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 i s found to drive the thermoelectricpower (TEP) strongly negative, indicatin g that the degassed metallic tubes in a bundle are n type. The magnitude of the negative TEP indicates that important asymmetry in the electronic carb on pi bands exists near the Fermi energy. Easily measurable increases in th e 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 th e nanotube wall can contribute significantly to the transport properties.