Preparation and characterization of polycrystalline anatase and rutile TiO ₂ thin films by rf magnetron sputtering

Titanium dioxide films with the anatase and rutile single phase were formed on Si substrates by rf sputtering through a precise control of critical parameters. The structure of the films was studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the optical properties were evaluated with spectroscopic ellipsometry (SE). Lattice distortion was found in both anatase and rutile films from TEM observation. The obtained refractive indices n exhibit higher values than those reported for thin films due presumably to the density structure of the sputtered films. Optical band gaps were calculated by Tauc plot using the obtained extinction coefficient separately for anatase and rutile, with values larger than those reported for bulk materials. The reasons for the larger band gap might be due to the strain from lattice distortion.