Phase transitions of dense systems of charged "dust" grains in plasmas

The behavior of "dust" grains (particulates) in microelectronics process plasmas has been studied using N-body simulations. Grains are assumed to be negatively charged and interact through a screened Coulomb potential Φ(r). The dimensionless parameters κ=a/λ and Γ=Φ(a)/k BT characterize the thermodynamics of the particulate system, where λ is the ion Debye length, a=(3/4πnD)1/3 is the mean intergrain distance, and nD and T are the dust density and temperature. The simulations exhibit a transition between "fluid" and "solid" phases at a critical value Γc that depends on κ and weakly on the system history (i.e., whether it "melts" from an ordered state or "freezes" from a random one).