Symposium NM3 : Nanotubes and Related Nanostructures

Catalyst is one of the most crucial factor governing the synthesis of carbon nanotube (CNT), as exemplified by our recent report on the preferential synthesis of semiconductor signle-walled CNT (SWCNT) via catalyst modulation using water ambient [1]. For the synthesis of long and vertically-aligned array (forest) of SWCNT, the stability is one of the most important factor in catalyst system, where long lifetime (typically >10 min) is required for the densely-packed array (spacing below 20 nm) of small (c.a. 3 nm) catalyst nanoparticle at high temperature (> 700 °C). To overcome the above strict requirements, Fe catalyst on AlO_x support layer was used as a common factor in the previous reports.
We have recently found out that the synthesis of mm-tall SWCNT forest can be possible using support layer not including Al atoms. Our recent studies showed the importance of AlO_x realizing a proper balance between Ostwald ripening and subsurface diffusion of iron catalyst to result in the formation of stable catalyst [2], and also demonstrated the controllability of the catalyst size and density by modulating the catalyst formation processes [3]. The above studies suggest that any materials other than AlO_x can also work as a support layer if we can precisely control Ostwald ripening and subsurface diffusion. Based on this idea, we have investigated the preparation process of MgO layer and achieved the synthesis of mm-tall SWCNT forest from Fe catalyst.
Furthermore, our recent investigation on the fundamental limitation in achieving both of the length and crystallinity in SWCNT forest is reported. Specifically, we have developed the novel catalyst system and process ambient to achieve the synthesis of tall (> 100 μm) SWCNT forest at high temperature (c.a. 1000 °C). Structural properties of the obtained SWCNT are compared with those of SWCNTs synthesized by floating catalyst method using similar process temperature and ambient, to provide an insight into the effect of catalyst-support interaction on the structure of CNT.

Acknowledgements
This presentation is based on results obtained from a project commissioned by the NEDO.

References
[1] S. Sakurai, M. Yamada, H. Sakurai, A. Sekiguchi, D. N. Futaba, K. Hata, Nanoscale 8 (2016) 1015.
[2] S. Sakurai, H. Nishino, D. N. Futaba, S. Yasuda, T. Yamada, A. Maigne, Y. Matsuo, E. Nakamura, M. Yumura, K. Hata, J. Am. Chem. Soc. 134 (2012) 2148.
[3] S. Sakurai, M. Inaguma, D. N. Futaba, M. Yumura, K. Hata, Small 9 (2013) 3584.

Fundamental understanding of the molecular routes by which carbon nanotubes (CNTs) are produced by catalytic chemical vapor deposition (CVD) is essential to their cost-effective production, and to tailored synthesis for applications. Oxygen-containing species, such as O₂, H₂O, and CO₂, have been shown to dramatically enhance CNT growth, but the underlying mechanisms of this enhancement are not well understood. Furthermore, these oxygen-containing species are thought to influence the recurrent poor reproducibility observed in standard CNT synthetic approaches, even at the laboratory scale. Here, we investigated the influence of O₂ on Fe/Al₂O₃ catalyst thin film annealing and resultant vertical CNT forest growth. Variable delivery of O₂ (0 to 800 ppm) to the gaseous atmosphere influenced the size distribution of the catalyst particles formed upon dewetting, but did not significantly affect the gaseous chemistry of the reactive growth atmosphere. As anticipated, the CNT diameter and alignment were strongly related to the annealed catalyst morphology, with catalyst particle diameters ranging from 12 ± 3 nm to 17 ± 3 nm and CNT diameters ranging from 4.8 ± 1.3 nm to 6.4 ± 1.1 nm (i.e., via a perpendicular nucleation mode, yielding CNTs smaller than the catalyst particles). At the lowest O₂ concentration, which resulted in the smallest catalyst particles, single- and double-walled tubes were found. At higher O₂ annealing atmospheres, larger catalyst particles were observed, and O₂ was found to significantly promote Ostwald ripening of Fe atoms. In contrast, O₂ had a minor influence on subsurface diffusion of Fe atoms, and this was confirmed via X-ray photoelectron spectroscopy (XPS) element depth profile analysis and cross-sectional transmission electron microscopy (TEM). Using XPS, X-ray diffraction (XRD), and thin film X-ray reflectivity (XRR) to characterize the catalyst-supporting substrates, we demonstrated reduced alumina densities at lower O₂ atmospheres, corresponding to higher O deficiencies in the alumina support. We postulate that these stoichiometric vacancies led to positive charge build up in the substrate and hindered the surface diffusion of Fe atoms during the high-temperature process. Results from a matrix annealing study at various H₂ (20 to 80%) and O₂ (0 to 100 ppm) partial pressure demonstrated that the promoting effect of O₂ on Ostwald ripening was diminished in high H₂ environments, confirming the importance of oxidation to the ripening of Fe atoms. Control experiments in a separate reaction system designed for the precision control of water vapor confirmed that the observed effects were due to the presence of O₂ rather than H₂O. Taken together, these results not only suggest that dimolecular O₂, rather than H₂O, could be responsible for day-to-day variations observed in CNT catalyst preparation, but also provide insights into the control of CNT diameter and density via the manipulation of catalyst formation process.

Single-walled carbon nanotubes (SWCNTs) exhibit many outstanding properties, therefore, they have a huge potential for electronics applications. To realize SWCNT devices compatible with LSI manufacturing processes, the synthesis of SWCNTs at low temperatures below 400°C is essential to prevent the degradation of interlayer dielectric films. Previously, we reported SWCNT growth by alcohol catalytic chemical vapor deposition (ACCVD) using Pt catalysts [1]. Recently, theoretical calculations have revealed that, compared to other transition-metal surfaces, Rh(111) face exhibits a low dissociation barrier for an ethanol molecule, promoting cleavage of ethanol C-C bonds [2]. In this study, we synthesized SWCNTs by ACCVD using Rh as a catalyst. By precisely optimizing the ethanol pressure, we successfully grew SWCNTs below 300°C.
Rh catalysts were deposited onto Al₂O₃/SiO₂/Si substrates using electron beam deposition. SWCNT growth was carried out on the Rh/Al₂O₃/SiO₂/Si in an ultra-high vacuum chamber equipped with a stainless steel nozzle for introducing the ethanol gas [1]. The base pressure was less than 1×10^-6 Pa, which enabled the precise control of the ethanol gas supply. The growth temperature was varied between 270 and 600°C. The grown SWCNTs were characterized using SEM and Raman spectroscopy.
SEM and Raman results showed that SWCNTs were grown at all temperatures by optimizing the ethanol gas supply and that the optimal ethanol pressure decreased with decreasing growth temperature. The catalyst activity of Rh is greater than that of Pt in the low-temperature region and, even below 300°C, RBM peaks were observed in Raman spectra, indicating the SWCNT growth. The estimated activation energy of SWCNT growth for Rh catalysts were lower than those reported for SWCNT growth by ACCVD using Co catalysts. Taking into account the theoretical calculations [2], the low energy barrier of the Rh surface for the dissociation of ethanol molecules enabled SWCNT growth below 300°C.

[1] A. Kozawa et al. Diamond Relat. Mater. 63 (2016) 159.
[2] J. –H. Wang et al. J. Phys. Chem. C 113 (2009) 6681.

Chemical Vapor Deposition (CVD) synthesis of CNTs is capable of producing aligned, densely packed, and very pure forests which have a variety of unique applications including drawing CNT yarns, as nearly ideal light absorbing coatings, and growing 3d CNT structures from patterned catalyst. While individual CNTs can be grown for extraordinarily long periods and up to 50 cm long using floating catalyst, aligned CNT forests exhibit rapid termination on the order of centimeters. CNT forests grow when the number density of active catalyst particles is above a critical value causing tubes to crowd together and self organize; growth terminates when catalyst poisoning, Oswald ripening, or diffusion into the support reduces the number density below that critical value. Femtosecond laser irradiation provides a new method to manipulate the energetics of CNT nucleation and growth in order to increase the time before termination, yield, and control CNT structure.
We have shown that pre-irradiation of catalyst in air leads to a 3-fold increase in the terminal length of CNT forests and that irradiation of catalyst with a single ultrashort pulse in-situ as growth begins increases terminal length up to 150-fold. Under conditions that do not result in an aligned forest but instead a diffuse mat, areas of catalyst irradiated with a single ultrashort pulse grew in an aligned CNT forest up to 3 mm in length. Continued investigation has shown that optimal timing for in-situ laser treatment of the catalyst in the growth step is accompanied by strong light emission attributable to the optical breakdown of CNTs. We propose that the generation of a large quantity of carbon containing products via laser breakdown along with the increased carbon solubility of laser heated iron catalyst particles creates conditions approaching Pulsed Laser Vaporization synthesis of CNTs. This environment could increase the number density of active catalyst prolonging the time before termination and thereby increasing the forest height in the laser spot. Electron transparent foils of SiO2 with Fe/Al2O3 catalyst were pre-irradiated and irradiated during growth; Transmission Electron Microscopy measuring the structure of catalyst nanoparticles and the population of active catalyst will be presented.

Conventional polymer-based lithography is widely used to define the location of carbon nanotube (CNT) synthesis. The feature size of patterning during synthesis is thus limited by the photoresist and the wavelength of light being used during lithography. To go beyond the currently used lithography, we have invented a new technique which can modify the surface chemistry with high precision. The process, termed “e-beam chemistry”, uses a focused electron beam from conventional electro-optics in the presence of water vapor to modify the surface chemistry of the substrate at precise locations thus activating heterogeneous catalysis for controlled synthesis of CNTs in selected areas. Using this process, inactive substrates like c-cut sapphire are activated it in selective areas using e-beam and H₂O (vapor pressure ~ 0.1 Torr). Exposing the activated sapphire to typical CNT growth conditions results in growth of vertical aligned CNTs only in those areas of the substrates that have selective activation of surface via e-beam chemistry. The proposed e-beam method enables spatial resolution beyond conventional photolithography and also beyond the values that is obtained using ion beam in Refs. 1,2. The process currently is only limited by the size of the probe. Using high resolution electron optics having ~0.1 nm probe size and minimum generation of secondary electrons, we will achieve single-atom precision during our e-beam chemistry for atomic (~ angstrom) scale engineering of materials properties.

[1] A. E. Islam, P. Nikolaev, P. B. Amama, S. Saber, D. Zakharov, D. Huffman, M. Erford, G. Sargent, S. L. Semiatin, E. A. Stach, and B. Maruyama, Nano Lett., 2014, 14 (9), pp 4997–5003.
[2] P. B. Amama, A. E. Islam, S. M. Saber, D. R. Huffman, and B. Maruyama, Nanoscale, 2016,8, 2927-2936.

Bimetallic catalysts such as Co-Mo have been used for efficient growth of bulk single-walled carbon nanotube (SWNTs) [1] and vertically aligned SWNTs [2, 3]. Recently, bimetallic catalysts such as Co-W [4] or Co-Cu [5] are employed for structure controlled growth of SWNTs. Roles of bimetallic catalysts are explored by newly proposed in-plane transmission electron microscopy (TEM) technique, which enables a direct TEM characterization of catalysts and CVD grown nanotubes on SiO₂ TEM grid. Sputtered and dip-coated cobalt-based catalysts, i.e., Co, Co-Mo, Co-Cu, Co-W, are studied in alcohol catalytic CVD (ACCVD).
The in-plane TEM result of the traditional Co-Mo bimetallic catalysts was consist with our previous report [3]; Co nanoparticle embedded in Co-Mo oxide which adhered to the substrate is the responsible to the nucleation of carbon nanotubes. By using Co-Cu catalysts, we can synthesize vertically aligned SWNTs with subnanometer diameters on quartz (and SiO₂/Si) substrates [5]. Scanning transmission electron microscopic energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into larger size, which contributed to the small diameter of SWNTs. High-melting point W₆Co₇ alloy is reported to grow a single chirality (12,6) with over 90 % abundance through high-temperature (1030 deg. C) reduction and growth [3]. Here, we show that a sputtered Co-W catalyst can selectively grow (12,6) SWNTs by CVD at lower reduction and growth temperatures [6]. Statistical Raman mapping analysis and optical absorption spectrum of the as-grown SWNTs reveal that the abundance of (12,6) is over 60 %. The morphology and structure of catalyst is investigated by the in-plane TEM before and after CVD growth. The catalyst alloy we produced was W₆Co₆C and the only metallic Co was left after the CVD of 5 min.

References:
[1] B. Kitiyanan, W. E. Alvarez, J. H. Harwell, D. E. Resasco, Chem. Phys. Lett., 317 (2000) 497.
[2] Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu, M. Ogura, T. Okubo, S. Maruyama, Chem. Phys. Lett., 385 (2004) 298.
[3] M. Hu, Y. Murakami, M. Ogura, S. Maruyama, T. Okubo, J. Catalysis, 225 (2004) 230.
[4] F. Yang, X. Wang, D. Q. Zhang, J. Yang, D. Luo, Z. W. Xu, J. K. Wei, J. Q. Wang, Z. Xu, F. Peng, X. M. Li, R. M. Li, Y. L. Li, M. H. Li, X. D. Bai, F. Ding, Y. Li,, Nature 510 (2014) 522.
[5] K. Cui, A. Kumamoto, R. Xiang, H. An, B. Wang, T. Inoue, S. Chiashi, Y. Ikuhara, S. Maruyama, Nanoscale, 8 (2016) 1608.
[6] H. An, A. Kumamoto, H. Takezaki, S. Ohyama, Y. Qian, T. Inoue, Y. Ikuhara, S. Chiashi, R. Xiang, S. Maruyama, submitted.

Single-walled carbon nanotubes (SWNTs) have shown great potentials in various applications attributed to their unique structure-dependent properties. Therefore the controlled preparation of chemically and structurally pristine SWNTs is a crucial issue for their advanced applications (e.g. nanoelectronics) and has been a great challenge for two decades. Epitaxial growth from well-defined catalyst nanocrystals is a possible strategy to produce structure-specified SWNTs. Only catalysts with desired atomic arrangements in their crystal planes can act as the structural templates for chirality specific growth of SWNTs, relying on the high selectivity in geometry match between catalysts and SWNTs. We developed a new family of catalysts, tungsten-based intermetallic compounds, which have high melting point and very special crystal structure, to synthesize facilitate the growth of SWNTs with designed chirality. The chirality-specific growth of SWNTs is realized by the cooperation of two factors: the structural match between SWNTs and the catalysts makes the growth of SWNTs with specific chirality thermodynamically favorable; and further manipulation of CVD conditions obtains optimized growth kinetics for SWNTs with this designed chirality. This idea has also been proved to be valid for SWNTs with other chiralities and other intermetallic catalysts. We expect that this advanced epitaxial growth strategy will pave a way for the ultimate goal of chirality control growth of SWNTs and also be applicable in the controlled preparation of other nanomaterials.

Since the invention of the first multi-channel carbon nanotube (CNT) field-effect transistor (FET), it has been one of the long pursued goals to scale the uniform inter-CNT pitch beyond 15 nm. Thin film-based depositions often yield CNT arrays with irregular-spaced pitches or with wide orientations. Therefore, the resolution and precision for placing CNTs, the key parameters determining the inter-CNT pitch, still fail to meet the requirements of scaling CNT FETs beyond 10 nm technology node. Here, we report a method called spatially hindered integration of nanowire electronics for uniformly scaling inter-CNT pitch. Specifically, by using sub-10 nm wide DNA nano-trenches to spatially confine the directional deposition of CNTs, we constructed parallel CNT arrays on DNA brick crystals with uniform programmable pitches ranging between 24.1 nm and 10.4 nm at the assembly yield over 95%. Furthermore, we assembled the aligned CNT arrays over millimeter-scale, through confined placement of the CNT-decorated DNA brick crystals on Si substrate. Finally, after DNA removal, we demonstrate CNT FETs with uniformly prescribed pitch for future nano-electronics.

Single-walled carbon nanotubes (SWNTs) have been considered as the likely candidate for miniaturizing nanoelectronics. However, one major obstacle to realization of SWNT-based nanotechnology has been the lack of technique for producing SWNTs with identical structures.This is partly due to the incomplete understanding of the SWNT nucleation mechanisms. In situ environmental transmission electron microscopy (TEM) is suitable for understanding SWNT growth process, but the low throughput of carbon nanotubes hinders obtaining consistent results and the data acquired so far are very fragmentary.

In this contribution, we demonstrate the reversible modulations of SWNT nucleation mode by regulating the carburization of catalyst particle during chemical vapor deposition processes. Particularly, by alternating carbon precursors, including CH4 and CO, which induce very different carbon chemical potentials at gas-catalyst interface, SWNT intramolecular junctions with significant diameter change along SWNTs are fabricated.

By performing a systematic TEM study, the size correlation between the SWNTs and the catalyst nanoparticles on which SWNTs grow reveals two nucleation modes: perpendicular mode and tangential mode [1], depending on the gas precursor used during chemical vapor deposition process. This is because different carbon chemical potentials at gas-metal surface lead to different carbon concentrations in catalyst particle. As demonstrated by Grand Canonical Monte Carlo simulations, high carbon content in nanoparticle favors the perpendicular mode of SWNTs nucleation and growth, different from the tangential mode promoted by nanoparticle with a low carbon concentration. The calculations are well consistent with the experimental findings, highlighting the importance of particle carburization in controlling the SWNT nucleation mode.

The understandings could provide guidelines for catalyst design and growth condition optimization, paving the way to success in structure-controlled synthesis of SWNTs [2,3].

[1] M.-F. Fiawoo et al., Phys. Rev. Lett. 108, 195503 (2012)
[2] M. He et al., Nanoscale 7 20284 (2015)
[3] M. He et al., submitted

In this contribution, we will first review methods of chiral structure analysis of single-walled carbon nanotubes (SWNTs) by electron diffraction (ED) technique. With that as a basis, we have established an approach using ED as a means to evaluate the validity of Raman spectroscopy for quantification of concentrations of metallic SWNTs (M%) or of semi-conducting tubes (S-SWNT%). We will also introduce a method to examine the relationship between the chirality of SWNTs and their intrinsic chemical reactivity. Such chirality dependence of chemical reactivity provides an effective approach towards controlling the chirality of SWNTs. After that, by introducing a certain amount of ammonia to a catalytic CVD process, we have succeeded in producing SWNTs with a narrow chirality distribution and large chiral angle, while maintaining the large diameter properties of high-temperature routes. Last but not least, we also demonstrated that structural control of SWNTs is achievable by fabricating nanoparticle catalysts with a defined structure on crystalline substrates via epitaxial growth techniques. In situ time-resolved environmental transmission electron microscope (ETEM) observation at atomic resolution of nanoparticle formation and SWNT growth were accomplished.

References:
1) Hua Jiang et al, PRB, 74 (2006), 035427;
2) Hua Jiang et al, Carbon, 45 (2007), 662;
3) Bilu Liu, Hua Jiang et al, Small 9 (2013), 1379;
4) Zhen Zhu, Hua Jiang et al, JACS 133 (2011), 1224;
5) Maoshuai He, Hua Jiang et al, Scientific Reports, 3 (2013), 1460

Research on epitaxial graphene (EG) on SiC substrates has been rapidly growing toward application to high frequency analog devices, due to its extremely high mobility of the carriers as well as to its robust interface between graphene and the substrate. While the EG on SiC (0001) (Si-face) has been the major target so far, the EG on SiC (000-1) (C-face) has attracted recent attentions due to its even higher carrier mobility as compared to that on Si-face. The drawback of the EG on C-face, however, is that the on-wafer uniformity of the layer number distribution is quite low. In this work, we propose a novel fabrication method for forming a uniform EG by using a sputtered SiC films on SiC substrates.
Graphene was grown on the C-face of semi-insulating 6H-SiC substrates with or without the sputtered SiC films at temperatures ranging from 1400 to 1900 °C under an Ar ambient at 90 kPa. The SiC films were deposited by an RF magnetron sputtering with the several different thicknesses from 1 to 5 nm. The EG were characterized by using a Raman scattering mapping, an atomic force microscope (AFM), an optical microscope, a transmission electron microscope (TEM) and a low energy electron microscope (LEEM).
The impacts of the sputtered SiC films on the layer number distribution was investigated by assuming that the Raman G’ peak intensities correspond to the layer number of the graphene. As a result, the fractional area of the graphene having the layer number three or less increased from 50% to 95% by introducing the sputtered SiC film. TEM analyses clarified that the layer number of the graphene grown from the sputtered SiC films is from 2 to 3. These results indicate that the use of the sputtered SiC film remarkably improve the uniformity of the layer number distribution, which is suitable for fabrication of high frequency analog devices.
As for the mechanism for the uniform growth of EG on the sputtered SiC films, we currently understand that the sputtered SiC film inhibits nucleation and graphitization at surface defects on the surface of the SiC substrates. We are planning to investigate the mechanism of graphene growth with sputtered SiC films and the electrical characteristic of graphene fabricated from sputtered SiC films and demonstrate an application to high frequency analog devices.

The mechanisms by which Cu catalyst pre-treatments control graphene nucleation density in scalable chemical vapor deposition (CVD) are systematically explored. CVD is emerging as the industrially dominant growth technique for “electronic-grade”, mono- or few-layer large-area films of 2D materials, and Cu is one of most widely used catalyst materials in particular for graphene growth.[1] A crucial aspect of such CVD process development is to control nucleation of the 2D material effectively, as this dictates the texture of the growing 2D film. Many reports have shown empirically the effectiveness of catalyst pre-treatment. However, there is little understanding what the key mechanisms are that allow achieving a low graphene nucleation density.

Here, we investigate and compare the most widely used polycrystalline Cu catalyst pre-treatments and develop the critically required understanding of what the key mechanisms are that control the mono-layer graphene nucleation density.[2] Unlike previous reports, we use time-of-flight secondary ion mass spectrometry (SIMS) to depth- and surface-profile the Cu foils after the various CVD process stages in unprecedented detail. This provides a detailed picture of the contamination present in the Cu catalyst, as well as on the effectiveness of various pre-treatments. We are thus able to unambiguously show the critical importance of extrinsic and intrinsic carbon impurities. We devise a new simple method to study the effects of oxygen in this context by selectively oxidizing the Cu foil. This allows us to clearly decouple Cu surface roughness effects from chemical effects, triggered by oxygen permeation through the Cu bulk. Our study is undertaken with a commercial CVD reactor, widely used within the nascent graphene industry, with 50 cm²-sized Cu foils over which graphene is grown homogeneously. The implications of these findings are discussed regarding high-throughput mono-layer graphene CVD with domain sizes >1 mm. The insights from our data allow us to rationalize the many seemingly contradictory reports in literature on this topic and devise generalized guidelines for the most efficient pre-treatment methods for Cu catalysed graphene CVD.

[1] Hofmann, S. et al., The Journal of Physical Chemistry Letters 14, 2714 (2015)
[2] Braeuninger-Weimer et al, submitted (2016)

Catalytic chemical vapor deposition (CCVD) has long been recognised as the most promising technique for controlled synthesis of single-walled carbon nanotubes (SWNTs). However, understanding the nucleation-growth mechanisms of SWNTs remains a very difficult task limiting our ability to control the tube’s structure. In this context, understanding the key role played by carbon solubility in the catalyst particle seeding the nucleation and growth of SWNTs is an essential step towards a better knowledge and control on the growth mechanisms of SWNTs.

To go beyond phenomenological approaches, we have performed simulations at atomic scale. Here, we use a carefully assessed tight binding model for nickel and carbon [1] to numerically investigate different aspects of the CCVD synthesis process. Grand canonical Monte Carlo calculations to model metal-carbon systems of the type NiC [1] have shown very accurate results. Among other thing, nanotube growth from Ni nanoparticles was very accurately described [2]. It was also noticed that solubility and wetting properties are important parameters in which regard the growth [3]. In the present work, we plan to expand this model to a more general metal-carbon systems studying the influence of the solubility on the thermodynamics properties metal-carbon nanoparticles along with the growth of carbon nanotubes. By considering metals with different solubilities, we highlight that controlling the level of dissolved carbon in catalytic particles is of key importance to enable nucleation and growth.

[1] H. Amara, et al., Phys. Rev. B, 73, 014109 (2009)
[2] M.-F. C. Fiawoo, et al., Phys. Rev. Lett., 108, 195503 (2012)
[3] M. Diarra, et al., Phys. Rev. Lett., 109, 185501 (2012)

The conventional synthesis route for graphene films is chemical vapor deposition (CVD) which usually requires high growth temperatures and relatively long deposition times. We have shown that disordered carbon materials may be deposited using the energetic physical vapor deposition (PVD) technique filtered cathodic vacuum arc deposition (FCVA) with the microstructure of the resulting carbon film determined by the energy of depositing plasma and growth temperature [1] . Here we show that it is possible to use FCVA to synthesize carbon films containing less than 10 graphene layers from a pure carbon ion flux with energies of ~20eV. The films analyzed using a range of analytical methods including Raman spectroscopy, X-ray absorption near edge structure (XANES) and electron microscopy. The films were grown at much higher rates (~1 nm/min) and lower temperatures (750^oC) than normally required using CVD. The lower growth temperature was made possible by the energetic carbon flux which assisted the arrangement of carbon atoms into graphene layers. The addition of hydrogen was found to have little effect on film growth. Several substrate types were employed for growth, however graphene only formed on copper and nickel metal surfaces, indicating that, as in CVD, templating is required to initiate growth. Graphene films were also grown on copper coatings prepared using the same FVCA system. This graphene was transferable to the underlying substrate, enabling the preparation of graphene films on other materials.

[1] D.W.M. Lau, A. Moafi, M.B. Taylor, J.G. Partridge, D.G. McCulloch, R.C. Powles and D.R. McKenzie, Carbon, 47, 3263, 2009.

Formation of the carbon nanotube sock is a prerequisite for continuous production of thread and sheet using the floating catalyst growth method. Although several studies have considered sock formation mechanisms, the dynamics of the sock behavior during the synthesis process are not fully understood. In this work, a computational technique is utilized to explore the multiphysics environment within the nanotube reactor affecting the sock formation and structure. Specifically the flow field, temperature profile, catalyst nucleation, and residence time are investigated and their influence on the sock formation and properties are studied. We demonstrate that it is critical to control the multiphysics synthesis environment in order to form a stable sock. Sock production rate was studied experimentally and found to be linearly dependent on the amount of effective catalyst (iron in the sock) inside the reactor. To achieve a high sock production rate, the proportion of effective iron has to be high when increasing the total amount of catalyst in the reactor. Based on the analysis, we suggest that using small size catalyst and growing longer CNTs by increasing temperature, increasing residence times etc. will increase the CNT production rate and improve properties.

Highly ordered porous carbons hold great promise for a wide range of applications including water purification, gas separation, catalysis, and electric energy storage due to their unique properties.¹ To enhance their performance in these applications, there have been considerable efforts to develop rational synthesis methods of high quality porous carbons with controlled surface properties and structural ordering. Among various synthetic strategies, zeolite-templated method has emerged as a promising route because the resultant carbon, which is an inverse replica of the zeolite template, exhibits a very high surface area and pore volume.² In principle, zeolite templated-carbon (ZTC) offers tunability of pore structures, depending on a choice of the zeolite template. To date, however, ZTCs have been synthesized by carbonization of organic molecules at high temperatures, causing serious external carbon deposition before carbon filling into the zeolite micropores completes. Such undesirable carbon deposition on the external surface has hindered the generation of high quality microporous carbons.
To realize this problem, we present a synthetic strategy of porous carbon using Ca²⁺ catalyst which is embedded zeolite template.³ For the synthesis, ethylene/acetylene gas was provided as a carbon source. The remarkable advantage of this method is to dramatically drop the carbonization temperature to 400 – 600 °C, preventing the external carbon deposition. This is attributed to the catalytic action of the embedded Ca²⁺ ions during the carbonization process, which enables highly selective carbon deposition into zeolite pores where the Ca²⁺ ions exist. The resulting carbons, synthesized without external carbon layers, have mainly graphene-like sp² characteristics and exhibit very high surface area and pore volume. More interestingly, they have the electrical conductivity two orders of magnitude higher than amorphous mesoporous carbon. We demonstrate such carbon synthesis for various types of zeolite template and systematically investigate the carbonization mechanism using several analytical tools. In addition, we demonstrate a large scale synthesis using current method towards more practical applications.

References
1. T. Ma, L. Liu & Z. Yuan, Chem. Soc. Rev., 2013, 42, 3977.
2. a) T. Kyotani, etc. Chem. Mater. 1997, 9, 609-615. b) K. Kim, M. Choi, & R. Ryoo, Carbon 2013, 60, 175-185. c) P. Hou, T. Yamazaki, H. Orikasa, & T. Kyotani, Carbon 2005, 43, 2618-2641. d) T. Kyotani, etc. Carbon 2009, 47, 1220-1230. e) J. Rodriguez-Mirasol, T. Cordero, L. Radovic, & J. Rodriguez, Chem. Mater. 1998, 10, 550-558. f) S.H. Joo, S. J. Choi, I. Oh, H. Kwak, Z. Liu, O. Terasaki, & R. Ryoo, Nature 2001, 412, 169-172.
3. R. Ryoo, etc. Nature in press, 2016.

Boron nitride nanotubes (BNNTs) are isoelectronic analogues of carbon nanotubes (CNTs) and exhibit a range of properties that are as compelling as those of CNTs. Despite having been first synthesized in 1995, their scalable synthesis is still far behind from their carbon counterparts. Recently, we reported scalable manufacturing of high-quality, small-diameter BNNTs (~5nm) directly from hBN powder by using atmospheric pressure induction plasma and demonstrated an unprecedentedly high-yield rate approaching to 20 g/h¹. The main finding was that the presence of hydrogen in the reaction stream is crucial for the rapid growth of BNNTs. Here we investigate such catalytic role of hydrogen in BNNT growth by examining the hydrogen-mediated plasma chemistry using in situ optical emission spectroscopy (OES). The OES study shows that in the early stage the process (T ~6,000 K) hydrogen prevents reformation of N₂ or N₂⁺ from the decomposed feedstock (e.g., N radical) and promotes the formation of NH and BH radicals. Compared to N₂ or N₂⁺ species, those radicals are much effective precursors for the hBN phase formation at the surface of B droplets (i.e., BNNT nucleation sites). Their interaction with a B cluster is investigated using density functional theory (DFT) calculation. The microscopy analysis also suggests that the presence of hydrogen significantly enhances the heat transfer rate between plasma and feedstock thereby improving the vaporization efficiency of feedstock.


1. K. S. Kim, C. T. Kingston, A. Hrdina, M. B. Jakubinek, J. Guan, M. Plunkett and B. Simard, ACS Nano, 2014, 8, 6211-6220.

Boron nitride nanotubes (BNNTs) are wide-bandgap structural analogues to carbon nanotubes. Importantly, the special chemical, optical, thermal and radiation-absorption properties of BNNTs make them far superior than their carbon counterparts for many applications. A host of other BNNT properties have been considered, including tunable thermal conductivity, piezoelectricity, biocompatibility, hosts for silocrystal structures, electron field emission, water purification, and reinforcements for structural composites, to name just a few. Despite of many novel properties and potential applications, an unfortunate constraint that has severely limited the scientific study and industrial application of BNNTs is the general lack of availability of the synthesized materials.
In the first half of this talk, I will present the successful operation of a high-throughput, scalable BNNT synthesis process whereby precursor materials (B-containing powders) are directly and continuously injected into a high-temperature, extended-pressure inductively-coupled (EPIC) thermal plasma. The high pressure (up to 10 atm) nitrogen plasma system has achieved a record output of over 35 g/h for pure, small diameter, few wall, highly crystalline BNNTs. The EPIC method should find further application in other synthesis challenges, for examples alloy BCN nanotubes and nitride nanowires.
In the second half of the talk, I will discuss several studies and applications enabled by high quality and high quantity BNNTs synthesized by EPIC system. First, I will describe a successful wet-chemistry post-tube-synthesis route to the encapsulation of metallic nanostructures (including short nanocrystals, rods, and long wires) within BNNTs for the first time. Secondly, large quantity of highly crystalline BNNTs also finds prospective utilization in mechanical enhanced polymer composites and desalination membranes.

In recent years, Graphene-based materials have attracted much attention due to their superior physical and chemical characteristics. However, these characteristics depend on their size and structure. Among these materials are zero-dimensional Graphene quantum dots (GQDs) with sizes defined lower than 100 nm. The electrons could be confined by the structure and let material possess semiconductor characteristic. They are also non-toxic and biocompatible making them widely applicable in biosensing, biomaging. Currently, most methods of synthesis GQD involve high temperature, costly and complex processes unfavorable to its development. Here we report a facile and rapid process to synthesize GQD through a microplasma-assisted electrochemistry method.
Microplasmas are defined as gaseous discharges formed in electrode geometries where at least one dimension is less than 1mm. It can be operated with an aqueous solution as an electrode. Energetic species including radicals, ions and electrons formed in the microplasma are capable of initiating electrochemical or non-electrochemical reactions below the electrolyte and produce GQD. Detailed materials characterizations including UV-Vis, Raman, and photoluminescence spectroscopies, and microscopies including TEM and AFM suggest the developed microplasma-assisted electrochemistry method possess the ability to produce GQDs. The analytic results demonstrate the as-product had blue emission under 365 nm UV-light. Raman spectrum show G, D and 2D band signals typical for carbon containing materials. Size distribution from TEM imaging show an average size of 4.9 nm. Finally, the PL spectrum show the emission property of as-product is excitation-dependent. Further functional group analysis will done by such as XPS and FTIR.

2D materials like graphene represent a new class of membrane materials with minimum material thickness (1 atom thin). Selective engineering of nanopores in these materials hence allows for the realization of size selective nanoscale transport with theoretical minimum transport resistance (proportional to membrane thickness).
Here we report on the development of a simple, cost effective and fast characterization technique to assess the quality of membrane grade 2D materials directly on the catalyst after synthesis by CVD and show size selective ion/molecular transport through sub nanometer pores formed via facile oxygen plasma treatment on centimeter sized graphene membranes grown via scalable chemical vapor deposition (CVD) processes. The density of such defects can be tuned to be >10¹² cm^-2. Further, by tuning the reaction conditions during CVD we show that such nanopores can be directly formed in-situ during material growth itself. Our approach addresses a significant challenge in the development of advanced atomically thin nano-porous membranes for a wide range of applications from gas separation, biochemical purification, water treatment and desalination .
Kidambi et al. (manuscript in preparation)
O’Hern et al. Nano Letters (2015).
Kidambi et al. Chemistry of Materials (2014).
Boutilier et al. ACS Nano (2014).
Kidambi et al. Nano Letters (2013).
O’Hern et al. Nano Letters (2013).
O’Hern et al. ACS Nano (2012).

One of the possible applications of single-walled carbon nanotubes (SWNTs) is their use as templates or containers to encapsulate polycyclic aromatic hydrocarbon (PAH) molecules, viz., coronene, perylene, sumanene, etc. Recent researches to aim at such applications are divided into the two directions; one is to synthesize graphene nanoribbons (GNRs) via fusion of PAH molecules, and another is to stack PAH molecules under van der Waals interactions. The experiment by Talyzin et al. (2011) is categorized as the former. They succeeded to synthesize hydrogen-terminated GNRs in SWNTs. Their GNRs were twisted and had helical configurations. On the other hand, the experiment by Okazaki et al. (2011) is categorized as the latter. They observed self-organized columnar stacks of coronene molecules within SWNTs through vapor-phase doping. Such columnar coronene molecules are applicable as fluorescent probes that are robust under harsh environments. Subsequently, his group published a series of the related works. Fujihara et al. (2012) showed experimentally that dimerization of coronene molecules prior to encapsulation assists the preferential growth of GNRs, whereas suppression of the dimerization leads to stacking of coronene molecules. Verberck et al. (2013) performed Monte Carlo simulations of coronene or dicoronylene molecules in SWNTs, and concluded that whether the encapsulated coronene molecules stack in the ordered way or not depends on the diameter of the encapsulating SWNT. Kigure et al. (2014) discussed the energetics of PAH molecules, coronene, sumanene, and corannulene, in SWNTs using density functional theory. They found the stacking morphology of the PAH molecules depends on the molecular species. In this paper, we study the morphology of coronene or sumanene molecules encapsulated in a SWNT by means of molecular-dynamics simulation. Edge-opened SWNTs of various diameters are placed in a coronene or sumanene atmosphere, and the dynamical processes of encapsulation of coronene or sumanene molecules into SWNTs are followed. The resulting stacking morphologies of the encapsulated molecules are examined; how their tilt angles, inter-molecular distances, and inter-molecular rotations depend on the diameter of the SWNTs is shown. The geometrical constraint condition for the columnar stacks of coronene or sumanene molecules in SWNTs is discussed.

Nanocarbon hybrids have attracted much attention of materials researhcers nowadays. A pillared-graphene nanosturucre is one of such hybrids, and it was proposed by Dimitrakakis et al.(2008) and experimentally synthesized by Kondo et al. (2008). This nanostructure consists of graphene sheets and carbon nanotubes(CNTs); the CNTs are bonded vertically to the graphene sheets. Although Dimitrakakis et al. anticipated its use as hydrogen storage, recent researches focus on its application to three-dimensional electronic devices. Prior to such an application, the mechanical properties of a pillared-graphene nanostructure under various loads should be known. In this paper, the hardness of a pillared-graphene nanostructure is studied via indentation simulation. In a simulation model, four single-walled carbon nanotubes (SWNTs) are bonded vertically to two rectangular graphene sheets the sides of which are fixed. SWNTs of armchair or zigzag type are selected. The chiral indices (n,n) of armchair type SWNTs range from (6,6) to (19,19), so that their diameters range from 0.814 nm to 2.577 nm. On the other hand, the chiral indices (n,0) of zigzag type range from (10,0) to (34,0), so that their diameters range from 0.783 nm to 2.662 nm. For each CNT type, models in which the distance between the SWNTs is changed from 8 nm to 16 nm are prepared. A pyramidal nanoindentor with the dihedral angle of about 136 deg is used. Indentation force is gradually increased. A simulation model is equilibrated at each constant load, and the deflection of the graphene sheet at the loading point is measured. The simulations for each model are performed at the temperatures 1 K, 100 K, 200 K, 300K, and 400K. The hardness of a model is calculated from the load-deflection curve using the equation of Oliver and Pharr (2004). It is revealed the hardness increases with increasing the SWNT diameter, whereas it decreases with increasing the distance between SWNTs and temperature, and the dependence of the hardness on the SWNT diameter weakens with increasing the distance between SWNTs and temperature. It is also found the hardness of a pillared-graphene cosisting of SWNTs of zigzag type is larger than that of a pillared-graphene consisting of SWNTs of armchair type, which is due to the difference between the backling behaviors of the SWNTs of the two types.

Graphene, a single atomic layer consisting of honeycomb lattices of carbon atoms, possesses many superior mechanical, electronic, and thermal properties that make its application to nanodevices possible. Especially, the thermal properties of graphene attract researchers'attentions nowadays because the thermal conductivity within its plane is of the same order of magnitude as of carbon nanotubes (CNTs), and one order of magnitude higher than those of metals. In addition, the potentiality of controling heat flows in electronic and energy devices by thermal rectification using some kind of graphene devices stimulates researchers'interest in its thermal properties. As Wang et al. proposed in 2014, one of the methods of realizing such thermal rectification using graphene is to change the width of a graphene nanoribbon (GNR) at its intermediate position. In this paper, the rectification of heat in GNRs of asymmetric geometries is investigated by means of molecular dynamics. Two kinds of the geometries of GNRs are our objects of study; a trapezoidal or a T-shaped step is inserted halfway in the longitudinal direction of a GNR. For the GNRs of these two kinds geometries with various widths, the thermal conductivities in the two longitudinal directions, forwad and backward, are calculated using noequilibrium molecular dynamics simulations (NEMD). The possibility of thermal rectification in the GNRs is addressed, and its mechanism is discussed by examining the phonon spectra.

In the last decade graphene has emerged as an exciting material revealing potential applications in various fields including in the polymer nanomaterials science.
The most commonly used method to produce graphene in large scale is through oxidation of graphite followed by exfoliation and reduction of the oxidation products. However, this method leads to the production of graphene with structural defects and remaining oxidation, and thus with lower electrical and mechanical properties compared to graphene.[1] Liquid-phase exfoliation of graphite is another mass-scalable approach for the production of graphene,[2] typically using organic solvents and application of shear. Still, the use of large volumes of organic solvents has negative environmental consequences.
Alternative approaches to produce good quality graphene by graphite exfoliation using “green” solvents such as water are thus necessary. Recently, the production of graphene based on graphite exfoliation through non-covalent interactions with pyrene derivatives was reported.[3] This approach was used for the exfoliation and stabilization of graphene in water, leading to the production of few- and single- layer graphene without structural damage. The suspension of graphene in water allows its easy mixture with water-soluble polymers and with polymers that form stable suspensions in water.Waterborne polyurethane (WPU) is a synthetic polymer used as high quality surface coating, providing an eco-friendly process without emission of volatile organic compounds (VOCs). The potential applications of waterborne polyurethane/ graphene thin films in antistatic coatings, electromagnetic shielding and corrosion-resistant coatings have been reported.[4,5]
The present work reports the preparation of stable aqueous suspensions of few-layer graphene (FLG) and its mixture with carbon nanotubes (CNT) using solutions of pyrene derivatives at low concentration.WPU / FLG; WPU / CNT, and WPU / FLG + CNT were prepared at loadings from 0,1% to 10% wt. The graphene and exfoliated graphite-based materials were deposited on substrates and characterized by Raman spectroscopy. The nanoparticles were observed by scanning transmission microscopy. The mechanical properties of the composite films were measured by tensile testing. The electrical properties as well as the water vapor permeability of the composite films were also investigated.
[1]F. Bonaccorso, A. Lombardo, T. Hasan, Z. Sun, L. Colombo, and A. Ferrari, Materials today, 15 (2012) 564-589
[2]A. Ciesielski, P. Samori, Chemical Society Review, 43 (2014) 381-398.
[3]D. Parviz, S. Das, H. Ahmed, F. Irin, S. Bhattacharia, and M. Green, ACS Nano, 6 (2012) 8857–8867.
[4]B. Ramezanzadeh, E. Ghasemi, M. Mahdavian, E. Changizi, M. Moghadam, Carbon, 93 (2015) 555-573.
[5]S. Hsiao, C. Ma, H. Tien, W. Liao, Y. Wang, S. Li, C. Yang, S. Lin, R. Yang, ACS Applied Materials and Interfaces, 7 (2015) 2817-2826.

Hollow micro/nano structures form an important family of functional materials. In this talk, we will present some advances achieved in the field. We have used the thermal oxidation process combined with the passage of electric current during a structural phase transition to disclose a colossal mass diffusion transfer of ions. This combination points to a new route for fabrication of hollow materials. A structural phase transition at high temperature prepares the stage by giving mobility to Ti ions and releasing vacancies to the system. The electric current would drive an inward delocalization of vacancies, condensing into voids, and finally turning into a big hollow. This strong physical phenomenon leading to a colossal mass transfer through ionic diffusion is suggested to be driven by a combination of phase transition and electrical current followed by chemical reaction. We show this phenomenon for Ti leading to TiO2 microtube formation, but we believe that it can be used to other metals undergoing structural phase transition at high temperatures.
On the other hand, we will also talk on both coaxial core-shell structured microwires and ZnO microtubes with growth of nanosticks in the inner and nanowires on the outer surface as a novel hierarchical micro/nanoarchitecture. First, a core-shell structure is obtained -the core is formed by metallic Zn and the semiconducting shell is comprised by a thin oxide layer covered with a high density of nanowires. Such Zn/ZnO core-shell array showed magnetoresistance effect. It is suggested that magnetic moments in the nanostructured shell superimposes to the external magnetic field enhancing the MR effect. Second, microtubes decorated with nanowires on the external surface are obtained. The thermal activated energy of the obtained semiconducting microtubes was estimated to be 0.5 eV. In an intermediate stage, a hierarchical morphology comprised of discrete nanosticks in the inner surface of the microtube has been found. Hyperfine interaction measurements disclosed the presence of confined metallic Zn regions at the interface between linked ZnO grains forming a chain and a ZnO thicker layer. Surprisingly, the metallic clusters form highly textured thin flat regions oriented parallel to the surface of the microtube as revealed by the electrical.

The preparation of novel 1D materials with exceptional functionalities has been the focus of an intense research effort during the last decades. Among the different synthesis approaches, soft-chemistry methods allowed the preparation of a plethora of materials using mild conditions and, in some cases, the organic solvents utilized in these methods also acted as templates for the nucleation and growth of the 1D structures.
On this regard, long-chain amines have been successfully used as templating agents for the synthesis of vanadium oxide, vanadium sulfide and copper sulfide nanotubes. However, despite the efforts devoted to the templated synthesis of gallium chalcogenides frameworks using aromatic and short-chain amines, the ability of long-chain amines to stabilize 1D networks still remained as a challenge in these systems.
In this work, we present the synthesis of gallium sulfide and gallium selenide nanotubes using long-chain amines (hexadecylamine and dodecylamine) as templating agents¹. The nanotubes have a multi-layered structure and diameters of tens of nm and lengths of up to 2 µm. Very interestingly, the amines are located between the gallium chalcogenide layers, creating an interlayer spacing of a few nanometers which, together with the quantum confinement of the 1D structure, causes an increasing of the band-gap of up to 2 eV respect to the bulk gallium chalcogenide phases. Moreover, preliminary tests on the use of these nanotubes as active materials for lithium ion batteries have been performed and will be discussed.


[1] Seral-Ascaso et al. Nanoscale, 2016, 8, 11698-11706.

The development of solvent-free approaches to functionalize covalently graphene oxide (GO) and nanodiamond (ND), is an important step toward creating a new carbon nanohybrid materials with novel properties and improved performance in drug delivery design, field emission displays, composite materials, sensors, biosensors, nanocatalysts, etc. The presence of oxygenated functionalities on GO and ND surfaces brings the possibility for selective attachment of other functional groups and molecular fragments for building up different nanostructures. In the present work, we applied the solvent-free functionalization technique, in order to take advantage of the possibility of amidation of COOH groups to functionalize covalently pristine GO and ND by using three amines of different structure: one monofunctional aliphatic amine, octadecylamine, and two monofunctional aromatic amines: 1-aminopyrene, and 2-aminofluorene. The distinctive feature of the proposed way of covalent attachment of amines is that the formation of amides takes place due to thermal activation without any additional chemical activation of COOH groups. A task of special importance from the point of view of practical applications of GO and ND is a detailed comparative characterization of physical and chemical properties of pristine and chemically functionalized nanomaterials. Accordingly, in this study we present the results of characterization of the functionalized GO and ND materials obtained by using different microscopic together with spectroscopic and spectrometric techniques, as well as comparative analysis of the conductivity properties of pristine and amide-functionalized GO and ND.
The approach proposed allows for a facile preparation of amide-functionalized GO and ND without contamination with other chemical reagents, detergents and solvents, which is especially important for a vast variety of applications.


