When double-wall carbon nanotubes can become metallic or semiconducting

Abstract

The electronic properties of double-wall carbon nanotubes (DWCNTs) are investigated viadensity functional theory. The DWCNTs are separated into four categories wherein theinner–outer nanotubes are metal–metal, metal–semiconductor, semiconductor–metaland semiconductor–semiconductor single-wall nanotubes. The band structure ofthe DWCNTs, the local density of states of the inner and outer nanotubes, andthe total density of states are calculated. We found that for the metal–metalDWCNTs, the inner and outer nanotubes remain metallic for different distancesbetween the walls, while for the metal–semiconductor DWCNTs, decreasing thedistance between the walls leads to a phase transition in which both nanotubesbecome metallic. In the case of semiconductor–metal DWCNTs, it is found that atsome distance the inner wall becomes metallic, while the outer wall becomes asemiconductor, and if the distance is decreased, both walls become metallic. Finally, in thesemiconductor–semiconductor DWCNTs, if the two walls are far from each other, thenthe whole DWCNT and both walls remain semiconducting. By decreasing thewall distance, first the inner, and then the outer, nanotube becomes metallic.