Atomic restructuring and localized electron states in a bent carbon nanotube: A first-principles study

We apply first-principles calculations to study structural and electronic p roperties of a semiconductor carbon nanotube bent to a large angle. The geo metry optimization results in fourfold carbon rings at the bend region. The se fourfold rings, seldomly seen in carbon structures, result from the coll apse of carbon hexagons at the most stressed region of the bend. Part of th e atoms at the fourfold rings are also fourfold coordinated, which indicate s a strong sp(3) character. Localized electron states are found at the bend region, making the bent tube behave as a quantum dot. This bending-induced quantum dot can be charged with one electron or one hole at most.