Carbon nanotubes have an exciting array of applications which span mechanical, electrical, thermal and chemical/sensing. However, full exploitation is slowed by a lack of control over synthesis. Despite the two decades since the explosion of work in the area, progress in controlled production of nanotubes is impeded by our lack of understanding of the fundamental mechanisms of nucleation and growth. Our group has endeavored to develop a method that addresses the critical bottlenecks impeding the speed of research by taking advantage of advances in robotics, artificial intelligence, data sciences and in-situ/in-operando characterization.
Our Autonomous Research System, ARES, is capable of designing, executing and evaluating its own CNT growth experiments. Artificial intelligence module based on random tree / genetic algorithm statistical approach analyses experimentally obtained kinetic parameters (rate, time constant, etc.) and proposes new experiments to achieve user-defined objective. These are then executed by ARES automatically and without human intervention, and fed back into the AI module to ensure machine learning.
Recent experiments utilized maximum growth rate as an objective. The normalized difference between the objective and experimentally observed growth rates behaves in a fashion similar to what is typically seen in the control systems, with experimentally observed growth rate oscillating around the target. The convergence can be expressed via cumulative root mean square (RMS) of the rate difference. RMS increases initially (divergence), followed by consistent decrease after ~50 experiments, indicating convergence. That is, after some unsuccessful experimentation, ARES was better able to supply experimental conditions that achieved the objective growth rate. We take this as a clear demonstration of autonomous AI learning: convergence on the objective via closed-loop iterative experimentation without human intervention.

We report the metal-catalyst free synthesis of carbon nanotubes by thermal CVD from uncapped carbon nanotube forest as template. The uncapped CNT forest was formed by SiC surface decomposition (CNT forest on SiC).^[1,2] CNT forest on SiC consists of nearly ideally close-packed, well-aligned, and catalyst-free CNTs. We estimated the synthesized CNTs by Raman spectroscopy and scanning/transmission electron microscopy (SEM/TEM). We also report the uncapped CNT edge activation analyzed by X-ray photoelectron spectroscopy.
CNT forests were formed on the C-face (000-1) of n-type 4H-SiC substrate with SiC surface decomposition. The length of CNT forest was approximately 30 nm. The CNT forests were uncapped by mild oxidation with 15 wt%, 100°C H₂O₂ solution.^[3] CNTs were grown from uncapped CNT surface by thermal CVD method with CH₄ and H₂ as source gases.
We explored the optimal proportion of these gases, temperature and pressure condition for growth, and growth time dependence. In thermal CVD method, CNTs were grown under wide range conditions; at 1000°C, CH₄ proportion of 10~100% (H₂ dilution, total flow 50 sccm). The best condition of these gases for metal-catalyst free CVD growth was 40% CH₄ at 1000°C. The CNT forest thickness increased homogeneously from 30 nm to 100 nm in this condition, various diameters CNTs grew rapidly from the surface of CNT forest. The ratio of the rapidly grown CNTs was estimated to be about 1/1000 of uncapped CNT edges.
Raman spectra after uncap, after CVD for 1h, and after CVD for 4h indicate that as the CVD growth time got longer, the intensity of G-band increased and G/D ratio became higher. This CNTs growth in CVD continued for a long period. Also, RBM spectra after 4h CVD growth was enhanced, where nearly zigzag chirality such as (10,1), (14,1), (15,1) were obtained and it indicates high quality CNTs were grown by spiral growth of one step Diels -Adler reaction.
[1] M. Kusunoki et al., Appl. Phys. Lett. 87, 103105 (2005)
[2] M.Inaba et al., Appl. Phys. Lett. 106, 123501 (2015)
[3] R. Marega et al., Carbon 47, 675 (2009).

Bi-metallic nanoparticles are reported to enhance catalytic synthesis of carbon nanotubes by chemical vapour deposition, and are considered a very promising route to control nanotube chirality in bulk quantities. Herein, we systematically study different alloy combinations of evaporated Fe, Co, and Ni films to grow nanotube forests. Our results show two regimes of catalytic activity enhancement. When the total thickness of catalyst is larger than ~1 nm, bi-metallic catalysts outperform the equivalent layers of a single metal, producing taller forests of multi-walled nanotubes. The enhancement appears to be irrespective of the catalyst evaporation sequence. In contrast, for films thinner than nominally 0.5 nm, we observe a significant difference in catalytic activity, only for the case in which the metals are co-evaporated or sequentially deposited. This is because alloy formation is more challenging on small-sized nanoparticles, as shown by both in-situ photoemission and secondary ion-mass spectroscopy. Optimised catalyst compositions allow the synthesis of millimetre-range forests with a growth rate twice as fast as that for the equivalent single layers. In addition, when the tubes are single-walled, they display a narrow distribution of chiral angles, hence suggesting bi-metallic catalysts are potentially useful to synthesise chiral-selective nanotube forests.

Carbon nanotubes (CNTs), with exceptional thermal and mechanical properties as well as inherently high surface area, are an attractive candidate for integrating into thermal structures of advanced power electronics. Growth of vertical aligned carbon nanotubes (VACNTs) directly onto bulk copper (Cu) substrates is a promising application of utilizing CNTs as novel thermal interface materials (TIMs) in electronics packaging. However, compared to growing CNTs on conventional inert substrates such as SiO₂, direct growth of CNTs onto Cu substrates is significantly more challenging for controllable array synthesis due to the diffusion of metallic catalysts into the substrate during CNT growth. In this study, by introducing appropriate controlled buffer layers deposited on the Cu substrate surface, VACNTs of good alignment and high quality were reproducibly synthesized on the Cu substrate via chemical vapor deposition method. The effect of different buffer layers (Al₂O₃, SiO₂ and Al etc.) on CNT growth, structure, and quality, especially on interfacial properties between the CNT layer and Cu substrate was investigated by SEM, Raman, and Uniaxial force testing system. The experimental results indicated that buffer layer material, deposition method, and thickness plays a key role for determining CNT layer growth/structure and results in varying mechanical and thermal properties. This fundamental understanding of the role of buffer layer on CNT growth allows us the successful synthesis of VACNT on the copper substrate with desired structure and optimum properties. The findings would provide a real-life VACNT application for thermal management of electronics devices.

High density carbon nanotube forests have many applications. I first briefly review forests grown by many groups on insulating substrates, due to the advantageous properties of the Fe catalyst/Al₂O₃ support combination, with densities up to 10¹³ cm^-2. On the other hand, some applications require electrical conduction, and the growth of forests on metals is much more difficult, primarily because the high surface energy of metals precludes the de-wetting that enables formation of catalyst nano-particles. Here, we review various means to circumvent this problem, including plasma processing, carburisation and catalyst immobilisation. We then describe the use of TiSiN or TaSiN supports which are amorphous (without grain boundary diffusion paths), and have a low surface energy which enables forest area densities of 5x10¹² cm², with volume filling fractions of up to 30%. Doping can allow high conductivity without need for chirality slection.

Recent advances in fabrication and characterization of a novel type of nano-carbon based composite are reported. Although carbon fibers are usually considered incompatible with elastomeric matrices, carbon fiber-reinforced elastomer composites were fabricated in this work due to preliminary modification of the fibers with nano-carbons, namely by multi-step carbon nanotube (CNT) grafting. Previous works on CNT grafting on carbon fibers reported persistently that the grafting leads to drastic deterioration of the fiber proper thus making composite properties rather poor [1-4]. This work reports near-zero deterioration due to introduction of a protective layer in a multi-step procedure.
Polyurethane and silicone matrices were used for composite manufacturing. The interfacial shear strength (IFSS) between carbon fibers and elastomeric matrix was enhanced by grafting CNT on the carbon fibers through several process steps including desizing of carbon fibers, introduction of a protective alumina layer, seeding iron nano-particles, and then chemical vapor deposition (CVD) for CNT growth. The considerable part of current research was dedicated to the process temperature optimization for better covering of the fiber surface with CNT and minimizing grafting-induced carbon fiber damaging. Single filament tests were carried out to investigate the influence of grafting process on the fiber tensile strength. Improvement of interfacial shearing strength up to 150% was achieved due to CNT grafting. Investigation of mechanical properties of the composites showed substantial improvement of delamination resistance due to application of CNT-grafted fibers. The structure of composites in both intact and fractured form was investigated by scanning electron microscopy (SEM), X-ray tomography and X-ray photoelectron spectroscopy (XPS). The composites are flexible, demonstrate high mechanical strength, elastic modulus and vastly improved thermal conductivity.
In conclusion the development of such composites is a perspective way for producing flexible, strong and cheap materials with advanced functionality.
References
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Although it is well known that growth temperature affects the synthesis of carbon nanotubes (CNTs), the effects of preheating the incoming hydrocarbon precursors and of forming water vapor from oxygen and hydrogen are less known. In this study, we use a sophisticated system of multi-zone thermal chemical vapor deposition (CVD) furnaces in parallel and in series to study the effects of thermal preheating of these precursors prior to their reaching the sample.
We analyzed a dozen of possible preheating combinations and showed how an appropriate combination of gas residence times for both hydrocarbons and water formation can increase the CNT carpet height by a factor of 3, exceeding 3 mm in height. Extensive HRTEM and HRSEM characterizations of the CNTs and GC-MS of the output gases indicate how preheating affects the CNT height, diameter, and crystallinity. This analysis helps to understand the mechanisms at play for the precursor gases prior to reaching the sample and helps to design more efficient synthesis systems for CNT growth.

We report on the synthesis of kilometers of continuous macroscopic fibers made up of carbon nanotubes (CNT) of controlled number of layers, ranging from singlewalled to multiwalled, tailored by the addition of sulfur as a catalyst promoter during chemical vapor deposition in the direct fiber spinning process. The progressive transition from single-walled through collapsed double-walled to multiwalled is clearly seen by an upshift in the 2D (Gprime;) band and by other Raman spectra features. The increase in number of CNT layers and inner diameter results in a higher fibre macroscopic linear density and greater reaction yield (up to 9%). Through a combination of multiscale characterization techniques (X-ray photoelectron spectroscopy, organic elemental analysis, high resolution transmission electron microscopy, thermogravimetric analysis, and synchrotron XRD) we establish the composition of the catalyst particles and position in the isothermal section of the Cminus;Feminus;S ternary diagram at 1400 °C. This helps explain the unusually low proportion of active catalyst particles in the direct spinning process (<0.1%) and the role of S in limiting C diffusion and resulting in catalyst particles not being in thermodynamic equilibrium with solid carbon, therefore producing graphitic edge growth instead of encapsulation. The increase in CNT layers is a consequence of particle coarsening and the ability of larger catalyst particles to accommodate more layers for the same composition.
We further present the distribution of CNT chiralities obtained from ED, Raman spectroscopy and Emission spectra and discuss these findings in the context of the current screw dislocation growth model accepted in the field.
Finally, we show the application of basic polymer fibre spinning principles to produce highly oriented CNT fibres by reducing entanglements in the gas phase through CNT dilution. The resulting fibres have tensile properties superior to those of Kevlar, high electrical conductivity and a very large surface area. The exploitation of these properties in sensors, supercapacitors and other devices is briefly demonstrated.
Chem. Mater. Reguero et la, 2014, 26(11), 3550-3557
ACS Nano Qiu et al 2013, 7(10), 8412-8422
ACS Nano Belén et al accepted

Carbon nanotubes (CNTs) have received wide attention both from academia and industry due to their exceptional mechanical, thermal and electrical properties.^[1] CNTs with floccus structure can be prepared in industrial conditions with fluidized bed technology, and thus they have great development potential in the practical applications due to their relatively low cost and batch-production in comparison with single-walled CNTs and CNTs arrays.^[2-3] At this stage, combined CNTs with polymer, metal and ceramics is still an effective approach to take full advantage of excellent properties of floccus CNTs. Therefore, the dispersion of floccus CNTs is a key step to put CNT application forward. For this reason, the achievement of appropriate dispersion of floccus CNTs has been regarded as a prerequisite for various industrial applications. Here, we compared four classes of mechanical dispersion methods to disperse commercialized floccus CNTs so as to investigate corresponded dispersion states of floccus CNTs, which are expected to provide insight into the influence of different dispersion states of floccus CNTs on the macro-performances of composites. We found that the dispersion states achieved by vortex-jet and cavitation are conductive to prepare highly conductive composites, whereas those obtained by impact-grinding contribute to prepare superior mechanical composites. Accordingly, the acquisition of appropriate dispersion state of floccus CNTs by optimized dispersion method and conditions should be a critical issue for different application requirements. Finally, dispersion states have been modeled and put forward to account for dispersion mechanisms. Our study was proposed to provide guidance for the preparation and application of commercialized floccus CNTs composites.
Key words: Floccus carbon nanotubes, Dispersion, Composites
Correspondence should be addressed to Ming Xu([email protected])
1. Sekitani T, Nakajima H, Maeda H, et al. Stretchable active-matrix organic light-emitting diode display using printable elastic conductors[J]. Nature materials, 2009, 8(6): 494-499.
2. Xu M, Futaba D N, Yamada T, et al. Carbon nanotubes with temperature-invariant viscoelasticity from-196 to 1000 C[J]. Science, 2010, 330(6009): 1364-1368.
3. Yoon H, Yamashita M, Ata S, et al. Controlling exfoliation in order to minimize damage during dispersion of long SWCNTs for advanced composites[J]. Scientific reports, 2014, 4.

Carbon nanotubes (CNTs) and graphite are both light weight carbon based material that processes low thermal expansion properties. Carbon nanotubes are fascinating materials that possess tremendous physical properties which can be of benefit to many applications. Significant strides have been made in recent years to shrink the size of electronic devices at an unprecedented rate. However, the need to quickly dissipate thermal energy is ever more important for devices&’ performance and lifetime. One way to address the thermal dissipation issues is to understand the thermal transport at those nano-junctions is by investigating materials that are connected at the nanoscale. However, growing CNTs directly on graphite surfaces has been challenging and largely left unexplored. Successful growth of CNTs on graphite allows for detailed studies for various carbon systems as light weight heat transfer devices with minimal CTE mismatch.
A recent study demonstrated CNT carpets can be grown on carbon substrates activated with silicon oxide coatings. It is also seen that carpet height can be tailored with SiO₂ film thickness and with CVD growth time. These parameters allow tuning of nano-engineered architecture suitable for thermal applications. The objective of this investigation is to identify and to correlate the influence of interfacial layer and CNT carpet height on the thermal diffusivity of the solid. Model structures consisting of CNT on flat carbon substrates and their thermal properties evaluated with Netzsch, Inc laser flash 457 systems. Variation of thermal behavior as a function of carpet morphology will be presented, with the idea of elucidating how the thermal behavior of these types of layered solids can be fine-tuned.

Every year Oil spill incidents causes serious environmental and ecological issues as a result of release of crude oil and toxic organic solvents in seawater. There is urgent need to develop novel and efficient oil remediation ways. . Use of porous materials have attracted great attention because of possibility of complete removal of oil from site and recyclability . The porous adsorbents include natural products such as straw , cotton , wood fiber and various synthetic organic and inorganic materials such as zeolites , silica , perlite , graphite, activated carbon , conjugated micro porous polymers , polypropylene and polyurethane but these conventional adsorbents suffer from various problems such as low adsorption capacity , high cost and complex synthesis methods. Graphene due to its extraordinary properties has made itself highly attractive for numerous applications such as lithium ion batteries , super capacitors , sensors and composite materials. It has also emerged as promising adsorption material due to its high surface area and hydrophobic surface. Pristine graphene cannot be used for oil spill on macroscopic scale however Assembling graphene into three dimensional macroscopic structures has been found promising in oil adsorption. Therefore , In this work graphene oxide solution is synthesized by Modified Hummers method . The graphene hydrogel is synthesized by reduction of graphene oxide and freeze drying technique is employed subsequenty to prevent the collapse of pores in drying. SEM and BET Tests shows porous structure morphology made of interconnected graphene sheets with high surface area . These porous materials have shown high adsorption capacity (40-70 g/g) for various oils and organic solvents . Adsorbate can be removed from material by heat treatment making it re-usable for adsorption again and this property of recyclability is retained for several cycles. Moreover Kinetic study is done to study the adsorption speed which is an important property as most spreading of oil occurs within first few hours of oil spill . When graphene aerogel was contacted with n-hexane sample , the entire adsorption process of n-hexane was completed within few seconds which reflects extremely fast uptake speed of material. Adsorption process mechanism is explained using kinetic sorption models . These characteristics of high adsorption capacity , fast uptake speed and recyclability makes this material much more useful for practical use in oil spill incidents.

Cleaving crystalline graphite via electrochemical reactions in acid conditions has proven to be an efficient way of producing high-quality graphene for different applications. Here we report a protocol to produce electrochemically exfoliated graphene with large crystal size (3mm), low oxygen content, and low sheet resistance (4.8 KW/Square aprox). In this work is investigated the mechanism that allows exfoliation process on carbon paper seeking electrochemical route in aqueous-acid media as an environmentally friendly alternative to produce large size-area graphene layers. Distinct Raman peaks are observed at 1350 cm^-1 (D peak) and 1590 cm^-1 (G peak) and 2707 cm^-1 (2D peak). The D peak can be associated with edge-effects due interstitial vacancies rather than functional groups as corroborated by FTIR measurements. Decoration of high quality graphene with metallic and magnetic nanoparticles is interesting for bio and gas sensing. Non-covalent decoration in this case is key to increase the quantum yield in fluorescence studies. Here we report liquid-phase, non-covalent, decoration of electrochemically exfoliated graphene using Ag, Au, Fe, Sr, and Co nanoparticles.

Graphene, a single-layer carbon film, is a promising material for many electrical, photonics, and biomedical applications due to its two-dimensionality and unique properties[1]. The number of graphene layers should be determined accurately because the number of layers strongly affects the electronic properties. In this paper, we report TEM(Transmission Electron Microscopy) analysis of Moiré patterns originating from two monolayer graphenes characterized as a monolayer Graphene by Raman measurement.
Graphene was synthesized by a CVD method on a copper substrate (Alfa Aesar, 99.8%, thickness: 25 mu;m). After the etching of Cu substrate by 100 mM ammonium peroxodisulfate solution, the specimen was rinsed thoroughly with distilled water. Next, it was transferred on a carbon-supported Cu TEM grid. The number of graphene layers on the TEM grid was preliminary determined by Raman measurements (inVia Reflex, Renishaw). TEM measurements were made continuously over the monolayer graphene area, using an FEI Titan Cubed 60-300 TEM, equipped with image and probe correctors. The TEM was operated at 80 kV with a monochromator for high-resolution TEM imaging.
We obtained selected area electron diffraction patterns from the monolayer graphene determined by the Raman mapping investigation. Two sets of hexagonal diffraction spots were observed in several areas. The number of graphene layers corresponding to each set of diffraction spots was also determined by comparing the intensity ratio of the diffraction peaks [2]. We found that each set belongs to single-layer graphene.
We examined the atomic-resolution TEM images of the graphene in the same area. The HRTEM image revealed the Moiré pattern in the graphene. The Moiré pattern revealed that each graphene was stacked toward the three-dimensional direction [3,4]. Thus, two layers of graphene were observed in the monolayer graphene area determined by the Raman spectroscopy.
We also performed a multi-slice TEM image simulation using MactempasX software to compare the 3D atomic structures of the two graphene membranes and the experimental HRTEM images. We found that the experimental Moiré image was constructed with a 10 Å interlayer distance between the graphene. Normally, the interval between graphene in graphite is 3.35 Å. Thus, the wide-interval graphene bilayer was treated as two ‘monolayer&’ graphene in the Raman measurements. This structure was constructed by CVD-grown graphene, formed on both sides of the Cu substrate. After graphene etching on the back side by acid treatment, we barely observed the Moiré pattern in the monolayer graphene area.
[1] K. S. Novoselov et al., Nature 490 (2012) 192.
[2]J. C. Meyer et al., Solid State Comm. 143 (2007) 101.
[3] J. H. Warner et al., Nano Lett. 9 (2009) 102.
[4] J. S. Alden et al., PNAS 110 (2013) 11256.

Oil and gas industry has many challenges that affect its production; one of them is the scale deposition. Scales are minerals that deposit in oil/gas infrastructure and cause clogging and corrosion in the pipelines and well bore. As a result, various solutions have been proposed to overcome these challenges; however, most of the current solutions have limitations. In this work, a new type of sensor and associated system for complete online monitoring of scale deposition with great accuracy and reliability is fabricated and characterized.
This system is based on Chemical Vapor Deposition (CVD) graphene film as active material for back-gated transistor like sensor systems. Graphene has unique sensing/electronic properties along with physical and chemical stability in corrosive and hostile environments present in the oil and gas application. The graphene films are synthesized and optimized using CVD reactor in various substrates with different surface finishes. These films were transferred to SiO₂ substrate for characterization such as optical assessment and conductivity measurements. The electrical resistance measurements are used as a response variable for presence of scale at the surface of graphene film.
The back-gate structured is fabricated by depositing and patterning a metal layer to act as the back gated structure. Then the graphene is exfoliated and patterned as the active channel for the sensor. Then metal source and drain contacts were deposited. This was followed by opening the back gate contact. In order to optimize and obtain the low source and drain parasitic contact resistance, which is measured to be in the range 10 kohm, Kelvin and TLMs structures are fabricated. These are used to select and optimize the electrical contact resistivity with graphene. These metals include Ti, Cu, Cr, Al and Ni. Initial results indicate that 200 nm Al with 10 nm Ti as an adhesion layer film provide very good contact resistance value in the range of 12 kohm.
The impact of chemical sensitivity, optimization of the device, various integration schemes and functionalization of the graphene for sensing selectivity are ongoing and will be reported in the conference.

It has been reported that reduced graphene oxide (rGO)-metal oxide composites are active for supercapacitor applications^{1, 2}. However, a systematic study is missing to understand how the pseudocapacitance of these composites may change with varying the degree of oxidation of the GO substrate and/or metal oxide loadings. We prepared GO using the classical Hummers&’ method³ (HGO) and the so-called improved method⁴ (IGO) thereby obtaining nanocarbon substrates with different degrees of oxidation (where HGO < IGO). Then, in the presence of HGO or IGO, rGO-CoFe₂O₄ composites were synthesized using a hydrothermal method. Different loadings of CoFe₂O₄, ranging from 0 to 16 wt%, were employed. The composites were characterized by X-ray diffraction, electron microscopy and zeta potential analysis. The electrochemical performance of the composites was investigated using cyclic voltammetry and galvanostatic discharge-charge tests in a three-electrode experimental setup using aqueous 1.0 M KOH electrolyte.
Our results show a significant difference in the specific capacitance of rHGO and rIGO composites during the discharge-charge tests. We observed that the specific capacitance is reduced with increasing degree of oxidation of the GO. In the same manner, the specific capacitance is reduced with increasing concentration of CoFe₂O₄: rHGO-CoFe₂O₄ (5 wt%) and rHGO-CoFe₂O₄ (16 wt%) exhibit ~452 Fg^-1 and ~200 Fg^-1, respectively. These results suggest that the pseudocapacitance behavior of rGO-metal oxide composites is dependent both on the degree of oxidation of the GO substrate and the metal oxide concentration.
1. He, P.; Yang, K.; Wang, W.; Dong, F.; Du, L.; Deng, Y. Russ J Electrochem 2013, 49, (4), 359-364.
2. Wu, Z.-S.; Zhou, G.; Yin, L.-C.; Ren, W.; Li, F.; Cheng, H.-M. Nano Energy 2012, 1, (1), 107-131.
3. Kumar, N. A.; Choi, H.-J.; Shin, Y. R.; Chang, D. W.; Dai, L.; Baek, J.-B. ACS Nano 2012, 6, (2), 1715-1723.
4. Marcano, D. C.; Kosynkin, D. V.; Berlin, J. M.; Sinitskii, A.; Sun, Z.; Slesarev, A.; Alemany, L. B.; Lu, W.; Tour, J. M. ACS Nano 2010, 4, (8), 4806-4814.

Transparent conducting films (TCFs) play an important role in numerous transparent electronic devices and have attracted considerable attention due to their potential application to touch screens, organic thin film transistors, and organic light-emitting diodes. At present, indium tin oxide (ITO) is the most commonly used material to form TCFs. However, the use of ITO is limited by its high cost and the depletion of ITO sources. In addition, owing to the huge increase in demand for flexible and stretchable electronic devices, there is a need for a novel material that can replace brittle ITO. Carbon materials such as carbon nanotubes and graphene have been suggested for the formation of TCFs due to their low cost, good electrical properties, and flexibility. However, their practical use in TCFs is limited by the difficulty of synthesizing large areas of these films and of obtaining a homogeneous dispersion of coating solution. On the other hand, silk fibroin (SF), a protein derived from the Bombyx mori silkworm cocoons, has been reported as a potential carbon precursor that can be processed into various forms such as aerogels, fibers, and films. In particular, SF can be easily fabricated into flexible TCFs using a facile solution process that occurs in an eco-friendly aqueous system, which imparts the SF-based TCFs with its conductive property through a facile carbonization process. In this study, we fabricated transparent conducting carbon thin films using SF and the as-prepared flexible TCFs were transferred onto polyethylene terephthalate (PET) substrates. The resulting as-prepared flexible TCFs that were transferred onto a PET substrate showed high electrical conductivity, high transparence, and superior flexibility.

Raman spectroscopy enables us to investigate the molecule or crystal structures by the difference of energy between incident light and scattering light. However, spatial resolution is limited to sub-micron range because visible laser beam is generally used. Recently, tip-enhanced Raman scattering spectroscopy (TERS), where Raman spectroscopy is combined with atomic force microscopy (AFM), has been recognized as a powerful tool. However, the TERS system has not been fully established at present, due to the absence of commercial tips showing the reproducible performance. Among three types of TERS configurations, bottom, top and oblique illumination, the last one is most preferable because it can be applied for any kinds of samples. Metal-coated (Ag or Au) cantilever tip is commonly used. Although silver is known to show much more enhancement in electric field than gold, it is more likely subjected to oxidation. In this study, we report on the reproducible TERS measurement using the custom-made Ag-coated tips. The catilever (Olympus AC240TM-R3) was first oxidized and coated with 30 nm Ag. Then a few nm of oxidation-resistant layer was coated. It is noted that 70-80 % of tips shows enhancement. The system we used was Renishaw inVia Raman spectrometer and Bruker Innova AFM. Based on the TERS imags at the edge of single layer graphene on SiO₂ grown by chemical vapor deposition, we discuss the spatial resolution in our TERS system, where much higher resolution is achieved compared with conventional Raman mapping.

Local modulation of charge carrier doping in ferroelectric field-effect devices opens the opportunity for realizing on-demand functional circuits. A local domain switching produced by a scanning probe tip on a graphene-ferroelectric field effect transistor (GFFET) can bring about targeted, local carrier density modulation on the graphene channel, either into p-type or n-type. A promising approach towards such goal is to switch the polarization through a local strain gradient, i.e. flexoelectric switching.
In our experiment, we studied graphene-PTO/STO superlattice FETs, where a good coupling between graphene and the ferroelectric gate material has been demonstrated by the ferroelectricity-driven switching direction of graphene transport hysteresis. Large regions with uniform “up” polarizations were written on ferroelectric 15 PbTiO₃ / 3 SrTiO₃ (15 PTO / 3 STO) superlattices, with electrically biased conductive atomic force microscope (AFM) tips. Fine features could then be mechanically written on such regions by applying a strain gradient and, consequently, polarizing some of the domains “down”. The mechanical writing was executed on an “up” polarized region by scanning with an insulated AFM tip that exerted a force of ~11mu;N. An electric field could erase the strain-gradient induced written features by restoring them in the “up” configuration, demonstrating ferroelectric switching. Dual AC resonance tracking (DART) piezoresponse force microscopy (PFM) was used to map out the domain features before and after writing. The samples used for this experiment were 100nm thick, significantly thicker than thin films used in prior experiments, and flexoelectric switching was enabled due to the relatively small coercive voltages of the superlattices. Having developed a method for local, rewriteable control of polarization beneath a graphene sheet, the transport properties of the graphene can then be studied as a function of the corresponding locally written domain structures.

Because of its superior characteristics, graphene is highly expected to apply in various fields, such as electrical wiring, transparent electrodes. Graphene is usually grown by CVD method using Cu or Ni as a catalyst. However, the transfer process of the graphene is a big problem for the applications of the mass production of devices. Not only the technical difficulties, but also the degradation of their properties during the process is the important point to be solved. In recent years, a direct growth of graphene on a substrate has been often studied as a substitutional method for the transfer process. We have been studying the precipitation method for forming high-quality multilayer graphene [1] and have succeeded in the direct growth of multilayer graphene using a W capping layer. In this report, the effect of the capping layer on the precipitation method is investigated with changing the materials for the capping layer.
Four types of samples were prepared to study the effect; W(25nm)/Ni(300nm) /amorphous carbon(a-C(5nm))/sapphire substrate (Sample A), Au(100nm)/Ni(300nm)/a-C(5nm)/sapphire substrate (Sample B), SiO₂(100nm)/Ni(300nm)/a-C(5nm)/sapphire substrate (Sample C), and Al₂O₃(100nm)/Ni(300nm)/a-C(5nm)/sapphire substrate (Sample D). Each layer was deposited by using electron-beam deposition. The samples were annealed at 900 ^oC for 30 minutes in a vacuum to precipitate graphene. By using Raman spectroscopy, the samples were evaluated especially whether the graphene was directly formed on the substrate or not. In order to study the presence of the graphene on the substrate, the catalysts were removed using a diluted aqua regia.
The results of Raman spectroscopy show that the majority of the carbon atoms precipitated on the surface of the sapphire as a multilayer graphene by the use of the W capping layer while a very small amount of carbons did on the sample surface (Sample A). The low D / G ratio of 0.17 suggests a high quality of the graphene. On the other hand, the use of the Au capping layer only brought a multilayer graphene on the surface of the sample without any formation of graphene directly on the sapphire substrate (Sample B). The use of the SiO₂ and Al₂O₃ capping layers (Sample C and D) also brought no formation of graphene on the substrate. Tungsten (W) didn&’t make any alloy with Ni during the annealing process because of its high melting point. The dense and firm interface made the carbon atoms difficult to precipitate. In contrast, Au easily alloyed with Ni and didn&’t work as a capping layer. Although SiO₂ and Al₂O₃ didn&’t dissolve into Ni, the imperfect interfaces possibly failed to force the carbons to directly precipitate on the sapphire substrate.
Acknowledgement: This work was supported in part by JSPS KAKENHI Grant Numbers 2660089, 15H03558, 26105002, 25000011.
Reference: [1] Jumpei Yamada et al., MRS spring Meeting & Exhibit., (2015) T14.03.

Graphene, which consists of one-atomic-layer carbon film, is expected to be used for flexible optoelectronic applications, since it has various superior electric, optical and mechanical properties [1, 2]. Optical adsorption of single layer graphene is almost independent on the wavelength between 300 to 2500 nm [1], which enables us to tune optical transmittance in wide wavelength ranges by changing layer numbers [2]. Therefore, graphene is expected to be used for optoelectronic applications. For the wavelength of the visible light, transparent conductive films were fabricated and high performance of light emitting device was reported [3]. Optical filters [4] and limiters [5] based on graphene for infrared regions are expected and the tunable optical properties by applying voltage were confirmed. In order to develop flexible optoelectronic applications using graphene, it is necessary to understand the effects of layer numbers and the incident angle-dependence of the optical properties of graphene. In addition, to understand the optical properties of interfaces between graphene and substrates are important.
Two kinds of graphene films were used in this study. One was thick (80~100 layers) graphene on Ni foil and the other was single layer graphene on Cu foil. The layer number of deposited graphene by CVD was able to control between single and several hundred by selecting appropriate substrates. By using PMMA as a supporting material, graphene films were transferred onto quarts glasses or PET films. The layer numbers were estimated by cross-sectional TEM observations.
The angular-dependence of the optical transmittances were measured in air at room temperature using UV-VIS-NIR spectroscopy (SolidSpec-3700DUV, Shimadzu). The optical transmittances of graphene/substrate structures were measured in the wavelength range between 250 and 2500 nm. The incident angle was varied from 0 to 70 degree in 10 degrees steps. Both thick and single layer graphene show almost flat optical transmittance between 300 to 2500 nm, which indicates that the optical transmittance can be tuned by changing layer numbers [2]. Optical transmittances of thick graphene/quarts structures for all wavelengths are decreased with increasing the incident angle, which consistent with those of other materials [6, 7]. We will discuss the interface between graphene and substrate.
Acknowledgement
This paper is partially based on results obtained from a project supported by New Energy and Industrial Technology Development Organization (NEDO).
References
[1] F. Bonaccorso et al., Nat. Photonics 4 (2010) 611-622.
[2] S. Bae et al. Nat. Nanotech. 4 (2010) 574-578.
[3] T.-H. Han et al., 6 (2012)105-110.
[4] H.-J. Li et al., Appl. Phys Exp. 7 (2014) 024301.
[5] Y. Xu et al, Adv. Mater. 21 (2009) 1275.
[6] H. Miyazaki et al., j. Ceramic Society of Jpn. 121 (2013) 17-20.
[7] G. Fanchini et al., Nano Lett. 8 (2008) 2176-2179.

Previously we have demonstrated that coating a Nafion membrane with partially reduced graphene oxide sheets that have gold or platinum nanoparticles chemically bound to their surface improves the power output of the PEM fuel cell by more than 70%.
Now we investigate the effects of graphene oxide applied to PEM fuel cells, testing in a fuel cell attached to H₂ and O₂ gases and measuring voltage and current. Here we report on the catalysis effect of graphene oxide, not only on the nafion membrane, but also on the electrodes. It has been speculated that the graphene oxide enhances the ion conduction through the membrane, but graphene oxide incorporated within the nafion membrane material produced only modest improvements in power output. We coated graphene oxide on the outside of the membrane, both on the anode and the cathode, and obtained more than 50% enhancement of the power output, suggesting that a different mechanism may be present. Theoretical calculations of the process will be performed.

Previously we have synthesized and characterized gold and platinum nanoparticles chemically bound to reduced graphene oxide sheets. Now we have synthesized iron nanoparticles chemically bound onto reduced graphene oxide. Characterization includes TEM, SEM, EDAX, FTIR, Raman spectroscopy, and measurement of magnetic properties. We will look at how the iron nanoparticles change the spectroscopic properties of reduced graphene oxide.

Graphene oxide (GO) has attracted much attention as a material for exploring a variety of physical properties including electric transport, wide energy range of photoluminescence (PL), and room-temperature ferromagnetism. The sp² and sp³ domains coexist in GO, and the sp²/sp³ domain fraction is crucially important for controlling the physical properties of GO. It should be possible to tune the various properties of GO in situ by adjusting the sp²/sp³ fraction, which is usually controlled chemically by thermal annealing, or by plasma treatment. Here, we report a method for in situ tuning of the sp²/sp³ fraction based on electrochemical reduction and oxidation (redox) caused by ion migration in a solid-state electrolyte.^1,2 The method can be applied not only to electronic devices but also to a wide range of nano-optoelectronic devices including nonvolatile PL memory devices and on-demand rewritable biosensors that can be integrated into nano- and microtips which are transparent, ultrathin, flexible, and inexpensive.³
[1] T. Tsuchiya, K. Terabe, M. Aono, Adv. Mater. 26, 1087-1091 (2014)
[2] T. Tsuchiya, K. Terabe, M. Aono, Appl. Phys. Lett. 105, 183101 (2014)
[3] T. Tsuchiya, T. Tsuruoka, K. Terabe, M. Aono, ACS Nano, 9, 2102-2110 (2015)

Hybridization of organic-inorganic halide perovskite and graphene can offer new functionalities that are not existing in either materials. Combining the large absorption of the perovskite layer and high mobility of graphene, hybrid devices exhibit a broad spectral photoresponsivity, which can be used in imaging sensors, UV detectors, and flexible applications. We studied the growth of organic-inorganic halide perovskite on exfoliated few-layer graphene with a focus of thin film (< 50 nm) condition. All the results were produced with vapor deposition of lead halide in a high vacuum chamber then converted into organic-inorganic halide perovskite in a tube furnace. Scanning electron microscopy, atomic force microscopy, and X-ray diffraction were used to characterize the perovskite/graphene structures. The growth of lead halide on few-layer graphene is mainly based on material nucleation at graphene edge where interaction with dangling bonds is expected. Moreover, we also observe direct synthesis of lead halide on few-layer graphene.

With a growing concern and urgent development of sustainable energy systems and next-generation energy storage technologies, such as lithium-sulfur (Li-S) batteries and metal-air batteries, sp² carbon (e.g. carbon nanotubes (CNTs) and graphene)-based nanomaterials have recently attracted enormous research interest. The promising applications of sp² carbon-based nanomaterials are highly dependent not only on their superior intrinsic physical properties, but also on their tunable structural characters. However, due to the intrinsic shortages of the low-dimensional nanomaterials, such as aggregation and aeolotropism, the wise hybridization of graphene and other components into 3D hierarchical nanomaterials is of great importance and also challenge to extend their excellent properties from nanoscale to macroscale and thereby the practical applications.
On the basis of above considerations, several graphene-based nanomaterials are scrupulously designed and facilely fabricated to fully demonstrate their intrinsic properties and also the hierarchical structural features. (1) Structural hybridization of alternative aligned CNTs and graphene into sandwich-like 3D framework (ACNT/G), rendering an excellent loading transfer and could be repeatedly compressed at high strains (ε > 90 %), with a highest mechanical energy absorption density of 237.1 kJ kg^-1 and an ultrahigh power density of 10.4 kW kg^-1.^[1] (2) Interfacial modulation of ACNT/G via nitrogen incorporation to obtain a scaffold for high-rate Li-S batteries, with a high initial capacity of 1152 mAh g^-1 at 1.0 C and a remarkable capacity of 770 mAh g^-1 can be achieved at 5.0 C. ^[2] (3). Spatial confinement of nanosized NiFe layered double hydroxide active centers into a graphene framework, resulting in a superior electrocatalyst for oxygen evolution reaction with a remarkably low Tafel slope (~45 mV dec^-1), a substantially decreased overpotential (~337 mV required for 10 mA cm^-2) and enhanced durability. ^[3] These processes open up fresh perspectives and inspiring avenues on hierarchical graphene towards superior energy storage and oxygen electrocatalysis.
References:
1. C Tang, Q Zhang, M-Q Zhao, G-L Tian, F Wei. Nano Energy, 2014, 7: 161-169.
2. C Tang, Q Zhang, M-Q Zhao, J-Q Huang, X-B Cheng, G-L Tian, H-J Peng, F Wei. Advanced Materials, 2014, 26(35): 6100-6105.
3. C Tang, H-S Wang, H-F Wang, Q Zhang, G-L Tian, J-Q Nie, F Wei. Advanced Materials, 2015, doi: 10.1002/adma.201501901.

Since the first exfoliation of monolayer graphene in 2004, a lot of studies about the graphene as an electronic device have been tried. The one of the representative device using graphene is gas sensor. It has been reported that graphene is so sensitive to adsorbates like NO₂, NH₃, CO, H₂O on its surface. In comparison with conventional gas sensor, however, its sensing characteristics like sensitivity and response, recovery time, selectivity are still under study. Moreover, the graphene is very sensitive to the water molecules, the graphene device as a humidity sensor could be considered.
It has also been reported that poly methyl methacrylate (PMMA) residues promote adsorption of water molecules on graphene. In this case, PMMA was used as a photoresist to pattern the electrodes on graphene and its residue on graphene after patterning the electrodes on mechanically exfoliated graphene. Separately, PMMA has been well known as a supporting layer on transferring chemical vapor deposited (CVD) graphene as wet transfer method, which is commonly used. PMMA residues, however, left on the CVD graphene after the transfer process. Such a residual PMMA has an important role to play in determining the sensor ability.
Here, we investigated the effect of PMMA on CVD graphene under various humidity environments. CVD graphene was transferred on Si/SiO₂ substrate by wet transfer using PMMA and connected copper wire with silver paste to measure the resistance of the graphene. The sample was put into humidity chamber. The range of relative humidity was between 40% and 90% at fixed temperature 30#8451;. We could directly measure the electrical resistance of CVD graphene in various humidity conditions. Finally we confirmed that the PMMA is one of the critical factor to determine the resistance change of the graphene but further experimental data is needed to find another factor and explain a major reason for the resistance change.

Low-dimensional structures of graphene attract interests by means of fundamental Dirac physics and perspectives of electronic device application. To produce FETs it is essential to open the bandgap, which can be induced by quantum size effects appeared in nanostructures such as graphene nanoribbons (GNRs)[1]. The GNR approach, however, falls into many difficulties in controlling ribbon shapes including width, line edge roughness, edge structure, and so on. Moreover, more serious intrinsic problem is a trade-off between the carrier mobility and the bandgap in GNRs, i.e. the narrower the GNR&’s width - the larger gap is opened, but the carrier mobility is reduced due to acoustic phonon scattering and heavier effective mass etc. [2]. Here we present a new type of graphene nanostructure, graphene lateral superlattices (GLSLs), which can potentially overcome the problems mentioned above. The new structure is formed on SiC(1-108) facets after surface decomposition of vicinal 4H-SiC(0001) [3] as a result of macroscopic step-bunching. The initial vicinal surface turns into the periodic wavy structure, consisting of (0001) and (1-108) (26° tilted from (0001)) surfaces. Scanning tunneling microscope (STM) imaging performed on a (1-108) facet indicates weakly corrugated surface with ~2.3 nm periodicity. Combined with the results of micro-Raman spectroscopy, indicating double layers of graphene, the detailed structure on the facet is modeled, i.e. a (1-108) macro-facet consists of ordered pairs of (0001) terraces and (1-102) facets with sim;2.3 nm periodicity, which are covered by an initial graphene layer and a locally laminated graphene top layer imaged by the STM. The electronic structure of the top layer at K-points is investigated by angle-resolved photoemission spectroscopy (ARPES). It indicates the valence band maximum located at sim;0.2 eV below Fermi level and dim states above, implying the bandgap of at least 0.2 eV. The similar structure is fabricated on semi-insulating 4H-SiC substrate and I-V measurement is performed by two- and four- terminal electrical methods along the (1-108) facets. The two-terminal I-V behavior indicates Schottky barrier height of ~0.2 eV, which is agreement with the result of ARPES. Band structure calculation around K-points on the simplified model by density functional theory (DFT) suggests band-gap opening essentially due to periodic potentials induced by corrugated lower graphene layer. The four-terminal I-V curve at several temperatures indicates no temperature dependence as confirmed by the conductance plot as a function of temperature. This result should imply ballistic electron transport in our GLSLs. References [1] T. Kakjiwara et al., Phys. Rev. B 87, 121407(R) (2013). [2] A. Betti et al., IEDM 10, 728 (2010). [3] S. Tanaka et al., Phys. Rev. B 81, 041406 (R) (2010).

Nanoscale carbon reinforcement using carbon nanotubes (CNTs) and graphene has shown great potential to improve the mechanical, thermal, and electrical properties of host polymer matrices. In particular, graphene nanoribbons (GNRs) have thin elongated strips of sp² carbon honeycomb structures, exhibit a high aspect ratio, and have a large interfacial area. Moreover, the outstanding electronic and spin transport properties of GNRs make them attractive for a wide range of device applications and for use as structural reinforcement in nanocomposites. However, there are a number of practical challenges that must be addressed before high-performance GNR-based polymer nanocomposites can be obtained. First, the GNRs must be dispersed homogeneously in their host polymer matrix as the intrinsic van der Waals interactions that typically exist between GNRs can lead to agglomeration. Such agglomeration lowers the effectiveness of GNRs for reinforcement. Second, the external load should be efficiently transferred via a strong interaction at the interface between the GNRs and the matrix. As such, the interfacial adhesion between the GNR and the surrounding matrix should be maximized. In this study, reduced graphene oxide nanoribbons (RGONRs) were prepared by unzipping multi-walled CNTs, which was followed by chemical or thermal reduction. Their dispersion stability in various organic solvents and their ability to reinforce a host polypropylene (PP) matrix were investigated. The RGONRs led to notable enhancements of the thermal degradation temperature and of the mechanical properties of the PP matrix.

A unique way to obtain metal oxide decorated nanocrystalline graphene under controlled conditions will be reported. Crystalline oxide nanoparticles (2-3 nm diameter) formed during the detachment of the graphene from the initial growth substrate reside preferentally at highly defective graphene sites. This material is candidate for heterogeneous catalyst, it allows to study theoretically and experimentally disputed transparency effects of graphene as well as is a candidate to shed light into electronic and magnetic interactions of quasi zero dimensional nanoparticles on 2D surfaces. Moreover this modified nanocrystalline graphene can promote charge transfer between specific gas species and functionalized graphene, proving effective in giving fast sensor response, and high selectivity. In contrast to nearly defect free CVD derived graphene it shows gas sensing behaviour under ambient conditions at 25°C, e.g. 5 ppm NO₂.

Cellulose, the most abundant carbohydrate in nature, is desirable for large-scale production of 5-hydroxymethylfurfural (HMF) without food supply problems. To convert cellulose to HMF, there are three key chemical reactions, including hydrolysis of cellulose, isomerization of glucose, and dehydration of fructose. Hydrolysis and dehydration steps need Broslash;nsted acid catalysts, while isomerization step requires Lewis acid as a catalyst. Most researches have focused on metal-based catalysts for producing HMF from cellulose such as chromium and lead based catalysts, however, they have been suffered from toxicity and high cost. For these reasons, developing novel, green and cost-effective heterogeneous catalysts for utilization of cellulose is necessary.
Carbon materials are attractive candidate to reduce the dependency of metal-based catalysts for environmental acceptability and sustainable catalysts. Among them, graphene oxide (GO) and its derivatives are fascinating to investigate in the context of catalytic performance and mechanism due to their unique properties such as two-dimensional structure, high surface area, and various functional groups. Furthermore, functional groups of graphene oxide is easily modifiable to different structures, and the graphitic platelets are useful to incorporation of heteroatoms by structural rearrangements to accommodate these atoms.
It has not been reported to develop graphene-based catalyst for producing HMF from cellulose in one pot reaction. Moreover, carbocatalysis allows facile recovery after reaction and contributes to develop green prototype for utilization of cellulose.
In this research, we successfully synthesized boron-doped sulfonated graphene oxide (BS-GO) and apply them to a catalyst for producing HMF in a single step. The empty orbital of boron atoms acted as Lewis acid, while sulfonated group works as Broslash;nsted acid, respectively. Doping ratio is identified by XPS and EA measurement, and HMF yield is confirmed by HPLC. Boron atom is doped into graphene lattice about 4.78% and sulfonated group is introduced about 1.02%. We control the reaction temperature (130 - 150 ^oC), time (0 - 12 h), loading of catalyst, and pressure (0.1 - 0.4 MPa) to obtain optimized yield of HMF, leading to the successful conversion of HMF with 89.7% yield within 3 h from fructose.

