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Graphene/Au(111) interaction studied by scanning tunneling microscopy

We have used scanning tunneling microscopy to study the structure of graphene islands on Au(111) grown by deposition of elemental carbon at 950°C. Consistent with low-energy electron microscopic observations, we find that the graphene islands have dendritic shapes. The islands tend to cover depressed regions of the Au surface, suggesting that Au is displaced as the graphene grows. If small tunneling currents are used, it is possible to image simultaneously the graphene/Au moiré and the Au herringbone reconstruction, which forms underneath the graphene on cooling from the growth temperature. The delicate herringbone structure and its periodicity remain unchanged from the bare Au surface. Using a Frenkel-Kontorova model we deduce that this striking observation is consistent with an attraction between graphene and Au of less than 13 meV per C atom. Raman spectroscopy supports this weak interaction. However, at the tunneling currents necessary for atomic resolution image of graphene, the Au reconstruction is altered, implying influential tip-sample interactions and a mobile Au surface beneath the graphene.