Synthesis and nitridation of nanocrystalline silicon produced via a tubular forced flow reactor

The design and operation of a novel, continuous reactor for scaling-up the production of nanocrystalline materials is outlined. The reactor operates using a replenishable thermal evaporation source in a forced gas flow. This alternative reactor design overcomes many of the production limitations of the batch reactor inert gas condensation process used widely in nanocrystalline synthesis. By achieving gas flow velocities of 12.5-40 m s^-1, particle size is kept in the nanometer range by quickly removing the particles from the hot growth zone and minimizing their agglomeration during synthesis. The effects of processing parameters on Si particle size and morphology are presented. Nanocrystalline Si₃N₄ was produced by subsequent nitridation and heat treatment. Complete nitridation of the Si was achieved by 1050°C. Upon moderate heat treatment (1600°C for 3 h), the SiO_x present in the material crystallized.