Synthesis and variable temperature electrical conductivity studies of highly ordered TiO2 nanotubes

Rafts of aligned, high aspect ratio TiO2 nanotubes were fabricated by an electrochemical anodization method and their axial electrical conductivities were determined over the temperature range 225-400 A degrees C. Length, outer diameter, and wall thickness of the nanotubes were approximately 60-80 mu m, 160 nm, and 30 nm, respectively. Transmission electron microscopy studies confirmed that the TiO2 nanotubes were initially amorphous, and became polycrystalline anatase after heat treatment at temperatures as low as 250 A degrees C in air. The activation energy for conductivity over the temperature range 250-350 A degrees C was found to be 0.87 eV. The conductivity values are comparable to those of nanocrystalline and nanoporous anatase thin films reported in literature.