Quantum Transport and Interaction in Carbon Nanotubes

被称为碳纳米管(CN)的石墨针是最近发现的，并已成为广泛研究的主题。CN是几个同心的二维(2D)石墨管，由碳原子六边形组成，绕轴螺旋排列。CN的直径通常在20~300Å之间，长度可超过1μm，相邻的片层或壁层之间的距离大于石墨片中最近邻原子之间的距离，因此CN的电学性质由单层CN的电学性质决定。这个项目的目的是从理论上研究碳纳米管的电子和输运性质。碳纳米管可以是金属或半导体，取决于它们的直径和螺旋排列。根据二维石墨片的能带结构和沿圆周方向的周期性边界条件，可以得到CN是金属的还是半导体型的条件。这一结果首先是通过忽略管曲率影响的紧束缚模型来预测的。这些性质可以在kp方法或有效质量近似下很好地再现。事实上，有效质量方案已经被成功地用于研究CN的各种电子性质。在这个项目中，我们基于紧束缚模型结合k-p方法讨论了纳米管的输运性质。研究了杂质散射的影响，指出除了势能范围小于晶格常数的散射体外，完全没有后向散射。预测了存在晶格空位时的电导量子化，即强散射体和短程散射体。通过一对拓扑缺陷，如五元环和七元环，不同直径的纳米管的输运也被阐明。

Graphite needles called carbon nanotubes (CN's) were discovered recently and have been a subject of an extensive study. A CN is a few concentric tubes of two-dimensional (2D) graphite consisting of carbon-atom hexagons arranged in a helical fashion about the axis. The diameter of CN's is usually between 20 and 300 Å and their length can exceed 1μm. The distance of adjacent sheets or walls is larger than the distance between nearest neighbor atoms in a graphite sheet and therefore electronic properties of CN's are dominatecl by those of a single layer CN.A single-wall nanotubes are produced in a form of ropes. The purpose of this project is to study electronic and transport properties of carbon nanotubes theoretically.Carbon nanotubes can be either a metal or semiconductor, depending on their diameters and helical arrangement. The condition whether a CN is metallic or semi-conducting can be obtained based on the band structure of a 2D graphite sheet and periodic boundary conditions along the circumference direction. This result was first predicted by means of a tight-binding model ignoring the effect of the tube curvatureThese properties can be well reproduced in a k p method or an effective-mass approximation. In fact, the effective-mass scheme has been used successfully in the study of wide varieties of electronic properties of CN.In this project we have discussed transport properties of nanotubes based on the k p method combined with a tight-binding model. Effects of impurity scattering have been studied and the total absence of backward scattering has been pointed out except for scatterers with a potential range smaller than the lattice constant. The conductance quantization in the presence of lattice vacancies, i.e., strong and short-range scatterers, has been predicted. The transport across a junction of nanotubes with different diameters through a pair of topological defects such as five-and seven-membered rings has also been clarified.