Solving the Puzzle of the Coexistence of Different Adsorption Geometries of Graphene on Ni(111)

Graphene and the Ni(111) surface have almost identical unit cells, enabling the synthesis of high-quality graphene layers in perfect registry with the Ni surface in simple 1 × 1 unit cells. The relative orientation of graphene to the Ni(111) surface, however, is an open puzzle: up to three different structures (top-fcc, top-hcp, and bridge-top) have been found experimentally. The present dispersion-corrected ab initio density-functional theory study on the adsorption of graphene on Ni(111) reveals a dependence of the adsorption geometry on the concentration of subsurface interstitial carbon and presents a possible solution to this puzzle. At very high local interstitial carbon concentrations, we observe only physisorption. At intermediate concentrations, chemisorbed top-hcp graphene is energetically most favorable whereas at low concentrations bridge-top and top-fcc are the preferred chemisorbed structures