Chapter 5 - Electronic Structures of Single-Walled Carbon Nanotubes

Abstract

This chapter summarizes the results of detailed research on the realistic electronic structure of single-walled CNT (SWCNT), with explicit consideration of carbon-carbon bond-alternation patterns accompanied by the metal-insulator transition inherent in low-dimensional materials including CNT. It has been shown that armchair-structural tubes (a, a) probably remain metallic after energetical stabilization in connection with the metal-insulator transition but that zigzag (3a, 0) and helical-structural tubes (a, b) change into semiconductive even if the condition 2a + b = 3N is satisfied. There is no so much difference in the electronic structures between MWCNT and SWCNT and these are regarded electronically similar at least in the zeroth order approximation. Doping to CNT with either Lewis acid or base would cause intriguing electronic properties including superconductivity. Studies on the electronic structure of carbon nanotube (CNT) are of much importance toward its efficient utilization in electronic devices. It is well known that the early prediction of its peculiar electronic structure right after the lijima's observation of multiwalled CNT (MWCNT) seems to have actually triggered the subsequent and explosive series of experimental researches of CNT. In that prediction, alternative appearance of metallic and semiconductive nature in CNT depending on the combination of diameter and pitch or, more specifically, chiral vector of CNT expressed by two kinds of non-negative integers (a, b) is described.