Electronic properties of magnetically doped nanotubes

Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered in this paper. In the case of semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic (except for Cr).     

Preparation of CdS doped carbon nanotubes and their electrochemical properties

A CdS doped carbon nanotube sol was synthesised by the sol-gel technique and applied to a titanium plate to synthesise a composite electrode. Energy dispersion X-ray spectroscopy and X-ray diffraction analysis confirmed that the electrodes contain CdS. Scanning electron microscopy revealed that the carbon nanotubes were uniformly dispersed on the surface of the plate. A two-chamber microbial fuel cell was constructed using the electrode as the anode, flexible graphite as the cathode and glucose solution as the substrate in the anode chamber. The effects of CdS dose, glucose concentration and temperature on the cell efficiency and organic degradation have been analysed. At 313 K, the two-chambered fuel cell possessed the optimum output voltage of 906 mV, with a power of 19·6 mW m^?2 and a removal rate of 81% for chemical oxygen demand in treatment of wastewater. The composite electrode was found to be stable and to perform reproducibly.     

Electronic, thermal and mechanical properties of carbon nanotubes

A review of the electronic, thermal and mechanical properties of nanotubes is presented, with particular reference to properties that differ from those of the bulk counterparts and to potential applications that might result from the special structure and properties of nanotubes. Both experimental and theoretical aspects of these topics are reviewed.     

Photorefractive properties of nanostructured organic materials doped with fullerenes and carbon nanotubes

The phenomenon of a significant increase in the photoinduced changes in refractive index, non-linear refraction, and nonlinear third-order optical susceptibility in organic materials based on polyimides, pyridines, and prolinols upon the introduction of fullerenes and carbon nanotubes (CNTs) into the organic matrix is briefly considered (with emphasis on the dominating effect of CNTs). It is established that the values of these photorefractive parameters determined in said fullerene- and CNT-doped materials using a four-wave-mixing scheme are close to the analogous values in bulk silicon-based materials. The results can be useful in developing thin-film nonlinear filters, thin diffraction gratings for passive data recording, and optically-addressed light modulators, in medical applications, and in display technology (e.g., for creating a three-dimensional medium prototype).     

Electronic transport properties of coupled quantum dots on carbon nanotubes

We investigate the electronic transport properties of coupled quantum dots, controlled by local gates on carbon nanotubes. The inter-dot coupling can be tuned from weak to strong by changing gate voltages, and oscillates in short and long period with the distance between two gates. We introduce a one-dimensional scattering model to describe the mechanism of the electron transport through the carbon nanotube quantum dots. We show that pi and PI* channels contribute differently to the inter-dot coupling and the transport phase plays a key role in the oscillations of the coupling.     

Electronic and magnetic properties of nitrogen-doped finite-size and open-ended zigzag carbon nanotubes

Density functional calculations have been used to investigate the effect of the N doping on the electronic and magnetic properties of finite-size and open-ended zigzag carbon nanotubes (CNT). The carbon atoms at the edge site are more easily replaced by N atoms energetically, compared to other sites. The single N atom substitution can reduce the magnetic moment of edge carbon atoms near the doping site and result in the suppression of spin polarization. Such spin suppression is independent of tube diameter and it can be ascribed into perturbation of the π/π^* state localized at the doped edge. At low N-doping concentrations, the finite-length zigzag CNTs can maintain an antiferromagnetic (AFM) ground state, but the conversion from AFM to a nonmagnetic state can occur at high impurity concentrations. More interestingly, the tunable electronic properties from the half-semiconducting to semiconducting state can be realized in these N-doped finite-size and open-ended CNTs if subjected to a variably external electric field along the tube axis.     

Electronic and optical properties of finite carbon nanotubes in an electric field

The effects, caused by the geometric structure and an electric field (E), on the electronic and optical properties of quasi-zero-dimensional finite carbon nanotubes are explored by employing the tight-binding model coupled with curvature effects. Electronic properties (state energies, symmetry of electronic states, energy spacing and state degeneracy) are significantly affected by the magnitude and the direction of the electric field and the geometric structure (radius, length and chirality). The electric field, by lowering the symmetry of finite carbon nanotubes, modifies the electronic properties. Thus, the optical excitation spectra, excited by electric polarization parallel to the nanotube axis, exhibit rich delta-function-like peaks, which reveal the characteristics of the electronic properties. Therefore it follows that geometric structure and E influence the low-energy absorption spectra, i.e. the change of frequency of the first peak, the alternation of the peak height and the production of the new peaks. There are more absorption peaks when E is oriented closer to the cross-section plane. Moreover, the very complicated optical absorption spectra are characteristic for the individual chiral carbon nanotube due to its specific geometric structure. Above all, the predicted absorption spectra and the associated electronic properties could be verified by optical measurements.     