Acknowledgements: Financial support from UNAM (grants DGAPA-IN100815) is greatly appreciated. N. A.-C. is indebted to the Doctorate Program in Chemical Sciences of UNAM and CONACyT for a Ph. D. fellowship.

Halloysite nanotubes (HNTs) have attracted attention for their potential use in a variety of applications owing to their mechanical robustness, thermal stability, natural abundance and low cost. HNTs have a small amount of negative fixed charges on their outer surfaces and can be well dispersed in solvents and polymers of medium to high polarity. The inclusion of HNTs into epoxy matrix at low concentrations was found to be effective in stiffening and hardening. At 1 vol% loading, composites showed improvements up to 50% in modulus and 100% in hardness compared to pure epoxy, based on nanoindentation measurements. In addition, tribology studies using TriboIndenter and AFM showed an increase of wear résistance; depending on their orientation in the composite, HNTs can decrease the scratch volume by 50% at fixed loading levels. The optical transmittance of composites was studied using UV-Vis. Adding HNTs into epoxy had almost no effect on the transmittance over the range of wavelength from 400 to 700 nm. Transmittance values of 91% were observed for HNT concentrations as high as 10 vol%.

Three-dimensional graphene sponges obtained by enhanced Hummer’s method and freeze-drying are a highly efficient tool for use during oil-water separation¹. Due to the hydrophobic nature of the graphene and contact angles with water in excess of 170 degrees, three dimensional graphene sponge is an invaluable and feasible substitute to various natural absorbers and organic materials such as expandable perlite and wool fibre². Due to the high porosity of the spongy graphene, it can absorb oils from 50 times up to a maximum of 120 times its own weight in various oils. For this study, a shape-mouldable and three dimensional spongy graphene with high specific surface area used as a protean and recyclable sorbent for not only oils but also toxic solvents such as chloroform is fabricated. The nanoporous characteristic allows spectroscopy and microscopic studies such as the use of Raman spectroscopy and Environmental Scanning Electron Microscopy (ESEM). We study the influence of various parameters ( porosity, hydrophobicity, surface area) on the absorption capability of the graphene sponge. Furthermore, we also report how to improve the regeneration efficiency( > 12 times) by heat treatment, adhering to the full release of absorbates (>99%) and still exhibiting the same micro and macro structure as before. In addition we will discuss how the introduction of halogen atoms to the graphene sponge enhances superhydrohobicity. The present work demonstrates that graphene sponges can be used in industry to separate oil-water mixtures and environmental cleaning of oil spills. Topics regarding environmental protection will also be addressed.

References:
1.Bi, Hengchang, et al. "Spongy graphene as a highly efficient and recyclable sorbent for oils and organic solvents." Advanced Functional Materials 22.21 (2012): 4421-4425.
2.Hong, Jin-Yong, et al. "Highly-efficient and recyclable oil absorbing performance of functionalized graphene aerogel." Chemical Engineering Journal 269 (2015): 229-235.

Since its discovery in 2004 graphene has generated huge interest in both academic institutions and industries due to its unrivalled physical properties. Graphene a 2-dimensional material is a one-atom-thick sheet of sp2-bonded carbon and has exceptionally good properties. Apart from the very high modulus of elasticity of ∼1 TPa and tensile strength of ∼125 GPa graphene also has a thermal conductivity of ∼3080-5300 W/mK which is 25 times that of Si. It has a carrier mobility at room temperature of 10,000 cm²/VS and a theoretical specific surface area is 2630 m²/g. Large scale economical production of high-quality graphene having few layers is essential for their real-world applications. Here, we report an effective and facile technique for the large-scale production of exfoliated graphite nanoplatelets. The processing route that has been adopted here for the synthesis of graphite nanoplatelets is based on the intercalation of the natural flake graphite (NFG) and solvent dispersion. Microcrystalline natural flake graphite is subjected to intercalation using concentrated sulfuric acid (H₂SO₄) along with hydrogen peroxide (H₂O₂) leading to the formation of a graphite intercalation compound (GIC). The GIC is later thermally exfoliated to obtain the graphite nanoplatelets. The graphite nanoplatelets are finally ultrasonicated in acetone for five different time periods to find the effect of vibrational mechanism on the exfoliation of the graphite nanoplatelets. Ultrasonication has been carried out at room temperature for 2, 5, 7, 12 and 20 h. Both HRTEM and AFM analysis confirm that the nanoplatelets obtained after ultrasonication for more than 12 h were well exfoliated and had a thickness less than 1 nm. The XPS analysis of various samples showed a maximum relative % of C (97.2 at. %) and a minimum relative % of O (2.8 at. %) in the case of 12 h sonicated sample. The surface area and pore size distribution were determined by the Brunauer-Emmet-Teller (BET) method. The extent of defects introduced in the nanoplatelets during ultrasonication was determined from the I_D/I_G intensity ratio using the Raman spectra obtained from the various ultrasonicated samples. Ultrasonication of the graphite nanoplatelets beyond 5 h shows a gradual increase in crystallinity and decrease in defect density as well as a decrease in the number of graphene layers in the graphite nanoplatelets. Beyond 12 h of ultrasonication both the intensity of the (002) X-ray diffraction peak and the ID/IG ratio of the Raman spectra come to a saturation suggesting that there is a limit to the extent of exfoliation possible by the ultrasonication process. Highly crystalline graphite nanoplatelets having low defect density and consisting of few layers of graphene could be synthesized by ultrasonication of the thermally exfoliated graphite. The process of thermal exfoliation followed by ultrasonication is very effective in producing few layer graphene (FLG) platelets in large quantities.

Boron nitride nanotubes (BNNTs) are structural analogs of carbon nanotubes (CNTs) with boron and nitrogen atoms instead of carbon atoms. Besides their structure, mechanical and thermal properties of BNNTs are very similar to the remarkable properties of CNTs. However, BNNTs have better resistance to thermal oxidation and BNNTs are also electrically insulating with uniform electronic properties independent of their size and chirality. Therefore, they are evaluated as suitable fillers for the fabrication of mechanically and thermally enhanced polymer composites, while preserving the electrical insulation of the polymer matrix.

In this study, polypropylene (PP) / boron nitride nanotube (BNNT) composites with different amount of loading (0.5, 1, 3 and 6 wt %) were prepared using a co-rotating twin screw extruder. The nanotubes incorporated into PP matrix were synthesized from the reaction of ammonia gas with a powder mixture of boron and iron oxide in an alumina boat which was centered in a tubular furnace. X-ray diffraction (XRD) results revealed that hexagonal boron nitride and the cubic iron were the solid phases formed in the synthesized material. Multi-wall cylindrical and bamboo-like boron nitride nanotubes with outer diameters ranging from 50 to 130 nm were observed with SEM and TEM analyses.

According to the tensile test results, slight increase in the Young’s modulus and yield strength of the composites was observed with 0.5 and 1 wt % of the as-synthesized nanotube addition into the PP matrix. On the other hand, due to the agglomeration of BNNTs, elongation at break and tensile strength values of the composites decreased with an increase in BNNT loading. However, after the as-synthesized nanotubes were purified, and modified with polyethylene glycol, slight improvement in all mechanical properties of neat PP with 0.5 wt % loading was observed. Differential scanning calorimetry (DSC) analysis revealed a noticeable increase in the crystallinity temperatures of the composites when compared to neat PP. Thermal gravimetric analysis (TGA) results of the composites at each BNNT loading displayed slight improvement in thermal stability over the neat PP.

Graphene is a novel member of the carbon family[1]. Various synthesis techniques of graphene have been detailed in literature such as mechanical exfoliation of graphite, epitaxial growth of graphene by chemical vapor deposition, solvothermal approach and so on.[2] However, those chemical approaches require harsh oxidizers and a strong reducer that are not environmentally benign. Inspired by the failure mechanism of batteries, an electrochemical exfoliation approach has been proposed to prepare graphene in different electrolytes[3]. It has been found that the solvation structure of cations plays a critical role in the exfoliation process of graphite and the subsequent morphologies of exfoliated graphene. The interactions among the solvent molecules, cations and graphene surface will be explored in this talk. The fundamental exfoliation mechanism will be discussed which provides new insights on the facile synthesis of high quality graphene.

References:
1. 1. H. Zhou, H. Deng, S. A. Ghetmiri, H.H. Abu-Safe, S.Q.Yu, X.Yang and Z.R.Tian, “Optimizing height and packing-density of oriented one-dimensional photocatalysts for efficient water photoelectrolysis,” J.Phys. Chem. C. 117, 20778−20783 (2013).
2. Cai, Minzhen, Daniel Thorpe, Douglas H. Adamson, and Hannes C. Schniepp. "Methods of graphite exfoliation." Journal of Materials Chemistry22, 48, 24992-25002 (2012).
3. Su, C.Y., Lu, A.Y., Xu, Y., Chen, F.R., Khlobystov, A.N. and Li, L.J. High-quality thin graphene films from fast electrochemical exfoliation. ACS nano, 5(3), 2332-2339 (2011).

Mechanical strain energy storage and dissipation capabilities are investigated
in carbon nanotube (CNT) polymer matrix composites fabricated by fused
deposition modeling (FDM) additive manufacturing (AM). CNT reinforced
acrylonitrile-butadiene-styrene (ABS) AM composites were studied, in terms of
microstructure and mechanical performance. Macro-scale dynamic properties of
the bulk nanocomposite specimens were determined using a dynamic mechanical
analyzer, while micro- and nano-scale load transfer and dissipation were
investigated using dynamic nanoindentation. To study the mechanical strain
energy dissipation of these nanocomposites, the ratio of loss to storage
modulus was measured at different applied strains. Results show permanent
damage in neat ABS samples at lower dynamic strains than that observed in
composites samples, suggesting the CNT fillers enhance the strength of the
build interfaces during the AM process. A comparison was made to samples
fabricated using an injection molding approach. The results of this research
provide the foundation to utilize AM in the design of composites with high
energy dissipation capability, especially for applications where dynamic
loading may compromise structural stability and functionality, such as rotary
wing structures.

Graphene has almost flat optical adsorption in wide range of wavelengths, therefore transparent conductive films based on graphene are demonstrated [1,2]. On the other hand, low reflectance applications used graphene nanostructures are proposed [3]. The reflectances of the fabricated graphene nanostructures are almost same as data of CNTs [4]. In addition, it is well known that graphene has high thermal conductivity. Therefore, the graphene is expected to be one of the most appropriate wide range of low reflectance materials for high power laser applications. Garphene nanostructures were fabricated by plasma etching of carbon substrate [3], which cannot be formed on the various substrate materials and structures. Thus, it is necessary to develop the coating of graphene nanostructures. In our previous study, low temperature graphene deposition technique using microwave plasma CVD was reported [5]. In this study, the direct formation of the vertically aligned graphene sheets on metal and dielectric substrates are developed based on the proposed CVD. In addition, optical properties of the fabricated vertically aligned graphene sheets are discussed.

The vertically aligned graphene sheets were deposied by microwave plasma CVD. It was confirmed from SEM and TEM observations that the samples are consists of vertically aligned multilayer graphene sheets on few layer graphene which are parallel to the substrate. The heights of the graphene sheets are tuned by the deposition periods. By wet-transfer process, the vertically aligned graphene sheets/dielectric substrates were fabricated.

UV-visible spectrometer was used to measure the optical properties. Total-reflectance spectra of the vertically aligned graphene sheets, having 5µm in height, on metal substrate are less than 1% in the range between 300 and 1000nm. This is one order higher than the reported value, however further reduction of the reflectance would be expected by increasing the heights and density. We also confirmed both reflectance and transmittance of the vertically aligned graphene sheets on quartz substrates depend on the incident angles.


Acknowledgement
This paper is partially based on results obtained from a project supported by New Energy and Industrial Technology Development Organization (NEDO).



[1] S. Bae et al., Nat.Nanotech.4(2010)574.
[2]Y.Okigawa et al., Jpn.J.Appl.Phys.54(2015)095103.
[3] T.Matsumoto et al., Optics Express DOI:10.1364/OE.21.030964.
[4] K.Mizuno et al., Proc.Natl.Acd.Sci.U.S.A.106(2009)6047.
[5]T.Yamada et al., J.Phys.D:Appl.Phys. 46(2013)063001

Electronic and Structural properties of Graphene as an actual carbon material rather than an ideal model for two dimensional systems with novel Dirac Fermion is significantly influenced by the presence of edges, defects and impurities [1], and so on. Especially, surrounding guest chemical species play an important role for two dimensional host materials like graphene, where the host-guest interactions though the surface and the interface between supporting substrate is classified into three types according to the energy scale of interactions; chemical modification by covalent bonding, charge transfer by electrostatic interaction, and mechanical strain by physisorption [3]. In this talk, I would like to focus mainly on the charge transfer interactions caused by guest chemical species facing with graphene. Indeed, surface modification of supporting substrate by self-assemble monolayer of molecules having various electric dipole and eigen frequency of molecular vibration enables tuning of the Fermi energy EF and carrier scattering of graphene [4, 5]. Interestingly, such molecular proximity effects for adsorbed molecules on the surface of graphene show significant dependence on EF experimentally tuned by gate voltage, where hole and electron doping by oxygen [6] and hydrazine molecules, respectively, exhibit opposite dependence on EF. In addition, the kinetic for the charge transfer induced by molecular adsorption is quite slower in comparison with usual time scale for the electron system. Moreover, the absolute value of the characteristic times of the charge transfer by hydrazine (1.25 min) is much faster than that for oxygen (18 min), in the former of which large amount of water molecules coexist as hydration water in contrast to oxygen as dry gas. This is explained by a mechanism by electrochemical process involving co-existing water molecule for charge transfer phenomena by molecular adsorption on graphene. Indeed, the is a graphene FET characteristic measurement under precise controlling of atmosphere in UHV chamber reveals that the oxygen induced charge transfer process is much accelerated accompanied with increasing in partial pressure of water in oxygen gas.

[1] T. Enoki, S. Fujii, and K. Takai, Carbon, 50, 3141-3145 (2012).
[2] Y. Kudo, K. Takai, and T. Enoki, J. Mater. Res., 8, 1097-1104 (2013).
[3] K. Takai, H. Kumagai, H. Sato, T. Enoki, Phys. Rev. B, 73, 035435 (2006).
[4] Y. Yokota, K. Takai, and T. Enoki, Nano Lett., 11, 3669-3675 (2011).
[5] Y. Yokota, K. Takai,Y. Kudo, Y. Sato and T. Enoki, Phys. Chem. Chem. Phys., 16, 4313-4319 (2014).
[6] Y. Sato, K. Takai, and T. Enoki, Nano Lett., 11, 3468-3475 (2011).

Given the outstanding mechanical properties, lustrous appearance, and biocompatibility of silkworm silk, it is gaining significant attention from both the textile industry and research society. The possibility of creating tougher silks attracts particular research interest. For further enhancing the performance of silk, two strategies have been developed to functionalize silk fibers: post-functionalization and in situ functionalization. Post-functionalization approaches generally require the usage of toxic chemical solvents and complex procedure. By contrast, in situ functionalization approaches, which is facile and green, enables the production of modified silk fibers through feeding specific diets to silkworms. Carbon nanotubes (CNTs) and graphene (GR) have been widely studied for using as reinforcement. Recently, mechanically reinforced spider silk was reportedly obtained through spraying spiders with single-walled-CNTs (SWNTs) and GR aqueous dispersions,^[1] although it is unclear whether the incorporation is happened post-spun or in situ. However, the practical production of spider silk is difficult because of the territorial and cannibalistic natural instincts of most spiders. In this work, we demonstrated that mechanically enhanced silk could be directly collected by feeding Bombyx mori larval silkworms with diets containing SWNTs or GR. The as-spun silk fibers containing nanofillers showed evidently increased fracture strength and elongation-at-break, demonstrating the validity of SWNT or GR incorporation into silkworm silk as reinforcement through an in situ functionalization approach. By analyzing the silk fibers and the excrement of silkworms, we conclude that parts of the fed carbon nanomaterials were incorporated into the as-spun silk fibers, while others went into excrement. FTIR spectroscopy of silks showed that SWNTs- and GR-modified silks contained more α-helix/random coil structures and fewer β-sheet than controlled silk. This composition may contribute to increased breaking elongation and toughness modules, as the coil conformation consists of more movable chains than β-sheet. Besides, the SWNTs and GR may work as “slipknots,” leading to increased breaking elongation. We also investigated the pyrolysis of modified silk, and a highly developed graphitic structure with superior electrical conductivity was obtained through the introduction of SWNTs and GR. The successful generation of these SWNTs/GR-embedded silks by in vivo feeding is expected to open up possibilities for the large-scale production of novel high-toughness functionalized silk fibers.
[1] E. Lepore, F. Bonaccorso, M. Bruna, F. Bosia, S. Taioli, G. Garberoglio, A. Ferrari, N. M. Pugno, arXiv preprint arXiv:1504.06751 2015.

We present a direct and scalable floating catalyst method to fabricate carbon nanotube (CNT) fibers, yarns and thin films and comprehensively investigate the effects of synthesis conditions and post-treatment processes on their structures and multi-properties. Kilometer-long CNT fibers are fabricated continuously with a production rate of 2 km/hour. After a combination of mechanical densification and epoxy infiltration treatments, the CNT fibers possess tensile strength of 5 GPa and young modulus of 444 GPa while their electrical conductivity could reach 12,000 S/cm. Besides, the knot-strength efficiency of the post-treated CNT fibers approaches 78%, much higher than that of many commercial high-strength fibers. In addition, the tensile strength of the CNT yarns, twisted from five CNT fibers, can achieve up to 3.7 GPa. Furthermore, a fast acid treatment increases the electrical conductivity of the CNT fibers to 18,000 S/cm with the maximum current density of 66,000 A/cm², competitive to the conventional copper wires. Highly dense and aligned CNT thin films with controllable density demonstrate superior multi-properties with high degree of anisotropies. After the mechanical condensation and acid treatment, the tensile strength and electrical conductivity reach up to 243 MPa and 4994 S/cm.
A new, robust, steady-state Joule heating infrared thermal metrology technique is successfully developed for simultaneously measuring the thermal conductivity of and convection coefficient from CNT fibers and films. The thermal conductivity of the as-prepared fiber ranges from 4.7 W/m K to 28.0 W/m K and depends on fiber volume fraction and diameter. Further, the measured convective heat transfer coefficients range from 25 W/m² K to 200 W/m² K, which are higher than the expected for macroscale materials and demonstrates the impact of the nanoscale CNT features on convective heat losses from the fibers. The acid treatment increases the thermal conductivity by as much as a factor of ~3 for the fibers and ~6.7 for the thin films. The acid-tread CNT film demonstrates thermal conductivity of up to 759 W/mK and specific thermal conductivity of up to 474 mW m²/kg K, which is even higher than the typical values of conventional metals and comparable with the highly conductive CNT assemblies reported in the literature.
The results of this study may have significant impact on both providing alternative approaches for fabricating super-strong and highly conductive CNT fibers and films and understanding the mechanisms of the load, electron and heat transfers in the CNT macroscale assemblies. The outstanding multi-properties of these continuous CNT fibers and films are very promising for further developing them into large-scale applications such as advanced composites, electrical wires and thermal interface materials.

Nucleation of bi/multilayer graphene (B/MLG) domains under a monolayer graphene in a flat Cu
foil during chemical vapor deposition (CVD) has long been presumed to have originated from the
top surface. On the contrary, we found the mechanism of B/MLG growth predominantly belongs
to other side of the coin, i.e. the backside of the Cu foil, hitherto completely overlooked. We have
observed that the nucleation of B/MLG under the monolayer graphene on top side of Cu foil is
primarily correlated with graphene growing on the backside. The invasion of carbon species to
backside leads to diffusion through the bulk Cu contributing to the formation of B/MLG domains
at the top. By supporting the Cu foil with a nickel (Ni) substrate, which acts as a “getter” for the
carbon species accumulating at the back of the Cu, we were able to suppress the carbon species
from diffusing into the top side through the bulk Cu foil during the CVD process. Furthermore,
depth profiling of the Ni substrate and quantum-mechanical calculations provide evidence of
carbon penetration into the Ni during the CVD process, corroborating our observation that the
backside growth is the main route mechanism for B/MLG nucleation. Finally, we devised CVD
method which does not require any prior surface treatment of Cu foil to realize large area exclusive
monolayer graphene with improved charge carrier mobility values of ~ 6800 cm2V-1s-1.

In energy storage devices, the interface between electrode and electrolyte is important. Electric double-layer capacitors depend on physical adsorption of electrolyte, and a battery utilizes an electrochemical reaction at electrodes. Carbon materials like graphite and its derivatives are widely used in electric storage devices such as negative electrode in a battery, where degradation mechanism of electrode and SEI (Solid electrolyte interphase) formation are crucial in device performance. However phenomena at the interface between carbon materials and electrolyte in energy storage devices are still unclear because of complicated structure of conventional carbon electrode materials. In this study, the electrochemical interaction at the interface between graphene electrode as the model structure of carbon electrode materials and electrolyte solution is investigated in order to clarify the phenomena in energy storage devices. Gate voltage dependence of the conductivity was measured for graphene FET on SiO₂ substrate with the bipolar electrochemical configuration, where the graphene channel and Pt wire in the electrolyte were applied as working and counter electrodes, respectively. 1 M KCl aqueous solution and 1 M LiCl aqueous solution, and 1 M LiBF₄ organic solution (EC / DMC) were used as electrolyte solution. Raman spectroscopy was carried out using excitation wavelength of 532 nm under an atmospheric condition. Similar results were obtained in the case of KCl and LiCl aqueous solution. A reversible behavior of the transfer curve upon cycles of sweeping top gate voltage (Pt counter electrode) was observed for smaller voltage region, where the electrochemical current between top electrode and graphene channel is negligible. This is attributed to the physisorption of electrolyte on the graphene surface. Applying larger gate voltage, irreversible gate-voltage dependence appears with electrochemical currents due to electrolysis of water at electrodes. However, no change in Raman spectra after larger voltage applying suggests less structural change for graphene. Increment of electrochemical current below – 2 V, which becomes suppressed after cycles of gate sweeping actual battery reactions between carbon and decrease in the LiBF₄ organic electrolyte solution. Namely, SEI is formed by reaction between graphene and electrolyte. But the position of Dirac point didn’t change in the transfer curve, indicating the absence of chemical doping. In this regard, it is consistent with that position of G band doesn’t change in Raman spectroscopy. On the other hand, D band appears at only edge parts in graphene in 2D-Raman mapping after cycles of gate voltage sweeping. Since edges in graphene is chemically active site, SEI is formed by reaction between graphene and EC/DMC, suggesting significant roles of edges of carbon electrode in actual energy storage devices.

Polymer films are commonly used to create barriers between different environments. For example, polyethylene films can be used to package meat products to extend shelf-life. In addition to keeping the surface of the meat free from atmospheric pathogens and other airborne contamination, the packaging can keep the environment around the meat free from oxygen when the meat is packaged under an inert atmosphere (as is the case when employing a modified atmosphere packaging strategy). Clearly, the better the barrier to oxygen diffusion, the longer the meat’s shelf-life can be extended as oxygen is a critical component in meat degradation processes. Similarly, polyurethane and epoxy films are often used to protect steel pipes from corrosion. Again, the polymer film is used to create a barrier that, in this case, inhibits corrosive agents from contacting the steel; the better the barrier, the lower the rate of corrosion. Even with decades of advancement in polymer science, however, there is still a need to improve such barrier materials. A common strategy for improving barrier films involves producing a composite material by compounding the polymer with a functional filler that provides a higher barrier relative to the polymer, creating a more tortuous path for the diffusing species, resulting in lower permeation. Nanoscale fillers with high aspect ratios are excellent candidates for these applications. In this work, we explore the use of modern graphenic materials for improving oxygen barriers in food packaging and anti-corrosion barriers in steel coatings by compounding and casting graphene nanoplatelets (GNP) with polyethylene (PE), polyurethanes (PU), and epoxies (EP). GNPs from various commercial suppliers are carefully characterized before being melt-processed into packaging films with low density PE and/or solution-processed into coatings with PU and EP. The melt-processing is performed on a twin screw extruder. The resulting films are characterized mechanically and physico-chemically. The oxygen transmission rates (OTR) are measured and compared with pure PE films. The measured OTRs are correlated with the GNP properties, the film structure, and the degree of GNP dispersion. The GNP-PU/EP coatings are produced by solution-processing the GNPs with PU/EP bases. After mixing with the curing agents, the solutions are cast onto substrates, cured, and characterized mechanically and physico-chemically. The anti-corrosion efficiencies of the films are established electro-chemically after deposition on metal substrates.

The incorporation of nanomaterials that are biocompatible with different types of biological compounds has allowed the development of a new generation of biosensors applied especially in the biomedical field. In particular, the integration of carbon nanomaterials onto field-effect devices (FED) can be interesting to develop (bio)chemical sensors with enhanced properties. The capacitive electrolyte-insulator-semiconductor (EIS) is a typical class of FED that is used for biomedical and environmental sensing systems.In this study we investigated the fabrication of sensitive nanocomposites combining carbon nanotubes (CNTs) or graphene oxide (GO) with different oxide nanoparticles, by means the layer-by-layer (LbL) technique incorporated onto an EIS structure for detection of biomedical substances and of environmental interest. The morphology of the nanocomposites were analyzed by microscopies techniques, while electrochemical methods were used to evaluate the sensor's properties, including output signal response, sensibility and selectivity. The advantages of employing nanostructured materials and their influence to achieve a (bio)chemical sensor with enhanced performance are also discussed.

The effect of acrylic acid (AA) and amine alcohol (DMAE) functionalization via plasma of carbon nanofibers (CNF) on physical and mechanical properties of polypropylene-CNF nanocomposites prepared by melt mixing was studied. The behaviour of these functionalized CNF via plasma was compared with a CNF functionalized by oxidation with a mixture of sulphuric acid (H₂SO₄) and Nitric acid (HNO₃). Two different types of compatibilizers were used: an amine alcohol modified PP (PPgDMAE) and a maleic anhydride grafted PP (PPgMA). The CNF functionalization was evidenced by Raman spectroscopy, comparing the ratio of peaks at 1371 and at 1590 cm^-1. Dispersion of the CNF was assessed using scanning microscopy, and the effect of the type of CNF functionalization on the dispersion was evidenced. A notorious increase in thermal stability, mechanical and electrical properties and crystallization rate were observed. A great effect on the storage modulus, with a remarkable increase of up to 60%, was obtained when using PPgDMAE and AA functionalized CNF. The mechanical properties of flexural and impact strength showed an effective load transfer when using this CNF and compatibilizer system, which was attributed to the better functionalized CNF dispersion and the strong interactions between CNF and polymer matrix.

Activated Carbon Fibers (ACFs) consisting of 3D random network of nanographenes is interesting host material because of its nanopores and localized spins originating from zigzag-edges [1]. Ferrocene (FeCp₂) having localized d -electron is expected to interact with nanographenes due to its electron-donating property, localized in cation form spin, and pi-conjugated system. In this study, we introduced ferrocene as guest molecule to ACFs host in order to clarify host-guest magnetic interaction between nanographene and magnetic molecule.
The FeCp₂-introduced ACFs (FeCp₂-ACFs) was synthesized by vapor transfer by controlling temperature and annealing time. The introduction of the guest molecule is confirmed by Fe_2p peaks in XPS, where the atomic ratio of Fe is 1.4×10^-2 / C-atom. The peak of C-C bond in plane of FeCp₂-ACFs shifts to lower energy. In addition, the increment in shake-up peak intensity of C_1s spectrum indicates the increase of conduction electrons. Thus, the emergence of charge transfer host-guest interaction is suggested in FeCp₂-ACFs, which is also supported by red-shift of G-band in Raman spectrum indicating weakening of C-C bonding by doped electrons filling antibonding states. The significant enhancement in spin concentration of FeCp₂-ACFs than that of ACFs indicates the presence of ferrocenium ion in which chemical form a spin magnetism of 3d electron appears in FeCp₂. It should be noted that our sample doesn’t show ferromagnetism, although it has been reported [2]. Assuming the simple dipolar interaction between nanographene’s edge and ferrocenium ion spins, ESR linewidth is expected to increase 5 times as large as that of ACFs. But, the ESR linewidth of FeCp₂-ACFs doped at 55 °C are 8-10 times larger than that of ACFs, suggesting the exchange interaction between nanographene’s spin and ferrocenium ion spins. In addition, The ESR intensity for FeCp₂-ACFs is easily saturated than ACFs by applying higher microwave power, indicating that spin relaxation to conduction electron system is suppressed by hybridization with spin states of FeCp₂ having isolated nature. Narrowing of the ESR linewidth of FeCp₂-ACFs upon higher microwave power suggests the presence of two kinds of spin species; spins with only dipolar broadening and spins broadened also by exchange interactions, the latter of which is easily saturated with the higher microwave power.
[1] T. Enoki and K. Takai, Solid State Comm., 2009, 149, 1144-1150.
[2] A. Nakayama et al., Synt. Met., 1997, 86, 2335-2336.

Earlier experiments have demonstrated the ability of pores with diameters range of 0.6-0.7 nm to offer the highest H₂ uptake per unit specific surface area at 77 K. However, the effect of pore geometry has remained unclear. We present experimental data that directly shows the effect of pore geometry on hydrogen (H₂) densification in nanoporous carbons with identical pore size but different pore types. Based on our previous research findings, which show evidence for solid-like H₂ in the pores of nanoporous carbon containing micropores of an optimum size (0.6-0.7 nm) at 77 K, we selected three nanoporous carbons with optimal pore size but different pore types to compare the effects of their pore geometry on H₂ densification. The selected carbons were TE7 carbon representing a disordered carbon structure, a titanium carbide-derived carbon (TiC-CDC) representing slit pores, and single-walled carbon nanotubes (SWCNTs) for cylindrical pores. This allowed a comprehensive analysis of the influence of pore geometry without any change in pore size. We used inelastic Neutron Scattering (INS) as one of the few experimental techniques that can provide direct access to confined H₂ molecules in the micropores. Data from INS was combined with volumetric high pressure gas sorption analysis, structural characterization and computer simulation to determine the effects of the three selected pore geometries on hydrogen densification. The INS spectra analysis suggests the solid-like H₂ molecules are confined in ultramicropores of TE7 and TiC-CDC but are not found in SWCNTs at 77 K. The quantities of confined, solid-like H₂ in micropores of TE7 and TiC-CDC increased with pressure and were directly evaluated using in situ INS and confirmed by analysis for gas sorption isotherms. It was noticed that the predicted density of H₂ contained in the pores of TE7 is much higher than that of TiC-CDC, indicating that the confinement of solid-like H₂ is stronger in disordered pores than in the slit pores between graphitic sheets. Even at 2 MPa, H₂ uptake on SWCNTs has not shown signs of strong densification due to hydrogen confinement inside the cylindrical pores, compared to solid-like H₂ confined in TE7 and TiC-CDC occurring at pressure as low as 1.6 kPa. We suggest H₂ is unlikely to have undergone pseudo-condensation inside the nanotubes at 77 K and up to 2 MPa H₂ pressure, which is in good agreement with other research. Thus, this investigation greatly supports the development of more accurate models for the evaluation and design of higher-capacity nanoporous adsorbents. In the next step, we will apply the methodology of INS technique combined with gas sorption measurement and simulation to complex pore geometries to optimize the pore size and pore geometry for enhanced hydrogen densification and meeting the US Department of Energy (DOE)’s requirements for on-board hydrogen storage.

Lintec of America has recently developed continuous processes for production of highly aligned, free-standing carbon nanotubes sheets (c-Silk) at an attractive low cost that enables the production of large amounts of coatings, composite yarns and sheets. C-Silk can be easily applied over complex shape substrates producing a robust and uniform conductive coating. Through a new manufacturing process called biscrolling [1], c-Silk can be used for producing continuous composite yarns and sheets comprising up to 99 wt % of otherwise unspinnable nanopowders or nanofibers that remain highly functional. These methods utilize the strength and electronic connectivity of sometimes minute amounts of 50 nm thick carbon nanotube sheets that are helically scrolled in the yarns or stacked on sheets confining nanopowders, micropowders, or nanofibers between the layers of aligned nanotubes. This new technology has been demonstrated on the manufacturing of ribbons yarns, superconductors, high performance battery materials, catalytic oxygen electrodes for fuel cells, TiO2 for release of active oxygen, and strong sutures containing biomedical agents. The observed mechanical properties enable yarn knotting and the weaving and sewing of biscrolled multifunctional yarns into textiles.
[1]. M. D. Lima et al., Biscrolling Nanotube Sheets and Functional Guests into Yarns. Science 331, (2011).

Graphene oxide (GO) having oxygen-containing groups is promising as metal-free and environment-compatible catalyst. Although the research for GO catalyst with high reactivity was progressed [1] [2], the detail mechanism for catalytic activity is not clear yet. Indeed oxidative coupling of benzylamine using GO catalyst in the lower temperature condition are limited about 30% yields in spite of higher yields for the higher temperature. Considering that GO is quite hydrophilic and has large amount of water molecules accommodated into galleries between layers, it reminds us that a catalytic reaction using GO as Brönsted acid in water medium. In this study, the change in the chemical structure of graphene oxide as catalyst is investigated before / after the synthesis of a xanthene derivative in water solvent in order to clarify the mechanism of the catalytic activity.
GO was synthesized from natural graphite flake by Hummers methods. A mixture of benzaldehyde (2 mmol), dimedone (4 mmol) and GO catalyst (4.9 wt%) dispersed in water was stirred at 80°C for 3h. After separation of GO catalyst from the reaction media by filtration and washing with dichloromethane, the water solvent was evaporated. The obtained product was characterized by GC-MS. The chemical structure of GO before / after the reaction was evaluated by XPS. This experiment was conducted three cycles.
The GC-MS peak for 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione (m/z = 350) appears in the product of the reaction using GO catalyst in spite of the absence of the peak on the condition without GO, indicating catalytic activity of GO as Brönsted acid. The first cycle yield and conversion are 12% and 99% respectively from GC-MS. However, the C/O ratio of GO estimated by XPS decreases after the reaction. Taking the fact that C/O ratio also decreases in the control experiment without reactants, the C/O decreasing is mainly attributed to the heat-induced reduction during the reaction. The intensity ratio of C1s peaks for oxygen-containing functional groups [3] (especially –COOH, C=O) to total intensity for C1s decreases for GO after the reaction more than that for control experiment as repeating reaction cycle. The xanthene derivatives reaction might relate to –COOH, -C=O functional groups of GO.

[1]C.Su, M.Acik, K.Takai et al, Nat. Commun. 2012, 3, 1298
[2]Shaabani, A.; Mahyari, M.; Hajishaabanha, F. Res. Chem. Intermed. 2013, 40, 8, 2799-2810
[3]Rodriguez-Postor, I.; Ramos-Fernandez, G.; Varela-Rizo, H.; et al. Carbon. 2015, 84, 299-309

Structure and electronic properties of Graphene oxide (GO) having oxygen-containing functional groups depend on synthesis method [1]. However, there is little research on properties of GO synthesized by different methods. In this study, we evaluated GOs synthesized by different method in terms of magnetism and chemical structure.
GO samples were synthesized by Brodie [2] and Hummers [3] methods, which are labeled as BGO and HGO, respectively. FT-IR spectra were recorded by the FT/IR6600 (JASCO co.). The magnetic susceptibility was measured using a squid magnetometer (Quantum Design, MPMS-XL). Raman spectra were recorded by the Lab RAM-HR-Evolution (HORIBA-JOINYVON co.) using a 532nm laser. UV-vis spectra were recorded by the V-770 (JASCO co.). In FT-IR spectra peaks for hydroxyl, carboxyl, epoxy and carbonyl groups [4] appear for GO in spite of absence of any peak for graphite. Interestingly, the peak around 1224 cm^-1 attributed to C-OH stretching for HGO is larger than that for BGO, while the peak around 1050 cm^-1 for C-O-C stretching is larger for BGO. Hydroxyl and epoxy groups are more likely to be introduced by Hummers and Brodie method, respectively. The temperature dependence of magnetic susceptibility indicates an order of magnitude larger localized spin concentration of HGO (Ns = 2×10¹⁹) than that of BGO (Ns = 2×10¹⁸). This indicates that p-electron state of GO differs according to oxidation methods. The difference of functional groups between HGO and BGO explains the larger spin magnetism for HGO. In the case of introduction of epoxy group, oxygen atom bonds to adjacent carbon atoms, remaining symmetry of A, B sub-lattice of graphene lattice. On the other hand, attaching hydroxyl group occurs randomly on carbon atoms of graphene and breaks symmetry of A, B-sublattice, resulting in the emergence of the localized states and the spin magnetism. The G band position in Raman spectra for GO do not change after oxidation in comparison with graphite, indicating that GO has the same fermi energy as Graphite. The UV-vis spectra of GO and Graphite show a sharp absorption peak at 230 nm and 260 nm, respectively, which are attributed to π-π* transition between maxim of DOS. It is suggested that the energy gap of π-π* energy state increases due to partial destruction of π-electron system by oxidation.

References
[1] A. V. Talyzin et al, Nanoscale, 6, 272, (2014)
[2] B. C. Brodie, Phil. Trans. R .Soc. Lond., 149, 249-259 (1859)
[3] D. C. Marcano et al, ACS Nano, 4, 8, 4806–4814 (2010)
[4] J. Guerrero-Contreras, F. Caballero-Briones, Mater. Chem. Phys., 153, 209 (2015).

Among the various sorting techniques for single-walled carbon nanotubes (SWCNTs) selective wrapping with conjugated polymers leads to very pure semiconducting and even monochiral dispersions with comparatively low effort. Polymer-sorted SWCNTs exhibit very low residual metallic content and little intertube interactions, which results in high photoluminescence quantum yields (PLQY) in ensemble average. Typically harsh sonication methods are used to disperse nanotubes in order to break up the SWCNT bundles of the raw material and enable polymer wrapping. In addition to reproducibility issues sonication damages the carbon lattice and shortens the SWCNTs resulting in a reduced PLQY.
Here, we use simple high speed shear force mixing (SFM) to disperse nearly monochiral (6,5) SWCNTs with poly [(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6’-{2,2’-bipyridine})] (PFO-BPy) in toluene with high yield and in large volumes. This highly scalable process disperses SWCNTs of exceptional quality with an average tube length of 1.8 µm and an ensemble photoluminescence quantum yield (PLQY) of 2.3% [Graf, A. et al., Carbon 105, 593 (2016)].
We further employ these exceptionally long SWCNTs, dispersed by SFM, to determine length-dependent optical properties of nanotubes from a hundred nm up to a few µm. Upon shortening of the SWCNT we find a characteristic shift and broadening of the absorption and emission peaks. Using data of numerous samples, we develop a metric for extracting the average SWCNT length in a dispersion by simple emission and absorption spectroscopy. This metric allows us to bypass tedious length-counting of SWCNTs in atomic force microscopy images for sample screening

Owing to the rapid paradigm shift in the field of nanocomposites, multi-functional composites are a much sought after commodity. The aerospace industry is one of the best examples of a field that benefits from robust structural materials which act as good thermal heat dissipation sinks in engine exhausts or provide excellent electromagnetic shielding against lightning strikes. With the limitations associated with obtaining superior composite properties from dispersing large aspect ratio nanomaterials, the current study involves composites that have been prepared by depositing multi-walled carbon nanotubes on alumina based fiber mat surfaces using a chemical vapor deposition process. The fiber mats are then stacked up and infiltrated with a high strength, epoxy resin to form “fuzzy” fiber composites that offer excellent structural properties in addition to remarkable thermal and electrical properties. The radially aligned MWCNTs wick the polymeric resin by capillary action, thereby providing excellent in-plane and out-of-plane structural properties.

Due to their application in aerospace industries, these composites are exposed to a variety of conditions including high humidities and temperatures. The current study involves understanding the changes in the properties of these hybrid composite materials when subjected to an aggressive environment at a high temperature (60^oC) in the presence of water. The short (15 days) and long term (90 days) studies both confirm a decrease in the mechanical properties of the alumina based composite (control) while denoting no change in the properties of the CNT fuzzy fiber composite. The alumina hydration reactions that occur at high temperatures lead to interfacial bond failure in the control specimens while, the presence of complex energy dissipation mechanisms (fiber pullout, fiber breakage, crack deflection etc.) in the CNT composites due to excellent CNT/polymer interfaces, helps maintain the integrity of these composites over both short and long term exposure conditions.

High quality dense and tall vertically aligned rapidly-grown spinning carbon nanotube (CNT) forests with the CNT layers varied from 2 to 5 were predominantly produced intentionally with selectivity above 70%. In addition, the high stability and reproducibility of the tube diameters are in the range of 3 to 7 nm but below 10 nm, was demonstrated by a water vapor free thermal chemical vapor deposition (CVD) using Fe catalyst with hydrogen as the process gas and acetylene as a carbon source with temperatures around 680 ^oC. Not only we can control the catalyst nanoparticle size with high areal density, but also fine-tuning of CVD process conditions can be done especially flow rate and duration (or residence time) of acetylene, it’s inlet temperature strongly affects the control of number of walls and tube diameters of CNTs due to the hydrocarbon decomposition on catalyst nanoparticles.
The wire-like macro scale assemblies of CNTs give them exceptional mechanical toughness, electrical conductivity and resilience to bending stress, and are recognized to have a potential to be used in electrical or structural applications. The ability to fabricate continuously dry spinning CNT fibers from a large scale CNT forest represents an important step in this direction. In this report, the diameter of the CNT fiber was measured to be 10-20 mm fabricated by pulling at a speed of 10 mm/min and twisting at a rate of 250 revolutions/min. The tensile strength of 700 MPa and Young’s modulus of 50 GPa with the surface twisting angle of 25° were measured to be the highest from the pristine CNT fiber and it consists of more than 70% of double wall CNTs. The processing of CNT fiber by high voltage (HV) was considered as possible ways to improve both the mechanical and electrical properties. Different HV was applied to CNT fiber in vacuum for several minutes to vary a current that directly goes through CNT fiber. Improvement in surface smoothness and disappearance fluff were clearly observed with increase in HV. The graphite component in CNT fiber which was determined by Raman study was found to be increased with increase in applied voltage this may be due to Joule heating effect by the direct electric resistance heating. The tensile stress of the CNT fiber increased from 620 MPa to 960 MPa with an increase in the applied voltage. The Young’s modulus was found to be improved from 34 GPa to 75 GPa by HV treatment. Generally when carbon fibers are HV treated they become rigid, but this HV-treated CNT fiber show flexibility. Based on our measurements it is indicated that pristine CNT fibers behave typically as semiconductors and have electrical conductivity less than the order of 10⁵ S/m at room temperature. The CNT fibers after applying HV treatment have improved more than 10⁶ S/m. The impact of crystallization of CNT fibers on the electrical conductivity was confirmed by a transmission microscopy (TEM).

Lithium-ion batteries (LIBs) with high energy density have become the important devices for energy storage and electric vehicles. Anode is a crucial part of LIBs. To improve anode performances further, structures and properties of electrode materials need to be designed and optimized to solve the extreme volume changes (e.g. SnO2>250%) problem of electrochemically active particles during Li+ insertion/extraction process, which always leads to a rapid capacity fade upon cycling due to mechanical fracture of electrodes and loss of electrical contact.
Single-walled carbon nanotube (SWCNT) is tagged with superior electrical properties and suitable to be used as electrode materials,[1] which can serve as a promising matrix for supporting electrochemically active materials as electrodes in LIB to improve the electrical conductivity and accommodate the strain of volume change during the alloying/dealloying with lithium.[2]
In our electrode design, SWCNT was introduced and combined with N-doped carbon coating on SnO2 to realize a coaxial nanocables structure, which is a conductive restrictive sheath to buffer volume change and improve electrical connection between SnO2 NPs and SWCNTs during process of charge-discharge cycles. And the N-doped carbon-coated SnO2/SWCNT aerogel was fabricated by hydrothermal treatment, PDA coating, freeze-drying and annealing. The material exhibits a capacity of 904 mA h g-1 at current density of 0.5 A g-1 after 260 cycles. In addition, its initial coulombic efficiency is 74.6%, which is higher than that of most reports. Our results demonstrated that the structural design was feasible and it could provide us with a new method and concept of fabricating SWCNT-based anode materials.

Key words: SWCNT, N-doped carbon coating, coaxial structure, lithium ion batteries
1. Odom T W, Huang J L, Kim P, et al. Atomic structure and electronic properties of single-walled carbon nanotubes. Nature, 1998, 391(6662): 62-64.
2. Rong J, Masarapu C, Ni J, et al. Tandem structure of porous silicon film on single-walled carbon nanotube macrofilms for lithium-ion battery applications. ACS Nano, 2010, 4(8): 4683-4690.

