LOCAL ATOMIC CONFIGURATION IN LASER SYNTHESIZED SI C/N POWDERS STUDIED BY X-RAY PHOTOELECTRON-SPECTROSCOPY/

Nanometric Si/C/N powders have been obtained from the laser synthesis of a liquid precursor: hexamethydisilazane. The chemical composition o f the products is a function of the experimental parameters: the C/N r atio in the powders is controlled in the range 0.34 to 1.34 by varying the ammonia content in the flowing gas (argon). This paper presents s ome results obtained by X-ray Photoelectron Spectroscopy (XPS) about t he local atomic structure of these powders. The evolution of the powde rs after annealing treatments at 1500 and 1600 degrees C under nitroge n atmosphere has been studied. The chemical composition deduced from X PS wide spectra are compared with chemical analysis. From the analysis of the Si-2p core level, information about the local atomic bonding a round silicon atoms are obtained. The different environments present i n the system and their evolution with temperature have been deduced fr om the comparison with data obtained for stoichiometric compounds (SiC , Si3N4 and SiO2). The existence of local chemical disorder is shown i n the as-formed powders. For powders with C/N approximate to 0.6, the samples remains amorphous until 1500 degrees C; crystallization which starts around 1500 degrees C is total at 1600 degrees C. The existence of C-N bonds at 1500 and 1600 degrees C is evidenced. This result is in good agreement with results obtained by neutron diffraction and X-r ay absorption (XAS).