Modification of the electronic structure of a carbon nanotube, induced by vacancy-related defects, was studied using first-principles calculations. Three defect configurations which were likely to occur in semiconducting carbon nanotubes were considered. A vacancy-adatom complex was found to produce a pair of localized states deep inside the energy gap. A pentagon-octagon-pentagon topological defect produced by the divacancy was structurally stable and gave rise to an unoccupied localized state in the gap. Also considered was the nature of partially occupied localized states produced by a substitutional impurity plus a monovacancy.

Deep Levels in the Band Gap of the Carbon Nanotube with Vacancy-Related Defects. G.Kim, B.W.Jeong, J.Ihm: Applied Physics Letters, 2006, 88[19], 193107