单壁纳米管的弹性性质

基于第一性原理计算了一系列单壁碳纳米管(椅型、锯齿型)和氮化硼锯齿型纳米管的杨氏模量.用实际的数值结果显示了杨氏模量与纳米管管径之间的依赖关系.还讨论了各类纳米管卷曲形变能以及平衡基矢长度a随管型的变化. 关键词： 单壁纳米管 平衡基矢长度 杨氏模量 形变能     

Elastic properties of single-wall nanotubes

3 , BC₂N, and C₃N₄. These studies have been carried out using a total-energy, non-orthogonal, tight-binding parametrisation which is shown to provide results in good agreement both with calculations using higher levels of theory and the available experimental data. Our results predict that of all types of nanotubes considered, carbon nanotubes have the highest Young’s modulus. We have considered tubes of different diameters, ranging from 0.5 to 2 nm, and find that in the limit of large diameters the mechanical properties of nanotubes approach those of the corresponding flat graphene-like sheets. Received: 30 November 1998 / Accepted: 14 December 1998     

Magnetic fullerenes inside single-wall carbon nanotubes

C(59)N magnetic fullerenes were formed inside single-wall carbon nanotubes by vacuum annealing functionalized C(59)N molecules encapsulated inside the tubes. A hindered, anisotropic rotation of C(59)N was deduced from the temperature dependence of the electron spin resonance spectra near room temperature. Shortening of the spin-lattice relaxation time T(1) of C(59)N indicates a reversible charge transfer toward the host nanotubes above approximately 350 K. Bound C(59)N-C(60) heterodimers are formed at lower temperatures when C(60) is coencapsulated with the functionalized C(59)N. In the 10-300 K range, T(1) of the heterodimer shows a relaxation dominated by the conduction electrons on the nanotubes.     

Measuring the uniaxial strain of individual single-wall carbon nanotubes: resonance Raman spectra of atomic-force-microscope modified single-wall nanotubes

Raman spectroscopy is used to measure the strain in individual single-wall carbon nanotubes, strained by manipulation with an atomic-force-microscope tip. Under strains varying from 0.06%-1.65%, the in-plane vibrational mode frequencies are lowered by as much as 1.5% (40 cm(-1)), while the radial breathing mode (RBM) remains unchanged. The RBM Stokes/anti-Stokes intensity ratio remains unchanged under strain. The elasticity of these strain deformations is demonstrated as the down-shifted Raman modes resume their prestrain frequencies after a nanotube is broken under excessive strain.     

High-field electrical transport in single-wall carbon nanotubes

Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10(9) A/cm(2). As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.     

Electron transport in armchair single-wall carbon nanotubes

The rates of electron scattering via phonons in the armchair single-wall carbon nanotubes were calculated by using the improved scattering theory within the tight-binding approximation. Therefore, the problem connected with the discrepancy of the scattering rates calculated in the framework of the classical scattering theory and ones predicted by experimental data was clarified. Then these results were used for the solving of the kinetic Boltzmann equation to describe electron transport properties of the nanotubes. The equation was solved numerically by using both the finite difference approach and the Monte Carlo simulation procedure.     

Ultrafast carrier dynamics in single-wall carbon nanotubes

Time-resolved carrier dynamics in single-wall carbon nanotubes is investigated by means of two-color pump-probe experiments. The recombination dynamics is monitored by probing the transient photobleaching observed on the interband transitions of the semiconducting tubes. This dynamics takes place on a 1 ps time scale which is 1 order of magnitude slower than in graphite. Transient photoinduced absorption is observed for nonresonant probing and is interpreted as a global redshift of the pi-plasmon resonance. We show that the opening of the band gap in semiconducting carbon nanotubes determines the nonlinear response dynamics over the whole visible and near-infrared spectrum.     

单壁碳纳米管中电子的有效质量

解析研究了单壁碳纳米管中电子的有效质量，以及导带底的电子有效质量与其管径和螺旋度的关系.结果表明，单壁碳纳米管的几何结构对其电子有效质量有重要的影响.特别是锯齿形窄隙半导体管，发现其导带底的电子有效质量与管径的平方成反比. 关键词： 单壁碳纳米管 电子有效质量     

Four-point resistance of individual single-wall carbon nanotubes

We have studied the resistance of single-wall carbon nanotubes measured in a four-point configuration with noninvasive voltage electrodes. The voltage drop is detected using multiwalled carbon nanotubes while the current is injected through nanofabricated Au electrodes. The resistance at room temperature is shown to be linear with the length as expected for a classical resistor. This changes at cryogenic temperature; the four-point resistance then depends on the resistance at the Au-tube interfaces and can even become negative due to quantum-interference effects.     

Dielectric response of aligned semiconducting single-wall nanotubes

We report measurements of the full intrinsic optical anisotropy of isolated single-wall carbon nanotubes (SWNTs). By combining absorption spectroscopy with transmission ellipsometry and polarization-dependent resonant Raman scattering, we obtain the real and imaginary parts of the SWNT permittivity from aligned semiconducting SWNTs dispersed in stretched polymer films. Our results are in agreement with theoretical predictions, highlighting the limited polarizability of excitons in a quasi-1D system.     

