Tailoring the crystal structure of TiO2 thin films from the anatase to rutile phase

TiO2 films with various Sn concentrations were deposited on quartz substrates using rf reactive magnetron sputtering. The crystal structure was investigated by using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the chemical states of Ti and Sn were analyzed by x-ray absorption near edge structure (XANES) spectroscopy. Without Sn doping, TiO2 films change the crystal structure from rutile to anatase as the total gas pressure increases in the sputtering deposition. On the other hand, Sn doping induces the transformation of TiO2 crystalline structure from anatase to rutile phase, where the XANES spectra implied that Sn substitutes into Ti site of rutile TiO2. Atomic force microscope analyses revealed that the Sn-doped TiO2 films exhibited a flat surface with the roughness of approximately 2 nm.