Carbon nanotubes show a large variation in the physicochemical properties as a function of the number of layers. Double-walled and triple-walled carbon nanotubes (DWNTs and TWNTs), consisting of two and three concentric nanotubes, have attracted much attention because of their unexplored properties (e.g., optical, electronic, and mechanical properties) caused by a coupling interaction between adjacent layers. Up to now, several methods (e.g., catalytic chemical vapor deposition, thermal treatment of single wall carbon nanotubes (SWNTs) or DWNTs encapsulating fullerenes and other compounds containing carbon elements) have been reported to synthesize DWNTs and TWNTs. However, there are no systematic report on the synthesis and properties of DWNTs and TWNTs due to the complex synthetic technique.
In this talk, I will describe the synthesis of double- and triple walled carbon nanotubes and their structural characterizations. To produce DWNTs, we have used two techniques; catalytic chemical vapor deposition and thermal treatment of SWNTs encapsulating fullerenes. We observed large difference in optical and thermal properties between two types of DWNTs. In addition, the coalescence between adjacent DWNTs by high temperature treatment and boron doping treatment will be described as a tool to create nanotube&’s junctions and also to control the diameter of DWNTs. Finally, the unique structural features of TWNTs will be also described in related with the thermal treatment induced coalescence.

Although the study of double wall nanotubes has been ongoing for many years, it is only recently that a large advance has occurred through the systematic studies carried out on many tubes and on many optical transitions by Feng Wang at the University of California, Berkeley. The implications of these findings on triple wall carbon nanotubes will be discussed.

In order to accommodate an increasing demand for carbon nanotubes (CNTs) with desirable characteristics one has to understand the origin of helicity of their structures. Here, through in situ atomic scale microscopy we demonstrate that the formation of carbon nanotube is initiated by the nucleation of the carbon cap. We observe that the nucleation is initiated by the formation of a graphene embryo, which is bound between opposite step-edges on the nickel catalyst surface. The embryo grows larger as the step-edges migrate along the surface, leading to the formation of a curved carbon cap when the steps flow across the edges of adjacent facets. Further motion of the steps away from the catalyst tip with attached rims of carbon cap generates the wall of the nanotube. Density Functional Theory calculations bring further insight into the process, showing that the step flow occurs by surface self diffusion of the nickel atoms via a step-edge attachment-detachment mechanism. Based on the revealed mechanism of carbon cap formation and the fact that it occurs first in the sequence of stages involved in nanotube growth, we suggest the angular distribution of catalyst adjacent facets as a key feature that is responsible for the symmetry of carbon cap and consequently, the helicity of the nanotube. This finding paves a new path towards the controllable growth of carbon nanotubes.

Carbon nanotubes (CNTs) have unique thermal/electrical/mechanical properties and high aspect ratios. Growth of CNTs directly onto reactive material substrates (such as metals, carbon based foam structures etc.) to create a micro-carbon composite layer on the surface has many advantages-the possibilities of eliminating processing steps and resistive junctions, or/and providing a thermally conductive transition layer between materials of varying thermal expansion rates etc. Compared to growing CNTs on conventional inert substrates such as SiO₂, direct growth of CNTs onto reactive substrates is significantly more challenging. Namely, control of CNT growth, structure, and morphology has proven difficult due to the diffusion of metallic catalysts into the substrate during CNT synthesis conditions. In this study, uniform CNT layers are successfully grown on copper foil and carbon foam substrates that were pre-coated with an appropriate buffer layer, using the chemical vapor deposition method. SEM images indicated that synthesis method, growth conditions, and most notably substrate surface pre-treatment all influence CNT growth and layer structure/morphology. The SEM image and pull-off testing results revealed that good bonding exists between the CNT layer and substrate material, and interfacial adhesion (0.2-0.5MPa) is affected by the buffer layer thickness. Additionally, the thermal properties of the CNT/substrate structure were evaluated using the laser flash technique and have shown that the CNT layer can reduce thermal resistance when used as a thermal interface material between bonded layers.

Carbon seeds like nano-diamond, fullerene fragments and nanotube segments have been used to synthesize carbon nanotubes (CNTs) [1-5]. This new route may produce high purity nanotubes free from metal impurities, which will promote the application of nanotubes. Pretreatment including air oxidation followed by water vapor annealing is proved to be essential. To investigate the process of CNT re-growth so as to better understand it, we conducted re-growth of CNT in conventional chemical vapor deposition (CVD) as well as in the in situ scanning electron microscope. By comparing growth conditions in these two systems, it might be helpful to comprehensively evaluate the influence of experimental parameters on the re-growth of carbon nanotube.
We carefully studied the influences of the experimental parameters on the re-growth of CNT. By varying these parameters, the new pretreatment as well as the growth condition suitable for CVD and in situ system was established, and the re-growth of nanotube from seeds with different chiralities was realized in these two systems. Furthermore, multi-times re-growth of nanotube was also achieved. In situ observation on CNT formation provided a direct evidence for the re-growth of nanotube. According to our experimental results, the efficiency of re-growth was closely related with pretreatment conditions and growth parameters, especially the carbon source. On the basis of these analyses, the growth mechanisms of nanotube synthesized from seed will be discussed.
References
[1] Takagi, D. et al. J. Am. Chem. Soc.131, 6922(2009).
[2] Yu, X. et al. Nano Lett.10, 3343(2010).
[3] Ibrahim, I. et al. ACS Nano6, 10825(2012).
[4] Yao, Y. et al. Nano Lett.9, 1673(2009).
[5] Liu, J. et al. Nat. Commun.3, 1199(2012).
Corresponding Author: Huafeng Wang
Tel: +81-3-5228-8244, Fax: +81-3-5261-1023
E-mail: [email protected]

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.
To this end, we have developed a method, Automated Rapid Experimentation and in-situ Spectroscopy (ARES) which speeds the rate of experimentation by 100 times. We are also exploring experimental parameter space autonomously, using the same artificial intelligence and machine learning approaches used in advanced robotics. Our intent is to integrate computation and simulation explicitly into our closed-loop experimentation system to direct the path of exploration, yielding faster results with better fidelity than conventional approaches. We use this to determine the conditions which discriminate between single wall and multiwall carbon nanotube synthesis.

CNT&’s are expected to revolutionize a range of technologies because of their unique mechanical and electrical properties. Using nanotubes in structural materials holds significant promise due to their extremely high modulus and tensile strength, however their cost, production rate and integration into a fiber form severely limit the current structural application opportunities. We report the investigation of the formation of carbon nanotubes from a polymeric precursor using an electrospinning production process. This CNT formation concept is based upon modeling studies performed by Sinnot. Reactive Empirical Bond order calculations show that for small diameter carbon fibers, less than about 60 nm, the SWNT and MWNT phases are thermodynamically favored relative to an amorphous or planar graphitic nanofiber structure. We have developed a novel process using continuous electrospun polyacrylonitrile (PAN) nanofibers as precursors to continuous SWNT and MWNT. The process for converting PAN nanofibers to SWNT's and MWNT's follows the process for typical carbon fiber manufacture. The PAN nanofibers, of 10 to 100 nm in diameter, are crosslinked by heating in air and then decomposed to carbon via simple pyrolysis in inert atmosphere. The pyrolyzed carbon nanofibers are then annealed to form the more energetically favorable SWNT or MWNT phase, depending upon the precursor diameter. We will discuss the process and characterization data.

Literature abounds with examples of mechanochemistry, in which chemical reactions are shown to be influenced by mechanical loads acting on the reacting surfaces/volumes. These mechanochemical effects promise to direct the reaction pathways of chemical synthesis processes, enabling unprecedented control of the produced structures. We study the effect of externally applied mechanical forces on the collective growth of aligned carbon nanotube (CNT) "forests" by chemical vapor deposition (CVD). Previous work on CNT growth under mechanical pressure showed that the final forest height decreased with applying compressive stresses, but did not measure growth kinetics. Motivated by these results, we use a custom-built cold-wall CVD reactor to apply measurable axial loads in situ during forest growth, while recording the growth kinetics in real-time. Compressive forces in the range of 0.2 to 20 grams are applied by a probe pushing on millimeter-size CNT forests growing on a resistively heated substrate from a mixture of ethylene, acetylene, hydrogen and helium at atmospheric pressure. The real-time growth kinetics are determined by measuring the forest height increase using a feedback loop controlled actuator that moves the probe vertically upwards to maintain a constant force during growth. Results show that a mechanical force influences both the growth kinetics and the resulting forest morphology. The maximum growth rate is found to be inversely related to the applied compressive force. These findings highlight the importance of studying mechanochemistry of CVD, in which the process activation energy at the catalyst is modulated by the mechanical stresses. The exact influence of mechanical stresses on the kinetics and energetics of CNT growth provides insights into the internal mechanical feedback within a growing forest, comprising billions of CNTs per square centimeter each having diameter-dependent growth rates. If the kinetics of CNTs subjected to compressive forces is slowed down, while the kinetics of those CNTs subjected to tensile loads is accelerated, a homogenizing effect ensues, which eventually leads to reducing the growth rate mismatch and contributes towards the coordinated forest growth at a single collective growth rate. Hence, understanding these collective mechanochemical effects is key to engineering the morphology of functional aligned CNT ensembles.

In the inner spaces of cylindrical hollow nanomaterials such as carbon nanotubes (CNTs), some kind of materials are encapsulated having anomalous structure by comparison with the bulk materials due to the confined nanospaces. For example, sulfur (S) is encapsulated within inner space of CNTs of less than 1 nm in inner diameters as one dimensional liner or zigzag structure, while S crystal has a orthorhombic structure at atmospheric pressure. Especially, although bulk S is insulator, the one dimensional S in the CNTs are expected to exhibit metallic conductivity. Since insulator-metal phase transition of bulk S has been observed only under ultra-high-pressure conditions (P>90 GPa), encapsulation of materials into the confined nanospace is expected to induce appearance of not only anomalous structure but also properties, which appear at ultimate state, of the materials even at atmospheric pressure.
In this study, we encapsulated tellurium (Te) in CNTs of various inner diameters. Our aims were to prepare anomalous phase of Te at ordinary pressure and to clarify the relation between CNT diameter and the crystal structure of encapsulated Te. As a result, we found that Te exists as ordinary phase when encapsulated within CNTs of greater than ~2 nm in diameter. In contrast, in CNTs of less than ~2 nm in diameter, the encapsulated Te had an unknown structure that could not be indexed to known tellurium phases, including high-pressure phases, Te oxides, and Te hydroxides. Here, we describe the unknown structure of Te discovered by transmission electron microscopy and Raman spectroscopy, as well as the relation between CNT diameter and the crystal structure of encapsulated Te.

Single-walled carbon nanotubes (SWNTs) have been anticipated for application in various electronic devices. To fabricate SWNT devices in a conventional LSI process, it is important to grow SWNTs at low temperatures under high vacuum. So far, using Pt as a catalyst, we have attained SWNT growth under an ethanol pressure of 1x10^-1 Pa [1]. However, the mechanism of SWNT growth from Pt catalysts have not been clarified. In this study, we investigated the growth process of SWNTs from Pt.
After deposition of Pt catalyst on the SiO₂/Si substrates, SWNT growth was carried out using the alcohol catalytic chemical vapor deposition (ACCVD) in a high vacuum. For fabrication of Pt catalysts, we used both EB and pulsed arc plasma (PAP) depositions to control the catalyst particle size. The grown SWNTs were characterized by FE-SEM, TEM and Raman spectroscopy.
Average particle size of Pt catalysts prepared by the EB deposition was smaller than that by the PAP deposition, but most of Pt particle sizes were below 3 nm in both methods. Irrespective of the catalyst particle size, the diameter distribution of SWNTs were almost same and the average diameter was below 1.0 nm, when the growth temperature was 700 0C. TEM and Raman results showed that most of SWNTs grown from Pt particles whose sizes were larger than the SWNT diameters. In addition, compared with Co catalysts, the SWNT growth from Pt endured for longer time under the same growth temperature, although the growth rate was lower. This indicates that growth process of SWNTs is different between Pt and Co catalysts, and the surface diffusion process on the catalyst particle would play an important role in the SWNT growth from Pt. Based on the experimental results, we will discuss the growth mechanism of SWNTs from Pt.
[1] T. Maruyama et al. Mater. Express 1 (2011) 267.

In this work, two different methods used for growth of carbon nanotubes are described, as well as a detailed analysis of the effect of changing any parameter (oven temperature, synthesis time, the concentration of catalyst, carrier gas flow and solution flow) on the CNT's morphology. An influence of the number of linear or aromatic carbons of the carbon source (n-pentane, n-hexane, n-heptane, cyclohexane, toluene and acrylonitrile were used) on the growth of carbon nanotubes was revealed. The employed catalyst was ferrocene; the applied method was spray pyrolysis. To perform the characterization, different equipment was used, in particular Scanning Electron Microscopy (SEM), Transmission Electron Microscopy, Infrared Spectroscopy (FTIR) and Raman spectroscopy.

Multi-walled carbon nanocoils and nanotubes (MWCNCs/MWCNTs) hybrid was synthesized by chemical vapor deposition (CVD). This material can find an application in the field of energy devices. The experimental parameters were optimized to reduce their fiber diameters.
Fe₂O₃/zeolite was prepared by mixing Y-type zeolite (Tosoh HSZ-390HUA) in an iron acetate ethanol solution with an iron acetate mass fraction of 5%. The mixture was homogenized by sonication for 10 min. Then, the mixture was calcined at 100°C for 20 h in a furnace. To produce the Fe/Sn catalyst on zeolite, Sn was evaporated onto the surface of Fe₂O₃/zeolite under vacuum. The synthesis of MWCNCs was carried out in a tubular electric furnace with a quartz tube connected to N₂ and C₂H₂ gas cylinders and a rotary pump for the evacuation of air. After reaching the required temperature, N₂ and C₂H₂ were introduced simultaneously. The total gas flow rate was 1000 mL/min [1].
The conditions for the synthesis of the thinnest MWCNC in this experiment were as follows: reaction temperature, 700°C; C₂H₂/N₂ pressure, 0.67 kPa; and C₂H₂/N₂ ratio, 0.01 [2]. A low C₂H₂ gas flow rate and a low partial gas pressure were important in reducing the fiber diameter. The reaction temperature affected both the MWCNC fiber diameter and the MWCNC composition ratio in the MWCNC/MWCNT hybrid. At high temperatures (750°C), MWCNTs were predominant and their crystallinity increased, which was confirmed by the detection of the radial breathing mode and high intensity ratios of the G peak to the D peak in the Raman spectra. By contrast, MWCNCs were produced preferentially at low temperatures (approximately 700°C). Transmission electron microscopy showed that the fiber diameter of the thinnest MWCNC was less than 5 nm at both the helix and tip and that the thinnest MWCNC had a triple walled structure. Under optimized conditions, the vacuum deposition of a thin film of Sn on a Si substrate and the mounting of Fe catalyst supported zeolite on a Sn/Si substrate effectively increased MWCNC composition ratio. MWCNC composition ratio was increased by up to 30% [2].
References
[1] Masashi Yokota, Yoshiyuki Suda, Hirofumi Takikawa, Hitoshi Ue, Kazuki Shimizu, Yoshito Umeda, The Journal of Nanoscience and Nanotechnology, 11 (2011) 2344-2348.
[2] Siew Ling Lim, Yoshiyuki Suda, Kotaro Takimoto, Yuichi Ishii, Hideto Tanoue, Hirofumi Takikawa, Hitoshi Ue, Kazuki Shimizu, Yoshito Umeda, Japanese Journal of Applied Physics, 52 (2013) 11NL04.

The control of structure morphology in 3-D nanomaterials has been studied in recent decade for the change of material characteristics e.g. superhydrophobicity and reinforcement properties. Previously, the modification of structure morphology was tried to improve the reinforcement properties by enhancing interconnect bonding between support matrix and reinforcement materials. Especially, carbon-based materials have been widely used to modify the properties of reinforcement materials due to extraordinary properties of carbon such as high tensile strength and young&’s modulus.
Herein, we propose a new concept of reinforcement materials containing carbon nanofibers (CNF) and spherical silica. Although there are many reinforcement materials based on only CNF, reinforced composites were well-broken due to their straight-shaped CNF. Therefore, CNF was tuned by adding spherical silica to reinforce the composite materials. The spherical silica/CNF was synthesized in the shape of dumbbell-type to enhance the adhesive strength via electrospinning. The dumbbell-type CNF was fabricated from colloidal electrospinning technique, followed by carbonization of poly(vinyl alcohol) (PVA) containing spherical silica. Before carbonization process, electrospun PVA nanofibers were treated by iodine to increase thermal resistivity of PVA. This process could easily help converting PVA nanofibers to CNFs. Furthermore, milling process was finally needed to fit the support matrix for the array of dumbbell-type CNF.

Thermodynamic modeling of the MOCVD process, using the standard free energy minimization procedure, cannot always explain the deposition of hybrid films that occurs. The present investigation explores a modification of the procedure to account for the observed simultaneous deposition of metallic iron, Fe₃O₄, and carbon nanotubes from a single precursor. Such composite films have potential application in various device architectures and sensors, and are being studied as electrode material in energy storage devices such as lithium ion batteries and supercapacitors.
With ferric acetylacetonate [Fe(acac)₃] as the precursor, MOCVD in argon ambient results in a nanocomposite of CNT, Fe, and Fe₃O₄ (characterized by XRD, TEM, SEM and Raman spectroscopy) for growth temperature T and total reactor pressure P ranging from 600⁰C-700⁰C and 5-30 torr, respectively. No previous report could be found for the single-step formation of a CNT-metal-metal oxide composite. Equilibrium thermodynamic modeling using available software predicts the deposition of Fe₃C, together with a large proportion of carbon, in contrast with experimental observations. To reconcile this contradiction, the modeling of the process was approached by taking the molecular structure of the precursor into account, whereas “standard” thermodynamic simulations are restricted to the total number of atoms of each element in the reactant(s) as the input. The molecular structure of Fe(acac)₃ suggests that, in inert ambient CVD, the oxygen present in the deposit can only come from the oxygen in the precursor. To describe the probability of oxide formation during the CVD process, we introduce the term “oxygen consumption” [O_con], which is the statistical average of the oxygen atom(s) taken up by each metal atom during CVD. When O_con is restricted to lie between 0 and 1, thermodynamic computations in predict simultaneous deposition of FeO_1-x, Fe₃C, Fe₃O₄ and C in the inert ambient. At high temperature and in a carbon-rich atmosphere, iron carbide decomposes to iron and carbon. Furthermore, FeO_1-x yields Fe and Fe₃O₄ when cooled below 567°C. Therefore, the resulting film would be composed of Fe₃O₄, Fe and C, in agreement with experiment. Relative proportions of the solid components in the deposit are found to vary as functions of T, P and O_con. A higher O_con yields a higher proportion of Fe₃O₄. Variation in iron content in the deposit is the cumulative effect of increasing and decreasing amounts of Fe_1-xO and Fe₃C with O_con, respectively. For a given O_con, the molar concentrations of different species do not vary much with T and P. The weight percentage of carbon (~40%) calculated from thermodynamic analysis matches well with experimental data from TG-DTA. It is to be noted that thermodynamic modeling can only predict the formation of elemental carbon, not of CNTs. The observed growth of MWNTs is due to the catalyitc (kinetic) action of nanocrystalline elemental iron formed during the CVD process.

Even though the devices made from individual nanotubes have shown outstanding performances such as high mobility, high current, high thermal conductivity, good chemical and mechanical stability, the high hope for the next generation of carbon nanotube based electronics is hampered by several major problems. Among them, is the lack of reliable methods to control the alignment and position of nanotubes as well as, and perhaps most problematically, the growth of nanotubes with controlled chiralities. Even though the post-growth separation of metallic from semiconducting SWNTs have made very good progress, the alignment and assembly of the separated nanotubes into devices are still challenging and not suitable for large scale fabrication. Consequently, a method that can directly produce well aligned arrays of pure semiconducting nanotubes is thought to be the ideal choice for large scale fabrication of nanotubes FETs. In recent years, through systematic studies, we proposed and confirmed a mechanism on the selective growth of semiconducting carbon nanotubes. Important rules were summarized for achieving a high selectivity in growing semiconducting nanotubes by systematically investigating the relationship among water concentration, carbon feeding rate, diameter of catalyst and the percentage of semiconducting nanotubes in the produced SWNT arrays. This understanding will help us to develop better approach to solve the most difficult problem which limited applications of carbon nanotubes in nanoelectronics - the coexistence of metallic and semiconducting nanotubes in samples produced by most, if not all, growth methods.

Perfect Carbon nanotubes (CNTs) is ideal nano materials for electronics and thin film application. Recently, it is demonstrated that CNTs can be growth in super-long and perfect structure, it can exhibits excellent electronic and mechanical properties. They are therefore considered as potential materials for flexible electronics application.
We developed a general strategy for fabrication of super-long perfect carbon nanotube by carefully control the operating conditions, and minimalized the deactivation of the catalyst. The super-long CNTs can be more than half meter in length. We realize the visualization and manipulation of individual super-long carbon nanotubes under optical microscopes by deposition of TiO₂ nanoparticles on them. The CNTs over 1 mm in length exhibited 120 GPa strength, over 1.2 TPa Young&’s modulus, and 17% breaking strain. The superlubricity can be realized in centimetres-long perfect double-walled carbon nanotubes (DWCNTs) under ambient conditions. Centimetres-long inner shells can be pulled out continuously from such nanotubes, with an intershell friction lower than 1 nN that is independent of nanotube length. The shear strength of the DWCNTs is only several pascals, four orders of magnitude lower than the lowest reported value in CNTs and graphite. The perfect structure of the super-long DWCNTs used in our experiments is essential for macroscale superlubricity.

Substitutional doping of boron into carbon nanotubes is reported to enhance their conductivity by lowering the Fermi level into the valence band for semiconducting tubes and introducing additional charge carriers in metallic tubes. Few-walled carbon nanotubes (FWNTs) possess a wall number of 2-5, and represent a unique structure that combines the high intrinsic conductivity and graphitic quality of single walled nanotubes with the robustness to chemical processing of multi-walled nanotubes. We implement a liquid-injected chemical vapor deposition process to form the first boron-doped few walled nanotubes through a single synthesis step. The intrinsic structural and electrical properties of boron-doped and undoped FWNTs were compared to determine changes in the metallicity or defect density in the individual nanotubes after doping. These tubes were then processed into ink dispersions and spray coated to form conductive films. The electrical properties of these films were then compared to undoped FWNT films to determine any decrease in the bulk resistivity upon substituting boron into the nanotube lattice. This is the first report of boron-doped FWNTs, and may have applications in batteries and thermal conductors.

Single-walled carbon nanotubes (SWNTs) have shown great potentials in various fields attributing to their unique structure-dependent properties, therefore, the structure-controlled preparation of SWNTs is a crucial issue for their advanced applications (e.g. carbon-based nanoelectronics) and has been a great challenge for about two decades. To fully utilize the outstanding performance of SWNTs, it is preferred to control the structure of SWNTs during growth rather than in post-synthesis treatments. However, up to date, the direct synthesis of SWNT samples with a single dominating chirality > 60% have never been realized. Here we report a strategy to produce SWNTs with specific chirality by using a new family of catalysts, tungsten-based bimetallic alloy nanoparticles of non-cubic symmetry, which have high melting points and consequently are able to maintain their crystal structure during the chemical vapor deposition (CVD) process, to regulate the chirality of the grown SWNTs. The (12,6) SWNTs are directly synthesized at an abundance of > 92% by using W-Co catalysts. Experimental evidence and theoretical simulation reveal that the (0 0 12) planes of W₆Co₇ nanocrystals extremely match the structure of (12,6) SWNTs, therefore facilitate the preferential growth of (12,6) tubes. This method is also valid for other tungsten-based alloy nanocatalysts to grow SWNTs of various designed chirality. Employing alloy nanocrystals with unique structure as catalysts paves a way for the ultimate chirality control in SWNT growth and thus may promote the development in SWNT applications.
References:
[1] F. Yang, X. Wang, D. Zhang, J. Yang, D. Luo, Z. Xu, J. Wei, J.-Q. Wang, Z. Xu, F. Peng, X. Li, R. Li, Y. Li, M. Li, X. Bai, F. Ding, Y. Li*, “Chirality-specific growth of single-walled carbon nanotubes on solid alloy catalysts”, Nature, DOI 10.1038/nature13434 (2014).
[2] Y. Li*, R. Cui, L. Ding, Y. Liu, W. Zhou, Y. Zhang, Z. Jin, F. Peng, J. Liu*, “How Catalysts affect the Growth of Single-Walled Carbon Nanotubes on Substrates”, Advanced Materials, 22, 1508-1515 (2010).

There have been various forms of carbon nanotubes (CNTs) reported, including conventional tubular-type[1], bamboo-type[2], cup-stacked[3], coiled[4] and beaded[5] CNTs. As physical and chemical properties of nanocarbon materials are related strongly to their microscopic structures, CNTs with unconventional structures are expected to have peculiar properties that are not prominent for the conventional tubular CNTs. For example, the cup-stacked CNT has many edges on the inner and the outer surfaces of the tube wall, which favors the application of the CNTs to material supporting catalysts[6].
In this paper, we report on the development of a new type of beaded CNTs. The CNTs have the diameter of 100 nm in the tube part and that of 50 nm in the bead part typically. The typical lengths of the tube part and the bead part are 200 nm and 100 nm, respectively. In TEM observation, we did not find any long CNTs with amorphous beads, which is the typical structure of beaded CNTs, but found plenty of carbon nanobells[7] and short CNTs together. The size of the two materials is corresponding well to that of the bead part and the tube part of the beaded CNTs that we found in FE-SEM observation. This good agreement suggests that the beaded CNT could be a hybrid nanocarbon material of a series of nanobell and short CNT. This structure is different from necklace-type CNTs[8], which has no components of straight tubes, and is quite unique.
This material was synthesized with the submarine-style CVD method developed originally. In the synthesis, graphene oxide supported cobalt-iron catalyst was heated in a small chamber submerged in 2-propanol. The bottom of the chamber was opened and the inner space of the chamber was filled with argon. Alcohol vapor was supplied to the heated catalyst as a carbon source from the liquid surface exposed at the bottom of the chamber. In this method, we design a strong non-equilibrium condition for the growth of nanocarbon materials. The unique beaded CNTs were synthesized at the substrate temperature of 1110-1120 K.
Recently, a work of corking carbon nanobells with gold nanoparticles was reported to find potential applications to nanoscale reaction containers or drag delivery vehicles[9]. The hybrid nanocarbon material of nanobell and short CNT could provide another approach to new applications of the nanospace.
[1] S. Iijima, Nature, 354, 56 (1991). [2] Y. Saito and T. Yoshikawa, J. Cryst. Growth, 134, 154 (1993). [3] M. Endo et al., Appl. Phys. Lett., 80, 1267 (2002). [4] X. Chen et al., Nano Lett. 3, 1299 (2003). [5] J.-M. Ting and J.B.C. Lan, Appl. Phys. Lett., 75, 3309 (1999). [6] C. Kim et al., J. Appl. Phys., 96, 5903 (2004). [7] X. Ma et al., appl. Phys. Lett., 77, 4136 (2000). [8] H. Okuno et al., Carbon, 42, 2543 (2004). [9] Y. Zhao et al., ACS Nano, 6, 6912 (2012).

