  The electrical transport properties of anodically grown TiO2 nanotubes was
investigated. Amorphous nanotubes were anodically grown on titanium foil and
transformed through annealing into the anatase phase. Amorphous and
polycrystalline single nanotubes were isolated and contacted for measurements
of the electrical resistance. Non-linear current-voltage characteristics were
explained using the fluctuation induced tunneling conduction model. A clear
enhancement of the conductance was induced in an insulating anatase nanotube
through low-energy Ar/H ion irradiation. Confocal Raman spectroscopy shows that
the annealed samples were in anatase phase and a blueshift due to phonon
confinement was observed.