There is growing interest in graphene-based coatings due to graphene’s high surface area, aspect ratio and impermeability, which make this material ideal for anti-corrosive barrier coatings.(Bohm, 2014, Raju et al., 2014, Su et al., 2014, Dumée et al., 2015, Nine et al., 2015, Ramezanzadeh et al., 2016) We have prepared polymer-based composite coatings with different flake size nanomaterials, including commercially available graphene nanoparticles, i.e. XGnP® 5M, 15M and 25M (XG Sciences, Inc., Lansing, Michigan, USA) that have a flake diameter of 5 µm, 15 µm and 25 µm. The nanomaterials were mixed into a thermosetting polymer matrix (“Gold Lacquer”, AkzoNobel Packaging Coatings Limited, UK). The polymer matrix was chosen to be compliant with new national legislation which requires the use of polymers which are not based on Bisphenol A. In order to obtain a better dispersion of the nanomaterials into the polymer matrix, a solvent, i.e. propylene glycol monomethyl ether acetate (Sigma-Aldrich Co Limited, UK), was used. The solvent was completely evaporated before the polymer/graphene nanocomposite suspensions were characterized and further used.
The polymer/graphene formulations were subjected to rheological characterization using a TA Discovery HR-3 rheometer with parallel-plate geometry (60 mm diameter and 1 mm gap). Preliminary tests showed that increasing flake diameter lead to high storage moduli at low and at high frequencies. The relative viscosity measured through steady shear rate flow was found to decrease with increasing flake size. Steel surfaces were coated with the polymer-based formulations and aged in a 0.1 M NaCl solution. Electrochemical impedance spectroscopy found that the presence of graphene improved the corrosion resistance of the materials with flake diameter strongly affecting the performance of the coating.
References
S. Bohm, Nat Nano, 2014, 9, 741-742.
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Nitrogen doping was carried out while the graphene grew on a copper foil. Mixture of melamine, C₃N₃ (NH₂)₃, and methane, CH₄, was used for N and C source of N-doped graphene. Here the mixing ratio was controlled by heating the melamine in the temperature range between 423 and 473 K and also a flow rate of carrier gas for melamine vapor. CVD was conducted at the pressure of 5 kPa under flowing a 2 sccm of H₂ and a 100 sccm of PR gas (10% CH₄ in Ar) including melamine vapor at 1273 K for 30 min. In advance, 0.05 mm thick copper foil was annealed at 1273 K for 9 hours under 1 atm of H₂ flow (50 sccm). Un-doped graphene was easily obtained by setting the furnace temperature of melamine at room temperature. After growing of N-doped or un-doped graphene, a flow of mixture gas was closed and increased H₂ rate to 10% in 50 sccm of Ar at 5 kPa, then the furnace power off. Cooling rate of furnace was ca. 40 degree/min by down to 1073 K.
In order to determine the number of stacking, Cu was etched away by using FeCl₃/HCl aqueous etchant, and the sample was transferred to quartz substrate. The number of stacked graphene layers was estimated at 7-9 by the transmittance at 550 nm (97.7 % for 1 layer graphene). Additionally, high resolution TEM images clearly showed hexagonally arranged lattice fringe, which guarantees commensurately stacked graphene layers. Raman scattering was measured for the sample on the Cu foil with a laser excitation of 532 nm. Clear D-band signal was detected for N-doped sample, and the D band intensity increased with increasing melamine concentration in methane. This feature is explainable by a model of substitutional N-doping to the carbon site. XPS using Al-K_a on the sample of Cu indicated weak N1s signals at the binding energy (BE) of 398 eV for the samples with N doping amount of 1-2 at%. On the other hand, N1s signal shifted to high BE at 401 eV when the doping amount decreased in the range of 0.2-0.5 at%. From such chemical shift of N1s, we can say that pyridinic and pyrrolic N with neighboring atomic vacancy are dominated for the sample including a few at% of N, and graphitic N for the sample with lower doping amount of less than 1 at%. Doping dependences of N on the electric conductivity and on the ORR feature will be opened as the results of sample characterization.

Chemical vapour deposition (CVD) has emerged in the recent years as the most promising method for the controlled and scalable synthesis of high quality films of two-dimensional materials (2DM), such as graphene [1] and hexagonal boron nitride (h-BN) [2]. While a lot of recent attention has focussed on 2DM growth mechanisms on the typically used catalyst materials, many applications require transfer of the 2DM films away from the growth substrate, which has become a serious bottleneck. In particular, there is currently very little in-depth knowledge of the fundamental mechanisms underlying transfer.
Based on a detailed understanding of 2DM/catalyst interactions, we devise here improved strategies for high-quality 2DM film transfer [3]. We thereby focus on graphene and h-BN mono-layer films grown directly on Cu, as it is currently the most widely used catalyst. Based on detailed in-situ investigations of 2DM/Cu interactions [4,5] we show how intercalation allows the local Cu oxidation at the interface followed by selective dissolution, which gently releases the 2DM film. This enables a method of transfer, which we refer to as Lift-Off Transfer (LOT). We introduce two pathways for LOT, either involving interfacial composition change and dissolution in one, or two process steps. Using LOT, we successfully demonstrate both the transfer of graphene and hBN films in very few simple process steps. We show that this method is not only highly versatile, but also yields layers of high quality regarding surface contamination, layer coherence, defects and electronic properties, without requiring additional post-transfer annealing. Furthermore, our experiments offer detailed new insight into open questions regarding the mechanisms of 2DM transfer.

[1] Hofmann, S. et al., J. Phys. Chem. Lett 14, 2714 (2015)
[2] Caneva, S. et al., Nano Lett. 15, 1867 (2015)
[3] Wang R. et al., submitted
[4] Kidambi et al., Nano Lett. 13, 4769 (2013)
[5] Blume et al., Phys. Chem. Chem. Phys. 16, 25989 (2014)

Carbon nanotubes (CNTs) are of considerable interest in the electronics industries, especially for field-effect transistors and as conductive layers for the touch screen market. However, a major obstacle in deploying CNTs in commercial applications is the current difficulty in sorting semiconducting CNTs from amongst metallic ones from their polydispersed mixtures. There have been numerous efforts targeted to either control their growth to a monodisperse type of CNT or to sort them. However, existing methods, using polymers or “nanotweezers” have their drawbacks. In addition, the mechanism by which even the existing methods act is not very well characterized at the molecular-scale. With that aim in mind, we undertook a fully atomistic Molecular Dynamics technique to understand the origin of size-selectivity among CNTs by a small organic semiconductor molecule (contorted hexabenzocoronene called c-OBCB, [Octabenzocircumbiphenyl]) featuring four side-chains. This molecule was discovered by Lynn Loo’s group at Princeton to be capable of selecting a (10,3) CNT variant with 97 per cent specificity from among a polydisperse CNT mixture, but only in one specific solvent (toluene). In order to uncover the underlying principles behind it we conducted a detailed computational study of the enthalpic and entropic contributions that contribute to the binding of c-OBCB to four differently sized and different chirality CNTs. We also studied the motion of the c-OBCB molecule over the surface of the CNT to investigate whether it offsets or enhances the thermodynamics of the system. We used Sandia’s LAMMPS Molecular Dynamics code to model the system and OPLS parameters for the CNT and c-OBCB. We found that the underlying molecular-scale causes of the experimentally observed selectivity is not traceable to a single dominant effect; rather, is a composite of effects. It takes a combination of two key factors: (1) the strength of the binding interactions between the core of the c-OBCB and the curved surface of the CNT and (2) the relative preference of the side-chains on the c-OBCB to stick to the carbon nanotubes (versus interacting with the solvent). The best combination for selectivity appears to be one in which there is strong binding of OBCB to the CNT in conjunction with a solvent that promotes side-chains adhering to the CNT surface. The worst combination is the one in which c-OBCB is weakly bound to the CNT variant and there is a good solvent for the side-chains. We were also able to capture the specific solvent effect for this system: Toluene allows significantly better binding than chloroform (which was not observed to be CNT variant-selective, experimentally). The results also highlight that the diffusivities obtained in either solvent show no correlation with CNT diameter or chirality and hence are not important for selectivity. This opens the door to using all-atom Molecular Dynamics to rationally design a molecule to select for a precise CNT variant.

Stretchable electrodes have been a substantial component for flexible electronics such as flexible displays, flexible energy devices, and wearable sensors. Carbon nanotubes (CNTs) and graphene have been considered as flexible electrode materials due to their outstanding properties such as good mechanical strength, high carrier mobility, and high thermal conductivity. ¹ However, a graphene film can only withstand up to 1% strain before cracks are introduced to the film. The combination of CNTs and graphene has potential to extend the original 1D and 2D materials into versatile 3D structures. ² Vertically aligned carbon nanotubes (VACNTs) with an optimized aspect ratio and mechanical flexibility can provide the possibility to serve as a strain relief support for graphene as stretchable electrodes.

In this work, we demonstrated that VACNTs supported graphene as stretchable electrodes. 50 µm thick VACNTs were grown on a SiO₂ wafer substrate with 3 nm Al as the supporting layer and 5 nm Fe as the catalyst layer via atmospheric pressure chemical vapor deposition (APCVD). ³ The VACNTs were then transferred to a PDMS substrate by curing liquid PDMS prepolymer on VACNTs. The VACNTs/PDMS was laminated from the SiO₂ wafer due to the strong bonding between VACNTs and PDMS. Graphene was then transferred to the surface of VACNT carpet to interconnect the VACNTs on the topside with graphene and serve as the electrical conductive layer. The VACNT-graphene hybrid structure was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Raman spectroscopy. The sheet resistance was then measured under different strains applied to the substrate by four-point probe method. The results demonstrated our VACNT-supported graphene could serve as a potential stretchable electrode in flexible electronics.

1. Jiang, J.; Li, Y.; Gao, C.; Kim, N. D.; Fan, X.; Wang, G.; Peng, Z.; Hauge, R. H.; Tour, J. M. ACS Appl. Mater. Interfaces 2016, 8, (11), 7356-7362.
2. Kumar, K.; Kim, Y.-S.; Li, X.; Ding, J.; Fisher, F. T.; Yang, E.-H. Chem. Mater. 2013, 25, (19), 3874-3879.
3. Fejes, D.; Pápa, Z.; Kecsenovity, E.; Réti, B.; Toth, Z.; Hernadi, K. Appl. Phys. A 2015, 118, (3), 855-861.

Decades of research since the 1940s has substantiated graphite as a low surface energy material. Its chemical structure led researchers to believe that airborne hydrocarbon contamination was inconsequential and contradictory reports were not convincing. Graphite gained renewed interest when graphene was first isolated in 2004. Being an atomically thin material, the surface properties of graphene are critical to its performance, thus elucidating surface properties of graphene and graphite became important topics in fundamental and applied research.

Fresh graphite is shown to be mildly hydrophilic and becomes hydrophobic upon exposure to ambient air. Similar behaviour was observed for graphene and MoS₂. Ellipsometry showed growth of an adsorptive layer on the fresh (clean) surface and ATR-FTIR indicated that the adsorptive layer was airborne hydrocarbon. Theoretical calculation further confirmed that adsorption of only a monolayer of hydrocarbon is enough to reproduce the hydrophobic behavior previously observed on HOPG.

Surface energy of fresh CVD graphene was calculated to be 62.2 ± 3.1 mJ/m² (Fowkes), 53.0 ± 4.3 mJ/m² (Owens-Wendt), and 63.8 ± 2.0 mJ/m² (Neumann), which decreased to 45.6 ± 3.9 mJ/m², 37.5 ± 2.3 mJ/m², and 57.4 ± 2.1 mJ/m², respectively, after 24 hours of air exposure. Similar behaviour also occurred for HOPG and MoS₂. The fresh surface exhibits highest surface energy which decreases upon adsorption of airborne hydrocarbons. Results also indicate that the fresh surface is mildly polar.

The physical phenomena of advancing and receding contact angles have been elucidated by other researchers on well-defined heterogeneous surfaces. We apply this theory to our experimental results and show that the intrinsic WCA of fresh sp²-hybridized carbon is 68.6° ± 7.1°. Furthermore, roughness and chemical heterogeneity do not cause the intrinsic hydrophilicity of graphitic surfaces, thus other explanations must be considered. This work unequivocally shows that fresh graphitic surfaces are mildly hydrophilic and slightly polar, findings that can have implications for the myriad of potential applications for 2D materials.

Paraffin is known to be a good energy storage phase change material (PCM) because of its high energy storage capacity and low cost. However, its low thermal conductivity and the potential for leakage of liquid paraffin can hinder applications of paraffin in energy storage systems. To combat these issues nanomaterials have been used to create PCM composites which enhance their thermal properties while also strengthening and shape stabilizing the PCMs. In this study, we developed a PCM composite using graphene aerogel (GA), in which the GA functions thermally as a heat conduction path and mechanically as nanofillers reinforcement of the PCM matrix. We show that chemical, molecular, and structural integration between the PCM and GA significantly affects the mechanical reinforcement and thermal transport of the GA-PCM composite.

The crystal and molecular structures, and the multiscale mechanical and thermal behaviors of the GA-PCM composite were characterized to evaluate the role of GA in the PCM composites. The crystal and molecular structures of GA, PCM and GA-PCM were characterized using XRD, FTIR, and Raman. The mechanical properties were studied using nanoindentation at the nano/microscale and a digital durometer at the macroscale from 25 °C to 70 °C. Thermal scanning microscopy (SThM) was used to study the thermal properties at microscale. The latent heats and thermal conductivities were analyzed using DSC and a Hot Disk transient plane source (TPS) technique at the macroscale.

There have been few fundamental studies on the mechanical and thermal behaviors of GA much less its composites. Based on the nanoindentation results, GA was found to exhibit an extremely low modulus (90-400 kPa) and hardness (0.3-0.9 kPa), while the hardness of paraffin is strongly strain-rate dependent and changes from 0.8 MPa to 5MPa when the strain rate changes from 1×10^-4s^-1 to 500×10^-4s^-1. Interestingly, the hardness of the composite is greatly enhanced above either component and is less strain rate sensitive, reaching 3-17 MPa in the same strain rate range (1×10^-4s^-1-500×10^-4s^-1). The GA-PCM is found to contain the liquid PCM within the GA matrix through capillary forces even above the melting temperature where the GA-PCM’s durometer Share A hardness reaches a non-zero plateau of 10.5. The GA exhibits a low thermal conductivity of 0.056 W/mK. However, the thermal conductivity of the composite is 0.27 W/mK, above the level of the paraffin alone (0.2 W/mK). Perhaps most interestingly, by integrating paraffin into GA, the effective latent heat storage capacity of paraffin in GA-PCM is increased by 3% over pure paraffin. These results all indicate a distinct molecular integration effect of the GA and paraffin. This study provides fundamental knowledge of the mechanical and thermal properties of GA, PCM and GA-PCM composite as well as inspirations for future designs of energy storage PCM systems using carbon nanomaterials.

The selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs) are widely able to be used for electronic due to solution processability and mechanical flexibility. However, separating semiconducting SWNTs from metallic SWNTs is need for the wide applications in SWNT based electronics. The semiconducting SWNTs sorting method using conjugated polymers can take advantages of high-selectivity, high-yield and simplicity of execution. As one of key strategies, we believe that molecular design of conjugated polymer will provide unique interaction for sorting ability with the nanotubes. In this study, we newly synthesized conjugated poly(thienylenevinylene)s to wrap semiconducting carbon nanotubes. The effect of poly(thienylenevinylene) and their different alkyl side-chain length have been examined including the extraction conditions on the purity and yield. For the study, two types of SWNTs with different diameter were dispersed using respective polymers by a mild centrifugation without additional surfactant and expensive processes. The dispersed SWNTs are systematically investigated with respect to their ability to selectively disperse SWNTs. Furthermore, we demonstrated that the sorting of semiconducting SWNTs was directly related to the length of the polymer's alkyl side chains. Polymers with longer alkyl side chains bound strongly to SWNTs due to the increased overall surface contact area with the nanotubes. Finally, we fabricated the sc-SWNTs based field effect transistors as a promising application of purified SWNT dispersions.

Alzheimer`s diseases is known to be induced by self-assembling of b-amyloid peptides to fibrils, which is accelerated by acetylcholinesterase (AChE) that hydrolyzes a neurotransmitter acetylcholine. Herein, we demonstrated graphene oxide (GO)-based optical biosensor for the optical detection of AChE activity and inhibitors via its fluorescence response. To this end, GO was non-covalently functionalized with phenoxydextran (PhO-dex-GO), leading to its outstanding colloidal and optical stability in various media solutions. The fluorescence of PhO-dex-GO increased as AChE enzyme hydrolyzed acetylthiocholine (ATCh) while its turn-on response decreased in the presence of an inhibitor, paraoxone, to AChE. The turn-on fluorescence response of PhO-dex-GO was found to be caused by its protonation by the product of the enzymatic hydrolysis reaction. The PhO-dex-GO sensor was able to provide the precise kinetic parameters such as a Michaelis constant, a maximum velocity, and an inhibition dissociation constant for the enzyme activity and the inhibition efficiency.

In the first part we present Raman spectra of graphite, graphene, and carbon nanotubes with UV excitation energies. Using excitation energies above 4.7 eV, i.e. above the M-point exciton, we can observe the vibrational density of states of these carbon materials[1]. We get access to regions of the first Brillouin zone that are not accessible with Raman spectroscopy in the optical visible range. Tuning the excitation energy towards lower energies activates double-resonant Raman scattering processes with ultra-short wavevectors. We analyze and explain the origin of the scattering processes by simulating corresponding spectra for various excitation energies.
In the second half we analyze the electronic and vibrational properties of double-bond coupled diamondoids[2,3]. The hybrid sp²-sp³ carbon nanostructures exhibit HOMO-LUMO transitions around 4.7 eV widely independent from the size or symmetry of the diamondoid constituents.
A strong enhancement of the characteristic C=C stretching mode occurs under UV excitation. This is associated with a localization of the π- HOMO and π^*- LUMO and an elongation of the carbon bond during the vibration[4]. We support our findings with density functional perturbation theory computations of both the vibrational modes and the electronic states. In the end we compare all carbon systems with respect to their (ultra-violet) optical properties and their characteristic vibrations.

[1] C. Tyborski et al., PRB, B 92,041401(R) (2015)
[2] M. A. Gunawan, J.-C. Hierso, D. Poinsot, A. A. Fokin, N. A. Fokina, B. A. Tkachenko, and P. R. Schreiner, New J. Chem. 38 (1), 28 (2014)
[3] H. Schwertfeger, A. A. Fokin, and P. R. Schreiner, Angew. Chem. Int. Ed. 47, 1022 (2008)
[4] R. Meinke, R. Richter, A. Merli, A. A. Fokin, T. V. Koso, V. N. Rodionov, P. R. Schreiner, C. Thomsen, and J. Maultzsch, J. Chem. Phys., 140, 034309 (2014)

For focused electron/ion beam applications, ring-cathode sources provide the exciting prospect of producing a high brightness-high resolution electron beam source. Recently a design of a graphene ring-cathode source made of a graphene microtube grown in-situ on a sharp Ni wire tip was reported by Shao et al [1]. One of the challenges reported in that paper was to improve the mechanical properties of the graphene microtube and enhance the lifetime of the emitter. In this paper, an improved design of the graphene ring-cathode, enriched by Ni nanoparticle on inner side of the graphene microtube is proposed. This process of enriching the graphene microtube using Ni-nanoparticles prevents deforming of the circular shape of the microtube and also significantly improves the overall lifetime of the ring-cathode emitter.

[1] Shao, X., Srinivasan, A., Zhao, Y., & Khursheed, A. (2016). A few-layer graphene ring-cathode field emitter for focused electron/ion beam applications. Carbon, 110, 378-383.

Research on the development of novel graphene-based nanocomposites is still a hotspot in materials science field due to their unique optical, electronic, thermal, mechanical and catalytic properties. In recent years, mostly of the reported graphene-based composites are based on binary composites. In contrast, much less efforts have been dedicated on the ternary nanocomposites, although they possibly possess much more abundant structures and superior performance. [1] Research on the preparation and investigation of the properties of graphene-based ternary nanocomposites in catalysis, supercapacitor and sensor fields it still very interesting and challenging. In this context, the present work aims at the development of a graphene-based ternary nanocomposite of gold nanoparticles-PEDOT/reduced graphene oxide (AuNPs-PEDOT-rGO) via the one-step approach and its assembly with horseradish peroxidase (HRP) for the detection of hydrogen peroxide (H₂O₂). The prepared nanocomposite was characterized by UV-Vis absorption and infrared spectroscopy, field-emission scanning electron microscopy, and electrochemical measurements. SEM images revealed that 10 nm-AuNPs were uniformly distributed on the surface of PEDOT and rGO nanocomposites. Cyclic voltammetry and electrochemical impedance spectroscopy revealed that the AuNPs-PEDOT-rGO shows superior electron transfer rate and better ability to retain the electroactivity of HRP in respect to rGO and PEDOT-rGO counterparts, due to the synergistic effects arising from the combination between the three single components at the nanoscale. The AuNPs-PEDOT-rGO/HRP modified electrode has been used for the amperometric detection of hydrogen peroxide and the apparent Michaelis–Menten constant (K_M) of HRP for the nanocomposite was estimated to be 0.011 mM using the Lineweaver–Burk equation. The novel simple and sensitive sensing platform showed potential applications for the detection of H₂O₂ in the pharmaceutical, clinical and industrial areas.

Acknowledgements:
The authors are grateful to FAPESP, CNPq, Capes, MCTI-SisNano and EMBRAPA.

[1] Zhang, M., Li, Y., Su, Z., Wei, G. Polym. Chem. 2015, 6, 6107.

A theoretical study of new compounds based some new allotropic forms of carbons in the form cage denominated Quasi-Fullerenes (C_48-q and C_60-q) [1] that due to their size have capacity to encapsulate metal nitride clusters [2] to form some new molecules denominate Nitride Cluster Quasi-Fullerenes (NCQF). They have very interesting chemical reactivity properties, which have not been seen in small carbon molecules. Full geometry optimizations of the systems were performed at the PBE level of theory. All formation energies are negative indicating that they are thermodynamically stable. The NBO calculations are done to understand the charge transferred from metal nitride cluster to the quasi-fullerenes. All calculations were performed using the software package Gaussian 09. [3]

A distinct advantage of nanosensor arrays is their ability to achieve ultra-low detection limits in solution by proximity placement at or near the generation source of an analyte. However, real-time optical detection of E. coli metabolites remains a challenge. Previous work has shown great promise for the use of near-infrared fluorescent nanomaterials for optical detection of biomolecules [1, 2]. In this work, we demonstrate label-free, zeptomolar (10-21M) protein detection from single Escherichia coli bacteria immobilized in a microfluidic chamber, measuring protein efflux from single organisms in real time. The array is fabricated using non-covalent conjugation of an aptamer-anchor polynucleotide sequence to near-infrared emissive single-wall carbon nanotubes, using a variable spacer of 0 to 5 hexa-ethyleneglycol abasic ligands shown to optimize sensor response. Unlabeled RAP1 GTPase and HIV-1 integrase proteins can be selectively detected, and RAP1 is detected from crude cell lysates, from single E. coli bacteria as efflux, and from the same after T7 bacteriophage infections, via a fluorescent turn-on response from the array as large as 182 ± 8%. We use the sensor array to show that the bacterial process of induction, protein synthesis, and protein export is a highly stochastic process yielding variability in protein secretion on a single-bacterium level, with cells undergoing division under starved conditions producing 66 % fewer secreted protein products than their non-dividing counterparts. In this way, nanosensor arrays can enable the real-time, single-cell analysis of a broad range of metabolic products.

The research for graphene nano-electronic devices has been paying attention enormously for futuristic device applications such as next-generation graphene-based electronics, optoelectronics, and spintronics. Especially, graphene nanoribbons (GNRs) have been focusing due to their nonzero band gap property, arising from its quantum confinement, and edge effect, unlike semi-metallic graphene. Zigzag GNRs (ZGNRs), particularly, are a semiconductor that creates flat band around Fermi level because of its edge-localized state; however, its band gap decreases as GNR’s width increases. In this study, we investigated band gaps of edge-oxidized ZGNRs and edge-nitrided ZGNRs using density functional theory (DFT). From our investigation of edge-oxidized and edge-nitrided GNRs, we compare the calculated band structures and electronic properties to provide information such as edge-conversion effects, which should be very useful to develop delicately tuned electronic devices for next generation.

Acknowledgement
This research was supported by Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (No. 2013M3A6B1078865 and No. 2013M3A6B1078869).

The GÙC base synthesized in our lab combines the Watson-Crick base pairing properties of Guanine and Cytosine to form a Janus type module. The directional nature of hydrogen-bonding enables molecular recognition of GÙC bases and formation of a cyclic hexamer. A second level of self-assembly driven by solvophobic effect and π-π interactions leads to stacking of the hexameric modules and formation of supramolecules, that feature a hollow core of 1 nm running the length of the stack and giving it a tubular structure, termed rosette nanotubes (RNTs). The non hydrogen-bonding face of the GÙC base offers opportunities for conjugation with a variety of functional groups that end up being expressed on the periphery of the RNTs. The nanoscale self-assembly and surface functionalization achieved with this class of materials has led to a range of applications in tissue engineering and drug delivery.
While the GÙC base consists of two fused pyrimidine rings, the tricyclic module xK1-RNT possessing a pyridine spacer between the two pyrimidine rings features a central core of 1.4 nm and possesses enhanced optoelectronic properties. A continuing endeavor of our lab is the engineering of RNTs with expanded inner diameters and the evaluation of their biophysical properties. In this regard our ongoing efforts were directed towards expanding the size of RNTs through synthesis and self-assembly of a water-soluble tetracyclic module. With this modification, the RNTs will feature 1.7-1.9 nm wide tubular core. Moreover, the two-pyridine ring expansion has effectively altered the optoelectronic profile of the resulting supramolecular structure. In this presentation the synthetic and theoretical efforts towards the synthesis and characerization of a tetracyclic-based RNTs will be described and the emergent optoelectronic properties discussed.

Thermoelectric materials can transform small amounts of dispersed thermal energy into electrical energy. Thus, they contribute to solving the energy problem and developing self-sustaining power sources for wearable devices, and so on. The challenge in this field is designing flexible and eco-friendly thermoelectric devices.
Graphene nanoribbons (GNRs) are a single-layered graphene, a two-dimensional honeycomb lattice consisting of carbon atoms, with a nanometer width. GNRs have recently been attracting great interest as a potential candidate for a thermoelectric nanowire with high thermoelectric capability^[1]-[2]. In addition to having high thermoelectric output, GNRs are nontoxic and flexible. However, the thermoelectric efficiency of GNRs is not sufficient, owing to their high thermal conductivity, comparable to those of diamonds and carbon nanotubes^[3]. In order to improve the thermoelectric efficiency, we have to develop techniques that reduce the thermal conductivity without reducing their output.
Even a small degree of edge disorder in GNRs is known to suppress thermal conductivity dramatically^[4]. GNRs that retain high output after the introduction of edge disorder (ED-GNRs) are promising candidates for high-performance thermoelectric applications. In this paper, we theoretically elucidate the effects of edge disorder on the thermoelectric power factor (PF) of GNRs at room temperature.
We modeled edge disorder by addition and removal of carbon atoms at the edges. Our simulation is based on the non-equilibrium Green’s function (NEGF) method combined with the tight-binding method. Using the method, we computed transmission of 1,000 ED-GNRs having different configurations of edge disorder. We then calculated electrical conductances, Seebeck coefficients, and the PFs from the transmission data. All the simulations are performed at 300K.
We found that the PF of an ED-GNR exhibits a maximum at a certain ribbon length. As edge disorder concentration increases, both the maximum PF and the optimum ribbon length decrease, owing to Anderson’s localization resulting from the interference of electron waves scattered by edge disorder.
[1] T. Kato, S. Usui, and T. Yamamoto, Jpn. J. Appl. Phys. 2013; 06GD05, 52.
[2] Y. Yokomizo and J.Nakamura, Appl. Phys. Lett. 2013; 113901, 103.
[3] J. Hu, X. Ruan and Y. P. Chen, Nano Lett. 2009; 2730, 9.
[4] H. Karamitaheri, M. Pourfath, H. Kosina, and N. Neophytou, Phys. Rev. B 2015; 165410, 91.

In the two dimensional material field, chemically doped graphene has been studied to applicate high performance electronic device. There are several powerful method to grow high quality graphene. For example, representative method would be Chemical Vapor Deposition (CVD)[1], gas phase growth with metal catalyst and Pulsed Laser Deposition (PLD) etc.
Each method has own merits and demerits. Gas-phase doping on graphene by CVD requires complicated transfer process which can cause unintentional doping and defects creation. In this work, we report a solid-phase synthesis of N-doped graphene on N-doped silicon carbide (SiC) substrate by pulsed laser (XeCl, 308nm) irradiation. Laser-induced synthesis provides a direct growth of nitrogen doped graphene on an insulating substrate without additional transfer procedure. The XPS analysis demonstrates that the C-N bonding conformation of the N-doped graphene was pyridinic-N type. Also, G band shift in Raman spectra shows that solid-phase doping can provide precise controllability of doping concentration by changing the dopant concentration of the SiC substrate

Graphene is attractive materials for oxidation barrier because defect-free graphene with one-atomic thickness is impermeable to gas molecules. However, it has been contradictorily reported that the existence of graphene on copper surface can accelerate and decelerate the oxidation of copper surface at room temperature. The mechanism underlying the contradictory oxidation behaviors of copper surface under graphene has remained unclear and has limited graphene oxidation barrier. Herein, we clarified the effects of graphene on underlying copper oxidation at room temperature by comparing the oxidation behaviors of graphene covered copper and bare copper. In addition, we investigated the correlation between the defects in graphene and the oxidation rate of the underlying copper surface because synthesized graphene inevitably has defects. As a result, oxidation of copper surface under graphene can be accelerated and decelerated compared to bare copper depending on defect density of graphene. Lastly, we found that transfer process is critical factors in determining oxidation of copper surface. Transferred graphene (wet transfer) almost passivated copper surface in contrast to as-grown graphene accelerated copper oxidation.

Hybrid quantum dot-graphene photodetectors have recently attracted substantial interest owing to their remarkable performance and low power consumption. However, the performance of the device greatly depends on the interfacial states and photogenerated screening field. As a consequence, the sensitivity is limited and the response time is relatively slow. In order to circumvent these challenges, herein, we have designed a composite graphene and graphene quantum dot (GQD) photodetector on Lead Zirconate Titanate (Pb(Zr_0.2Ti_0.8)O₃) (PZT) substrates to form a ultra-sensitive photodetector over a wide range of illumination power. Under 325 nm UV light illumination, the device shows sensitivity as high as 4.06x10⁹ AW^-1, which is 120 times higher than reported sensitivity of same class of devices. Plant derived GQD has broad range of absorptivity and is an excellent candidate for harvesting photons generating electron-hole pairs. Intrinsic electric field from PZT substrate separates photogenerated electron-hole pairs as well as provides the built-in electric field that causes the holes to transfer to the underlying graphene channel. The composite structure of graphene and GQD on PZT substrate produces a simple, stable, and highly sensitive photodetector over a wide range of power with short response time, shows a way to resolve the shortcomings.

Although there are numerous reports of high performance supercapacitors with porous graphene, there are few reports to control the interlayer gap between graphene sheets with conductive molecular linkers (or molecular pillars) through a pi-conjugated chemical carbon-carbon bond that can keep a high conductivity which can explain the enhanced capacitive effect of supercapacitor mechanism about accessibility of electrolyte ions. For this, we designed molecularly gap-controlled reduced graphene oxides (rGOs) via diazotization of three different phenyl, biphenyl, and para-terphenyl bis-diazonium salts (BD1-3). The graphene interlayer sub-nanopores of rGO-BD1-3 are 0.49, 0.7, and 0.96 nm, respectively. Surprisingly, the rGO-BD2 of 0.7 nm gap shows the highest capacitance in 1 M TEABF4 having 0.68 nm size of cation and 6 M KOH having 0.6 nm size of hydrated cation. The maximum energy density and power density of the rGO-BD2 were 129.67 Wh kg^-1 and 30.3 kW kg^-1, respectively, demonstrating clearly that the optimized sub-nanopore of the rGO-BDs corresponding to the electrolyte ion size resulted in the best capacitive performance.

We have demonstrated the efficiency of the scalable floating catalyst chemical vapor deposition (FC-CVD) method for direct facile manufacturing of the self-supporting carbon nanotube (CNT) aerogels. High process rates and conditions implemented for the synthesis of the high performance CNT fibers have been shown to be effective for aerogel formation with controllable density and porosity.
In this work, the CNT aerogels are synthesized via FC-CVD method using methane as a carbon-source, hydrogen as a carrier gas and ferrocence and thiophene as a catalyst and promoter, respectively. The CNT aerogel/polydimethylsiloxane (PDMS) composites are made by direct polymer infiltration. Through the established process, the highly porous and ultralight CNT aerogels are synthesized with densities ranging from 0.55 to 32 mg/cm³. The weightless CNT aerogels are lighter than 1 mg/cm³, comparable with the lightest graphene aerogels ever reported. The aerogels exhibit high porosity (>98%) and surface areas up to 170 m²/g with tortuous pores. In addition, the electrical conductivity can achieve up to 106 S/m, which are suitable for energy applications. The thermal conductivity of the obtained aerogels is within the range of 0.127-0.137 W/m.K.
Besides, the CNT aerogel is completely infiltrated with the polymer at 4.5% weight fraction of CNTs. Polymer infiltration does not disturb the three-dimensional (3D) CNT network, however, it can cause its compaction, enhancing electrical and thermal transport within the composite. The electrical conductivity of CNT aerogel/PDMS composites can reach up to 33 S/m and their electrical conductivity has enhanced by ~16 orders of magnitude and thermal conductivity double that of pure matrix that are used in bio-integrated devices and flexible composites. The easily accessible fabrication method can be used for the production of various lightweight polymeric composites.

Large area graphene sheets were obtained from graphite by electrochemical exfoliation in acid media. The obtained graphene was decorated with gold nanoparticles (AuNP) using sodium cholate as a buffer layer resulting in non-covalent functionalization that preserves the desirable electronic properties of the graphene sheets. SEM and HR-TEM imaging revealed highly exfoliated crystalline samples of ~5 μm. Raman and FTIR and XPS analyses confirmed the high quality of obtained graphene. The AuNP-Graphene samples were characterized with various techniques including absorbance and fluorescence spectroscopy (samples displayed a fluorescence signal using an EW l 290 nm). The calculated quantum yield (Φ) for these samples was 40.04%, high when compared with reports for other solution processable graphene.

Graphene, a single layer of carbon atoms bonded in a hexagonal lattice, is simultaneously the thinnest, strongest and stiffest known material, as well as being an excellent conductor of both heat and electricity. Reassembly of individual 2D graphene sheets into 3D macroscopic structures such as films or fibers offers immense potentials for many important applications such as structural composites, electrodes for batteries and super-capacitors, stretchable/foldable electronics and membranes. Due to its intrinsically exceptional thermal conductivity, high quality graphene macroscopic structures also show immense potential as effective thermal management materials for high power electronics. However, key challenges exist in the scalable assembly of 2D graphene nanosheets into highly ordered 3D macroscopic structures, limiting practical applications of graphene-based systems. Superior properties of high quality single/few layer graphene have yet to be realized for graphene-derived macroscopic structures due to non-optimized microstructure, graphene alignment and existence of defects and functional groups.
Finding solutions to address these key challenges, we report various novel strategies to assemble individual graphene sheets into highly ordered 3D structures, e.g., films and fibers, with exceptional thermal management performance. An innovative strategy by combining two well-established industrial-scale processes of electrospray deposition and a continuous roll-to-roll process for scale-up assembly and manufacturing of the largest area graphene papers ever reported. Post-assembly strategies of high temperature annealing and mechanical compaction are employed to improve graphene sheet alignments, remove defects and thus achieve breakthrough electrical (1.83×10⁵ S/m) and thermal conductivities (1434 W/mK). The highly-aligned and defect-free graphene paper displays superior thermal management performance in removing hot spot as a heat spreader. We also fabricate highly thermally/electrically conductive and mechanically strong graphene fibers by a scalable wet spinning process. A new fiber structure is designed consisting of large-sized graphene sheets forming a highly ordered fiber arrangement intercalated with small-sized graphene sheets filling the space/micro-voids. The graphene fibers exhibit a sub-micron crystallite domain size through high temperature treatment, achieving an enhanced thermal conductivity up to 1290 W/mK, outperforming the best carbon fibers and carbon nanotube fibers. The tensile strength of the graphene fiber reaches 1080 MPa. A thermal bimorph actuator has been fabricated using the graphene fibers showing a sub-second response, exceptional actuation capability and cyclic stability. The highly thermally conductive and mechanically strong graphene fibers have many potential applications including thermal management materials in high power electronics and reinforcing components for high performance composite materials.

Yi Zhang, Zhi Zhang, B. N. Chandrashekar and Cheng Chun*

Department of Materials Science and Engineering, South University of Science and Technology of China, Shenzhen, Guandong – 518055, P.R. China
Corresponding author: [email protected]

Abstract

A decade ago, researchers have greatly exploited various excellent properties of graphene such as high electronic conductivity and elasticity [1]. Chemical vapor deposition (CVD) graphene is one atomic thick layer gained much attention to study and elaborate the mechanical properties. CVD graphene grown on copper and transfer onto the target substrates induces wrinkles and ripples, alters the exceptional properties such as mechanical and electrical conductivity. Here we concentrated on designing wrinkle modifications in graphene to study the mechanical properties such as bending strength. As we can directly perceive, folding of single-layer or few-layers graphene needs very small energy and force, and the fact do shows that unmodified graphene has relatively low bending strength. However, after transfer step which induces wrinkles and ripples, we find a large increasing in bending strength which can be indicated from a large diminish in γ, a ratio between in-plane stretching stiffness and out-plane bending stiffness. Moreover, we find that the texture along certain directions can improve the bending stiffness of selected folding direction. Rationally, a random texture on the whole plane of graphene will bring a higher bending stiffness in any direction. Quantitatively, the γ shows that fabricated ripples can promote the bending stiffness more than a thousand times comparing to its originality. This γ is similar to that of paper we daily used, so we interpreted the principle mechanically, in a macro scale, replacing the graphene with a piece of paper. Consequently, this material with special nanostructure can be applied in the fabrication of hinge or bone of nano-robots. Its large perspective in the application of nanoscale tools is extremely large to be discovered.

References:
1. MK. Blees, AW.Barnard, PA. Rose, SP. Roberts, KL McGill, PY. Huang, AR. Ruyack, JW.Kevek, B. Kobrin, DA. Muller, PL. McEuenm, Nature 524 (2015) 204

Graphene oxide (GO) exhibits great functionalities due to the oxygen-containing functional groups. Since its surface is hydrophilic due to those groups, it has a high potential to adsorb and store water molecules. In this study, we characterized the water absorbing properties of graphene oxide in the form of papers and found that the moisture absorption capacity of GO paper is higher than that of the widely used desiccant silica gel. Interestingly the moisture adsorption isotherm of microporous GO paper is found to be consistent with Type IV adsorption isotherm which traditionally describes monolayer and multilayer adsorption and capillary condensation in mesoporous materials. In order to examine the characteristics of moisture adsorption of GO paper with different conditions of surface functionalization, we fabricated three kinds of graphene oxide papers, two with rich oxygen functional groups and one with partial chemical reduction and found that the paper with high oxygen/carbon ratio has higher moisture absorbance capability. For the GO paper with reduction, the overall moisture absorbance was reduced. However, the absorbance at high humidity was significantly improved due to direct formation of multilayer water vapor in the system, which derived from the different polarities between the adsorbent and the adsorbate. In the food experiment to see the performance as a desiccant, we tested grape fruits with and without GO paper. The fruits with a GO paper exhibited longer-term preservation with delayed mold gathering because of desiccation effect from the paper. Our results suggest that GO will find numerous practical applications as a desiccant and is a promising material for moisture desiccation and food preservation.

Producing a usable form of semiconducting graphene has plagued the development of graphene electronics for over a decade. Only in the last year has progress been made to overcome this hurdle. Improved growth of the first graphene “buffer” layer of SiC(0001) revealed that it was a true semiconductor rather than an unusable wide gap insulator with significant mid gap surface states. To date, no theory has predicted that the buffer should be semiconducting. We resolve this contradiction through surface x-ray diffraction. Our measurements reveal that the buffer structure is not the commensurate structure assumed for the past forty years. We show conclusively that the buffer is incommensurate with SiC and engages in a mutual modulation of the SiC(0001) interface layers. Within this new context, model calculations demonstrate that a semiconducting buffer can be explained through the formation of unperturbed graphene islands surrounded by partially hybridized incommensurate boundaries. The strong interaction of the buffer with SiC suggests that the properties of the buffer can be controlled through modifying the SiC interface. For example, we find that the band gap changes when a monolayer forms above the buffer. This novel effect testifies to the capability of band gap engineering in buffer graphene and provides inspiration for a new era of graphene based electronic devices.

Formation of defects during material production is inevitable as imperfection in cryastalline structure is very natural. In graphene, various kinds of defects such as vacancy, adatom and impurity have been observed in many experiments as well. Graphene has been paid attention for a long time because of their exceptional material properties, and defects can influence on unique characteristics of graphene and change its electronic, optical, or thermal properties. For this reason, investigation of defects in graphene has been still actively performed for defect engineering.
Divacancy (DV) is one of the common structural defects in graphene formed by eliminating neighboring two carbons. It was reported that divacancies are thermodynamically favorable rather than single vacancies. Also, the pore size is large enough to embed external single impurity atoms. Recently, atomic Si-DV defects were routinely found in electron microscopy experiments, and transition metal (TM) incorporated divacancy complexes in graphene-like system, showing good catalytic activity, were also frequently detected.
In this work, using results of first-principles density functional theory (DFT) calculations, we analyzed why graphene prefer elements with four valence electons as atomic impurities. Calculations for single atomic and diatomic divacancy complexes in graphene were performed with various divacancy pores. We investigated formation energetics of divacancy complexes in graphene to confirm thermodynamic and kinetic stability. Our theoretical study suggests that divacancy complexes including elements with four valence electrons are very stable in terms of formation energy and binding energy, compared to other defect configurations. Atomic and electonic structures support this result because of the charge balance

Abstract
In this work we present a theoretical study results of the growth of graphene bilayer over GaN(0001) surfaces. The calculations were performed by Density Functional Theory calculations. Two models emerged as the most favored¹: for Ga poor conditions a 3sqr3x3sqr3 graphene structure on top of a 4x4(0001)GaN surface and for Ga rich condition a sqr21xsqr21 graphene structure on top of a 2sqr3x2sqr3 GaN(0001) double bilayer¹ with a -1.10% and -0.72% mismatch respectively. The gallium rich model exhibit a magnetic moment of 0.19 Bohr magnetons/cell whereas the stable structure for Ga poor conditions does not presents magnetic behavior².
To model the GaN(0001) surface, a repeated slab geometry was used. Each slab consisted of four GaN double layers with adatoms on the surface. For the Ga-rich conditions, a bilayer of Ga was added. Dangling bonds on the bottom of the surface were saturated with pseudo-H atoms, with a fractional charge of 0.75e. The bottom GaN bilayer and the saturated pseudo-H atoms were frozen to simulate a bulk-like environment. Two consecutive slabs were separated by an empty space ~9.0 Å wide to reduce the slab-slab interactions.
The introduction, some years ago, of the Scanning Tunneling Microscope (STM) was a breakthrough tool in developing nanoscience and nanotechnology, so in order to reinforce the calculations predictive power we are working in simulations of STM images from the calculated pure 4x4 (0001) GaN surface and 2sqr3x2sqr3 GaN(0001) double bilayer and then the STM images of the same surfaces with graphene monolayer and bilayer deposits. Additionally we are calculated the effect of bias voltage and the tip distances from the surface (from as low as 0.1V up to 3.0V bias).
Acknowledgments: DGAPA project IN102714. The authors are grateful to A. Rodriguez for his technical assistance. Calculations were performed at the DGCTIC-UNAM under project SC16-1-IR-57.
References
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1. Espitia-Rico, M.; Rodríguez-Martínez, J.A.; Moreno-Armenta, M.G.; Takeuchi , N., Applied Surface Science 326 (2015) 7–11

Physical properties of reduced graphene oxide (rGO) are strongly dependent on the ratio of sp² to sp³ hybridized carbon atoms and the presence of different functional groups in its structural framework. This research for the very first time illustrates successful wafer scale integration and remarkable p to n type conversion of 2D rGO employing pulsed laser deposition followed by laser annealing using nanosecond ArF excimer laser. Reduced graphene oxide is grown onto c-sapphire employing pulsed laser deposition in laser MBE chamber and is intrinsically p type in nature. Subsequent laser annealing using different laser energy densities: 0.6Jcm^-2, 0.8Jcm^-2 and 1.0Jcm^-2 at room temperature and pressure converts p type rGO to n type semiconductor. The XRD, SEM, and Raman spectroscopy indicate the presence of large area rGO onto c-sapphire having Raman active vibrational modes: D, G, and 2D. High resolution SEM depicts the morphology and formation of rGO from zone-refined carbon formed after nanosecond laser annealing. Temperature dependent resistance data of rGO thin films follow Efros-Shklovoskii variable range hopping (ES-VRH) model in the low-temperature region and Arrhenius conduction in the high-temperature regime. The photoluminescence (PL) spectra also reveal a less intense and a broader blue fluorescence spectra, indicating the presence of miniature sized sp² domains present in the near vicinity of π* electronic states which favor the VRH transport phenomena. XPS results reveal reduction of the rGO network after laser annealing with C/O ratio measuring as high as 23% after laser assisted reduction. The p to n type conversion is due to the reduction of rGO framework which also decreases the ratio of the intensity of D peak to the intensity of G peak as evident from the Raman spectroscopy. This wafer scale integration of rGO with c-sapphire and p to n type conversion employing laser annealing technique at room temperature and pressure will be useful for large area electronic devices and will open a new frontier for further extensive research in these functionalized 2D materials.

Confined assembly in the intersheet gallery spaces of two-dimensional (2D) materials represents a new templating route for the creation of novel material architectures. Herein, a facile fabrication method is demonstrated for replicating complex, hierarchical graphene wrinkled/crumpled textures in metal oxide films. The fabrication involves: (1) texturing of graphene oxide films by programmed compression of underlying polymer substrates, (2) spontaneous intercalation of hydrated metal ions into these GO films in water-swollen state, (3) dehydration of cation-GO complexes and thermal decomposition of GO to dissociate the complexes, (4) calcination to remove the graphene template by O₂ oxidation. To determine the generality and versatility of this method, a variety of mono- and multi-valent metal ions were explored as intercalants (Ag⁺, Zn²⁺, Al³⁺, Mn²⁺, and Cu²⁺), and a range of GO templates was applied with pre-fabricated textures that include uniaxial wrinkles, isotropic crumples, and complex hierarchies. We find that many but not all of the metal ions and synthesis conditions produce textured metal oxide films, and the optimal precursors and concentration for successful replication are identified and reported here. Remarkably, even the finest structural features in multi-scale hierarchical GO templates can be replicated with high fidelity in Zn, Al, Mn, and Cu oxide films when using the optimal ion loading. The final films are shown to consist of unique nanosheet-like aggregates of distinct metal oxide nanoparticles, whose mobility, attachment, and sintering are guided by the 2D confinement imposed by the template during their assembly. Overall, this intercalation templating approach has broad applicability for the creation of complex, textured metal oxide films, and provides a generalized synthetic route that can replicate textures already realized in highly flexible graphene sheets into other material systems.

