Surface coating of small SiO2 particles with TiO2 thin layer by using barrel-sputtering system

Surface coating of small SiO2 particles with a thin TiO2 layer was carried out by using a hexagonal barrel-sputtering system. In order to determine suitable sputtering conditions, the TiO2 layer was deposited on a glass substrate by reactive sputtering under given total pressures, oxygen fractions, and substrate temperatures. The analysis of X-ray diffraction patterns and ultraviolet–visible absorption spectra showed that the preparation of a TiO2 layer with the rutile phase requires a high total pressure at room temperature whereas that with the anatase phase requires a moderate total pressure at 498 K. The surface coating of SiO2 particles by TiO2 layer was performed under the conditions suitable for either the rutile or anatase phase. It was found from scanning electron microscope, energy-dispersion spectrometer, and ultraviolet–visible absorption measurements that the surface of SiO2 particles was successfully coated with a thin uniform TiO2 layer with the rutile or anatase phase.