Morphology of graphene thin film growth on SiC(0001)

Epitaxial films of graphene on SiC(0001) are interesting from a basic physics as well as applications-oriented point of view. Here we study the emerging morphology of in-vacuo prepared graphene films using low energy electron microscopy (LEEM) and angle-resolved photoemission (ARPES). We obtain an identification of single and bilayer of graphene film by comparing the characteristic features in electron reflectivity spectra in LEEM to the PI-band structure as revealed by ARPES. We demonstrate that LEEM serves as a tool to accurately determine the local extent of graphene layers as well as the layer thickness

Origins of anomalous electronic structures of epitaxial graphene on silicon carbide

On the basis of first-principles calculations, we report that a novel interfacial atomic structure occurs between graphene and the surface of silicon carbide, destroying the Dirac point of graphene and opening a substantial energy gap there. In the calculated atomic structures, a quasi-periodic $6\times 6$ domain pattern emerges out of a larger commensurate $6\sqrt{3}\times6\sqrt{3}R30^\circ$ periodic interfacial reconstruction, resolving a long standing experimental controversy on the periodicity of the interfacial superstructures. Our theoretical energy spectrum shows a gap and midgap states at the Dirac point of graphene, which are in excellent agreement with the recently-observed anomalous angle-resolved photoemission spectra. Beyond solving unexplained issues of epitaxial graphene, our atomistic study may provide a way to engineer the energy gaps of graphene on substrates.Comment: Additional references added; published version; 4 pages, 4 figure

Electron states of mono- and bilayer graphene on SiC probed by STM

We present a scanning tunneling microscopy (STM) study of a gently-graphitized 6H-SiC(0001) surface in ultra high vacuum. From an analysis of atomic scale images, we identify two different kinds of terraces, which we unambiguously attribute to mono- and bilayer graphene capping a C-rich interface. At low temperature, both terraces show $(\sqrt{3}\times \sqrt{3})$ quantum interferences generated by static impurities. Such interferences are a fingerprint of $\pi$-like states close to the Fermi level. We conclude that the metallic states of the first graphene layer are almost unperturbed by the underlying interface, in agreement with recent photoemission experiments (A. Bostwick et al., Nature Physics 3, 36 (2007))Comment: 4 pages, 3 figures submitte

The interaction of Xe and Xe + K with graphene

We have investigated the electronic properties of monolayer graphene with adsorbed layers of xenon or potassium, or a combination of the two. The formation of the first Xe layer is characterized by a dipole polarization which is quenched by a second Xe layer. By comparing K on Xe on graphene to K on bare graphene, we determine the K contribution to trigonal warping and mass renormalization due to electron–phonon coupling. The former is found to be small but significant, while the latter is shown to be negligible. Thus, previously determined values of electron–phonon coupling for K on graphene are shown to be intrinsic to doped graphene and not determined by the proximity of K ions to the graphene

Graphene: Status and Prospects

Graphene is a wonder material with many superlatives to its name. It is the thinnest material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have the smallest effective mass (it is zero) and can travel micrometer-long distances without scattering at room temperature. Graphene can sustain current densities 6 orders higher than copper, shows record thermal conductivity and stiffness, is impermeable to gases and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a bench-top experiment. What are other surprises that graphene keeps in store for us? This review analyses recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.Comment: pre-edited version of the review published in Science Please note that only 40 references are allowed by the magazine. Sorr

Epitaxial graphene: a new material

Graphene, a two-dimensional sheet of sp2-bonded car-bon arranged in a honeycomb lattice, is not only the building block of fullerenes, carbon nano tubes (CNTs) and graphite, it also has interesting properties, which have caused a flood of activities in the past few years. The possibility to grow graphitic films with thick-nesses down to a single graphene layer epitaxially on SiC{0001} surfaces is promising for future applications. The two-dimensional nature of epitaxial graphene films make them ideal objects for surface science techniques such as photoelectron spectroscopy, low-energy electron diffraction, and scanning probe microscopy. The present article summarizes results from recent photoemission studies covering a variety of aspects such as the growth of epitaxial graphene and few layer graphene, the elec

Electron-Phonon Coupling in Highly-Screened Graphene

Photoemission studies of graphene have resulted in a long-standing controversy concerning the strength of the experimental electron-phonon interaction in comparison with theoretical calculations. Using high-resolution angle-resolved photoemission spectroscopy we study graphene grown on a copper substrate, where the metallic screening of the substrate substantially reduces the electron-electron interaction, simplifying the comparison of the electron-phonon interaction between theory and experiment. By taking the nonlinear bare bandstructure into account, we are able to show that the strength of the electron-phonon interaction does indeed agree with theoretical calculations. In addition, we observe a significant bandgap at the Dirac point of graphene.Comment: Submitted to Phys. Rev. Lett. on July 20, 201