(130e) Continuous Flow Plasma Microreactor Synthesis of Magnetic Nanoparticles

We have synthesized magnetic nanoparticles in a continuous flow plasma microreactor by non-thermal disassociation of vapor phase precursors. The synthesis technique employs a direct-current (dc) hollow cathode microplasma consisting of a stainless steel cathode with a pin hole (d~180 microns) and an arbitrarily-shaped anode. Microplasmas are miniaturized glow discharges characterized by large radial electric fields and high concentrations of energetic electrons which permit rapid decomposition of gaseous precursors. Under appropriate precursor saturation conditions, radicals polymerize to nucleate particles homogenously in the gas phase. Particle growth is limited to the small reactor volume (less than 1 nL) created by the microplasma geometry. As a result of the large concentration gradients and short residence time, the technique is capable of producing very small (2-20 nanometer diameter) nanoparticles with narrow size distributions. Particle size and distribution are determined in situ using a gas-phase electrophoretic mobility macromolecular analyzer (GEMMA). Aerosol classification allows experimental parameters to be rapidly optimized to obtain narrow size distributions. We have recently explored the formation of alloy nanoparticles such as CoPt for catalytic applications. Optimization results for the plasma microreactor and material properties of the nanoparticle alloys will be presented in this talk.