双壁碳纳米管电浸润现象的分子动力学模拟

在单壁碳纳米管电浸润现象原子模拟的基础上,对双壁碳纳米管的电浸润现象进行了计算机模拟.运用经典分子动力学方法结合一个宏观的电毛细管模型模拟了双壁碳纳米管在水银中的电浸润过程,对不同内管尺寸情况下的浸润现象作了研究和比较.计算结果表明双壁碳管和单壁碳管的电浸润过程存在很大的不同,双壁碳管的内管在电浸润过程中起到重要的作用：当改变双壁碳管中内管的尺寸时,浸润现象会产生很大的改变. 关键词： 双壁碳纳米管 电浸润 分子动力学     

Transport of liquid mercury under pressure in double-walled carbon nanotubes

In this paper, transport of liquid mercury under pressure through double-walled carbon nanotubes is studied using classical molecular dynamics simulations in conjunction with a pressure control model. The results indicate that wetting of double-walled carbon nanotubes by mercury occurs above a threshold pressure of liquid mercury. Liquid mercury can be transported through the inner tube of double-walled carbon nanotubes with the continuous increase of its pressure. The threshold pressure of liquid mercury decreases and the transport efficiency increases greatly with enlarging the inner tube size. The space between the two walls of double-walled carbon nanotubes can also transport the liquid mercury while the distance between the two walls is much larger than the radius of the inner tube. Transport efficiency of double-walled carbon nanotubes is a little lower than that of single-walled carbon nanotubes while double-walled carbon nanotubes transport liquid more steadily than single-walled carbon nanotubes.     

Frequency change by inter-walled length difference of double-wall carbon nanotube resonator

Ultrahigh frequency nanomechanical resonators based on double-walled carbon nanotubes with different wall lengths were investigated via classical molecular dynamics simulations. For a double-walled carbon nanotube resonator with a short outer wall, the free edge of the short outer wall plays an important role in the vibration of the long inner wall. For a double-walled carbon nanotube resonator with a short inner wall, the short inner wall can be considered as a flexible core, thus, the fundamental frequency is influenced by its length. By controlling the length of the inner or outer wall, various frequency devices can be realized by a single type of double-walled carbon nanotube with walls of equal length.     

Vibrations of single- and double-walled carbon nanotubes with layerwise boundary conditions: A molecular dynamics study

In the present work, the vibration characteristics of single- and double-walled carbon nanotubes under various layerwise boundary conditions at different lengths are investigated. This is accomplished by the use of molecular dynamics simulations based on the Tersoff-Brenner and Lennard-Jones potential energy functions. The effects of initial tensile and compressive strains on the resonant frequency of carbon nanotubes are also taken into consideration. From the results generated, it is observed that the natural frequency of carbon nanotubes is strongly dependent on their boundary conditions especially when tubes are shorter in length. The natural frequency and its dependence on tube end conditions reduce by increasing the tube length. The natural frequency of DWCNTs lies between those of the constituent inner and outer SWCNTs and is nearer to those of the outer one. It is further observed that the natural frequency is highly sensitive to tensile and compressive strains. The frequency shift occurring in the presence of small initial strains is positive for tensile strains and negative for compressive strains. The results obtained provide valuable information for calibrating the small scaling parameter of the nonlocal models for the vibration problem of carbon nanotubes.     

On the role of interband surface plasmons in carbon nanotubes

We review the properties of collective surface excitations—excitons and interband plasmons—in single-walled and double-walled carbon nanotubes. We show that an electrostatic field applied perpendicular to the nanotube axis can control the exciton-plasmon coupling in individual small-diameter (≲nm) singlewalled nanotubes, both in the linear excitation regime and in the non-linear excitation regime with the photoinduced biexcitonic states formation. For double-walled carbon nanotubes, we report a profound effect of interband surface plasmons on the inter-tube Casimir force at tube separations similar to their equilibrium distances. Strong overlapping plasmon resonances from both tubes warrant their stronger attraction. Nanotube chiralities possessing such collective excitation features will result in forming the most favorable innerouter tube combination in double-walled carbon nanotubes. These findings pave the way for the development of new generation of tunable optoelectronic and nano-electromechanical device applications with carbon nanotubes.     