Significant progress has been made recently in the synthesis of single wall carbon nanotube (SWNT) by catalytic chemical vapor deposition (CCVD), along with a rise of commercially viable applications. A property selective synthesis seems still elusive, though, because of specific issues. High synthesis temperatures, nanometric sizes and a large number of correlated growth parameters make the experimental investigation of the growth mechanisms specially challenging. Theoretical approaches are not easier, but I will show here that dedicated computer simulations, including tight binding models [1], as well as DFT based calculations can provide a useful insight. Different aspects have been investigated.
It starts with the complex stability pattern of atomic carbon dissolved in subsurface layers of crystalline Ni, that depends on the presence of a graphene layer on top of it [2]. For catalyst nanoparticles below 3 nm, relevant for the CCVD growth, the presence of carbon dissolved in the surface layers induces a gradual melting at temperatures well below the melting temperature of pure nanoparticles of the same size. Calculated size dependent phase diagrams for Ni-C nanoparticles [3] indicate that facetted crystalline nanoparticles are unlikely to be observed in this size range under growth conditions.
This raises the question of the role of the carbon dissolved in the catalyst during the growth, that is shown to have a strong influence on the wetting properties of the metal-SWNT interface [4]. Through careful Transmission Electron Microscopy observations [5], so called tangential and perpendicular growth modes were identified. Computer simulations were used to analyze these growth modes at the atomic scale, demonstrating that the tangential mode corresponds to a weak carbon supply and slow growth, while the perpendicular one is observed when the carbon fraction in the nanoparticle is larger [6]. Growth experiments designed to tune the carbon fraction in the nanoparticle by changing the carbon feedstock (CO and CH₄) confirm this analysis.
Finally the role of the different contributions to the stability and dynamics of the nanotube/nanoparticle interface on the possibility of a chiral selectivity will be discussed.

References
[1] Amara, H. et al. Phys. Rev. B 2009, 79, 014109.
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[3] Magnin, Y. et al. Phys. Rev. Lett. 2015, 205502, 1–5.
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[6] He, M.; Magnin Y.; Amara, H.; Jiang, H.; Fossard, L.; Castan, A.; Kauppinen, E. I.; Loiseau, A.; Bichara C. submitted.

How do carbon nanobes grow, what factors possibly predetermine their helical symmetry, and what are the mechanisms of growth termination -- this aspects are of sustained interest and remain central issues in synthesis. I will discuss theoretical views emerging from concurrent account for thermodynamics and kinetic requirements [1]. In addition to carbon nanotubes, other related nanostructures and their intriguing properties will be theoretically analyzed. This includes magnetic field generation with graphene solenoids [2] , and metal-insulator variability of monoatomic carbon chains of carbyne [3], recently synthesized in bulk quantity.
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The unique size, large surface area, remarkable chemical and physical properties make nanomaterials one of most important areas of modern materials science. Many advancements have been made in the last decades in the synthesis of nanomaterials, which led to new innovative applications in various fields such as; catalysis, chemical sensing, photonics, electronic devices and drug delivery, among others. One of such improvements has been made through chemical functionalization approaches, which overcome some limitations of carbon nanostructures, such as poor solubility. However, there are only few studies [1,2] investigating in details the whole processes of the chemical reactions between differently functionalized nanostructures. Recently [3], we reported an experimental and theoretical study on how chemical reactions between two functionalized (-COOH and –OH) multiwalled carbon nanotubes (MWCNT) could lead to carbon nanoribbons. It was demonstrated that these reactions produce tube unzipping and that this process occurs through a simple solid state mechano-chemical reactions, then followed by two elimination steps: water condensation and decarboxylation. In this work we present a detailed theoretical analysis of these processes, considering different functional chemical groups, such as chloride/hydroxyl and amine/carboxylic directly attached to tube walls [4]. In order to carry out these analyses we used ab initio and reactive molecular dynamics methods. Our results have showed that the energy barrier for the activated reactions are in the range of the energy mechanically provided by simply grinding of the reactants. Our results also show that the energy released from these reactions is more than the necessary to trigger the spontaneously tube unzipping leading to the nanoribbon formation. We also discuss how to use these results in the proper choice of functional groups in order to optimize the fabrication of nanoribbons from unzipped tubes.
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Growing graphene on a metal surface is one possible way to obtain high quality graphene, with a controllable number of layers. The synthesis usually relies on a chemical vapor deposition of a carbon bearing gas on the surface of a metal such as Ir, Cu, or Ni. We investigate here the case of graphene on Ni that is of particular interest because the role of carbon solubility in subsurface layers is both difficult to investigate experimentally, and important to understand how to produce high quality graphene.

Experimentally, it has been observed that below temperatures of 460 C, the Ni (111) surface displays a reconstruction in presence of C, forming a surface carbide layer [1]. The exact role of this surface carbide during the growth of graphene is not yet understood, though it plays an important role in the synthesis process [2], and on the coupling of graphene with the metallic substrate [3], thus having a significant impact in its electronic properties [4]. To study the interaction of carbon with nickel at the atomic level, we developed a tight binding model [5] implemented in a Grand Canonical Monte Carlo code. With this approach, we investigate the CVD synthesis of graphene on a reconstructed Ni (111) surface. We identify thermodynamic conditions (temperature, carbon and nickel chemical potentials) to obtain a graphene monolayer. Nucleation sites are identified to be C atoms already present in the carbide, or steps in the substrate. Possible removal of Ni atoms from the system is also included, since the carbide layer has been proposed [2] to give rise to graphene by replacing Ni atoms by C. Depending on both chemical potentials (Ni and C) and temperature, graphene can grow etching the carbide, grow over a carbide step or grow only on bare Ni (111) regions.

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Nanostructures configured as triply periodic minimal surfaces, such as gyroidal systems, possess a broad range of potential applications as energy and storage materials and can be used as elementary building blocks for complex electronics. Here, I will present our recent developments made in the modeling of the effect of structure size and material density on the electronic and water purification properties of a number of sp2 carbon gyroid nanostructures.

I will first describe a general Monte Carlo method for discovering atomic structures of carbon gyroids of arbitrary size that obey the prescribed space group symmetry for gyroid surfaces. A total of 19 structures are investigated, among which we find three types of ground state structures corresponding to a given number of atomic cycles present in the asymmetric unit cell. Each type is characterized by the distribution of non-hexagonal rings: type I structures present a minimum number of non-hexagonal rings (octagons), while type II (type III) structures include square and heptagon (pentagons and octagons) in addition to hexagons. Density functional theory is used to establish how electronic, topological, geometric, and energetic properties of these gyroids vary with size and density. We determine that most studied systems feature occupied and unoccupied three-dimensional Dirac hyper-cones and metallic and semi-conducting behaviors.

We also establish that the local curvature induced by the presence of specific carbon ring sizes imposes highly specific behavior on electrolyte diffusion inside the gyroid channels. We find that gyroidal carbon nanostructures (GCN) materials containing carbon square and heptagon motifs are globally more rigid and locally more flexible than GCN materials containing octagonal rings. The most rigid GCN’s present a faster water diffusion, indicating that the diffusion properties can be controlled by a proper choice of gyroid size and density. The analysis emphasizes that a fine balance between water permeation and ionic conduction can lead to GCN materials with attractive properties for nanofluidic applications. The impact of these findings are discussed in terms of their ionic transport, water filtration, and energy storage properties.

New red-shifted emitting states in carbon nanotubes, introduced by chemically stable and tunable covalently-bound dopants,^1,2 are gaining attention for their potential to boost photoluminescence quantum yields,^1,2 add new functionality,^3,4 and serve as single photon emitters.⁵ These sites present a rich array of new photophysics for exploration. As examples, we will present low-T photoluminescence (PL) probes of defect-state electronic structure and a demonstration of exciton localization or trapping at individual dopant sites, critical for enabling new functionality.⁶ As a consequence of trapping, exciton dynamics are significantly altered, with PL lifetimes being extended significantly.⁵ We will present results on defect-state relaxation dynamics, with exciton trapping increasing PL lifetimes by around a factor of 10 in comparison to E₁₁ exciton lifetimes. Dependence of lifetimes on nanotube chirality, specific dopant, and dielectric environment will be presented and shown to exhibit a strong dependence on emission energy. Trapping and detrapping dynamics will be discussed in the context of new functionality including room-temperature single photon emission.⁵


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We studied the oxygen etching of individual single-walled carbon nanotubes on silicon oxide substrates using atomic force microscopy and high-temperature environmental scanning electron microscopy. [1] Our in situ observations show that carbon nanotubes are not progressively etched from their ends, as frequently assumed, but disappear segment by segment. Atomic force microscopy, before and after oxidation, reveals that the oxidation of carbon nanotubes on substrates proceeds through a local cutting that is followed by a rapid etching of the disconnected nanotube segment. Unexpectedly, semiconducting nanotubes appear more reactive under these conditions than metallic ones. We also show that exposure to electron and laser beams locally increases the chemical reactivity of carbon nanotubes on such substrates. By analogy with the reactivity of monolayer graphene on oxide substrates, we propose that the chemical reactivity of SWCNTs on substrates is controlled by substrate-trapped charges and that laser and electron beams can increase the reactivity by increasing the surface density of substrate charges. An interesting question is whether the observed effect is limited to reactions involving charge transfer (e.g., oxidation, reduction, or reactions involving a charge-transfer complex intermediate). We believe that these results may have important consequences not only for the functionalization and purification of SWCNTs but also for their growth selectivity.

1. H-A. Mehedi, J. Ravaux, K. Yazda, S. Tahir, T. Michel, V. Jourdain, R. Podor, Increased chemical reactivity of single-walled carbon nanotubes on oxide substrates: in-situ imaging and effect of electron and laser irradiations. Nano Research 9 (2016) 517-529.

Hypervelocity impacts (HVI) can cause extreme material deformations, sometimes much larger than their ultimate strength [1]. Especially for the designers of aerospace structures, the advanced materials with multifunctional capabilities and high resistance to HVI are of great interest. Carbon nanotubes (CNT) being lightweight and with high strength properties are ideal candidates. Although CNT have been extensively studied in the last two decades for possible use in different types of engineered materials and applications, including for spaceships, their mechanical behavior at high impact is still not completely understood [2,3]. Recently, we have reported [3] that impacts at 7 km/s induced high mechanical strain, causing crack propagation and can result in totally unzipped CNT. Experimental data and molecular dynamics (MD) simulations revealed that the impact outcome depended on the relative orientation of the CNT and the substrate. In this work we expand these analyses, we carried out a detailed study on the mechanical behavior of CNT at impact collisions for different velocity ranges. Our results have showed that the highly energetic impacts cause bond breakage and rehybridization of the carbon atoms. We also observed the formation of several different nanostructures depending on impact conditions, such as: nanodiamonds, nanoribbons, and covalently interconnected nanostructures. The mechanisms behind the CNT structural transformations were investigated through fully atomistic reactive MD simulations. From the simulations was possible to establish the velocity and impact angle ranges that favors the formation of specific type of nanostructures.

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[2] Khatiwada, Suman, Carlos A. Armada, and Enrique V. Barrera. Procedia Eng 58 (2013): 4-10.
[3] Ozden, Sehmus, et al. Nano Lett 14.7 (2014): 4131-4137.

The real-time and spatially-resolved detection and identification of analytes in biological media present important goals for next-generation nanoscale probes and sensors. To this end, we employ the intrinsic near-infrared fluorescence of single-walled carbon nanotubes which is photostable yet sensitive to the immediate environment. To build biomedical technologies that employ carbon nanotube photoluminescence, a better understanding of the optical response, as well as new methods to measure it in biological systems, are needed. We have developed new imaging platforms to quantify nanotube emission, including a method to conduct photoluminescence excitation/emission spectroscopy on living samples. We synthesized carbon nanotube-based photoluminescent sensors to interrogate analytes and processes in living specimens, including mammalian cells, 3D tumor spheroids, and mice.

The intentional incorporation of impurities and defects can serve as a powerful tool for modification of the electronic and optical properties of host nanomaterials and enabling of new functionalities¹. Introduction of Sp³ defects by covalent functionalization to single-walled carbon nanotubes (SWCNTs) generates new emission states with energies lower than the optical bandgap (E₁₁) of SWCNTs by 100 to 300 meV². With controllable emission wavelengths and high quantum yield, these defect states open up new opportunities for the applications of SWCNTs in photonics such as lasing, photon upconversion and single photon emission³.
Recently, it has been shown that such doping sites are capable of emitting single photons at room-T, which opens the possibility of building room-T electrically-driven single photon emitters based on doped-SWCNTs⁴. The realization of these devices needs the fine control of doping densities, to the point of introduction of solitary dopants on individual SWCNTs. Furthermore, it requires the high emission quality from doping states, such as sharp linewidth of the emission spectra and non-blinking of the emission intensity.
In this work, we demonstrated a chemical approach capable of creating solitary dopants on the sidewalls of single-chirality SWCNTs. Our method was based on the fine control of the doping of surfactant-suspended and poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) wrapped SWCNTs with different diazonium salts. We investigated the photoluminescence (PL) spectra of doped-SWCNTs at room temperature and low temperature (4K). Individual, bright and stable emission peaks were observed from doped SWCNTs at room-T. The linewidth of the PL peaks decreased to a few meV at 4K. Next, Hanbury Brown-Twiss (HBT) experiment was performed to explore the single photon nature of the emissions. Extremely strong photon ant-bunching behavior with g⁽²⁾ less than 0.1 were observed on these doping sites at room temperature (295k).
[1] Piao, Yanmei. et al. Nature Chem. 2013, 5, 840.
[2] Hartmann, Nicolai F. et al. Nanoscale. 2015, 7,20521.
[3] Kim, Mijin. et al. J. Phys. Chem. C . 2016, 120, 11268.
[4] Ma, Xuedan. et al. Nature Nanotech. 2015, 10, 671.

Exciton-polaritons are quasiparticles that form upon strong coupling between electronic excitations of a material and photonic states of a surrounding microcavity. The special nature of excited states of organic semiconductors leads to particularly strong coupling and facilitates condensation of exciton-polaritons at room temperature, which may lead to electrically pumped organic polariton lasers. However, charge carrier mobility and photo-stability in currently used materials is limited and exciton-polariton emission so far has been restricted to visible wavelengths. Interestingly, the stable near-infrared luminescence of semiconducting single-walled carbon nanotubes (SWCNTs) incorporates all properties necessary for strong coupling, in particular a large oscillator strength as well as a very narrow line width.
Here, we demonstrate for the first time strong exciton-photon coupling in metal clad microcavities filled with purified monochiral SWCNTs in a polymer matrix. Exciton-polaritons are unambiguously observed in angle-resolved reflectance measurements. We find an upper and a lower polariton branch that correlate well with the coupled oscillator model and transfer-matrix simulations. Bright, near-infrared polariton emission from the lower polariton mode is measured by off-resonant excitation. The exceptional oscillator strength and sharp excitonic transition of (6,5) SWCNTs enables large Rabi splitting (> 110 meV), efficient polariton relaxation and narrow band emission (< 15 meV). Given their high charge carrier mobility and excellent photostability, SWCNTs represent a highly promising new material for practical exciton-polariton devices operating at telecommunication wavelengths

Recently optoelectronic devices and electronic power devices using GaN-based materials have attracted much attention because they exhibit high optical and electrical power with high efficiency due to the wide band-gap. These power devices are generally used in high temperature operation by the heat dissipation of devices. Therefore, for high device reliability, it is important to design the mounting structure for heat sink to obtain efficient heat spreading. Carbon nanotube is expected to be excellent heat conductor for heat spreading of the power device because of extremely high thermal conductivity. Therefore, it is thought that carbon nanotube is very useful for electrode material with high thermal conductivity in the GaN power device. However, to our knowledge, there are no reports on detail electrical properties and band-structure for the hetero-interface between the carbon nanotube and the GaN. The Schottky barrier height is expected to depend on the workfunction of the electrode material. Then, studies of the Schottky barrier of metalic multi-wall carbon nanotubes (MWCNTs)/GaN interface become of interest. And there is also possibility to exhibit ohmic property to p-GaN if the MWCNTs workfunction is relatively large. In this paper, we present results of electrical characterization and Schottky barrier height for band-structure in carbon nanotube/GaN hetero-interface. We also demonstrate low contact resistance of the MWCNTs ohmic contact to p-GaN film.
Schottky diode property using the interface between MWCNTs and n-GaN were investigate. We obtained I-V characteristics of the MWCNTs electrode on the n-GaN film. Schottky diode behavior was observed. From the Schottky diode property, the barrier height φ_B and n value were estimated by the thermionic emission model. Finally, the Schottky barrier height φ_B was determined to be 0.737 eV. By using a value of the GaN electron affinity of 4.10 eV, the work function of the MWCNTs was determined to be as high as 4.84 eV. Previously, the work function of the MWCNTs was reported to be the value of 4.8 eV and 4.95 eV measured by photoelectron emission. Therefore our result is in good agreement with the value from the photoelectron emission. From these results, the MWCNTs electrode with relatively large workfunction could be useful for an ohmic contact of p-GaN because the metal electrode with the large workfunction such as Au, Pd and Ni is generally used for the p-GaN contact.
Since the workfunction of the MWCNTs were estimated to be large enough to obtain ohmic contact of p-GaN, the specific contact resistance values of the MWCNTs/p-GaN interface were measured by the transmisson line method (TLM). A 0.4 μm thick p-type GaN film doped with Mg at a concentration of 9×10¹⁹ cm³ was used. The MWCNTs electrode layer was prepared on the p-GaN. Finally, the specific contact resistance of the Mg electrode was as low as 2.6×10^-3 Ωcm². We demonstrated low contact resistance of the MWCNTs ohmic contact to p-GaN.

Current innovations in carbon nanotube applications for reinforcement composites, energy and electronics require mass production of this material exceeding ten thousand tons. Besides, there are some facts that carbon nanotubes may be cytotoxic, so its mass usage may result in potential ambient pollution during the fabrication, exploitation, and disposal. Thus, an efficient and rapid method for detection carbon nanotubes have to be formulated and developed.
Herein, our team has proposed an efficient mechanism for detection of single wall carbon nanotubes (SWNT) that involves amplification of their photoluminescent signal through the formation of organic complexes with tailorable polymethine dyes [1,2]. The complexes are formed due to Coulomb force attracting ionic polymethine dyes (like astraphloxin) to SWNT covered by charged surfactant in water, so the dyes excitation can be transferred to the nanotubes. The resonant energy transfer is clearly evidenced experimentally via excitation-emission photoluminescence mapping in visible and near-infrared range. As a result of the excitation transfer to SWNT, a selective and strong enhancement (up to a factor of 6) of the nanotubes photoluminescence in the near-infrared range is observed. Only the dye molecules stacked to the nanotube micelles contribute to the photoluminescence amplification (the dye monomers present in the mixtures at high concentration do not transfer the energy to SWNT). The uncharged dyes of similar molecular structure or the nanotubes covered with neutral surfactant do not form the complexes and there are no transfer of the energy. So, the Coulomb attraction of the charged dye and SWNT is crucial in formation of the energy transfer complexes. In addition, this amplification is sensitive to both nanotube chirality and the surfactant that the nanotubes are dispersed in. The highest photoluminescence multiplication was achieved for (7,5) chirality, however the high selectivity of this method of SWNT sensing relies also on specific wavelength of excitation and emission of intrinsic photoluminescence for each SWNT chirality/diameter. Thus, the complexation results in selective detection for the particular nanotubes with limit of detection in the range of (1-4) ng per mL.
Easily tailorable π-conjugated systems of polymethine dyes allows us to tune the energy levels for energy transfer in studied complexes towards desirable opto-electronic task. Furthermore, carbon nanotube functionalization towards breaking the limitation of low photoluminescence quantum yield is a key issue for engineering of novel applications including rapid in situ sensing of SWNT in aqueous environment.
Acknowledgements: The work was supported by NATO SPS project (NUKR.SFPP 984189) and EU FP ‘Horizon-2020’ Marie Sklodowska-Curie Individual Fellowship (FOC4SIP, 654733).
References:
[1] P.Lutsyk, et al. Light: Science & Applications (2016) 5, e16028;
[2] M.P.Shandura, et al. Sensor Letters (2014) 12, 1361-1367.

Single-walled carbon nanotubes (SWNTs) have shown oustanding capabilities in the realization of new functional devices but are extremely sensitive to any slight changes in their environment, altering their physical properties. A strategy to overcome this difficulty is to use double-walled carbon nanotubes (DWNTs), consisting of two concentric tubes. In order to better know the basic properties of this kind of tubes in linkage with their structure, we have developed a systematic and robust procedure using acHR-TEM (aberration corrected Transmitting High Resolution Electron Microscopy) to determine the atomic structure of several tens of tubes. Statistical analyses of their diameters and twist angle between inner and outer tubes show that whatever the synthesis technique, some configurations are strongly favored whereas some other are never observed. These results reveal the existence of strong coupling between the two concentric tubes in a DWNT for the smaller diameters below 2 nm. To complete this analysis, we performed Monte Carlo calculations with an empirical model in order to understand the nature of the coupling and explain the selectivity of observed configurations.

During the last 20 years or so, carbon nanotubes (CNTs) have attracted a huge attention due the dramatic effects of their structure and environment on their physical properties (electrical, optical and chemical). For instance, due to their one-dimensional nature, the scattered light is strongly polarized along the nanotube. This theoretically opens the possibility to image and characterize individual CNTs in various environments using cross-polarization microscopy and spectroscopy. Recently, Wang and coworkers [1] provided the experimental demonstration of this prediction by reporting optical imaging and spectroscopy of individual CNT on substrates with an unprecedentedly high throughput. This work notably opened the door to in situ studies of individual CNTs during growth, functionalization, doping or filling which are crucial processes for the control, understanding and application of CNTs.
In our work, we developed a model to better understand the nature of the CNT scattering excited with a supercontinuum laser. Our main focus was put on the depolarization induced by the optical elements as well as the nature of the substrate. With this model, we were able to predict some of the effects of the depolarization on the signal from the CNT and refine the experimental setup. Notably, we demonstrated that optical elements such as the microscope objective are crucial and impact strongly the polarization of the light. The depolarization, instead of strongly reducing the signal, actually gives information on the CNT observed. By developing our own setup while choosing carefully our detectors and optics, we managed to investigate the different conditions involved in the observation and characterization of nanotubes. We successfully observed nanotubes on different substrates (Si, SiO₂, quartz, glass) and under different atmospheric conditions (composition and temperature), thus allowing us to study the behavior of CNTs while being oxidized or burnt at different temperature and oxygen concentration. We are also further improving the conditions to manage to observe in situ the growth of CNTs.

[1] Liu et al., Nature Nanotechnology, 2013; 8:917-22

Single-walled carbon nanotubes (SWNTs) have stable and robust fluorescence in the near infrared (IR), but the quantum yield is very low compared to other emissive nanoparticles. We have previously found that the fluorescence efficiency of DNA-wrapped SWNTs can be significantly enhanced upon addition of small molecular reducing agents, such as dithiothreitol (DTT) and Trolox. In this presentation we will discuss the molecular-induced changes in fluorescence from SWNTs suspended in various commonly used surfactants. Upon addition of the reducing agents, sodium dodecyl sulfate (SDS) wrapped SWNTs showed a 4-fold fluorescence intensity increase while sodium cholate (SC) wrapped SWNTs showed fluorescence decrease by ~45%. Minimal change in fluorescence was observed for SWNTs dispersed in sodium dodecylbenzene sulfonate (SDBS) and sodium deoxycholate (DOC). Concurrent measurements of the fluorescence lifetime for each case suggest that the added molecules are affecting both the non-radiative and radiative rates of the SWNTs. For fluorescence brightening of individual SDS wrapped SWNTs, we found the fluorescence efficiency enhancement varied among individual nanotubes, with some brightening by up to 6.5 times while others brightened by only 16%. Surprisingly, fluorescence images of individual SWNTs longer than the diffraction limit exhibit a single step, uniform brightening along the entire nanotube upon addition of the reductants. This single step and uniform brightening event suggests that the fluorescence brightening is likely a consequence of as little as a single reductant molecule interacting with the SWNT sidewall.

The occurrence of Dirac point in band structure of graphene has lead to exotic electronic properties in graphene such as anomalous quantum Hall effect, occurrence of super currents etc. Graphene is currently being considered as a potential candidate for exploration of spintronics and related applications such as spin qubits due to low spin-orbit interaction and low hyperfine interactions. Recent experiments have also demonstrated spin injection into graphene layers. Here we attempt to understand spin transport in graphene nanoribbons under different bias conditions, systematically using first principles calculations. The elementary device geometry to understand spin transport consists of ZGNR and AGNR contacted by two electrodes. Analysis of conductance and spin currents under different bias voltages will be presented.

Ionic and molecular transport through nanochannels and nanopores differs from micro- and macroscale transport due to the dominance of surface forces responsible for novel physical phenomena. Single-walled carbon nanotubes (SWCNTs) with their unique structure and physical properties appear as particularly interesting channels for gaining a deeper understanding of fluidic and ionic transport at the nanoscale and potentially for the development of nanofluidic applications. The possibility of transporting ions and molecules through SWCNTs has already been reported by several groups but our understanding is still limited by the difficulty to prepare well-controlled SWCNT-based nanofluidic and by the discrepancy between experimental observations on different platforms. An easier and more reproducible method of fabrication of experimental platforms both robust and data-rich would represent a critical step for the field.
At the meeting, we will present a new fabrication protocol of nanofluidic devices allowing to study ion transport through one or several SWCNTs in parallel and to characterize them by optical means. We measured relatively high ionic conductance values supporting that the nanotube surface is both charged (surface charge of the order of 0.05-0.2 C/m²) and slippery (slip length of the order of 10-150 nm). Contrary to simulation predictions for SWCNT of diameters of 1.2-2 nm, we found that the transport of cations was selective compared with bulk transport. This additionally supports that cations are the main charge carriers and that the nanotube surface is negatively charged. We observed a sublinear dependence of the conductance on the salt concentration which could be explained by a charge regulation model. Most devices displayed a voltage-activated ion transport in contrast with the ohmic behaviour commonly reported in the literature. Our theoretical models and simulations show that this can be related to the presence of energy barriers for the transport of cations along the nanotube length. To determine the origin of these energy barriers, we performed Raman spectroscopy measurements which showed significant variations of the nanotube Raman features along their length. This revealed a strong and heterogeneous effect of the environment (polymer matrix and substrate) on the nanotubes in terms of strain and doping.

There has been significant research interest in graphene for electronics applications, due to its good electrical conductivity, high optical transparency, mechanical flexibility, high thermal stability, and two-dimensional planar structure. However, the potential of graphene as a planar channel material replacing silicon is limited due to the absence of a bandgap. On the other hand, graphene is an excellent candidate as a transparent, conductive, and flexible electrode for silicon-based electronic and optoelectronic devices, including solar cells, gas sensors, and photodetectors.

Unlike conventional metals, whose Fermi level is typically pinned at the surface, the Fermi level and hence workfunction of graphene can be tailored by electrostatic gating, chemical or contact doping, surface engineering, or by varying the number of graphene layers. As a result, graphene is also a promising candidate as a replacement for the gate electrode in metal-oxide-semiconductor (MOS) devices. Due to its transparent nature, graphene could also be used as the gate electrode in transparent gate MOS transistors for photodetector and sensing applications.

In this talk, we fabricate and characterize MOS devices with graphene as the metal gate electrode, silicon dioxide as the dielectric, and p-type silicon as the semiconductor. We find that Fowler-Nordheim (F-N) tunneling dominates the gate tunneling current in these devices for oxide thicknesses of 10 nm and larger, whereas for devices with 5 nm oxide, direct tunneling starts to play a role in determining the total gate current. Furthermore, we study the temperature dependence of the F-N tunneling current in these devices in the temperature range 77 to 300 K. We extract the pre-exponential and exponential F-N coefficients and the effective tunneling barrier height as a function of temperature. We find that the effective barrier height decreases with increasing temperature, which is in agreement with results previously reported for conventional MOS devices with polysilicon or metal gate electrodes. In addition, by performing high frequency capacitance-voltage (C-V) measurements on these MOS devices, we observe a local capacitance minimum under accumulation for thin oxides. By fitting the data using numerical simulations based on the modified density of states of graphene in the presence of charged impurities, we show that this local minimum results from the contribution of the quantum capacitance of graphene. Finally, we extract the workfunction of the graphene gate electrode by determining the flat-band voltage as a function of oxide thickness. These results provide important insights for the heterogeneous integration of graphene into conventional silicon technology.

Multi walled carbon nanotubes functionalized isocyanate groups (MWCNTs-NCO) were synthesized by reacting pristine MWCNTs with methylene diphenyl diisocyanate (MDI) for use in the nylon 6,6 (PA66) composites. It has been shown that the isocyanate groups on the MWCNTs were reacted with amine groups, and as a result, MWCNTs grafted with PA66 (PA66-g-MWCNTs) were formed during melt extrusion. Formations of MWCNTs-NCO and PA66-g-MWCNTs were confirmed with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analyses. The interfacial adhesion energies between PA66 and various MWCNTs were estimated by a drop-on-fiber method. PA66/PA66-g-MWCNT composite exhibited the highest interfacial adhesion energies among the composites examined. As a result, PA66/PA66-g-MWCNT composite exhibited the best dispersion of MWCNTs in the PA66 matrix and the highest level of reinforcement.

Multi-walled carbon nanotubes (MWCNTs) grafted with poly(methylmethacrylate) (PMMA) (PMMA-g-MWCNT) were prepared by reacting MMA monomer and MWCNT functionalized with 3-Methacryloxypropyltrimethoxysilane (MWCNT-MPS). The PMMA-g-MWCNTs were incorporated into bisphenol-A polycarbonate (PC) matrix by melt mixing to improve mechanical strength and electrical conductivity of PC. The formation of MWCNT-MPS and PMMA-g-MWCNT were confirmed by the Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analyses. The interfacial adhesion energy between PC and PMMA-g-MWCNTs calculated by using drop-on-fiber method was higher than that between PC and pristine MWCNTs. As a result of higher interfacial adhesion energy, the dispersion of MWCNTs in the PC matrix and interfacial adhesion between the MWCNTs and PC matrix were better in the case of the PC/PMMA-g-MWCNT composite than in the case of the PC composite with pristine MWCNTs. The former also exhibited better mechanical properties and electrical conductivity than the latter at the same MWCNT content.

Activated carbons have long been recognised as one of the most effective methods of water treatment. Contaminants adsorb onto the surface of these materials, removing them from the water supply. Activated carbons are nanoporous, and thus have very high surface areas, which makes contaminant removal very effective. Some contaminants however, such as the pesticide metaldehyde, are difficult to remove from water with standard carbon materials. Our work focuses on tuning the size and shape of the pores in activated carbons to target these elusive toxins, and selectively remove them from the water supply.

Lignin, an integral part of lignocellulosic biomass, is produced in large quantities by the paper and pulping industry. The wide-spread availability and low cost of lignin makes this a promising feedstock for industrial-scale production of activated carbons. Uniquely, the lignin structure varies depending on the plant species it is isolated from. This leads to the exciting possibility we will be able to tune the activated carbon structure, including the size and shape of its pores, simply by adjusting the feedstock. The structure of four lignins systematically isolated using the same method, but from different feedstocks, was investigated using GPC, 2D-NMR, FTIR and other advanced characterisation techniques. Despite a similar chemical composition, it became clear that each lignin was composed of different numbers of aromatic units.

On lignin carbonisation, only the aromatic backbone remains, thus lignin from different feedstocks is likely to produce carbons with distinct structures. Initial experiments support this possibility, since the lignins exhibited different behaviours on carbonisation. A design of experiments methodology will be used to optimise the structure of carbons derived from an industrially produced lignin. A series of carbons prepared from lignins isolated using different feedstocks will then be prepared. A complete characterisation of these carbons using a variety of techniques including gas sorption, small angle scattering, and electron microscopy will yield information on any structural differences between the resulting chars and activated carbons. This work shows promise for using selection of the biomass feedstock to tune activated carbons porosity for selective removal of water contaminants.

The deformable conductive features have received considerable attention due to their potential of being utilized in a wide-variety of applications such as foldable display, flexible photovoltaics and wearable electronics. For this reason, various conductive materials such as carbon nanotube (CNT), graphene and metal nanowires were researched for deformable electrode. However, single material system often has difficulty satisfying both high conductivity and high mechanical stability that seem to mutually exclusive properties at the same time. Therefore, composite materials such as metal nanoparticle(NP)-CNT and metal NP-graphene have been suggested. Metal NPs can be mainly contributed towards the development of high conductivity in composite material and CNT or graphene can act as conducting bridges between metal NPs, resulting in the preservation of electrical property under mechanically severe conditions such as bending, and twisting and folding deformations. For this reason, those composites can satisfy the both high conductivity and mechanical stability at the same time.
In this study, we have successfully developed deformable conductive electrodes using Ag NP-CNT composites. Intense pulsed light (IPL) irradiation was employed as the post treatment process for sintering of NPs and decomposition of remaining organic stabilizing agents to achieve desired conductivity. CNTs with high mechanical stability could minimize the significant reduction of conductivity owing to cracks that can generate under mechanical stress in pure Ag NPs film. In addition, because CNTs has excellent absorption property at the wide wavelengths region, the photonic sintering efficiency of the composite film could be enhanced so that less IPL photonic energy was required. Moreover, the added CNT concentration was optimized by analyzing the change in electrical and mechanical properties of composite. The fabricated composite electrodes exhibited high electrical performance (6.8 μΩ_*cm) and mechanical stability even under folding condition. In addition, after IPL irradiation, strong adhesion property between the Ag NP-CNT and underlying substrate was remarkably developed owing to inter–fusion at interfaces between the composite/substrates by photo–thermal energy. By different adhesion property between the irradiated and non–irradiated area in the composite film irradiated selectively by IPL using photomask, micro–scale patterns could be developed. Finally, we demonstrated the deformable light emitting diode arrays and tested them under the bending, twisting, rolling, and folding conditions. It is believed that our result not only provide the effective way for large scale production of patterned deformable electrodes, but also facilitate their widespread in the various future electronics such as foldable display, flexible photovoltaics and wearable electronics.

We have used molecular modeling as a design tool for proposing a strategy that can help alleviate the problem of graphene stacking in a polar PMMA matrix. The idea is to leave the graphene sheets (GSs) intact (i.e., without destroying their perfect crystal structure) and, instead, to functionalize the PMMA chains with proper end groups such as pyrene end-functional groups, with a strong tendency to adsorb on graphene sheets. It turns out that the resulting α,ω-poly(methyl methacrylate) (py-PMMA-py) chains are excellent dispersing agents for GS. This was verified by detailed by performing atomistic molecular dynamics (MD) simulations of py-PMMA-py/GS nanocomposites with the LAMMPS [1] code using the DREIDING force-field [2] (which was previously employed to compute the mechanical properties of syndiotactic sPMMA nanocomposites with functionalized and non-functionalized GS with remarkable success [3]) in the isothermal-isobaric (NPT) statistical ensemble at T=550K and P=1atm. Nanocomposites with several %wt. loadings in GS and py-PMMA-py were tested.
The simulations showed that the pyrene end-functional groups adsorb strongly on the two faces of GS and, as a result of the intervening polymer mass, GS are kept separate and well dispersed in the nanocomposite at all conditions studied. Several interesting structures were observed in the MD simulations [4]: a) py-PMMA-py chains adsorbed on the same face of a GS through their end pyrene groups (a loop), b) py-PMMA-py chains adsorbed on the two faces of the same GS (an extended loop), and c) py-PMMA-py chains connected through their two end pyrene groups to two different GS (a bridge). It is these loop and bridge structures that prevent GS from coming together in the polymer matrix to self-assemble and form stacks. Simulation results for the mechanical properties of the simulated systems will also be presented through a method [5] based on small-strain deformations of microscopically detailed model structures which leads directly to the calculation of elastic constants of glassy polymers.

REFERENCES

[1] http://lammps.sandia.gov/; LAMMPS Molecular Dynamics Simulator.
[2] Mayo, A.; Olafson, B. D.; Goddard, W. A. J. Phys. Chem. 94, 8897-8909 (1990).
[3] Skountzos, E. N.; Anastassiou, A.; Mavrantzas, V. G.; Theodorou, D. N. Macromolecules 47, 8072-8088 (2014).
[4] Papadimitriou, K. D.; Skountzos, E. N.; Gkermpoura, S. S.; Polyzos, I.; Mavrantzas, V. G.; Galiotis, C.; Tsitsilianis, C. Acs MacroLetters 5, 24-29 (2016).
[5] Theodorou, D. N.; Suter, U. W. Macromolecules 19, 139-154 (1986).

Graphene is atomically thin and chemically inert, consists of light atoms and possesses a completely ordered structure; as a result of these special properties, 2D graphene support has greatly contributed to the single-atom imaging of target specimens by TEM. Many experimental and theoretical reports have described the changes that can be realized in chemical activities and reactions through the downsizing of materials. “Single-atom catalysis,” for example, has recently attracted attention as a potential solution to energy depletion. Nonetheless, the large-scale fabrication and characterization of single-atom materials remain major challenges, because single atoms generally have high mobility and easily aggregate. To begin to overcome these problems, we here report a simple method for the fabrication of dispersed Pt single atoms supported by graphene films. We also analyze the chemical properties of the fabricated atoms by XPS.
Graphene films were synthesized by a CVD method on a copper substrate (purity 99.8%, thickness 25 μm; Alfa Aesar). After etching the Cu substrate with 100 mM ammonium peroxodisulfate solution, the specimen was rinsed thoroughly with distilled water. Next, it was transferred onto a carbon-supported Cu TEM grid. We deposited single atoms of dispersed Pt on graphene by magnetron sputtering using a pure Pt thin film (t = 0.1mm). The metal Pt atoms were sputtered by strong magnetic and electric fields between a Pt target and the TEM grid. TEM and STEM observations of Pt single atoms were performed by an FEI Titan Cubed 60-300 TEM equipped with image and probe correctors. We were operated at 80 kV with a monochromator for high-resolution TEM and STEM imaging. XPS analysis was conducted on a JEOL JPS-9200. The peak position and intensity of Pt 4f peaks were confirmed between single atoms and nanoparticles in the Pt dispersion.
We also confirmed the formation of dispersed Pt single atoms by HAADF-STEM observation. The dispersed Pt atoms were shown to be uniformly located across the entire graphene support. Pt atoms moved along the graphene edges, at the boundary of graphene layers, during the STEM observation, but they did not immediately aggregate when exposed to a focused electron probe. The dispersion of Pt single atoms was maintained for more than 2 months under ambient conditions. The Pt 4f-binding energy in dispersed Pt single atoms was significantly shifted to an energy higher than that of Pt clusters and nanoparticles in XPS measurement. On the other hand, the peak intensity and position of O 1s peaks were not changed by Pt structure. Therefore, we considered that this significant shift in Pt 4f-binding energy was not attributable to the oxidation of Pt atoms.
In conclusion, we synthesized and characterized uniformly dispersed Pt atoms by a simple physical vapor deposition method on a graphene support.
[1] K. Ding et al., Science 350 (2015) 189.

The discovery of graphene in 2004 has initiated great research thrust towards an array of applications including transparent conducting electrodes (TCEs), owing to its unique electronic properties, high optical transmittance, chemical stability and mechanical flexibility. Over the recent years, it has become a strong candidate as an emerging TCE in lieu of indium – tin oxide TCEs that could resolve the drawbacks of the later in terms of lacking mechanical flexibility, chemical stability and continuously increasing cost. Herein, we investigate the intercalation of CVD few layers graphene with Ferric Chloride in a two-zone vapor transport process as a viable doping route to reduce the sheet resistance and modulate the work function, towards application as TCE in photovoltaic devices. In doing so, we use Hall effect measurement, Raman Spectroscopy, Kelvin probe, X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) to evaluate the changes in the electrical transport, electronic and morphological properties. Our results show a significant decrease of sheet resistance by more than 80% achieving a minimum value of 70 Ohm/sq. FeCl₃ - acting as a p-dopant- lowers the Fermi level of FLG, and thereby increases the work function from 4.5 eV to 5.0 eV. The optical transmittance of doped FLG was maintained within 5% of that for pristine FLG at 550 nm leading to nearly 10-fold increase of the TCE figure of merit. On the contrary, the transmittance increases by 10% in NIR region. Intercalation is confirmed by the increase of the interlayer spacing as deduced from XRD and STM in addition to the upshifting of the Raman G-peak. This study demonstrates a facile and effective route to reduce the sheet resistance of graphene with minimal optical losses and to tune its work function, paving the way towards graphene based transparent conductors.

Recently decades, boron nitride (BN) nanomaterials have become attractive due to their excellent properties such as high thermal conductivity, semiconductivity, high oxidation resistance at high temperatures, and radiation protective etc. With these properties BN nanomaterials have diverse area of applications like filler material in polymer/ceramic composites for high temperature applications, electrical nano insulator, electron field emission etc. The aim of this study is to investigate the effect of BN nanomaterials in polymeric materials on thermal conductivity and mechanical properties. Just about to use as reinforcement materials for composite material fabrication, vertical aligned (VA) and randomly growth boron nitride nanotubes (BNNTs) were achieved by chemical vapor deposition (CVD) method. Besides, boron nitride nanofibers (BNNFs) were produced by electrospinning method and followed with nitridation process. Epoxy resin was used as matrix material for the production in BNNTs and BNNFs containing composites. Effects of nano materials in composites were also investigated by changing total amount and orientation of reinforcement materials. BNNFs and BNNTs were dispersed randomly oriented in epoxy resin to understand the effect of nanomaterial form on properties. Besides, vertically aligned BNNTs and randomly BNNTs were used in epoxy resin to investigate the effect of orientation of reinforcement material on mechanical and thermal properties. Scanning electron microscopy (SEM) was used for morphological analysis for evaluating the uniformity of fiber and tube formation in the matrix. Fourier Transformation Infrared (FTIR) spectroscopy was also conducted to identify phase formation of BN nanomaterials and it proved the existence of B-N bonds. Mechanical properties were determined by applying tensile tests. As a result, it was demonstrated that addition of BNNTs and BNNFs improved the both mechanical and thermal properties of composite material compared to neat epoxy.

Water scarcity is a debilitating issue that affects millions of people worldwide. Fortunately, technological advancements have made large-scale seawater desalination a reality and mitigated some of our water woes. Despite this, popular desalination technologies such as reverse osmosis and thermal distillation are expensive and energy intensive. A more sustainable alternative is Capacitive Deionization (CDI) which promises to be more thermodynamically efficient. One of the main strategies used to improve the desalination performance is to synthesize materials that are electrically conductive, have high surface areas and are chemically stable. In this work, porous carbon hollow spheres of various sizes were synthesized via a modified Stöber process. The morphology, porosity and electrochemical properties of the spheres were studied using SEM, TEM, BET and CV techniques while their desalination performances were evaluated based on batch-mode CDI experiments. The largest surface area of 809.91 m² g^-1 was obtained for a carbon hollow sphere of approximately 230 nm and a salt removal capacity of up to 18.88 mg g^-1 was observed. A study of the electrosorption isotherms and kinetics was also performed.

Two years ago, we pioneered the concept of thin film reservoir where we describe how we doubled the height of carbon nanotube (CNT) forests by using a thin film reservoir of iron positioned below the alumina underlayer.¹ We are now submitting a new paper where we show how, by using a copper/silver thin film as a reservoir, we can inhibit CNT growth for the areas positioned above.² Using this technique, we show how we pattern the thin film reservoir (using lithography and lift-off) to then replicate this pattern on the CNT forest above.
We also present our most recent development where we use a molybdenum thin film reservoir to further enhance CNT growth, up to 4X (manuscript in preparation). What is most remarkable, and different compared to the iron reservoir mentioned above, is that by varying the thickness of the Mo film, we can modulate the CNT height and grow taller CNTs with thicker Mo layers.
By patterning the reservoir, we show how we can grow patterned CNT carpets with varying heights, all from the same catalyst layer. We will discuss the complex mechanisms based on diffusion from the reservoir to the surface and how the reservoir material interacts with the catalyst material to either inhibit or enhance CNT growth. We believe these findings are significant as they provide a simple way to locally control CNT growth on the third dimension (height) with lithographic precision.


1. Shawat, E.; Mor, V.; Oakes, L.; Fleger, Y.; Pint, C. L.; Nessim, G. D., What Is Below the Support Layer Affects Carbon Nanotube Growth: An Iron Catalyst Reservoir Yields Taller Nanotube Carpets. Nanoscale 2014, 6, 1545-1551.
2. Shawat Avraham, E. S., L.; Mor, V.; Girshevitz, O.; Westover, A.; Pint, C. L.; Nessim, G. D., Thin Reservoir Copper-Silver Thin Film as a Growth Inhibitor to Synthesize Lithographically Patterned Carbon Nanotube Forests. Under submission 2016.

Ethylene-vinyl acetate (EVA) is extensively used in the manufacturing of wire and cables because of its high ductility and low processing temperature. Yet, flame retardants must be used to reduce the high flammability of EVA. In recent years, aluminum and manganese hydroxide (ATH, MH) have been studied as the halogen-free flame retardant for EVA blend. However, to achieve an acceptable flame retardancy level, over 50 wt% loading of ATH or MH is needed, which greatly compromised the mechanical properties. In our research, the combination effect of MoS₂, graphene and ATH is studied. A series of flame retardant EVA composites were melt blended with different concentration of ATH, MoS₂ and graphene. With only 2 wt% loading of both MoS₂ and graphene, the weight percentage of EVA could be increased to 60% and still achieve the V-0 grade in UL-94 flame test. Scanning electron microscopy (SEM) confirmed the homogenous dispersion of all particles inside the blend. Dynamic mechanical analysis (DMA) showed a 127% increase in the storage modulus. Also, the tensile modulus and tensile strength were both maintained same with pure EVA. From the TGA measurement, the incorporation of MoS₂ and graphene has increased the thermal stability and char residue yield. Cone calorimetry showed that the peak heat release rate has an 80% reduction compare to pure EVA. Limiting oxygen index (LOI) is also increased.

