In-situ transmission electron microscopy gives valuable information about many important issues of carbon nanomaterials. Dynamic phenomena are getting accessible to direct observation. The presentation shows the application of different in-situ techniques such as heating, irradiation, or electrical probing of carbon and related nanostructures under observation in the microscope. The focus is on one- and two-dimensional carbon nanomaterials such as monoatomic carbon chains and graphene and on related non-carbon materials such as two-dimensional silica.
The nucleation and growth of carbon nanotubes or graphene can be made visible in the solid-state growth of carbon structures on catalytically active metals [1]. The heating of suitable metal-carbon precursors allows us to observe the growth of single- or multi-wall carbon nanotubes on small metal particles or the growth of mono- and multilayer graphene on flat metal surfaces. Electron irradiation can be used to tailor the precursor systems prior to the growth of carbon. Diffusion processes, i.e., carbon atoms in or on metals or, conversely, metal atoms on graphitic surfaces, play a decisive role and can also be observed in-situ [2].
Interesting yet hardly explored carbon species are linear sp1-bonded chains of carbon atoms. The in-situ electrical probing by an STM tip in a TEM allows us to generate such carbon chains that are the only real one-dimensional allotrope of carbon [3]. The chains can be pulled out from graphenic aggregates by electrically biased metal contacts. While the chains are generated and observed, their electrical characteristics can be measured. The analysis of current-voltage curves shows that a Peierls distortion leads to an opening of the bandgap so that the chains are normally semiconducting.
Two-dimensional silicon dioxide films have recently attracted much interest due to their hexagonal structure that has many common characteristics with graphene, e.g., the same types of non-hexagonal defects. A new route is explored towards the synthesis of 2D silica in a solid-state growth process that is carried out in-situ in a TEM [4]. The experiments allow us to obtain detailed information on the nucleation, growth, and the epitaxial relationship with the crystallographic symmetry of the metal surface.
[1] J. A. Rodríguez-Manzo, C. Pham-Huu and F. Banhart, ACS Nano 5, 1529 (2011).
[2] O. Cretu, A.V. Krasheninnikov, J.A. Rodríguez-Manzo, R. Nieminen and F. Banhart, Phys. Rev. Lett. 105, 196102 (2010).
[3] O. Cretu, A. R. Botello-Mendez, J.-C. Charlier, I. Janowska, C. Pham-Huu, F. Banhart, Nano Lett. 13, 3487 (2013).
[4] F. Ben Romdhane, T. Björkman, J. A. Rodríguez-Manzo, O. Cretu, A. V. Krasheninnikov, F. Banhart, ACSNano 7, 5175 (2013).

Carbon nanotubes (CNTs) have rich structural diversity represented by their chirality range and number of walls. The electronic properties of CNTs are heavily influence by these structural characteristics and therefore it is important to study the atomic configuration with detail. Defects, such as vacancies and bond rotations perturb the perfect crystalline structure of CNTs and influence properties, therefore prompting their study. In this talk I will show how the atomic structure of CNTs can be imaged in high detail using aberration-corrected transmission electron microscopy (AC-TEM) to answer important structure questions. We utilize Oxford's JEOL 2200MCO AC-TEM, equipped with an image aberration corrector and bespoke monochromation of the electron beam at an accelerating voltage of 80 kV. The chirality of individual nanotubes are determine directly from AC-TEM images, which also provide spatial mapping of the atomic structure by tracking deviations in the Moire patterns. By obtaining high quality images of CNTs using AC-TEM, we have been able to reveal the presence of shear strain in single-walled carbon nanotubes arising from bending, the presence of defects hidden within the inner wall tubes of double-walled carbon nanotubes, and the presence of molecules attached to the outside (and inside) of SWNTs.

Carbon Nanotubes (CNTs), especially single walled CNTs (SWNTS) have attracted interest for a wide range of technological applications because of their novel mechanical, electrical, optical properties. Synthesizing high yield, high purity, and monodispersed chiral SWCNTs is critical to exploit these properties to their full extent. A common route for CNT synthesis is catalytic chemical vapor deposition (C-CVD), which involves metal catalyst (i.e. Ni, Fe, Co) to decompose carbon precursors and to provide a nucleation site for SWCNTs formation. Researchers have achieved super growth of very long and pure SWCNT bundles [1]. Only a few reports on monodispersed SWCNT of same chirality are available. Co/MgO is one of the catalyst-support systems that selectively grow mainly semiconductor SWCNT [2]. Yet, the exact relationship between the tube growth and the catalyst-support system is still missing. We have employed an Environmental Scanning Transmission Electron Microscope (ESTEM) operated at 300 kV, which permits us to introduce C2H2 over the Co/MgO system at reaction temperatures and record real-time atomic resolution videos to capture nanotube cap nucleation, lift-off, and growth. We observed that the catalysts remained faceted during the whole process. The caps nucleated at the junction of two different facets of the catalyst. The caps grew laterally from the nucleation site and stopped growing larger when the cap rims reached another facet edge on the catalyst. The final cap geometry comprises a graphene sheet that is attached to epitaxially well-matched facets but that has lifted off from the mismatched facets. The cap then guides the subsequent growth of the SWCNT. In addition to the metal-graphene interfacial energies, other factors, such as a preferential adsorption of carbon at low-coordination metal sites, higher diffusion rates on specific metal surfaces or subsurfaces, are involved in SWCNT nucleation and growth. Therefore, we hypothesize that tuning the orientation and size of the catalyst particle facets can significantly improve chiral selection of SWCNTs. More details of the mechanism of SWCNT nucleation and growth, and chirality control will be presented.
References
1. Hata et al., Science 2004, 306, 1362
2. He et al., Nature Science Report, 2013, 3, 1460

Because of their extraordinary electrical and thermal conductance graphite and more in general graphitic nanomaterials, such as carbon nanotubes (CNTs) or graphene, are discussed for various applications, one example being electrical conductors. For many applications it is necessary to contact them with a metal. Copper and nickel are metals used in electronic devices and are also interesting because of their different valence electron occupancy. The contact between copper/nickel and CNTs shows a contact resistance and is currently not well understood [1]. This work emends the knowledge about these interfaces. Samples with copper and nickel interfaces towards MWCNTs and graphite were analysed. The comparison of the multiwalled CNT (MWCNT) metal interfaces with the ones of graphite points out the effect of the bent graphite layers in the CNTs.
An interfacial nickel carbide layer at the nickel-graphite interface could be observed by core-loss electron energy loss spectroscopy (EELS). Carbide formation at the copper-graphite interface was not observed by monochromated valence electron energy loss spectroscopy (VEELS) and core-loss EELS. The different behaviour of nickel and copper can be explained by the full valence d-shell of copper, which prevents it from covalent bonding without changing its electron configuration. Disturbances of the graphitic system could be detected by high resolution transmission electron microscopy (HRTEM) images. Those results from the graphite interfaces are compared with the ones from the MWCNT-metal samples.
[1] Lim S. C., et al. Appl Phys Lett, 95, 264103-264103-3 (2009).

In this study, we investigate the charge transport behavior in a disordered one-dimensional (1D) chain of metallic islands using the newly developed multi-island transport simulator based on semi-classical tunneling theory and kinetic Monte Carlo simulation [1]. The 1D chain is parameterized to model experimentally-realized devices consisting of randomly sized gold nanometer-sized islands deposited on an insulating boron nitride nanotube [2]. The effects of disorder, device length, temperature and source-drain bias voltage (V_SD) on the current are examined. Preliminary results of random assemblies of gold nano-islands in two dimensions (2D) are also examined in light of the 1D results.
At T = 0 K and low bias the disordered 1D chain shows charge transport characteristics with a well-defined Coulomb blockade (CB) and Coulomb staircase (CS) features that are manifestations of the nanometer size of the islands. In agreement with the experimental observations, the CB and the blockade threshold voltage (V_th) at which the device begins to conduct increases linearly with increasing chain length. The CS structures are more pronounced in longer chains, but disappear at high V_SD. Due to tunneling barrier suppression at high bias, the current-voltage characteristics follow a non-linear behavior. Smaller islands have a dominant effect on the CB and V_th, while wider junctions with their large tunneling resistances predominantly determine the overall device current. The study indicates that smaller islands with smaller inter-island spacings are better suited for practical applications. Temperature has minimal effects on high-bias current behavior, but the CB is diminished as V_th decreases with increasing temperature.
In 2D systems with sufficient disorder, our studies demonstrate the existence of a dominant conducting path (DCP) through which most of the current is carried, making the device effectively quasi-1-dimensional. The existence of a DCP is sensitive to the device structure, but can be robust with respect to changes in V_SD.
Acknowledgements: Simulation studies were performed in part using the computing cluster wigner.research.mtu.edu in Information Technology Services and rama.phy.mtu.edu in the Department of Physics at Michigan Technological University. Y. K. Yap acknowledges the support from the U.S. Department of Energy, the Office of Basic Energy Sciences (Grant DE-FG02-06ER46294, PI:Y.K.Y.), the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory (CNMS at ORNL) (Projects CNMS2009-213 and CNMS2012-083, PI:Y.K.Y.), and the ORNL&’s Shared Research Equipment (ShaRE) User Program (JCI).
References:
[1]. Savaikar et al., J. Appl. Phys. 114, 114504 (2013).
[2]. Lee et al., Advanced Materials 25, 4544 (2013).

Some of the grand challenges in nanoscience are the ability to control movement of atoms either to propel nanometer-sized machines, or to synthesize novel electronic devices and materials. To that end, electrical current can be used to move a wide range of metals along a carbon nanotube (Fe, Cu, W, In, Ga). In this talk I will present our finding of a peculiar way in which these metals move. For example, we find that an iron nanocrystal is able to pass through a constriction in the carbon nanotube with a smaller cross-sectional area than the nanocrystal itself. Remarkably, through in situ transmission electron imaging and diffraction, we find that, while passing through a constriction, the nanocrystal remains largely solid and crystalline and the carbon nanotube is unaffected. I will also discuss implications of this work on synthesis of nanocomposite materials, and on the stability of carbon-based electronic devices.
More details can be found in these publications:
Phys. Rev. Lett. 110, 185901 (2013)
http://link.aps.org/doi/10.1103/PhysRevLett.110.185901
Phys. Rev. B 88, 045424 (2013)
http://link.aps.org/doi/10.1103/PhysRevB.88.045424
This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by the DOE at Lawrence Berkeley National Laboratory's NERSC facility.

We present the results of an extended investigation of point defects in carbon nanotubes (CNTs) and their effects on mechanical and electronic properties. This study is based on large-scale calculations using density-functional theory (DFT) with exchange and correlation functionals of the GGA - including empirical corrections for van-der-Waals interactions - and of the hybrid type. We also carried out simulations using classical interatomic potentials: this has allowed us to obtain a critical comparison between the outcome of DFT and force-fields. The CNT models adopted have a range of sizes and chiralities. In particular, (i) our simulations of oxygen chemisorption have revealed a tendency to clustering and also the existence of kinetic traps (epoxide configurations), which explain scanning tunneling spectroscopy data [1]; (ii) the extension to oxygen isovalent species on CNTs and other graphitic surfaces has suggested a simple predictive model for the chemisorption pattern [2]. Moreover, (iii) our analysis shows an intrinsic difficulty of available force-fields to account for the energetics of vacancies and adsorption site preferences. Additional results aiming at characterizing the interaction of nitrogen oxides (NOx) with the CNT surface will also be presented.
We acknowledge support from Nano-Tera.ch, a program of the Swiss Confederation, evaluated by the SNSF, and the Swiss National Supercomputing Centre (CSCS) under project ID 245.
[1] J. M. H. Kroes, F. Pietrucci, A. Curioni, R. Jaafar, O. Gröning and W. Andreoni, J. Phys. Chem. C 117, 1948 (2013)
[2] J. M. H. Kroes, F. Pietrucci, A. Curioni and W. Andreoni, (to be published)

Carbon nanotubes (CNTs) are considered to be a very promising material due to their exceptional thermal, electrical, optical and mechanical properties. Many studies have been performed in the past decade in an effort to explore and develop devices which could leverage the excellent properties of CNTs. Particularly, CNT network based thin film transistors (CN-TFTs) has been explored in great detail as they may find applications in flexible displays, sensors, e-clothing, antennas, etc. In addition, recent advances in synthesis, purification and assembly of CNTs have also underscored the importance of CNT arrays or densely aligned CNTs based TFTs for high performance logic devices [1, 2]. Fewer studies have focused on (self-heating) thermal considerations of these devices which is an important aspect since CNTs are typically deposited on thermally insulating substrates. We have previously investigated the heat dissipation issues and associated thermal reliability in CNT random network based TFTs [3, 4]. In this work, we aim to investigate the performance and thermal reliability issues of perfectly aligned or semi-aligned CNTs based TFTs; we will consider the dense arrays of CNTs where CNT-CNT interaction is greatly pronounced and have not been appropriately simulated in the previous studies [5]. This interaction can not only significantly affect the electrical performance but can also lead to thermal reliability problems. We plan to develop and employ a self-consistent electro-thermal model to understand the transfer characteristics of CN-TFTs along with the potential heat dissipation issues which could affect the device performance. Our electro-thermal model has been successfully used to explain experimental observations and to provide useful insights for design and optimization of CNT random network based TFTs. The present work will help in bridging the gap between electrical and thermal transport and reliability aspects of aligned/semi-aligned CN-TFTs.
[1] Shulaker, M.M.; Hills, G.; Patil, N.; Wei, H.; Chen, H.Y.; PhilipWong, H.S.; Mitra, S. Carbon nanotube computer. Nature 2013, 501, 526-530.
[2] Cao, Q.; Han, S.J.; Tulevski, G.S.; Zhu, Y.; Lu, D.D.; Haensch, W. Arrays of single-walled carbon nanotubes with full surface coverage for high-performance electronics. Nat Nanotechnol 2013, 8, 180-186.
[3] Gupta, M.P.; Behnam, A.; Lian, F.F.; Estrada, D.; Pop, E.; Kumar, S. High field breakdown characteristics of carbon nanotube thin film transistors. Nanotechnology 2013, 24.
[4] Gupta, M.P.; Chen, L.; Estrada, D.; Behnam, A.; Pop, E.; Kumar, S. Impact of thermal boundary conductances on power dissipation and electrical breakdown of carbon nanotube network transistors. J Appl Phys 2012, 112.
[5] Shekhar, S.; Erementchouk, M.; Leuenberger, M.N.; Khondaker, S.I. Correlated electrical breakdown in arrays of high density aligned carbon nanotubes. Appl Phys Lett 2011, 98.

One defining characteristic of nanomaterials is that their properties often vary as a function of shape and size. For single-walled carbon nanotubes (SWCNT) such variations modify the electronic and optical properties mainly in a discontinuous manner. Metallic character can switch into semiconducting properties and vice versa. Since most technologies require predictable and uniform performance parameters, scientists have been intensively researching strategies for the preparation of SWCNTs with well-defined diameter, length, chirality, and electronic properties (uniform metallic, and especially uniform semiconducting nanotubes).[1] The separation can be achieved by different methods including strategies borrowed from biochemistry (encapsulation by surfactants followed by ultracentrifugation or encapsulation with DNA) or in our case by spontaneous wrapping of conjugated polymers such as the fluorene-based homo- and co-polymers around SWCNTs with diameters around 1 nm.[2]
The side chains of the conjugated polymer in these hybrid structures allow solubilization in common organic solvents. In previous reports, many different polymer structures have been tested with the ability to discriminate SWCNTs of different diameter and helicity on demand. PFO (poly(9,9-dioctylfluorene-2,7-diyl) has been demonstrated to be the a very efficient polymer for separation of SWCNTs with small diameters (0.8 - 1.2 nm). Earlier studies ascribed the discrimination mechanism to the nature of the polymer backbone. Recent research showed indications, that the side chain of the polymers also plays an important role in the wrapping and selection mechanism.
Within this report we demonstrate the selection of semiconducting SWCNTs in a wider diameter range (0.8 - 1.6 nm) using polyfluorene derivates with alkyl chains of increasing length (hexyl to octadecyl side chains). By tuning the length of the alkyl side chains SWCNTs of different diameter can be selected. SWCNTs with diameters > 1.2 nm, for whom post-synthetic separation methods did not exist up to date, can now be selected efficiently. The high amount of semiconducting SWCNTs in the prepared dispersions, which is extremely important for applications, is demonstrated by optical spectroscopy and by fabrication of high performing field-effect transistors with mobilities up to 14 cm2V-1s-1 for holes and 16 cm2V-1s-1 for electrons (on/off ratio: 105).[2]
[1] Marc C. Herasm, Nat. Nanotech. 2008, 3, 387
[2] W. Gomulya, G. D. Constanzo, E. J. Figueiredo de Carvalho, S. Z. Bisri, V. Derenskyi, M. Fritsch, N. Fröhlich, S. Allard, P. Gordiichuk, A. Herrmann, S. J. Marrink, M. C. dos Santos, U. Scherf, M. A. Loi, Adv. Mat. 2013, 25, 2948

As a sustainable, non-polluting alternative to fossil fuels, hydrogen has many benefits: it can be produced from water using a variety of renewable sources such as wind and solar power and when used in fuel cells or internal combustion engines, the only by-product is the regeneration of water. The critical barrier to the widespread use of hydrogen as a fuel is that it is a gas at room temperatures and pressures and so is challenging to efficiently and economically store and transport.
One heavily researched method of storing hydrogen is using nanoporous materials (materials with pore dimensions on angstrom or nanometre length scales, such as zeolites, metal-organic frameworks and nanostructured carbons), which can act as “molecular sponges” for adsorptive storage of hydrogen. The evaluation of the capacities of different porous hydrogen storage materials is generally based on modelling experimental gas adsorption isotherms using assumptions about the density of the hydrogen inside the pores. As this density is very difficult to experimentally determine, it is generally assumed that the maximum or limiting amount that can be stored in a porous material occurs when the density of the hydrogen in the pores reaches liquid-like densities.
However, our recent models and inelastic neutron scattering experiments have shown that in certain carbon nanomaterials containing optimally-sized pores, the adsorbed hydrogen inside the pores can be compressed to the point where it behaves as solid hydrogen under relatively mild conditions of temperature and pressure - where classically, this should not be possible. This new description of the density of hydrogen inside the pores has led to improvements in the ways in which hydrogen capacities can be modelled and predicted to allow more accurate comparisons of the maximum capacities of different nanoporous hydrogen storage materials. This will ultimately inform the design and development of new materials for on-board hydrogen storage solutions for transportation applications.

Recently, environmental topics have become more imperative. Photocatalysis is an environmentally friendly procedures that uses irradiation energy to perform catalytic reactions. Therefore, photocatalysis has been widely applicated for pollutant eradication. The magnetite is a common mineral in the nature and it has great potential to be used as photocatalysts under visible-light irradiation.
In this study, nano-magnetites with crystal morphologies of rods and tubes are synthesized via the nano-hematites with carbon reduction method. The magnetite nano-rod is fabricated with glucose/sample=1/6 at 5000C for 4 hrs, while magnetite nano-tube is synthesized with glucose/sample=1/12 at 5000C for 4 hrs. The specific surface area of nano-rod and nano-tube is 21.4 and 25.3 m2/g, respectively. The efficiency of photocatalytic degradation on M.B. is 88% for nano-rod and 90% for nano-tube within the first 510 mins. Moreover, the photocatalytic rate constant is 0.0042 and 0.0044 1/min for nano-rod and nano-tube, respectively, which increases with an increase of surface area. The results show that the photocatalytic activity of nano-magnetite is influenced by its crystal morphology. In addition, the photocatalytic ability of nano-magnetites is comparable with the literatures. This suggests that the nano-magnetite is the potential candidate in the application of the environmental remediation.

Recently, many researchers have been interested in the self-assembled 3D supramolecular structures to synthesis of helical silica nanotubes. And the use of organic compounds as templates for the generation of inorganic structures and materials has received increasing attention over the last decade.
We have been studied the solvent-effects on the synthesizing of helical silica nanotubes via polycondensation of tetraethoxysilane (TEOS) on self-assembled structures that were composed 1,2-diphenylethylenediamine based neutral (G1) and cationic (G1N) gelators. By controlling parameters such as ratios of each gelator or the concentration of the reactants, we could finely fabricate the helical silica nanotubes.
In this study, we synthesized helical silica nanotubes by self assembly of organic gelators that prepared by heating a mixture of G1 and G1N using sol-gel condensation protocol with TEOS. The sol-gel reactions were carried out in ethanol solvent. And then, triethoxyoctylsilane was used to derivatized on the surface of nanotubes. The morphological structure of nanotubes was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TEM images taken after remove the gelator. In order to confirm the reaction of silica nanotube fabrication, the nanotubes were analyzed using elemental analyzer, LC, HPLC and TOF-SIMS.
This work was supported by the grant No. R0001026 from the Ministry of Trade, Industry & Energy and Busan Metropolitan City, Korea.

The attachment (both covalent and noncovalent) of crown ethers and other heteromacrocyclic compounds to carbon nanostructures such as fullerenes and carbon nanotubes is studied in context of the design of supramolecular donor-acceptor systems to approach artificial photosynthesis. As a rule, the covalent attachment has obvious advantages due to superior bonding strength. On the other hand, the functionalization methodologies explored up to now include several derivatization steps, and thus are labor-consuming, as well as require large amounts of solvents and a number of auxiliary operations. The main goal of our work was to test the feasibility of simple, one-step and solvent-free covalent functionalization of pristine MWNTs and oxidized SWNTs, ND and fullerene C60 with amino-substituted crown ethers, namely, 4prime;-aminobenzo-15-crown-5 and 4prime;-aminobenzo-18-crown-6. The functionalization was carried out by preparing 1:1 (w/w) mixture of the carbon nanomaterial and amino-crown ether under vacuum and heated during 4 h at 160-170 C. The covalent attachment technique proposed is based on thermal instead of chemical activation. It is fast, does not require the use of organic solvent reaction medium and auxiliary operations (washing, centrifugation, drying, etc.), and therefore can be considered as ecologically friendly. The specific covalent bonding mechanism depends on carbon nanomaterial employed. It relies on the formation of amide bonds between amino-crown ether molecules and carboxylic groups of SWNTs and ND, whereas in the case of MWNTs and C60, the chemistry of pentagonal (and probably other) structural defects is explored. The covalent attachment of crown ethers to the carbon nanostructures modified FTIR spectra of the latter, where new absorption bands due to NH, CH, aromatic ring and other vibrations appeared; the spectral changes were especially evident in the case of ND and C60. On the other hand, the corresponding Raman spectra were generally featureless. According to TGA, the mass fraction of amino-crown ethers is about 15-25% for SWNTs, 10-20% for MWNTs, and about 20% for ND and C60 functionalization. The changes observed in SEM images were generally insignificant, but more visible in TEM microphotographs of the functionalized nanotube samples. In particular, pristine MWNTs used in the present work as a starting material are composed of 8-12 well-defined layers, which became less distinguishable after crown ether addition to the nanotube sidewalls. Changes in LDI-TOF mass spectra of fullerene due to functionalization were especially dramatic, where we found evidences of the addition of up to four molecules of amino-crown ether to a single fullerene cage.
Acknowledgements: We appreciate financial support from the grants UNAM-DGAPA-IN101313 and CONACyT-127299. L.V. H.-H. thanks CONACyT for a doctoral fellowship

The noncovalent attachment of tetraazamacrocyclic systems, including porphyrins and phthalocyanines, to carbon nanotubes is a subject of significant research effort, stimulated by the possibility to combine unique electronic and optical properties of the interacting components. The resulting new nanocomposites exhibit interesting and potentially useful properties related to photoinduced electron transfer, solubilization of single-walled carbon nanotubes (SWNTs), among others. However, their high complexity limits the possibility to experimentally afford detailed information on molecular level, thus making theoretical studies an indispensable tool for understanding the macrocycle-nanotube interactions. In the present work, we performed a theoretical study of Ni(II)-tetramethyldibenzotetraaza[14]annulene complex (NiTMTAA), which can serve as a simple model for metal porphyrins and phthalocyanines, with short closed-end SWNT models, using density functional theory (DFT) techniques. The aim was to estimate the most preferable (of six possible) orientation of saddle-shaped NiTMTAA molecule with respect to armchair and zigzag SWNT models. The DFT calculations were performed within the Gaussian 09 package, by using long-range dispersion-corrected generalized gradient approximation correlation functional LC-BLYP and hybrid meta exchange-correlation functional M06-2X. Both DFT functionals were used in conjunction with the LANL2MB basis set. The geometries were fully optimized and formation energies ΔEcomplex were calculated according to the following formula: ΔEcomplex = Ecomplex - (ESWNT + ENiTMTAA), where E is the corresponding absolute energy. The results were analyzed in terms of closest contacts between NiTMTAA and SWNT models, formation energies for the complexes, as well as HOMO-LUMO gap energies. The formation energies showed variable stability of NiTMTAA+SWNT complexes, the most stable being those in which NiTMTAA contacts armchair and zigzag nanotubes through its o-phenylene groups, with energies values of about -13 and -18 kcal/mol. An interesting finding was that if NiTMTAA contacts the closed end of zigzag SWNT model through its methyl groups, such an orientation gives rise to the formation a new carbon-carbon bond with a bond distance of about 1.6 Å; this result was obtained with both functionals tested in this work. Armchair-type structures showed closest intermolecular contacts C...H of about 2.7-3.5 Å, while for zigzag models these distance were slightly lower by 0.2 Å. The calculated values of HOMO-LUMO gap energies were generally higher in the case of LC-BLYP functional, where the gap values calculated for zigzag models varied in a wide range from 0.05 to 0.23 eV, and those for armchair models were more uniform, of 0.10 to 0.19 eV.
Acknowledgements: Financial support from CONACYT of Mexico (grant 127299) and UNAM (grant DGAPA-IN101313) is greatly appreciated. L. V. H.-H. is indebted to the PhD Program in Chemistry of UNAM.