Catalytic Chemical Vapor Depostion(CVD) is a popular method for producing aligned Carbon nanotube (CNT) forests. CVD is a highly repeatable process and yields large volumes of CNTs making it an ideal process for investigating how growth parameters including temperature, catalyst structure, and gas composition influence CNT type and dimensions. Increasing the activity and lifetime of the catalyst is a critical challenge before carbon nanotubes can realize their potential in electronic and mechanical applications. We have observed that a single 150 fs ultrashort laser pulse incident on a growing CNT forest dramatically enhances the final height of the forest. The most extreme enhancement is observed if the forest is irradiated within a very narrow time window 17 to 24 seconds after the initiation of CNT growth. Over the subsequent 10 minute growth period the CNT forest in the irradiated area grows taller than the surrounding forest by a factor of 50; irradiated areas reached 1mm in length vs. 20 µm in pristine areas. As observed in previous studies¹ irradiation of the catalyst film in air with a single ultrashort pulse long before annealing and growth also enhanced the final forest height; we observed approximately a factor of two increase in the final forest height; pre-irradiated areas reached 40 µm in length over a 10 minute growth period. The efficiency of CNT growth will be presented as a function of the laser parameters and CVD growth parameters. Scanning Electron Microscopy, Transmission Electron Microscopy, Atomic Force Microscopy, and Raman Spectroscopy of nanotubes and catalyst from irradiated and unirradiated areas will be presented.
1.Rouleau, C. M. et al. Altering the catalytic activity of thin metal catalyst films for controlled growth of chemical vapor deposited vertically aligned carbon nanotube arrays. Applied Physics A 93, 1005-1009 (2008).

Scalable fabrication of microstructures with freeform geometries, in particular curved and re-entrant shapes, is limited by the constraints of fabrication methods that present a tradeoff between structural complexity and throughput. We present a scalable fabrication technique to produce freeform Carbon Nanotube (CNT) microstructures with exceptional uniformity by controlling the growth rate of aligned CNTs via engineered catalyst film stack. The growth rate of CNTs can be controlled by introducing a growth retardant layer underneath the regular catalyst film stack. Offset patterning of the CNT growth catalyst and growth retardant layer with varying thicknesses is used to locally modulate the CNT growth rate at inter- and intra-structural level which enables multi-height scale structures and curved structures whose trajectories depend on the strain mismatch within the structures. The final shape of the curved CNT microstructures can be designed via finite element modeling, and compound catalyst shapes produce microstructures with multi-directional curvature and unusual self-organized patterns. Conformal coating of the CNTs enables tuning of the mechanical properties independently from the microstructure geometry, representing a versatile principle for design and manufacturing of complex microstructured surfaces. This principle can be applied toward applications demanding uniform arrays of complex structures over large areas, such as micro-architectured composite materials for maximized stiffness and damping properties, and nature-inspired superhydrophobic surfaces with intricate micro- and nanoscale features for directional wetting properties.

Chemical vapour deposition (CVD) is probably the most promising technique to synthesize large scales of carbon nanostructures as graphene, thin films, nanotubes or their hybrid. Together with the use of metallic foils as catalytic substrates, CVD offers a high control [1] and scalability [2].
We studied the role of an oxidized stainless steel foil (SS) as a substrate for the synthesis of vertically aligned carbon nanotubes (VACNTs) and carbon thin films by CVD. Here, a reduction-synthesis process was carried out in a tubular CVD reactor for several temperatures between 7000C-8300C.
VACNTs and nanocrystalline amorphous carbon (a-C) thin films were directly and simultaneously obtained on the SS foil. The a-C thin films were synthesized on the stainless steel at all temperatures (7000C-8300C), and consisted on nanocrystalline and amorphous carbon film (thickness < 100 nm) filled with Cr-Fe carbides. Contrary, CNTs forests were only obtained at low temperatures (7000C-7800C). Raman spectroscopy and TEM analysis confirmed the graphitic carbon on SS as multi-walled CNTs and nanocrystalline a-C. We also performed a study of the SS evolution by XPS and XRD. It is shown that the oxidation-reduction steps created an oxide layer where metallic Fe was surrounded by a thick cationic Cr layer. At synthesis step, a temperature-dependant carbon diffusion inward the substrate is found, that led to carbides precipitation on grain boundaries. We are currently applying wet etching routes on the stainless steel to extract the VACNTs/a-C film hybrid structure to study their connection, the growth mechanism and their properties.
A simple and feasible method to simultaneously synthesize a hybrid structure consisting on VACNTs and nanocrystalline a-C thin film on low-cost SS foil is demonstrated. Further work is proposed to understand the growth mechanisms in these heterogeneous substrates, so high quality and inexpensive carbon nanostructures and their related materials can be obtained.
[1] V. Jourdain and C. Bichara, “Current understanding of the growth of carbon nanotubes in catalytic chemical vapour deposition,” Carbon, vol. 58, pp. 2-39, Jul. 2013.
[2] R. Guzma#769;n de Villoria, A. J. Hart, and B. L. Wardle, “Continuous High-Yield Production of Vertically Aligned Carbon Nanotubes on 2D and 3D Substrates,” ACS Nano, vol. 5, no. 6, pp. 4850-4857, Jun. 2011.

In this talk, we will describe the synthesis of carbon nanotubes and nanotube networks using different dopants during chemical vapor deposition. In particular, we will discuss the effects of sulfur, boron and nitrogen. It will be shown that these dopants are responsible for significant changes in the nanotube morphology and electronic properties. For example, sulfur induces the formation of pentagons and heptagons, whereas boron aids the growth of heptagonal carbon rings, and nitrogen promotes the formation of pentagonal cusps. It will be demonstrated that it is indeed possible to assemble/grow carbon nanotube networks if a careful control of dopants is achieved during chemical vapor deposition (CVD) growth. High resolution electron energy loss spectroscopy (HR-EELS) studies on these nanotube materials will be presented, and the locations of boron, sulfur and nitrogen within nanotubes will also be shown. First principles theoretical calculations on nanotubes containing pentagon, hexagons and heptagons in the presence of these dopants will be discussed. Recent experiments on different doped graphene layers will also be presented. We will discuss the citotoxicity and applications as molecular sensors of these doped nanocarbons.

Carbon nanotube forests may find applications as interconnects in integrated circuits, heat spreaders, and supercapacitors. However, to outperform the materials currently used in these technologies, the tubes need to be grown at low temperatures, on conductive supports, and in the form of high-density forests with all of the tubes holding the same metallic properties. Despite the advancements in nanotube synthesis [1,3], control over structural selectivity of the tubes remains elusive. This give rise to resistivity values of forests orders of magnitude greater than that of Cu, regardless of the fact that nanotubes themselves can sustain much higher current densities. To overcome this issue, we dope nanotube forests using MoO₃ as doping material, evaluate the doping stability at different pressure and temperature conditions, and its impact on the electrical properties of the tubes. By in-situ photoemission spectroscopy, we first determine the minimum necessary MoO₃ thickness to dope a tube ensemble. We then study the variation of forest resistivity upon annealing in vacuum at various temperatures and times, and find that MoO₃-doped forests increase their conductivity at least two orders of magnitude thus reaching values comparable to that of Cu. In addition, the doping is significantly more stable than other dopants (e.g. iodine) during thermal cycling. As MoO₃ is employable at a large scale production of devices, this report represents a step towards the use of nanotubes in interconnects of next generation electronics.
[1] S. Esconjauregui, R. Xie, Y. Guo, S. Pfaendler, M. Fouquet, R. Gillen, C. Cepek, C.Castellarin-Cudia, J. Robertson. Applied Physics Letters 102, 113109 (2013).
[2] H Sugime, S Esconjauregui, J Yang, L D'Arsié, RA Oliver, S Bhardwaj, C Cepek, J Robertson. Applied Physics Letters 103, 073116 (2013).
[3] S. Esconjauregui, M. Fouquet, B. Bayer, C. Ducati, R. Smajda, S. Hofmann, J. Robertson. ACS Nano 4, 7431 (2010).

Single-walled carbon nanotubes (SWNTs) have been promising candidates in near-IR optoelectronic applications due to their unique optical, electronic and material properties. However, the reported fluorescence quantum yield has been very low which limits their applications. Recently, studies on covalent doping of SWNTs revealed an exciting method to overcome this problem by enhancing the nanotube (NT) intensity an order of magnitude compared to pristine emission. But, these studies have been mostly limited to ensemble measurements. On the other hand, to controllably tune the photo-physical behaviors of NTs, it is important to understand the nature of the dopant site, exciton migration and trapping dynamics on an individual NT level with mild doping chemistry. Therefore, we have studied low level covalently doped individual (6,5) nanotubes with different doping chemistry. We can resolve single dopant sites while simultaneously observing the pristine emission along individual SWCNTs. These studies enable insight into the spatial extension and mobility of the different trap states as well as their photophysical stability.

As the trend toward the miniaturization of electronics progresses at a rapid pace, the demand for nanoscale materials with desirable physical and chemical properties continues to grow. One class of materials that has shown promise is single-wall carbon nanotubes (SWNTs) due to their unique electronic, surface, optical and mechanical characteristics. Because of these characteristics, significant effort has been made to incorporate SWNTs into a multitude of commercial platforms such as sensors, biomedical devices, super capacitors, conductive composites and thin-film transistors. However current production methods for SWNTs yield a mixture, composed of a broad range of nanotube species (chiralities) where each one exhibits its own distinctive characteristics. In platforms where precise control over the properties of SWNT is required for success of the nascent technology, the inability to conveniently characterize a batch of SWNT can have a deleterious impact on its development. Therefore a method that allows the researcher to acquire a wealth of information about the sample in question would be strongly advantageous. In this talk, we will introduce a new technology that integrates Raman spectroscopy and DLS measurements for simultaneous analysis of a single, small quantity sample of SWNT. From these measurements, important attributes such as diameter, length, relative purity, quality and hydrodynamic diameter of the SWNT can be easily obtained for use in applications that incorporate nanomaterials with properties of interest.

SWCNTs are produced with wide distribution in diameter/chirality resulting in variability in the starting material chirality distributions with respect to production batch and method. The separation methods (gel chromatography, DGU) to isolate nearly single-chiralities that have been reported require high cost instrumentation and long separation times to achieve high purity, thereby preventing low-cost scalability of the method. Recently aqueous two-phase (ATP) separation has been shown as a new promising method to separate single-wall carbon nanotubes (SWCNTs) by diameter. We reported that the ATP separation mechanism is driven by the hydrophobicity of the surfactant, or combination of surfactants, covering the SWCNTs, which can be tuned by mixing different surfactants in well-defined ratios. As such, variations of parameters that influence hydrophobicity result in different SWCNT isolation. This rationalization on hydrophobicity dependence is instrumental in designing tuned ATP procedures toward desired SWCNT isolations comparable to or better than DGU that are scalable without high cost instrumentation.

The purification of single-wall carbon nanotubes (SWCNTs) of different chiralities is both scientifically interesting and technologically important. Recent demonstrations in nanotube sorting using polymer aqueous two-phase (ATP) systems enabled the isolation of metallic, semiconducting, and single-chirality species. In this work, we report a systematic study of sequence-dependent partition of DNA-wrapped SWCNTs in several polymer ATP systems. The DNA-controlled partition of SWCNTs in ATP system suggests the sensitive dependence of hydration energy on the exact spatial distribution of hydrophilic groups which are determined by the DNA sequence and the SWCNT chirality (n,m). In addition, the spontaneous partition of DNA-SWCNT hybrids in a given polymer ATP system can be further modulated by salt and polymer additives. This unique approach of combining DNA sequence and polymer ATP system led to the purification of many single-chirality SWCNT species at high purity.

Current large scale, single walled carbon nanotube (SWCNT) production methods generate a mixture of nanotubes with diverse properties; in particular, a mixture of metallic and semiconductor materials are produced Many important applications require that only one type of SWCNT be utilized without the presence of the other type. We report on a novel approach, based on the method of “electric tweezers” [1] that employs AC dielectropheresis, that can be used to transport and separate SWCNTs in suspension. The dielectropheretic forces acting on metallic and semiconducting nanotubes are of opposite sign and of significantly different magnitude, which allows for purification based on the type of conductor. This approach has promise with regard to providing an efficient and cost-effective process to provide purified material of both semiconducting and metallic SWCNTs for a variety of technologically imortant devices. Details of the purification system will be presented along with electronic and spectroscopic characterization results which illustrate the efficiency and selectivity of the method.
[1] D.L. Fan, F.Q. Zhu, R.C. Cammarata, C.L. Chien, "Electric Tweezers", Nano Today6, 339 (2011).

We investigated the arrangement of methyl-terminated terthiophenes inside a nanotube by using density functional theory (DFT) including dispersion corrections. After conducting DFT calculations, a variety of arrangements of the inner terthiophene chains was found, depending on host-tube diameters and the number of chains. Because of the various inner thiophene arrangements, the terthiophene chains interact differently. The interactions are stronger in a smaller nanotube compared to within a larger nanotube, indicating importance of nanotube confinements to the interchain couplings. The interchain interactions split the orbitals of the multimeric terthiophene chains, which are built from single-chain frontier orbitals, to broaden their energy levels. Therefore, nanotube confinements are key factors in determining the energy levels of the frontier orbitals of contained multimeric terthiophenes. As a result, their electronic transitions are affected by the encapsulation into a restricted nanotube space. According to time-dependent DFT calculations, a specific electronic transition occurs from a HOMO-built orbital to a LUMO-built orbital. The broadening of the orbital energies by the aggregation of terthiophene chains in a nanotube leads to a widened range of excitation energies (E_x) in their electronic transitions relative to the single-chain. With respect to the strongest transition of multimeric terthiophenes, the excitation energy is enhanced by confinement to a nanotube. The E_x enhancement within a smaller nanotube is more significant than within a larger nanotube due to the stronger interchain interactions in a smaller nanotube. Therefore, it is proposed from the DFT calculations that nanotube confinements can modulate electronic and absorption properties of multimeric terthiophene chains by changing the interchain interactions.

Individual carbon nanotubes (CNTs) have outstanding mechanical strength (~ 50 GPa). As a result, continuous CNT yarns are promising candidates for replacing high strength carbon-based fibers in load bearing applications. While the hierarchical mechanics of CNT yarns provide an interesting platform for tunable properties, their strength still remains less compelling in comparison with Kevlar (~3N/Tex) and Dyneema (~3.5N/Tex). Therefore, understanding what governs and practically limits the strength of CNT yarns remains a vital area of research. Load transfer within the CNT yarn involves mechanics at multiple length scales, including van der Waals adhesion at nanoscale contacts between individual CNTs and micro-scale waviness of CNTs and anisotropy of the yarn. Here we present a hierarchical quantitative model that enables the derivation of structure-property relationships for the stiffness and strength of CNT yarns. Using a mathematical representation of the wavy shape of CNTs, contact locations are determined geometrically. At each contact location, the cross-section of the nanotube is deformed due to van der Waals adhesion. The contact width and contact length along the CNT axis are determined by finding the 3D equilibrium geometry, resulting from the balance between van der Waals adhesion energy and elastic strain energy. We find that the contact width is dependent on the diameter and number of walls of the CNT, with single walled nanotubes yielding the highest contact strength due to low wall stiffness. The contact length is found to depend on the adhesion energy of the contact, bending stiffness of the nanotubes and the number density of CNTs in the yarn. The analytically described geometry of the yarn, contact locations and contact strength and stiffness distributions are then assembled into a finite element model enabling direct simulation of internal load transfer in the yarn. Upon loading, failure is observed by relative sliding between CNTs and fracture of individual CNTs. Furthermore, this initial failure results in a new contact distribution, reflecting the morphological changes due to loading. In order to predict the dynamic evolution of morphology, the contact locations and strength are re-calculated at the end of each loading step. We observe that the number of contacts increases initially as the nanotubes become aligned with the loading axis, however the load capacity soon begins to drop due to CNT-CNT sliding as well as fracture of individual CNTs. The evolution of morphology predicted by the simulation reflects our experimental observations via in-situ tensile testing and small-angle X-ray scattering. Our results point towards identification of the load transfer mechanism and failure propagation as well as the key morphological parameters influencing the mechanical properties of CNT yarns. In addition quantitative understanding of the effects of yarn morphology can inform synthesis efforts to achieve tunable properties.

Recent studies of single-walled carbon nanotubes (CNTs) in aqueous media have showed that water can significantly affect the mechanical properties of the tubes [1, 2]. CNTs under hydrostatic compression can preserve their elastic properties up to large pressure values, while exhibiting exceptional resistance to mechanical loadings.
It was experimentally observed that CNTs with encapsulated carbon linear atomic chains (CLACs), when subjected to high hydrostatic pressure values, present irreversible red shifts in some of their vibrational frequencies. In order to address this phenomenon, we have carried out fully atomistic reactive (ReaxFF) [3] molecular dynamics (MD) simulations.
We have considered the cases of finite and infinite (cyclic boundary conditions) CNTs with encapsulated CLACs of different lengths (from 9 up to 40 atoms). Our results show that for pressure around 10 GPa causes the coalescence of two chains. The calculated vibrational spectrum shows that the longer chains (after coalescence) present a smaller resonant frequency, consistent with experimental observations. Also we show that for extreme high pressures (up to 10 times higher than the experimental one) the CNTs are deformed in an inhomogeneous way due to the CLAC presence. The CLAC/CNT interface regions exhibit convex curvatures, which results in more reactive environments [4], thus favoring the formation of covalent bonds between CLACs and CNTs. This process is irreversible with the new formed covalent bonds continuing to exist even when the external pressure is released. A red shift from 1850 to 1750 cm^minus;1 in the C-C mode of the chain was calculated, thus suggesting new interaction between chains and carbon nanotubes.
[1] V. Vijayaraghavan and C. H. Wong, Comp. Mater. Sci. v79, 519 (2013).
[2] C. H. Wong and V. Vijayaraghavan, Phys. Lett. A v378, 570 (2014).
[3] A. C. T. van Duin, S. Dasgupta, F. Lorant, and W. A. Goddard, J. Phys. Chem. A v105, 9396 (2001).
[4] D. Srivastava, D. W. Brenner, J. D. Schall, K. D. Ausman, M. Yu, and R. S. Ruoff, J. Phys. Chem. B v103, 4330 (1999).

In recent years, studies on the thermal properties of single wall carbon nanotubes are of great research interest in the area of thermal management. The heat energy in solids is transferred by the quantized lattice vibrations called phonons and it is possible to estimate the lattice thermal conductivity by Raman spectroscopy. Here we estimate the thermal conductivity of nanometer thick suspended single wall carbon nanotube mat by laser Raman spectroscopy. From the temperature and laser power dependent frequency shift of the A_1g mode of the G band, the thermal conductivity is estimated to be about 18.3 Wm^-1K^-1. The obtained result is supported by our theoretical study that suggests the thermal conductivity of the carbon nanotube mat is contributed both by the intra and inter-tube thermal transport. The calculated inter-tube thermal conductivity is about 0.7 Wm^minus;1K^minus;1, which is much less than the intra-tube thermal conductivity.

Carbon nanotubes (CNTs) represent a nearly ideal material for enabling high-performance micro/nano-electromechanical (MEMS/NEMS) devices because of their extraordinary mechanical and electrical properties. The mechanical properties of carbon nanotubes allow one to make MEMS devices that operate at extremely high speed with a potential for far lower power dissipation. Early device demonstrations used discrete CNTs placed randomly until one happened to bridge a pair of electrodes. More recently, techniques depositing continuous films of CNTs have been investigated. This approach allows the use of standard lithography and etching processes to produce arbitrary patterns at any desired locations on a substrate. In order to grow continuous CNT films, high temperature process such as chemical vapor deposition is often required. These processes are incompatible with many substrates including metallized wafers. A low-temperature (<300 °C) CNT film deposition process such as electrophoretic deposition is well suited to fabricate continuous CNT films even on flexible substrates.
This paper reports a method enabling rapidly production of a carbon nanotube thin film by electrophoretic deposition at room temperature. Electric field and time were precisely controlled to obtain an accurate, reproducible film thickness. To investigate the electrical and mechanical properties of such films, we recorded electric resistance and Young&’s modulus using IV characterization and a nanoindenter, respectively. The measured resistivity of the films was 2.14×10^-3 to 7.66×10^-3 Omega;#9679;cm, and the Young&’s modulus was 4.72 to 5.67 GPa, independent of film thickness from 77 to 134 nm. These results indicated that the mechanical and electrical properties of film are comparable with previously reported methods such as layer by layer deposition even though we achieved much higher deposition rated. We also measured the film mass density which is usually unrecorded even though it is an important parameter for MEMS/NEMS device actuation. The film density was found with conventional thickness measurement and Rutherford backscattering spectrometry. It varied from 0.12 to 0.54 g/cm³ as the film thickness increased. This method could be extended to flexible electronics or high frequency RF MEMS devices.

Ordered carbon nanotube (CNT) growth by deposition of nanoparticle catalysts using dip pen nanolithography (DPN) is presented. DPN is a direct write, tip based lithography technique capable of multi-component deposition of a wide range of materials with nanometer precision. A NanoInk NLP 2000 is used to pattern different catalytic nanoparticle solutions simultaneously to provide nucleation sites for CNT synthesis. To generate a uniform pattern of nanoparticle clusters, various conditions need to be considered. These parameters include, modulating the level of humidity in the vessel, temperature, and tip-surface dwell time. By simultaneously patterning different nanoparticle solutions next to each other, identical growth conditions can be compared for different catalysts in a streamlined analysis process. Solutions of Fe, Ni, and Co nanoparticles are patterned onto silicon, mica, and graphite substrates. These nanoparticle patterns serve as nucleation sites for CNT growth. Synthesis of CNTs is achieved by a chemical vapor deposition (CVD) reaction. Each nanoparticle patterned substrate is placed in a tube furnace held at 725#730;C during CNT growth. The carbon source used in the growth chamber is toluene and is injected at a rate of 5 mL/hr for 45 minutes. Growth is observed for Fe and Ni nanoparticle patterns, but is minimal for the Co patterns. The results of these reactions provide important information regarding efficient and highly reproducible mechanisms for future aligned CNT growth using patterned nanocatalysts.

We directly synthesized large self-assembled, conductive, and superhydrophobic three-dimensional mats of entangled carbon nanofibers (CNFs) using thermal chemical vapor deposition (CVD). We show that the yield obtained from the catalysis of an unconstrained thin Ni-Pd film is over an order of magnitude higher compared to the same thin film when bound to a substrate. The growth mechanism differs from substrate-bound growth, where catalysis occurs only the top surface of the catalytic film, as the full Ni-Pd catalyst layer participates in the reaction and is totally consumed to bi-directionally grow CNFs. Therefore, the yield further increased with the thin film thickness, in contrast with substrate-bound growth. The unconstrained growth occurred thanks to a weak adhesion layer that delaminated during the thermal process. Additionally, we showed that the supporting substrate material strongly affected the nanostructure morphology obtained. The as-grown CNF mats were used as a three-dimensional electrode for lithium-ion batteries. We envisage these CNF mats to be an ideal platform to be functionalized for multiple applications including high-performance electrodes, sensors, electromagnetic shields, and conductive polymer-coated composites.

Novel methods for fabricating graphene nanosheets and unzipped carbon nanotubes (CNTs) coated with nanoparicles have been developed using chemical and thermal treatments. Through longitudinal unzipping of single- and multi-walled CNTs using sonication with nitric acid or 1,2-dichlorobenzene, unzipped CNTs were fabricated after an annealing process on a copper substrate. The width of unzipped CNTs can be controlled by changing the condition of chemical and thermal treatments. The unzipped CNTs were mixed with metal nanoparticles and were annealed at the high temperature. During the annealing process, both evaporation and redeposition of the metal nanoparticles occur and the unzipped CNTs coated with nanoparticles were synthesized.

We synthesized millimeter-tall, dense carpets of crystalline CNTs on non-polished copper substrates with a thin Al₂O₃ (below 10 nm) underlayer and Fe (1.2 nm) layer as a catalyst using chemical vapor deposition (CVD). Preheating of the hydrocarbon precursor gases and in-situ formation of controlled amounts of water vapor were critical process parameters. High-resolution microscopy showed that the CNTs were crystalline with lengths up to a millimeter. Electrical conduction between the CNTs and the copper substrate was demonstrated using three methods. (1) Probe-station measurements using microprobes showed electrical conductivity from the CNTs to the copper substrate. (2) Successful electrodeposition of copper from aqueous solution and cyclic voltammetry measurements confirmed electrical conductivity between the CNTs and the copper substrate. (3) Electrochemical hydrolysis of water on copper foils covered with CNT carpets exhibited a much higher current compared to the sample without the CNTs. Through TEM characterizations of cross-sections, we demonstrated that copper diffusion into the alumina layer during the thermal process was the key to explain the observed electrical conductivity. Additionally, the high conductivity of a thermal processed sample compared to the insulating behavior of a pristine sample confirmed the mechanistic hypothesis. Adsorption isotherm measurements showed the mesoporous structure of the vertically aligned carbon nanotubes (VACNTs) with a surface area of 342 m²/g. Electrical conduction and high surface area of this nanostructure make it a promising platform to be functionalized for future battery electrodes.

Carbon nanotube (CNT) based macroscopic solids with a light weight, high porosity and large surface area are of great importance for many applications.For instance, regarding energy applications they can serve as electrodes in batteries, fuel cells and supercapacitors, in medicine, as scaffolds for tissue regeneration and in environment for absorption and filtration materials. However, establishing 3-Dimensional interconnected CNT structures with controlled porosity and functionality is still in its infancy. Here we report a reproducible and inexpensive method to obtain macroscopic 3D solids consisting of CNT and sodium alginate polymer. The CNT-alginate hydrogel is formed by mixing CNT dispersion in aqueous solutions of sodium alginate. The hydrogel is then subjected to freeze-drying that results in an ultralight (estimated density ~30 mg/cc), macroporous and stable solid. The porosity of the 3D solid can be controlled by the freezing protocol.When using a thermal gradient during freezing (unidirectional freezing), homogenous pore alignment within the solid is achieved.Field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) are employed for characterizing the materials. Processing of similar solids with nitrogen-doped CNTs and functionalized CNTs will also be presented.

