Compounds produced by the photoinduced diffusion of silver into a germanium sulfide film have been found to be promising photoresist materials for microfabrication technology. Thin films of silver, on the order of 40 nm in thickness, were grown on a GeS_1.7 substrate in a thermal vapour deposition system. The resultant samples were then illuminated using a xenon arc lamp for different periods of time to initiate the photodiffusion process. AFM images show that the Ag overlayer becomes discontinuous during diffusion, first forming discrete islands of Ag and finally diffusing completely to form a Ag–Ge–S overlayer. Nanoindentation tests were used to determine the nanoscale mechanical properties of the film samples and to probe the diffusion kinetics. Samples of different compositions and varying degrees of silver diffusion can be distinguished using this technique. The elemental composition of the thin films as a function of depth and the layer thickness were also determined using Rutherford backscattering analysis (RBS). The photo-diffused sample has a step-like compositional profile with a Ag-rich intermediate formed during the initial period of photodiffusion. The reaction slows down after illumination for 180 s as Ag atoms migrate deeper into the germanium sulfur substrate, and the composition of the reacted overlayer changes from GeS_1.7Ag to GeS_1.7Ag_0.5.