Incorporating heteroatoms such as Boron as "dopants" in the crystalline lattice of a single-walled carbon nanotube (SWCNT) induces changes in its intrinsic properties . Understanding the bonding environment of the dopants and their distribution in the wall of B-doped SWCNTs is crucially important for applications. However, the tube's heterogeneity, their bundling, and the presence of catalytic by-products hinder their direct application. We have optimized the production of SWCNTs doped with B using a high-vacuum assisted chemical vapour deposition method developed in- house and this work shows our progress regarding the subsequent purification processes we have tried. The density gradient ultracentrifugation method has been investigated in this work as an alternative to the conventional chemical purification treatment that could possible affect to the functionalized material. In order to characterize this material, multifrequency Raman spectroscopy was performed followed by optical absorption studies before and after the purification treatments, as well photoluminescence analysis has been done to assign the semiconducting chiralitys. This analysis has allowed us to understand the changes in the tubes' morphology and physical properties. To the best of our knowledge, this study provides the first relevant results regarding the scalability of this purification process over a B-doped SWCNT keeping the most species on the resultant material and has become a significant step toward the chirality sorting.

CNT dispersion limits and/or blend ratios in polymer matrices for the development of new composite materials with property improvements approaching theoretical predications is very important. However, despite the amount of process optimization studies to date for polymer/CNT-based composites, non-interacting bulk polymer or filler agglomerations phases still exists within these materials restricting property improvements. To address this problem, in this work, a liquid/solid phase separation method was developed to separate well-blended interacting polymer/CNT micro-phases from non-interacting bulk CNT and polymer matrix phases in the polymer/CNT dispersions prior to composite fabrication. Experimental analysis shows that within the blended polymer/CNT micro-phase polymer interactions with CNT are selective. In addition to experimentation, molecular dynamics studies were employed to investigate the onset and selectivity of polymer-CNT interactions as a function of the phase separation conditions used. From computational analysis as well as theoretical calculations, a model was developed to visualize the blended polymer/CNT micro-phases. This analysis was also used to demonstrate that there is a geometrically dependence governing the selective interaction between the polymer-CNT leading to this well-dispersed/blended micro-phase. In other words, coupling the dimensions corresponding to the polymer radius of gyration (R_g) to specific CNT bundle aspect ratios can be used to ensure formation of a polymer/CNT micro-phase. This work demonstrates that understanding the role of phase separation is important to address the nano-filler dispersion limits, which are critical toward the processing of superior polymer-based composite materials with fully-utilized CNT reinforcement.

Due to recent concerns relating to both the environment and biosafety, there is a growing demand for efficient technologies for protecting and reusing water and oil resources. Within various technologies, membrane-based filtration has been extensively developed and used as a result of their versatility and cost-efficiency [1]. However, membrane fouling is a major problem encountered in the membrane filtration process, which impairs the performance, and cleaning or replacement may add extra cost and reduce efficiency [2]. Developing a membrane that is less prone to fouling and has a self-cleaning ability would be pivotal for the membrane-based filtration process.
In this work, we demonstrated a membrane with self-cleaning ability for oily water treatment and oil recovery. First, carbon nanofibers (CNFs) were grown on commercially available stainless steel (SS) meshes using atmospheric pressure chemical vapor deposition (APCVD), followed by a deposition of polypyrrole-dodecylbenzenesulfonate (PPy(DBS)) via electropolymerization. CNFs enhanced the conductivity of SS mesh, facilitating a uniform growth of PPy(DBS) on the mesh surface. Subsequently, the polymer surface was treated via oxygen (O₂) plasma to form nanowire (NW) structures onto already ‘rough’ surfaces, in order to enhance the efficiency of water/oil separation and the subsequent self-cleaning ability. To fabricate such PPy(DBS) NWs, SS-CNFs-PPy(DBS) surfaces were etched using a one-step maskless O₂ plasma etching process in reactive ion etching (RIE) [3]. The length of NWs was accurately controlled by varying power and duration of the RIE etching process. Using the unique tunable wetting property of PPy(DBS) [4], the optimized membrane selectively trapped oil under oxidation, and released the trapped oil, regenerating itself under reduction. We measured contact angles for various lengths of NWs, and found that the membrane surface was switched between high adhesion Wenzel state and low adhesion Cassie–Baxter state, which was not observed from flat PPy(DBS) surfaces.
We will further study parameters including mesh pore sizes, CNFs lengths, PPy(DBS) thickness, and NW lengths to optimize the separation performance and regeneration ability.

[1] M. O. Adebajo, R. L. Frost, J. T. Kloprogge, O. Carmody, and S. Kokot, “Porous materials for oil spill cleanup: A review of synthesis and absorbing properties,” Journal of Porous Materials, 10 (3), 159–170 (2003).
[2] R. W. Baker, Membrane technology and applications. John Wiley & Sons, 2004, (2004).
[3] K. Du, I. Wathuthanthri, Y. Liu, Y. T. Kang, and C.-H. Choi, “Fabrication of polymer nanowires via maskless O2 plasma etching,” Nanotechnology, 25, 165301 (2014).
[4] W. Xu, J. Xu, C.-H. Choi, and E. H. Yang, “In situ control of underwater-pinning of organic droplets on a surfactant-doped conjugated polymer surface,” ACS Applied Materials & Interfaces, 7 (46), 25608–25617 (2015).

Engineered nanoparticles such as graphene and related materials (GRMs), nanodiamonds (NDs), and carbon nanotubes (CNTs) are already used in many kinds of commercial applications and products available on the market. It is thus rather likely that they may get into the environment at any step of their life cycle, from their production to their disposal, and also during their use. Because the aquatic compartment is known to concentrate pollutants, it is expected to be especially impacted. The toxicity of a compound is conventionally evaluated using mass concentration as a quantitative measure of exposure. This is mainly for practical reasons, especially when the substance is initially available in dry form. However, several studies have highlighted that such a metric is not the best descriptor at the nanoscale.
Here we compare the inhibition of Xenopus laevis (amphibian) larvae growth after in vivo exposure to different carbon nanoparticles of different morphology from 0D to 2D (few-layer graphene (FLG), NDs, CNTs) for 12 days (standardised assay [1]), using different dose metrics to express the concentration of carbon nanoparticles: weight concentration (mg/L), number of particles concentration (number/L) and finally surface area concentration (m²/L).
Our results clearly show that surface area is the most relevant metric for comparing the toxicity (growth inhibition) of these different types of carbon allotropes, whith all the data fitting on the same plot. We were even able to propose an effective area concentration (EC₅₀) of 7.5 m²/L, above which 50% of the exposed population would encounter significant growth inhibition after exposure to carbon nanoparticles in our experimental conditions [2]

[1] ISO 21427-1
[2] A. Mottier, F. Mouchet, C. Laplanche, S. Cadarsi, L. Lagier, J-C. Arnault, H. Girard, V. Léon, E. Vazquez, C. Sarrrieu, E. Pinelli, L. Gauthier and E. Flahaut,
Nano Letters. 2016

Fullerenes that contain other species inside them are known as endohedral fullerenes. These compounds are of interest by their potential applications¹, from molecular electronics to pharmacy ¹. Recently mass spectrometry experiments have shown^2,3 the presence of fullerenes doped with group-3 elements (Sc, Y and La). The smallest compounds obtained in these experiments are those formed with a fullerene C₃₆ and an endohedral group-3 atom. Similarly the fullerene C₄₄ can encage these species.
We studied their electronic properties, geometries and stabilities with the density functional theory, using the functional PBE with the dispersion correction D3(BJ) and the basis def2-TZVP for all atoms. We analyzed uniquely the lowest energy minima, with all their vibrational frequencies real.
Our results show that the most suitable C₃₆ isomer to host group-3 elements has D_6h symmetry. In the compounds, only La is located at the fullerene's center and the other two atoms are displaced in direction of a hexagonal ring. These interactions metal-fullerene are very similar to metal-benzene. In addition, Hirshfeld charge distributions and electrostatic potential maps have shown that La@C₃₆ is an ionic compound and the others mostly covalent. Similarly, the properties of the endohedral compounds formed with C₄₄ and these atoms have been studied preliminarily in order to explain the large abundance observed in experiments³.

Keywords: Endohedral fullerene, C₃₆, Density Functional Theory, Electronic Structure.
1. Popov, A. A., Yang, S. & Dunsch, L. Endohedral fullerenes. Chem. Rev. 113, 5989–6113 (2013).
2. Klingeler, R., Bechthold, P. S., Neeb, M. & Eberhardt, W. Mass spectra of metal-doped carbon and fullerene clusters. J. Chem. Phys. 113, 1420 (2000).
3. Dunk, P. W. et al. Bottom-up formation of endohedral mono-metallofullerenes is directed by charge transfer. Nat. Commun. 5, 5844 (2014).

The null band gap of graphene precludes its application to the development of electronic devices. This has motivated the search for other nanostructures that possess, at the same time, the most of the good properties of graphene and non-null band gap. A new structure called graphyne (GY), a bi-dimensional carbon allotrope proposed in the 80’s by Baughman et al. [1], has been shown to present non-null band gap [2]. Formed by sp¹ and sp² hybridized carbon atoms, GYs and its similar “cousin” structure, the graphdiynes (GDYs), have gained special attention because of their electronic properties as well as their bi-dimensionality and porosity [2]. GY and GDY structures can be simply imagined as being formed by the substitution of certain carbon-carbon bonds in graphene by acetylene (–C≡C–) and diacetylene (–C≡C–C≡C–) chains, respectively. Mechanical and thermal properties of some GYs and GDYs have been predicted in the literature [2,3]. However, the mechanical properties of some GYs and GDYs were not calculated yet. In this work, using classical molecular dynamics, we present calculations of the Young’s modulus of all original seven types of GYs [1] and corresponding GDYs, along two main directions. The results show good agreement with the available data in the literature for some GYs [3]. The Poisson's ratio of all GYs and GDYs are computed for the first time. The results show that the Young's moduli of GYs and GDYs are smaller than that of graphene, and decrease, in general, with structure density. Also, an asymmetry of the Young’s modulus along two different directions in some GYs and GDYs are observed. Most GYs and GDYs Poisson's ratio are similar to that of graphene, but some GYs and GDYs present interesting giant (larger than one) Poisson’s ratio behavior. A mechanical honeycomb model is used to understand and explain these last Poisson’s ratio results.
[1] R. H. Baughman, H. Eckhardt and M. Kertesz, J. Chem. Phys. 87, 6687-6699 (1987).
[2] A. L. Ivanovskii, Progress in Solid State Chemistry, 41(1), 1-19 (2013).
[3] Y. Y. Zhang, Q. X. Pei, and C. M. Wang. Appl. Phys. Lett. 101(8), 081909 (2012).

Diamond nanocylinder forest (DNF) is energetically and mechanically viable structures like porous carbon composites, which is candidate for electrode materials for fuel cells due to its high surface area high porosity and electrochemical stability ^[1]. planar boron-doped diamond film is good electrochemical electrode with large voltage window, it is supposed that boron doped DNF (BDDNF) will also show high electrochemical performance ^[2].

Nowadays there are two popular approaches to fabricate these structures, one of them is diamond substrate etching, for which the main disadvantage is the introduction of damage and impurities to product. The other one is the template-assisted chemical vapor deposition(CVD) growth method ^[3], which will result in more uniform cylinders with less damage to surface and is adopted in this study.

During the experiment, porous alumina membrane was set on the diamond substrate as template. The growth of diamond was conducted in the atmosphere of H₂ and CH₄ (3%) with a substrate temperature ranging from 750 to 1000°C. The antenna-edge-type microwave plasma assisted CVD apparatus which is able to create a continuous and highly focused plasma body, was used to enhance the nucleation of diamond growth. After removing the template, the as–grown cylinders were identified to be tube structure or rod structure depending on the morphology. Coupled with the Raman spectra, it was confirmed that the cylinders obtained at the temperature of 750~900°C were diamond like carbon (DLC) tubes, while DLC rods was observed when the temperature ranged from 800 to 950°C. When temperature rose up to 1000°C, the product turned to be diamond rods. Moreover, the SEM images showed that the higher temperature, the better quality of cylinders within the range of growth temperature. The diamond cylinders will be characterized by X-ray diffraction (XRD) and Transmission Electron microscope (TEM) to examine the fine details and crystallinity as well.

Reference：
[1] Tang, Jing, et al. Nano Today 9.3 (2014): 305-323.
[2] Luo, Daibing, et al. ACS nano 3.8 (2009): 2121-2128.
[3] Masuda, Hideki, et al. Advanced Materials 13.4 (2001): 247-249.

Transparent conductive films (TCFs) are widely used in electronic devices, such as organic light emitting diodes, liquid crystal displays, touch screens and solar cells. Today, the industry standard materials for TCFs are doped metal oxides, most commonly indium tin oxide, which provides excellent electrical conductivity while being optically transparent. Metal oxides, however, have several drawbacks, including high refractive index and haze, spectrally non-uniform optical transmission and restricted chemical robustness. Moreover, they are scarce, require expensive processing methods, and their properties deteriorate after bending, limiting their applications in flexible and wearable electronics. These disadvantages of classic transparent conductors have triggered numerous efforts in discovering alternative materials for TCFs. Materials such as conductive polymers, nanocarbons, metal nanogrids and nanowires were explored as potential replacements for ITO. Among these, carbon nanotubes (CNTs) and graphene are particularly promising due to their unique properties: they have neutral color, can be easily transferred to flexible substrates, and retain their conductivity even after repeated bending. However, to be adopted in the industry, CNT- and graphene-based TCFs have to demonstrate optoelectrical performance that matches or is superior to that of ITO-based TCFs. There are several approaches that can be employed to improve the optoelectrical performance of CNT- and graphene-based TCFs. We have created hybrid CNT/graphene materials that take advantage of the synergistic effects between CNTs and graphene, and demonstrate better optoelectrical performance than the individual constituents.

We have developed a novel, scalable and commercially feasible process for the fabrication of hybrid CNT-graphene TCFs using aerosol-synthesized single-walled CNTs (SWNTs) and commercially available graphene oxide solutions. The method involves dry transfer of as-synthesized SWNT films onto a substrate, spray deposition of graphene oxide (GO) on top of the SWNTs, reduction of GO and, finally, doping of the hybrid with gold (III) chloride. We have investigated the optoelectrical performance of the hybrids, as well as their morphology and elemental composition. We have demonstrated that our method yields transparent and conductive films with state-of-the-art sheet resistance value of 73 Ohm/square at 90% transmittance (at 550 nm). Fabricated films satisfy most of the requirements for applications as TCFs in various devices. Moreover, the hybrids show better performance than reduced graphene oxide or than any of the rGO-CNT hybrids reported previously. The method introduced in our study has a potential for industry applications due to straightforward materials processing and low equipment requirements.

Boron nitride nanotube (BNNT) which has high thermal conductivity but is electrically insulating is a promising material. BNNT can be synthesized via laser ablation, RF plasma, and ball milling-annealing process. Among them, the ball milling-annealing process where BNNT is synthesized using a pulverized/mechanically activated boron powder would be a most possible commercial production process because it is easy to scale-up. Synthesized BNNT are contaminated by milling ball debris such as zirconia or iron compounds during the milling process and boron compounds during the annealing process. Here, BNNT was purified by several methods such as centrifugal separation, polymer wrapping, and solvent extraction. Purity and morphology of BNNT were measured by SEM, TEM, EDX analysis, and Raman spectroscopy. Morphological dependence of the purified BNNT on thermal conductivity was investigated. And polymer composite was prepared using BNNT alone or mixed with boron nitride nanosheet which was prepared by exfoliation of hexagonal BN. Thermal conductivity of the composite was measured in terms of each volume fraction.

Carbon nanomaterials, such as graphene and carbon nanotubes (CNTs), are formed on silicon carbide (SiC) by high temperature thermal annealing without any surface cap layer. Si atoms combine with oxygen from chamber residual and sublimate as silicon mono-oxide (SiO).^[1] The remaining carbon atoms reform the nanocarbon materials. Also, for diamond surface, graphene layers parallel to the diamond (111) surface is formed by high temperature annealing.^[2] In this study, we fabricated the new structure of vertically oriented graphite layers (VOG) on (001) diamond by hot implantation and high temperature annealing.
Aluminum ions were implanted to (001) diamond substrate with the density of 10¹⁹ cm^-3 for 300-nm thickness at the temperature of 500 °C. The direction of the implantation was tilted by approximately 7 degrees to avoid channeling effect. The implanted samples were annealed at the temperature of 1700 °C in Ar for 2 hours. The sample was observed by high resolution TEM.
Cross-sectional TEM image of the VOG showed clear lateral lines with the thickness of ~10 nm. The interval of the lateral lines were ~0.34 nm, which corresponds to the graphite interlayer distance. From Raman spectrum, no G-band from graphite structure was observed and broad peak emerged at 1440 cm^-1 for all samples with VOGs. In case no implantation was directly annealed, VOG Raman peak of 1440 cm^-1 was not observed, which means that implantation is the key factor to form VOG structure. The formation mechanism of VOG we suspect is as follows. The initial structure was formed in hot implantation, and part of the intercalating atoms caused by implantation moved to the surface and increased VOG structure by high temperature annealing. This structure is useful for ohmic electrodes of diamond power devices.

[1] M. Kusunoki, M. Rokkaku, and T. Suzuki, Appl. Phys. Lett. 71, 2620 (1997).
[2] N. Tokuda, T. Inokuma et al., Jpn. J. Appl. Phys. 52, 110121 (2013).

Graphene is a monoatomic two-dimensional material showing strong sensitivity for molecular adsorbents. Raman micro-spectroscopy revealed that oxygen molecules selectivity adsorb at graphene edges with the support of UV irradiation [1]. Such inhomogeneous adsorption behavior provides us with important insights for the development of graphene transistors. In order to control physical properties of graphene in molecular adsorption, it is essential to understand the chemical bonding state and electronic structure of carbon-oxygen systems on a nanometer scale.
We here performed soft X-ray scanning photoelectron spectroscopy on UV irradiated graphene field effect transistors using “3D nano-ESCA” (Three-dimensional nano-scale spatially resolved electron spectroscopy for chemical analysis), installed at University-of-Tokyo Outstation Beamline for Materials Science (BL07LSU) of SPring-8 [2]. 3D nano-ESCA provides us with the information on local electronic and chemical states with the spatial resolution of about one hundred nm and the energy resolution of a few hundreds meV.
Exfoliated graphene samples were fabricated on the SiO₂/p⁺-doped Si substrate (0.5 mm in thickness), and Au electrodes (100 nm in thickness) pattern were formed by electron-beam lithography. Then, UV light was irradiated under negative gate voltage (-60 V).
We obtained a C 1s photoelectron intensity map and identified microstructures, where the electrode, the substrate and the graphene channel were clearly distinguished. Furthermore, we have found that there exists three differently-oxidized parts, namely strongly, mildly and weakly oxidized regions recognized in the combination of C 1s core level photoelectron spectra and Raman micro-spectroscopy. In the strongly oxidized region, carbon-oxygen components in C 1s photoelectron spectra were increased upon oxidation. In the mildly oxidized region, sp² hybridization is transformed to sp³ hybridization. In the weakly oxidized region, hole doping in graphene without structural change was indicated by the C 1s core level peak shift.
In the presentation, we will discuss the details of 3D nano-ESCA results including energy shifts and components of photoelectron spectra.

[1] N. Mitoma and R. Nouchi, Appl. Phys. Lett. 103, 201605 (2013).
[2] K. Horiba et al., Rev. Sci. Instrum. 82, 113701 (2011).

In this paper, a unique solar cell that is a paper dye-sensitized solar cell(DSSC) based on a carbon-nanotube (CNT)-composite paper and improvement its conversion efficiency are described.
Nowadays, clean power, e.g., solar power, wind power, and so on, has been attracting much attention as “renewable energy” because of recent environment problems. Here, we focus on solar power generation, i.e., solar cells. As the targeted device, we study the DSSC. Generally, the DSSC consists of conductive and dye-absorbed-semiconducting electrodes facing each other. In addition, an electrolyte is poured between two electrodes. For our DSSC, a metallic-CNT-composite paper for a conductive electrode and a semiconducting-CNT-composite paper with dye for a dye-absorbed-semiconducting electrode are used, respectively (i.e., “PAPER DSSC”). The metallic- and semiconducting-CNT-composite papers can be fabricated easily by using the following paper-making method based on the traditional Japanese washi paper-making method. At first, a pulp suspension is prepared by soaking and dispersing paper fibers in water. Next, a metallic- or a semiconducting-CNT suspension is prepared. Then, the pulp and the CNT suspensions are mixed. After that, the mixed suspension is scooped up by wire netting and dried by a heating press. As a result of this process, very unique, flexible, and usable CNT-composite papers are obtained.
In previous study, we have clarified and discussed that the paper-DSSC based on the CNT-composite papers have been able to be fabricated and generate power. However, its conversion efficiency has not been so good yet. We here aim to overcome the problem of its low power generation. One of the reasons we consider is leak current. Ideally, almost all excited electrons in the negative electrode move into semiconductors from dyes, when the dyes receive light. However, in our paper-DSSC, some electrons may recombine in the dyes or move into the electrolyte. Therefore, we improve the negative electrode of our DSSC to increase its conversion efficiency in this study. For this, we focus on the following two points. One is improvement of the making process of negative electrode. The amount of contents in the semiconducting-CNT-paper electrode with dyes and the structure of it should be controlled strictly, we consider. Another is preventing undesired flow of excited electrons from the dyes or the negative electrode to the electrolyte. According to a report, a special chemical, 4-tert-butylpyridine (TBP), can prevent the undesired flow as a block layer by adding the electrolyte. In this study, we clarify whether these approaches are effective for the paper-DSSC because they have never been tested. We believe these approaches will give us many hints to overcome the problems. Finally, our paper-DSSC will be able to increase its conversion efficiency.

The realization of the uniform nanomaterials with specific topology useful for high-performance nanoscale devices is currently one of the main challenges in nanotechnology [1]. The search for thermally and chemically robust structures requires an access to complex mono-disperse building blocks with desired topology and size. Carbon-based materials, such as fullerenes, carbon nanotubes, and graphene are very exciting molecular-level building blocks for nanoscale materials design [2-4]. The variety of basic 1D, 2D, and 3D shapes and geometries needed to build any specifically designed molecular architecture is possible due to the large number of accessible hybridizations of the carbon atom. However, the separation of a synthetic mixture of the major and minor products into mono-disperse or single chirality components, especially in the case of carbon nanotubes, is still a big challenge for researchers and hence provides some limitations to access the pure carbon nano-materials for technological applications.
The organic supramolecular assemblies, which consist of covalently or non-covalently bounded functional monomeric building blocks materials, can be rival to the pure nanocarbon-based systems. Porphyrins and phthalocyanines may consider as one of the most interesting building blocks for such assemblies. These thermally and chemically robust molecules found a variety of applications ranging from traditional dyes and pigments to more contemporary cancer therapies, environmental and biochemical sensors, nonlinear optics and light-harvesting.
Here, we have presented a general design for functional 3D tetraazaporphyrin-based nanostructures, which would bridge the gap between the well-known fullerenes and nanotubes and a new class of the functional nanomaterials. We have explored three major motifs for functional nanostructures which vary by three- or four-fold topology, porosity, degree of conjugation, and electronic structures. The stability of proposed nanocages, nanobarrels and nanotubes generated by conversion from nanobarrels was revealed on the basis of DFT and MD calculations, whereas their optical properties were assessed using a TDDFT approach [5]. It was shown that the electronic structures and optical properties of studied structures could be easily tuned via their size, topology, and the presence of bridging sp³ carbon atoms. Based on DFT and TDDFT calculations, the optical properties of the new materials can rival those of known quantum dots. The ability to store large quantities of methane (106–216 cm³(STP)/cm³) was observed in all cases with several compounds being close to or exceeding the DOE target of 180 cm³(STP)/cm³.

REFERENCES
[1] P. A. Alivisatos, ACS Nano 2 (2008) 1514.
[2] H. W. Kroto et al. Nature 318 (1985) 162.
[3] S. Iijima, Nature 354 (1991) 56.
[4] K. S. Novoselov et al. Science 306 (2004) 666.
[5] R. V. Belosludov et al. Phys. Chem. Chem. Phys. 18 (2016) 13503.

We report a polyhedral porous carbon electrode engineered from molecular design and graphitization evolution. Using a series of bimetallic metal-organic frameworks (BMOF) based on zeolitic imidazolate frameworks (ZIFs) ZIF-8 and ZIF-67 with varied ratios of Zn/Co as the precursors, nano-scaled porous carbons were precisely synthesized with tunable size and graphitization degree. Their intense impacts on the morphology, specific surface area, porosity and electrochemical properties were systematically explored using SEM, BET and CV techniques while their desalination performances were investigated by conducting batch-mode membrane capacitive deionization (MCDI) experiments. The results show that the porous carbon derived from the bimetallic MOF with Zn/Co molar ratio of 3.0, exhibited superior electrosorption capacity of 34.24 mg g^-1 with the existence of ion-exchange membranes when the initial NaCl concentration is 750 mg l^-1 and voltage applied is 1.2V, due to its optimal combination of large specific surface area and high electrical conductivity. Moreover, the BMOF-templated porous carbon electrode can be reused for at least 22 cycles due to its good stability.

To widen the spectrum of its applications, it is important to functionalize graphene, while preserving its superior properties, and retaining its planar lattice (for high mobility) and its carbons’ sp² hybridized state (for high carrier density). Such a functionalization mechanism, when conducted in compliance to the needs of semiconductor manufacturing processes will enable graphene’s incorporation into diverse applications. Here, we develop a unique eta-6 organometallic approach to functionalize graphene in a vapor-phase process, which retains the structural and electrical properties, while offering chemical sites for interaction and interfacing with other chemical or biochemical systems. In contrast to other functionalization processes, the eta6-functionalized graphene maintained its high charge carrier mobility (1000 cm²V^-1s^-1 at 300 K). We will discuss the mechanism of charge transfer in eta-6 functionalization of chromium carbonyl on graphene. This process will unveil graphene’s previously unknown potential to hierarchically interface with physical and biological components to produce novel systems and applications. Results will also facilitate gate-fabrication for FETs via atomic-layer-deposition (currently a major challenge).

In this paper, we have tried to demonstrate the possibility of using graphene nanoribbons as an effective material in gas sensing devices. There are lots of theoretical reports that show the potential of graphene nanoribbons but one can hardly find any experimental investigation on this manner. In order to achieve that, proper carbon nanotubes are grown using plasma enhanced chemical vapor deposition and sonicated in H2SO4/HNO3 (4:1) solution for 6 hours and then dried. Then, the produced carbon nanotubes are drowned in liquid nitrogen for 10 min and in less than 30 sec the temperature are increased up to 80 degree by adding proper boiling water. The abrupt thermal expansion, as reported before, unzip the carbon nanotubes and proper graphene nanoribbons are achieved after 1hour sonication. We dropped the resulted materials on proper comb-shaped inter-digits and 2nm gold are sputtered on it. Then, the device are checked for dynamic gas sensing toward methane with nitrogen as carrier. Same process did for pristine carbon nanotube films. We have shown that decorated graphene nanoribbons can have good sensitivity to methane in acceptable concentration. Compared with carbon nanotubes, the response of graphene nanoribbons are better that show the potential of these materials as gas sensors.

Single-walled carbon nanotubes (SWCNTs) have been investigated for use as polarized electrodes in electric double-layered supercapacitor (EDLCs). In chemically functionalized SWCNTs, it is reported that the specific capacitances are larger than those of unfunctionalized SWCNTs. The reason for this is believed to be the greater electrolyte ion adsorption on the surface of functionalized SWCNTs as a result of the improved wettability of the surface of SWCNTs. The DOS of SWCNTs changes with chemical functionalization, and the injection and ejection of electrons into and from the functionalized SWCNTs lead to further change in the DOS, which is inferred to have an effect on the properties of the EDLCs. Since in-situ Raman measurements can be used to investigate the physical properties of chemically functionalized SWCNTs as well as their DOS, the obtained results should help to elucidate whether or not chemically modified SWCNTs improve the characteristics of the polarized electrodes used in EDLCs. Here, we report not only the influence of air oxidation on the electrochemical doping of the air-oxidized SWCNTs using in-situ Raman spectroscopy but also the relationship between the in-situ electrochemical Raman data and the properties of EDLCs.

We oxidized approximately 90% semiconducting, highly crystalline SWCNT (hc-SWCNT) bundles in the atmosphere at 450 °C for 30 min to obtain SWCNTs modified with oxygen-containing functional groups and investigated not only the influence of air oxidation on the electrochemical doping of the air-oxidized SWCNT (AO-SWCNT) bundles in aqueous sulfuric acid solution using in-situ Raman spectroscopy with a three-electrode electrochemical cell. We focused on the 100–300 cm^-1 range for the radial breathing mode (RBM) and the 1200–1800 cm^-1 range for the TG mode of the SWCNTs for every 0.1 V between -0.2 and +1.0 V in one go.

By oxidizing the hc-SWCNTs in air, AO-SWCNTs with a small diameter distribution could be prepared. When a negative charge was applied to the AO-SWCNTs used as a working electrode, a large downshift of the G⁺ line of the AO-SWCNTs was observed compared to that before air oxidation. On increasing the ratio of small-diameter nanotubes/total nanotubes, the Raman data obtained in situ revealed that the effect of the weakening of the C-C bond was stronger than that of the renormalization of the phonon energy. In contrast, in the case of applying a positive charge to the AO-SWCNTs, the magnitude of the upshift of the G⁺ line for the AO-SWCNTs was slightly larger than that for the hc-SWCNTs. The influent electric charges per unit mass and the specific capacitances of the AO-SWCNT electrodes for the maximum magnitude of the shift of the G⁺ line (10.7 cm^-1) were 60.1 C/g and 50.1 F/g, respectively, which are larger than those of hc-SWCNT electrodes.

Graphene nanoribbon (GNR) represents a unique form of carbon materials and have spurred intensive interests due to their exceptional electronic property, thermal stability, and low percolation threshold. Recent theoretical and experimental works demonstrated that GNRs are promising materials for many applications such as energy generation and storage, chemical and biosensors, catalysis, nanocomposites, and nanoelectronics. To further boost the advantages of GNRs, metal nanoparticles (NPs) were selected to form various types of composite material for plenty applications including, energy storage, photocatalyst, electrochemical sensors, and especially catalysis. The unique nature of GNR-NP composite materials with high surface area and exceptional conductivity can assist the chemical reaction to lower the activation energy and increase reaction rate constant.

Here we report a facile synthesis of GNR-PtNP composites as a green catalyst for catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). 4-NP has been a persistent wastewater constituent from various industries. Consequently, a catalytic method is sought-after in reducing 4-NP to less toxic and commercially important 4-AP. GNR was prepared by an intercalation-assisted longitudinal unzipping of single-walled carbon nanotubes (SWCNTs). KNO₃ was used as intercalation agent that weaken Van der Waals attraction between CNT walls to facilitate the GNR formation. The process generated oxygen-containing groups on the GNR surface, providing the anchoring site for Pt-NPs nucleation and growth via a wet-chemical reaction. Detailed materials characterizations and systematic catalysis study indicate that GNR-PtNP composites show superior catalytic performance with a normalized reaction rate constant (k_n) of 120 x 10^-3 mmol.s^-1g^-1. Our work suggests that GNR-PtNP composite materials show a great potential to develop an effective and stable catalyst for environmental protection.

In general, a carbon black (CB) is used as a Pt catalyst support in a polymer electrolyte fuel cell (PEFC) electrode. However, its low durability, originated in its poor crystallinity, is obstructing the practical use of PEFC. Instead of the CB, we focused on carbon nanowalls (CNWs) as a catalyst support, because of its high crystallinity and high-specific surface area. We have succeeded supporting of Pt nanoparticles with a diameter of 2-3 nm and ultra-high-density over 10¹³ cm^-2 on the whole surface area of the CNWs using a supercritical fluid (SCF) metal-organic chemical fluid deposition (MOCFD) method [1]. In this study, electrochemical characteristics and durability of Pt-supported CNWs synthesized by a C₂F₆/H₂ mixture gas plasma are investigated.
The CNWs were grown on Ti substrates by a radial-injection plasma-enhanced chemical vapor deposition (RI-PECVD) system [ref.]. In this system, two types of plasmas, surface wave excitation plasma (SWP) and capacitively-coupled plasma (CCP), are used to precisely and independently control density ratios of radical species. H₂ (100 sccm) and C₂F₆ (50 sccm) gases were introduced to the SWP and CCP regions, respectively. The total gas pressure was 99.5 Pa, and the powers applied to the SWP and CCP regions were 250 W and 300 W, respectively. The substrate temperature was kept at 800 °C. The deposition time was 15 min and the height of the resultant CNWs was approximately 500 nm. Pt nanoparticles are supported on the CNWs employing the SCF-MOCFD system. As a Pt precursor, 1 wt% (CH₃C₅H₄)(CH₃)₃Pt solution diluted by n-hexane was used. For the Pt support, 30 min of Pt support were done. Electrochemical measurements were carried out by three-electrode cell using the Pt supported CNWs. Pt wire and reversible hydrogen electrode (RHE) were used as counter and reference electrodes, respectively. At the potential cycle test, a potential is swept between 1.0 and 1.5 V with a speed of 2 s/cycle.
The potential cycle test was applied to Pt-supported CNWs and electrochemical surface areas (ESA) were calculated for evaluating the degradation. As a result, normalized ESA values gradually increased up to 11.7 times until 30,000 cycles. Then, they showed only 12.8% decrease after the following 30,000 cycles (totally, 60,000 cycles), although the conventional CB generally showed over 50% decrease only after five thousands cycles. Pt supported CNWs showed very high performance on durability, which should be promised to be applied for the highly durable fuel cell electrode.
[1] K. Mase et al., Appl.Phys. Lett. 98, 193108 (2011)
[ref.]

Ultrafine particles are widely used as lubricant oil additives since they can infiltrate and separate
tribological contacts, thereby reducing the friction and wear between surfaces. They are more
thermally and mechanically stable compared to molecular additives under high friction, and the
good dispersibility of ultrafine particles without molecular ligands is highly desirable. Based on
our previous report, ultrafine particles with miniaturized crumpled structure should self-disperse
in lubricant oil, just like how crumpled paper balls do not readily stick to each other. Meanwhile,
they could reduce friction and wear like miniature ball bearing. Here we report the use of
crumpled graphene balls as a high-performance additive that can significantly improve the
lubrication properties of polyalphaolefin base oil. In friction test, crumpled graphene’s
tribological performance excels that of other carbon additives including graphite, reduced
graphene oxide, and carbon black. Notably, polyalphaolefin base oil with only 0.01–0.1 wt. % of
crumpled graphene balls outperforms a fully formulated commercial lubricant in terms of friction
and wear reduction.

Top-down graphene production via the exfoliation from graphite produce a mass of graphene, but with structural variations in layer number, sheet size, edge type, and defect density, which strongly affect the electronic structure of graphene. For the useful application, the subsequent structural separation of graphene is mandatory.
In this study, we demonstrated simple separation of graphene using multicolumn gel chromatography. Platelet-type carbon nanofiber, starting material of graphene, was dispersed in the aqueous sodium dodecyl sulfate (SDS) solution using an ultrasonic homogenizer. During the sonication, graphene was exfoliated from the nanofiber and dispersed in the solution. To remove the untreated nanofiber, we conducted centrifugation and the supernatant was used for gel chromatography.
The graphene dispersion was separated via flowing through the allyl dextran-based gel columns in series. This method is based on the structure dependent interaction strength of graphene with the gel. At the first column, by the filtering effect, the thick graphitic fragments are separated out, and the unbound fragment consisted of thin graphene sheets. By the chromatographic separation at the subsequent columns, it was observed that the large-size graphene tends to be unbound by the gel.
In this chromatographic separation, the surfactant affinity affects the adsorption priority on the gel. It has been reported that the SDS adsorbs onto the graphene, but does not adsorb onto the graphene oxide [1]. This selective adsorption depends on the degree of oxidation, which can be explained by electrostatic repulsion between the negatively charged SDS head groups and the negatively charged hydroxyl groups on oxidized graphene[2]. The reduction of surfactant adsorption density on the graphene caused by the edge with the oxygen functional group is supposed to result in the preferential attachment on the gel surface. This scalable simple separation method will contribute to the further precise separation of graphene structure, and promote the useful applications of graphene.

[1]A. G. Hsieh et al., J. Phys. Chem. B 117, 7950 (2013).
[2]A. J. Glover et al., J. Phys. Chem. C 116, 20080 (2012).

Cymatics, proposed by Hans Jenny in 1967, is the study of the wave mechanics and visualization of sounds through vibrational phenomena of plate surface. The resultant patterns made by displacement node/antinode of the waves show highly symmetric images depending on the geometry of the plate and the driving frequency. Famous example is the Chladni patterns in which the powders or particles move due to the vibration and accumulate progressively in nodal points of the applied wave, and thus lead to spatially periodic arrangement.
In this study, we are motivated by potential of this cymatics to introduce a new approach to the micro- and nanomaterial assembly that has been a long-standing goal in the field of nanoscience and nanoengineering in general. In this work, we utilize the combination of silicon substrate as a vibrating surface and materials with different length scales from micrometer to nanometer and different geometry from particles to nanowires. Analogous to the definition of crystallographic ‘lattice’, symmetric and periodic points comprised of accumulated building blocks can be seen as ‘lattice equivalent’, resulting from material assembly. By virtue of the tailorability of the system, we deliberately control the pattern size and dimensionality and understand the wave mechanics as well. This approach is technologically unique in that (i) it is a method that enables the construction of three-dimensional nanomaterial assembly, which has never before been observed in the field of cymatics and (ii) a massively parallel method that creates arrays over macroscale areas where the total patterned area is only limited by the size of the plate surface.
Our new assembly approach has the following distinctive features that we believe provide a new route bottom-up construction. Periodic and symmetric patterns are easily made in Cartesian coordination system, where liquids on the centimeter scale plate are employed as a medium. Such founding distinguishes 2D liquid from single liquid droplet in Spherical coordination system that previous studies have focused on. Coffee-ring effect in 2D liquid is utilized to enhance the periodicity and symmetry of patterns. Strong coffee-ring effect makes the particles dispersed inhomogeneously, and thus makes the patterns composed of the particles homogeneously. We show how transparent polymer can be used as ‘three-dimensional spacer’ within nanoparticle superlattices assembled, which has never before been observed in cymatics. Consequently, we expect this versatile strategy to be widely adopted by academic and industrial researchers for rapid prototyping.

Key to achieving the hoped for improvements by using graphene as a filler in polymer composites is an understanding of the effect that processing has on the underlying composite properties. While graphene and its related materials possess superb mechanical strength, barrier properties and thermal and electrical conductivity, its structure and interactions within the polymer environment can all affect the bulk properties.^1–4

Here we study the electrical impedance and rheological properties of composites of polystyrene (PS) and graphene nanoplates (GNPs) under steady shear. We find a number of different processes occurring both rheologically and electrically within the composite, dependent on the shear rate and subsequent annealing. At lower shear rates the impedance of the composite drops under shear – a consequence of the break-up of larger discrete aggregates of the GNPs within the composite, increasing the interfacial area of the GNPs and establishing a more effective network. At higher shear rates the impedance is seen to increase, a result of alignment of the GNPs within the polymer network. Upon cessation of the shear, the impedance of the composites again changes. At lower shear rates, the impedance gradually increases to a plateau. For the higher shear rates, the behaviour is more complex, involving multiple alignment and aggregation effects. We relate these changes to the evolution of the GNP structure within the polymer, linking changes in the network structure to the stress relaxation of the polymer following cessation of the shear, and also the relaxation of the impedance under annealing.

These results add important insight and understanding to processing methods for these materials and are directly related to the composite electrical properties. Such understanding is vital for achieving the desired property improvements in the composite.

References
(1) Li, Z.; Young, R. J.; Wilson, N. R.; Kinloch, I. A.; Vallés, C.; Li, Z. Compos. Sci. Technol. 2016, 123, 125–133.
(2) Yoo, B. M.; Shin, H. J.; Yoon, H. W.; Park, H. B. J. Appl. Polym. Sci. 2014, 131 (1), 1–23.
(3) Compton, O. C.; Kim, S.; Pierre, C.; Torkelson, J. M.; Nguyen, S. T. Adv. Mater. 2010, 22, 4759–4763.
(4) Kim, H.; Macosko, C. W. Polymer 2009, 50 (15), 3797–3809.

Single-walled carbon nanotubes (SWCNTs) have been expected for various applications because of their unique characteristics. In SWCNT growth, Al₂O₃ buffer layers have been widely used to increase SWCNT yield, but the mechanism of yield increase has not been understood enough. Previously, we reported SWCNT growth using Rh catalyst on SiO₂/Si substrates and found that the SWCNTs from Rh catalyst have narrow diameter distribution [1]. In this study, we carried out SWCNT growth from Rh catalysts on Al₂O₃ buffer layers prepared by various methods and investigated the influence of Al₂O₃ types on catalyst activity.
SWCNT growth was performed using Rh/Al₂O₃/SiO₂/Si substrates at 700°C by the alcohol gas source method [1]. We used five kinds of Al₂O₃ layers; (i) Electron Beam (EB) deposition of Al, followed by oxidation in air, (ii) EB deposition of Al, followed by thermal oxidation, (iii) EB deposition of Al₂O₃, (iv) RF-sputtering deposition of Al, followed by oxidation in air, (v) RF-sputtering deposition of Al, followed by thermal oxidation. Rh catalysts were deposited on those Al₂O₃ layers by EB evaporation. The grown SWCNTs were characterized by SEM and Raman spectroscopy. The Al₂O₃ layers were analyzed by XPS, AFM and XAFS.
Raman and SEM results showed that, except for the sample (i), SWCNTs were grown and that SWCNT yield increased in the order that the samples (v) > (iv) > (iii) > (ii). XPS results indicated that Al was oxidized for all samples, but that a portion of Rh diffused into the Al₂O₃ in the sample (i), indicating that thermal oxidation process suppressed diffusion of Rh. Al K-edge XAFS spectra showed that crystallinity of the Al₂O₃ layer deposited by RF-sputtering was superior to that by EB deposition. Our results showed that crystallinity of Al₂O₃ depends on the fabrication method_, which affects the catalyst activity for SWCNT growth.

[1] A. Kozawa et al. Diamond Relat. Mater. 63 (2016) 159.

The unique properties of single-walled carbon nanotube (SWCNT) films, such as high porosity and specific surface area, low density, high ratio of optical transmittance to sheet resistance, high thermal conductivity and chemical sensitivity, and tuneable metallic and semiconducting properties, open up a new avenue for a wide range of applications. SWCNT networks have been demonstrated to show potential advantages in performance and fabrication cost reduction in comparison with ITO as well as most of organic materials that have been extensively studied as low-cost alternatives. Furthermore, high flexibility of the SWCNTs opens avenues beyond the ITO, i.e. creation of completely new components, urgently needed in the flexible and transparent electronics.

The optoelectronic performance of the produced SWCNT films depends on many parameters: quality, length, diameter, metallicity and chirality of SWCNTs comprising the film, morphology and diameter of bundles, orientation of the SWCNTs and their doping. We report the improvement of the film conductivity by tuning the parameters of SWCNTs.

We demonstrated an aerosol CVD process to dry-deposit large area SWCNT-networks with tuneable and the state-of-the-art conductivity and optical transmittance on wide range of substrates including flexible polymers. Wide application potential of our SWCNT films is demonstrated by successful applications in photovoltaic devices, supercapacitors, and the field effect transistors.

This research was supported by the Ministry of Education and Science of Russian Federation (Project DOI: RFMEFI61815X0003).

Due to their unique optoelectronic properties, single-walled carbon nanotubes become more and more popular as a sensor material for the photodetectors. Several mechanisms are responsible for the photocurrent generation in nanotubes. Although the photocurrent of individual single-walled carbon nanotubes (SWCNT) is predominantly photovoltaic in nature, in macroscale assembles of SWCNT the absorbed energy is effectively transferred to the crystal lattice and the photothermal mechanism dominates in this case. The present research is devoted to the development of a bolometric infrared detector based on free-standing aerosol synthesized carbon nanotubes and hybrid materials consisting of graphene, deposited on the surface of free-standing nanotubes film. The SWCNT films obtained with aerosol CVD method can be quickly and easily transferred to almost any substrate including structures with holes of different shapes and dimensions. It makes them convenient for mass fabrication of bolometers and microbolometers with suspended thermal isolated sensors.
Graphene in hybrid materials served as an absorber. The influence of the absorber amount on the spectral characteristics, voltage sensitivity, response time and noise equivalent power of the bolometer was investigated. The best response time was observed for the sample of pristine carbon nanotubes, whereas the hybrid sample with the largest amount of graphene showed the highest sensitivity to radiation.
The bolometric characteristics and parameters were measured for the sensors made from nanotubes of different diameters from 1 to 2 nm. It is well known that the electrical properties of the SWCNT assembles namely the temperature dependence of the resistance strongly depend on the size of the tubes. The film made from thick SWCNT demonstrates metallic behavior consisting in the resistance increasing proportional to the temperature, whereas the thin tubes have semiconducting properties and their resistance decrease as temperature rises. The temperature coefficient of resistance (TCR) of semiconducting nanotubes in low temperatures is higher than TCR of the metallic tubes. Thus, the bolometric sensors made from semiconducting tubes perform much higher sensitivity in liquid nitrogen temperatures than metallic tubes sensors. Additionally, the dependencies of bolometric parameters on the ambient pressure and temperature were measured and analyzed, which allowed us to define the most optimal conditions for bolometers.

Because of its outstanding characteristics, graphene is highly expected to apply in a wide range of fields, such as electrical wiring, and transparent electrodes of light emitting diodes (LEDs). In recent years, a direct growth of graphene on a substrate has been studied for the advantages of device applications. We have already succeeded in a direct growth of multilayer graphene on sapphire substrate by precipitation method using W capping layer [1]. However, it is necessary to lower the process temperature, for example, less than 700 ^oC in order to avoid a thermal-destruction of devices in opto-electric integrated circuits. Although there are some reports about low-temperature direct-growth of graphene, their properties are still inferior to those of high-temperature grown ones [2]. This study examines to improve the quality of multilayer graphene directly grown at low temperature by using crystalized Ni catalyst and changing the cooling rate during precipitation.
Ni (300 nm) layer was deposited on a sapphire (0001) substrate using electron-beam deposition. The layer was crystalized with annealing at 700 ^oC. After the crystallization of the Ni layer, amorphous carbon (a-C) (1 nm) and W (20 nm) were deposited. Then, the samples were annealed at 700 ^oC for 30min in vacuum and cooled with cooling rate of 10 ^oC / min (slow cooling). Finlay, the catalyst layers were removed using a dilute aqua regia solution in order to directly observe the graphene on the substrate. The samples were evaluated using Raman scattering spectroscopy.
The narrow G and G’ peaks in Raman spectra indicate that multilayer graphene was successfully precipitated on the sapphire substrate. D/G ratio of the sample precipitated with a slow cooling was as low as 0.10, which was lower than that of 0.14 of the sample precipitated with a conventional rapid fan-cooling. However, these values were much smaller than that of 0.30 of a sample grown without the Ni crystallization. The estimated grain size of the graphene from its D/G ratio [3] was 62 nm for the conventional process, while those of the samples with Ni crystallization were 184 nm and 140 nm with and without slow-cooling, respectively. The grain size of the graphene was possibly increased by the smooth and large-size of grains of the crystallized Ni layer. The small supersaturation during the precipitation caused by the slow cooling is thought to be beneficial for controlling the low density of nucleation and, consequently, the large size of the grains.
Acknowledgement: This work was supported in part by JSPS KAKENHI Grant Numbers 2660089, 15H03558, 26105002, 25000011.
Reference:
[1] J. Yamada et al. MRS Fall Meeting & Exhibit, (2015) Q3.69.
[2] J. Sun et al. Nano Research, 8 (2015) 3496-3504.
[3] M. A. Pimenta et al, Phys. Chem. Chem. Phys., 9 (2007) 1276–1291.