Single-walled carbon nanotubes (SWCNTs) have been one of the key building blocks for nanoscale science and technology over the past two decades due to their interesting physical and chemical properties. SWCNTs are particularly promising for high speed and low power semiconductor electronics. A challenge, however, is the hierarchical organization of these building blocks into organized assemblies and, ultimately, useful devices. Ordered structures are necessary as random network SWCNTs thin films result in sub-optimal electronic properties including reduced channel conductance and mobility. Numerous techniques for aligning SWCNTs have been explored to solve this shortcoming and achieve higher conductance and mobility. These approaches can be divided into two main categories: (a) direct growth via chemical vapor deposition and arc-discharge, and (b) post synthetic assembly. In the case of direct growth, both metallic and semiconducting SWCNTs are produced. In this case, the performance of SWCNT field effect transistors (FETs) is limited by metallic SWCNTs (m-SWCNTs), thus motivating attempts to purify semiconducting SWCNT (s-SWCNT) samples with homogeneous electronic properties.
We introduce a novel yet simple method to deposit aligned s-SWCNTs on substrates via dose-controlled, floating evaporative self-assembly. The unique advantage of this method is that it allows for the deposition of s-SWCNTs with exceptional electronic-type purity that are prepared using conjugated polymers as semiconductor-selective agents in organic solvents. Unlike s-SWCNTs sorted using anionic surfactants in aqueous solution, conjugated polymers like polyfluorene-derivatives are advantageous because they sensitively and selectively “pick out” semiconducting species directly during dispersion from raw s-SWCNT powders, thereby avoiding the need for subsequent post-dispersion sorting. This method shows that the s-SWCNTs were predominantly aligned within ±140, were packed at a density of ~50 s-SWCNTs µm^-1, and constituted primarily a well-ordered monodispersed layer. The dose-controlled, floating evaporative self-assembly method is a substantial evolution over standard evaporation-driven self-assembly, which has been used to deposit surfactant-encapsulated s-SWCNTs from aqueous solution.

The development of new techniques for the preparation of monochiral single-walled carbon nanotube (SWCNT) suspensions in a scalable, reproducible and simple manner remains an ongoing challenge to the carbon nanotube community. In our contribution to scale up we have recently shown that the number of required Sephacryl gel columns can be reduced to one by altering the pH of the sodium dodecyl sulfate (SDS) eluent and demonstrated the separation of 15 different nanotube (n, m) species with a purity of 17 - 72 %. In our recent work we now demonstrate that this technique can be applied to gel permeation chromatography system. This automated procedure requires no pre-centrifugation, is scalable, and is found to yield monochiral SWCNT fractions of semiconducting SWCNTs with a purity of 61 - 95 %. Unsorted and resulting monochiral fractions are characterized using optical absorption and photoluminescence spectroscopy.

There is a growing interest in synthesizing three-dimensional (3-D) carbon nanotube structures with multi-functional characteristics. Here, we report the fabrication of a novel composite material consisting of 3-D interconnected multi-walled carbon nanotubes (MWNTs) with Silicon Carbide (SiC) nano- and micro-particles. The materials were synthesized by a two-step process involving the chemical coating of MWNTs with Silicon oxide, followed by Spark Plasma Sintering (SPS). SPS enables the use of high temperatures and pressures that are required for the carbothermal reduction of silica and for the densification of the material into a 3-D composite block. Covalent interconnections of MWNTs are facilitated by a carbon diffusion process resulting in silicon carbide formation as silica coated MWNTs are subjected to high temperatures. The presence of SiC in the sintered composite has been confirmed through Raman spectroscopy, which shows the characteristic peak close to 800 cm^-1 and also Energy Filtered Transmission Electron Microscopy maps. X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy and High Resolution Transmission Electron Microscopy have also been used to characterize the produced material. Interestingly, the thermal property measurements of the sintered composite reveal a high thermal conductivity value (16.72 W/mK) for the material. From the electrical point of view, a 3-D variable range hopping (VRH) electron hopping was observed in the composite.

The nanorods are a modified shape of the graphene. The size of nanorods varies between 1 and 100 nm according to the classic data. Some potential applications of these particles are in the medical area, using gold nanorods for cancer therapies by their absorption property in the near infrared. In this work, the nanorods were obtained by a chemical treatment of functionalized multiwall carbon nanotubes to achieve their splitting. Also, we have observed the self-assembling of these structures in a temperature gradient that occurs during the synthesis process. The obtained materials have been characterized by Scanning Electron Microscopy (SEM) and we can observe nanorods, structures like nanoflowers shape and nanoplates, with a size between 200 and 500 nm.

Flavin mononucleotide (FMN) and its derivatives present one of the highest order surfactant organization around different chirality of SWNTs, stemming from: (i) the cooperative H-bonding, vdW and electrostatic interactions between adjacent isoalloxazine moieties; and (ii) concentric π-π stacking interactions with the underlying graphene sidewalls. To gain a meaningful understanding in terms of the structure-property relationships, we investigate the structure of FMN assembly around various (n,m)-SWNTs.^[1] Given the fact that, the FMN creates 7/1 and 8/1 helices around (6,5) and (8,6)-SWNTs, herein we introduce the formation of FMN fractional helices around intermediate NT diameters (i.e. from 0.8 - 0.9 nm). The fractional U/T FMN helices can be realized via translating the FMN dimer by (2.5 nm×T)/U along the z-axis, while rotating by (360°×T)/U around the z-axis using a radius of d_t/2 (of the given (n,m)-SWNT) + 0.34 nm (helix-SWNT π-π distance). Such FMN fractional helices show different H-bonding patterns, which imparts varying FMN helical packing density onto given diameter nanotube, and subsequently different FMN helical stability. These findings indicate that the lateral FMN-FMN packing stability is mostly governed by how close the isoalloxazine moieties approach each other within the given helical organization, and to a lesser extent from H-bonding. This opens up a unique insight into the molecular engineering of self-organizing surfactants around various diameter and chirality nanotubes.
^[1] Sharifi, R.; Samaraweera, M.; Gascoacute;n, J. A.; Papadimitrakopoulos, F.; J. Am. Chem. Soc., 2014, 136(20), 7452-7463.

Flexible and stretchable electronics have drawn great attention due to their potential applications in various fields ranging from skin sensors and wearable devices to bio-integrated devices. Previously, electrodes of stretchable electronics were fabricated using metal, carbon-based material and conducting polymer, etc. Especially, CNTs/CNWs have been regarded as suitable nanomaterials for the application of flexible and stretchable devices because of their superior electrical properties and mechanical performance. Nevertheless, CNTs/CNWs in stretchable electronics still have limitations in that CNTs/CNWs themselves are not stretchable.
In this study, new types of coiled carbon nanotube (CCNT)-containing electrode were proposed. The stretchability or flexibility of electrode was improved by changing the structure from straight to coiled shape. We have synthesized coiled CCNTs to apply for stretchable electronics using chemical vapor deposition (CVD). Various kinds of catalysts including Fe, In and Se were used for the synthesis of CCNT. As-synthesized CCNTs were then transferred onto a patterned PDMS substrate. Uniaxial-oriented CCNTs on patterned PDMS substrate had a key role of the performance of stretchable electronics, and might be promising materials for stretchable electronics in the future.

Although single wall carbon nanotubes (SWCNTs) attracted enormous research interest, but due to several difficulty of the separation of individual chirality hindered their practical applications. To separate individual SWCNTs with single chirality quantitative understanding of surfactant morphology morphologies of various diameter nanotubes (NTs) is essential. Different surfactants yield a variety molecular structure on SWCNTs surface. Here we explored the morphology of different surfactant in the surface of two different chirality SWCNTs (6,5) and (7,6) by monitoring their spatiotemporal photoluminescence, obtained via single molecule imaging techniques. To image single NTs, samples were immobilized by preparing gel of tetra methyl orthosilicate (TMOS). Changes of fluorescence signal serve as surface sensitive probe at the surfactant-NTs interface. Our primary analysis of single NTs intensity profile results shows that some surfactant wrap uniformly all along the NTs, while others yield disordered aggregates. Possible roles played by different surfactant structure on the surfactant morphology at the NTs surface will be discussed.

Hollow N-doped graphitic carbon nanomaterials have attracted considerable technological interest owning to their many applications, such as catalysts, sensors, hydrogen storage materials, and electrochemical devices. In this paper, we report a novel approach to control Ni diffusion in the N-doped amorphous carbon nanofibers, which can graphitize the amorphous carbon into graphitic carbon and form the hollow structures. We use in situ TEM to study the detail process of Ni diffusion in electrospun carbon nanofibers and thus observe the motion of Ni particles like worms. In addition, the typical morphology of Ni nanoparticle during Ni diffusion process changes from initial sphere, to sphere with small tip, to elongated shape, finally to sphere. The prepared materials as anodes show high capacity, good rate capability, and long cycle life.
Acknowledgements
The authors are grateful for the support received from the Research Grants Council of the Hong Kong Special Administration Region (grant: PolyU 5312/12E) and the Hong Kong Polytechnic University (grants: G-YK47 and G-YBA1).

Recent advances in organic photovoltaics render them promising for flexible solar cells. Exciton separation into a free hole and electron are crucial in the design of organic photovoltaics involving nanostructured materials, such as single walled carbon nanotubes (SWNTs). Organic heterojunctions based on C₆₀ and SWNTs have been reported as viable photovoltaics candidates. Such heterojunctions, however, are not well defined. In an effort to improve molecular understanding of these heterojunctions, our group has engineered a number of flavin-C₆₀ complexes (FC₆₀) that can interact with the nanotube in a more defined manner, through the isoalloxazine helix.^[1] These compounds contain a medium-length aliphatic chain (composed of 17 carbons and one oxygen) that links the isoalloxazine with C₆₀. The molecular conformations of such flexible aliphatic chain are presently studied in order to permit the isoalloxazine to come in close proximity (i.e. π-π interaction) with C₆₀, using molecular dynamics. Furthermore, we also study (using ab initio calculations) the electronic structures of various FC₆₀ configurations and their propensity to result in photo-induced charge transfer. These calculations are similarly extended onto flavin-wrapped SWNTs,^[1] which presents an even richer conformational and electronic structure landscape.
Reference
1) Ju, S.-Y.; Doll, J.; Sharma, I.; Papadimitrakopoulos, F., Selection of carbon nanotubes with
specific chiralities using helical assemblies of flavin mononucleotide. Nat. Nanotech. 2008, 3, 356-362

The work under consideration is in line with the ever increasing demand of environmental protection regarding the immense amount of waste water generated and the specific heavy metals&’ content found in it. Carbon materials have been long used for water treatment purposes. The very fast growing use of carbon nanotubes (CNTs) has been utilized in this research. A new direction to the use of these CNTs is tested where these nanotubes are modified by impregnating their surfaces with iron oxide. Different percentages of iron oxide have been used for this purpose with 1 weight % and 10 weight % impregnation on the CNT surface. The samples fabricated as a result of the sol-gel method were subjected to various characterization methods before exposing the robust materials to the removal of divalent lead (Pb(II)) from water. The topography, composition and thermal analysis of each sample was conducted. The thermal analysis performed via TGA upto 900°C indicated the retention of 1.6% and 32% of the materials of 1% and 10% composition respectively. SEM images clearly indicated the modified surfaces of CNTs depicting the presence of iron oxide particles. The elemental analysis of EDX showed that on an average, weight percent of 1% iron and 10% oxygen were present in the sample of 1% impregnated CNTs whereas 18% oxygen and 11% iron were indicated in the sample with 10% impregnation. The characterization of the modified carbon nanotubes indicates the successful preparation of the desired materials. The use of these prepared materials is hoped to be highly beneficial for the removal of lead as a heavy metal from water.

Hybrid nanostructured materials offer unique opportunities to leverage properties of the constituents to create higher levels of performance than are attainable with a single nanomaterial. One inherent limitation in quantum dot (QD)-based devices is that the carriers must hop from dot to dot in what is often a relatively tortuous transport pathway. In solar cells this leads to significant losses in collection efficiency and, thus, fill factor due to low carrier mobility and the recombination of carriers via surface traps on the QDs [1]. On the other hand isolated QDs tend to exhibit longer photoluminescent lifetimes than is typical of thin films of the same material. The microsecond scale carrier lifetimes present in high-quality PbS QDs allow for some collection of the carriers in spite of the poor transport through the QD film. Carbon single walled nanotubes (SWNTs) are just the opposite in that they exhibit very short excitonic lifetimes and carrier mobilities that are orders of magnitude higher than those of QD films [2, 3]. Here, we seek to couple QDs with SWNTs in an effort to efficiently collect the long lived photogenerated carriers, enabling high efficiency QD based photovoltaic devices.
We report on the coupling of PbS colloidal QDs to SWNTs with the goal of optimizing photogenerated charge collection efficiency. We observed self-assembly and attachment of QDs to the surface of the SWNTs in organic solutions without covalent functionalization of the SWNT surfaces and with the QDs in their initial purified state capped with oleic acid. For this work, both laser generated SWNTs consisting of 33% metallic SWNTs (m-SWNTs) and 66% semiconducting SWNTs (s-SWNTs) and enriched CoMoCAT SWNTs consisting of 5% m-SWNTs and 95% s-SWNTs were employed. TEM was used to show that the QDs were closely packed on the surface of the SWNTs. After coupling to the SWNTs, the luminescent emission (PL) from the QDs was quenched by >85% relative to the QD solution. From this we deduce that electronic coupling existed between the PbS QDs and the SWNTs. The time dependence of the PL from the QDs in the hybrid structures was investigated with time resolved photoluminescent spectroscopy (TRPL), which revealed a faster bi-exponential decay in the hybrid solutions than observed in the free QD solution. An energy transfer rate of le;150 ± 20 ns was calculated for exciton energy transfer from the QDs to the SWNTs. The PL quenching can be attributed to energy or charge transfer from the QDs to the SWNTs; however, the subsequent increased PL response of the SWNTs has not been detected due to the presence of m-SWNTs and bundles. Experiments to couple QDs to high purity, highly dispersed polymer wrapped s-SWNTs have begun and will be discussed.
1. Zhao, N., et al. ACS Nano, 2010. 4(7): p. 3743-3752.
2. Liu, Y., et al., Nano Letters, 2010. 10(5): p. 1960-1969.
3. Wang, C., et al., Nano Letters, 2009. 9(12): p. 4285-4291.

The use of carbon nanotubes (CNTs) as electrodes in electrochemical energy storage and conversion systems have been demonstrated, where the CNTs are either deposited electrophoretically on a metal collector, or grown directly on a support or binders, such as polyvinylidene chloride is used to hold the powder together. Furthermore, filtration of a surfactant-dispersed CNTs, super acids and the densification of CNT forests via liquid-induced collapse techniques have been used to fabricate free standing CNT mats/films.
We present a liquid phase post synthesis self-assembly (LP-PSSA) technique that transforms CNTs into flexible, robust and binder-free membrane with limited or no impact on the intrinsic properties using high density organic liquids. The density of the membrane is greater than that of water (ρge;1g/cc). A correlation of the concentration of the CNTs in the liquid to the diameter and thickness reveal a transition from high packing density to low packing density, and from high flexibility to brittleness. This is confirmed by mechanical testing analysis of the flexural modulus using 3-point bending.

Carbon nanotubes of different origin were subjected to variable frequency microwave (5.85 to 7.0 GHz) treatment.
The purpose of this research was to find out whether the origin and morphology of carbon nanotube deposits influences their microwave-induced transformations.
SEM, TEM and Raman spectroscopy were used to characterize the samples before and after variable frequency microwave treatment. The samples before treatment represented either CNT forest or CNT felt comprising double-walled or multiwalled nanotubes, as well as significant impurities of non-CNT carbon (with the exception of CNT forest samples, which did not contain any non-CNT carbon). All the samples contained traces of iron catalyst, which was used for the nanotube growth.
As a result of the research we can conclude that the variable frequency microwave irradiation has considerably different effect on carbon nanotubes of different origin. It was found that the irradiation may impact either iron particles or non-CNT carbon or nanotubes depending on the power, atmosphere and other conditions. In particular, a 1-minute irradiation could vaporize selectively the non-CNT carbon along with iron out of the deposit thus making it a 100 % nanotube sample in one step. This "purification" effect is accompanied with certain relaxation in nanotube bends resulting in visible straghtening of the nanotubes, presumably along the axis of the irradiating wave.This kind of result is achievable in a double-walled nanotube felt of fluidized-bed origin. In contrast, a multiwalled nanotube forest sample underwent substantial corrugation of constituting nanotubes (initially the nanotubes of the forest were straight) with no loss of iron (EDX iron signature stayed the same after irradiation).
These observed differences can be related with different nature of microwave-susceptible centers in different nanotube deposits. The mechanism is discussed in the paper, as well as prospectives for purification and alignment technology on this principle.

Manufacture of electrospun carbon nanofibers (CNFs) involves three process steps: fiber formation, stabilization and carbonization. After the initial fiber formation, structure relaxation and volatilization of noncarbon elements occur during stabilization and carbonization respectively. These phenomena consequently lead to a reduction in the strength of the CNF. In this study we evaluate the effect of constraining the CNFs during the stabilization and carbonization steps on their mechanical properties. To this effect, tensile tests were conducted on constrained carbon nanofibers (CCNFs) in situ scanning electron microscope (SEM) using a microelectromechanical system (MEMS) tensile testing platform. The CCNFs used in this study were produced via electrospinning of polyacrylonitrile (PAN) into fibers, which were subsequently stabilized at 270°C in an oxygen environment and carbonized in nitrogen at 800°C, under constraint. To understand the relationship between diameter and mechanical properties, CCNFs of diameters ranging from ~70 nm to 150 nm were mounted on a MEMS device inside the SEM by nanomanipulation and subsequently tensile tested in situ SEM. The results show that the modulus and strength of CCNFs increase with decreasing diameter. Also, when compared to unconstrained CNFs, CCNFs have better mechanical properties. In order to understand the reason for the enhancement in mechanical properties of CNFs under constraint and further improvement with decreasing diameter, the molecular orientation of the graphitic structure in individual CCNFs were evaluated using Selected Area Electron Diffraction (SAED) inside a Transmission Electron Microscope (TEM). The results indicate that the orientation of 002 graphitic planes along the fiber axis increases with both constraint and decreasing fiber diameter.

The synthesis of a novel nanowire heterostructure is reported which was created by employing a chemical vapor deposition process that is a modification of a method successfully used to grow a variety of pure boron nanostructures [1]. 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 product of this reaction, when imaged by scanning and transmission electron microscopy, was found to be a core-shell nanowire, where the interior of the structure consists of a boron nanowire and the exterior is essentially a multiwalled carbon nanotube. The interior boron nanowire has lattice spacings of 0.38, 0.48, and 0.44-0.45 nm, and is similar to the product obtained without the addition of methane. The layers of the carbon nanotube which formed on the outside of the heterostructure are distorted and wavelike in appearance, most likely because of a lattice mismatch. 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 carbon nanotubes 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 heterostructure is a few microns. Each nanowire heterostructure has a bulbous tip filled with catalyst, indicating a vapor-liquid-solid growth. This new nanowire is a novel form of boron-carbide, and its exterior could be considered as a new form of carbon, with the possibility that this material will have interesting thermal and electrical properties which are currently under investigation.
References:
[1] R. B. Patel: Synthesis and Characterization of Novel Boron-Based Nanostructures and Composites. 2013, PhD Dissertation New Jersey Institute of Technology.

There has been an active interest in determining the physical, chemical, electronic and thermal properties of single walled carbon nanotubes (1) as these properties lead to the development of technological applications. Herein we report an interesting nanothermal sensor that is made by depositing pristine carbon nanotubes on silicon wafer having lithographically deposited gold fingers. The nanothermal sensors were made by depositing a) carbon nanotubes were deposited from methylene chloride b) carbon nanotubes deposited from the medium containing sodium dodecyl sulfonate and c) Baytron-P assisted medium. The nanothermal sensors showed d.c. electrical resistance independent of temperature in the range 293 K to 313 K when the sensors were made by procedures (a) or (b). The electrical resistivity has been independent of temperature. When the nanosensor is made with carbon nanotubes by assisted method (C), the d.c. electrical resistance decreased with temperature. The results obtained can be fitted into the following expression
[R/R_o]= e^-a[1/T_o^] e^a[1/T] (1)
where R is the resistance at temperature T, R_o is the resistance at temperature T_o and a is the temperature of coefficient. The negative temperature coefficient is manifested in the semiconducting property. The sensor behavior is linear with temperature and is reproducible over a good number of iterations. The nanosensor maintained its sensitivity and reproducibility over a number of operations. The nanosensor made by non-assisted carbon nanotube showed zero temperature coefficient of resistance; in the previous studies (2,3) with thin films it has been observed that microcrystalline structure resistors exhibited zero TCR, with amorphous structure showing a negative and polycrystalline structure showing positive TCR. The single walled carbon nanotubes that are deposited are having microcrystalline structure exhibiting insensitivity to temperature. This is probably the first instance of assisted thermal sensor made with single walled carbon nanotubes.
1. K.S.V. Santhanam and G. Lein, Encyclopedia of Nanoscience and Nanotechnology, 24, p.249, (2011).
2. B. Fu, L. Gao, Scripta Materialia, Volume 55, Issue 6, September 2006, Pages 521- 524
3. Q.X. Jia, Z.Q. Shi, K.L. Jiao, W.A. Anderson, F.M. Collins, Thin Solid Films, 196, 29-34 (1991)

Flexible strain gauges made of silicone rubber and carbon nanotubes have been studied for structural health monitoring in aeronautical area, or even for sensors in rehabilition engineering [1,2]. Therefore, studies are needed to investigate the electrical properties of these composites under mechanical deformation in order to optimize the sensitivity and, consequently gauge factor, besides decreasing hystereris of the sensor element[3]. In this work, we produced and characterize the electrical properties of silicone rubber composites with vertically aligned carbon nanotubes (VACNTs) under tensile strain. The silicone rubber composites with VACNTs were produced by both capillar driven infiltration of PDMS (kit Ezsil 44) and vacuum assisted resin transfer moulding in closed molds, depending on the substrate used to grown the VACNT film. The first method is indicated for plain substrate, and the last one for fibrous substrates.
The carbon nanotubes were produced by two methods: thermal and microwave plasma CVD. In thermal CVD[4], the VACNTs were grown on a felt of quartz fiber, using a mixture of camphor and ferrocene. The mixture was evaporated at ~200^oC and carried by a N₂ flow to the pyrolysis zone of a furnace at 850 ^oC at atmospheric pressure. In microwave plasma CVD[5], CH₄/H₂/N₂ gas mixture were used to produce VACNT films on Ti substrates. The morphology and crystalline ordering of the VACNT were investigated by scanning electron microscopy and Raman spectroscopy, respectively.
DC measurements using a Keitlhey multimeter, impedance spectroscopy using a Solartron equipment and softwares of equivalent circuit fitting were used to investigated the electrical properties of each composites under tensile strain. In a large range of frequencies (1Hz to 10KHz) a resistive character is preponderant for both type of composites, and, therefore, they can be used as piezoresitive strain gauges. Composites obtained with VACNT from thermal CVD revealed inductive character, while the composites obtained with VACNT from MW-CVD has a capacitive behavior. The gauge factor was obtained for DC measurements at strain ranges from 0,05 to 0,5, and at certain frequencies where the sensitivy was maximized. For range at microstrains, an apparatus based on a plates deformation was implemented including simulation with Catia software.
[1]I. Kang, M. J Schulz, J. H. Kim, V. Shanov,D. Shi. Smart Mater. Struct. 15 (2006)737-748.
[2]T. Yamada, Y. Hayamizu, Y. Yamamoto, Y. Yomogida, A. Izadi-Najafabadi, K. Hata. Nature Nanotechnology 6(2011)296-301
[3] W. Obitayo and T. Liu. Journal of Sensors (2012) Article ID 652438, 15
[4] V.G. de Resende, E.F. Antunes, A. O. Lobo, D.A.L. Oliveira, V. J. Trava-Airoldi, E. J. Corat. Carbon 48 (2010)3655-3658
[5] E.F. Antunes, A.O. Lobo, E.J. Corat, V.J. Trava-Airoldi I Carbon 45 (2007) 913-921

Due to their exceptional physical and mechanical properties carbon nanotubes have been the subject of considerable attention. Those properties observed at the nanoscale have motivated researchers to utilize carbon nanotubes as reinforcement in composite materials [1]. Previous research has shown that the change in length scale of carbon nanotubes, relative to carbon fibers, enables selective reinforcement of the polymer matrix surrounding a carbon fiber [2]. Some obstacles need to be overcome so that carbon nanotubes can be used as reinforcement in polymer matrix. One of the most significant challenges towards improving the properties of nanocomposites is to obtain a uniform deposition of nanotubes onto the fiber. As the deposition temperature of the nanotubes is very high an elevated exposure time can lead to degradation of the carbon fiber. To overcome this obstacle we have developed a deposition technique where the fiber is exposed to an atmosphere of growth for just one minute. Initially the carbon fiber receives a layer of amorphous silicon, which acts as a diffusion barrier deposited in a plasma assisted reactor, then the fiber is pre-heated at 450 °C and then is exposed to an atmosphere rich in carbon and iron, that works as catalyst particles, at 800 °C for one minute, and the deposition of carbon nanotubes occurs. Density growth and length of carbon nanotubes can be controlled by varying the carbon concentration in the precursor solution. The length of the nanotubes varies from 3 to 15 micrometers. This deposition method can allow us to generate reinforced fibers that can be used in structural composites.
[1] THOSTENSON, E. T. and CHOU, T-W.; Aligned multi-walled carbon nanotube- reinforced composites: processing and mechanical characterization. J. Physics D: Appl. Phys., v. 35, p. L77, 2002.
[2] THOSTENSON, E. T et al., Advances in the science and technology of carbon nanotubes and their composites: a review. Composites Sci. Technol. v. 61, p. 1899, 2001.

The synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and graphene from catalyst on substrate using CVD has massively progressed in the past decade, especially the ability to control the nature of these structures on all length scales and in all aspects of their composition, structure, and morphology. Dense carpets of CNTs/CNFs are an ideal electrically-conductive scaffold for active electrode material. Graphene provides a massive surface area that can be functionalized.
The focus of this presentation is to introduce the audience to the scientific aspects of the synthesis of carbon nanostructures. I will guide the audience through the nucleation and growth mechanisms using a unified model focused on the roles of catalysts, underlayers, reservoirs, and precursor gases using chemical vapor deposition. The mechanisms will be supported by numerous experimental results, such as dense carpets of crystalline CNTs on insulating and metallic substrates, role of thin film reservoirs to enhance CNT growth, self-delaminating growth of large mats of CNFs, and the synthesis of high-quality few layers graphene at reduced temperature.
Finally, I will show applications of these nanostructures as a platform material to energy devices such as batteries and supercapacitors using functionalized dense carpets of mm-tall and vertically aligned CNTs, 3-dimensonal self-assembled CNF mats, and functionalized graphene.

Advances in nanomaterials hold the key for resolving many formidable energy challenges in the 21st century. Although many revolutionary technologies have been developed for a clean, secure and sustainable energy future, economically viable devices with sufficient high energy and power densities for automobiles, portable electronics, and other power tools are still lacking. Supercapacitors (SCs) are poised to address our current energy storage and delivery needs by combining the high power, rapid switching, and exceptional cycle life of a capacitor with the high energy density of a battery. While activated carbon and carbon nanotubes (CNTs) are extensively used as supercapacitor electrodes due to their superior properties, their low specific capacitance (100-120 F/g) fundamentally limits the energy density of SCs. Defects in nanomaterials, which are often dismissed as material performance limiters, can enhance electrochemical properties and are central for improving the current SC performance. Here, we show that the structural, compositional, and morphological defects in carbon nanomaterials can improve the performance from 100-120 F/g to beyond 650-800 F/g. For instance, while helically coiled CNTs improve the double layer capacitance, N-doped CNTs exhibit an enhanced pseudo-capacitance and vacancies in graphene alter the quantum capacitance. Accordingly, we demonstrate that by controlling type, nature, and bonding environment of defects in carbon nanomaterials, one can efficiently tune the double-layer (via changes in surface area), pseudo (by inducing new redox activity) and quantum (through altering the density of states) capacitance of SCs. Most importantly, we developed scalable roll-to-roll processes for producing nanocarbon-based SCs employing various Al current collectors (ranging from simple kitchen Al foil to industry-standard Al cathode) for high energy and power density SCs at a low cost < $1 Wh/Kg. This work is supported by NSF-CMMI scalable nanomanufacturing SNM # 1246800 award, and is a result of strong collaboration with an industrial partner Cornell Dubilier, Liberty, SC. Co-authors include the team members of Profs. P. Bandaru (UCSD), Mark Roberts (Clemson) and R. Podila (Clemson).

Fullerenes and carbon nanotubes (CNTs) have different electronic structures; C60 is known to be a semiconductor and a good electron acceptor while SWCNTs can be either metallic or semiconducting. C60/CNT hybrid nano structures such as peapods constitute a system with different physical properties, accounting from a different band structure. This opens up for engineering materials for a variety of applications in electronics. We will present preliminary results on a novel variant of Peapods. The structures are characterized by high resolution transmission electron microscopy (HRTEM) to track the filling of C60. We also present transport measurements of the hybrid structures. The electrical properties of the structures observed by HRTEM are tested at low temperatures.

Carbon nanotube (CNT) cables with ultrahigh conductivity and light weight are desired in various applications, especially in aerospace, biomedical, MEMS, and electricity transmission. Individual or small bundles of carbon nanotubes (CNTs) are nanocables with high conductivity and ultrahigh current carrying density. However, when they assemble into macroscopic fibers, the conductivity of CNTs drop sharply, mainly due to loose shrinkage and disorder alignment. Here, we fabricated well-aligned, densely-packed, highly-conductive and light-weight CNT cables. These cables were made from continuously grown CNT films by combining mechanically drawing through a series of diamond drawing dies, rolling, and post chemical treatment. Our experimental results show that both mechanical drawing and rolling help to make the loose nanotube films into dense fibers. The loose CNT films are densely shrunk into cables and CNT bundles aligned along the cables after drawing or rolling and the density of CNT cables increase significantly from 0.1~0.3 g/cm³ to 0.8~1.3 g/cm³, which is still only ~1/9 to that of copper. Meanwhile, the post-treatment, such as chemical purification, acid doping, and iodine doping can improve the electrical conductivity of CNT cables independently. Although most of the CNTs are semiconducting according to Raman spectra, the electrical conductivity of the macroscopic cables still reach to (~2×10⁶ S/m), which is 1~2 order of magnitude higher than most of the CNT fibers reported in literature. The CNT cables shows great potential applications in the near future if ones can controllably grow metallic CNTs.

Thomas Swan & Co. Ltd. are a world leader in the supply of single wall carbon nanotubes (SWNT). Our Advanced Materials Division were early investors in the technology, forming a strong collaboration with the University of Cambridge to develop a scalable process for SWNT manufacture. Launched in 2004, our carbon nanomaterials business continues to add capabilities as we target a variety of market applications. Today, Thomas Swan has multi-kilogramme capabilities in manufacturing both SWNT and MWNTs which deliver value for our customers in new and emerging markets, from printable electronics, memory devices and storage to advanced coatings and composite systems.
On-going fundamental R&D is crucial to the success of our business. In-house R&D programs target a number of core areas including CNT growth control and optimisation, CNT purification and CNT functionalisation. We also work with a range of academic and industrial partners on similar research streams as well as more targeted product development programs.
This presentation will give an overview of the range of CNT activities on-going at Thomas Swan, from the early days of scale up through to market adoption and commercialisation.

The vast majority of industrial scale Carbon Nanotube (CNT) production involves short nanotubes (< 100 microns) that appear as a powder. These products are typically utilized as minor components (usually less than 2%) in polymers where they may or may not impart marginal improvements in composite properties. At Nanocomp Technologies we produce large-format CNT material by floating catalyst chemical vapor deposition. This technique produces very long CNT&’s (> 1 mm) in the gas phase, where entanglement produces large format material of exceptional strength and electrical conductivity. By manipulating the physics and chemistry of the process, the format and properties of the material can be controlled. Post-production processing further enhances the desired material properties. In this way applications such as Ballistics, Wiring and Cables for aerospace, and Integrated Energy Storage can be realized.

The unique optical properties of carbon nanotubes (CNTs) are very promising for the development of novel opto-electronic components and sensors with applications in many fields. Despite numerous studies performed using photoluminescence or Raman and Rayleigh scattering, knowledge of their optical response is still partial, in particular direct and quantitative access to the intrinsic absorption characteristics of CNTs is still challenging. Nevertheless, the understanding of absorption processes occurring in carbon nanotubes is crucial for future applications, and more precisely this comprehension should occur at the individual nanotube level.
We show here that the spatial modulation spectroscopy (SMS) technique applied to the investigation of individual CNTs, provides direct access to the absolute absorption properties of these materials^1,2. Using this approach, we have determined, over a broad optical spectral range, the absorption spectrum of semiconducting individual SWNTs and the oscillator strength of their different excitonic resonances. A non-resonant background is also identified and its cross-section comparable to the ideal graphene optical absorbance. Furthermore, investigation of the same SWNT either free-standing or lying on a substrate shows large broadening of the excitonic resonances, as well as strong weakening of polarization-dependent antenna effects, due to SWNT-substrate interaction. At last, the combination of the SMS absorption method and Raman spectroscopy provides an all-optical characterization of individual double-wall carbon nanotubes. The latter materials might provide a new route for the development of carbon-nanotube-based structure with hybrid optical and electrical properties.
[1] D.Christofilos , J-C.Blancon , J.Arvanitidis, A.San Miguel, A.Ayari, N.Del Fatti and F.Vallée, Journal of Physical Chemistry Letters 3, 1176 (2012).
[2] J.-C. Blancon, M. Paillet, H.N.Tran, X.T.Than, S. Aberra-Guebrou, A. Ayari, A. San Miguel, N-M. Phan, A-A. Zahab, J-L. Sauvajol, N. Del Fatti and F. Vallée, Nature Communications 4:2542 doi:10.1038/ncomms3542 (2013).

Triplet excitons and triplet-triplet interactions in single-wall carbon nanotubes have eluded detection for many years. Here we report on spin sensitive study of different triplet excitons in (6,5) SWNTs with lifetimes of (30±10)µs and asymp; 1 ms as determined from the modulation frequency dependence of optically detected magnetic resonance (ODMR). The quantum yield of triplet exciton production of the shorter lived species of (5±2)% is likewise obtained using ODMR. We also observe long lived photoluminescence signals attributed to delayed fluorescence from triplet-triplet annihilation. The power-law decay of pump-probe and time-resolved photoluminescence from this long lived process is characteristic of diffusion-limited annihilation in one-dimensional systems and allows an estimation of the triplet diffusion constant of 0.1 cm² s^-1. We will also present preliminary results of ODMR experiments on oriented SWNT samples.

Carbon nanotubes have been studied by researchers and experiments have shown a strong interaction between tubes and substrate inducing important deformation of the nanotube on top of substrate [1, 2]. In this work, carbon nanotubes were grown by catalytic chemical vapor deposition (CVD) on quartz substrate [3]. Nanotube epitaxy combined with gas flow directed leads to the formation of serpentines, i.e. SWNTs with parallel straight segments connected by alternating U-turns [3-6]. We employed confocal Raman spectroscopy with atomic force microscope (AFM) setup to study single wall carbon nanotubes (SWNTs) serpentines deposited on quartz. SWNT was pulled with a tip. The manipulation was performed dragging the SWNTs serpentines at xy-direction on the substrate and structural modifications were observed. The Raman spectrum change along the SWNT when manipulated with a gold tip. We observed a modification in the G-band frequency along the tube and not only in a specific point where dragged the tube. Under uniaxial stretch, only a downshift is observed for certain G modes due to the elongation of C-C bonds in the axial direction [7]. These results can be attributed to an interaction between the SWNT and substrate. When we drag the tube in a specific place, we change this interaction along the carbon nanotube, but the tube moves just at the point where it was pulled. This confirms the strong electronic interaction between the carbon nanotubes and the quartz surface.
Acknowledgments
J.S.S., N.M.B.N. and A.J. acknowledge financial support from CNPq, CAPES and FAPEMIG. E.J. acknowledges support from the Israel Science Foundation, the US-Israel Binational Science Foundation, the Kimmel Center for Nanoscale Science, and the Legrain, Djanogly, Alhadeff and Perlman Family foundations.
References
1. J. S. Soares et al. Nano Lett.10, 5043 (2010).
2. M. Steiner et al. Appl. Phys. A 96, 271 (2009).
3. N. Geblinger et al. Nature Nanotech. 3, 195 (2008).
4. S. Jeon et al. Nano Res.1, 427 (2008).
5. J. Huang et al. Nanotechnology19, 505601 (2008).
6. J. Xiao et al. Nano Lett.9, 4311 (2009).
7. X. Duan et al. Nano Lett. 7, 2116 (2007).

We have modulated the diameters and morphologies of SWNTs for the applications of SWNT/Si solar cells [1, 2], organic bulk heterojunction solar cells, dye-sensitized solar cells and perovskite-type solar cells. Highly transparent-conductive SWNT films from controlled bundle-diameter and long bundle length were synthesized by floating catalyst CVD. The SWNT films with a sheet resistance of 134 Omega;/sq. at the 81.5% transparency were dry-transferred onto Si substrate to form a diode. The power conversion efficiency (PCE) of the solar cell is 11% and is stable after 1 year, which is attributed to the high purity pristine SWNTs. Moreover, the solar cell performance under different light intensities is investigated to evaluate both the series and shunt resistance of the device. The interfacial oxide layer between the SWNT film and the Si substrate is also discussed [1].
In order to further improve the performance of the solar cell, we investigated the effect of the SWNT morphology. Using the vertical-aligned SWNT arrays synthesized by alcohol catalyst CVD method, we have obtained a hierarchical 3D honeycomb-like architecture of SWNTs using the breath figure technique, where water vapor condenses on the surface of vertical-aligned SWNT and forms hexagonal pattern. The micro-honeycomb network consists of vertical aggregated SWNT walls and a buckypaper bottom. This hierarchical structure exhibits lower sheet resistance and higher optical transmittance compared with the buckypaper. The honeycomb networked SWNT film was transferred onto the 3 mm by 3 mm n-type silicon substrate by hot water thermocapillary method. The pristine SWNT-Si solar cell shows a record-high fill factor of 72% as well as a PCE of 6%. The PCE remains stable for months in ambient condition. A PCE exceeding 10% is achieved in the dry state after dilute nitric acid treatment. Through modeling, the honeycomb-networked SWNT film shows much smaller series resistance than random-oriented SWNT film [2].
By using cobalt-copper binary metallic catalysts, we have reduced the diameter of the VA-SWNT from 2 nm to less than 1 nm, with the E₁₁ of SWNTs increasing from 0.5 eV to 1.2 eV. The effect of the diameter change on the solar cell performance will be discussed. Moreover, we fabricated both bulk heterojunction solar cells and dye-sensitized solar cells using the SWNT films to replace the ITO layer, with little degradation in performance. The application of SWNT films as hole-collector in the perovskite-type solar cells is also promising.
References:
[1] K. Cui, A. S. Anisimov, T. Chiba, S. Fujii, H. Kataura, A. G. Nasibulin, S. Chiashi, E. I. Kauppinen, S. Maruyama, J. Mater. Chem. A, (2014), DOI: 10.1039/C4TA01353K.
[2] K. Cui, T. Chiba, S. Omiya, T. Thurakitseree, P. Zhao, S. Fujii, H. Kataura, E. Einarsson, S. Chiashi, S. Maruyama, J. Phys. Chem. Lett., 4 (2013) 2571.

New composite materials made by adding carbon nanotubes (CNT) to various materials such as alloys, polymers, and metals are expected to have enhanced mechanical strength, electrical and thermal conductivity, and chemical stability in comparison to its base constituents. Unfortunately, pure CNT are not soluble in water or in organic solvents and have tendencies to aggregate. This drastically limits its usage in industrial applications. Chemical functionalizations of CNT allow for improved bonding of CNT into the composite matrix, however, may weaken the stiffness of pure CNT[1]. Carboxylation is an important process[2].
There are few theoretical studies of carboxylated CNT, however, the picture which they present is incorrect. Many people have falsely believed that the common oxidizing acid functionalization treatment yields CNT with -COOH groups added to the sidewall. In particular, carboxylation is done by reagents not containing carbon (i.e. nitric acid) so the C in the -COOH linkage is one of the CNT backbone carbons. The three bonds in the CNT wall are broken and this introduces major damage to the wall which affect structural, electronic and mechanical properties, and has been even shown to lead to spontaneous degradation[3].
We present results of extensive theoretical studies of structural and mechanical properties of carboxylated CNT. They are based on the ab initio calculations in the framework of the density functional theory. We have performed calculations for various metallic and semiconductor, single- and multiwall CNT, imperfect and carboxylated at various concentrations, including disorder. We analyze morphology, determine the stability (binding energy) of carboxylated CNT and calculate their elastic moduli (Young&’s, Shear, Bulk & Poisson&’s ratio). We also compare properties of grafted (-COOH, -OH, -O) and imperfect (vacancy defects) CNT with carboxylated ones. In particular, we show that both, structural and elastic properties, especially, dependence of Young&’s modulus on concentration of grafted groups or vacancies differ much between previously studied systems and those which are truly carboxylated. We explain experimental observations showing that small concentration of -COOH groups will improve strength on CNT in comparison to defected one. We find out the critical concentration above which the carboxylation of CNT will lead to significant changes in structure of tube, resulting in significant decrease in Young&’s modulus making it unsuitable as enforcement in composites. Moreover, we show the governing mechanisms of reduction of CNT toxicity in the case of carboxylation. These studies shed light on physical mechanisms governing the carboxylation process and also provide valuable quantitative predictions that are of importance for design of novel composite materials and functional devices.
[1]K.Z.Milowska et al.,PCCP,15,14303(2013)
[2]S.W.Kim et al.,Carbon,50,3(2012)
[3]X.Liu et al.,Carbon,48,1961(2010)

Single-walled carbon nanotubes (SWCNT) are the subject of a wide range of researches due to their unique properties and versatility. Functionalized SWCNT have been broadly explored in various researches areas because of advantages they present in respect to non-functionalized ones. In general, obtaining a good dispersion of SWCNT in polymeric matrices is a difficult task to accomplish. However, functionalized SWCNT are more easily dissolved than non-functionalized ones, helping to attain such task. A uniform distribution is desired for optical applications, since SWCNT agglomerates reduce the optical quality of the composite materials. Furthermore, functionalized SWCNT can be employed also in electronic, optical and biological applications. As a promising microfabrication technique, two-photon polymerization (2PP) has been used in the production of various types of functional polymeric microstructures. The use of doped polymers in the production of microstructures opened up a range of new possibilities in the fabrication of microdevices. Combining SWCNT special properties with the fabrication of microstructures paves the way for the development of a whole new class of functional microdevices. In the present work, we report the fabrication of 3D polymeric microstructures with carboxylic acid functionalized SWCNT, using a range of SWCNT concentrations from 0.01 up to 1 wt%, evaluating its distribution into the structures. The structures present good surface quality and integrity, even when a high SWCNT concentration was employed. The Raman analysis indicated a good distribution of SWCNT throughout the microstructure. These results show that such doping might be useful to provide microstructures with enhanced mechanical and electrical properties, bringing new possibilities for microdevices fabrication. Also, using functionalized SWCNT, we can expand the application of two-photon polymerized microstructures, for instance, in optical and biological applications.

Multi-wall carbon nanotubes (MWCNT) can be used to create ceramic nanocomposites with improved fracture toughness. In the present work, we altered the nanotube surfaces with atomic layer deposition (ALD); the coated CNTs were used then made into nanocomposites using a polymer derived ceramic (PDC) to create the matrix. The hardness and elastic modulus of the nanocomposites were measured by nanoindentation and the matrix-CNT interfacial properties were tested with a novel in-situ pullout apparatus. By systematically changing the ALD coating materials (Al₂O₃, TiO₂ and HfO₂) and varying the coating thickness, the overall mechanical properties of the composite were varied. Our findings also provide overall guidance on controlling the strength and toughness of ceramic nanocomposites by modifying CNT surfaces.

The electrical performance of semiconducting materials can be strongly affected by point defects. In carbon nanotubes (CNTs), a wide variety of defects are possible (both chemical and electrostatic) with an equally wide variety of electronic consequences. Understanding these electronic consequences is critical for high performance CNT transistor applications, as well as CNT sensor application. I will discuss our recent measurements of three types of carbon nanotube defects: (1) oxidative point defects, (2) electrostatic barriers generated by charge traps, (3) sp3-bonded phenyl groups. The defects we study are either naturally occurring, created by scanning probe modification, or created by chemical modification of the CNT sidewall. In all cases, real-time electrical measurements are invaluable for monitoring defect creation and identifying single defects. We show that a single sp3-bonded phenyl groups has minimal effect on device properties, while certain oxidative defects dominate global device properties. We also confirm recent theoretical predictions for carrier scattering from a Coulomb barrier in a CNT, and the dependence of this scattering probability on gate voltage.

There has been growing interest in recent years in reinforcing polymers with different types of nanostructures to produce nanocomposites. At the same time there have been new developments in the field of carbon-based nanomaterials with the discovery of carbon nanotubes and graphene with impressive mechanical properties. The presentation will show how Raman spectroscopy can be used to characterize these carbon-based nanomaterials and in particular how it can be employed to follow their deformation in nanocomposites from stress-induced Raman bands shifts. The aim of this presentation is to determine how stress transfer takes place both between the nanomaterials and the polymer matrix and between the different carbon layers within the reinforcement. In particular, the mechanics of the deformation of single-, double- and multi-walled carbon nanotubes will be compared and it will be shown that inter-wall stress transfer by shear between the individual walls of the nanotubes has an important effect upon controlling their ability to reinforce polymers. Large stress-induced Raman bands shifts are found during deformation as a result to stress transfer from the matrix to the nanotubes. Band broadening is found during deformation with the single-walled nantoubes whereas it is found that band narrowing occurs for the double- and multi-walled nanotubes. This has been interpretated as being due to lower levels of stress in the inner walls as the result of poor internal stress transfer and the behavior has been modelled fully. In general it is found that this internal stress transfer is only up to 70% efficient leading to inferior mechanical properties for double- and multi-walled nanotubes in nanocomposites compared with their single-walled counterparts.

Novel electromechanical properties of Carbon nanotube (CNT) enable their great potential in many fields. However, correlating the property and the structure of the same CNT is still challenging. Here, using our newly developed in situ platform inside a scanning electron microscope (SEM) [1], we study the strain-induced bandgap change and electric induced vibration of CNT and correlate them with the atomic structure of the CNT. Individual CNTs are placed across the pre-fabricated source and drain electrodes on the platform by nanomanipulation [2]. The CNT is stretched precisely by changing the distance between the source and drain electrodes [3] and its electrical property is measured at each strain. On one hand, the strain-induced bandgap change, dE_gap/dε, is extracted from the measured transfer curves of the CNT devices at different axial strain [4]. On the other hand, the theoretical predicted dE_gap/dε of the same CNTs are calculated [5] using the diameter and chirality of the CNTs determined through transmission electron microscopy [2]. For the first time, the experimental obtained dE_gap/dε agrees quantitatively with the theoretical prediction. We also find that dE_gap/dε of double-wall CNT and triple-wall CNT are mainly determined by their outer wall chirality. Electric induced vibration of CNT is studied using a resonator structure similar to that reported previously [6]. The resonance frequency of our CNT resonators is tuned not only transversally by a gate voltage, but also by the axial strain of the CNT. The resonance frequency of a single-wall CNT resonator is tuned by more than 20 times when the axial strain of the CNT is only increased from nearly zero to 2%. The transversal gate-tuning ability is weaker than the axial-tuning ability, and decreases with increasing the axial strain. The obtained relationship among the resonance frequency, the gate voltage and the axial strain will allow for the design of novel CNT resonators.
References:
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[3] Z. Y. Ning, M.Q. Fu, T. W. Shi, Y. Guo, S. Gao, X. L. Wei, Q. Chen: Nano Lett., 14 (2014), 1221.
[4] E. D. Minot, Y. Yaish, V. Sazonova, J.-Y. Park, M. Brink, P. L. McEuen: Phys. Rev. Lett., 90 (2003), 156401.
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Despite the exceptional mechanical properties exhibited by individual Carbon Nanotubes&’ (CNTs), weak van-der-Waals forces greatly reduce their macro-scale performance. We have conducted carbon-ion implantation to achieve enhanced inter- and intra-wall shear interaction in CNT systems. In situ Transmission Electron Microscopy (TEM) was used to perform tensile, shear and frictional studies on joule-heated/post-irradiated and as-irradiated CNT bundles. A substantial increase in the tensile and shear strength for as-irradiated CNTs bundles up to ~14.73 GPa and ~318.95-578.37 MPa, respectively, and a shear strength exceeding ~1.17 GPa when exposed to additional amorphous-carbon binding, was observed. The static friction, residual adhesive force and adhesion energy increased remarkably, from 132.4 nN to 585.8 nN, from 5-30 nN to 315 nN, and from ~0.71-1.64 J m^-2 to >~136.96 J m^-2, respectively, for two joule-heated bundles in contact compared against a joule-heated bundle in contact with an as-irradiated bundle. The results exceed theoretical expectations for improvements in the tensile strength of CNT bundles by means of carbon-ion irradiation, are comparable to the strength of CNT bundles irradiated with electrons, verify the validity of carbon-ion irradiation as a means of addressing weak load transfer and reveal the extent to which high energy points such as defects, a-C and oxygen-containing functional groups can improve the interfacial adhesion between CNTs. These findings will provide new routes for large-scale fabrication of high strength, stiffness and toughness CNT mats, yarns and composites, high-friction gecko-like CNT-based components and adhesives, and super-strong welds.

Fibres and other macro-assemblies composed of CNTs are often questioned regarding their tensile strength, as the initial hype over carbon nanotubes arose from predictions of the strength of individual graphene layers, encouraged by measurements of individual MWCNTs and SWCNT bundles in AFM [1, 2]. Further inspired in the famous space elevator article [3], the publicity assumed that these figures could also be readily realized in materials made from these components.
It&’s against a background of this enthusiasm, and against the opposing fact that carbon-carbon surfaces are used as lubricants, DWCNTs being even suggested as super-lubricants [4], that we examine the gradual improvement in strength of macroscopically useful materials. Yarn-like fibres composed of carbon nanotubes produced by the direct spinning process [5] have been used as the subject of this study. Here, we will re-examine the response of nanotube aggregates to applied tensile stress comparing FEA models with experimental work, in an attempt to answer how to ideally transfer the properties of individual nanotubes into macro-assemblies.
[1] M.-F. Yu, O. Lourie, M. J. Dyer, K. Moloni, T. F. Kelly, R. S. Ruoff, Science 287, p.637 (2000)
[2] M.-F. Yu, B. S. Files, S. Arepalli, R. S. Ruoff, Phys. Rev. Lett. 84, p.5552 (2000)
[3] B. I. Yakobson, R. E. Smalley, Amer. Sci. 85, p.324 (1997)
[4] R. Zhang, Z. Ning, Y. Zhang, Q. Zheng, Q. Chen, H. Xie, Q. Zhang, W. Qian, F. Wei, Nat. Nanotech. 8, p.912 (2013)
[5] Y.-L. Li, I. A. Kinloch, A. H. Windle, Science 304 p.276 (2004)

Carbon nanotube research community is spending lots of resources to develop purification and dispersion processes for bulk synthesized SWCNTs to realize high performance devices consisting of individualized SWCNTs. Bundling is especially detrimental for the SWCNT network transistors, where it leads to increased leakage currents and poor gate field coupling. Ideally, the synthesis processes should be optimized to produce - directly and without additional processing steps - pure and highly individualized SWCNTs. Floating catalyst CVD synthesis process has the potential to meet these goals.
Here, we present our recent progress on synthesis of individual, ultra-pure and long SWCNTs with a floating catalyst reactor by implementing real-time concentration and particle size control by utilizing a differential mobility analyzer and a condensation particle counter. This approach enabled us to controllably reduce the SWCNT concentration of the aerosol, leading to reduced bundling probability and formation networks consisting of dominantly individual SWCNTs with mean diameter of 1.3 nm and a narrow helicity distribution near armchair edge, as observed with high resolution AFM, TEM and electron diffraction techniques.
The SWCNT networks exhibit excellent performance as transparent conductive films with sheet resistances as low as 60 Ohm/sq. a 90 % transparency with high uniformity and low surface roughness. We also fabricated thin film transistors on silicon substrate using the low density SWCNT networks as the channel material. The SWCNT TFTs exhibit high charge carrier mobility of >100 cm^2/Vs and ON/OFF ratios up to 10^7, suggesting application potential of these devices for integrated electronics.

