Obtention d'alliages réfractaires SiCxNy(O) par dépôt chimique à oartir d'une gazeuse Si(CH3)4-NH3

By pure thermal CVD from Si(CH/sub 3/)/sub 4/NH/sub 3/ mixtures SiC/sub x/N/sub y/(O) films have been prepared at 1475 K. Using electron microprobe analysis a continuous composition variation between SiC and Si/sub 3/N/sub 4/ is shown. The difficulty of quantitative analysis due to the conductivity of the samples is underlined. By selecting the right conditions, precise measurements were obtained. These films have an optical energy band gap in the range 2.2-4.1 eV and a constant photoluminescence peak. The film structure is discussed and these materials may be probably ascribed to an alloy phas

Periodic formation of FeSi bands in diffusion couples Fe (15 wt.% Si) - Zn

During the reaction in Fe(15 wt.% Si)-Zn diffusion couples at temperatures between 623 and 723 K thin regularly spaced parallel bands containing very small FeSi precipitates are observed throughout the 6 and ~ reaction layers. The periodic nature of this effect is strongly reminiscent of the well-known Liesegang phenomenon. A detailed analysis of our results with respect to the principles underlying the Liesegang mechanism, however, shows that such a mechanism cannot explain the observed phenomenon in our case. A more probable explanation is found in the action of shear and tenSile stresses in the diffusion couple which lead to a periodic release ofthe continuously formed FeSi precipitates from the Fe(15 wt.% Si) substrate. Preliminary results obtained with substrates of varying thicknesses are strongly in favour of the latter explanation