Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC

Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping

Electrical properties of the graphene/4H-SiC (0001) interface probed by scanning current spectroscopy

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

Room temperature tunable detection of subterahertz radiation by plasma waves in nanometer ingaas transistors

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InSe as a case between 3D and 2D layered crystals for excitons

InSe is a promising material in many aspects where the role of excitons is decisive. Here we report the sequential appearance in its luminescence of the exciton, the biexciton, and the P-band of the exciton-exciton scattering while the excitation power increases. The strict energy and momentum conservation rules of the P-band are used to reexamine the exciton binding energy. The new value >= 20 meV is markedly higher than the currently accepted one (14 meV), being however well consistent with the robustness of the excitons up to room temperature. A peak controlled by the Sommerfeld factor is found near the bandgap (similar to 1.36 eV). Our findings supported by theoretical calculations taking into account the anisotropic material parameters question the pure three-dimensional character of the exciton in InSe, assumed up to now. The refined character and parameters of the exciton are of paramount importance for the successful application of InSe in nanophotonics

Up and Down, Old and New: Values and Value Systems of MPs and Voters in France

MPs are often criticised as being homogeneous. This is well known in terms of social background or gender, but the criticism also holds for values and norms. MPs are said to share normative agreements on the essential points and demonstrate differences on second-order issues. This criticism is even more widespread regarding the new politics based on the cultural divide, notably vis-à-vis politicians from the extreme right as far as immigration, European integration or globalisation are concerned. In this contribution, these criticisms are addressed by investigating the degree of normative agreements and disagreements of French MPs. Furthermore, the differences both in old and new politics between MPs on the one hand and the electorate as a whole and their supporters on the other hand are evaluated. It is concluded that MPs are definitely not all the same and the degrees of difference among MPs or with the electorate are far from being those expected

Module Éducation à la Transition Écologique (ETE) à l'université de Montpellier : retour d'expérience.

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