Abnormal Oxidation of Ag Films and Its Application to Fabrication of Photocatalytic Films with <i>a</i>-TiO₂/<i>h</i>-Ag₂O Heterostructure

Abstract

Metallic Ag films were observed to be layer-by-layer oxidized by reactive-sputtering deposition of TiO2, leaving a layer of Ag2O with hexagonal structure (h-Ag2O), which is rarely reported in literature. The oxidation of Ag film behaved rather abnormally because it was not until the Ag film was completely oxidized that amorphous TiO2 (a-TiO2) could form on the h-Ag2O layer, thus providing an effective method for fabrication of h-Ag2O films and a-TiO2/h-Ag2O heterostructures. O atoms in the plasma were proved to be responsible for the oxidation of Ag film, and the formation of TiO2 on the film that was not completely oxidized was disenabled, probably due to the formation of a new kind of oxide, (TiAg)O2. The optical properties of h-Ag2O films were studied for the first time, and the photocatalysis was found to be better than that of TiO2 films. The a-TiO2/h-Ag2O heterostructures exhibited excellent photocatalytic activity under ultraviolet and visible-light irradiation, much better than that of the a-TiO2 and the h-Ag2O single-layer films. The photocatalysis was discussed using the special electronic structure built in the a-TiO2/h-Ag2O heterostructures. In addition, decomposition of Ag2O was suggested to play an important role in the photocatalysis.