Optical properties of anatase, rutile and amorphous phases of TiO2 thin films grown at room temperature by RF magnetron sputtering

Anatase (A), rutile (R) and amorphous phase TiO2 thin films have been prepared by RF magnetron sputtering on unheated glass substrates by controlling the total pressure of sputtering gases (Ar + O-2) and the substrate bias. The crystal structures of the films were confirmed by x-ray diffraction and Raman scattering. The analysis of optical absorption data for A- TiO2 film shows an energy bandgap (E-g) of 3.2 eV (indirect extrapolation) and similar to 3.5 eV (direct extrapolation). On the other hand, R-TiO2 film shows E-g similar to 2.9 eV (indirect) and 3.2 eV (direct). The latter film also shows the presence of amorphous regions with E-g similar to 3.0 eV (indirect) and 3.8 eV (direct). The bandgap of both the films, obtained using indirect extrapolation, has a value range consistent with the previous measurements.