Mechanics and strain engineering of bulk and monolayer Bi2O2Se

Abstract High-mobility semiconductive ultrathin films of bismuth oxyselenide (Bi2O2Se) have attracted great interest due to their potential applications in advanced electronic and photoelectronic devices. Enthusiasm aside, future success of such applications hinges upon the fundamental understanding of two dimensional (2D) Bi2O2Se, which is far from mature. In particular, unlike many other 2D materials with a van der Waals gap, 2D Bi2O2Se features a weak electrostatic stacking interaction, which gives rise to a significantly different mechanical response. The unique mechanical response of 2D Bi2O2Se has a strong influence on its band gap, a critical property toward its device applications. Here, using ab initio calculations, we investigate the mechanical and electronic responses of both bulk and monolayer Bi2O2Se under uniaxial and biaxial tension as well as those of monolayer Bi2O2Se under in-plane shearing. The distinct mechanical responses of bulk and monolayer Bi2O2Se under different mechanical deformation are explained by the associated study of the evolution of electron localization function and charge density analysis. We reveal that the band gap of both bulk and monolayer Bi2O2Se decreases as the applied tensile strain increases. The critical uniaxial and biaxial tensile strains, above which bulk and monolayer Bi2O2Se transform from being semiconductive to being metallic, are determined. These findings suggest fertile yet largely unexplored opportunities of strain engineering of 2D Bi2O2Se toward new device applications.