Metallization of the semiconducting carbon nanotube by encapsulated bromine molecules

We use ab initio density-functional calculations to investigate the electronic structure of the bromine-adsorbed carbon nanotubes. When a Br₂ molecule is inside the (10,0) carbon nanotube, a trace of electron charge transfers from the nanotube to the Br₂ adsorbate, resulting in an increased Br–Br bond length. When the supercell contains two Br₂ molecules, total energy calculations reveal the formation of a linear chain of bromine atoms inside the carbon nanotube. Electron transfer from the nanotube to the atomic chains of the bromine adsorbates is much enhanced even in large-diameter nanotubes. We suggest that an exposure of the tip-opened carbon nanotube samples to a modest Br₂ partial pressure could result in a strong hole-doping of the nanotube, which makes the semiconducting nanotubes nearly metallic.     

Terahertz applications of carbon nanotubes

We formulate and justify several proposals utilizing unique electronic properties of carbon nanotubes for a broad range of applications to THz optoelectronics, including THz generation by hot electrons in quasi-metallic nanotubes, frequency multiplication in chiral-nanotube-based superlattices controlled by a transverse electric field, and THz radiation detection and emission by armchair nanotubes in a strong magnetic field.     

Molecular dynamics study on the field effect ion transport in carbon nanotube

We investigated potassium ion transport in the (5, 5) carbon nanotube by using classical molecular dynamics simulations under applying external force fields. This can be applied to nanoscale ionic-field-effect devices. As the applying external force field increases, the potassium ions rapidly go through the nanochannel. Under the low external force fields, the thermal fluctuation of the nanochannel affected on the tunneling of the potassium ions, whereas the effects of the thermal fluctuation were negligible under the high external force fields.     

Terahertz radiation from armchair carbon nanotube dipole antenna

This paper investigates the electromagnetic radiation characteristics of a metallic, large aspect ratio single walled carbon nanotube antenna in the terahertz frequency region below 12.5 THz. The key features of terahertz pulse have been revealed on the carbon nanotube antenna in comparison with conventional photoconductive switching. The terahertz waveforms, radiation power and their field distributions have been evaluated and are analysed. The Fourier transformed spectra over the whole frequency range demonstrate that the carbon nanotube antenna can be used as radiation source for broadband terahertz applications.     

Radiation Properties of Carbon Nanotubes Antenna at Terahertz/Infrared Range

The geometric structure and the terahertz/infrared radiation characteristics of carbon nanotubes dipole antenna arrays have been investigated by CST MICROWAVE STUDIO based on finite integral methods. In terahertz and infrared frequency span, the antenna properties such as electrical field distributions, scattering parameters, standing wave ratio, gain, and two dimension directivity patterns are discussed. Our results show that N × N antenna arrays have higher radiation efficiency than single carbon nanotube dipole antenna. This work was supported by National Natural Science Foundation of China (60571026, 10396160).     

Electrical transport and noise in semiconducting carbon nanotubes

We investigate electrical transport and noise in semiconducting carbon nanotubes. By studying carbon nanotube devices with various diameters and contact metals, we show that the ON-currents of CNFETs are governed by the heights of the Schottky barriers at the metal/nanotube interfaces. The current fluctuations are dominated by 1/f noise at low-frequencies and correlate with the number of transport carriers in the device regardless of contact metal.     

Recent advances in carbon nanotube photophysics

A review is given of how resonance Raman spectroscopy (RRS) and photoluminescence (PL) can be used to reveal unique information about nanostructures, 1 nm in diameter, thus providing new techniques for probing the electronic and vibrational properties of nanostructures. Special attention is given to recent advances made in this field.     

Behavior of H2O molecule in carbon nanotube/boron nitride nanotube heterostructure

We perform total-energy electronic-structure calculations of a water molecule inside a (7, 7) carbon nanotube/boron nitride nanotube (CNT/BNNT) heterojunction. The van der Waals interaction is also considered in this study. We find that the equilibrium distance between the water molecule and the wall of the CNT (BNNT) is ≈ 3.3 Å, and the encapsulation energy is 0.22 eV (0.25 eV). The energy profile along the tube axis exhibits a dramatic change in the vicinity of the heterojunction. A speed change of water flow is expected to occur near the heterojunction. Such information would provide valuable insight in nanostructure design for nanofluidics.     

