Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 33: Graphene

O 33.18: Poster

Dienstag, 17. März 2015, 18:15–21:00, Poster A

Transition of image-potential states from free-standing graphene to the graphene/metal interface — •Nico Armbrust, Jens Güdde, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg

We present a theoretical study of the formation of image-potential states on a graphene layer at varying distance to a metal surface. For this purpose we have constructed an analytical one-dimensional model-potential on the basis of the two-band model for the metal and a parametrized potential that reproduces the double Rydberg-like series of even and odd image-potential states of free-standing graphene. This enables us to calculate energies and wavefunctions of the combined system for arbitrary distances between graphene and the metal surface by solving the one-dimensional Schrödinger-equation numerically. For large distances, the image-potential states are typically located at the graphene sheet since its work function is lower than that of most metals. We show, how this double series of free-standing graphene evolves into a single series of the semi-infinite graphene/metal system when a flat graphene layer approaches the metal surface. Our model can quantitatively reproduce experimental data on graphene/Ir(111) and graphene/Ru(0001) which strongly differ in the interaction strength and therefore the binding distance. In particular, the model can explain the different binding energy and lifetime of the first (n=1) image-potential state in the valley and hill areas of the moiré superlattice of graphene/Ru(0001).