Additive-enhanced coarsening and smoothening of metal films: Complex mass-flow dynamics underlying nanostructure evolution

Exposure of Ag/Ag(100) thin films to molecular oxygen (O₂) at 220--250 K is shown to activate low-temperature coarsening of submonolayer island distributions, and a smoothing of multilayer films with ``mounded'' morphologies. Dissociation of O₂ at kink sites populates step edges with atomic oxygen (O), modifying the step-edge energetics, and facilitating Ostwald ripening of film nanostructures. We propose that ripening occurs by ``easy'' detachment and terrace diffusion of an AgₙO species. Cluster diffusion does not play a significant role, contrasting with the O-free system.