Single Particle Transport Through Carbon Nanotube Wires: Effect of Defects and Polyhedral Cap
The ability to manipulate carbon nanotubes with increasing precision has enabled a large number of successful electron transport experiments. These studies have primarily focussed on characterizing transport through both metallic and semiconducting wires. Tans et al. demonstrated ballistic transport in single-wall nanotubes for the first time, although the experimental configuration incurred large contact resistance. Subsequently, methods of producing low contact resistances have been developed and two terminal conductances smaller than 50 k-ohms have been repeatably demonstrated in single-wall and multi-wall nanotubes. In multi-wall nanotubes, Frank et al. demonstrated a resistance of approximately h/2e(exp 2) in a configuration where the outermost layer made contact to a liquid metal. This was followed by the work of de Pablo et al. where a resistance of h(bar)/27e(exp 2) (approximately 478 ohms) was measured in a configuration where electrical contact was made to many layers of a multi-wall nanotube. Frank et al. and Pablo et al. note that each conducting layer contributes a conductance of only 2e(exp 2)/h, instead of the 4e(exp 2)/h that a single particle mode counting picture yields. These small resistances have been obtained in microns long nanotubes, making them the best conducting molecular wires to date. The large conductance of nanotube wires stems from the fact that the crossing bands of nanotubes are robust to defect scattering.