Sonochemical production of a carbon nanotube

Sonochemical production of a carbon nanotube has been studied. The carbon nanotube is produced by applying ultrasound to liquid chlorobenzene with ZnCl₂ particles and to o-dichlorobenzene with ZnCl₂ and Zn particles. It is considered that the polymer and the disordered carbon, which are formed by cavitational collapse in homogeneous liquid, are annealed by the inter-particle collision induced by the turbulent flow and shockwaves.     

Structural and surface features of multiwall carbon nanotube

We present the direct evidence of defective and disorder places on the surface of multiwall carbon nanotube (MWCNT), visualizing the presence of amorphous carbon at those sites. These defective surfaces being higher in energy are the key features of functionalization with different materials. The interaction of the π orbital electrons of different carbon atoms of adjacent layers is more at the bent portion, than that of regular portion of the CNT. Hence the tubular structure of the bent portion of nanotubes is spaced more than that of regular portion of the nanotubes, minimizing the stress.     

Field emission characteristic of screen-printed carbon nanotube cathode

The fabrication of carbon nanotube emitters with excellent emission properties is described. The multi-walled carbon nanotubes (MWNTs) produced by chemical vapor deposition (CVD) method were purified with oxidation method and mixed with organic binding pastes and then screen-printed on glass substrates with ITO film. We applied anode voltage gradually to refine the emission behavior of the emitter by cleaning the top surface of screen-printed carbon nanotubes (CNTs). The density of the carbon nanotubes is about 2.5×10⁸/cm². Diode field emission experiments were performed in dynamic vacuum system to study the emission current, the emission uniformity, etc. Bright and stable character emission images were obtained in the diode structure and the emission current could approach 1 mA/cm².     

Nonlinear resonances of a single-wall carbon nanotube cantilever

The dynamics of an electrostatically actuated carbon nanotube (CNT) cantilever are discussed by theoretical and numerical approaches. Electrostatic and intermolecular forces between the single-walled CNT and a graphene electrode are considered. The CNT cantilever is analyzed by the Euler–Bernoulli beam theory, including its geometric and inertial nonlinearities, and a one-mode projection based on the Galerkin approximation and numerical integration. Static pull-in and pull-out behaviors are adequately represented by an asymmetric two-well potential with the total potential energy consisting of the CNT elastic energy, electrostatic energy, and the Lennard-Jones potential energy. Nonlinear dynamics of the cantilever are simulated under DC and AC voltage excitations and examined in the frequency and time domains. Under AC-only excitation, a superharmonic resonance of order 2 occurs near half of the primary frequency. Under both DC and AC loads, the cantilever exhibits linear and nonlinear primary and secondary resonances depending on the strength of the excitation voltages. In addition, the cantilever has dynamic instabilities such as periodic or chaotic tapping motions, with a variation of excitation frequency at the resonance branches. High electrostatic excitation leads to complex nonlinear responses such as softening, multiple stability changes at saddle nodes, or period-doubling bifurcation points in the primary and secondary resonance branches.     

Effects of electromigration on copper atoms in carbon nanotube channels

The effects of electromigration on copper in carbon nanotube (CNT) channels are investigated using molecular dynamics simulations. The study shows that the potential energy of copper and the resistive forces on copper are dependent on the shape of the CNT junction, and the increase in bias voltages magnifies these effects. Bias voltages affect the density of copper in the downstream CNT. The velocity of copper in the downstream CNT is relatively lower than that in the upstream CNT when the biased voltage is high.     

Planar trivalent polygonal networks constructed from carbon nanotube Y-junctions

This work is the first step towards proving that general planar polygonal networks can be constructed as patterns of carbon nanotubes. A subset of the planar polygonal networks, namely the trivalent planar networks, are studied. These patterns can be constructed from carbon nanotubes such that every intersection point of the networks is replaced with a carbon nanotube Y-junction. Accordingly the basic task is to show the basic connections of the carbon nanotube Y-junctions. The basic set of connected Y-junctions is defined and models of the structures are shown. Nanorings with two, three or more branches are constructed from two, three or more Y-junctions such that two tubes of every Y-junction are joined to the neighbouring tubes with the third tube being free. Because of the known, exceptional electronic behaviour of carbon nanotubes, combinations of basic elements of planar nanotube networks could motivate new experimental and theoretical works having the goal of finding the basic electronic tools for nanocircuits.     

