Electronic structure of graphene on single-crystal copper substrates

The electronic structure of graphene on Cu(111) and Cu(100) single crystals is investigated using low-energy electron microscopy, low-energy electron diffraction, and angle-resolved photoemission spectroscopy. On both substrates the graphene is rotationally disordered and interactions between the graphene and substrate lead to a shift in the Dirac crossing of similar to-0.3 eV and the opening of a similar to 250 meV gap. Exposure of the samples to air resulted in intercalation of oxygen under the graphene on Cu(100), which formed a (root 2 x 2 root 2)R45 degrees superstructure. The effect of this intercalation on the graphene pi bands is to increase the offset of the Dirac crossing (similar to-0.6 eV) and enlarge the gap (similar to 350 meV). No such effect is observed for the graphene on the Cu(111) sample, with the surface state at Gamma not showing the gap associated with a surface superstructure. The graphene film is found to protect the surface state from air exposure, with no change in the effective mass observed, as for one monolayer of Ag on Cu(111).