Konstantin V. Emtsev

Large area quasi-free standing monolayer graphene on 3C-SiC(111)

Large scale, homogeneous quasi-free standing monolayer graphene is obtained on cubic silicon carbide, i.e., the 3C-SiC(111) surface, which represents an appealing and cost effective platform for graphene growth. The quasi-free monolayer is produced by intercalation of hydrogen under the interfacial, (6 root 3 x 6 root 3)R30 degrees-reconstructed carbon layer. After intercalation, angle resolved photoemission spectroscopy reveals sharp linear pi-bands. The decoupling of graphene from the substrate is identified by x-ray photoemission spectroscopy and low energy electron diffraction. Atomic force microscopy and low energy electron microscopy demonstrate that homogeneous monolayer domains extend over areas of hundreds of square-micrometers

Revealing the electronic band structure of trilayer graphene on SiC: An angle-resolved photoemission study

In recent times, trilayer graphene has attracted wide attention owing to its stacking and electric-field-dependent electronic properties. However, a direct and well-resolved experimental visualization of its band structure has not yet been reported. In this paper, we present angle-resolved photoemission spectroscopy data which show with high resolution the electronic band structure of trilayer graphene obtained on alpha-SiC(0001) and beta-SiC(111) via hydrogen intercalation. Electronic bands obtained from tight-binding calculations are fitted to the experimental data to extract the interatomic hopping parameters for Bernal and rhombohedral stacked trilayers. Low-energy electron microscopy measurements demonstrate that the trilayer domains extend over areas of tens of square micrometers, suggesting the feasibility of exploiting this material in electronic and photonic devices. Furthermore, our results suggest that, on SiC substrates, the occurrence of a rhombohedral stacked trilayer is significantly higher than in natural bulk graphite. (Less)

Large Area Quasi-Free Standing Monolayer Graphene on 3C-SiC(111)

Large scale, homogeneous quasi-free standing monolayer graphene is obtained on a (111) oriented cubic SiC bulk crystal. The free standing monolayer was prepared on the 3C-SiC(111) surface by hydrogen intercalation of a -reconstructed carbon monolayer, so-called zerolayer graphene, which had been grown in Ar atmosphere. The regular morphology of the surface, the complete chemical and structural decoupling of the graphene layer from the SiC substrate as well as the development of sharp monolayer p-bands are demonstrated. On the resulting sample, homogeneous graphene monolayer domains extend over areas of hundreds of square-micrometers.

Mini-Dirac cones in the band structure of a copper intercalated epitaxial graphene superlattice

The electronic band structure of an epitaxial graphene superlattice, generated by intercalating a monolayer of Cu atoms, is directly imaged by angle-resolved photoelectron spectroscopy. The 3.2 nm lateral period of the superlattice is induced by a varying registry between the graphene honeycomb and the Cu atoms as imposed by the heteroepitaxial interface Cu/SiC. The carbon atoms experience a lateral potential across the supercell of an estimated value of about 65 meV. The potential leads to strong energy renormalization in the band structure of the graphene layer and the emergence of mini-Dirac cones. The mini-cones band velocity is reduced to about half of graphenes Fermi velocity. Notably, the ordering of the interfacial Cu atoms can be reversibly blocked by mild annealing. The superlattice indeed disappears at∼220 °C. (Less)

Manipulation of plasmon electron–hole coupling in quasi-free-standing epitaxial graphene layers

We have investigated the plasmon dispersion in quasi-free-standing monolayer graphene (QFMLG) and epitaxial monolayer graphene (MLG) layers by means of angle resolved electron energy loss spectroscopy. We have shown that various intrinsic p- and n-doping levels in QFMLG and MLG, respectively, do not lead to different overall slopes of the sheet plasmon dispersion, contrary to theoretical predictions. Only the coupling of the plasmon to single particle interband transitions becomes obvious in the plasmon dispersion by characteristic points of inflections, which coincide with the location of the Fermi level above or below the Dirac point. Further evidence is given by thermal treatment of the QFML graphene layer with gradual desorption of intercalated hydrogen, which shifts the chemical potential toward the Dirac point. From a detailed analysis of the plasmon dispersion, we deduce that the interaction strength between the plasmon and the electron–hole pair excitation is increased by about 30% in QFMLG compared to MLG, which is attributed to a modified dielectric environment of the graphene film.

Tailoring the Electronic Structure of Epitaxial Graphene on SiC(0001): Transfer Doping and Hydrogen Intercalation

Graphene grown on the (0001) basal plane of silicon carbide, i.e. on the SiC(0001) surface, is an extremely promising candidate for future nano-electronic applications. However, hurdles such as strong electron doping and low carrier mobility might sensibly limit the prospects of graphene on SiC(0001). In this work we present and discuss two different approaches that allow for a precise tailoring of the band-structure of graphene on SiC(0001): non-covalent functionalization of the graphene surface with a strong acceptor molecule, i.e. tetrafluorotetracyanoquinodimethane (F4-TCNQ), and passivation of the SiC interface via hydrogen intercalation. Both approaches effectively eliminate the intrinsic n-type doping in graphene and might have a positive impact in the charge carrier mobility. The molecular functionalization approach also leads to an enlargement of the band-gap of bilayer graphene to more than double of the original value. Hydrogen intercalation yields graphene layers decoupled from the SiC substrate and hence quasi-free standing. Furthermore, this work investigates a combination of the two approaches and demonstrates that quasi-free standing bilayer graphene can be hole doped by depositing F4-TCNQ.