Characteristics of TiO2 coatings produced by the reactive ionized cluster beam method

The epitaxial growth of TiO2 rutile films on sapphire substrates and single-crystal aluminium film substrates is reported. The films were grown by titanium deposition in an O2 environment. O2 gas was supplied to keep the pressure at 2x10-4 Torr during the deposition. The electron current and voltage for gas ionization were kept at 400 mA and 500 V respectively. Depositions were made with acceleration voltages of 0-3 kV and substrate temperatures of 200-500degC. The growth rate was 6.6 nm min-1 and typically the film thickness was 200 nm. High quality epitaxial films on sapphire substrates were obtained at 0-0.5 kV and 400degC. The epitaxial relation between the grown film and the substrate was TiO2 rutile (200)parallelAl2O3(0001). The refractive index was up to 2.7, the same value as for rutile single crystal. In the case of deposition onto an aluminium film surface, the epitaxial relation was TiO2 rutile (200)parallelAl(111). A substrate temperature of 450degC was necessary. These epitaxial TiO2 rutile films have three crystal structures which were rotated by 60deg relative to each other on the (200) plane. (orig.)