Significant enhancement of gravimetric hydrogen storage capacities of carbon nanotubes (CNT) is achieved by a stepwise process including acid treatment and polymer coating. The influence of each step on the structural parameters of multi-walled CNT and their composites is investigated by changing the feeding ratio of polymer and type of oxidation process. It is found that polypyrrole (PPy) coating decreases both surface area and pore size of CNT but improves hydrogen uptake capacity by increasing the distance between CNT bundles. Acid treatment leads to reduction of carbon to oxygen ratio and the formation of hydrophilic surface. Therefore, hydrogen absorption/desorption kinetics of CNT and their composites are enhanced by increased absorption sites after chemical functionalization, and hydrogen is not released from functionalized CNT during desorption process due to chemical interactions. On the other hand, non-functionalized CNT absorb hydrogen physically and then release it easily. The hydrogen sorption measurements at ambient conditions by Intelligent Gravimetric Analyzer (IGA) demonstrate that hydrogen uptake of CNT/PPy composite is 1.66 wt.% which is almost 3 times higher than that of pure CNT. IGA measurements proves the effect of polymer coating on hydrogen uptake values of CNT and the relationship between the functionalized surface and hydrogen sorption characteristics of CNT.

Carbon nanotubes (CNTs) create a unique nanofluidic system for studying the dynamics of ion transport in nanochannels due to their well-defined and simple chemical structure, atomically smooth and chemically inert surface, easily functionalizable ends and similarity to transmembrane protein pores. Carbon nanotube based smart membrane devices were designed as an outstanding architecture for ion transport studies. Molecular transport through hollow cores of crystalline carbon nanotubes is of considerable interest from the fundamental and application point of view.
The fabricated devices contain an array of densely packed, open-ended and vertically aligned carbon nanotubes (~4E+10 tubes/cm²). Each individual CNT has an inner core diameter of ~5 nm, incorporated across a polymer film to form a well-ordered, nanoporous membrane structure. The concentration gradient ion diffusion study was done by applying the potassium ferricyanide aqueous solution as feed ions. Ionic flux through the CNT membrane was monitored using a differential pulse voltammetry (DPV) technique to define the transported ion concentration. In order to explore the effect of CNT ends chemical modification on the ion transport through the CNT membrane, ionic flux through a composite membrane structure was studied with and without the presence of chemical end groups at the entrance of CNT cores. Plasma oxidation was applied in order to open the tips of carbon nanotubes and also activate the ends with carboxylic groups. Results indicated that the molar flow rate of ions through the CNT cores with carboxylic groups was 4.74E-4 mmol/h. These carboxyl groups were functionalized by an amine-modified molecule that bonded to a bulky receptor. These molecules enabled the pore entrance to open and close. In particular, to design a smart CNT membrane, the core entrances of aligned CNT membranes were functionalized with amine-modified probe single stranded DNA (ssDNA) that binded reversibly to complimentary DNA (cDNA). Thereby, the functionalization enabled a reversible closing and opening of the CNT core entrance. When the amine-modified ssDNA was covalently bonded to the CNT, the flux was reduced to 2.82E-4 mmol/h. Interestingly, membranes with CNT tips that were functionalized with ssDNA indicated a 100% reduction in the ion flux when bounded with cDNA; release of cDNA increased the flux, demonstrating a reversible ion-channel flow. Therefore, this study demonstrated the ability to gate molecular transport through CNT cores for potential applications in time releasing mechanism for drug delivery systems, chemical separations and DNA sensing.

Self-propagating exothermic chemical reactions can generate electrical pulses when guided along a conductive conduit such as a carbon nanotube. However, these thermopower waves are not described by an existing theory to explain the origin of power generation or why its magnitude exceeds the predictions of the Seebeck effect. In this work, we present a quantitative theory that describes the electrical dynamics of thermopower waves, showing that they produce an excess thermopower additive to the Seebeck prediction. Using synchronized, high-speed thermal, voltage, and wave velocity measurements, we link the additional power to the chemical potential gradient created by chemical reaction (up to 100 mV for picramide and sodium azide on carbon nanotubes). This theory accounts for the waves&’ unipolar voltage, their ability to propagate on good thermal conductors, and their high power, which is up to 120% larger than conventional
thermopower from a fiber of all-semiconducting SWNTs. These results underscore the potential to exceed conventional figures of merit for thermoelectricity and allow us to bound the maximum power and efficiency attainable for such systems.

Introducing intra-molecular junctions between carbon nanotubes in the form of organic molecular linkers allows for simultaneous de-bundling and connecting of the nanotubes at tunable distances. Careful engineering of the molecular linker controls the geometry of the assembly and influences the electronic, optical, thermal and mechanical properties of nanotubes.
We present a comparison of different synthetic approaches towards obtaining interconnected single wall carbon nanotubes (SWCNTs) with the use of diamine molecular linkers. For example, a comparison of the effectiveness of 1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) versus thionyl chloride application as coupling reagents is studied. The commercially obtained tubes that are used in this research are thoroughly cleaned and subjected to mild nitric acid reflux treatment. It ensures retention of basically pristine mechanical and electronic properties of tubes while opening the caps and forming oxygen-containing groups at defect sites along the sidewalls. We carefully choose purification techniques to obtain composites of the best quality without the precursor impurities. Better understanding and control over local covalent functionalization density and distribution may be the key to successful fabrication of electronic devices based on SWCNTs such as molecular diodes or single electron transistors. Therefore we attempt to quantitatively estimate the interlinking extent using the Near Edge X-Ray Absorption Fine Structure (NEXAFS) technique and Fourier Transform Infrared Spectroscopy (FTIR). To assess the quality of the obtained material various other analytical techniques are applied, such as: Transmission Electron Microscopy (TEM), Raman Spectroscopy, and Thermogravimetric Analysis (TGA).

The helical assembly of self-organized flavin mononucleotide (FMN) around single-walled carbon nanotubes (SWNTs) presents among the highest organization order in nanotube surfactants. In this contribution, we quantitatively analyze and model for the first time the cooperative hydrogen bonding of adjacent flavin moieties as well as the concentric π-π interactions between the isoalloxazine moieties and the underlying graphene lattice as a function of (n,m)-SWNT chirality. For this we use dissociation thermodynamics of FMN-wrapped (n,m)-SWNTs dispersed in both H₂O and D₂O as a function of FMN concentration. The binding strength of these FMN assemblies has been assessed in terms of ΔH, ΔS and ΔG. Atomistic molecular simulations were used to modeled these data and link their dependence in terms of nanotube diameter (dt) the chiral angle (theta;). The findings of this study provide the first quantitative proof of the quasi-epitaxial assembly of FMN around various (n,m)-SWNTs.[1] This study demonstrates the architectural fidelity of FMN-wrapped SWNTs that closely emulates the dissociation mechanics of double-stranded DNA in its aqueous solutions.
^[1] Sharifi, R.; Samaraweera, M.; Gascoacute;n, J. A.; Papadimitrakopoulos, F.; J. Am. Chem. Soc., 2014, 136(20), 7452-7463

Single-Wall Carbon nanotubes (SWCNTs) can be dispersed with the help of nanofibrillated cellulose (NFC), resulting in dispersions with high colloidal stability and quality that can be exploited into preparation of composites with high electrical conductivity and strength.
Dispersing SWCNTs from bundles into individualized tubes in polymer matrices is challenging. Therefore, alternatives such as chemical functionalization and using surfactants have been used to improve its dispersion, both of which have their own repercussion on mechanical and electrical properties of the final composite. We hereby report a self-assembly route for creating inexpensive, strong and highly conductive NFC composites. This is made by showing the novel discovery that NFC itself can act as a superior dispersion and purification agent for SWCNTs in water. The quality of the NFC/SWCNT dispersions were carefully analyzed using Raman spectroscopy, UV-vis-NIR spectroscopy and dynamic light scattering. All the hybrids were further analyzed in terms of structural morphology, mechanical and electrical performance. We demonstrate that this dispersion is suitable for self-assembly of functional nanocomposites including random-network nanopaper, aerogel and anisotropic microfibers. These can be used in many applications such as electronic textiles, nanopaper substrates, energy storage devices and supercapacitors.
Another step is to analyze the dispersion in order to understand the mechanism behind the favorable SWCNT dispersion. The effect of processing parameters are studied. The goal is to reduce agglomeration of SWCNTs and increase SWCNT content. Molecular interaction between nanocellulose and SWCNT is therefore studied. This can open new possibilities for nanocellulose-assisted dispersions of other inorganic nanoparticles such as multi-wall carbon nanotubes, graphene and other nanoparticles and nanorods.

Carbon fiber reinforced polymer composites (CFRPs) are replacing traditional structural materials, due to their outstanding in-plane strength and stiffness. However they lack sufficient out-of-plane and interlaminar performance. Recently, integrating nano-sized reinforcement into the CFRP structures was shown to eradicate these weaknesses. Zin oxide (ZnO) nanowires and carbon nanotubes (CNTs) are among nano reinforcement additives. In the present study, a low temperature (85°C) hydrothermal synthesis technique is utilized to grow ZnO nanowires on the surface of woven carbon fiber fabrics. A relatively low temperature CNT synthesis; graphitic structures by design (GSD), is also employed for grafting multi-walled carbon nanotubes (MWCNTs) on top of the carbon fibers and on the ZnO nanowires. These two synthesis techniques induce different surface treatment on the carbon fibers including the exposure to elevated temperatures, amorphous ZnO coating, water-soaking, ZnO nanowires growth and CNTs growth. Carbon fiber fabrics based on these different surface treatments were utilized to fabricate composite laminates. The energy absorption capabilities of the different hybrid composites were examined via out-of-plane high velocity (~90m/s) impact tests. A 20% improvement in the impact absorption energy of the CFRPs comprising surface grown ZnO nanowires and MWCNTs was achieved, compared to the composite laminates based on the raw fibers with no surface treatments.

Desalination of seawater remains the only source of potable water for many Gulf countries. Improvement of desalination technologies performance will increase not only the quality of the potable water that communities get access to, but also will reduce the high cost of desalinated water production for human consumption. Capacitive deionized (CDI) techniques stand in need of electrodes with very specific requirements, among which high surface area, excellent electrical conductivity and increased electro-sorption capacity; improved chemical stability; reduced pore size for better ion separation; and material and processing costs comparable with other potable water production techniques, are in the top of the list. In the present work, a wide range of material characterization techniques are implemented to determine the properties of a noble highly aligned carbon nanotube - cellulose thin film membrane intended for CDI electrodes. The sample is imaged using scanning electron microscopy (SEM) and atomic force microscopy (AFM), indicating multi-wall carbon nanotubes with a diameter of 30-50 nm. The electrical conductivity of the sample is determined by both, macroscopic and high spatial resolution (conductive AFM) techniques, leading to values of σ=10⁴ - 10⁵ S/m. This result in addition to the SEM and AFM images allow us to determine whether the CNT based membrane yields a local metallic behavior. Brunauer-Emmett-Teller (BET) is used to determine the surface area of the aligned carbon nanotubes raw material leading to ~100 m²/g, again in compliance with CDI electrodes application. Preliminary porosity estimations indicate it is in the range of 65 to 80%. The high porosity is evidenced in an evolving macroscopic static contact angle whose change with time is related to membrane water absorption. Static contact angle measurements of droplets grown within an environmental scanning electron microscope (ESEM) show a more precise story of the evolution of the droplets indicating a super-hydrophobic initial behavior (theta; ~ 140^o), which evolves up to the initial values of macroscopic contact angles of 100^o. Finally, the electro-sorption capacity is determined by cyclic voltammetry using Stern model.

An improved, high strength, carbon fiber derived from islands-in-a-sea bi-component gel spun polyacrylonitrile (PAN) - carbon nanotube (CNT) precursor fibers containing 1 wt % mixture of single, double and few walled CNTs has been developed. While in most composite systems CNTs are used as a reinforcing element, the presence of CNTs in the present carbon fibers aimed at modifying the structure of the carbon matrix and consequently the properties of the carbon fiber itself. Novel microscale experiments provided the properties of individual carbon-CNT fibers of 1 mu;m diameter. The highest strength and Young&’s modulus values were 7.3 GPa and 318 GPa, respectively, which exceeded the properties of the highest strength commercial carbon fibers. The statistics of mechanical strength were described by a cumulative Weibull probability density function that resulted in Weibull characteristic strength of 6.2 GPa and Weibull modulus of 4.5. The highest strength carbon fibers contained a large number of long and oriented CNTs that protruded from the failure cross-sections. In high strength fibers carbon matrix was attached to the CNTs after fiber failure suggesting strong CNT-carbon matrix interaction. The role of CNTs in the failure process was investigated in situ by mechanical experiments inside a transmission electron microscope (TEM). The experiments showed sword-in-sheath failure of the CNTs which was followed by telescopic pullout from the carbon fiber. This mode of failure controlled the ultimate fiber strength. Furthermore, in situ scanning electron microscope (SEM) single nanotube pullout experiments provided a lower limit for the average interfacial shear strength between the CNTs and the carbon matrix as 110±15 MPa.

Carbon nanotubes have been considered for applications such as electronics, sensors, and composites due to their superlative properties that have been the focus of research efforts over the past 20 years. Nanotubes are routinely added to polymeric materials for enhanced mechanical and thermal properties. One application of carbon nanotubes has been as an additive to slow the thermal degradation of polymers under slow heating rates typically experienced in thermogravimetric analysis and flammability research. However, rapid heating rates induced by laser pulse heating have not hitherto been studied. In our work, the carbon nanotube composites are subjected to heating rates five orders of magnitude higher than traditional studies. The heating rates are achieved with a 1064 nm Nd-YAG variable pulse millisecond laser. We have found that the carbon nanotubes form a protective networked layer on the surface of the composite, which, in return, reduces heat input to the underlying polymer and slows mass loss. The effectiveness of the network layer has been found to be a function of nanotube loading and dispersion quality. Microscopy and spectroscopy studies have shown that the nanotubes remain intact on the surface. The behavior of the nanotubes under single pulse and multi-pulse conditions, as well as in thermo-oxidative and inert atmospheres, will be presented.

Filler-matrix interactions are key for dictating the composite mechanical, thermal and electrical properties, as well as related applications such as high strength fibers, multifunctional coatings, and thermoelectric devices. Full fundamental understanding of the filler-matrix interfacial interactions through studies of the microstructure in common composites remains a challenge. One reason for this is due to the presence of non-interacting components such as bulk-polymer or filler agglomerations. In this work, a new technique for preparing polymer-based single-wall carbon nanotube (SWNT) buckypapers (BP) is outlined. This hybrid polymer/SWNT buckypaper (hPBP) exhibits a unique structure and through-thickness variation in properties. The hPBP is fabricated using a new processing approach involving a simple one-step filtration method combined with liquid-solid phase separation step. As a result a graded architecture is formed in the hBPB ranging from a nano-carbon rich to a polymer rich layer. Scanning electron microscope and wide-angle X-ray diffraction results provide details about the hPBP structural make-up. Thermogravimetric analysis and tensile tests have also been utilized to study the thermal and mechanical properties of resultant materials. In addition, through thickness, electrical properties were also probed.

Single wall carbon nanotubes (SWNT) functionalized with azobenzene chromophores offer a diversity of optoelectronic applications based on optical modulation of the cis/trans isomerization dynamics of the chromophore. We have developed a hybrid system utilizing noncovalent binding between the chromophore Disperse Red 1 (DR1) and SWNT using a pyrene tether to facilitate coupling with the SWNT via π-π stacking interactions. Evidence supporting our model for photoisomerization-induced tuning of the SWNT electronic environment was provided by optical second harmonic generation (SHG) experiments, in which the relative trans/cis population ratio of the DR1P-SWNT hybrid was reversibly modulated by randomly polarized light within the main absorbance band of DR1P. This demonstrated that the pyrene tether coupling DR1 to the SWNT affords considerable orientational flexibility to the chromophore, thereby raising the possibility that these hybrid materials may also exhibit photoinduced birefringence.
Here we report photoinduced birefringence in a DR1P-SWNT system deposited in a 10 nm thin film. In photoinduced birefringence, linearly polarized light near lambda;_max of the azobenzene absorbance window causes repeated trans-cis-trans isomerizations that ultimately rotates the trans isomer perpendicular to the field vector of the linearly polarized light. The coupling of the chromophore to the SWNT without an intermediary polymer host leverages the inherent flexibility of the pyrene tether, resulting in fast, reversible photoinduced birefringence of order Δn asymp; 0.1 at 633 nm using moderate intensity of linearly polarized 488 nm light. The birefringence follows biexponential dynamics, with rise times as fast as 0.12 s at 4 mW. The slower component reflects dipolar interactions between chromophores, translational motion of the chromophores along the nanotube surface, and possibly bulk movement of individual nanotubes. The dark decay of birefringence is also biexponential, with a small residual birefringence of 3% remaining 1500 hours following illumination. The residual birefringence could be completely erased using circularly polarized 488 nm light. The photoinduced writing and erasure of birefringence was stable for up to 750 cycles on the same sample location without chromophore degradation. This demonstration of photoinduced birefringence in functionalized nanotubes without any polymer host opens up new routes to the development of materials for optoelectronic modulation, with considerable progress expected as the effects of the pyrene tether length are more fully investigated.

We prepared polyer matrix composites in which multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed, and their morphologies, thermal properties, and mechanical properties were investigated. The incorporation of MWCNTs into the polyer matrices improved their thermal and mechanical properties with appropriate flexibility. These drastic improvements in the variousproperties of MWCNT/polymer composites were assumed to have been caused by the formation of a three-dimensional structure at the
interfacial phase of the polymer matrix along the MWCNTs, which we designated as a cell structure. These numerous nano-cells were thought to have behaved individually and collectively.

Carbon nanotubes (CNTs) have been shown to impact the electro-optic properties of nematic liquid crystals (NLCs). This is due to a number of physical phenomena, including electrically-induced rotation of the nanotubes, agglomeration, and dynamical and surface effects. Which effects are the predominant ones is not yet completely understood. We studied the effects of time-varying and static electric fields on the electro-optical properties and Freedericksz transition of 5CB NLCs with different concentrations of multi-walled carbon nanotubes (0%, 0.01%, and 0.1%). Test devices with ~12 µm cell gap and poly(vinyl alcohol) alignment layers were fabricated. Transmission optical ellipsometry was used to measure the optical retardance of the 5CB as the peak voltage and frequency of an applied AC electric field were varied from 0-10 V and 1-100 kHz, respectively. The critical voltage of the Freedericksz transition was noted by a sharp decrease in the retardance from an initial plateau, which approached zero as the voltage was increased. Numerical simulations of CNT-facilitated switching show that induced polarization on the nanotubes from capacitive effects can significantly reduce the critical voltage in DC electric fields, in agreement with experimental results. We will also discuss how the frequency response of the devices provides insight into the physical mechanism behind the modification of the critical voltage.

Metal matrix nanocomposites (MMC) were successfully fabricated using high energy planetary ball-milling and hot pressing. Aluminium magnesium alloy AlMg5 was used as matrix material to investigate the effect of 1 vol% carbon nanotube (CNT) reinforcement. Different milling times from 1 to 20 hours, process control agents (PCA) amount and milling media sizes (10 or 20 mm balls) were investigated. Raman spectroscopy, X-Ray diffraction, optical microscopy, HR-SEM and HR-TEM were used to characterize the processed composite materials. Mechanical properties such as Vickers hardness (HV₂₀) and ultimate tensile strength (UTS) were measured. Hardness and UTS values were increased by a factor of 3 over pure alloy achieving macro-hardness around 170 HV₂₀ and UTS around 560 MPa. The influence of the milling time was ascertained and showed that the highest mechanical responses were achieved using 2 to 6h of high energy milling with 10 mm milling media and 15 wt% heptane as PCA.

Nanostructured carbon materials, especially activated carbon, carbon nanotubes, and graphene, have been widely studied for supercapacitor applications. To continue improving the properties of these materials for electrochemical energy storage, a detailed understanding of the relationship between nanostructure and performance is needed. A fundamental structural parameter obtained from the Raman spectra of these materials, the in-plane correlation length, also known as the nanocrystalline domain size, has been quantified for various carbon nanostructures grown by microwave plasma-enhanced chemical vapor deposition (MPECVD) and correlated with their nanostructural characteristics and electrochemical properties. The types of carbon examined in this research included multiwalled carbon nanotubes, graphenated carbon nanotubes, graphene nanosheets, and amorphous carbon. In examining the electrochemical double-layer capacitance of these films determined from cyclic voltammetry and galvanostatic charge-discharge curves, a linear trend was discovered between specific capacitance and nanocrystalline domain size. This correlation for a common and fundamental nanostructural characteristic is believed to be the first result of its kind to span many representative nanostructured carbons, and may allow more effective nanoscale engineering of supercapacitor electrode materials.

We propose a new authentication system based on an artifact-metrics system using carbon nanotube (CNT)-composite papers. Nowadays, an advanced authentication technology is required with the development of the information society. Currently, a biometric authentication has been often used as an authentication technology that uses physical features of the human body such as fingerprints, irises, and veins. This authentication system is possible to authenticate a high level. However, some researcher indicated that the biometrics has some weak points. For example, the finger prints can be counterfeited by using gelatin. As a technology to solve these problems, an artifact-metrics authentication has been proposed. The artifact-metrics is an authentication system that uses specific features of the artifacts. Typically, specific random patterns of the artifacts are used for verification as a "fingerprint" of the artifact. In this study, as the material for a new artifact-metrics authentication, we focused on CNT-composite papers. Because they have specific Raman spectroscopic characteristics of the CNTs, performed an authenticity judgment using keys obtained by Raman mapping from them. We measured the CNT patterns in the samples by a Raman microscopy (inVia Reflex). We have found that anyone cannot make the completely same CNT patterns. Further, we used a calculated correlation-coefficient and pattern-matching in the comparison of the authentication data. In previous work, we mapped patterns by the peaks of G-band (around 1590cm^-1) and RBM-band (around 280cm^-1) from the gained spectra. We estimated the error rate (accuracy) of this system about 10^-2. However, it was inferior value compared to the fingerprint authentication. The cause of these, we considered that the correlation coefficient between genuine-genuine was decreased and the correlation coefficient between genuine-counterfeit was increased because Raman peaks were buried in noise that it was derived from compounded of CNTs and a pulp. To solve this problem, we introduced a tolerant measurement system and authentication system for noise and an error. For tolerant measurement system to noise, we used CNTs indicating a strong reaction especially in 532nm laser excitation wavelength of the Raman microscope, and optimized measurement parameters. In addition, for tolerant authentication system to the error, we introduced the multi-modal metrics system. The system can be expected to increase the correlation coefficient between genuine-genuine and decrease the correlation coefficient between genuine-counterfeit because this system be able to complement each other's data, by combining use of plural Raman peaks. This time, in particular, we succeeded in reduce to less than half the average values of the correlation coefficient between genuine-counterfeit. By these efforts, we estimated the error rate of this system about 10^-8 order. We succeeded in raising the authentication accuracy significantly.

The field emitter based on the carbon nanotubes (CNTs) has been investigated as field-emission (FE) X-ray source due to its small form factor and low power consumption. However, long term stability of CNT emitters should be further improved for the practical application, when they operate at high current density. The former studies on CNT emission failure mechanism have revealed that CNT emitters are ruptured at a weak point such as defect site of CNT by Joule heating or ion bombardment. So, we anticipate that the life time of CNT emitters could be enhanced by covering the defect sites of CNT with robust material, such as metal oxide. In this study, we chose ZnO as protective material, because the work function of ZnO differs from that of CNT by only 0.3 eV, which would result in little change in the emission characteristics.
The ZnO protective layer was coated by using hydrothermal method on the surface of CNTs after AZO seed layer was coated by radio-frequency sputter system. From the scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) images, we were able to observe AZO and ZnO amorphously grow near the defect sites of CNT. The emission stability measurement results show that the life-time of ZnO-coated CNT emitters is enhanced more than 2 times when it is compared with that of bares CNT emitters.
In this experiment, the emitter&’s life-time is defined as the time taken for the emission current to drop from 100mA to 50mA. While a large number of the bare CNT emitters are kinked or broken after emission measurement starting from 100mA for 10 min, which can be characterized from HRTEM images, most of the ZnO-coated CNT emitters maintain their shape at the same emission condition.
In this presentation, the role of ZnO-coating in the enhancement of emission life-time of CNT emitters will be discussed in detail.

Wet scrubbers and electrostatic precipitators (ESPs) are commonly used to remove particulates in the acidic and corrosive gases generated by IT manufacturing industries. However, these devices suffer from low collection performance for ultrafine particles and corrosion caused by the gases. We have developed a novel non-metallic ESP composed of separate charging and collection stages made by carbon fiber-based materials. This ESP uses carbon fiber chargers at the center of the grounded channels of carbon fiber-reinforced polymer (CFRP) and PVC collection plates into which metallic films are inserted. The collection efficiency of the ESP was measured using SiO₂ dusts, and mists (0.01-10 mu;m) by varying operation and design parameters. Finally, the ESP (400 x 400 m²) was demonstrated with a bypassed gas of 1,200 m³/hr from the exhaust line of acidic and PFC gas scrubbers of a semiconductor manufacturer in Korea. Ozone emission performance of a carbon fiber charger was experimentally investigated by comparing to the emission performances of general chargers with different materials (Silver, Copper, Tungsten, and Carbon etc) and with different diameters of high voltage electrodes, and the results showed that lower ozone emission of a charger with carbon fibers than the general metals was possible not by material effect but by sharpness effect of the high voltage electrode. Also, electrical and collection performances of the carbon fiber charger (400 x 400 mm²) were not changed with different materials (stainless steel, CFRP) that were used for 16 ground channels and with reduction of the channel lengths to 140, 90, and 50 mm. Furthermore, by increasing the voltage applied to the charger and the collection plates and by increasing the length of the collection plates, an improvement in the collection efficiency of the ESP could be achieved for a high air flow velocity of 2 m/s. In particular, when the ESP with the carbon fiber charger (400 x 400 m², CFRP, 16 channels with 100 mm length) and collection plates (400 x 400 m², 400 x 540 mm² with 10-mm gap) was operated with 10 and 12 kV applied voltages to the charger and collection plates, respectively, it removed >90% of the ultrafine particles at 2 m/s of gas velocity. Finally, during 1 month of operation at the demonstration site, the ESP had average collection efficiencies of 97% based on particle numbers of 0.3, 0.5, and 1 mu;m and 92% based on total particle mass; these collection efficiencies were achieved with a much smaller specific corona power of 0.028 W/m³/hr compared with the 0.05 to 0.3 W/m³/hr of conventional ESPs. These results indicate that the non-metallic ESP with carbon fiber chargers in CFRP channels and PVC collection plates with inserted aluminum sheets could be a promising technology to remove particles in corrosive gases generated by IT manufacturing industries while emmiting low ozone and consuming low power.

