Functional multi-walled carbon nanotube/polyaniline composite films as supports of platinum for formic acid electrooxidation

Embedding of carbon nanotubes in conducting polymeric matrices for various nanocomposites material is now a popular area. In this article, a concise chemical method has been described for the preparation of homogeneous nanocomposite of multi-walled carbon nanotube (MWNT)/polyaniline (PANI) by electrochemical codeposition. For this we functionalized the MWNTs via the diazotization reaction. This helped to disperse the nanotubes in aniline. The composite films were dispersed Pt by electrodeposition technique. The presence of MWNTs and platinum in the composite films was confirmed by XRD analysis and transmission electron microscopy (TEM). Four-point probe investigations revealed that the MWNT/PANI composite films exhibited a good conductivity. Cyclic voltammograms (CV) showed that Pt-modified MWNT/PANI composite films perform higher electrocatalytic activity and better long-term stability than Pt-modified pure PANI film toward formic acid oxidation. The results imply that the MWNT/PANI composite films as a promising support material improves the electrocatalytic activity for formic acid oxidation greatly.     

The dynamics simulation of Ne atom injected into single-wall carbon nanotube

The dynamical processes of Ne atom injected into single-wall carbon nanotube (SWCNT) are modeled with molecular dynamics simulations. The threshold energies to encapsulate rare-gas atoms in SWCNT are presented. The range of tube radius for stable oscillation is revealed, which is independent of the type of carbon nanotubes. And the oscillatory frequency is sensitive to the change in the diameter, the length and chirality of the tube.     

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyacrylate composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in pure acrylic emulsion by ultrasonication to prepare MWCNT/polyacrylate composites applied on building interior wall for electromagnetic interference (EMI) shielding applications. The structure and surface morphology of the MWCNTs and MWCNT/polyacrylate composites were studied by field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). The electrical conductivity at room temperature and EMI shielding effectiveness (SE) of the composite films on concrete substrate with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in two different frequency ranges of 100-1000 MHz (radio frequency range) and 8.2-12.4 GHz (X-band). The experimental results show that a low mass concentration of MWCNTs could achieve a high conductivity and the EMI SE of the MWCNT/polyacrylate composite films has a strong dependence on MWCNTs content in both two frequency ranges. The SE is higher in X-band than that in radio frequency range. For the composite films with 10 wt.% MWCNTs, the EMI SE of experiment agrees well with that of theoretical prediction in far field.     

Towards ideal hexagonal self‐ordering of TiO2 nanotubes

The present work reports on key factors that influence the degree of order in anodic TiO₂ nanotube layers. We show that the anodization voltage and the Ti purity are of crucial importance for the ideality of self‐organization within the nanotube layers and that repeated anodization can significantly improve hexagonal ordering. Optimizing each factor significantly reduces the variation in the average pore diameter and strongly reduces the areal density of polygon ordering/packing errors. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Charge-carrier dynamics in single-wall carbon nanotube bundles: a time-domain study

We present a real-time investigation of ultra-fast carrier dynamics in single-wall carbon nanotube bundles using femtosecond time-resolved photoelectron spectroscopy. The experiments allow us to study the processes governing the sub-picosecond and the picosecond dynamics of non-equilibrium charge carriers. On the sub-picosecond time scale the dynamics are dominated by ultra-fast electron–electron scattering processes, which lead to internal thermalization of the laser-excited electron gas. We find that quasiparticle lifetimes decrease strongly as a function of their energy up to 2.38 eV above the Fermi level – the highest energy studied experimentally. The subsequent cooling of the laser-heated electron gas to the lattice temperature by electron–phonon interaction occurs on the picosecond time scale and allows us to determine the electron–phonon mass-enhancement parameter λ. The latter is found to be over an order of magnitude smaller if compared, for example, with that of a good conductor such as copper. Received: 4 March 2002 / Accepted: 7 March 2002 / Published online: 3 June 2002     

Pulsed laser CVD investigations of single-wall carbon nanotube growth dynamics

The nucleation and rapid growth of single-wall carbon nanotubes (SWNTs) were explored by pulsed-laser assisted chemical vapor deposition (PLA-CVD). A special high-power, Nd:YAG laser system with tunable pulse width (>0.5 ms) was implemented to rapidly heat (>3×10⁴°C/s) metal catalyst-covered substrates to different growth temperatures for very brief (sub-second) and controlled time periods as measured by in situ optical pyrometry. Utilizing growth directly on transmission electron microscopy grids, exclusively SWNTs were found to grow under rapid heating conditions, with a minimum nucleation time of >0.1 s. By measuring the length of nanotubes grown by single laser pulses, extremely fast growth rates (up to 100 microns/s) were found to result from the rapid heating and cooling induced by the laser treatment. Subsequent laser pulses were found not to incrementally continue the growth of these nanotubes, but instead activate previously inactive catalyst nanoparticles to grow new nanotubes. Localized growth of nanotubes with variable density was demonstrated through this process and was applied for the reliable direct-write synthesis of SWNTs onto pre-patterned, catalyst-covered metal electrodes for the synthesis of SWNT field-effect transistors.     

