Identifying and Visualizing the Edge Terminations of Single-Layer MoSe 2 Island Epitaxially Grown on Au(111)

Recently, single-layer transition-metal dichalcogenides have drawn significant attention due to their remarkable physical properties in the monolayer as well as at the edges. Here, we constructed high-quality, single-layer MoSe islands on the Au(111) surfaces in ultrahigh vacuum by molecular beam epitaxy. All of the islands have hexagonal or triangular shapes with two kinds of well-defined edges. Scanning tunneling spectroscopy (STS) curves show notable differences in positive sample bias for the two types of edges. Density functional theory calculations for several edge configurations of MoSe confirm that the STS differences are attributed to the coupling between the p orbital of Se atoms and the d orbital of Mo atoms, and the two types of observed edge terminations are the bare Se edge and selenium-saturated Mo edge.