The rehybridization of electronic orbitals in carbon nanotubes

Rehybridization of electronic orbitals in carbon nanotubes contains tilting angles of π orbital, electrons wavefunctions of π orbital and a orbital, degrees of hybridization, etc. In this paper, we have obtained analytical formulas of tilting angle of π orbital relative to tube surface, electrons wavefunctions of π orbital and a orbital, degrees of hybridization, separately, as well as the numerical results.     

卷曲效应对单壁碳纳米管电子结构的影响

利用计入卷曲效应的单壁碳纳米管(SWCNT)的能量色散关系,计算最低导带的电子速度及有效质量,并与不计入卷曲效应的结果进行了比较.计算结果表明:卷曲效应对电子速度及有效质量的影响与SWCNT的类型密切相关,金属锯齿型SWCNT对卷曲效应最为敏感,其次是扶手椅型SWCNT,最不敏感的是半导体锯齿型SWCNT.由此可以推断,卷曲效应对金属锯齿型SWCNT电子结构及低偏压输运特性影响最大,其次是扶手椅型SWCNT,影响最不明显的是半导体锯齿型SWCNT.这些结果与实验测量及密度泛函理论计算结果完全一致. 关键词： 单壁碳纳米管 卷曲效应 电子速度 电子有效质量     

单壁碳纳米管单原子空位缺陷的紧束缚理论研究

文章在紧束缚势模型基础上系统地研究了非手性单壁碳纳米管上单原子空位缺陷结构和电子结构性质.计算表明,单原子空位缺陷会自发地形成5-1DB型缺陷, 且该缺陷的局域结构和形成能强烈地依赖于碳纳米管的尺寸、旋度和电学性质.同时作者发现这类缺陷在费米能级以上约0.2eV处产生局域的电子态.     

Influencing range of vacancy defects in zigzag single-walled carbon nanotubes

The influencing range of a vacancy defect in a zigzag single-walled nanotube is characterized with both structural deformation and variation in bandstructure. This paper proposes a microscopic explanation to relate the structural deformation to the bandstructure variation. With an increasing defect density, the nanotubes become oblate and the energy gap between the deep localized gap state and the conducting band minimum state decreases. Theoretical results shed some light on the local energy gap engineering via vacancy density for future potential applications.     

Direct transition of potential of water droplets to electric energy using aligned single-walled carbon nanotubes

In this paper, we report that an electromotive force (EMF) can be induced in a rope of aligned single-walled carbon nanotubes (SWNTs) when water droplets fall on this rope. The magnitude of this EMF depends sensitively on the slant angle of the SWNTs. Most interestingly, both the magnitude and the direction of the induced EFM can be modulated by applying a current to the SWNTs. The concepts of electrical slip and no-slip are proposed and can be quantitatively described by ``electrical slip resistance'. This kind of generator does not need any magnet, rotor, {etc} and shows quite a different operating mechanism and design compared with a conventional large scale hydroelectric power generator.     

Electronic transport properties of metallic single-walled carbon nanotubes

We have calculated the differential conductance of metallic carbon nanotubes by the scatter matrix methon.It is found that the differential conductance of metallic nanotube-based devices oscillates as a function of the bias voltage between the two leads and the gate voltage.Oscillation period T is directly proportional to the reciprocal of nanotube length.In addition,we found that electronic transport properties are sensitive to variation of the length of the nanotube.     

扶手椅型单壁碳纳米管中的B/N对共掺杂

利用第一性原理电子结构计算方法,研究了扶手椅型单壁碳纳米管（SWCNT）的B/N对掺杂效应.研究发现,对于扶手椅型SWCNT两个不同的掺杂位点,B/N对更容易发生在与管轴线成30°角的P₁位点上.B/N对的掺杂使得金属性SWCNT能隙打开,且能隙随着B/N对轴向掺杂浓度的升高而逐渐增大.同时,还发现两B/N对掺杂后SWCNT的电子结构敏感地依赖于B/N对在圆周上的相对位置,能隙随着B/N对相对距离的增大而增大.这归结于B/N对的掺入影响了原有的电荷分布,这种影响是局域的 关键词： 单壁碳纳米管 B/N对掺杂 电子结构 第一性原理     

Potential energy distributions within and on single-walled and double-walled carbon nanotubes