液体水银在碳纳米管中传输的压力控制模型

碳纳米管在纳米技术中有一个很重要的应用,就是它可以作为纳米管道传输液体. 本文用分子动力学模拟方法,结合一个液体压力控制模型,对液体水银由于外部压力作用在碳纳米管中传输的现象进行研究. 研究结果表明,当液体水银的内部压强超过一个临界值时,液体水银能够浸入到碳纳米管内部;不断增大液体内部的压强,碳纳米管可以连续地传输液体;而当对液体水银进行循环加压时,碳纳米管可以间断地传输液体水银. 关键词： 碳纳米管 流体传输 分子动力学     

液体水银在碳纳米管中传输的压力控制模型

碳纳米管在纳米技术中有一个很重要的应用，就是它可以作为纳米管道传输液体. 本文用分子动力学模拟方法，结合一个液体压力控制模型，对液体水银由于外部压力作用在碳纳米管中传输的现象进行研究. 研究结果表明，当液体水银的内部压强超过一个临界值时，液体水银能够浸入到碳纳米管内部；不断增大液体内部的压强，碳纳米管可以连续地传输液体；而当对液体水银进行循环加压时，碳纳米管可以间断地传输液体水银.     

Codoping of Potassium and Bromine in Carbon Nanotubes： A Density Functional Theory Study

We investigate the co-doping of potassium and bromine in single-walled carbon nanotubes （SWCNTs） and doublewalled carbon nanotubes （DWCNTs） based on density functional theory. In the co-doped （6,0） SWCNTs, the 4s electron of potassium is transferred to nanotube and Br, leading to the n-type feature of SWCNTs. When potassium is intercalated into inner tube and bromine is put on outer tube, the positive and negative charges reside on the outer and inner tubes of the （7,0）@（16,0） DWCNT, respectively. It is expected that DWCNTs would be an ideal candidate for p-n junction and diode applications.     

Electron-energy characteristics of double-walled carbon nanotubes doped with alkali metal atoms

A computational scheme based on density functional theory adapted for systems with translational symmetry is applied to calculating the electronic structure and energy spectrum of double-walled carbon nanotubes doped with alkali metal atoms (Li, Na, and K). The specific features of the electron-energy characteristics, including the potential curves for the interaction of nanotubes with “guest” atoms moving in the radial direction or along the circumference of the tube, are established. It is shown that doped double-walled nanotubes have an increased electron emissivity.     

Radial breathing vibration of double-walled carbon nanotubes subjected to pressure

A theoretical vibrational analysis of the radial breathing mode (RBM) of double-walled carbon nanotubes (DWCNTs) subjected to pressure is presented based on an elastic continuum model. The results agree with reported experimental results obtained under different conditions. Frequencies of the RBM in DWCNTs subjected to increasing pressure depend strongly on circumferential wave numbers, but weakly on the aspect ratio and axial half-wave numbers. For the inner and outer tubes of DWCNTs, the frequency of the RBM increases obviously as the pressure increases under different conditions. The range of variation is smaller for the inner tube than the outer tube.     

Curvature-induced metallization of double-walled semiconducting zigzag carbon nanotubes

We report total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled carbon nanotubes consisting of semiconducting (n,0) nanotubes. We find that optimum spacing between the walls of the nanotubes is slightly larger than the interlayer spacing of the graphite. We also find that the electronic structures of the double-walled nanotubes with the inner (7,0) nanotube are metallic with multicarrier characters in which electrons and holes exist on inner and outer nanotubes, respectively. Interwall spacing and curvature difference are found to be essential for the electron states around the Fermi level.     

