Paper EM+NS-TuA11
Controlling the Electronic Structure of Graphene Layers

Tuesday, October 16, 2007, 5:00 pm, Room 612

Much recent attention has been given to the electronic structure of graphene, the honeycomb carbon sheet which is the building block of graphite, carbon nanotubes, C₆₀, and other mesoscopic forms of carbon. Following recent developments in synthesizing or isolating graphene films, experiments have revealed many interesting and physical properties, including an anomalous quantum Hall effect, ballistic electron transport at room temperature, and micron-scale coherence lengths. These unconventional properties are the direct consequence of graphene's peculiar and structure, with massless "Dirac Fermions" as charge carriers at the Fermi level. We have determined the layer-dependent electronic properties of graphene sheets prepared on silicon carbide, using angle-resolved photoemission spectroscopy. We examine this unique two-dimensional system in its development from single layers to multilayers in the π band, the highest occupied state, and the dispersion relation in the out-of-plane electron wave vector in particular.¹ By exploiting the sensitivity of graphene’s electronic states to the charge carrier concentration, changes in the on-site Coulomb potential leading to a change of π and π* bands can be examined. We demonstrate that, in a graphene bilayer, the gap between π and π* bands can be controlled by selectively adjusting relative carrier concentrations, suggesting a potential application in switching functions in electronic devices.²

¹T. Ohta, A. Bostwick, J. L. McChesney, T. Seyller, K. Horn, E. Rotenberg, Phys. Rev. Lett., 2007, in press.
²T. Ohta, A. Bostwick, T. Seyller, K. Horn, E. Rotenberg, Science 313, 951, 2006.