Electronic structures and transport properties of carbon nanotube

Abstract

The electronic structure of carbon nanotube (CN) (5, 5) with a finite length is studied on the basis of Hückel molecular orbital (HMO) method. Highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap oscillates and decreases as the length l of tube increases, where l is the number of cis-polyene rings of the circumference of CN. For tube (5, 5, l) without a cap the gap vanishes at l=3 n+1, where n is a positive integer. On the other hand, the minimum appears at l=3 n for capped tube (5, 5, l). The band gap oscillates with the periodicity of 3 for either capped one or one without a cap. Such behaviors are similar to the one-dimensional (1-D) graphite systems starting from polyphenanthrene. The electronic structures of porous CNs, nanotubes perforated periodically on the cylindrical surface, are studied on the basis of the tight-binding model within the Hückel approximation. Depending on the pitch and the helicity, various band structures appear in porous nanotube with two atoms taken away from the unit cell. Completely flat band also appear in some cases. In those systems flat band ferromagnetism could be expected. Perforation enables us to control the electronic structure of nanotube.