Vibrational analysis of fluid-filled carbon nanotubes using the wave propagation approach

This paper presents a method for vibrational analysis of fluid-filled double-walled carbon nanotubes using the wave propagation approach. Simplified Flügge shell equations are proposed as the governing equations of vibration for the carbon nanotubes. The double-walled nanotubes are considered as a two-shell model coupled together through the van der Waals interaction between two adjacent nanotubes. Based on the proposed theoretical approach, we investigate the influences of parameters, such as fluid properties and vibrational modes, on the vibrational characteristics of carbon nanotubes. In this study, we consider the double-walled nanotubes with an inner diameter of 2.2 nm and an outer diameter of 3.0 nm. The theoretical investigation may give a useful reference for potential application and design of nanoelectronics and nanodevices. PACS 62.30.+d; 62.25.+g; 62.40.+I     

Nonlocal shear deformable shell model for thermal postbuckling of axially compressed double-walled carbon nanotubes

An investigation is reported of the thermal buckling and postbuckling of axially compressed double-walled carbon nanotubes (CNTs) subjected to a uniform temperature rise. The double-walled carbon nanotube is modeled as a nonlocal shear deformable cylindrical shell, which contains small-scale effects and van der Waals interaction forces. The governing equations are based on higher order shear deformation shell theory with a von Kármán–Donnell-type of kinematic nonlinearity and include thermal effects. Temperature-dependent material properties, which come from molecular dynamics (MD) simulations, and an initial point defect, which is simulated as a dimple on the tube wall, are both taken into account. The small-scale parameter, e ₀ a, is estimated by matching the buckling temperature of CNTs observed from the MD simulation results with the numerical results obtained from the nonlocal shear deformable shell model. The numerical illustrations concern the thermal postbuckling response of perfect and imperfect, single- and double-walled CNTs with different values of compressive load ratio. The results show that buckling temperature and postbuckling behavior of nanotubes are very sensitive to the small-scale parameter. The results reveal that temperature-dependent material properties have a significant effect on the thermal postbuckling behavior of both single- and double-walled CNTs.     

Nanotube nanoscience: A molecular-dynamics study

Carbon nanotubes, fullerenes, and other nanostructured carbon materials are now the most important material phases in the field of nanoscience and nanotechnology. We study the structural stabilities and the interconversion of carbon nanotubes and various other carbon nanostructured phases at elevated temperatures as well as under high pressure using the molecular dynamics method combined with a newly parametrized transferable tight-binding model. The model can deal with not only sp² and sp³ covalent bonds but also the interaction between sp² layers, which plays an important role in the structural and electronic properties of carbon nanostructured materials. It is found that, during a thermal transformation process of carbon nanotubes with C₆₀ fullerenes trapped inside into double-walled carbon nanotubes, the outer carbon-nanotube wall is chemically active and forms covalent bonds with inner carbon atoms, and that most vacancies on the initially imperfect outer tube wall are eventually filled with atoms migrated from inner fullerenes. It is also found that external pressure of about 20 GPa induces a variety of structural transformations in carbon nanostructures. On the other hand, pressure of 30 GPa or higher usually results in sp³-rich amorphous carbon materials. Finally, the rotational interlayer friction force in double-walled carbon nanotubes is studied for the system of (4,4)@(9,9), and the torque of the friction force per unit area acting on each nanotube of the system is found to be as small as . This small value indicates the importance of carbon nanostuctured materials not only for nanoelectronics but also for nanometer-scale machines in the future.     

Carbon nanotube film synthesized from ethanol and its oxidation behavior in air

In this paper, we propose an efficient way to synthesize carbon nanotube films using ferrocene and ethanol. The as-grown film is free-standing, semi-transparent, and of macro scale size. The tubes in the film are mostly singleor double-walled. The oxidation behavior of the film is studied via Raman spectroscopy, and the result indicates that the inner wall of the double-walled tube is effectively protected from oxidation by the outer wall.     

