Chemical vapor deposition has proved to be successful in producing graphene samples on silicon carbide (SiC) homogeneous at the centimeter scale in terms of Hall conductance quantization. Here, we report on the realization of co-planar diffusive Al/ monolayer graphene/ Al junctions on the same graphene sheet, with separations between the electrodes down to 200 nm. Robust Josephson coupling has been measured for separations not larger than 300 nm. Transport properties are reproducible on different junctions and indicate that graphene on SiC substrates is a concrete candidate to provide scalability of hybrid Josephson graphene/superconductor devices.

Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn.

In this communication, we will illustrate how Raman spectroscopy can be used tostudy the doping of graphene. We will first report data recorded by in situ Ramanexperiments on single-layer (SLG) graphene during exposure to rubidium vapor. Bythis way, we have been able to follow continuously the changes of the G and 2Dbands features over a broad doping range (up to about 1014 electrons/cm2). Previoustheoretical predictions have shown that the evolution of the G-mode in SLG resultsfrom the competition between adiabatic and non-adiabatic effects. We emphasizethat a possible substrate pinning effect, which inhibits the charge-induced latticeexpansion of graphene layer, can strongly influence the G band position [1].In the second part, we will show that the charge carrier density of grapheneexfoliated on a SiO2/Si substrate can be finely and reversibly tuned between electronand hole doping with visible photons. This photo-induced doping happens undermoderate laser power conditions but is significantly affected by the substratecleaning method. In particular, it requires hydrophilic substrates and vanishes forsuspended graphene. These findings also suggest that Raman spectroscopy is notalways as non-invasive as generally assumed [2].Finally, we will discuss how these results can be useful to extract information aboutgraphene doping and strain from Raman measurements.References[1] R. Parret, M. Paillet, J.-R. Huntzinger, D. Nakabayashi, T. Michel, A. Tiberj, J.-L.Sauvajol, A.-A. Zahab, ACS Nano, 7 (2013) 165.[2] A. Tiberj, M. Rubio-Roy, M. Paillet, J.-R. Huntzinger, P. Landois, M. Mikolasek, S.Contreras, J.-L. Sauvajol, E. Dujardin, A.-A. Zahab, Scientific Reports, 3 (2013)2355.

The structural, optical, and transport properties of graphene grown by chemical vapor deposition (CVD) of propane under hydrogen on the Si face of SiC substrates have been investigated. We show that little changes in temperature during the growth can trigger the passivation of the SiC surface by hydrogen. Depending on the growth condition, hole or electron doping can be achieved, down to a few 1011 cm−2. When the growth temperature is high (T≈1500–1550∘C), we obtain electron-doped graphene monolayers lying on a buffer layer. When the growth temperature is slightly lowered (T≈1450–1500∘C), hole-doped graphene layers are obtained, lying on a hydrogen-passivated SiC surface, as confirmed by the enhancement of the mobility (of the order of 4500 cm2/Vs) and the persistence of weak localization almost up to room temperature (250 K). The high homogeneity of this graphene allows the observation of the half-integer quantum Hall effect, typical of graphene, at the centimeter scale in the best cases. The influence of the SiC steps on the transport properties is discussed.

While the integration of graphene on semiconductor surfaces is important to develop new applications, epitaxial graphene has only been integrated on SiC substrates or 3C-SiC/Si templates. In this work, we explore the possibility of growing graphene on AlN/Si(111) templates. Using a chemical vapor deposition process with propane as the carbon source, we have obtained graphitic films (from 2 to 10 graphene layers) on AlN/Si(111) while preserving the morphology of the AlN layer beneath the graphitic film. This study is an important step for the integration of graphene with semiconductors other than SiC.