Thermal stability and electrical properties of dodecyl-benzene-sulfonic-acid doped nanocomposites of polyaniline and multi-walled carbon nanotubes

Electrically conductive dodecyl-benzene-sulfonic-acid (DBSA) doped polyaniline (Pani) nanocomposites were prepared with multi-walled carbon nanotubes (MWCNTs) by in situ oxidative polymerization of aniline in the presence of different amounts of MWCNTs. The stability of the nanocomposites in terms of DC electrical conductivity retention was studied in ambient atmosphere by isothermal accelerated aging and cyclic accelerated aging techniques. The MWCNT/Pani nanocomposites were observed to be thermally more stable under ambient environmental conditions than Pani. Such nanocomposites with high thermal stability may find a place as future materials for the replacement for Pani.     

Thermal stability and electrical properties of dodecyl-benzene-sulfonic-acid doped nanocomposites of polyaniline and multi-walled carbon nanotubes

Electrically conductive dodecyl-benzene-sulfonic-acid (DBSA) doped polyaniline (Pani) nanocomposites were prepared with multi-walled carbon nanotubes (MWCNTs) by in situ oxidative polymerization of aniline in the presence of different amounts of MWCNTs. The stability of the nanocomposites in terms of DC electrical conductivity retention was studied in ambient atmosphere by isothermal accelerated aging and cyclic accelerated aging techniques. The MWCNT/Pani nanocomposites were observed to be thermally more stable under ambient environmental conditions than Pani. Such nanocomposites with high thermal stability may find a place as future materials for the replacement for Pani.     

Electro-optical properties and frequency response of polymer-dispersed liquid crystal gratings doped with multi-walled carbon nanotubes

In this paper, a model developed for establishing the lowest possible driving voltage of Holographic polymer-dispersed liquid crystal (H-PDLC) based on the Maxwell–Wagner effect doped with specific nanotubes. The dependences of the turning point frequency on the doping concentration and the distribution of multi-walled carbon nanotubes (MWCNTs) are discussed. The MWCNTs can effectively adjust the relaxation frequency of grating, increase its LC droplet size, and decrease its dielectric permittivity. The diffraction efficiency and threshold voltage of the prepared switchable Bragg grating were found to reach 91% and 0.77 V μm^?1, respectively, at 5 kHz. By comparing the results of experiments and simulations, we obtained the mass distribution ratio of MWCNTs in the LC and polymer regions. It was found that the MWCNTs diffuse into the LC regions during the polymerization process, and the use of a suitable driving frequency and doping concentration can minimize the driving voltage. This work provides a reference for studying the dynamic range optical tuning and polymerization kinetics of nanoparticles in switchable gratings.

     

Biocompatibility and toxicological studies of carbon nanotubes doped with nitrogen

In this report, we compare the toxicological effects between pure carbon multiwalled nanotubes (MWNTs) and N-doped multiwalled carbon (CNx) nanotubes. Different doses of tubes were administered in various ways to mice: nasal, oral, intratracheal, and intraperitoneal. We have found that when MWNTs were injected into the mice's trachea, the mice could die by dyspnea depending on the MWNTs doses. However, CNx nanotubes never caused the death of any mouse. We always found that CNx nanotubes were far more tolerated by the mice when compared to MWNTs. Extremely high concentrations of CNx nanotubes administrated directly into the mice's trachea only induced granulomatous inflammatory responses. Importantly, all other routes of administration did not induce signs of distress or tissue changes on any treated mouse. We therefore believe that CNx nanotubes are less harmful than MWNTs or SWNTs and might be more advantageous for bioapplications.     

Biological properties of carbon nanotubes

Carbon nanotubes are novel materials with unique physical and chemical properties, and have been considered for use in numerous technological applications. More recently, attention has turned to the unique biological and medical properties of these materials. In this review, the processing, chemical properties, physical properties, nucleic acid interaction, cell interaction, and toxicologic properties of nanotubes are described. Finally, future directions in this area are discussed.     