The growth of graphitic structures on Ni and Fe catalysts are compared with respect to their chemical states and morphologies. In the first part, nanoislands with a nominal thickness of 1 nm supported on an AlN scaffold layer are used for the CNT growth. Ni appears metallic, has weak interactions with AlN, and forms large island leading to large diameter CNT growth with the tip-growth mode. Fe is slightly oxidized, has stronger interactions with AlN, and forms small islands leading to small diameter CNT growth with the base-growth mode. In the second part, thin films were used for simultaneously growing graphite and FLG. This time, the AlN layer acts as a diffusion against the Si substrate underneath. In both cases, metal 3d/C 2p hybridization of the first layer leads to work function values for few layer graphene that are significantly lower than that of graphite. For Fe, small amount of metastable cementite phase also appears, whereas Ni remains pure metallic. Graphite layers are thicker for Ni because of higher surface corrugation, albeit the catalytic activity is higher on Fe films because of the domed surface geometry. The defect density of the graphitic structures grown on Fe thin films is higher than those grown on Ni thin films. In both parts, 790 oC surface temperature and 0.059 mbar acetylene pressure are used. Characterizations involve x-ray photoelectron spectroscopy, micro-Raman microscopy, scanning electron microscopy and Kelvin probe force microscopy measurements.

The design of biological architectures from electrogenerated polymers and self-assemblies of nanomaterials such as functionalized or non-functionalized carbon nanotubes, nanodiamonds and nanoparticles are promising to enhance the sensitivity and specificity of the devices. These designs allow immobilizing a maximum amount of biological entities within minimized volume by enabling unhindered permeation of analyte and substrate through the porous structure. We present alternative approaches to form such nanostructured scaffold structures. These include construction of three dimensional structures onto the electrodes by classical drop casting to nanotube forests and entangled nanotube networks, grown on conductive surfaces by chemical vapor deposition (CVD). The spatially controlled deposition of nanoparticles or nanodiamonds on the nanotube deposits has been optimized. The clearances between the nanoparticles and the size of the nanoparticles will determine the pore size of the structure. Prototypes of such nanostructured electrodes are then constructed with different pore sizes and optimized due to the envisioned applications in biodetection (biosensors) and bio-energy conversion (biofuel-cells). However, pores size control of these structures is not possible with nanotube forests. These resulting scaffolds were then reinforced by non - covalent π-stacking interactions using functionalized pyrene monomers to obtain densely packed anchoring points to immobilize biomolecules using affinity interactions. An impressive current densities (465 µA cm-2) and sensitivities upto (85.78 mA M-1 cm-2) were obtained. The high performance biocathodes for oxygen reduction by electron transfer with maximum current density 0.35 mA cm-2 were also constructed. These nanostructures provide an efficient way of immobilizing and wiring a large amount of biomolecules like DNA, enzymes, antibodies etc. onto the electrodes.

Single-wall carbon nanotube (SWNTs) applications in electronics require a thorough understanding of how SWNTs interact with the environment, the substrate and the contacts, and how metallic SWNTs could be removed to enable all-semiconducting circuits. In the above cases the thermal interaction between SWNTs and their substrate (e.g. SiO2) is essential, as is their reaction with O2 which most commonly serves to remove (“burn”) metallic SWNTs [1, 2]. While much work, including from our group [3] has been devoted to the former, little is quantitatively known about the latter.
In this study we investigate the interactions between the carbon atoms in pristine SWNTs (verified by Raman spectroscopy) with ambient O2 molecules, and how these contribute to Joule breakdown of SWNTs. For that purpose, we study the breakdown of two-terminal SWNT devices (with lengths varying between 1-4 mu;m and diameters varying between 1-2 nm) in environments with varying oxygen partial pressure from 2.1 mu;Torr to 760 Torr. (The ambient temperature is 300 K and the humidity was kept constant and below 5%.) We discover that Joule breakdown in our SWNTs occurs when the combined energy from the C atoms and the ambient O2 molecules exceeds an activation energy of ~1.2-1.5 eV, consistent with reported values (1.5 eV) for bulk multi-walled carbon nanotubes combustion study [4]. In our experiments, we apply a constant voltage across the SWNT until it breaks down, while monitoring the current. Through extensive thermal modeling [3], we estimate the temperature of the SWNT due to Joule heating and thus calculate the energy of the individual C atoms. From the O2 partial pressure and bias duration, we build a statistical model to extract the threshold energy of the bombarding O2 molecule that eventually triggers the Joule breakdown of the SWNT.
We find that with decreasing O2 partial pressures, Joule breakdowns of SWNTs with similar geometry take place at significantly higher voltage and power. This occurs because with fewer oxygen collisions, the probability of finding an energetic O2 molecule is low. Therefore we need to raise the temperature and energy of the SWNT to meet the activation energy and induce a breakdown. This work provides essential insights on how SWNTs interface with ambient gas molecules and how to improve SWNT reliability, both critical in the design of SWNT-based sensors and for the removal of metallic SWNTs in circuit applications.
References:
1 N. Patil et al, IEEE IEDM 573-576 (2009).
2 S. H. Jin et al, Nat. Nanotech. 8, 347-355 (2013).
3 A. Liao et al, Phys. Rev. B 82, 205406 (2010).
4 A. Vignes et al, Chem. Eng. Sci. 64, 4210-4221 (2009).

Field emission current from single walled carbon nanotubes (SWCNTs) is simulated via the OCTOPUS code implementation of time-dependent density functional theory (TD-DFT), a quantum many electron algorithm capable of solving problems with hundreds to thousands of electrons in the presence of time varying external potentials on massively parallel computer architecture. Simulations were performed in a finite computational domain such that imaginary absorbing potentials were necessary to allow charge migration out of volume boundaries and long time evolution. A real space grid of resolution 0.2 Å was found to properly converge all systems considered in this work. Adsorbed atoms, SWCNT defects as well as SWCNT chirality were investigated to determine the influence each has on work function and subsequent field emission current magnitude. Results indicate that Ag, Al adsorbates were especially useful for increasing field emission current over standard SWCNTs. As much as an order of magnitude current increase over standard (no adsorbate) CNTs was observed with these adsorbates at an Electric field of 1 V/Å. Differences from the Fowler-Nordheim relation were observed for low field emission. Such results demonstrate the utility of CNT based cathodes for improving output power and efficiency in future high power microwave devices.

Despite of the increasing popularity of other forms of carbon (e.g. graphene), carbon nanotubes (NTs) continue to attract much attention for their great commercial potential in a large variety of nanotechnology applications.
Raman spectroscopy is widely utilized for the fast and non-destructive characterization of all forms of carbon [1]. It allows easily identifying its allotropes and evaluating effects of disorder/defects that are of great interest in all fields where localization matters.
Some years ago, Ferrari and Robertson [2] proposed a phenomenological three-stage model for the interpretation of the visible Raman spectra in disordered, amorphous and diamond-like carbon. They pointed out that clustering of the sp² phase, bond disorder, presence of sp² rings or chains, and the sp²/sp³ ratio act as competing forces on the shape of the Raman spectra of nanocarbons [2]. Hence, they defined an “amorphisation trajectory” to depict the spectral changes accompanying the evolution from graphite to tetrahedral amorphous carbon (or diamond), ideally conceived as the result of the introduction of defects (bond-angle disorder, bond-length disorder, and sp³ hybridization) into perfect graphite.
As type and density of structural defects in NT walls change with growth conditions and post-growth treatments causing the shape of their Raman profiles to vary, we wondered if also NTs follow an amorphisation trajectory as other nanocarbons do.
In order to answer this question we carried out a systematic investigation by means of Raman spectroscopy, kinetic thermal analysis and complementary techniques on various typologies of nanocarbons, including crystalline graphite, amorphous activated carbon and several (laboratory-prepared and commercially available, pristine and heat treated) multi-wall NTs, featured by different purity degree (81.7minus;99.7 wt%), crystalline quality (amorphous fraction: 0minus;5 wt%), size (outer diameter: 5minus;100 nm) and morphology.
The comparative discussion of the results obtained proves the existence of a sharp correlation between strength of C bonding, as measured by the G-band position (omega;_G) in Raman spectra, and oxidative resistance of the samples, as monitored by maximum the oxidation-rate temperature (T_M) in kinetic thermal profiles.
As the thermal stability is commonly attributed to the aromaticity of C bonds [3], we conclude that the changes of omega;_G with T_M can be understood, within the framework of a three-stage model, inspired to that proposed by Ferrari and Robertson for other nanocarbons, as the effect produced by the introduction of curvature, lattice defects and edges, accompanying the evolution from crystalline graphite to highly crystallized NTs and from poorly crystallized NTs to amorphous activated carbon.
[1] Dresselhaus M.S. et al. Physics Reports 2005, 409, 47.
[2] Ferrari A.C.; Robertson J., Phys. Rev. B 2001, 61, 14095.
[3] Lehman J.H.et al. Carbon 2011, 49, 2581.

Carbon nanotube-incorporated conductive composites have been of interest for decades due to the unique mechanical and electrical properties of carbon nanotubes. We previously demonstrated the combination of microscale Ag particles and multi-walled carbon nanotubes decorated with nanoscale Ag particles as conductive fillers for composites [1-3]. The one-dimensional, flexible and conductive nanotubes constructed effective electrical networks among the micron-sized Ag particles, and the contact interface was improved by the Ag nanoparticles self-assembled on the sidewall of nanotubes [1-3]. This strategy was successfully realized in epoxy matrix-pastes [1], stretchable [2] and flexible [3] composites. Here we characterized electromagnetic interference shielding properties of flexible conductive composites [4]. There was a logarithmic relationship between the conductivity and shielding effectiveness which could be controlled by Ag concentration. The achieved maximum shielding effectiveness was about ~75 dB at 1 GHz. The dominant mechanism of electromagnetic interference shielding was reflection, and there was an excellent agreement between the theory and experimental data [4]. [1] Oh et al, Journal of Materials Chemistry, 20, 3579 (2010) [2] Chun et al, Nature Nanotechnology, 5, 853(2010) [3] Ma et al, Advanced Materials, 24, 3344 (2012) [4] Kwon et al, Carbon, In-press (2013)

The microscopic origin of the p-type doping of AuCl₃ functionalized carbon nanotubes (CNTs) is investigated using first-principles self-interaction corrected density functional theory (DFT). Although the system has been studied as potential candidate for highly sensitive and selective gas sensors, a clear identification of the source of the p-type doping is not achieved. Recent experimental and theoretical works suggest that it is due to the adsorbed Cl atoms. We test this hypothesis and show that adsorbed Cl atoms only lead to a p-type character for very specific concentrations and arrangements, which furthermore are not the lowest energy configurations. We therefore propose and investigate alternative mechanisms while considering all possible configurations and concentrations. In particular, we study the possible formation of different conformations of AuCl₃ as well as the effect of the adsorbate concentration. As a result, we find that especially AuCl₄ molecules bind strongly to the CNT and that they lead to an electron transfer to the molecules and thus a shift of the Fermi energy below the valence band maximum. We conclude that the origin of the p-type doping in AuCl₃ functionalized CNT is due to the adsorption of AuCl₄ molecules. Knowing the exact nature of the p-doping adsorbates is a key step for the further development of AuCl₃ functionalized CNTs in water vapor sensor applications and in understanding the mechanisms behind their resistivity changes.

In recent years, one-dimensional carbon nanomaterials such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have received a great deal of attentions in application of supercapacitor, because of its unusual structure and unique physical and chemical properties. This paper introduces the latest research works in our group on applications of one-dimensional carbon nanomaterials in supercapacitor, including:
1) High concentration nitrogen-doped coiled CNFs were directly synthesized from amine flames. The results revealed that: (1) the CNFs exhibited a stable screw-pitch with diameters in a range from 40 to 100 nm and length longer than 10 mu;m. (2) The N content was as high as 11% and it was dominated as a ‘graphite-like&’ structure. (3) the CNFs showed a larger capacitance and more excellent electrochemical properties than that of the electrode prepared by using conventional CNTs from CVD process.
2) We systematically studied the synthesis, morphology and structure characteristics and electrochemical properties of CNTs grown on nickel foam by CVD method, and demonstrated the improvement of its capacitance and impedance characteristics for the good conductive contact between CNTs and nickel foam. Our study provides a new way to shorten the electrode fabrication into one-step.
3) The CNTs/TiO2 composites were synthesized by hydrothermal reaction. It is found that the capacitance of this composite was improved and which could be enhanced through UV pretreatment. Therefore, a new technique to improve electrode surface chemical characteristic and electrochemical properties by aid of UV light treatment is introduced.

Over the past few years, one-dimensional (1D) nanostructures, such as nanowires, nanofibers, and nanotubes, have been considered as a building block in the nanotechnology because of their potential for fabricating future micro/nano-scale electronic devices. Although promising advance has been investigated from many researchers, aligning and patterning the randomly dispersed solution-based nanostructures in large scale still have been difficult obstacles. One of the most critical limitations in conventional techniques is that they used specific shape substrate (i.e., templates) or complex experimental system. To overcome these restriction, electrohydrodynamic (EHD) jet printing has a promising technology to make that desired pattern on even non-conductive substrate (i.e., glass or plastic) without any templates or many processes. In this study, we carried out experimental investigation for aligning and patterning metal nanowire suspension with polymer host matrix composite by EHD jet printing. The nanowires within these polymer fiber jet could be aligned and patterned due to the coupled balancing between flow field and electric field of EHD system. Using this technique, it will be applied fabricating micro/nano-scale devices such as nanowire-based transistor or electronic skin in the near future.

True solutions of single-walled carbon nanotube (SWCNT) anionic polyelectrolytes can be generated via reductive chemical (alkali metal/liquid ammonia[1,2] and alkali metal naphthalide/THF[3]) or electrochemical[4] processes. On the other hand, only superacids have been reported to dissolve carbon nanotubes oxidatively via proton transfer. Protonation does not permanently remove electrons from the carbon nanotube frameworks, but generates a polarised protonated-carbon nanotube moiety.
To complement electrochemical reduction of carbon nanotubes, an oxidative dissolution[5] process was developed to generate discrete SWCNT cations using a highly stable lithium hexafluoroarsenate/propylene carbonate electrolyte system. As observed in chemical and electrochemical reductive dissolution, initial fractions predominantly contained metal catalyst particles and amorphous materials, typically found in as-synthesised materials. Preferential dissolution of larger diameter or metallic species was also observed using Raman spectroscopy. The reactivity of the SWCNT cations towards nucleophiles was confirmed through their covalent assembly on amine-modified silicon surfaces. Generation of these SWCNT cations opens up new opportunities for surface modification. In addition, this electrochemical approach offers a scalable and non-destructive route to purify and process carbon nanotubes.
[1] Fogden, S.; Howard, C. A.; Heenan, R. K.; Skipper, N. T.; Shaffer, M. S. P. ACS Nano 2011, 6, 54.
[2] Wunderlich, D.; Hauke, F.; Hirsch, A. J. Mater. Chem. 2008, 18, 1493.
[3] Pénicaud, A.; Poulin, P.; Derré, A.; Anglaret, E.; Petit, P. Journal of the American Chemical Society 2004, 127, 8.
[4] Hodge, S. A.; Fogden, S.; Howard, C. A.; Skipper, N. T.; Shaffer, M. S. P. ACS Nano 2013, 7, 1769.
[5] Hodge, S. A.; Bayazit, M. K.; Tay, H. H.; Shaffer, M. S. P. Nat. commun. 2013, 4.

Carbon nanocoils (CNCs) have remarkable mechanical, electrical and thermal properties for its special 3-D structure and sizes, making them widely used in nanospring, sensor, microwave absorber and other application areas . Our previous work used CNCs as heating elements to generate microbubble and demonstrated that their power consumption is lower than carbon nanotube based microbubble generator. Then we paid attention to the thermal property of CNCs. However, quantitative study on the thermal properties of carbon nanocoils is still a vacancy. As four points third harmonic method has already successfully used in measuring the thermal conductivity of individual carbon nanotubes, the first effort to measure the thermal conductivity of carbon nanocoils by using four-point third harmonic method is presented in this paper.
CNC is approximately modeled as one dimension electric conductor similar to CNT. A microdevice for the third harmonic measurement is fabricated on an oxidized silicon wafer. W/Ti metal film (~200 nm) was sputtered as four point electrodes. Dielectrophoretic force (DEP, 18V peak to peak, 1MHz) was used to deposit the nanocoils over the electrodes. Using an experimental setup built in our lab, the typical third harmonic voltage appears when input current is 400uA. The experimental result and calculation indicate that the thermal conductivity of carbon nanocoils is in the same order of the thermal conductivity of multiwalled cabon nanotubes. In addition, the value exhibits a strong dependance on the geometry parameters of the species.

One-dimensional vertically aligned carbon nanostructures (1D-VACNS) such as carbon nanotubes (CNTs) and carbon nanofibers have attracted a lot of interest for advanced micro/nano electronic applications. Despite the huge progress in carbon research over the years, production of controlled 1D carbon nanostructures with well-defined properties in large quantities by a cost-effective technique is still a challenging task. The usage of toxic gasses, the presence of their byproducts and C-deposition on the furnace interior along with the targeted area are among the most important disadvantages of Chemical Vapor Deposition technique. High temperature annealing of silicon carbide (SiC) single crystal wafer in a vacuum furnace is another attractive method for controlled synthesis of carbon; however, due to the high covalent bond strength of Si-C, decomposition requires high temperatures (T>1250 °C) and high vacuum (P<10-4 Torr) conditions [1,2]. Hence, this process cannot be accomplished in a simple quartz tube furnace but rather requires a special/expensive vacuum furnace. Moreover, for aligned CNT formation, extra carbon source is required similar to CVD [1]. The objective of this study was to develop a technique to decrease the temperature and vacuum values for 1D-VACNS formation by thermal decomposition of SiC. With respect to this, the effect of catalyst on the SiC decomposition was studied. Application of catalyst on SiC wafer resulted in the formation of one-dimensional (1D) vertically aligned carbon nanostructures at low temperature and vacuum values (compared to SiC decomposition) without extra carbon supply into the system [3]. Resulting nanostructures were characterized using scanning electron microscopy and Raman spectroscopy. The effect of catalyst amount is discussed and a mechanism for the 1D carbon nanostructure formation through SiC decomposition in the presence of catalyst is proposed.
1. G.Cambaz, G.Yushin, S.Osswald, V.Mochalin, Y.Gogotsi, Noncatalytic Synthesis of Carbon Nanotubes, Graphene and Graphite on SiC, Carbon, 46, p.841, 2008.
2. G.Cambaz Buke, G.Yushin, V.Mochalin, Y.Gogotsi, Effects of Defects on Graphitization of SiC, Journal of Materials Research, JMR focus issue DeNovo Carbon Nanomaterials, 28, 7, p. 952, 2013.
3. G. Cambaz Buke, Growth of one dimensional carbon nanostructures on SiC - Catalyst effect, Journal of vacuum science and technology A, 31, 060603 (2013); http://dx.doi.org/10.1116/1.4819375

The surface energies of pristine multi-walled carbon nanotubes (MWCNTs) and MWCNTs functionalized with carboxylic acid (MWCNT-COOH), acyl chloride and ethyl amine were characterized, and the effects of the changes in MWCNT surface energies on the interfacial adhesion and reinforcement of the composites were explored. When the surface energy of pristine MWCNTs was compared to that of functionalized MWCNTs, a decrease in the dispersive surface energy and an increase in the polar surface energy were observed. Interfacial adhesion energies between MWCNTs and various polymers were estimated from surface energy values of MWCNTs and various polymers. Among the MWCNTs, polyethylene, polystyrene and bisphenol-A polycarbonate (PC) had the highest interfacial energy with pristine MWCNTs, while nylon 6,6 and polyacrylamine exhibited the highest interfacial energy with MWCNT-COOH. When tensile properties and adhesion at the interface of PC and nylon 6,6 composites containing MWCNTs were examined, composites having high interfacial adhesion energy exhibited greater adhesion at the interface and reinforcement.

Microinjection molding is one of the key engineering technologies for producing the micro polymeric parts with product miniaturization trend. In the application of micro injection molded parts, the replication quality of their micro features is an important factor to determine the reliability of the selected manufacturing route. To improve the replication quality, the injection speed and holding pressure are considered as the main parameters affecting the surface quality in the microinjection molding with regard to process optimization. Among various polymer materials for microinjection molding, biomass derived polylactide has received much attention and is expected to replace petroleum-based commodity polymers, because of its biodegradability and biocompatibility. Although polylactide is a very promising material in the field of biocomposites, it has an extremely slow crystallization rate and relatively poor physical properties than petroleum based commercial polymers, providing a shortcoming for industrialization of polylactide composites. To overcome these drawbacks, polylactide nanocomposites reinforced by the carbon nanotube (CNT) was prepared by melt compounding process and injection molded into a mold with micro needle patterns. Effects of CNT and process conditions on processability, morphology, and surface properties of molded polylactide/CNT nanocomposites have been evaluated. The replication ratio of surface micro patterns was increased with increasing injection speed and holding pressure while it was decreased with increasing CNT content. The incorporation of CNT enhanced the surface hardness and modulus of polylactide because of reinforcing effect of CNT as well as enhanced crystallinity by the nucleating effect of CNT. This study accounts for the effect of CNT and various processing conditions on the polylactide matrix, providing a design guide for micro injection molded polylactide/CNT nanocomposites in industrial fields. This research was supported by National Research Foundation of Korea (Project No. 2012-047656).

The homogeneous dispersion of carbon nanotubes (CNTs) in a polymer matrix is a critical parameter that significantly affects the electrical and mechanical properties of CNT-based composite materials, and represents an important challenge to overcome during the manufacturing process of these materials. In our work we used double-stranded DNA to facilitate the dispersion of multi-walled CNTs in solution prior to the integration in epoxy resin PRIME 20 LV. Composites containing DNA-wrapped CNTs were prepared using sonication at different CNT loading and the morphology of the composites after cure was observed under an optical microscope. Nanoindentation experiments were conducted to determine the local mechanical properties of the CNT/PRIME 20 LV composites, showing a significant improvement in their distribution across the sample surface as a result of the enhanced dispersion of the multi-walled CNTs by DNA. An electrical test to assess the stability of the CNTs dispersion in the resin was developed by measuring the conductivity of the composite mixture before cure in time. Results of the electrical measurements indicate that the mixture with DNA-wrapped CNTs is stable for several days after preparation.

Unlocking the full potential of low-density cellular materials requires realization of specific combinations of cell size, density and composition. Such design, however, remains challenging and time consuming. Here we show that atomic layer deposition (ALD) based templating of complex architectures formed by self-organization can provide access to the previously unoccupied space on the feature size vs. surface area material selection chart. Our approach combines the cell size, density, and compositional control that is characteristic for engineered microlattices with high surface area that is the domain of aerogels. Specifically, we report on the fabrication of millimeter to centimeter sized low-density nanotubular alumina and titania bulk materials with densities ranging from 5 to 400 mg/cm3 and narrow unimodal pore size distributions ranging from 30 nm to 4 micron. The materials are thermally stable and one order of magnitude stronger and stiffer than traditional aerogels of the same density by virtue of their unimodal feature size and nanotubular morphology which enables the realization of monoliths with ultra-low density and ultra-high surface area. The tunability of the materials opens the door to many promising applications in the fields of energy harvesting, catalysis, sensing and filtration.

Contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed. Main attention is paid to ultrasonic, plasma techniques and other physical techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and organic salts, mineral and organic acids, oxides, inorganic and organic peroxides, organic sulfonates, polymers, dyes, natural products, biomolecules, and coordination compounds). Special studies on CNTs solubilization are examined. Experimental data on the dispersion of the carbon nanotubes, functionalized with 4-anisidine, 4-aminobenzoic acid, 1,3-dimethyl-5-aminobenzene-1,3-dicarboxylate, 4-aminopyridine, 2-aminothiazole, and 4-sulfanylamide, in a series of organic solvents and water, are presented. Practical applications of carbon nanotube hybrids with 4-anisidine for car paints are shown.
References
1. Boris I. Kharisov, Oxana V. Kharissova, Hector Leija Gutierrez, Ubaldo Ortiz Méndez. Recent advances on the soluble carbon nanotubes. Ind. Eng. Chem. Res. 2009, 48(2), 572-590.
2. Oxana V. Kharissova, Boris I. Kharisov, Edgar Gerardo de Casas Ortiz. Dispersion of carbon nanotubes in water and non-aqueous solvents. RSC Advances, 2013, in press.

The surface functionality and interlayer spacing changes induced by functionalizing groups were investigated for multi-walled carbon nanotubes (MWCNTs). A comparison of available experimental data for interlayer distances in pristine and functionalized MWCNTs, obtained by distinct techniques, has been carried out. The reported values for MWCNTs, produced by pyrolysis, CVD, laser evaporation and other methods were compared with our experimental data on the synthesis of MWCNTs by microwave heating procedure. Influence of number of carbon shells, as well nature of functionalizing groups (-OH, -COOH, 4-anisidine, 4-aminobenzoic acid, 1,3-dimethyl-5-aminobencene-1,3-dicarboxylate, 4-aminopyridine, 2-aminothiazole, and 4- sulfanilamide) on the inter-layer distance, was analyzed. The measured distance spread around a constant value of around 0.35-0.37 nm. We use an interlayer Morse potential previously developed from a local density approximation (LDA) treatment of a bilayer of graphite. We have fit this Morse potential to experimental high-pressure compressibility data for graphite and to a more extensive LDA equation of state (EOS) for graphite, and excellent agreement has been observed. We employed this potential to treat the interlayer mechanics of MWCNTs, where the MWCNT is so highly deformed that interlayer separation well below ~0.34 nm, such as down to ~0.26 nm, is occurring. This, to our knowledge, is the first treatment that attempts to account for deformations that have the layers approaching each other at very high local (interlayer) stress levels. Since evaluating the interlayer potential for a large MWCNT system is computationally intensive, a continuum simulation approach is proposed that saves on computational time and thus on cost. Comparisons with experimental results of buckled and highly kinked MWCNTs are presented.
References
Carbon Nanotubes. Synthesis, Structure, Properties, and Applications. Series: Topics in Applied Physics. Dresselhaus, Mildred S.; Dresselhaus, Gene; Avouris, Phaedon (Eds.). 2001, Vol. 80, 448 pp.
Carbon Nanomaterials, Second Edition. Yury Gogotsi and Volker Presser (Eds.). CRC Press, 2013, 529 pp.

In this research, the main objective was to obtain Fe/MWCNT and Fe/TNT (5 wt.%) nanocomposites, which were prepared by incipient wetness procedure. Both composites were successfully synthesized via microwave-hydrothermal route. The microwave irradiation generated tubes with relatively smoother surface. The nanotubes in both procedures have diameter range of 7-10 nm and length of a few mcs. Nanotubes tended to agglomerate forming bundles. The tubes were randomly distributed and have a specific surface area of about 300 m2/g. All obtained nanotubes were open-ended. These nanocomposites showed a certain activity for water treatment and also can be applied for inforcement of polymers used in sport articles.

For over two decades CNT`s and single-walled carbon nanotubes (SWNT) have been extensively researched, as evidenced by the over 10,000 papers published each year. However CNT are not yet a material used heavily in industry, particularly for SWNT`s still only research grade material is available. I envision that this situation is going to change quickly, since the first industrial scale SWNT production plant is planned to be in operation in 2015. At the same time, a couple of SWNT applications would hit the market. These “first” SWNT industrial applications are going to be very different from what we researchers had thought they would be useful for. It is interesting to note that most of the developed applications do not even care much of the electrical or thermal properties of the SWNTs.
In this talk I would briefly overview about the first industrial scale SWNT production plant based on the super-growth CVD, and then focus on what I envision would be the first industrial scale application of SWNT applications, and more importantly why?

Growth of vertically aligned carbon nanotube (CNT) forests is highly sensitive to the nature of the substrate. This constraint narrows the range of available materials to just a few oxide-based dielectrics and presents a major obstacle for applications requiring their growth on conductive surfaces. In this study we present a way to overcome this problem by using graphene as the thinnest conductive barrier to promote CNT forest growth on a variety of substrates [1]. Chemical vapor deposition-grown graphene is used to enable CNT forest growth directly on Cu substrates, which are otherwise incompatible for CNT forest growth. Furthermore, graphene is also shown to intermediate forest growth on other key substrates such as Pt, and diamond. Our results imply that it should be possible to grow vertically aligned CNTs on an almost any substrates, constrained only by the CNT growth conditions.
We find that the growth depends strongly on the degree of crystallinity and number of layers of graphene. The synergistic effects of graphene are revealed by its endurance after CNT growth and low contact resistances between the vertically aligned CNTs and Cu. This work establishes graphene as a unique interface that extends the class of substrate materials for carbon nanotube growth and opens up important new prospects for applications.
[1] R. Rao et al., Sci. Rep. (2013) 3, 1089

The utilization of conventional conductors copper and aluminum to transmit power to the ultra-deep water systems is presently a challenge and stresses the need for a more conductive and lighter materials. A number of recent developments are leading to a new electrical conductor based on continuous carbon nanotubes (CNT) fibers. CNT has a low density and its specific strength is the best of known materials. In theory, metallic nanotubes are more conductive and can carry an electric current density 1,000 times greater than the metals. The CNT therefore has emerged as promising candidate with high potential to replace the above said prevalently used conducting metals as a super-strong, light-weight and ultrahigh conductive electrical conductor.
The development of continuous, macroscopic CNT conductor for a wide variety of applications is in progress whose electrical conductivity is superior to copper. The study encompasses optimization of CNT growth via chemical vapor deposition (CVD) to produce continuous, high purity, well aligned and uniform fiber material, a variety of chemical and thermal treatments and their combinations for purification to remove amorphous carbon and remnants of catalysts, doping techniques to improve the overall strength and conductivity, and analysis of the effects of these treatments on mechanical and electrical properties of the wire.

Controlling the chirality of carbon nanotubes during growth is a challenging problem limiting their use in a wide variety of applications. Previous work in chiral-selective growth demonstrates a relationship between growth rate and chirality. Furthermore, chiral-selective growth is extremely difficult for multi-walled carbon nanotubes (MWNTs), therefore, considering only single-walled carbon nanotubes (SWNTs) reduces the complexity of the chiral-selective growth process. Prior to solving the growth rate, determining the proper parameters for SWNT growth is paramount. A machine learning based approach for selectively growing SWNTs using a laser-induced Chemical Vapor Deposition (CVD) growth system is introduced. This approach models the complex relationships between growth parameters to predict SWNT growth. The growth parameters under consideration are: argon, ethylene, hydrogen and carbon dioxide partial pressures, growth chamber pressure, growth temperature, and water content. Determination of SWNT growth is performed through in-situ Raman spectroscopy using a 532 nm excitation laser. The catalyst consists of 10 nm of alumina and 1 nm of nickel deposited onto 10 µm by 10 µm silicon pillars with a height of 50 µm. A total of 150 growth experiments are used as training data for the SWNT vs. MWNT Support Vector Machine (SVM) classifier. The SVM model is applied to a range of simulated inputs and the subset of these inputs that meet a 99% probability of SWNT growth are investigated further. The simulated inputs consist of 147,521,405 unique growth parameter combinations spanning the entire parameter space producing an accuracy of 80.67% with this SVM model. A reduced dataset of 65,767 growth parameter combinations meets the 99% probability of SWNT growth. Randomly chosen input parameters from this reduced dataset result in SWNT growth in all performed experiments. Specifically, two SWNT growth regions, predicted by this model, consist of a high temperature, high pressure region, and a low temperature, low pressure region, which is also validated through lab experimentation.
The views expressed in this paper are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government.

The use of carbon nanotubes (CNTs) as nanoscale electrical conductors - for example to replace copper in microelectronics interconnects - is much desired owing to the higher current-carrying capacity of CNTs compared to metals. This application however requires to parallel many CNTs (i.e. conduction channels) in order to mitigate the deleterious effect of the CNTs quantum resistance and contact resistance. In this talk, we present key achievements towards this goal.
First, an original implementation of hot wire chemical vapour deposition that allow the growth of high density CNT forest on metallic aluminium films at low temperature is presented. Used in conjunction with innovative multilayer catalyst design, this process results in a drastic reduction in the CNT/metal contact resistance while keeping ultra high CNT area density. In particular, the selective growth of CNTs on aluminium in < 300 nm diameter via hole with CNT shell density > 10^13 cm-2 is demonstrated. This density is close to the theoretical maximum density and is the highest reported so far for CNT growth on conductive supports. As an illustration, we will demonstrate the integration of paralleled CNTs in both vertical and horizontal interconnects with associated electrical characterization. The in-situ grown few-walled CNT nanoscale strands showcase good electrical performances with current-carrying capacity ~10^8 A.cm-2 and specific contact resistance < 5.10^-8 Omega;.cm2 [1]. However, the resistivity values obtained - which lie in the 0.5-1 mOmega;.cm range and are thus among the lowest reported [2] - are still far from copper performances. We will show that doping of the CNT strands is one possible route to improve the electrical performances and that a fourfold reduction of the resistivity can be obtained with halogen doping. The temporal and thermal stability of the doping process will finally be presented.
[1] J. Dijon et al, MRS Proc. 1559 (2013) ; Carbon 60, 139 (2013)
[2] Y. Awano et al, Proc. IEEE 98, 2015 (2010)

Structurally uniform and chirality-pure single-wall carbon nanotubes are highly desired for both fundamental study and many of their technological applications, such as electronics, optoelectronics, and biomedical imaging. Considerable efforts have been invested in the synthesis of nanotubes with defined chiralities by tuning the growth recipes but the approach has only limited success. Recently, we have shown that chirality-pure short nanotubes can be used as seeds for vapor-phase epitaxial cloning growth, opening up a new route toward chirality-controlled carbon nanotube synthesis. In this talk, we will first present our strategy on the chirality-controlled synthesis of carbon nanotubes combining DNA based nanotube chirality separation and vapor phase epitaxial growth. [ref 1] Then, we will present our recent results [ref 2] on the chirality-dependent growth and termination behaviors of various kinds of single chirality nanotubes. We will show how the chiral angles, diameters, as well as the electronic structures of nanotubes influence their growth and termination behaviors. Finally, we will show our ongoing work on the use of end caps molecules of nanotubes for their controlled synthesis. Our studies aim at a much deeper understanding on the growth and termination mechanism of carbon nanotubes and may pave the way for their controlled synthesis and practical applications.
References.
1. Liu, J.; Wang, C.; Tu, X. M.; Liu, B. L.; Chen, L.; Zheng, M.; Zhou, C. W. Nat. Comm. 2012, 3, 1199.
2. Liu, B. L.; Liu, J.; Tu, X. M.; Zhang, J. L.; Zheng, M.; Zhou, C. W. Nano Lett. 2013, 13, 4416-4421.

The physical properties of novel carbon-based materials (nanotubes, graphene) strongly depend on their structure: chirality for SWNTs, number of layers and stacking for graphene. However, materials produced are far from being ideal and a direct synthesis of nanotubes with designed structure and properties is not yet achieved. The tremendous progress made is still limited by our poor understanding of nucleation and growth mechanisms, at an atomic scale not easily accessed experimentally. Atomistic computer simulation is ideally suited for investigations at this level, but the complexity of the synthesis methods, such as the most commonly used Catalytic Chemical Vapour Deposition, makes these studies quite challenging.
Here, we use a carefully assessed tight binding model for nickel and carbon [1] to numerically investigate different aspects of the CCVD synthesis process. We have extended previous calculations [2] of carbon adsorption isotherms to nanoparticles (NPs) up to ~2.5 nm diameter, in a broad temperature range. We thereby study the chemical and physical states of the metal catalyst as a function of size, temperature and carbon chemical potential conditions corresponding to nucleation and growth of SWNTs [3]. We then study the interfacial properties of the NPs with respect to sp2 carbon walls, show that they strongly depend on the amount of carbon dissolved, and emphasize their role in the growth of tubes. Finally, we try and identify conditions in the growth parameter space that lead to the formation of defectless nanostructures, in order to investigate the chiral selectivity issue.
[1] H. Amara et al., Phys. Rev. B 79 (2009) 014109; J. H. Los et al., Phys. Rev. B 84 (2011) 085455
[2] H. Amara et al., Phys. Rev. Lett., 100 (2008) 056105
[3] M. Diarra et al., Phys. Stat. Sol. B 249 (2012) 2629; M. Diarra et al., Phys. Rev. Lett. 109 (2012) 185501

Aligned single-walled carbon nanotube (SWNT) arrays provide a great potential for the carbon-based nanodevices and circuit integration. Aligning SWNTs with selected chirality and identifying their helical structures remains a daunting issue. The widely used gas-directed and surface-directed growth modes generally suffer the drawbacks of mixed and unknown helicities of the aligned SWNTs. Here we develop a rational approach to anchor the SWNTs on graphite surfaces, on which the orientation of each SWNT sensitively depends on its helical angle and handedness. This approach can be exploited to conveniently measure both the helical angle and handedness of the SWNT simultaneously at a low cost. We believe that this approach has a great prospect for the future carbon-based nanoelectronics. Additionally, by combining with the resonant Raman spectroscopy, the (n,m) index of anchored SWNT can be further determined. Handedness and theta; were quickly measured based on the chirality-dependent alignment of SWNTs on graphite surface. By combining their measured d and Eii, (n,m) indices of SWNTs can be independently and uniquely identified from the (theta;,d) or (theta;,Eii) plots, respectively. This approach offers intense practical merits of high-efficiency, low-cost, and simplicity.

Here we investigate the behavioral differences between two classes of nanoparticle (NP) catalysts that can be used to synthesize carbon fibrils by chemical vapor deposition (CVD). High-resolution transmission electron microscopy is used to compare the structure and morphology of carbon fibrils, such as nanofibers (CNFs) and nanotubes (CNTs), synthesized using both zirconium oxide (zirconia) NPs and commonly used metal NPs (iron, chromium, and copper) under identical conditions. The results elucidate that the two types of catalysts have very distinct morphologies: metal NPs form a graphitic cage, while the zirconia NPs form a carbon onion like structure. Our results also indicate that synthesis of fibrils using zirconia NP catalysts is a surface-bound process, and that the melting and subsequent solvation of NP catalysts with carbon atoms is unlikely. Finally, we observe that smaller zirconia NPs do not form a carbon onion like structure, but that CNFs are synthesized instead of CNTs, indicating that NP geometry effects strongly influence the growth mechanism and synthesized fibrils form non-metallic catalysis.

Combined resonant Raman spectroscopy, high resolution transmission electron spectroscopy (HRTEM) and electron diffraction experiments on the same suspended (free-standing) individual carbon nanotubes is an efficient method to determine unambiguously the intrinsic features of phonons in these nano systems.
In this talk, a special attention is focusing on multi-walled carbon nanotubes, mainly on double-walled carbon nanotubes (DWNT), because they provide a unique model system for studying the role of the coupling between the layers on the phonons.

Solution-processed networks of purely semiconducting single-walled carbon nanotubes (SWNT) are interesting for high-mobility field-effect transistors (FETs) for flexible electronics. Here, we use confocal Raman microscopy to investigate charge accumulation and doping in electrolyte-gated FETs with graded layers of semiconducting (7,5) SWNTs that were selected by dispersion in poly(9,9-dioctylfluorene). These nanotube FETs exhibit hole mobilities of up to 7.5 cm²V^-1s^-1 and on/off ratios of 10⁵. For negative gate voltages, i.e. hole accumulation, we observe a linear shift of the G&’-peak toward higher wavenumbers. Using this shift we map the charge carrier distribution in an operating FET at different gate and source-drain voltages with high spatial resolution and over large areas. With this simple technique we are able to visualize directly the channel pinch-off and onset of the saturation regime depending on the assignment of source and drain electrode in an FET with nonuniform carbon nanotube distribution along the channel. In addition to nanotube networks we apply this in-situ mapping technique to reduced graphene oxide layers and other two-dimensional semiconductors.

Carrier-doping on single-walled carbon nanotubes (SWCNTs) can be used for controlling and switching the optical properties of nanotube devices[1]. Recent studies[2, 3] revealed that oxygen doping of SWCNT leads to the emergence of a bright photoluminescence (PL) peak at wavelengths 10 to 15% longer than that of the pristine SWCNTs&’ band-edge exciton emission (noted as E11). As this new peak (noted as E11*) is characterized with a PL quantum yield one order of magnitude higher than that of the E11 emission[3], it become very attractive for wide variety of optoelectronic applications. Studies to dates have attributed this E11* peak to the emission of zero-dimension-like local states generated by the oxygen doping of carbon nanotubes. Aiming to understand the intrinsic nature of these zero-dimiensional states, we performed low temperature PL imaging and spectroscopy studies on individual oxygen doped SWCNTs. Our detail analysis on spectral lineshapes as well as the PL intensity and energy fluctuation of E11 and E11* emission peaks reveals many new spectral features that have not been reported in earlier room temperature[2] and ensemble level low temperature[3] studies. For example we observed that ozonation of SWCNTs leads to splitting of the original band-edge exciton peak at 990 nm into three distinct peaks. These findings have significant implication toward understanding the effects of oxygen doping in modifying the optical properties of SWCNTs.
1. Ostojic, G. N. et al. Interband Recombination Dynamics in Resonantly Excited Single-Walled Carbon Nanotubes. Phys. Rev. Lett. 92, 117402 (2004).
2. Ghosh, S. et al. Oxygen Doping Modifies Near-Infrared Band Gaps in Fluorescent Single-Walled Carbon Nanotubes. Science 330, 1656 (2010).
3. Miyanchi, Y. et al. Brightening of Excitons in Carbon Nanotubes on Dimensionality Modification. Nature Photonics 7, 715 (2013).

This work focuses on showing our recent progress on establishing the prerequisites for studying the rich low-dimensional physics of pristine vs. doped SWCNTs using photoemission and X-ray absorption in order to use them as sensing objects. We will discuss the changes in the site selective electronic structure within various types of metallicity pure SWCNTs (metallicity-sorted and functionalized) and substitutionally doped SWCNTs (with B and N). From these elements, nitrogen is the most studied experimentally as substitutional dopant. However, it can also be part of specific molecules like NO2 or NO, which can present distinctive adsorption kinetics and alter the functionalization of a tube. The mechanisms governing NOx-adsorption had always been thought to be related to chemisorption and with the present study we compellingly prove that this mechanism must be rethought. With a study supported by density functional theory calculations, we have been able to correlate that an additional signal observed in the higher binding energy region of the core level C1s in photoemission is due to the formation of carbonyl groups [C=O] as reaction by-products during adsorption on the tube defects, and not to a naturally expected C-N type of bond. Strikingly, Franck Condon satellites, never detected before in nanotube-NOx systems, were resolved in the N1s X-ray absorption signal revealing a weak chemisorption intrinsically related to NO dimer molecules. Furthermore, I will focus on substitutional doping of B in single-walled carbon nanotubes contemplating the possibility of the formation of an acceptor state in the SWCNT' s electronic structure even at very low B concentrations. B substitution in the tube's lattice is not necessarily uniform, and the formation of B nano-domains has been considered for a long time. For this reason, quantifying the amount and bonding environments of B in the SWCNT lattice has been challenging, particularly when the doping concentration is below 1 at%. In B doped samples, EELS studies carried out in a TEM failed to detect the substituted B in the C network. For this reason, B induced changes in the intensity of the RBM and shifts in G' band have been used as indirect proof of substituted B in the SWCNT lattice so far. We will see how the direct detection of B in the SWCNT lattice from the core level signal recorded with high resolution x-ray photoelectron spectroscopy (XPS) can be achieved. I will also show how the corresponding line shape analysis and the changes in the electronic properties of B doped SWCNTs allow elucidating the site selective bonding environments with unprecedented, detail even when the B concentration is below 1at%. The case of ultra-low doping (comparable to the doping levels in Si semiconductor technology) will be discussed based on X-ray absorption spectroscopy findings.

High-throughput optical imaging and in-situ chirality characterization of individual carbon nanotubes on substrate or in active device is essential for improving chirality-controlled nanotube growth and for understanding nanotube device physics. However, its realization is still of great challenges nowadays. In this talk I will discuss our recent progress towards this aim by establishing an atlas of nanotube optical transitions [1] and developing a high-contrast polarization microscopy/spectroscopy [2].
References:
1. Kaihui Liu, et. al “An atlas of carbon nanotube optical transitions”, Nature Nanotechnology 7, 325-329 (2012).
2. Kaihui Liu, et. al “High-throughput optical imaging and spectroscopy of individual carbon nanotubes in devices”, Nature Nanotecnology (accepted) and arXiv:1307.5353.

One of the assets of nanotubes is that their properties depend on their geometry - the so-called chiral species (defined by their diameter and chiral angle)- which allows an unprecedented flexibility in the nanoworld. However, so far most of the technological developments are hindered by the fact that most samples consist of an uncontrolled mixture of a large number of species.
Optical spectroscopies are the most suited methods for a fast and non invasive diagnostic of the species content of both pristine or processed samples. However, the variation of the absorption cross-section with the chiral species has been a long-standing unresolved issue. Although theoretical studies have predicted a strong variation of this cross-section with the chiral species, no clear cut experimental study on this key property has been reported so far. Actually, there is a multitude of entangled parameters (species concentration, PL quantum yield,...) that usually hamper such experimental measurement.
Here, we present an original method to tackle the chirality dependence of the absorption cross-section of carbon nanotubes [1], which opens the way to the quantitative analysis of the chiral species content of samples. This method is based on a non covalent functionalization of the nanotubes with porphyrin molecules, that induces an ultra-efficient energy transfer to the nanotube upon excitation of the porphyrins. This provides a new handle to excite uniformly the whole chiral species distribution. By comparing the luminescence of the sample obtained through the energy transfer scheme with that obtained through regular nanotube absorption, we can get rid of the unknown parameters (species concentration, quantum yield...) and we are able to trace back the variations of the intrinsic absorption of the nanotubes with the chiral species. In particular, we show that this cross-section varies by up to a factor 2.5 with the chiral angle. This effect was predicted -though underestimated- by theory. In particular, we show that a sub-set of the semi-conducting species (type I) shows a larger absorption whereas the other sub-set (type II) has a reduced absorption. This sheds a new light on the long-standing controversy about a possible preferred growth of near armchair nanotubes that was essentially based on photo-luminescence analysis assuming a chiral independent absorption coefficient. In addition, the method developed in this study not only provides the relative variation of the absorption with the chiral species, but it also allows us to obtain an absolute estimate of absorption cross-section of 13 chiral species from the comparison with the well established absorption cross-section of the porphyrin molecules used as reference absorbing units in the compounds. We deduce an empirical formula for predicting the absolute absorption cross-section of carbon nanotubes as a function of their chiral angle.
[1] Vialla et al., Phys. Rev. Lett. 111, 137402 (2013)

Luminescent devices operating at sub-250nm wavelength present a strong commercial interest. Applications such as antibacterial properties, high density optical storage or nanofabrication possibilities require reliable, portable and efficient devices. Actual Deep UltraViolet (DUV) sources are based on gas active regions, which are difficult to integrate in mobile devices, exhibit poor efficiencies and are harmful for environment. Thus, the development of solid state based DUV emitters is getting more and more relevant.
Hexagonal boron nitride is a wide band gap semiconductor (~ 6.5 eV), which meets a growing interest for DUV applications. In contrast to carbon nanotubes, Boron Nitride Nanotubes (BNNTs) are all semiconductors whatever their diameter and chirality with a luminescence between 200 nm and 250 nm governed by strong excitonic effects. Until recently, the optical properties were poorly known due to both the scarcity of samples and suitable investigation tools. This situation has changed thanks to the development of dedicated photoluminescence (PL) and cathodoluminescence (CL) experiments running at 4K and adapted to the detection in the far UV range [1, 2, 3].
The previous studies on boron nitride nanotubes have mainly dealt with multi-wall BNNTs with a large number of walls (20-120 walls) [2]. These tubes luminesce between 226 and 234nm and this spectral range has been assigned, in hBN, to transitions involving defects. A critical point to further study the confinement effect on the excitonic transitions is therefore to elucidate the luminescence origin of these multiwalls. Furthermore it is important to investigate the luminescence of small diameter BNNTs (with a reduced number of walls), which actually appears to be very challenging.
Cathodoluminescence from a single BNNT with a large number of walls have been measured with a spatial resolution of about ten nanometers, thanks to an UV dedicated SEM system. Different areas along the tube were investigated, from which luminescence is detected at few wavelengths. From 224 to 228 nm, monochromatic cathodoluminescence images exhibit features, which can be linked to the crystallographic structure, separately observed by Transmission Electron Microscopy (TEM) on the same tube. HRTEM observations and tomography experiments have revealed that the BNNTs exhibit a peculiar shape. The section of the tube is polygonal with a number of facets between 6 and 9. These facets form an helix along the axis of the nanotube. An important consequence of this faceting is the formation of a large number of defects along the tube.
We will discuss the relations between these structural properties and the luminescence.
References
[1] P. Jaffrennou el al., J. Appl. Phys. 102 (2007) 116102
[2] P. Jaffrennou and al., Phys. Rev. B, 77 (2008), 235422.
[3] K. Watanabe and al., Phys. Rev. B, 79 (2009), 193104.

