Unravelling the roles of surface chemical composition and geometry for the graphene-metal interaction through C1s core-level spectroscopy

Here we show that by using a combined experimental and theoretical approach it is possible to separate the contributions to the interaction strength between epitaxial graphene and transition metal surfaces arising from the geometrical and chemical properties of the supporting surfaces. This has been achieved by performing photoelectron measurements and numerical simulations of the C1s core level spectral distribution for a large number of graphene-metal systems, which have been obtained by systematic intercalation of different metals (Co, Rh, Ir and Ru) at the graphene-Ir(1 1 1) and graphene-Ru(0 0 0 1) interfaces. We demonstrate that the chemical species of the substrate's topmost layer plays a major role in determining the coupling between graphene and its substrate. Moreover, we show that both the experimental and the theoretical C1s spectral centres of mass are in linear relationship with the d-band centre of the transition metal substrate, which is considered a reliable descriptor of the graphene-substrate interaction strength. Our results provide a simple method to determine and tailor the properties of graphene-metal contacts.