Anisotropic hole growth during solid-state dewetting of single-crystal Au-Fe thin films

Thin Fe-Au bilayers were deposited on c-plane sapphire substrates. The layers were found to be quasi-single crystalline, with a 〈1 1 1〉 texture and strong heteroepitaxy to the substrate. When annealed, these films dewetted from the substrate via the formation of faceted hexagonally shaped holes, which grow anisotropically with increasing annealing time. The studied Fe-Au films exhibited significantly higher thermal stability against dewetting than polycrystalline Au films prepared and annealed under identical conditions. We developed a thermodynamic diffusion model describing the growth kinetics of an individual hole. This model, in conjunction with experimental results, allows estimation of the effective surface self-diffusion coefficient.