Observation of Mg-induced structural and electronic properties of graphene

We report the formation of superstructures induced by Mg adatoms on a single layer graphene (SLG) formed on Ni(111) substrate, where a strong metallic parabolic band is found near the Fermi level at the Γ-point of the Brillouin zone. Our valence band and core level data obtained by using synchrotron photons indicate that Mg adatoms intercalate initially to lift the SLG from the Ni substrate to produce a well-defined π-band of SLG, and then the parabolic band appears upon adding extra Mg atoms on the Mg-intercalated SLG. Our scanning tunneling microscopy images from these systems show the presence of superstructures, a 2√3 × 2√3 phase for the intercalated Mg layer below the SLG and then a √7 × √7 phase for the Mg overlayer formed on the Mg-intercalated SLG. We discuss the physical implications of these superstructures and the associated parabolic band in terms of a possible graphene-based two-dimensional superconductivity.