Epitaxial graphene on SiC(0001) and SiC(000(1)over-bar): from surface reconstructions to carbon electronics

Graphene with its unconventional two-dimensional electron gas properties promises a pathway towards nanoscaled carbon electronics. Large scale graphene layers for a possible application can be grown epitaxially on SiC by Si sublimation. Here we report on the initial growth of graphene on SiC basal plane surfaces and its relation to surface reconstructions. The surfaces were investigated by scanning tunneling microscopy (STM), low energy electron diffraction (LEED), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and x-ray photoelectron spectroscopy (XPS). On SiC(0001) the interface is characterized by the so-called (6 root 3 x 6 root 3)R30 degrees 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 role of three structures with periodicities (6 root 3 x 6 root 3)R30 degrees, (6 x 6) and (5 x 5) present in this phase. The graphitization process can be observed by distinct features in the STM images with atomic resolution. The number of graphene layers grown can be controlled by the conical band structure of the pi-bands around the (K) over bar point of the graphene Brillouin zone as measured by laboratory-based ARUPS using UV light from He II excitation. In addition we show that the spot intensity spectra in LEED can also be used as fingerprints for the exact determination of the number of layers for the first three graphene layers. LEED data correlated to the ARUPS results allow for an easy and practical method for the thickness analysis of epitaxial graphene on SiC(0001) that can be applied continuously during the preparation procedure, thus paving the way for a large variety of experiments to tune the electronic structure of graphene for future applications in carbon electronics. On SiC(000 (1) over bar) graphene grows without the presence of an interface layer. The initial graphene layer develops in coexistence with intrinsic surface reconstructions of the SiC(000 (1) over bar) surface. In high resolution STM measurements we show atomically resolved graphene layers on top of the (3 x 3) reconstruction with a Moire type modulation by a large superlattice periodicity that indicates a weak coupling between the graphene layer and the substrate.