Coupling Epitaxy, Chemical Bonding, and Work Function at the Local Scale in Transition Metal-Supported Graphene

Resonance tunneling spectroscopy and density functional theory calculations are employed to explore local variations in the electronic surface potential of a single graphene layer grown on Rh(111). A work function modulation of 220 meV is experimentally measured, indicating that the chemical bonding strength varies significantly across the supercell of the Moire pattern formed when graphene is bonded to Rh(111). In combination with high-resolution images, which provide precise knowledge of the local atomic registry at the carbon metal interface, we identify experimentally, and confirm theoretically, the atomic configuration of maximum chemical bonding to the substrate. Our observations are at odds with reported trends for other transition metal substrates. We explain why this is the case by considering the various factors that contribute to the bonding at the graphene/metal interface.