Effects of tube diameter, external pressure and boron-nitrogen doping on electronic structures of single-walled carbon nanotubes

Abstract

Electronic band structures of zigzag and armchair single-walled carbon nanotube (SWCNT) with tube diameter from 3-10 Å were investigated by density function theory with numerical basis set. The periodic boundary condition was implemented for all calculations. The electronic properties depend on chiral vectors and tube diameters. The dependence of SWCNTs band gap energy on tube diameters shows the maximum at certain tube diameter. The band gap energy converges to a particular values at large diameter. Band gap energies of (3i+1) and (3i+2) zigzag SWCNTs seems to converge to the same values at large diameter. Their band gap energies vary inversely with tube diameter, whereas those of armchair SWCNT vary inversely with (tube diameter)2. Zigzag (8,0) and armchair (5,5) SWCNTs were used to investigate the effect of boron and nitrogen (B-N) doping. The electronic band structures of B-N doped SWCNTs change with the position of doping only on the XY plane for zigzag SWCNTs while it depends on both of XY plane and Z axis for armchair SWCNTs. The favorable B-N doping position on SWCNTs is that with the smallest B-N distance in singlet spin state. Electronic band structures of undoped and B-N doped zigzag (8,0) and armchair (5,5) SWCNT were also calculated at various strain ratio (?) to investigate the effect of external pressure. The change in band gap energies at various strain conditions has been observed. The B-N doping has almost no effect on Young's modulus, and its magnitude remains in the order of TPa. For zigzag SWCNTs, external pressure with both positive and negative strain ratios could reduce its band gap energy whereas no regular patterns are observed for armchair SWCNTs. This understanding could be applied for selection of appropriate SWCNTs which could be useful for electronic devices application.