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

Abstract

Sn-doped titanium oxide thin films were deposited on glass by dc/radio frequency (rf) magnetron cosputtering, in which dc and rf were utilized for and Sn targets, respectively. The samples were postannealed from 400 to for in ambient air. Glancing incidence X-ray diffraction revealed an amorphous phase in the as-deposited films and a polycrystalline phase for films postannealed at temperatures higher than . Furthermore, the film postannealed at was found to have anatase/rutile duplex phases with a fine grain microstructure and amorphous structure by using transmission electron microscopy. The heat-treatment also induces a change in the surface morphology of the Sn-doped thin films observed by field-emission scanning electron microscopy. The optical properties of the Sn-doped thin films were characterized by UV/visible spectrophotometry. The average transmittance of all the films was higher than 85% and a small absorbance zone occurred in the visible region. A sudden rise in the bandgap was obtained for the film postannealed at due to phase transformation, resulting in better photocatalytic activity under visible-light irradiation.