An ab initio study of the electronic properties of carbon nanotubes activated by hydrogen-passivated vacancies

The effect of multi-vacancies on the electronic structure of semiconducting carbon nanotubes is studied using the ab initio pseudopotential density-functional method. The di-vacancy is found particularly effective in changing the band gap of the semiconducting nanotubes, while mono-, tri-, or tetra-vacancies introduce gap-states. A significant modulation of band gap is observed for a certain type of zigzag nanotube upon varying concentration of di-vacancy. The hydrogen passivation is found critical for stabilizing the vacancies. Based on present calculations, a conceptual model is proposed for semiconductor–semiconductor junctions that do not involve the chirality change of the tube.