Thermally induced growth of graphene on the two polar surfaces of 6H-SiC is investigated with emphasis on the initial stages of growth and interface structure. The experimental methods employed are angle-resolved valence band photoelectron spectroscopy, soft x-ray induced core-level spectroscopy, and low-energy electron diffraction. On the Si-terminated ͑0001͒ surface, the ͑6 ͱ 3 ϫ 6 ͱ 3͒R30°reconstruction is the precursor of the growth of graphene and it persists at the interface upon the growth of few layer graphene ͑FLG͒. The ͑6 ͱ 3 ϫ 6 ͱ 3͒R30°structure is a carbon layer with graphene-like atomic arrangement covalently bonded to the substrate where it is responsible for the azimuthal ordering of FLG on SiC͑0001͒. In contrast, the interaction between graphene and the C-terminated ͑0001͒ surface is much weaker, which accounts for the low degree of order of FLG on this surface. A model for the growth of FLG on SiC͕0001͖ is developed, wherein each new graphene layer is formed at the bottom of the existing stack rather than on its top. This model yields, in conjunction with the differences in the interfacial bonding strength, a natural explanation for the different degrees of azimuthal order observed for FLG on the two surfaces.

A hallmark of graphene is its unusual conical band structure that leads to a zero-energy band gap at a singleElectrons in metals and semiconductors undergo many complex interactions, and most theoretical treatments make use of the quasiparticle approximation, in which independent electrons are replaced by electron-and holelike quasiparticles interacting through a dynamically screened Coulomb force. The details of the screening are determined by the valence band structure, but the band energies are modified by the screened interactions. A complex self-energy function describes the energy and lifetime renormalization of the band structure resulting from this interplay.Bohm and Pines (1) accounted for the short-range interactions between quasiparticles through the creation of a polarization cloud formed of virtual electron-hole pairs around each charge carrier, screening each from its neighbors. The long-range interactions manifest themselves through plasmons, collective charge density oscillations of the electron gas that can propagate through the medium with their own band-dispersion relation.These plasmons can in turn interact with the charges, leading to strong self-energy effects. Lundqvist predicted the presence of new composite particles called plasmarons formed by the coupling of the elementary charges with plasmons (2). Their distinct energy bands should be observable using angle-resolved photoemission spectroscopy (ARPES), but so far have only been observed by optical (3, 4) and tunneling spectroscopies (5), which probe the altered density of states.Understanding the coupling between electrons and plasmons is important because of new "plasmonic" devices proposed to merge photonics and electronics. Graphene in particular has been proposed as a promising candidate for such devices (6-8). Plasmarons have been predicted to occur in graphene and to be observable in ARPES (9, 10), yet their detailed dispersion and interaction with defects remain unknown. Here we present a

We report on an investigation of quasi-free-standing graphene on 6H-SiC(0001) which was prepared by intercalation of hydrogen under the buffer layer. Using infrared absorption spectroscopy we prove that the SiC(0001) surface is saturated with hydrogen. Raman spectra demonstrate the conversion of the buffer layer into graphene which exhibits a slight tensile strain and short range defects. The layers are hole doped (p = 5.0-6.5 x 10^12 cm^(-2)) with a carrier mobility of 3,100 cm^2/Vs at room temperature. Compared to graphene on the buffer layer a strongly reduced temperature dependence of the mobility is observed for graphene on H-terminated SiC(0001)which justifies the term "quasi-free-standing".Comment: 3 pages, 3 figures, accepted for publication in Applied Physics Letter

We investigate the transport properties of high-quality single-layer graphene, epitaxially grown on a 6H-SiC͑0001͒ substrate. We have measured transport properties, in particular charge-carrier density, mobility, conductivity, and magnetoconductance of large samples as well as submicrometer-sized Hall bars which are entirely lying on atomically flat substrate terraces. The results display high mobilities, independent of sample size. The temperature dependence of the conductance indicates a rather strong coupling to the SiC substrate. An analysis of the Shubnikov-de Haas effect yields the Landau-level spectrum of single-layer graphene. When gated close to the Dirac point, the mobility increases substantially and the graphenelike quantum Hall effect occurs.

Electron-plasmon coupling in graphene has recently been shown to give rise to a "plasmaron" quasiparticle excitation. The strength of this coupling has been predicted to depend on the effective screening, which in turn is expected to depend on the dielectric environment of the graphene sheet. Here we compare the strength of enviromental screening for graphene on four different substrates by evaluating the separation of the plasmaron bands from the hole bands using Angle Resolved PhotoEmission Spectroscopy. Comparison with G0W -RPA predictions are used to determine the effective dielectric constant of the underlying substrate layer. We also show that plasmaron and electronic properties of graphene can be independently manipulated, an important aspect of a possible use in "plasmaronic" devices.

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Metal nanoantenna plasmon resonance lineshape modification by semiconductor surface native oxide J. Appl. Phys. 112, 044315 (2012) Asymmetric interfacial abruptness in N-polar and Ga-polar GaN/AlN/GaN heterostructures Appl. Phys. Lett. 101, 091601 (2012) On the mechanisms of energy transfer between quantum well and quantum dashes J. Appl. Phys. 112, 033520 (2012) Enhanced internal quantum efficiency in graphene/InGaN multiple-quantum-well hybrid structures

Graphitization of the 6H-SiC(0001) surface as a function of annealing temperature has been studied by ARPES, high resolution XPS, and LEED. For the initial stage of graphitization – the 6√3 reconstructed surface – we observe σ-bands characteristic of graphitic sp2-bonded carbon. The π-bands are modified by the interaction with the substrate. C1s core level spectra indicate that this layer consists of two inequivalent types of carbon atoms. The next layer of graphite (graphene) formed on top of the 6√3 surface at TA=1250°C-1300°C has an unperturbed electronic structure. Annealing at higher temperatures results in the formation of a multilayer graphite film. It is shown that the atomic arrangement of the interface between graphite and the SiC(0001) surface is practically identical to that of the 6√3 reconstructed layer.