Different from zero-dimensional systems such as atoms, molecules, and quantum dots, semiconducting single-walled carbon nanotubes (SWNTs) are ideal one-dimensional systems that allow free diffusion of excitons along their length. Studies have also shown that multiple excitons exist within the diffusion length can annihilate via Auger process. Interplay of Auger process and exciton diffusion therefore could have interesting effects on photon emission statistics of SWNTs. Current existing studies[1] on photon emission statistics were conducted at low temperature where excitons were localized to quantum-dot-like states. To this end we conduct room temperature 2nd order photon correlation spectroscopy studies on high quality SWNTs capable of emitting continuous photoluminescence along their length which could extend up to several micrometers. We observed the degree of photon-bunching lower than 0.5 at the lowest pumping powers. We will also present a correlation between the diffusion length and the degree of photon-bunching. Our study could have implications toward utilizing SWNTs as room temperature single photon sources.
1. A. Hoegele, C. Galland, M. Winger, A. Imamoglu, Phys. Rev. Lett. 2008, 100, 217401.

Nature has inspired many scientists to create a new type of artificial materials mimicking the unique biological structures. It is also possible to directly combine various functional materials with naturally occurring biological platforms. In particular, the incorporation of carbon nanomaterials such as carbon nanotubes (CNTs) into biological polymers has been intensively studied for various biomedical applications. However, the previous hybrid structures between CNTs and biopolymers were mostly fabricated by simply mixing two components or immersing one to another, which often resulted in inhomogeneous aggregations rather than well-dispersed hybrid structures. Here we report the fabrication of highly homogeneous hybrid structures between bacterial cellulose (BC) and CNTs by in situ growing of BC fibers from G.xylinus bacteria in CNT-dispersed culture medium. As a result, the CNTs are well incorporated not only on the surface of but also inside the microporous BC nanofiber scaffolds, which are evidenced by Raman spectroscopy, scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). We also found that the compressive mechanical strength of CNT-BC composite was about 6 times higher than the bare BC scaffolds, and 3 times higher than the CNT-immersed BC. For this reason, the homogenous CNT-BC scaffolds showed outstanding osteogenic conductivity and inductivity when implanted in mouse calvarial defects. We expect that the outstanding structural properties and bio-compatibility of the CNT-BC scaffolds would be very useful for various biomedical applications including regenerative medicine and cell engineering.

Multiwall WS2 nanotubes were discovered two decades ago and are nowadays produced in large scale synthesis [1]. Theoretical calculations and experiments showed that such nanotubes become more stable than the corresponding nanosheets at a threshold outer diameter of about 15 to 20 nm and having made of at least 5-10 layers [2]. Generation of nanotubes of small size and number of layers (<4) requires highly exergonic conditions. In this study, short (20-100 nm) 1-3 layers WS2 nanotubes with diameter of 3-7 nm were produced, by inductively coupled radio-frequency Ar plasma irradiation of multiwall WS2 nanotubes. High resolution transmission electron microscopy (HRTEM) of the plasma-treated nanotubes reveals tiny (“daughter”) nanotubes attached to the outer surface of the multilayer WS2 nanotubes. The amount of such daughter nanotubes increased with the treatment time from 10 to 40 min and with increased plasma power from 400 W to 600W. Rough statistical estimate shows that 80% of nanotubes were covered by daughter nanotubes, when treated at 600 W for 40 min. Some of the nanostructures seem to be nanoscrolls as could be seen when visualized along their axis, while still attached to the multiwall nanotube. However, the majority of the daughter nanostructures are nanotubes, having at least one perfectly closed layer. Many of the daughter nanotubes were found to have either a common growth axis with the multiwall nanotube or tilted by 30° or 60° relative to its axis. The tiny nanotubes could be detached from the large multiwall WS2 nanotubes by dispersion in ethanol and ultrasonication for 10 min. The layer to layer distance in the daughter nanotubes varied between 6.3-6.5Å, which is larger than the interlayer spacing of multiwall nanotubes (6.31Å ), suggesting that they were not fully relaxed during the growth process.
Our proposed growth mechanism of the daughter nanotubes involves strong interaction of the plasma with point or line defects, causing unzipping and exfoliation of the outermost layers of the multiwall nanotube, release of the elastic strain, followed by scrolling and closure into small nanoscrolls or nanotubes.
[1] R. Tenne, L. Margulis, M. Genut, and G. Hodes, Nature 360, 444-446 (1992).
[2] G. Seifert, Th. Köhler, and R. Tenne, J. Phys. Chem. B 106, 2497-2501 (2002).

Graphene is a zero-bandgap semiconductor, no optical luminescence is observed in pristine graphene. A bandgap, however, can be engineered into graphene quantum dots (GQDs) due to quantum confinement and edge effects. As a result, luminescent GQDs have attracted great attention as one of highly promising nanomaterials due to their exceptional advantages of low cytotoxicity, excellent solubility, stable photoluminescence (PL), fine biocompatibility as well as low-cost.[1] Above these fascinating merits in GQDs distinguish themselves from traditional fluorescent materials, making them perfect alternatives for numerous exciting applications: bioimaging,[2] fluorescence sensors,[3] fuel cells,[4] photovoltaic devices.[5]
Doping carbon materials with heteroatoms can effectively tune their intrinsic properties, thus producing new phenomena and unexpected characteristics. Although veriouse heteroatom-doped carbon materials have been reported, doped GQDs have been much less studied. Herein, we report a facile one-pot electrochemical approach for the synthesis of boron(B) doped GQDs (B-GQDs) with B content of 5.24 at %, in which only borax was used as the electrolyte without any other chemical additives. The as obtained water-soluble B-GQDs feature intriguing tunable fluorescence, act as a Al3+ fluorescent sensor, cellular imaging and electrocatalysts for the oxygen reduction reaction. With the existence of borax, they show strong green luminescence with a quantum yield as high as 13%. Significantly, green fluorescent crystals were obtained from evaporating the aqueous solution in the presence of borax at room temperature.
Acknowledgements
This work is supported by NSFC (21073018), the Major Research Plan of NSFC (21233003), Key Laboratory of Theoretical and Computational Photochemistry.
References
[1] D. Pan, J. Zhang, Z. Li, M. Wu, Adv. Mater. 2010, 22, 734-738.
[2] S. Zhu, J. Zhang, C. Qiao, S. Tang, Y. Li, W. Yuan, B. Li, L. Tian, F. Liu, R. Hu, H. Gao, H. Wei, H. Zhang, H. Sun, B. Yang, Chem. Commun. 2011, 47, 6858-6860.
[3] Y. Dong, G. Li, N. Zhou, R. Wang, Y. Chi, G. Chen, Anal. Chem. 2012, 84, 8378-8382.
[4] Y. Li, Y. Zhao, H. Cheng, Y. Hu, G. Shi, L. Dai, L. Qu, J. Am. Chem. Soc. 2011, 134, 15-18.
[5] Y. Li, Y. Hu, Y. Zhao, G. Shi, L. Deng, Y. Hou, L. Qu, Adv.Mater. 2011, 23, 776-780.

By filling the central pore of a single walled carbon nanotube (SWCNT) it is possible to form nanowires of a wide range of inorganic materials that are one unit cell in diameter. These are extreme nanowires, i.e. at the limit of miniaturisation of nanowires. Nanowires of these diameters show extreme quantum confinement effects and in some cases have crystal structures which cannot be stabilised as 3D crystals. A wide range of scientifically and technologically interesting materials have already been used to produce such nanowires. These include ferromagnetic materials, e.g. Fe and Co, phase change materials, e.g. GeTe, ferroelectric materials, e.g. SbSeI, and semiconductors, e.g. HgTe. It is likely that extreme nanowires will have entirely new properties, not just modified versions of the properties of the materials from which they are formed. Such properties would be interesting both fundamentally and technologically. However, as yet there has only been very limited characterisation of the properties of nanowires formed inside single walled carbon nanotubes and the fundamental physics is not yet really understood.
We will present the first Raman spectra of the vibrational modes of HgTe nanowires inside single walled carbon nanotubes alongside atomic resolution TEM of the samples. Both TEM and the vibrational spectra clearly indicate that HgTe forms nanowires with an entirely new crystal structure when infiltrated into 1.3-1.4nm diameter SWCNTs. The strength of the Raman scattering is strongly dependent on incoming photon energy, with a strong resonance centred at 1.77eV which tails off more slowly to low energy than to high. Whilst all of the fundamental and combination modes are resonant at the same basic energy, the shape of the resonance varies for different features. It is clear that the form of the resonance has a lot to tell us about the electron-phonon coupling in these 1-Dimensional structures. We will present the dependence of the Raman scattering on excitation and scattered polarisation, which is entirely in line with what would be expected for nanowires. However the temperature dependence of the Raman scattering is anomalous, showing a decrease in scattering intensity by a factor of ten with increasing temperature from 4K to 300K. In addition to a comprehensive discussion of Raman scattering from HgTe nanowires, we will also present Raman scattering from PbI2 and CoI2 nanowires formed in SWCNTs and prove that the physics demonstrated by the HgTe nanowires is more generally applicable.

Hematite, which is the most stable iron oxide with n-type semiconductor&’s feature, is of great interest due to its low cost and strong corrosion resistance. Most recently, hematite has been extensively investigated in the photoelectrochemical water splitting, catalysts, Li-ion batteries, pigments and chemical sensors. For these applications, since the device performance largely depends on the surface-to-volume ratio of the hematite electrodes or catalysts, tremendous efforts have been devoted to synthesize hematite nanomaterials with large specific surface areas.
Among them, hematite nanotubes have attracted great interest owing to the facile synthesis of them using anodic oxidation processes. Most of studies on hematite nanotubes were based on anodization of Fe or Fe-alloy foils, which results in hematite nanotubes on thick metal substrates. For high-quality chemical sensors or solar water splitting cells, the separation and transfer of hematite nanotube arrays from the metal substrates onto Si or glass substrates are needed. However, using the synthesis-and-transfer method, obtaining vertical hematite nanotubes on the Si or glass substrates is challenging because hematite nanotubes are very fragile and thus the separation of large-area hematite nanotubes is difficult. Alternatively, vertically synthesis of hematite nanotubes on Si or glass substrates have been reported, but the quality of the hematite nanotubes fell far behind those from anodization of Fe foils.
Here we report synthesis-in-place of vertically aligned hematite nanotubes. By anodizing Fe films on Si or glass substrates, we could obtain vertical hematite nantubes on the substrates. The orderness of the hematite nanotubes is unparalleled with those of the previously reports. Furthermore, the vertically synthesized hematite nanotubes on the Si or glass substrates could be used as chemical sensors and without additional processes. The experimental results reveal that the chemical sensors based on the high-quality hematite nanotubes exhibits ultra-sensitive gas sensing properties to flat hematite thin films. In addition, it will be shown that the hematite nanotubes are very promising as high-quality solar water splitting for hydrogen production.

Interest in development in the use of nanoparticles in structural composites for the improvement of thermal conductivity, mechanical properties and electrical properties has recently stimulated some research efforts. Such improvements require the introduction of functional groups and the proper selection and concentration of the nanoparticles, as well as their uniform dispersion. The identification and verification of uniformity of dispersion is very important in the efficient processing for improved performance. Recently, new methods for studying and evaluating the interfacial properties between the reinforcing fibers and the epoxy matrix, have been developed. Distinct from FE-SEM observation, electrical resistance methods are being developed which can be applied for to measure interfacial shear strength (IFSS) and degree of dispersion. The main principle, on which the electrical resistance measurement is based, is Kirchhoff&’s laws, which considers conductive materials as electrical circuits. In this research, the self sensing character of the conductive carbon nanotubes (CNT) and conventional carbon reinforcing fibers has been successfully used as a method for evaluating the dispersion of nanoparticles and interfacial adhesion. The electrical resistance in these composites was observed to be dependent on differences in wetting and interfacial adhesion between matrix and fillers. In summary, a correlation was observed between the electrical resistance and dispersion and degree of cure. It is felt that these methods, along with the electro-micromechanical methods, provide valuable tools for investigating the role of interfacial behavior on thermal conductivity, electrical and mechanical properties. Optical observations by FE-SEM of degree of dispersion and interfacial adhesion are consistent with the electrical resistance results. Additionally, it may be possible to use electrical resistance circuit analysis to detect the location of and extent of micro-damage within composite materials. Acknowledgements: this work was supported by the Agency for Defense Development (ADD) via Korean Institute of Materials Science (KIMM) under contract UE135026GD, 2013.

High energy electron irradiation to carbon nanomaterials is expected to become a technique to tailor the structure with desirable properties. However, the mechanical properties of electron-irradiated carbon nanomaterials are not well understood. In our previous study, we developed molecular dynamics (MD) simulation including electron collision effects to study the structural changes of carbon nanotubes (CNTs) under electron beam irradiation. In the present work, the vibrational properties of electron-irradiated CNTs are studied with the simulation. In the CNT cantilever, the frequency of the CNTs irradiated at the base get lower than that irradiated at the end. The simulations show the capability of mechanical modification of CNTs to a variety of vibrational modes by electron irradiation.
Acknowledgments
This work was supported by JSPS KAKENHI Grants number 25249052.

We report a very efficient synthesis method of millimeter-scale synthesis of vertically aligned carbon nanofibers (CNFs) using thermal chemical vapor deposition. Less than 60 nm thick CNFs are readily grown on palladium thin film catalyst supported on Al2O3, which activate the stackings of conical graphitic nanostructures. The field emission performance of the as grown CNFs is better than that of vertically aligned carbon nanotubes. The maximum emission current density from the CNF carpet was 0.44 µA at 2 V/µm, with the field enhancement factor of over 3000.

The implementation of single-walled carbon nanotubes (SWCNTs) into potential applications is still a great challenge due to the polydisperse nature of the pristine material and its insolubility in any processing solvent. Therefore it is of fundamental interest to elaborate elegant and facile methods for the exfoliation of bundled SWCNTs and for the stabilization of the individualized species in order to address a specific type with respect to their diameter, helicity and electronic type. In the last two decades, a variety of different protocols in the field of covalent and noncovalent nanotube functionalization has been shown to address the aforementioned challenges.
In respect to the polydispersity of the SWCNTs regarding electronic type, diazonium chemistry provides a suitable functionalization scenario for the covalent attachment of a variety of different functional groups to the scaffold of predominantly metallic nanotubes. In principle, the introduction of solubilizing addends, covalently attached to the nanotube framework, provides a suitable scenario for the fast and easy separation of selectively derivatized nanotubes on the basis of simple extraction steps. However, so far such processes still lack efficiency and involve elaborate pre-treatments of nanotube dispersions such as ultracentrifugation.
We herein report on a selective diazonium functionalization sequence in combination with a supramolecular host-guest separation process. Covalently grafted Hamilton receptor units on the scaffold of predominantly metallic SWCNTs, allows for the recognition of cyanuric acid derivatives based on a typical key-lock principle via H-bonding. With the combination of several donor-acceptor components such as fullerenes and porphyrines we recently were able to build up functional supramolecular architectures based on this strong six-point recognition motif. Adapting this concept to SWCNTs, we can achieve highly soluble nanotube architectures in common organic solvents - opening the road for a very efficient and high yielding separation scenario. Furthermore, the variation of cyanuric acid guest molecules, bearing different donor-acceptor components, allows for the construction of quite complex hybrids with potential applications in the field of future smart electronic materials.

As carbon nanotubes attract attention as potential materials in radio frequency applications, linearity studies of carbon nanotube field-effect transistors are needed over a large frequency range with different metal contacts. In our work, horizontally aligned carbon nanotubes grown on quartz substrates are used to fabricate top-gated field-effect transistors. The combined set-up of external mixers and a spectrum analyzer enables detection of higher order harmonics up to 110 GHz. Single-tone harmonic distortion tests show that the amplitude of second harmonic follows the trend in a traditional transistor model. However, third order and higher order harmonics are also observed which may be attributed to the Schottky barrier between carbon nanotubes and the metal contact. In addition, two-tone mixing measurements also display higher order harmonics. Controlled measurements demonstrate that the non-linearity is due to the nanotubes. Thus, the observed harmonic generation shows characteristics of both a field-effect transistor and a Schottky diode. To distinguish between the two non-linear effects, different metals are used as source/drain contacts to form asymmetrical contacts devices. High frequency measurements and corresponding dc characterization data are combined to quantify the contribution of the non-linear elements on the measured output signal. Our findings indicate that high-frequency nanotube electronics may find useful applications as nonlinear frequency mixers and generators.

Integrating or self-assembling carbon nanotubes onto patterned nanoparticles on a substrate could be a unique approach for creating higher order architectures and also facilitating selective placement of nanotubes on a substrate. These hetero-assemblies could be extremely beneficial for advanced sensors and devices, micro/nano-electromechanical systems, and controlled nanoarchitectures applications. Here we report the self-assembly of single-walled CNTs on a patterned array of graphene shell encapsulated gold nanoparticles (GNPs). The GNPs were directly patterned onto a silicon substrate in a high throughput chemical vapor deposition. These patterned nanoparticles were further tagged with affinity biomolecule as a receptor and a solution of CNTs bound with target biomolecules was linked with these receptors. This process also resulted in rapid separation of biomolecule-functionalized CNTs via target-receptor affinity. Morphology and structure of the nanoarchitectures was observed using SEM, TEM, and Raman spectroscopy. The binding chemistry was characterized by FTIR and fluorescence microscopy. In addition, these novel CNT-GNP architectures could be of significant interest for plasmonics as demonstrated by the mathematical modeling conducted in this research, where the intense hot spots were estimated at the interface of CNT and GNP.

The main goals of optimizing chemical vapour deposition (CVD) growth of single-walled carbon nanotubes (SWNTs) are control over the diameter and the type (metallic/semiconducting) of nanotubes. A myriad of parameters can be tuned but a fundamental understanding of the SWNT growth mechanism and specific role of the catalyst particle size and composition is still missing.
Here we investigate the evolution of iron catalyst particles on quartz substrates during the reduction step with hydrogen and its effect on subsequent SWNT growth. We find a strong dependence of particle size and size distribution on the reduction time and temperature. Statistical analysis of the Raman radial breathing modes over large sample areas using different laser excitations (532 nm, 633 nm and 785 nm) enables reliable extraction of the diameter distributions and type (metallic/semiconducting) of the grown SWNTs. The diameter distribution of nanotubes grown with isopropanol as the carbon source directly reflects the catalyst particle size distribution. Depending on reduction temperature and time we can reproducibly shift the SWNT diameter distribution from 1.1(± 0.2) nm to 1.5(± 0.3) nm and the nanotube density from 1-2 SWNT/µm to 5-6 SWNT/µm. Based on these data we propose a model describing the size evolution of the catalyst particles. In addition, the impact of different carbon sources (ethanol, isopropanol, acetone, acetonitrile) and carbon feed rates on nanotube diameter distribution and the ratio of semiconducting to metallic SWNTs will be discussed.

Carbon nanotubes (CNTs) have attracted much interest in a broad range of domains of material sciences due to their exceptional properties. We focus here on one of the most promising properties, which is the ballistic transport of electrons over microns. Such conductors could revolutionize the microelectronic by replacing the copper if a huge number of tubes can be aligned in a connection in order to achieve very low resistance. The ultimate density [1] can be obtained with small diameter single walled-CNTs but the perfect control of their integration in components still remains a challenge. The goal of this work is thus to obtain a dense CNTs carpet growth mode and to control the CNTs diameter and their number of walls [2][3] with accuracy in order to synthesise SWCNTs.
The catalyst particles necessary for the nanotube growth are prepared by dewetting a thin iron film deposited by Ion Beam Sputtering (IBS) on a substrate made of an alumina thin film, used as a diffusion barrier and also deposited on a silicon substrate by IBS. Dewetting is achieved by pretreating the film in the CVD reactor, which is equipped with an heated substrate holder. The holder can be polarized to initiate a confined plasma. Hot filaments can be inserted at the vicinity of the substrate holder to activate decompositions.
An acetylene / hydrogen / helium gas mixture is used to grow the CNTs. The hot filaments are used here to increase the gas phase reactivity and thus the nucleation rate thanks to radicals resulting from the decomposition of species. The importance of the gas mixture will be discussed as well as the particles pretreatment.
The nanotubes obtained by this process were then characterized by SEM, which allows us to control the carpet growth mode and to measure their length. Moreover, we used a FEI CM20 transmission electron microscope (TEM) operating at 200 kV in the high resolution mode to determine the statistical distribution of the tube diameter and to correlate it with the catalyst film thickness and its pretreatment conditions. We will show how we could turn these conditions to decrease the nanotube diameter below 2nm while keeping a dense carpet growth mode. The key role of the acetylene dilution to activate smaller nanoparticles obtained by this way will be highlighted. We will also show that when the same pretreatment is applied directly on the substrate, the alumina densification inhibits the catalyst diffusion and leads to bigger nanoparticles.
References
[1] G. Zhong, J. H. Warner, M. Fouquet, A. W. Robertson, B. Chen, J. Robertson, J. Am. Chem. Soc. 6 (2012) 2893
[2] A. Okamoto, H. Shinohara, Carbon, 43 (2005) 431
[3] Y. Chen, J. Zhang, Carbon, 49 (2011) 3316

Single wall carbon nanotubes (SWCNTs) have shown extraordinary electronic and optical properties since their discovery in 1991 by Iijima et al [1]. However, these properties are highly sensitive to any slight fluctuation in their environment, making their control difficult. On the contrary, double wall nanotubes (DWCNT) offer the advantage that the outer layer can be used as a sacrificial layer, preventing any degradation of the electronic structure of the inner layer [2]. However, interaction between the layers and its impact on their respective properties require to be known in detail.
This is the purpose of the study we have undertaken. DWCNT have been elaborated using CVD techniques [3] In this process, CH4 is thermally decomposed on Co:Mo-MgO catalysts, in order to reach a fraction of DWNTs close to 80%. As a first step, we performed a detailed analysis, by TEM, of the CNT population.
We have found a population of DWNT close to the forecast of 80%. We have observed that nanotubes with an homogeneous diameter distribution, are often grouped into bundles. Statistical analysis of the diameter distribution indicates that diameter of DWNTs down to 1.4 nm can be obtained.
Moreover, thanks to a Cs-corrected JEOL ARM200 operating at 80kV, we have been able to image directly the chiralities of either the inner or the outer wall for different tubes. Numerical FFT of the images have been compared to diffraction simulations using a Fortran code, developed by Lambin and Kociak [4]. Results show an excellent agreement between measurements and simulations, which confort us in the reliability of this study.
In order to rely diameter distribution, chirality and optical properties, we sorted the primary solution, using the density gradient ultracentrifugation (DGU) and performed optical absorption measurements and HRTEM analyses for different populations of DWCNTs extracted by this process. We present our first results on optical and structural characterization of sorted DWCNTs.
References
[1] S. Iijima, Nature, 354 (1991) 56
[2] T. Hertel, A. Hagen, V. Talalaev, K. Arnold, F. Hennrich, M. Kappes, S. Rosenthal, J. McBride, H. Ulbricht and E. Flahaut, Nano Lett., 5 (2005) 511-514
[3] E. Flahaut, R. Bacsa, A. Peigney, and C. Laurent, Chemical Communications, 2003 (2003) 1442-3
[4] M. Kociak, K. Hirahara, K. Suenaga, and S. Iijima, Eur. Phys. J. B 32, 457-469 (2003)

The stimuli responsive polymers are polymers which change dimensions in response to environmental stimuli, such as temperature and pH: a property that makes them useful materials in a wide range of applications and consequently attracts much scientific interest. We demonstrate the synthesis of Methacrylic bacid based co-polymeric nanotubes to form pH activated nanotubes. The nanotubes are fabricated by conformally coating the pores of anodic aluminium oxide membranes with stimulie responsive polymers using initiated chemical vapor deposition. These nanotubes can swell extensively in high pH range. The swelling of the nanotubes is the strong function of pH of the medium and the methacrylic composiion of the polymer. The physical, chemical and morphological properties of nanotubes are studied using various characterization tools such as FTIR, Ellipsometer and SEM. Furthermore, The pH response of the co-polymer nanotubes is studied through the time release of a Hydrophobic phloroglucinol dye encapsulated and adsorbed by the SRP co-polymer nanotubes for the potential application of nanotubes as nanocarriers.