Field-emission characteristics of carbon nanotubes and their applications in photonic devices

Based upon the field-emission investigation of carbon nanotubes, several prototype devices have been suggested that operate with low swing voltages with sufficiently high current densities. Characteristics that allow improved current stability and long operating lifetime as electrical and opto-electronic devices are presented. The aim of this paper is to illustrate the useful characteristics of carbon nanotubes and their possible applications.     

Electronic structures and three-dimensional effects of boron-doped carbon nanotubes

Abstract

We study boron-doped carbon nanotubes by first-principles methods based on the density functional theory. To discuss the possibility of superconductivity, we calculate the electronic band structure and the density of states (DOS) of boron-doped (10,0) nanotubes by changing the boron density. It is found that the Fermi level density of states D(?_F) increases upon lowering the boron density. This can be understood in terms of the rigid band picture where the one-dimensional van Hove singularity lies at the edge of the valence band in the DOS of the pristine nanotube. The effect of three-dimensionality is also considered by performing the calculations for bundled (10,0) nanotubes and boron-doped double-walled carbon nanotubes (10,0)@(19,0). From the calculation of the bundled nanotubes, it is found that interwall dispersion is sufficiently large to broaden the peaks of the van Hove singularity in the DOS. Thus, to achieve the high D(?_F) using the bundle of nanotubes with single chirality, we should take into account the distance from each nanotube. In the case of double-walled carbon nanotubes, we find that the holes introduced to the inner tube by boron doping spread also on the outer tube, while the band structure of each tube remains almost unchanged.     

碳纳米管掺杂纳米WO3气敏材料的制备及其应用

为降低WO3气敏元件的工作电压,改善WO3基敏感材料的气敏性能,采用化学吸附沉淀-水热法合成WO3和WO3/SWCNT复合材料,并研究矿化剂用量和SWCNT掺杂量对其气敏性能的影响.结果表明,大剂量矿化剂的使用会降低WO3的气敏性能;碳纳米管掺杂可以使WO3在较低的工作温度下有较高的灵敏度.SWCNT掺杂量为1％的元件...     

Optical properties of carbon nanofiber photonic crystals

Carbon nanofibers (CNFs) are used as components of planar photonic crystals. Square and rectangular lattices and random patterns of vertically aligned CNFs were fabricated and their properties studied using ellipsometry. We show that detailed information such as symmetry directions and the band structure of these novel materials can be extracted from considerations of the polarization state in the specular beam. The refractive index of the individual nanofibers was found to be n(CNF) = 4.1.     

稀土掺杂碳纳米管/聚氯乙烯复合材料的吸波性能研究

利用La(NO3)3和Ce(NO3)3掺杂的碳纳米管(MWCNTs-La(NO3)3和MWCNTs-Ce(NO3)3)作为吸收剂、聚氯乙烯(PVC)作为基体,制备出MWCNT-La(NO3)3(或Ce(NO3)3)/PVC复合材料。运用透射电子显微镜和X射线衍射仪对MWCNTs、MWCNTs-La(NO3)3、MWCNTs-Ce(NO3)3的微观结构进行表征分析,使用同步热分析仪和矢量网络分析仪对MWCNT/PVC、MWCNT-La(NO3)3/PVC、MWCNT-Ce(NO3)3/PVC复合材料的热解行为和吸波性能进行测试分析。结果表明,在2～18GHz频率范围内,适量掺杂La(NO3)3或Ce(NO3)3可以使MWCNT/PVC复合材料的吸波性能大幅度提高,而热解行为变化不明显。在反射率R<-10dB的范围内,MWCNT-Ce(NO3)3/PVC复合材料的吸收频宽(约为5.4GHz)虽然不及MWCNT-La(NO3)3/PVC的吸收频宽(约为5.6GHz)宽,但是吸收频段和吸收峰峰值均向高频区域移动,有利于提高复合材料的高频吸波性能。     

Thermodynamic properties of multiwalled carbon nanotubes

The experimental study of the heat capacity of multiwalled carbon nanotubes has been conducted at a constant pressure and a temperature in the range from 60 to 300 K. The derived temperature dependence of the heat capacity has been shown to differ from that of graphite. The explanation of the fact has been given in terms of the special features of phonon spectra of the above materials. Based on the experimental results and reliable literature data standard values of the basic thermodynamic functions of multiwalled carbon nanotubes (enthalpy, entropy, and Gibbs reduced energy) have been calculated.