Regensburg 2010 – scientific programme
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O: Fachverband Oberflächenphysik
O 52: Graphene II
O 52.8: Talk
Wednesday, March 24, 2010, 16:45–17:00, H31
Effect of Noble-Metal Contacts on the Electronic Structure of Graphene — •Andrei Varykhalov1, Markus R. Scholz1, Timur K. Kim2, and Oliver Rader1 — 1Helmholtz-Zentrum Berlin für Materialien und Energie — 2Institute for Solid State Research, IFW Dresden
Graphene-metal contacts are crucial for a future planar bipolar nanoelectronics. We investigated these contacts by angle-resolved photoemission at high resolution using noble-metal intercalation. We observe that doping level and band gap depend strongly on which noble metal is intercalated. As predicted from first principles, strong electron doping is provided by Cu (Δ EF ∼ −310 meV) and Ag (∼ −560 meV) but also unexpected large gaps appear (Eg=180 and 320 meV, respectively). Au affects the neutral state of graphene much less than predicted moving the Dirac point ED by only Δ EF ∼ +55 meV above the Fermi level. In order to investigate whether or not graphene/Au is gapless also above ED, we adsorbed potassium and gadolinium on top of the graphene. Both act as efficient donors but potassium opens a substantial band gap due to symmetry breaking while ED is well below EF and gapless after doping by gadolinium. We propose that the large 9×9 unit cell of the graphene/Au interface amplifies via quantum interference the decoupling of the graphene from its substrate which leads to the quasifreestanding electronic structure of graphene.