Dynamic probe of atom exchange during monolayer growth

In heteroepitaxy, impinging beam atoms can either wet the surface or swap with substrate atoms. Herein, we present a dynamic study of these phenomena throughout the assembly of the first atomic layer of Ge on Si(111). In situ spectromicroscopic analysis demonstrates that, at a sufficiently high temperature, atom exchange is more significant at the early stages of growth and attenuates as deposition proceeds. Our result highlights the role of propagating monolayer edges in the entropy-driven atom swapping and demonstrates that substitution of Si by Ge is a low-energy pathway to incorporate Ge in the growing monolayer. These observations are confirmed by molecular dynamic simulations.