  Exposing single-walled carbon nanotubes to room temperature UV-generated
ozone leads to an irreversible increase in their electrical resistance. We
demonstrate that the increased resistance is due to ozone oxidation on the
sidewalls of the nanotubes rather than at the end caps. Raman and x-ray
photoelectron spectroscopy show an increase in the defect density due to the
oxidation of the nanotubes. Using ultraviolet photoelectron spectroscopy we
show that these defects represent the removal of pi-conjugated electron states
near the Fermi level, leading to the observed increase in electrical
resistance. Oxidation of carbon nanotubes is an important first step in many
chemical functionalization processes. Since the oxidation rate is controllable
with short exposures, UV-generated ozone offers the potential for use as a
low-thermal budget processing tool.
