Density-functional calculations of multivalency-driven formation of Te-based monolayer materials with superior electronic and optical properties

Abstract

Contemporary science is witnessing a rapid expansion of the two-dimensional (2D) materials family, each member possessing intriguing emergent properties of fundamental and practical importance. Using the particle-swarm optimization method in combination with first-principles density functional theory calculations, here wepredict a new category of 2D monolayers named tellurene, composed of the metalloid element Te, with stable 1T-MoS2-like ( {\alpha}-Te), and metastable tetragonal (\b{eta}-Te) and 2H-MoS2-like ({\gamma}-Te) structures. The underlying formation mechanism of such tri-layer arrangements is uniquely rooted in the multivalent nature of Te, with the central-layer Te behaving more metal-like (e.g., Mo), and the two outer layers more semiconductor-like (e.g.,S). In particular, the {\alpha}-Te phase can be spontaneously obtained from the magic thicknesses truncated along the [001] direction of the trigonal structure of bulk Te. Furthermore, both the {\alpha}- and \b{eta}-Te phases possess electron and hole mobilities much higher than MoS2, as well as salient optical absorption properties. These findings effectively extend the realm of 2D materials to group-VI monolayers, and provide a new and generic formation mechanism for designing 2D materials.