AVS 56th International Symposium & Exhibition
    Graphene Topical Conference Wednesday Sessions
       Session GR+AS-WeA

Paper GR+AS-WeA8
Mapping the Geometric and Electronic Structures of Epitaxial Graphene

Wednesday, November 11, 2009, 4:20 pm, Room C3

Session: Graphene: Surface Characterization
Presenter: M. Caffio, University of St Andrews, UK
Authors: B. Wang, University of St Andrews, UK
M. Caffio, University of St Andrews, UK
R. Schaub, University of St Andrews, UK
Correspondent: Click to Email
A single layer of graphite is known as graphene [1]. It is acknowledged that graphene is a candidate for future electronic devices when supported. Hence a detailed understanding of its geometric and electronic properties is essential. Many studies have in common the observation of moiré superstructures with parameters depending on the mismatch between graphene and substrate [2]. However, an in-depth characterization of the monolayer and its interaction with the support has so far been hampered by experimental limitations, and is strongly debated. We report on a low temperature STM study of graphene grown by low-pressure CVD of ethylene on Rh(111).

Topography measurements show that the C-Rh interactions lead to distortions of the ideal, free-standing graphene, resulting into two sets of superstructures: one is characterized by a coincidence lattice expanded to (12×12)/(11×11), while the other is contracted to (11×11)/(10×10). The coexistence of several graphene superstructures on a transition metal substrate is in contrast to previous reports. Both superlattices exhibit remarkable coherence lengths, in excess of 1000 nm. However, high-resolution images allow us to precisely monitor the registry of the C atoms with respect to the underlying substrate, revealing that the atomic arrangements are subject to local distortions. Resonance transmission microscopy and spectroscopy, in combination to DFT calculations, were further used to obtain deeper insight into the altering environment at the graphene/Rh(111) interface. Our results show how variations of the local work function within the overlayer unit cell provide invaluable information on the electronic coupling between graphene and Rh(111) substrate.

[1] K.S. Novoselov et al., Nature 438, 197 (2005)

[2] J. Coraux et al., Nano Letters 8, 565 (2008)