Effect of photo-oxidation on the photodiffusion of silver in germanium chalcogenide glasses

We report results on photoinduced changes in Ge-chalcogenide glasses, which occur in ultra high vacuum (UHV) vs. in air. They demonstrate the important role of oxygen that determines the magnitude and the type of the photoinduced effects. To observe photodiffusion without the presence of oxygen, Ag/glass thin films were prepared, subjected to photodiffusion, and chemically analyzed, all within the chamber of high resolution X-ray Photoelectron Spectroscopy (XPS) equipment. Under these oxygen-free conditions, Ag is introduced in the Ge-Se hosting network. The results show that the diffusion product is homogeneous, comprising of Ge-chalcogen tetrahedra and ethane-like units (GeSe3)2 with Ag ions attached to them. In oxygen containing ambient, Ge rich glasses oxidize more easily than the chalcogen rich glasses, since oxygen reacts primarily with Ge. Under these experimental conditions, which are likely to exist in practical applications, a higher concentration of Ag can be introduced, with the formation of Ag containing products like α and β Ag2Se and Ag8GeSe6. Raman spectroscopy reveals that because of interaction between Ge and oxygen, the initially Ge-rich chalcogenide network becomes chalcogen-rich after the oxidation of Ge.