The potential fields arising from dispersion forces induced by single- and double-walled carbon nanotubes of various chiral configurations and sizes on an argon test atom have been calculated, employing a discrete summation method that takes into account the translational symmetry of the carbon lattice of the different armchair and zigzag chiral conformations. The total interaction potential was considered to be pair-wise additive and described by the Lennard–Jones 6–12 potential expression. This has yielded radial field distributions as a function of axial distance within, outside, and between the walls these carbon nanotubes. It was found that these distributions depended not only upon position but also upon orientation of the axes with respect to the graphene sheets. The potential barriers at the open end of the carbon nanotubes have also been studied. The effect of surface curvature was evaluated by comparing a single graphite sheet to the corresponding segments of nanotubes containing the same number of carbon atoms. Using the calculated data, the Henry constants and diffusion coefficients have been computed together with their temperature dependencies and compared to other planar and microporous carbon systems.     

Influence of chirality on the thermal conductivity of single-walled carbon nanotubes

The influence of chirality on the thermal conductivity of single-walled carbon nanotubes(SWNTs) is discussed in this paper, using a non-equilibrium molecular dynamics(NEMD) method. The tube lengths of the SWNTs studied here are 20, 50, and 100 nm, respectively, and at each length the relationship between chiral angle and thermal conductivity of a SWNT is revealed. We find that if the tube length is relatively short, the influence of chirality on the thermal conductivity of a SWNT is more obvious and that a SWNT with a larger chiral angle has a greater thermal conductivity. Moreover, the thermal conductivity of a zigzag SWNT is smaller than that of an armchair one. As the tube length becomes longer, the thermal conductivity increases while the influence of chirality on the thermal conductivity decreases.     

On the size of small single-walled carbon nanotubes

We derive a formula relative to the diameter/length ratio of a small single-walled carbon nanotube by means of calculations referring to Fermi energy. These calculations arise from the consideration of the Fermi's velocity for a multiwalled carbon nanotube.     

单、双原子空位缺陷对扶手椅型单层碳纳米管屈曲性能的不同影响

采用分子动力学方法,对完善和含缺陷扶手椅型单层碳纳米管进行轴向压缩的数值模拟,对比研究三种不同的温度环境下单、双原子空位缺陷对碳纳米管轴压变形性能的特殊影响.研究结果表明管壁缺陷显著降低了纳米管低温时的承载能力,由于单原子空位缺陷造成的特殊应力集中效应会引发纳米管过早发生局部屈曲,单原子缺陷管的屈曲强度反而小于双原子管的屈曲强度. 关键词： 分子动力学 碳纳米管 屈曲 缺陷     

Numerical distortion and effects of thermostat in molecular dynamics simulations of single-walled carbon nanotubes

In this paper, single-walled carbon nanotubes （SWCNTs） are studied through molecular dynamics （MD） simulation. The simulations are performed at temperatures of 1 and 300K separately, with atomic interactions characterized by the second Reactive Empirical Bond Order （REBO） potential, and temperature controlled by a certain thermostat, i.e. by separately using the velocity scaling, the Berendsen scheme, the Nose-Hoover scheme, and the generalized Langevin scheme. Results for a （5,5） SWCNT with a length of 24.5 nm show apparent distortions in nanotube configuration, which can further enter into periodic vibrations, except in simulations using the generalized Langevin thermostat, which is ascribed to periodic boundary conditions used in simulation. The periodic boundary conditions may implicitly be applied in the form of an inconsistent constraint along the axis of the nanotube. The combination of the inconsistent constraint with the cumulative errors in calculation causes the distortions of nanotubes. When the generalized Langevin thermostat is applied, inconsistently distributed errors are dispersed by the random forces, and so the distortions and vibrations disappear. This speculation is confirmed by simulation in the case without periodic boundary conditions, where no apparent distortion and vibration occur. It is also revealed that numerically induced distortions and vibrations occur only in simulation of nanotubes with a small diameter and a large length-to-diameter ratio. When MD simulation is applied to a system with a particular geometry, attention should be paid to avoiding the numerical distortion and the result infidelity.     