Reduced graphene oxide (rGO) was looked at as a capacitor electrode material due to its high theoretical surface area. RGO can be thought of stacked sheets of imperfect graphene with irregular layer spacing. Graphene oxide (GO) started as an aqueous solution and was dropcasted onto Kapton films. Once dried, RGO was synthesized from GO using four different methods, a chemical etch using .1 M ascorbic acid (AA), a thermal reduction using a heat gun, and two laser methods: using a LightScribe CD/DVD burner and another using a CNC controlled laser cutter. The rGO samples were used to make 2.5 cm x 2.5 cm parallel plate capacitors and their capacitances were compared. Kapton dielectrics of 25.4 micrometer thicknesses were used and allowed for the theoretical capacitance of 765 pF to be calculated. Reduction by AA resulted in a capacitance of 360±31.3 pF, the thermal reduction returned a capacitance value of 148±7.5 pF, the LightScribe method returned a capacitance value of 630±400 pF, and the laser etch returned a capacitance of 270 pF. For comparison, a parallel plate capacitor of the same size was created using aluminum foil electrodes which measured 188 pF, roughly 25% of the theoretical value. An electric double layer capacitor was also created using paper soaked in KOH as a separator and electrolyte returning a capacitance value of 7000 pF.

Graphene-like nanoribbons and nanostructures with 3D epitaxy were produced in copper, silver and aluminum metals by the application of a high DC current to the liquid metal containing particles of activated carbon. This technique allows for incorporation of carbon in concentrations up to ~30 at% in metals such as Ag and Cu, far in excess to the solubility limit in the ppm range indicated by the binary phase diagrams. These materials, referred to as “covetics”, show high conductivity compared to composites or alloys containing the same amount of carbon. The incorporation of carbon in silver covetic gives rise to 3D epitaxial structures of highly defective graphene-like ribbons and sheets.^[1] These nanostructures have primarily sp2 bonding as evidence from EELS and Raman spectroscopy data. We present simulations from Density functional theory which predict bonding between carbon and silver at vacancies and edges of the graphene-like ribbons. First principles calculations of the dynamic matrix of Ag and Al covetics predict a phonon density of states with Raman active modes corresponding to bonding between C and Ag/Al and which agree with our Raman scattering results that show weak modes in the region of 500 to 1,000 cm^-1. Copper covetic with C content up to ~15 at % shows a different structure for the incorporation of C in the lattice compared to Ag and Al covetics. We have used the bulk Cu covetic as target for the deposition of copper covetic films by e-beam evaporation and PLD. The films show higher transparency and greater stability compared to pure copper films of the same thickness.^[2] We present a comparison of the structure and electrical properties and the strain of the graphene-like regions of covetics with different host metals.
* Funded by DARPA/ARL under Grant No. W911NF-13-1-0058, and ONR Award No N000141410042.
[1] L. G. Salamanca-Riba, R. A. Isaacs, M. C. LeMieux, J. Wan, K. Gaskell, Y. Jiang, M. Wuttig, A. N. Mansour, S. N. Rashkeev, M. M. Kuklja, P. Zavalij, J. R. Santiago, H. Liangbing, Advanced Functional Materials 2015, in press.
[2] R. A. Isaacs, H. Zhu, C. Preston, A. Mansour, M. LeMieux, P. Y. Zavalij, H. M. I. Jaim, O. Rabin, L. Hu, L. G. Salamanca-Riba, Applied Physics Letters 2015, 106, 93108.

The unique chemical and physical properties associated with carbon based materials has led to the increased interest in the fabrication and characterisation of novel carbon nanomaterials. Of particular importance has been the morphology associated with these materials, since it is the morphology of the carbon material that dictates its properties and applications [1]. With attempts mainly yielding zero, one and two dimensional structures (e.g. fullerenes, carbon nanotubes, graphene etc.), the exploitation of complex, free-standing three dimensional carbon morphologies (network structures) is still finite. This is due in part to the limitations associated with conventional synthesis techniques (e.g. arc discharge, laser ablation, chemical vapour deposition (CVD) etc.) and mechanistic models still being used [1]. Consequently, researchers have begun to focus more attention on the implementation of other methods for the synthesis of carbon structures. In particular, the use of template structures, in an endeavour to gain greater control over the shape of carbon-based nano/micromaterials.
As such, in this study, we seek to demonstrate the array of uniquely shaped carbon materials that one can synthesize via the templating approach, making use of both traditional and non-traditional templates to fully explore the uncharted area of eccentrically designed carbon material.
References
1. Shaikjee, A. and N.J. Coville, The synthesis, properties and uses of carbon materials with helical morphology. Journal of Advanced Research, 2012. 3(3): p. 195-223.

To measure the Raman scattering spectra of a monolayer graphene sample, we describe the design and development of a high-efficiency optical measurement device for operation within the small bore of a high-power magnet at low temperature. Magneto-optical measurements have revealed various novel properties of graphene materials [1]. However, the scattering cross section of monolayer graphene on Raman scattering is rather small. Consequently, the intensity of Raman scattering emitted from monolayer graphene becomes much smaller than the intensity emitted from multilayer graphenes with about 100 layers. It is true that high-efficiency light collection and sub-micrometer depth of focus are easily achievable using high-NA objective lenses and laser sources. However, in practice, the small cryogenic measurement volumes of a sample insert inside a high-field magnet and the destructive thermal shrinking in the cryogenic operation prevent the use of high-quality microscope objectives. Moreover, the long distances of telescopic lens optics within a sample insert can be influenced by the mechanical vibration of high-power magnets. For the high-efficiency measurement of light emitted from this small region, we designed a compact confocal optics with lens focusing and tilting systems, and used a piezodriven translation stage that allows micron-scale focus control of the sample position. We designed a measurement device that uses 10 m-long optical fibers in order to avoid the influence of mechanical vibration and magnetic field leakage of high-power magnets, and we also describe a technique for minimizing the fluorescence signal of optical fibers. The operation of the device was confirmed by Raman scattering measurements of monolayer graphene on quartz glass with a high signal-to-noise ratio. Though the light collection efficiency of the device is about 240-fold smaller than that of a conventional optical microscope, the device has a sufficient collection efficiency for detecting the Raman scattering light of monolayer graphene at the same level as for the HOPG sample.
[1] C. Faugeras, M. Amado, P. Kossacki, M. Orlita, M. Sprinkle, C. Berger, W. A. de Heer, and M. Potemski, Phys. Rev. Lett. Vol.103, (2009) art.186803.
[2] T. Mitsui, Review of Scientific Instruments, Vol.85, (2014) art.113111. DOI: 10.1063/1.4902342

The synthesis of glassy nanosheets of boron, carbon, and sulfur using a modification of a method successfully used to grow a variety of pure boron nanostructures is reported [1]. The process was originally a thermal vapor deposition reaction, performed in an inert atmosphere, and this was altered through the addition of methane and hydrogen sulfide gas. These 2-D nanomaterials have been characterized using the following techniques: Scanning electron microscopy, Raman spectroscopy, Transmission electron microscopy, Optical microscopy, Two probe electrical measurements, Capacitance measurements, Ellipsometry, and UV-Vis spectroscopy. Microscopy revealed that the product consists of flat, very thin (<10 nm), large area amorphous (based on electron diffraction patterns) optically transparent sheets with numerous folds. Electron energy dispersive and electron energy loss spectroscopy indicated that the sheets are composed primarily of carbon and boron with sulfur, magnesium, and nickel impurities. FTIR and Raman spectroscopy showed that the material possesses the following bonds: C-C, S-S, B-C, C-C, and C-S. Electrical measurements indicate these materials are highly insulating, with a potentially large dielectric constant. Ellipsometry and UV-Vis spectroscopy show that the nanosheets possess optical properties similar to fused quartz glass but are strong absorbers of UV radiation with a two shouldered peak absorption of 230 and 260 nm. The unique combination of properties of this novel glass material mean it could find use in optoelectronic applications.
References:
[1] R. B. Patel: Synthesis and Characterization of Novel Boron-Based Nanostructures and Composites. 2013, PhD Dissertation New Jersey Institute of Technology.

In the asymmetric charge storage configuration, faradic reactions are much slower than non-faradaic capacitive charge storage. Thus, a rate capability imbalance occurs between the two different electrodes. Therefore, to create an asymmetric charge storage system, there is a need to develop a rapid-response faradaic electrode. To this end, nanostructured carbon materials (NSCMs) can exhibit a high power density as a faradic electrode due to the short transport path of ions and electrons. Moreover, the pseudocapacitive reaction that occurs at the surface of the NSCMs has a low volume change during the charge insertion and extraction processes, which leads to a stable cyclic performance. Furthermore, one interesting observation is that sodium ions can be stored in NSCMs as fast as lithium ions despite the relatively large size of sodium ions. This is likely due to the pseudocapacitive behavior of the NSCMs, which is less sensitive to the bulk diffusion of ions.
Here, we report ultra-thin hollow carbon nanospheres (UTH-CNs) that can be used as the faradaic electrode of asymmetric sodium-ion supercapacitors. The UTH-CNs were fabricated from regenerated silk proteins and silica nanospheres as carbon precursors and templates, respectively. Due to the ultra-thin, ~3 nm, carbon walls and the hollow morphology of the UTH-CNs, they exhibited fast sodium ion storage behavior, which occurred via a pseudocapacitive reaction. As a result, the asymmetric pseudocapacitors that used UTH-CNs as a faradaic electrode exhibited a capacitance of 186 Fg^-1, a specific energy of 43 Whkg^-1, and a power density of 10 kWkg^-1 as well as superior rate performance, which lasted for more than 1000 cycles.

The modification of individual oxygen functional groups and the resultant optical properties of graphene oxide (GO) suspension were investigated using controlled photothermal reduction by infrared irradiation. The evolution of optical characteristics of GO suspensions was obtained from optical absorption, steady state and time resolved photoluminescence spectroscopy. The results suggest the gradual restoration of sp² clusters within the sp³ matrix with increase of reduction time and illumination power density. The yellow-red emission ( ~ 610 nm) originated from the defect assisted localized states in GO due to epoxy/hydroxyl (C-O/-OH) functional groups, while that of blue one ( ~ 500 nm) was ascribed to the carbonyl (C=O) assisted localized electronic states. With increase in reduction time and IR power density, the intensity of yellow-red emission was found to decrease, with the blue emission being the prominent one.
We have also investigated the nonlinear optical properties of both graphene oxide as well as the reduced graphene oxides by single beam Z-scan measurement in the femto-second region. The results reveal that both saturable absorption and two-photon absorption are strongly dependent on the intensity of the pump pulse. The saturable absorption occurs at lower pump pulse intensity, whereas two-photon absorption dominates at higher intensities. Intriguingly, we find that the two-photon absorption coefficient and the saturation intensity vary with IR induced reduction, which is ascribed to the varying concentrations of sp² domains within the sp³ matrix in the reduced graphene oxides. These experimental findings may open up a new dimension for controlling the optical absorption and emission properties of graphene oxide by tailoring the oxygen functional groups, leading to the potential application of graphene based optoelectronic devices.

After the Noble Prize for graphene isolation in 2004, this one-atom thick graphitic material has received great attention world-wide due to its exceptional optical, mechanical, electrical and thermal properties. Huge potential has been recognized from both academia and industry in different field like polymer composites, optoelectronics, transparent conductive electrodes, etc. The addition of graphene/graphene nanoplatelets (GNPs) into epoxy, the most used matrix in aerospace area, promises to improve its mechanical, electrical and thermal properties. The GNPs/epoxy nanocomposites possess not only improved mechanical performance, but also the potential to further reduce the weight of current composite components in aircraft, leading to a more sustainable composite design. However, best production methods for graphene/few layer graphene (e.g. ultrasonication) require the use of large quantity of organic solvent, resulting in difficulties in industrial scale application due to costs and environmental impact. Moreover, the yield of these methods is very low, typically 1 to 3%, the control of graphene morphology and dispersion in epoxy remains extremely challenging. Direct in-situ exfoliation/dispersion of graphene in epoxy or other polymeric matrices could promise to tackle the above drawbacks and lead to a viable route to applications. Among the in-situ exfoliation and dispersion methods, three roll mill (TRM) was proven to be very efficient in dispersing 1D nanofillers, carbon nanotubes (CNT) in epoxy, and could be even more efficient in dispersing 2D nanofillers like graphene/GNPs, moreover, the yield is 100%. Unfortunately, very little effort has been dedicated so far to in-situ exfoliation and dispersion of graphene via TRM, and in particular to the optimisation of processing conditions.
A systematic study of the relationship between various processing parameters, structure and final properties of nanocomposites is provided. The optimised processing conditions resulted in five time larger in lateral diameter (from 0.7 to 3.5 µm), three times increase in aspect ratio (from 51 to 153), leading to an eight orders of magnitudes increase in electrical conductivity (from 10^-12 to 10^-4 S/m) and decrease in percolation threshold (from 2.5 to 1.5 wt%). The mechanical reinforcement efficiency of composites manufactured with optimised processing conditions was studied using simple micromechanical models. The storage and flexural modulus were significantly increased by 160 % and 170 % with only 4.0 wt % GNPs loading, which, to the best of the authors&’ knowledge, is the best result ever reported in the scientific literature. The thermal diffusivity of resulting composites was increased by 88-96% from 80 to 100 0C with 5.0 wt.% GNPs loading#65292;and the thermal conductivity was increased by ~100%. In conclusions, this research work provides a guideline for the effective in-situ exfoliation and dispersion of graphene, with great potential on industrial scale-up.

Hereby we report a method to enhance the electronic properties of graphene by increasing the concentration of negative charge carriers. Nitrogen-doped large-area bilayer graphene was achieved by adding NH₃ to the Hot Filament Chemical Vapor Deposition (HFCVD) technique. A systematic study of the concentration of charge carriers as a function of nitrogen doping was carried out, and the corresponding structural characterization using Raman spectroscopy, FT-IR and X-ray Photoelectron Spectroscopy was performed. The electrical measurements confirm the n-type behavior induced by nitrogen doping in bilayer graphene in comparison to pristine HFCVD graphene. Nitrogen-doped graphene is a promising material for applications in different fields such as electrochemical energy devices (fuel cells, metal-air batteries) and biosensors.

Graphene has attracted considerable attention in recent years due its extraordinary electronic properties, that might potentially turn super-high-speed devices into reality. The hope is that this carbon allotrope hasten a future generation of computer chips, since silicon was pushed to its physical limits. Graphene nanoribbons belong to a growing class of nanoscale carbon based materials with novel electronic, optical and vibrational properties as well as technological potential. Structurally, the nanoribbons stand between the quasi-one dimensional conducting polymers such as polyacetylene and the two dimensional graphene sheet [1]. Graphene nanoribbons might work as a template where it is possible to study how physics is affected by the dimensionality of system.
A great source of physical interest in this type of material is the charge transport. In a recent theoretical work, the charge transport on armchair graphene nanoribbons (AGNR) was investigated. Besides obtaining the experimentally expected charge distribution throughout the lattice, it was found a collective behavior of charge carriers, when subjected to external electric fields. Another theoretical investigation has shown that it is possible to obtain a phase transition between subsonic and supersonic regimes, depending on the electric field applied. It was, thus concluded that the collective behavior presented by charge in AGNR is, in many aspect, similar to what occurs in conducting polymers. Therefore, it is only natural to investigate, in AGNR, phenomena that are already known to affect the charge transport in organic semiconductors in general. An important example of such phenomena that have not yet been explored is structural defects. In this sense, the present work is dedicated to the study of vacancy effects on electronic and transport properties of armchair graphene nanoribbons with several different widths and intensities of external electric fields. It is known that the size of the AGNR is very important to the formation and stability of excitons. Therefore, it is expected that structural vacancies also play important role on the nature of such quasiparticles.
The study will be conducted by using a tight-binding model, which has been successfully applied for the treatment of electronic properties in grapheme. Within this model, it is considered a two-dimensional Hamiltonian with relaxation in a first order of expansion. Concerning the Ehrenfest molecular dynamics, the lattice degrees of freedom are treated by Euler Lagrange equations while the pi-electrons are described by the time dependent Schrodinger equation.

Several extraordinary properties of Graphene (G) have recently been investigated such as their conductivity, mechanical, thermal, and optical properties. Even though these unique properties of G have been explored, there remain many questions to be answered, particularly with regards to the magnetic properties. Moreover, only a few limited experimental studies exist that explore their magnetic properties and these experiments dealt with G on a substrate rather than as "flakes", or with Graphene Oxide (GO) flakes modified by thermal annealing or adatoms instead of direct chemical functionalization. Therefore, we chose to examine the properties of the flakes of GO before and after their "chemical modification" in order to systemically investigate the impact of such changes on their magnetic properties.
GO flakes dispersed in the water phase were used as a starting material in this study. There are several different oxygen functional groups on both basal planes and edges of GO and these are good starting points for the chemical reaction. Moreover, GO is a promising precursor for the mass production of more graphene-like materials (single layer of material) from graphite (multi layers). The various types of electro-withdrawing and donating chemicals with GO at different reaction conditions were systemically investigated. We have observed enhance magnetic properties (moment) after modifying GO with our chemicals.
By adding these means of modifying G&’s magnetic properties to the already known methods for GO, we seek to open a new field for graphene-based materials for device applications such as spintronic, magnetoresistance, and magnetic memory devices. The GO samples were analyzed by Vibrating Sample Magnetometer (VSM), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Solid Nuclear Magnetic Resonance (Solid NMR).

The thermal expansion coefficient (TEC) establishes the relationship between dimensional changes and temperature variations in a material. Most materials present a positive TEC, i.e., they expand (contract) when heated (cooled). However, some materials exhibit negative values for this property (contracting upon heating) or “zero thermal expansion” (ZTE) behavior in specific temperature ranges. ZTE materials are characterized by small values of TEC (<~ 2×10^-6 K^-1), and are suitable for technological applications requiring small dimensional changes when subjected to large and/or quick temperature variations. Here, we report a combined Density Functional Theory (DFT) and classical Molecular Dynamics (MD) study of the thermal expansion properties of two-dimensional carbon-based nanostructures created upon insertion of interlayer covalent C-C bonds in bilayer graphene. Recent experimental studies support the feasibility of such materials, and theoretical studies have shown that the electronic and mechanical properties of the material can be tuned by the fraction and spatial arrangement of sp³-hybridized interlayer bonds. Here, we demonstrate that these nanostructures exhibit ZTE behavior in a wide range of temperatures. We show that by controlling the density of interlayer bonds, it is possible to tune the sign of the TEC of the system (from negative to positive) in a given temperature, and the range of temperatures where the ZTE property is observed. Several materials have been found to present ZTE or near ZTE behavior, but none of them combine special electronic, thermal and mechanical properties as these graphene-based configurations do. Since the miniaturization trends in technology has already reached the nanoscale, the ZTE property of this graphene-based nanostructure can be of great utility in several applications such as in nanoelectronics, nanoelectromechanical systems, sensors and thermoelectric nanodevices.

Graphyne (GY) is a two-dimensional one-atom-thick carbon allotrope that possesses both sp and sp2 hybridizations. Its structure can be formed by coherent replacement of different carbon-carbon bonds in a graphene hexagonal network by acetylenic linkages (-Cequiv;C-).^1,2 Although its structure has been proposed in the 80s,³ the recent interest on GYs comes from the prediction of non-zero band gap and mechanical and thermal transport properties not so different from those of graphene.^1,2 One interesting property of GYs is the thermal expansion. It relates the dimensional changes of an object to the variation of temperature. GYs have been shown to present negative thermal expansion behavior.^4,5 In this work, we present the calculation of the thermal expansion coefficient (TEC) of seven different GY structures by means of classical molecular dynamics (MD) simulations. To our knowledge, it is the first thermal expansion study of GYs based on a classical MD study. Also, we present the TEC of some different GYs not considered in the previous studies. We have obtained negative values of the TEC, at room temperature, for all types of GYs in agreement with the results from previous ab initio methods.^4,5 However, the absolute values of the TEC of all GYs are larger than that of graphene, what agrees only in part with the previous studies. An interesting trend in the dependence of the TEC of GYs with their density is observed and discussed.
References
[1] A. L. Ivanovskii, Progress in Solid State Chemistry41, 1-19 (2013).
[2] Y. Li, L. Xu, H. Liu and Y. Li, Chem. Soc. Rev.43, 2572-2586 (2014).
[3] R. H. Baughman, H. Eckhardt and M. Kertesz, J. Chem. Phys.87, 6687-6699 (1987).
[4] T. Shao, B. Wen, R. Melnik, S. Yao, Y. Kawazoe and Y. Tian, J. Chem. Phys.137, art. n. 194901 (2012).
[5] N. K. Perkgöz and C. Sevik, Nanotechnology25, 185701 (2014).

Simple and facile synthesis of stacked MnO2/reduced graphene oxide composites driven by the surface charge-induced mutual electrostatic interaction is presented. The electrochemical performance demonstrated that the given composite exhibited an enhanced specific capacity and improved cycling stability as an anode material compared with other graphene-mixed MnO2 composites or nanostructured MnO2. The resultant composites exhibit excellent reversible capacity as high as 1100 mAh g-1, even after 100 cycles at 123 mA g-1 with good rate capability for lithium ion battery anodes.

With the advent of scanning helium ion microscopy, maskless lithography of nanoelectronic devices based on 2-dimensional materials such as graphene has become commonplace. The shorter de Broglie wavelength of ion beams such as He⁺ and Ne⁺ enables the fabrication of features smaller than those achievable with e-beam lithography. Furthermore, the positive charging nature of ion beams may be utilized in qualitatively testing the conductivity of milled graphene nanoelectronic devices in situ. Here, we will discuss the use of energetic ion beams in engineering the local properties of devices and explore the mechanical, electromechanical and chemical properties of the ion-milled devices using scanning probe microscopy (SPM). By using SPM-based techniques such as band excitation (BE) force modulation microscopy, Kelvin probe force microscopy (KPFM) and Raman microscopy, we demonstrate that the mechanical, electrical and optical properties of the exact same devices can be quantitatively extracted. Additionally, the effects of defects inherent in ion beam direct-write lithography, on the overall performance of the fabricated devices will be elucidated.
Acknowledgements
This work was conducted at the Center for Nanophase Materials Sciences, which is a Department of Energy (DOE) Office of Science User Facility

Hysteresis in the channel conductance as a function of gate voltage sweeps is usually observed in graphene field effect transistors, which is detrimental to their deployment in electronic devices. The origin of such hysteresis has been variously attributed to graphene-insulator interface traps, adsorbed molecules and bulk charges in the dielectric. While exfoliation gives rise to pristine graphene samples, scalable and large area synthesis of graphene is realized using CVD which gives rise to defects, such as grain boundaries, in the as-grown graphene samples. These defects commonly act as trap centres and are hence expected to influence the hysteretic behaviour of fabricated graphene devices.
Here we demonstrate for the first time the effect of graphene defect density on device hysteresis. Intentionally tailoring the defect densities in graphene enables us to establish a linear correlation between the defect density and conductance hysteresis. For example, graphene devices with higher defects had lower mobility, higher intrinsic carrier concentration and larger hysteresis and vice-versa. The trap charge densities as calculated from hysteresis in the electrical transfer characteristics was found to both follow the same qualitative trend, and give reasonable quantitative agreement, with the defect density as extracted from Raman spectroscopy. This increase in hysteretic behaviour can be explained as the interplay between defect-induced trap states in graphene and graphene-insulator interface states. Hence, lower defect density in graphene is shown to be attractive for high frequency devices not only due to their intrinsically higher mobilities, but also due to lower hysteresis in the transport characteristics.

We report on the investigation of contact resistance of monolayer CVD grown graphene with a metal-on-bottom topology. The effects of metal-semiconductor work function difference and graphene defect density on the contact resistance have been investigated. We find the contact resistance to decrease with work function difference as well as defects in CVD grown graphene. In comparison with the contact resistance of 6500±2400 #8486;mu;m obtained with the conventional metal-on-top architecture on a 25 mu;m wide device, the lowest contact resistance of 1200±250 #8486;mu;m obtained with Palladium on a defective graphene, is not only lower in the absolute value, but also on consistency of the measured values. The lower contact resistances observed on defective graphene with the same metal was attributed to the increased number of modes of quantum transport in the channel.

Although polycrystalline graphene generated by chemical vapor deposition features defects at grain boundaries, experimental results show that the strength of polycrystalline graphene is comparable to that of the pristine graphene. This is in contrast to the widespread knowledge that defects typically weaken a material&’s strength. Here, we examine why polycrystalline graphene has high strength and high fracture toughness, by combining an innovative algorithm with classical molecular dynamics simulation to systematically build well-stitched (99.8% heptagon and pentagon defects without void) polycrystalline graphene models with regular and irregular grain boundaries, and use these models to systematically examine the fracture toughness of polycrystalline graphene composed of grains of different characteristic length. Our study reveals that polycrystalline graphene under fracture releases up to 50% more energy than the pristine graphene. Per mechanism, we find that grain boundaries increase the critical energy release rate to fracture by reducing stress concentration and making branches near the crack tip. We conclude that these effects are likely governed by the out-of-plane deformation of polycrystalline graphene.

Carbyne is an allotropic form of the carbon based on the sp-hybridization of carbon atoms. It can be linear or form cycle structures which can be semiconductors or metals depending on the type of chemical bonds between carbon atoms. Diagnostics of carbyne is technically rather complicated due to transfer of carbyne into other forms of carbon under use of high-energy methods.
The present paper suggests a new nonobservational method of the carbyne electronic structure calculation taking into account effects of the spin-orbit coupling. The method is illustrated by calculations of splitting of states at the Fermi level in cumulene and polyyne carbynes having semiconductor and metal electronic structures accordingly.
Linear method of augmented cylindrical waves is a distribution of the Slater method of augmented plane waves in the case of nanotubes and realized in the form of a specially configured computer program.
Calculations have shown that spin and orbit motions of electrons are interacted that leads to splitting of fourfold degenerate energy levels. Nevertheless, each p subband possesses a two-fold degeneracy that is a consequence of the Kramers theorem on symmetry in relation to time reversal and presence of the inversion center in carbynes. As a result, the spin degeneracy remains and directions of the spin polarization of degenerate bands are opposite to each other. Spin-orbit splitting of the orbitally nondegenerate s band is absent.
A polyyne carbine has a semiconductor type of the band group structure with a gap equal to 1.14 eV between the bonding state and antibonding state. Spin-orbit interaction leads to spin-orbit splitting of states of the valence band and conduction band. In particular, at the boundary of the Brillouin zone, disintegration energy induced by the spin-orbit interaction is different for the highest level of the valence band (3.1 meV) and the lowest level of the conduction band (2.1 meV). In the absence of spin-orbit interaction, there is a band intersection at the Fermi level in the center of the Brillouin zone in a metal cumulene carbyne. Taking into account spin-orbit interaction, the band structure becomes more complicated and Fermi energy intersects two bands. The present calculation has shown an appearance of the direct optical gap 2.5 meV in the area of Fermi energy, but metal character for the cumulene system is not broken by the spin-orbit interaction.
So, the paper studies theoretically the electronic structure of cumulene and polyyne carbynes taking into account effects of the spin-orbit coupling. The obtained values of spin-orbit gaps equal to 2 - 3 meV reasonably match to the inverse relationship of the spin-orbit splitting diameter in carbon nanotubes. So, spin-orbit gaps in carbynes are expected to be about 2 meV. This value is enough for significant influence on the carbine quantum conductivity.

Graphene oxide (GO) is a versatile, solution-processable, candidate material for next-generation, large-area ultrathin electronic, optoelectronics, or energy technologies. To characterize the GO, as dependent on the synthesis method, we calculated the Raman spectroscopy intensity ratio I(D)/I(D') based on realistic material models. First, generation of realistic GO material models, including functional group formation, concentration, and distribution is reported, based on molecular dynamics (MD) simulations with the LAMMPS package using the reactive ReaxFF force-field, chosen for its ability to accurately describe bond-breaking and formation events in hydrocarbon systems. To model chemically grown GO, the initial structure was set-up with randomly distributed epoxy and hydroxyl groups attached to both sides of the single-layer graphene (SLG) sheet. The structure was then annealed computationally at 300°K by MD simulations. To model oxygen plasma and oxygen gas synthesized GO, bombardment of the SLG sheet with hyperthermal atomic oxygen was performed. The so-called epoxide, defect formation and growth regimes before breakup of the SLG sheet into a number of gaseous species, were observed in the simulations. Based on resulting realistic GO models, the defect-induced Raman intensity ratio demonstrated that GO generated by different synthesis methods can be distinguished. Finally, the Raman I(D)/I(D') intensity ratio evolution with time in the continuous bombardment of the SLG sheet with hyperthermal atomic oxygen can explain the observed dependence on the time of exposure of graphene to oxygen plasma.

Graphene is a promising material for energy storage due to its exceptionally interesting and unique properties. Our present work is focused on rapid, chemical free and low temperature method for high throughput production of graphene by the reduction of graphene oxide using focused solar radiation. The simple method of preparation, easy scalability, cost effectiveness and high electrical conductivity of solar power reduced graphene holds great promise for supercapacitor applications. At first, graphite oxide is synthesized by simplified Hummers method at room temperature. Then, as prepared graphene oxide is reduced by focused solar radiation using a common magnifying convex lens. The obtained graphene is characterized by Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectroscopic (FTIR) techniques for surface, structural and functional group analysis. Charge storage measurements have been studied in detail. The fabricated supercapacitor cell shows high specific capacitance of 269.5 F g^-1 . Ultra high energy density has been ontained using ionic liquid as electrolyte, where it reaches 81.3 Wh Kg^-1.

Zigzag graphene nanoribbons (ZGNRs) are receiving attention for carbon-based spintronics materials due to the spatial edge states. In view of the revelation of the half-metallicity in ZGNRs, we have studied the angle dependency and layer selectivity in bilayer ZGNRs with AB-β stacking forms by means of the density functional theory (DFT) calculations. As a result, it was shown that properly chosen electric field strength and direction can reduce the required field intensities and give rise to layer-selective electrical currents. In bilayer ZGNRs, only the AB-β stacking form shows the edge states contrasting to other stacking forms. We expand our work to multilayer ZGNRs and show that they also exhibit angle dependency and layer selectivity as in the bilayer ZGNRs. In particular, the trilayer ZGNRs with distinct stacking forms were investigated by means of the density functional theory (DFT) calculations
Reference
[1] Jeon. G. W., Lee. K. W., Lee, C. E., Layer-selective half-metallicity in bilayer graphene nanoribbons, Scientific reports. 5, 9825

We report on Molecular Dynamics (MD) simulation studies aimed at understanding how and under what conditions graphene layers separate during polymer stamp assisted large area mechanical exfoliation. Our reported experimental results [1] using this technique have shown clear evidence of separation of large area (~ square centimeters) albeit multi-layer graphene from a highly ordered pyrolytic graphite (HOPG) substrate. The exfoliation technique separates the layers from the HOPG substrate by manipulating the adhesion properties of a Polydimethylsiloxane (PDMS) stamp and other key process parameters such as the normal contact force, exfoliation speed, and stamp dwell time. The exfoliated layers, albeit of varying thickness, possess regions that are tens of nanometer thick and contain various topographical features such as bubbles, wrinkles, and compressed regions. Understanding the exfoliation process through atomistic modeling and simulation can provide considerable qualitative (and potentially quantitative) insight into the roles of the different process variables and pre-existing geometric defects in the starting material on the exfoliated layer characteristics (e.g. number of exfoliated layers, features produced, etc.).
The MD model of the PDMS stamp-HOPG interaction was built using the LAMMPS software. The AIREBO potential function was used to model the interactions of the carbon atoms in a given layer while the Lenard Jones potential was used to model the van der Waals interactions between the layers. The results suggest that a number of different mechanisms are active during the separation of layers. Although the physical exfoliation experiments were performed as a pull test, the simulated layer separation mechanisms are seen to be a variant of the traditional peel test. These mechanisms are classified based on the starting location of the crack, which determines the nature of its propagation. MD simulations also indicate that gradual control of the exerted normal contact force between the PDMS stamp and the HOPG results in exfoliation of few-layer graphene. Initial raw material imperfections such as discontinuous layers play a significant role in determining the number of exfoliated layers. In such cases, layer separation occurs right below the discontinuous layers. These layers move laterally before exfoliation occurs. The trend of the simulated exfoliation force is seen to be in qualitative agreement with the experimentally obtained force signatures. The fundamental understanding derived from this study will serve to inform the experimental campaign as well as aid in fine-tuning the process as scale-up of the PDMS-based mechanical exfoliation process is attempted.
This work is supported by the Morris M. Bryan Jr. Professorship of the second author.
[1] B. Jayasena and S. N. Melkote, "An Investigation of PDMS Stamp Assisted Mechanical Exfoliation of Large Area Graphene." Proceedings NAMRI/SME, June 2015, to appear in Procedia Manufacturing

Graphene has attracted a lot of attention due to its exceptional electronic properties, and it is one of the most promising candidate materials for large-scale integration (LSI) interconnects. High crystallinity graphene is required because of its low resistivity. Presently, “in-plane” high crystallinity has been achieved by chemical vapor deposition (CVD). However, the stacking order of multi-layer graphene (MLG) is also expected to have an influence on the electrical properties of MLG. Here, we demonstrate the low-temperature synthesis of MLG by CVD on 300 mm wafers and discuss the relationship between in-plane crystallinity and the stacking order of MLG.
MLG was synthesized by thermal CVD at 650 °C, using C₂H₂, H₂, and Ar as source gases, on a physical vapor deposition (PVD-) or CVD-Ni catalyst deposited on 300 mm Si wafers^[1][2]. It is well-known that the in-plane crystallinity of graphene can be evaluated from the ratio of G peak intensity and D peak intensity (G/D ratio) in the Raman spectrum. By changing the CVD process conditions and controlling the surface conditions of a Ni catalyst, the G/D ratio can be controlled from 1 to 50 or more. Conversely, the stacking order of MLG can be evaluated from the shape of the G&’ peak in the Raman spectrum. The G&’_3DB peak signal and the G&’_2D peak signal are components of the G&’ peak of MLG, and the ratio of G&’_3DB peak intensity and G&’_2D peak intensity (G&’_3DB/G&’_2D ratio) correlates with the stacking order of MLG^[3]. The G&’_3DB/G&’_2D ratio tended to increase with an increase in the G/D ratio, but it was not always the case. In addition, the G&’_3DB/G&’_2D ratio showed a large difference between high crystallinity (G/D ratio > 50) CVD-MLG and mechanically exfoliated highly oriented pyrolytic graphite (HOPG) with the equivalent G/D ratio. This indicates that the stacking order of MLG, determined during growth, depends not only on in-plane disorder such as defects or grain boundaries but on other elements probably due to the growth mechanism of the layer-structure material.
This work was performed as “Ultra-Low Voltage Device Project” funded and supported by METI and NEDO. A part of this study was supported by AIST, Japan.
[1] D. Nishide et al., Abstract of ICDCM 2014, O8B.1 (2014).
[2] T. Matsumoto et al., Abstract of 2014 MRS Fall Meeting, K10.25 (2014).
[3] L.G. Canccedil;ado et al., Carbon, 46 (2008).

A novel approach to manipulating the electronic properties (conductivity and work function) of graphene paper suggested here allows for the facile fabrication of large area flexible conductive films with a wide range of conductivities from common insulators to semiconductors and semi-metals. A layer of anodic metal deposited on the surface of the graphene oxide paper is used to fast and ambient reduction of graphene oxide to the electrically conductive state at predetermined depth. By controlling the treatment duration and defect-removal rate, the electrical conductivity can be increased over six orders of magnitude from about 10^-2 S/m for the pristine graphene oxide film up to 1.5x10⁴ S/m for the fully reduced graphene paper, which is one of the highest among those achieved by the reduced graphene oxide papers. The work function of the reduced graphene paper monotonously decreases from 4.9 eV to 4.2 eV by varying the acidity of the reducing environment. This spontaneous electrochemical reduction process involves no toxic reagents, or any external energy input, differentiating from the conventional graphene oxide reduction techniques. We suggest the mechanism responsible for this process involves the balance of the internal potential drop due to the electric resistance of the reduced layers of graphene oxide and the diffusion of oxygen containing species to the reduced monolayers. The vast adjustable range of the electrical properties resembles the similar capability of silicon through heavy doping, opening a new avenue in the post-treatment of the graphene oxide flexible films. This metal-assisted electrochemical reduction technique is facile, environmentally friendly, and adaptable for large-scale fabrication of the flexible and lightweight thin film electronic devices for sensing, energy storage, wearable electronics, and logic processing where the interfacial charge transportation characteristics are critical.

Ionic transport properties and ionic selectivity are major attributes to consider when developing novel materials for separation technologies, used in a wide range of such as water purification and pharmaceutical and fuel separation. Recently, lamellar nanoporous materials made from graphene oxide (GO) nanosheet were shown to have ultrahigh water permeability, while ionic and molecular permeability has a sharp size cutoff at hydration radii of ~ 4.5#8491;. [1] GO membrane consists of percolative network of channels with narrow height distribution in sub-nanometer regime; it has been postulated that the size-exclusion mechanism is governing the membrane&’s filtration properties.
In this work, we demonstrate that the charge-selection is an important transport mechanism, which could be used to further enhance the membrane&’s properties, particularly for desalination applications. Although we observe exponential ionic size-dependence in permeability of cationic species, this relation does not hold when comparing anions and cations. GO membranes have order of magnitude smaller permeability for negatively charged Cl^- ions compared to that of positively charged K⁺ ions with very similar hydration radius. We postulate that the negatively charged functional groups inside the GO nanochannels are responsible for electrostatically repulsing co-ions. The charge selectivity of the membranes is modulated by electrolytes&’ solute concentration and pH, which influence the surface charge density of the oxygen groups. We will discuss how this observation could help us to further increase membrane&’s ionic rejection rate, while retaining the ultrahigh water flux.
References
1. Joshi, R.K. et al. Precise and Ultrafast Molecular Sieving through Graphene Oxide Membranes. Science 343, 752-754 (2014)

Graphene oxide (GO) is incorporated into polyamide-11 (PA11) via in-situ polymerization to make a composite that has significantly reduced hydrolytic degradation during accelerated aging. To determine hydrolytic aging, the material was first immersed in water at elevated temperatures of 100 and 120 #730;C. The extent of hydrolytic degradation was then characterized by multi angle laser light scattering measurements of the decrease in the PA-11&’s mass-average molecular weight (Mm). Unloaded PA11 had an aged equilibrium molecular weight of 23 and 24 kDa at 100 and 120 °C. At a loading of 0.1 percent by weight, a significantly higher equilibrium molecular weight of 33 and 34 kDa at 100 and 120 #730;C was observed. The decrease in the rate of degradation and resulting 50% increase over unloaded PA11&’s equilibrium molecular weight is attributed to the highly asymmetric and planar nanosheets of GO, which we suggest inhibits the mobility of water. Similar changes in the GO-PA11&’s properties were found by measuring the changes in the polymer's crystallinity, water uptake, and gas transmission. Techniques to reduce degradation and extend the polymer lifetimes are of fundamental and practical importance. PA11 is commonly used in flexible pipes for transporting oil, particularly from wellheads to offshore platforms. A GO-PA11 composite with significant resistance to hydrolysis degradation has important implications for longer and safer material lifetimes.

In this work, we investigate the structure and electrochemical properties of hybrids from graphene (supercapacitive) and transition metal oxides such as cobalt oxide (pseudocapacitive) polymorphs namely, cobalt(II) monoxide; CoO with periclase (rock salt) and cobaltosic(II,III) oxide; Co₃O₄ with spinel structures as high-performance electrochemical electrodes for alternative energy, electrochemical sensing and electrocatalysis owing to their higher specific capacitance, wide operational potential window and stability through charge-discharge cycling, environmentally benignity, cost-effective, easily processable and reproducible on a larger scale. To accomplish this, we design and synthesize by direct anchoring of CoO and Co₃O₄ on the surface functional groups of graphene oxide (GO) and reduced graphene oxide (rGO) result in CoO/GO, Co₃O₄/GO, CoO/rGO and Co₃O₄/rGO. This approach affords chemical/ physical adsorption with enhanced coupling between pseudocapacitive metal oxides and graphene derivatives leading to higher surface reactivity by creating tailored interfaces. We used a range of complementary analytical techniques to characterize structural and physical properties include electron microscopy combined with electron diffraction, x-ray diffraction, atomic force microscopy, electrical properties, Fourier transform infrared and resonance Raman spectroscopy with Raman mapping. All of these techniques reveal surface morphology, local and average structure, and local charge transfer due to the physically (and/or chemically) adsorbed cobalt oxide highlighting the surface structure and interfaces. The latter allows determine the charge transfer properties by plotting the variation of prominent Raman bands (i.e. 2D vs. G). The present findings are indicative of grade-quality of the synthesized hybrids as advanced electroanalytical platforms. We acknowledge WKU RF and the department in parts for financial support.

In this work the strutural and thermodynamic properties of adamantane molecule have been investigated using the density functional theory (DFT) formalism considering both the generalized gradient (GGA) and local density (LDA) approximations. One or ten carbon atoms have been substituted with Si to form C₉Si₁H₁₆ or Si₁₀H₁₆ (sila-adamantane), respectively. The values obtained to structural stability showed that the sila-adamantane and C₉Si₁H₁₆ are more stable than pristine adamantane. The enthalpy, entropy, free energy and specific heat at constant pressure are also calculated, whose dependence with the temperature are discussed.

In order to understand the surface chemical properties of graphitic nanoribbons (GNRs), adsorption of two model aromatic compounds e.g. nitrobenzene (electron withdrawing) and aniline (electron donating) has been studied on pristine GNRs, nitrogen doped GNRs (N-GNRs) and GNRs oxidized by hydrogen peroxide and ultraviolet radiation (ox-GNRs). High pressure liquid chromatography (HPLC) methodology was employed for determining the amount of adsorbed aromatics. Adsorbent&’s point of zero charge was determined by the mass titration method with aqueous dispersions. The surface chemistry of all types of GNRs was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction techniques (XRD) and Raman spectroscopy. The chemical surface characteristics of GNRs were also compared with two commercially available activated carbons with predetermined acidic and basic surfaces.

There is growing interest in the scalable synthesis of graphene oxide membranes for separation applications by understanding and controlling the selective transport of small molecules. In an effort to shed light on water molecule transport through graphene oxide nanochannels, we have used classical molecular dynamics simulations of model systems containing water molecules between graphene oxides membrane layers. The simulations considered 6 different hydration levels. The simulation cell had 45000 to 65000 atoms with a C/O ratio of 4 and hydroxyl group functionalization. The layer spacing was found to vary from about 8 Å in dry membrane to 11 Å in well-hydrated membrane in good agreement with experimental observations. These simulations have been augmented with Born-Oppenheimer molecular dynamics simulations of smaller model systems, with hydroxyl group and epoxy group functionalization to explore the water-graphene oxide interaction. This hierarchical modeling scheme has shed light on the proportions of bound and free water molecules, water clustering, proton hopping, and the diffusion of water molecules. When seen in light of experimental spectroscopy studies, these simulations offer insights into two-dimensional water channels and water transport in the confined environment of graphene oxide membranes.

Several techniques can be used to transfer CVD graphene, among them the polymer supportive layer-based transfer, usually poly(methyl methacrylate) (PMMA) is widely reported. In this technique, first PMMA is spin coated on graphene/metal substrate surface, followed by the metal etching. PMMA/graphene stack is scooped onto a target substrate, followed by PMMA/graphene baking step in order to improve graphene-substrate adhesion. In the last step the supportive layer is etched away by annealing or dissolution in acetone. This fast low-cost method can produce high quality graphene, but has some drawbacks related to the presence of PMMA residues whose total removal is still challenging. PMMA residues on graphene surface can induce p-doping effect and act as centers of carrier scattering, decreasing carrier mobility and leading to a low-quality graphene. Due to the strong interaction between the PMMA and the graphene layer, the etching process can introduce structural discontinuities such as tearing and cracks which are not desirable. In this work we studied the influence of each parameter regarding the PMMA transfer technique. The discussion is centered on the evaluation of how the concentration of a second layer of PMMA affects transfer results. The influence of baking time and temperature of PMMA/graphene/SiO₂/Si stack in order to enhance graphene/substrate contact was also evaluated. This work aims to identify the influence of each step of PMMA-based transfer in graphene morphology, structure and electrical properties thus proposing an optimization of the graphene transfer process. Optical microscopy and atomic force microscopy (AFM) results showed that a double layer of PMMA can enhance or degrade graphene quality depending on its concentration. When properly diluted (15% in anisole, resulting in a PMMA layer of 1.35%) the transfer technique using double layer PMMA produces high quality graphene with fewer PMMA residues, non-cracked surface and sheet resistance around 247 ohm/square. By Raman results we observed that adding a second PMMA layer did not result in G mode shift, although the so-called disorder-induced Raman mode (D band) at 1350 cm^-1 (laser excitation at 2.41 eV) has been found to be more pronounced when using two layers of PMMA 4.5%, thus suggesting that PMMA residues contributed with the rising of D band intensity. We also investigated the influence of different baking times and temperatures, and our results pointed out that increasing baking time (up to 45 minutes) can degrade graphene quality thus leaving higher amounts of PMMA residues on the graphene surface

Producing large-scale graphene films with controllable patterns is an essential component for graphene-based nanodevice fabrication. The patterning of graphene is a powerful approach for tuning its physical and electronic structure and for device-integration, including ultrahigh frequency analog amplifiers, electrical interconnects and conduits for heat dissipation. In parallel with top-down nanotechnology for patterning graphene, significant advances in the bottom-up approaches or directly patterning graphene have made it possible to produce patterns with long-range order. On directly patterning graphene, since the patterning step is carried out before graphene growth, the amount of contamination is potentially minimized, which could produce higher quality graphene devices. Electron-beam evaporation and ink-jet printer have been reported as the main techniques to passivated metallic substrates prior graphene growth. Despite of potentially minimizing the contamination on graphene surface, there are some limitations on barrier guided growth of graphene patterns such as difficulties in controlling growth orientation or assembly and high cost of some deposition techniques, such as electron-beam evaporation which can be an obstacle for large-scale fabrication. In this work we present a further study on this subject focusing on atomic layer deposition (ALD) and spray-pyrolysis as deposition techniques of Al₂O₃ to produce patterned graphene through area-selective CVD growth. In this report, a systematic study was conducted to determine how key process parameters, number of cycles and purging time for ALD, and deposition time and concentration of precursor solution for spray-pyrolysis, affect the morphology and the electrical properties of both graphene and Al₂O₃ layers. Our results showed that by ALD, the passivation layer deposited with 120 cycles proved to be unstable and was damaged during transfer process, which eventually contaminates graphene layers as shown by AFM and electrical measurements. On the other hand, using 200 cycles was possible to obtain more continuous and uniform layer of Al₂O_3, and even with Raman spectroscopy showing the growth of disordered graphene structures, conductivity was significantly hindered. Also, it was possible to conclude the importance of purging time to protect efficiently pre-selected areas on copper during Al₂O₃ deposition, which resulted in high quality graphene upon growth step. Purging times of 30 sec led to copper contamination by ALD by-products, while purging times of 45 sec efficiently protected the pre-selected areas on copper. Our results also suggested that spray-pyrolysis as deposition technique has high potential to produce large area patterns. Properly tuning deposition parameters (5mg/mL for initial precursor concentration and 30 sec of deposition time) it was possible to suppress graphene growth on passivated regions and obtain high quality graphene grown on pre-selected areas.

