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Chemical Vapor Deposition (CVD) of graphene on copper is one of the most efficient technologies for producing high quality graphene for large areas. Nevertheless, still high pressures and big quantities of precursor gas are currently required. The objective of this work is to deposit graphene using the monolayer-formation-time concept (t) from the kinetic theory of gases, which leads to an economization of the precursor gas, a minimization of the process pressure and the time needed to grow a graphene monolayer. Our process has been designed taking into account the dependence of t on the pressure, the mass particle of the gas, the sticking coefficient, and the growth temperature. Thus, with this alternative method, based on CVD but using very-low pressure instant pulses of precursor gas (~10^-4 Pa), we have reduced the deposition time to the order of 10 s. We carried out the processes at temperatures below 1000 Grad Celsius with methane (CH4) as a precursor gas under High Vacuum (HV) conditions. After Raman spectroscopy and mapping, and Scanning Electron Microscopy (SEM) characterization of the samples, the results point to the formation of high quality monolayer graphene on sputtered copper and silicon substrates covering domain areas of 10^4 micron^2.

The Solar Diameter Imager and Surface Mapper (SODISM) on board the PICARD space mission provides wide-field images of the photosphere and chromosphere of the Sun in five narrow pass bands (centered at 215.0, 393.37, 535.7, 607.1, and 782.2 nm). PICARD is a space mission, which was successfully launched on 15 June 2010 into a Sun synchronous dawn-dusk orbit. It represents a European asset aiming at collecting solar observations that can serve to estimate some of the inputs to Earth climate models. The scientific payload consists of the SODISM imager and of two radiometers, SOVAP (SOlar VAriability PICARD) and PREMOS (PREcision MOnitor Sensor), which carry out measurements that allow estimating the Total Solar Irradiance (TSI) and the Solar Spectral Irradiance (SSI) from the middle ultraviolet to the red. The SODISM telescope monitors solar activity continuously. It thus produces images that can also feed SSI reconstruction models. Further, the objectives of SODISM encompass the probing of the interior of the Sun via helioseismic analysis of observations in intensity (on the solar disc and at the limb), and via astrometric investigations at the limb. The latter addresses especially the spectral dependence of the radial limb shape, and the temporal evolution of the solar diameter and asphericity. After a brief review of its original science objectives, this paper presents the detailed design of the SODISM instrument, its expected performance, and the scheme of its flight operations. Some observations with SODISM are presented and discussed., Comment: 37 pages, 14 figures, more information at http://picard.projet.latmos.ipsl.fr/

A simple and most promising oxide-assisted catalyst-free method is used to prepare silicon nitride nanowires that give rise to high yield in a short time. After a brief analysis of the state of the art, we reveal the crucial role played by the oxygen partial pressure: when oxygen partial pressure is slightly below the threshold of passive oxidation, a high yield inhibiting the formation of any silica layer covering the nanowires occurs and thanks to the synthesis temperature one can control nanowire dimensions.

The synthesis of Si3N4 nanowires from the reaction of silicon nanoparticles with N2 in the 1200-1440 C temperature range is reported. The nitridation conditions are such that the reaction with nitrogen is favoured by the presence of silicon oxide in the particles and by the active oxidation of silicon without a catalyst. It is shown that the Si to Si3N4 conversion rate depends on the amount of silicon particles used in the experiments and that, in general, the reaction slows down for greater amounts. This trend is explained by particle stacking, which restricts the exchange of gases between the furnace atmosphere and the atmosphere around the inner particles. In a first stage, local oxygen partial pressure increases around the inner particles and inhibits nitridation locally. If the amount of reactant Si nanoparticles is small enough, this extrinsic effect is avoided and the intrinsic nitridation kinetics can be measured. Experiments show that intrinsic kinetics does not depend on temperature.