Ultrathin film graphene-polymer nanocomposites demonstrate the ability to make highly stretchable and electrically conductive thin films as a potential organic electrode using facile and cost-effective layer-by-layer (LbL) assembly of graphene nanoplatelets (GNPs), stabilized with poly(4-styrenesulfonic acid), and assembled with poly(vinyl alcohol). This technique integrated high electrical conductivity, controllable resistance sensitivity, efficient energy conversion due to noticeable triboelectric performance, excellent oxygen barrier property, and good flame retardancy into a single film, which was rarely reported in other kinds of thin films prepared by solution processing.
A 200 nm film has ~ 1000 Ω/sq sheet resistance following brief exposure to nitric acid (HNO₃) vapor. Raman and x-ray photoelectron spectroscopy proved that the effects of HNO₃ treatment originated from the removal of polymeric components, restricted to the film surface, rather than chemical doping of graphene. These unique thin films are potentially useful as flexible electrodes for a variety of electronic applications. One possible application is a graphene strain sensor. The research reports the fabrication of thin film graphene strain sensors coated on stretchable yarns. Highly stretchable, sensitive, and wearable sensors are realized by a graphene LbL assembly method, indicating up to 150% stretchability and versatility available of detection of both large- and small scale human motions. Another application can be a triboelectric nanogenerator (TENG) by the different triboelectric series between a graphene LbL electrode and a flexible plastic substrate. This nanosheet-dispersed film also provides a tortured pathway for oxygen gas molecules that reduced the gas permeation rate and an increasing char forming that preserved the structure of cotton fabric by ceramic surface layer char.

There is significant interest in the use of carbon nanotube (CNT) based cathodes for improving output power and efficiency in high power microwave devices. In the current work, we explore the effects of tube-tube interactions on the characteristics of field emission using density functional theory (DFT). We obtain predictions of field emission current structures consisting of multiple tubes in selected relative orientations and spacing. We employ DFT+D2 to correctly describe the graphitic dispersion surface interaction and thus achieve correctly optimized inter-tube configurations. We simulate field emission current from multiple CNT arrangements via time-dependent DFT (TD-DFT). TD-DFT simulations were performed in a finite computational domain with appropriately shaped absorbing boundary potentials to allow charge migration out of volume boundaries and allow long time evolution. Configurations studied include chemically bridged arrays and simulated substrates.

Electrically conducting lightweight materials that provide reduce manufacturing costs, processing flexibility, and durability in harsh environments demonstrates a great potential for aerospace applications. Although many attempts have been made to manufacture light weight polymer composites, fabrication of light weight metal composites remains a challenge toward further enriching their industrial application. Here, we introduced the deterministic approach to fabricate an electrically conducting light weight halogen intercalated graphite incorporated metal composites, and their electrical properties have been tailored precisely to match or exceed significantly with the electrical properties of pure metal. Composites have been prepared by two steps. In first steps, we did the production of halogen intercalated graphite filler, and it was then confirmed by TEM, SEM-EDS, XRD, and Raman. The charge transfer between halogen and graphene layers in graphite alters the number of charge carriers, which expands the Vander Waals gap between two graphitic layers, resulting decrease in the resistivity of graphite. In second step, consolidation of such halogen intercalated graphite filler with metal nanopowder shows a low electrical resistivity, which surpasses the best values of metals, and also with reduced density than other carbon-based metal composites. Importantly, this approach is facile and providing a universal route for the rational design and engineering of highly conductive light weight metal composites.

In this presentation, we introduce our results on the temperature (T) dependence of electrical resistance in graphene, measured between 10 and 400 K. Graphene samples were prepared on various substrates; SiO₂, h-BN and HfO₂. The resistivity of graphene shows a linear T-dependence at low T and becomes superlinear above ~100 K for graphene prepared on HfO₂ substrate. The transition temperature strongly depends on the substrates. We find ~150 and ~200 K for graphene on SiO₂ and on h-BN, respectively. Surface optical phonon energies of HfO₂, SiO2 and h-BN are 21, 59 and 101 meV, and our results can be explained by the remote interfacial phonon scattering by the surface optical phonons of the substrates.

Graphene based photodetectors have attracted wide interests due to their high-speed, wide-band photodetection, and potential as highly energy-efficient integrated devices. However, the inherently low absorption cross section and non-selective spectra response hinder its utilization of high performance pho todetector. Here, we report a solution-processed and high spectral selectivity photodetector based on gold nanorods (Au NRs)-graphene heterojunction with near-infrared (NIR) detection. Au NRs are used as subwavelength scattering source and nanoantennas with wide light absorption range from ultraviolet to near infrared via tuning their geometry. And photons couple into Au NRs excite resonant plasmas and generate hot carriers, which pump into graphene, resulting into selective NIR photodetection. A flexible NIR photodetector is also demonstrated based on this simple structure. Au NRs can achieve variable resonance frequencies by designing different aspect ratio as nanoantenna for graphene, which promises selectively amplifying the photoresponsivity and enabling highly specific detection.

In this presentation, we discuss Raman spectra of scrolled graphene structure. We scrolled monolayer graphene by applying a droplet of isopropyl alcohol (IPA) solution (IPA/water~1:3) to the exfoliated graphene on substrate. In Raman spectroscopy, we have observed peculiar low-frequency Raman peaks below 120 cm^-1 only at certain positions of the scrolled graphene. The low-frequency Raman properties of the scrolled graphene are clearly distinguished from the radial breathing mode (RBM) of carbon nanotubes, but similar to the layer breathing mode and the shear mode in twisted multi-layer graphene. From the similarities of Raman spectra between the scrolled graphene and the twisted multi-layer graphene, we argue that in such specific locations layers in the scrolled graphene encounter specific twisted angle between layers and result in the peculiar low frequency Raman peaks.

Ionic liquid (IL) has been adopted as gate dielectric layer for graphene field-effect transistors (GFET).[1] Due to its short effective distance (~7 Å) between charged ion and graphene surface, the dielectric can accumulate charge on graphene with lower gate voltage than SiO₂ layer[2]; thus, IL gated GFET can be operated in low voltage condition. In this study, we obtained dielectric constant of IL layer by applying dual-gate-electrodes on the GFET.

For back gate electrode, we prepared h-BN layer on SiO₂/Si substrate and transferred graphene on top of the h-BN to improve flatness and electrical properties of graphene, where h-BN and SiO₂ is gate dielectric and Si substrate with high doping level is gate electrode; both graphene and h-BN are mechanically exfoliated. And we patterned electrode on graphene by e-beam lithography method and deposited Pd/Au metal electrode with e-beam evaporator. After lift-off process, we dropped ionic liquid compound on top of device and harden as gel state by exposing UV light.

We applied both top- and bottom-gate voltage through IL and h-BN/SiO₂ layer, respectively, to obtain dielectric constant ratio between top and bottom dielectric. We measured Dirac point of graphene by varying top-gate voltage with fixed bottom-gate voltage. Then, we observed the Dirac point increases as we decrease the bottom-gate voltage. By comparing how sensitively the Dirac point moves according to the top- and bottom-gate voltage, we measured the ratio of top- and bottom-gate dielectric as 53.66. In this way, we obtained dielectric constant of IL as 0.4578; it is that of 5.46-nm SiO₂.


References
[1] B.J. Kim, J.H. Cho et al., High-Performance Flexible Graphene Field Effect Transistors with Ion-Gel Gate Dielectrics Nano Lett. 2010, 10 (9), 3464-3466
[2] P. Simon and Y. Gogotsi, Materials for electrochemical capacitors Nature Materials 2008, 7, 845-854

A method is described to fabricate self-organized titanium dioxide (titania; TiO₂) nanotube arrays for energy storage applications. This facile method enables modification of the crystal structure of titania nanotubes in order to overcome their limitation of high resistivity and harvest high charge storage accumulation. The titania nanotubes are grown by anodic oxidation of titanium foil in a fluorine-containing electrolyte and subsequently exposed to an inert atmosphere under various heat-treatment regimes. Integrating these nanostructures into a binder-free working electrode results in a capacitance of up to 2.6 mF cm^-2, which exceeds the values so far reported for unadulterated titanium oxides in the literature [1,2]. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), cyclic voltammetry (CV), charge discharge (CD), and electrochemical impedance spectroscopy (EIS) reveal the structural as well as the physical and electrochemical properties of the tailored TiO₂ nanotube materials.

1. Salari, M., et al. Enhancement of the electrochemical capacitance of TiO2 nanotube arrays through controlled phase transformation of anatase to rutile. Physical Chemistry Chemical Physics, 2012,14, pp.4770-4779
2. Salari, M., et al., Enhancement of the capacitance in TiO₂ nanotubes through controlled introduction of oxygen vacancies. Journal of Materials Chemistry, 2011, 21(13): pp. 5128-5133.

Due to high mobility and atomic thickness, graphene is a promising candidate for the next-generation electronic material. While considerable effort has been devoted to achieve higher mobility in graphene films, relatively little attention has been paid to the effect of forming contacts between graphene and metal, which are indispensable to the electric devices. In general, at a graphene/metal interface, mainly due to the difference in work functions, carriers are injected from the metal to graphene. The resulting shift of local Dirac point is not limited at the graphene/metal interface but extends by ~1 micron into the graphene channel. This carrier doping affects more significantly the performance of graphene field effect devices with shorter channel, as well as may conceal Dirac physics at the graphene/metal interface such as the relativistic superconducting proximity effect.
Here, we experimentally investigate the channel length dependence of graphene transport properties and extract the effect of metal contact. Several metal species are investigated and results are compared with numerical models. We reveal that the metal contact causes additional Dirac point in the gate voltage dependence of conductivity, and discuss the effective work function of graphene (4.93 eV) and the chemical interaction in a graphene/metal interface. Furthermore, we succeed in removing the influence of metal contact by inserting a thin nano-carbon layer (amorphous carbon or multilayer graphene (MLG)) at the interface. We conclude that the MLG interfacial layer is more suitable due to smaller increase in the contact resistance.

Graphene is a two-dimensional carbon nanomaterials with superior electronic, thermal, and mechanical properties and currently explored in advanced electronics, transparent protective coating, energy storage devices and polymer composites. It is highly desirable to economically produce high-quality graphene in industrial quantities to commercially realize its applications; however, no scalable method exists. Mechanochemical approaches to graphene nanosheets synthesis offer the promise of improved yields, new reaction pathways, and greener and more efficient syntheses, making them potential approaches for low cost production of graphene nanosheets.
Here we report the scalable production of single- and few-layer graphene nanosheets with low defect densities by an efficient water-assisted mechanochemical exfoliation of graphite in N-methylpyrrolidinone (NMP). The mechanochemical exfoliation could be further improved by applying high speed homogenization and ultrasonication as pretreatments. It is found that the former step homogenized the graphite-solvent solution while the latter provided sufficient energy to weaken the van der Waals interactions and promoted the intercalation of solvent molecules into the graphene sheets within bulk graphites. Significantly, when NMP with water was employed as the cosolvent in the mechanochemical exfoliation, it was found to be possible to produce graphene nanosheets with less defect.
Detailed materials characterization including transmission electron microscopy, Raman spectroscopy, and UV-Vis absorbance spectroscopy suggest that single- and few-layer graphene nanosheets were successfully prepared with the concentration and yield up to 15.8 mg/mL and 31.5%, respectively. The yield may be further improved by optimizing the process conditions. Our work provides a guide of rational design of a solvent system to improve the yield and stability of the exfoliated materials.

Due to high mobility, graphene is a promising candidate for electronic materials. However, for successful application of graphene to switching devices, gap formation is indispensable. In this study, we explore the gap formation in graphene based on strain engineering. We focus on two kinds of strain configurations: uniaxial local strain and periodic uniaxial strain.
From our previous study, it is known that the gap formation by uniaxial local strain requires a long electron mean free path. To elongate the electron mean free path, we used graphene sandwiched between hexagonal boron nitride (hBN) films with corresponding convex-concave surfaces. In the sample fabrication, we used van der Waals dry transfer and edge contact techniques. From micro Raman spectroscopy, the maximum strain was estimated to be ~ 0.13 %. In transport measurement, the conductance decreased with decreasing temperature within the whole gate voltage range. The minimum conductance exhibited thermal activation behavior within a high temperature range (300 K - 40 K), indicating the existence of a transport gap. The estimated gap value of 3.2 meV was consistent with the value expected from the spatial variation of strain in this sample.
For the periodic uniaxial strain, a band gap has been observed only in scanning tunnel spectroscopy, while it has not been confirmed in actual field effect devices. This missing gap is presumably due to the relaxation of strain in device fabrication processes. Here, we develop a novel device fabrication method which makes graphene largely strained even after the formation of electrical contacts. In this method, a graphene film is placed on a periodic array of resist HSQ bars. The introduction of strain was confirmed with micro-Raman spectroscopy. The back gate voltage dependence of the conductance in the strained graphene exhibited remarkable difference from the conventional V-shaped curve observed in graphene placed on SiO2. The minimum conductance showed thermal activation behavior at high temperatures (> 50 K). From the Arrhenius plot, the band gap was estimated to be ~ 2.4 meV. Besides, the current-voltage characteristics became nonlinear around the origin. The high resistance region extended within +/- 2 meV at the gate voltage corresponding to the minimum conductance. This value agreed well with the band gap estimated from the temperature dependence. These observations confirm the formation of the band gap in our graphene with periodic uniaxial strain.

Graphene-based nanostructures have been investigated as very promising candidates for water filtration and separation membranes. Experimental evidences have shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules [1-2]. This phenomenon has been attributed to the formation of a network of nano-capillaries that allow nearly frictionless flow water while blocking other molecules by steric effects. It is supposed that water molecules are transported through the percolated two-dimensional channels formed between graphene-like sheets. Despite the last evidences of fast permeation of water in such materials, the flow rates are strongly dependent on how the membranes are fabricated. Also, some fundamental issues regarding the nanoscale mechanisms of water permeation are still not fully understood and their interpretation remains controversial. In this work we have investigated the dynamics of water permeation through graphene and GO model membranes. We have carried out fully atomistic classical molecular dynamics (MD) simulations of system composed of multiple layered graphene-based sheets having nano-slits in a staggered alignment, with a variety of inter-layer distances, and into contact with a water reservoir under different thermodynamics conditions (e. g. T, P). We have systematically analyzed how the transport dynamics of the confined nanofluids depend on variables such as; interlayer distances, slit widths and oxide functional groups percentage. Our results are consistent with the available experimental conditions and clarify some important aspects of the anomalous behavior of confined water in GO membranes [3].
[1] R. R. Nair et. al. Science 2012, 335 (6067), 442-444
[2] R K. Joshi et. al. Science 2014, 343 (6172), 752-754
[3] D. D. Borges, C. Woellner, P. A. S. Autreto and D. S. Galvao, submitted.

Millimeter sized single crystal graphene has promising technological values as it can directly be integrated in the nanoscale devices for various applications. The synthesis of large sized single crystal graphene by chemical vapor deposition (CVD) is largely limited by the substrate topography, its cleanliness, and defects on it. Here, we report the synthesis of submillimeter sized single crystal single, bilayer, and few-layer graphene at low methane concentration and moderate chamber pressure in the hot filament chemical vapor deposition on the copper foil cleaned by electropolishing method. The electropolishing of copper was performed in order to obtain ultraclean, defect minimized, and smooth surface. In the cleaning process, phosphoric acid was used as an electrolyte and stainless still as the counter electrode. Ethylene glycol was also added to the solution to reduce the defects formed on the copper substrate during the electropolishing process. The synthesized graphene crystals vary in size ranging from about 50 to 400 . The synthesized graphene single crystals were characterized by Raman spectroscopy, confocal optical microscopy, and high resolution transmission electron microscopy. Our results show possibility of millimeter sized single crystal graphene synthesis on copper foil suitable for fabricating highly efficient practical devices.

Graphene's unique optoelectronic properties have spurred interest in a range of photodetection applications. Here we present progress towards incorporating high-responsivity, high-speed graphene photodetectors on photonic integrated circuits. First, we demonstrate a waveguide-integrated graphene detector on a zero-change commercial foundry CMOS chip. The silicon device layer of an SOI CMOS process is used to construct waveguides as well as electronics to amplify the photodetector signal. Removal of the silicon substrate and thinning of the burried oxide layer allows graphene to be placed within the waveguide mode. To our knowledge, this is the first demonstration of a waveguide-integrated graphene detector on a commercial CMOS chip and paves the way for integrated photonics based on graphene active devices. Second, we demonstrate integration of graphene photodetectors with chalcogenide glass waveguides to detect light at a wavelength of 5.2 μm. Calcium fluoride is used as the substrate due to its transparency at the desired wavelength and its low refractive index. This research has applications in chip-integrated mid-IR spectroscopy, useful for medical chemical sensing.

Kirigami is the Japanese technique of cutting, folding and gluing papers to generate 3D structures. It has emerged as a potential tool for the design of mechanical metamaterials whose properties can be tailored using purely geometric principles [1-3]. Recently [1], the experimental realization of different graphene kirigamis was reported. Graphene membranes possess exceptional mechanical properties, being the ultimate 2D planar material (just one atom thick). They exhibit very high stiffness and strength, making them suitable to various mechanical and structural applications. However, graphene is also known to be brittle, fracturing easily at small deformations. The kirigami concept has been applied to dramatically enhance its stretchability. In this work we have used fully atomistic reactive molecular dynamics simulations to investigate the mechanical properties of graphene pyramid kirigamis.
The pyramid kirigami structures were generated from a large graphene sheet where parts were removed (cut) accordingly to a pattern to form a 2D projected pyramid-like structure. This initial 2D structure assumes a characteristic 3D pyramidal shape when subject to an external force applied perpendicular to its basal plane.
We then used classical molecular dynamics simulations to characterize the response of the material when subject to externally applied loads. Our results show that the structure can exhibit very large deformations even with small load values and it goes much beyond the breaking deformation limit of its parent graphene structure. We have also simulated ballistic impacts using a large silicon projectile shot against the kirigami structures. Our results showed that the kirigami configuration is many times more efficient than its equivalent graphene form to absorb impacting kinetic energy and/or to stop ballistic projectiles, making it a very good candidate for ballistic protection applications [4].
[1] M. K. Blees et al., Nature v525, 204 (2015).
[2] T. C. Shyu, Terry C., et al., Nature Mater. v15, 785 (2015).
[3] Z. Qi, D. K. Campbell, and H. S. Park. Phys. Rev. B 90, 245437 (2014).
[4] F. A. Moura, P. A. S. Autreto and D. S. Galvao, submitted.

New types of textile fibers that conduct electricity have been an emerging topic that has occurred in the last decade or so. This newfound interest is mainly due to the discovery of graphene and carbon nanotubes (CNTs) and the astounding electrical properties that it provides, which allows for textiles that are strong as well as able to carry electrical current without much resistance. These advances are useful because in the field these textiles have a variety of potential uses, mainly the ability to be structurally strong while at the same time be sensors for a variety of measurement types. Sensors such as conductive fibers for measuring joint movements, unobtrusive vital sign detection systems, and the ability to detect damage in a textile or composite material are all uses for conductive fibers that have been investigated. In the context of flexible body armor, which is mainly made of Kevlar weaves, the ability to electronically detect damaged fibers could be useful in assessing whether or not the integrity of the armor has been compromised.
Kevlar by and large is an insulator and is known for its low thermal conductivity. The first part of this study will be to investigate methods and procedures to dye Kevlar KM2 yarns in order to make them conductive. Current methods call for coatings with CNTs or graphene nanoribbons. The coating methods will be developed and experimented with in-house in our Advanced Materials and Structures Laboratory (AMSL). The infusion of graphene nanopowders as well as graphite flakes will also be investigated.
The second part of this study involves first determining the base resistivity range of the fibers that are produced and investigating the relationship between stress applied to the fibers, the strain exhibited by the fibers, and the change in resistance as these fibers are strained. An Instron tensile test machine outfitted with fiber clamps in conjunction with a four-probe resistance testing multi-meter would be used to perform these kinds of tests. Additionally, standard tensile tests will be able to determine if graphene-infused fibers are structurally as strong as standard Kevlar fibers. Preliminary tests have been performed on proprietary conductive fibers supplied by NASA. Currently there needs to be more construction on this experimental aspect of the setup; results are not conclusive since data recording by the multi-meter needs to be synchronized to the time-load-displacement data output by the Instron machine to achieve accurate results.

Hot filament chemical vapor deposition (HFCVD) is a versatile technique suitable for industrial scaling of high quality carbon nanomaterials including graphene, due mainly to its filaments which can be heated to a wide range of temperature for dissociating the precursor gas molecules. We report here the layer number controlled synthesis of high quality and large area graphene of large crystallite size on copper foil by using methane as the carbon precursor gas. We show that suitable combinations of different growth parameters such as substrate to filament distance, substrate heater temperature, temperature of the filaments, methane concentration, deposition time, and total gas pressure in the chamber lead to the controlled growth of monolayer, twisted bilayer, and few-layer graphene of crystallite size ranging from about 1 to 10 μm. The graphene was characterized by Raman spectroscopy, optical, atomic force, and high resolution transmission electron microscopy for determination of the quality and number of layers. The grain size of the graphene was measured by optical imaging of the selectively oxidized underlying copper foil through graphene grain boundaries via ultraviolet irradiation under moisture-rich ambient conditions. The measured sheet resistance of monolayer and bilayer graphene are 460 Ω/sqr and 285 Ω/sqr respectively, and goes as low as 120 Ω/sqr for few-layer graphene. Based on the results obtained, a detailed mechanism of graphene synthesis in the HFCVD is proposed, and a miraculous role of filaments on the graphene growth is explained. We conclude that HFCVD has an advantage over conventional thermal CVD especially for high quality bilayer and few-layer graphene growth on copper.

Efficient exfoliation of graphite in solutions to obtain high quality graphene flakes is desirable for technologies such as printable electronics, catalysis, energy storage, and composites where large quantities of the material are required. However, low yields of single-layered graphene, submicron lateral dimensions, and poor electronic properties remain as major challenges for solution exfoliated graphene flakes. Oxidation of graphite and its subsequent exfoliation into monolayered graphene oxide (GO) with large lateral dimensions has an exfoliation yield of ~ 100% but despite numerous efforts, it has not been possible to completely remove the oxygen functional groups so that the reduced form of GO (rGO) remains a highly disordered material with properties that are generally far inferior to chemical vapor deposited (CVD) graphene. While rGO has been widely demonstrated to be potentially useful material for catalysis and energy storage even in its disordered form, efficient reduction of GO into high quality graphene should lead to substantial enhancement in performance. Here, we demonstrate a simple and quick method to reduce GO into pristine graphene using 1 – 2 second pulse of microwaves. The microwave reduced GO (MW-rGO) exhibit pristine CVD graphene-like features in the Raman spectrum with sharp G and 2D peaks and nearly absent D peak. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission microscopy (HR-TEM) suggest highly ordered structure in which oxygen functional groups are almost entirely removed. These results suggest that reduction of GO using microwaves is highly efficient and realizes the goal of achieving high quality graphene with excellent properties by solution exfoliation.

Graphene has attracted a tremendous attention as nanofiller due to its special properties. However, untreated graphene has a tendency to aggregate each other by π–π interaction. In this work, hyperbranched polymer (HBP) was grafted on the surface of graphene oxide (GO) for improving dispersion capability of graphene nanosheets. HBP-functionalized GO (HGO) was synthesized by ring-opening polymerization of latent AB₂ type monomer using hydroxyl groups of GO as initiators. FT–IR, XPS, TGA, Raman, XRD analyses indicated that GO was successfully functionalized with HBP and HBP exfoliated the graphene nanosheets individually. In order to investigate filler effects of HGO for poly(vinyl chloride) (PVC), a series of PVC/HGO was prepared by the variation of HGO content from 1 to 5 wt%. From DSC and TGA, the glass transition temperature (T_g) and thermal stability of PVC/HGO were considerably increased indicating that HGO can improve the thermal properties of PVC. Moreover, the tensile strength and toughness was increased with an increase in HGO content until 3 wt%. The results indicated that homogeneous dispersion and strong interfacial interaction of HGO enhanced the mechanical properties of PVC. Gas barrier property was estimated by the oxygen transmission rate. PVC/HGO composites also exhibited better gas barrier property than neat PVC. Therefore, we expected that hyperbranched polymer-functionalized graphene oxide would be a promising nanofiller for improving the thermal, mechanical, and gas barrier properties of PVC.

Abstract
Transparent electrodes with excellent flexibility as well as good electrical and optical properties are required for application of wearable electronics. Graphene has attracted much attention in the field, but still modification of graphene is required to solve conductivity or stability problems.¹ Dopamine, which contains catechol and amine groups, and its polymerized form, known as polydopamine, form strong covalent and noncovalent interaction with arbitrary substrates. Inserting dopamine between two graphene layers would improve the mechanical property of graphene layers and change the electronic band structure of graphene by the strong interaction between dopamine and graphene. In this presentation, we show graphene/dopamine/graphene (GDG) and graphene/polydopamine/graphene (GPDG) sandwich structures and investigate their electrical and mechanical properties. The GDG sandwich structure was prepared by coating dopamine on a graphene layer and transferring another graphene layer. And, the GPDG sandwich structure was prepared by heating the GDG at 180 celsius degree for 3 hours. Polymerization of dopamine was characterized by C 1s and N 1s binding energy peaks by X-ray photoelectron spectroscopy. Improved conductivity was confirmed by measurement of the sheet resistance. The sheet resistance values of the GDG and GPDG structures were 295 and 344 ohm/square, respectively, which are lower than the sheet resistance value (~640 ohm/square) of the graphene/graphene (GG) structure. The improved conductivity remained constant for 45 days. Furthermore, the GDG and GPDG structures showed better stability in the bending test than the GG structure. Nanoindentation measurement also exhibited that the GPDG structure has higher Young’s modulus value (~105 GPa) compared to the GDG (~85 Gpa) and GG (~70 GPa) structures.

Reference
[1] Xu, Y., Liu, J. Small 12, 1400 (2016).

Recent work shows that graphene grown on Ge(001) is epitaxially oriented in several domains with respect to the substrate. In addition, graphene growth induces a 4-fold faceting of the Ge surface with facets being identified as {107}.[1]

To expand our understanding of the faceting, we synthesize graphene via chemical vapor deposition on Ge(001) miscut 6 degrees towards [110]. The resultant surface is faceted with a 2-fold symmetry. We identify the facets by using reflection high-energy diffraction (RHEED). The 6-degree miscut Ge(001) can also be called a ~ (1 1 13) oriented surface. The 2-fold facets are observed with the incident beam in the azimuthal direction pointing up or down the miscut-induced staircase, e.g., (13, 13, -2). They are consistent with (2, 0, 13) and (0, 2 13) orientations. These orientations are nearly the same as those on Ge(001) and in the same family as the commonly observed {1 0 5} facets found for Ge growth on Si(001). This faceting will be compared to that observed on other low-index germanium facets after graphene synthesis.

We also investigate the effect of post-growth annealing at different temperatures on the faceting, for both full and partial coverages of graphene. Facet angles and morphology are explored with RHEED and atomic force microscopy; the strain in the graphene is determined using Raman spectroscopy. Mechanisms that may lead to the faceting, including processes that are thermodynamically driven and strain driven, will be discussed in the context of our results.

[1] R. M. Jacobberger, B. Kiraly, M. Fortin-Deschenes, P. L. Levesque, K. M. McElhinny, G. J. Brady, R. R. Delgado, S. S. Roy, A. Mannix, M. G. Lagally, Direct oriented growth of armchair graphene nanoribbons on germanium. Nature communications 6, (2015).

Supported by DOE

Atomically thin materials such as graphene, silicene, transition metal dichalcogenides, and phosphorene have greatly attracted attention due to rich physical properties. One of the important aspects of those materials is their extraordinal flexibility owing to their single atomic layered structure. There have been studied of the strain effect on electronic properties in atomically thin materials. These include, for instance, the modification of electronic properties in various materials, the enhancement of a chemical reactivity, and the improve of the thermoelectric performance in phosphorene. However, phonon properties of atomically thin layered materials associated with the strain have not extensively been investigated.
In the present paper, we examine the strain dependence on phonon dispersions and a specific heat by performing the first principles calculation based on the density functional theory. For the phonon dispersion, we focus on the high-energy and low-energy region of the phonon modes. We found that the high-energy phonon modes show the softening due to the strain. In particular, the G-modes exhibit the red-shift with the energy splitting as a function of the strain. Furthermore, it has been shown that the split of these are different for the strain of the zigzag direction and armchair direction. On the other hand, the low-energy acoustic modes exhibit the hardening; the dispersion relation of the out-of-plane mode essentially changes from the quadratic to the linear associated with the strain. The comparison between the first principles result and the analytical result explains this modification in terms of the ratio of the nearest-neighbor and the next-nearest-neighbor force constants. To see the effect of the strain-induced phonon modification on thermal properties, we calculated a specific heat. We show that the classical limit of a specific heat achieves faster for the larger strain. This originates with the softening of the phonon mode due to the strain. We also elucidate that the temperature dependence of the low-temperature specific heat also changes from the linear to the quadratic. We ascribe this to the different wavenumber dependence of the phonon dispersion in the presence of the strain.

In this talk, I will discuss our recent progress in carbon nanotube sorting. Our method using recoverable polymers and low cost large-scale available carbon nanotubes can produce high purity semiconducting carbon nanotubes at large scale and low cost. This opens up possibilities for scalable practical applications for flexible and stretchable electronics.

Scaled separation of single-wall carbon nanotube (SWCNT) populations with completely specified physical structures is a primary milestone necessary for enabling SWCNT-based technologies. Aqueous two-phase extraction (ATPE), in which the spontaneous phase separation of an aqueous polymer mixture is utilized to spatially separate solutes on the basis of their chemical potential difference for the two phases, is a promising technology for achieving this milestone. By implementing multistage iterative separations using surfactant composition gradients, either stepwise or through an automated process, many individual species of SWCNT have been isolated, with isolation for some species to the level of specific left, or right,-handed enantiomer. Additionally, combination of ATPE with separately developed methods for length separation and endohedral volume specification will demonstrate the progress towards the total structure control goal.

Single-walled carbon nanotubes (SWCNTs) have considerable potential in future nanoscale electronics because of their superior electrical characteristics. However, there are two main challenges facing SWCNTs-based transistors. The first challenge is the coexisting of metallic (m-) and semiconducting (s-) SWCNTs in the as-synthesized samples. For the separation of s- and m-SWCNTs, the regular separation methods are easy to introduce damage or contamination. The second challenge is the difficulty to place the SWCNTs over a large area. Therefore, it will be a significant advancement for the development of a highly efficient and nondestructive method to prepare high percentage s-SWNTs on arbitrary substrates without any post-synthesis purification or separation.
Magnetic field, as a facile and nondestructive tool, could be an ideal strategy to separate m-/s-SWNTs that based on their difference of magnetic susceptibilities. Here, we design a novel magnetic field-assisted floating catalyst chemical vapor deposition (CVD) system to separate m-SWCNTs from s-SWCNTs. Briefly, the m-SWCNTs are attracted toward the magnetic pole, leaving the s-SWCNTs to the substrate. By using this strategy, the s-SWCNTs with purity of 99% have been obtained, which is enough to construct a high-performance transistor with mobility of 230 cm² V^–1 s^–1 and on/off ratio of 10⁶. We also establish a model to quantitatively calculate the percentage of the m-SWCNTs on the substrate and this model show a good match to the experimental data. Furthermore, our rational design also provides a new avenue for the growth of SWCNTs with specific chirality and manipulated arrangement due to the difference of magnetic susceptibilities between different diameters, chiralities, and types.

Single-walled carbon nanotube (SWCNT) networks deposited from a purple (6,5) single chirality SWCNT aqueous solution were electrically characterized as pure semiconductors based on metal/semiconductor Schottky contacts using both complex instrument and portable device. Both large scale PMOS (p-type metal-oxide-semiconductor) and NMOS (n-type metal-oxide-semiconductor) devices were fabricated on these (6,5) SWCNT thin films showing fA off current and I_ON/I_OFF ratio > 10⁸. The CMOS (complementary metal-oxide-semiconductor) inverter was demonstrated by wire bonding PMOS and NMOS (6,5) SWCNT TFTs together to achieve the voltage gain as large as 52. The single chirality and uniform diameter of (6,5) SWCNT can mitigate the variation of carbon nanotube electric properties, and chemical and bio interfaces, rendering promising carbon nanotubes for practical applications in electronics and bio-sensing.

Despite many years of worldwide efforts, there is still no established method available for producing large-area single-domain films of highly aligned, densely packed, and chirality-enriched single-wall carbon nanotubes (SWCNTs). Here, we have developed a new process of vacuum filtration to produce a wafer-scale (i.e., inch-size) film of aligned SWCNTs [1]. This method works for SWCNTs synthesized by various methods and can be scaled up in all three dimensions. We fully characterized the produced large-area films through different microscopy, spectroscopy, and transport methods, demonstrating nearly perfect global alignment with extraordinary photonic and optoelectronic properties. The strikingly high degree of alignment of our films with a nematic order parameter of ~ 1 and a thickness of ~ 100 nm distinguishes our method from both existing two-dimensional and three-dimensional post-growth assembly techniques. We investigated the underlying mechanisms based on a proposed model of two-dimensional confinement induced phase transitions. We identified the factors that affect the degree of alignment, including the filtration speed, the SWCNT concentration, the surfactant concentration, the hydrophilicity of the filter membrane surface, the SWCNT length, and the SWCNT diameter.

1. X. He, W. Gao, L. Xie, B. Li, Q. Zhang, S. Lei, J. M. Robinson, E. H. Hároz, S. K. Doorn, R. Vajtai, P. M. Ajayan, W. W. Adams, R. H. Hauge, and J. Kono, “Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes,” Nature Nanotechnology, published online on April 4, 2016, doi:10.1038/nnano.2016.44.

Complex surface topographies emerge in ultrathin-layered materials undergoing large mechanical deformations. Yet, the ability to independently engineer feature size and orientational order across multiple length scales remains a challenge. In this study, we demonstrate hierarchical graphene surface architectures generated using various sequences and combinations of extreme mechanical deformation. The method involves multiple cycles of compression driven by thermal actuation of pre-stretched polymer substrates followed by polymer dissolution, graphene film transfer, and recompression. In each generation, the compression can be biaxial (2D) or unidirectional (1D), and the 1D contraction step can be aligned parallel or perpendicular to the previous step, leading to a family of different hierarchical wrinkle/crumple textures. Analysis of the three-generational genealogy of these graphene films shows that both directionality and sequence play a role in final texture, and that the characteristic length scale of the features increases with subsequent generations. This behavior can be explained through the increase in effective film thickness (which is directly related to feature size) as complex, out-of-plane textures are added in each successive generation. These films show systematic increases in hydrophobicity and electrochemical current density with each successive generation, and the final product of three-generational extreme compression shows superhydrophobicity (static contact angle >160 degree) and high electrochemical activity (20-fold increase in comparison with planar GO film). We believe this texturing concept can be extended to other 2D material films and has potential applications in anti-fouling substrates, stretchable electronics and advanced electrode architectures.

Reliable contact formation and controlled interfacing with conventional dielectrics or barrier films remains a critical issue for almost any nanomaterial, in particular 2D materials on which physical or atomic-layer deposited (ALD) thin films typically show Volmer-Weber-type island growth. Early attempts to grow ALD layers directly on graphene resulted in inhomogeneous film growth, hence often seed layers are used which however can negatively affect the as-grown interface. Here we present a detailed study of ALD Al₂O₃ nucleation on supported CVD graphene films. By optimizing H₂O or ozone exposure to promote Al₂O₃ nucleation, we show that we can grow high-quality, dense ALD films directly on graphene without the need of seed layers. We have successfully used this new understanding to grow sub-nanometre Al₂O₃ tunnel junctions directly on graphene for use in spintronic devices [1]. Upon increasing the film thickness to 40nm we can virtually eliminate gate hysteresis for CVD graphene-based field-effect devices [2]. Levels of unintentional graphene doping are at the same time significantly reduced and the room temperature field-effect mobility of encapsulated devices greatly increases. We discuss the relevance of these results to a range of graphene applications, targeting a holistic picture of 2D/non-2D oxide interactions and further optimization of 2D materials integration with conventional thin film and ultra-large-scale integration (ULSI) technology.

[1] Martin et al. ACS Nano 8, 7890 (2014)
[2] Alexander-Webber et al and Aria et al, submitted (2016)

A novel method to manufacture composite carbon nanotubes yarns (cYarns™) by spinning vertically aligned nanotube forests allows the large scale manufacturing of multifunctional yarns that can be introduced into textiles using conventional techniques. Addition of guest materials during the spinning process produces unique yarns with the guest material content as high as 99%wt. Such hybrid yarns can be used as electrodes for batteries, supercapacitors and fuel cells, catalytic membranes, magnets, highly porous absorbers, and strong structures containing biomedical agents. When spun with elastomers and submitted to a special twisting process, cYarns™ can be also used as actuators capable to respond either to electrical or chemical stimuli. By applying electrical pulses, contractions up to 10% and a mechanical work capacity of 1.36 kJ/kg were achieved, which exceed by two orders the performance of biological muscle. When driven chemically by absorption of solvents cYarn™ containing silicon rubber can generate up to 50% stroke and 1.2 kJ/kg work capacity at a efficiency of chemical to mechanical energy conversion of 16%.

Lima, M.D., et al. Science 338 (2012) 929
Lima, M.D., et al. Small 11 (2015) 3113

Among the different possible ways to give Carbon Nanotubes (CNTs) additional properties, filling (that is to say putting something inside the inner channel) is among the most interesting - yet most challenging ones. A wide range of metal oxides, metal halides and other compounds have been introduced into carbon nanotubes already, either from the molten or gas phases, or from solutions [1-4]. The role of parameters such as the available inner space and number of walls of the CNTs on the crystallisation of confined inorganic nanocrystals has already been addressed in our earlier work [5]. However, important parameters driving the filling efficiency have not been identified yet.

After a brief introduction to the Double-Walled CNTs (DWCNTs) we have especially used in this work [6], we will focus here on different examples of 1D-nanocrystals confined within DWNTs and prepared by a 2-step method involving (i) filling of the DWCNTs by molten halides then washing in order to remove all the excess of material outside the nanotubes and (ii) in situ transformation inside the nanotubes when needed, in order to produce metal nanocrystals by reduction in hydrogen atmosphere.

Our results, based on HRTEM observation using different imaging modes (bright field, dark field, STEM) and associated analytical tools (EDS, EELS), reveal that the reality of nanotube filling is much more complex than expected. For some halides (e.g., NiI₂), earlier decomposition even during the filling step is observed, which could not be anticipated from the known data on the bulk material. Others (e.g., iodine) show a variety of atomic structuration inside and outside the CNTs which is driven by the available space being filled. Overall, the whole study reveals a variety of filling efficiencies, the reason of which was identified [7].

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[2] M. Monthioux, E. Flahaut, J.P. Cleuzioux, J. Mater. Res., 21, (11), (2006), 2774-2793
[3] A. Tonkikh et al., Carbon, 94, (2015), 768-774
[4] J. Sloan, M. Monthioux, In Carbon Meta-Nanotubes: Synthesis, Properties, and Applications (editor: M. Monthioux), Wiley-Blackwell (UK), 2012, pp. 225-271.
[5] E. Flahaut et al., Chemistry of Materials, 18, (8), (2006), 2059-2069
[6] E. Flahaut, R. Bacsa, A. Peigney, Ch. Laurent, Chem. Commun., (2003), 1442-1443
[7] C. Nie et al, submitted to Carbon (2016)

The outstanding electronic properties of single wall carbon nanotubes (SWCNTs) have made them attractive candidates for future nanoelectronics technologies. Much progress has been made toward achieving this goal, with advances in such areas as SWCNT device structure and performance, separation of semiconductor vs. metallic tubes, and diameter control, to name a few. One as yet unsolved impediment to the implementation of advanced carbon nanotube electronics is the inability to arrange SWCNTs on a substrate in a manner suitable for forming complex circuits.
We are presently exploring new techniques based on lithographically directed, DNA-mediated assembly of length sorted and chirality monodisperse SWCNT segments, such that the location and orientation of each and every nanotube is precisely controlled. One technique exploits end-functionalization of the SWCNT segments to bind them to nanoparticle anchors (~ 5 nm in diameter) patterned on a substrate by a combination of nanolithography and self-aligned pattern transfer. Both monovalent and bivalent binding are explored using covalent and non-covalent binding chemistries. Placement efficiency is assessed in terms of overall yield of SWCNT binding, as well as binding specificity and orientational control. In another approach, DNA-wrapped SWCNT segments are adsorbed onto 10–40 nm-wide hydrophilic lines defined by nanolithography and site-selective surface energy modulation. Placement of individual SWCNT segments at predetermined locations is achieved with nanometer accuracy. Three terminal electronic devices, consisting of a single SWCNT segment placed either beneath or on top of metallic source/drain electrodes display the expected behavior for semiconducting and metallic nanotubes, respectively. These scalable, high resolution techniques for controlling individual nanotube placement represent an important step forward toward the formation of complex SWCNT circuits.

Teslaphoresis is the directed motion and self-assembly of matter by radiofrequency energy transmitted from a Tesla coil. Carbon nanotubes placed within the Teslaphoretic field polarize and rapidly self-assemble into wires (< 5 s) that span from the nanoscale to the macroscale, the longest thus far being 15 cm. We also show the self-assembly of long nanotube wires at a remote distance (> 30 cm away from the antenna) and that the transmitter wirelessly powers nanotube-based LED circuits that harvest energy directly from the Teslaphoretic field. Furthermore, we found that individualized carbon nanotubes in suspension self-organize into large-scale, parallel arrays on a substrate with high fidelity alignment to the direction of the transmitted electric field. Thus, the Teslaphoretic system may be an effective tool for scalable manufacturing of carbon nanotube transistors and conductive fibers.

Atomic force microscopy (AFM) has become a common tool to visualize and measure the shape and the size of nanometer scale materials. However, errors of up to 50% are commonly reported for AFM height measurements of some nanoscale 1D materials such as DNA. Our AFM height measurements at different values of applied force demonstrate that similar errors occur when measuring diameters of single wall carbon nanotubes (SWCNTs) or thicknesses of 2D materials such as graphene oxide and graphene. The main sources of these errors are identified and an approach to significantly reduce the uncertainty in height measurements is presented. Using this approach an uncertainty of approximately 0.1 nm can be achieved. This increased accuracy in AFM height measurements has facilitated measurements of the thickness of polymer that remains wrapped on SWCNTs in highly semiconducting enriched polyfluorene/SWCNT dispersions [1]. It has also enabled monitoring of the thermal reduction of graphene oxide into graphene. While the height measurement protocol has been developed on nanocarbon materials, the experimental and analysis methods that we have developed are more generally applicable to a wide range of 1d and 2d materials.

[1] Nanoscale, 2014, 6, 2328–2339

Miniaturization of silicon field-effect transistors (FETs) is encounter with various fundamental limitations, including i) high power consumption due to leakage in the semiconducting channels; ii) short channel effects as the conduction length approaches the scale of the depletion layer width, and iii) high contact resistance at the semiconducting channels. The development of nano-FETs by various nanowires (NWs) and carbon nanotubes (CNTs) are still hindered by surface defects and difficulty in controlled synthesis of semiconducting CNTs, respectively.

Apparently, beyond the box approaches should be explored to overcome the above mentioned limitations. Here we discuss about creation of transistors and electronic switches without semiconductors. Furthermore, these devices are based on quantum tunneling, potentially bypass most if not all the above mentioned limitation. Specifically, we will discuss about room-temperature tunneling FETs by metallic quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) [1]. These QDs-BNNTs can also be designed for use in flexible electronics [2]. Finally, graphene-BNNTs heterojunctions are also created to convert metallic graphene into digital switches [3]. All these results are made possible after the success in controlled synthesis of high-quality BNNTs by catalytic chemical vapor deposition (CCVD) [4-6].

This work is supported by the U.S. Department of Energy, the Office of Basic Energy Sciences (DOE-BES Grants DE-FG02-06ER46294, and DE-SC0012762). Part of this work was conducted at the Center for Nanophase Materials Sciences (Projects CNMS2009-213 and CNMS2012-083), which is sponsored at Oak Ridge National Laboratory (ORNL) by the DOE-BES Scientific User Facilities Division, and by ORNL’s Shared Research Equipment (ShaRE) User Program.

References:
[1] C. H. Lee et al, Adv Mat 25, 2544 (2013).
[2] B. Hao et al, Sci Rep 6, 20293 (2016).
[3] V. Parashar et al, Sci Rep 5, 12238 (2015).
[4] J. Wang et al, Nanoscale 2, 2028 (2010)
[5] B. Hao et al, Chapter 20 in Nanotubes and Nanosheets: Functionalization and Applications of Boron Nitride and Other Nanomaterials, (CRC Press) pp 551-572 (2015).
[6] S. Bhandari et al, Chapter 1 in Boron Nitride Nanotubes in Nanomedicine, (Elsevier) pp 1-16 (2016).

