First-principles Study On Saturated Adsorption Of Alkali Metal Atoms On Silicene

Silicene is a two dimensional wrinkled silicon film with only a single atomic layer. It’s a kind of graphene-like material, and has been successfully obtained in the experiments. Silicene has the excellent Dirac electronic properties, and behaves stronger spin-orbit coupling effects(SOC) than graphene. In experiment, quantum spin Hall effect(QSHE) of silicene has been observed due to its structural warping of the honeycomb lattice. In order to tune the electronic properties of silicene, doping and adsorption on silicene have attracted broad attention in recent years.In this work, we performed first-principles pseudopotential calculations within density-functional theory and containing SOC. We firstly study the stabilities, micro-geometries and electronic properties of alkali metals atoms adsorption on silicene. On this basis, we performed the comparison of our results with pure silicene and hydrogen saturated silicene. We found that all the formation energies of SiX(X=Li, Na, K and Rb) are negative, indicating that the relative structural of these new compounds when compared with silicene are stable. Bader charge analysis shows that charge is transferred from Si atoms to H atoms in SiH compound, but in SiX the direction of charge chansfer is opposite, i.e., the charge is transferred from alkali metals atoms to Si atoms. From the viewpoint of chemical bonding, we found that valence bond is formed between Si atoms and H atoms, but the bonds between Si atoms and alkali metal atoms are mainly ionic. From the band structure calculations, we found that the SiH open an indirect band gap, the new type compound Si Li is a semiconductor with a direct band gap of 0.34 eV. However, all the other compounds SiX(X=Na, K and Rb) exhibit metallic properties.For germanene also has carried on the related research, we find that the condition of germanene due to the higher buckling height, so have a larger band gap than silicene. GeH and GeF have a direct band gap opening different with SiH open a indirect band gap. Bader charge analysis shows that charge is transferred from Ge atoms to H and F. From the viewpoint of chemical bonding, we found that valence bond is formed between Si atoms and H atoms.