GEOMETRIC BOUNDARY EFFECTS ON THE ELECTRONIC-PROPERTIES OF FINITE CARBON NANOTUBES

Quantum finite-size effects in carbon nanotubes are studied as a funct ion of tube length L and of the type of end structure used to terminat e the tube. The ''end'' structures considered are: tori, open tubes te rminated with H atoms, and various caps formed from hemispherical piec es of fullerenes. With different geometric boundaries there arise dist inct asymptotic band-gap behaviors as a function of L: damped oscillat ions decaying as 1/L, monotonic 1/L decay, exponentially decaying, and constant. These asymptotic scaling behaviors are categorized and expl ained in terms of general characteristics of the frontier orbitals. Im plications for nanoscale devices are briefly discussed. (C) 1997 Elsev ier Science Ltd.