Polarisation du nitrométhane sous choc

Shock induced electrical polarization of nitromethane has been investigated in the 3 to 8.3 GPa range of pressure. Experimental results agree with Allison's phenomenological theory and lead to a polarization relaxation time of about 10 nanoseconds. We point that other works on the polarization of nitromethane have been published. Our results disagree in interpretation and relaxation time (30 picoseconds) but an agreement, within 15 %, is found for the dielectric constant.La polarisation du nitrométhane soumis à une onde de choc plane d'amplitude 3 à 8,3 GPa a été étudiée expérimentalement. Les résultats obtenus montrent que ce phénomène peut être décrit par la théorie phénoménologique d'Allison et conduisent à un temps de relaxation de la polarisation du nitrométhane d'environ 10 nanosecondes. Ces résultats contredisent les observations et les conclusions d'autres auteurs qui ont proposé pour interpréter leurs mesures une théorie différente et un temps de relaxation de l'ordre de 30 picosecondes. Par contre, nos résultats sur la constante diélectrique s'accordent à 15 % près avec les leurs

Fresnel diffraction in phase-space

Fresnel Diffraction is worked out in phase space by simple calculations based on the Wigner Distribution Functions for the transfer functions of an at-ray of ideal lenses, which allow the simulation of a composite material and of a continuous medium

Low-pressure chemical vapour deposition of mullite coatings in a cold-wall reactor

Nitrous oxide, together with aluminium and silicon chlorides, as precursor gases, while hydrogen and nitrogen as carriers, have been fed into a cold-wall reactor, in order to produce crystalline deposited layers of mullite (3Al2O3.2SiO2) on silicon carbide and aluminium nitride substrates. The corresponding deposition kinetics has been studied, for fixed flow rates of nitrous oxide, hydrogen and nitrogen, as a function : of the substrate temperature, from 1100 to 1300 °C ; of the gas pressure, from 10 to 90 hPa and of the AlCl3 to SiCl4 input ratio. The coating's chemical composition, crystal structure and morphology was precisely determined by means of WDS, XRD and SEM. The aluminium content of the deposits increases first as a function of pressure. It reaches a maximum for P = 20 hPa, whence it decreases steadily, to finally vanish completely for P = 100 hPa. The best experimental conditions to produce mullite coatings were then interpolated, experimentally tested, and the side compounds, under such conditions, identified

Chemical Bath Deposition of PbS:Hg2+ Nanocrystalline Thin Films

Nanocrystalline PbS thin films were prepared by Chemical Bath Deposition (CBD) at 40 ± 2°C onto glass substrates and their structural and optical properties modified by in-situ doping with Hg. The morphological changes of the layers were analyzed using SEM and the X-rays spectra showing growth on the zinc blende (ZB) face. The grain size determined by using X-rays spectra for undoped samples was found to be ~36 nm, whereas with the doped sample was 32–20 nm. Optical absorption spectra were used to calculate the Eg, showing a shift in the range 1.4–2.4 eV. Raman spectroscopy exhibited an absorption band ~135 cm−1 displaying only a PbS ZB structure