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 O₂ 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, ∼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 O₂, 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.