Mechanisms of solid-state dewetting of thin Au films in different annealing atmospheres

We studied the initial stages of solid-state dewetting of thin nanocrystalline Au films deposited on sapphire substrates during annealing in air and in the flow of forming gas. The interrupted annealing technique was employed to study the evolution of the size and morphology of individual holes in the film. The holes exhibited comparable expansion rates and similar topographies comprising an elevated rim in both annealing atmospheres. In particular, we observed a terraced topography of the hole rim with sharp steps associated with individual grain boundaries. The holes in the film annealed in air exhibited more branched, tortuous lateral morphology than their counterparts in the film annealed in forming gas. We interpreted these experimental finding in terms of the effect of annealing atmosphere on the surface anisotropy of Au. We developed dewetting models which consider Au self-diffusion along the Au-sapphire interface as a factor controlling the kinetics of the dewetting process. The predictions of our models are in a good agreement with experimental findings.