Nitrocellulose aerogel is a robust, sponge-like porous material.[1] It has a very high surface area and tunable nanopore features, and offers an ideal matrix for incorporating various nanomaterials for targeted applications, such as for enhanced detection of explosives and mitigation of explosive events. Carbon nanotubes (CNTs) possess excellent thermal, electrical and mechanical properties. The composite aerogel of nitrocellulose and CNTs has recently been reported to exhibit mechanoresponsive conductivity and pressure sensing.[2] To our knowledge, there have been no reports on the promoted laser initiation of the composite aerogel of nitrocellulose and CNTs.
In this work, multi-wall CNTs (MWCNTs) are carboxylated using a wet chemistry [3] and are characterized by X-ray photoelectron spectroscopy. The thus-functionalized MWCNTs are infiltrated uniformly into nitrocellulose aerogels directly from alcohol-based sol-gel mixtures, forming nitrocellulose-based, homogeneous composite aerogels. Although the composite aerogels exhibit similar surface areas and mechanical strengths as pure nitrocellulose aerogels, they become more sensitive to laser stimuli than pure nitrocellulose aerogels. The gel morphologies of the composite aerogels are similar to those of pure nitrocellulose aerogels, as evident in the preliminary micrographs of scanning electron microscopy. The surface areas of the composite aerogels are determined by nitrogen sorption analysis. No significant changes in surface areas are found with increasing the concentrations of MWCNTs. In all, the presence of infiltrated MWCNTs does not seem to alter the aerogel&’s structure to a significant extent; it does enhance the aerogel&’s initiation and combustion behavior.
Reference:
[1]. Peterson, G.R., et al., Chem. Commun. 2012, 48, 11754.
[2]. Wang, M., et al., Adv. Mater. 2013, 25, 2428.
[3]. Hung, N.T., et al., Inorg. Mater. 2008, 44, 219.
Acknowledgement:
This research was performed under an appointment to the U.S. Department of Homeland Security (DHS) Science & Technology (S&T) Directorate Office of University Programs Summer Research Team Program for Minority Serving Institutions, administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy (DOE) and DHS. ORISE is managed by Oak Ridge Associated Universities (ORAU) under DOE contract number DE-AC05-06OR23100. All opinions expressed in this paper are the author&’s and do not necessarily reflect the policies and views of DHS, DOE or ORAU/ORISE.

Single walled carbon nanotubes (SWNTs) possess unique electrical properties, which makes them attractive building blocks in electronic devices. The large-scale assembly of nanotubes with controlled orientation on surfaces is therefore essential for their integration into practical devices. Templated growth of SWNTs on certain crystalline substrate represents the most efficient way to offer the levels of perfection in alignment needed by most applications in electronics. The researchers have demonstrated that the alignment is due to guided growth along either step edges or lattice directions, with only one alignment mode predominantly in different research system for most of the cases. Here we present a comprehensive study of the alignment process on quartz and the observation that both step edges guided growth (graphoepitaxial effect) and lattice guided growth (epitaxial effect) can coexist and compete with each other. In our growth systems with either Cu and Co/Mo catalyst, water vapor was discovered to have strong effect on the alignment mode. The mechanism that explains how water vapor affects the growth mode will be discussed in the presentation. This is the first time that strong dependence of SWNT alignment on the surface topology due to steps is fully investigated. These findings provide important insights into understanding of guided growth mechanism of SWNTs, and possibly pave the way to highly controlled nanotube configurations with potential applications in electronics, sensing, and other fields.

Carbon nanotube (CNT) forests have outstanding thermal, electrical, and mechanical properties, which have generated significant interest as thermal interface materials (TIMs). Some TIM applications, however, require low thermal resistance and high electrical resistance to protect electronic components. It is thus useful to be able to modify CNTs to reduce their electrical conductivity while maintaining high thermal conductivity and interface conductance, and high mechanical compliance. We recently showed that nanoscale oxide coatings could be applied to CNTs in forests without changing the mechanical deformation behavior of the forests (P. Pour Shahid Saeed Abadi et al., Nanotechnology, in press). In this study, we investigated the thermal and electrical resistance of CNT forests with an oxide coating. Low-pressure chemical vapor deposition (LPCVD) was used to produce CNTs on high-conductivity Si substrates. Plasma-enhanced atomic layer deposition (PALD) was used to conformally deposit Al2O3 on individual CNTs in arrays. This process is facilitated by O2 plasma pretreatment to functionalize the surface of the CNTs and nucleated the oxide growth.. Several analytical techniques were used to characterize the carbon nanotube-oxide composites, including scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Thermal conductivity and thermal interface resistance were measured for pristine and oxide-coated CNT array using a modified photoacoustic technique. The oxide coating was found to increase the effective thermal conductivity of the forests, in contrast to expectations of increased phonon scattering in the CNTs as a result of the oxide boundary. Thermal interface resistance increased modestly as expected due to the additional interfaces and phonon scattering at the CNT tip contacts. Electrical resistivity measurements were made and a significant increase in electrical resistivity was observed for the oxide-coated forests, which makes this approach a promising route to create a viable TIM for thermally conductive and electrically insulating applications.

Single-walled carbon nanotubes (SWNTs) have excellent electrical properties for a wide range of applications, such as transistors, solar cells, photodetectors and sensors. However, for all these applications, it is necessary to separate semiconducting SWNTs from metallic ones. A scalable and efficient approach for sorting high-purity semiconducting SWNTs still remains a challenge. Sorting with conjugated polymer is one of the most simple and low-cost processes and can be used to sort large amounts of semiconducting SWNTs. Here, we explore different factors that affect both the yield and selectivity of SWNTs by polythiophenes. We found that the dispersion yield was directly related to the length of the polymer&’s alkyl side chains. Molecular dynamics simulations in both implicit and explicit toluene indicate that polythiophenes with longer alkyl side chains bind to the nanotube more strongly, due to the increased surface contact area with the nanotube. Solvent type is also important for realizing high dispersion yield. With careful and strategic choice of solvent, we managed to achieve a dispersion yield up to 44% while maintaining the selective dispersion of semiconducting SWNTs. This increased yield is likely due to the more flexible polymer conformation in certain solvents as observed from Small Angle X-ray Scattering (SAXS) measurements. Additionally, this technique permitted selective sorting of small-diameter semiconducting SWNTs in a high concentration, which is ideal for solar cell applications.

Recent advances have led to sorting of single-wall carbon nanotubes (SWNTs) into chirally purified (e.g. all-semiconducting or all-metallic) solutions and networks [1,2]. However, until now, studies have only focused on the electrical and optical properties of such sorted SWNT films, without reports of their thermal properties to the best of our knowledge.
In this work, we use infrared (IR) thermal imaging to simultaneously study thermal and electrical transport in chirality-sorted SWNT networks for the first time. SWNTs are sorted by density gradient ultracentrifugation [1] to assemble SWNT films through a vacuum filtration method. We suspend the films between two Pd-coated copper blocks that serve as both electrical contacts and heat sinks. We use Joule heating and IR microscopy to obtain the temperature pro-files of the suspended SWNT films [3]. We use the transfer length method to obtain the electrical contact resistance, and a finite element model to extract the thermal conductivity of the film and the thermal boundary conductance between the film and Pd/Cu contacts.
We characterized the thermal and electrical properties of 90% semiconducting, 90% metal-lic, and unsorted (66% semiconducting) SWNT films. The electrical conductivity of these films ranges from 8.5×104 to 1.3×105 S/m. For the semiconducting films the thermal conductivity is ~180 Wm-1K-1 and the thermal contact conductance is 2700 WK-1m-2 between the film and the Pd/Cu contacts. The metallic films have thermal conductivity of ~140 Wm-1K-1 and a contact conductance of 3000 WK-1m-2. Finally, the unsorted films have a thermal conductivity of 290 Wm-1K-1 and a thermal contact conductance of 1500 WK 1m 2. We uncover that metallic films have lower thermal conductivity but higher electrical conductivity due to greater SWNT junction density and greater mass density (~2 g/cm3 instead of ~1 g/cm3 for the other networks). In addi-tion, we find that chirality plays a lesser role on thermal properties than the individual SWNT lengths and overall junction density. Our results are in good agreement with mesoscopic models relating the SWNT film thermal conductivity to mass density [4].
The thermal conductivity of the materials studied here is comparable to that of metals like Al while having one-half the mass density, making SWNT films attractive as lightweight thermal and electrical conductors. In addition, unlike metals, the SWNT film thermal properties can be tuned over several orders of magnitude by varying the SWNT length and junction density [4,5].
[1] M. C. Hersam, Nature Nanotech. 3, 387-394 (2008)
[2] H. Wang et al., ACS Nano 26, 2659-2668 (2013)
[3] F. Lian et al., MRS Spring Meeting (2013)
[4] A. N. Volkov et al., App. Phys. Lett. 101, 043113 (2012)
[5] R. Prasher et al., Phys. Rev. Lett. 102, 105901 (2009)

Hydrothermal treatment of Manganese nitrate in the presence of ZnO nanorod templates results in free standing cavity MnO2-ZnO composite arrays on copper substrate. Tuning the molar concentration of cobalt nitrate and hydrothermal temperature can controllably prepare one dimensional MnO2-ZnO cavity structure arrays. The electrochemical properties of the resultant arrays are investigated. Due to free space between adjacent tubes or rods, short insertion and extraction length for Lithium ions, the as-prepared one-dimensional cavity MnO2-ZnO composites exhibit good cycling performances and high capacities as electrode materials for Li-ion batteries.

Ingenious electrical innovations as the imaginations of public have been materialized by the evolution of material science and production process (e.g. photolithography) over the past half-century, starting with transistor. Recently wearable electronics, the most-talked-about categories of Electronics, have been emerged as new technology for dimension-free electronic device as it shown in movies which represent the public imaginations. Unfortunately, the conventional materials (e.g. silicon, metal) are not suitable for the wearable electronics due to difficulty of maintaining the electrical properties under the external force induced transformation. To realize a wearable electronics such, all components must comply with not only bending to some degree without losing their function, but also slightly stretchability to apply to fit the nature&’s life forms. Discovery of low dimensional carbon materials, one-dimensional carbon nanotubes, two-dimensional graphene, and three-dimensional graphite, inspired the development thin electronic devices with opening potentials (e.g. superb electrical and mechanical properties) for wearable electronics beyond the limits of conventional materials.
The ultimate goal of our approach is to develop the key technical solution for realization of the wearable device that is possible to alternate the conventional materials based device. The in-situ synthesis of single walled carbon nanotubes (as channel materials) - graphite (as electrode materials) structure offers unique potential for flexible electronics with superb mechanical flexibility and also provides a promising strategy toward flexible, wearable electronic devices including chemical and biosensors, only using single walled carbon nanotube - graphite structures, without fragile metal contact or others so that can be applied to fit the nature&’s life forms. Particularly, our wearable device acts as a chemical sensor by detecting the abrupt change in environment (~5%, at 5ppm DMMP), fitted with wildlife (lucanus maculifemoratus dybowskyi parry, stag beetle and Dracaena sanderiana cv. Virens, lucky bamboo). The fully functional device comprises carbon nanotube-based chemical sensors with interconnect of graphite and passive RLC circuit system, also based on graphite, for wireless data transmission. These results represent substantial progress toward all-carbon electronics through chemical synthesis and suggest the future promise of the electronic interfaces with ecosystem.

Our research is focused on the engineering of novel, highly sensitive and miniaturized hybrid materials from carbon nanotubes (CNTs) and DNA molecules for applications in biosensors and medical devices. These hybrid sensors allow for a high degree of miniaturization, a key factor in the design of lightweight components while maintaining the advantages of in-situ and real-time analysis capabilities. In the first phase of the sensor design process, we investigated the structural and electrical properties of the supramolecular complexes made of amide-functionalized CNTs and double-stranded DNA. The solubilization properties of the hybrid nanotubes in aqueous solutions with different concentrations of DNA were studied, and an optimal ratio of nanotubes and biomolecules to achieve a good level of dispersion was found. Complexes formed in aqueous solution from CNTs and DNA are highly stable and maintain their properties up to one month from preparation. The morphology of the CNT-DNA composites was investigated at the nanoscale level using atomic force microscopy (AFM) and electron microscopy (SEM). Results from these investigations show the strong affinity between the surface of the amide-functionalized CNTs and the DNA strands, which results in a characteristic pearl-like configuration of the hybrid assemblies. Further, the local conductive properties of the CNT-DNA films were mapped by atomic force microscopy in the PeakForce TUNA mode, revealing the excellent conductivity of the films.

Hollow micro-/nano-structures have recently gained tremendous interest because of their great potential in various applications such as catalysis, drug delivery, gas sensor, energy conversion and storage systems, and so on. In the past decade, there have been great successes on developing effective methods for the synthesis of hollow structures including hollow spheres, cubes and one-dimensional (1D) micro-/nanotubes.However, most of these reported hollow structures are relatively simple. Hollow structures with higher complexity in terms of structure and composition are anticipated to offer exciting opportunities for both fundamental studies and practical applications. As an example, multi-shelled hollow structures are shown to exhibit enhanced lithium storage and gas sensing performance compared to simple hollow structures. With this interest, researchers worldwide have recently devoted rapidly increasing efforts on the rational design and synthesis of complex hollow structures. In particular, tubular structures (e.g., micro-/nanotubes) could be regarded as special hollow structures that might inherit the benefits from both hollow and 1D structures. Despite the great advances on complex hollow structures with isotropic architectures, it appears less developed for the fabrication of 1D complex hollow structures. Therefore, it will be highly desirable to develop a simple but general strategy to effectively synthesize novel 1D hollow structures with high complexity for different functional materials.
In this work, we develop a facile and general tempated assisted strategy to grow novel complex tube-in-tube hollow structures for many binary and mixed metal oxides, including Mn2O3, Co3O4, NiO, Fe2O3, CuCo2O4, ZnCo2O4, CoMn2O4, MnCo2O4 and NiCo2O4. The promising applications of these novel tubular structures are investigated including MnCo2O4 for oxygen reduction reaction and ZnCo2O4 for lithium ion batteries.

Polyacrylonitrile (PAN) is the major precursor in the processing of carbon fibers because of its good spinnability, easy carbonization, and high carbon yield. However, many potential applications of PAN based carbon fiber are underdeveloped due to their high cost of PAN. In contrast, the cellulose precursor for carbon fiber has a well-ordered crystalline structure, high thermal conductivity, mechanical flexibility, and low precursor cost despite its lower yield on carbonization. The properties of the PAN precursor play a crucial role in the production of carbon fiber because enhancement of the PAN precursor properties could translate into corresponding enhancements in the produced carbon fibers. Nanocellulose is well known as an excellent reinforcement to improve the mechanical properties of polymer composites. Therefore, nanocellulose is expected to reinforce the PAN precursor and be used simultaneously as a cellulose precursor for carbon fiber.
In this research, the PAN precursor was reinforced by nanocellulose as cellulosic reinforcement that was separated from microcrystalline cellulose. The nanocellulose reinforced PAN precursor fiber was prepared by a wet-spinning process from PAN-nanocellulose solution. The strong polar interaction between the nitrile groups of PAN and the hydroxyl groups of nanocellulose resulted in the formation of an interconnected structure. In addition, the mechanical properties of nanocellulose reinforeced PAN precursor were investigated and the nanocellulose reinforced PAN precursor effectively because of its high aspect ratio and good interfacial adhesion to the PAN matrix. The spun PAN-nanocellulose fibers, containing nanocellulose in different concentrations, were oxidatively stabilized at 280oC in air and carbonized at 1000oC in nitrogen. The Tuinstra-Koenig equation was used to estimate graphite crystallite size of PAN-nanocellulose carbon fiber and the graphitic content (sp2 carbon) was increased after carbonization process. The intensity of graphitic carbon peak in the Raman spectroscopy and graphite crystallite size of PAN/nanocellulose carbon fiber were increased with increasing nanocellulose contents. This research was supported by the National Research Foundation of Korea. (Project No. 2010-0028182 and 2012-047656)

Irradiating carbon nanomaterials with energetic electrons is expected to become a technique to tailor the structure with desirable properties. However, the technique is not well established. It is important to study atomic level behavior of the materials under electron irradiation. Molecular dynamics (MD) simulation is suitable for such kind of studies. In the present work, we study the interaction volume of electron beam in carbon nanomaterials with the MD simulation.
The interaction between incident electron and carbon atom in the target materials during electron irradiation is introduced by the relativistic binary collision theory. The motion of each atom in the material under electron irradiation is calculated with the MD simulation.
Interaction volume of electron beam in the carbon nanotube and the multi-layered graphene are studied. The interaction volume increases with an increase in the electron energy. For example, when the beam diameter is 1 nm, the diameters of the interaction volumes in the multi-layered graphene are 1.13 and 1.98 nm at 150 and 500 keV irradiation, respectively. The secondary damages caused by the knock-on atoms largely affect to enlarge the interaction volume.
This work was supported by JSPS KAKENHI Grants number 25249052.

Since the electrical, physical and optical properties of single-walled carbon nanotubes (SWNTs) are dependent on their diameter and chirality, a number of researches to control the diameter or chirality has been performed so far. As a catalyst for SWNTs synthesis, the transition metals have been mostly used. However, recent reports demonstrated the wide ranges of nanoparticles including some precious metals and various metal oxide nanoparticles can act as catalysts for SWNTs growth. Recently, we used Au nanoparticles for SWNTs growth since Au has a low melting temperature so that we can easily tune the particle size by thermal annealing. In addition, it is expected that a melting point decrease phenomena would take place in a nanoscale environment, which is helpful for particle size change with relatively lowered temperature ranges.
Here, we demonstrate the growth of SWNTs having narrow distribution on diameter and chirality using the uniform-sized Au nanoparticles below 1-nm diameter via repetitive annealing of e-beam deposited Au thin films. The monodispersed Au nanoparticles were obtained using optimized spincasting recipe to prevent surface diffusion-derived particle agglomeration during both particle-annealing and tube-growth stages. We performed repetitive thermal annealing to induce the gradual decrease of the Au particle size. Finally, we grew SWNTs from the size-controlled Au nanoparticles with methane CVD. As for substrates, we employed ST-cut quartz wafer to obtain parallel-aligned SWNTs to fabricate electronic device through tube-transfer from the quartz to SiO2 covered Si wafer. It is found that both Au nanoparticle size and tube diameter linearly decreased with prolonged annealing time. We carefully characterized the diameter and chirality of as-grown SWNTs through the systematic analysis using AFM, Raman spectroscope and photoluminescence. Moreover, we present electronic transport property from field effect transistor device fabricated by using the diameter-controlled SWNTs channel and CVD-graphene electrodes.

Most recent experimental and theoretical works performed by our group and related to the synthesis, microscopic analysis and property studies of nanotubes and nanosheets made of BN [1,2], WS2 [3,4] and MoS2 [5] compounds will be reviewed. The emphasis will be put on the in-situ experiments performed in a high-resolution transmission electron microscope toward understanding and control of electrical, mechanical and optical properties of these nanomaterials [6]. The author is grateful to Drs. D.Tang, Z. Xu, W. Wei, M. Yamaguchi, C. Zhi, A. Pakdel, N. Kawamoto, M. Mitome, C. Nethravathi, K. Kimoto, D. Kvashnin, P. Sorokin, and Profs. Y. Bando, R. Tenne, J. Lou and B. Yakobson for their valuable contributions and discussions with respect to the regarded projects.
[1] Yamaguchi et al. Acta Mater. 61, 7604 (2013)
[2] Pakdel A., Bando Y., Golberg D. 29, 7529 (2013)
[3] Tang D.M. et al. Nano Lett. 13, 1034 (2013)
[4] Nethravathi C. et al. ACS Nano 7, 7311 (2013)
[5] Tang D.M. et al. (2013), submitted for publication
[6] Golberg D. et al. Adv.Mater. 24, 117 (2012)

We demonstrate a novel method to create flexible conduction channel for tunnel field effect transistors (TFETs) without using semiconductors. This was obtained by functionalizing boron nitride nanotubes (BNNTs) with iron (Fe) quantum dots (QDs) at their outer surfaces.
Silicon-based field effect transistors (FETs) have been playing a crucial role in the modern electronic devices since over fifty years ago. However, the performance of Si FETs degrades as reducing their feature size due to high power dissipation, short channel effects, high contact resistance, etc.. Semiconducting nanomaterials, such as nanowires and single walled carbon nanotubes (SWCNTs), have been proposed as the conduction channels in the next generation switching devices. BNNTs are structurally similar to SWCNTs with a uniform wide band gap (~6eV) that is not sensitive to the change of chirality, diameter, and number of nanotubular walls [1, 2]. Furthermore, BNNTs are mechanically and chemically stable, and ideally free of dangling bonds at their surfaces. However, BNNTs are electrical insulating, and not applicable for FETs as doping has proven to be a failure. We have shown that BNNTs functionalized with gold quantum dots (QDs-BNNTs) can form the conduction channel of tunnel field effect transistors (TFETs) recently [3].
Here, we demonstrate that individual QDs-BNNT is a flexible conduction channel applicable for TFETs using a scanning tunneling microscopy stage inside transmission electron microcopy (STM-TEM) system. In addition, the gold QDs can be replaced by other metallic QDs, for example, the ferromagnetic Fe QDs in this work. Firstly, high-quality BNNTs were grown by the growth vapor trapping (GVT) approach using conventional tube furnaces [4, 5]. The quality of the as grown BNNTs has been confirmed by Raman spectroscopy, Fourier transformed IR (FTIR), and field emission scanning electron microscope. Secondly, we have deposited a thin layer of iron film by pulsed laser deposition (PLD) method, followed by annealing at appropriate temperatures. By doing so, one-dimensional (1D) array of Fe QDs are formed on the surface of BNNTs. Then, we have performed the I-V test in our STM-TEM system at Michigan Technological University. Results indicate that Fe QDs-BNNTs are new class of electronic materials with high on-off ratios (~signal up to submicron Ampere). Furthermore, their switching behaviors are evaluated at by various bending angles. Details of such in-situ study will be discussed in the meeting.
Y. K.Yap acknowledges supports from National Science Foundation (Award 1261910), and the U.S. Department of Energy, the Office of Basic Energy Sciences (Award DE-FG02-06ER46294).
References:
[1]. Wang et al, Nanoscale 2, 2028 (2010).
[2]. Wang et al, in Chapter 2 of B-C-N Nanotubes and Related Nanostructures (Springer, 2009).
[3]. Lee et al, Adv. Mater. 25, 4544 (2013).
[4]. Lee et al, Nanotechnology 19, 455605 (2008).
[5]. Lee et al, Chem. Mater. 22, 1782 (2010).

Next generation electroactive materials for aerospace applications require a simultaneous increase in electroactive performance paired with a decrease in power consumption. Many prototypical electroactive materials have poor mechanical/thermal properties and unsatisfactory electroactive performance. In contrast, synthesized boron nitride nanotubes (BNNTs) exhibit excellent mechanical, electronic, optical, and thermal properties. BNNTs possess high strength-to-weight ratio, high temperature resistance (~800°C in air), radiation shielding capabilities and can be incorporated into various composites. Previous theoretical studies have predicted that BNNTs exhibit intrinsic piezoelectric properties. However, the piezoelectric properties of BNNT-containing composites have rarely been studied experimentally.
In this presentation, the electroactive characteristics of novel BNNT-based materials are physically demonstrated. A molecular dynamics model was developed to illustrate the piezoelectric nature of BNNTs as a function of chirality, diameter, and temperature. The model introduces a strain-dependent dipole potential term to simulate the piezoelectric response resulting from deformation. Furthermore, a series of BNNT/polyimide composite materials with varying degrees of nanotube alignment were prepared. The incorporation of BNNTs produced electroactive materials that exhibited high piezoelectric coefficients (d33 asymp; 22 pm/V) and high electrostrictive coefficients (M33,asymp; 4.2 x 10-16 m2/V2)) when compared to conventional piezoelectric and electrostrictive polymers. The effect took the form of a change in refractive index (delta n and psi) under the influence of an applied electric field. It is anticipated that the BNNT-containing electroactive material will lead to new sensors, actuators, and energy harvesting devices capable of operation in high temperature environments.

