Re-entrant semiconducting behavior of zigzag carbon nanotubes at substitutional doping by oxygen dimers
Seung-Hoon Jhi
Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
The electronic structures of carbon nanotubes doped with oxygen dimers are studied using the pseudopotential density functional method. The fundamental energy gap of zigzag semiconducting nanotubes shows a strong dependence on the concentration and configuration of oxygen dimer defects that substitute for carbon atoms in the tubes as well as on tube chiral index. For a certain type of zigzag nanotubes, the energy gap is closed and the tubes become semimetallic when doped with oxygen dimers. At higher oxygen-dimer concentrations the gap reopens, and the tubes exhibit semiconducting behavior again. The change of band gap of the zigzag tubes is understood in the frame of their response to the strains caused by the dimer substitutional doping.