Particle formation paths in the synthesis of silicon nitride powder in a laser-heated aerosol reactor

Abstract

The Laser-chemical vapour precipitation of Si 3N 4 powder by reacting SiH 4 and NH 3 was studied using a newly developed laminar gas mixing system. Thermophoretic sampling enabled monitoring of the formation process on a milli-second basis and shows the existence of two synthesis paths: the nitridation of Si particles and the sintering of directly formed Si 3N 4. The latter route leads to almost stoichiometric α- and β-Si 3N 4, with particle sizes up to 150 nm. The Si 3N 4 particles do not decompose above the thermodynamic decomposition temperature, probably due to kinetic reasons since the residence time is of the order of milliseconds.