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A. Garhofer:
"Ab initio studies of Graphene-Metal Interfaces";
Vortrag: Seminar Institut für Allgemeine Physik (IAP), TU Wien, Institut für Angewandte Physik; 25.06.2013.

Graphene (Gr) is a 2D allotrope of carbon with unique electronic and mechanical properties. The isolation of graphene in 2004 has led to a remarkable surge of interest in the scientific community. High quality graphene sheets can be produced via epitaxial growth on metal substrates. The Gr-metal interaction has either been classified as "weak" interaction, e.g. on Au, Ag, Cu, and Pt with merely shifted Gr pibands, or as "strong", e.g. on Ni, Ti, and Co, with strongly perturbed graphene bands. However, the interaction of graphene with a metallic surface is still not well understood on a fundamental level. In this talk, I will present density function (DFT) theory calculations of different Grmetal interfaces. Gr/Ni(111) usually grows in 1x1 structures, because of a negligible lattice mismatch. Semi-local functionals don´t account for van der Waals forces and are not able to describe the interaction correctly, while vdW-DF functionals reproduce the benchmark calculations. Common concepts of adsorption cannot be applied to this system, as we observe strong signs of chemisorption but with adsorption energies typical for physisorption. While in free-standing graphene the formation energies for single vacancies and Stone-Wales defects are large, these defects are stabilized when a nickel substrate is present. Furthermore, the energy barriers to heal the defects are decreased significantly. Besides 1x1 structures also moiré patterns are observed for Gr/Ni(111). A new growth model of graphene on Ni(111) is presented, where surface nickel carbide plays an important part. An artificially Gr/Ni(111) system, obtained by the intercalation of 1ML Ni leads to a pronounced buckling of graphene due to locally strongly enhanced Gr-Ni interactions for specific adsorption configurations. Theweakly coupled Gr/Ir(111) configuration shows contrast inversion in STM/AFM measurements which could be assigned via DFT calculations.