Two-Dimensional Noble Metal Chalcogenides in the Frustrated Snub-Square Lattice

We study two-dimensional noble metal chalcogenides, with compositions {Cu, Ag, Au}(2){S, Se, Te}, crystallizing in a snub-square lattice. This is a semiregular two-dimensional tesselation formed by triangles and squares that exhibits geometrical frustration. We use for comparison a square lattice, from which the snub-square tiling can be derived by a simple rotation of the squares. The monolayer snub-square chalcogenides are very close to thermodynamic stability, with the most stable system (Ag2Se) a mere 7 meV/atom above the convex hull of stability. All compounds studied in the square and snub-square lattice are semiconductors, with band gaps ranging from 0.1 to more than 2.5 eV. Excitonic effects are strong, with an exciton binding energy of around 0.3 eV. We propose the Cu (001) surface as a possible substrate to synthesize Cu2Se, although many other metal and semiconducting surfaces can be found with very good lattice matching.

Automated summary

In this study, we investigate the structure and properties of two-dimensional noble metal chalcogenides. We find that they can form a unique geometric lattice structure in the two-dimensional plane and exhibit semiconductor behavior. Among them, Ag2Se is considered the most stable compound with a small band gap. We also observe strong excitonic effects, which may have implications for the application of these materials in optoelectronic devices.