Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 22: Focused Session: Epitaxial Graphene III

O 22.2: Topical Talk

Dienstag, 24. März 2009, 11:00–11:30, SCH 251

Unraveling the strong interaction between graphene monolayer and Ru(0001) : a DFT-based STM and STS study — •Marie-Laure Bocquet and Bin Wang — Laboratoire de Chimie, Ecole Normale Supérieure de Lyon, Lyon, France

In this talk, I will refer to recently published experimental Scanning Tunneling Microscopy experiments resolving the (12x12)C / (11x11) Ru Moiré superstructure and will propose a detailed comparison with large-scale ab initio periodic calculations.

I will show that, in contrast to expectations, the measured electronic corrugation of the Moiré pattern mainly originates from a geometric buckling of the graphene sheet of 1.5 Å, induced by alternating weak and strong chemical interactions with Ru. This finding holds when considering smaller ((10x10) Ru) and larger ((12x12) Ru) coincidence structures in the calculations. The chemical bonding in the strong contact regions, leads to three recently measured properties nicely reproduced by the calculations :

- the STM transparence of carbon atoms directly above surface Ru atoms;

- the asymmetry between low- and high- lying carbon electronic states probed by STS spectroscopy ;

- the considerable band gap opening in the graphene states.

Finally I will review similar studies of graphene monolayer on various metal surfaces which allow us to classify the metals in two separate classes, one in which graphene is chemisorbed and one in which it is physisorbed.