Effects of gas adsorption and collisions on electrical transport in single-walled carbon nanotubes

Degassing of bundles of single-walled carbon nanotubes in vacuum at 500 K is found to drive the thermoelectricpower (TEP) strongly negative, indicating that the degassed metallic tubes in a bundle are n type. The magnitude of the negative TEP indicates that important asymmetry in the electronic carbon pi bands exists near the Fermi energy. Easily measurable increases in the TEP (similar to 5-19 mu V/K) and resistivity (2%-10%) are observed at 500 K upon exposure to N-2 and He, suggesting that even gas collisions with the nanotube wall can contribute significantly to the transport properties.