Nanocrystalline titanium dioxide (TiO2) is frequently used as a photoanode material in dye-sensitized solar cells (DSCs) due to its excellent electrical properties and high thermal and chemical stability. However, random photo-induced electron diffusion through a disordered architecture increases the possibility of interfacial recombination with oxidized species (e.g., I3-) or cationic sensitizers. In previous work, we demonstrated doubly open-ended TiO2 nanotube (DNT) based DSCs showed great charge collection efficiency compare with that of conventional TiO2 nanoparticle (NP) based DSCs due to direct electron pathway of DNT. The DNT-DSCs yielded higher power conversion efficiency (PCE) than was observed from TiO2 nanoparticle-based DSCs, for comparable film thicknesses, despite the use of less amount of dye. Although efficient structure characteristics of DNT as a photoanode, one limiting factor of DNT based DSCs is insufficient internal surface area for anchoring large amount of dye. To overcome this drawback, in this work, DNT decorated with few nm-sized TiO2 nanoparticles (sNP@DNT) were prepared as a photoanode and applied in dye-sensitized solar cells (DSCs). The sNP@DNT electrode is achieved by Ti(OH)4 precursor solution. The sNP@DNT-DSCs showed about 9% increased dye loading, and the PCE was exhibited 10.0% (which is a record efficiency for NT-based DSCs up to date), about 47% improvement from the corresponding bare DNT-based DSC (6.8% of PCE). This value was even 23% greater than the conventional TiO2 NP-based DSC with light scattering layer (8.1% of PCE). The enhanced PCE in the sNP@NT was not only due to the enlarged surface area with increased dye-loading (thus, increased light-harvesting ability), but also low electron transfer resistance (thus, retarded recombination reaction).

In catalysis, solar energy harvesting, health care, and nanofluidics, investigation of nanotubes as well as nanochannels embedded in solid state membranes is of high relevance for both basic research and industrial applications. On the way to novel applications, systematic studies on these nanostructures as well as development of suitable fabrication techniques to precisely tailor their dimensions, orientation, and surface properties are required.
We present the integration of high aspect ratio (> 500) inorganic nanotubes in a polymeric etched ion-track membrane by using atomic layer deposition (ALD). Polycarbonate membranes with cylindrical nanochannels of 30 µm length and diameter varying between 400 and 20 nm are fabricated by swift heavy ion irradiation at the UNILAC accelerator of GSI, and subsequent chemical etching. The resulting nanochannels exhibit defined aspect ratios between 75 and 1500. In order to functionalize the surface, these membranes are coated by ALD with layers of controlled thickness of alumina (Al2O3), titania (TiO2) and silicon dioxide (SiO2). We investigate the homogeneity of the ALD surface modification process inside the nanochannels by various methods. Average channel diameter and diameter distribution are studied by small angle X-ray scattering before and after coating. Furthermore, X-ray photoelectron spectroscopy is applied to analyse the surface composition. In addition, the supporting polymer templates are dissolved by wet-chemical methods and the resulting inorganic nanotubes with exactly defined diameters and wall thicknesses are visualized by scanning electron microscopy (SEM) and scanning transmission electron microscopy in SEM. The nanotube composition is analysed by energy dispersive X-ray spectroscopy, evidencing the homogeneity of the ALD process inside the nanochannels.

Three successive generations of twist-spun artificial muscles are described that provide both torsional and tensile actuation. Our first generation of twist-spun muscles, which are electrochemically powered by volume changes induced by double-layer charge injection, provide torsional rotation speeds of 590 rpm, and torsional strokes of 250° per millimeter of actuator length, which is 1000 times that for earlier artificial muscles. Our second generation muscles, which require no electrolyte and are based on guest-infiltrated carbon nanotube yarns, can torsionally actuate at 11,500 rpm and deliver 85 times higher power density during contraction than natural muscles. Our third generation muscles, which are thermally, electrothermally, or chemically powered polymer fibers, can rotate at 50,000 rpm, contract by up to 49%, lift 100 times heavier loads than the same length and weight human muscle, or actuate at 7.5 cycles/s for millions of cycles.

Carbon nanotubes (CNTs) have been received worldwide attention due to their outstanding mechanical, electrical and thermal properties. Ever since CNT yarns, composed of axially aligned and highly packed CNTs, were fabricated, the transfer of CNT&’s superior properties to macroscale CNT yarns was expected. However, the tensile strength of CNT yarn is inferior to individual CNTs. Although the individual CNTs are ultra-strong, they are connected by weak inter-molecular interaction, van der Waals forces. Therefore, stronger linkage between CNTs is necessary for the high strength of CNT yarns. To increase the interaction between CNTs, covalent cross-linking was applied to CNT yarns using bi-functional crosslinker. The detailed reaction mechanism will be discussed. The covalent cross-linked CNT yarns were characterized by FT-infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy, and also examined for their mechanical properties. Mechanical measurement showed that the tensile strength of CNT yarns was increased after the covalent cross-linking, achieving 3~4 GPa.

Carbon fiber-reinforced epoxy composites (CFEC) were fabricated infusing 0, 0.15, 0.30, and 0.40 wt% amino-functionalized XD-grade carbon nanotubes (NH2-XDCNTs) using the compression molding process under 16 kips. The thermo-mechanical and inter laminar shear strength properties of CNT incorporated carbon/epoxy composite samples were evaluated by performing dynamic-mechanical thermal analysis (DMTA) and short beam shear (SBS) tests. XD-CNTs were infused into Epon 862 resin using a mechanical stirrer followed by a high intensity ultrasonic liquid processor for better dispersion. After the sonication, the mixture was placed in a three roll milling processor for 3 successive cycles at 140 rpm, with the gap spaces incrementally reduced from 20 to 5 µm, to obtain the uniform dispersion of CNTs throughout the resin. Epikure W curing agent was then added to the modified resin and mixed using a high-speed mechanical stirrer. Finally, the fiber was reinforced with that modified resin using the compression molding process. The results obtained from the DMTA test were analyzed based on the storage modulus, glass transition temperature, and crosslink density. The analysis indicated that the thermo-mechanical properties were linearly increasing from 0 to 0.3 wt% XDCNTs loading. The SBS test results exhibited that the incorporation of XDCNTs into the composite increased the interlaminar shear strength (ILSS) by up to 22% at 0.3 wt% CNTs loading. Better dispersion of XDCNTs might be attributed to more crosslinking sites and better interaction between fiber and matrix resulting in an improved fiber-matrix interface, whereas, the reaction between functional groups -NH2 of XDCNTs with epoxide groups of resin and epoxy silanes of fiber surfaces improved the crosslinking and thereby ILSS properties of carbon/epoxy composites.

Ideal garments for simultaneous health hazard and heat stress prevention are lightweight clothing that combines high protection with excellent breathability. Conventional protective garments restrict evaporative heat loss, thus greatly limiting the main mechanism of human body thermoregulation in thermally stressing environments. Advancements in moisture-management performance of protective fabrics need new materials that are able to rapidly transport water vapor out and still provide a good degree of protection from harmful environments. Recently, in our laboratory, we have demonstrated exceptionally-fast gas and water flow rates in carbon nanotube pores (CNT). These results suggest that CNTs may sustain very large water vapor transport rates (MVTR) while maintaining a high degree of protection from biological and large chemical warfare agents thanks to their very small, nanometer-sized diameter.
To validate this concept, we have developed flexible, robust, and large-area membranes having vertically aligned CNT arrays as pores in polymer matrix. To fill the voids between the CNTs without disturbing orientation of nanotubes, we used parylene as flexible and impermeable polymeric materials. SEM images indicate that well aligned CNTs are embedded in a flexible parylene matrix free of any macroscopic voids or structural defects. Our measurements show that our CNT membranes provide MVTR that are comparable to or exceeding state-of-art breathable fabrics at all relative humidities. Moreover, CNT membranes have excellent wind-proof properties because the moisture conductive pores are only few nm. Analyte rejection data for 1-5 nm CNTs show that 7-nm Au nanoparticles and 3-nm dyes are completely excluded by these pores, suggesting that CNT membranes will provide full protection from viruses or biological threat agents. Our results suggest that CNT incorporation in flexible polymeric matrices as selective, moisture-conductive pores may provide a breakthrough toward the development of next generation breathable and protective fabrics.

Vertically aligned arrays of multi-walled carbon nanotubes (MWNT forests) possess uncommon properties. Upon infiltration of forests with polymer binder, we obtained highly elastic, electrically conductive composites that provided reproducible changes of resistivity at stretching for strains over 40%. The composites can be used for high deformation strain sensors and skin-like smart materials. When heated with alternating current, nanotube forests generated loud, audible sound typical for thermo-acoustic transducers. The latter can be applied for sound generation, noise cancellation, heat dissipation. If irradiated with low-intensity laser, forests exhibited bolometric response that became significant with decreasing temperature. High responsivity of 42 V/W with signal bandwidth of about 2600 Hz was observed in the region with a surprisingly small temperature coefficient of resistance. This fact along with peculiar current dependences of material differential photoresistance can be explained by lifting Coulomb blockade in carbon nanotube junctions irradiated with light. A combination of significant bolometric response and nonlinear electrical transport are characteristic features of nanostructured junction array system needed for design of advanced infrared detectors.

Carbon Nanotubes (CNTs) and graphene have remarkable electrical, thermal, and mechanical properties, more so than previously known polymers and colloids. Realizing these properties in applications requires understanding and control of fluid phases, so as to enable effective solution processing.
CNTs and graphene behave as hybrids between polymers and colloids. At low concentration, CNTs form complex fluids with intriguing properties. In crowded environments (e.g., gels), CNTs reptate like stiff polymers; surprisingly, their small bending flexibility enhances rotational diffusion and decouples it from the network pore size. In strong acids, CNTs and graphene dissolve spontaneously.
At low concentration, CNT solutions can be processed into transparent, conducting films, e.g., by dip-coating. The film performance and morphology (including alignment) are controlled by the CNT length, solution concentration, coating speed, and level of doping. Long CNTs (sim;10 mu;m) yield uniform films with excellent optoelectrical performance (sim;100 Omega;/sq sheet resistance at sim;90% transmittance in the visible), in the range of applied interest for touch screens and flexible electronics.
At higher concentration, biphasic (isotropic and liquid crystalline) CNT solutions can be used to fabricate porous foam-like, three-dimensional structures consisting of interconnected pristine carbon nanotubes (CNTs). Solution processing preserves the length and quality of the CNTs and yields robust, yet soft macroscopic foams with record electrical conductivity for low-density materials (~1900 S/m at 14.7 mg/cm3 and 99% porosity). These CNT foams match the specific thermal conductivity of metal foams but are ten to a hundred times lighter. Polymer infiltration yields structures with conductivities 100 times higher than traditional composites, and infiltrated CNT foams form electrically triggered shape memory materials with record performance.
At high concentration, CNTs and graphene form liquid crystals that can be spun into macroscopic fibers. Long, pristine CNTs yield high-performance multi-functional fibers that combine the specific strength, stiffness, and thermal conductivity of carbon fibers with the specific electrical conductivity of metals. These fibers are positioned for high-value applications, such as aerospace electronics and field emission, and can evolve into engineered materials with broad long-term impact, from consumer electronics to long-range power transmission. Solution processed fibers of graphene, graphene nanoribbons, and graphene oxide show remarkable green strength and may yield a novel path to manufacturing new-generation carbon fibers.

Single-walled carbon nanotubes (SWCNTs) have attracted significant attention as building blocks for future nanoscale electronics due to their small size and unique electronic properties [1-4]. However, current SWCNT production techniques generate a mixture of two types of nanotubes with divergent electrical behaviors due to structural variations [2, 5]. Some of the nanotubes act as metallic materials while others display semiconducting properties. This random mixture has prevented the realization of functional carbon nanotube-based nanoelectronics [3, 6-7]. Here, a method of purifying a continuous flow of semiconducting nanotubes from an initially random mixture of both metallic and semiconducting SWCNTs in suspension is presented. This purification uses AC dielectrophoresis (DEP), and takes advantage of the large difference of the relative dielectric constants between metallic and semiconducting SWCNTs. Because of a difference in magnitude and opposite directions of a dielectrophoretic force imposed on the random SWCNT solution, metallic SWCNTs deposit onto the electrodes while semiconducting SWCNTs remain in suspension [3]. This work presents a significant advancement in nanotube purification in a facile and scalable manner, and can therefore significantly increase the feasibility of manufacturing reliable semiconducting SWCNT-based nanoelectronic devices. A detailed discussion of these techniques will be presented, along with the fabrication of a dielectrophoretic force-utilized microfluidic lab-on-a-chip device that can accomplish purification of semiconducting nanoparticles at industrially relevant processing rates. The effectiveness of the device is characterized using ultraviolet-visible (UV-Vis) spectroscopy analysis on separated samples.
References:
[1] P. Avouris, Physics World 20, 40-45 (March 2007).
[2] P. Avouris and J. Appenzeller, The Industrial Physicist, June/July 2004, American Institute of Physics.
[3] R. Krupke et al., Science 301, 344-347 (2003).
[4] N. Peng et al., J. Appl. Phys. 100, 024309 (2006).
[5] M. S. Dresselhaus, G. Dresselhaus, and M. Pimenta, Euro. Phys. J. D 9, 69-75 (1999).
[6] R. Krupke et al., Nano Lett. 3, 1019-1023 (2003).
[7] T. Tanaka et al., Appl. Phys. Expr. 1, 114001 (2008).

High resolution fluorescence imaging of the brain has relied on craniotomy and has been limited to < 1 mm penetration depth by light scattering. Here, by chemical separation of SWNTs based on electronic type and diameter, semiconducting SWNTs with fluorescence emission in the >1300 nm region have been successfully enriched. The long-wavelength fluorescence emission of separated SWNTs has much reduced photon scattering in animal tissues, allowing for clear visualization of the mouse brain through intact scalp and skull at unprecedented penetration depths. Reduced photon scattering in the >1300 nm near-infrared window using biocompatible SWNTs allows fluorescence imaging reaching a depth up to ~ 3 mm in mouse brain with sub-10 um spatial resolution. Fast tracking of injected SWNTs inside the blood stream allows video-rate recording of blood perfusion in the cerebral vessels with high temporal resolution, providing direct real-time assessment of vascular and blood flow anomaly in a mouse middle cerebral artery occlusion stroke model.

Because of the extraordinary properties of the nanomaterials, research activities and applications of nanomaterials have continued to increase. However, the impacts of nanomaterials to the environment (air, water, plants, and living organisms) have not being carefully evaluated. This means, the possibility that water becomes contaminated with various nanomaterials will be increased due to the increase use of nanomaterials. Here we demonstrate a simple and quick technique to clean such contaminated water with almost 100% efficiency.
Five different types of nanomaterials were prepared in the laboratory, including carbon nanotubes (CNTs) [1], boron nitride nanotubes (BNNTs) [2], graphene, boron nitride nanosheets (BNNSs), and zinc oxide nanowires (ZnO NWs) [3] were used in the investigation. Firstly, 1mg of each of nanomaterials was separately dispersed in 4ml of distilled water without adding surfactants. Then, 4ml of semisynthetic hydrocarbon oil was added into each of these suspensions. The extraction of these nanomaterials is then performed by shaking the mixtures and then allowed the self-separation of the oil and the water phases in room temperature. As view by the color of the water phase and the oil phase, we can visualize that nanomaterials in the water phase was transferred into the oil phase. After observing for the stability for few days, 0.1ml of the solution from the water phase of each case was carefully extracted and coated on a clean oxidized silicon substrate for inspection. The dried samples are then analyzed under field emission scanning electron microcopy (FESEM), Raman specstrocopy, and Fourier transformed IR (FTIR). We found no nanomaterials on these samples, concluding that all the nanomaterials contaminated in the water phase were totally removed and be transferred into the oil phase. The experiments are repeated and compared to cases where CNTs, BNNTs, graphene, BNNSs, ZnO NWs were functionalized in sodium cholate solutions (concentration = 10mg/ml). Details of these results, the effect of surfactants, and the extraction mechanism, will be discussed in the meeting.
Y. K.Yap acknowledges supports from National Science Foundation (Award 1261910).
References:
[1] V. Kayastha, et al, Appl. Phys. Lett. 85, 3265 (2004).
[2] C. H. Lee, et al, Nanotechnology 19, 455605 (2008).
[3] S. L. Mensah, et al, J. Phys. Chem. C (Letter) 111, 16092 (2007).

Carbon based nanomaterials, namely carbon nanotubes and graphene, exhibit the highest charge carrier mobilities of any semiconductor, and are structurally and chemically extremely robust. Despite these advantageous properties however, there are no known examples where carbon materials genuinely out-perform conventional semiconductors in their own right when incorporated within an optimized optoelectronic device. Perovskite based solar cells have recently emerged at the forefront of photovoltaics research, but currently employ a low mobility amorphous hole transporter, which in part limits the efficiency through a high series resistance. Here, we report a new approach for achieving efficient hole extraction in perovskite solar cells by combining polymer-functionalized single-walled carbon nanotubes (SWNTs) within the amorphous organic hole-conductor matrix.
By means of polymer (P3HT) functionalization we are able to solution-process the generally insoluble SWNTs, and simultaneously tune their electronic properties such that they become highly selective for p-type charges (holes). We observe that the random dispersion of SWNTs in the dedicated hole transport material enhances the performance of perovskite solar cells. Interestingly, we find that a two-layer deposition of SWNTs and hole transport material leads to an even larger improvement yielding an efficiency of 12.8%.
This seems to indicate that highly efficient hole transfer occurs from the perovskite directly to the nanotubes when the SWNTs directly contact the perovskite interface. We confirm this finding by photoinduced absorption studies, which show a distinct bleaching of the ground state absorption of the SWNTs. We infer from these results that the role of the SWNTs goes beyond increasing the conductivity of the hole transporting layer, instead we come to believe that most of the hole transfer occurs rapidly through the SWNT network. To test this hypothesis, we replace the dedicated hole transporting material (spiro-OMeTAD) with an electronically inert polymer (PMMA), and find that carbon nanotubes alone are able to selectively and efficiently transfer holes in perovskite solar cells achieving a power-conversion efficiency of up to 14.2%.
With this we have demonstrated a means by which carbon nanotubes can be employed as a highly effective p-type charge collection layer in thin film solar cells. This concept may soon prove to be effective for a wide range of photovoltaic systems. In particular the inherent chemical and thermal robustness of SWNTs may be a key aspect for achieving long-term stability of performance and device integrity of hybrid solar cells. Beyond broad usefulness in photovoltaics, this concept may be just as relevant for charge injection layers in light emitting diodes or organic transistors. This work will certainly encourage renewed effort in achieving application specific properties from SWNTs through electronic modification via surfactant nanotube interactions.

After brief introduction about the strategy to solubilize CNTs in solution, we report our recent study on the following three topics.
i) Determination of precise electronic states of individually dissolved (n,m)single-walled carbon nanotubes (SWNTs) and their empirical prediction
ii) Rational concept to recognize/extract single-walled carbon nanotubes with a specific chirality
iii) Remarkably Durable High Temperature Polymer Electrolyte Fuel Cell Based on
Topic (i) : Electronic structures of SWNTs, one of the fundamental features of nanotubes, strongly depend on the chirality of the nanotubes. We have discovered that we can determine the precise electronic states of isolated SWNTs having their own chirality indices by in situ near-IR photoluminescence spectroelectrochemistry at the fabricated modified ITO electrode. We also present empirical equations that predict electronic states of (n,m)SWNTs.
Topic (ii): The facile separation of a mixture of SWNTs into specific chirality components has recently attracted great attention. We report that certain chiral polyfluorene copolymers can well recognize SWNTs with certain chirality preferentially, leading to solubilization of specific chiral SWNTs. This is the first example showing the rational design and synthesis of novel fluorene-based copolymers toward the recognition/extraction of targeted (n,m)-chirality of the SWNTs.
Topic (iii) : Low durability of polymer electrolyte fuel cell (PEFC) is a major drawback that should be solved. we describe the finding that a novel PEFC free from acid leaching shows remarkable high durability (single cell test: .400,000 cycling) together with a high power density at 120 degree Celsius under a non-humidified condition. This is achieved by using a membrane electrode assemblywith Pt on poly(vinylphosphonic acid)-doped polybenzimidazole wrapped on carbon nanotube and poly(vinylphosphonic acid)-doped polybenzimidazole for the electrocatalst and electrolyte membrane, respectively. Such a high performance PEFC opens the door for the next-generation PEFC for ‘‘real world&’&’ use.

Chemical functionalisation is critical to many nanotube applications, but needs to be versatile and applicable at scale. Existing approaches tend to rely on liquid phase reactions, often requiring damaging sonication or lengthy work up through filtration or centrifugation. The formation of individualized functionalised single wall nanotubes (SWNTs) is a particular challenge.
One approach is to shift the modification reaction into the gas phase. We have developed a generic, scalable furnace treatment, based on the thermochemical activation of the CNTs, followed by reaction with functional organic monomers (1). This approach allows the introduction of a wide variety of functional groups onto the CNT surface whilst maintaining the excellent properties of the untreated materials. The underlying mechanism of the reaction has been established and the distribution of the functionalised sites studied using tagging experiments. The reaction is extremely versatile and can be carried out with a variety of monomers. The reaction and the subsequent product purification can be carried out entirely in the gas-phase, greatly simplifying work-up and improving scalability; the approach is fundamentally compatible with the scale and equipment of many industrial nanotube synthesis processes, and is applicable to multi-walled nanotubes, SWNTs, and other carbon-based materials. The surface properties of these products have been studied by direct wetting experiments on the nanoscale, dispersion studies, and inverse gas chromatography (IGC) (2). Water dispersible materials with cationic, anionic, and non-ionic surface functionalities provide simple processing routes to a range of applications, and are particularly well suited to studying biological interactions.
A different approach to nanotube processing, relies on reductive charging. Using a liquid ammonia process (3), pure nanotubides can be redissolved, purified, or optionally functionalised without sonication. A key step is to control the ratio of charge to carbons, as it determines both the yield and the nature of the dissolved material. The G/D ratios observed during the dissolution sequence, as a function of metal:carbon ratio, demonstrate a new purification method for removing carbonaceous impurities from pristine SWNTs. The production of individualised SWNT solutions has been confirmed by neutron scattering. A similar approach can be applied to graphene nanoplatelets (4). Interestingly, the chemical charging agent can be avoided by a pure electrochemical process that yields both nanotube anions (5) and cations (6). The resulting nanocarbon ions can be readily chemically grafted for a variety of applications.
1. R. Menzel et al, Chem. Sci., 2010, 1, 603
2. R. Menzel et al, Langmuir, 2009, 25(14), 8340; R. Menzel et al, Carbon, 2012, 134(20) 8302
3. S Fogden al, ACS Nano, 2012, 6, 54
4. E Milner et al, J Am Chem Soc, 2012,8302
5. Hodge et al, ACS Nano, 2013, 1769-1778
6. Hodge et al, Nature Comm, 2013, 1989

Sensors based on functionalized carbon nanotube field effect transistors have already shown great promise. They combine high sensitivity due to the reduced dimensionality and exceptional electronic properties of the nanotubes with high molecular affinity, conferred by surface functionalization with biomolecules such as single-stranded DNA. Here we show that dilute vapors of volatile organic compounds can be reliably detected down to part-per-billion concentrations. We extend this work by studying vapors from complex fluids of human origins, including sweat and blood. Synthetic versions of these fluids are also used to test the ability of the devices to differentiate solutions that are extremely similar but differ in a known way. We show that the devices are able to detect changes in the concentration of one compound, at part-per-billion levels, even in a background of many similar compounds. This opens up the tantalizing possibility of tracking volatile biomarkers in bodily fluids quickly and cheaply using a solid state sensor, which could have a huge impact in medical diagnostics. This research was supported by the Department of Defense US Air Force Research Laboratory and UES through Contract Nos. FA8650-09-D-5037 as well as support from the Army Research Office through grant #W911NF-11-1-0087.