Reply to ＂Comment on ＇Electrical Conductivity and Current-Voltage Characteristics of Individual Conducting Polymer PEDOT Nanowires＇＂

Recently we reported electrical properties of an individual PEDOT nanowire .Ohlckers and Pipinys suggested that the temperature-behavior of I- V curves and resistance can be described in the framework of a phonon-assisted tunneling （PhAT） model. However, there are two points which need to be addressed. First, as shown in Figs. 1 and 2 of Ohlckers and Pipinys＇s Comment, obvious deviations have been observed between the experimental data and the fitting curves obtained from this model especially at low temperatures. Second, the PhAT model is based on the assumption that a source of charge carriers is the local electronic traps in the electrode-nanowire interface layer, the carriers enter the conduction band of the nanowire due to the PhAT through the barrier from these traps. This model has not considered the structure characteristics and conduction mechanism in polymer nanowires.     

Electrical Conductivity and Current--Voltage Characteristics of Individual Conducting Polymer PEDOT Nanowires

We report the current-voltage （Ⅰ-Ⅴ） characteristics and electrical conductivity of individual template-synthesized poly（3,4-ethylenedioxythiophene） （PEDOT） nanowires （190 ± 6 nm in diameter and δRT = 11.2 ± 2Ω^-1 cm^-1） over a wide temperature range from 300 to 10K. With lowering temperature, the Ⅰ - Ⅴ characteristics become nonlinear around 50K, and a clear Coulomb gap-like structure appears in the differential conductance （dI/dV） spectra. The temperature dependence of the resistance below 70 K follows In R α T^-1/2, which can be interpreted as Efros-Shklovskii hopping conduction in the presence of a Coulomb gap. In addition, the influences of measurement methods such as the applied bias voltage magnitude, the two-probe and four-probe techniques used in the resistance measurements are also reported and discussed.     

Adsorption and electrochemistry of hemoglobin on Chi-carbon nanotubes composite film

This study describes the noncovalently functionalization of carbon nanotubes (CNTs) with natural biopolymer chitosan (Chi) as substrate for hemoglobin (Hb) immobilization. The noncovalently Chi-functionalized CNTs possessed an improved solubility in aqueous solution and was beneficial to form three-dimensional configuration of the CNTs film electrode. The adsorbed Hb in Chi-CNTs interface showed a pair of quasi-reversible redox peak with a formal potential of −0.34 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution and possessed good bioelectrochemical catalytic activities toward the reductions of H₂O₂.     

A simple approach for synthesis of TiO2 nanotubes with through‐hole morphology

The present work reports a simple approach for fabrication of self‐standing titania (TiO₂) nanotube membranes with through‐hole morphology. The method is hydrofluoric acid free and the pore opening of TiO₂ nanotubes is performed by electrochemical thinning of the oxide barrier layer. A reduction of anodization voltage was applied at the end of the anodization process to cause a successful removal of the remaining barrier layer from the TiO₂ nanotubes during their detachment from the underlying titanium substrate. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhanced self‐ordering of anodic ZrO2 nanotubes in inorganic and organic electrolytes using two‐step anodization

This work reports on the optimized growth of self‐ordered ZrO₂ nanotubes in inorganic water‐based and organic electrolyte systems containing small amounts of fluoride employing a two‐step anodization process. We show how surface pretreatments of the metallic Zr substrate can drastically improve the growth and morphology of the resulting anodic ZrO₂ nanotube arrays. Using two step anodization and employing organic electrolytes, highly regular and ordered nanotubular ZrO₂ oxide layers can be grown to significantly increased tube lengths compared with aqueous electrolytes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical properties of transparent carbon nanotube networks prepared through different techniques

Ultra‐thin, optically transparent and electrically conducting films of pure carbon nanotubes (CNTs) are widely studied thanks to their promise for broad applications. In the present work, we study and compare different deposition techniques for the production of these networks: dip‐coating, spray‐coating, vacuum filtration and electrophoretic deposition on a quartz glass using single‐walled carbon nanotubes (SWCNTs) produced by the HiPCo method. In order to optimize the networks, besides the various deposition techniques we also investigate how the optical and electrical properties vary if the networks are fabricated from different CNTs, all synthesized by the CVD method: SWCNTs, DWCNTs and MWCNTs. As the main criteria for evaluating the quality of these CNT networks we measure the electrical surface resistance at a certain optical transmittance and correlate it to the morphology (homogeneity and roughness) of the networks. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

250 µm long anodic TiO2 nanotubes with hexagonal self‐ordering

In this work we show that the growth of more than 250 µm thick self‐organized TiO₂ nanotube layers is possible, using an electrochemical approach in organic electrolytes. The tubes can grow as a hexagonal close packed pore array. Crucial parameters that decide on the dimensions are the fluoride ion concentration, the voltage and the anodization time. Self‐organized tube formation is restricted to a critical parameter range. Highest aspect ratio tubes can be achieved under a set of very optimized conditions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

     

Microstructure and wear property of carbon nanotube carburizing carbon steel by laser surface remelting

Carbon nanotube was used to carburize the surface of medium carbon steel and mild steel, respectively, by means of laser surface remelting. The slurry of carbon nanotube of ethanol was coated on the surface of the materials prior to laser irradiation. Microstructures, microhardness and wear property of the surface layers treated by different laser performance parameters were studied. Graphite coating was also used for carburizing. The results showed that both carbon nanotube and graphite were dissolved in the surface molten layer, leading a carburized hardening layer on the surface of the substrate. However, different microstructures formed in the carburizing layers, depending mainly on the type of carburization materials, carbon nanotube or graphite. The carbon nanotube hardening layer exhibits a little higher hardness than the graphite hardening layer. The carburized layer greatly increases the wear resistance of the base material.     

