Amorphous and crystalline TiO2 coatings synthesized with the RF PECVD technique from metalorganic precursor

Abstract

Thin films of titanium dioxide (TiO2) were synthesized with the help of plasma enhanced chemical vapour deposition (RF PECVD) technique, using titanium (IV) ethoxide and gaseous oxygen as precursor compounds. The glow discharge power and the flow rate of oxygen were used as process operational parameters. Phase composition of the films was studied with the X-ray diffraction (XRD) technique, their morphology was followed with the scanning electron microscopy (SEM), elemental composition was investigated with the energy dispersive spectroscopy (EDS) and their thickness and optical properties were assessed with the help of variable angle spectroscopic ellipsometry (VASE) and UV-VIS spectroscopy.The coatings obtained at the glow discharge power of 300 W and the oxygen flow rate of 400 sccm were characterized by the best titanium dioxide stoichiometry and the highest refractive index of 2.2. As deposited, the films had strictly amorphous character. They crystallized after thermal annealing at 500 °C, with an increase of their refractive index to 2.35. Thermal treatment also modified water wettability of the coatings: annealing produced a decrease of water contact angle by more than 30°. An illumination of the films with UV radiation brought about further drop of water contact angle which eventually resulted in a strongly hydrophilic surface.