The molecular hybrids of biomolecules and carbon nanotubes (CNTs) have led to the developments of various functional hybrids, including for applications in solar cells, superconductors, bioelectronics and medical diagnostics. The architecture of individual hybrids, as well as their inter-molecular aggregation, plays a crucial role in device performance. We employ Raman and Photoluminescence spectroscopy to characterize the optical properties of single-walled carbon nanotubes (SWNTs) complexed with DNA or proteins. Using this information, the doping of SWNTs as well as the dispersion quality of the hybrids are revealed. Further, we demonstrate the nanocapillary as a 'non-invasive' sensing technique, which detects the molecular structure of the biomolecule-SWNTs in their native states at the single molecular level.
By adapting the strong G-band Raman signature of the SWNTs, a study was performed to evaluate the cellular uptake of bovine serum albumin (BSA)-SWNTs by macrophages (a type of white blood cells). We observe that macrophages effectively uptake BSA-SWNTs, with the average number of nanotubes internalized per cell remaining virtually constant over consecutive cell generations. The number of SWNT internalized is found to be ~40 x 10^6 SWNTs/cell for a 60 cells/mm^2 seeding density and ~140 x 10^6 SWNTs/cell for a 200 cells/mm^2 seeding density. In vitro experiments demonstrated that incubation of BSA-SWNTs with macrophages neither affects the cellular growth, nor the cellular viability over multiple cell generations. Our results show that BSA-SWNTs are an efficient molecular transport system with relatively low cytotoxicity maintained over multiple cell generations in vitro.

Recent theoretical and experimental studies have suggested that heteroatom-doped carbon nanomaterials including carbon nanotubes (CNTs) and graphenes as novel materials with exceptional electrochemical property due to the heteroatom doping. For example, heteroatom-doped CNTs have been demonstrated as efficient catalysts for the simultaneous electrochemical detection of glucose, hydrogen peroxide, L-cysteine, and dihydronicotinamide adenine dinucleotide (NADH), making them particularly attractive from both scientific studies and innovation applications.
Here we show that boron-doped CNTs (BCNTs) with tunable boron atomic concentration ranging from 0.4 to 21.1 atomic percentage (at%) can be synthesized by an atmospheric-pressure carbonthermal reaction. The as-produced BCNTs exhibit superior electrocatalytic activity for dopamine (DA) sensing than the pristine CNTs and conventional glassy carbon electrodes. Mixtures of pristine CNTs and boron oxide (boron precursor) were heated at elevated temperatures (900~1200 ^oC) in argon (Ar) and ammonia (NH₃) atmospheres. We found that boron atomic concentrations in the nanotubes could be tuned by simply controlling the NH₃ concentrations in the reaction flows.
High-resolution transmission electron microscopy (HRTEM) characterization reveals the BCNT sidewalls are essentially free of amorphous carbon over coating. Detailed electron energy loss spectroscopy (EELS) characterization indicates that boron substitution doping mainly occurred on the nanotube surface, suggesting the formation of electrocatalytic activation sites. Extensive X-ray photoelectron spectroscopy (XPS) characterization confirms that boron atoms were successfully doped into the sp2 graphene lattice of CNTs, and boron atomic concentrations in CNTs can be tuned from 0.4 to 32.2 at% by simply controlling the NH3 concentration from 0 to 15%, respectively.
Electrochemical characterization indicates a significant enhancement of 25% in the amperometric response for BCNTs with 2.1 at% boron atomic concentration than pristine CNTs, suggesting its potential as efficient catalysts for electrochemical detection of DA. It is also noteworthy from a practical point of view that the developed atmospheric-pressure synthesis method is amenable to industrial-scale production since it avoids the need for a vacuum system.

Due to their excellent mechanical, thermal, and electrical properties in nanoscale, carbon nanotubes (CNTs) have offered various potential applications in macroscale, including structural composites, thermal interfaces, energy storages, artificial membranes, etc. For these applications to be successful, assembled CNTs (e.g., CNT mats or yarns) are preferred because such assemblies are mainly free from the dispersion problem. This research aims to explore a potential application of CNT mats (so called buckypapers) to a heat spreader that can transport heat rapidly in-plane directions.
In this work, CNT mats were fabricated using a filtration process, during which covalent bondings between CNTs were introduced to facilitate the phonon transfer. The thermal conductivity of the CNT mats was then measured using a laser flash method, showing very large diffusivity and also moderately high thermal conductivity. However, it was found that the CNT mats couldn&’t be applied to heat spreaders due to porous structure of CNT mats and their extremely large surface, i.e., thermal radiation occurred faster than the phonon transfer. We tried to solve this radiation problem using radiation-reflective metal nanoparticles.
Radiation-reflective metal nanoparticles such as Ag and Ni (indexes: 0.98-0.99 and 0.90-0.95) were incorporated into CNT mats and sintered into the metal matrix using a simple process as follows. First, CNTs and Ni and Ag nanoparticles were prepared. They were mixed into a solution and dispersed by sonication. The dispersed solution was then filtered through a filter paper in vacuum condition, producing CNT-nanoparticle mats. It was confirmed that using this filtration process, Ni and Ag nanoparticles were located in the pores of CNT matrix. Finally, CNT-nanoparticle mats were converted into CNT mat reinforced metal matrix composite by a sintering method. The effect of the nanoparticles and their contents on the thermal conductivity of the CNT- mat metal matrix composites was investigated using a laser flash method. Further detailed results will be presented at the Conference.

Single-walled carbon nanotubes (SWNTs) have been extensively studied due to their outstanding properties and potential applications in many areas. In special, a number of researches has been dedicated to control the diameter or chirality because electronic, physical and optical properties of SWNTs are determined by their diameter and chirality.
As for methodology toward SWNTs&’ diameter control, tuning the catalytic nanoparticle (NP) size has been thought to be one of the most effective approaches owing to the size correlation between NP and SWNTs. However, the catalytic NP generally exists as a semi-liquid phase due to a melting point decrease under the high temperature environment for SWNT synthesis. This may give rise to undesirable particle aggregation which causes the broadening of diameter distribution of SWNTs.
In this study, we used nanoporous materials, such as zeolites and nanoporous silica, to confine the size and shape of the catalytic NP. To change the NP size on the templates, we deposited Fe thin films over the templates with different thickness by e-beam deposition method and obtained the mean size of 1-5 nm NP. SWNTs were synthesized by CVD using methane and hydrogen gases. As a result, catalytic particles having 5-nm in size produce a bunch of SWNTs with relatively wide diameter distribution which ranges from 0.95 to 2.77 nm. On the other hand, the particles less than 2-nm in mean size produce SWNTs having narrower diameter distribution from 1.19 to 1.75 nm. In the meeting, we additionally present the effect of pore sizes on diameter distribution of nanoparticles and SWNTs as well.

The electronic and optical properties of single-walled carbon nanotubes (SWNTs) depend strongly on their dielectric environment. In particular polar substrates such as silicon dioxide are known to quench photoluminescence and cause charge carrier scattering, which reduces carrier mobility in field-effect transistors (FETs). To avoid these effects nanotubes can be separated from polar surfaces, for example, by self-assembled monolayers (SAMs) with long alkyl chains.
Here we use aligned arrays of long (>100 mu;m), chemical vapour deposition-grown SWNTs. Pristine SWNTs are transferred onto densely packed self-assembled monolayers using an optimized polymer transfer process. The transferred SWNT arrays are then used to fabricate electrolyte-gated FETs with ionic liquids as well as bottom-gate FETs, where the SAM acts as an ultrathin, high-capacitance gate dielectric. Both device types enable low voltage (<2 V) operation with high transconductance and ambipolar charge injection and transport in ambient air. We study the effect of the transfer process and SAM-end groups (-CH3, -CF3, -CN, -NH2) on hole and electron transport as well as near-infrared emission of the SWNTs. The significant increase of photoluminescence intensities of at least one order of magnitude for SWNTs on alkyl-SAMs compared to those on bare silicon dioxide highlights the potential of efficient near-infrared light-emitting FETs based on aligned SWNTs.

Carbon nanotubes (CNTs) have great potential for aerospace applications because of their unique combination of high strength and stiffness, low density, and high electrical and thermal conductivity. Great strides have been taken recently in the scaling up of CNT yarns and sheets to the point where macroscopic test specimens can be routinely fabricated and commercial components contemplated. As a recent example, Harvey has recently fabricated and characterized coaxial cable with a carbon nanotube yarn core and carbon nanotube paper sheath. Yet the conductivity of these materials is still too low to make practical electrical power conductors, which require about 100,000 S/cm. Recently very high quality macroscopic fibers have been fabricated through a chlorosulfonic acid solution process that have electrical properties that surpass conventional carbon and graphite fibers, about 30,000 S/cm. Doping the fibers with iodine improved the conductivity to about 40,000 S/cm, but this is still too low. An additional complication is that the conductivity of both the as-spun and I₂-doped fibers increases over time. The goal of this study was to explore ways to further improve both the electrical conductivity and the stability of the fibers with an eye towards fabricating electrical power conductors.
CNT fibers were fabricated using a variety of spinning conditions and post-spinning processing with the goal of creating a high conductivity yet environmentally stable fiber. These fiber variants were then doped with Br₂, I₂, ICl, or IBr under a variety of conditions with the goal of improving further on the electrical conductivity and stability of fibers. Since high and stable electrical conductivity was the goal, the conductivity of the fibers was monitored over a period of time exceeding 30 days. Additionally, the fibers were imaged with a field emission scanning electron microscope and energy dispersive x-ray spectra and Raman spectra of the fibers were measured for structural changes. Conditions were found where the conductivity of the undoped fiber was both high (50,000 S/cm) and stable. Doping with the mixed halogens ICl and IBr improved the conductivity of the fibers more than that of Br₂ or I₂. Although I₂ doped fiber attained their residue compound in the shortest time, both ICl and IBr ultimately had more conductive residue compounds (60,000 S/cm). It is suspected that more improvements can still be made.

We have developed a carbon nanotube (CNT) film-based biosensor with a metal semiconductor field effect transistor structure (MESFET). A gold top gate was deposited on the middle of the CNT channel and probe antibodies were immobilized on the gold top gate with an antibody-binding protein, protein or Escherichia coli outer membrane (OM) with autodisplayed Z-domains of protein A. These CNT-MESFET biosensors exhibited a higher sensitivity than the CNT-FET biosensor with probe antibodies immobilized using a chemical linker, since the orientation of immobilized antibodies was controlled by the antibody- binding proteins. In addition, nonspecific binding was effectively inhibited by E. coli OM. Using the CNT-MESFET biosensors with E. coli OM containing Z domain, we detected amyloid-β (Aβ) in human serum, one of the biomarkers for early diagnosis of Alzheimer's disease. Aβ at the level of 1pg/mL in human serum could be measured in real-time and without labeling, which was lower than a limit of detection for plasma Aβ using an enzyme-linked immune sorbent assay. These results suggested that our CNT-MESFET biosensors might be applicable for an early diagnosis of Alzheimer's disease.

Polyacrylamide (PAM) is a water-soluble polymer that shows high viscosity, low toxicity and low cost. [1]. This polymer has been used as mobility control agent as well as for permeability profile correction agent in improved oil recovery [2]. However, its use is limited due to the low stability under several harsh conditions, e.g. temperature and salinity. This problem can be overcome by copolymerizing acrylamide with monomer groups such as AMPS (2-Acrylamido-2-methylpropane sulfonic acid) that is a hydrolysis-resistant monomer. On the other hand they are noticeably more expensive and less efficient viscosifiers than hydrolyzed PAM.
Carbon nanotubes (CNT) show a nanometer scale and high aspect ratio. They can be used as reinforcing agents for polymer composites due their extraordinary proprieties as mechanical and electrical [3]. A homogeneous dispersion and a good interaction between the CNT and polymer matrix is desirable to obtain improved material. Surface modification of CNT allows the direct modulation of their hydrophilic properties and improves their suitability in various applications.
A PAM covalent attached to the CNT has been synthesized [4]. The nanomaterial was characterized by i) TGA, that show an increase of mass loss in characteristic region for functionalization, ii) DSC that allow the determination of the glass transition for polymer produced, iii) TEM, where was possible to see the structure modification, iv) XPS that show the presence of amine and amide groups. This functionalization increases the dispersion of the carbon nanomaterials in water what allowed a stable suspension preparation.
With the goal of improving the stability of PAM solutions we have used the modified CNT (CNT-TEPA-AM) as a nano-additive in polyacrylamide aqueous solution. An aqueous acrylamide-AMPS copolymer (with 10 wt% AMPS) in concentration of 1.0 g L-1 was used. CNT-TEPA-AM in the concentrations of 0.05 wt% and 0.10 wt% were added to various aqueous solutions containing polyacrylamide. The nanofluids viscosity was measured with a Brookfield rheometer during 180 days at 7.34 s-1 shear rate and showed that the small amount of the CNT-TEPA-AM improved the viscosity and the stability of these suspensions in distilled water at 70 oC. After 30 days from the fluid preparation under inert atmosphere the fluid that has 0.05 wt% of CB-EDA-AM show its viscosity 32% higher than the fluid without nanofiller, therefore an increase in stability as well as viscosifying was observed for aqueous solution at 70 oC. Our preliminary preparation has shown that small amounts of CNT-TEPA-PAM are able to increase the PAM viscosity significantly and the nanofluid still show temperature-tolerance behavior, showing its potential for technological application.
References
1. Savart,T.; Macromol Mater Eng; 295 (2010)146-152.
2. Ball, J.T.; SPE 12650-MS, 1984.
3. Sahoo,N. G.; Prog. in Polymer Sci. 35 (2010) 837-867.
4. Pei, X.; European Polymer J. 44 (2008) 2458-2464

Ultrafast fluid transport inside carbon nanotubes (CNTs) makes them ideal one-dimensional nanopores, yet flow enhancements in CNTs reported in literature differ by orders of magnitude. Much of the controversy over flow enhancement in aligned CNT membranes arises due to insufficient information regarding the following critical parameters: CNT number density, CNT inner diameter, and true serpentine length of CNTs. Toward precise quantification of flux through CNTs, we developed nondestructive techniques employing synchrotron radiation at the Advanced Light Source for determination of these structural characteristics in vertically aligned CNT (VACNT) arrays, from which we fabricate nanocomposite membranes. These characterization techniques are now being extended for probing these parameters directly in CNT composite membranes. The latter are fabricated by infiltrating the void space between VACNTs with a polymer and then opening the ends of a large number of single- and double-wall CNTs [O(10^10-10^12) cm^-2] to expose their core volume for fluid transport.
Using simultaneous small- and wide-angle X-ray scattering in a novel grazing-transmission configuration (GT-SAXS/WAXS), we probed the hierarchical structure of VACNT arrays and thereby quantify crucial parameters of the CNT nanochannels, namely inner diameter and true length (related to tortuosity). We modeled the form factor scattering as that from a normal population of core-shell cylinders to extract mean and variance of the diameter distribution, which has not previously been shown for double- and single-wall CNTs. The mean serpentine length L of CNTs is proportional to the height H of the VACANT array by the tortuosity factor tau; (i.e., L = tau;H), which we calculate from the azimuthal distribution of scattered intensity about the beam&’s axis. Complementary electron microscopy corroborated information extracted from X-ray images: high-resolution TEM revealed CNT diameter and number of graphitic walls, while SEM enabled quantification of CNT tortuosity by performing fast Fourier transforms of SEM images.
Our ongoing efforts build on these advanced synchrotron metrology tools toward precise evaluation of mass transport properties of CNTs as a function of their structural features. Armed with quantitative information of the hierarchical structure of CNT arrays as well as of CNT nanocomposite membranes, we will be able to uniquely study the disputed roles of diameter and length in rapid transport through CNT nanochannels.

We employ ab-initio self-interaction corrected density functional theory combined with the non-equilibrium Green's function method, as implemented in the SMEAGOL code, to study the electronic and transport properties of carbon nanotubes functionalized with AuCl₄ molecules. In particular, we characterize the transmittance for different concentrations and configurations of randomly distributed AuCl₄ molecules and analyze to which extend the properties of the tube can be tuned. Our results are in good agreement with recent theoretical work that suggests that AuCl₄ molecules can enhance the sensitivity and selectivity of carbon nanotube gas sensors. We clarify the origin of the resistance changes and predict optimal concentrations for obtaining a high sensitivity. Moreover, we investigate how the presence of water affects the transport properties.

Hexagonal boron nitride (h-BN) is known as a material with structural similarity with graphite. Herein, the boron and nitrogen atoms are alternately structured in a hexagonal ring and they are also bound together in the hexagonal lattice plane by strong covalent bonds to form h-BN sheets, whilst an interaction within different sheets is governed by a weak van der Waals force. There are various fabrication methods to take advantages of those properties in order to fabricate perfect and thin h-BN layers for promising application purposes. However, most of the works have been done are realized by a chemical vapour deposition (CVD) method where various source gases are reacted to form h-BN nanosheets or nanowalls [1,2]. In contrast, there are a few demonstrations using a physical vapour deposition (PVD) technique [3,4]. We recently reported that h-BN can be synthesized using the PVD method, leading to vertically oriented nanowalls when hydrogen is added to the gas mixture. Surprisingly, the resulting nanowall structure seems independent of the used substrate material or its orientation during deposition. This work reports on the detailed growth behaviour of h-BN nanowalls deposited on Si (100)-substrates using unbalanced radio-frequency magnetron sputtering.
Here, to discriminate between possible chemical and physical processes governing the growth of the h-BN nanowalls , variations of target-substrate distance (TSD), substrate stage orientation (i.e. 0° or 90°-tilted), and substrate temperature (T_sub) were used, followed by detailed investigations with scanning and transmission electron microscopy (S/TEM). Despite the large tilt, the walls retain their vertical position with respect to the substrate, pointing to a large influence of chemical reactions governing the growth, rather than a pure ion flux dominated growth process. The growth rate as a function of TSD is experimentally determined, showing linear dependence. Interestingly, the microstructure of the h-BN nanowalls are strongly correlated to the substrate temperatures (T_sub< 600 °C), an effect which is probed by varying the latter . Higher T_sub clearly leads to more porous layers, and in case of small TSD, even to a granular morphology instead of walls. As the addition of hydrogen is indispensable in the actual wall formation [4], this behaviour exposes a significant role of hydrogen absorption or desorption with respect to the growth mechanism. As a merit of this work, these results suggest a new route-map for estimating the transition boundary between h-BN nanowalls and planar films in the presence or absence of external thermal substrate heating.
[1] A. Pakdel, et al., Mater. Today 15, 256 (2012).
[2] Y. Lin, et al., Nanoscale 4, 6908 (2012).
[3] M. Sajjad, et al., J. Mater. Sci. 48, 2543 (2013).
[4] B. BenMoussa, K. Haenen, et al., J. Phys. D Appl. Phys. 45, 135302 (2012).

Nanoidentation was used to study the viscoelastic properties of poly(methyl methacrylate), PMMA, filled with multi-walled carbon nanotubes, MWNT. The incorporation of MWNT has been shown to improve various mechanical properties of PMMA in the literature. However, our results show that the reduced Young&’s modulus and hardness of the MWNT/PMMA composites are on average lower than that of neat PMMA samples when analyzed using the unloading portion of the nanoindentation load function. Quasi-static measurements of hardness and reduced modulus as well as nano-dynamic mechanical analysis have shown no trend with increasing MWNT concentration up to 2% by weight. Possible reasons for this observation could be the sample surface roughness and surface defects, and MWNT agglomeration (dispersion and distribution quality). However, through the use of various loading patterns, the viscoelastic properties of neat PMMA and filled PMMA nanocomposites can still be explored but significant differences between samples exists depending on concentration of carbon nanotubes in the tested location.

Already first study of a field emission from carbon nanotube (CNT) was showed the abnormally high density of emission current. Thus far, the nature of this effect is not understand and actively discussed. The peculiarity of the carbon nanotube emitter is non-linear character of nanotube conductivity having the potential barriers at both ends. In this case the current-voltage characteristics of vacuum diode with nanotube emitter is determined by the quantum processes across and along nanotube. The object of this work was to study of the peculiarities low-voltage field emission from carbon nanotube emitter, which were caused by quantum-size effects into them.
Experimental study of low-voltage field emission were carried out on the model of nanodiode with 1D nanotube emitter which was deposited on 3D metal cathode in the presence electrostatic or high-frequency electric fields at room temperature. The distribution of the charge density along the nanotube was studied by STM and REM methods.
Our study showed the following: (i) the equidistant resonance peaks are present on I-E curve. The sign of differential conductance near the resonance peak changes the sign from positive to negative; (ii) threshold voltage of the start of emission observed and had an abnormally low magnitude; (iii) near threshold voltage the periodic oscillations of charge density along the nanotube observed. The period of these oscillations was inversely proportional to charge density; (iiii) at field emission process the DC emission current was accompanied by AC current; (iiiii) at area resonance peak the field electron emission was accompanied by the light emission.
Based on experimental data the mechanism of low-voltage field emission may be explained by the coherent transport of charge along nanotube in condition of Luttinger liquid and their collective tunneling through the potential barrier to vacuum.

Vertically aligned arrays of carbon nanotubes (CNTs) reported in the literature are typically entangled, have poor crystalline quality, and consist of CNTs of varying lengths. These issues degrade electrical and thermal conductivity, as well as the ability to make good contact to the entire array. Such problems severely limit their usefulness for applications. Conversely, we report the fabrication of completely un-entangled, planarized, high crystalline quality, vertically-aligned multiwall arrays of CNTs. The nanotubes are grown at temperatures ranging from 350 - 600 C in anodized aluminum oxide templates directly on various substrates, including silicon, sapphire, and aluminum. Post-growth planarization provides uniform heights for all the CNTs within a given array. Arrays consisting of CNTs with independently-controlled diameters and site densities ranging from 10 - 75 nm and 10^11 - 10^9 cm-2, respectively, are demonstrated. The arrays are studied with electron microscopy and Raman spectroscopy, and their properties correlated with growth temperature and CNT diameter.
This work is supported by the Laboratory Directed Research and Development Program at Sandia National Laboratories. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the United States Department of Energy&’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

The operating mechanism of the carbon nanotube enabled vertical field effect transistor (CN-VFET) requires gate field access to the channel layer without too much screening from the intervening single wall carbon nanotube source electrode layer. Hence, while the nanotube surface density can be well above the electrical percolation threshold the layer must still be rather dilute (sub-monolayer). For large area arrays of devices this places more severe constraints on the nanotube deposition method in terms of attaining homogeneous films over the entire array. To demonstrate nanotube layers exhibiting the requisite homogeneity we have been exploring ultrasonic nozzle spray deposition of the single wall carbon nanotubes in a home built spray station from single wall carbon nanotube ink.
Film quality was characterized by atomic force microscopy, sheet resistance, UV-Vis spectroscopy, a specially developed larger-area uniformity test that samples microscopic “pixels” over macroscopic areas and by the fabrication of CN-VFETs. In all cases comparison is made between spray fabricated and more conventional filtration fabricated nanotube electrode layers. The results, which are quite encouraging, will be discussed.
This work was supported by Nanoholdings LLC.

Covalently interconnected three-dimensional (3D) scaffolds of nanomaterials have received much attention of late, and carbon nanotubes (CNTs), graphene, graphene oxide (GO) etc. are some of such materials that could be interconnected to produce 3D carbon structures. These nanoengineered 3D architectures could have high and tunable surface area, porous structure and interesting electron transport and mechanical properties and several applications related to electrical, mechanical, electrochemical, sensor and bio-medical could be explored using these structures. Although there are some recent efforts to build covalent junctions between nanotubular structures of CNTs, graphene and GO, the creation of three-dimensionally engineered nanoporous architectures via covalently interconnected nanoscale building blocks remains one of the fundamental challenges in nanotechnology. Another popular approach is the creation of covalent junctions between CNTs and graphene. Recently, a significant part of the research has been paid attention on the intermolecular junctions of CNTs which involves the creation of two-dimensional (2D) and three-dimensional (3D) intramolecular junctions. In most reported works, additive elements such as boron, sulphur are used to create the interconnections and hence the 3D nanostructured architecture. Here, we shall discuss the synthesis of highly porous and covalently interconnected 3D-Carbon framework. Combination of outstanding physical and chemical properties of such 3D porous architecture will be discussed here.

