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

Abstract

Sn-doped titanium oxide (TiO2) thin films were deposited on glass by dc/radio frequency (rf) magnetron cosputtering, in which dc and rf wereutilized for Ti and Sn targets, respectively. The samples werepostannealed from 400 to 500 degrees C for 1 h in ambient air. Glancingincidence X-ray diffraction revealed an amorphous phase in theas-deposited films and a polycrystalline phase for films postannealed attemperatures higher than 450 degrees C. Furthermore, the filmpostannealed at 400 degrees C was found to have anatase/rutile duplexphases with a fine grain microstructure and amorphous structure by usingtransmission electron microscopy. The heattreatment also induces achange in the surface morphology of the Sn-doped TiO2 thin filmsobserved by field- emission scanning electron microscopy. The opticalproperties of the Sn-doped TiO2 thin films were characterized byUV/visible spectrophotometry. The average transmittance of all the filmswas higher than 85% and a small absorbance zone occurred in the visibleregion. A sudden rise in the bandgap was obtained for the filmpostannealed at 400 degrees C due to phase transformation, resulting inbetter photocatalytic activity under visible-light irradiation. (c) 2007The Electrochemical Society.