title: Time-resolved two-photon photoemission of unoccupied electronic states of periodically rippled graphene on Ru(0001).
abstract: The unoccupied electronic states of epitaxially grown graphene on Ru(0001) have been explored by time- and angle-resolved two-photon photoemission. We identify a Ru derived resonance and a Ru/graphene interface state at 0.91 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.
authors.affiliation: Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, 35032 Marburg, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Armbrust
authors.forename: J
authors.initials: J
authors.lastname: Güdde
authors.forename: P
authors.initials: P
authors.lastname: Jakob
authors.forename: U
authors.initials: U
authors.lastname: Höfer