Carbon nanotubes (CNTs) were synthesized by chemical vapor deposition (CVD) of benzene over Cu, Fe, and Fe-Cu/SBA-16 nanocatalyst. The synthesis of CNTs was carried out at 750^oC with ambient pressure.. The CNTs were synthesized under same reaction conditions from these three catalysts.. The synthesized CNTs were purified by multistep process. The morphology and structure of these purified CNTs was characterized by the scanning electron microscopy (SEM) technique. SEM results showed that CNTs with shorter length and narrow diameter were produced from bimetallic catalyst as compared to the CNTs from monometallic catalysts. Then these purified CNTs were functionalized by treating the CNTs with mixture of H₂SO₄/HNO₃. As a result of this acidic treatment, functional groups were introduced on the surface of CNTs. The presence of oxygen containing functional groups was confirmed by FTIR. These functionalized CNTs were used in the synthesis of polymer nanocomposites. These nanocomposites were prepared in two steps. In the first step, silver nanoparticles were incorporated on the surface of functionalized CNTs. In the second step, these Ag/CNTs were covered with layer of polypyrrole by oxidative polymerization process. These Ag/CNTs nanohybrid and CNTs/Ag/PPy composites were characterized by FTIR and SEM and their electrical properties are measured to extract important information.

Continuous carbon fiber polymer-matrix composites are lightweight structural materials that are well-known for their high strength, high modulus and low density. The permittivity of these composites has been studied by numerous workers at radio wave and microwave frequencies due to the relevance to electromagnetic interference shielding and radar radiation absorption. The relative dielectric constant and the capacitance of these composites in the through-thickness direction (i.e., the direction perpendicular to the plane of the fibers) have been studied in prior work, due to their relevance to structural capacitors for electrical energy storage. These structural capacitors do not involve the embedment of capacitors in the composite. Rather, the composite material is modified such that electrically conducting and insulating components in the composite material are stacked so as to achieve a dielectric capacitor with the configuration of a parallel-plate capacitor. This approach is to be distinguished from the embedment of a device, such as a battery, in a composite material, in order to achieve the energy storage function. In this work, negative permittivity (real part) has been discovered in continuous carbon fiber epoxy-matrix structural composite laminates. The relative dielectric constant as negative as -300 at frequencies up to 2 MHz is obtained in the through-thickness direction when a cellulosic paper interlayer of thickness 25 or 35 mu;m is present at every interlaminar interface of the laminate. The greater is the moisture content in the paper at the time of incorporation into the laminate, the more negative is the permittivity. When the paper has been dried just prior to incorporation, the permittivity is positive, up to +400. When the paper is 60 mu;m thick and used as received (without drying), the permittivity is positive, up to +30. The paper by itself, whether wet or dried, exhibits low positive relative dielectric constant ranging from +1.2 to +1.4. The highly positive permittivity observed in the composite with dried paper is attributed to the functional groups of the fibers. The negative permittivity observed in the composite with wet paper is attributed to the interaction of the functional groups on the carbon fiber surface and the residual water in the paper in the fabricated laminate. Thus, composites with highly positive and highly negative values of the relative dielectric constant have been achieved, thereby allowing positive and negative forms of energy storage and a new dielectric form of data storage that uses the two signs of the capacitance to store 0 and 1. In prior work, negative permittivity is mostly observed in metals, such as silver, as enabled by the plasma oscillation of the free electrons. It is recognized to have the potential of revolutionizing electronics and photonics. This work's discovery of negative permittivity in a structural composite will advance the field of structural electronics.

Recent years have seen the development of several experimental systems capable of tuning local parameters of quantum Hamiltonians, including ultracold atoms, trapped ions, superconducting circuits and photonic crystals. These systems excel in studying the physics of bosons in disorder-free settings. A solid state analog, in which Hamiltonians of interacting electrons are designed and studied, remains a major open challenge, since in conventional solids electrons exist inside an imperfect host material that generates uncontrolled disorder. In this talk I will describe our newly-developed platform for realizing in suspended carbon nanotubes such disorder-free, locally-tunable electronic systems. This platform becomes possible due to a new technique for nano-assembly of one or several carbon nanotubes on complex electrical circuits without damaging the nanotubes&’ pristine electronic behavior. I will demonstrate how these systems allow us to localize individual electrons at arbitrary positions along suspended nanotubes, to shape the electronic wavefunctions and their mutual interactions, and to tailor their coupling to the nanotube&’s mechanical motion, thereby engineering artificial electron-phonon interactions. These capabilities open the door to a broad spectrum of quantum experiments on electronics, mechanics, and spins in artificially engineered settings.

A multiprobe scanning probe microscope (SPM) system has been used to perform multiprobe electrical measurement of carbon nanotubes. In this system two probes can be used across an isolated carbon nanotube. A variety of probes have been developed that are compatible with multiprobe operation. These include probes for writing single single-walled carbon nanotubes which have a high degree of alignment and this is demonstrated with on-line Raman. The interconnection of the multiprobe system with the Raman System will be described in detail. The combination has the potential to cross the fabrication/measurement gap that will allow for both production and nanocharacterization of such single molecule carbon nanotube molecular devices both with chemically sensitive Raman measurements (with and without plasmonic enhancement) and with on-line electrical transport on isolated carbon nanotubes. The results will be described that will relate the chemical alteration under electrical transport in these nano devices.

Near-infrared emission from semiconducting single-walled carbon nanotubes (SWNTs) usually results from radiative relaxation of excitons. By binding an additional electron or hole through chemical or electrochemical doping charged excitons, so-called trions, are created that can emit light at lower energies. Due to the short-range Coulomb interaction in carbon nanotubes the energy difference between trions and excitons is large enough (100 - 200 meV) to observe weak trion photoluminescence from doped SWNTs even at room temperature. Here, we demonstrate strong trion electroluminescence from electrolyte-gated, light-emitting SWNT transistors based on three different nearly monochiral carbon nanotube networks, namely (6,5), (7,5) and (10,5). The red-shifted trion emission is equal to or even stronger than the exciton emission. This effect can be attributed to the high charge carrier density in the transistor channel even in the ambipolar regime, which also leads to strong Auger quenching. Carrier density-dependent photoluminescence and absorption spectra for both hole and electron accumulation further corroborate the generation of trions in these devices. The ratio of trion to exciton emission can be tuned by the applied voltages. This allows us to create voltage-controlled near-infrared, polarized light sources with narrow linewidths (le;70 meV) that are processed from solution, very robust against sample imperfections and operate at low voltages (le;3V).

Single-wall carbon nanotubes (SWCNTs) have been extensively investigated for more than two decades and hundreds of possible applications have been proposed. For example, proof-of-concept studies illustrated their viability as high-efficiency electron emitters, due to their high aspect ratio, or wire interconnects in nano-sized electronics circuits. In both cases, one of the key processes in their electric/electronic application is the mechanism of charge transfer between neighboring SWCNTs. Therefore, in this work, using SPM nanomanipulation, such charge transfer process was investigated as a function of SWCNT nature (metallic or semiconducting) and anode/cathode distance. Electric force microscopy (EFM) characterization sorted out metallic from semiconducting SWNTs (atop a Si/SiOx substrate), which were then cut into two halves via SPM nanomanipulation, forming the anode and cathode of the charge transfer experiment. Using the EFM tip to inject charges on the cathode SWCNT, the charge transfer to the anode SWCNT was investigated via EFM characterization. It was found that above an injected density threshold, charge transfer from the cathode SWCNT to the anode SWCNT occurs. Subsequently, the anode-cathode distance was also varied via SPM nanomanipulation and the injection/transfer experiment repeated. For metallic SWCNTs, the charge transfer occurs via electron tunneling, following a Fowler-Nordheim mechanism regardless the anode-cathode distance. Additionally, the charge density threshold (to initiate charge transfer to the anode) weakly depends on the anode-cathode separation. Semiconducting SWCNTs, however, show a different behavior: 1) the charge transfer only follows a Fowler-Nordheim mechanism for anode-cathode distances above 50nm. Below such distances, charge diffusion via the substrate might be the leading charge transfer process. 2) The charge density threshold strongly depends on the anode-cathode distance (the larger the distance, the larger the density threshold). In summary, the results show that charge transfer mechanisms in SWCNTs are dependent on their metallic/semiconducting nature and that electron tunneling may not be the dominant process in all cases. These results may have an important impact on the design and operation of SWCNT-based electronics.

Near-infrared photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g. C₆₀). However, little is known about crucial photochemical events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (tau;_pet) and yield (#981;_pet) in photoexcited SWCNT-C₆₀ bilayer films. The process of trion formation proceeds by a series of steps: 1. formation of SWCNT excitons by the pump pulse; 2. dissociation of the excitons at the SWCNT-C₆₀ interface by PET to the C₆₀ layer, and 3. direct optical excitation of trions in the SWCNT by the probe pulse. The rise time of the trion induced absorbance enables the first determination of the photoinduced electron transfer (PET) time of tau;_pet le; 120 fs, while an experimentally determined trion absorbance cross section reveals the yield of charge transfer (#981;_pet asymp; 38 ± 3 %). The fast PET times between SWCNTs and C₆₀ and are on par with some of the best donor:acceptor pairs currently used in excitonic photovoltaics and are consistent with low reorganization energies and/or strong electronic coupling. Technologically, our results suggest tremendous potential for SWCNT-C₆₀ heterojunctions in applications such as thin-film photovoltaics.

The optical properties of carbon nanotubes offered the possibility of using in different applications such as nonlinear optical switching device, biomedical imaging, fluorescent bio markers and sensors [1]. Single wall carbon nanotubes (SWNT) show strong photoluminescence (PL) when nanotubes isolated or present in small bundles in solutions.
In this study, we mix SWNT solution with the water soluble DiOxaBorine dye (DOB-719) at different concentrations. The DOB-719 has strong optical absorption with maxima at 630 and 680 nm usually assigned with dye in dimeric and monomeric form respectively. The mixing of DOB-719 with the SWNTs results in change of the ratio for monomers and dimers in resulting dispersion. The PL excitation-emission observation of initial SWNT and SWNT-DOB-719 system reveals about 50 nm red shift in emission spectra of SWNT and new efficient excitation of PL bands for all SWNT chiralities at 750 nm after mixing with DOB-719. The obtained results demonstrate a promise of DOB-719 for formation of novel molecular complexes with SWNTs with enhanced PL.
The work was partially supported by NATO SPS project (NUKR.SFPP 984189) and Marie Curie IRSES TeLaSens project (FP7 Project # 269271).
References
1. S. Yamashita, Y. Saito, J H Choi, Carbon Nanotubes and Graphene for Photonic Applications, Woodhead Publishing (2013).
2. M.P. Shandura, et al., Sensor Letters, (2014) In press.

Introduction of new photoluminescent (PL) states upon low-level covalent doping of carbon nanotubes^1,2 is gaining interest due to their chemical stability and potential for tube brightening. The nature of these optical states is not yet well-understood. We present PL imaging and spectroscopic studies of oxygen¹ and aryl diazonium² doped tubes at the single-tube and single-dopant site levels. Dynamic and static emission behaviors will be presented as modulated by the relative dopant concentration. Results will be discussed as the interplay of 1-D bright exciton behaviors and 0-D trap states introduced at the dopant sites. PL spectroscopy of single doped tubes at cryogenic temperatures reveals fine structure that further indicates exciton localization at dopant sites. A comparison of the emission fine structure to expectations from quantum chemical modeling of the new dopant-induced optical states may also be used to identify the chemical functionality of the dopant sites.
References:
[1] S. Ghosh, et al., Science, 330, 1656 (2010).
[2] Y. Piao, et al., Nature Chem., 5, 840 (2013).

The recently-reported exceptionally fast fluid transport rates in narrow carbon nanotubes (CNT) spurred great interest for their application as nanofluidic channels in several areas ranging from desalination and carbon capture, to drug delivery, protein separation, and breathable fabrics.
Here, we highlight experimental work performed in our laboratory directed toward: a) a fundamental understanding of the selectivity of these pores for electrolyte solutions under a pressure driving force; b) elucidating electric-field driven ion transport in a single CNT nanopore; c) the development of breathable and protective fabrics based on CNT arrays. For our studies, we used ceramic or polymeric membranes with well-aligned, a-few-nm wide CNTs as only through-pores. We demonstrate that ion selectivity in narrow CNT pores is dominated by electrostatic interactions between carboxylic groups at the CNT tips and the ions in solution. Ion selectivity can be tuned by acting on solution pH and by employing a controlled surface functionalization with atomic layer deposition (ALD) without loss of their unique ultrafast fluid transport properties. Single-pore ionic conductance measurements revealed a usual power law concentration dependence ~cⁿ, n<1. Finally, flexible CNT membranes under development for the breathable and protective fabric application provide water vapor transport rates that are comparable to or exceeding state-of-art breathable fabrics at all relative humidities even if the moisture conductive pores are only a-few-nm wide and the membrane porosity <1%. Moreover, these tiny pores enable simultaneous passive protection from biological threats by size exclusion.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

A growing number of contaminants are entering water supplies from human activity, among which most can have bio-accumulative, persistent, carcinogenic, mutagenic and detrimental effects on the survival of aquatic organisms, flora, fauna as well as human health. Hence, effective, low-cost, robust methods to disinfect and decontaminate waters from source to point-of-use are needed, without further stressing the environment or endangering human health by the treatment itself [1]. In this work, single-walled carbon nanotube/graphene hybrid papers prepared by vacuum filtration are used as adsorbents for the removal of a series of aromatic compounds from aqueous systems. The configuration of these carbon nanostructures into flexible free-standing papers enables their direct use and easy recollection in water treatment, avoiding the need for additional solid-liquid separation procedures such as gravitational sedimentation, #64257;ltration, or coagulation [2]. Experimental data are collected via changes in optical absorption spectra of the different aqueous solutions and are used to extract all parameters required to implement a semi-empirical mass-transfer model. Agreement between experiment and theory is excellent and data from all compounds can be cast on a universal adsorption curve [3]. Results indicate that the as-prepared hybrid papers demonstrate the highest adsorption capacity of aromatic compounds to date [2,3]. Furthermore, spent hybrid papers are successfully regenerated by thermal oxidation and microwave irradiation after treatment such that the original adsorption capacity is significantly exceeded with a regeneration efficiency above 200% even after several saturation/regeneration cycles [4]. The prospect of using carbon nanotube/graphene free-standing papers as new generation adsorbents for organic compounds offer not only fast adsorption rates, improved stability and larger capacity, but also exhibit very high regeneration efficiency, potentially providing a sustainable/renewable solution for future purification systems.
References:
1. S. Chowdhury and R. Balasubramanian, Adv. Colloid Interface Sci.2014, 204, 35.
2. A. B. Dichiara, T. J. Sherwood and R. E. Rogers, J. Mater. Chem. A, 2013, 1, 14480.
3. A. B. Dichiara, T. J. Sherwood, J. Benton-Smith, J. C. Wilson, S. J. Weinstein and R. E. Rogers, Nanoscale, 2014, 6, 6322.
4. A. B. Dichiara, J. Benton-Smith and R. E. Rogers, Environ. Sci.: Nano, 2014, 1, 113.

We study electron emission from the side surface of individual Joule-heated carbon nanotubes (CNTs) by using multi-probe measurement techniques inside a scanning electron microscope. By ingeniously combing three electric probes and one optical probe, electron emission current density (J) and temperature (T) of individual hot CNTs heated by self-Joule heating are simultaneously determined.¹ It is found that experimental ln(J/T²)-1/T plots exhibit an upward bending feature deviating from the straight lines in Richardson plots, and that our measured electron emission density is more than one order of magnitude higher than that predicted by Richardson&’s law. The results indicate the breakdown of classical Richardson&’s law in electron emission from individual hot Joule-heated CNTs. To describe the regarded electron emission, a new kinetic model based on the coupled Boltzmann equations of electrons and phonons is proposed and can well simulate the experimental curves.² Based on theoretical calculations, it is found that, in contrary to normal thermionic emission from macroscopic metallic filaments which solely relies on thermal effect, both thermal effect and internal electric field co-contribute to the electron emission from Joule-heated CNTs due to the presence of hot electrons under electric drive and the low-dimensionality of CNTs. This is thought to be partially responsible for the breakdown of Richardson&’s law. Due to the contribution of internal electric field to electron emission, the model also predicts that electron emission density distribution along a Joule-heated CNT is asymmetric along tube axis and depends on the direction of electric field in CNTs. The prediction is subsequently verified in experiments by measuring the spatial distribution of electron emission density of individual Joule-heated CNTs using four electric probes.³ The direct contribution of internal electric field to electron emission from Joule-heated CNTs may provide a new way of achieving cold electron source with low working voltage and high emission density.
References:
[1] X. L. Wei, S. Wang, Q. Chen, L. M. Peng Sci. Rep.2014, 4, 5102.
[2] X. L. Wei, D. Golberg, Q. Chen, Y. Bando, L. M. Peng Nano Lett. 2011, 11, 734.
[3] X.L. Wei, D. Golberg, Q. Chen, Y. Bando, L. M. Peng Phys. Rev. B2011, 84, 195462.

Carbon nanotubes (CNTs) exhibit a range of interesting properties and have attracted significant attention in recent years [1,2]. Of note are their highly desirable conducting and semiconducting electronic characteristics; however, in order to realize these properties, the CNTs must be converted into an ink to allow for application-specific CNT film deposition and device fabrication.
Exploiting the electronic properties of as-produced CNTs is challenging. Raw, powdered CNTs must be dispersed into an appropriate medium in a controlled and scalable manner in order to prepare CNT films for electronic applications. However, raw CNTs exhibit very poor solubility in common solvents and are insoluble in water without either prior chemical modification or the use of a dispersing agent such as a surfactant. Unfortunately, chemical modification of CNTs or use of surfactant each negatively impacts the desirable electronic properties of the CNTs.
Our team has developed several new methods to prepare stable, concentrated, CNT-based inks for different deposition techniques. We have developed a functionalization procedure that preserves the electronic properties of raw tubes and can be used to generate aqueous inks that are suitable for spray-coating and Optomec&’s Aerosol Jet^® deposition techniques. Our process is scalable and can be used to reproducibly cast conductive CNT films with conductivity values that exceed 300,000 S/m. Moreover, these dispersions can be further formulated to give stable ink-jettable inks. Additionally, we have developed a novel technique to prepare screen-printable CNT-based inks that easily generate CNT films with resistivity of <6 ohms/square after one coat. Our screen-printable inks only require curing at a mild temperature after deposition and do not contain any additives that require a special treatment step. All electrical characterization to be presented is based on methods developed and validated by Brewer Science using measurements systems analysis (MSA) protocols.
[1] D. Tasis, N. Tagmatarchris, A. Bianco, and M. Prato, “Chemistry of Carbon Nanotubes,” Chemical Reviews, v. 106, no. 3, pp. 1105-1136, 2006.
[2] L. Hu, D.S. Hecht, and G. Gruner, “Carbon Nanotube Thin Films: Fabrication, Properties, and Applications,” Chemical Reviews, v. 110, pp. 5790-5844, 2010.

Electronics devices based on graphene and carbon nanotubes (CNTs) have attracted significant attentions for potential radiofrequency (RF) applications [1-4]. It is shown that intrinsic current-gain and power-gain cutoff frequencies above 1 THz should be possible, but experimental demonstration using field-effect transistors (FETs) based on individual CNTs suffered from excessive parasitic effects and impedance mismatch problems. In order to overcome these limitations, great efforts have been concentrated on FETs made from aligned arrays of CNTs. Since all of the published CNT RF circuits were designed to work at linear region, it is often stated that it is necessary to use dense arrays of all-semiconducting nanotubes to achieve high performance. While impressive progress has been made in achieving high density arrays of CNTs, for example in several cases the required density of tens of nanotubes per mu;m has been realized, it is still challenging to eliminate all metallic CNTs without damaging semiconducting CNTs and thus severely degrading the performance of the CNT array FETs. Therefore most of the published RF integrated circuits based on CNT array on quartz only can operated at a relative low frequency far below 1 GHz owing to the low cut-off frequency of FETs. Here we argue that rather than trying to avoid the requirement of pure semiconducting CNTs, we may indeed make a good use of the natural growing CNTs for RF applications. We demonstrate that perfect ambipolar modulation may be achieved using FETs based on as-grown CNTs arrays on quartz near the minimum current point (MCP). Using the ambipolar region rather than linear region of these FETs, RF circuits including frequency multipliers and mixers are batch-fabricated and shown to outperform all previously reported carbon based RF circuits [5].
References:
[1] C. Kocabas, H. Kim, T. Banks, J. A. Rogers, A. A. Pesetski, J. E. Baumgardner, S. V. Krishnaswamy, H. Zhang, Proc. Natl. Acad. Sci. U. S. A. 2006, 105, 1405.
[2] Z.X. Wang, Z.Y. Zhang, H. Zhong, T. Pei, S.B. Liang, L.J. Yang, S. Wang and L.-M. Peng, Adv. Func. Mater. 23 (2013) 446-450
[3] Z.X. Wang, L. Ding, T. Pei, Z.Y. Zhang, S. Wang, T. Yu, X.F. Ye, F. Peng, Y. Li and L.-M. Peng, Nano Letters 10 (2010) 3648
[4] Z.X. Wang, Z.Y. Zhang, H.L. Xu, L. Ding, S. Wang, and L.-M. Peng, Appl. Phys. Lett. 96 (2010) 173104
[4] Z.X. Wang et al., Adv. Mater. 26 (2014) 645

With recent developments in single-walled carbon nanotube (SWNT) sorting technology, SWNT thin-film transistors (TFTs) fabricated by these sorted carbon nanotubes demonstrate high mobility and on/ off ratios. However, challenges still remain for their practical use, including: i) control of the threshold voltage for robust and low-power circuits; ii) reduction of the operational large hysteresis; iii) consistent device polarity (unipolar/ambipolar) in different environments.
Our first approach is to n-dope SWNTs using 1H-benzoimidazole derivatives processed via either vacuum evaporation or solution coating¹. The threshold voltages of our polythiophene-sorted SWNTs TFTs can be continuously tuned over a wide range. Photoelectron spectroscopy (PES) measurements confirmed that the SWNT Fermi energy decreases with increased doping concentration. Utilizing this approach, we proceeded to fabricate SWNT complementary inverters by inkjet printing of the dopants with a noise margin of 28 V at V_DD = 80 V (70% of 1/2 V_DD) and a gain of 85. Additionally, equally robust SWNT CMOS inverters (noise margin 72% of 1/2 V_DD), NAND and NOR logic gates with rail-to-rail output voltage swing and sub-nanowatts power consumption were fabricated onto a highly flexible substrate for the first time.
Our second approach is to utilize Poly(trifluoroethylene) (PTrFE) polymer as a top-gate dielectric to fabricate hysteresis-free devices at different sweep rates. These devices also exhibit excellent bias-stress stability under ambient conditions. Ambipolar SWNT transistors are observed when Poly(vinylidene-trifluoroethylene-chlorotrifluoroethylene), P(VDF-TrFE-CTFE), is utilized as a top-gate dielectric in air. Furthermore, we demonstrate the continuous tuning of threshold voltages of both unipolar and ambipolar SWNT TFTs by application of a second gate voltage.
Reference:
1.H. Wang, Z. Bao et al., Tuning the threshold voltage of carbon nanotube transistors by n-type molecular doping for robust and flexible complementary circuits, PNAS, 111(13), 4776-4781, 2014
2.H. Wang, Z. Bao et al., Highly Stable Carbon Nanotube Top-Gate Transistors with Tunable Threshold Voltage, Advanced Mateirals, doi: 10.1002/adma.201400540, 2014

Single-walled carbon nanotubes (SWNTs) have attracted a lot of attention in the last years, owing to their unique mechanical, thermal and opto-electronic properties. The ability to disperse SWNTs in water and in organic solvents makes solution-based processes very promising for the fabrication of SWNT-based devices. Here, we demonstrated the technological potential of solution-processed semiconducting SWNTs with single chirality, selected by means of conjugated polymer wrapping [1]. Employing a network of randomly oriented polymer-wrapped (7,5) SWNT deposited by spin coating, we fabricated and characterized thin film transistors (TFTs) and integrated circuits on rigid as well as flexible plastic substrates. Bi-functional devices such as blue color light-emitting field-effect transistors have also been realized using the same materials and device architectures.
In order to investigate the charge transport mechanisms in these solution-processed semiconducting systems, we have studied the percolation behavior in the randomly formed polymer-SWNT network. Primary aim of this analysis was to quantify the impact of the small amount of metallic carbon nanotubes present in the solution even after separation. To achieve this, we have studied the dependence of several key device parameters including: the channel ON (I_ON) and OFF (I_OFF) currents, the channel ON/OFF current ratio (I_ON/I_OFF) and the linear field-effect charge carrier mobility (µ_lin), as a function of the increasing transistor channel length (L_C) from 0.75 µm to 40 µm [2]. Devices with L_C = 40 µm showed, on average, I_ON as high as 1 mA, I_ON/I_OFF ratios up to 10⁷, and mu;_lin close to 0.2 cm²V^-1s^-1. On the other hand, devices with L_C < 2 µm exhibited a low I_ON/I_OFF ratio (~1) due to the presence of metallic SWNTs.
Finally, the surface topography and lateral charge transport in polymer-SWNT films were investigated using atomic force microscopy (AFM) and lateral-current AFM techniques. From the surface topography images we were able to extract the diameter of SWNTs/bundles, but also confirm the presence of the conjugated polymer along the nanotubes axis. Mapping of the current percolation pathways along the polymer-SWNT network, on the other hand, enabled the extraction of the intrinsic resistivity of the semiconducting polymer-SWNT network with nanoscale spatial accuracy. Our work highlights the tremendous potential of semiconducting polymer-SWNTs blends for application in large-area plastic microelectronics.
[1] A. Nish, J.Y. Hwang, J. Doig and R.J. Nicholas, Nature Nanotechnology 2 (2007), pp. 640-646.
[2] D.M. Sun, M.Y. Timmermans, Y. Tian, A.G. Nasibulin, E.I Kauppinen, S. Kishimoto, T. Mizutani and Y. Ohno, Nature Nanotechnology 6 (2011), pp. 156-161.

