NMR CHARACTERIZATION OF SI-BASED ULTRAFINE LASER FORMED POWDERS

Ultrafine SiC, Si3N4 and Si/C/N powders in the nanometric range (<100 nm) have been synthesized by laser driven reactions. Mixtures of SiH4C2H2 (or CH3SiH3), SiH4NH3 and SiH4CH3NH2NH3 have been irradiated by a high power continuous wave CO2 laser in a crossflow configuration cell. By varying the reaction conditions (flow rates and ratios of the reacting gases, laser power), amorphous to crystalline powders of variable size were formed. The powders were investigated by 29Si and 13C solid state NMR. A comparison of the different spectra obtained provides information on the local structure and composition of the materials. © 1992.