Transient Surface Faceting, Near-Surface Layering, and Atomic Ordering in Au1-xGex Binary Alloy Melts

Abstract The behavior of molten metals is relevant to the science of crystallization and to technological processes spanning from soldering to environmental chemistry and crystal growth. In all these contexts, the near-surface structure and composition of the melt are particularly important. Here, we investigate binary Au-Ge alloys in the liquid state and upon crystallization. In situ electron microscopy on nanoscale Au-Ge drops shows ubiquitous transient surface faceting in the liquid state, where facet sizes increase with Ge content. Freezing of such drops involves surface-induced crystallization templated by the facets. Simulations demonstrate the formation of a Au/Ge bilayer with periodic atom arrangements at the melt surface. During freezing, these surface motifs guide crystallization in the bulk. The results identify distinct near-surface structures of alloy melts characterized by layering and segregation, which can direct crystallization of the melt as well as nucleation and growth of other crystals at the surface of the molten metal.