Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 10: Semiconductor Substrates: Epitaxy and Growth

O 10.13: Talk

Monday, February 25, 2008, 16:15–16:30, MA 042

Spatial variation of the Dirac-gap in epitaxial graphene — •Lucia Vitali, Christian Riedl, Robin Ohmann, Ulrich Starke, and Klaus Kern — MPI for Solid State Research, Stuttgart, Germany

The unconventional electronic properties of graphene make it a promising candidate for the realization of novel nanoelectronic circuits which was first realized using single layer graphene samples produced by mechanical exfoliation. An alternative method has been established with the epitaxial growth of graphene on SiC basal-plane surfaces by thermal decomposition of the topmost SiC bilayers. The electronic structure of mono- and few-layer graphene on SiC shows the typical linear dispersion of the π-bands at their crossing at the Dirac point. The opening of a gap as a function of the layer thickness and charge distribution can be observed by high-resolution photoemission experiments. However, the conditions and layer thickness required for the gap opening and the detailed values of gap size and Dirac energy shift are currently under debate. In the present communication we use scanning tunneling spectroscopy (STS) at low temperatures to obtain insight in the local electronic structure of mono- and bilayer graphene on SiC(0001). We show that already for the first graphene layer grown on top of the (6√3×6√3)R30^∘ buffer layer a gap opening is observed. The size of this gap, however, is varying with the periodicity of the interface structure, possibly due to a spatially dependent potential induced into the graphene layer. For the second layer we also observe the Dirac gap but no local spatial variation, i.e. the interface potential is too weak to modulate the electronic structure of the bilayer.