We show experimentally that multilayer graphene grown on the carbon terminated SiC(0001[over ]) surface contains rotational stacking faults related to the epitaxial condition at the graphene-SiC interface. Via first-principles calculation, we demonstrate that such faults produce an electronic structure indistinguishable from an isolated single graphene sheet in the vicinity of the Dirac point. This explains prior experimental results that showed single-layer electronic properties, even for epitaxial graphene films tens of layers thick.

Recent transport measurements on thin graphite films grown on SiC show large coherence lengths and anomalous integer quantum Hall effects expected for isolated graphene sheets. This is the case eventhough the layer-substrate epitaxy of these films implies a strong interface bond that should induce perturbations in the graphene electronic structure. Our DFT calculations confirm this strong substrate-graphite bond in the first adsorbed carbon layer that prevents any graphitic electronic properties for this layer. However, the graphitic nature of the film is recovered by the second and third absorbed layers. This effect is seen in both the (0001)and (0001) 4H SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. It causes the graphene to be doped and gives rise to a gap opening at the Dirac point after 3 carbon layers are deposited in agreement with recent ARPES experiments (T.Ohta et al, Science 313 (2006) 951).PACS numbers: 73.20. At, 71.15.Mb The possibility of carbon nanotubes (CNT) switching devices has been pursued in the last decade because of their attractive electronic properties. Nevertheless, problems with large intrinsic resistance in contacts and the inability to control tube helicity, and thus whether or not they are metallic or semiconducting, have made large scale circuit designs problematic. The proposed solution to these problems is an all carbon nanoelectronics paradigm based on the planar 2D form of carbon, graphene. [1] Graphene consists of a single carbon plane arranged on a honeycomb lattice. From a fundamental point of view, graphene ribbons can be seen as an unrolled CNT but with different boundary conditions (finite versus cyclic). Therefore, their electronic properties should be similar. In fact this has been demonstrated in recent experiments on single and multi-graphene sheets that show the existence of Dirac Fermions, large electron coherence lengths and anomalous integer quantum Hall effect [2,3,4]. The advantage of graphene over CNTs for electronics resides in its planar 2D structure that enables circuit design with standard lithography techniques. This enables the graphene to be cut with different shapes and selected edge direction. By simply selecting the ribbon edge direction it is possible to design metallic or semiconductor graphene ribbons [5,6] (analogous to helicity in CNTs).Since single or multiple sheets must be supported on a surface for fabrication, the pressing question becomes: how does the interface between a graphene sheet and its support affect its electronic properties? In other words can the symmetry of an isolated graphene sheet be maintained in the presence of an interface? It is this question that is the focus of this paper. Specifically we have studied the system of graphite grown on both polar faces of hexagonal SiC.The graphene layers are produced by sublimating Si from either the 4H-or 6H-SiC (0001) (Si terminated) or (0001) (C terminated) surfaces at sufficiently high temperatures to graphitize the excess car...