Epitaxial graphene on SiC(0001) and : from surface reconstructions to carbon electronics

Abstract

Graphene with its unconventional two-dimensional electron gas properties promises apathway towards nanoscaled carbon electronics. Large scale graphene layers for a possibleapplication can be grown epitaxially on SiC by Si sublimation. Here we report on the initialgrowth of graphene on SiC basal plane surfaces and its relation to surface reconstructions.The surfaces were investigated by scanning tunneling microscopy (STM), low energyelectron diffraction (LEED), angle-resolved ultraviolet photoelectron spectroscopy(ARUPS) and x-ray photoelectron spectroscopy (XPS). On SiC(0001) the interface ischaracterized by the so-called reconstruction. The homogeneity of this phase is influenced by the preparation procedure.Yet, it appears to be crucial for the quality of further graphene growth. We discuss the roleof three structures with periodicities , (6 × 6) and (5 × 5) present in this phase. The graphitization process can be observed bydistinct features in the STM images with atomic resolution. The number ofgraphene layers grown can be controlled by the conical band structure of theπ-bands around the point of the graphene Brillouin zone as measured by laboratory-based ARUPS using UVlight from He II excitation. In addition we show that the spot intensity spectra in LEEDcan also be used as fingerprints for the exact determination of the number of layers for thefirst three graphene layers. LEED data correlated to the ARUPS results allow for an easyand practical method for the thickness analysis of epitaxial graphene on SiC(0001)that can be applied continuously during the preparation procedure, thus pavingthe way for a large variety of experiments to tune the electronic structure ofgraphene for future applications in carbon electronics. On graphene grows without the presence of an interface layer. The initial graphenelayer develops in coexistence with intrinsic surface reconstructions of the surface. In high resolution STM measurements we show atomically resolved graphene layers on topof the (3 × 3) reconstruction with a Moiré type modulation by a large superlattice periodicitythat indicates a weak coupling between the graphene layer and the substrate.