Ag diffusion in amorphous As 50Se 50 films studied by XPS

Abstract

X-ray photoelectron spectroscopy and depth profile analysis were used to investigate the X-ray-induced silver photodiffusion into an amorphous As 50Se 50 thin film. At the initial stages of irradiation an induction period was observed while core level spectra analysis revealed the existence of a mixed As–Se–Ag interlayer between the metal and the chalcogenide matrix. It was found that during the induction period this interlayer is enriched in silver and the existing As–Se–Ag intermediate species are transformed to Ag–Se–Ag that form the metal source for the effective silver photodiffusion. With further irradiation photodiffusion proceeds by the disruption of Ag–Se bonds and the recombination of As atoms with Se to stable As–Se units. Ultimately, silver concentration reaches a plateau when the diffusion stops. A separated Ag 2Se phase on the film’s surface is identified at this stage. Depth profile analysis shows that silver has been homogenously diffused into the chalcogenide matrix and the Ag 2Se phase exists only at the top surface layers probably in the form of quasi-crystalline clusters that prohibit further Ag diffusion.