Annealing effects on the photoresponse of TiO2 nanotubes

The present work investigates the influence of different annealing treatments on the photoresponse of electrochemically formed TiO2 nanotubes. The "as prepared" TiO2 nanotube layers have an amorphous structure and show a comparably low photocurrent magnitude. Annealing the tubes in air or dry Ar at 450 degrees C converts the structure to anatase and increases strongly the photocurrent conversion efficiencies. Significant differences between annealing in air and in dry Ar were found. Annealing in Ar results in green layers that show lower photon to current efficiencies than the layers annealed in air. Extended annealing in Ar at 450 degrees C leads to morphological changes of the nanotube structure. These differences in the behaviour (photoresponse and mechanical stability) are attributed to the reductive nature of the Ar environment (leading to a partial reduction and vacancy formation). (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.