Hydrothermal synthesis and electrochemical characterization of VO2 (B) with controlled crystal structures

Three different VO₂ (B) nanostructures, including urchin-like VO₂ (B), VO₂ (B) honeycombs and VO₂ (B) nanorods have been successfully fabricated through hydrothermal process by adjusting the concentrations of the oxalic acid. The microstructure and morphology of the VO₂ nanostructures were evaluated by using X-ray diffraction and scanning and transmission electron microscopies. Electrochemical properties measurements of urchin-like VO₂ (B) and VO₂ (B) honeycombs showed excellent cycling performance, especially the urchin-like VO₂ (B) exhibited higher discharge capacity and better capacity retention.     

Electrochemical synthesis of polypyrrole/carbon nanotube nanoscale composites using well-aligned carbon nanotube arrays

Polypyrrole/carbon nanotube nanoscale composites were successfully fabricated by electrochemical deposition of polypyrrole over each of the carbon nanotubes in well-aligned large arrays. The thickness of the polypyrrole coating can be easily controlled by the value of the film-formation charge. For both thin (low film-formation charge) and thick (high film-formation charge) films, the polypyrrole coating on the surface of each nanotube is very uniform throughout the entire length, as observed by transmission electron microscopy. Received: 2 May 2001 / Accepted: 4 May 2001 / Published online: 20 June 2001     

On the compressive response of carbon nanotube tangles

The nonlinear bulk compressibility of entangled multiwalled carbon nanotubes is studied. The analogy with textile fibre assemblies is explored by means of the well established van Wyk model. In view of the small diameter of the nanotubes, the possible effect of adhesive van der Waals interactions at tube-tube contacts is analysed. It is found, however, that the contribution of adhesive contacts to the bulk stress should be negligible. Compression experiments are performed on multi-walled carbon nanotubes and show that van Wyk's model is able to describe the response, although the values of the dimensionless parameter k of van Wyk's model were lower than expected. There is indeed no indication that van der Waals interactions play any significant role.     

Investigation of Schottky-Barrier carbon nanotube field-effect transistor by an efficient semi-classical numerical modeling

An efficient semi-classical numerical modeling approach has been developed to simulate the coaxial Schottky-barrier carbon nanotube field-effect transistor (SB-CNTFET). In the modeling, the electrostatic potential of the CNT is obtained by self-consistently solving the analytic expression of CNT carrier distribution and the cylindrical Poisson equation, which significantly enhances the computational efficiency and simultaneously present a result in good agreement to that obtained from the non-equilibrium Green's function (NEGF) formalism based on the first principle. With this method, the effects of the CNT diameter, power supply voltage, thickness and dielectric constant of gate insulator on the device performance are investigated.     

Field emission from single-walled carbon nanotubes aligned on a gold plate using a self-assembly monolayer

Field emission from single-walled carbon nanotubes (SWNTs) aligned on a patterned gold surface is reported. The SWNT emitters were prepared at room temperature by a self-assembly monolayer technique. SWNTs were cut into sub-micron lengths by sonication in an acidic solution. Cut SWNTs were attached to the gold surface by the reaction between the thiol groups and the gold surface. The field-emission measurements showed that the turn-on field was 4.8 V/μm at an emission current density of 10 μA/cm². The current density was 0.5 mA/cm² at 6.6 V/μm. This approach provides a novel route for fabricating CNT-based field-emission displays. Received: 3 May 2002 / Accepted: 6 May 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +82-54/279-8298, E-mail: ce20047@postech.ac.kr     

Synthesis and Raman scattering study of double-walled carbon nanotube peapods

Double-walled carbon nanotubes (DWNTs) encapsulating C₆₀ fullerenes were successfully synthesized by gas phase diffusion method. The obtained peapods were examined using high-resolution transmission electron microscopy (HRTEM). The HRTEM images indicate that the ordered packing phases of fullerene molecules inside are sensitively related to the inner-tube radius of DWNTs. Also, Raman measurements were carried out for the first time to characterize DWNTs peapods. There are obvious differences between the Raman spectrum of DWNTs peapods and that of SWNTs peapods. The intensities of resonances from C₆₀ in the former are much stronger than those in the latter. In addition, changes of tangential mode (TM) and radial breathing mode (RBM) of DWNTs after C₆₀ doping were observed. The possible reasons are discussed in the text.