Structural evolution and optical properties of TiO2 thin films prepared bythermal oxidation of sputtered Ti films

A dense rutile TiO2 thin film was synthesized by the thermal oxidation of a sputtered titanium metal film in ambient air. The effects on optical prope rties of TiO2 films of the crystal structure and microstructural evolution at various oxidation temperatures were investigated. The Ti films transform ed into single-phase rutile TiO2 at temperatures greater than or equal to 5 50 degrees C without going through an anatase-to-rutile transformation. Ins tead, an additional crystalline Ti2O phase was detected at 550 degrees C on ly. An increase in the oxidation temperatures ranging between 700 and 900 d egrees C led to an increase in both the refractive index and absorption coe fficient, but a decrease in the band gap energy (E-g). According to the coh erent potential approximation model, the band gap evolution of the oxidized films was primarily attributed to the electronic disorder due to oxygen de ficiency at a higher oxidation temperature rather than the presence of an a morphous component in the prepared films. (C) 2000 American Institute of Ph ysics. [S0021-8979(00)07920-2].