Graphene, the few carbon atomic layers in a honeycomb lattice, is regarded as an excellent candidate for the applications of chemical sensing and biosensing, because of its extremely high surface area to volume ratio, readily molecular adsorption and sensitive electrical response to adsorption. Typically, the gas molecules are physisorbed (weakly bound) on graphene and become the electron donors or acceptors to graphene. Oxygen molecules are the dominant adsorbates on conductance response of graphene. The carrier density of graphene is correlated to the density of O₂, so adsorption results in the change of carrier density. It is assumed that the number of electron transferred per O₂ is constant and the adsorbed O₂ does not affect the charge mobility of graphene. Hence the conductance change is proportional to the area density of O₂ on graphene. Therefore the conductance response of graphene can be utilized to observe and monitor the O₂ adsorption and desorption, making graphene an ideal system to study the kinetics and mechanism of adsorption and desorption.
In this work, we study the UV-laser photodesorption kinetics by conductance response in air. The conductance response of graphene on photodesorption has been studied recently. Photodesorption is a photophysical/photochemical process to efficiently achieve surface treatments. The density of adsorbates on surface can be controlled by photodesorption. The graphene is grown on Cu foil by chemical vapor deposition and transferred to SiO₂/Si substrate. The graphene is placed in an air-tight chamber to keep the relative humidity at 40 % at room temperature. A 325 nm UV He-Cd laser is applied to desorb the gas on graphene. The conductance response of graphene on photodesorption follows the exponential function e^-t/td of exposure time t, where t_d is the photodesorption time constant. Analytical expressions of the power-dependent photodesorption kinetics of graphene in ambience are derived. The photodesorption time constant t_d can be expressed as a function of the adsorption time constant t_a, desorption cross section, and photon flux density. In addition, the steady occupation fraction on graphene is equal to t_d/t_a. It is suggested that the photodesorption of O₂ on graphene is attributed the injection of photogenerated hot electrons and is restricted by the density of antibonding states of O₂.

Silicon carbide (SiC) is a primary substrate for high quality epitaxial graphene growth. Grown on the carbon face of silicon carbide (SiC(000-1)), graphene features higher carrier mobilities compared to graphene grown on the silicon face.[1] However, graphene growth on SiC(000-1) is significantly different from the well controlled monolayer graphene growth on the silicon face. On the carbon face, a (3x3) surface precursor phase precedes graphene growth, significantly altering the growth thermodynamics compared to the Si face.[2] Despite more than a decade of research, the precise atomic structure of the (3x3) surface reconstruction of SiC(000-1) is not yet clear. Here, we perform an ab initio random structure search (AIRSS) employing the van der Waals corrected PBE density functional to identify the reconstruction in the C-rich regime close to graphene growth. Our search reveals a new lowest-energy surface reconstruction model that was not reported previously,[3] explaining the very different graphitization behavior compared to the Si face. Simulated STM images are in excellent agreement with previously reported experimental findings.[4,5]
[1] J. Kedzierski, et al, and W. A. de Heer, Electron Devices, IEEE 55, 2078 (2008).
[2] L. Nemec, V. Blum, P. Rinke, and M. Scheffler, PRL 111, 065502 (2013).
[3] L. Nemec, F. Lazarevic, P. Rinke, M. Scheffler, and V. Blum, PRB 91, 161408 (2015).
[4] F. Hiebel, P. Mallet, L. Magaud, and J.-Y. Veuillen, PRB 80, 235429 (2009).
[5] F. Hiebel, L. Magaud, P. Mallet, and J.-Y. Veuillen, J. Phys. D 45, 154003 (2012).

Trilayer graphene can express two discrete phases having different stacking orientations, a metallic Bernal phase and a semi-metallic rhombohedral phase. Existing studies demonstrate that the application of perpendicular electric fields can switch the more thermodynamically stable Bernal phase to the less stable rhombohedral phase. However, the reverse transition, from rhombohedral to Bernal, has only been actualized through cumbersome, thermally-activated surface functionalization using triazine. In this study, DFT simulation is used to assess the possibility of inducing reversible phase change through the virtual application of electric fields of various intensities and unique geometries to Bernal, rhombohedral and mixed graphene trilayers. An experimental assessment is then conducted to evaluate the efficacy of applied electric fields in inducing this reversible phase transition in chemo-mechanically exfoliated Bernal and rhombohedral trilayer graphene using transmission electron microscopy (TEM), scanning tunneling microscopy (STM), and Raman spectroscopy. A memory device employing the controlled phase transition between Bernal and rhombohedral trilayer graphene phases promises superiority to other emergent phase-change memory devices in its speed, reliability, and power economy. The results of this ongoing exploratory study are to be presented at the conference proceedings.

The peculiar band structure of graphene allows for it p or n doping depending on the electronic structure of the supporting substrate which may affect the graphene reactivity. In the case of SiO₂ and Al₂O₃ surfaces, for example, it has been observed (1) that the underlying substrate affects the reactivity of graphene. The use of appropriate substrate patterns with regions with strong and weak coupling with graphene could allow for the selective functionalization of graphene and the development of functionalization patterns.
In this work we use Density Functional Theory to evaluate the influence of Au(111), Cu(111) and MoS₂ substrates on the reactivity of supported graphene as well as on graphene ribbons. As test reactions we consider the dissociative adsorption of H₂, H₂O and O₂.
As a key parameter in surface reactivity is the activation energy barrier of elementary reaction steps, we performed extensive Nudged Elastic Band calculations to obtain the energy profiles along the reaction coordinate of the dissociative adsorption reactions considered. In all cases the reactivity was compared to that of bare graphene.
When graphene is supported on the metal surfaces, the general trend is a decrease of activation energy barriers, being more pronounced on the copper surface. In the case of the dissociative adsorption of O₂, the nature of the metal substrate not only affects the energy barriers but also the reaction mechanism. During the course of the reactions, the graphene height above the surface decreases up to 0.5 A in the case of the Cu(111).
As an example of the influence of the metal substrate on the graphene reactivity, the energy barriers for the dissociative adsorption of H₂O into adjacent H and OH species are 3.19 eV, 2.83 eV and 2.44 eV on bare graphene, graphene on Au(111) and graphene on Cu(111), respectively. The influence of the MoS₂ substrate is less pronounced. The observed differences in reactivities are correlated to the charge transfer processes which occur during the course of the reactions.
In the case of supported graphene nanoribbons, we focused on the reactivity of the edges.
(1) Q. H. Wang et al. Nat. Chem., 2012, 4, 724.

Recently, the thermal decomposition of a SiC surface has been extensively studied, because it allows us to synthesize graphene sheets on a SiC wafer that can be utilized for the fabrication of graphene-based electronic devices. In particular, Si-face of SiC has been utilized for tailoring a large-scale, uniform monolayer graphene sheet. However, the electronic properties of graphene on Si-face are largely different from those of a freestanding graphene. In addition, in spite of many years of efforts, the carrier mobility of graphene on Si-face has remained almost two orders of magnitude smaller than an ideal value. These are ascribed to the existence of buffer layer between the top-layer graphene and the SiC substrate. On the other hand, graphene can be also formed on C-face on SiC and the achievable carrier mobility is one order of magnitude higher than that on Si-face. A weak coupling of graphene layers with the substrate and the absence of the buffer layer are considered the main causes of higher carrier mobility. Here, we investigate graphene on C-face by using noncontact scanning nonlinear dielectric potentiometry (NC-SNDP). NC-SNDP can simultaneously image topography and potentials in an atomic-scale by measuring tip-sample capacitance [1]. Unlike Kelvin probe force microscopy, NC-SNDP is selectively sensitive to potentials induced by dipoles rather than those by monopole charges and contact potential differences. We measured graphene on C-face of a diced n-type 4H-SiC wafer, which was formed by annealing the wafer in Ar atmosphere. The topographic image shows a graphene sheet was formed on C-face. In contrast to Si-face [2], we could not find super-periodic structures of the top-layer graphene. The top layer seems to continuously extend over the surface to some extent but the underlying structures seems to be inhomogeneous. The spatial average of the measured potentials is +0.27 V. This suggests that the existence of positive surface or interfacial dipole moments, oriented from bulk to surface. The existence of the positive dipoles is consistent with a numerical result that work function is reduced by graphene formation on C-face [3]. On the other hand, the detected dipoles have an opposite direction to that of spontaneous polarization in 4H-SiC along c-axis. In addition, each graphene layer has symmetric sp2 charge distribution with no dipole moments. The potential image shows spatially inhomogeneous potential variations ranging from 0.1 V to 0.4 V, which are significantly larger than the contribution from charge density modulating the measured potentials. Thus, our result indicates that spatially inhomogeneous electronic interfacial structures exists between the graphene layers and the substrate, which are responsible for these dipoles.
[1] K. Yamasue et al., (under review).
[2] K. Yamasue et al., Phys. Rev. Lett. 114 (in press).
[3] A. Mattausch et al., Phys. Rev. Lett. 99, 076802(2008).

We synthesized large area and uniform bilayer graphene by hot filament chemical vapor deposition (HFCVD) on copper substrates and oxidized it to obtain ultrathin, uniform and large area graphene oxide (GO). The symmetric and narrow 2D band in the Raman spectrum shows that it is a misoriented bilayer graphene, which was further confirmed by the Moore pattern in the high resolution transmission electron microscopy (HRTEM) images. The angle of rotation between the two graphene layers is 30 degrees as measured by fast Fourier transform (FFT) of the HRTEM image. The as synthesized graphene was transferred onto SiO₂/Si substrate and chemically oxidized to obtain large area graphene oxide ultrathin film. We characterized the large area GO sample by Raman spectroscopy, X-ray photoelectron spectrostrocopy (XPS), and studied its electrical properties by four probe Van der Pauw method. The possible applications of the fabricated GO material will be discussed in light of the modifications of its electronic properties in such ultrathin film.

Graphene oxide (GO) films have attracted significant interest because of their extraordinary mechanical properties. In particular, GO films are known to be highly stable in water, which is a prerequisite for their membrane applications in solution. However, this is counterintuitive because GO sheets become negatively charged on hydration and the electrostatic repulsion between the sheets should make the membrane disintegrate. This apparent contradiction can now be well explained by a long-overlooked factor we have discovered in this study. Our findings show that while neat GO membranes do, indeed, readily disintegrate in water, the films become stable if they are crosslinked by multivalent cationic metal contaminants. Such metal contaminants can be introduced unintentionally during synthesis and processing of GO, most notably on filtration with anodized aluminium oxide (AAO) filter discs that corrode to release significant amounts of aluminium ions. This finding has wide implications in interpreting the processing-structure-property relationships of GO and other lamellar membranes. Strategies to avoid and mitigate metal contamination are also discussed. Further, we demonstrate that this crosslinking effect can be exploited for the template-assisted synthesis of new 2D materials and lamellar structures with macroscopic dimensions, providing new opportunities to study wet-chemical reactions confined in the few nanometers of space between layers.

Understanding of the nucleation and growth mechanisms of nanomaterials in arch plasma synthesis is in its infancy. Coherent Rayleigh-Brillouin scattering (CRBS) can potentially probe the shape and size of the nanoparticles in-situ during the early stage of the nanomaterial growth. Since CRBS probe is essentially dependent on the polarizability of the material [1], theoretical spectroscopy can complement such experiments. Here, we have used time-dependent density functional perturbation theory (TDDFPT) to compute the frequency dependent polarizability and absorption spectra of nanomaterials of different shapes and sizes in a wide range of frequency from static electric field to untraviolet including the relevant frequencies for the CRBS. Comparisons made from spherical objects like C₆₀ and non-spherical objects like carbon nanotubes provide estimate of the anisotropy in polarizability and absorption spectra of these nanostructures. We find a 4-5 times enhancement in the static and dynamic (omega;=3 eV) polarizabilty in the longitudinal direction of carbon nanotubes in comparison to C₆₀, which will help in detection of nanoscale objects in plasma synthesis via CRBS as well as in a wide range of applications.
[1] Shneider and Gimelshein, Appl. Phys. Lett. 102, 173109 (2013).
Supported by the grant through U.S. Department of Energy contract DE-AC02-09CH11466

Effects of an ion bombardment of various materials are explored for the purposes of creating new materials that have advanced properties. In this study, features of the defects&’ formation in the samples of graphene, graphene oxide and silicon by Ar cluster ions irradiation are given. Irradiation was performed by Ar cluster ions with acceleration energy E ~ 30 kV (Exogenesis nAccel00, Boston, USA) and total fluence of Ar cluster ions ranged from 1x10⁹ cm^-2 to 1x10¹³ cm^-2. Samples of multi-layer graphene oxide, mono- (SLG), few-layer (FLW) of graphene and polished Si are used for irradiation experiments. The study of the irradiated samples was conducted by the methods of Raman spectroscopy and atomic force microscopy. In our experiments on irradiation of samples of graphene, graphene oxide and silicon evenly distributed craters/defects formation over the surface by cluster beams is observed. Small pores on the surface of the graphene oxide samples were formed under such parameters, with the mean pore size of 10-20 nm and depth of 2-4 nm. AFM results clearly prove the presence of nanopores on graphene oxide structure. AFM images of irradiated silicon shows formation of craters on surface of silicon with crater dimension of 20 nm in diameter and 1 nm deep. The distribution of craters was concordant with the Gaussian distribution of the mass-to-charge ratio for individual clusters measured using TOF and the size distribution ranging from about 1000 atoms per cluster to 10 000 atoms per cluster. Additionally to AFM irradiated samples of graphene, graphene oxide and silicon was characterized by Raman spectroscopy. Molecular dynamics simulations of individual gas cluster ion impact on suspended graphene sheet and a graphene on a substrate are used for comparison with obtained craters cross section and surface shape.
In addition, in this study characteristics of the defects formation in the samples of graphene oxide by highly charged ¹³¹Xe ⁺²² ions are presented. During irradiation experiments multi-layer graphene oxide were used. Graphene oxide samples with highly charged Xe^q+ (q = 22) at flunces 10¹²-10¹⁵ ions/cm² and with kinetic energy 1.75 MeV were conducted at Eurasian National University (ENU) Astana, Kazakhstan, by using DC-60 Accelerator. The analysis of irradiated samples was conducted by using Raman spectroscopy and the near edge X-ray absorption fine structure (NEXAFS).

As a result of the measurement of the induced acoustoelectric (I_AEC) current in graphene under the influence of a surface acoustic wave (SAW) fluctuation character of acoustoelectric current at low bias voltage (V_bias) is found. The fluctuation nature of I_AEC is manifested in all cases of measurements depending on the action of a SAW and the application of an external electric field near the point of electrical neutrality. Steady electric and fluctuating character of acoustoelectric currents near the electrical neutrality is due to the fluctuation of the electric potential of the electrons and holes in graphene. Large bias voltage V_bias of external electric field is applied to the graphene to effectively suppress the occurrence of the fluctuation potential of electrons and holes, and for large values #8203;#8203;of V_bias strict linear dependence of the I_AEC on V_bias is observed. The parabolic dependence of the induced acoustoelectric current I_AEC in graphene on amplification current I_saw a SAW power is due to the nature of the relaxation of acoustic phonons of piezoelectric substrate, which is dominant in the process of electron-phonon scattering in comparison with analogous process in graphene and inducing acoustoelectric current in it. The sign and magnitude of the induced acoustoelectric current in graphene when exposed to a SAW and an external bias voltage of the electric field are caused by the magnitude and direction of the electromagnetic fields induced by a SAW and an external electric field. At concurrence of a SAW direction and the external electric field, the process of acoustoelectric current induction is intensified while at the opposite direction - I_AEC is dumped by applied bias voltage V_bias and processes of the interaction of these fields between themselves. It is shown that changing the amplitude of a SAW allows you to control the amount and direction of the current in graphene on the surface of the piezoelectric crystal and create a SAW device with graphene coatings.
Also, the in-situ study of graphene Raman spectra under the influence of a SAW and an external bias electric field is conducted. The significant change of the nature of Raman spectra of the graphene and the piezoelectric substrate is associated with the phonon-plasmon in graphene and phonon-electron interaction in piezoelectric crystal, respectively.
These results are of great interest to radio acoustoelectronics and graphene plasmonics for creating a contactless an acousto-optical and communications, acoustoelectronic, nanostructured materials and nanosystems.

Friction and wear are the primary modes of mechanical energy dissipation. Researchers around the globe have been attempting to realize an ultra-low friction state termed “superlubricity”(coefficient of friction <0.01) at the macroscale ever since its first experimental demonstration at nanoscale in 2004, however, the exact mechanism of such realization has been missing so far. In the present study, we discuss the theory aspect of the experimentally observed superlubricity at macroscale in a system consisting of graphene, nanodiamond, and diamond like carbon (DLC). Our simulations suggest that the macroscopic superlubricity originates from an intriguing nanomechanical phenomenon: graphene patches at a sliding interface, wrap around the tiny nanodiamond particles and form nanoscrolls with reduced contact area that slide easily against the amorphous DLC surface, achieving an incommensurate contact (a necessary condition to achieve superlubricity) and near zero coefficient of friction (0.004). The energetics and dynamics of scroll formation leading to the superlubric condition will be presented.
Reference:
Macroscale superlubricity enabled by graphene nanoscroll formation
Diana Berman, Sanket A Deshmukh, Subramanian KRS Sankaranarayanan, Ali Erdemir, Anirudha V Sumant
Science,

The exceptional mechanical, electronic, and thermal properties of graphene render it a highly promising filler for polymer-matrix nanocomposites. While preliminary experiments indeed show significant enhancement in the thermomechanical properties of graphene-polymer nanocomposites even at relatively low loading of filler, our fundamental understanding of structure-property relationships that govern such enhanced material response is yet in its infancy. In this presentation, we report the results of molecular-dynamics simulation studies of the mechanical behavior of grapheneshy;-polymer nanocomposites with the aim of elucidating the underlying mechanisms that govern the mechanical response of these materials. Using a model glassy polymer matrix, we delineate systematic trends in the enhancement of the mechanical stiffness and yield strength of the polymer composite as a function of polymer molecular weight, filler concentration, filler size, and matrix-filler interfacial interaction strength. While the mechanical properties of the polymer composite are inevitably enhanced with filler loading, a key finding of our work is that the filler size has an even stronger effect: substantial enhancement in the mechanical response of the nanocomposite can be achieved even at low loadings of monolayer graphene flakes over the size range of 10-100 nm. For comparison of different filler reinforcement effects in such polymer-matrix nanocomposites, we also present systematic mechanical behavior studies of fullerene-polymer composites and show that, for fullerene fillers, the response is only weakly dependent on filler size with relatively high loadings required for appreciable improvement in mechanical properties. We explain the differences in the response of (0D) fullerene- and (2D) graphene-reinforced polymer-matrix composites through detailed atomic-scale characterization of the nanocomposites and present a simple mechanics model for understanding the filler-size dependent response of the polymer nanocomposites.

Due to its high stiffness, strength and surface area along with its multifunctional properties, graphene is clearly a strong candidate to be employed as a filler in polymer nanocomposites. It is difficult, however, to disperse graphene homogeneously in a polymer matrix because it tends to re#8209;agglomerate and its chemically inert surface can be incompatible with the matrix. In contrast, its derivative, graphene oxide (GO), facilitates dispersion remarkably because of the functional groups on its basal plane. This structural modification, however, reduces its intrinsic stiffness by a factor of ~4 over monolayer graphene. Hence, there is a compromise to balance the improvement in interfacial adhesion with the reduction of intrinsic stiffness, when GO or reduced GO (rGO) are employed as reinforcements.
The mechanics of graphene has been studied extensively, both free-standing and in nanocomposites. We have shown by using the strain sensitive 2D Raman band that the deformation of graphene still follows continuum mechanics on the microscale, and that the interfacial shear strength with a polymer matrix is only of the order of 2 MPa. For multilayer graphene, its reinforcement efficiency is less as a result of the poor interlayer stress transfer, due to the reversible loss of the Bernal stacking of the graphene during deformation. Theoretical studies of the deformation behaviour of GO have predicted a Young&’s modulus of ~250 GPa for monolayer GO. Indentation studies upon GO membrane have found a similar value of Young&’s modulus, but the fundamental mechanisms of deformation of monolayer GO at the molecular level have still not been investigated experimentally.
This study presents a method to monitor the deformation mechanics of monolayer GO using Raman spectroscopy. Individual flakes of monolayer GO have been deposited upon a rigid polymeric substrate. The flakes have been strained by deforming the substrate, with Raman spectra being obtained simultaneously from the GO flakes. It has been demonstrated that the Raman D band undergoes downshift with tensile strain, similar to the behaviour of the 2D band in graphene monolayers. The fundamental rate of band shift per unit strain, however, is only 1/2-1/3 of that of the monolayer graphene. This is likely to be the direct result of damage in the GO lattice due to the oxidation, reflected also in the reduction in Young&’s modulus for GO. Stress-induced Raman band shift have also been used to map the deformation of monolayer GO flake and to determine the strain distribution across a GO flake during deformation on the substrate. In general it is found that there is a better stress transfer efficiency of GO with the substrate compared to that of monolayer graphene as a result of the functional groups on the GO basal plane. The ability to monitor the deformation of GO in nanocomposites will be demonstrated and it will be shown how this is able to elucidate the fundamental mechanisms of reinforcement in such materials.

Demand of graphite is increasing explosively with the energy applications including lithium-ion battery, fuel-cell and nuclear reactor, so that British geological study announced that graphite is a supply risk material which has higher rank than platinum group materials. The manufacturing process of artificial graphite (the Acheson process) was established in 1960s, and it has been used without major modifications, though it is highly energy inefficient. In this work, full graphitization of carbon powders was achieved using microwave heating. Activated carbon powders (G60 and KB) were graphitized by microwave irradiation with the help of impregnated metals. After 5 min of microwave irradiation, the interlayer spacing (d-spacing, d₀₀₂) of G60 decreased from 3.6899 Å to 3.3610 Å, and that of KB decreased from 3.6209 Å to 3.3662 Å. Also, the intensity ratio between the G-band and the D-band in Raman spectra (I_G/I_D ratio) of G60 increased from 0.92 to 3.29, and that of KB increased from 1.54 to 3.26. These values are almost identical to the values of reference graphite powder. (The interlayer spacing is 3.3612 Å, and the intensity ratio between the G-band and the D-band is 3.34.) Graphitization of pitch-based amorphous carbon exhibited similar results in interlayer spacing and I_G/I_D ratio. In addition, we propose critical concepts including the heating mechanism and the penetration depth for better nano carbon fabrication with microwave heating.

Graphene is most interesting two dimensional (2D) material due to its unique properties such as excellent conductivity, ultrahigh carrier mobility, outstanding mechanical and optical properties. Several methods have been used to produce graphene layers such as mechanically exfoliated graphene, epi-growth on SiC, reduced graphene oxide, and chemical vapor deposition (CVD) method. Among them, CVD is a promising process for the growth of large area and high quality monolayer graphene. However, absence of band gap and high sheet resistance of graphene limit its wide optoelectronic applications. One potential solution is to tune the graphene energy structure by controlling the stacking order as in AB bernal stacked bilayer and rhombohedral staked trilayer. Multilayer grown graphene also decreases the high sheet resistance of a monolayer graphene.
In this report, we demonstrate a completely controllable large scale multi-stacked graphene growth by a two-step growth process using a low pressure CVD having two zones of low and high temperatures. On the first step, monolayer graphene is grown on Cu foil using a conventional growth method at 1000#8451;. Then, second growth step is conducted with graphene/Cu foil placed in a heating zone at a reduced temperature of 800#8451;. Activated carbons from the higher temperature zone nucleate and merge on a monolayer graphene surface to produce bilayer graphene. Most of bilayer graphene has been shown to provide a bernal stacking structure over 95%. Controlled synthesis of multilayer graphene has been characterized by scanning electron microscopy (SEM), Raman spectroscopy, UV-Vis spectrophotometer, Fourier transform infrared spectroscopy (FTIR), and aberration corrected scanning transmission electron microscopy (Cs-corrected STEM).
This research was supported by the MSIP (Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (IITP-2015-R0346-15-1008) supervised by the IITP (Institute for Information & Communications Technology Promotion).

A single atom thick, graphene is the youngest allotrope of carbon and has attracted great interest among the scientific community because of its excellent optical, mechanical, and electrical properties. The applications such as transparent and current spreading electrodes, solar cells, and sensors require large-area, defect-free, and single-layer graphene. However, synthesis of graphene to meet the required industry standards is still a challenge. Several previous attempts have focused on exploring polycrystalline or single-crystal Cu, Ni and their alloy to produce graphene. Here, epitaxial chemical vapor deposition (CVD) growth of high-quality and defect-free single-layer graphene with maximum coverage is achieved on thin films (100-300 nm) of cobalt (Co) on SiO₂/Si substrate via high temperature, and low-pressure chemical vapor deposition. The X-ray diffraction analysis reveals the single crystalline Co film on SiO₂/Si substrate, which subsequently enables the formation of very-high quality graphene. A superior Raman 2D to G-band peak ratio (I_2D/I_G) > 7.5 and no defect induced D-band is observed. In comparison, I_2D/I_G for exfoliated graphene is about 3 - 4. An epitaxial growth mechanism is proposed through the combination of microscopic and spectroscopic analysis. This work not only provides valuable information for understanding graphene nucleation and growth mechanism on cobalt, but also gives an effective alternative to exfoliated graphene for future nanoelectronics applications.

Since the inception of graphene research, the goal has been to use this 2D material for next generation electronics. While many theoretical approaches have been suggested to open a bandgap, no gap sufficiently large, scalable, or ordered has been produced. This has led the National Science Foundation to limit funding for graphene and instead focus on other 2D materials that are even more difficult to grow. What is ironic is that this decision is based on very little information about graphene. The lack of a band gap is not due to any fundamental physical reason but is instead due to a lack of ordered material that makes testing theoretical prediction extremely difficult. Disorder makes employing almost all traditional surface science probes nearly impossible; a situation particularly distressful for a pure 2D system. The inability to determine materials properties outside of simple transport measurements is particularly problematic once it is understood that isolated graphene does not exist. It then becomes critically important that we understand the substrate-graphene interaction to make any substantive progress towards graphene electronics. In this talk I will focus on producing a bandgap in highly ordered epitaxial graphene grown on the SiC(0001) surface. I will talk about two works in our group; graphene grown on the sidewalls of SiC steps and new work showing that the first graphene (buffer) layer is a true semiconductor. Graphene grown on sidewalls of trenches shows ballistic transport, exceptional mobilities, low intrinsic doping, and the opening of a band gap. We use a bottom-up, scalable growth method to improve edge order in graphene ribbons. I will present data from both zig-zag and armchair geometries obtained using LEEM, micro-LEED, ARPES, PEEM, micro-ARPES and dark-field PEEM showing that the ribbon geometry is very different in the two forms of edge growth. The results from these experiments complicate simple models for the exceptional transport in these ribbons. I will also present new ARPES data that shows a band gap greater than 0.5eV opening in the pi-bands of the buffer graphene layer. This result is very different from earlier work on less ordered graphene buffer layer films. Surface x-ray data shows that the buffer is not a single-layer system as usually modeled but is instead a two-layer system of graphene and reconstructed SiC bilayer. Both layers are incommensurate with the bulk. This work offers some insight into why the band gap forms in this buffer graphene layer.

Graphene grown on heteroepitaxial 3C-SiC films have attracted considerable interest due to its ability to be synthesized on large-scale, low-cost silicon substrates [1, 2]. We have recently reported a novel alloy-mediated (Ni/Cu) catalytic approach to obtain transfer-free, wafer level, high-quality bilayer graphene on silicon wafer [3, 4]. In contrast with sublimation-based routes, our alloy-mediated graphitization takes place at moderate temperatures (1100 °C) which is compatible with the conventional Si technology. The obtained bilayer graphene demonstrated exceptionally low sheet resistance (~25 #8486;/#9633;) and high carrier concentration (~10¹⁵ cm^-2), which qualifies it as leading alternative to classic metals for efficient conduction at the nanoscale.
We have investigated in-depth the graphene synthesis mechanisms by analysing the morphological, structural and elemental composition of the samples. A bilayer graphene is found on top of a ~20 nm thick amorphous Si-O-C layer. The two graphene layers found to be separated by 0.9 nm, indicating the presence of a dense intercalation. The elemental profile uncover a significant amount of oxygen in the top 20 nm layer along with silicon and carbon, which is not normally found in crystalline 3C-SiC film. The distribution of oxygen atoms concentration decreases with depth, from ~35 atomic % in the top 5 nm layer to about 15 atom % at a depth of 20 nm, suggesting different degrees of oxidation achieved during the annealing process. Thus, we explain how the oxidation and amorphization of the SiC surface is a crucial intermediate step towards graphitization in our alloy-mediated approach.
[1] A. Ouerghi, et al., "Epitaxial graphene on single domain 3C-SiC (100) thin films grown on off-axis Si (100)," Applied physics letters, vol. 101, pp. 021603, 2012.
[2] B. Gupta, et al., "Evolution of epitaxial graphene layers on 3C SiC/Si (111) as a function of annealing temperature in UHV," Carbon, vol. 68, pp. 563-572, 2014.
[3] B. V. Cunning, et al., "Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers," Nanotechnology, vol. 25, pp. 325301, 2014.
[4] F. Iacopi, et al., "A catalytic alloy approach for graphene on epitaxial SiC on silicon wafers," Journal of Materials Research, vol. 30, pp. 609-616, 2015.

Substrates significantly affect the properties of low-dimensional systems, as well as the chemical species
that can become attached to such surfaces. Some insights into surface and environmental effects on
monolayer, bilayer, and trilayer graphene have provided detailed information on this topic along with new
tools to probe these issues. A discussion of the use of spectroscopy to study these issues will be presented.

The performance of optimized graphene devices is ultimately determined by the quality of the graphene itself. Graphene grown on SiC has a single orientation, but its thickness cannot be limited to one layer. We have developed a method for manipulating these graphene layers with a single-atom-thickness precision. A graphene film of one or two monolayers grown on SiC is exfoliated via the stress induced with a nickel film. The excess graphene is selectively removed with a second exfoliation process with a gold film, resulting in a flat, single-oriented, monolayer graphene film.
This single-oriented graphene can be a template for the growth and transfer of single-crystalline films if the films can be epitaxially grown on graphene. We, for the first time, demonstrated direct van der Waals growth of high-quality single-crystalline GaN films on this graphene. The GaN film was released and transferred onto Si substrates. The post-released graphene/SiC substrate was reused for multiple growth and transfer cycles of GaN films. This technique will be generally applied for growing other single-crystalline 3D and 2D materials on graphene and transfer.
References
1. Jeehwan Kim, Hongsik Park, James B. Hannon, Stephen W. Bedell, Keith Fogel, Devendra K. Sadana, Christos Dimitrakopoulos, “Layer#8208;resolved graphene transfer via engineered strain layers”, Science, Vol. 342, 833 (2013)
2. Jeehwan Kim, Can Bayram, Hongsik Park, Cheng#8208;Wei Cheng, Christos Dimitrakopoulos, John A. Ott, Kathleen B. Reuter, Stephen W. Bedell, and Devendra K. Sadana, “Principle of direct van der Waals epitaxy of single#8208;crystalline films on epitaxial graphene”, Nature Communications, Vol. 5, 4836 (2014)

Graphene is a promising material for commercial applications in electronics, composite materials, photovoltaics, energy storage, biological engineering and many other fields. CVD synthesis of graphene on catalytic metal substrates remains to be the cheapest, large-scale and high fabrication yield method. In order to transfer graphene from copper or nickel foil onto a target substrate, numerous approaches have been proposed and tested. Two of them such as (i) Poly(methyl methacrylate) (PMMA) film based method [1] and (ii) direct transfer method on perforated carbon mesh by IPA droplet [2] are currently widely used to fabricate devices with supported and suspended graphene. Nevertheless, the cleanness of CVD graphene transferred by either method is still an issue since the hydrocarbon residue or polymer remnants at surface of transferred graphene are routinely observed. Here we report on comparative examination of these most widely-used transfer and cleaning techniques using surface sensitive low energy SEM equipped with true secondary electron detector. We also propose a method of the graphene transfer based on anthracene film as a sacrificial layer. The main advantage of our approach is based on facile sublimation of the anthracene layer upon heating the sample with transferred graphene to moderate temperatures of 100-150 ^oC. This protocol is particularly advantageous when the transfer is needed onto the moister-sensitive substrate such as elements of Li based all-solid-state batteries. The cleanness of this three transfer methods are comparatively studied under identical conditions. In addition the effectiveness of the cleaning procedures by platinum catalysis [3] and activated carbon adsorption [4] have been compared. Both SEM and TEM characterization have demonstrated the advantage of anthracene method to obtain clean suspended CVD graphene.
[1] “Transfer of CVD-Grown Monolayer Graphene onto Arbitrary Substrates”, Ji Won Suk, Alexander Kitt, Carl W. Magnuson, Yufeng Hao, Samir Ahmed, Jinho An, Anna K. Swan, Bennett B. Goldberg, and Rodney S. Ruoff, ACS Nano, 2011, 5 (9), pp. 6916.
[2] “A direct transfer of layer-area graphene”, William Regan, Nasim Alem, Benjamín Alemán, Baisong Geng, Ccedil;aglar Girit, Lorenzo Maserati, Feng Wang, Michael Crommie, and A. Zettl, Appl. Phys. Lett., 2010, 96, 113102.
[3] “Ultraclean freestanding graphene by platinum-metal catalysis”, Jean-Nicolas Longchamp, Conrad Escher, and Hans-Werner Fink, J. Vac. Sci. Technol. B 31, 020605 (2013).
[4] “Dry-cleaning of graphene”, Gerardo Algara-Siller, Ossi Lehtinen, Andrey Turchanin, and Ute Kaiser, Applied Physics Letters 104, 153115 (2014).

Graphene has drawn great attention over the past decade because of its potential applications in areas including electronics, biological engineering, filtration, light-weight and strong composite materials, photovoltaics and energy storage. Graphene has been made by micromechanical cleavage of graphite, annealing SiC substrates, chemical vapor deposition, growth on metal supports, and liquid phase exfoliation of graphite. However, the development of scalable and effective methods for production of graphene with high electrochemical quality suitable for energy storage is still one of the major challenges of graphene science and technology.
In this study, we have developed a new method to produce few-layer graphene by shear exfoliation using a high-pressure homogenizer. The exfoliation of graphite takes place in two steps. In the first step, a large number of structural gaps are formed on the edges of graphite flakes, leading to weakening of the cohesion between layers of graphite and being beneficial for the following exfoliation process. In the second step, the shear forces lift the monolayer or few-layer graphene sheets, leading to peeling-off of these monolayer or few-layer graphene sheets from graphite.
At a pressure of 100 MPa exfoliated graphene was obtained with a yield of about 15% (corresponding to a concentration of 1.5 g/L) after 120 min treatment using NMP as solvent in which graphene sheets can be well dispersed. Transmission electron microscopy and atomic force microscopy showed that the product contains both monolayer and few-layer graphene with most graphene sheets having fewer than 12 layers. Furthermore, Infrared and Raman spectroscopies analyses indicate that no basal-plane defects or oxides are introduced in the process. In addition, this method can process large liquid volumes in both batch and continuous ways, which is very important for the large-scale industrial production.

For numerous applications of graphene such as composites, electrochemical energy storage, etc., it is often necessary to synthesize graphene in bulk quantities, whereas the variation of the number of layers in a certain range affects the application insignificantly. However, among the methods of graphene synthesis available to date, only the creation of colloidal suspensions can be rather easily scaled to mass production.
The majority of graphene suspensions are produced from graphite oxide (GO). This technological route has several disadvantages. In the first place, the production of graphite oxide is ecologically unfriendly and rather noneffective. It requires large amount of reagents beside graphite (HNO₃, H₂SO₄, KClO₄), the process is slow (up to 120 hours), it generates large amount of chemical waste that requires for neutralization (mixtures of acids and gases). On the other hand, the technological process consisting of graphite oxidation, GO exfoliation, and GO reduction by design generates defective graphene structure affecting its mechanical and electrical properties.
This report is dedicated to a cryogenic method of graphite exfoliation for the production of graphene-like materials targeted at bulk application cases. The method consists of the following major stages: graphite intercalation by sodium solution in liquid ammonia under the temperature of about -33 °C, graphite intercalate drying, graphite intercalate exfoliation via explosive decomposition, and finally, material washing out and drying. The unique property of Na-NH₃ solution to form a solvated electron/ solvated sodium ion system drives the process of effective graphite intercalation. The technological cycle from the intercalation to the exfoliation lasts about 0.5 hours. The process generates only hydrogen gas and NaOH as the by-products that can be readily commercialized. The method does not include graphite oxidation/ reduction and thus, graphene-like material produced largely preserves the structure of the pristine graphite. On the other hand, interaction of graphite/ graphene with metal-ammonia complex under certain conditions leads to its in situ covalent functionalization by amino groups that is strongly advantageous, for example, for energy storage and nanocarbon-polymer composite applications.
Another important advantage of the cryoexfoliation method is its flexibility with regard to the microstructure engineering of the final material. We have shown, that easily implemented modifications to the process, such as changing the regime of the exfoliation, using different intercalation metals, and solving additional compounds in the intercalation solution, allows for tailoring the microstructure of the material produced. Flake-like, sponge-like, “foamy”, “shaggy” materials as well as double-level microstructures such as diamond-like carbon on graphene-like matrix and carbon nanotubes on graphene-like matrix have been synthesized.

The 2D allotrope of carbon, graphene, can be naturally formed on silicon carbide (SiC) substrates by thermal decomposition during which silicon leaves due to sublimation, while carbon resides on the substrate in an ordered manner. Despite the arguments that 2D carbon film on SiC is not graphene there exist numerous evidences that it is an epitaxial form (in particular on the Si- terminated face) of true graphene. One carbon atom thick honeycomb structure of the crystal lattice, similarly to free standing graphene, provides an energy band structure of linear dispersion resulting in peculiar physical properties and shows the finger print of graphene (2D peak) in Raman spectra. Formation mechanism is a top down solid state phase transition in which every next carbon monolayer is completed in a reversed growth mode under the previous one. The first step is surface reconstruction of SiC providing a template (buffer layer) for epitaxial growth on the Si-face terminated substrate. C-terminated face has different growth mechanism of which better understanding is needed. Due to the peculiar deposition mechanism and the difference in the faces, the topology of the films is different which implies different physical properties of the films obtained even at similar fabrication conditions.
Here we are going to discuss the main consequences of the topological diversity and ways to control the process of uniform material formation. The role of the surface reconstructed C-rich layer as a precursor of graphene and its effect on graphene properties will be enlighten. Depending on the buffer layer integrity the subsequently formed graphene may contain defects. The impact of the buffer layer on the graphene thickness evolution of larger area SiC substrates, e.g. diameter of 100mm is of particular interests.
We will address formation of bilayer inclusions in Si-face grown graphene and their influence on the electronic properties and sensitivity to ambient conditions. Our recent results encompass an improved graphene thickness uniformity with a bilayer occurrence down to 1% over an substrate area of 15x15mm2. This will have a significance concerning different applications, as well as understanding adsorption of functional groups at exposure to atmosphere. The latter effect has been studied in detail and the most interesting results will be communicated. Other means of graphene functionalization will be discussed. We will present examples of gas sensing ability and surface bio-functionalization. C-face grown graphene will be compared in terms of formation mechanism and characteristic properties.
Finally, conclusions reflecting the current progress of the material development and a brief outlook will be given.

The ability to manipulate materials with atomic precision is central to nanoscience. Hyperthermal ion implantation (HyTII) is a kinetic approach to doping with sub-nanometer control and is ideally suited for modifying 2D nanomaterials like graphene. HyTII consists of implanting surfaces with hyperthermal (~10 - 500 eV) ions with precisely tunable energies (|ΔE| le; 2 eV). At the low end of the ion energy scale (10-25 eV), ions have insufficient energy to directly displace an atom from the lattice of a 2D material and instead can either embed shallowly into the subsurface, functionalize the surface through chemical or physical adsorption, or scatter off the surface. For substitutional doping of graphene, the ionic species (e.g., nitrogen for n-type doping) must be within an energy window (~25-70 eV) in which it has sufficient energy to displace the primary knock-on atom from the lattice, yet still come to rest near the original site to fill the vacancy. At the higher energy scale (~70-500 eV), vacancy-producing glancing-angle collisions become more probable, thus substitutional doping via HyTII gradually transitions into lattice damage and sputtering as the energy is increased.
Much of our understanding regarding the mechanistics of the HyTII process is garnered through molecular dynamics studies¹ along with only a few experimental demonstrations that confirm the ability to substitutionally dope graphene via HyTII.^2-4 In this presentation, we expand upon the experimental work by performing a systematic characterization of the effects of nitrogen ion implantation (N-HyTII) with energies ranging from 25 - 100 eV and doses ranging from zero to ~1×10¹⁵ N⁺/cm². We obtain such a large dose range by focusing the energy filtered N⁺ ion beam onto a CVD-grown graphene film with a Cu substrate, allowing the natural ion flux gradient to generate a smoothly varying dose across the sample. Following N-HyTII and graphene transfer to a SiO₂/Si substrate, we collect Raman spatial maps over the entire sample surface, and perform XPS and STM analysis on a subset of the variable-energy samples along with HOPG as a control. The STM and XPS analysis confirm the substitutional incorporation of N into the graphene lattice at 45 eV, while the Raman D-peak to D`-peak ratios reveal distinct differences over the full energy range that are consistent with the different hyperthermal ion-substrate interactions described above. We conclude this study by demonstrating the use of HyTII in graphene device processing, and highlight the effects of N-doping on the magnetotransport properties of graphene.
References:
¹ E. Åhlgren et al., Phys Rev B 83, (2011).
² Y. Xu et al., AIP Advances 3, 072120 (2013).
³ U. Bangert et al., Nano Lett. 131001102242007 (2013).
⁴ C.D. Cress, et al., GOMACTech-14 (2014).

Being an atomically thin 2-dimensional layer, graphene has no 3-dimensional bulk. Hence, properties of graphene like, e.g., charge carrier density or charge carrier mobility are easily influenced by its environment, in particular by the substrate. Epitaxial graphene grown on silicon carbide substrates has been studied widely in the past. It has been observed, that the charge carrier type and concentration depends on the details of the interface. While epitaxial graphene on SiC(0001) is n-type doped due to charge transfer from interface states [1,2], quasi-freestanding graphene (QFG) on H-terminated SiC(0001) is p-type doped [3]. We have explained this surprising result by the spontaneous polarization of the hexagonal SiC substrates, which are typically used for the growth of epitaxial graphene [4]. In short, the spontaneous polarization of the hexagonal SiC substrate acts like a pseudo-charge located just at its surface. On the Si-face, this pseudo-charge is negative. As a consequence, in the absence of donor-like interface states, the negative pseudo-charges at the SiC(0001) surface are compensated by positive charges in the graphene. Because the spontaneous polarization of SiC depends on the polytype - being largest for 4H-SiC, of lower magnitude for 6H-SiC, and basically zero for 3C-SiC - the charge carrier concentration should vary in a characteristic manner with the polytype of the substrate. In order to test this hypothesis, we have carried out a systematic study using angle-resolved photoelectron spectroscopy of QFG on H-terminated 3C-SiC(111), 6H-SiC(0001), and 4H-SiC(0001). The measurements provide qualitative and quantitative support for our model. [5] Furthermore, by using both n-type and semi-insulating substrates we shed light on the role of the substrate doping.
______
[1] K.V. Emtsev, et al., Phys. Rev. B 77 (2008) 155303.
[2] S. Kopylov, et al., Appl. Phys. Lett. 97 (2010) 112109.
[3] F. Speck, et al., Appl. Phys. Lett. 99 (2011) 122106.
[4] J. Ristein, et al., Phys. Rev. Lett. 108 (2012) 246104.
[5] S. Mammadov, et al., 2D Materials 1 (2014) 035003.

Electronic properties of graphene nanoribbons (GNRs) can be tuned by their doping with heteroatoms, such as nitrogen. This possibility has been extensively studied theoretically, but only a few experimental attempts to synthesize nitrogen-doped GNRs (N-GNRs) by bottom-up approaches have been reported. This talk will be focused on the recently developed bottom-up solution method for gram quantities of narrow GNRs [1] and N-GNRs [2] that are less than 2 nm wide and have atomically precise armchair edges. The method is based on Yamamoto coupling of presynthesized molecular precursors followed by cyclodehydrogenation using Scholl reaction [1,2]. GNRs and N-GNRs were characterized by a number of microscopic (STM, AFM, SEM, TEM) and spectroscopic (XPS, UPS/IPES, UV-vis-NIR, IR and Raman spectroscopy) techniques. GNRs and N-GNRs have large electronic bandgaps, which makes them promising for applications in field-effect transistors with high on-off ratios and photovoltaic devices.
This work was supported by the National Science Foundation (NSF) through CHE-1455330.
[1] T. H. Vo, et al., Large-Scale Solution Synthesis of Narrow Graphene Nanoribbons. Nat. Commun. 2014, 5, 3189.
[2] T. H. Vo, et al., Bottom-up solution synthesis of narrow nitrogen-doped graphene nanoribbons.Chem. Commun. 2014, 50, 4172.

Graphene-based van der Waals heterostructures have recently attracted much attention due to their potential applications in high-speed modulators of terahertz (THz) and infrared (IR) radiation, transistors, and THz photomixers. This paper reviews recent advances in theoretical and experimental studies on double-graphene-layer (DGL) van der Waals heterostructures for the terahertz (THz) device applications. The DGL consists of a core shell in which a thin tunnel barrier layer is sandwiched by the two GLs being independently connected with the side contacts and outer gate stack layers at both sides. The DGL core shell works as a nano-capacitor, exhibiting inter-GL resonant tunneling (RT) when the band offset between the two GLs is aligned. The RT produces a strong nonlinearity with a negative differential conductance (NDC) in the DGL current-voltage characteristics. The excitation of the graphene plasmons by the THz radiation resonantly modulates the tunneling current-voltage characteristics. When the band offset is aligned to the THz photon energy, the DGL structure can mediate photon-assisted RT. We demonstrate that the photon-assisted resonant radiative inter-GL transitions enable the applications of such devices for THz/IR lasers and photodetectors (PDs).
The measured I-V curves of the fabricated two DGL devices exhibiting no trace of NDC in the reference device while a clear NDC peak is seen in the other device. The NDC strongly depends on the relative crystallographic orientation between the two GLs. In order to observe it the two layers have to be aligned so that their crystallographic axes are parallel. The misalignment angle between the two GLs crystallographic axes is about 30° in the reference sample while this angle is about 1° for the other sample.
We conducted THz emission experiments using a Fourier transform far-IR spectrometer to observe the spontaneous emissions associated with the photon assisted resonant tunneling transitions. For band offset (Δ) conditions when the energy of the final state of the tunneling inter-GL transition is lower than the initial state, the tunneling is associated with emission of the electromagnetic photons. Our results show THz emission exclusively in this case, when the energy of the final state is higher, the tunneling is preceded by an absorption of photons. The detection experiments were conducted in an oblique incidence configuration to maximize the THz electric field perpendicular to the GLs and thus the resonant tunneling transitions associate with the absorption of the THz photon.
In summary, the DGL devices can exhibit advantages over the devices exploiting the intra-GL interband vertical radiative transitions proposed and analyzed previously. This work was supported by JSPS GA-SPR (#23000008), Japan.

