INSITU LIGHT-SCATTERING STUDY OF PARTICLES SYNTHESIZED IN A RF SILANE AMMONIA GLOW-DISCHARGE

Glow-discharge synthesis is an attractive candidate technology for making ultrafine ceramic precursors. Using light scattering, we studied in situ the size, mass, and structure of submicron particles generated in a radio frequency glow discharge of a silane-and-ammonia gas mixture. By dynamic light scattering, we found that large particles congregated near the ion sheath boundary with smaller particles in the bulk of the plasma. No anisotropy in particle velocities was observed, and we found excellent agreement between the intensity correlation data and a theory based on an isotropic Maxwell-Boltzmann velocity distribution. Of particular interest was the transport behavior of the particles, which, in the rarefied environment of the glow discharge, exhibited kinetic behavior persisting up to 100-mu-s and hydrodynamic behavior for longer times. The equipartition mass of the particles was obtained in the kinetic regime, and a drag factor was derived from the hydrodynamic regime. Near the ion sheath boundaries, where an intense band of scattering could be seen, static light scattering indicated a relatively large radius of gyration that could be reconciled with the mass only by assuming a low density, ramified particle structure. Ex situ small-angle neutron scattering showed that the particles were slightly rough.