Effect of Annealing on the Nb-Doped TiO2 Films Prepared by DC/RF Cosputtering

Abstract

Nb-doped titanium oxide thin films were deposited on glass by dc/radio-frequency (dc/rf) magnetron cosputtering, in which dc and rf were utilized for Ti and Nb targets, respectively. The coated samples were postannealed at temperatures ranging from 473 to for in ambient air. Glancing incidence X-ray diffraction revealed a polycrystalline phase for the Nb-doped films postannealed at , in contrast to the undoped one that has to be annealed at , indicating that Nb dopant can enhance the crystallization of amorphous . Furthermore, the as-deposited -doped film postannealed at was found to have an anatase-dominated phase with a fine-grain microstructure observed by transmission electron microscopy. Heat-treatment also induces a change in the surface morphology of the films examined by field-emission scanning electron microscopy. The optical properties of the films were characterized by UV/visible spectrophotometry. The average transmittance of the films is higher than 85%, and a small absorbance zone occurs in the visible region. Under visible light irradiation, all the Nb-doped films exhibit better photocatalytic activity than that of undoped ones. Among them, the Nb-doped film annealed at shows the best photocatalytic performance.