AVS 51st International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThM

Paper PS-ThM6
Atmospheric-pressure Microdischarges as Short-residence Time Reactors for Silicon Nanoparticle Synthesis

Thursday, November 18, 2004, 10:00 am, Room 213A

Session: Atmospheric and Microdischarges
Presenter: R.M. Sankaran, California Institute of Technology
Authors: R.M. Sankaran, California Institute of Technology
D. Holunga, California Institute of Technology
R.C. Flagan, California Institute of Technology
K.P. Giapis, California Institute of Technology
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Microdischarges are investigated as short-residence time reactors for the synthesis of nanoparticles. The application is attractive since nucleation and growth can be limited in the reaction zone, while charging of particles in the plasma may reduce coagulation downstream. We report here on the gas-phase synthesis of silicon nanoparticles in an atmospheric-pressure dc microdischarge. The discharges are formed in silane/argon gas mixtures between a metal capillary tube (d=180 microns) that serves as the cathode and an anode tube of larger size. Incorporation of gas flow through the discharge results in a continuous production of aerosol particles which are size classified in situ using a radial differential mobility analyzer (RDMA). Based on their electrical mobility, the particles were found to possess relatively narrow distributions (@sigma@@sub g@=1.3-1.5) with mean sizes between 2 and 5 nm depending on reactor conditions. Electrical measurements after synthesis in the microreactor show that the particles are charged both negatively and positively. To further characterize the particles, the aerosol stream is bubbled into solvents directly after synthesis in the microreactor. These colloidal dispersions exhibit strong blue photoluminescence with maximum intensity at 440 nm (2.8 eV). Atomic force microscopy on solutions drop cast on silicon substrates have verified that the particles are as small as 2 nm. In this talk, we will discuss features of this new synthesis technique including effects of discharge conditions on particle growth and optical properties.