Recently, the driving frequency of electronic device is drastically increased due to high performance requirement and new applications in various fields. Ultra fast driving diode structure can be a key technology as basic electrical unit for those various applications. p-n junction diode structure has been used generally to convert alternating current (AC) signal to direct current (DC) signal. The structure is also a core technology of Si based transistor, which is employed widely to various electrical components. However, the working mechanism is not suitable for high-speed driving since the speed limit is induced by the mobility of hole and electron in semiconductor. Here we report a new diode structure based on multi-wall carbon nanotube (MWCNT) employing tunneling mechanism. Applying the structural asymmetric effect induced by the high aspect ratio of CNT to metal-insulator-metal(MIM) diode concept, better electrical asymmetric characteristic was achieved in metal-insulator-CNT (MIC) structure. For the MIC diode, high contrast ratio between on- and off-current is as high as about forth-order at room temperature. Its temperature dependence is quite good up to 423K, compared to the other results. In addition, rectifying performance of the MIC diode through AC signal is good up to 10MHz with few negative current. The estimated cut-off frequency of the MIC diode is 4.74THz. Ultra fast structural asymmetric diode using all metallic materials can be applied to various high frequency applications, such as a communication device, high speed electrical switch, energy harvesting structure, and so forth.

Graphyne is a generic name for a carbon allotrope family of 2D structures, where benzenoid rings are connected by acetylenic groups, with the coexistence of sp and sp2 hybridized carbon atoms. [1]. Although these materials have been proposed in 1987 [1], due to difficulties in their synthesis, they have been synthesised only recently [2]. The successful synthesis of the graphynes has sparked new interest in these structures due to its remarkable electronic properties which can be quite similar to graphene ones. Graphyne nanotubes [2,3] have already been successfully produced [3], but other possibilities remain to be explored. Among these new structures there is the possibility of the existence of graphyne nanoscrolls, which are structures obtained by rolling graphyne sheets into papyrus-like structures. Nanoscrolls [4] present high radial flexibility and large solvent accessible surface area, which opens the possibility of many applications. This kind of structure has been already observed to other materials, such as graphene and hexagonal boron nitride, the latter being first predicted from theoretical investigations and recently experimentally realized.
In this work we have investigated the structural and dynamical aspects of graphyne scroll formation through fully atomistic molecular dynamics simulations. Our results show that graphyne nanoscrolls can be formed from different type of graphyne sheets (alpha, beta and gamma configurations). Possible technological applications of these hypothetical new structures are also addressed.
[1] R. H. Baughman, H. Eckhardt, and M. Kertesz. J. Chem Phys. v87, 6687 (1987).
[2] G. Li, Y Li, H. Liu, Y. Guo, Y. Li, and D. Zhu, Chem. Commun. v46, 3256 (2010)
[3] V. R. Coluci, S. F. Fraga, S. B. Legoas, D. S. Galvao, and R. H. Baughman, Phys. Rev. B v68, 035430 (2003).
[4] S. F. Braga, V. R. Coluci, S. B. Legoas, R. Giro, D. S. Galvao, and R. H. Baughman, Nano Lett. v4, 881 (2004).

Polyethylenimine (PEI) has been shown previously to be an effective n-type dopant for carbon nanotubes, however, the temperature dependent behavior of the electrical conductivity and Seebeck coefficient has not been reported on previously. Here, we showed that the electrical conductivity of the PEI doped SWNTs follows either a standard variable range hopping model or fluctuation assisted tunneling model, depending on the concentration of SWNTs in the composite. For the Seebeck coefficient, a rapid transition from +40 µVK-1 to -38 µVK-1 is observed for PEI/SWNT concentrations ranging from 0-0.5. The temperature dependent behavior appears to follow that of the standard heterogeneous model, yet the physical interpretation of this model does not satisfactorily describe the system. Instead, a previously derived diffusion thermoelectric power model was used consisting of a small and constant linear metallic term plus a varying and potentially large density of states term which combine to fit the range in values observed quite well.

New methods for drugs detections are necessary to improve the time and sensitivity for drug testing. Our work is focused in the development of a simple strategy to produce bimetallic silver-gold core-shell nanoparticles for the study of drugs interactions. Formation of the nanoparticles was achieved by the reduction of the AgNO3 with NaBH4 and HAuCl4 with sodium citrate with polyethylene glycol. A conventional microwave was applied for complete the synthesis. This technology offers minimization of reaction times and stabilization of nanoparticles. In this research, we explore the interactions with cephalexin, ciprofloxacin and clindamycin with the silver-gold core shell nanoparticles. Characterization of the nanoparticles was performed using UV-Vis absorption spectroscopy, nanoparticle size analyzer and transmission electron microscopy. New band formations and red shift was observed from the optical studies.

The aerospace industry is always interested in increasing the strength while reducing the weight of carbon fiber composite materials. Adding single walled carbon nanotubes (SWCNT) to a polymer matrix can achieve that goal by improving delamination properties of the composite. The SWCNTs increase the fiber/polymer ratio, hence the strength, and create fiber linking in cured resin, strengthening the fiber/polymer interface. Because of the complexity of polymer molecules and the curing process, few 3-D Molecular Dynamics simulations of a polymer-SWCNT composite have been run. We will present the effort conducted to set up a model of a matrix, made of aerospace-grade EPON-862 cured with a diethyltoluenediamine (DETDA) curing agent, embedded with a SWCNT. The polymer is set up as an uncured 2:1 ratio of EPON-862 to DETDA. The model is set up to run with the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), with a COMPASS (Condensed phase Optimized Molecular Potential for Atomistic Simulations Studies) potential to represent the interactions between the atoms of the polymer and the SWCNT. This potential includes non-bonded interactions (9-6 Lennard-Jones), bond interaction (class2), angles (class2) and dihedrals (class2). A density of 0.3 g/cm³ is obtained by packing several uncured polymer molecules, and a curing process is then conducted at 600K. The cured polymer can be used to conduct different simulations, and was tested with a pull-out test to calculate the interfacial shear stress.

Single-walled carbon nanotubes (SWCNTs) are considered as one of the promising materials for printed electronics due to solution processibility as well as their superior electrical, mechanical, chemical properties. High-performance SWCNT thin-film transistors (TFTs), with high carrier mobilities and large on/off current ratios, have been recently demonstrated by employing sorted SWCNTs. SWCNTs easily exhibit unipolar p-type behavior under ambient condition due to adsorption of oxygen and moisture, whereas they are known as intrinsically ambipolar materials. Ambilpoar TFTs have been attracting significant attention due to their property to enable electron and hole transport in a single device. In this work, we present bilayer ambipolar transistors and circuits, operating under ambient condition, based on inkjet printed zinc tin oxide (ZTO) and SWCNTs. Both ZTO and SWCNT semiconductor layers are deposited by inkjet printing. Solution-processed zirconium dioxide is employed as a gate dielectric and facilitates low voltage operation (< 5 V). These TFTs exhibit balanced electron and hole mobilties exceeding 3 cm^2 V^-1 s^-1. Ambipolar TFTs are integrated into inverters, amplifiers and ring oscillator circuits and show high gain and operating speed. The performance of ambipolar circuits is compared with that of conventional complementary circuits, which employ n-channel ZTO and p-channel SWCNT TFTs.

Nanoporous carbon has been widely studied and used in various applications such as gas separation, catalyst supports, and electrode materiala. It has been conventionally prepared by pyrolysis and physical or chemical activation of organic precursors such as polymers in which the pore size and pore structure can be controlled during the process at very high temperature in inert atmosphere. In this study, the solventless process was used to prepare polybenzoxazine precursor which can be synthesized from formaldehyde, phenol and aromatic diamine to produce nanoporous carbon with high chair yield. The effects of the pyrolysis temperatures on the microstructure of the obtained nanoporous carbon have been investigated. The physical properties of the products were also investigated by SAA and SEM. In addition, XRD was used to demonstrate the characteristic d spacing of the resulting nanoporous carbon. The electrochemical properties of the electrodes have been investigated by the cyclic voltammetry and electrochemical impedance spectroscopy.

When the first carbon nanotube FETs were presented more than a decade ago they were considered a candidate for the ultimate scaled transistor. Very quickly it became clear however that the intrinsic material problems associated with the carbon nanotubes presented a formidable challenge and interest waned. With performance scaling slowing down, driven by serious power constraint on the system level and manifest in a constant clock frequency for more than the last half decade, academia and industry intensified the search for the “next switch”. Many candidates emerged over the recent years. The dream is, of course, to find a new switching element that can replace the conventional transistor. Preferably with out any change of the existing infra structure - new materials and fabrication methods would be tolerated. The goal is to find a switch that can give high performance at low supply voltage and high integration density that is consistent with the power constraint of the system. Due to its superb scaling behavior and electrical transport properties carbon nanotubes are a natural successor of the current available technology solutions for the digital application space if the material problems could be solved. Carbon nanotube devices can be build that resemble very closely the exiting device structures and would therefore fit into the exiting CMOS technology ecosystem with out major interruptions. To move carbon nanotubes into a main stream technology many challenges lie ahead. The foremost are: (1) to obtain an extremely high purity population of semiconducting carbon nanotubes and (2) to place these carbon nanotubes at precise positions to build the circuits. Although device scaling beyond a 10nm gate length has been shown there are a number of questions unanswered related to the integration of carbon nanotubes into high density digital technology. My presentation will address the fundamental material questions and the still open integration issues that need to be addressed to make carbon nanotubes a main stream technology by 2020.

The miniaturization of electronic devices has been the principal driving force behind the semiconductor industry, and has brought about major improvements in computational power and energy efficiency. Although advances with silicon-based electronics continue to be made, alternative technologies are being explored. Digital circuits based on transistors fabricated from carbon nanotubes (CNTs) have the potential to outperform silicon by improving the energy- delay product, a metric of energy efficiency, by more than an order of magnitude. Hence, CNTs are an exciting complement to existing semiconductor technologies. Owing to substantial fundamental imperfections inherent in CNTs, however, only very basic circuit blocks have been demonstrated. By overcoming these inherent imperfections, though the use of the imperfection-immune design paradigm and CNT-specific fabrication processing, we demonstrate the first computer built entirely using CNT-based transistors. The CNT computer runs an operating system that is capable of multitasking: as a demonstration, we perform counting and integer-sorting simultaneously. In addition, we implement 20 different instructions from the commercial MIPS instruction set to demonstrate the generality of our CNT computer. This is the most complex carbon-based electronic system yet demonstrated. It is a considerable advance because CNTs are prominent among a variety of emerging technologies that are being considered for the next generation of highly energy-efficient electronic systems.

Single-walled carbon nanotubes (SWCNTs) possess exceptional electronic characteristics and have been explored for applications in solution processable, flexible, high performance electronics. In particular, advances in semiconducting SWCNT sorting and integration techniques have enabled the fabrication of random network unipolar and ambipolar logic devices ranging from transistors to a functional computer. Due to adventitious atmospheric doping of SWCNT TFTs under ambient conditions, p-type unipolar devices have dominated prior efforts for integration of SWCNT TFTs into functional circuits. However, when implemented in logic circuits, unipolar devices sustain high steady-state currents, which lead to significant steady-state power consumption during operation. In contrast, CMOS logic is the backbone of modern microelectronics since either the constituent p-type or n-type transistor is turned off in each logic gate, resulting in intrinsically low power consumption and thus the ability to be implemented in efficient large-scale integrated circuits. Moreover, CMOS logic offers wide noise margins, which allows robust and reliable operation in highly complex circuitry that inevitably encounters large parametric shifts. These enabling advantages of CMOS technology not only require the realization and integration of p-type and n-type transistors, but also precisely tuned, well-separated threshold voltages to ensure that the complementary devices are not concurrently passing current and thus not dissipating steady-state power. Here, we demonstrate thin-film SWCNT CMOS logic devices with sub-nanowatt static power consumption and full rail-to-rail voltage transfer characteristics as is required for logic gate cascading. These results are enabled by a local metal gate structure that achieves enhancement-mode p-type and n-type SWCNT thin-film transistors (TFTs) with widely separated and symmetric threshold voltages. These complementary SWCNT TFTs are integrated to demonstrate CMOS inverter, NAND, and NOR logic gates at supply voltages as low as 0.8 V with ideal rail-to-rail operation, sub-nanowatt static power consumption, high gain, and excellent noise immunity. This work provides a direct pathway for solution processable, large area, power efficient SWCNT advanced logic circuits and systems.

One of the more promising uses of semiconducting single walled carbon nanotubes (SWCNTs) is as active channel semiconductor materials in field-effect transistors (FETs). Many groups have reported results on SWCNT FETs formed by different fabrication methods. We have focused on inkjet printed SWCNT FETs, in which the semiconductor material consists of SWCNTs deposited from solution by inkjet printing on pre-patterned electrodes defined on a suitable substrate. The fraction of semiconducting nanotubes is > 98%, and the preparation and purification of these materials have been described elsewhere [1]. The pre-patterned electrodes can be the source and drain electrodes of individual FETs or they can be part of prefabricated circuits - such as ring oscillators - which becomes complete upon the deposition of the nanotubes. [2]
In this work we report on results of FETs with channel lengths of 150-250 nm, far less than the average SWCNT length. We would expect many individual nanotubes to span the length between source and drain. High purity semiconducting SWCNTs were dispersed in an organic solvent and inkjet printed on a gate dielectric layer of Al₂O₃, formed by atomic layer deposition. We have designed two kinds of device structures: bottom-gated top contact and top-gated bottom contact. The SWCNT channel was formed by single droplet inkjet printing. The channel between source and drain electrodes was mostly comprised of several (10-30) SWCNTs extending between S and D. TFTs with bottom-gated top contact structure possess a linear mobility exceeding 20 cm²/V-s, and an Ion/Ioff > 10³ with around 30 single tubes in the channel region. On the other hands, top-gated bottom contact devices exhibit a linear mobility, exceeding 340 cm²/V-s, and an Ion/Ioff ~ 10³ with around 10 single tubes in the channel region. In order to fabricate the top contact devices, SWCNT ink was printed on a dielectric layer and the exact location of printed CNTs was confirmed using SEM to form S/D electrodes on the nanotubes. In the case of bottom contact device, however, we prefabricated S/D electrodes before the inkjet printing. This bottom contact process offers huge advantages in terms of ease of processing and the formation of complex device arrays and circuits.
The ability to inkjet print a semiconductor onto prefabricated contacts and not have processing temperatures exceed 200^oC is another major advantage of our process. We present a comparison of the device characteristics between these two structures (top gate and bottom gate) and discuss the reasons for the difference. We also describe the temperature-dependent TFT characteristics and discuss the nature of the charge carrier transport in these devices.
[1] A. A. Green and M. C. Hersam, Adv. Mater. 23, 2185 (2011)
[2] B. Kim, S. Jang, P. L. Prabhumirahi, M. L. Geier, M. C. Hersam, A. Dodabalapur, Appl. Phys. Lett. 103, 082119 (2013)

We present our recent results on SWNT floating catalyst synthesis and dry deposition of flexible and transparent thin films for touch sensor and field effect transistor (TFT-FET) applications. High quality SWNTs with tunable diameter, length and bundle size have been produced from carbon monoxide (CO) using Fe cluster catalyst produced both via physical evaporation and via ferrocene vapour thermal decomposition in laminar flow of CO. State-of-the-art flexible SWCNT films on PET (1) show transparency-sheet resistance properties surpassing those of ITO-PET films. We demonstrate the use SWCNT transparent films as capacitive touch sensors for mobile devices and as transparent OLED electrodes. We fabricate high performance transparent, flexible and even moldable all-carbon TFT-FETs with metallic-type conductivity CNT films as source, drain and gate electrodes and with thick PMMA polymer gate insulator, in addition to using SWCNT network as FET active i.e. semiconductor material (2). We discuss tube-to-tube contact resistance dependence on the tube as well as the bundle diameter and the influence of chemical doping, based on conducting AFM experiments (3).
1. Kaskela, A., A.G. Nasibulin, M. Zavodchikova, B. Aitchison, A. Papadimitratos, Y. Tian, Z. Zhu, H. Jiang, D.P. Brown, A. Zakhidov and E.I. Kauppinen (2010) Aerosol synthesized SWCNT networks with tuneable conductivity and transparency by dry transfer technique. NanoLetters 10, 4349-4355.
2. Sun, D.-M., M. Y. Timmermans, A. Kaskela, A. G. Nasibulin, S. Kishimoto, T. Mizutani, E. I. Kauppinen and Y. Ohno (2013) Moldable, all-carbon integrated circuits. Nature Comminications 4, 2302.
3. Znidarsic, A., Kaskela, A., Laiho, P., Gaberscek, M., Ohno, Y., Nasibulin, A.G., Kauppinen, E.I., and Hassanien, A. (2013) Spatially Resolved Transport Properties of Pristine and Doped Single-Walled Carbon Nanotube Networks. The Journal of Physical Chemistry C 117, 13324-13330.

In this contribution I will present recent progress on unraveling the influence of metallicity on the electronic transport properties of functionalized single walled carbon nanotubes. Photoemission and x-ray absorption spectroscopy where applied on fully metallicity sorted starting material to determine the bonding environment, influence of charge transfer, hybridisation and the influence of basic correlation effects on the two particle excitation and the nature of the metallic ground state as a function of metallicity and functionalisation.
As examples a gas sensing model based on external functionalisation shows how reactive gases like nitric oxides are predominantly physisorbed with a weak chemisorption which depends on the metallicity of the SWCNT. The chemical reaction with the metallic SWCNT is stronger. Similar trends are observed regarding the charge transfer and hybridisation in metallicity sorted metallocene and Eu filled SWCNT. Last but not least, the nature of the metallic ground state of filled as well as intercalated SWCNT was determined as function of the interaction of purely metallic and semiconducting SWCNT with the fillers and n- and p-type intercalant.

Tuning the threshold voltage of a transistor is crucial for realizing robust digital circuits. For silicon transistors, the threshold voltage can be accurately controlled by doping, mainly through ion implantation. However, it remains challenging to tune the threshold voltage of single-wall nanotubes (SWNTs) thin-film transistor (TFTs). Here, we report a facile method to controllably n-dope SWNTs using 1H-benzoimidazole and benzimidazolium derivatives processed via either solution coating or vacuum deposition, respectively. The threshold voltages of our polythiophene-sorted SWNT TFTs can be tuned accurately and continuously over a wide range. Photoelectron spectroscopy (PES) measurements confirmed that the SWNT Fermi level shifted to the conduction band edge with increasing doping concentration. Utilizing this approach, we proceeded to fabricate SWNT complementary inverters by inkjet printing of the dopants. We observed an unprecedented noise margin of 28V at VDD = 80V (70% of 1/2VDD) and a gain of 85. Additionally, robust SWNT CMOS inverter (noise margin 72% of 1/2VDD), NAND and NOR logic gates with rail-to-rail output voltage swing and sub-nanowatt power consumption were fabricated onto a highly flexible substrate for the first time.

Carbon nanotube network (CNN) devices are of great interest for multiple applications, such as integrated circuits and display drivers on transparent or flexible substrates, especially because CNNs have shown higher carrier mobility than organic or amorphous silicon thin-film transistors [1,2]. However, the performance of CNN devices is often limited by high electrical [3-5] and thermal [6,7] resistances at the junctions between individual carbon nanotubes (CNTs). These junction resistances are at least an order of magnitude higher than those of individual CNTs, causing high power dissipation and ultimately degrading the overall device performance [3,4].
In this study, we present a novel method to reduce the resistance of CNT inter-tube junctions through a nanoscale chemical vapor deposition (CVD) process. In the presence of CVD precursors under reduced pressure, localized nanometer scale Joule heating is induced at crossed CNT junctions by passing current through the CNNs. This results in selective deposition of metallic nanosolder at the hot inter-tube junctions. This deposition is self-limited by the fact that the junction cools upon deposition due to its reduction in electrical resistance. We show that the effectiveness of this nanosoldering process is dependent on the workfunction of the deposited metal, and that our technique can improve the overall device performance by nearly an order of magnitude. This new nanoscale CVD technique may also find applications for other nanocomposites where junction or grain boundary resistances are limiting performance and reliability.
[1] D. Sun, et al., Nat. Nanotechnol. 6, 156 (2011); [2] Q. Cao, et al., Nature 454, 495 (2008); [3] P. Nirmalraj, et al., Nano Lett. 9, 3890 (2009); [4] M. Stadermann, et al., Phys. Rev. B: Condens. Matter Mater. Phys. 69, 201402 (2004); [5] A. Kyrylyuk, et al., Nat. Nanotechnol. 6, 364 (2011); [6] R. Prasher, et al., Phys. Rev. Lett. 102, 105901 (2009); [7] J. Yang, et al., Appl. Phys. Lett. 96, 023109 (2010).

Highly concentrated colloidal suspensions of nanocarbon (NC) materials are of great interest for a variety of applications ranging from flexible electronics and flexible conducting fibers to electrochemical catalysts for energy harvesting or storage devices. Prior to this, it is very contingent to fabricate the highly conductive and chemically compatible pastes. However, until now, NC pastes were fabricated by conventional severe oxidation process and stabilization techniques with organic dispersant, which are not optimal for high performance NC pastes. Dispersant-free fabrication of highly conductive and chemically compatible NC pastes has never been tried and still a big challenge for scientist and engineer. Here, we report a new method for fabricating printable, spinnable, and chemically compatible conducting pastes containing high quality carbon nanotubes (CNTs) and graphene nanoplatelets in organic solvents without the need for additional dispersion agents. Our approach is based on the self-assembly of donor-donor-acceptor-acceptor arrays of hydrogen bonding sites introduced onto the NC materials. We found that the printed CNT/graphene hybrid coating showed a high electrical conductivity (>20,000 S m^-1) that could be dramatically improved to ~500,000 S m^-1 by hybridization with a small amount of silver nanowires. Importantly, the defect formation within the NC materials was minimized even after attachment of the quadruple hydrogen bonding motifs, which contributes to the high electrical conductivity of the CNT/graphene film. In addition, we found that screen-printed NC pastes could be used as high performance electrochemical electrodes in dye-sensitized solar cells and electrochemical capacitors.

Membrane-based separation processes are more economic than conventional thermal distillation techniques for desalination of brackish water and seawater. Currently, polymeric membranes dominate the desalination market because they exhibit reasonable water flux and salt rejection rates, and are easy to fabricate. Especially, polymeric membranes used in reverse osmosis (RO) are typically polyamide (PA) thin-film composites (TFCs); these membranes are selected primarily because of their high permeability to water and relative impermeability to various dissolved impurities such as salt ions and other small molecules as well as chemical stability in a broad pH range. Nevertheless, desalination industries are demanding much higher flux polymeric membranes with high salt rejection for energy-saving purposes. Recently, various approaches have been studied to obtain high water flux as well as high rejection.
Amongst them, ultrafast water transport through carbon nanotubes (CNTs) has attracted many interests. Although ultrafast water transport through CNTs have been both theoretically and experimentally proven, vertically-aligned CNTs (VA-CNTs)-based membrane devices have still a great challenge for practical applications such as desalination, particularly demanding high salt rejection as well as high water flux. Theoretically, for NaCl rejection, the inlet pore size diameter of CNTs should be as low as 0.6 nm, however it is not easy to develop VA-CNTs with sub-nano pore structural membrane. As another route to use such unique properties of CNTs, the proper engineering of CNTs with conventional polymeric membranes would be more favorable, but many previous trials have failed to achieve high-performance desalination membranes. Here we show that CNTs, if open at both ends and well-dispersed, can significantly enhance the water flux of conventional polymeric desalination membranes without any loss of high salt rejection, even at randomly distributed manner. This could be achieved by using cap-opened CNTs and their outer surface hydrophilization for better compatibility with polymeric organic phases and water molecules, as a result, leading to significantly improved water flux by almost two-fold as compared to pristine polymeric membranes. Further, we demonstrate the water flow can transport through the randomly oriented CNTs in polymer mixed matrix using molecular dynamics (MD) simulation. These results can help understand an actual role of CNTs embedded in polymeric matrix on the water transport.

Nanomaterial based devices often require a greater degree of nanoscale geometric order and placement control than often possible by traditional lithographic methods. This is especially true for carbon nanotubes (CNT) devices where their anistropic shape and purity (i.e. chirality, length) leads to further challenges. The precise programmable assembly of biomolecules, like DNA, have been successfully used as an alternate bottom-up approach to self-assemble CNT devices . Recently, we have reported surface based self-assembly of DNA wrapped CNT rafts using reversible DNA interactions on mica. However, placement of biomolecules on technologically relevant substrates and their surface-based self-assembly on such substrates is still challenging , . Herein, we will present a rationally designed, stimuli-responsive chemical modification which enables the assembly of DNA-wrapped CNTs on technologically relevant surfaces necessary for building devices. The physicochemical characterization of the substrate will be presented. This approach overcomes the current limitation, and enables DNA-mediated assembly of CNTs to be used for semiconductor devices.