Vacancy complexes in carbon and boron nitride nanotubes

Abstract

The effect of divacancies on the stability, structural and electronic properties of carbon and boron nitride nanotubes is studied using the ab initio density functional method. VBBN is more stable in the boron-rich and less stable in the nitrogen-rich growth conditions, and VNNB is more stable in the nitrogen-rich than in the boron-rich conditions. We find that stoichiometric defects VBVN, VBCN and VNCB are stable in both the boron and nitrogen rich environments. The relaxation energy in the VCVC is lower in the armchair than in the zig-zag and the opposite trend is seen for VCBC and VCNC. The divacancy is found to be particularly effective in changing the band gap of the semiconducting nanotubes due to the appearance of additional energy levels within the band gap region. For the zig-zag systems, we observe a drastic reduction of the band gap in VBBN, VNNB and VNCB and a complete removal of the band gap in VBVN and VBCN, negating the semiconducting behaviour of the nanotube.