Electronic structure and localized states at carbon nanotube tips

Topology related changes in the local density of states near the ends of closed carbon nanotubes are investigated using spatially resolved scanning tunneling spectroscopy and tight binding calculations. Sharp resonant valence band states are observed in the experiment at the tube ends, dominating the valence band edge and filling the band gap. Calculations show that the strength and position of these states with respect to the Fermi level depend sensitively on the relative positions of pentagons and their degree of confinement at the tube ends.