In Situ Observation of the Layer-by-Layer Melting of the Au(200) Surface in Nanoporous Gold

Melting is a fundamental phenomenon in condensed matter physics, chemistry, and other disciplines, which preferentially occurs at surfaces or interfaces. However, the correlation between surface microstructure and the melting behavior of nanomaterials remains elusive due to a limited understanding of surface melting at the atomic level. Herein, the surface melting process of the Au(200) facet was observed at atomic resolution using an in situ transmission electron microscopy. The results showed that a dynamically evolving step structure formed and persisted on the Au(200) surface during the melting process. Theoretical calculations indicated that the elastic energy generated by lattice distortion at the step structure was partially transferred to the Au(200) facet, thereby facilitating surface melting. Interestingly, melting occurred exclusively at the top surface of the Au(200) facet, while the inner atoms remained completely unaffected until the melted layer detached.