Electronic band structure change with structural transition of buckled Au2X monolayers induced by strain

Abstract

This study investigates the strain-induced structural transitions of η ↔ θ and the changes in electronic band structures of Au₂X (X = S, Se, Te, Si, Ge) and Au₄SSe. We focus on Au₂S monolayers, which can form multiple meta-stable monolayers theoretically, including η-Au₂S, a buckled penta-monolayer composed of a square Au lattice and S adatoms. The θ-Au₂S is regarded as a distorted structure of η-Au₂S. Based on density functional theory (DFT) calculations using a generalized gradient approximation, the conduction and the valence bands of θ-Au₂S intersect at the Γ point, leading to linear dispersion, whereas η-Au₂S has a band gap of 1.02 eV. The conduction band minimum depends on the specific Au–Au bond distance, while the valence band maximum depends on both Au–S and Au–Au interactions. The band gap undergoes significant changes during the η ↔ θ phase transition of Au₂S induced by applying tensile or compressive in-plane biaxial strain to the lattice. Moreover, substituting S atoms with other elements alters the electronic band structures, resulting in a variety of physical properties without disrupting the fundamental Au lattice network. Therefore, the family of Au₂X monolayers holds potential as materials for atomic scale network devices.