Copper / silver alloy thin films form with a fine, polycrystalline, metastable crystal structure. The expected effects of annealing include grain growth, transformation into the two stable phases, coarsening of the phases, texture formation, and the formation and growth of pinholes or voids. Copper/silver alloy films were deposited on single crystal sodium chloride substrates, via pulsed laser deposition ablation of an alloy target, of the eutectic composition. Free-standing films of 20-30 nm thickness were studied as-deposited and after annealing on copper TEM grids at 100°C for various times. Although several of the expected degradation processes involve short-range diffusion – essentially single atomic jumps – these were not observed, while other, longer-range diffusion effects were clearly identifiable. In particular, void shrinkage was observed in the films at short times, and void growth occurred at longer times.