Photochemically induced oxidation and silver deposition on amorphous germanium sulfide films studied using atomic force microscopy and ion beam methods

Abstract

Amorphous thin films of composition GeS 1.7 deposited using a thermal evaporation technique were studied using a combination of atomic force microscopy (AFM), Rutherford backscattering (RBS) and nuclear reaction analysis (NRA). The effects of photo-induced oxidation and metal deposition on these films were also studied by these techniques. This combination of experimental methods allows us to identify the chemical nature of surface structures, and correlate changes in morphology to those of sample stoichiometry for various chemical and photochemical reactions. We find that the GeS 1.7 films grow in a layer-like structure when deposited at rates of less than 0.02 nm/s on a Si(111) substrate held at 298 K. The films are quite inert to further reaction in the dark, however exposure to oxygen in the presence of ultraviolet radiation results in formation of an oxide which begins to nucleate at defect sites and then grows in a fractal pattern across the surface. Correlation of surface coverage from the AFM images and absolute oxygen density from NRA demonstrates that the reacted overlayer formed is an oxide consisting of approximately 20 at.% of oxygen. Deposition of Ag on these films results in formation of a reacted overlayer, as determined by AFM and RBS, followed by growth of Ag islands.