Abstract Submitted to the NANOTUBE-99 Workshop:

The tip of a carbon nanotube can either be open or capped. Methods of constructing polyhedral caps have been suggested and there has been recent evidence for the existence of capped nanotubes. Characteristic features of electron flow through nanotubes is of relevance to both molecular electronics and experiments using nanotubes tips as a probe. To the best of our knowledge, there have been no studies of electron transmission through a nanotube cap, although there have been studies of the local density of states in a capped nanotube. In this talk, we calculate electron transmission between polyhedrally capped carbon nanotubes and a substrate. The main issues we address are:
(a) The relationship between local density of states and transmission probability through cap atoms.
(b) The effect of localized discrete energy levels in the cap. For a capped carbon nanotube that is not connected to a substrate, the localized states do not couple to the coexisting continuum states. However, close proximity of a substrate causes hybridization between these groups of states. As a result, new transmission paths open from substrate states to nanotube continuum states via the localized states in the cap. We show that the interference between various paths gives rise to transmission antiresonances with the minimum equal to zero at the energy of the localized state.
(c) The effect of defects on tunnel current or transmission. The presence of defects that are located close to the cap transforms antiresonances into resonances. Depending on the spatial position of defects, these resonant states are capable of carrying a large current.

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