PARTICLE PARTICLE INTERACTIONS IN DUSTY PLASMAS

High densities Of submicron particles have been created in an Ar/SiH4 parallel plate radio-frequency (rf) discharge. The particles were collected and measured by electron microscopy and the mean particle diameter was found to be 230 +/- 60 nm. Laser scattering from the dense clouds of such particles showed that the concentration was 1 X 10(8) cm-3. A laser Doppler anemometer was used to measure the particle velocity distribution and hence the mean particle mass. This is consistent with the specific density of the hydrogenated amorphous silicon. The mean velocities of particles were measured at two different gas flows when the discharge was extinguished, so that the particles are neutral and do not interact, and the particles move with the gas velocity. However, during the discharge the particles have almost no mean axial velocity, even though the gas flow is as large as before. This is due to the strong interparticle interactions that keep the particle cloud, as a whole, stationary. The charge on the particles is estimated, leading to a value of the Coulomb coupling parameter of GAMMA = 10. This large value suggests that the particle cloud can be viewed as a Coulomb liquid.