B/N pair and Si doped ultra-small-diameter single-walled carbon nanotubes: a density functional theory study

The structures and electronic properties of Si-doped ultra-small-diameter single-wall carbon nanotubes (SWCNTs) are studied through the first principle calculations based on density functional theory. To investigate their structural properties, a detailed calculation of bond length is performed for Si-doped (3, 3) armchair and (5, 0) zigzag nanotubes. The total energy and the formation energy show us that the doping configurations are energetically stable structures. The results reveal that Si-doped metallic carbon nanotubes can open their band gap, converting them into semiconductors. In addition, we also discuss the electronic structures of Si and B/N co-doped SWCNTs. B/N pair doping SWCNTs, in which Si has been doped, can increase or decrease their band gaps. For doping atoms, the band gap increases the closer they get to the vertical direction of the nanotube axis. (paper)