The exceptional transport properties of single-walled carbon nanotubes (SWCNTs) make them excellent candidates for future electronic devices and technologies. The key bottlenecks impeding their application are primarily materials related and include isolating the desired population of SWCNTs, selective placement and device-device variation. This talk will will describe recent progress in addressing these challenges along with implementation of these materials into low-power electronic devices. Isolation of semiconducting SWCNTs is achieved via column chromatography. The method is simple, scalable and yields purity levels approaching 99.99% (verified via high-throughput electrical testing). The materials are then used to build thin-film transistors that yield high-performance at low power. The work highlights the potential of these materials in a variety of applications.

Single-walled carbon nanotubes (SWCNTs) have been widely recognized over the last two decades as promising candidates for next-generation field-effect transistors (FETs). Recent work performed by Franklin et al. at IBM suggests that aggressively scaled and pitched arrays of SWCNTs are expected to outperform silicon in logic circuits, which could enable next-generation electronic technologies with low power consumption and high performance.[1] Realizing the full potential of SWCNTs for these applications, however, has been challenging and many limitations that persist require further advances in the materials science of nanotube sorting, alignment, and assembly. Recently, we have made such advances by employing polyfluorene polymer wrappers to selectively isolate large-diameter semiconducting-SWCNTs to greater than 99.9% purity and controllably depositing the SWCNTs into aligned arrays using a novel method that we have pioneered titled “dose-controlled, floating evaporative self-assembly”.[2, 3] Using these methods, we have recently demonstrated[4] FETs with unprecedented, high on-state conductance with simultaneous high on/off ratio. At a SWCNT packing density of 42 nanotubes/mu;m and a channel length of 230 nm and width of 4 µm, we demonstrate champion SWCNT FETs with on-state conductance of 242 mu;S/mu;m and on/off ratio of 7x10⁵. Average on-state conductance and on/off ratio for 13 devices with lengths ranging from 160-240 nm are 193±35 mu;S/mu;m and 3x10⁵±2.5x10⁵, respectively. At a channel length of 1 µm, we demonstrate on-state conductance of 112 mu;S/mu;m and on/off ratio of 2x10⁷. Average on-state conductance and on/off ratios at this channel length are 95±10 mu;S/mu;m and 5x10⁶±7x10⁶, respectively. Our average devices achieve 1400x greater conductance modulation than the previous state-of-the-art, at comparable on-conductance of ~200 µS/µm. Likewise, our average devices achieve 30-100x greater on-conductance, at comparable conductance modulation of 10⁵-10⁶.
These promising results are due to the exceptionally high purity and alignment of the SWCNTs in the channel. For example, we have measured 4071 SWCNTs in 400 nm channel length FETs and 1612 SWCNTs in <240 nm channel length FETs and found no metallic SWCNTs. A transmission line method indicates that the on-conductance is limited by a contact resistance of 80 k#8486; per nanotube per palladium electrode. By improving upon this contact resistance and optimizing the nanotube packing density, we believe that our methods, which are scalable to large areas, are a promising pathway towards aggressively scaled and pitched SWCNTs for next-generation microelectronics and thin-film transistor applications.
1. Franklin et al. Nano Lett 12(2) 758 (2012).
2. Brady et al. APL 104 083107 (2014).
3. Joo et al. Langmuir 30(12) 3460 (2014).
4. Brady, G.J.; Joo, Y.; Wu, M.; Gopalan, P.; Arnold, M.S., In preparation. (2014).

Single-wall carbon nanotubes (SWCNTs) is a promising channel material for future high speed electronic applications owing to its ultra-high mobility and thin, one-dimensional structure. In order to gain the maximum performance benefit from scaled carbon nanotube field-effect transistors (CNFETs), systems of CNFETs must be realized using complementary (both p-type and n-type) logic. However, n-type doping of CNTs has long remained a challenge since as-made carbon nanotube field-effect transistors (CNFETs) are intrinsically p-type in ambient. Recently we successfully demonstrated a novel n-type solid-state doping method with yttrium oxide (Y₂O_x). In this technique a thin layer (5 nm) of yttrium is evaporated at 3×10^-7 Torr on CNTs and subject to partial oxidation. Devices encapsulated with Y₂O_x film show excellent NFET electrical characteristics with I_on/I_off of 10⁶ and subthreshold slope of 95 mV/dec. We have carried out detailed material analysis on these films and revealed that yttrium is only partially oxidized to form a sub-stoichiometric oxide. Thus metallic yttrium reduces the carbon nanotubes (donate electrons to CNTs) that results in strong n-type doping behavior. This mechanism was further verified by Raman and UPS spectroscopy. The profound understanding of the doping mechanism provides us with crucial information to engineer the doping of CNT technique with controllable doping strength in future.
Demonstrating silicon CMOS compatibility is an important consideration for the feasibility of introducing a future technology. We also demonstrate a VLSI-compatible approach for monolithic three-dimensional (3D) integration of CNFETs with silicon CMOS for high-performance digital logic applications. Fine-grained monolithic 3D integration is demonstrated at the logic gate level, whereby individual logic gates comprise both CNFETs and silicon FETs. Monolithic 3D integration is additionally achieved at the circuit-level, with CNFET logic gates cascaded with silicon CMOS logic gates, creating hybrid CNFETminus;silicon CMOS logic circuits. All the CNFET fabrication steps are VLSI-scalable and silicon CMOS compatible. Following standard silicon CMOS fabrication using LOCOS (local oxidation of silicon), an inter-layer dielectric (ILD) is deposited, followed by etching and filling of ILVs. CMP and sputter etching are performed to smooth the wafer surface in preparation for the CNFET process. Then grown CNTs (875 °C) are transferred (125 °C) on a wafer-scale from a growth substrate to the silicon CMOS wafer. This transfer decouples the high-temperature CNT growth from the silicon CMOS wafer. CNFETs are then fabricated directly on top of and overlapping the silicon FETs. Metal wires are used to connect CNFETs to other CNFETs, or CNFETs to the ILVs for integration with the silicon CMOS underneath. This work demonstrates the compatibility of CNFETs with silicon CMOS and the ability to achieve monolithic 3D ICs simultaneously using silicon CMOS and CNFETs.

Semiconducting carbon nanotubes (scCNTs) have been shown to be well suited for the fabrication of one-dimensional field-effect transistors (FETs) where the conducting channel is exposed to ambient conditions. Because the current through the device strongly depends on the distribution of charges near to the channel, those CNTFETs can be used to detect biomolecular species with high sensitivity and selectivity [1].
Here we describe the assembly of CNTFETs and first successful steps towards their use as biomembrane sensors for the detection of curvature-sensitive proteins. Membrane proteins are responsible for communication and transport of chemicals or ions between and within cells. Their functions are so manifold that the majority of medicine sold worldwide targets membrane proteins. Membrane curvature is important for the lateral organization of proteins in membranes, e.g., during budding.
Sorting of single-walled, arc-discharge CNTs is accomplished by a two-step density gradient ultracentrifugation [2] with a yield of 98% scCNT. CVD-grown CNTs are sorted in a one-step gel column chromatography with a yield of 76% scCNT [3]. We present an advanced UV-Vis characterization to quantify the yield which incorporates absorption intensities calculated by Verdenhalven et al. [4] and allows to determine the chirality fractions without the need of additional peak fitting.
We use ac dielectrophoresis (DEP) for the assembly of CNTFETs. Since DEP does not allow for a selective deposition of scCNTs between electrodes, we work at frequencies where both semiconducting and metallic tubes are deposited. When the distance between the electrodes is larger than the length of the CNTs, the assembled FET channel consists of multiple tubes aligned in series [5,6] which causes a very interesting feature. Because incorporation of a single scCNT into the channel is enough to get reasonable FET characteristics, it is still possible to obtain a transistor performance, when the sorting yield is considerably less than 100%. Even the yield of 76%, as obtained for the CVD-grown CNTs, turns out to be sufficient to assemble functional multi-tube CNTFETs in a single DEP deposition step.
A supported lipid bilayer (SLB) was used to cover the CNTFET with a membrane and membrane mobility was proven by FRAP. Incorporation of curvature sensitive proteins into the SLB leads to an accumulation of proteins within the curved membrane parts located on top of the CNTFET channel. Thus, self-organization forces the proteins to localize along the CNT, the place where the electrical detection will take place.
[1] A. Star et al., Nano Lett. 3 (2003) 459-463
[2] J. Posseckardt et al., Phys. Status Solidi B 247 (2010) 2687-2690
[3] F. Ostermaier et al., Phys. Status Solidi B 250 (2013) 2564-2568
[4] E. Verdenhalven et al., J. Phys.: Condens. Matter 25 (2013) 245302
[5] S. Taeger et al., Int. J. Mater. Res. 98 (2007) 742-748
[6] N. Ranjan et al., Phys. Status Solidi B 245 (2008) 2311-2314

Human mesenchymal stem cells (MSCs) show promise for applications such as regenerative medicine, drug discovery, cellular therapy and disease modelling. Expansion of stem cells and maintenance of their self-renewal capacity in vitro requires specialized robust cell culture systems. Conventional approaches consisting of animal derived matrices and a cocktail of growth factors have limitations such as consistency, scalability, and pathogenicity. Furthermore, to achieve high cell densities for practical therapeutic applications, 3D culture systems are desired. To overcome the above limitations, multifunctional 3D porous scaffold, fabricated using synthetic materials that permit stem cell expansion and maintenance in vitro would be a significant advancement. In this study, we present the development of innovative 3D, macroporous, all-carbon scaffolds assembled using single- and multi- walled carbon nanotubes (SWCNT and MWCNT) that are cytocompatible and show multi-functional attributes that allow adipose-derived stem cell (ADSC) expansion and maintenance. ADSCs cultured on SWCNT and MWCNT scaffolds show negligible cell death quantified by LDH assay after 1, 3, and 5 days, compared to poly(lactic-co-glycolic) acid (PLGA) scaffolds (control group). Calcein-AM staining shows the presence of live ADSCs on SWCNT and MWCNT scaffolds, corroborating LDH results. Immunofluorescence results confirm the expression of cell attachment (vinculin) and proliferation marker (Ki-67) indicating that ADSCs attach and proliferate on SWCNT and MWCNT scaffolds. SEM of ADSCs showed that cytoplasmic extensions attach to the underlying nanotube network. ADSCs cultured on SWCNT and MWCNT scaffolds express stem cell markers (CD105+, CD73+, CD90+, CD45-, CD34-, CD14- and CD19-) after 15 days. Additionally, SWCNT and MWCNT scaffolds can be de-assembled into smaller components to allow harvest of ADSCs throughout the scaffold; hitherto not possible with polymeric scaffolds such as PLGA. The harvested ADSCs are capable of in-vitro expansion. Tri-lineage differentiation studies show that the ADSCs differentiate towards adipocytes, osteoblasts and chondrocytes, and indicate that the scaffolds do not affect differentiation capabilities of ADSCs. Our results demonstrate that 3D macroporous carbon nanotube scaffolds, fabricated using SWCNTs and MWCNTs, are cytocompatible and can be used as an artificial 3D matrix for human stem cell expansion and maintenance. The nanotube scaffolds can be de-assembled to retrieve the expanded ADSCs. The nanotube networks may be functionalized with therapeutic ligands to control stem cell fate and simultaneously imaged non-invasively at nano- to macro-scopic length scales using MRI/CT/Photoacoustic imaging, and thereby exploited as multifunctional scaffolds for theragnostic tissue engineering applications.
References:
Lalwani et. al., Carbon, 53, 90-100, 2013.
Talukdar et. al., Biomaterials, 35 (18), 4863-4877, 2014.

Thermal degradation kinetics of polypropylene (PP) and PP with multi-walled carbon nanotubes (MWNT) have been well characterized for heating rates below 10 K/min. Military applications have also examined thermal degradation kinetics for PP-MWNT at heating rates similar to a ballistic event through laser pulse heating. This study examined the kinetics at heating rates ranging from 30 K/min to 195 K/min in order to bridge a gap between the low heating rates and the laser pulse heating experiments. The degradation experiments were completed with a Thermogravimetric Analyzer. The rate constants and activation energies were determined through the use of kinetic software. The results show that the MWNT increase the thermal stability of the polymer, as measured by the increased decomposition temperature. The results of the study are compared to the traditional lower heating rates and laser pulse heating experiments.

Carbon materials including graphite, carbon nanotubes and graphene possess high thermal conductivity, which is desirable for diverse thermal management applications. One of the promising applications of these carbon structures is their use in thermal energy storage systems based on phase change materials (PCMs). Conventional organic PCMs, such as paraffin and fatty acids have relatively low thermal conductivities that limit their power capacity. Integration of PCMs with high-thermal conductivity carbon nanostructures fillers can potentially yield composites with improved thermal properties. However, a number of challenges associated with larger interface thermal resistance between the fillers and between the fillers and the PCM need to be addressed by rational structural and compositional design of such composites.
Here we demonstrate the synthesis of carbon nanotubes (CNTs) on the ultra-thin graphite foam (UGF) with a pore size of 450 µm, and integration of these hybrid structures in composite phase change materials (PCMs) used for thermal energy storage. CNTs were grown on UGF foams using a CVD method at 750 °C with 5 nm thick Fe and 10 nm thick of Al₂O₃ films as catalysts and acetylene as a hydrocarbon gas. The CVD process yields high quality multi-walled nanotubes with the bottom end seamlessly connected to the UGF struts and the top end containing the Al₂O₃ layer. Overall, the fabricated hybrid structure represents a combination of macroscopically three dimensional UGF with one-dimensional CNTs extended toward the pores of the UGF. The length of the grown CNT can reach up to 500 µm, which is longer than the UGF pore sizes, allowing the tubes to bridge the opposite walls of the pores. The synthesized hybrid carbon structures have been assembled with erythritol, a PCM, to produce UGF/CNT/PCM composites. Thermophysical properties, such as a heat fusion, thermal conductivity, melting and crystallization temperatures of the composite have been investigated. The combination of strong interface bonding and large surface to volume ratio provided by the hybrid structure has been found to enhance the thermal conductivity, diffusivity, and transient phase change processes of the composite PCM materials.

Recently, highly efficient invertors made of SiC power devices are expected to contribute to the energy problems. To exhibit the high performance of SiC device, new electrodes for high current density, high temperature, and heat dissipation are desired. Carbon nanotube (CNT) is the candidate. CNTs synthesized on SiC by surface decomposition method (CNTs on SiC)^[1][2] exhibit the most densely packed CNT forest (surface density: ~3x10¹² cm^-2) and is suitable for electrodes because of their high current density durability. In this work, we evaluated the dependence of the contact resistivity on SiC dopant concentration and Schottky barrier height at CNT/SiC interface.
CNTs on SiC were formed by annealing the C-face of n-type 4H-SiC substrate in vacuum at the temperature of 1600 ^oC. Ti/ Au was deposited on CNTs on SiC as the top contact electrode. To restrict the contact area of CNT forest on SiC, electrically isolated areas were fabricated with focused ion beam. The electric properties were measured by 2-point-probe method to obtain size dependence of total resistance, which includes top/bottom contact resistances and CNT bulk resistance, and then the contact resistivity at CNT/SiC interface was separated.
The contact resistivity at CNT/SiC interface was evaluated as ~3×10^-4 Omega;cm² when SiC dopant concentration is ~3×10¹⁸ cm^-3, and was decreased as the dopant density increases. Schottky barrier at CNT/SiC interface becomes thinner and tunneling current increase as the doping concentration in SiC increases. Schottky barrier height can be revealed as 0.40 ~ 0.45 eV. This value is equivalent to NiSix which is the most major ohmic contact to SiC. Therefore, this Schottky barrier height is very low for SiC and indicates that CNTs on SiC ohmic-contact to SiC with high dopant concentration of >10¹⁹ cm^-3. CNTs on SiC can be desirable electrode for SiC power devices.
[1] M. Kusunoki et al., Appl. Phys. Lett.77, 531 (2000)
[2] M. Kusunoki et al., Appl. Phys. Lett. 87, 103105 (2005)

Carbon nanotubes have shown promising properties as electrochemical electrodes such as the rapid electron transfer kinetics, wide potential window, high sensitivity, biocompatibility, and manufacturing versatility [1]. CNT-based flexible devices have been investigated extensively for varieties of application in gas sensors [2], pH sensor [3] and electronics devices, but there are few reports on electrochemical applications (chemical and bio sensors) [4-7]. In addition, the conventional solution-based process to form CNT thin film may degrade the performance and the uniformity in electrochemical activity on the electrode surface due to the contamination associated with dispersal substances. In this study, we demonstrate high-performance flexible microelectrodes based on a CNT thin film for electrochemical biosensor applications, and apply them to detect dopamine, an important neurotransmitter.
The CNT microelectrodes were fabricated on a PEN substrate by dry transfer method, and standard microfabrication process [8]. In the electrode structure, only CNT surface is exposed to electrolyte and performs electrochemical reaction. To minimize the contamination of CNT surface due to photoresists, the CNT surface was covered with an oxide film during the fabrication process [9]. An array of 35 microelectrodes was fabricated on the PEN substrate in size of 10×15 mm².
The electrochemical properties of CNT microelectrodes were characterized by cyclic voltammetry with K₄[Fe(CN)₆]. The results showed the well-defined sigmoidal voltammetric curves, the steady-state characteristic of ultramicroelectrode, and reversible properties with the difference in quartile potentials |E_3/4 - E_1/4| ~ 60 mV, close to the ideal value (59 mV). This means that the fabricated CNT microelectrodes have high electron transfer rate. Electrodeposition of gold nanoparticles on electrode confirmed the uniformity in electrochemical activity of the CNT surface, especially after an activation process. These CNT microelectrodes also exhibited high sensitivity in detection of dopamine.
[1] J.J. Gooding, Electrochimica Acta, 50 (2005) 3049.
[2] Y. Sun and H.H. Wang, Advanced Materials, 19 (2007) 2818.
[3] D. Lee and T. Cui, Biosensors and Bioelectronics, 25 (2010) 2259.
[4] X.B. Yan, X.J. Chen, B.K. Tay and K.A. Khor, Electrochemistry communications, 9 (2007) 1269.
[5] J.-Y. Lee, E.-J. Park, C.-J. Lee, S.-W. Kim, J.J. Pak and N.K. Min, Thin Solid Films, 517 (2009) 3883.
[6] M.-P.N. Bui, X.-H. Pham, K.N. Han, C.A. Li, Y.S. Kim and G.H. Seong, Sensors and Actuators B: Chemical, 150 (2010) 436.
[7] M.-P. NgocáBui, K. NamáHan, C. AiáLi and G. HunáSeong, Chemical Communications, (2009) 5549.
[8] D.-m. Sun, M.Y. Timmermans, Y. Tian, A.G. Nasibulin, E.I. Kauppinen, S. Kishimoto, T. Mizutani and Y. Ohno, Nature nanotechnology, 6 (2011) 156.
[9] N.X. Viet, Y. Ukita, M. Chikae, Y. Ohno, K. Maehashi, K. Matsumoto, P.H. Viet and Y. Takamura, Talanta, 91 (2012) 88.

Supercapacitors are important energy storage devices due to their high specific power and moderate energy storage capabilities. They are applicable to electric vehicles, pulse power systems and portable devices. A lot of effort has been spent to develop main components of many flexible and transparent electronic devices; however, energy and power sources in those devices have retained their classic form factor. Therefore, it is of great interest to develop both transparent and flexible supercapacitors. Supercapacitors with single walled carbon nanotube (SWNT) thin film electrodes are highly appealing candidates for this purpose owing to their high conductivity, ion permeability (resulting in high power density) and chemical inertness (long cycle lifetime).
In this work, we fabricated flexible and transparent SWNT thin film based supercapacitors using a polymer based gel electrolyte on polydimethylsiloxane (PDMS) substrates. High electrical conductivity of SWNT thin films allowed the possibility of fabrication of supercapacitors without a separate charge collector. Electrochemical properties of symmetric solid-state supercapacitors with SWNT electrodes were then investigated using cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. A detailed analysis of the electrochemical properties of the fabricated supercapacitors will be presented. Supercapacitors with SWNT thin film electrodes had a specific capacitance of 34 F/g with an optical transmittance of 74%. We will present a detailed analysis of electrochemical properties of the fabricated supercapacitors to underline their capacitive behavior. Our results reveal the potential of the use of SWNT thin films in transparent and flexible supercapacitor electrodes that can be fabricated through simple solution based methods.

Lithium-Sulfur (Li-S) batteries, consisting of lithium metal as anode and sulfur as cathode, are extensively being investigated because of their superior theoretical capacity (1675 mAh/g) and energy density (2500 Wh/kg). Meanwhile, in combination with the natural abundance, low cost, light weight and environmental friendliness of elemental sulfur, Li-S batteries have become one of the most attractive candidates for next generation rechargeable batteries. However, despite these advantages, the performance of Li-S batteries is limited by two main problems. One is the poor active material utilization caused by the insulating nature of sulfur and its discharge products Li₂S. The other one is poor cycle life and low system efficiency related to dissolution and shuttling problem with polysulfides in conventional organic electrolytes. To overcome this, considerable research efforts have placed on improving the cathode conductivity and stabilizing the active material within cathode.
In this work, we report a novel dual protection structured sulfur composite developed with cut carbon nanotube (CCNT) and a conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The process involves the modification of Multi-wall CNTs by acid treatment and loading of sulfur on CCNT by chemical reaction deposition. Then the conducting PEDOT is coated on the surface of S/CCNT particles by in-situ polymerization. Within this structural design, the CCNT undertakes the role of carrying the sulfur into the conductive carbon network, whereas the conducting PEDOT contributes to direct coverage of sulfur to inhibit the diffusion of polysulfides out of the cathode and enhance the capacity and cycling stability. TGA, XRD, BET, FTIR, SEM and TEM are respectively carried out for examining the obtained PEDOT/S/CCNT ternary composite. Cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) experiments are used to evaluate the electrochemical performance of the ternary composite in half cells. More detailed results will be discussed in the meeting.

The potential roll-to-roll, low-cost fabrication of organic photovoltaics has become increasingly attractive for power generation to even the most remote locations. P3HT (poly(3-hexylthiophene)) and PCBM ([6,6]-phenyl-C-61-butyric acid methyl ester) are the most widely used donor/acceptor materials in organic photovoltaics (OPVs). One of the biggest challenges of organic semiconductors is their low charge carrier mobility. The four to five orders of magnitude higher charge carrier mobility of semiconducting (sem-) single walled carbon nanotubes (SWNTs) can potentially address this issue, if one manages to appropriately configure them in heterojunction structure with the proper carrier extraction architecture. To this effect, the supramolecular organizations of flavin mononucleotide (FMN) around single walled carbon nanotubes (SWNTs) was shown to provide effective nanotube dispersions and the ability to impart selective enrichment of sem-SWNTs by recognizing the underlying nanotube helical pattern. Utilizing this approach, we herein present our recent work in outfitting the organic analogue of FMN (FC12)^[1] with a terminal PCBM functionality. Such seemingly straightforward coupling, presents a number of challenges associated with both charge transfer and H-bonding interactions between the C₆₀ and flavin moieties. Various approaches are discussed along with successes and failures in their different synthetic routes.
^[1] Ju, S.-Y.; Kopcha, W.; Papadimitrakopoulos, F.; Science, 2009, 323, 1319-1323.

Carbon nanotube (CNT) has remarkable electrical properties, making it an attractive material for electrode fabrication, thus numerous efforts to implement it in various electrochemical device such as an electric double layer capacitor has been developed. In this study, we propose a new device utilizing vertical aligned CNTs as the electrode, to generate micro/nano bubbles by means of an electrochemical method. Micro/nanobubbles have unique electrochemical properties originated in their size, and have been garnering attention in fields such as medical science and agriculture. Research regarding its application, such as wound sterilization, cell activation of edible rice, and seawater conduit cleaning is well underway, but further development of their application will require detailed fundamental information regarding their size derived characteristics. Therefore, a device that can control individual bubble size at a certain address will be an invaluable tool for this purpose. In this study, we use vertically aligned CNTs as an electrode for water electrolysis in order to enable some control over bubble generation.
Vertically aligned CNT of about 300 mu;m height were synthesized on an Si substrate by means of chemical vapor deposition. It is then covered by polydimethylsiloxane (PDMS) using spin coating so as to produce a resin composite film in which vertically aligned CNT is trapped while retaining its original structure. This method enables us to obtain a surface structure in which the tip of each vertically aligned CNT slightly protrudes from the PDMS matrix by adjusting the viscosity of the PDMS solution and spin speed used for spin coating. Furthermore, when the resulting film was peeled off from the Si substrate, the base surface shows that individual CNT tips were slightly exposed. By conducting water electrolysis using the CNT-PDMS electrode as cathode, electric field concentration occurs at the tips of each CNT protruding from the PDMS surface and bubbles are generated selectively following chemical reaction. When voltage is applied in a 10% NaOH aqueous solution, visible bubbles appeared instantaneously at over than 1V. When viewed under optical microscopes, two types of region have been found, an area that formed a large amount of bubbles of 1 mu;m or less diameter, and an area in which large bubbles grow rapidly. SEM observation of the electrode surface suggested that this variance is derived from the difference in shape of the exposed CNT. This CNT-PDMS electrode also requires lower voltage compared to pure CNT electrode to initiate bubble generation, and can be used continually without deterioration, even after repeated drying and cleaning.
This work was supported by JSPS KAKENHI Grant No. 26286024.

Silicon is emerging as a very attractive anode material for lithium ion batteries due to its low discharge potential, natural abundance, and high theoretical capacity of 4200 mAh/g, more than ten times that of graphite (372 mAh/g). This high charge capacity is the result of silicon&’s ability to incorporate 4.4 lithium atoms per silicon atom; however, the incorporation of lithium also leads to a 300-400% volume expansion during charging, which can cause pulverization of the silicon material and loss of electrical contact between the silicon and current collecting substrate. The architecture of the anode must therefore be able to adapt to this volume increase. Here we present a low cost, high-rate, and scalable process for constructing silicon anodes using directed assembly techniques to create a layered carbon nanotube and silicon nanoparticle structure. This layered architecture increases the surface area available for electrochemical reactions, and also provides a conductive path to the current collecting substrate.

