Carbon nanotubes and their interaction with the surface of diamond

Abstract

Calculations based on density-functional theory have been used to model armchair carbon nanotubes existing in isolation, close-packed into nanoropes, and lying prone on both the hydrogen-terminated and clean (001) surfaces of diamond. In the combined nanotube:diamond systems, the electronic band structures are indicative of electron transfer from the hydrogen-terminated diamond to the physisorbed nanotubes; that is, carbon nanotubes---like ${\mathrm{C}}_{60}$---appear to be capable of transfer doping diamond $p$ type. Total-energy comparisons with separated systems suggest that the nanotubes are positively bound to the diamond substrate. Diffusion techniques have been used to model movement of the (7,7) nanotube across the hydrogen-terminated diamond surface, with the results suggesting that this substrate presents a rather smooth energy surface to the nanotube; this is consistent with the fact that no covalent bonding across the interface has been found. For comparison, the same nanotube has been modeled above a completely clean diamond (001) surface, and while the nanotube remains bound to the diamond substrate, there is no charge transfer across such an interface.