Optical Band Gap Energies in Quasi-Metal Carbon Nanotubes

Abstract

The structure of carbon nanotubes is described by two positive integers (n₁, n₂). The π-electron model of the nanotube band structure predicts that when the difference n₁–n₂ is multiple of three, the energy gap between the valence and conduction bands vanishes so that such tubes should exhibit quasi-metal properties. The band structure of 50 chiral and achiral (n₁, n₂) nanotubes with 4 ≤ n₁ ≤ 18 and n₂ = n₁–3q has been calculated by the linearized augmented cylindrical wave method. Nanotubes have been identified for which the optical band gaps are in the terahertz range (1–40 meV) and which can be used for design of emitters, detectors, multipliers, antennas, transistors, and other nanoelements operating in the high-frequency range.