The collective behaviour of weakly ionized RF dusty plasmas is investigated. Negatively charged SiO2 fine particles are generated and suspended in an SiH4/O2/Ar discharge. At high pressure (300 mTorr), the random fluctuations of the discharge and particle motions are suppressed. Coulomb solids with particle diameters from a few micrometres to a millimetre have been observed. At low pressure, the coupling between particles and the background plasma causes large-amplitude low-frequency fluctuations of the dusty plasma.
