Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 86: Graphene VI

O 86.4: Vortrag

Freitag, 30. März 2012, 11:15–11:30, MA 041

Time-Resolved Two-Photon Photoemission of Unoccupied Electronic States of Periodically Rippled Graphene on Ru(0001) — •Nico Armbrust, Jens Güdde, Peter Jakob, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg

The well characterized graphene layers epitaxially grown on Ru(0001) have attracted a lot of interest up to now due to their periodically rippled structure caused by the strong interaction with the metal substrate. Here, the dynamics of unoccupied electronic states of graphene on Ru(0001) have been explored by time- and angle-resolved two-photon photoemission (2PPE). We identify a Ru derived resonance and a Ru/graphene interface state at 0.91 eV and 2.58 eV above the Fermi level, as well as three image-potential derived states close to the vacuum level. The most strongly bound, short lived and least dispersing image-potential state is suggested to have some quantum-well character with a large amplitude below the graphene hills. The two other image-potential states are attributed to a series of slightly decoupled states. Their lifetimes and dispersions are indicative of electrons moving almost freely above the valley areas of the moiré superstructure of graphene.