Since its experimental realization, graphene became one of the most important subjects in materials science due to its extraordinary electronic, thermal and mechanical properties. However, in its pristine form graphene is a gapless semiconductor, which limits its use in several technological applications. There are many ways to address this gap problem, for example through chemical functionalization (hydrogenation [1] and fluorination [2], among others). Graphane and graphone are the most studied hydrogenated graphene forms. Graphane is the graphene fully hydrogenated form, while graphone has just one hydrogenated side. Graphone presents interesting electronic and mechanical properties, such as non-zero electronic gap and high Young&’s modulus. These properties can be exploited for different applications in nanoelectronics. Recent studies on graphene hydrogenation processes [1] showed that hydrogenation occurs via island growing domains, however how the substrate can affect the hydrogenation dynamics and/or patterns has not been yet properly addressed. In this work we have addressed these issues through fully atomistic reactive molecular dynamics simulations. We investigated the structural and dynamical aspects of the hydrogenation of graphene membranes (graphone-like) on different substrates (graphene, few-layers graphene, graphite and platinum) and at different temperatures. Our results show [3] that a significant number of randomly distributed H clusters are formed during the early stages of the hydrogenation process, regardless of the type of substrate and temperature. These findings suggest that, similarly to graphane formation [1], large perfect graphone-like domains are unlikely to be formed. Our results also show that the observed hydrogenation rates are very sensitive to the substrate type and temperatures. For all the cases we have investigated here (substrates and temperatures), the largest fraction of hydrogenated carbon atoms was observed for platinum substrates.
[1] M. Z. S. Flores, P. A. S. Auteto, S. B. Legoas, and D. S. Galvao, Nanotechnology 20, 465704 (2009).
[2] R. Paupitz, P.A. S. Autreto, S. B. Legoas, S.G. Srinivasan, A. C. van Duin, and D. S. Galvao, Nanotechnology 24, 035706 (2013).
[3] C. F. Woellner, P. A. S. Autreto, and D. S. Galvao, to be published.

Atomically thin membranes have generated a lot of interest in filtration and separation applications. 2D materials like graphene offers the minimum theoretical membrane resistance along with the opportunity to tune pore sizes at the nanometer scale in complete contrast to solution-diffusion of molecules through conventional membranes.
While several methods of synthesis for 2D materials exist, chemical vapor deposition has emerged as the preferable route towards scalable, cost effective synthesis. Here, selective molecular transport through precise and controllably engineered, high-density, sub nanometer diameter pores in graphene grown via chemical vapor deposition processes is demonstrated. The density of such defects can be tuned to be >10¹² cm^-2 and a combination of pressure and diffusive transport measurements shows evidence for size selective transport behavior.
The possibility of tuning the selectivity of atomically thin membranes through controlled creation of sub nanometer pores, addresses a significant challenge in the development of advanced nano-porous atomically thin membranes for nanofiltration, desalination, gas separation and several biological applications. These membranes hence offer opportunities to study and elucidate the complex dynamics and transport phenomena at the nanometer length scales.
O&’Hern et al. Nano Letters (2015).
Kidambi et al. Chemistry of Materials (2014).
Boutilier et al. ACS Nano (2014).
Kidambi et al. Nano Letters (2013).
O&’Hern et al. Nano Letters (2013).
O&’Hern et al. ACS Nano (2012).

One of the main issues of proton exchange membrane (PEM) fuel cells is their limited durability caused by agglomeration and/or loss of platinum catalyst particles and corrosion of carbon supports. Here we report on carbon nano-onions (CNOs) as a carbon-allotropic support for platinum catalysts to address the challenging issue. We successfully synthesized nanodiamond-derived CNOs having the 0-D structure composed of sp²-bonded concentric carbon shells surrounding a hollow core. Their morphological microstructure as well as electrochemical properties relevant to oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in both acid and alkaline media were studied in comparison with a commercial carbon-supported platinum catalyst (Etek, Pt 20 wt. %). Even with a half Pt contents, our CNO-supported Pt (Pt/CNO) was comparable to the commercial Pt/C in terms of ORR activity in both media. The plentifully exposed edge planes of CNOs and formation of Pt nanoparticles of higher catalytic activity on CNOs were responsible for the higher activity. More significantly and interestingly, the highly graphitized surface of CNOs improved durability of ORR and tolerance against MOR, decreasing Pt migration and agglomeration during ORR.

Graphene-like two-dimensional materials have shown high mechanical strength, good chemical stability and superior electrical properties. Extensive applications such as high-mobility transistors, smart sensors, catalysis and photonic devices have been exhibited. In this study, three-dimensional, free-standing, foam-like graphene/h-BN structures with area of tens of square centimeters were synthesized by nickel-template assisted chemical vapor deposition (CVD) method. Both the graphene foams and h-BN foams consist of interconnected suspended mono-to-few-layer graphene-like networks. Bene#64257;t from the foam structure, the graphene foam could generate loud sound at low driving voltage of 3 V via thermoacoustic process, the h-BN foam could sustain its thermal stability up to 1200 °C with superelasticity and ultralow density of 1.6 mg/cm³.
Refs:
1. Fei WW, Zhou JX, Guo WL, Low-voltage Driven Graphene Foam Thermoacoustic Speaker, Small, 11, 2252-2256 (2015).
2. Yin J, Li XM, Zhou JX, Guo WL, Ultralight Three-Dimensional Boron Nitride Foam with Ultralow Permittivity and Superelasticity, Nano Lett. 13, 3232 (2013)
3. Yin J, Li XM, Yu J, Zhang ZH, Zhou JX, Guo WL, Generating electricity by moving a droplet of ionic liquid along graphene. Nature Nanotech. 9, 378-383 (2014).

Since their discovery carbon nanotubes (CNTs) have fascinated many researchers due to their unprecedented electrical, optical, thermal, and mechanical properties. Recently, a complete computer based on CNT circuits has been demonstrated. However, a major drawback in utilizing CNTs for practical applications is the difficulty in positioning or growing them at speci#64257;c locations or in locating them on the substrate such that the circuit can be built around them.
Here we present a simple, rapid, non-invasive, and scalable technique that enables optical imaging of CNT. Instead of relying on the CNT chemical properties to bind marker molecules we rely on the fact that the CNT is both chemical and physical defect on the otherwise flat and uniform surface. Namely, it may serve as a seed for nucleation and growth of small size, optically visible, nano-crystals. As the CNT surface is not used to bind the molecules they can be removed completely leaving the surface intact and thus the CNT electrical and mechanical properties are preserved. By choosing a small molecule with suitable vapor pressure it is self-removed via sublimation off the CNT surface. The successful and robust optical imaging allowed us to develop a dedicated image processing algorithm through which we are able to demonstrate a fully automated circuit design resulting in field effects transistors and inverters. Moreover, we demonstrate that this imaging method allows not only to locate CNTs but also, as in the case of suspended ones, to study their mechanical motion including mode shapes, resonance frequencies, dissipation phenomena, and nonlinear behavior.

Because of their exceptional electrical, thermal, mechanical, and fluidic properties, carbon nanotubes provide ideal 1-D nanofillers for composite fabrication. CNT type, orientation, and concentration dictate the nanocomposite properties and, for several applications (e.g. thermal interfaces, dry adhesives, and films with anisotropic electrical conductivity), vertical alignment of nanotubes is critical to meet performance requirements. In particular, to exploit CNT as fast mass-transport conduits in highly permeable and selective membranes, small-diameter SWNTs need to be organized in high density, vertically-aligned arrays that span the entire composite thickness. Unfortunately, achieving high loading of long, well-oriented CNTs in a large scale membrane remains a challenge.
Here, we demonstrate cm², free-standing, flexible SWNT/parylene membranes with well-aligned nanotubes at loadings 10x greater than previously reported films. To fabricate these membranes, 1-3 nm SWNT forests with number densities surpassing 10¹²/cm² are grown on a 4-inc wafer with a LPCVD process. A following highly conformal coating with parylene-N produces pinhole-free composites that, after opening the CNT pores, are tested for their transport performances. Pressure-driven water and gas permeability measurements confirm that narrow SWNTs sustain flow rates exceeding predictions of continuum hydrodynamics models for liquids and Knudsen theory for gases by several orders of magnitude. In addition, these membranes fully reject test analytes with dimensions larger than the SWNT diameters without loss of their outstanding water permeances. Finally, recorded water-vapor diffusion rates surpass state-of-art breathable fabrics at all relative humidities and match those of ePTFE. These results provide a step forward toward realizing the promises of CNTs for next generation high-performance membranes.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Ever since the wide range applications of laptop computers and cell phones, seeking of power sources for driving portable electronics is becoming increasingly important. The current technology mainly relies on rechargeable batteries. But for the near future, micro/nano-systems will be widely used in health monitoring, infrastructure and environmental monitoring, internet of things and defense technologies; the traditional batteries may not meet or may not be the choice as power sources for the following reasons. First, with the increasingly shrinkage in size, the size of the total micro/nano-systems could be largely dominated by the size of the battry rather than the devices. Second, the number and density of micro/nano-systems to be used for sensor network could be large, thus, replacing batteries for these mobile devices becoming challenging and even impractical. Lastly, the power needed to drive a micro/nano-system is rather small, in the range o f micro- to milli-Watt range. To meet these technological challenges, the author proposed the self-powering nanotechnology in 2005, aiming at harvesting energy from the environment to power the micro/nano-systems based sensor network. This talk will introduce the piezoelectric nanogenerator developed using 1D and 2D nanomaterials toward the goal of self-powered systems.
[1] Z.L. Wang and J.H. Song, Science, 312 (2006) 242-246.
[2] X.D. Wang, J.H. Song J. Liu, and Z.L. Wang, Science, 316 (2007) 102-105.
[3] Y. Qin, X.D. Wang and Z.L. Wang, Nature, 451 (2008) 809-813.
[5] Z.L. Wang, Advanced Functional Materials, 18 (2008) 3553-3567.
[4] R.S. Yang, Y. Qin, L.M. Dai and Z.L. Wang, Nature Nanotechnology, 4 (2009) 34-39.
[5] S. Xu, Y. Qin, C. Xu, Y.G. Wei, R.S. Yang, Z.L. Wang, Nature Nanotechnology, 5 (2010) 366 - 373
[6] W.Z. Wu⁺, L. Wang⁺, Y.L. Li, F. Zhang, L. Lin, S. Niu, D. Chenet, X. Zhang, Y. Hao, T.F. Heinz, J. Hone, and Z.L. Wang “Piezoelectricity of single-atomic-layer MoS₂ for energy conversion and piezotronics", Nature, 2014, DOI: 10.1038/nature13792.

Charge-transfer reactions have been shown to alter the electronic structure of carbon nanotubes in a bandgap-dependent fashion. Such electronic modification holds great promise for isolating single nanotube structures from their heterogeneous synthetic mixtures. This study investigates the role of redox chemistry in the aqueous two-phase extraction of both single-wall carbon nanotubes (SWCNTs) and double-wall carbon nanotubes (DWCNTs). We demonstrate a multi-step oxidative extraction procedure to successfully separate SWCNTs by semiconducting bandgap and metallicity. We additionally show that redox-modulation can be applied to separate small diameter SWCNTs from DWCNTs, while also facilitating the enrichment of DWCNTs by outer-wall electronic type. We propose that electron transfer between redox molecules and the nanotubes induces reorganization of the surfactant coating layer, which in turn affects the partitioning of the nanotubes between the two different polymer phases. Redox-induced modulation of the dispersant coating is a generally observed phenomenon in many different nanotube sorting processes which can be further tuned to improve separation reproducibility and purity.

In this presentation the use of electron irradiation to grow 1D and 2D nanostructures will be presented. The fabrication of these nanostructures is accomplished by using the electrons used to image specimens in a (Cs aberration corrected) transmission electron microscope. No specialized holders or systems are required making the technique relatively cheep and easy.
As examples of the technique I will demonstrate of electron irradiation can be used to form 1D coaxial B/BOx nanowires and BOx nanotubes. In addition, I will show how 1 atom thick Fe membranes can be formed and also the catalytic activity of a single atom for the growth of or etching of graphene can be accomplished. The electron microscopy technique provides unprecedented insight in to nanostructure formation at the atomic scale.

The ability to control the quantity and location of molecular flux to a precise location in space has important applications to nanoscale 3D printing, catalysis, and sensor design. Barrier materials containing pores with molecular dimensions have been used to control molecular compositions in the gas phase, but unlike their aqueous counterparts, none has enabled an ability to observe or control discrete single pore transport. Herein, we demonstrate gas transport through atomically thin, monolayer graphene opened with discrete Å-sized pore(s) demonstrating the ability to detect and control the gas flux. This is accomplished using ~nm sized gold clusters formed on the surface of the graphene. Such clusters migrate and partially block the pore. We also observe stochastic switching of the magnitude of the gas permeance in a sample without gold clusters, attributed to molecular rearrangements of the pore; the stochastic switching is fit to discrete and repeatable states. These discrete angstrom pore molecular valves open possibilities for unique sensors, catalytic processes, and approaches to molecular synthesis based on the controllable switching of a molecular gas flux reminiscent of ion channels in biological cell membranes and solid state nanopores.

Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multi-valent crosslinker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 ^oC with record-high surface area (4073 m² g^-1), large pore volume (2.26 cm^-3) and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity > 3 times more than activated carbons, very high electrochemical activity at high mass loading and high stability, as demonstrated by supercapacitors and lithium-sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.

Chemical vapor deposition (CVD) synthesis of vertically aligned carbon nanotubes (CNTs) using lithographically-patterned catalyst films directly creates bulk microstructures having high porosity (>99%). The mutual control of microscale geometry and nanoscale porosity is attractive for materials for battery and supercapacitor electrodes, surfaces, with controlled wettability, and direct contact printing of liquid inks. However, as-grown CNT forests are susceptible to significant shrinkage due to surface tension forces exerted during liquid infiltration and evaporation, and this has prevented development of applications that leverage the porosity of the CNT forest within a liquid environment. We show that elastocapillary densification of CNTs can be prevented by conformal deposition of an ultrathin, low surface energy, and protective layer of poly-perfluorodecylacrylate, poly-(1H, 1H, 2H, 2H-perfluorodecylacrylate) (pPFDA) on the CNTs via initiated chemical vapor deposition (iCVD). Energy-dispersive X-ray spectroscopy is performed to verify conformal and uniform coating of the CNT pillars with the fluorine-rich polymer (pPFDA).
Two scenarios are studied. In the first scenario, entangled CNTs on top of the pillars coated with pPFDA clusters form surfaces possessing re-entrant features which prevents infiltration of low surface tension liquids (i.e. tetradecane, hexadecanethiol, dimethoxyethane) resulting in oleophobicity. Goniometric measurements with drops of dimethoxyethane (surface tension = 20 mN/m) on coated CNT pillars exhibit a contact angle of 121°±2.5°. Confocal microscopy imaging is also performed to verify prevention of liquid infiltration into the pPFDA-coated CNT pillars. Environmental SEM images captured during drying of a tetradecane macrodroplet on the pPFDA-coated pillars exhibit capillary bridging. Further drying of the macrodroplet leads to formation of microdroplets with size of 1-2 µm, which is at the same order of magnitude with the size of the bundles of entangled CNTs coated with pPFDA clusters on top of the pillars.
In the second scenario, oxygen plasma treatment is employed before and after pPFDA deposition to remove the entangled CNTs and pPFDA clusters on the top surface, enabling infiltration of wetting liquids into the CNT pillars. The mechanical reinforcement provided to the CNT-CNT junctions stabilizes the CNT forest against shrinkage during liquid infiltration and evaporation. Scanning electron microscopy images obtained after wetting of the pPFDA-coated CNT pillars with silver containing liquid, and subsequent drying, verify infiltration of the liquid without densification in the CNTs. We discuss the potential applications of pPFDA-CNT composite microstructures, including printing stamps for electronics fabrication.

We synthesized nanocarbon-coated titanium oxide nanowire aerogel (NWAG) by chemical vapor deposition (CVD) at 750#730;C. Samples after CVD for different reaction times were investigated by aberration-corrected transmission electron microscopy (Cs-corrected TEM). We observed amorphous carbon islands for short CVDs (<675 sec), and graphitic nanostructures for longer CVDs on the surface of the nanowires. Raman spectrums also evidenced that graphitization proceeded as the reaction time extended. Electric conductivity increased from 1.79×10^-4 S/m for bare NWAG to 2.16 S/m after graphitization, suggesting that the nanocarbon was continuously deposited through the 3D structure of NWAG. Growth of the graphitic nanostructures terminated at 3 to 4 graphene layer at 1125 sec. Even longer CVDs deposited amorphous carbon layer on top of the graphitic nanostructures, indicating that the graphitization was catalytically occurred on titanium oxide nanowire surface. These observations provide insights not only into graphitization on metal oxide, but also into a fabrication of conductive 3D nanocarbon-metal oxide composite.

Graphene growth has been intensively investigated to produce high quality wafer for electronic device applications in the past years. The common techniques to produce graphene include: (a) exfoliation from graphitic materials, (b) chemical vapor deposition on metal surface and (c) thermal annealing from SiC. Since graphene growth in the synthesis techniques could be considered as a 2-D confined graphitization progress, it is known that amorphous carbon is a common by-product in the graphitization progress which is difficult to be characterized and removed. In this talk, various amorphous carbon structures and their structural evolutions in graphitization processing will be briefly discussed. Due to the structural disordered nature, amorphous carbon is difficult to be characterized at the atomic and nanometer scales by the commonly used technologies. The diffraction based technologies, such as TEM and XRD usually do not effectively detect a small amount of amorphous carbon at the atomic scale. Since the cross section of Raman scattering of sp³ is about 2 orders smaller than it of sp², sp³ carbon is usually not observed in the presence of sp²carbon. Therefore, amorphous carbon with co-existing sp² and sp³ states and their conversion is often ignored in structural characterizations of graphene growths on SiC and metals. In commercial graphitic carbon for graphene exfoliations, the amount of amorphous carbon is not provided. However, a small amount of amorphous carbon associated graphene structures affects electronic properties. Examples are given by discussions of electronic contact properties of sputtered amorphous carbon thin film on SiC after annealing and graphene formed on SiC by thermal decomposition. As progressing in graphitization process of amorphous carbon, the ideal factor of Schottky barrier height (SBH) of carbon on SiC decreases with increasing the degree of graphitization when annealing temperatures increases. Since amorphous carbon at the nanoscale is observed on the interface of graphene and SiC substrate by HR-TEM, it is assumed that amorphous carbon at the atomic scale exists too. Then, the electronic transport properties on graphene/SiC are discussed from the viewpoint that an atomic and nano-structure of amorphous graphitic carbon is considered as a part of the interfacial structures of graphene/SiC.

Membrane-based dehumidification of gas streams has several advantages in terms of technology, economy, and energy over conventional dehumidification processes such as electro-osmotic dehumidification, desiccants, or condensation. Several polymer membranes are commercially available for drying compressed air, e.g. polyimide membrane (UBE Industries Ltd, Japan), and poly ether block amide, PEVAX® 1074 (Foster Polymer Corp, CT, USA). Graphene oxide (GO) sheets, which are oxidative exfoliation products of graphite, have attracted growing interest in energy storage and separation technology. In particular, carboxyl, hydroxyl, and epoxide functionalities generated by the oxidation of graphite have shown potential for making functional composite membrane materials that have excellent water transport properties. The two-dimensional channels between the stacked GO sheets may allow water to pass through while rejecting unwanted solutes. This property suggests high water flux in stacked GO sheets. In addition, GO sheets can be mass-produced via chemical oxidization and ultrasonic exfoliation of graphite, thereby significantly lowering the material manufacturing cost and facilitating scale-up of the membrane synthesis process. Therefore, GO becomes a target material for making high-performance membranes for water vapor separation.
We prepared a range of different GO membranes from different GO sources with the goal of obtaining various flake sizes, from 100 nm to a few hundreds of mu;m in nominal diameter. Two different methods, a simple vacuum filtration and a casting on a PTFE plate were utilized to isolate free-standing GO membranes. In addition to the variable flake sizes, membranes were made with various thicknesses, from 2 µm to 50 µm. These membranes were evaluated using mixed gas permeability testing (with air plus H₂O) and exhibited very high selectivity for H₂O with N₂ and O₂ at or below the system measurement limit, correlating to selectivities above 10⁴. The Hshy;₂O vapor permeabilities were up to ~10⁶ Barrer.
In this presentation, we will discuss the effects of flake size, thickness, level of oxidation, and temperature on water vapor selectivity of various GO membranes over other gasses_.

Graphene-based laminates, with ultralong and tortuous nanocapillaries formed by stacking GO flakes and abundant oxygen-containing functionalities, have great promises in filtration, separation and biomimetic selective ion transportation. In this talk, I will introduce my recent work on selective mass transport through GO-based membranes. We found that for small ions, excellent selectivity can be achieved with GO membranes based on delicate ion-GO interactions, beyond the functioning stage of the physical size effect. In detail, transition metal cations prefer to bind to the sp³ C-O matrix of GO sheets via a coordination interaction, whereas cations lacking d electrons (e.g. alkali and alkaline earth cations) prefer to interact with the sp² aromatic clusters via a cation-π interaction. For anions, due to the ionization of oxygen-containing functional groups in aqueous environment, the GO membranes are charged negatively, further leading to the electrostatic repulsion towards different anions. The diverse interactions between different ions and GO lead to excellent selectivity of GO membranes.
In addition to the research on selective ion transport through GO membranes, the diffusion of liquid water is investigated based on a novel isotope labelling technique. This is the most fundamental problem and of crucial importance in solution-based mass transport. By dissolving certain amount of deuterium oxide (D₂O) as a tracer to label the source water, the trans-membrane permeation of D₂O is investigated to extrapolate that of water. We found that liquid water can afford an ultrafast permeation through graphene-based nanochannels with a diffusion coefficient 4~5 orders of magnitude greater than the bulk case. The results present here may indeed lay a foundation on nanofluidic device design and biomimetic fast mass transportation based on engineering the nanochannels within GO membranes.
Finally, I will introduce my recent work on water desalination with GO-based membranes. In terms of water desalination, as-synthesized GO membranes cannot perform well at the present state due to the fast ion flows. By intercalating monolayer titania nanosheets (TO) into GO laminates, assisted with mild ultraviolet (UV) reduction, we found that the as-prepared RGO/TO hybrid membranes exhibit excellent water desalination performances. Under no external hydrostatic pressures, the ion permeations through RGO/TO hybrid membranes can be reduced to <5% compared to the GO/TO cases, while the water permeation can be retained up to ~60%. The mechanism for the excellent water desalination performances of RGO/TO hybrid laminates is discussed, indicating that the photoreduction of GO by TO is responsible for the effective rejection of ions, while the photoinduced hydrophilic conversion of TO under UV irradiation is responsible for the well-retained water permeabilities. These excellent properties make RGO/TO hybrid membranes promising for practical water desalination.

Graphene is an ultrathin, impervious membrane. The controlled introduction of nanoscale pores in graphene would lead to various applications such as water purification, chemical separation, DNA sequencing, etc. However, it is also known that such tiny holes in graphene are unstable against filling by carbon adatoms. Thus, the stabilization of tiny holes is a critical issue to be resolved to facilitate the applications [1]. Here, using extensive molecular dynamics simulations [2] and by employing rigorous many-body potentials (e.g. AIREBO [3] and Tersoff model [4, 5]), we propose a novel method to form and stabilize a nanopore in graphene by using the silicon nanoparticle bombardment: A silicon ball, whose diameter is less than 10 nm, is impinged onto the graphene with sufficiently high velocity. When the ball hits the graphene, it penetrates the membrane by forming a hole with the disruption of the ball. Then, as a result of the competition between two covalent interactions of Si-C and C-C pairs, the detached Si atoms are bonded with the dangling C atoms in the perimeter of the hole. The hole remains stable until the end of the simulations. The stability depends on the type of balls: When a carbon ball hits the graphene, the formed hole shrinks suddenly after the penetration, i.e. the hole is not stable. The comprehensive quantitative analysis and explanation regarding these phenomena will be presented at the conference. The observations in this study are quite similar to the findings by aberration-corrected scanning transmission electron microscopy and density-functional calculations [1]. It confirms that even the classical MD simulations with proper force field employed, can successfully present the nanopore formation and stabilization in graphene. The proposed method in this study would be useful for the development of stable nanopores, and it would be a major step toward reliable graphene-based molecular translocation devices.
References:
[1] J. Lee, Z. Yang, W. Zhou, S. J. Pennycook, S.T. Pantelides, and M. F. Chisholma, Proc. Nat&’l Acad. Sci. U.S.A., 111, 17522 (2014).
[2] S. Plimpton, J Comp Phys, 117, 1 (1995).
[3] S. J. Stuart, A. B. Tutein, and J. A. Harrison, J. Chem. Phys., 112, 6472 (2000).
[4] J. Tersoff, Phys. Rev. B 37, 6991 (1988).
[5] J. Tersoff, Phys. Rev. B 38, 9902 (1988).

Narrow graphene nanoribbons (GNRs) constructed by atomically precise bottom-up synthesis from molecular precursors have attracted significant interest as promising materials for nanoelectronics. GNRs with zigzag edges are predicted to exhibit low-dimensional magnetism, while semiconducting behavior with bandgaps that strongly depend on the width of the ribbons is realized in narrow armchair GNRs.
To date, there has been little awareness of the potential of GNRs to serve as nanoscale building blocks of novel materials. Here we show that the substitutional doping with nitrogen atoms can trigger the hierarchical self-assembly of GNRs into ordered 3D metamaterials. We used GNRs doped with 8 N atoms per unit cell (8N-GNRs) and their undoped analogues, synthesized using both surface-assisted and solution approaches, to study this self-assembly on a supporting surface and in an unrestricted 3D solution environment.¹ Scanning tunneling microscopy on surface synthesized GNRs shows that hydrogen bonding drives 8N-GNRs to self-assemble edge-to-edge into ordered 2D arrays. In solution, sheets of side-by-side coordinated GNRs can in turn assemble via van der Waals and π-stacking interactions into 3D stacks, a process that ultimately produces macroscopic crystalline structures.² Spectroscopy shows the opening of a confinement-induced bandgap that is not significantly affected by the assembly process. Thus, the optoelectronic properties of our semiconducting 3D GNR crystals are determined entirely by those of the individual GNR constituents, which are widely tunable by varying properties such as width, edge orientation and termination, etc. The atomically precise bottom-up synthesis of bulk quantities of basic nanoribbon units and their subsequent self-assembly into crystalline 3D structures suggests that the rapidly developing toolset of organic and polymer chemistry can be harnessed to realize families of novel carbon-based materials with engineered properties.
1. T.H. Vo et al., Nature Commun. 5, 3189 (2014).
2. T.H. Vo et al., submitted (2015).

The electronic and optical properties of graphene and multi-layer graphene are highly dependent on the presence and coordination of heterodopant atoms such as silicon, nitrogen, fluorine, nickel, copper or oxygen. These dopants can be intentionally introduced, but are also common contaminants introduced during material growth and processing. To measure the effects of these intentional or contaminant dopants, techniques such as Raman spectroscopy or x-ray photoelectron spectroscopy are utilized. While these techniques are powerful on a mesoscopic scale, they do not directly measure the manner in which dopants and contaminants are incorporated on or into the graphene lattice, and are not sensitive enough to detect individual contaminant atoms.
Recent advances in single-atom sensitivity imaging with coordinated spectroscopy allow direct chemical identification and bonding measurements of single heteroatoms[1]. Aberration-correction in scanning transmission electron microscopy (STEM) enables the sub-Å spatial resolution and direct imaging of single atoms in and on graphene and functionalized graphene. The addition of energy dispersive x-ray spectroscopy (EDXS) allows the unambiguous identification of heteroatoms in graphene and other 2-D materials without a priori knowledge of the chemistry of the species. Using a 0.7 sr windowless Bruker EDXS detector on a Nion UltraSTEM 200, we have identified single impurity atoms with spectral collection times under 10 seconds and high signal-to-noise. This technique is very powerful for measuring both fixed and mobile heteroatoms, through the use of sub-image scanning and tracking techniques. When a heteroatom&’s mobility and orientation is known, its chemical coordination can then be directly measured by electron energy loss spectroscopy. (EELS). This technique is applicable to almost all of the elements of the periodic table to atomic numbers as low as 3 (Li). Using this approach, we have measured mobile calcium, sulfur, silicon and phosphorous heteroatoms on low dimensional carbon samples. This atom-by-atom STEM-EDXS-EELS approach can also be applied to the characterization of other 1 and 2-dimensional nanomaterials, such as transition-metal dichalcogenides and quantum dots.
[1] Zhou, W., et al.,. Physical Review Letters. 109(20): p. 206803.

One of the major challenges in applied graphene research is producing graphene-based materials with pre-defined physical properties. In this work we have introduced several methods for altering optical properties and band gaps of graphene oxide (GO) through controlled processing. This was achieved by stepwise ozone treatment of reduced graphene oxide (RGO) in aqueous suspensions. After exposure of initially non-emissive RGO to ozone for the periods of 5 to 50 minutes, an appearance of the broad photoluminescence feature in the visible and near-infrared was observed. Due to ozone-induced oxidation, RGO became water soluble and experienced a dramatic change in color caused by the bleaching of its UV-Vis absorbance. The intensity and the wavelength of photoluminescence emission was also found to be highly dependent on the treatment conditions suggesting a possibility for adjusting optical properties of the resulting GO material for the needs of specific optoelectronics applications. Semi-empirical modeling of graphene oxide sheets with sp² carbon cluster size estimated from the photoluminescence spectra has shown localization of the electronic density in the regions surrounding functional groups, suggesting a possibility of emission from electronically confined defect-induced environments.
In addition to ozone treatment, a significant change in optical properties of graphene oxide was observed while varying pH of the GO solution: sharp and structured emission features resembling the spectra of molecular fluorophores were present at basic pH values, but in acidic conditions below pH 8 GO emission was significantly broadened and red-shifted. These reversible changes consistent with excited state protonation of the emitting species in acidic media were proposed to arise from quasi-molecular fluorophores, similar to polycyclic aromatic compounds with pKa* ~8, formed by the electronic coupling of carboxylic acid groups with nearby carbon atoms of graphene. Such coupling was depicted by computational modeling showing a region of confined electrostatic potential enclosing a section of the graphene sheet around deprotonated carboxylic functional group, which was also in the agreement with the above-mentioned defect-induced emission model.

Multi-layer graphene with relative rotations between carbon layers, known as turbostratic graphene, can effectively decouple the electronic states of adjacent layers, preserving properties similar to that of SLG. Here, we investigate the growth of turbostratic graphene on heteroepitaxial Ni(111) thin films utilizing physical vapor deposition (PVD). Varying the carbon deposition temperatures between 800°C-1100°C, a sharp transition in the graphene quality and domain size is shown. Combination Raman modes of the as-grown graphene within the frequency range of 1650 cm^-1 to 2300 cm^-1 along with features of the characteristic Raman 2D mode demonstrate the prevalence of turbostratic graphene. High-resolution TEM cross-sectional imaging directly identifies bilayer and multi-layer graphene from regions that exhibit turbostratic graphene Raman signatures. Raman maps of pertinent Raman modes reveal large-area, domain-like growth of turbostratic graphene on Ni(111) thin films at high carbon deposition temperatures.

Graphene and other two-dimensional (2D) materials, have been touted as promising ultra-thin passivation coatings due to their extremely low permeability to gases, and their ultimate thinness which offers the opportunity to preserve the physical properties of surfaces with only a single atomic layer separating them from their surroundings. Catalytic chemical vapor deposition (CVD), offers a promising direct integration route for reducing a catalyst surface and forming a uniform, conformal 2D material layer, enabling simplified device integration strategies.[1-4] Indeed, we have shown that few-layer graphene prevents the oxidation of Ni electrodes exposed to air for 7 days, with tunnelling spin valve devices successfully demonstrated based on these passivated electrodes.[5] However, studies of graphene on other surfaces (e.g. Cu) have highlighted that the expected passivation is not necessarily achieved, and may not be maintained over the long-term.[6]
We demonstrate here the long-term (>18 months) protection of Ni surfaces against oxidation under atmospheric conditions by coverage with a single-layer of graphene, formed by CVD.[7] In situ, depth-resolved X-ray photoelectron spectroscopy of various graphene coated transition metals (Cu, Co, Fe, Ni, Pt) reveals that of key importance to achieving this long-term protection is a strong graphene-metal interaction[1], which prevents the intercalation of oxidizing species at the graphene-metal interface and thus suppresses oxidation of the substrate surface.[7] Furthermore, the ability of the substrate to form a passivating oxide is critical in preventing oxidation from proceeding instead through the bulk, fed through defects or damaged regions in the graphene overlayer. We thus provide a clear rationale for understanding the extent to which two-dimensional materials can protect different substrates, and highlight the key implications for applications of these materials as barrier layers.
(1) Weatherup et al. Nano Lett. 2011, 11, 4154
(2) Weatherup et al. ACS Nano 2012, 6, 9996
(3) Weatherup et al. ChemPhysChem 2012, 13, 2544
(4) Weatherup et al. J. Am. Chem. Soc. 2014, 136, 13698
(5) Dlubak et al. ACS Nano 2012, 6, 10930
(6) Kidambi et al. Nano Lett. 2013, 13, 4769
(7) Weatherup et al. In Preparation

Carbon-based metal-free electrocatalysts for oxygen reduction reaction (ORR) have attracted significant attentions and have been vigorously investigated to replace precious metal-based catalysts. To enhance ORR activities of the metal-free catalysts into the level close to those of precious metals, it is crucial to understand active sites of the carbon-based electrocatalysts. To test a null hypothesis that defects of carbon play an important role of ORR, we used carbon balls, the defects of which are controlled by temperature. The carbon balls were prepared from glucose solution via a hydrothermal process followed by heat treatment between 400#8451; and 1000#8451; in argon. Carbon balls of higher D/G (disorder/graphitic) ratios measured by Raman spectroscopy showed higher ORR activities. For example, carbon balls prepared at 1000 #8451;, which contain the highest level of defects, showed the highest ORR activity among a series of carbon balls. Preferential adsorption of oxygen on defects was proved to be responsible for the ORR activity improvement by temperature programmed desorption technique (TPD). The role of defects was also confirmed by comparing ORR activities between bare carbon balls and defect-blocked carbon balls obtained by atomic layer deposition (ALD).

Freestanding films of reduced graphene oxide (rGO) have attracted much attention as electrodes for electrochemical capacitor, especially for flexible device applications. However, graphene paper electrodes are usually limited in thicknesses to less than 10 mu;m, as increasing the electrode thickness hinders its performance due to restacking of rGO sheets and slow diffusion of ions [1]. To prevent this problem, carbon nanoparticels such as carbon nanotubes (CNTs) are frequently used as nanospacers between the rGO sheets to increase the electrolyte accessibility and electronic conductivity of the films [2]. However, CNTs have a much lower capacitance compared to rGO and their addition limits the overall capacitance of the freestanding electrodes.
In this study, for the first time, we have used highly porous carbide derived carbon (CDC) nanoparticles as spacer between graphene sheets and fabricated thick rGO/CDC hybrid electrodes. The electrodes were made by thermal reduction of GO/CDC papers fabricated by vacuum-assisted filtration of aqueous solutions of GO and CDC containing 10, and 20 wt. % of CDC. Utilizing the high surface area and conductivity of rGO and the accessible pores of the CDC [3], the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a high scan rate of 100 mV/s in an aqueous electrolyte. The addition of CDC between the rGO layers increases the accessibility of active material to the electrolyte ions and we observed good performance of the electrodes with the thickness of 40-50 mu;m.
References:
1. Oh, Y.J., et al., Oxygen functional groups and electrochemical capacitive behavior of incompletely reduced graphene oxides as a thin-film electrode of supercapacitor. Electrochimica Acta, 2014. 116: p. 118-128.
2. Wang, Y., et al., Preventing Graphene Sheets from Restacking for High-Capacitance Performance. Journal of Physical Chemistry C, 2011. 115 (46): p. 23192-23197.
3. Chmiola, J., et al., Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer. Science, 2006. 313 (5794): p. 1760-3.

Because of particularly high theoretical energy density, metal-air batteries are considered one class of promising power sources for energy related application such as electronics, electrified transportation and energy storage of smart grid in next-generation. The attracted several benefits of metal-air batteries are high energy density, cost-effective design, easy handling and eco friendliness. Also, it is generally regarded that the most distinct aspect of a metal-air battery is the air electrode using oxygen from surrounding air infinitely. However, the performance of these electrochemical devices shows limitation by the sluggish oxygen reduction reaction (ORR) kinetics. At present, the most effective and used ORR catalyst for air electrode of metal-air batteries is Pt, Pt based alloys and oxides; they, however, are very expensive and have limited availability. Recently, nitrogen doped carbons have been remarkably attracted as efficient metal-free electrocatalysts because of the disordered carbon nanostructures and electron donation from nitrogen to adjacent carbon. Although various method for nitrogen doping into carbon are available such as pyrolysis, carbonation, CVD and etc., these method are required many step and high cost. We recently proposed a facile method for synthesizing carbon materials using solution plasma processing (SPP). Here, we successfully synthesized the nitrogen doped sheet like nanocarbon without any pre-treatment and future annealing process and apply these easily scalable materials as metal-free electrocatalysts for ORR in alkaline media. Nitrogen doped sheet like nanocarbon was formed irregularly stacked with small sheet morphology after solution plasma process. From the CV measurements, the ORR onset voltage corresponding to ORR activity increased from -0.22V to -0.17V and the current density also increased about 4 times when the solution plasma was discharged in higher electrical energy. Our results demonstrated that the solution plasma process we proposed shows high possibility for the synthesis of carbon based catalyst for metal-air battery and fuel cell.

Carbon nanotubes (CNTs), a new allotrope of carbon, exhibit tunable electrical, optical and mechanical properties. All these properties are interrelated with the structure of the as-fabricated carbon nano-materials and the network. Controlling the alignment and bonding of the carbon conjugated system, optical as well as electrical properties can be tuned. Surface roughness of the nano-surface plays an important role in tuning optical properties. Vertically aligned carbon nanotube forest can behave like a black body and it originates from the sparseness and alignment. This kind of nano-surface is ideal for minimizing optical reflection and could have important consequences in maximizing solar energy harvesting.
We experimentally demonstrate that light reflection from the top Carbon Nanostructured (CNS) thin surface is nearly wavelength independent in the range of 250-2300 nm. UV-vis-NIR specular and diffuse reflectance spectra of as fabricated thin CNS surface (200µm -300µm) show tunable reflectivity. Tunability of surface reflectivity originates from the roughness, mesh like network structure and the alignment. Thin CNS surface has mesh like network structure with specific directional orientation that exhibits substantially low reflectance (about 6.5%). Transmission electron microscopy (TEM) and atomic force microscope (AFM) has been employed to investigate mesh like structure, specific alignment and the roughness. CNS surface has been compressed to reduce the roughness to study the dependence of specular reflectance on roughness. CNS surface with reduced roughness potentially increases the reflectance (about 14%) and shows a linear dependency on wavelength.
Carbon nanostructured surface has been decorated with TiO₂ (diameter is about 120 nm), and iron (III) oxide (Fe₂O_3, diameter is about 50 nm) nanoparticles to increase the surface roughness. Effect of the surface roughness has been studied to tune the optical properties. Incorporation of nanoparticles improves the thermal stability and has been determined by using thermogravimetric analysis (TGA). By this work, we demonstrate a scalable method to fabricate thin carbon nanostructured surface that can be tuned to have low reflectivity.

Graphene nanoplatelets (GNPs) are a novel nanofillers including single or multilayers of a graphite plane which possesses exceptional functionalities, high mechanical strength (1 TPa in Young&’s modulus and 130GPa in ultimate strength), and chemical stability, for the following reasons: their abundance in nature and thus their cost effectiveness and their extremely high-specific surface area, which carries high levels of transferring stress across interface and provides higher reinforcement than other carbon materials. Because of their high absolute strength, large surface area and cost-effectiveness, graphene nanoplatelets (GNPs) have high potential for improving the material properties of polymer-based composites. In this study, the graphene nanoplatelets (GNPs) modified with maleic acid (MA) were used to reinforce epoxy composite to enhance their mechanical properties. The mechanical properties of GNPs/epoxy nanocomposite, such as ultimate tensile properties, flexure properties and impact strength were investigated. Significant improvement in the mechanical properties of nanocomposites containing different proportions of GNPs (0.25, 0.5, 0.75 and 1 wt%) were increased over that of neat epoxy resin.
The fracture surfaces of the neat epoxy composites (without adding GNPs) and the GNPs/epoxy nanocomposites were comparatively examined using Scanning electron microscope (SEM). The images showed that nanofillers exhibited higher solubility and compatibility in epoxy matrix. Therefore, embedding GNPs can restrain creviced growth in the GNPs/epoxy nanocomposites and prevent the expansion of these cracks.

In order to achieve both efficient utilization of light absorption and controlled contacting of graphene and titania nanoparticles, layer-by-layer (LbL) technique was applied to fabricate hybrid photocatalytic films with either altanative graphene and P25 nanoparticles (NPs) layers or mixed graphene and P25 NPs. The structures and photocatalytic properties of different lbl hybrid fims were compared and discussed.

We are motivated to screen from the organo-metal reagent family, which displays good reactivity to water and the hydroxyl group, to design a new type of graphene oxide framework (GOF) compounds. In this presentation, we report a highly expanded GOF compound formed via intercalation of different organo-Ti reagents into GO accompanied by an intra-gallery hydrolysis process. Such new GOFs can be transformed into nanocomposites of TiO₂ and carbon nanosheets under controlled conditions, which are promising as synergetic photocatalysts towards the treatment of trace organic contaminates in a water environment.

Carbon nanowalls (CNWs) synthesized by plasma-enhanced chemical vapor deposition (PECVD) have attracted much interest due to the unique structure consisting of nanographite domains with several tens of nanometers [1,2]. Recently it was reported that CNWs also play a role as platinum (Pt) catalyst supports of electrodes in fuel cells [3]. According to the report, Pt nanoparticles are preferentially absorbed along the domain boundaries in CNWs. In addition, the Pt nanoparticles supported on CNWs (Pt/CNW) exhibit relatively high catalytic activity for anodic oxidation of hydrogen. Therefore, the control of domain structure of CNWs can lead to further improvement of the catalytic activity of Pt/CNW. In this paper, we report the control of domain size in CNWs by PECVD, Pt loading on them, and the measurements of the catalytic activity.
CNWs with different domain sizes were synthesized by PECVD. The Pt loading on the CNWs was carried out by the solution reduction method. As result, the Pt nanoparticles were preferentially absorbed along domain boundaries in CNWs as reported previously. It should be noted that the Pt particle size strongly depend on the domain size. Namely the smaller the domain size is, the smaller the Pt particle size is. The Pt/CNWs with smaller Pt particles exhibit high catalytic activity. Especially the cathodic activity for oxygen reduction reaction is high and reach two times as much as that of commercial available T-Pt/CNWs with good performance. This suggests that Pt/CNWs is a promising catalytic electrode for fuel cells.
[1] S. Kurita et al., J. Appl. Phys. 97, 104320 (2005).
[2] K. Kobayashi et al., J. Appl. Phys. 101, 094306 (2007).
[3] S.C. Shin et al., J. Appl. Phys. 110, 104308 (2011).

The fabrication of carbon nanofiber arrays with controlled geometrical structures has attracted much interest owing to their applicability to various types of functional devices. Although there have been many reports on the fabrication of carbon nanofibers, a high-throughput preparation process of carbon nanofibers with controlled geometrical structures has not be established so far. In the present report, we describe the preparation of carbon nanofiber arrays based on the nanoimprinting using anodic porous alumina as a mold. Nanoimprinting is a promising technique for the high-throughput preparation of polymer nanopatterns on a surface of substrate. In our previous reports, we showed the preparation of polymer nanostructures with high aspect ratios by nanoimprintng using anodic porous alumina molds [1-3]. Anodic porous alumina is a typical self-ordered nanohole array material [4]. The nanoimprinting using anodic porous alumina molds allows the preparation of ordered polymer nanofiber arrays with high aspect ratios on the surface of substrates. In this work, the carbon nanofibers were formed by heat treatment of the obtained polymer nanofibers. The geometrical structures of carbon nanofibers could be controlled by changing the anodic porous alumina molds. The carbon nanofibers obtained by the present process will be useful for the various application fields. [1] T. Yanagishita K. Nishio, and H. Masuda., Jpn. J. Appl. Phys. 45, L804 (2006)., [2] T. Yanagishita K. Nishio, and H. Masuda, Appl. Phys. Exp., 1, 067004 (2008)., [3] T. Yanagishita, K. Nishio, and H. Masuda, Appl. Phys. Express, 2, 022001 (2009)., [4] H. Masuda and K. Fukuda, Science 268_, 1466 (1995).

The investigation of carbon-based materials at atomic scale has been subject of intense theoretical and experimental research in recent years. Among these structures carbon nanoscrolls (CNSs) [1, 2] present very unique and interesting properties. CNSs are graphene sheets rolled up into a papyrus-like shape. Due to their open ended topology, they exhibit large radial flexibility (their diameter easily tunable through physical and/or chemical processes) and large accessible surface area. These properties can be exploited to use them as nanoactuators [3] or for hydrogen storage [4]. However, CNS mechanical properties have not been yet fully investigated. Recent experimental/theoretical works showed that under certain conditions carbon nanotubes (CNTs) can be unzipped when shot at high velocities against metallic targets [5]. These investigations showed that the key parameters which determine the resulting structures from these collisions are the velocity values and the relative orientation of the CNT axis with relation to the target. In this work we have investigated the dynamical and structural properties of CNSs shot at high velocities against different targets. We have considered cases that mimic the similar conditions of the CNT experiments [5]. We have carried out fully atomistic molecular dynamics (MD) using the reactive force field ReaxFF as implemented in the well-known LAMMPS code. Our results show that the velocity and scroll axis orientation remain key parameters to understand the resulting CNS structures after impact, but the relative orientation of the scroll open ends and the substrate is also very important. We observed that for appropriate velocities and orientations, the nanoscrolls can either be unscrolled back into graphene layers or be unzipped into nanoribbons. Another interesting result was that if the CNS impacts the substrate with its open end, for certain velocities, fused scroll walls were observed. For comparison purposes we also considered BN scrolls. For all the cases investigated here, BN fused scrolls were never observed.
[1] S. F. Braga, V. R. Coluci, S. B. Legoas, R. Giro, D. S. Galvao, and R. H. Baughman, Nano Lett. 4, 881 (2004).
[2] E. Perim, L. D. Machado and D. S. Galvao, Frontiers in Materials 1, 31 (2014).
[3] R. Rurali, V. R. Coluci, and D. S. Galvao, Phys. Rev. B74, 085414 (2006).
[4] V. R. Coluci, S. F. Braga, R. H. Baughman, and D. S. Galvao, Phys. Rev. B 75, 125404 (2007).
[5] S. Ozden, et al., Nano Lett. 14, 4131 (2014).

