Laser synthesis and characterization of Si/C/N ceramic powders

We presented both laser synthesis and characterization of ultrafine nanomet ric (12 to 20 nm diameter) Si/C/N powders starting From NH3, SiH4 and C2H2 gas mixture, using a continuous-wave CO2 laser. The main parameters affecti ng this process are: the reactant flow ratio R = Phi (NH3)/Phi (SiH4), the C2H2 flow rate, the pressure cell and the laser power. These parameters str ongly influence and change the temperature of the reaction which affects th e size, stoichiometry and crystallinity of the particles. Infared Fourier t ransform reflection spectroscopy and X-ray diffraction analysis have been e mployed to investigate the final composition of the powders. Our results po int out that for low values of R (R = 0.5 to 1) Si/C/N powders are a mixtur e of amorphous phase, ascribed to ternary compound and crystalline beta -SI C, while for higher R values (R > 1) C atoms enter substitutionally into th e matrix of amorphous Si3N4 giving rise to a ternary compound where most Si atoms have the local structure CxS-Si-N4-x.