First-Principles Calculation on Geometric, Electronic and Optical Properties of Fully Fluorinated Stanene: a Large-Gap Quantum Spin Hall Insulator

The searches for large-gap quantum spin Hall insulators are important for both practical and fundamental interests. In this work, we present a theoretical observation of the two-dimensional fully fluorinated stanene (SnF) by means of density functional theory. Remarkably, a significant spin-orbit coupling is observed for the SnF monolayer in the valence band at the \it \Gamma point, with a considerable indirect band gap of 278 meV. The direct gap of the SnF monolayer is at the \it \Gamma point, which is slightly larger by as much as 381 meV. In addition, the elastic modulus of the SnF monolayer is about 20 J/m^2, which is comparable with the in-plane stiffness of black phosphorus monolayer along the x-direction (\sim28.94 J/m^2). Finally, the optical properties of stanene, SnF monolayer and stanene/SnF bilayer are calculated, in which the stanene/SnF bilayer is supposed to be an attractive sunlight absorber.