Operating glove boxes that contain radioactive isotopes offers a risk to an operator for exposure, and the use of thick gloves or robot teleoperation may prove prohibitive. In our work, we study the benefits of carbon nanomaterial additives to a reference butyl rubber matrix for improvements in impermeability, protection of the glove from radiolysis, and mechanical properties to help prevent a rupture failure in the use of glovebox gloves used to isolate an operator from radioactive substances. We employ several strategies, using composites of carbon nanotubes, graphene and mixtures of the above with carbon black blended with butyl rubber. Also, we employ a second strategy where we produce laminate graphene layers formed directly on the butyl rubber gloves as a permeation barrier. We investigate the mechanical properties with puncture tests, tensile, DMA, and wear testing before and after exposure to beta radiation to determine the capabilities of these gloves to stand up in such an operating environment.

3D graphene materials and structure become the hot research with the study of graphene and the excellent thermal, optical and electrical properties of graphene itself. The construction of 3D material including the pore size distribution, pore volume, etc., is especially important for the field of energy storage and sorbents.
The most common structures of 3D graphene materials are graphene foam and graphene gel, and these 3D structure are obtained with a series chemical treatment procedures. In this report, we had developed a novel hot solvent fast separation method to prepare graphene composite microspheres with fine structure and uniform size, to achieve perfect combination of graphene sheets and other nanomaterials. The procedure is performed by mixture single layer graphene with selected nanomaterials and then treated with special procedure. Then microsphere graphene with diameter varies from several hundred nanometer to several microns, and the specific surface area varies from 1000 to 2400 m²/g are obtained in bulk scales. This simple and versatile method had effectively avoided the disadvantages of conventional solution mixing, such as low efficiency, high pollution and structural disorder, etc. In addition, the graphene sphere also exhibit high packing density, low oil-absorbed value and controllable morphological structure. Therefore, it is possible to achieve the effective use of graphene in the field of supercapacitors, conductive inks, sorbents for removal organic pollutants and as supporting materials for various catalysts.

Carbon nantubes (CNTs) and graphene have the excellent mechanical properties, e. g., high flexibility and high toughness. These superior mechanical properties evoke trials of fabrication of nanocarbon hybrids. Lv et al. (2014) reviewed examples of graphene-CNT hybrid nanostructures such as 3-dimensional CNT networks, a hybrid of graphene with vertical CNTs, a hybrid of graphene with horizontal CNTs, rebar graphene, and a graphene-multi-walled carbon nanotubes (MWNT) hybrid film. In these hybrids except the last, the connections between CNTs or between CNTs and graphene are realized by sp2 bonds. On the other hand, in the graphene-MWNT hybrid films, the van der Waals interactions or pi-pi interactions are the interaction force connecting the building blocks. This connecting manner leads to the flexibility of fabricated macroscopic films. Tristán-Loacute;pez et al. (2013) prepaired large-area hybrid films in the form of alternating layers of graphene and multi-walled carbon nanotubes. Their films show superior electronic conduction and are also applicable to electric field emission sources. However, their films are not transparent because the CNTs consisting of their alternating layers are MWNTs. Hence, one of the ideas to secure the transparency of hybrid films is to intercalate SWNTs between graphene sheets. In this paper, the mechanical properties of the alternating layers of grahene and SWNTs are addressed via molecular-dynamics simulation. In simulation models, SWNTs are interacalated parallel to each other between graphene sheets. The periodic boundary condition is applied in the direction of the axes of the SWNTs. The indentation forces are imposed on the carbon atoms on one or two columns of the uppermost graphene sheet. Thus, the simulation models are quasi-two dimensional. How the load-deflection curves depend on the number of layers and the diameter of SWNTs is discussed. Our results will serve as the fundamental data of the deformation and strength of the graphene-SWNTs hybrid films.

The geometry and conformation of biological materials determine their correct functioning in highly selective biological environments. Therefore, understanding the correlation between the geometry and properties of such biomaterials is crucial for exploring their potential applicability in various biologically-relevant processes. For example, developing nanoscale vectors for the targeted delivery of drugs requires a good understanding of their flow behavior in biological channels. Since the targeted tissues are commonly accessed through the blood capillaries, the study of the flow properties of the biomaterials in such confined conduits could provide important insight as to their efficacy as both drug delivery vectors and therapeutic modalities.
Carbon nanomaterials (CNMs) are emerging as materials of interest in biological applications, particularly with respect to their toxicity in cancer tissues. The selective uptake of CNMs in cancer tissue can be utilized for multi-fold applications such as drug delivery and ablation therapy. Also, Gold Nanoparticles (Au NPs) have been extensively utilized in cancer treatment via Thermal and Radio frequency ablation.
This work describes the decoration of graphene oxide sheets and gold nanoparticles in-situ to give geometrical variants of the Au-CNM composite materials. Micro and Nano-scale graphene oxide was synthesized using Modified Hummers Method. Uniform in-situ synthesis of 10-50 nm gold nanoparticles on graphene oxide sheets is reported. Characterization techniques such as electron microscopy, dynamic light scattering and atomic force microscopy have been used to study size, morphologies, and elemental analysis. Comparision of Raman Spectras show intercalation of gold nanoparticles in between graphene oxide sheets. Rheological measurements of such geometrical variants of CNMs, Au-NPs and Au-CNM composites in polyethylene glycol (PEG) solutions having blood-like viscosity were conducted, as a step towards observation, simulation and study of geometry effects of nanomaterials on blood flow. Furthermore, combined efficacy of Au-CNM composite for RF ablation of cancer cells has also been explored.

Supercapacitor, also called electrochemical capacitor, is considered to be very promising energy storage devices, as they have excellent power density and life-cycle stability. The development of supercapacitors has focused on the utility of graphene, as an electrode material, because of its outstanding electrical properties and high specific surface area. Recently, gaphene material is most easily produced by the reduction of graphene oxide (GO) and can be manufactured by cost-effective chemical methods with a high yield, making them potentially promising active materials for the energy storage field. However, the typical two-dimensional (2D) sheet-like graphene tend to aggregate and restack irreversibly due to strong van der Waals attraction, which leads to the loss of the available surface area and their solution accessibility. In order to solve these problems, many approaches have been proposed for converting the 2D graphene sheet into 3-dimentional (3D) structures to prevent aggregating and restacking during process.
In this study, we describe a novel strategy for the synthesis of 3D crumpled structure, namely crumpled graphene ball (CGB), from 2D GO sheet via aerosol spray pyrolysis. CGB with different reduction levels have been effectively produced through thermal reduction of 2D GO sheet in the temperature range of 100-300 ^oC. Also, it was found that both the morphology and the size of CGB are predominantly governed by the initial concentration of GO sheet. The effects of structural parameters such as interlayer spacing, oxygen content, surface area and disorder degree on their specific capacitance were explored systematically.

Conductive porous carbon plays critical roles as electrode material for energy storage devices that include supercapacitors and lithium-ion batteries. Using commonly available cellulous fibers as the raw material to produce porous carbon, which is further doped to enhance the electrode conductivity, is a promising approach to achieve high-performance and low-cost electrodes. Herein, cotton is used as a precursor to fabricate heavily nitrogen doped porous carbon (NPC) in a one-step process by pyrolysis in ammonia environment. The nitrogen content and specific surface area of the NPC can be well controlled by adjusting the pyrolysis temperature and duration. The NPC was further used as electrode to assemble supercapacitors and lithium-ion batteries. Their electrochemical characteristics were studied, including cyclic voltammograms, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. Promising results, including high capacity and excellent cycling stability were obtained. Through experimental and theoretical analysis, we find that nitrogen content and surface area have a synergetic effect on the performance of NPC electrodes. This study opens a new route to economically produce high-performance carbon electrodes for energy storage devices.

The report is dedicated to an experimental study of supercapacitors based on the functionalized nanostructured carbon materials such as activated carbon (AC), carbon nanotubes (CNT), and activated carbon cloth (ACC) as the electrodes and novel types of water-based electrolytes with increased electrochemical window of operation.
Two types of chemical functionalization of the nanocarbon materials (AC, CNT, ACC) were carried out. In the first functionalization scheme, grafting the nitrogen containing ionizable groups such as nitro and amino groups onto the nanocarbon materials surface was performed. The functionalized and pristine nanocarbon materials were used as the electrodes in symmetrical supercapacitors on the base of standard acid-water electrolyte. It is shown that the functionalization leads to the increase of the specific electric capacity of approximately 1.5 times for AC, 3 times for CNT, and 1.6 times for ACC.
The second functionalization scheme consisted in the halogenation of the nanocarbon materials via treatment with fluorine, chlorine, bromine, or iodine. Distinct decrease of the electrolysis process intensity under overpotentials of up to 1.8 V is shown for halogenated carbon nanomaterials in comparison with the pristine ones in the standard acid-based water electrolyte. The physical-chemical processes leading to the effects observed for functionalized materials such as material porosity change, wettability increase, specific interactions between the grafted functional groups and electrolyte ions, redox processes as well as passivation of the active electrolysis centers are discussed.
Regarding the increase of the supercapacitor operating voltage, the most widespread to date electrolytes with large electrochemical window are based on ionic liquids. However ionic liquids are expensive and characterized by low electric conductivity. To increase the operating voltage of the supercapacitor while maintaining the conductivity relatively high, we propose a new type of electrolytes based on high-concentration water solutions of organic substances and metal perchlorates. It is thought that the high degree of water bounding to solvated ions will impede the electrochemical processes in the dense electric double layer charge.
Indeed, it is shown that the electrolytes proposed can operate at up to 2 V in pulsed regime without significant influence of electrolysis. At the same time, the conductivity of the supercapacitors based on the new electrolytes decreases by no more than 2 times in comparison with the standard acid-based water electrolyte that is significantly better than the conductivity of ionic liquids. Moreover, the eutectic water solutions of organic substances and metal perchlorates are shown to significantly decrease the lower temperature limit of supercapacitor operation down to approximately -40 °C.

Recently, a lot of R&D activity is dedicated to gas sensors based on different forms of nanocarbons. Special attention is paid to graphene owing to its unique properties and large investments. However, the price for graphene remains relatively high owing to lack of mass production. Moreover, manipulating graphene nanosheets to build them into sensor structures can be a challenging process. The present report is dedicated to experimental study of gas sensor structures formed using activated carbon fibers (ACF) as the functional sensing element.
ACF is a highly porous nanostructured material. ACF is produced via viscose fiber pyrolysis and carbonization at 1000 °C with subsequent activation by water vapor at 800 °C. Specific surface area of ACF is up to 2000 m2/g. Taking into account its high surface area, ACF can be considered as a 3D carbon mesh with graphene-like regions. Hence, ACF is a candidate for graphene replacement in less demanding applications. At the same time, ACF is a macroscopic object with the thickness of 1-100 mu;m and therefore, it can be easily handled and manipulated.
Gas sensing structures were produced by housing the ends of an ACF inside graphite paper electrodes mounted onto a nonconducting substrate. The length of the ACF between the electrode housings was 2-3 mm. The sensing structures produced were included into a bridge measuring circuit so that the change of the resistance of the ACF upon exposure to different gases could be easily measured.
The ACF-based sensors were exposed to a number of gases and saturated vapors of liquids: bromine, hydrochloric acid, ammonia, nitrogen dioxide, water, ethanol, propane, butane, triethylamine. It is shown that the response of the sensors can be described the best taking into account donor-acceptor properties of the gas under measurement. Under exposure to “acceptor” gases, the resistance of the ACF decreases, whereas under exposure to “donor” gases, the resistance increases. The kinetics of ACF resistance upon exposure is generally characterized by the initial irreversible change that is thought to be defined by the chemisorption of the gas analyzed. The following change of the resistance is thought to occur owing to physical sorption. It is completely reversible upon “ventilation” of the sensor by dry air and thus, can be used for recurring measurement.
As the sensors were found to be selective mainly to the donor-acceptor properties of the gases, different types of ACF chemical activation were studied. It is shown that chemical activation such as nitrosulphuric or hydrazine treatment changes the response of the sensor significantly. Such chemical modification thus opens a way to build “electronic nose” gas recognition systems based on arrays of ACF sensing structures that were subjected to various chemical activation procedures. The perspectives of ACF application in other graphene-connected areas, such as FET, is discussed as well.

Carbon fibers (CF) are lightweight materials and are associated to excellent mechanical properties, high thermal and electrical conductivity and low thermal expansion coefficient. These characteristics have been attracted attention of many research groups in different science field and application [1-5]. One of the most applications used for CF is the activating. The activated carbon fibers (ACF) have an interesting adsorption capacity. The adsorption capacity is due to the ACF have well-defined pore structures which provide a high specific surface area in contrast with CF. ACF is one of the most widely used adsorbent materials around the world. Normally, ACF is used for the drinking and waste water treatment and in many other applications where the removal of generally dispersed contaminant molecules is desired [6]. The goal of this work was to produce inexpensive activated carbon fibers and characterization the fibers for future applications in metallic substance removal from water. In this work, the carbon fibers were produced from the carbonization of Brazilian textile polyacrylonitrile fiber. Carbon fiber were produced from PAN fiber oxidation in air (260°C) and carbonized in argon atmosphere at 900°C. The activation process was performed immediately after carbonization by shifting the argon gas to CO₂ and rising up the temperature to 1000°C during 50 min. The morphologies of activated and not activated carbon fiber were characterized by scanning electron microscope (SEM). The morphological surface analyze indicated the existence of pore on the surface of the ACF increasing the surface roughness and wetting ability. X-ray photoelectron spectroscopy (XPS) was used to measure presence of oxygen content on the fibers. It was observed by XPS a high intensity in the capture of the carbon electrons of the ACF this shown a significant reduction of oxygen in the ACF. Raman spectroscopy and X-ray diffractometer (XRD) were used to structural characterization. By using the Raman spectroscopy was possible to analyze fibers superficially while XRD analyzed more internal structures. The Raman spectrums were fitted in four Gaussian and one Lorentzian curve as reported in literature. The Raman results showed that the ACF presented an increase on D peak, which is linked to the disorganization of the graphitic structure. According to the DRX the CF had higher crystallites that the ACF, this decrease in crystallite was due to the surface tension during the activation process. These results are in according to the SEM and XPS results giving additional information about the influence of the activating for adsorption property of the ACF.

Detection of volatile organic compounds (VOCs) emitted from cancerous tumor cells in exhaled human breath allows for early diagnosis of various types of cancers. Graphene has much potential for use in sensor technology, but typical graphene sheet has limited surface area for gas sensing. Recently, three-dimensional (3D) graphene with the electrical properties like graphene has been synthesized from graphene oxide and polymer composite. 3D graphene with a large surface area would be a suitable material for creating novel sensitive VOCs sensors. In this study, 3D graphene was synthesized employing a reduction method as follows. Graphene oxide, formaldehyde and, hydroquinone, were mixed and heated in a sealed ambient at 85^oC to promote, a polymerization reaction. The polymerized compound was then reduced at 1050^oC under flowing Ar/H₂ gas, which was characterized by various techniques. A six-membered carbon ring structure and a decrease of oxygen-containing functional groups were confirmed by X-ray photoemission and Raman spectroscopies, and electrical conductivity increased by reduction. The surface area was 300 cm² calculated based upon BET surface area measurement of a sample area of 3 mm × 5 mm. A simple 3D graphene gas sensor was fabricated by applying Ag paste as electrodes to the edge of the sample. The capability of gas sensing was evaluated by measuring the electrical current response in flowing N₂ gas over a range of concentrations of acetone or 1-butanol at room temperature which are VOC markers used for lung cancer. It was observed that the device drain-source current correlated well with the VOC concentration. The adsorption of acetone decreased the current, but the adsorption of 1-butanol increased the current. The 3D graphene sensor gave larger current change than a previously fabricated graphene based FET sensor because more VOC molecules adsorbed on the graphene surface indicating potential applications for VOC sensing.

Recent theoretical and experimental works have been demonstrated that graphene nanoribbons (GNRs) are semiconducting with tunable bandgap controlled by their dimensions, making them interesting materials for various applications including nanoelectronics, energy storage, sensing, and nanocomposites (reference). However, pristine GNRs without functionalization are insoluble in polar solvents. Such poor processability has precluded the pristine GNR for applications. By introducing the oxygen-rich groups around a GNR, the resultant graphene oxide nanoribbon (GONR) should show a synergistic effect to have the bandgap of GNR and solution processability of graphene oxide (GO) (reference). It has been showed the chemical oxidative unzipping of carbon nanotube (CNTs) is an effective way to produce GONRs in a high yield. However, conventional chemical unzipping of CNTs were treated large amount of concentrated sulfuric acid (normally 1 mg/ml of CNT concentration in H2SO4) as a de-bundled agent to reduce the strong van der Waals force of bundled CNTs structure and unzipping CNTs completely. Moreover, it is still lacking a facile synthesis to produce GONRs in a high yield with controllable dimensions.
In this study, we show a facile solution-based chemical oxidative process for producing a nearly 100% yield of GONRs with controllable dimensions by lengthwise unzipping the starting CNT with different diameters. We aim to develop a green, facile and high-yield synthesis of dimension-controllable GONRs. Recently our group has developed a green and facile synthesis to produce GONRs by oxidative unzipping multi-walled carbon nanotube with 20 nm average outside diameter (O.D.) using a low amount of strong acids (10 mg/ml of CNT concentration in H₂SO₄). The key is to introduce nitrate salts as the de-bundled and intercalation agents in H₂SO₄, allowing the nitrate and sulfate ions to unzip CNTs completely in a low amount of H₂SO₄ (cite the Nature Chemistry paper). Significantly, we found that it is possible to produce GONRs with smaller width by unzipping the single walled carbon nanotube with 1.5 nm average O.D using the same approach. Detailed high resolution transmission electron microscopy (HRTEM) characterizations indicate that it is possible to produce GONRs with different widths by simply changing the starting CNTs with different diameters in our method. Systematic high resolution X-ray photoelectron spectroscopy (HRXPS) characterization suggests that the types and concentrations of functional groups attached on the surface of as-produced GNRs were controllable. The powder X-ray diffraction (XRD) shows a nearly 100 % yield of GONRs produced in our method and suggest an intimate relationship between the GONR yields and the initial concentrations of de-bundled and intercalation agents. Our developed method provides a useful strategy for structure modification of carbon nananometerials.

The combination of the control of CNT assembly density and the control of intrinsic carbon properties by doping can synergistically enhance the supercapacitive properties of CNT-based electrodes. In this study, we prepare CNT spheres and subsequently performed nitrogen (N) doping to fabricate CNT based supercapacitor. We control the doping content in the CNT spherical assembly and characterize the doping and its configuration, as well as the doping effect on the electrochemical capacitive properties. We confirm the morphological advantage of N-doped CNT spherical particles over CNT films in the electrochemical capacitive properties. Our approach is a facile and high-throughput method for producing compact packing of CNTs and, simultaneously, multiscale porous morphologies.

Super-absorbent polymers (SAPs) are often prepared by minimal crosslinking of hydrophilic polymers. It can absorb an extremely large amount of water compared to most hydrophilic materials, and the absorbed water is hardly removable even under some pressure. SAPs are widely used in various applications such as hygienic, foods, cosmetics, agriculture and architecture.
Polyacrylonitrile (PAN) is one of the most important fiber forming polymers. PAN fibers have many outstanding properties including their high strength, abrasion resistance, and good insect resistance. The stabilization process of PAN fiber is normally performed in the temperature range of 200 ~ 300#8451; under an oxidative atmosphere. During the process, PAN precursor fibers experience significant chemical and physical changes. Therefore, the stabilized PAN (Oxy-PAN) fibers are chemically and thermally stable while they are exposed to low or high temperature and alkaline solution.
There are many methods of manufacturing SAP such as hydrolysis, graft polymerization and crosslinking. One of the common methods for manufacturing a SAP was hydrolysis of PAN, and SAPs were commonly prepared in a granular shape and powders. It is desirable for fibers to possess high surface areas in many applications such as reinforcing fibers in composite, filter materials, and absorbent materials. The PAN nanofibers with high surface area can be a promising precursor for SAP application. However, this hydrolysis method has a difficulty to maintain the nanofibrous structure of PAN.
To overcome this drawback, Oxy-PAN nanofibrous webs fabricated by electrospinning were firstly stabilized by heat treatment, and subsequently hydrolyzed with various sodium hydroxide solution concentrations to impart the ability to highly absorb water. This was achieved through the chemical conversion of the nitrile groups on the surface of the PAN nanofibrous web. Attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) were used to confirm the chemical conversion on the surfaces of hydrolyzed Oxy-PAN (H-PAN) before and after hydrolysis. Water uptake was used to determine the water absorbing capacity. Also, the dimensional stability of H-PAN was observed by optical microscopy.

We have investigated quantum oscillations of the Hall conductivity in highly-oriented pyrolytic graphite (HOPG) with a mosaic spread (ZYH). High energy proton irradiations were performed on the samples to study the effects of point defects on the quantum transport properties. The components of the Hall conductivity tensor were calculated from the Hall resistance and magnetoresistance measured in a van der Pauw-configuration at 3 K. The Hall conductivities were then separated in terms of electron and hole contributions by applying band-pass filtering of Shubnikov-de Haas magnetoresistance oscillation. The integer quantum Hall effect-like plateaus were observed in both pristine and irradiated samples.

In this work has been investigated the synthesis and characterization of the potential photocatalytic of innovative catalysts composite materials based on the zinc oxide and/or metallic zinc dispersed in a matrix of amorphous carbon as the degradation of the phenol red dye. ZnO/Zn/amorphous carbon matrix nanostructured composite powder was prepared by partial pyrolysis method based on the classical Pechini method. Composite was characterized by infrared spectroscopy and X-ray diffraction. XRD pattern displays only some more intense diffraction lines ascribed to the ZnO and Zn metallic. The photocatalytic activity of the commercial ZnO (Vetec), ZnO/Zn/C and Zn/C composites were evaluated by the degradation reaction of the phenol red dye in the alkaline medium (pH = 9), using a low power reactor, equipped with a 15 W lamp type T8. A comparison of the photocatalytic activity of 100 mg/L of ZnO (Vetec), ZnO/Zn/C and Zn/C composites showed that the degradation rate of phenol red dye between 30 and 150 min reaction of the ZnO/Zn/C and Zn/C composites showed a higher phenol red conversion than that on pristine ZnO, being close to 82% for the ZnO/Zn/C and of 79% for the Zn/C, while the ZnO showed a conversion only about 66 %. These phenomena can be ascribed to a higher mass diffusion of phenol red induced from solution to the amorphous carbon playing the catalytic support role.

Reliable switching of high voltage and/or high current electrical power in a small form factor package in harsh environments remains an unresolved problem. Among the proposed technical solutions, ohmic RF microelectromechanical systems (MEMS) switches stand out compared with FET and PIN diode switches due to their low insertion loss and relatively fast switching speed in a small form-factor. However, there is to date no commercial supply of RF MEMS switches that will withstand harsh environments due to reliability issues in terms of switch lifetime.
Reliability is closely related to the metal-to-metal contacts of the switch, where micro welding, friction, wear and contamination can lead to reduced performance. [1]
Research groups across the globe have strived to overcome this specific obstacle in differing ways; ranging from alternate and improved switch architectures to various contact materials. [2-4]
In this work we focus on the study of integrated carbon-based and printed nanocomposites as contact materials that will be used to develop manufacturable RF MEMS switches with an aim to provide high reliability. A small portfolio of materials will be developed which have appropriate strength, surface texture, conductivity and hardness characteristics.
Specifically the materials to be investigated as contacts are; Carbon nanotubes (CNTs), Graphene and Diamond like Carbon (DLC). Each have previously demonstrated properties that make them extremely attractive for contacts in MEMS switches. These properties include high hardness and conductivity. The durability of these materials either alone or in a metallic composite configuration is speculated to improve the lifetime of the switch by several fold. [5]
Manufacturability will be incorporated as an objective of the material engineering. The use of composites opens up new routes to manufacture including both 2D and 3D printing in combination with more traditional lithographic patterning. Devices will be fabricated using these engineered nanomaterials and accelerated lifetime testing.
As a result of this work, the impact of integrating the aforementioned carbon-based nanocomposites into the microstructure of RF Ohmic MEMS Switches will be discussed.
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3. Chow, L. L. W., Volakis, J. L., Saitou, K. &
Kurabayashi, K. Lifetime Extension of RF
MEMS Direct Contact Switches in Hot
Switching Operations by Ball Grid Array
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479-481 (2007).
4. Leung, C. H., Shi, J., Lorincz, S. & Nedelescu, L.
Integrated microrelays: concept and initial
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(2002).
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resistance and contact force on Au coated
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2007.

The realization of large-area and low-cost flexible macroelectronics relies on both the advancements in materials science and the innovations in manufacturing techniques. In this study, we demonstrate extremely bendable and foldable carbon nanotube integrated circuits fabricated on a piece of ultrathin polyimide substrate through an all-printed process. We further demonstrate that the electrical characteristics of each integrated logic circuit can be tuned and optimized individually by using different numbers of carbon nanotube printing passes for different transistors in the circuit, manifesting the unique adaptability of ink-jet printing methods. Additionally, the adoption of a hybrid gate dielectric layer consisting of barium titanate nanoparticles and poly(methyl methacrylate) has led to not only excellent gating effect but also superior mechanical compliance. The circuit characteristics show negligible amount of change after up to 1,000 cycles of bending tests with curvature radius down to 1 mm, as well as very aggressive folding tests. This report on fully-printed and foldable integrated circuits represents a big advancement towards the practical applications of carbon nanotubes for high-performance and low-cost ubiquitous flexible electronics.

Expanded graphite intercalation compound (xGIC) /Polydimethylsiloxane (PDMS) nanocomposites was prepared by low temperature curing process. The effects of functionalized xGIC filler and cyclic stretching on the morphology and thermal properties of PDMS were investigated. The xGICs were uniformly dispersed in PDMS matrix and the degree of filler connection increased with increasing filler content. Fourier transform infrared spectroscopy (FTIR) confirms the Si functionalization presence on the surface of the xGICs. The sheet resistance of nanocomposite decreased from ~10¹⁷ ohm/sq. to 3 x 10¹³ ohm/sq. and the thermal conductivity was decreased from 0.80 W/mK to 0.65 W/mK after 1000 cycles stretching when the xGIC content was 20 wt%.Thermal stability enhancement with increasing xGIC was observed in thermogravimetric graph. This study reveals the importance of void formation at the interface on the thermal conductivity.

High-pressure studies on fullerene crystals have led to various interest phases such as polymer [1], amorphous and super-hard [2]. Recently, nano/microcrystals of fullerene C₆₀ have attracted much interest due to their unique shapes, structures and properties. Thus, high-pressure studies on such solvated fullerene nanocrystals are of very interest for the production of polymerizations and new materials [3]. In this paper, we report the structural change of Fc-doped C₆₀ nanosheets obtained by Liquid- Liquid Interfacial Precipitation (LLIP) method [4] under high pressure up to 5.0 GPa, where Fc is Ferrocene.
For high-pressure studies, the pressure was generated by a CLOCK type diamond anvil cell (DAC) and Ruby luminescence method was used for pressure determination. Raman experiments were carried out at room temperature using a Raman spectrometer (NRS 1000) with a 532 nm green laser line as excitation.
In the pressure dependence of Raman peaks of Fc-doped C₆₀ nanosheets, we observed two points of the change in the slope of the peak frequency with pressure at around ~0.5 and ~1.0 GPa. Moreover, the A_g(2) mode also exhibits clear splitting at ~2.8 GPa. In addition, we also observed the appearance of new peaks around ~450, ~600 and ~900 cm^-1 at the same pressure range. Furthermore, the effect of photo irradiation on the phase transition was also observed under high pressure.
These origins of some transitions will be discussed in the light of the charge transfer and polymerization.
[1] Y. Iwasa et al., Science 264, 1570 (1994).
[2] L. Wang et al., Science 337, 825 (2012).
[3] K. Kato et al., Trans. MRS-J (in press).
[4] T. Wakahara et al., J. Am. Chem. Soc. 131, 9940 (2009).

The vapor-phase deposition of carbon nanofibers from hydrocarbons is often accomplished using discrete nanoparticles, each of which forms a single nanofiber. While effective, this approach does have limitations. It would be simpler to form nanofibers from bulk catalysts having dimensions which greatly exceed the fiber size as their production is fast and easily scalable. Controlling fiber growth on this type of catalyst becomes much more difficult as the fiber size is no longer constrained by the particle size. Rather, the fiber forms from a small subunit of the catalyst particle. It is known that low surface area catalysts, like foil, will often form carbon as a solid film rather than a collection of fibers, but that under the right condition fibers will form. In this work, the mechanisms of growth are studied and methods for controlling microstructural factors are accomplished through mechnical alloying. Nonequilibrium processing allows for unique control over the catalyst composition and its micro/nanostructure. The challenges and successes of applying nonequilibrium processing to create efficient catalysts (including the Fe-Cu and Ni-Cu systems) are described. The optimized catalysts are then employed to rapidly deposit carbon nanofibers and create bulk components (cm dimensions) which are entirely fibrous and structurally coherent.

The oxygen reduction reaction (ORR) is the key cathode reaction in various types of fuel cells. Platinum (Pt) and its alloys have been used for practical electrocatalysts for the ORR. However, non-noble metal electrocatalysts are strongly desired since Pt is scarce and expensive. So far metal-nitrogen macrocyclic compounds, such as iron (Fe)-phthalocyanines, exhibiting relatively efficient eletrocatalytic activities has been studied as candidates of non-Pt electrocatalysts [1]. However, to make the electrodes in fuel cells, they are further deposited on carbon paper by wet process with solution. The process is complicated. The direct synthesis of carbon alloy catalysts on carbon paper is very attractive for the fabrication of fuel cell. In this paper, we report the direct synthesis of Fe-and N-doped nanocarbon catalysts on carbon paper by plasma-enhanced chemical vapor deposition (PECVD), and the high catalytic activity.
Fe- and N-doped nanocarbon catalysts were synthesized directly on carbon paper by the PECVD. The electrochemical evaluation for nanocarbon catalysts on carbon paper was carried out by using three electrode cell. The nanocarbon catalysts exhibit unique morphology and structure which are different from those of carbon nanowalls synthesized without Fe- and N-doping [2,3]. The linear sweep voltammogram shows that the onset potential is high and exceeds 0.88 V which is comparable to highest one in this field. X-ray photoelectron spectroscopy data also show that the graphite-like N is predominant as doping sites in the nanocarbon catalysts. In addition, the coordinate and/or function of Fe in the nanocarbon catalysts with high catalytic activity will be discussed in light of X-ray absorption and transmission electron microscopy observation.
[1] F. Sedona et al., Nat. Mater. 11, 970 (2012)
[2] S. Kurita et al., J. Appl. Phys. 97, 104320 (2005).
[3] S.C. Shin et al., J. Appl. Phys. 110, 104308 (2011).

Low-dimensional carbon nanomaterials such as fullerenes, nanotubes, graphene and diamondoids have extraordinary physical and chemical properties. Compression-induced polymerization of aromatic molecules could provide a viable synthetic route to ordered carbon nanomaterials, but despite almost a century of study this approach has produced only amorphous products. We recently reported recovery to ambient pressure of macroscopic quantities of a crystalline one-dimensional sp³ carbon nanomaterial formed by high-pressure solid-state reaction of benzene. Preliminary characterization revealed close-packed bundles of subnanometre-diameter sp³-bonded carbon threads capped with hydrogen, crystalline in two dimensions and short-range ordered in the third. These nanothreads promise extraordinary properties such as strength and stiffness higher than that of sp² carbon nanotubes or conventional high-strength polymers. They may be the first member of a new class of ordered sp³ nanomaterials synthesized by kinetic control of high-pressure solid-state reactions. Further investigation of this new 1-D carbon material has been conducted through inelastic neutron scattering, computational studies, and high-resolution transmission electron microscopy. These experiments have revealed higher crystalline order in the material, which has aided in the analyses of the chemical structure and the mechanism behind the compression-induced reaction.

Single graphene sheet had a theoretical specific area or about 2620 m²/g, and is considered as an ideal supercapacitor material. However, it was found that most graphene based supercapacitors only with capacitance values of approximately 130 -200 F/g in aqueous selectrolytes. These capacitance vales are lower than that the theoretical values of graphene based supercapacitors, partially because of that the flat graphene sheet significant lower its specific surface area. Higher capacitance of graphene-based supercapacitor can be fabricated with special treatment of graphene sheet, it was found that after converting flat graphene sheet into crumpled paper ball like graphene, graphene exhibit stability performance as supercapacitor materials with higher capacitance.
In this reports, we report a novel procedure to fabricate graphene composites with nanomaterials. We had found that with special treatment procedure and carefully selected nanomaterials. The as-prepared graphene composite exhibit fine structure, uniform size, higher packing density, better and easily controlled morphological structure, low oil-absorbed value. The specific surface area of graphene composites can reach to 2300 m²/g. These graphene composites give significantly capacitances of 300-350 F/g. In constant, the dried graphene gives a capacitance of 100-200 F/g only.

Carbon electrode materials demonstrate exceptionally high energy and power densities as supercapacitors and attract significant. However, their practical implementation is impeded by synthesis costs, limited operating voltage windows, and trade-offs between aerial capacitance and rate handling abilities. Subsequently, most conventional supercapacitor electrode materials implement expensive micrometer 1-10 µm porous carbons or nanometer (5 - 100 nm) sized carbon particles (graphene, onions or nanotubes) with finely tuned porosities and high accessible specific surface areas.
We present a novel internal surface area electrode with 50 - 100 µm diameter particles, a finely tuned microporosity, a specific surface area in excess of 1700 m²/g, and high capacitive performance. We obtained these carbide-derived carbon (CDC) materials via Cl₂ etching of coarse titanium carbide powder at 800 °C and subsequent annealing in H₂ at 600 °C. The carbon particles, which retained their coarse-grained structure, exhibited a narrow pore size distribution (d_av = 0.67 nm) that allowed for electrosorption of organic electrolytes and room temperature ionic liquids. Electrochemical testing using tetraethylammonium tetrafluoroborate ([NEt₄⁺]][BF₄^-]) solvated in acetonitrile showcased low ionic resistance, capacitance exceeding 120 F/g (at 10 mV/s), and high rate handling capability that allowed the material to store 60 F/g at a 1 V/s charge/discharge rate. We evaluated the performance of this carbon material using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm⁺][TFSI^-]) in neat and solvated configurations. Despite the viscous nature of the electrolyte, the material showcased over 110 F/g charge storage densities in a solvent-free state and 140 F/g while solvated in acetonitrile at a 10 mV/s sweep rate. Furthermore, neat RTIL electrolyte extended the voltage window of the material above 3.0 V, showcasing little electrochemical breakdown and improving the material&’s operational capability and energy density. We further explore the fundamental properties of this novel model system by mechanically milling or vacuum annealing the material to determine the influence of pore length and surface defects on fundamental properties of ion electrosorption in supercapacitors. We completed small-angle neutron scattering and X-Ray pair distribution function analysis to characterize the nanoscale structure of these porous particles. In addition to showcasing high capacitance, the coarse-grained carbon electrodes offer a less expensive supercapacitor fabrication approach and maximize resulting gravimetric and volumetric charge storage densities.

Heteroatom doping into carbon matrix has become one of the hot topics, because it endows carbon materials with a variety of positive effects, such as the improvement of catalytic activity of oxygen reduction reaction (ORR) and electrochemical capacitance for supercapacitors. From the practical point of view, both of nanostructural design and control of heteroatom doping are required, which are however very challenging.
To date, two dominant approaches to fabricate heteroatom-doped carbon materials have been developed: (i) carbonization of heteroatom-enriched compounds and (ii) post-treatment of carbons with reactive heteroatom sources. Regarding the former strategy, the amount of doped heteroatoms generally reduces as elevating the carbonization temperature. On the other hand, the latter approach can alleviate this restriction; the optimized reaction condition enables high-level doping without a remarkable change of pore properties. Hence, the post-treatment approach allows to control both of nanostructure and heteroatom doping. However, the use of toxic reactive gas (e.g. NH₃ or HCN for N-doping, and H₂S and SO₂ for S-doping) makes researchers hesitate to choose this approach. As a more favorable way, the use of urea or melamine as the reactant in the post-treatment to obtain N-doped carbon has been reported. In this case, however, thoroughly mixing the solid reactant with precursor carbon materials is difficult, which cannot be applied to monolithic carbons but only to powdery carbons.
In the present study, we have developed a new method for N-, P- and S-doping into carbon via a versatile post-treatment without using toxic gas flow conditions. The heat-treatment of carbon materials with a reagent, which is stable in an ambient atmosphere and evolves reactive gases on heating, in a vacuum-closed tube allows the introduction of various heteroatom-containing functional groups into carbon matrix. This method does not significantly change the nanostructure of original carbon materials, which indicates that independent tuning of heteroatom doping and nanostructural design can be achieved in various carbon materials. In addition, the sequential reactions of carbon materials allow for the binary- and ternary-heteroatom doping, which expands the versatility of the new technique. Furthermore, we have also investigated the effects of heteroatom doping on electrochemical capacitance by applying the obtained heteroatom-doped carbon monoliths to monolithic electrodes for supercapacitors

Here we present a comprehensive meta-analysis of the most diverse range of nanomaterials, to date, for field electron emission, including 1D, 2D and 3D/bulk materials. In the 132 papers considered, effects of the various deposition methods, aspect ratio and geometry, uniformity, as well as operating conditions have been considered in detail to unify an otherwise disparate field. New definitions of the turn on and threshold electric fields allow direct comparison between materials, resulting in a comprehensive and novel comparison. Factors affecting the field emitting capabilities, as defined relative to Fowler Nordheim theory, are considered, with specific interest into the effect of the work function and the morphology of the emitter. We find that there is little direct correlation between low work function and high field emission current and low turn-on field, and that of the wide range of materials available, the nanographitic allotropes, and in particular the carbon nanotubes, are some of the most promising.
The morphology of the emitter is similarly influential on the efficiency of the field emission. However, intimate details of the effect of emitter morphology are little known or explored. Indeed, patterning of emitters is not a novel concept. Our studies have explored the emitter geometry using carbon nanotubes, due to their ability to be readily patterned and grown at the nanoscale. By undertaking measurements related to the aspect ratio, electrostatic screening effect, number of defect sites, and edge emission, we gain an insight into these workings.
In addition to this, the effect of plasma etching on graphitic materials has also been explored with regards to further enhancing the field emission. Plasma treatment was found to, on average, decrease the turn-on field by 20 %, with an associated average increase in measured current density of 14 mA/cm². The best performance was shown by graphene-based materials, using a nitrogen plasma, with an exposure time between 1 and 3 minutes, and a plasma power of < 200 W.

Despite displaying superior strength, conductivity, flexibility and durability, carbon nanofiber (CNF) applications have been limited due to the cost intensive complexities of their synthesis. Here we show that common metals act as CNF nucleation sites in molten media to efficiently drive the unexpected, high yield electrolytic conversion of CO₂ dissolved in molten carbonates to CNFs, and that CNT yield and conformation is controlled by oxide concentration and current density. We present an inexpensive, high-yield and scale-able synthesis of CNFs. We accomplish this by electrochemically reducing CO₂ on steel electrodes in a lithium carbonate electrolyte. The structure is tuned by controlling the electrolysis conditions, such as the addition of trace common metals to act as CNF nucleation sites, the concentration of added oxide, the addition of initiators and the control of current density. It is demonstrated that the process can be driven by efficient solar, as well as conventional, energy in a STEP, solar thermal electrochemical process. Scalability of the process is demonstrated from 1 A to 100A. An inexpensive source of CNFs made from carbon dioxide will facilitate the rate of its adoption as an important societal resource for the building, aerospace, transportation, renewable energy, sporting and consumer electronics industries, while concurrently consuming carbon dioxide.

There have always been great concerns about the element carbon, especially since the discovery of fullerenes, carbon nanotubes and graphene. Many new carbon allotropes have been proposed, the sp-sp² hybrid structure of carbon is theoretically predicted to be of characteristic properties and stable at ambient environment. First, we adopted bottom-up assembly approach to fabricate this structure. Through coupling polymerization reactions among terminal alkynes and aryl halides, the C-C bond was formed and the hybrid materials were synthesized. The produced sp-sp² hybrid structure was confirmed by Raman spectra. Different precursors and catalysts were employed to investigate the different among final products. Actually, the morphology of the hybrid materials could be controlled by reaction conditions. We investigated their application in energy storage fields. Silicon particles and conductive additives were coated by the in situ coupling polymerization of terminal alkynes, and the composite was applied in lithium ion battery anodes. Finally, the 2D sp-sp² hybrid materials are well known as graphyne, which was first proposed in 1980&’s. Here we designed a route to constructed graphyne like sp-sp² hybrid structures.

Electrocatalytic hydrogen evolution using non-precious metals or metal-free catalysts is critically necessary because platinum-based electrocatalysts are greatly limited in scalable commercialization of hydrogen generation due to their high cost. Here, we report the facile synthesis of metal-free hybrid catalysts, in which the graphitic carbon nitride (g-C₃N₄) is coupled with nanoporous graphene doped by S and Se. The S and Se co-doped hybrid catalyst (g-C₃N₄@S-Se-pGr) reveals superior electrocatalytic performances, including an exchange current density of 6.27×10^-6 A cm^-2, on-set potential of 0.092 V, Tafel slope of 86 mV/dec, adsorption free energy of -0.13 eV, and long-term stability comparable to those of commercial Pt/C catalysts. Volcano plots showing the hydrogen evolution activity versus adsorption free energy are also compatible with those of the conventional metal catalysts. Our strategy has the potential to allow a new paradigm for the development of high-performance metal-free electrocatalyst for energy conversion devices.

Scarcity of fresh water and its pollution is one of the major problems globally. Several methods such as reverse osmosis (RO), multistage flash distillation (MSF), mediated electrochemical oxidation (MEO), electrolysis and ion exchange have been proposed and implemented commercially for desalination and purification of water to meet these demands. However these have large energy footprints, resource and capital intensive. Thus there is an urgent need to devise novel techniques for efficient water desalination and purification economically. Graphene has recently been found to effectively filter ions from sea water. Here we report a working device made of hierarchically linked intrinsically defected graphene sheets by long microchannels for efficient and economical desalination and purification of sea water. This is easy to fabricate, reusable and economically viable for point of use application. The details of material processing and device fabrications will be discussed.

Well-developed surface area as well as suitable porosity of activated carbons stay at the origin of their wide application in electrochemical capacitors. Although the mechanism of energy storage in these devices is quite well understood, there are still some issues related especially with carbon electrode ageing which need more in depth studies.
It is widely accepted that ion transport within the carbon electrode bulk strongly depends on the porosity structure and interconnection of ions. However, it seems that there are some more specific criteria for effective ion transportation. It seems that some ions approach the interface easily and can be reversibly transported from/to electrolyte bulk, dependently on polarization applied. On the other hand, some ions - once interface is reached - tend to remain at the interface and cannot be reversibly desorbed. Such ‘memory effect&’ of the electrode has rather negative influence on the supercapacitor cyclability and charging/discharging efficiency.
This paper will report on electrochemical performance of various anions such as Cl, I, Br, SO₄, NO₃ as well as cations such metals as Li, Na, K, Cs, Mg, and Cu at electrode/electrolyte interface studied by various frequency-dependent methods such as electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance (EQCM). Several activated carbons with various type of porosity have been investigated in order to correlate porosity-related features with electrochemical parameters such as capacitance value, various type of resistance (ESR, EDR) and frequency response (mass change). Finally, aforementioned considerations will be discussed in direct regard of cyclability issues of carbon electrodes.

Hybrid nanostructures, especially the inorganic metal oxide nanostructure incorporated with graphene and/or reduced graphene oxide (rGO) sheets have received tremendous attractions since it is proposed that the drawbacks of these transition metal oxides (TMO) as anode materials originated from their intrinsically poor electricity and the large volume change could be simultaneously solved in the hybrid structure, which is quite attracting and exciting. During the past few years, there have been certain degrees of progress achieved on the metal oxide/graphene based hybrid nanostructures through which cycling stability and rate performance can be improved compared with those of the simple metal oxide nanostructures. However, the performance enhancement is still unsatisfactory in terms of long-term cycling stability and excellent rate capability for TMOs based anode materials, where much effort still needs to be devoted.
Manganese oxide (MnO) has been intensively exploited as a promising anode material due to its various advantages including high theoretical capacity, low conversion voltage, low voltage hysteresis and high density, which could be adopted for high energy density batteries. More importantly, MnO is quite cost-effective and environmentally benign compared with other TMOs such as Co₃O₄, NiO, MoO₃ and so on, which will fulfill the requirement of scalable applications. However, similar to other TMOs, MnO based anode for LIBs also has the drawbacks of poor cycling stability and inferior rate capability due to the pulverization effect resulting from large volume charge during Li⁺ insertion/extraction process and its intrinsically poor electrical conductivity. Hybrid structure of MnO nanostructure with carbon species could improve the lithium storage performance to some extent, but still be far away from the requirement of practical applications in terms of high rate, long term cycling stability and remarkable rate performance. Therefore, it remains an urgent and challenging task to build well defined MnO nanostructure based hybrid structure aiming to achieve long term cycles (> 1000 cycles) and excellent rate performance (> 500 mA h g^-1 at 3000 mA g^-1). In this work, we successfully fabricated the sandwich-like hybrid structure by paving a monolayer of MnO nanoparticles onto the surfaces of rGO sheets through a cost-effective glycol process followed by a simple thermal annealing treatment under nitrogen gas protection. Benefitting from the well defined structural features, the lithium storage performance of the rGO@MnO nanoparticle sandwiched structure exhibits impressive cycling stability and excellent rate performance.

Carbon nanomaterials have excellent conductivity and amenability for functionalization, making them desirable for applications in sensors and energy storage. We have explored paper-based sensing using carbon nanotubes (CNTs) as sensor medium. A novel dry plasma jet is used to deposit CNTs on paper substrates as an alternative to conventional inkjet printing, which may face clogging issues for excessive CNT lengths. Results show low ppm level sensitivity for ammonia, methane and other vapors and gases. We have also developed CNT based biosensors on paper for DNA detection and early diagnostics of heart disease. Our 2D carbon nanomaterial work focuses on vertical graphene (VG) by plasma enhanced chemical vapor deposition directly on metal substrates such as copper, nickel and stainless steel. The VGs appear like the blade of a knife, thick near the bottom of the substrate and tapering off to a few layers at the top, and a growth mechanism is proposed. The VGs appear to be suitable for the construction of supercapacitors, and preliminary results on storage capacity will be presented. The author acknowledges Jessica Koehne, Ram Ghandiraman, Jin-Woo Han, Beomseok Kim, Ami Hannon and Mike Oye.

