Some properties of TiO2 layers prepared by medium frequency reactive sputtering

One of the most extensively used coating materials with a high index of ref raction is titania (TiO2). It is transparent in the visible range and has g ood mechanical properties and chemical stability. Among the several crystal structures of this oxide, rutile has the highest density and microhardness , the highest index of refraction and the highest temperature stability. Fo r TiO2, it is known that different types of deposition techniques create fi lms with different properties. The aim of this work was to analyze the prop erties of TiO2 films prepared by twin magnetron sputtering. The films were prepared by medium frequency (MF) twin magnetron reactive sp uttering. This method offers two special properties which may strongly infl uence the growth of the film. First, the substrate is continuously bombarde d by positively charged ions of high energy. The values obtained are up to 200 eV. Second, using this method it is possible to prepare transparent TiO 2 films in the metallic or transition mode of the cathode characteristic wi th a very high deposition rate. X-ray diffraction patterns show that, depen ding on the preparation conditions, the films contain different amounts of rutile, mixed with anatase and amorphous phases. The film morphology, i.e. microstructure and surface roughness, was investigated by scanning electron microscopy (SEM). It was shown that samples with a highly homogenous micro structure and with a very smooth surface could be produced. The optical con stants were calculated from the measured optical transmission and reflectio n spectra. The film density was determined by weighing. The values obtained were around 90% of the density of bulk TiO2 with rutile structure. All fil ms showed a compressive stress. The microhardness was measured by the Vicke rs method. (C) 1999 Elsevier Science S.A. All rights reserved.