Boron nitride nanotubes (BNNTs) are of engineering interest for applications requiring high thermal conductivity, resistance to oxidation at high-temperatures, and electrical insulation. The last few years have seen the development of large-quantity synthesis methods of BNNTs for the purpose of providing high-quality material for use as single molecules, incorporation into composites, and fabrication of BNNT macroscopic articles such as fibers, films, and aerogels. However, the large-scale production techniques currently employed yield a high concentration of non-nanotube reaction products. These impurities drastically limit BNNT viability for use as single molecules and fabrication of macroscopic articles, while also reducing the achievable properties in composite materials. Until now, the chemical similarity of the hexagonal boron nitride impurities to BNNTs has confounded purification attempts.

Here we present a purification method, where BNNTs synthesized via the high temperature-pressure method at the National Institute of Aerospace/NASA Langley Research Center are introduced to high temperatures in a wet oxygen environment. A high purity BNNT product was obtained with total yield of ~5 wt% where the elemental boron and hexagonal boron nitride impurities removed. Characterization of the synthesized and processed BNNTs via scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and infrared spectroscopy indicate a high purity of the processed material with no noticeable damage to the BNNTs from the purification technique. Whereas 5% yield is poor for engineering applications, this yield permits additional scientific studies to develop characterization techniques for further optimization to improve the yield and future engineering solutions. Via cryogenic transmission electron microscopy we were able to see individualized, dissolved BNNTs in chlorosulfonic acid (CSA), similar to what has previously been observed for carbon nanotubes. Additionally, we observed liquid crystalline behavior, when the purified BNNTs are dissolved in CSA, and have produced the first-ever aligned thin films and short BNNT fibers, leading to the fabrication of macroscopic objects from purified BNNTs.

Graphene is a zero-band gap semiconductor exhibiting an ambipolar transport behavior. Graphene doping is important in order to tune its electrical properties, such as carrier density and Fermi level position, which can be achieved with boron or nitrogen atoms to obtain p or n-type doping, respectively. Boron-doped graphene can be employed in number of applications, namely: optoelectronic devices, field effect transistors (FET), solar cells, lithium batteries and hydrogen storage [1]. However, controlling the level of doping can be challenging, specially maintaining at the same time graphene unique superior properties. In this way, it is of fundamental importance to understand and control the doping process in graphene. In the present work we investigated boron doped graphene grown by molecular beam epitaxy (MBE).
Starting samples were α-Al2O3 (0001) substrates. Growth and doping takes place in a MBE growth chamber equipped with an e-beam evaporator (for carbon) and an effusion cell (for boron). Samples were heated up to 950oC and then a power of 750 W is applied to the e-beam. Under these conditions (at a pressure of 5 x 10-8 mbar) a 3 monolayer thick graphene film is grown after 10 min. Boron was controllably introduced in the films in order to achieve p-type doping. Two different approaches were used. A one-step doping approach where the boron and carbon source shutters were opened simultaneously and the growth/doping process was kept for 10 min. A two-steps doping approach, where first only the carbon beam was directed to the sample surface for 5 min. After 5 min, boron is added to the process and the growth/doping lasts for another 5 min, finally yielding the same 10 min used in the first approach. The influence of the boron flux on the electrical and physico-chemical properties of the MBE-grown films were then investigated for both approaches. Raman analyses were carried out using a 473 nm laser, and X-ray photoelectron spectroscopy (XPS) measurements were performed using Al Kα X-ray source. Carrier density and mobility were obtained by magneto transport measurements in van der Pauw geometry.
XPS measurements suggest the formation of B-O and B-C bonds. Raman analysis shows that both, the G and 2D bands, up shift for both growth approaches as a function of the boron flux. This is attributed mainly to the boron doping effect in graphene as p-type [2]. B-doping also affects the intensity of these bands, where a decrease in the 2D/G area ratio is observed, consistent with the B doping effect. Magneto transport measurements show a decrease in the carrier mobility, accompanied with an increase in the charge carrier concentration for increasing the boron flux during growth. Mechanisms of boron incorporation as well as the role of each doping approach will be discussed.

References

[1] Ruitao Lv, et. al Proceedings of the National Academy of Sciences 112 (2016) 14527.

[2] Beams, R., Cançado, L.G., Novotny, L. J. Phys.: Condens. Matter 27 (2015) 083002.

A label-free molecular detection platform based on the fluorescent emissions of single wall carbon nanotubes will be presented. The carbon nanotubes are non-covalently modified with chelating polymers and single-stranded DNAs, which provides a specific recognition site for protein molecules. The bindings of the target biomolecules with the surface modified nanotubes disturb the dielectric environment of carbon nanotubes and hence cause their fluorescent emission property change. By monitoring their emission intensities, the specific recognition event on the nano scale is transduced to measurable macroscopic signals. In this presentation, we will demonstrate a miniature microarray platform to integrate multiple recognition sites onto a small area of glass slide. Using only a few microliter of the target sample, we are able to quickly detect multiple analytes using our nanosensor platform. The label-free detection system will be of great potential for product quality control and clinical diagnosing applications in the future.

Nanomaterials such as carbon nanotubes (CNTs) have found many potential biomedical applications in bio-sensing and delivery of drugs, proteins, and genes. Boron nitride nanotubes (BNNTs) are chemically inert like CNTs because of their defect-free surface, making them a very promising candidate for biomedical applications.¹ Biomedical study of BNNTs is relatively unexplored due to the difficulty in the synthesis of high-quality BNNTs.² Here we report on quantification of short (~500nm and shorter) and high-quality BNNTs in aqueous suspension with a measurement level down to sub-µg/ml.

Ultraviolet-Visible (UV-Vis) light absorption spectroscopy has been widely used for the quantification of biological molecules such as proteins, and DNAs. This is based on the presence of absorption bands in the visible spectra. However, BNNTs are wide band gap materials (~6 eV)^2-3, therefore UV-Vis absorption spectra in the visible range is not accessible for quantification. Here we will present a novel approach to quantify cut BNNTs by UV-vis spectroscopy. High-quality (6eV band gap with no intra-band defects) BNNTs were grown by catalytic chemical vapor deposition (CCVD).³ The as-grown BNNTs can be extracted in water and weight can be precisely measured in mg level. The extracted BNNTs was then functionalized with biocompatible PEGylated phospholipid [methoxy-poly(ethylene glycol)-1,2-distearoylsn-glycero-3-phosphoethanolamine-N conjugates (mPEG-DSPE, Mol. Wt. 5000) to make them water dispersible.⁴ As functionalized BNNTs were cut by sonication to a nominal length below ~500 nm. The as cut BNNTs were examined by field emission scanning electron microscope (FESEM) and analyzed for their length distribution. These cut BNNTs are then used to generate our UV-Vis calibration curves from sub-gram per ml to sub-µg per ml levels. These calibration curves were further improved by a series of repeatable experiments to refine their accuracy. Our results has proven that the refined calibration curves can be used to quantify concentration of cut BNNTs based on selected spectra range. Quantification results based on the absorption band of BNNTs at 213nm will also be discussed. The details of these quantification experiments and the cytotoxicity test of these cut BNNTs will be presented in the meeting.

Y.K.Y. acknowledges the support from the National Science Foundation, Division of Materials Research (Award No. 1261910).

References:
1. Bhandari, S. Tiwari, B.; Yapici, N.; Zhang, D.; Yap, Y. K., Boron Nitride Nanotubes in Nanomedicine 2016 (Elsevier), 1-15.
2. Wang, J. S.; Lee, C. H.; Yap, Y. K., Nanoscale 2010, 2 (10), 2028-2034.
3. Lee, C. H.; Xie, M.; Kayastha, V.; Wang, J. S.; Yap, Y. K., Chem Mater 2010, 22 (5), 1782-1787.
4. Lee, C. H.; Zhang, D.; Yap, Y. K., The Journal of Physical Chemistry C 2011, 116 (2), 1798-1804.

A molecular dynamics simulation technique has been used to study the thermal and mechanical properties of multi-walled carbon nanotubes- polycarbonate composites system. The composition of multi-walled carbon nanotubes in polycarbonate varied by 1 to 5% by weight and 5 to 15% by volume. Discover module of modelling and simulation software Materials Studio 7 has been used for calculating the mechanical properties. The simulations results show the 91 and 12% increase in elastic modulus by 3% addition of MWCNT by weight and volume, respectively. The reason for this increase can be the load transfer characteristics of MWCNTs and interaction between reinforcement with base matrix.

Boron is low-abundance element in the Earth’s crust and in the Solar system. It has potential applications such as neutron absorption. Boron nanostructures have attracted a lot of theoretical and experimental interest. Recently, it has been predicted that single layer of boron composed of triangular and hexagonal motifs, known as ‘α-sheets’, more stable than flat triangular and hexagonal sheets. These sheets can be obtained by detaching atoms from a triangular flat sheet. These α-sheets are metallic and flat in nature. Here we present electronic and transport properties of boron nanoribbons derived from stable configuration ‘α-sheet’. Transport properties of different spin configuration of α-sheet, as a function of energy and under different bias conditions have been investigated using first principle calculations. The effect of bias voltage on conductance along with effect of spin-orbit coupling (SOC) on transmission will be presented.

Corona phase molecular recognition (CoPhMoRe) uses a heteropolymer adsorbed onto and templated by a nanoparticle surface to recognize a specific target analyte. This method has not yet been extended to macromolecular analytes, including proteins. We develop a variant of a CoPhMoRe screening procedure of single-walled carbon nanotubes (SWCNT) and use it against a panel of human blood proteins, revealing a specific corona phase that recognizes fibrinogen with high selectivity. In response to fibrinogen binding, SWCNT fluorescence decreases by >80% at saturation. Sequential binding of the three fibrinogen nodules is suggested by selective fluorescence quenching by isolated sub-domains and validated by the quenching kinetics. The fibrinogen recognition also occurs in serum environment, at the clinically relevant fibrinogen concentrations in the human blood. These results open new avenues for synthetic, non-biological antibody analogues that recognize biological macromolecules, and hold great promise for medical and clinical applications.

Recently, carbon allotropes including highly oriented pyrolytic graphite (HOPG), graphene monolayers (GML) and multi walled carbon nanotubes (MWCNT) have drawn substantial attention for their desirable electrical, optical, thermal, and mechanical properties. Understanding the surface properties is essential to fully realize the potential of these materials,. Despite the fact that they have identical bonding structure, these allotropes have been observed to display divergent surface properties. Despite significant study, attempts to fully explain these divergent surface properties have remained inconclusive even when dealing with parameters as fundamental as adhesion.
In order to better address this challenge, we provide in this work conclusive experimental results regarding the time evolution of the surface properties of these allotropes as we expose these materials to airborne contaminants. We present evidence of variations in the surface properties of HOPG in the presence of airborne contaminants by submitting the data, from the atomic force microscopy (AFM) measurements, to an inferential algorithm that allows estimating the net error while ensuring self-consistency across the data set. By comparison of data from the three samples, we demonstrate the similarity of the surface properties of the three allotropes when contaminant adsorption resulting from exposure to air is considered

Carbon Nanotubes have a great potential to affect our future in a wide variety of applications such as fuel cells, electronics, and materials. Therefore the understanding of how CNT’s are grown, and created are of great interest. Carbon nanotubes can come in two basic varieties Single Walled (SWCNT) and Multi-Walled (MWCNT). The different types of tubes have various physical and chemical properties. The way the CNT’s are grown can affect the type of tubes that are created.
In this study we have grown carbon nanotubes on various substrates using transition metal nanoparticles as nucleation sites for the growth. The nanoparticles were deposited on the substrates using a template of block copolymers. The block copolymers self assemble on the substrate to form nanometer sized micelles on the surface which the nanoparticles can fill in and form an array on the substrate. The average size of the nanoparticles formed by filling the micelles was found to be 30 nm.
The method of deposition starts by using a solution of block copolymer (Polystyrene-b-poly(4-vinyl pyridine)) in toluene. Different transition metal salts were then mixed with the block copolymer solutions. The different transition metal salts used in this study was Fe, Ni, and Co nitrates, some solutions were created with specific mole ratios of the various metal salts to create complex nanoparticles. Once the solutions were created, a glass syringe was used to coat the block copolymer transition metal salt solutions onto the substrates using a spin coating technique. Next the samples were placed into a vacuum chamber with an oxygen plasma that is used to burn off the block copolymer and leave the transition metal nanoparticle on the substrate surface in an arranged pattern. Lastly, the substrates with the patterned nanoparticles are placed into a CVD growth system.
The carbon nanotubes are grown in a tube furnace at a temperature of 750 C. A mixture of Argon, Hydrogen and Ethylene gas is flowed into the tube furnace to grow the carbon nanotubes. The samples are allowed to grow for 45 min in the CVD system.
The samples were characterized using AFM and SEM. Images were taken of the block copolymer surfaces to examine the micelles formed prior to plasma cleaning, and then after plasma cleaning to examine the nanoparticle size left behind. The grown carbon nanotubes were then characterized with the SEM. It was found that the CNT’s ranged in diameter from 30 nm to 35 nm depending on the identity of the nanoparticle. The use of the TEM showed that the CNT that were grown as multi-walled.

Surface-enhanced Raman scattering (SERS) provides high sensitivity and selectivity on molecule detection, making it attractive for biomedical and chemical detections. Generally there are two mechanisms to influence the SERS enhancement: electromagnetic mechanism (EM) created by the metals with surface plasmon resonance (SPR) property and chemical mechanism (CM) due to the charge transfer between the molecule and the substrate. Consequently, the development of synthetic method to produce nanostructures with controllable EM and CM properties will lead to important advances on both fundamental study and innovative applications for SERS-based biomedical detections. Graphene nanoribbons (GNRs) represent a unique structure of carbon nanomaterials with controlled electronic properties by tuning their widths, making them can be potentially useful as the SERS-active substrate and used in other applications including energy, composites, biomedical and electronics.
Here we report a rational design to develop a SERS-active nanocomposite with improved EM and CM properties. Toward this goal, we prepared silver (Ag)/Boron-doped GNR (B-GNR) composites using a sequential reaction route. First we synthesized GNRs with averaged width around 4 to 5 nm by the chemical unzipping of singled-walled carbon nanotubes (SWCNTs). Additionally, the prepared GNRs were doped with B atoms by a controlled carbonthemic reaction under argon (Ar) flow at atmospheric pressure and the B dopant concentration was about 1.7 atomic percentage (atom%) according to the X-ray photoelectron spectroscopy (XPS) analysis. Ag NPs with range of 15 to 30 nm averaged size were decorated onto the B-GNRs surface through an atmospheric-pressure microplasma-assisted redox reaction. Detailed materials characterizations including transmission electron microscopy and UV-Vis spectroscopy show that Ag/B-GNR composites were successfully synthesized in our experiment. We further systematic studied the Raman response of the Ag/B-GNR composite using Rhodamine 6G (R6G) as the Raman probe molecules. The result indicates that the Ag/GNR composite shows superior SERS performance with low detection concentration of 10^-10 M of R6G and high enhance factor (EF) of 1.0510⁹.

The layer-by-layer (LbL) technique is a simple and versatile way to produce tailored nanostructures with fine tune in thickness, composition and structure. Graphene has attracted considerable attention due to extraordinary mechanical and electrical properties, which can be explored to improve electron transfer mechanisms in sensor applications. We present herein the synthesis and characterization of graphene nanoplatelets wrapped by chitosan (G_chit) and poly(styrenesulfonic acid) (GPSS), producing, positively (G_chit) and negatively charged (GPSS) suspensions stable in water, making them suitable materials for LbL film fabrication. Raman scattering indicated a successful formation of the graphene platelets, while FTIR had shown the occurrence of van der Waals interactions between the nanoplatelets and PSS, granting chemical interactions between the former and chitosan. The materials presented also good LbL film formation and different electrical properties, which can be exploited in distinct applications involving graphene derivatives.

One of the most common techniques for the synthesis of carbon nanotubes (CNTs) is chemical vapor deposition (CVD), in which the CNTs grow from metallic catalyst particles. In order to have control over the properties of the grown CNTs, it is essential to control the catalyst particles themselves. For the synthesis of single-walled CNTs (SWCNTs), the diameter of the catalyst particles is the most important parameter to control and should typically be around 1 – 3 nm.
The most common catalyst materials include Fe, Co and Ni, but many more metals have been demonstrated to be effective catalysts. Furthermore, bimetallic catalysts such as Fe/Co, Co/Mo and Fe/Pt are reported to yield a more narrow CNT diameter distribution and possibly selectivity toward semiconducting CNTs. The catalyst particles are conventionally prepared by either physical vapor deposition of an ultrathin metal(oxide) film, or from solutions of metal salts However, the amount of catalyst metal required for SWCNT growth is extremely small (several monolayers), and it is challenging to deposit such thin layers in a reproducible way.
In this work, we have explored the use of atomic layer deposition (ALD) to deposit the catalyst films for CNT synthesis on flat SiO₂/Si substrates. In ALD, ultrathin films can be deposited by cycle-wise exposures to a precursor and reactant gas. Self-limiting surface reactions enable a layer by layer growth with sub-monolayer control over the thickness, even in high aspect ratio and 3D structures. Furthermore, bimetallic materials can be easily deposited by alternating different cycles.
First, we have investigated ALD of cobalt oxide (CoO_x) films using CoCp₂ and O₂ plasma. CoO_x films can be deposited with a growth rate of 0.055 nm/cycle at low temperatures (< 100 °C) and exhibit almost no growth delay. The CoO_x is reduced to metallic Co particles during a H₂ anneal in the CVD process. We found that Co particles resulting from just 1 cycle CoO_x ALD (< 0.05 nm) are already sufficient to act as a catalyst for the growth of a high density of SWCNTs. For thicker CoO_x films the density first increases, but after several cycles the particles become too large and start forming multi-walled CNTs instead.
Next, we added Pt by ALD using MeCpPtMe₃ and O₂ gas in order to form bimetallic CoPt catalyst particles. Compared to the CNT growth from 2 cycles CoO_x, we found that the addition of a small amount of Pt (~10 cycles) suppressed the CNT growth, while a larger amount of Pt (~50 cycles) dramatically increased the density and number of CNTs. Interestingly, we were not able to grow CNTs on samples with just Pt catalyst (without CoO_x) which indicates the synergetic effect of both materials. TEM images of the ALD catalysts hint at the formation of CoPt alloys and reveal that the density of the CoPt particles is indeed much larger compared to Co alone.
These results show that ALD is an excellent tool for the reproducible and controllable deposition of CNT catalysts.

Recently, short aromatic peptides have attracted significant interest because they can spontaneously form fascinating discrete and well-ordered structures at the nanoscale: nanotubes, nanospheres, nanofibrils, and hydrogels. Peptide nanotubes (PNTs) based on diphenylalanine possess unique biological and physical properties such as inherent biocompatibility, high aspect ratio and remarkably rigid structure. Strong piezoelectricity found recently in aromatic PNTs adds a new important functionality useful for the development of sensors, actuators and micromechanical systems. Piezoefect was found to be surprisingly stable as a function of temperature and applied electric field being strongly dependent on the chemical modifications and synthesis conditions. Higher chemical reactivity of PNTs as compared to carbon nanotubes (CNTs) or silicon nanowires makes easier to carry out their modification with receptor molecules, and more versatile synthesis protocols, whereby a lot of novel devices can be produced. Thus, biocompatible, lightweight and highly mechanically stable PNTs are an attractive material for the fabrication of piezoelectric transducers for future generation of chemical sensors and biosensors.
In this work, we present the results of the high-resolution Piezoresponse Force Microscopy (PFM) study of diphenylalnine (FF) peptide microtubes prepared from the solution. Different configurations were used to study both longitudinal and transverse piezoeffects as a function of temperature and frequency. Special attention was paid to spatially resolved PFM images that provide a link between topographical features (molecular clusters or defects) and polarization. Head-to-head and antiparallel polarization directions were observed in microtubes and these were attributed to the peculiarities of their growth. Polarization instabilities were observed in the temperatures above room temperature and attested to the 1D-water aligned along nanochannels. Composites consisting FF microtubes with graphene were studied as well.

The work was supported by the Portuguese-NSF grant FLAD 299/2015 and RFBR, according to the research project No. 16-32-60188 mol_a_dk.

In this work, we report vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) on silicon substrate by thermal chemical vapor deposition (T-CVD) technique without any carrier gas. Solution prepared by liquid precursor xylene as carbon source and ferrocene as catalytic source, has been used for the growth of VA-MWCNTs at growth temperature of 850 °C with growth time of 25 min. Firstly, growth has been carried out for different quantities of the solution ranges from 2 ml to 3.5 ml in steps of 0.25 ml at fixed concentration 0.02 gm/ml. To understand the growth mechanism, growth has also been carried out for different concentrations of the solution by changing only the ferrocene quantity, ranges from 0.1 gm/ml to 0.3 gm/ml at fixed quantity of the solution 2.5 ml. Scanning and transmission electron microscopic techniques have been used for morphology and micro structural analysis. Micro-crystalline analysis has been done using Raman measurements. Enhanced field emission properties in terms of emission current density (~7mA/cm²), and temporal stability have been observed for this VA-MWCNT films. It has been observed good vertical alignment for the quantity of solution ranges from 2.25 ml to 2.75 ml with concentration 0.2 gm/ml. Growth mechanism has been explored for VA-MWCNT films on the basis of precursors used and their parameters. The observed results are explained in the frame work of Fowler-Nordheim model of field emission. This method is easily scalable, safe and cost-effective. Hence, this growth of VA-MWCNT cathodes has to be optimized and probed further to replace as an alternative to conventional electron sources in many device applications, nano-interconnects, energy storage, composite materials etc.

Graphene has a number of remarkable properties; however, its electronic structure of a zero band gap semiconductor limits its use in optoelectronics applications. Unlike graphene, its functional derivative graphene oxide (GO) possesses a band gap and exhibits photoluminescence, which makes it a highly attractive material for photovoltaic devices and nanoscale optoelectronic transistor applications. In order to be able to adjust optical properties of GO for a particular application we introduced a controlled solution-based ozone processing of reduced graphene oxide (RGO) yielding the appearance and further increase of photoluminescence as RGO was oxidized into GO. This transformation was followed by a shift in the absorption spectra with consecutive change in color from black to light yellow, and an improved water solubility. Thermal solution treatment of ozonated GO introduced a reverse effect with a notable decrease in emission and the darkening of sample color. These techniques allow for the controlled modification of the optical properties of GO and help elucidate the origins of its photoluminescence. FTIR spectra of ozone-treated RGO showed stepwise enhancement of 1736 cm⁻¹ (C=O) and ~1230 cm⁻¹ (C-OH) features and the disappearance of ~1570 (C=C) peak confirming gradual increase in the amount of oxygen addends accompanied by the loss of sp² carbon structure. The corresponding increase in fluorescence lifetimes with the degree of oxidation indicated the change in the GO structure facilitating the stabilization of fluorophores. These structural variations were modeled via semi-empirical PM3 calculations. Modeling results attribute the appearance of optical band gap in GO to either localized electronic environments surrounding functional groups or addend-confined graphitic islands. The latter model is supported by ~20 nm blue shift in GO emission appearing upon ozone treatment, which could result from oxidation-induced size decrease of confined sp² regions.

Stray light absorption is essential to reduce signal to noise degradation in optical instruments. To date the best commercially available solution are black paints, which present an absorption coefficient of ~60%. Much work has focused on producing a superior absorber using Carbon Nanotube (CNT) forests, with some results indicating an absorption coefficient of over 99%. The main setback of using the CNT forests is that they are grown on a rigid substrate whose shape does not conform onto most optical devices. We present a method for creating a CNT light absorbing material with over 99.96% absorption of incident radiation that can be easily placed onto any surface, including flexible and rigid plastics, glasses and metals. Furthermore, the material exhibits Lambertian diffusive reflection and essentially a zero grazing angle of radiation. In addition, the material can be modified so that the absorption coefficients have a strong correlation with angle by controlling the orientation of the CNTs in the forest. The extraordinary light absorbing properties, ease of application and the customization of absorption to angle of incident radiation make this material highly suitable for commercial application in optical instruments.

Carbon nanotube-based materials exhibit properties far below theoretical predictions and even much lower than those for some conventional carbon materials [1, 2]. So it is one of the most challenging targets of carbon materials science to translate outstanding properties of carbon nanotubes into macroscopic composite or fiber features. One can suggest rather obvious idea that the synthesi of longer nanotubes helps. Recently, some works like [3, 4] showed that it works and brings higher electric conductivity and better mechanical strength. Although there are several methods discovered for synthesizing millimeter- and centimeter-long nanotubes including our own technique [5], the macroscopic material requires the nanotubes in quantities, which are difficult or impossible to produce in laboratory bench scale. So it is necessary to scale up, which is a difficult chemical engineering problem for any process, and is especially difficult for such a delicate topochemical reaction.
This work reports a scaled up process of the longer carbon nanotube synthesis. A suspended-bed synthesis rig is reported capable of producing carbon nanotube cotton in spools or piles in kilogram amounts. A possibility to produce free-standing non-woven nanotube thin films is demonstrated. The embryonation and initial growth periods are recorded.
The carbon nanotube cotton was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, thermal analysis (TGA/TSC) and X-ray photoelectron spectroscopy (XPS). It was shown that the material is dominated by double- and triple-walled carbon nanotubes. Various methods of final treatment/purification from residual catalyst were investigated, the residual catalyst level of less than 0.2 % weight are reachable. It was also shown that the carbon nanotube cotton is electrically conductive and shows more that 1 kS/cm even in loose form with multiplication if densified. Opportunities of combing, roving and spinning the carbon nanotube cotton are discussed.
In conclusion this successful scale-up development paves the way for intensification of research and development in macroscopic carbon nanotube-based fubers and composite materials.

References
1. V.Z. Mordkovich, S.A. Urvanov, V.D. Kravchenko, N.V. Kazennov, E.A. Zhukova and A.R. Karaeva, Materials Research Innovations (2016) 20, 14
2. M. Zhang, K.R. Atkinson, and R.H. Baughman, Science (2004) 306, 1358.
3. J. N. Wang, X. G. Luo, T. Wu & Y. Chen, Nature Communications (2014) 5, Article number: 3848.
4. L. Liu, W. Ma and Z. Zhang, Small (2011) 7, 1504.
5. A.R. Karaeva, M.A. Khaskov, E.B. Mitberg, B.A.Kulnitskiy, I.A.Perezhogin, L.A. Ivanov, V.N. Denisov, A.N. Kirichenko and V.Z. Mordkovich, Fullerenes, Nanotubes and Carbon Nanostructures (2012) 20, 411.

The advancements of semiconducting electronic devices are interlocked with the development of top-down process for physical miniaturization represented by Moor’s law. Accordingly, electronic devices have become ever smaller and faster. Silicon-based semiconductor technology, however, has reached its physical limitation in terms of degree of integration and performance. Thus, significant efforts have been made to meet the rising demands using various types of carbon nanomaterials such as carbon nanotubes and graphene because of its excellent charge carrier mobility. Currently, of particular interest is the potential use of graphene for field-effect transistors. Although graphene intrinsically has a zero-band gap, some interesting investigations theoretically and experimentally demonstrated the band gap opening of graphene; that is, the opening of a band gap could be realized by reducing the width of graphene into nanoscale ribbons. Thus, many researchers have studied on graphene as a semiconducting channel material applying newly developed fabrication processes. Electron-beam lithography as a top-down method is the most commonly used means of patterning graphene at tens of nanometer scale. However, it is also well known that the graphene may be damaged due to the irradiation from electron-beam exposure. Hence, the development of alternative lithographical methods is emphasized in producing graphene nanoribbons (GNRs). Here, we suggest a method to produce GNRs in a large area by using polymeric nanowires as a passivation mask through dynamic assembly and transfer printing process. Followed by O₂ plasma etching process, we successfully crafted GNRs with a high degree of feature-size controllability and a low level of defects. Finally, a flexible two-channel device and bottom-gated field-effect transistors on a SiO₂/Si substrate were fabricated by capitalizing on these aligned arrays of GNRs formed by polymeric nanowire array-enabled lithography.

Platinum (Pt) nanostructures on conducting supports are widely used in electroanalysis and electrocatalyst for sensing, fuel cell and solar cell applications. Among conducting supports, Single-wall Carbon nanotube (SWCNT) is considered as nearly ideal supporting material for catalysts due to its high surface area, good conductivity, and chemical inertness. Therefore, there is increasing demand for simple fabrication method to form Pt-SWCNT nanocomposites on flexible substrates. The formation of Pt-SWCNT composite on paper have several advantages as compared to traditional electrode materials: 1) The use of paper instead of electrode material leads to significant reduction of cost of electrode material 2) It eliminates the requirement of pre-treatment of electrode surface before modification 3) It eliminates the requirement of binding polymers to incorporate CNT on electrode surfaces. 4) The prepared nanocomposite can easily be transferred into preferable substrates which otherwise is technologically challenging 5) It is disposable and environment-friendly.In this report, we use paper based CNT thin film, prepared by vacuum filtration method, both as conducting support and electrode material to incorporate Pt nanostructures. Two different methods, electrochemical deposition and vacuum filtration assisted assembly, were used to incorporate platinum nanostructures on the surface of SWCNT. The morphology and state of platinum nanostructures were characterized by Scanning Electron Microscope (SEM) , XPS (X-ray photoelectron spectroscopy) , X-ray Diffraction (XRD) and Cyclic Voltammetry (CV). Methanol was used as a model molecule to demonstrate electrocatalytic properties of paper-based Pt-SWCNT composites

Raman spectroscopy is commonly used to study chemical composition of materials with a high degree of specificity, but it suffers from low sensitivity due to an inherent weakness of Raman scattering and its spatial resolution is diffraction-limited by far field optics to ~0.5λ. These drawbacks can be overcome by nanoRaman or tip-enhanced Raman spectroscopy (TERS), where a Scanning Probe Microscope (SPM) tip functionalized with a noble metal such as gold or silver is brought into contact with the material of interest. Due to a high spatial confinement of an enhanced electromagnetic field directly under the apex of the functionalized tip, Raman spectra from the material with as much as six orders of magnitude enhancement can be obtained. The spatial resolution in TERS is believed to be governed by tip dimensions and experimental values better than 20 nm is commonly reported.

Carbon-based materials such as carbon nanotubes and graphene oxide have potentially a wide variety of applications in nanotechnology due to their unique properties; they have also been some of the most widely studied materials using TERS. However, for a long time since its inception in 2000, TERS measurements were reported only from single points or from a series of points along a line. More recently, TERS imaging has been demonstrated, using which it is possible to obtain a hyperspectral near-field Raman image which provides a spectrum from every pixel of the image. TERS images reveal much more information as they can be used for better correlation of chemical information with morphological features, and they provide information that cannot be obtained from SPM or electron microscopy alone.

Here, TERS images of carbon nanotubes and graphene oxide as pure components are shown. Besides correlation of chemical information with morphological features, they reveal inhomogeneity on the surface of carbon nanotubes in the nanometer scale as well as greater enhancement along the edge of graphene oxide flakes relative to adjacent flat portions, which cannot be captured using SPM alone. Similar differences in TERS response is also obtained from folds and wrinkles in graphene oxide flakes as well as from areas that are patterned by pulsed force lithography compared to flat or unpatterned areas, and possible reasons are discussed. Finally, TERS images of multi-component samples are discussed, which show the ability of TERS to detect individual components among them due to the inherent specificity of Raman scattering to different chemical compositions, in addition to improved sensitivity and spatial resolution.

Single-walled carbon nanotubes arranged in spaghetti bundles are investigated as anode materials for Li-ion batteries. Electrochemical experiments are used to measure the charge and discharge curves during the first 5 cycles, and in situ Raman spectroscopy is used to characterize the chemistry of intercalation as well as side interfacial reactions. Raman spectroscopy demonstrates a significantly high capacity from the first discharge, where Li intercalation features and also the signature of side reactions have been clearly observed. However, the capacity is dramatically reduced at the 2nd cycle and is then slightly less affected but still decreases during successive cycles up to the 5th. These experimental results are explained by the density functional theory analyses. In agreement with in situ Raman in the 2nd cycle, the theoretical model demonstrates a much lower capacity of the nanotube bundle compared to graphite. Therefore we attribute the excess capacity measured in the first cycle to the presence of defects and unsaturated edges and to the formation of a solid-electrolyte interphase where both of these effects irreversibly trapping a significant amount of lithium.
[1] G. Ramos-Sanchez, G. Chen, A. Harutyunyan, and P. B. Balbuena, RSC Adv., 2016, 6, 27260–27266

Low density graphene materials have gained large interest due to their application in electrochemical storage, including supercapacitors and battery anodes, oil adsorption and gas sensing. In this poster I will present a solution processable method of synthesizing graphene aerogels with tunable densities ranging from 5 mg/mL to over 1000 mg/mL . Polycyclic aromatic hydrocarbons can be incorporated into aerogels during synthesis resulting in a monotonic decrease in density with increased loading. This method also allows control over pore sizes and can even increase the number of mesopores, which is ideal for Li-ion battery anodes. Aerogels still maintain high surface areas and conductivities necessary for many applications. A similar method can be adopted to synthesize doped graphene aerogels with controlled doping density. The mechanical, electrical, and gas sensing properties of these materials are studied to highlight the precise control of aerogel density that allows control over the physical properties of the material and can be tailored towards the application of the aerogel.

The wetting dynamics of surfaces is an important area of fluid dynamics, which many times determines the potential use of a specific material [1]. Because of that, the engineering of texturized structures on the micro/nanoscopic level tries to obtain surfaces with extraordinary properties, like rapid detachment [2], superhydrophilicity and superhydrophobicity [3]. Some of these properties can be very useful to applications concerning anti-icing, antifogging and self-cleaning materials. On this matter, patterned surfaces, for instance, patterns created by uniformly spaced pillars, represent an effective and feasible strategy to design materials with such properties [4]. In order to understand, at atomic level, how a liquid like water behaves when into contact with such materials, we investigated through classical molecular dynamics simulations the permeation behavior of water nanodroplets on carbon nanotubes forests (our patterned surface). We considered different tube arrays, varying tube diameters and the spacing between them, as well as, different functional groups (hydrogen termination, carboxyl, etc.) to achieve different degrees of wettability and/or hydrophilic or hydrophobic behaviors. Besides that, the droplet diameter and impact velocity were also varied trying to mimic, as much as possible, our simulations to related experiments [4]. From our preliminary results we observed three different regimes: complete rebound (where droplet penetrates totally on the surface and rise again at the top), complete penetration (the droplet remains completely inside the patterned surface) and internal fragmentation (where the droplet fragments inside the patterned structure). These results are consistent with the available experimental data [4]. We have also discussed how to exploit these ideas to design nanopatterned surfaces with specific behavior (hydrophobic or hydrophilic, or even superhydrophilic one).

1. L. Duta, A.C. Popescu, I. Zgura, N. Preda and I.N. Mihailescu, Wettability of Nanostructured Surfaces, Wetting and Wettability, (InTech, 2015) pp. 207-252.
2. Y. Liu, L. Moevius, X. Xu, T. Qian, J. M. Yeomans, and Z. Wang, Nature Physics 10, 515 (2014).
3. Z. Wang, M. Elimelech, and S. Lin, Environmental Science & Technology 50, 2132 (2016).
4. Y. Nonomura, T. Tanaka, and H. Mayama, Langmuir, ASAP article (2016).

Several potential applications have been suggested for carbon nanotubes, including electrical applications and mechanical reinforcement for composites. When combined with other materials, these nanotubes can provide improvements and functionalization of structures made from various materials. Several methodologies have been applied to produce composites devices, mainly using polymeric matrices. Photopolymerization techniques, using linear or nonlinear optics phenomena, have been frequently used to fabricate composites in nano or micro scale [1]. Multiphoton absorption polymerization (MAP) have been widely used for this purpose. Thus, the objective of this work is to focus on the production f-SWCNT/acrylate micro-composites using MAP and the investigation of the mechanical and electrical properties, comparing with the pure polymer. To fabricate f-SWCNT/acrylate micro-composites we used a mixture in equal proportions of two three-acrylate monomers. These monomers are mixed with an aclyphosphine oxide photoinitiator. Functionalized SWCNT dispersed in water are added to liquid resin. After solvent evaporation, this resin is placed between a glass substrate and a cover slip for the microfabrication process. The laser source used is a Ti:Sapphire oscillator operating at a repetition rate of 86 MHz delivering 100 fs pulses, centered at 780 nm. The laser beam is focused through a microscope objective into the liquid resin and scanned during the photopolymerization procedure. As a result, fabricated composites present good surface quality and integrity, even when a high SWCNT concentration (1.00 wt%) was employed. Raman analysis indicates a good distribution of SWCNT throughout the microstructure. Phase AFM images for the pure polymer, as well as for the composite containing f-SWCNT indicate changes in the micro-mechanical properties of the structures containing SWCNT, such as in the elastic modulus and viscoelasticity. Besides, nanoscratches mechanical essays are being made using AFM to show the benefits of reinforcement with nanotubes. The electrical conductivity of these composite is higher than pure polymer. Even using low concentration of f-SWCNT in these composites (0.01 wt%), we observe a significantly improvement electrical conductivity. The results obtained in this work show that SWCNT incorporated in acrylate polymers might be useful to provide microstructures with mechanical and electrical improvement, opening new possibilities for microdevices application. The authors acknowledge FAPESP (Grants # 2011/12399-0, 2011/23587-1 and 2014/21439-1), CNPq, CAPES and the Air Force Office of Scientific Research (FA9550-07-1-0374) for financial support and Andre Romero for technical assistance.

[1] Otuka, A. J. G., et al., Single-Walled Carbon Nanotubes Functionalized with Carboxylic Acid for Fabricating Polymeric Composite Microstructures. Journal of Nanoscience and Nanotechnology, 2015. 15(12): p. 9797-9801.

Carbon nanotube (CNT) yarns are a flexible, high-strength, conductive and chemically inert alternative to conventional metal wires. The most common techniques currently used to enhance CNT yarn conductivity involve increasing the amount of CNT for every yarn or adding metallic materials. Although effective, these techniques have major shortcomings, the most serious are the high cost of CNT’s and the corrosion of the metals over time. To overcome these challenges, our team has developed a novel approach of incorporating graphene flakes into the CNT yarns. This unique technique allows us to take advantage of the structural properties of the CNTs with the conductive properties of the graphene flakes. This serves to increase the amount of carbon material in the yarn without greatly increasing costs.

Graphynes and graphdiynes are carbon 2D allotrope forms presenting both sp2 and sp hybridized atoms, which leads to distinct geometries. The main difference between graphynes and graphdiynes are the number of acetylenic (one and two, respectively) groups connecting benzene rings. These materials have been theoretically predicted [1] but due to difficulties in the synthesis process, only recently they have been produced [2]. The successful synthesis of the graphdiynes has sparked new interest in these structures and remarkable electronic properties have been predicted for some of them.
Graphyne-like nanotubes [3] have already been successfully produced, but other structures remain to be explored. Among them is the possibility of the existence of graphyne/graphdiyne nanoscrolls, which are structures obtained by rolling graphyne/graphdiyne sheets into papyrus-like structures. Nanoscrolls present high radial flexibility and large solvent accessible surface area, which opens the possibility of many applications. This kind of structure has been already experimentally realized with different materials, such as graphene, graphene oxide and hexagonal boron nitride. For a recent review see ref. [4].
In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics of nanoscroll formation for a series of α, β, and δ graphyne and graphdiyne nanoscrolls. We have also investigated their thermal stability for a temperature range of 200-1000K. Our results show that stable nanoscrolls can be formed for all structures considered here. Their stability depends on a critical value of the ratio between width and height of the graphyne/graphdiyne sheets. Our findings also show that these structures are less stable then graphene-based nanoscrolls, which is attributed to the strong pi-pi stacking interaction presented between the nanoscrolls walls, which in the present case become less effective due to the higher structural porosity. Also, for high temperatures we observed interlayer cross-links formation resulting from the chemical reactions of the acetylenic groups, forming a new class of quasi-3D nanostructures.

[1] R. H. Baughman, H. Eckhardt and M. Kertesz,^, J. Chem. Phys., v87, 6687 (1987).
[2] G. Li, Y. Li, H. Guo, Y. Li and D. Zhu, Chem. Commun., v46, 3256 (2010).
[3] V. R. Coluci, S. F. Braga, S. B. Legoas, D. S. Galvão, and R. H. Baughman, Phys. Rev. B v68, 035430 (2003).
[4] E. Perim, L. D. Machado and D. S. Galvao, Frontiers in Materials, v1, 31 (2014).

Graphene as a two-dimensional sheet of carbon atoms is found to be arranged in a honey-comb shaped planar lattice. When such a sheet of graphene is rolled, it can be used to explain the many different and often varying properties of another allotrope of carbon called carbon-nanotube (CNT) that exists in different chiral forms. These differences in the CNTs arise primarily because of the chiral vectors with ‘m’ equal to ‘n’ being metallic and ‘m’ not equal to ‘n’ being semiconducting. During the growth of CNTs, different chirality often exist together in a mixture making their separation a challenging task. Techniques such as gel chromatography and electrophoresis have been used on an industrial scale for achieving this. Furthermore, semiconducting properties of a CNT are important for the electronics industry to enhance the performance of electronic devices. However, efficient and inexpensive separation of a mixture of CNTs remains a problem. Here we show through molecular dynamics and circular dichroism how the outermost domain of flagellin (D3) interacts specifically with m-CNT (metallic CNT) in a mixture through glycine. Based on the residues that are adsorbed onto the CNTs, nine different combinations of tripeptides including glycine with its flanking residues were extracted from the amino acid sequence of D3. Simulations were carried out using visual molecular dynamics (VMD) and NAMD between m-CNT as well as s-CNT (semiconducting CNT) and all the nine combinations of tripeptides for a period of 50 ns at a temperature of 300 K and a pressure of 1 atm. As glycine interacted specifically with m-CNTs, the flanking residues energetically improved the binding events. It was observed that hydrophobic flanking residues established stronger interactions between glycine and m-CNTs whereas polar flanking residues weakened the binding events. On the other hand, for s-CNT, the non-binding interactions with the tri-peptides were lower compared to m-CNT with lesser contact time. The presence of hydrophobic flanking residues completely disrupted the already weak interactions between glycine and s-CNT. It is thus found that the flanking residues of glycine play a major role in its interaction with m-CNT and s-CNT. Such a phenomenon can be explained by the band-gap theory of metals and semiconductors where the activation energy of tri-peptides being closer to the band-gap energy in metals helps the tri-peptides interact in an energetically favorable manner with the m-CNT. However, s-CNT being stable with the least energy, the band-gap energy is higher than the activation energy of the tri-peptide making it difficult to interact with the tri-peptide in excitation state. This study of the interactions between D3 and CNTs can pave a way for a biological method separating CNTs based on their chirality giving crucial insights into the effect of the primary structure of a protein on the non-binding interactions with CNTs.

One of the greatest challenges with single-walled carbon nanotube (SWNT) based nanostructured devices is maintaining the nanotubes in their pristine state so that their unique opto-electronic characteristics are preserved. Recent studies have shown that organization of special surfactants around single walled carbon nanotubes allows individualization of single-walled carbon nanotubes (SWNTs) that exploit their unique properties. These surfactants adapt different organizational patterns from random to tubular. Our group has shown that flavin mononucleotide (FMN) and its aliphatic (dodecyl) analog FC12 self-organize in a helical pattern that forms a tubular assembly around SWNTs. Such helical wrapping originates from four sets of H-bonds that “stitch” the neighboring FMN moieties into a continuous helical ribbon, and the π-π interaction of the isoalloxazine ring with the underlying graphene sidewalls. Understanding of molecular motifs and relative interactions involved in their formation may allow us to enhance the organization complexity of these assemblies. Along these lines we investigated a smaller analogue of FC12, i.e. lumazine (LC10) where the terminal phenyl ring of flavin has been removed, resulting in a bicyclic, rather than a tricyclic, moiety. Using Molecular Mechanics simulations the aim of this study is to elucidate the organizational pattern of lumazine (LC10) in comparison to that of FC12. In addition, this contribution intends to address whether the shorter lumazine repeat introduces a gap between helical repeats, which can be studied via spectroscopic techniques.

Significant advances in organic photovoltaic materials make them the potential candidate for next generation photovoltaics. Our group recently reported a Flavin-C₆₀ (FC₆₀) compound, which shows efficient photoluminescence (PL) quenching as a potential candidate towards organic photovoltaics devices. FC₆₀ links the isoalloxazine with C₆₀ moiety through a flexible aliphatic chain. Flavin-C₆₀ complexes (FC₆₀) can interact with the SWNTs in a more defined manner, through the isoalloxazine helix .This study aims to explain the efficient isoalloxazine PL quenching in dilute FC₆₀ solutions and its interactions with SWNTs. Molecular mechanics and Molecular dynamics were used to study the various conformations of aforementioned systems. These calculations indicate flexible aliphatic chain of FC₆₀ can adopt different conformations in order to bring the isoalloxazine moiety in close proximity with the fullerene group. This makes a stable ground state complex compared to its extended conformation via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix and the C₆₀ cage, that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C₆₀ in π-π overlap with the isoalloxazine helix.

Conjugated polymer extraction (CPE) has been shown to be a highly effective method to isolate high purity semiconducting single-walled carbon nanotubes (sc-SWCNTs). In both literature reports and industrial manufacture, this method has enabled large scale enrichment of sc-SWCNTs of high purity (≥ 99.9%) but exclusively in non-polar solvents such as toluene. Very little has been reported regarding the usage of polar solvents and thus the preparation of hydrophilic inks. Using the conjugated polymer with hydrophilic side chains we have investigated the enrichment of SWCNTs (synthesized via the plasma torch method) in polar solvents. Various conditions (polymer-to-SWCNT ratio, solvent type, silica gel treatment) were explored in order to maximize yield and purity of enriched sc-SWCNTs. This presentation will report on the scope and limitations of using the conjugated polymer with hydrophilic side chains in polar solvents to obtain sc-SWCNTs with high purity and high yield comparable to the non-polar solvent counterparts. The prepared hydrophilic inks demonstrate high performance in thin film transistor devices.

