Ballistic transport in metallic nanotubes with reliable Pd ohmic contacts

Contacting metallic single-walled carbon nanotubes by palladium (Pd) affords highly reproducible ohmic contacts and allows for the detailed elucidation of ballistic transport in metallic nanotubes. The Pd ohmic contacts are more reliable than the titanium (Ti) previously used for ballistic nanotube devices. In contrast, Pt contacts appear to give nonohmic contacts to metallic nanotubes. For both ohmic and nonohmic contacts, the length of the nanotube under the metal contact area is electrically turned off. Transport occurs from metal to nanotube at the edges of the contacts. Measurements with large numbers of Pd-contacted nanotube samples reveal that the mean free path for defect scattering in SWNTs grown by chemical vapor deposition can be up to 4 mum. The mean free paths for acoustic phonon scattering are on the order of 500 nm at room temperature and much greater than4 mum at low temperatures.