On the nature and origin of Si surface segregation in amorphous AuSi alloys

We examined the surface segregation behavior of Si in amorphous AuSi alloys using ab initio molecular dynamics simulations within density functional theory. For a thin Au₇₀Si₃₀ film, our simulations predict Si surface enrichment that leads to a stoichiometry close to Au ₆₀Si₄₀ in the surface layer. The surface structure exhibits a rather ordered Au3Si2 phase, which somewhat differs from the bulk Au₆₀Si₄₀ structure that exhibits a tendency of random hard-sphere packing. We also discuss the origin of the Si surface segregation based on analysis of segregation-induced changes in the atomic and electronic structure of the AuSi alloy surface.