Carbon nanocoils (CNCs) are an exotic class of low dimensional nanocarbons with helical shape. Typical thicknesses and coil diameters of CNCs fall within the ranges of 100–400 nm and 400–1000 nm, respectively, and their full lengths are on the order of several tens of micrometers [1].
We have developed a precise resistivity measurement system for quasi-one-dimensional nanomaterials using a focused ion beam [2]. The system enables the resistivity of CNCs to be measured and its dependence on coil geometry to be elucidated. At room temperature, the resistivity of CNCs tended to increase with coil diameter, while that of artificially graphitized CNCs remained constant. These contrasting behaviors indicate coil-diameter-induced enhancement in structural disorder internal to CNCs. Low-temperature resistivity measurements performed on the CNCs revealed that electron transport through the helical axis is governed by the variable range hopping mechanism. The characteristic temperature in variable range hopping theory was found to systematically increase with coil diameter, which supports our theory that the population of sp2-domains in CNCs decreases considerably with coil diameter.
References
[1] Taiichiro Yonemura, Yoshiyuki Suda, Hiroyuki Shima, Yasushi Nakamura, Hideto Tanoue, Hirofumi Takikawa, Hitoshi Ue, Kazuki Shimizu, Yoshito Umeda, Carbon, 83 (2015) 183-187
[2] Yasushi Nakamura, Yoshiyuki Suda, Ryuji Kunimoto, Tamio Iida, Hirofumi Takikawa, Hitoshi Ue, Hiroyuki Shima, Applied Physics Letters, 108 (2016) 153108-1-4

In this work, we report on the mechanical behavior of a dense brush of small-diameter (1-3 nm) non-catalytic multiwall (2-4 walls) vertically aligned carbon nanotubes (VACNTs), measured using spherical nanoindentation and SEM in-situ micro-pillar compression testing. These VACNT brushes were produced using high temperature vacuum decomposition of 6H SiC single crystals which results in very high density of close to 0.95 g/cm³, which is 10 or more times higher than CNTs produced by other techniques, and a very small 0.35 nm inter-tube distance. At these small inter-tube distances, electron beam irradiation has been shown to introduce stable links between neighboring carbon nanotube. The purpose of this current work is to study the mechanical behavior of VACNTs subjected to such inter-tube bridging. This work will also seek to study the viscoelastic response of the VACNTs in regards to the volume of the crosslinked region.

Both spherical nanoindentation and micro-compression experiments demonstrate a significantly higher loading modulus (~17-20 GPa) and orders of magnitude higher buckling resistance in these dense CNT brushes, as compared to vapor phase deposited CNT brushes or carbon walls. Indentations using indenters of varying sizes show a considerable increase in the buckling strength values of the CNT turf with decreasing indenter radii.

For in-situ SEM micro-compression experiments we utilize focus ion beam (FIB) micromachining technique to fabricate VACNT micro-pillars of varying diameters. Exposure to ion beam is expected to introduce stable links between neighboring CNTs within the VACNT bundle. Thus micro-compression testing of VACNT pillars of varying diameters allows us to study the mechanical and viscoelastic response of the VACNT bundle as a function of the amount/degree of intertube bridging. The micro-compression results demonstrate a significantly higher buckling strength for pillars with smaller diameters, suggesting reinforcement from the outer rim containing of crosslinked CNTs. Decreasing the pillar diameter is also seen to cause a more brittle failure in the VACNT pillars. The compression experiments were also used to characterize the change in the viscoelastic response in terms of the (i) VACNT pillar diameter (volume of crosslinked region), (ii) frequency dependence, and (iii) the stress/strain applied on VACNT pillars with varying diameters and a nominal height 1μm.
As such, the ability of these dense CNTs to dissipate energy, while withstanding such elevated loads, is highly promising for energy-absorbing applications, especially in MEMS devices.

In recent years, nanomaterial-based strategies have emerged as an attractive approach in combating hematology-related diseases, such as thrombosis and malaria. With their unique physico-chemical properties and biocompatibility [1-4], graphene and its related derivatives, specifically graphene oxide (GO), have been increasingly explored for this purpose. Here, we examine the nano-bio interactions between GO and blood plasma proteins to elucidate the bio-physico-chemical activity of GO for hematological applications [5-6]. We investigate numerous facets of the GO-protein interactions, particularly, protein adsorption, binding kinetics and equilibrium, and conformational stability [5]. We observe that GO possesses a high loading capacity and affinity for the three plasma proteins of albumin, globulin, and fibrinogen. Also, we note that these molecular interactions are significantly influenced by the lateral size and concentration of GO. On the basis of the robust protein adsorption on GO and the size- and concentration-dependent nano-bio interactions, we probe the antithrombotic and antimalarial properties of GO and then show its potential in combating these hematological disorders [6]. We foresee that this study will offer a broad perspective on nano-bio interactions and potentially facilitate the exploration into the development of nanotechnology-based strategies for hematological and other biological applications.

[1] A.M.H. Ng, Kenry, C.T. Lim, H.Y. Low, K.P. Loh. Biosensors and Bioelectronics, 65:265-273 (2015).
[2] W.C. Lee, C.H. Lim, Kenry, C. Su, K.P. Loh, C.T. Lim. Small, 11:963-969 (2015).
[3] Kenry, P.K. Chaudhuri, K.P. Loh, C.T. Lim, ACS Nano, 10(3):3424-3434 (2016).
[4] Kenry, K.P. Loh, C.T. Lim, RSC Advances, 6:46558-46566 (2016).
[5] Kenry, K.P. Loh, C.T. Lim, Nanoscale, 8:9425-9441 (2016).
[6] Kenry, K.P. Loh, C.T. Lim, Small, 11:5105-5117 (2015).

Single-walled carbon nanotubes (SWNTs) have a hollow space in the nanometer size that can be encapsulated various functional molecules. The confined molecular assemblies exhibit unique low-dimensional structures and solid state properties that can not be realized in the bulk states. Synthesis and structures of ionic crystals encapsulated SWNTs have been reported [1-3]. However, tube diameter, chirality or temperature dependence on the local structure and properties of ionic crystals encapsulated SWNTs have not been systematically investigated. In this study, we report the effects of the diameter and chirality of SWNTs on the local structures and the electronic states of the encapsulated cesium iodide (CsI) and the other ionic crystals by using molecular dynamics (MD) and first-principles density functional theory (DFT) simulations.
In the MD simulation, we used the Born-Mayer-Huggins-Tosi-Fumi intermolecular potential between the alkali halide ions and the Dreiding potential between carbon atoms in SWNT. We have designed on the armchair and zigzag nanotubes with diameters ranging from 1.1 to 1.6 nm. One SWNT and any number of alkali halide ion pairs (Cs-I) around SWNT were set in a rectangular cell as initial configuration. Stable structure at 300 K was calculated with the NVT ensemble after the relaxation calculation at 1000 K. Stable structures was calculated to raise the temperature by 100 K from 300 K to 1000 K. The detailed results on the local structures of encapsulated CsI crystals and the values of the melting points will be presented.
In the DFT calculation, we used a code package PWscf and GIPAW in Quantum ESPRESSO. We also made claculations of NMR chemical sift and Electric field gradient (EFG) tensors.
Detailed results on the simlations, including the experimental results on TEM and solid-state NMR spectroscopy will be presented.

We propose a new type of an electromagnetic shielding (EMS) sheet that consists of carbon-nanotube (CNT)-composite papers (CNTCPs). Nowadays, electromagnetic environment has become increasing complexity. Undesired electromagnetic noise is generated and spread in the air constantly. It causes error for electronic devices. Therefore, such noise must be prevented strictly. As one of the solutions, EMS sheets based on metallic materials are used usually. In the previous study, we focused on the use of CNTs instead of the metallic materials to develop a new type of the shielding sheets because they have electromagnetic wave absorption ability caused by its high electrical conductivity. However, generally, it is difficult to handle the CNT because it is nanoscale material. As a solution of that, we have developed the CNTCP that can be fabricated easily by our composite-paper-making method based on a traditional Japanese washi paper making method. To make our CNTCP, a pulp suspension is prepared by soaking and dispersing paper fibers in water at first. Next, a CNT suspension is prepared. Then, the pulp and the CNT suspensions are mixed. Finally, the mixed suspension is scooped up by wire netting and dried by a heating press. As a result of this process, our CNTCPs are obtained. The proposed shielding papers have shown up to about 70 dB shielding effectiveness (SE) for the near field (~1 GHz). Moreover, they have unique properties, e.g., flexible and light weight, in addition to showing SE. In the recent information society, EMS sheets for a high frequency band, i.e., the far field (more than a few GHz), are wanted because the information and communication technology needs and uses such band for example.
We here study and evaluate the far field SE of our CNTCP. Moreover, we design a new type of an EMS-CNTCP, i.e., a stacking type of a shielding paper, to increase SE. Generally, thickness of the shielding sheet is made thicker to increase SE. However, in case of the “paper,” it is difficult. As a solution of this, “stacking” is very effective we considered. In this study, we prepare our shielding papers having two-, four- and eight-layers and measure SE of them (targeted frequency band is from 0.5 GHz to 18 GHz), respectively.
As results of measurements, we have found that our CNTCP has had the SE for the targeted far field, i.e., our EMS paper can be used for the frequency band from 0.5 GHz to 18 GHz. Moreover, we have also found that we can control not only its thickness but also the magnitude of SE easily by changing the stacking numbers of papers. We now consider that our EMS paper may also obtain an additional effect for shielding by “stacking.” In case of making an EMS sheet thicker, its construction should be as one. However, in case of our EMS paper, its construction must not be quite as one, i.e., the air or something must be put between papers. We are checking the effect caused by “something,” and we will clarify it in near future.

Carbon nanotubes (CNT) are currently being exploited for a large number of applications due to their

excellent mechanical and electrical properties. Direct use of these nanomaterials necessitated the

development of nano-composites with different bonding and matrix materials. In this work, multiwall

CNTs are used in combination with N-methyl- 2-pyrrolidone(NMP) and polyurethane(PU) for preparing

nanocomposite films. The uniform dispersion of CNTs and the solubility of PU is achieved by NMP,

which is used as a solvent. High flexibility, damping and elastic properties of polyurethane were

considered during its selection as the polymer matrix of the composite. Polyurethane/ multi-walled

carbon nanotube elastomer composite films are synthesized on polyimide and glass substrates using

spin coating methods. For the first time, this paper is reporting the use of Ultraviolet-Ozone Plasma

treatment(UVO) for enhancing the surface energy of the substrate. This was found to enhance the

adhesion strength of the deposited PU-CNT nanocomposite films after a systematic optimization of the

UVO duration. These studies are carried out from 5 mins to 40 minutes. The surface energy of the

substrate was determined to be 86.5mN/m for the polyimide substrate. The microstructure of these

films are examined using optical and scanning electron microscopes. The conductivities of the films are

examined using Van der Pauw method. The AC conductivity of 1wt%, 5wt% and 8wt% CNT loaded PU

nanocomposite films were found to be 3.86, 5.90 and 5.38 S/m respectively which are few orders

higher than the values reported in the literature. These values were confirmed with the Nyquist plot

and equivalent circuit modelling. This shows the frequency independent conductive nature of the

composite films. The quality of the films is analyzed using Laser Raman spectroscopy. The effect of

substrate (Polyimide or Glass), UVO exposure (Ultraviolet-Ozone plasma treatment, carbon nanotube

loading (1-8%), ultra-sonication time(20 min to 1 hour), annealing conditions (80 to 130 o C) on the

quality of the films are presented in detail in this paper. The results of these studies are further

analyzed and discussed.

Single-walled carbon nanotubes(SWNTs) have a hollow space in the nanometer size that can be encapsulated various functional molecules. The confined molecular assemblies is expected to exhibit unique low-dimensional structures and solid state properties that can not be realized in the bulk states. Recently, syntheses of sulfur encapsulated SWNTs or selenium encapsulated DWNTs and unique one-dimensional conductive sulfur chain structure or double-helices selenium structure were reported. In this study, we report the effects of chirality and diameter of CNTs on the local structure and molecular structure and electronic states of the chalcogens encapsulated by SWNTs by using molecular dynamics(MD) simulations and First-Principles DFT calculations.
In the MD simulations we used SCIGRESSVer2.3.0(Fujitsu). GEAR method of the fifth order in the numerical integration method and the speed scaling method were used as the temperature control methods. One SWNT and slufur or selenium atoms in rectangular cell as initial configurations and structural relaxation were performed at 1 K, 800 K and 297 K by using NTV ensembles. In the First-Principles DFT calculations, we used a code package PWscf and GIPAW in Quantum ESPRESSO. We have calculated the electronic states of encapsulated chalcogen assemblies and their solid-state NMR parameters(chemical sift and electric field gradient (EFG) tensor). The detailed results will be presented.

Jacob Gissinger, Chandrani Pramanik, Satish Kumar, Hendrik Heinz

The unrealized potential of polyacrylonitrile (PAN) based carbon fibers is investigated through molecular dynamics simulations using the PCFF-INTERFACE force field.¹ A novel polarized model for carbon nanotubes (CNTs) is used in order to observe nanoscale behavior at the solid-state PAN/CNT interface. The role of this interface on stress transfer is confirmed to be crucial to composite mechanical properties. Interfacial shear strength is found to be dependent on the pre-orientation of the PAN precursor, indicating that a highly aligned polymer matrix will encourage the templating of chains even prior to the carbonization process. The mechanism behind this dependence is observed at the molecular level with particular attention paid to the behavior of PAN’s reactive nitrile groups. Voronoi analysis of these groups reveals patterns which could be correlated to the fiber’s eventual carbonized morphology. Trends in binding energy and glass transition temperature with respect to CNT diameter are also interpreted and related to experimental process parameters.<sup>2

[1]</sup> Heinz, H.; Lin, T.-J.; Mishra, R. K.; Emami, F. S.; Langmuir, 2013, 29,1754
² Chae, H. G.; Newcomb, B. A.; Gulgunje, P.V. ; Liu, Y., Gupta, K. K.; Kamath, M.G. ; Lyons, K. M.; Ghoshal, S.; Pramanik, C.; Giannuzzi, L.; Sahin, K.; Chasiotis, I.; Kumar, S. Carbon , 2015, 93, 81

Arc discharge is one of the most efficient and environmental friendly method to synthesize Single Wall Carbon Nanotube (SWCNT). However, due to the ultra-fast synthesis procedure, localization of the SWCNT synthesis in an arc discharge plasma volume in situ has been a long standing problem. This relates to the ability of controlling volumetric synthesis of nanostructures in plasmas in general. In order to better understand the mechanism of the nanotube growth in plasma, we have developed an actuator driven high-speed system that is able to extract material from the arc plasma volume during the synthesis procedure. The majority of the SWCNTs produced using arc discharge method are semiconducting with diameter of about 1.5nm. It is shown that the growth region of SWCNTs is between 3mm to 11mm away from the center of the arc discharge. Dependent on the origin, the length of SWCNTs increases non-monotonically up to 500nm, while diameter and chirality only slightly depend on the growth position.
An actuator driven high-speed system has been developed that is able to extract material from the arc plasma volume during the synthesis procedure. Scanning Electron Microscope (SEM) and RAMAN spectrum has been used as the characterization device. Along each substrate, the wide and obtuse D and G bands transfer into thin and sharp peaks. This phenomenon indicates that the extracted material along each sample transferred from amorphous carbon to perfect SWCNTs. Time dependent numerical simulation of the probe temperature in the presence of hot arc plasma has been performed in order to prove that nickel nanoparticles collected from the arc plasma are likely solidified and thus cannot promote SWCNT growth at the probe’s surface.
In this paper, we describe the direct experimental localization of the nucleation and the synthesis of carbon nanotubes by in situ extracting the growth products from the discharge plasma. This work presents measurement of SWCNT formation region in arc discharge plasma and obtaining the relationship between the SWCNT length and the distance from the center of the arc.
Acknowledgment:
The authors benefited from fruitful discussions with Dr. Y. Raitses and Dr. M. Shneider. The authors thank Dr. M. Kundrapu for help with numerical simulations of arc discharge. This work was supported the US Department of Energy, Office of Science, Basic Energy Science.

The influence of various dispersion parameters on the evolution of multi-walled carbon nanotubes (MWCNTs) in titanium (Ti) metal matrix composites (TMCs) prepared via powder metallurgy routes have been investigated. Ti-MWCNTs powder mixtures were synthesized by sonication and high energy ball milling (HEBM). The impact energy provided to the powder mixtures during the dispersion processing was quantified and optimized to disperse 0.5 wt.% MWCNTs into Ti matrix in two controlled ball milling processes: with and without in-situ formation of TiC during HEBM. The effect of dispersion processing parameters on the sp² C-C network in MWCNTs, resultant microstructures and mechanical properties of TMCs was investigated. The interfacial reactions between MWCNTs and Ti matrix were controlled by retaining the crystallinity of MWCNTs during the processing stages of TMCs. The defects induced in MWCNTs during the synthesis of TMCs were quantified and their relationship was established with the interfacial reactions with Ti matrix during high temperature consolidation stages. The mechanical properties of MWCNTs in the composites consolidated from the powder mixtures with in-situ TiC formation during HEBM and pre-sonicated MWCNTs were significantly enhanced as opposed to the composites consolidated from the powder mixtures without formation of TiC during HEBM.

Graphene is expected to have various electronic applications such as supercapacitors, field-emission devices, and sensor devices due to its excellent material properties. Various processing methods such as filtration, inkjet printing, dip coating have been developed to make graphene films. However, graphene films made by these methods show lower electrical conductivity than the expected value due to the poor connectivity between graphene particles. Results from some researchers showed that the electrical conductivity of graphene fibers can be enhanced by hybridizing large graphene particles with small graphene particles. In that work, they claimed that the reason for the increase in the electrical conductivity is that the small graphene particles are filling the microvoids between the large graphene particles. We have studied to make predictive model for calculating size difference and composition where it shows optimum electrical conductivity. We have fabricated graphene hybrid films composed of graphene of different size to verify this theoretical model. The electrical conductivity from the experimental results showed similar trend with the theoretical model we have proposed, showing that optimal size difference and composition of graphene particles can be predicted theoretically.

Epoxy adhesive can be used to connect two different materials in composite structures. Comparing with other mechanical fastening methods, such as bolt or rivet, the adhesive does not need to use them. It leads to reduce the weight and decrease the stress concentration along the connecting line. This work studied mechanical, interfacial and deformation properties of bisphenol-A type neat epoxy, CNT-epoxy adhesives and an acrylic-type adhesive for comparison. Static contact angle, and work of adhesion between either neat epoxy or CNT-epoxy and acrylic adhesives were measured to verify the water durability on the interfacial adhesion. Lap shear and their fatigue strengths of 3 adhesives were measured for mechanical test. Different elastic waves which occurred during fracturing were evaluated by acoustic emission (AE) and fractured patterns were observed by microscope. Shear and fatigue strength of CNT-epoxy adhesive was better than neat epoxy adhesive, whereas fatigue strength used by acrylic adhesive was better than CNT-acrylic adhesive. In terms of fracture elastic energies, AE outcomes were consistent well with lap shear and fatigue testing results. Reinforcement by CNT in epoxy adhesive exhibited the improvement in interfacial adhesion as well as adhesive modulus under both ambient and wet conditions. Acknowledgements: this work was supported by National Research Foundation of Korea under, 2016-2022 (2016R1D1A1B01012620). This work was also supported by BK 21 plus project, 2016-2020.

Since their discovery in 1991, an intense effort has been spent on investigating the unique and advantageous properties of single-wall carbon nanotubes (SWCNTs). Apt examples include 20-times stronger than steel, 10-times higher thermal conductivity than copper, half the density of aluminum, and 10-times more carrier mobility of silicon. As such, over the past 25 years, the use of SWCNTs in a wide range of applications has been expected and anticipated, and many research projects have been carried out world-wide to harness the potential of one of the most promising materials in nanotechnology.
In November 2015, Zeon Corporation (ZEON) completed and begun operation of an industrial-scale mass production plant for SWCNTs based on the Super-growth (SG) method developed by the National Institute of Advanced Industrial Science and Technology (AIST). This approach affords high efficiency and large quantity synthesis where the SWCNTs possess high purity, high specific surface area, and high aspect ratio compared with other commercial carbon nanotubes.
To promote the development of commercially available mainstream SWCNT-based applications, as well as to overcome the bridging between basic science and industry, this presentation will discuss our strategy for understanding targeting applications needed by industry. In addition, my presentation will contain discussion on the technological advances in areas, such as rubber and metal-based composite materials.
This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

An overview of carbon nanostructures, from nanotubes to graphene to carbon aerogel, will be given. Various applications of these carbon nanostructures, especially in the area of energy storage will be summarized and compared. Achieving important function, rather than only focusing on the nanoscale structures, will be the key consideration in developing these desired structures.

NASA is currently working on developing motors for hybrid electric propulsion applications in aviation. To make electric power more feasible in airplanes higher power to weight ratios are sought for electric motors. One facet to these efforts is to improve (increase) the conductivity and (lower) density of the magnet wire used in motors. Carbon nanotubes (CNT) and composites containing CNT are being explored as a possible way to increase wire conductivity and lower density. Presented here are measurements of the current carrying capacity (ampacity) of a composite made from CNT and copper. The ability of CNT to improve the conductivity of such composites is hindered by the presence of semiconductive CNT (s-CNT) that exist in CNT supplies naturally, and currently, unavoidably. To solve this problem, and avoid s-CNT, various preferential growth and sorting methods are being explored. A supply of sorted 95% metallic CNT (m-CNT) was acquired in the form of thick film Buckypaper (BP) as part of this work and characterized using Raman spectroscopy, resistivity, and density measurements. The ampacity (A/cm²) of the Cu-5vol%CNT composite was 3.8% lower than the same gauge pure Cu wire similarly tested. The lower ampacity in the composite wire is believed to be due to the presence of s-CNT in the composite and the relatively low (proper) level of longitudinal cooling employed in the test method. Although Raman spectroscopy can be used to characterize CNT, a strong relation between the ratios of the primary peaks G/G’ and the relative amounts of m-CNT and s-CNT was not observed. The average effective conductivity of the CNT in the sorted, 95% m-CNT BP was 2.5 times higher than the CNT in the similar but un-sorted BP. This is an indication that improvements in the conductivity of CNT composites can be made by the use of sorted, highly conductive m-CNT.

Thermal interface materials (TIMs), which are applied between contacting surfaces of heat-generating devices and heat sinks, have become important research topics for efficient electronics cooling.[1] However, state-of-the-art TIMs have demonstrated significantly lower thermal conductivity (κ) than intrinsic κ of fillers due to the incomplete thermal percolation pathway and high interfacial thermal resistance. Here we adopted a multi-dimensional filler design composed of 3D microscale Ag flakes, 1D multiwalled carbon nanotubes (MWNTs), and 0D silver nanoparticles (Ag NPs).[1] MWNTs decorated with Ag NPs (nAgMWNTs) were successful in increasing electrical conductivity of polymer matrix composites in our previous studies.[2-4] However, this combination provided an even greater opportunity to enhance κ due to the significantly higher intrinsic κ (~3000 W/mK) of MWNTs than that of Ag flakes (429 W/mK).[1] We achieved ultrahigh κ (160 W/mK) of epoxy-matrix TIMs with a significantly greater lattice thermal conductivity (144.5 W/mK) than electronic thermal conductivity (15.4 W/mK).[1] nAgMWNTs constructed efficient phonon transport pathways between microscale Ag flakes. [1] Adv. Mater., DOI: 10.1002/adma.201600642 (2016) [2] Adv. Mater., 24, 3344 (2012) [3] Nano Lett., 14, 1944 (2014) [4] ACS Nano, 9, 10876 (2015)

Flexible, body-worn healthcare/medical devices have the potential to revolutionize preventive medical care and health promotion. Carbon nanotube (CNT) thin films are promising bio-electronic materials for transistors, biosensors, and other passive components to build such wearable devices because of the excellent electronic and mechanical properties and biocompatibility. In the recent works, we have studied CNT thin film technologies from the growth of CNTs and the thin film formation to device fabrication and characterization on flexible and stretchable films. High-mobility flexible thin-film transistors (TFTs) and their integrated circuits have been realized on a transparent plastic film. We have also demonstrated extremely stretchable CNT TFTs. Highly-sensitive, flexible biosensors with excellent uniformity in the sensing property have also been realized.
First, we have developed a method to realize high-mobility CNT thin films, based on a gas-phase filtration and transfer process. CNTs were grown by a floating-catalyst CVD technique. The CNT film was collected by filtering through membrane filters at room temperature, and transferred to the substrate with electrodes of TFTs. This technique enables to form CNT films with high mobility (>600 cm²/Vs) and controllable threshold voltage on a plastic film.
CNT films can also be used as electrodes and interconnections, which are flexible, transparent, stable, and free of rare metals. By using CNT transparent conductive films, we realized all-carbon TFTs and ICs, in which the electrodes and interconnections consist of CNT film and the insulators consist of PMMA. The all-carbon device was able to be formed into three-dimensional dome-shape devices by the thermo-pressure forming technique. We also demonstrate extreme stretching ability of all-carbon devices fabricated on PDMS thin film.
One of critical issues of CNT biosensors is reproducibility in terms of device fabrication and characteristics. In this work, uniform and ultra-clean CNT thin film was formed on a plastic film by the dry transfer process. Both amperometric (electrochemical) and potentiometric (field-effect transistor) sensors were fabricated using the CNT thin film. To prevent the contamination, the CNT thin film was covered with an oxide layer during the fabrication process.
The electrochemical property of the CNT-thin film electrode exhibited almost ideal characteristics. The quartile potential was 60.4 mV, which was close to an ideal value of 56.4 mV. The steady-state current (I_SS) of the micro-electrodes well-agreed with the theoretical diffusion-controlled I_SS. The device-to-device variation in steady state current was less than 6%, showing excellent reproducibility of CNT amperometric sensors. We also fabricated CNT TFT-based potentiometric sensors on a plastic film. High-sensitivity (10 pM) and wide-range (10⁶) detection of dopamine was confirmed by using CNTs decorated with pyrene-1-boronic acid.

Carbon nanotubes (CNT) and graphene have emerged as materials for next-generation electrodes in organic solar cells (SCs) and perovskite SCs, offering a possible alternative to indium tin oxide (ITO)-based SCs. CNTs and graphene have excellent mechanical flexibility and are composed entirely of highly abundant carbon. Single-walled CNTs (SWCNTs) have advantages in terms of stretchability, ease of synthesis, and suitability for direct roll-to-roll deposition onto substrates, which translate to lower costs. SWCNTs as transparent conductive films in photovoltaics have been the subject of active research.
For the research in SCs, they have attracted a great deal of attention as solution-processable and flexible light-harvesting devices that have the potential to meet the world’s energy needs. The efficiency of SCs has increased tremendously with the emergence of perovskite SCs. As the result, power conversion efficiency (PCE) has reached as high as 20%. However, SC flexibility is still limited by the use of ITO, which is bendable but not completely flexible nor stretchable like CNTs.
Here in this work, we demonstrate applications of SWCNTs as transparent electrodes in organic SCs and perovskite SCs. Moreover, we show the SWCNT films can be used to replace ITO as well as the metal electrode. Because doping in CNT to improve its transparency and conductivity is crucial, we also investigate several dopants and the methods of application. Our ITO-free SWCNT organic SCs showed a PCE of 6.04% with the PTB7:PC71BM photoactive layer in which MoOx thermal doping was applied. On the other hand, metal-free window-like SWCNT organic SCs produced a PCE of 4.1%. For the application in perovskite SCs, diluted HNO3 (35 v/v%)-doped SWNT-based device produced the highest PCE of 6.32% which was about 70% of the ITO-based device (9.05%).

How to create a high performance and multifunctional sp² carbon nanostructured fiber (Nanotube/Graphene) is one of the most exciting topics for realizing light weight, strong, and multifunctional cable, wire, textile and structural material to electronic systems such as sensors, medical devices and energy harvest and storage platforms. Here we demonstrate a novel approach enabling an intrinsic structural transformation of carbon nanotubes inside the fibers creating structurally seamless and macroscopically continuous multilayered graphene nanoribbon and/or multi-walled nanotube fibers by applying highly controlled electrical energy. High Resolution Transmission Electron microscope (HRTEM), small angle X-ray diffraction (XRD), and Raman spectroscopy (the intensity ratio of D band and G band) reveal that, after applying controlled alternate voltage with certain frequency, most of the original double-walled carbon nanotubes are transformed to the continuous graphitic nanoribbon and multi-walled structures showing increased number of graphene layers and significantly decreased the wall distance with Significantly improved sp² lattice crystallinity over the large area. This novel continuous structure, which is impossible to synthesize using conventional methods, leads to up to 10 times higher thermal conductivity (150-200 W/mK) and 20-30% decreased electrical resistivity compared to intrinsic nanotube fibers.

Previous reports for pressure-driven transport through CNT membranes demonstrated CNT permeability values that were orders of magnitude larger than those predicted by Knudsen diffusion theory for gases (~10² fold enhancement) and by Hagen-Poiseuille equation for liquids (10³-10⁵ fold). While these results spurred great interest in CNTs for efficient membrane separations, it remains an open question if driving forces other than pressure could result in similar transport rate enhancements. A positive answer would greatly extend the promises and application space of CNTs as fluidic channels.
In this work, we provide the first experimental evidence of enhanced gas transport in CNTs driven by a concentration rather than a pressure gradient. We fabricated cm², free-standing, flexible, 1-5 nm SWNT/parylene membranes with well-aligned nanotubes as only transporting pores, and we measured the water vapor diffusion rate through the membrane when each surface is exposed to a different relative humidity. Our measurements demonstrate that these membranes exhibit rates of water vapor transport (~8000 gr/m²day) that surpass those of commercial breathable fabrics, even though the CNT pores are only a few nm wide and the overall porosity is less than 5.5%. Measured permeability of our CNT channels is 24 times larger than Knudsen diffusion prediction, and this flow enhancement is close to that measured for pressure-driven transport of nitrogen.^[1] Membranes made from 1-3 nm SWNT forests with higher number densities (> 10¹²/cm²) display even larger gas-transport enhancements.
This ultrafast rate of water vapor transport in CNTs suggests that CNT membranes hold great potential for pervaporation, membrane distillation, and as building block of breathable and protective fabrics. For the last application, a membrane shall be able to block dangerous components while permitting perspiration. By demonstrating complete rejection of 3-nm charged dyes, 5-nm uncharged gold (Au) nanoparticles, and ~40-60-nm Dengue virus from aqueous solutions during filtration tests, we provide evidence that, in addition to outstanding breathability, our CNT membranes provide a high degree of protection from bio-threats by size exclusion.^[1]

This work was supported by the Defense Threat Reduction Agency (DTRA) D[MS]² project under Contract No. BA12PHM123 and was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.


[1] N. Bui, E. R. Meshot, S. Kim, J. Pena, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater. 2016, DOI: 10.1002/adma.201600740.

Miniaturization of electronic devices using nanotubes is still hindered by difficulty in controlled synthesis of semiconducting carbon nanotubes. On the other hand, boron nitride nanotubes (BNNTs) are electrical insulators and cannot be used in electronic devices [1, 2]. Recently, we demonstrated that metallic quantum dots functionalized BNNTs (QDs-BNNTs) are potential candidates for conducting channels in tunneling field effect transistors (TFETs) [3]. Here we show that QDs with monolayer and multilayer gold atoms can be formed on BNNTs. The formation of these QDs and their function as TFETs will be discussed.
Controlling the size, spacing and uniformity of gold QDs on the surface of BNNTs are important for their application in TFETs. In our experiments, gold QDs are deposited on as-grown, vertically-aligned BNNTs by pulsed laser deposition (PLD). Results indicate that a careful selection of laser power, deposition duration and subsequent annealing temperatures allow rational control on the size, spacing and uniformity of QDs. By scanning tunneling electron microscopy (STEM), monolayer of gold atoms, gold chains and crystalline QDs are detected. Crystalline gold QDs as large as ~5-15 nm can also be formed simultaneously but located at the opposite surface of BNNTs. The electronic transport properties of these QDs-BNNTs are also investigated by using four-probe scanning tunneling microscopy (4-probe STM). Results suggest that the formation of these gold QDs on BNNTs has enabled electronic switching behavior at room temperature. Subsequent modeling suggests that the local density of states (LDOS) of these QDs-BNNTs are tunable. The growth mechanism of these QDs and their function in TFETs will be discussed in the meeting.
This work is supported by the U.S. Department of Energy, the Office of Basic Energy Sciences (DOE-BES Grants DE-FG02-06ER46294, and DE-SC0012762, PI:Y.K.Y.). Part of this work was conducted at the Center for Nanophase Materials Sciences (Projects CNMS2009-213 and CNMS2012-083, PI:Y.K.Y.), which is sponsored at Oak Ridge National Laboratory (ORNL) by the DOE-BES Scientific User Facilities Division, and by ORNL’s Shared Research Equipment (ShaRE) User Program.

References:
1. Wang, J.S., et al., Low temperature growth of boron nitride nanotubes on substrates. Nano Letters, 2005. 5(12): p. 2528-2532.
2. Wang, J.S., C.H. Lee, and Y.K. Yap, Recent advancements in boron nitride nanotubes. Nanoscale, 2010. 2(10): p. 2028-2034.
3. Lee, C.H., et al., Room-Temperature Tunneling Behavior of Boron Nitride Nanotubes Functionalized with Gold Quantum Dots. Advanced Materials, 2013. 25(33): p. 4544-4548.

Rare metals have high socio-economical and technological importance, while being prone to supply-demand fluctuations. Indium is currently used as ITO (indium-tin oxide) to provide transparent conducting films for a wide variety of consumer electronics devices, such as displays and touch screens for mobile phones and ipad-style portable computers. Recent introduction of bendable and flexible - and even formable and stretchable – devices requires novel materials to replace ITO, due to its brittle nature. In order to replace ITO, we have developed single-walled carbon nanotube (SWNT) and carbon nanobud (CNB) thin films. CNB material combines SWNTs and fullerenes with covalent bonding (Nasibulin, Kauppinen et al. 2007). Here we introduce our industrial scale, ISO 9001:2008 certified direct dry printing (DPP) manufacturing of CNB-based transparent conductive films (TCF) developed at Canatu Ltd. (http://www.canatu.com), enabling flexible and formable touch devices and the manufacturing of TCFs with electrical properties on par with those of ITO-on-PET, and with optical properties better than those of ITO, metal nanowires and metal mesh.
We present optically unsurpassed quality, CNB thin film based flexible capacitive touch solution for emerging flexible and 3D formable applications, including flexible active matrix organic electroluminescent (AMOLED) displays and automotive touch solutions. We also present various flexible and thin touch integration options for reflective electrophoretic displays (EPD) and AMOLED displays, including CNB integration on flexible cover window and on 12 µm moisture barrier film.


Nasibulin, A.G., Pikhitsa, P.V., Jiang, H., Brown, D.P., Krasheninnikov, A.V., Anisimov, A.S. , Queipo, P. , Moisala, A. , Gonzalez, D., Lientschnig, G., Hassanien, A., Shandakov, S.D., Lolli, G., Resasco, D.E., Choi, M., Tománek, D. and Kauppinen, E.I. (2007) A Novel Hybrid Nanomaterial. Nature Nanotechnology 2, 156-161.

We present a post synthesis self-assemble protocol that transforms the trillions of CNTs in powder form into densely packed flexible, robust and binder-free macroscopic membranes with hierarchical pore structure. The processing protocol has limited or no impact on the intrinsic properties of the CNTs. The binder-free CNT membranes could be as thin as < 10mm with mass density greater than that of water (1.0g/cc). As the thickness of the CNT membrane is increased, we observed a gradual transition from highly flexible to buckling and brittleness in the flexural properties of the membranes. We correlate the mass of the CNTs to thickness of the CNT membrane. We have demonstrated the use of the CNT membranes as electrode in two-electrode 1M H₂SO₄ aqueous double layer supercapacitor that shows very high power density ~1040 kW/kg based on the mass of both electrodes and time constant of ~ 15 ms with no degradation in performance even after 10,000 cycles. Furthermore, we will show the designing of flexible 3-stack solid-state ultracapacitor and 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 with very low leakage current ~ 10nA.

Graphene’s linear, gapless dispersion near the Dirac point endows it with unique properties desirable for detecting single photons. This band structure allows graphene to absorb photons of nearly any wavelength and through the use of resonant structures this absorption can reach nearly 100%. As an example, our simulations show that graphene critically coupled to a photonic crystal cavity and waveguide will have an absorption of 93% for 1550 nm light. Graphene’s energetic landscape also leaves it with a small density of states near the Dirac point translating into an exceptionally low heat capacity and thus a large temperature change upon absorbing just a single photon. For instance, calculations show that a 10 μm² sheet of graphene at 3 K could experience a temperature rise of up to 500% upon absorbing a single 1550 nm photon. To detect such temperature changes we propose using graphene as the weak link in a Josephson junction (JJ). We present a model demonstrating that a graphene-based JJ (gJJ) single photon detector could operate at the readily achievable temperature of 3 K with near zero dark count, sub-50 ps timing jitter, and sub-5 ns dead time. In addition, we present preliminary experimental results of an illuminated gJJ showing switching characteristics consistent with single photon detection.

The burgeoning of wearable health technology has made direct current (DC) driven nanoelectronic chemical detection one of the most attractive candidates due to its simple circuitry. To date, nearly all existing DC sensing methodologies are based on charge transfer between the sensor and the adsorbed vapor molecules. However, the high binding energy at the charge-trapped sites significantly limit those sensors’ response to tens to hundreds of seconds and also makes it inherently difficult for non-polar molecule detection, of which donor and acceptor effect is quite poor. Here we report a radically different sensing mechanism by exploiting the incomplete screening effect due to the semi-metallic nature of graphene. Molecular absorption induces capacitance change on the graphene transistor, which can be amplified intrinsically by the graphene transistor’s transconductance and measured conveniently as DC current change. Rapid (down to sub second) and sensitive (down to ppb) detection of a broad range of vapor analytes, including 17 polar and non-polar molecules, are achieved on a centimeter-area graphene field effect transistor covered with a micro fabricated flow channel. Specifically, we demonstrated, for the first time, alkane detection based on pristine CVD graphene. Our results not only pave the way to a universal gas sensor technology which offers high speed and high sensitivity to nearly all types of analytes, but also provide an ideal test bed for probing physisorption kinetics between hydrocarbon and π system.

Boron nitride nanotubes (BNNTs) are a type of light, strong, chemically and thermally stable tubular nanostructures, and are promising for disruptive fiber-reinforced polymer nanocomposites technologies. Although substantial advances have been achieved, the bulk mechanical properties of nanotube-reinforced polymer nanocomposites remain far from their anticipated levels. Lack of understanding of the nanotube-polymer interfacial strength is considered as one of the critical challenges in realizing their reinforcing effects. In this talk, we present recent experimental studies of the mechanical strengths of the interfaces formed by individual BNNTs with poly(methyl methacrylate) (PMMA) and epoxy resin, respectively. The nanotube-polymer interfacial strength was characterized by using in situ electron microscopy nanomechanical single-tube pull-out techniques. By pulling out individual tubes from polymer matrices using atomic force microscopic force sensors inside a high resolution scanning electron microscope, both the pull-out force and the embedded tube length were measured with resolutions of a few nano-Newtons and nanometers, respectively. The nanomechanical measurements reveal the shear-lag effects on nanotube-polymer interfaces. The analysis shows that the interfacial strengths of BNNT-polymer interfaces are statistically higher than those of the comparable carbon nanotube/nanofiber polymer interfaces. The superior load transfer capacity of BNNT-polymer interfaces is ascribed to both the strong van der Waals interactions and Coulomb interactions on BNNT-polymer interfaces, which is supported by molecular dynamics simulations. The research findings suggest that BNNTs are excellent reinforcing nanofiller materials for light-weight and high-strength polymer nanocomposites.

Conventional scaling of Si complementary metal-oxide semiconductor (CMOS) devices provided ever-improved transistor performance, density, power, and cost in the last four decades. However, it has become very difficult in recent 10 years with Si devices approaching their physical limits. In search for the next switch beyond silicon, carbon nanotubes are a very promising candidate, with a saturation velocity several times faster than silicon and intrinsic thinness (~ 1 nm in diameter) which enables superior electrostatic control to minimize the off-state leakage current even at ultra-small device dimensions. Here we discuss our recent advances in building high-performance nanotube transistors with extremely scaled device dimensions including both device channel length (L_ch) and contact length (L_c), separation of nanotubes based on their electronic types, and assembly techniques for forming nanotube arrays with high semiconducting nanotube purity and tight pitch. These results suggest that replacing Si with carbon nanotubes in high-performance logic devices at 5 nm technology node and beyond is feasible.

Calculations have indicated that aligned arrays of semiconducting carbon nanotubes (CNTs) promise to outperform conventional semiconducting materials in short-channel, aggressively scaled field effect transistors (FETs) like those used in semiconductor logic and high frequency amplifier technologies. These calculations have been based on extrapolation of measurements of FETs based on one CNT, in which ballistic transport approaching the quantum conductance limit of 2G_o=4e²/h has been achieved. However, constraints in CNT sorting, processing, alignment, and contacts give rise to non-idealities when CNTs are implemented in densely-packed parallel arrays, which has resulted in a conductance per CNT far from 2G_o. The consequence has been that it has been very difficult to create high performance CNT array FETs, and CNT array FETs have not outperformed but rather underperformed channel materials such as Si by 6x or more.

Here, we report nearly ballistic CNT array FETs at a density of ~50 CNTs µm^-1, created via CNT sorting, assembly, and treatment. The on-state conductance in the arrays is as high as 0.46 G_o per CNT, and the conductance of the arrays reaches 1.7 mS µm^-1, which is 7x higher than previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density reaches 900 µA µm^-1 and is similar to or exceeds that of Si FETs when compared at equivalent gate oxide thickness and off-state current density. The on-state current density exceeds that of GaAs FETs, as well. This leap in CNT FET array performance is a significant advance towards the exploitation of CNTs in high-performance semiconductor electronics technologies.

When a thin semiconducting layer acts as a tunnel barrier between two ferromagnetic (FM) contacts, the resistance in the circuit depends upon the relative orientation of the electron-spins between the contacts. Typically, the resistance changes from maximum to minimum depending upon whether the spins in the magnetic contacts are in anti-parallel or parallel spin configuration. The relative difference in resistance between these two magnetic configurations is known as tunnel magnetoresistance (TMR)-a phenomenon, which plays a vital role in high density data storage device. Intrigued by the weak spin-orbit and hyperfine interaction in carbon nanotube (CNT), researchers have used CNT as a spin transport channel between FM leads to design a next generation magneto resistive device [1, 2]. A spin flip scattering length of up to 250 nm has been reported [1] in the case of multiwall carbon nanotubes contacted to ferromagnetic (Co) leads. In addition, sign reversal of magnetoresistance is also observed [2] in both single-wall and multiwall carbon nanotubes contacted to PdNi leads. Despite these pioneering experimental efforts, the complete control over chirality and incomplete understanding of the FM-CNT interface make it harder to reproduce these results for practical applications. Understanding the role of spin-interface [3] at the CNT-FM junction is fundamental to developing a next generation magnetoresitive device. Herein, we have used a semiconducting single-wall CNT as a channel between two ferromagnetic electrodes to investigate the spin injection efficiency and tunnel magnetoresistance behavior in a prototypical CNT junction. A first-principles spin polarized density functional theory in conjunction with a single particle many-body Green’s function approach is used to probe the electric field manipulation of spin polarized current in a CNT-FM junction. Our calculations show that the sign of the tunnel magnetoresistance can be switched from positive to negative, which is consistent with the experimental observation.

References:
[1] K. Tsukagoshi, B. W. Alphenaar and H. Ago, Nature 401 (1999) 572-574.
[2] S. Sahoo, T. Kontos, J. Furer, C. Hoffmann, M. Gräber, A. Cottet and C. Schönenberger, Nature Physics 1 (2005) 99-102.
[3] S. Mandal and R. Pati, ACS Nano 6 (2012) 3580-3588.

Due to their outstanding transport properties, carbon nanotubes (cnt) are leading candidates to be employed as channel materials in future nanoelectronic devices. Key bottlenecks to realizing device integration is the sorting and placement of carbon nanotubes. This talk will describe our efforts in using polymer-based sorting methods to isolate high-density and high-purity semiconducting cnt solutions. We explore the dependence of starting material and polymer to cnt ratio on the effectiveness of the separation. We confirm optically and electrically that the semiconducting purity is > 99.99% through several thousand individual device measurements. I will discuss our recent results on the selective placemen of carbon nanotubes into redefined locations. In addition to single-cnt devices, thin-film transistors were also fabricated and tested. Due to the high purity of the solutions, device switching (~ 10⁵ I_ON/I_OFF) was observed at channel lengths below the percolation threshold (< 500 nm). Operating below the percolation threshold allows for devices with much higher current densities as transport is now the result of direct transport as opposed to through cnt/cnt junctions.

There is a clear need for fast, high efficiency, and broadband sensitive detectors and graphene demonstrates great promise to fill this void. Graphene possesses high room temperature carrier mobility, up to 60000 cm^2/(Vs),[1] and large absorption of incoming radiation, ~2.3%.[2] This absorption is impressive considering graphene is only one atomic layer thick. In the Gigahertz (GHz) frequency range, the absorption is enhanced due to the Drude contribution of the free carriers.[1] Synthesizing epitaxial graphene from SiC has the advantage wafer scale size, being defect free and single crystal.[3]
There are multiple viable detection mechanisms for graphene devices in the GHz range. To investigate this further, two types of GHz detectors were fabricated on epitaxial graphene. The first device is an antenna coupled device. It utilizes two dissimilar contact metals, one for the source and the other for the drain, and the work function difference produces asymmetry. The other device is a field effect transistor constructed with an asymmetric top gate that creates a PN junction and facilitates tuning the photovoltaic response. Both device types were fabricated using a lift off resist-based clean lithography process to produce low contact resistance[4] and use asymmetry for detection, consistent with recent studies of the photothermoelectric effect (PTE) mechanism.[5] By breaking the device’s symmetry, a net current is produced through the diffusion of hot electrons.
The devices were electrically characterized and then irradiated with a Backwards Wave Oscillator (BWO). The response of both device types were tested from 100GHz to 177GHz. The antenna coupled devices demonstrated variable response with respect to frequency and power of incident radiation as well as distinct antenna coupling. The response of the PN junctions depends on the radiation frequency and the gate voltage. At a fixed frequency, the device response can be doubled by tuning the gate voltage.

[1] P. Avouris Nano Lett. 10, 4285-4294 (2010).
[2] K. F. Mak, et al Solid State Comm. 152, 1341 (2012).
[3] L. O. Nyakiti, et al.,MRS Bulletin 37, 1149-1157 (2012).
[4] A. Nath, et al Applied Physics Letters 104, 224102 (2014).
[5] X. Cai, et al Nature Nanotechnology 9, 814 (2014).