Graphene On Weakly Interacting Metals: Dirac States Versus Surface States

We investigate the interplay between graphene and different, weakly interacting metal substrates by measuring the local density of states of the surface with scanning tunneling spectroscopy. Energy-resolved Friedel oscillations, confined states, and a prominent signal in point spectra are found after intercalating several monolayers of silver between graphene and Ir(111) and correspond to the shifted surface state of silver. These features outweigh spectroscopic signatures of graphene, which are retrieved when the amount of silver is reduced to one monolayer. Hence, suppressing the surface states of the metal substrate enhances the sensitivity to the Dirac states of quasi-free-standing graphene.