Graphene and its composites have great potential as anode materials for Li-ion batteries (LIB) since their capacity was reported to exceed that of graphite, currently used as anode in most LIB [1].There are many methods to synthesize graphene, but there are still challenges to produce graphene at a large scale with desired properties that suit its perspective applications. Since there is yet no universal method for graphene production, especially that gives high yield, it would be reasonable to develop methods adjusted to specific applications e.g. electrochemical energy storage.
Liquid ultrasonic exfoliation of graphene is very popular technique however satisfactory yield of exfoliation is usually achieved with either toxic organic solvents or in the water solutions of surfactants, the latter results in contaminated final product, which is unacceptable for electrochemical applications.
In our work we used sodium carboxymethyl cellulose (NaCMC) as a water soluble “green” exfoliating agent for the high-yield graphene preparation. Since NaCMC is known to be a good binder for active electrode masses there is no need to remove it from as prepared graphene. Such approach allowed us simultaneous synthesis of graphene and preparation of electrode material for LIB.
Microwave assisted method for the liquid phase graphite exfoliation was developed in the present work. Addition of microwave heating step to sonication of graphite dispersions in solutions of sodium carboxymethyl cellulose (NaCMC) resulted in formation of concentrated graphene dispersions of up to 4.3 mg/ml after 10 hours of sonication; concentration of graphene was increased for 34% compared to using sonication alone. HRTEM and Raman spectroscopy revealed formation of few-layer graphene (3-4 layers). It was found as well that graphene yield depends on the molecular weight of the NaCMC - the higher molecular weight the higher graphene yield (up to 59% increase of graphene yield was observed for NaCMC with 250000 molecular weight compared to NaCMC with 90000 molecular weight). Drying of prepared dispersions resulted in the graphene/NaCMC composites with graphene content up to 38.65%. Yield and concentration of graphene can further be improved by increasing sonication time and recycling of sediment.
Graphene/NaCMC composite was tested as electrochemically active binder for using with Si nanoparticles in LIB electrodes. Si showed up to 51% capacity increase in the presence of graphene/NaCMC binder comparing to conventional NaCMC binder.
1. N. Lavoie et al. in Y. Abu-Lebdeh and I. Davidson (eds) Nanotechnology for Lithium-ion batteries,117 (Springer, NY, 2013).
2. A. Cieselski, P. Samori, Chem. Soc. Rev. 43, 381 (2014).

Carbon-based materials, including heteroatom-doped carbon, hard carbon, carbon nanotube, graphene and some other forms, have excellent conductivity, robust chemistry, good mechanical stability and great abundance, which show potential applications in the fields of energy storage, such as lithium-ion battery (LIB) and supercapacitor (SC). Doping with heteroatoms and fabricating various microstructures are efficient ways to functionalize the carbon materials, which can greatly improve the electrochemical performance.
For LIB electrode materials, carbons are commonly employed to fabricate multi-phase composites to achieve superior electrochemical performance. Porous or nano-structured carbons are helpful to accommodate the volume or stress change during charge and discharge especially for the LIB anode materials and hence to enhance the cyclability. Hard carbon is another alternative candidate for commercial graphite anode. Heteroatom doping and microstructure design are effective for performance improvement. For example, N-doped porous carbon with interconnected 3D nanofiber framework exhibits a specific capacity as high as 943 mAh g^minus;1 at 2 A g^minus;1 after 600 cycles.
For Li-S batteries, by constraining sulfur within carbon frameworks, the sulfur electrode shows greatly enhanced conductivity and reduced dissoluble loss of intermediate sulfur species in liquid electrolyte, leading to a much improved electrochemical performance. For the carbon matrices, morphology, porous structure and functionalization play important roles in determining sulfur loading, electrical conductivity, specific capacity and cycle life.
For SCs, carbon materials are also crucial to the performance. For example, functionalized 3D hierarchical porous carbon (THPC) prepared with polypyrrole microsheets as precursor presents large surface area, high-level heteroatom doping, good electrical conductivity, and hierarchical porous nano-architecture. It delivers specific capacitance up to 224.5 F g^-1 at current density of 0.2 A g^-1 and 152.5 F g^-1 at 30 A g^-1. Such unique features make the THPC become ideal electrode material for high-performance SCs.

The large specific surface area and excellent conductivity have made graphene a promising electrode material. We are developing graphene supercapacitors with large energy density and ionic liquid is used as the electrolyte to expand the operating voltage. Oxygenous functional groups are usually introduced in graphene-based materials and they are often involved in the interactions between the electrode and the electrolyte, which are affecting the performance of graphene supercapacitors. In this study we analyze the surface conditions of various graphene-based materials and probe the mechanism of chemical reactions between the ionic liquid electrolyte and the graphene electrode in order to increase the energy density of the supercapacitor.
The influence of functional groups on morphology and properties of graphene-base materials has been investigated. Epoxy and hydroxyl groups can prevent the re-stacking of graphene via twist and wrinkles, which are result from changed bond angles due to the introduced oxygen atoms. We also carried out structural and electrochemical characterization of the assembled graphene supercapacitors. Both Fourier transform infrared spectroscopy (FT-IR) and mass spectroscopy (MS) were used to detect the functional groups before and after charging, which are indicative of the interactions between graphene and the ionic liquid electrolyte. The hydroxyl groups are usually connected to EMI⁺ in electrolytes. At the same time, the double bonds between sulfur and oxygen in TFSI^#8209; will break up to lose oxygen atoms to graphene, while little reaction would occur on BF₄^- or MPPp⁺ under charging. The chemical reactions are indicated by the redox peaks between 1.5 and 2.0 V in cyclic voltammetry (CV), while electrochemical impedance spectroscopy (EIS) shows that the equivalent series resistance (ESR) stayed almost the same even though the reactions had taken place. These chemical reactions are suggested to have contributed to the electrode capacitance and the supercapacitor using EMI-TFSI electrolyte showed the highest energy density (156 Wh/kg) among the three examined ionic liquid electrolytes under the same operating voltage.

The confinement and uniform dispersion of Si nanoparticles (NPs) in a carbon matrix is one of the promising strategies to accommodate the problematic large volume change of high-capacity Si-based anodes during charging/discharging in lithium-ion batteries. Here, we introduce an inverse opal carbon (IOC) matrix for Si NPs dispersion. We study a dispersion of Si NPs in the macroporous, highly interconnected porous IOC matrix. The Raman and XRD analyses are used to characterize carbon and Si properties of the Si NPs/IOC composite electrode. Finally, we compare the specific capacity of the bare Si NPs electrode and Si NPs/IOC composite electrode to discuss the IOC effect on lithium-ion battery performance.

The fabrication of three dimensional (3D) carbon-based architectures (such as carbon nanotubes (CNT)-sponges, graphene foams, aerogels, aerographite, etc.^[1]) is an extensively studied field due to their broad range of applications in the areas of energy storage, healthcare, catalysis as well as environmental protection^[1]. However, the utilization of these carbon nanomaterials and their extraordinary properties, like the high tensile strength of 63 GPa for CNTs or graphenes lowest electrical resistance, is typically limited by the lack of advanced structural design^[2]. Macroscopic foams based on carbon nanotubes are typically manufactured either by rather complicated chemical vapor deposition (CVD) processes, leading to superior compressive strength, or solution-processed hydrogels, which however tend to collapse under stress^[3]. This study introduces a new strategy for fabricating highly porous (93%) 3D CNT-networks using a simple dripping procedure as well as sacrificial ceramic templates based on 3D microparticles^[4]. During this process self-entangled CNT-networks are homogenously formed around the macroscopic structure of the template. Thereby the mechanical as well as the electrical properties compared to those of the template are increased by several orders of magnitude, resulting in a highly porous, conductive as well as mechanically stable (compressive strength up to 250 kg/cmsup2;) composite structure. Furthermore, the structure-property correlation has been understood. Removing the template results in a highly porous 3D CNT-architecture consisting of self-entangled carbon nanotubes, showing superior mechanical properties compared to those of similar carbon-based structures. On top of that it is demonstrated that this material is suitable as a sulfur-host scaffold for lithium-sulfur batteries^[5], being able to incorporate unwanted polysulfides along with high current densities and low series resistances, owning to its high mechanical stability, excellent conductivity as well as its high surface area.
References:
[1] Advanced Materials 26, 2014, 6100-6105
[2] Advanced Materials 24, 2012, 3486-3490
[3] Nature Nanotechnology 7, 2012, 562-566
[4] Particle & Particle Systems Characterization 30, 2013, 775-783
[5] Nano Letters 11, 2011, 4288-4292
*Corresponding Author: [email protected]

The hybrid lithium ion capacitors (LIC) have drawn great attention for energy storage since they can provide high energy density and high power density. It fills in the gap between electric double-layer capacitors (EDLC) and lithium ion batteries (LIB). In an LIC system, the anode electrode material of LIB is used as the source of high energy density, while the electrode material of EDLC is used as the cathode to deliver high power density.
Here we present a dual-graphene LIC based on three-dimensional (3D) single-wall carbon nanotube and graphene (SWNT/graphene) composite that is fabricated through a chemical method and denoted SWNT/G. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) examinations showed that the SWNT/G composite has a porous structure with well dispersed SWNT acting as a spacer to prevent the graphene sheets from restacking. The BET surface area measurement revealed the mesoporous structure in SWNT/G.
We assembled half-cells to evaluate the performance of electrode. The SWNT/G composite with a large specific surface area and excellent conductivity is demonstrated to be a promising candidate as the cathode material of LIC with a specific capacitance of 242 F/g in contrast to 80 F/g from activated carbon that has been commonly used in commercial LIC. On the other hand, we have also pre-lithiated the SWNT/G as the anode of LIC that can allow the Li⁺ ions to be stored on both sides of graphene in order to improve the electrochemical performance of the device. The SWNT would support the three-dimensional (3D) structure during the intercalation and de-intercalation of Li⁺ ions to avoid structural degradation during charge and discharge. In order to understand and interpret the reactions between the electrolyte and the electrode during pre-lithiation, X-ray photoelectron spectroscopy (XPS) was used to analyze the SWNT/G electrode before and after pre-lithiation and the results indicated that the Li⁺ ions have been inserted into the SWNT/G structure.
The efficacy of electrodes on both sides would influence the electrochemical performance of the LIC full cell. The capacitance of dual graphene LIC retained 84% when the current density increased from 0.03 to 0.6 A/g, while the capacitance of LIC using graphite as anode retained 60%. The dual-graphene LIC showed an energy density of 126 Wh/kg with a power density of 169 W/kg.

Two-dimensional (2D) materials with uniformly decorated heteroatoms attract immense interest beyond graphene due to their multifunctionality such as exceptional electrocatalytic, electronic, optoelectronic and magnetic properties. Despite recent explorations in 2D materials science and engineering, easy and scalable methods to produce uniformly doped 2D materials are limited. To overcome these problems, a new layered 2D network structure with uniformly distributed holes and nitrogen atoms was synthesized and its stoichiometry of basal plane is C₂N.[1] The structure of the C₂N was confirmed by scanning tunneling microscopy (STM). Its calculated and experimental band-gaps are 1.7 and 2.0 eV, respectively, in the semiconductor region, suggesting a clear advantage over conducting graphene and insulating h-BN. The C₂N structure was used to encapsulate iron (Fe) and cobalt (Co) particles by in situ reducing and subsequent annealing to give Fe@C₂N and Co@C₂N, which were used as catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Furthermore, another 2D structure with C₃N stoichiometry with uniformly placed nitrogen atoms in the carbon framework was synthesized by ‘direct&’ carbonization of hexaaminobenezene trihydrochloride single crystal at 500 °C. The topological and electronic structure of the C₃N 2D structure was studied by STM.[2] The C₃N structure could be a new class of 2D materials with novel properties that can be emerged from the unique structure.
[1] Mahmood, et al.,Nat. Commun.6, 6486 (2015).
[2] Mahmood, et al., Submitted (2015).

This talk will discuss the various possibilities of creating three dimensional nanostructured solids from nanoscale carbon building blocks of differenty sizes and dimensionalities. In particular we will discuss the properties of nanosclae junctions formed between carbon nanotubes and nanotubes and graphene and the properties of macroscopic solids formed from large number of these junctions. Some of the challenges involved in engineering these structures in scalale ways and the tunability of properties of such solids will be discussed. In addition, we will also discuss various possibilities of creating foams and porous solids made from such building blocks and various opportunities these solids present for applications.

Flexible and binder-free reduced graphene oxide (rGO) films have attracted significant attention as electrodes for supercapacitors due to their unique properties. Nonetheless, the tendency of rGO sheets to restack minimizes the surface area accessible to the electrolyte and hinders their overall performance[1]. To overcome this drawback, nanospacers such as carbon nanotubes (CNTs) are often introduced between rGO sheets to enhance the electrolyte accessibility and electronic conductivity of the films [2]. However, capacitance of CNTs is lower than rGO and its addition to the electrode structure limits the overall capacitance of the freestanding electrodes.
Herein, we have used highly porous carbide derived carbon (CDC) nanoparticles as spacers between graphene sheets and prepared thick rGO-CDC hybrid electrodes. The electrodes were made by thermal reduction of GO-CDC paper produced by vacuum-assisted filtration of aqueous solutions of GO-CDC composite containing 10 and 20 wt. % of CDC. Taking advantage of the high surface area and conductivity of rGO and the accessible pores of the CDC[3], the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a scan rate of 100 mV/s in an aqueous electrolyte. The addition of CDC between the rGO layers enhances the accessibility of electrodes to the electrolyte ions and good performance of the electrodes with the thickness to 40-50 mu;m was observed.
References:
1. Oh, Y.J., et al., Oxygen functional groups and electrochemical capacitive behavior of incompletely reduced graphene oxides as a thin-film electrode of supercapacitor. Electrochimica Acta, 2014. 116: p. 118-128.
2. Wang, Y., et al., Preventing Graphene Sheets from Restacking for High-Capacitance Performance. Journal of Physical Chemistry C, 2011. 115(46): p. 23192-23197.
3. Chmiola, J., et al., Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer. Science, 2006. 313(5794): p. 1760-3.

Distinctive from their 1D and 0D counterparts, 2D nanomaterials (2DNs) exhibit surface corrugations (wrinkles, ripples and crumples). These corrugations on graphene can modify its electronic structure, create polarized carrier puddles which lead to enhancement of chemical activities. Here, we apply cymatics - a process of actuating/patterning liquid-surfaces via sound waves (water, silicone oil or sand) - to create controlled wrinkles on floating graphene. The pattern and attributes of wrinkles on floating-graphene can be manipulated by changing frequency and amplitude of vibration source and the viscosity of the medium. Further, we also show graphene wrinkles via chemical vapor deposition growth on copper-covered-silicone oil droplets. The pattern of wrinkled graphene can be controlled via manipulating the size of silicone oil drops, thickness of copper, pressure in copper sputtering chamber and surface wettability of substrate. Well-arranged transverse wrinkled graphene ribbons with wavelength of 1 micrometer were fabricated. Further, wrinkles induced curvature can modify the functionalizability of graphene. Analysis of the shifts in G and 2D Raman peaks confirmed the change in functionalization affinity of graphene after wrinkle formation. These wrinkles can lead to novel nano/microelectromechanical systems with pattern functionalization on graphene and can be transferred to arbitrate substrates.

We present direct synthesis of graphene on vertically-aligned carbon nanotube (CNT) forest to form 3D CNT-graphene network for the first time. The multi-dimensional material assemble process is achieved by chemical vapor deposition for CNT forest; electroplating for uniform metal film coating around individual CNTs; and a second CVD process for the synthesis of graphene. This work has the following unprecedented accomplishments: 1) direct assembly of 1D and 2D carbon-based materials by CVDs; 2) combination of large surface areas (CNTs) and high electrochemical reaction sites (graphene) for electrochemical electrodes; and 3) embedded metal particles as the pseudocapacitor materials to further enhance the electrochemical capacitance.
Multiwall carbon nanotube (MWNT) forest is synthesized on SiO₂/Si substrate. As grown CNT forests are coaxially coated with nickel by electroplating. A second CVD is performed under various conditions with two gases, H₂ and C₂H₄; and different temperatures. For the case of H₂:C₂H₄ at 50:5 sccm at 800^oC, graphene sheets are synthesized on nickel particles, while the case of H₂:C₂H₄ at 500:50 sccm at 700^oC results in the second CVD synthesis of CNTs on nickel particles. It is observed that higher partial pressure of C₂H₄ and H₂ results in the synthesis of CNTs instead of graphene. Furthermore, when the synthesis temperature is lower than 720^oC under low pressure (H₂:C₂H₄=5:50sccm), amorphous carbon is formed due to the incomplete pyrolysis of ethylene.
Results show the enhancements of capacitance after the graphene and second CNT synthesis processes by 2.24 and 3.19 times, respectively, as compared with the electrodes made of CNT/Ni forests or 16.1 and 25.5 time as compared with the electrodes made of bare CNT forests. In the two CNT-graphene networks, the newly synthesized graphene and second CNTs clearly increase the surface area and also modify the electrochemical reactivity to improve the performance in the charge-discharge process. This paper will detail the synthesis process, material characterizations and system performances.

Ion sensors are attracting tremendous interest due to their widespread applications in the environmental monitoring, material identifying, and space exploration, etc. There are two major types of ion sensors: one is Faraday cup, which generates small current equivalent to the number of impinging ions, it has simple structure with low working voltage (several tens voltages) but almost without gain; the other is the electron multiplier, which multiply the incident ions through secondary emission process, it has complex structure with very high gain (10⁶~10⁸) but need very high working voltages (several kilovolts). So there is strong demand for ion sensors to combine high sensitivity and low working voltages. Recent development of nanotechnology has created huge potential to build highly sensitive and low power consumption ion sensors. Carbon nanotube is one of promising nanomaterials, which has a lot of advantages as the sensing material in the diverse sensors, such as gas sensor, optical sensor, etc., due to its very high surface-to-volume ratio, high carrier mobility and low electronic noise. Here we present a new microscale ion sensors made from carbon nanotubes are capable of detecting ions at small working voltage (0.2V) when ions attach on the surface of carbon nanotubes. The absorbed ion change the current of carbon nanotube sensor and meanwhile the number of incident ions was measured by Faraday cup. Through our calculation, the effective gain of carbon nanotube sensor can be up to 10⁹ and the detection limit of sensor can be down to two individual ions. By further decreasing the number of incident ions, step-like changes in current was found, which proves that the carbon nanotube sensor can be used as ion counter that makes carbon nanotube sensor as a very promising candidate for future high sensitive and low working voltage ion sensor.

Graphene derivatives are excellent candidates for supercapacitor electrodes because of their high specific surface area, high conductivity, and relative chemical and electrochemical stability. However, devices based on graphene electrodes also suffer from fundamental charge storage limitations that are connected to the unique electronic structure of graphene. Using ab initio simulations, we explore charge storage in pristine and defective graphene to understand the detailed origins of these limitations and suggest specific strategies for improvement. We show how proper description of the capacitance of graphene-based devices depends not only on the properties of the electrode and electrolyte individually, but also on the nature of their interaction at the charged electrode-electrolyte interface. We will discuss two distinct strategies for improving graphene-based supercapacitor performance: first, by changing the local structure and chemistry to improve the screening properties; and second, by properly engineering the electrolyte to alter the interfacial coupling. Finally, we will show how combining advanced theory with in operando X-ray spectroscopy can give insights into nanoscale chemical changes and mesoscale morphological changes occurring in 3D graphene supercapacitor electrodes during charging.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Carbon aerogels are a unique class of high-surface-area materials derived by sol-gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents and desalination. Since the first carbon aerogels were made via pyrolysis of resorcinol-formaldehyde-based organic aerogels, in the late 80&’s, the field has really grown. Recently, in addition to RF-derived amorphous carbon aerogels, several other carbon allotropes have been realized in aerogel form: carbon nanotubes, graphene, and diamond. Furthermore, functionalization of these new carbon aerogels via surface engineering has led to a host of composite, carbide, sulfide, and nitride aerogels that could make aerogels promising candidates for an even wider array of applications. Here, we will present recent work covering the synthesis of RF-derived, CNT, graphene, diamond, and composite aerogels, as well as their performance in a variety of applications.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Carbon with its electron configuration and unprecedented capability of forming different hybridization states (i.e., sp, sp², sp³, and their mixtures) can exist in various allotrope forms such as diamond, graphite, graphene, carbon nanotubes, etc.. Among well-known carbon allotropes are also fullerenes, the simplest one being C60, a nanosphere consisting of 60 carbon atoms with each carbon atom covalently bonded to its three neighbors. Related to fullerenes are carbon nanocages, a form of carbon consisting of a three-dimensional (3D) network of interconnected hollow single- or few-layer nanoshells. In recent years, carbon nanocages, have attracted significant attention due to their unique properties and promising applications, including electrode materials for supercapacitors. Recently, following a series of systematic in situ transmission electron microscopy (TEM) experiments, we developed a simple, scalable and low-cost thermolysis-based method of obtaining ultra-fine carbon nanocages. We used this method to produce highly homogenous nanocages with uniform internal diameters of ~ 3 nm and shells consisting of bi- or tri-layers of carbon, as observed directly by high-resolution TEM. BET measurements confirmed highly porous open structure of this material and the analysis of the adsorption isotherms, obtained from initial samples, yielded a mono-modal pore distribution with a peak at ~ 2.5 nm and high specific surface area of ~ 1150 m²/g. As expected based on the morphology-structure analysis, the nanocages showed promising performance as the active electrode material for electrochemical double layer supercapacitors. For this, supercapacitor electrodes were prepared from the nanocages and electrochemical measurements were conducted in the full cell configuration using charge/discharge cycling between 0 and 3.5 V at the current density of 100 mA/g. The measurements showed the first cycle capacity of ~ 280 F/g followed by the capacity stabilization at ~ 180 F/g for over 1000 cycles. Current efforts focus on further improvement of electrochemical performance of this material. In particular, attempts are made to modify the synthesis method to obtain nitrogen-doped carbon nanocages.

Nanodiamonds synthesized by detonation have emerged as promising additives to a variety of base lubricants. Recent laboratory experiments have shown that detonation nanodiamonds as lubricant additives are capable of eliminating wear and drastically reducing friction. The resulting reductions in wear and friction can increase the durability of a wide range of industrial and transportation systems as well as reduce fuel consumption. Several mechanisms have been suggested for this observation, including creation of protective surface films, surface roughness reduction by abrasion and by filling in surface regions between asperities, and by acting as spacers that roll and slide between contacting surfaces.
To better understand how nanodiamond&’s surface chemistry and shape influence the tribological performance, we have carried out molecular dynamics simulation of solvated nanodiamonds between sliding interfaces. Our initial simulations have focused on understanding the role of particle shape (round versus faceted) and surface chemistry on viscosity of base fluid, friction coefficient between sliding surfaces and water, and the motion of the nanodiamonds (sliding versus rolling). We have observed that faceted nanodiamonds experience more rotation than round nanodiamonds. In addition, nanodiamonds with surface functionalization (to saturate dangling bonds) result in an enhanced reduction in local viscosity of water compared to nanodiamonds with unsaturated carbon atoms on the surfaces. Simulation results for nanodiamonds with different surface functional groups, different shapes and morphologies, agglomerated nanodiamonds, and nanodiamonds reacting with metal surfaces during sliding will be discussed.
This work is supported by the G8 Research Council through the National Science Foundation under Grant No. CMMI-1229889.

This work is focused on high-energy electrochemical capacitors utilizing graphite (G) as negative electrode material and activated carbon (AC) with well-developed surface area as positive electrode. Furthermore, reduced graphite oxide (RGO) obtained by two different methods i.e. by thermal and chemical reduction was also investgated as the electrode material. The electrochemical exfoliation of graphite realized by reversible intercalation of lithium ions has been chosen as the main method of negative electrode material preparation. Electrochemical measurements i.e., cyclic voltammetry and galvanostatic charging/discharging reflected an improved energy efficiency when compared with results for symmetric cells (i.e. AC/AC capacitor). All measurements were performed in organic electrolyte to provide a wide range of operating voltage. In case of the hybrid system energy density has been remarkably improved and approaches 90 Wh kg^-1 accompanied by good power profile. Moreover, good cycle performance was also achieved.

Carbon nanotubes (CNTs) have attracted tremendous interest because of their outstanding electrical and mechanical properties. Despite the great potential of this material towards applications in sensing, catalysis, and future electronic devices, its drawbacks such as poor solubility and difficult processing have limited their use. Covalent functionalization allows the surface of CNTs to be modified with different chemical groups. These approaches increase the solubility of CNTs as well as offering the capability to tune the properties of the material for specific function. In this presentation, we present a novel method using aryl iodonium salts to functionalize CNTs covalently. In this method, CNTs were reduced with sodium naphthalide follow by addition of iodonium salts. Efficient covalent functionalization was achieved using sub-stoichiometric amount of iodonium salts

A facile electrolyte-accessible porous structure with a large surface area, in conjunction with a high conductivity, is required to develop high-rate electrical double layer supercapacitor with a large capacitance that can be charged-discharged at frequencies more than 100 hertz. In our study, commonly available cellulose papers were carbonized and deposited with perpendicularly oriented grapehen (POG) in a one-step plasma-enhanced chemical vapor deposition (PECVD) process. Microstructure characterization indicates that the carbonized paper consists of entangled hollow fibers with a diameter at the micrometer scale, while the surface of these fibers is covered with POG network. Such a hierarchical structure provides both high conductivity and a large surface area with a facile electrolyte-accessible porous structure, ideal for developing high-rate supercapacitor with a large capacity. Their microstructure and electrochemical characteristics were studied, including cyclic voltammograms, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. Promising results were obtained indicating the supercapacitor based on these POG network on carbonized paper is promising for working at frequencies above 100 hertz.

Due to their functionality, lightweight, ease of processing and low cost, polymers have replaced conventional materials in packaging applications over the last twenty years. However, despite their enormous versatility, a limiting property of polymeric materials in food packaging is their inherent permeability to gases and vapors. The barrier properties of polymers can be significantly enhanced by inclusion of impermeable lamellar fillers, such as clay and graphene. These nanofillers make the diffusing molecules follow tortuous pathways to pass through the nanocomposite film. As a result, a decline in permeability is achieved. Compared with clays, graphene-incorporated polymers show not only enhanced gas-barrier properties but also reinforced mechanical strength and improved electrical conductivity and thermal properties when properly dispersed in a polymer matrix. For example, graphene has a high mechanical strength (Young`s modulus ~1,100 GPa and fracture strength 125 GPa), thermal conductivity (~5,000 W m^-1 K^-1) and electrical conductivity (6000 S/cm) with a high transparency. In this study, polyethylene (PE) filled with carbon nanotubes (CNTs) and graphene was synthesized via a liquid mixing process. It is found that the gas barrier performance of the composites filled with hybrid nanofillers is much higher than that of the composites filled with only one filler. The introduction of long CNTs into the composites prevents the aggregation of graphene nanoplatelets in polymer matrix. This in turn leads to better dispersion of graphene nanoplatelets in polymer matrix and provides a larger area of the effective tortuous paths. Thus, the gas barrier performance of polymer nanocomposites increases significantly. Concurrently, the CNTs bridge the gaps between graphene nanoplatelets, maximizing the load carrying capacity of composites. Thus, remarkably enhanced mechanical properties of CNTs-graphene/PE composites are achieved at low hybrid nanofiller volume fraction.

We have reported a novel nanocomposite structure in which thin graphene oxide (GO) layer is sandwiched by periodic mesoporous silica (PMS) films with their mesoporous channels perpendicular to the flat or curved carbon substrate. The peculiar structure is supposed to be related to the surface chemistry of GO and depends on the synthesis conditions. In this presentation, we demonstrate the successful synthesis of GO-PMS nanocomposites with tailored pore size by selecting surfactant molecules with different alkyl-chain length as structure directing templates and controlled mesochannnel thichness by adjusting synthesis conditions.

Monodispersed N-doped porous carbon spheres are prepared by the carbonization of polymer particles in the presence of nitrogen-enriched molecule and subsequent activation. The doping enhances the pseudocapacitance and the electrical conductivity of carbon, and the activation enhances the surface area, thereby enhancing the electrochemical capacitance. The elemental composition and nitrogen bonding configurations are quantified by X-ray photoelectron spectroscopy measurements and the pore characterization is achieved by Brunauerminus;Emmettminus;Teller adsorption/desorption measurement. The effects of N-doping and activation on the capacitance is analyzed.

Efficient water desalination constitutes a major challenge in the next years and reverse osmosis membranes will play a key role to achieve this target. In this work, a high-performance reverse osmosis nanocomposite membrane was prepared by interfacial polymerization in presence of multiwalled carbon nanotubes. The effect of carbon nanotubes on the chlorine resistance, antifouling and desalination performance of the nanocomposite membranes was studied. We found that the addition of carbon nanotubes not only improves the membrane performance in terms of flow and antifouling, but also inhibits the chlorine degradation on these membranes. Several reports have acknowledged the benefits of adding carbon nanotubes to aromatic PA nanocomposite membranes, but little attention has been paid to the mechanisms related to the improvement of flow rate, selectivity and chlorine tolerance. We carried out a comprehensive study of the chemical and physical effects of carbon nanotubes on the fully crosslinked polyamide network. The chemical structure, chlorine resistance and membrane degradation was studied by several analytical techniques, permeation and fouling studies, whereas the microstructure of the nanocomposite was studied by small and wide angle X-ray scattering, high resolution transmission electron microscopy, and molecular dynamics. We found that the addition of the nanotube affects the interfacial polymerization, resulting in a polymer network with smaller pore size and higher sodium and chlorine rejection. We simulated the hydration of the membrane in seawater and found that the radial distribution function of water confined in the pores of the nanocomposite membrane exhibited smaller clusters of water molecules, thus suggesting a dense membrane structure. We analysed the network mobility and found that the nanotube provides mechanical stability to the polymer matrix. This study presents solid evidence towards more efficient and robust reverse osmosis membranes using carbon nanotubes as mechanical reinforcing and chlorine protecting additive.

The design and optimization of 3D graphene nanostructures are critically important since the properties of electrochemical energy storages such as supercapacitor can be dramatically enhanced by tunable porous channels. In this work, we develop porous graphene aerogels from graphene suspensions obtained via electrochemical exfoliation and explore their application as supercapacitor electrodes. By adjusting the content of the electrolyte in the exfoliation process, the aspect ratio of graphene sheets and the porosity of the graphene network can be optimized. Furthermore, the freezing temperature in the freeze drying step is also found to play a critical role in the resulting pore size distributions of the porous networks. The optimized conditions lead to meso- and macro-porous graphene aerogels with high specific surface area, extremely low densities and superior electrical properties. As a result, the graphene aerogel supercapacitors exhibit a specific capacitance of 325 F g^minus;1 at 1 A g^minus;1 and an energy density of 45 Wh kg^minus;1 in 0.5 M H₂SO₄ aqueous electrolyte with high electrochemical stability and electrode uniformity required for the practical usage. This research provides a practical method for lightweight, high-performance and low-cost materials in the effective use of energy storage systems.

In the synthesis of carbon nanotube (CNT) forests, we have achieved siginificant control of morphology parameters such as diameter, height, and areal density, which is important for a broad range of applications (e.g., energy storage). However, modulating CNT height witin a forest, i.e., synthesizing on the same forest areas with CNTs of different heights has not yet been demonstrated. What has been shown is that the catalyst can be patterned (e.g., by lithography) and then CNTs will grow only in the regions where there is a catalyst, thus discriminating two regions: (1) regions with CNTs of fixed height and (2) regions without CNTs.
Building on our demonstrated research on using a thin film iron reservoir to grow taller CNTs (up to 2X - presented at MRS Fall 2013), we show here how different materials used as thin film reservoirs can either enhance or inhibit CNT growth with different degrees. For instance, we will show how a thin film copper reservoir can inhibit CNT growth while a molybdenum thin film reservoir can significantly enhance CNT growth, up to 4X compared to no reservoir, while a thin film iron reservoir can enhance CNT growth up to 2X . Based on this, by using a uniformly deposited iron catalyst on alumina above patterns in the reservoir with thin films of different materials (using masks during thin film deposition), we can obtain regions of CNTs with heights varying from 0 to 4mm on the same sample.
Using HRSEM, HRTEM, and EDAX, we will show the effects of the reservoirs on the catalytic layer. We will focus on the mechanism based on upward diffuson of reservoir material via pinholes in the alumina underlayer and its effect (alloying / deweting / Ostwald ripening) with the iron catalyst. This technique opens new doors in the synthesis of CNT forests as it now allows a further level of control on the z-direction using a simple and elegant technique.

The ever increasing demand for faster electronics with more integrated functionality and larger data storage density calls for emerging technologies that would allow fabrication of higher density nanodimensioned structures. Attainment of smaller length-scale features by top-down approaches is getting increasingly challenging and time consuming due to the intrinsic serial nature of the top-down methodology.
Intrinsically parallel bottom-up methodologies based on self-assembled block copolymers (BC) as nanostructure templates, have the potential to generate predictable sub-10 nm structures at high throughput and low cost. BC based lithography is directly mentioned as a possible route to next-generation chip fabrication in the International Roadmap of Semiconductor Technology.
One of the key challenges in BC based nanolithography is how to control the out-of-plane alignment of the BC thin film structure relative to the substrate. The contributions from BC-substrate and BC-air interface free energies complicate the analysis of the system and in most cases limit predictability of the out-of-plane alignment. Substrate surface modification, mostly by grafting of polymer brushes prior to spin-casting of the BC is reported in almost all the publications in the field, as a means to improve the alignment.
I&’ll show two approaches we have been developing in my group that allow to successfully apply the BC thin film directly onto the substrate to be etched, without any complicated preliminary surface modification of the substrate.
- The first is a conceptually simple approach utilizing ex-situ fabricated nanoporous masks from polybutadiene-polydimethylsiloxane block copolymers. The BC masks show predictable morphology, independent of substrates&’ surface properties. The masks are prepared by microtoming of pre-aligned macroscopic nanoporous polymer monoliths of hexagonal morphology. Masks cut perpendicular to the cylindrical axis show outstanding long-range mono-crystalline hexagonal packing of 10 nm pores with a principal period of 20 nm. Transfer of the hexagonal pattern onto silicon and on graphene is accomplished by means of reactive ion etching through the masks. The first transfer of moiré patterns from block copolymer masks to silicon is also demonstrated.
- The second approach proves the formation of regular hexagonally packed dots or lines from polystyrene-polydimethylsiloxane (PS-b-PDMS) block copolymers, directly spin-cast on different substrates, like silicon, graphene and a number of common polymers. PS-b-PDMS block copolymers with different compositions were synthesized in our labs, with structures varying from lamellae to PS cylinders in a PDMS matrix and viceversa. Appropriate selection of film thickness and selective solvent vapor annealing allows for the formation of very uniform films with line or dot morphologies. The patterns are successfully transferred to silicon, graphene and polymer substrates by reactive ion etching.

Adsorption is a fundamental phenomenon and forms a basis for various fields like catalysis, energy storage, sensors and gas separation. Its variable morphology has given the element carbon a central position as probably the most flexible material offering a high degree of chemical and structural functionality important in all of these fields. 3D vertically aligned CNT arrays are solely carbon based model structures and are ideal candidates to unravel a variety of gas/carbon interactions. They possess a combination of micro, meso and macro pores and multiple well-defined adsorption sites all of which can be controlled with a high chemical homogeneity and reproducibility.^1,2 Moreover, 3D CNT architectures are minimal footprint areal structures nevertheless offering high specific surface area (ca. 500-800 m²/g). They are ideally suited for usage in a variety of microsized devices. In the first step, we are focusing on structural modifications of the CNT arrays by investigating the influence of diameter, intertube distance and open/close ended tubes on gas adsorption. Subsequently, the effect of various functional groups is explored. Plasma functionalization is used as it is a flexible method for grafting various functional groups without distorting the vertical alignment.³ Finally, the influence of changes in local electronic concentration by doping or creation of defects, on gas interaction is investigated. These studies are complimented by various characterization techniques like N₂ adsorption measurements, Raman spectroscopy, SEM, TEM, XPS surface and depth profiling measurements for an in-depth understanding of the mechanisms of adsorption on structured CNTs.
References
(1) Babu, D. J.; Lange, M.; Cherkashinin, G.; Issanin, A.; Staudt, R.; Schneider, J. J. Gas Adsorption Studies of CO₂ and N₂ in Spatially Aligned Double-Walled Carbon Nanotube Arrays. Carbon 2013, 61, 616-623.
(2) Rahimi, M.; Singh, J.; Babu, D. J.; Schneider, J. J.; Mu#776;ller-Plathe, F. Understanding Carbon Dioxide Adsorption in Carbon Nanotube Arrays: Molecular Simulation and Adsorption Measurements. J. Phys. Chem. C 2013, 117, 13492-13501.
(3) Babu, D. J.; Yadav, S.; Heinlein, T.; Cherkashinin, G.; Schneider, J. J. Carbon Dioxide Plasma as a Versatile Medium for Purification and Functionalization of Vertically Aligned Carbon Nanotubes. J. Phys. Chem. C 2014, 118, 12028-12034.

Advances in the synthesis and processing of nanomaterials have led to their strong consideration for printed electronics in recent years. Single-walled carbon nanotubes (CNTs), as one of the most promising nanomaterials, have high charge mobility, good thermal conductivity and chemical stability, and can be printed as semiconducting channels in field-effect, thin-film transistors (TFTs). Printed CNT-TFTs of many varieties have been successfully fabricated in the past decade; however, there has been limited effort towards improving overall CNT-TFT performance. In particular, contact resistance can play a dominant role in determining the performance and degree of variability in the TFTs. In this work, we have systematically investigated the contact resistance and overall performance of fully printed CNT-TFTs in three distinct contact geometries: double, bottom and top. The back-gated CNT-TFTs on Si/SiO₂ wafers were fabricated using an aerosol jet printer. For each of the contact geometries, source/drain contacts were printed with three different kinds of inks, including silver nanoparticles, silver nanowires and metallic CNTs. The active channel for each device was printed from the aqueous dispersion of high-purity (99%) semiconducting CNTs. A series of devices with different channel lengths (from 20 to 500 mu;m) and widths (50 to 300 mu;m) were fabricated for extraction of contact resistance and determination of related contact effects. Experimental results show that, compared to single (top or bottom) contacts, double contacts can offer a significant decrease in contact resistance and a moderate increase in transconductance for the CNT-TFTs with different electrode materials. This finding for the contact resistance of fully printed CNT-based transistors can help minimize the impact of contacts on the performance of nanomaterial-based devices and guide further development of printed nanomaterial electronics.

The unique electronic, optical, structural, and thermal properties of single-walled carbon nanotubes (SWNTs) render their (n,m)-chirality separation as an important first step towards their use in advance nanostructured devices. Flavin mononucleotide (FMN), a common redox cofactor, is known to exhibit a strong helical wrapping around SWNT through strong π-π interactions between the isoalloxazine moiety and the underlying graphene side-walls.¹ Here, we examine the effect of pH on the selective stability of the FMN wrapping around various (n,m)-SWNTs using the recently developed thermal dissociation method.² Three distinct H-bonding configurations exist as part of the various fractional helices that span between the two most stable 7/1 and 8/1 FMN helices.² At pH of 6, the FMN wrapping has three ionized hydroxyls for every two phosphate groups. This provides the ideal charge repulsion between adjacent FMN&’s phosphate moiety to afford maximum helical stability for 8/1 FMN helices, that naturally accommodate (8,6)-SWNTs. At pH of 9, excess charge repulsion (i.e. two negatives charges for each phosphate group) favor the more tightly wrap 7/1 FMN helices, which naturally select (6,5)-SWNTs. Such phosphate repulsion together with varying ionic strength can ultimately afford the selective enrichment for different diameter and chirality SWNTs.
Cited References:
Ju, S.-Y.; Doll, J.; Sharma, I.; Papadimitrakopoulos, F. Nat. Nanotech.2008, 3, 356
Sharifi, R.; Samaraweera, M.; Gascon, J. A.; Papadimitrakopoulos, F. JACS, 2015, 136, 7452

The electronic and optical properties of single-walled carbon nanotubes (SWNTs) are strongly depended on the diameter and chiral angle of the rolled graphene lattice, defined by the (n,m) integers. Extensive research efforts have been applied toward post-growth separation in order to afford single chirality SWNTs. In all separation techniques, quasi-epitaxial recognition of the underlying nanotube lattice is typically underemphasized. The original report of flavin mononucleotide (FMN) wrapping around carbon nanotubes suggested that the strength of helical FMN binding around various (n,m)-SWNTs can be utilized to afford selective enrichment of the (8,6)-species.1 More recently, our thermal dissociation method has enabled us to quantify the thermodynamic stability of the FMN organization in terms of individual contributions stemming from quasi-epitaxial πminus;π stacking interactions, H-bonding and lateral FMN packing.2 In this contribution, we employed the thermal dissociation method to afford high-purity enrichment of (8,6)-SWNTs (from HiPco samples) in a single step. Our results were modeled using molecular dynamics and ab initio calculations to explain the profound (8,6)-enrichment in contrast to the other (n,m)-species that are also wrapped with FMN helices. This methodology affords a novel pathway to obtain molecular understanding of the effects of quasi-epitaxial recognition around various nanostructured materials.
References:
1. Ju, S.-Y.; Doll, J.; Sharma, I.; Papadimitrakopoulos, F. Nat. Nanotech.2008, 3, 356
2. Sharifi, R.; Samaraweera, M.; Gascon, J. A.; Papadimitrakopoulos, F. JACS, 2015, 136, 7452

Multiwall carbon nanotubes that contain both trapped and substitutional nitrogen were synthesized using acetonitrile as the precursor and ferrocene as the catalysis. The average diameter of the nanotubes ranges between 20 nm and 150 nm. X-ray photoelectron spectroscopy (XPS) and Electron dispersion spectroscopy analysis reveals ~ 2 at% nitrogen in the carbon nanotubes with ~ 1 at% of the nitrogen as substitutionally doped in the form of pyridinic, pyrrolic and graphitic type defect substitution in the carbon nanotubes skeletal structure, and ~1 at% present as gaseous nitrogen trapped inside the nanotubes. Furthermore, the temperature dependent thermoelectric properties and micro-Raman spectroscopy are used to estimate the carrier concentration to substantiate the XPS results.

Carbon quantum dots (C-dots) are a new class of carbon nanomaterial and have been subject of intense multidisciplinary research due to their promising luminescence properties, biocompatibility, low cost and ease of synthesis. Thus, C-dots have potential application for bioimaging, nanomedicine, design of biological and chemical sensors, photocatalysis and electrocatalysis. Herein, 3 simple, fast, labour and energy efficient methodologies were used to prepare C-dots using an aqueous beetroot extract as the carbon source: alkali-assisted (AA), microwave-assisted (MA) and alkali-microwave-assisted (AMA) synthesis. For the preparation of the beetroot extract, 700 mg of beetroot were blended with 50 mL of Milli-Q water and then vacuum filtered. For the C-dots synthesis, 1 mL of 5M NaOH was mixed with 15 mL of the beetroot extract for AA and AMA synthesis. For MA and AMA, samples were heated at 200 °C for 30 min using a microwave oven. All the samples were purified by dialyze for 24h. After mixing NaOH with the beetroot extract, it is observed a quick change of the color, varying from purple to dark yellow, and also a green emission when the samples are exposed to UV-light. Those points evidence the formation of carbon nanoparticles. TEM images shows nanoparticles with a nearly spherical morphology and diameters bellow 5.0 nm. FTIR spectra show characteristic peaks of C-H, C-O, O-H and C=C bonds for all the samples. The emission spectra show an interesting feature of the by-prepared samples: the emission band position can be tunable by changing the excitation wavelength. This property is communally called as excitation wavelength dependent photoluminescence and its origin is believed to be related to the surface traps in the radiative transition of carbon dots. For all the samples, the emission band varies from 510 nm to more than 560 nm when the sample is excited from 380 nm to 510 nm. Comparing the 3 different methodologies in terms of photoluminescence properties, the one based only on the microwave-assisted heating has showed the most improved emission.
This work was financially supported by CNPq, Capes and Fapitec. Authors are also thankful to CMNano (project number 82)

In this paper, hydrothermal method has been employed to synthesize oxygen-modified carbon dots (O-CDs) from citric acid and nitrogen and sulfur modified carbon dots (N,S-CDs) from citric acid and cysteine. Both as-prepared carbon dots achieve naked-eye observable blue-green luminescence. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) are used to exhibit the chemical composition of carbon dots. The structure and size of both carbon dots are similar via transmission electron microscopy (TEM) and dynamic light scattering (DLS), which indicates that the function of size effect can be neglected in this study. Fluorescence properties, UV-vis absorption and solubility are systemically studied to investigate the influence of surface modification. The N,S-CDs show high quantum yield and excitation independent photoluminescence, however, the O-CDs present low quantum yield and excitation dependent photoluminescence, and both carbon dots achieve strong photo-stability. The cytotoxicity of carbon dots is also performed on U87-MG brain tumor cells, which shows that both carbon dots process good biocompatibility and low toxicity in live cell. The bright cellular imaging photos indicate that both carbon dots have great potential to serve as high quality optical imaging probes.

Nitroaromatics explosive compounds are the most common explosives in the world. The low-cost, portable and reliable method of nitroaromatics sensing has attracted a lot of attention in many fields.
This study shows the fabrication and sensing results of a high-performance chemiresistive sensor for nitroaromatics vapors based on oligomer/carbon nanotube hybrids. The fabrication is very simple. Just drop the oligomer/carbon nanotubes solution on interdigitated electrodes and let the solution dry out. The sensor shows parts per billion levels of sensitivity to NT and parts per trillion levels of sensitivity to DNT and TNT. This is attributed to the swelling of the oligomer in between the carbon nanotubes. As the oligomer swells, the charge carrier barrier will become larger and the conductivity of the device will decrease.
The oligomer (named carbazolylethynylene) used in this project has several features that are important. First, the oligomer can non-colvalently bind with carbon nanotubes, and can disperse carbon nanotubes well in common solvents like chloroform, which makes the thin film dropped on the electrodes very uniform. Second, the oligomer tends to bind with nitroaromatics such as 4-nitrotoluene (NT) vapor, 2,4,6-trinitrotoluene (TNT) vapor and 2,4-dinitrotoluene (DNT). Thus, this makes the device very sensitive and selective to nitroaromatics. Third, the oligomer is an insulation material which creates a charge carrier barrier between the carbon nanotubes.
This study demonstrate a new mechanism of carbon nanotube-based sensors, which may bring new design ideas for making sensors.

Carbonaceous materials deposit on cathode surface during the carbon arc discharge. The cathode deposit exhibits distinct spatial variations. Three different morphologies with an axial symmetry where a rim of pyrolytic carbon separates the innermost multiwalled carbon nanotubes containing core and the outmost powdery amorphous carbon soot. Based on the deposit temperature observed during the discharge, it is found that the deposit core has the highest temperature and decreases as one moves away from the center. Further study on the cathode current distribution during discharge reveals a strong correlation between the major current conducting area and the nanotube forming area. Cathode energy balance show the primary heating and cooling mechanisms at the cathode surface are plasma conduction and electron emission, respectively.

Single-walled carbon nanotubes (SWCNTs) own unique properties and show great potentials in the development of, including but not limited to, electronic and biomedical applications. However, the major challenges of devices based on SWCNTs are to precisely control the variability of their structures, dimensions and locations on insulating, flexible and high-k dielectric substrates, with high throughput and decent yield/ reproducibility. Here we report a new method of fabricating ultra-long bundles of SWCNTs in controllable shapes by lithographically patterned electrophoretic deposition. SWCNTs are first solubilized in aqueous solution by adding surfactants and sonication. The fabrication processes start from that, a sacrificial nickel (Ni) layer, the thickness ranged from 10-40nm, is vapor evaporated onto glass or silicon oxide wafer. Then a positive photoresist (PR) layer is spun coated on top of the nickel layer followed by soft-baking process. After that the PR layer is lithographically patterned and developed, and the exposed Ni layer is removed by wet etching for a few minutes, in order to produce an undercut beneath the PR layer. SWCNTs bundles are electrophoretically deposited along the edges of patterned Ni nano-electrodes by programmed DC voltage pulses. The density and width of SWCNTs bundles can be controlled by manipulating the DC pulse duration and total number of pulses. SWCNTs can be patterned to produce inches-long 2D arrays, and SWCNTs on SWCNTs junctions by repeating the lithographical patterning processes twice, and other complex patterns. We measure the resistance and source-drain current under different gating bias of 50 mu;m sections of single SWCNTs bundles.

