Atomic and electronic structure of simple metal/graphene and complex metal/graphene/metal interfaces

Structural, electronic, and magnetic properties of simple interfaces (graphene on top of a metallic substrate) and complex interfaces (a single metallic adlayer on a simple graphene/metal system, either on top or between the graphene and metallic substrate) have been studied using density functional theory. Two types of simple interface with strong (Ni/graphene) and weak (Cu/graphene) bonding were considered. In addition to binding energies and interface distances, which are used to quantify the strength of graphene-substrate interactions, the bonding in simple and complex interfaces was analyzed using charge density distributions and bond orders. Substantial enhancement of the metallic substrate/graphene binding was observed in complex interfaces, consisting of a Ni monolayer on top of a simple {Ni or Cu}/graphene interface. The increase of substrate-graphene bonding in such complex interfaces is accompanied by weakening of in-plane C-C bonds in graphene, as quantified by the bond orders. A weak ferrimagnetism in graphene, i.e., unequal magnetic moments $\ensuremath{-}0.04{\ensuremath{\mu}}_{B}$ and $+0.06{\ensuremath{\mu}}_{B}$ on the C atoms, is induced by a ferromagnetic Ni substrate. The strength of graphene-substrate interactions is also reflected in simulated scanning tunneling microscopy images.