Much stronger binding of metal adatoms to silicene than to graphene: A first-principles study

First-principles calculations have been performed to study the structural, energetic, and electronic properties of 15 different metal atoms adsorbed on silicene. Among the 15 metal adatoms on silicene, Li, Na, K, Ca, Co, Ni, Pd, and Pt obtain a larger binding energy than the cohesive energy of the bulk metal. While the binding of Au and Sn to graphene is rather weak, they bind strongly and covalently to silicene. For the alkali metal adatoms on silicene, the bonding is approximately ideal ionic. When the Ca atom is adsorbed on silicene, hybridization between the Ca 3d states and the silicene states occurs around E-F besides charge transfer from Ca to silicene. The Al, Ga, In, and Sn adatoms bind most strongly at the top site above a Si atom in silicene and form strong covalent bonds with the nearest Si atoms. For the Ti, Fe, Co, and Au adatoms on silicene, the adatom d states are strongly hybridized with the silicene states around E-F, while the hybridization states lie rather far below the E-F with E-F located approximately at the Dirac point for the Ni, Pd, and Pt adatoms on silicene. The strong binding of metal adatoms to silicene and the rich electronic properties of the systems suggest possible experimental exploration of functionalization of silicene with metal adatoms.