We analyze and interpret resonant Raman-Brillouin scattering by folded acoustic vibrations in short-period GaAs/AlAs superlattices. Analysis of the spectra and their resonance behavior is performed using a Raman-Brillouin electronic density constructed by combining thousands transitions between electronic eigenstates of the system according to their weight in the light-scattering process. We show that plots of this effective electronic density allow for capturing the essential physics of the electron-phonon interaction and of the resonant light-scattering process in a situation where complex effects are simultaneously present: electronic confinement in the quantum wells and wave-function delocalization due to interlayer coupling, folding of acoustic dispersion and symmetry changes in the deformation fields, resonant selection of optical transitions. Comparison between the measured spectra and those simulated using the Raman-Brillouin quantum model and the photoelastic model are presented. Activation and/or deactivation of the scattering by acoustic vibration doublets and changes in their intensity ratio with excitation energy are directly related to the Raman-Brillouin electronic density distribution along the superlattices axis. Limitations of the photoelastic model are discussed by comparing the steplike variation in the photoelastic coefficient to the Raman-Brillouin electronic density profiles.

Epitaxial graphene was grown on the surface of on-axis and off-axis SiC (0001) by solid state graphitization at high temperatures (2000 degrees C) in Ar ambient. The effect of the miscut angle on the lateral uniformity of the few layers of graphene (FLG) was investigated by combined application of micro-Raman spectroscopy and Torsion Resonance Conductive Atomic Force Microscopy, the latter method enabling a quantification of the FLG coverage on SiC with submicrometer lateral resolution. While the on-axis samples result in uniform coverage by thin (similar to 3 monolayers) FLG, the coverage for off-axis samples is much less uniform, following closely the step bunching morphology of the SiC surface.

Epitaxial graphene growth is significantly different depending on the polarity of the 6H-SiC surface: Si- or C-face. On the Si-face, a uniform coverage of few layers on the whole sample can be obtained, but with electrical properties disturbed by the presence of a Carbon-rich buffer layer at the interface. On the contrary, on the C-face, we demonstrated that almost free-standing very large monolayers of graphene can be obtained by covering the sample with a graphitic cap during the growth.

We studied the in-plane magnetoresistance R(B, T) anisotropy in epitaxial multilayer graphene films grown on the Si face of a 6H-SiC substrate that originates from steplike morphology of the SiC substrate. To enhance the anisotropy, a combination of argon atmosphere with graphite capping was used during the film growth. The obtained micro-Raman spectra demonstrated a complex multilayer graphene structure with the smaller film thickness on terraces as compared to the step edges. Several Hall bars with different current/steps mutual orientations have been measured. A clear anisotropy in the magnetoresistance has been observed, and attributed to variations in electron mobility governed by the steplike structure. Our data also revealed that (i) the graphene-layer stacking is mostly Bernal type, (ii) the carriers are massive, and (iii) the carriers are confined to the first 2-4 graphene layers following the buffer layer.

Using a graphite cap to cover the silicon carbide (SiC) sample, it is shown that large isolated graphene anisotropic ribbons can be grown on the C face of on-axis, semi-insulating, 6H-SiC wafers. The role of the cap is to modify the physics of the surface reconstruction process during Si sublimation, making more efficient the reconstruction of few selected terraces with respect to the others. The net result is the formation of a strongly step-bunched morphology with, in between, long (up to 600 mu m) and large (up to 5 mu m) homogeneous monolayers of graphene ribbons. This is shown by optical and scanning electron microscopy, while a closer view is provided by atomic force microscopy (AFM). From Raman spectroscopy, it is shown that most of the ribbons are homogeneous monolayers or bilayers of graphene. It is also shown that most of the thermal stress between the graphene layer and the 6H-SiC substrate is relaxed by wrinkles. The wrinkles can be easily displaced by an AFM tip, which demonstrates evidence of graphene ironing at the nanoscale. Finally and despite the very low optical absorption of a single graphene layer, one shows that differential optical microtransmission can be combined to the micro-Raman analysis to confirm the monolayer character of the thinnest ribbons.

The current transport across the graphene/4H-SiC interface has been investigated with nanometric lateral resolution by scanning current spectroscopy on both epitaxial graphene (EG) grown on (0001) 4H-SiC and graphene exfoliated from highly oriented pyrolytic graphite deposited on the same substrate [deposited graphene (DG)]. This study reveals that the Schottky barrier height (SBH) of EG/4H-SiC (0.36 +/- 0.1 eV) is similar to 0.49 eV lower than the SBH of DG/4H-SiC (0.85 +/- 0.06 eV). This result is discussed in terms of the Fermi-level pinning similar to 0.49 eV above the Dirac point in EG due to the presence of positively charged states at the interface between the Si face of 4H-SiC and the carbon-rich buffer layer, which is the precursor for EG formation.

We report a comparative investigation of Few layers graphene grown on 6H, 4H, and 3C-SiC substrates. We show that the size of the graphitic domains depends more on the < 0001 > SiC Surface orientation than the polytypism.