Coverage-dependent electronic and optical properties of H- or F-passivated Si/Ag(111) from first principles

Chemical functionalization of silicene can be devised to tune the intrinsic properties for optoelectronic applications of this material, as well as for optimizing the interface formed by ultrathin Si and a substrate. This work is focused on the (2 root 3 x 2 root 3)R30 degrees phase of silicene grown on Ag(111), and the adsorption of H or F atoms, at half and full coverage, is simulated within density functional theory. The optical response is constructed through the independent particle-random-phase approximation and analyzed thoroughly. The connection between the electronic structure and the features in the optical absorption and reflection is therefore investigated in order to highlight either the role of the adatoms or the effect of the metallic surface. As the coverage is increased, the silicene phases are effectively decoupled from Ag by H or F adatoms and the freestanding properties of the corresponding systems are recovered, for which a coverage-dependent band gap is opened in the states of the overlayer. However, despite being effectively decoupled from the substrate, the properties of functionalized silicene do not show the peculiar characteristics expected from the ideal freestanding Si layer.