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Trilayer graphene is of particular interest to the 2D materials community because of its unique tunable electronic structure. However, to date, there is a lack of fundamental understanding of the properties of epitaxial trilayer graphene on silicon carbide. Here, following successful synthesis of large-area uniform trilayer graphene, atomic force microscopy (AFM) showed that the trilayer graphene on 6H-SiC(0001) was uniform over a large scale. Additionally, distinct defects, identified as flower-shaped domains and isolated wrinkle structures, were observed randomly on the surface using scanning tunneling microscopy and spectroscopy (STM/STS). These carbon nanostructures formed during growth, has different structural and electronic properties when compared with the adjacent flat regions of the graphene. Finally, using low temperature STM/STS at 4K, we found that the isolated wrinkles showed an irreversible rotational motion between two 60° configurations at different densities of states.

International audience; A Grazing Incidence Fast Atom Diffraction (GIFAD) system has been mounted on a commercial molecular beam epitaxy chamber and used to monitor GaAs growth in real-time. In contrast to the conventionally used Reflection High Energy Electron Diffraction, all the GIFAD diffraction orders oscillate in phase, with the change in intensity related to diffuse scattering at step edges. We show that the scattered intensity integrated over the Laue circle is a robust method to monitor the periodic change in surface roughness during layer-by-layer growth, with oscillation phase and amplitude independent of incidence angle and crystal orientation. When there is a change in surface reconstruction at the start of growth, GIFAD intensity oscillations show that there is a corresponding delay in the onset of layer-by-layer growth. In addition, changes in the relative intensity of different diffraction orders have been observed during growth showing that GIFAD has the potential to provide insight into the preferential adatom attachment sites on the surface reconstruction during growth. (C) 2014 AIP Publishing LLC.

The effect of oxygen adsorption on the local structure and electronic properties of monolayer graphene grown on SiC(0001) has been studied by means of Low Energy Electron Microscopy (LEEM), microprobe Low Energy Electron Diffraction (\muLEED) and microprobe Angle Resolved Photoemission (\muARPES). We show that the buffer layer of epitaxial graphene on SiC(0001) is partially decoupled after oxidation. The monitoring of the oxidation process demonstrates that the oxygen saturates the Si dangling bonds, breaks some Si-C bonds at the interface and intercalates the graphene layer. Accurate control over the oxidation parameters enables us to tune the charge density modulation in the layer., 12 pages, 4 figures

International audience; A new table top technique is used to simultaneously analyze the local morphology of crystalline surfaces as well as the misalignment of large scale domains at the topmost surface layer. The approach is based on fast atom diffraction at grazing incidence (GIFAD); the diffraction pattern yields the structural characteristics and the topology of the surface electronic density with atomic resolution. If superficial mosaicity is present, diffraction patterns arising from each mosaic domain can be distinguished, providing high sensitivity to the properties of each of the domains. Taking NaCl(001) as an example, we observe a discrete tilt angle distribution of the mosaic domains following an arithmetic progression with a 0.025° ± 0.005° difference; a twist mosaic angle of 0.09° ± 0.01° is also observed.

In close analogy with the catalytic growth of graphene over-layer on several metal surfaces we have grown a two-dimensional silicon sheet in a honeycomb lattice, i.e. in a graphene-like structure, which could be a silicene layer. Two atomic ball models of this silicon single layer accounting for the atomically resolved scanning tunneling microscopy images and the low energy electron diffraction patterns are presented.

International audience; The optical properties of stacked InAs/InP quantum sticks (QSs) are investigated as a function of the spacer layer thickness. The stacked structures are grown by solid source molecular beam epitaxy and studied by photoluminescence (PL), polarized photoluminescence and photoluminescence excitation. Like for single QS plane structures, the stacked structures show PL spectra consisting of several peaks attributed to ground and excited states. The lowest full-width at half-maximum (FWHM=25 meV for the ground state) is measured for the intermediate 15 nm spacer layer thickness. High room temperature PL intensity is recorded. The results are promising for the use of such structures as active media in laser devices.

Using low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), and x-ray absorption spectroscopy (XAS) techniques, we have studied the first steps of silicon adsorption onto Cu (001) single crystal substrate. For low coverage (∼0.5 ML) and after annealing at 100 °C, STM images and LEED patterns reveal the formation of an ordered quasi commensurate (5×3) superstructure. From a quantitative analysis of XAS data, we extract the Si-Cu distance and detail the local atomic arrangement of the (5×3) structure.