We have demonstrated the use of binder-free CNT membranes as electrode in two-electrode 1M H₂SO₄ aqueous double layer supercapacitor that shows very high power density ~1040 kW/kg based on the mass of both electrodes and time constant of ~ 15 ms with no degradation in performance even after 10,000 cycles. We will present results on energy/power densities, voltage and cyclability of transparent and 3-stack bipolar all-solid-state supercapacitor. Preliminary results indicate CV voltage ~3V with very low leakage current ~ 10nA.

Since the discovery of fullerene and carbon nanotubes (CNT), carbon nanomaterials have attracted enormous interest in sensor application and subsequently resulted into new classes of sensors [1]. An important class of sensors are gaseous sensors due to the vital roles they play in environmental monitoring, bioengineering and medical applications, chemical and physical process controls. Graphene and CNTs have been studied for gas sensing applications due to their outstanding physical, electronic, mechanical and optical properties[2].
In this study, the focus would be on graphene sheets (GS) for ultrasensitive (ppb range) gas detection in vacuum environment. The high surface-to-volume ratio (giving a large exposed area) and mono-atomic thickness of graphene sheets makes it suitable for sub-ppm gas sensing as graphene membranes are easily deflected under small pressure, resulting in change in its electronic properties[3]. Two GS synthesis techniques would be used: Chemical Vapor Deposition and Inkjet Printing. The CVD-synthesized graphene on copper foil will be transferred onto already etched cavities of oxide on silicon. Beyond applications in atomic transportation and drug delivery, this opens up other applications such as hermetic sensors in nano/micro-electromechanical systems (like gyroscopes) that operate under vacuum. The goal of this project is to integrate the hermetic sensor in the encapsulation layer that isolate the device from the environment.
Ongoing work has successfully established Through-Silicon-Vias (TSVs) process flow for backside interconnect using carbon nanomaterials. This will be used for the inkjet printing of graphene with thickness of approximately 20nm after curing. The exposed GS over the cavities and TSVs will be part of a wheatstone bridge setup, which is balanced at a specific vacuum pressure without exposure to any gas, to capture the piezoresistive and vibratory properties (that is, resistance and frequency changes) of the device. This technique improves the selectivity of the sensor because the sensitivity is dependent on atomic masses of the gases which are different at constant volume. The effect of GS thicknesses, sizes, flow rate and concentration of the gases and boundary condition of GS will be studied. The output signal of the wheatstone will be fed into an amplification circuit to improve the resolution.
References
[1] B. Arash, Q. Wang, and W. H. Duan, "Detection of gas atoms via vibration of graphenes," Physics Letters A, vol. 375, pp. 2411-2415, 2011.
[2] S. Basu and P. Bhattacharyya, "Recent developments on graphene and graphene oxide based solid state gas sensors," Sensors and Actuators B: Chemical, vol. 173, pp. 1-21, 10// 2012.
[3] A. D. Smith, F. Niklaus, A. Paussa, S. Vaziri, A. C. Fischer, M. Sterner, et al., "Electromechanical Piezoresistive Sensing in Suspended Graphene Membranes," Nano Letters, vol. 13, pp. 3237-3242, 2013/07/10 2013.

In the present study, hydrogenation properties of Pd-C core-shell nanoparticles having controllable Pd nanoparticle core and carbon shell thickness have been investigated. An integrated gas phase synthesis method comprising of spark generator, neutralizer, differential mobility analyzer (DMA), sintering furnace and electrostatic precipitator (ESP) is used for the synthesis of the nanoparticles. A carbon precursor gas (CH₄) is introduced in the furnace which gets dissociated into carbon atoms at high temperatures and covers the compacted Pd nanoparticles to form Pd-C core-shell nanoparticles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) studies on Pd-C nanoparticles of mobility equivalent diameter of 20, 40 and 60 nm and carbon shell thickness of 0, 1.5 and 2.1 nm have been investigated and the results have been understood in terms of size and surface effects. A larger H/Pd ratio in Pd-C nanoparticles having larger carbon shell thickness and smaller nanoparticle size has been obtained from the elastic recoil detection analysis (ERDA). These results are explained on the basis of lowering of coordination number of Pd surface sites at Pd-C core-shell interface and size induced lattice distortion effects resulting in changes in the position of Pd 4d level. By combining the modification in electronic properties due to the size with that due to carbon shell thickness, Pd-H interaction can be significantly enhanced.

Supercapacitors are emerging as promising devices to conventional battery technology for energy storage systems. The development of new energy storage materials is the key to achieve supercapacitors with enhanced properties. In this sense, carbon-based nanomaterials (i.e. carbon nanotubes and graphene) arranged with transition metal oxides have being investigated to improve on efficiency of these devices. In this study we investigated the electrochemical properties for supercapacitor application of modified electrodes with nanostructured films containing an LbL multilayer fashion made with ZnO nanoparticles embedded into polymeric matrix of polyallylamine hydrochloride (PAH) and alternated with single-walled carbon nanotubes (CNTs). The morphology of PAH-ZnO/CNT LbL films with different bilayers was analyzed by atomic force microscopy (AFM), while cyclic voltammetry was used to evaluate the specific capacitance, rate capability and cyclic stability. The advantages of combining ZnO nanoparticles and CNTs and their influence in the film structure for a high performance supercapacitor are also discussed.

Despite their long length (> 100 µm) and low defect density the photoluminescence of as-grown aligned single-walled carbon nanotubes (SWCNTs) on quartz is strongly quenched and barely detectable. We found that simply transferring these SWCNTs to other substrates such as glass or even another quartz wafer resulted in a clear increase of PL emission of up to a hundred times. SWCNT arrays were grown as dense arrays (5-6 SWNT/µm) from iron catalys particles with an optimized chemical vapour deposition process that resulted in small diameters of 1.2 (±0.2) nm. The transfer of the as-grown SWCNT arrays was carried out either with poly(methyl methacrylate) (PMMA) or polystyrene (PS) as transfer polymers. After every step of the transfer process the SWCNT arrays were analyzed by Raman spectroscopy and photoluminescence was recorded over large areas (200x200 µm) using a confocal detection system with single photon sensitivity. The dielectric environment provided by the substrate only has a limited influence on the photoluminescence efficiency. Various mechanisms for the observed PL enhancement, such as creation of localized states and strain relaxation are discussed. The transferred arrays were subsequently used to fabricate field-effect transistors that showed balanced electron and hole transport and strong electroluminescence from electron-hole recombination along many individual nanotubes.

The bonding environment in the carbon nanotube lattice is changed when heteroatoms such as Boron atoms (B) knew as “dopant” is incorporated. This dopant affects the bonding environment and induces changes in the intrinsic properties of a single-walled carbon nanotube (SWCNT). Understanding the bonding environment, the dopant distribution of B atoms and the doping levels in the B-doped SWCNTs is particularly important to bring to reality their potential applications. However, the tubes' heterogeneity, their bundling, and the presence of catalytic by-products hinder their direct application. We have mastered the production of B-doped SWCNTs using high-vacuum assisted chemical vapor deposition and this work shows our progress regarding their purification processes. The density gradient ultracentrifugation method has been used in this work as an alternative to the conventional chemical purification treatment. In order to characterize this material, multifrequency Raman spectroscopy has been done followed by optical absorption studies before and after the purification treatments, which has allowed us to understand the changes in the tubes&’ morphology and their physical properties. Element analysis using X-ray photoelectron spectroscopy and Energy Dispersive X-Ray Spectroscopy ( for a bulk overview in Scanning Electron Microscopy have been used. To the best of our knowledge, this study provides the first attempts to scale up the purification process of doped nanotube material as significant step toward the application stage of this material.

Carbon nanotubes have been in the limelight for several decades, owing to their outstanding properties.^1-3 However, it is often necessary to manipulate these nanostructures through chemical modification in order to exploit their interesting properties at a tangible scale. Elemental doping of carbon nanotubes has proven to be an effective route towards achieving this goal.⁴ In this regard, the effects of silicon (Si) doping in single walled carbon nanotubes (Si-SWNTs) have not been explored in great detail previously. Theoretical calculations of Si-SWNTs⁵ showed that substitutional Si atoms protrude out from the carbon lattice due to the Si sp³ pyramidal hybridization, longer Si-C bonds, as well as to its larger ion size. The stress induced by this protrusion makes the presence of smaller diameter tubes within Si doped samples more favorable, and it is also likely that the lone orbital from Si could act as an amphoteric center for inter-tube bridging. Here we report the successful synthesis of Si-SWNTs by aerosol assisted chemical vapor deposition (AACVD). Si-SWNTs were characterized via Raman spectroscopy and TEM. Analysis of the radial breathing modes in the Raman spectra suggests the incorporation of Si into the carbon lattice. Electronic transport measurements of the Si-SWNT bundles show drastically different electronic transport properties when compared to undoped SWNTs, which corroborates the doping of Si atoms in the carbon lattice.
References
1. Iijima, S., Nature 354, 56-58 (1991).
2. Terrones, M., Int. Mater. Rev. 49, 325-377 (2004).
3. Baughman, R. H., Zakhidov, A. A. & Heer, W. A. de., Science 297, 787-792 (2002).
4. Terrones, M., Filho, A. G. S. & Rao, A. M., Topics in Applied Physics Vol.111, 531-566 (2008).
5. Baierle, R. J., Fagan, S. B., Mota, R., da Silva, A. J. R. & Fazzio, A., Phys. Rev. B 64, 085413 (2001).

The global water demand is nowdays one of the main problems all over the world. Due to the exponential growth of the population more clean water is needed every day. The aim of this study is to develop innovative nanocomposite multi-walled carbon nanotube based filters to remove viruses from water, since these organisms present a major risk for human health and public safety.
In the present work TiO₂ and Fe₂O₃-coated multi-walled carbon nanotube (MWCNT) composite films with various MWCNT contents were synthesized via a simple impregnation and filtration method and evaluated with respect to MS2 bacteriophage removal from contaminated water. As prepared TiO₂/MWCNT and Fe₂O₃/MWCNT nanocomposites with different weight ratios were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction techniques.
Exploiting the unique properties of carbon nanotubes (CNTs), an entire new class of composite materials is conceivable. Carbon nanotubes have large surface area which can increase the adsorption properties and additionally take part in the charge transfer processes. The coating process also increases the specific surface area of the filters, thereby also potentially increasing their adsorption capacity. The main goal of this study was to test the feasibility of modifying MWCNT based nanocomposite filters to promote adsorption of viruses from water. The efficiency of water purification was studied using model viruses, such as MS2 bacteriophages. These viruses are not human pathogenics and thus safe for the experimental work.
Removing or inactivation of the adsorbed viruses on the surface of composite filters will be achieved by photocatalytic degradation using UV light. MWCNTs could efficiently adsorb pollutants in water and also increase the photocatalytic activity of TiO₂ by acting as electron traps, thus stabilising the charge carriers and suppressing the rate of electron-hole recombination.

A new type of nanostructure synthesized using a one-step chemical vapor deposition process is reported, a boron carbide hybrid-nanotube (BCHN). The method of synthesis of these structures is a modification of a method successfully used to grow a variety of pure boron nanostructures. The process was originally a thermal vapor deposition reaction, performed in an inert gas atmosphere, which was altered by the addition of methane gas. The following analytical techniques have been used to characterize BCHNs: electron microscopy, Raman spectroscopy, 2 point electrical probe measurement, and compressive stress strain mechanical property tests (performed in the radial direction). The product of this reaction, when imaged by electron microscopy, was found to be a core-shell hybrid nanotube, where the interior of the structure consists of a boron nanowire and the exterior is essentially a distorted multiwalled carbon nanotube (CNT). The interior boron nanowire has lattice spacings of 0.38, 0.48, and 0.44-0.45 nm, indicating it is similar to the product obtained without the addition of methane. The layers of the CNT which formed on the outside of the BCHN are distorted and wavelike in appearance, most likely because of a lattice mismatch and the presence of excessive missing carbon atoms. This distortion is further manifested in the spacing between the layers of carbon, which range from 0.36 to 0.39 nm, as opposed to regular, straight CNTs which have a spacing of 0.34 nm. The boron nanowire interiors have a thickness of 20-30 nm, and are each surrounded by a 10-20 nm layer thick coating of carbon. The length of the entire hybrid-nanotube is a few microns. Each hybrid-nanotube has a bulbous tip filled with catalyst, indicating a vapor-liquid-solid growth. The carbon layer on the outside of the hybrid structure was found to be insulating, which is unusual for a layered carbon. Modeling was used to confirm a connection among defects, bandgap, and the waved structure of the BCHN. From a scientific standpoint, BCHNs are exciting because they could be considered to be a novel form of boron carbide and carbon. Furthermore, they may portend the discovery of other hybrid-nanotube structures.
Practically, BCHNs have some important differences from CNTs. They are highly insulating, making them suitable for applications where that is a requirement. More impressively, BCHNs are expected to have a number of uses exploiting their mechanical properties, as they address several problems with CNTs. CNTs are weak in compression and in the radial direction, and do not bond easily to each other or to matrices. BCHNs are shown to be up to 31% stiffer and 233% stronger than CNTs and maintain superior mechanical properties at elevated temperatures. BCHNs have a waved structure, which may help with bonding in composites and bundling. Due to their unique properties and structure, BCHNs are a significant advance in the field of nanocarbon science and engineering.

Non-covalent modification of nanomaterials provides the opportunity to modify their surface properties to improve dispersion and interfacial adhesion to a polymer host without modifying their structural and electronic properties. We use a suite of polymers with the same backbone and similar pendant groups with varying chemical properties to study the effect of different nanofiber surface chemistries on the dispersion and mechanical properties of the composites. Here we present data showing the confirmation of polymer wrapping by several polymers at a few percent by mass relative to the carbon nanofiber. This surface modification was confirmed by x-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis, and inverse gas chromatography (IGC).
Vapor grown carbon nanofibers were sonicated with a horn sonicator to disentangle the bundles, then mixed with a selected polymer for a period of time to allow the polymer wrapping around the fiber to occur. The polymers chosen had a flexible, 4-vinyl backbone to allow conformal wrapping to the CNF surface, an aromatic ring to allow p-p binding to the CNF, but a range of chemical properties to investigate the interfacial adhesion to sundry polymer hosts. The wrapping polymers include polystyrene (p-p binding), poly(vinylphenol) (hydrogen bond acid/base), and poly(vinylpyridine) (hydrogen bond base). The material was then centrifuged to separate material that was not successfully wrapped, and the supernatant decanted and vacuum filtered to produce a paper of wrapped material. This paper was then refluxed with solvent to remove any residual polymer, a process verified by UV-Vis spectrophotometry.
Thermal gravimetric analysis-mass spectrometry was used to qualitatively and quantitatively confirm the polymer wrapping. The mass of the polymers on the wrapped material was determined to be between 2-5 wt.%, in agreement with our calculations of complete single-layer surface coverage of the polymer. The mass spectral analysis of the thermal decomposition products of both the neat polymer and the polymer-wrapped CNF confirmed that the mass loss of the wrapped material was indeed consistent with the expected signatures of the neat polymers, confirming that the CNFs were wrapped.
XPS analysis of the wrapped-CNF showed the expected elemental and chemical shift signatures for the respective polymers, confirming that the polymers were indeed retained on the CNF surface after the filtration and rinsing stages.
The IGC analysis of the wrapped and unwrapped CNFs confirmed the surface modification by the reduced dispersive energy values, and the specific interaction parameters to tested probe solutes were in agreement with expected response to the various chemical probes.
These wrapped-CNF materials have been designed to target the chemical properties of many desirable host polymer materials. We will present data showing how the modified surface chemistries of the CNFs translates the performance of composite materials.

In order to harness the unique quantum-confined properties of single-walled carbon nanotubes (SWNTs), one needs to reduce bundling while providing them with a uniform physicochemical environment. The sharpness of the SWNT electronics transitions comes from the homogeneity of the surrounding environment. The larger linewidths of solution-suspended SWNTs typically arise from light aggregation as well as a variety of defects in the coverage of physisorbed surfactants that wrap around SWNTs. Moreover, the susceptibility of exposed SWNT regions to differential doping by H⁺/O₂ and other reagents (i.e. amines, conjugated molecules, nanoparticles, etc.) further enlarge linewidth broadening. Tubular surfactant assemblies such as flavin mononucleotide (FMN) and single-stranded (ss)-DNA are good surfactant candidates since their helical repeat approaches the SWNT exciton Bohr radius, self-organizing on top of the graphene sidewalls to anneal out vacancies that expose the bare nanotube to entities like O₂. Since tubular organization implies the need for surfactant cooperativity, elucidation of factors that affect such assembly holds great promise towards involving SWNTs in increasingly complex architectures. A C12 aliphatic analog of FMN (FC12) was already shown to possess the narrowest linewidth currently reported. In the case of FC12, the π-π stacking with lateral electrostatic and H-bonding interactions facilitates the formation of ordered helical assemblies that exhibit quasi-epitaxial recognition to the underlying (n,m)-cylindrical graphene lattice, resulting extremely tight FC12 assembly around SWNTs that prevents nanotube bundling through surfactant dissociation as well as leaves no room for O₂ to diffuse through the helix. Hence in this contribution, our target is to show high self-assembled surfactant order with the introduction of controlled defect within the Bohr radius of SWNT exciton or in other word, introduction of ribbon of defect within the ribbon of self-assembled surfactants. For this purpose, we designed a Flavin analogue that while wraps the carbon nanotubes in the same way, it exposes well-defined portion of pristine-SWNT that are amenable to physicochemical interactions with the surrounding environment as the wrapping remains intact. The structure of lumazine is exactly the same as that of flavin, with the notable exception that the phenyl ring has been removed, resulting in a bicyclic, rather than a tricyclic, moiety. Structurally, this obviously makes the lumazine head moiety smaller and more electron-deficient than its three-ringed cousin and diminish its π-stacking ability while conserves the planar pyrazine moiety and the hydrogen-bonding imide, enabling similar attachment of the alkyl tail and providing the potential to also conserve the same self-assembly pattern as flavin.

Scale formation in pipelines presents a very serious problem in gas and oil industry. [1] Our group has chosen to tackle this issue by means of real-time sensing of specific ions in brine. In order to do so, scale sensors based on Carbon Nanotubes (CNTs), taking advantage of their unique properties facilitated by various fabrication methods.[2]
One of these promising methods is inkjet printing of CNT layers, which is relatively new. This method, indeed seems to be a very promising.[3] Overall, it offers unique advantages over other methods of depositing the CNT layers. It does not require prefabrication of templates, and allows for rapid process at significantly lower cost.[4]
As scale sensors are usually exposed to hostile environment, the stability of the CNT layers is of great importance, as it undergoes continuous exposure to brine.
In this study, we present a comprehensive investigation of the stability of inkjet-printed CNT surfaces when exposed to brine. We attempt to identify the various effects of this exposure on chemical, electrical and mechanical properties of the surfaces as a function of exposure time and brine chemical composition. Our approach relies on investigating the surface electrical resistivity using four probe measurements, surface chemistry using Atomic Force Microscopy and Energy-dispersive X-ray spectroscopy, in addition to topography using Scanning Electron Microscopy and wettability using a Goniometer.
For this purpose, the properties of both freshly printed surfaces and the same surfaces immersed in brine for at least 24 hours were looked at as a function of time and brine composition. Our preliminary topography and roughness characterization using SEM and AFM results indicate a decrease in the roughness of these surfaces with prolonged exposure. The static contact angle observed with a goniometer shows an increase of more than 200%, while the electrical resistance also increases.
Based on our observations, the stability of inkjet-printed films seems to be compromised by exposure to brine, and show a noticeable degradation after prolonged exposure. These observations can provide a full-scale assessment of the stability of this deposition technique in the context of scale sensing applications.
References:
[1] Crabtree, Mike, et al. "Fighting scale—removal and prevention." Oilfield Review 11.3 (1999): 30-45.
[2] R. Tortorich and J.-W. Choi, “Inkjet Printing of Carbon Nanotubes” Nanomaterials, vol. 3, pp. 453-468, 2013.
[3] K. Kordás, T. Mustonen, G. Toacute;th, H. Jantunen, M. Lajunen, C. Soldano, S. Talapatra, S. Kar, R. Vajtai, and P. M. Ajayan, “Inkjet printing of electrically conductive patterns of carbon nanotubes” Small, vol. 2, pp. 1021-1025, 2006.
[4] J. Li, F. Ye, S. Vaziri, M. Muhammed, M. C. Lemme, and M. Östling, “Efficient inkjet printing of graphene” Adv. Mater., vol. 25, no. 29, pp. 3985-92, Aug. 2013.

aluminium ions exert several neurotoxic effects, such as neurofibrillary, enzymatic and neurotransmitter changes when introduced into the sentral nervous system. It is also believed to be the main cause for illnesses like Alzheimer disease, Guamanian amyotrophic lateral sclerosis and Parkinsonism dementia. Therefore, is greatly needed development of selective and cheap sensing devices that are able to detect the Al³⁺ ion in water. Carbon nanodots (C-dots) discovered in 2004 that quasispherical shape with size below 10 nm. C-dots are have great potential in cell imaging, chemosensor, optical sensing, bioimaging, diagnosis, cancer therapy and optoelectronics. Because their highly luminescence, biocompatibility, non-toxicity, photostability, water solubility and cost effective preparation.
C-dots can be prepared by various method, such as arc-discharge, combustion, hydrothermal, microwave pyrolysis, laser ablation, plasma treatment. C-dots were used in many applications in various areas such as bioimaging, chemosensor, temperature sensor, photocatalyst, cell imaging, magnetic resonance imaging and photothermal therapy. However this new nanocarbon is still need to explore the full potential for developing.
Fluorescence resonance energy transfer (FRET) involves the nonradiative transfer of excitation energy from an excited donor fluorophore to ground-state acceptor fluorophore. FRET processes are depended on the degree of spectral overlap between donor photoluminescence and acceptor absorption. FRET-based ratiometric probes are benefits observation of the fluorescence signal change at two different emission wavelength, which could provide correction for eliminating the environmental effects.
Paper-based sensor strips have been developed controls simultaneously for detecting toxins, disease markers, illicit drugs and for monitoring health. In this work, we prepared paper-based sensor strip containing rhodamine-appended carbon nanodots as ratiometric fluorescence probe based on FRET, which fluorescent response to Al³⁺. C-dots were chosen as the energy donor and Rhodamine 6G derivatives were energy acceptor. We choose commercial filter paper as a sensing platform due to its widely available, easy to use, store, transport and light weight. This paper-based sensor strip is a promising sensor in a practical application.

The development of effective coating processes for uniform thin films is a critical issue for fabricating transparent conductors. As a new class of thin film coating process, meniscus-dragging deposition (MDD) technique can offer the precise control of film thickness and the large-scale formation of conducting thin films with a tiny volume of coating solution. Such transparent thin films can be formed directly on a rigid or flexible substrate within a short time by applying the MDD method. Here, we report that highly uniform and conducting thin films with surfactant-stabilized single-walled carbon nanotubes (SWCNTs) can be achieved by controlling a dewetting velocity of the thin liquid layer. The film deposition using the MDD method was driven by dragging a meniscus of microliter SWCNTs dispersion trapped in the wedge between two plates. When the drying time was greater than the dewetting time, the SWCNTs thin film showed large defects and rupture during the drying process because of the dewetting forces and nonuniform solvent evaporation causing the secondary-flow in the aqueous layer. Such breakage of the films was successfully suppressed by increasing the dewetting time of the drying thin films, leading to the preparation of highly uniform SWCNTs films.

Carbon nanodots (C-dots) are a new class of fluorescent carbon nanomaterials, attracting tremendous attention because of their excellent biocompatibility, innocuousness and photostability. They have been recently described as paracrystalline carbon, composed of angstrom-sized polyaromatic carbon domains surrounded by amorphous carbon frames; however, their precise structure is still debatable. While general paracrystalline carbons (e.g., coal, carbon black and etc.) are hardly fluorescent, their nanometer-sized debris have exhibited a certain “optical” energy gap, presumably depending upon their size, shape and surface states, due to either the quantum confinement or the auxochromic effect. This artificial band gap leads to a number of interesting properties such as strong UV absorption, blue-to-green photoluminescence, excitation-energy-dependent photoluminescence and so on. There are still, however, challenges ahead such as blue-biased photoluminescence, spectral broadness, undefined energy gaps and etc. In this report, we chemically modify the surface of C-dots with a series of para-substituted anilines to control their photoluminescence. Our surface functionalization endows our C-dots with new energy levels, exhibiting long-wavelength (up to 650 nm) photoluminescence of very narrow spectral widths. The roles of para-substituted anilines and their substituents in developing such energy levels are thoroughly studied by using transient absorption spectroscopy. We finally demonstrate light-emitting devices exploiting our C-dots as a phosphor, converting UV light to a variety of colors with internal quantum yields of ca. 20%.

Single-walled carbon nanotubes (SWNTs) have been anticipated for application in a lot of future nanodevices. To fabricate SWNT electronics devices, it is important to grow SWNTs with uniform chirality and diameter at low temperature. So far, we have reported SWNT growth using Pt catalysts and succeeded in obtaining SWNTs with small diameters below 1.2 nm [1]. This suggests that metal catalysts with high-melting points are effective to grow SWNTs with small and uniform diameters. However, SWNT yield from Pt catalysts was small at a growth temperature of less than 6000C. In this study, we carried out SWNT growth by CVD using Rh catalysts, whose melting point is 19660C. By optimizing growth conditions, we obtained SWNTs with narrow diameter distribution at a growth temperature of 4000C.
After deposition of Rh catalyst on Al₂O₃/SiO₂/Si substrates, SWNT growth was carried out using the alcohol gas source method in a high vacuum [1]. The growth temperature was set between 4000C and 6000C, and the ethanol pressure was varied between 1×10^-5 Pa and 1×10^-2 Pa. The grown SWNTs were characterized by FE-SEM, TEM and Raman spectroscopy.
When the growth temperature was 600 0C, both G band and RBM peaks were observed in Raman spectra, indicating the growth of SWNTs from Rh catalysts. From Raman shifts of RBM peaks, SWNT diameters were estimated, which were distributed between 0.6 nm and 1.6 nm. SEM observation showed that the SWNT yield decreased as the growth temperature was reduced. In spite of the yield reduction, both G band and RBM peaks were still observed in the Raman spectra even at a growth temperature of 4000C, confirming the SWNT growth. In addition, the SWNT diameter distribution became narrower as the growth temperature was reduced, and SWMTs of diameter about 1.0 nm was dominant at 400 0C. Our results indicate that Rh catalyst is useful for low temperature growth of SWNTs with smaller-diameter and narrower diameter distributions.
[1] T. Maruyama et al. Mater. Express 1 (2011) 267.

The objectives of this research are the preparation and characterization of multiwalled carbon nanotubes (MWCNTs), functionalized MWCNTs, graphene, and functionalized graphene/epoxy nanocomposite for application to the thermal interfacial materials. This dissertation investigates the functionalized multi-walled carbon nanotubes (MWCNTs) which are used as cross-links between MWCNTs/epxoy interfaces to achieve homogeneous dispersion and strong interfacial bonding for developing fully integrated MWCNTs/epoxy nanocomposites. The monomer of glycidyl methacrylate (GMA) was grafted onto MWCNTs by free radical polymerization, and various grafted GMA quantities of functionalized MWCNTs by different compositions were obtained. In the GMA-MWCNTs/epoxy nanocomposites, GMA-MWCNTs can react with epoxy and becomes part of the cross-linked structure, rather than just a separate component. It was found that GMA-MWCNTs exhibited better dispersion in the epoxy matrix than that of pristine MWCNTs. The low grafted GMA quantity (7wt% organic compound on MWCNTs was obtained by TGA) of functionalized MWCNTs possesses better dispersion than that of higher grafted GMA quantity (8.2wt% organic compound on MWCNTs which was investigated by TGA) of functionalized MWCNTs. Moreover, results demonstrate that the thermal conductive property of the epoxy nanocomposite was improved dramatically, especially, adding low grafted quantity of functionalized MWCNTs. The thermal conductivity of MWCNTs/epoxy is increased from 0.19W/mK to 0.43W/mK, exhibiting 115 % improvement and the thermal interfacial resistance of nanocomposites is reduced from 0.51 to 0.16.

Carbon nanotubes (CNTs) have unique properties especially for electronic devices and sensors. Printing using inkjet offers a significant cost advantage over conventional fabrication but suffers from scalability and large line width (20 micron line width which is the line width used in Silicon devices in 1975). There is a need to print devices at today&’s silicon line width (20nm). We have introduced a multi-scale offset printing process capable of printing any material suspended or dissolved in solvents or water. The printing process is a multi-layer offset printing process designed to realize mass production of flexible CNT devices, based on directed electrophoretic assembly and a transfer. Reusable damascene templates, with templates that have different multi-scale patterns (down to 20 nm); one for each layer are created for multi-layer offset printing. The template can be fabricated on a hard substrate such as silicon wafer, or flexible substrates, such as polyimide, PEN or PET to fit on curved surfaces such as roll-to-roll process. Highly controlled thickness and alignment of CNTs is achieved by controlling assembly parameters, such as the applied voltage, pulling speed, nanomaterial concentration such as carbon nanotubes, nanoparticles or polymers. We printed Band-Aid CNT sensor that could read glucose, urea and lactate levels using sweat as well as an inexpensive micro CNT chemi-resistive two-terminal sensor for detecting H2S with a detection limit that&’s less than 1 ppm has also been developed.

Topological defects such as Stone-Wales defects play a central role in plastic deformation, chemical fucntionalization, and junction formation between carbon nanotubes. Here, we couple density functional theory with transition state theory to systematically investigate the thermodynamic formation energy and kinetic activation barrier of topological Stone-Wales defect in single-wall carbon nanotubes. We find that both the formation and activation energies depend critically on the nanotube chairality, diameter and defect orientation. The kinetic activation barrier follows empirical Broslash;nsted-Evans-Polanyi type correlation with the corresponding thermodynamic formation energy, and can be explained by overlapping energy-coordinate parabolas representing the structures with and without the defect. Further, we propose a possible route to substantially decrease the kinetic activation barrier for Stone-Wales defects. Such accelerated rates of formation of these defects are desirable in many novel electronic, mechanical and chemical applications, and also facilitate the formation of three-dimensional nanotube superstructures.

Solution-processable, high purity semiconducting single-walled carbon nanotubes (SWNTs) are promising candidates for electronic and optoelectronic devices in the post-silicon era. In the last few years, we have witnessed tremendous progress in the ability to sort SWNTs with polymer-based dispersants. The ability to specifically sort for semiconducting SWNTs has led to field-effect transistors exhibiting carrier mobilities > 10 cm²/v s and current on/off ratios > 10⁶. [1] Yet, the charge transport mechanism in such polymer/SWNTs networks is not well understood. We carried out temperature dependent electrical characterization of field-effect transistors having SWNT networks pre-sorted with poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6&’-{2,2&’-bipyridine})], PFO-BPy, or poly(9,9-dioctylfluorene-alt-bithiophene), F8T2. Sorting with PFO-BPY results in preferential selection of SWNTs having a diameter of 1.4 nm, while sorting with F8T2 leads to preferential selection of SWNTs having a diameter of 1 nm. While the mobilities and source-drain currents of thin-film transistors comprising these two types of SWNT networks are both thermally activated between 78 K and 293 K, we observe subtle differences in their temperature dependencies. Specifically, the temperature dependence of the electrical characteristics of devices with PFO-BPy-sorted SWNTs specify fluctuation-induced tunneling as the mechanism for charge transport, [2] while the temperature dependence of the hole mobility of devices comprising F8T2-sorted SWNTs is best described by the simpler Arrhenius equation in the same temperature range. Given that tube-tube junctions are generally believed to be bottlenecks for charge transport in carbon nanotube networks, [3] the presence of polymers on the surfaces of carbon nanotubes must affect inter-tube charge transport. Considering the percolative nature of carbon nanotube networks, hole transport must be preceded by overcoming the energy level offset between the Highest Occupied Molecular Orbital (HOMO) of the polymer and the valence band maximum of the semiconducting SWNTs for macroscopic charge transport. Spectroscopic characterization reveals this energy level offset to be as high as 1.2 eV in the PFO-BPy-sorted SWNT networks, and 0.5 eV in the F8T2-sorted SWNT networks. [4] We thus believe this difference in energy level offset to plays a critical role in dictating the temperature dependence of charge transport in these polymer-sorted SWNTs networks.
[1] Hang Woo Lee et. al., Nat. Commun. 2011, 2, 541-8.
[2] Jia Gao and Yueh-Lin Loo, Adv. Funct. Mater. 2015, 25, 105-110.
[3] Sung-Jin Choi et.al., Appl. Phys. Lett. 2012, 101, 112104.
[4] Jia Gao and Yueh-Lin Loo, unpublished data.

Quantum dots have been applied in sensing with success, but their use in environmental applications has been questioned due to their toxic heavy metal content, that could leach out of the device as a consequence of partial dissolution of the nanomaterial under natural water conditions. Carbon dots are fluorescent nanoparticles that offer a promising alternative to quantum dots for sensing, due to their low cost, benign fabrication process and negligible environmental impact. Fluorescence sensors are specially suited for detection of nitroaromatic compounds such as TNT and DNT, due to its ability to quench emission of excited species. When combined to Molecularly Imprinted Polymers (MIPs), the sensors become specific to the imprinted target molecules. An ideal chemical sensor will be highly specific, stable (no leaching of fluorescent labeling) and pose no toxicity to the user and the environment.
Amino-functionalized carbon dots (CDs) with high fluorescence were synthesized by pyrolysis of citric acid at low temperature (170 °C), in the presence of branched polyethylenimine (BPEI) in one simple step. The obtained BPEI-CDs are capped with abundant BPEI at their surfaces. We investigated the surface charge, surface chemistry and functionalization, particle size distribution, suspension stability in natural waters, photoluminescence properties (PL), emission wavelength, intensity and stability. The amino groups allow BPEI-CDs react with carboxyl groups in the presence of two catalysts 1-(3-Dimethylaminopropyl)-3 -ethylcarbodiimide hydrochloride (EDC) and 1-(3-Dimethylaminopropyl)-3 -ethylcarbodiimide hydrochloride (NHS). A molecularly imprinted polymer (MIP) with template of DNT was prepared using acrylic acid as the functional monomer. In order to prepare a robust fluorescent sensor, covalent bonds between carbon dots and MIPs need to be formed. The MIP was combined with fluorescent carbon dots via a simple covalent reaction. The fluorescent-labeled MIPs were tested for their performance in detecting aqueous 2,4-dinitrotoluene (DNT) by fluorescence quenching. The mechanism of quenching involves the formation of a charge-transfer complex between the fluorophore and quencher. The strong electron-withdrawing ability of nitrated compounds enables them to form strong charge-transfer complexes with c-dots. The quenching effect of DNT as a function of concentration of above-mentioned contaminant was investigated. Other environmental factors were considered including pH, ionic strength, and natural organic matter (NOM). Variations of those are expected in natural waters and alter the quenching levels of target compounds with respect to the pure water situation. The limits in detection and interference due to similar compounds were assessed. It can be concluded that the fluorescent-labeled MIP system is a feasible method for detecting DNT, with the potential for future use in detecting the nitroaromatic compounds in environmental water samples.

Carbon nanodots (CNDs), as fluorescent paracrystalline zero-dimensional carbon nanoparticles, have attracted much attention in optoelectronics, photocatalysis, and bioimaging due to low cost, biocompatibility, low toxicity, photostability, and etc. So far, many methods have been developed for the preparation of CNDs, including laser ablation, chemical oxidiation, electrochemical treatment, thermal pyrolysis, and microwave. Through these methods, high-quality CNDs have been obtained; however, there are still numerous challenges in improving their optical properties such as the lack of visible light absorption, blue-biased light emission, and so on.
Generally, the optical properties of CNDs are directly related to their electronic structure, originating from their polyaromatic carbon domains, defective states, and surface states. Currently, doping heteroatoms, especially nitrogen and/or sulfur, in a carbon framework has been found to be an attractive strategy to control photoluminescence (PL) of CNDs. Such dopants can be considered to generate defective states, where their different electronegativity, lone pairs of electrons, and etc. change the electronic structure of CNDs. Many research groups have attempted to synthesize a variety of heteroatom-doped CNDs with distinguished optical properties, however, there have been limitations on a degree of doping because dopant molecules and carbon precursors were separated to participate in the reaction independently.
In this work, we have synthesized nitrogen and sulfur-doped CNDs from ethylenediamine-N,N&’-diacetic acid and 2,2&’-(ethylenedithio)diacetic acid, respectively. Our method features the use of “single” molecular precursors that contain both carbon and dopant atoms, which allows us to examine the effects of doping in a molecular level. The effects of doping on the electronic structure of CNDs could be examined by a series of spectroscopic measurements including UV-vis absorption and photoluminescence. It is found that doping gives rise to new light absorption and photoluminescence bands at around 500 nm. Finally, we have demonstrated light-emitting didoes (LEDs) with our CNDs to show that the electronic states induced by doping directly influences their electroluminescence. Such LEDs successfully exhibits broad electroluminescence covering the visible light range from 500 to 700 nm, resulting in bright white light with maximum external quantum efficiency of 0.32%.

Charge storage devices like batteries and capacitors are widely used in applications like electric vehicles and smartphones. In particular, supercapacitors combine the high energy densities that can be achieved with batteries with the high power densities that can be obtained from conventional capacitors. Supercapacitor electrodes are typically made up of activated carbon materials that possess high surface areas for charge storage. With the advent of carbonaceous nanomaterials like carbon nanotubes (CNTS), graphene and aerogels, there is a potential to reach even higher charge and power densities. However, many challenges like agglomeration and microstructural instability needs to be overcome before the performance of supercapacitors based on carbonaceous nanomaterials can approach their theoretical limit. Therefore, strategies based on the manipulation of the morphological characteristics of these carbonaceous materials have been developed in order to optimise their performance in charge storage devices. In this context, this work investigates composites of CNTs and resorcinol formaldehyde (RF)-based carbon aerogels (CNT/CAG) as materials for supercapacitor electrodes. This strategy aims to combine the structural stability to withstand repeated charge/discharge cycles and high surface area mesoporous structure of RF-based CAG to enable effective charge storage with the high conductivity that CNTs provide. Typically, the formation of CNT/CAG composites involves the polycondensation of RF in the presence of CNTs to form an RF-based aerogel followed by a final pyrolysis step to convert the RF-aerogel to a carbon aerogel. Achieving a uniform dispersion of CNTs at a controllable loading in the RF resin in the initial step is a considerable challenge. Hence, most studies that have been done with CNT/CAG composites employ surfactants to aid in the dispersion which may be detriment to the integrity of the internal structure of the composite during pyrolysis. Furthermore, surfactants add to parasitic weight and hence reduce the specific capacitance. In this study, a novel strategy of combining CNT with RF-resin to form a stiff CAG/CNT composite via a resin infusion system has been investigated. Infusing a CNT-construct with RF-resin negates the challenge of pre-dispersing the CNT in the resin using a dispersant before casting into an electrode. The combination of CNT with RF-based CAG results in a mesoporous structure penetrating a conducting network which is ideal for electric double layer charge storage. With only a 2 wt% loading of CNTs, a high conductivity of 182 S m^-1 has been obtained. In addition, a reasonable specific and areal capacitance of 8.98 F g^-1 and 0.15 F cm^-2 has been measured using this method. This work can potentially be a quantum leap in the development of high CNT loading CNT-polymer composites which will aid the advancement of structural energy storage devices for future generations of electric vehicles.

Due to the importance of phenomena associated to carbon dioxide, this gas has since long ago attracted the attention of the scientific community and the consequent technological effort developed in the investigation of its properties allowed the understanding of the CO2 production as a result from coal and hydrocarbons combustion. As a consequence, CO2 concentration in the atmosphere became an important problem in terms of global warming. In order to solve this CO2 related environmental problems an accurate and reliable detection of this gas in a scale that allows mapping its concentration in any media is highly desirable. An efficient method to do so is the nanostructural arrestment of carbon dioxide (1). In this sense, carbon nanotubes stands (SWNT) up as a promising structure. Provided an important adsorption energy is observed between the gas molecule and the nanotube lattice, the other physical and chemical features of this system are favorable to this nanotechnology application. In a previous study, we observed that, whereas pristine SWNT present low reactivity, the effect of doping this system with transition metals yielded excellent results [2].In the present work, we propose a new route to functionalize SWNT in order to arrest carbon dioxide. By means of electronic structures calculations in the scope of the Density Functional Theory, we applied structural deformations to the lattice and conducted an analysis on whether or not the originated system was suitable to CO2 detection. The feasibility of this system to the actual application is measured in terms of the interaction energy, energies levels profiles and spectroscopic constants. By means of this procedure we observed a reasonable adsorption energy, of about an order of magnitude higher than that of the pristine nanotube. This indicate that the conformational functionalization is an reasonable choice to obtain efficient gas sensors.

Chemiresistive sensors were created from single-walled carbon nanotubes (SWCNTs) by non-covalent modification with late first-row transition metal complexes of meso-tetraarylporphyrins. An array device fabricated from metalloporphyrins bearing metal centers from Cr through Zn demonstrated strong responses to vapors of various volatile organic compounds (VOCs). The responses were subjected to statistical analyses that enabled the successful classification of representative VOCs into five different categories (alkanes, alcohols, ketones, aromatic hydrocarbons, and amines) with 98% accuracy. With the exception of amines, which are capable of strong charge transfer interactions, the basis of classification appears to correlate with the differences in the solubility properties of the porphyrin compounds in the various VOCs as solvents, suggesting that solvent vapors modulate the strength of interactions between the porphyrins and the nanotubes. This hypothesis is corroborated by Raman spectroscopic and field-effect transistor (FET) measurements. These results demonstrate the potential for porphyrin-functionalized SWCNT-based electronic noses as inexpensive, portable chemical sensors for the identification of VOCs in applications such as environmental monitoring and medical diagnostics.
Additionally, chemiresistive detectors targeted toward the detection of amine vapors were created from SWCNTs by non-covalent modification with Co meso-arylporphyrin complexes. We show that through changes in the metal&’s oxidation state, the electron-withdrawing character of the porphyrinato ligand, and the counteranion, the magnitude of chemiresistive response to ammonia gas could be improved. The resulting devices were also shown to have sub-ppm sensitivity and high selectivity toward amines as well as good stability to air, moisture, and time. The application of these chemiresistors in the detection of biogenic amines (i.e., putrescine and cadaverine) and in the monitoring of spoilage in various raw meat samples (chicken, pork, salmon, cod) over several days was also demonstrated.

Using first principles calculations, we show that the overlapping defects in bi-layer graphene (both AA- and AB-stacked) interact forming inter-layer covalent bonds, giving rise to two-dimensional (2D) clipped structures [1]. At the optimal separation between the mono-vacancies, the electronic properties of the connected bilayer structure are similar to pristine bi-layer graphene. The mechanical properties are significantly better in the 2D connected structures when compared with the defected mono-layer analog. These clipped structures can be transformed into one-dimensional (1D) double wall nanotubes (DWCNT) or multi-layered three dimensional (3D) bulk structures. These structures show good mechanical strength due to covalent bonding between multi-layers. Clipping also provides a unique way to simultaneously harness the conductivity of both walls of a double wall nanotube through covalently bonded junctions. With additional conducting channels and improved mechanical stability, these clipped structures can lead to a myriad of applications in novel devices.
1. #8203;Rahul P. Hardikar, Atanu Samanta, Aaditya Manjanath, and Abhishek K. Singh, Carbon, In press 2015.

Single-walled carbon nanotubes (SWCNTs) have recently been used as hole-transport layers (HTLs) in efficient and stable perovskite solar cells. Large SWCNT hole mobility and tunable energetics could allow for more efficient extraction from the perovskite layer and slower charge recombination times relative to many other organic HTLs such as P3HT and spiro-OMeTAD. However, the fundamental mechanisms and time scales underpinning charge extraction and recombination for SWCNT HTLs remain unclear. Here, we report the use of time resolved microwave conductivity (TRMC) and transient absorption (TA) spectroscopy to directly study hole-transfer from the photoexcited pervoskite layer to variable band gap semiconducting SWCNT thin films. Spectral signatures of charges in the SWCNT film from TA measurements indicate efficient hole transfer and slow recombination. Combining TRMC photoconductance transients with the TA measurements allow us to follow specific charge carriers over many decades of time (femtoseconds to microseconds), and demonstrate both efficient electron and hole extraction and very slow recombination. The results emphasize the potential for tunable SWCNT hole transport layers in efficient perovskite solar cells.

The perspective of merging graphene and carbon nanotubes (CNTs) into novel 3D sp2-hybridized carbon structures is regarded as a way to extend the outstanding physicochemical properties of those materials to the third dimension. Numerous applications could benefit from such 3D structures for energy storage and conversion, thermal management, or electrical interconnects.
The synthesis of vertically-oriented CNT forest on graphene layers is one of the main building blocks to fabricate 3D graphene-CNT hybrid structures. It is also a challenging one owing to the absence of dangling bond and low surface energy of graphene that strongly affect the restructuring of the catalyst used for CNT growth. In this talk, we introduce a new technique for the growth of high density (10¹² cm^-2), few-walled CNT forest on graphene by catalytic CVD (chemical vapor deposition). It allows the low temperature synthesis (< 600°C) of CNT forest on high quality monolayer graphene supported on both metals and insulators. The CNT growth mechanism and its impact on the quality of the underneath graphene will be presented. The electronic properties of the graphene-CNT hybrid structures are analysed and we will show that an ohmic contact is obtained between CNTs and graphene. The potential of this unique synthesis method for advanced interconnects application will be demonstrated through the fabrication of hybrid 3D structures composed of graphene horizontal lines connected by vertical CNT bundles.

Recent developments in monolayer graphene production allow its use as the active layer in field-effect transistor technology. Favorable electrical characteristics of monolayer graphene include high mobility, operating frequency, and good stability. These characteristics are governed by such key transport physical phenomena as electron-hole transport symmetry, Dirac point voltage, and charged impurity effects. Doping of graphene occurs during device fabrication, and is largely due to charged impurities located at or near the graphene/substrate interface. These impurities cause scattering of charge carriers, which lowers mobility. Such scattering is detrimental to graphene transistor performance, but our group has shown that coating with fluoropolymer thin films or exposure to polar organic vapors can restore favorable electrical characteristics to monolayer graphene. By partially neutralizing charged impurities and defects, we can improve the mobility by approximately a factor of 2, improve the Dirac voltage by up to 30 V, and cut the residual carrier density value in half. We hypothesize that this phenomena results from screening of charged impurities by the polar molecules. To better understand such screening interactions, we performed computational chemistry experiments to observe interactions between polar organic molecules and monolayer graphene. The strength of interaction for polar molecules with doped or defective graphene was over 1000% greater than with pristine graphene. We also computationally demonstrated charge screening of defects atop graphene by polar molecules. These computational observations correlate well with our experimental results to strongly support our hypothesis that polar molecules can act to screen charged impurities on or near monolayer graphene. Such screening favorably mitigates charge scattering, improving graphene transistor performance. Furthermore, this work could be extended to other 2-D electronic systems or nanoribbons.