Electronic transport properties of single-wall boron nanotubes

Electronic transport properties of single-wall boron nanotube(BNT) with different chiralities, diameters, some of which are encapsulated with silicon, germanium, and boron nanowires are theoretically studied. The results indicate that the zigzag(3, 3) BNT has more electronic transmission channels than the armchair(5, 0) BNT because of its unique structure distortion. Nanowires encapsulated in the BNT can enhance the conductance of the BNT to some extent by providing a significant electronic transmission channel to the BNT. The effect of the structure of nanowires and the diameter of BNTs on the transport properties has also been discussed. The results of this paper can enrich the knowledge of the electron transport of the BNT and provide theoretical guidance for subsequent experimental study.     

非共振条件下单壁碳纳米管拉曼散射强度的计算

利用非共振情况下的键极化模型理论，对单壁碳纳米管的拉曼光谱强度进行了研究.考察了碳纳米管结构、入射光和散射光的偏振方向以及管轴的取向对散射光强度的影响.计算结果表明，光的偏振方向对拉曼散射强度影响较大，而手性对拉曼光谱的影响较小.针对碳管样品的实际情况，给出了无规取向碳管的拉曼散射光谱. 关键词： 碳纳米管 拉曼散射 声子 键极化     

功能化单壁碳纳米管的热导率

采用基于BrennerⅡ势的非平衡态分子动力学方法，模拟研究了300K温度下经氢化学修饰的(10,0)单壁碳纳米管的热导率.研究显示功能化后碳管的热导率有明显减小，当有一列碳原子被氢化后（功能化程度为5%），碳管的热导率减小了大约1/3，为了进一步解释这种功能化对碳纳米管热导率的影响，计算了不同功能化程度下碳纳米管的声子谱.     

Optical transitions in single-wall boron nitride nanotubes

Optical transitions in single-wall boron nitride nanotubes are investigated by means of optical absorption spectroscopy. Three absorption lines are observed. Two of them (at 4.45 and 5.5 eV) result from the quantification involved by the rolling up of the hexagonal boron nitride (h-BN) sheet. The nature of these lines is discussed, and two interpretations are proposed. A comparison with single-wall carbon nanotubes leads one to interpret these lines as transitions between pairs of van Hove singularities in the one-dimensional density of states of boron nitride single-wall nanotubes. But the confinement energy due to the rolling up of the h-BN sheet cannot explain a gap width of the boron nitride nanotubes below the h-BN gap. The low energy line is then attributed to the existence of a Frenkel exciton with a binding energy in the 1 eV range.     

功能化单壁碳纳米管的热导率

采用基于BrennerⅡ势的非平衡态分子动力学方法,模拟研究了300K温度下经氢化学修饰的(10,0)单壁碳纳米管的热导率.研究显示功能化后碳管的热导率有明显减小,当有一列碳原子被氢化后（功能化程度为5%）,碳管的热导率减小了大约1/3,为了进一步解释这种功能化对碳纳米管热导率的影响,计算了不同功能化程度下碳纳米管的声子谱.     

Channeling in single-wall nanotubes: Possible applications

The relevant potentials are calculated and used to investigate the trajectories and various characteristics of axial channeling of high-energy positively charged particles in the recently discovered single-wall nanotubes (SWNTs). The application of SWNTs in high-energy physics, specifically, in future colliders, is discussed, in view of the fact that the dechanneling length in SWNTs is much longer than in single crystals. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 304–307 (10 September 1997)     

Chromatographic size separation of single-wall carbon nanotubes

Received: 18 May 1998/Accepted: 22 May 1998     

Phonon density of states of single-wall carbon nanotubes

The vibrational density of states of single-wall carbon nanotubes (SWNT) was obtained from inelastic neutron scattering data from 0 to 225 meV. The spectrum is similar to that of graphite above 40 meV, while intratube features are clearly observed at 22 and 36 meV. An unusual energy dependence below 10 meV is assigned to contributions from intertube modes in the 2D triangular lattice of SWNT bundles, and from intertube coupling to intratube excitations. Good agreement between experiment and a calculated density of states for the SWNT lattice is found over the entire energy range.     

Structure and thermophysical properties of single-wall Si nanotubes

In this work, molecular dynamics (MD) simulation based on the environment-dependent interatomic potential is carried out to explore the structure, atomic energy distribution, and thermophysical properties of single-wall Si nanotubes (SWSNTs). The unique structure of SWSNTs leads to a wider range energy distribution than crystal Si (c-Si), and results in a bond order in the range of 4.8–5. The thermal conductivity of SWSNTs is much smaller than that of bulk Si, and shows significantly slower change with their characteristic size than that of Si films. Out of the three types of SWSNTs studied in this work, pentagonal SWSNTs have the highest thermal conductivity while hexagonal SWSNTs have the lowest one. The specific heat of SWSNTs is a little larger than that of bulk c-Si. Pentagonal and hexagonal SWSNTs have close specific heats, which are a little larger than that of rectangular SWSNTs.