Hydrophilicity of TiO2 thin films obtained by radio frequency magnetron sputtering deposition

This paper reports results of the macroscopic and microscopic studies of the UV-light-induced hydrophilicity of TiO2 thin films prepared by radio frequency magnetron sputtering of a pure TiO2 in an Ar-O-2 mixture gas at different pressure values. The gas pressure affects the crystallographic structure as well as the surface topography and UV-light-induced hydrophilicity of the deposited films. The microscopic study of the film hydrophilicity is based on friction force microscopy measurements, which are used to microscopically distinguish regions of different hydrophilicity on the film surfaces. These measurements make use of the observation that for a hydrophilic tip, the more hydrophilic the sample surface is, the larger the tip-sample friction force is. The films deposited at a relatively high value of gas pressure (10 mtorr) had an amorphous structure, a good UV-light-induced hydrophilicity and a microscopically smooth and homogeneous surface. The films deposited at lower gas pressure values had mixed crystalline and amorphous structures and relatively rough and inhomogeneous surfaces. The effect of the gas pressure on the plasma particle bombardment of the growing films is discussed to account for the dependence of the structure and surface properties of the films on the gas pressure. (C) 2002 Elsevier Science B.V. All rights reserved.