Facing-target sputtering deposition of ZnO films with Pt ultra-thin layers for gas-phase photocatalytic application

In this paper, various zinc oxide (ZnO) films are deposited by a versatile and effective dc-reactive facing-target sputtering method. The ratios of Ar to O(2) in the mixture gas are varied from 8:2 to 6:4 at a fixed sputtering pressure of 1.0 Pa. X-ray diffraction, spectrophotometer and scanning electron microscope are used to study the crystal structure, optical property and surface morphology of the as-deposited films. The Pt ultra-thin layer, approximately 2 nm thick, is deposited on the surface of ZnO film by dc diode sputtering with a mesh mask controlling the coated area. The photocatalytic activity of ZnO films and Pt-ZnO films is evaluated by decomposition of methanol under UV-vis light irradiation. The variation of photocatalytic activity depends on the ratios of Ar to O(2), which is mainly attributed to the different grain size and carrier mobility. Though the pure ZnO film normally shows a low gas-phase photocatalytic activity, its activity is significantly enhanced by depositing Pt ultra-thin layer.