Adsorption of alkali adatoms on graphene supported by the Au/Ni(111) surface

We study alkali-metal adsorption on supported graphene by means of density-functional-theory calculations that include dispersion corrections. Graphene supported by the Au/Ni(111) surface is an important system for fundamental studies because this surface allows one to support graphene, preserving the electronic properties of freestanding graphene. We investigate the binding energetics as well as the structural and electronic properties of Li, Na, K, and Rb atoms adsorbed or intercalated at the graphene/Au/Ni(111) interfaces and compare the results to those obtained on freestanding graphene. Both the adsorption and intercalation of the alkali atoms induce electron doping to the graphene pi bands that display a quasirigid-energy shift. Electron doping by alkali atoms preserves the Dirac cone of graphene, which shifts downwards due to the negative polarity of the doping. The metallic or ionic character of the alkali dopant is controlled by its position relative to graphene. All of the investigated alkali atoms display an energetic preference to intercalate between graphene and the Au/Ni support. These results shed light on the relationship between graphene electron doping, the alkali-atom adsorption site, and the charge transfers at the graphene/support interface.