Characterization of inhomogeneity in TiO2 thin films prepared by pulsed dc reactive magnetron sputtering

This article discusses an analytical method for characterizations of TiO2 thin films and determinations of the degree of their inhomogeneity. The TiO2 films were prepared by a pulsed dc magnetron sputtering with an operating pressure as a main experimental parameter. The obtained films were primarily characterized for film crystallinity, microstructures and optical properties by spectroscopic ellipsometry. The measured ellipsometric data were analyzed by the single-, the double, and the triple-layer models in order to match with the inhomogeneous film structure proposed in the Thornton structure zone model. The results were then compared with those obtained from grazing-incidence X-ray diffraction, field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The study revealed that the pulsed dc sputtered TiO2 films could be best described by the inhomogeneous triple-layer physical model. Although the films deposited at lower operating pressure had a dense structure with a mirror-like surface topography, the films deposited at higher operating pressure had the porous structure with the rough surface and the void.