We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10 12 cm −2 per graphene sheet. The most highlyordered sample exhibits Shubnikov -de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

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...

With expanding interest in graphene-based electronics, it is crucial that high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001) (Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce epitaxial graphene sheets on a semiconductor. In this paper we show that graphene grown from the SiC(0001) (C-terminated) surface are of higher quality than those previously grown on SiC(0001). Graphene grown on the C-face can have structural domain sizes more than three times larger than those grown on the Si-face while at the same time reducing SiC substrate disorder from sublimation by an order of magnitude.

Graphene quantum dots (GQDs) interacting with molybdenum disulfide (MoS2 ) monolayers induce an effective photoexcited charge transfer at the interface. Both the photoluminescence (PL) and valley polarization of this GQDs/MoS2 heterostructure can be modulated under various doping charge densities. The photon-exciton interaction is used to explain and calculate the heterostructure PL control, and is further applied to the valley-polarization tuning.

We present a structural analysis of the multi-layer graphene-4HSiC(0001) system using Surface X-Ray Reflectivity. We show for the first time that graphene films grown on the C-terminated (0001) surface have a graphene-substrate bond length that is very short (1.62Å). The measured distance rules out a weak Van der Waals interaction to the substrate and instead indicates a strong bond between the first graphene layer and the bulk as predicted by ab-initio calculations. The measurements also indicate that multi-layer graphene grows in a near turbostratic mode on this surface. This result may explain the lack of a broken graphene symmetry inferred from conduction measurements on this system [C. Berger et al., Science 312, 1191].