Theoretical surface area of an individual single wall carbon nanotube (SWNT) is 1313 m²/g, however, surface area of the buckypapers made from SWNT powder without altering their structure by conventional methods is only half of its theoretical value. In this research a novel procedure is developed to disperse the SWNT and to make buckpapers with ~50% higher surface area than that of buckypapers made from the conventional method. Poly(methyl methacrylate) (PMMA) was used to prevent the SWNT aggregation, resulting in buckypapers of BET specific surface area as high as 900 m²/g. Buckpapers with single-wall and few-wall carbon nanotubes were made using conventional and developed methods and the effect of the surface area on electrochemical properties of the supercapacitors were investigated. A unique crystalline signature never observed previously in PMMA or PMMA/CNT composites was observed in the X-ray diffraction of the high surface area SWNT buckypapers, indicating a strong interaction between the PMMA and SWNT.

In order to selectively disperse semiconducting single-walled carbon nanotubes (SWNTs), wrapping by conjugated polymer have been researched widely. As introducing the wrapping SWNT via conjugated polymers, the sorting of semiconducting SWNTs can be achieved efficiently for using SWNTs in solution processing printed electronics. Although the field-effect transistors (FETs) based on sorted SWNTs have shown high charge carrier mobility, on/off ratio, and excellent mechanical flexibility, still a number of challenges are remained such as controlling threshold voltage or achieving highly stable devices. As one of strategies, especially, solution processed doping using various dopants is considered as efficient method for continuous processing of printed electronics. This method can be effectively applied to SWNT based FETs. In this study, the high performance top-gated and bottom contact (TG/BC) SWNT-FETs, wrapped by conjugated polymer for efficient sorting of semiconducting SWNTs, have been researched by introducing solution processed doping with various dopants. As applying doping SWNT approach by solution processing with various dopants into fabrication TG/BC SWNT-FETs, significant effect was observed such as converting polarity, and shift of threshold or turn-on voltages. In addition, it is applied to fabricate SWNT base complementary metal-oxide-semiconductor (CMOS) like inverters and logic gates.

Research on energetic material has focused on enhancing the power of its composite, increasing its insensitivity and stability and recycling decayed energetic materials through eco-friendly methods. Carbon nanotubes can offer advantages as new energetic materials due to their increased surface areas, enhancement of chemical reactivity by high thermal conductivity, and the ability to form composites with fuels by surface functionalization.
We explore the exothermic chemical reaction of fuels, which are deposited on the surface of single-walled carbon nanotubes (SWNTs) used as thermally conductive nanoconduits. We synthesize the vertically aligned SWNT forest using chemical vapor deposition and cover SWNT surfaces with nitrophenyl energetic materials via physical and chemical methods to produce SWNT-energetic material composites.
We reveal for the first time that there is a critical ratio of energetic materials to SWNT and composite morphology for enhanced energy release. Composites show explosive exothermic reaction when the ratio of energetic materials to SWNT is higher than 2 and when energetic materials are deposited mostly inside the SWNT forest, that is, between SWNT bundles.
In addition, we demonstrate that the inside as well as outside of SWNT forest can be uniformly coated with energetic materials when nitrophenyl energetic materials are chemically attached on SWNT surfaces via diazonium chemistry, while only outside of SWNT forest can be exclusively coated by physical method. Accordingly, the energy density as well as uniformity of the composites is higher with chemically decorated composites over physically decorated ones.
When SWNT-energetic material composites, prepared by chemical methods, are ignited by electrical discharge, energetically functionalized SWNTs release exceptional high energy, while energetic materials without SWNTs do not show any energy release, providing evidence for carbon nanotube-guided chain reactions.

We propose a development of a new mechanical sensor by using a “thread transistor.” It can be constructed by using a composite material of a carbon nanotube(CNT) and a thread, i.e., a CNT-composite thread(CNTCT). The CNT is expected to be a next-generation material because it has a lot of useful characters, e.g., it can have both metallic-(M-) and semiconducting-(S-) characters. In contrast, a lot of threads exist in our life. And the thread is flexible. Our CNTCTs that we have recently developed have characteristic of both CNTs and threads. Moreover, we have also succeeded to develop the “thread transistor” by using a M-CNTCT and a S-CNTCT. Therefore, in the near future, the thread transistor may be used around us.
In this study, we prepare the CNTCT by dipping cotton threads into the CNT dispersion. After that, we also prepare our “thread transistor.” Here, we develop and demonstrate a new type of a mechanical sensor by using our "thread transistor". In concrete, we observe the characteristic change by tensing the threads. To do this, we prepare M-CNTCT and the S-CNTCT. To construct thread transistor, we coat non-conductive paint to S-CNTCT. After the paint dried, we tense the S-CNTCT and tied the M-CNTCT round the S-CNTCT. In the thread transistor, the S-CNTCT play a role of channel and the M-CNTCT play a role of gate electrode. The source and drain electrodes can also be materialized by tying the M-CNTCT. In this time, we measured resistance of the M-CNTCT and the characteristic of the thread transistor. Furthermore, we tensed the M-CNTCT and measured the characteristic of thread transistor. As results of the measurements, the resistance of the M-CNTCT was about 650[Omega;/cm]. And we confirmed that our thread transistor could operate as a kind of a p-type MISFET. In addition, we measured the characteristic of thread transistor when the thread was tensed. In this case, we used an enameled wire instead of M-CNTCT and non-conductive paint for simplicity. When we tensed the S-CNTCT, the thread transistor did not behave as a FET. But when we quitted tensing, the thread transistor behaved as a FET once again. This phenomenon may be caused by two factors. First, we considered, the path of the S-CNT in the thread was torn by tensing the thread. Second, the gate voltage did not apply because the S-CNTCT may become thin by tensing. In contrast, when we tensed the enameled wire, the value of the drain-to-source current became small. Because the channel width became thin by tensing. Thus, when the threads are tensed, the characteristic of thread transistor is change. Therefore, we aim to apply this phenomenon to some devices, e.g., a mechanical sensor in the future work.

#12288;#12288;We propose a new electromagnetic shielding (EMS) sheet using carbon-nanotube (CNT)-composite paper. Recently, the electromagnetic environment surrounding devices such as mobile phones and personal computers has become increasing complexity because of the complicated electromagnetic noise. The noise can cause unexpected behavior in electronic devices, and the electromagnetic waves emitted by electronic devices can also reveal sensitive information about the device to the environment. Therefore, the noises need to be decreased. We focus on CNT-composite paper [1] as a new type of EMS sheet bases on the high electrical conductivity of CNTs. Furthermore, our paper combining pulp (paper fibers) and the CNTs have many advantages comparing with the metallic materials which are commonly used for EMS sheets. For example, the paper has good electrical conductivity in spite of a paper, the weight is light, and there is no deterioration problem because of both the CNT and the pulp properties.
#12288;#12288; In this study, we aim to make a new sheet that has a good shielding effectiveness (SE) over 30 dB in the whole frequency from 0.1 MHz to 1 GHz by using the paper. Our paper can reflect the electromagnetic wave on the surface of the paper and convert the electromagnetic energy to heat energy in the paper efficiently. The paper can be manufactured easily by a simple method that is based on a traditional method for making Japanese washi paper [1]. To make it, we use the multi-wall CNT (NC-7000, Nanocyl co.). Firstly, we prepare pulp dispersion by soaking and dispersing pulp in water. Secondly, we prepare CNT dispersion by dispersing the CNTs and TritonX-100 in water by irradiating with ultrasonic waves for 30 minutes. Thirdly, we mix the pulp and the CNT dispersion to make a mixed dispersion. Fourthly, we scoop up paper fiber and CNTs with a net from the mixed dispersion and dry it. Finally, we prepare some samples that have some CNT concentration and some shapes. To test the samples, we measure their SE with the Kansai Electronic Industry Development Center (KEC) method [2] which can check both the electric field and magnetic field. As results, our papers represented a good SE (over 30 dB) from 0.1 MHz to 1 GHz frequency.
References
[1] T. Oya and T. Ogino, Carbon 46, 169 (2008).
[2] Techno-Trading News. EMC Information No.24 (2003).

Recently carbon nanotubes (CNT) have attracted enormous attention due to their outstanding mechanical and electrical properties for strain sensors. With their unique quasi one dimensional structure and piezoresistive behavior, transition of conductive path ways allows CNT based composite as highly stretchable strain sensor. Here, we report an ultra-high stretchable and wearable device fabricated from dry spun carbon nanotube (CNT) fibers. The dry spinning technique is a solid state fiber spinning technique that provides an adjustable aligned structures. This aligned CNT fiber on a flexible substrate offers ultra-high stretchable properties with strain dependent resistivity. As a function of stretching distance, we observed constant increase of resistivity due to their transition of conductive path ways. This strain sensor exhibited over 800% stretching with high durability after 10000 cycles. We demonstrated applications from general strain gauge for monitoring status in architectures to wearable motion sensing devices. This device will open up applications for monitoring cracks, detecting motions and many other strain sensors where their capacities are limited to the strain.

We demonstrate a novel technique for quantitative detection of carbon nanotubes (CNTs) in biological samples by utilizing the thermal response of CNT under microwave irradiation. In particular, rapid heating of CNT due to microwave absorption is employed to quantify CNT uptake in agricultural samples with excellent sensitivity. The threshold for detectable CNT concentration is much lower (<0.1 µg) than common analytical methods such as electron microscopy and Raman spectroscopy. Considering the lack of effective detection methods for CNT uptake in plants, this method is not only unique but also practical, as it addresses a major problem in the field of nanotoxicology risk assessment. The microwave technique also holds promise for quantifying the microstructure of CNT/polymer nanocomposites.

Carbon nanotubes have attracted lots of attention from various fields of scientists because they exhibited extraordinary physical and chemical properties due to their intrinsic nano-sized feature. It should be noted that lots of carbon nanotube-derived products are already in use and their viability strongly depend on their commercialization. However, at present, several critical hurdles in the successful business of carbon nanotubes are considered to be (1) the large scale production of high quality carbon nanotubes in a low cost, (2) their limited end uses and (3) their safety issue. Thus, it is now urgently needed to speed up their current applications as well as find out their new end uses.
In this talk, I, first, describe the current status of industrial production of various types of carbon nanotubes in the world. Then, the controllability in the electrical, thermal and mechanical properties of carbon nanotubes will be described under various environments. Finally, recent practical uses of carbon nanotubes in Japan including super rubber sealant will be described.

Infrared and terahertz photodetectors are used extensively for applications in defense, communications, medical imaging, component inspection, and thermal imaging. Such detectors are often based on exotic semiconductor materials operated at low temperatures, and new approaches are sought that could lead to uncooled detectors or improved ease of integration with CMOS technology. In this presentation, I will discuss our recent efforts at developing and understanding carbon nanotube infrared and terahertz detectors. The detectors are based on macroscopic, optically-thick films of aligned single-wall carbon nanotubes, and are actualized using asymmetric contact electrodes or in p-n junction format. Responsivities of several Volts/Watt are observed in these devices, with a broadband spectral response spanning the visible to the terahertz. A combination of experiment and theory is used to demonstrate the origin of the responsivity and to discuss the performance attributes of such devices.

Carbon nanotubes can be envisioned as wave-guide integrated light sources for future on-chip data communication due to their unique structural, electrical and optical properties. The challenge thereby is to integrate and electrically contact solution processed nanotubes across CMOS compatible waveguide structures and to enforce efficient coupling of light from the nanotube into the waveguide. We will show how light from an electrically-driven carbon nanotube can be coupled directly into a photonic waveguide [1]. We realize wafer scale, broadband sources integrated with nanophotonic circuits allowing for propagation of light over centimeter distances. Moreover, we show that the spectral properties of the emitter can be controlled directly on chip with passive devices using Mach-Zehnder interferometers and grating structures. The direct, near-field coupling of electrically generated light into a waveguide, opposed to far-field fiber coupling of external light sources, opens new avenues for compact optoelectronic systems in a CMOS compatible framework.
[1] S. Khasminskaya, F. Pyatkov, B. S. Flavel, W. H. P. Pernice, R. Krupke, Advanced Materials 26 (2014) 3465

It is aimed to prepare polyvinyl alcohol/carbon nanotube (PVA/CNT) conductive nanofibers using the electrospinning process. Prior to composite preparation, carbon nanotubes were synthesized by chemical vapor deposition method. Then, carbon nanotubes are dispersed homogeneously in N-Methyl-2-pyrrolidone (NMP) and mixed with polyvinyl alcohol solution. A series of PVA/CNT film and nanofiber with various carbon nanotube composition are prepared using the spin-coating and the electrospinning process, respectively. Electrical conductivity and specific capacitance of spin-coated PVA/CNT films and electrospun PVA/CNT fibers increase with an increase in carbon nanotube content. Electrospun PVA/CNT nanofibers with larger electrode surface result in a higher specific capacitance when compared with spin-coated PVA/CNT films. According to the morphology analysis, homogeneous and highly porous PVA/CNT mat containing 50-300 nm diameter nanofibers are obtained by the electrospinning process.

The time scales and mechanisms for interfacial charge separation and recombination play crucial roles in determining efficiencies of excitonic photovoltaics. Semiconducting SWCNTs are robust light absorbers that have garnered increasing attention as the electron-donating or electron-accepting components in excitonic solar cells. In particular, near-infrared photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g. C₆₀). While the reported AM1.5 power conversion efficiencies of such devices are steadily increasing, significant improvements remain to be made if a better fundamental understanding is reached for the kinetics and thermodynamics of exciton dissociation and charge recombination. In this presentation, I will discuss a number of time-resolved spectroscopic studies on SWCNT:fullerene donor:acceptor heterojunctions, aimed at understanding the time scales and quantum yields for interfacial charge transfer, recombination rates and mechanisms, and the dependence of charge transfer rates and yields on interfacial energetics. In general, for optimized SWCNT:fullerene interfaces, we observe extremely fast charge transfer times, consistent with low reorganization energies and/or strong electronic coupling. Low reorganization energies are confirmed through measurements on SWCNT:fullerene heterojunctions where the charge transfer driving force is tuned by utilizing SWCNTs and fullerenes with widely varying electron affinities. Finally, recombination is found to depend sensitively on the charge density within the SWCNT film and appears to be mediated by traps of unknown origin. Our results provide routes toward improving upon current state-of-the-art PV devices and photodetectors based on SWCNT absorbers.

Effective heat removal from electronics is increasingly important as voltage, current, and frequency scale to increase grid efficiency. Without an efficient thermal interface material (TIM) between devices and their packaging material, the advantages of advanced power electronics are obscured due to the performance and lifetime reductions that occur with increasing temperatures. Vertically aligned multiwall carbon nanotube array-based TIMs are a promising alternative to conventional metal/epoxy-based TIMs because of the large thermal conductivity of multiwall carbon nanotubes (MWNTs) and the ability to eliminate the epoxy, a major thermal bottleneck. We are developing MWNT-based TIMs from untangled arrays of vertically-aligned nanotubes grown by thermal chemical vapor deposition (CVD) from catalysts embedded in the pores of anodized aluminum oxide templates directly on a heat-sink packaging material. The arrays have controllable geometry, can be planarized to facilitate thermal contact to heat-producing device surfaces, and have nanotubes that exhibit higher crystalline quality than those grown via plasma-enhanced CVD, as typically reported in nanotube TIM research. In this work we prepare MWNT arrays and study the effect of post-annealing to further improve MWNT crystalline quality, as evidenced by Raman spectroscopy. Scanning probe measurements on individual nanotubes correlate the resulting electrical and thermal transport properties with annealing conditions. Thermal conductivity measurements of MWNT arrays and device cooling tests are currently underway.
This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Isolated individual carbon nanotubes (CNTs) have shown exceptional thermal conductivity along their axis, but have poor thermal transfer between adjacent CNTs. Thick bundles of aligned CNTs have been used as heat pipes, but the thermal input and output areas are the same, providing no heat spreading effect. We demonstrate the use of energetic argon ion beams to join overlapping CNTs in a thin film to form an interpenetrating network with an isotropic thermal conductivity of 2150 W/m-K. Such thin films may be used as heat spreaders to enlarge the thermal footprint of laser diodes and CPU chips, for example, for enhanced cooling. At higher ion energies and fluence, the CNTs appear to collapse and reform, aligned parallel to the ion beam axis, and form dense high aspect ratio tapered structures. The high surface area of these structures lends themselves to applications in energy storage, for example. We consider the mechanisms of energetic ion interaction with CNTs and junction formation of two overlapping CNTs during the subsequent self-healing process, as well as the formation of high aspect ratio structures under more extreme conditions.

Nanostructured materials comprised of aligned carbon nanotubes (CNTs) are promising candidates for next-generation multifunctional applications. Extreme environment operation, enhanced stiffness, and low density motivate the study of aligned CNT carbon matrix nanocomposites (A-CMNCs). Here we report the synthesis of CNT A-CMNCs from polymer matrix precursors via a synthesis route compatible with industrial polymer derived ceramics processing. Structure-property relations are established, and the impact of CNT confinement on the morphology of the graphitic crystallites that comprise the carbon matrix is evaluated. A theoretical framework is used to analyze the impact of CNT packing on the specific hardness of the nanostructure, enabling the fabrication of a material that outperforms current generation carbon fiber reinforced carbon composites, and common engineering metal alloys, by more than a factor of 5× (from < 1 MPa * m³/kg to > 5 MPa * m³/kg). Morphological and structural features that limit the performance of this nanomaterial will be presented, and further work that could enable their better understanding, and ultimately control, is proposed.

We have discovered how to efficiently harvest photons using semiconducting carbon nanotubes.[1-3] Usually, when a film of nanotubes is illuminated, the photogenerated electron/hole pairs (excitons) are “stuck” to each other and rapidly lost to heat. We have overcome this problem and unlocked nanotubes&’ potential as absorbers by (i) dramatically reducing their structural and electronic heterogeneity and (ii) discovering how to drive the dissociation of excitons in the materials using type-II donor/acceptor heterojunctions. The efficiency of exciton dissociation and electron transfer from nanotube to C₆₀ exceeds 85% at the E₁₁ or E₂₂ transition of nanotubes when E₁₁ is > 1 eV.[2,3] We have learned that the propensity of nanotubes to aggregate into parallel arrays (fibers) dictates the flow energy in the films, occurring via inter-nanotube exciton energy transfer over 5 - 10 nm.[4] This flow of energy occurs across a complex energy landscape, which we have temporally resolved using two-dimensional white light ultrafast spectroscopy.[5] We have demonstrated the first proof-of-principal solar cells driven by nanotube excitons, based on simple bilayers between C₆₀ and ultrathin (~5 nm) films of semiconducting nanotubes that achieve a 1% solar power conversion efficiency (7% at the nanotube bandgap).[3,6] High internal quantum efficiency arising from the ultrathin nanotube layers indicates that future work on blended or multijunction solar cells exploiting multiple such layers will be many times more efficient. Work on blended heterojunctions with microstructure controlled by first creating extremely porous aerogels of semiconducting nanotubes (2.5 mg/ml) and then backfilling with C₆₀ derivatives shows promise in this direction.[7] Due to low dark current and external quantum efficiency as high as 50%, photodetectors with room temperature specific detectivity of 1E12 Jones at 1055 nm has been demonstrated.
1.M. S. Arnold, et al., Nano Lett. 9 (2009).
2.D. J. Bindl, M. S. Arnold, et al., Nano Lett. 11 (2011).
3.D. J. Bindl, M. S. Arnold et al., J. Phys. Chem. C 117 (2013).
4.R. D. Mehlenbacher, M. S. Arnold, M. T. Zanni et al., Nano Lett. 13 (2013).
5.R. D. Mehlenbacher, M. S. Arnold, M. T. Zanni et al., In Prep. (2014).
6.M. J. Shea, M. S. Arnold, APL 102, 243101 (2013).
7.Y. Ye, M. S. Arnold et al. Small (2014).

We have recently demonstrated for the first time the design of an aqueous electrochemical capacitor using the CNT electrodes with polyvinyl alcohol (PVA) based hydrogel membranes as separator, that has a relaxation frequency of 63 Hz (time constant ~ 15 ms and power density as high as 1040 kW/kg based on the mass of both electrodes. The CVs exhibit a rectangular shape indicating a capacitive response with excellent power capability at even 1V/s. The designed aqueous capacitors showed excellent cyclability (> 10,000 cycles) with good energy (~100%), and coulombic (~94%,) efficiencies at 10A/g.
We present a novel design of CNT-based flexible 3-stack bipolar solid state supercapacitor. We will present results on energy/power densities, voltage, cyclability, temperature stability in relation to flexibility and weight. Preliminary results indicate high temperature stability >85^oC and CV voltage ~3V.

There has been an increasing demand to develop sustainable energy sources with high energy-conversion efficiency. Direct ethanol fuel cells (DEFCs) are one of the promising clean power sources for diverse systems. To realize the utility of DEFCs in these applications, they will need to be cheap and lightweight as well as have high efficiency and long operation lifetime. We will present results on enhanced electrochemical performance of DEFCs with palladium (Pd) nanoparticle based catalysts supported on graphene-coated carbon nanotube aerogels. These three-dimensional, porous aerogels are lightweight, and provide easy transport pathways for fuel and ions. The ultra-high surface area of the aerogels allows deposition of small Pd nanoparticles, and the graphene coating hinders coarsening of the nanoparticles during operation and improves DEFC lifetime. The current density of our DEFCs was measured to be ~150 mA cm^-2, which is 70 times higher than DEFCs that utilizes the commercial electrodes that typically comprises of Pd nanoparticles on carbon black support. Further, the performance of our fuel cell showed minimal degradation over a 1000 cycles. This work has been partially supported by the NSF through Grants DMR 0645596 and CMMI 1335417.

The fabrication conducting pastes based on carbon nanotube(CNT) hybrid materials in organic solvents has been hindered by detrimental agglomeration. Here, we report a straightforward method for fabricating CNT-based conducting pastes without the need for organic dispersants promising the excellent electrical conductivity of the printed film. The proposed approach involves functionalizing the carbon nanotube materials with quadruple hydrogen bonding motifs without sacrificing the electrical conductivity. The judicious use of supramolecular interactions has allowed us to fabricate printable, spinnable, and chemically compatible conducting pastes with high-quality carbon nanotube hybrid materials, which could be useful for application in flexible electronics and textile electronics. The resulting pastes could be easily hybridized with a polymer for fiber spinning, or with metal and a metal oxide material to increase the electrical conductivity to 80000 S/m. Highly conductive polymer-composite fibers containing large amounts of conducting nanomaterials have not been produced without dispersant, however, because of the severe aggregation of conducting materials in high-concentration colloidal solutions. Here we show that highly conductive polymer-composite fibers containing CNT hybrid materials can be fabricated via a conventional solution-spinning process without any other treatment. The dispersant-free fabrication of conducting pastes opens up new possibilities for high-performance applications of nanocarbon materials in soft electronics, such as flexible, stretchable, or textile electronics.

At the Fraunhofer Institute for Material and Beam Technology (Fraunhofer IWS, Dresden) a new method for the integration of electrical surface conductivity into polymer surfaces was developed. The method is based on nanomaterial deposition into the molding tool for injection molding. Within the injection molding process, a highly conductive network of carbon nanotubes (CNT) is integrated as a thin film into the polymer surface. The method applied is cost efficient, technically applicable and can be easily integrated into existing industrial facilities. Compared with conventional conductive additives, which are added to the bulk polymer, material costs are very low, as the CNT layer has only a few nanometer of thickness. Providing a surface of 1m² with a 50nm CNT layer requires only a few milligrams of CNTs.
A further advantage, in addition to the low price is that the mechanical and optical properties remain almost unchanged and the achievable surface resistance of significantly less than 10⁹ #8486; is highly advantageous as well. With conductivities lower than 10⁹ #8486; materials are deemed to be not electrostatically chargeable and the achieved conductivities, gained with this new method, have a value of 10³ #8486;.
SWCNTs used in the process are produced at the Fraunhofer IWS and achieved the lowest resistance. For the production route, a pulsed arc system was developed to vaporize a doped graphite target. Depending on the used gases, 250g SWCNT can be produced per day in the Fraunhofer pilot plant. The diameters of the SWCNTs are 1.3nm ±0.1nm, they have a length of 10µm and are particularly of low defect, which is reflected in a G/D ratio of 25/1 (Raman spectroscopy).
The achieved transparency and the high flexibility of the CNT networks allow for their application in components, for example, as transparent electrodes, devices with antistatic surface, and antistatic packaging materials.

Since 2008, study of carbon nanotube (CNT) based thermophones has demonstrated the ability to produce thin, highly flexible, transparent loudspeakers. Contrary to conventional magnet based speakers, these loudspeakers or thermophones operate by what is known as the thermoacoustic effect in which a modulated change in temperature in an active element induces a pressure wave in the surrounding medium. Encapsulating nanotube sheets within an enclosure protects the relatively fragile active element from external hazardous environments and additionally creates a resonant system. We explore the effect of the device design and dimensions on the sound generation and cooling capabilities of the device. Additionally we discuss some potential applications for flexible thermophones as well as their inherent tradeoffs and limitations and compare the performance of thermoacoustic projectors with other thin and flexible loudspeakers. (ONR sponsored project, N00014-14-1-0152 ).

Strengthening behavior of composite containing discontinuous reinforcement is strongly related with load transfer at the reinforcement-matrix interface.We selected multi-walled carbon nanotube (MWCNT) and few-layer graphene (FLG) as a reinforcing agent. By varying a volume fraction of the reinforcement, aluminum matrix composites were produced by a powder metallurgy method. Although the reinforcements have a similar molecular structure, FLG has a 12.8 times larger specific surface area of volume more than MWCNT due to geometric difference. Therefore an increment of a yield stress versus a reinforcement volume fraction for FLG shows 3.5 times higher than that of MWCNT. Consequently, for both reinforcements, the composite strength proportionally increases with the surface area per composite unit volume.

The current study focuses on the influence of low nano-carbon loading (<0.5 wt%) to influence the structural development in the nano-composite fiber. Post fiber-spinning procedures including hot-stage drawing and annealing are used to induce ordered polymer domains assisted by the nano-carbon in the materials. The subsequent fibers exhibit stiffness and toughness well above the theoretically predictions. It was found that drawing and annealing procedures significantly enhanced the dimensions of fibrils, sub-fibrillar lamellar, and sub-lamellar grain size for the nano-composites as compared to control samples. This work discusses the role of the nano-filler toward the structural evolution of the polymer matrix during processing. The relationships between processing approaches and subsequent properties also provide new perspective for the use of nano-carbon as spinning aides to facilitate polymer ordering. It also brings to light the potential for producing high-performance composite materials from flexible polymers by minimal inclusion of carbon nano-fillers, which is attractive for commercial production in terms of cost.