螺旋上升对自激发锯齿型双壁碳纳米管振荡行为的影响

运用分子动力学方法模拟了锯齿型双壁碳纳米管体系的振荡行为,其中旋转的内管施加了不同大小的螺旋上升长度.不同于以前关于扶手椅型碳纳米管的工作(Zeng Y H,et al.2016 Nanotechnology 27 95705),锯齿型的内管在施加了不同大小的螺旋上升长度之后,其管壁结构会产生畸变或缺陷.模拟过程中,锯齿型内管在施加一定的旋转速度以后保持自由,而固定的外管为无任何缺陷的理想锯齿型碳纳米管.分子动力学模拟结果显示锯齿型内管的轴向振荡行为与内管施加的螺旋上升长度密切相关.内管的振荡频率随着内管螺旋上升长度的增加而增加.但当内管的螺旋上升长度较大时,由于螺旋上升所引起的内管缺陷结构造成整个内管的破裂,从而导致其无法进行稳定的轴向振荡.模拟结果还显示,对于无螺旋上升的理想锯齿型碳管,虽然其轴向振荡效果非常微弱,但却可以作为一种具有恒定旋转频率的旋转致动器.此外,对螺旋上升长度为0.5 nm的内管在不同温度下的振荡性能进行了模拟分析,结果表明内管振荡的幅度随温度的升高而相应地增加,但当温度超过一定的临界值后,内管不能保持稳定的振荡.     

Vibrational analysis of double-walled carbon nanotubes with inner and outer nanotubes of different lengths

In this study, the Euler-Bernoulli beam model is used to analyze the resonant vibration of double-walled carbon nanotubes (DWCNTs) with inner and outer nanotubes of different lengths. The resonant properties of DWCNTs with different inner and outer nanotube lengths are investigated in detail using this theoretical approach. The resonant vibration is significantly affected by the vibrational modes of the DWCNTs, and by the lengths of the inner and outer nanotubes. For an inner or outer nanotube of constant length, the vibrational frequencies of the DWCNTs increase initially and then decrease as the length of another nanotube increases. A design for nanoelectromechanical devices that operate at various frequencies can be realized by controlling the length of the inner and outer nanotubes of DWCNTs. This investigation may be helpful in applications of carbon nanotubes such as high frequency oscillators, dynamic mechanical analysis and mechanical sensors.     

4A碳纳米管及相关结构的嵌锂特性(英文)

碳纳米管独特的一维结构和强烈的卷曲效应为外来原子提供了理想的嵌入通道。本文全面总结了近年来我们对直径仅为4A的三种单壁碳纳米管嵌锂特性的密度泛函研究工作。我们具体讨论了体系嵌锂后的结构、能量、电子、电化学等特性。由于这些超小直径的碳纳米管最初合成于沸石晶体的纳米管道,我们也讨论了碳纳米管?沸石晶体复合体系的嵌锂特性。另外,我们还研究了由(5,0)和(14,0)碳纳米管组成的双壁碳纳米管体系的嵌锂特性。我们的理论计算表明,超小直径碳纳米管及相关结构作为锂离子电池负极材料具有很好的应用前景。     

多壁碳纳米管储氢的物理吸附特性

采用巨正则蒙特卡罗方法 ,模拟常温、1 0MPa下氢在扶手椅型多壁壁碳纳米管中的物理吸附过程 .氢分子之间、氢分子与碳原子之间的相互作用采用Lennard Jones势能模型 .研究了双壁碳纳米管外 (内 )径固定而内 (外 )径改变时的物理吸附储氢情况 ,发现氢分子主要储存在双壁碳纳米管的管壁附近 ,当双壁碳纳米管的内外管壁间距由 0 .34nm增大到 0 .6 1或 0 .88nm时可有效增加物理吸附储氢量 ,并给出了相应的理论解释 .在此基础上 ,计算了管壁间距为 0 .34、0 .6 1和 0 .88nm时的三壁碳纳米管的物理吸附储氢量 ,并与相同条件下单壁和双壁碳纳米管的物理吸附储氢量作了比较 ,发现多壁碳纳米管的物理吸附储氢量随碳管层数的增加而减小 .     

Gate-dependent magnetoresistance phenomena in carbon nanotubes

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under a magnetic field as large as 50 T. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidence for unconventional magnetoresistance is presented and interpreted by means of theoretical calculations.