Laser Synthesis and Characterization of Si/C/N Ceramic Powders

Abstract

We presented both laser synthesis and characterization of ultrafine nanometric (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 affecting this process are: the reactant flow ratio R = Φ//\mitPhiΦ, the C2H2 flow rate, the pressure cell and the laser power. These parameters strongly influence and change the temperature of the reaction which affects the size, stoichiometry and crystallinity of the particles. Infared Fourier transform reflection spectroscopy and X-ray diffraction analysis have been employed to investigate the final composition of the powders. Our results point out that for low values of R (R = 0.5 to 1) Si/C/N powders are a mixture of amorphous phase, ascribed to ternary compound and crystalline β-SiC, while for higher R values (R > 1) C atoms enter substitutionally into the matrix of amorphous Si3N4 giving rise to a ternary compound where most Si atoms have the local structure Cx–Si–N4–x.