Effect of Annealing on the Sn-Doped TiO[sub 2] Films Prepared by DC/RF Cosputtering

Sn-doped titanium oxide (TiO2) thin films were deposited on glass by dc/ radio frequency (rf) magnetron cosputtering, in which dc and rf were utilized for Ti and Sn targets, respectively. The samples were postannealed from 400 to 500 degrees C for 1 h 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 450 degrees C. Furthermore, the film postannealed at 400 degrees C was found to have anatase/rutile duplex phases with a fine grain microstructure and amorphous structure by using transmission electron microscopy. The heattreatment also induces a change in the surface morphology of the Sn-doped TiO2 thin films observed by field- emission scanning electron microscopy. The optical properties of the Sn-doped TiO2 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 400 degrees C due to phase transformation, resulting in better photocatalytic activity under visible-light irradiation. (c) 2007 The Electrochemical Society