Quantum walk transport on carbon nanotube structures

We study source-to-sink excitation transport on carbon nanotubes using the concept of quantum walks. In particular, we focus on transport properties of Grover coined quantum walks on ideal and percolation perturbed nanotubes with zig-zag and armchair chiralities. Using analytic and numerical methods we identify how geometric properties of nanotubes and different types of a sink altogether control the structure of trapped states and, as a result, the overall source-to-sink transport efficiency. It is shown that chirality of nanotubes splits behavior of the transport efficiency into a few typically well separated quantitative branches. Based on that we uncover interesting quantum transport phenomena, e.g. increasing the length of the tube can enhance the transport and the highest transport efficiency is achieved for the thinnest tube. We also demonstrate, that the transport efficiency of the quantum walk on ideal nanotubes may exhibit even oscillatory behavior dependent on length and chirality.     

Effect of sp-hybridized defects on the oscillatory behavior of carbon nanotube oscillators

Using molecular dynamics simulations, we investigate the oscillatory behaviors of carbon nanotube oscillators containing sp³-hybridized defects formed by hydrogen chemisorption. It is found that the presence of these defects significantly affects the kinetic and potential energies of the nanotube systems, which in turn affects their oscillation periods and frequencies. We have also studied the oscillatory characteristics of the oscillators containing sp³-hybridized Stone-Wales defects. Our results show that it is possible to control the motion of the inner nanotube by introducing sp³-hybridized defects on the outer nanotube, which provides a potential way to tune the oscillatory behavior of nanotube oscillators.     

Preparation of large-area double-walled carbon nanotube films and application as film heater

Large-area (larger than 30×30 cm²) double-walled carbon nanotube (DWCNT) films are prepared and application as a heating element for film heaters is demonstrated. A high heating efficiency is observed. Measurements indicate that the use of the DWCNT film heater would save energy consumption up to 20–30% when compared with a commercial film-like metal-based heater. Morphological analysis reveals that the special surface structure, appropriate electric and high thermal conductivities of the film formed by the network of entangled nanotube bundles may lead to the high heating performance. Considering large-area, shape flexibility, negligible weight and easy manipulation, the film exhibits promising potential applications as a film heater for thermal control in aircrafts, medical equipment, home appliances and other industrial fields at low temperature (below 400 °C).     

接触电阻对碳纳米管场发射的影响

基于改进的悬浮球模型,计算了碳纳米管和衬底间的接触电阻存在时碳纳米管顶端的局域电场, 并结合Fowler-Nordheim (F-N)场发射规律研究了接触电阻对碳纳米管场发射的影响.研究表明,接触电阻的存在,在高电场区域接触电阻抑制了碳纳米管的电子场发射,导致在高电场区域出现电流饱和及FN直线偏折现象.其原因可归结为接触电阻使得在碳纳米管顶端的局域电场相对于没有接触电阻时相对地减少. 关键词： 碳纳米管 场发射 接触电阻 电流饱和     

Ethylene glycol reflux synthesis of carbon nanotube/ceria core-shell nanowires

Carbon nanotube (CNT)/ceria core-shell nanowires were prepared facilely on a large scale under the boiling reflux of ethylene glycol. The composites are characterized by transmission electron microscopy, X-ray diffraction as well as Fourier transformed infrared spectra. It is found that the entire outer surface of CNTs is fully sheathed with a dense layer of uniform nanosized CeO₂, and that the thickness of the coating sheath can be readily manipulated by tuning the molar ratio of ceria to CNTs. Finally, a possible formation mechanism has been suggested as follows: with the high reaction temperature, ethylene glycol is partially converted to oxalic acid, and the surface hydroxyl groups of CeO₂ tiny particles react with oxalic acid to form the polymer-like inorganic-organic compounds. Subsequently, in view of the low-energy point, the polymer-like inorganic-organic compounds are coated on the surface of CNTs, and thus CNTs/ceria core-shell composites are obtained.     

Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes

Thorn-like, organometallic-functionalized carbon nanotubes were successfully developed via a novel microwave hydrothermal route. The organometallic complex with methyl orange and iron (III) chloride served as reactive seed template, resulting in the oriented polymerization of pyrrole on the modified carbon nanotubes without the assistance of other oxidants. Morphological and structural characterizations of the carbon nanotube/methyl orange-iron (III) chloride and polypyrrole/carbon nanotube composites were examined using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), infrared spectroscopy and X-ray diffraction (XRD). The electrochemical property of the polypyrrole/carbon nanotube composite was elucidated by cyclic voltammetry and galvanostatic charge-discharge. A specific capacitance of 304 F g⁻¹ was obtained within the potential range of −0.5-0.5 V in 1 M KCl solution.