Effect of surface Se concentration on stability and electronic structure of monolayer Bi2O2Se

Abstract

Structural stability is one of the most fundamental issues to explore the applications of two-dimensional (2D) materials. Se-terminated bismuth oxychalcogenide, Bi2O2Se, attracts extensive attention as its quasi-2D nature, which links traditional three-dimensional (3D) and van de Waals 2D materials. Herein, we systematically constructed Bi2O2Se monolayers with different surface Se concentrations and studied their structural stability under different chemical environments. The stability of Bi2O2Se monolayer is found to be sensitive to the surface Se concentration, i.e., its formation energy decreases linearly until the Se concentration increases to 50% and then remains flat. Five monolayers with 0%, 12.5%, 50%, 87.5% and 100% Se concentrations are found to be highly stable at different chemical environments from Se-poor to Se-rich. Among them, the 50% Se concentration is high-symmetry with a neat BiO layer sandwiched between two Se layers, showing a direct-gap semiconducting nature. Structural deformation occurs in the other four Se concentrations, resulting in a p-type semiconductor characteristic with in-gap states. Scanning tunneling microscope simulations characterize the arrangement of atoms on the surfaces, and reflect the distribution of the local electronic structure. Our work is expected to provide further insight into the stability of Bi2O2Se monolayers and advance the understanding on other quasi-2D materials.