Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 86: Graphene VI

O 86.7: Talk

Friday, March 30, 2012, 12:00–12:15, MA 041

Sheet plasmon dispersion in epitaxial graphene and graphene nanostructures — •Jens Baringhaus, Thomas Langer, Herbert Pfnür, and Christoph Tegenkamp — Institut für Festkörperphysik, Leibniz Universität Hannover, 30167 Hannover, Germany

The dispersion of the two-dimensional sheet plasmon in epitaxial graphene on SiC substrates has been investigated by means of angle resolved high resolution electron energy loss spectroscopy. The dispersion shows a characteristic point of inflection whose position in phase space depends on the interface (Si-face, C- face, H-intercalation). The plasmon dispersions can be quantitatively described by the model of a nearly free electron gas assuming in addition a resonant coupling to long-lived electron-hole pairs. As the characteristic point appears when entering the interband regime, the effect is related to the chemical potential of the graphene film, i.e. the interface structure. This is in agreement with experiments where the chemical potential has been shifted both by adsorption of F4-TCNQ on epitaxial monolayer graphene and heating of quasi freestanding monolayer graphene films. In undoped or barley doped graphene sheets such as graphene on C-face SiC a point of inflection is not visible at all. Furthermore, the uniaxial dispersion on self-assembled multilayer graphene nanoribbons with an average width of 100 nm has been studied as well. In perpendicular direction a strong damping of the plasmon is observed which can be attributed to the roughness of the ribbons whereas in parallel direction the plasmon dispersion is shifted to higher energies. This shift has its origin in the multilayer characteristic of the ribbons.