锯齿型单壁碳纳米管的广义层错能计算

基于密度泛函理论的第一性原理方法,计算了两种不同半径的锯齿型单壁碳纳米管以及单层石墨的广义层错能曲线。对小位移处广义层错能曲线进行斜率拟合所得切变模量与其它文献值一致。对三条广义层错能曲线的对比可知,锯齿型碳纳米管与单层石墨的广义层错能曲线相近,锯齿型单壁碳纳米管的曲率效应不明显。     

利用场发射显微镜研究O2对单壁碳纳米管场发射的影响

利用场发射显微镜和四极质谱计研究了充入高纯O2的四极质谱和O2对单壁碳纳米管场发射的影响.单壁碳纳米管经过约1000℃的热处理得到清洁态场发射像后，充入O2，分别测量了O2吸附和脱附后场发射的I V特性.实验观测到在单壁碳纳米管上O2的吸附使场发射电流减小，说明逸出功增加.在10-4Pa的O2压强下对单壁碳纳米管进行约1000℃的热处理，可以产生氧化刻蚀作用，观测到场发射像的变化，并测量了氧化刻蚀产生的I V特性变化. 关键词： 单壁碳纳米管 场发射显微镜 场发射 四极质谱     

单壁碳纳米管微分电导在高压和强磁场下的实验研究

单壁碳纳米管在高压下会发生结构相变，导致金属型的碳纳米管变成半导体.相变后碳纳米管中电子的库仑关联的表现形式发生变化，从Luttinger liquid行为转变成环境量子涨落行为.同时，相变后电子波函数的相位关联导致弱局域化行为的出现.为了研究库仑关联和相位关联之间是否有相互影响，使用金刚石对顶砧和液压自锁高压包在0—10 GPa准静压范围内测量了单层碳纳米管样品在低温和不同磁场下的微分电导随偏压的依赖关系.实验结果表明，相位关联和库仑关联是两种独立的效应，各自影响着电子的输运行为. 关键词： 单层碳纳米管 高压 微分电导     

单壁碳纳米管在场发射显示器中的应用研究

采用丝网印刷法将利用电弧放电法制备的单壁碳纳米管印刷在玻璃板上作为场发射显示器阴极材料，利用荧光粉阳极测试了其发光亮度，并研究其场发射性能.实验结果表明，单壁碳纳米管作为场发射显示器阴极材料具有较低的开启电场和较大的场发射电流密度，显示出良好的场发射特性.     

Parametric instabilities in single-walled carbon nanotubes

Parametric instabilities induced by the coupling excitation between the high frequency quantum Langmuir waves and the low frequency quantum ion-acoustic waves in single-walled carbon nanotubes are studied with a quantum Zakharov model. By linearizing the quantum hydrodynamic equations, we get the dispersion relations for the high frequency quantum Langmuir wave and the low frequency quantum ion-acoustic wave. Using two-time scale method, we obtain the quantum Zaharov model in the cylindrical coordinates. Decay instability and four-wave instability are discussed in detail. It is shown that the carbon nanotube＇s radius, the equilibrium discrete azimuthal quantum number, the perturbed discrete azimuthal quantum number, and the quantum parameter all play a crucial role in the instabilities.     

单壁纳米碳管的声子谱研究

通过五步旋转操作方便地得到了不同位置原子间的力常数矩阵，从而可以使对各种不同类型管的声子谱的计算变得简便. 计算表明，非螺旋的扶手椅型（n, n）管与锯齿型(n, 0)管的非简并和二重简并模式数分别为12和6(n-1)，这与从群论等方法所得结果相符. 关键词： 纳米碳管 声子谱 振动模式密度 动力学矩阵     

Selection of isolated and individual single-walled carbon nanotube from a film and its usage in nanodevices

Individual and isolated single-walled carbon nanotubes (SWNTs) are important for fabricating relevant nanode- vices and studying the properties of the SWNT devices. In this work, we demonstrate that individual and isolated SWNT can be selected and obtained from a film containing a huge number of SWNTs. By using both the polymethyl-methacrylate (PMMA) as a negative resist and the electron beam lithography, the selected SWNT can be fixed on a substrate, while the other SWNTs in the film can lift off. The selected SWNT can be used to fabricate nanodevice and a gas sensor of oxygen is demonstrated in this work.     

单壁碳纳米管环离散谱和连续谱间的转变

考虑卷曲效应，构造了扶手形单壁碳纳米管环的单Π轨道紧束缚模型.利用波函数分解方法导出了原子间相互作用矩阵元，由此研究了扶手形碳纳米管环的电子性质.随环半径改变，观察到电子结构发生从离散谱到连续谱之间的转变.计算也表明随管半径改变，其能谱也有类似的变化. 关键词： 碳纳米管环 卷曲效应 电子结构