Dependence of target–substrate distance on crystallographic and optical properties of WO3 films prepared by reactive radio frequency magnetron sputtering

WO3 films were deposited on glass substrates using radio frequency magnetron sputtering in a mixed gas of 80%Ar–20%O2. From the X-ray diffraction patterns, the WO3 films deposited at source to substrate distance (DT–S) of 40 mm were polycrystalline, crystallizing in the monoclinic crystal structure, with highly preferred c-axis orientation perpendicular to the film plane. On the other hand, amorphous films were observed in the WO3 films deposited at 70 mm. The crystallite sizes of the WO3 films deposited at DT–S of 40 mm were larger for films deposited at lower working gas pressures (PW). The optical absorption edge of the films shifted to shorter wavelength region with increase in PW irrespective of the DT–S. The oxygen deficient films are obtained when the films are deposited at DT–S of 40 mm and PW of 0.3 Pa and stoichiometric films are formed at higher PW. The photocatalytic oxidation of methanol proceeds via CO and formaldehyde as the intermediate species on WO3/TiO2 bilayer films and CO2 is identified as the final product.