Carbon nanofibers (CNFs) are ideal candidates for a range of important applications; However, to realize industrial application of these materials, processes must be developed to produce CNTs with desired structural characteristics, and with high yields.
Using a specific weak adhesion layer between the CNT catalyst and the substrate, we produced a catalytic thin film that delaminates inside our chemical vapor deposition (CVD) reactor during synthesis. Following delamination, removal of the mechanical constraint of the catalyst layer to the substrate led to mats of carbon nanofibers that were 3X to 5X larger than the substrate they originated from. The mass of these three-dimensional (3-D) CNF mats was over an order of magnitude that of micron-tall entangled CNFs we obtained using the same process on samples with stronger adhesion layers. Following an extensive characterization of the morphology and structure of the CNF mats in concert with a parametric study of the effect of temperature, pre-anneal conditions, growth duration, and substrate materials, we found evidence of a correlation between growth conditions and the 3-D mat morphological properties. This work gives insight into a new growth process whereby high yields of 3-D carbon nanostructures can be directly obtained from an unconstrained catalytic thin film, utilizing a rational choice of catalyst/underlayer combinations and growth conditions. Based on the extensive characterizations done to date, we can explain specific aspects of the new growth mechanisms based on thin film evolution, simultaneous delamination, and carbon nucleation of the catalytic thin film. Such materials have significant promise as conductive material scaffolds for a wide-range of next-generation materials that can take advantage of the high surface area and good mechanical robustness of such CNF structures.

Since the discovery of carbon nanotubes and the fundamental understanding of their growth mechanism, most researchers focused on the influence of different growth parameters and variety of substrates on vertically aligned carbon nanotubes (VACNTs) growth. Most research has focused on understanding the role of catalysts, underlayers, gases, and most recently thin film reservoirs position below the alumina underlayer. In this study, we demonstrate the effect of different metallic bridges positioned above the catalytic layer on the growth of VACNTs using thermal chemical vapor deposition (CVD). We show that the growth of CNTs can be enhanced or inhibited by using different materials. Using patterned metal foils or wires we were able to pattern regions with CNTs of varying height with regions without CNTs. For instance, we show how copper inhibited CNT growth while titanium bridges led to taller CNTs beneath. Using HRTEM and HRSEM we will show the effect of these metallic bridges on the catalyst morphology and on the CNT structure. We will discuss mechanisms of how the bridges affect the precursor gases in proximity of the catalytic layer. This research shows how we can control CNT growth on different regions of the same sample, without the need to pattern the catalyst.

Years ago, we showed how preheating precursor gases helped to synthesize carbon nanotubes (CNTs) at lower temperature and with increased crystallinity. We recently demonstrated how by applying a similar technique, we synthesized high quality, few-layer graphene at reduced temperature with full reproducibility on nickel thin films.
Raman spectroscopy showed that the graphene films synthesized using gas preheating exhibited 50% less defects compared to those obtained without gas preheating. However, the most important outcome is that all experiments performed using gas preheating were fully reproducible, while less than 15% of the experiments performed without gas preheating led to graphene of only acceptable quality. Gas chromatography/mass spectrometry (GC-MS) of the preheated gases showed an increased formation of polycyclic aromatic hydrocarbons (PAHs), as it did in our previous studies on CNTs.
From the results obtained, we postulated a new growth mechanism that fits previous density functional theory (DFT) reports of hydrocarbon stability on a nickel surface. The results presented are an important step in the direction of graphene synthesis at lower temperatures with full reproducibility. In this presentation, we will focus on the parallels between CNT and graphene synthesis and discuss how other insights on CNT growth could be leveraged to improve graphene synthesis.
This work has been published in the Journal of Materials Chemistry A (M. Somekh, et al., Fully reproducible, low-temperature synthesis of high-quality, few-layer graphene on nickel via preheating of gas precursors using atmospheric pressure chemical vapor deposition, Journal of Materials Chemistry A, P.19750-19758, Issue 36, December 2014).

Methods of in situ transmission electron microscopy (TEM) have become a powerful tool for the detailed analysis of electrical, mechanical and thermal properties of diverse 1D, 2D and 3D carbon nanomaterials, i.e. nanotubes, graphenes, and foam-like nanostructures. These methods combine the highest spatial resolution peculiar to a high-resolution TEM instrument and unique possibilities of precise manipulations with an individual nano-object, including its electrical biasing, resistive heating, bending and stretching [1].
I will present our group recent progress with respect to thorough studies of various carbon nanomaterials using different in-situ “Nanofactory Instruments” TEM holders. Mechanical properties of nanotubes and their junctions, and graphene-like nanosheets under direct mechanical tests using an atomic-force microscope (AFM)-TEM setup [2-5] will be presented and discussed. Ultimate increase in the nanostructure temperature up to ~2000^oC or more, using resistive heating in a scanning tunneling microscope (STM)-TEM holder has allowed us to shed a new light onto temperature gradients, intra-diffusion and metal amorphization/crystallization kinetics in the nanotube channels [6,7], and the peculiarities of the graphene oxide to graphene transformation [8]. Prototype field-emitters, using carbon onion- nanotube- or graphene- like nanostructures [9,10], and Li-ion batteries, using nitrogen-doped graphenes, were also constructed inside TEM and their functional performances were investigated in situ [11,12].
The author is grateful to many colleagues, e.g. D.M. Tang, Z. Xu, M.S. Wang, X.L. Wei, P.M.F.J. Costa, X.D. Bai, F. Banhart, N. Kawamoto, X. Wang, X.B. Wang, M. Mitome, Y. Bando, C. Zhang and O. Cretu for their key contributions to the regarded experiments at different stages of the in situ TEM Project accomplishment within MANA-NIMS over the last decade.
References:
[1] Golberg D. et al. Adv. Mater. 24, 177 (2012).
[2] Wei X.L. et al. Nano Lett. 15, 689 (2015).
[3] Wang M.S., Golberg D., Bando Y. Adv. Mater. 22, 5350 (2010).
[4] Wang M.S., Golberg D., Bando Y. Adv. Mater. 22, 4071 (2010).
[5] Nikiforov I. et al. Phys. Rev. Lett. 109, 025504 (2012).
[6] Costa P.M.F.J. et al. Nature Commun. 2, 421 (2011).
[7]Tang D.M. et al. (2015), submitted for publication
[8] Xu Z. et al. ACS Nano 5, 4401 (2011).
[9] Wang M.S., Golberg D., Bando Y. ACS Nano 4, 4396 (2010).
[10] Wei X.L., Bando Y., Golberg D. ACS Nano 6, 705 (2012).
[11] Wang X. et al. Adv. Funct. Mater. 22, 2682 (2012).
[12] Wang X. et al. Nano Lett. 14, 1164 (2014).

Single-walled carbon nanotubes (SWNTs)/graphene hybrid structures have been anticipated for various applications such as supercapacitors and electrode materials for rechargeable battery. However, previous attempts to grow carbon nanotubes (CNTs) on graphene using chemical vapor deposition (CVD) produced multi-walled CNTs or mixtures of CNTs with different wall numbers. In this study, using Pt as catalyst particles, we attempted to grow SWCNTs on graphene by CVD and synthesized semiconducting SWCNTs with a narrow diameter distribution on chemically treated graphene layers.
After acid treatments of graphite substrates, Pt catalysts were deposited on them by a pulsed arc plasma gun. Then, SWCNTs were grown on them at 7000C using the alcohol catalytic chemical vapor deposition (ACCVD) in a high vacuum [1]. The grown SWNTs/graphene hybrid structures were characterized by SEM, TEM, Raman spectroscopy and X-ay photoelectron spectroscopy (XPS).
SEM observations showed that SWCNTs were grown only on graphene layers which were exfoliated from the graphite surface even though Pt particles were well distributed all over the surface of the graphite substrates. TEM and Raman measurements showed that most SWCNTs grown on the graphene layers were semiconducting and that their diameters were less than 1.1 nm with a narrow distribution. In addition, the SWCNTs seemed to be attached to the graphene surface. C 1s core-level XPS spectra showed that graphite surface was oxidized at first, but, after SWCNT growth, the graphite oxide was reduced. These results showed that SWNTs/graphene hybrid structures were formed by this process. We will also discuss the selective growth mechanism of SWCNTs from Pt catalysts on the graphene layers.
[1] R. Ghosh et al. Chem. Comm. 51 (2015) 8974.

Carbon nanocapsules (CNCs), which are nanometer-sized airtight graphitic shells, encage various metals and carbides in their hollow centers. The properties of CNCs are influenced by both encapsulated materials and interfaces. In this study, we investigated the interfaces in the CNCs encapsulating α-iron (Fe) and Fe carbides (Fe₃C), which have been expected as next-generation magnetic materials.
The CNCs were synthesized by arc-discharge evaporation of Fe and C. The CNCs were identified by high-resolution transmission electron microscopy. The encapsulated materials were found to be α-Fe, Fe₃C, and their bicrystals. The average diameter of the CNCs was 19 nm, with the maximum 44 nm and the minimum 6 nm.
The interlayer spacings of the interfaces between graphitic layers and α-Fe and the interfaces between graphitic layers and Fe₃C were found to be 0.24 nm and 0.29 nm, respectively. These values are similar to the interlayer spacings of the chemisorbed (0001) graphitic layers on the (110) surfaces of α-Fe estimated by Vinogradov et al. using a density functional theory (approximately 0.23 nm) ¹⁾. This suggests that the observed interfaces in this study were chemisorbed ones. The interlayer spacings in Fe₃C-encapsulated CNCs were larger than that of α-Fe-encapsulated CNCs. This shows that the C-C bonds contribute to the increase in interlayer spacing. We observed strains of the graphitic layers at the steps on flat surfaces and the corners of the encapsulated crystals with polygonal shapes, resulting in larger interlayer spacings.
Reference
1) N. A. Vinogradov et al., Phys. Rev. Lett. 109 (2012) 026101.

In this work, we fabricate electrostatically actuated microelectromechanical resonators from nanographite, deposited using plasma-enhanced chemical vapour deposition (PECVD) directly onto an insulating substrate (SiO₂), establishing this as a route towards integration of nanographene/graphite using CMOS-compatible fabrication. The nanographite is conductive and has graphitic domains ~10 nm in diameter. Material characterisation is performed using Raman spectroscopy and atomic force microscopy. To fabricate devices, a continuous nanographite film is deposited by PECVD onto 6-inch silicon/SiO₂ wafers. Methane is the carbon precursor with hydrogen diluent. The film is patterned into doubly-clamped and cantilever beams via optical lithography and etched using reactive ion etching, nickel electrodes are deposited and the beam is released using HF vapour. The nanographite is under a relatively high compressive stress which causes buckling of the doubly-clamped beam. However, we over-etch the SiO₂ to achieve a ~30 mu;m undercut of the beam anchors. The stress gradient in the film creates an upward deflection of the anchors and imparts an effective tension to the suspended beam. Finite element simulation has been undertaken to take account of the added ‘length&’ which is added to the beam. We then model the fundamental mode of vibration as a beam under tension. To measure the resonant frequency of the resonators, we apply DC bias plus a time varying AC voltage, between the beam and substrate, causing a varying electrostatic force at the frequency of the AC voltage. The velocity of the beam is measured using laser Doppler vibrometry and becomes large at mechanical resonance. Natural frequency of vibration has been measured for a range of devices: 257 kHz for 150 mu;m beams, 420 kHz for 100 mu;m, 595 kHz for 75 mu;m beams and 15 kHz for 100 mu;m cantilevers. Quality factors have been calculated from a fitted Lorentzian curve and at ambient pressure are 20 and 1300 at 70 mTorr. Application of increasing DC Bias (up to 50 V) enables tuning of the natural frequency by electrostatic spring softening, with an average tunability of 1.19 kHz per volt across this range.

we demonstrate a simple and efficient solvent annealing method to manufacture highly ordered PS-PDMS masks with various length scales. The selective solvent to the majority domain shift the morphology from cylinder to sphere phase and thus the perpendicular orientation can be trapped during this transition. Only a simple dry etch process enables formation of the hard mask, removal of one block and patterning on substrate simultaneously. This method is particularly suitable for patterning on two-dimensional (2D) materials where part of the single atom layer is removed in a controlled way to give tunable properties. Graphene nanomesh is a typical example, in which high-density arrays of nanoscaleholes are punched to open bandgap. The available BCP lithography for graphene nanomesh is tedious, involving multiple deposition and etching steps. Most of all, it is difficult to reach sub-20 nm feature size since PS-PMMA mask is used. Here, SD12 and SD15 are directly deposited on CVD-grown single layer graphene. Lage-area mask covers on graphene without defects after solvent annealing. The pattern is well adjusted on grain boundaries, muti-layer islands and substrate defects. We use Raman spectroscopy to analyze the hole punching process. After the BCP deposition, the spectrum stays the same. Increase oxygen plasma etching time results in the increase of D peak, which typically characterizes the hole enlarging process. The high process control is evidenced by the unchanged width of the G peak. The patterned graphene after removing the mask by scotch tape, represents high fidelity of the mask morphology. The obtained graphene nanomesh can be used as filed-effect transistor in semiconductor industry or for atomic-layer membrane separation.

The absence of a band-gap and the lack of an adequate synthesis method of high quality graphene on silicon substrates have held back the applications of graphene in electronics and integrated micro- and nanosystems [1]. We have pioneered a novel approach to the synthesis of high-quality and highly uniform few-layer graphene on silicon wafers, based on solid source growth from hetero-epitaxial SiC films [2, 3]. Using a Ni/Cu catalytic alloy we realize high-quality, uniform bilayer graphene directly on silicon wafers, at temperatures compatible with conventional semiconductor processing. The obtained graphene is characterized by unprecedented and stable sheet resistances below 30 Omega;/square and an exceptional adhesion to its substrate, which is essential for wafer -level fabrication of nanodevices. We show how the exceptional properties of the catalytic graphene on silicon substrates can advance a wide spectrum of practical applications ranging from efficient metal replacement at the nanoscale for MEMS/NEMS [2] to miniaturized devices for on-chip energy storage [4].
[1] K. S.Novoselov, et al., A roadmap for graphene, Nature 490(7419): 192-200 (2012).
[2] B.V.Cunning, M.Ahmed, N.Mishra, A.R.Kermany, B.Wood, and F.Iacopi, Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers, Nanotechnology 25, 325301, 2014.
[3] F.Iacopi et al, A catalytic alloy approach for highly uniform graphene on epitaxial SiC on silicon wafers, Journal of Materials Research, Invited Feature Paper, J.Mater.Res. 30 (5), 609-616, 2015.
[4] M.Ahmed, F.Iacopi, “A thin film approach for SiC -derived graphene as on-chip electrode for supercapacitors”, patent pending, 2015.

The theoretically proposed graphene/single-walled carbon nanotube (G/SWCNT) hybrids by placing SWCNTs among graphene planes through covalent C-C bonding or meso 3D graphene structures are expected to be with extraordinary physical properties and promising engineering applications. Herein, Chemical vapor deposite(CVD) growth of 3D sp² nanocarbon structure such as graphene carbon nanotube(G-CNT) hybrids, unstacked double-layer graphene (UDG), graphene nanofiber (GNF) with meso single crystal layered double oxide (LDO) or MgO as hard templates with tunable structures, surface area, pore size and the conductivity was explored. The as obtained G-CNT-S cathode exhibited excellent performance for Li-S batteries with a capacity as high as 650 mAh g^-1 after 100 cycles even at a high current rate of 5 C. The UDG separated by a large amount of mesosized protuberances and can be used for high-power lithium-sulphur batteries with excellent high-rate performance. Even after 1,000 cycles, high reversible capacities of ca. 530mAh g^-1 and 380mAh g^-1 are retained at 5 C and 10 C, respectively.While the high conductive GNFs made from MgCO₃ nanofiber hard templates have the short diffusion distance for ions of ionic liquids electrolyte to the surface which yield high surface utilization efficiency and have a capacitance up to 15 mu;F/cm², higher than single-walled carbon nanotubes.
A rationally designed N-ACNT/G sandwich was proposed and fabricated via a two-step CVD growth. Aligned CNTs and graphene layers were in situ anchored to each other, constructing a sandwich-like hierarchical architecture with efficient 3D electron transfer pathways and ion diffusion channels. The moderate chemical modulation induced by nitrogen doping introduced more defects and active sites to the carbon framework, thereby improving the interfacial adsorption and electrochemical behaviors. When the novel N-ACNT/G hybrids were used as cathode materials for Li-S batteries, greatly enhanced cyclic and rate performances were demonstrated.
These types of 3D sp² structures are expected to be an important platform that will enable the investigation of stabilized three-dimensional topological porous systems and demonstrate the potential of sp² materials for advanced energy storage, environmental protection, nanocomposite and healthcare applications.

Since its discovery, graphene has held great promise as a two-dimensional (2D) metal with massless carriers and, thus, extremely high-mobility. This promise has led to only limited electronic device applications due to the lack of an energy gap which prevents the formation of conventional device geometries. Thus, several schemes for inducing a semiconductor band gap in graphene have been explored. These methods do result in samples whose resistivity increases with decreasing temperature, the expected temperature dependence of a semiconductor. However, this temperature dependence can also be caused by highly diffusive transport that, in highly disordered materials, is caused by Anderson-Mott localization and which is not desirable for conventional device applications. In this presentation, we demonstrate that in the diffusive case, the conventional description of the insulating state is inadequate and demonstrate a method for determining whether such transport behavior is due to a conventional semiconductor band gap.

Graphene Growth on SiC(0001) via thermal silicon sublimation results in the formation of an electrically insulating buffer layer (BL) at the interface between graphene and the substrate. This BL is a graphene-like layer covalently bound to the SiC [1]. Consequently, it does not exhibit the electrical properties of freestanding graphene [2].
Decoupling of the BL from the substrate can be achieved by hydrogen intercalation. During this process, the BL is converted into quasi-freestanding monolayer graphene (QFMLG) [3] by annealing in an ultra-pure hydrogen atmosphere. QFMLG is characterized by an improved charge carrier mobility as compared to regular epitaxial graphene on a BL [2], paving the way for electronic applications.
Here we present a study of the initial stages of hydrogen intercalation applying low energy electron microscopy (LEEM), low energy electron diffraction (LEED) and x-ray photoemission spectroscopy (XPS). Very short annealing times lead to only partially intercalated buffer layer patches with a unique signature in both LEEM as well as LEED and XPS.
[1] K. V. Emtsev et al., Phys. Rev. B 77, 155303 (2008).
[2] F. Speck et al., Appl. Phys. Lett. 99, 122106 (2011).
[3] C. Riedl et al., Phys. Rev. Lett. 103, 246804 (2009).

The effect of Fe catalyst application on SiC vacuum decomposition was investigated. Fe catalyst films with various thicknesses (1, 3, 6, and 9 nm) were deposited on SiC single crystalline wafers using thermal evaporator. SiC wafers with Fe coatings were annealed first in hydrogen and then in vacuum. The obtained nanostructures were investigated using Raman spectroscopy, AFM and SEM. Studies showed that we are able to produce various 1D carbon nanostructures. We also showed that the application of Fe decreased the SiC decomposition temperature down to 1100 ^oC from 1300 ^oC. Another important output of Fe application as a catalyst is the alignment of the produced 1D carbon nanostructures. These 1D aligned carbon nanostructures produced at lower temperatures may find various applications including field emitters, thermoelectric materials and sensors. Supported by TUBITAK grant no 213M481 and TUBA GEBIP award to Oren EE.

Boron and nitrogen doped graphene and carbon nanotubes are popularly in focus as metal-free electro-catalysts for oxygen reduction reactions (ORR) central to fuel-cells. N doped CNTs have been also reported to chemisorb mutually, promising a route to their robust pre-determined assembly into devices and mechanical reinforcements. We propose from first-principles a common mechanistic understanding of these two aspects pointing further to a generic chemical activation of carbon atoms due to substitution by nitrogen in experimentally observed configurations. Wannier-function based orbital resolved study of mechanisms suggests increase in C-N bond-orders in attempt to retain $\pi$-conjugation among carbon atoms, causing mechanical stress and loss of charge neutrality of nitrogen and carbon atoms, which remedially facilitate chemical activation of N coordinated C atoms, enhancing sharply with increasing coordination to B or N and proximity to zigzag edges. Activated C atoms facilitate covalent adsorption of radicals in general, diradicals like O$_2$ relevant to ORR, and also other similarly activated C atoms leading to self-assembly of graphenic nano-structures, while remaining inert to ordinary graphenic C atoms.
Activation of Graphenic Carbon Due to Substitutional Doping by Nitrogen: Mechanistic Understanding from First Principles,
Joydeep Bhattacharjee, J. Phys. Chem. Lett., 6, pp 1653-1660

Commercial aluminum alloys such as the Al-6061 and Al-7075 series have been doped with activated carbon during melting in the presence of a high DC current. The C doped materials are known as ‘Covetics&’. These Covetic materials can exhibit superior mechanical, electrical and anticorrosive properties andshow promise in lightweight applications for aerospace and naval building materials and coatless electrical wiring. Previous studies showed that for nominal 5 wt.% C incorporated in Al-7075, the ultimate tensile strength and hardness increased by 40% and 30%, respectively [1]. As-extruded Al-6061with 3 wt.% C showed improvements in tensile strength and electrical conductivity by 30% and 23%, respectively [2]. We performed a detailed study of the crystal structure by TEM and XRD, chemical bonding by XPS and Raman scattering, surface analysis using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Key results to be presented include, but are not limited to 1)TEM observations show the presence of crystalline graphene-like nanoribbons (GNR) with preferred orientation along the <110> and <112> directions of Al. 2) In Al-6061, mostly sp2 graphitic carbon was observed while Al-7075 contained both sp2- and sp3 bonding. 3) Both XPS and Raman indicated partial oxidation of the carbon nanostructures. A strong D peak in the Raman spectra indicates a high density of defects in the graphitic structures. Highly strained regions are surrounded by unstrained regions and showed variations of intensity indicating different number of layers. 4) Complimentary studies by AFM and KPFM mapped the presence of lower potential regions for the covetic samples in both stripe like features and 100-200 nm spots. 5) Density functional theory (DFT) modeling suggested covalent bonding between carbon and Al as seen from the experimental results. 6) Modulus and hardness data from the samples with different carbon content is obtained from nanoindentation.
1 Iwona Jasiuk, S.N., Lourdes Salamanca-Riba, Romaine Isaacs, and Sid Siddiqi: ‘Novel Aluminum-Carbon Materials&’, Nanotech Conference & Expo 2013, May 12-16, Washington D.C., 2013
2 Brown, L., Joyce, P., Forrest,D., Salamanca-Riba, L.: ‘Physical and Mechanical Characterization of a Nanocarbon Infused Aluminum-Matrix Composite&’, Materials Performance and Characterization, 2014, 3, (1).
* Supported by DARPA/ARL under contract W911NF13100, and ONR under contract N000141410042

The bottom-up synthesis of graphene nanoribbons (narrow strips of sp² hybridized carbon) has attracted much attention in recent years, with a number of contemporary demonstrations of the preparation of all-carbon systems. However, a limited number of studies have addressed the solution-phase synthesis of heteroatom-doped graphene nanoribbons; the design and preparation of such constructs is a significant challenge. We have recently developed new synthetic methodologies for the synthesis of oligobenzoquinolines via the aza-Diels-Alder (Povarov) reaction, producing oligobenzoquinoline precursors whose length and sequence are precisely controlled. Our straightforward approach also provides access to crowded macromolecular polybenzoquinoline scaffolds, which are key intermediates for the preparation of nitrogen-doped nanoribbons. Altogether, these findings hold implications for the bottom-up synthesis of graphene nanoribbons whose edge character, terminal functionalities, doping, and length are precisely defined.

Graphene has excellent and unique properties, such as high intrinsic charge mobility (200,000 cm²/sv) and extremely high Young&’s modulus (sim;1.0 TPa). CF reinforced composites (CFRCs) are currently used in aerospace applications and replacing traditional materials. The idea of adding graphene into CFRCs is to build up network within the composites, meanwhile providing hierarchical structures to further enhance the mechanical performance of the materials. Graphene could be localised and delivered into CFRCs through three effective methods, directly vacuum infusion of GNPs/Epoxy mixture (in-situ exfoliation/dispersion) into CF fabrics, free of organic solvent, automated spray coating graphene/polymer suspension and inserting interleaf carrier methods.
Automated spray coating with heating system has been set up to manufacture graphene/CF fabrics with almost unlimited working scale. The thickness of the films could be controlled from nano- to microscale and this effective layer by layer spray coating method could influence the orientation and distribution of graphene within the polymer matrix. A ratio of 50 wt.% graphene/ PEDOT: PSS masterbatch has been prepared and then diluted to 30 wt.% and 10 wt.% solutions to produce graphene reinforced polymer films using an airbrush onto CF fabric substrates. Graphene/phenoxy PKHH interleaf carrier was manufactured by bar coating methods, followed by infusion pure epoxy to produce CFRPs. The thickness of the phenoxy and GNP/phenoxy films ~25 and ~35µm, respectively. 80% films are homogeneous and smooth, several are uneven and with small holes.
Spray coating process does not destroy the lateral size of GNPs, keeping the integrity of GNPs. No substantial change of maximum compressive load and interlaminate shear strength (ILSS) after spray coating GNPs on CF fabric. Vacuum Infusion is the easiest method to deliver and localise graphene/GNPs into CFRPs. The CFRPs produced by vacuum infusion has higher ILSS comparing to other two methods when adding similar graphene in epoxy matrix. However, vacuum infusion for manufacturing CFRPs with higher maximum compressive load. The 10 layers UD CFRPs Ref has less maximum compressive load 1229N than that of 2773N of 8 layers [0°/90°] ₁₀ CFRPs Ref.
The surface conductivity of these composites was obtained through the four-point probes method. The aim of the research is to develop graphene delivery system via three different methods, and provide a guideline for an effective method to deliver and localise graphene/CNPs into CFRPs composites with potential for industrial scale-up.

The one-dimensional carbon nanotube CNTs and two-dimensional graphene sheets can be used to create three-dimensional (3D) nano networks. The resulting 3D pillared CNT-graphene network nanostructures could possess desirable out-of-plane properties while maintaining in-plane properties, attractive for numerous innovative applications, including electrodes for fuel cells, nanoporous structures for hydrogen storage and supercapacitors, and tailored orthogonal thermal transport materials. For these applications, covalently-bonded junctions, especially seamless C-C covalently bonded junctions, are needed to enhance the mechanical properties and stability, and thermal electrical transport. Growth process of 3D junctions of carbon nanotube (CNT)-graphene on copper and alumina templates with nano-holes was simulated with classical molecular dynamic (MD) simulation. The CNT, graphene and their seamlessly C-C bonded junction can forms simultaneously on the templates without catalysts. There are two mechanisms of the junction formation: i) CNT growth over the holes that are smaller than 3nm, and ii) CNT growth inside the holes that are larger than 3nm. Tensile strength and thermal properties of the as-growth C-C junctions as well as the junctions embedded with metal nanoparticles (catalysts) was determined via a quantum mechanics MD simulation method. Metal nanoparticles as catalysts remaining in the junctions significantly reduce the fracture strength and fracture energy, as well as thermal conductivity, making them brittle and weak. Among the junctions, the seamlessly C-C bonded junctions show the highest tensile strength and fracture energy due to their unique structures. This work provides a theoretical base and a route for synthesizing high-quality single-layer CNT-graphene nanostructures.

The exceptional electronic, chemical and mechanical properties of carbon nanotubes (CNTs), graphene and reduced graphene-oxide have triggered their intensive study as building blocks of future applications in electronics and energy conversion and storage devices. Solution-based versions of these nanomaterials have decisive advantages: (i) they can be modified by chemical functionalization to acquire additional properties; (ii) they can be processed through large-scale deposition techniques on multiple substrates. In this talk I will present some of our recent results on carbon nanomaterials with emphasis on examples combining chemistry and device-oriented studies.
One of the fields in which carbon nanomaterials will make a difference is flexible electronics, either for large-area applications or at high-frequency [1] where the charge mobility in graphene and CNTs is a key advantage over alternative solution-based options. For CNTs, it supposes to cope with the presence of metallic chiralities in the raw material which can be achieved using either covalent selective chemistry [2,3] or non-covalent selective polymer extraction [4]. In the latter case, the sorted semiconducting CNTs also have optical properties adapted to IR emission at telecom wavelength. In this context of large-area electronics, reduced graphene oxide does not reach the same level of performances due to a lower charge mobility but its large-scale processability, chemical reactivity and adjustable conductivity [5,6] are complementary assets.
In the second part of the talk, I will illustrate how carbon nanomaterials chemical functionalization also allows preparing new materials for energy conversion and storage purposes. For example, functionalized CNTs and graphene can be envisioned as electro-catalytic electrodes for oxygen reduction in the context of noble-metal-free hydrogen fuel cells [7] or as very stable electrodes in lithium-sulfur batteries.
[1] Sire et al, Flexible GHz Transistors Derived from Solution-Based Single-Layer Graphene, Nano Lett. 12, 1184 (2012)
[2] Darchy et al, A highly selective non-radical diazo coupling provides low cost semi-conducting carbon nanotubes, Carbon 66, 246 (2014)
[3] Hugot et al, Gram scale carbon nanotubes as semi-conducting material for versatile integration in plastic electronics, submitted.
[4] F. Sarti et al, High selective sorting of semiconducting single walled carbon nanotubes for light emission at telecom wavelength, submitted.
[5] Bourgeteau et al, New Insights into the Electronic Transport of Reduced Graphene Oxide Using Scanning Electrochemical Microscopy, J. Phys. Chem. Lett. 5, 4162 (2014)
[6] J. Azevedo et al, Localized Reduction of Graphene Oxide by Electrogenerated Naphthalene Radical Anions and Subsequent Diazonium Electrografting, J. Am. Chem. Soc. 136, 4833 (2014)
[7] I. Hijazi et al, Carbon Nanotube-Templated Synthesis of Covalent Porphyrin Network for Oxygen Reduction Reaction, J. Am. Chem. Soc. 136, 6348 (2014)

Recently, we discovered a new method to prepare N-doped carbon tubes with large diameters (up to 500 nm) and relatively thin walls (less than 10 layers), which we call N-doped graphene tubes (N-GTs). Although the large-diameter tubes contain multiple graphene layers, their wall thickness and ratio of wall thickness to tube diameter are very small compared to conventional multi-walled carbon nanotubes (MWNTs). As a result, their surface areas are much higher than conventional MWNTs. We also demonstrate an effective strategy for tuning the size of large-diameter nitrogen-doped graphene tubes (N-GT) from 50 to 200 nm by varying the transition metal (M=Fe, Co, Ni or Mn) used to catalyze the graphitization of dicyanamide. Fe yielded the largest tube size, followed by Co and Ni. Rather than generating tubes, Mn produced a clot-like carbon morphology. We correlate the carbon morphology to electrochemical properties to guide the development of high-performance precious metal-free catalysts for the oxygen reduction reaction (ORR). The Fe-derived N-GTs, which had the largest diameter, also exhibited the highest activity for the ORR in alkaline media as well as in a more challenging acidic electrolyte. A clear trend of Fe > Co > Ni > Mn for the ORR catalytic activity was observed. The Fe-derived carbon material also exhibited the highest BET surface area (~870 m²/g) and electrochemically accessible surface area (~450 m²/g). More importantly, the Fe-derived G-NTs had the highest concentration of nitrogen incorporated into the graphene planes. Thus, in addition to the intrinsic high activity of Fe catalysts, the high surface area and nitrogen doping contribute to high ORR activity. This effort demonstrates optimal manipulation of morphology and surface area provides an effective approach to further improving the performance of M-N-C precious metal-free catalysts. Furthermore, aiming to improve the activity and stability of conventional Pt catalysts, the ORR active N-GT is used as a matrix to disperse Pt nanoparticles in order to build a unique hybrid Pt cathode catalyst. This is the first demonstration of the integration of a highly active Fe-N-C catalyst with Pt nanoparticles with much improved activity and stability, relative to traditional Pt/C catalyst. This work provides a new concept to design and synthesis novel cathode catalysts for fuel cells.

Multi-walled nanotubes are composed of two or more concentric single-walled nanotubes. Unlike single-walled nanotubes, the multi-walled nanotubes usually do not have a well-defined common lattice periodicity since the periodicity of individual tubes therein generally do not match except for very few cases. Since lattice periodicity is a prerequisite for calculating the material properties, such as electronic structures, optical absorption/emission profiles, Raman spectrum, and cyclotron resonance, the lack of exact periodicity posed a significant challenge to understanding the material properties of incommensurate multi-walled nanotubes for almost twenty years since the first discovery of multi-walled carbon nanotubes [1].
Here we show that the interference between the periodicity of individual tubes is decisive in determining the electronic structures of multi-walled nanotubes. When repetitive structures are overlaid against each other, a new superimposed moiré pattern emerges and is observed by scanning tunneling electron microscopy [2]. We developed a theoretical model that can be applied to general moiré superlattices [3, 4] and calculated the electronic structures double-walled carbon nanotubes as an example [5]. We show that their electronic properties varies from metallic to semiconducting and further to insulating states depending on their moiré patterns, even when they are composed of only semiconducting nanotubes with almost similar energy gaps and diameters. Our study puts forth a new classification of nanotubes as the first example of one-dimensional moiré crystals and paves a firm ground to utilize superb technological merits of double-walled carbon nanotubes.
[1] S. Iijima, Nature 354, 56 (1991).
[2] K. Schouteden, A. Volodin, Z. Li, and C. Van Haesendonck, Carbon 61, 379 (2013).
[3] P. Moon and M. Koshino, Phys. Rev. B 87, 205404 (2013).
[4] P. Moon and M. Koshino, Phys. Rev. B 90, 155406 (2014).
[5] M. Koshino, P. Moon, and Y.-W. Son, Phys. Rev. B 91, 035405 (2015).

Chemical vapour deposition (CVD) growth continues to provide a real pathway towards large scale manufacturing and integration [Kidambi et al. APL 106, 063304] of novel 2D materials. As the scalable growth of graphene by CVD [Kidambi et al. NanoLett 13, 4624] begins to become technologically and commercially viable a number of open challenges remain as entry barriers to industry. In particular the large area homogeneity and statistical testing of electronic properties, including the importance of grain boundaries, contacts, and the number of layers. We have performed device fabrication and statistical probing of wafer scale monolayer CVD graphene transferred onto Si/SiO2, with sputtered Ni contacts. At room temperature we find an average mobility of 5500±900 cm²/Vs at an as-transferred carrier density of 2.2±0.3x10¹²cm^-2.
If the growth of monolayer graphene is stopped before full coverage is reached individual domains or grains of graphene are clearly visible both in scanning electron microscopy and Raman spectroscopy on the growth substrate as well as by using optical microscopy when transferred onto Si/SiO2. With the knowledge of grain locations we designed and fabricated devices to test the properties of individual grain boundaries. Our findings suggest that there is up to a 30% reduction in hole mobility across a single grain boundary compared to devices fabricated within a single monolayer graphene domain. Furthermore, particular grain boundaries appear to cause a strong enhancement of electron scattering with up to a 60% decrease in electron mobility, where the magnitude of this effect is strongly dependent on the nature of the individual grain boundary. This highlights the importance of fully understanding these structures and their effects on device performance when considering graphene for large area electronics applications.
Whilst the growth of high quality continuous monolayer graphene is already beginning to be used in an industrial setting, controllable growth of bilayer graphene remains a significant challenge. We have tuned the CVD growth of graphene on Cu to obtain large area (>40 micron) domains of bilayer graphene. Raman mapping of these bilayer regions reveals that the stacking of the graphene layers (Bernal-stacked or twisted bilayer) is maintained within each large area domain, and fabricated devices show a consistently high field effect mobility and a low carrier density of 2.5±0.4x10¹²cm^-2. Recently, we have shown that bilayer graphene exhibits fast electron-phonon relaxation rates which are highly tuneable with carrier density [Huang et al. JPhysCondMat 27, 164202] with considerable importance for a variety of applications including high frequency and high power electronics, high-speed sensors, and thermal management of electronic devices. These results suggest that large area growth of high quality bilayer graphene is within reach for use in high power applications exploiting the fast hot-electron energy-relaxation.

Control of graphene oxidation is important for electronic, sensing and energy storage applications. Current methods of oxidation of graphene generate ~ 10-100 nm pores due to etching of the graphene layer [1]. In this work, we present a method to controllably oxidize graphene and convert it into pore-free graphene oxide. We use in-situ Raman spectroscopy [2] to monitor the target degree of oxidation and also to study the kinetics of oxidation using temporal evolution of D/G ratio in different oxidation environments (i.e., temperature and oxygen partial pressure). The kinetic study enables extraction of the energy of incorporation of oxygen atoms into graphene defect sites for the first time. The extracted energy varies with the oxygen partial pressure and compares well with first principle calculations [3]. The atomic force microscopy scans show clear phase contrast between the oxidized and un-oxidized areas and confirms the presence of no pores in the oxidized areas. Our method enables understanding the mechanism and energetics of oxygen-related defects in graphene, which will enable pathways for defect engineering in graphene which is critical for many envisaged applications.
[1] Liu et al., Nano Lett., 2008, 8, p. 1965; Zandiatashbar et al., Nature Comm., 2014, 5, p. 3186.
[2] Rao et al., Nature Mat., 2012; Nikoleav et al., ACS Nano, 2014.
[3] Carlsson et al., Phys. Rev. Lett., 2009, 102, 166104.

Highly conductive epoxy composites reinforced with a combination of CVD-grown carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) have been fabricated by controlled shear mixing process. The electrical conductivity studies of epoxy composites were based on the varied combinations of GNPs and CNTs with different aspect ratio, length and diameter. Given specific processing routes, a remarkable synergistic effect was found on the epoxy based composite with addition of GNPs into the CNT network. Such synergistic effect arises from the use of large-size CNTs and GNPs with optimized loadings. In addition, planar GNPs deliver the ability to maximize contact areas and increase the size of CNT agglomerates by means of non-covalent interactions. On the other hand, the conductive network formation for small-size CNTs (i.e., reduced aspect ratio, diameter and length) with GNPs lies in the continued growth of agglomerates accompanied with increasing filler loading fractions. In this case, no synergistic effect was found due to the dramatic increase in the number of contacts required for sufficient electron tunnelling within a conductive network. This work demonstrates an effective method to fabricate macroscopic epoxy composites using fillers with enhanced electrical conductivity and paves the way into composite manufacture with low cost, lightweight and ease of processability.

In this study, the synthesis of carbon nano-tubes (CNTs), which originated from environmentally friendly precursor, was done through the decomposition of botanical hydrocarbons, turpentine oil (C₁₀H₁₆) using activated carbon as a substrate. The oil decomposition was carried out by nebulised spray pyrolysis operated at temperature of 700^oC for 30 minutes of reaction time in the presence of ferrocene. The carbon products were characterized by Transmission Electron Microscopy (TEM), Raman spectroscopy and X-Ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS), respectively. The TEM observations showed that the as grown materials were formed as agglomerated CNTs. Raman analysis revealed that the intensity ratio between disorder and graphite like structure (I_D/I_G) was in the range 0.87-0.93. On the other hand, XRD results shows that the as grown products contains no contaminants.

The exceptional properties - mechanical, thermal or electronic - of graphite or graphene are well-known. However many materials, deriving from these ideal structures have crystallite sizes of a few nm only. It is often the case of bulk carbon phases obtained by chemical vapor deposition (CVD) like the pyrolytic carbons (PyC) found in composite materials for aerospace (re-entry heat shields), aeronautical (braking devices) or nuclear (plasma facing components in fusion experiments, HTR or UNGG fission technologies) applications. The properties of such materials having a ratio of crystallites over defects close to one are poorly known.
In this talk we will present realistic atomistic models of such materials generated from HRTEM data using the recently introduced Image Guided Atomistic Reconstruction (IGAR) method [1-3] and carefully validate them against diffraction data in both real and reciprocal spaces. We will then present recent results on their elastic properties obtained from tensile tests simulations [4] and discuss the interesting relationship existing between elasticity and some structural parameters, namely the in plane and out-of-plane coherence lengths, the textural anisotropy and the degree of interconnections (screw dislocations) between graphitic layers.
The evaluation
[1] Leyssale et al., App. Phys. Lett.95, 231912 (2009).
[2] Leyssale et al. Carbon50, 4388 (2012).
[3] Farbos et al. Carbon80, 472 (2014).
[4] Farbos et al. Carbon Accepted (2015).

Characterization of single-layer graphene with point defects, impurities or dopants is important for understanding the material&’s behavior for application. For example, nanoporous graphene was considered for DNA sequencing, molecular sieving, gas separation, proton transfer, desalination or atomic species transport, while boron- or nitrogen- doped graphene was used for catalysis or nanoelectronics, among other applications. To quantify defect-induced Raman band intensities and distinguish between defect types, we developed a method combining defect potentials calculated by density functional theory with electron-defect matrix elements and Raman intensities predicted within a tight-binding framework. I(D)/I(D') intensity ratios, as dependent on defect topology and impurity adsorption, as well as substitutional doping, were analyzed. Monovacancy, divacancy, Stone-Wales, and so-called 555-777 and 5555-6-7777 reconstructed point defects were considered, as well as larger vacancies, specifically tri- and tetra-vacancies that were identified experimentally, and penta-, hexa-, and heptavacancies, having pore sizes from 0.1 nm to 0.5 nm. To elucidate effects of O₂ adsorption, mimicking experimental conditions such as etching by oxygen plasma, as well as of B- and N- doping, calculated I(D)/I(D') Raman intensity ratios were examined. Our results distinguished between defect types and were found to be consistent with measured values as available, rendering the calculated I(D)/I(D') Raman intensity signature a metric to assist in experimental characterization of single-layer graphene.

Graphene possesses properties making it attractive for molecular and optical sensing applications. Here, we present two examples using large area epitaxial graphene synthesized on semi-insulating (0001)6H-SiC via Si sublimation in an Ar ambient.
In contrast to conventional 3D materials which retain their bulk properties when patterned to form devices, anything that interacts with the 2D graphene surface during fabrication modifies its properties. Such surface sensitivity poses significant difficulties for the fabrication of molecular sensing devices, as well as impedes understanding the intrinsic interaction of graphene with other materials such as metals. Here, we describe femtosecond laser patterning of epitaxial graphene to fabricate electrically isolated, pristine epitaxial graphene surfaces. The non-equilibrium heating ablates graphene on a sub-micron scale to form precisely defined regions without damaging the unilluminated and/or partially illuminated material or substrate. Using these pristine graphene surfaces, we discovered the interaction of Ni on epitaxial graphene is quite different from CVD formed graphene. From these results, we propose a model to understand key parameters affecting contact resistance.
Terahertz radiation can be used in a range of sensing applications including radio astronomy and security; however, sensitive room-temperature detection at these frequencies is challenging. We have previously shown that epitaxial graphene can be employed to make large area plasmonic structures. Here we show that hydrogen-intercalated epitaxial graphene is more attractive for THz applications since the mobility is higher than that of conventionally formed graphene on SiC implying sharper plasmonic resonances in the THz. Van der Pauw devices fabricated on fully H-intercalated samples using standard photo-lithography revealed mobilities of ~3500 and ~3900 cm²V^-1s^-1 at 300 and 10 K, respectively, and both temperatures had a p-type sheet density ~ 8 × 10¹² cm^-2. We find that Drude model fits to THz transmission spectra for these samples agreed with measured Hall values of mobility.

The atomically-thin nature of graphene gives rise to new behaviours and assembly modes not seen in other carbons, and that are more characteristic of macromolecular soft matter. These behaviours include penetration of biological membranes with low energy barrier, depositional stacking and conformal coverage of complex surfaces, and conformational changes that include folding, wrinkling, crumpling, and wrapping/encapsulation. This talk explores the soft matter behavior of graphene-based materials and its applications in barrier materials, emulsion technologies, catalysis, and biomedicine. First, graphene oxide readily undergoes colloidal-phase assembly into uniform stacked structures with controlled inter-sheet gallery spaces that are being explored for barrier and selective membrane technologies. We show that this concept can be extended to 3D by covering curved droplet surfaces with multilayer GO films that control molecular transport between the dispersed and continuous phases in emulsions. This approach can be used to inhibit evaporation, inhibit liquid mixing, suppress interphase chemical reactions, and can even create wholly new metastable two-liquid phases that cannot be realized using conventional molecular surfactants. The flexibility of graphene oxide also allows compression-controlled wrinkling of thin GO films on elastic substrates. This approach can be used to produce wavelength-tunable surface topographies that direct cell alignment and morphology of interest in tissue engineering. While unidirectional shrinkage causes wrinkling, multidimensional shrinkage causes chaotic crumpling. We have developed a method to encapsulate nanoparticle ensembles in graphene nanosacks with applications in bio-imaging and catalysis. We have recently shown that these structures serve as nanoreactors, defined as material structures that provide engineered internal cavities that create unique confined nanoscale environments for chemical reactions. Crumpled graphene nanoreactors enable particle-carbon, and particle-particle electron transfer interactions that give rise to novel behaviors such as galvanic protection of Ag nanoparticles in Ag/Ni-filled nanoreactors, and the photochemical control of Ag-ion release in Ag/TiO₂-filled nanoreactors. Finally the ability of graphene material to penetrate cell membrances through atomically thin edge and corner sites will be shown to govern uptake and internalization of graphene materials into human cells, and the implications for inhalation exposures and safe material design will be discussed.

Diverse methods have been used to produce carbon nanoribbons, including the unzipping of nanotubes. Chemical unzipping of CNTs [1] can be obtained through the use of oxidative techniques in concentrated acid (H2SO4) and post treatments with harsh reagents such as highly concentrated potassium permanganate (KMnO4). Solid-state reaction templates with specific chemical surface functionalities to induce direct coupling between the functional groups and concomitant breakdown of the cylindrical structure, however, has never been used before. Here [2], we report for the first time, the demonstration of unzipping of CNTs via a solid-state room temperature reaction between multi-walled CNTs (MWCNTs) containing different reactive functionalities of COOH and OH groups. The reaction is mechano-chemically induced, initiated at room temperature in ambient air, facilitated by the simple grinding of two chemically variant CNT reactants and leading to the unzipping of the nanotubes. Fully atomistic reactive molecular dynamics and ab initio method have been also carried out to address the dynamics aspects of this process. Our results show that the released heat during the process can result in C-C bond breaking, which subsequently leads to CNT unzipping. The method proposed here is completely general and can be applied to develop new theoretical and synthetic frameworks where reactions could be designed and controlled via chemically modified solid reactants.
[1] D. V. Kosynkin et al., Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons. Nature, vol. 458, 872 (2009).
[2] M. A. Kabbani et al., Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes. Nature Comm., vol. 6, 7291 (2015).