Plasma properties and discharging of dust particles in an Ar/C2H2 plasma afterglow

Abstract

A global (volume averaged) model is developed for an argon-acetylene plasma afterglow. The model is used to study the electron and ion densities, electron temperature and densities of argon metastable atoms in the afterglow plasma. The calculated time dependence for the electron density is found to be in agreement with the existing experimental data. These calculated plasma characteristics are used to investigate the dust charge distribution function (DCDF) for particles with radii of 10–200 nm. The DCDF is found by solving numerically the master equation describing dust discharging as a one-step stochastic process and is also calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. The time dependences for mean dust charge, variance and dust charging time are obtained and analysed. If the electronegativity of the plasma in the steady-state is low, negative ions do not affect much discharging of dust particles in the afterglow, while at large electronegativity their role is essential. In the case of low electronegativity, discharging of dust particles is mainly due to deposition of positive ions with small and moderate masses (less than the mass of C10H6 + ions). Increasing electronegativity, the effect of heavy positive ions on dust discharging in the late afterglow is important. Secondary electron emission from dust surface at collisions of metastable atoms appears to be negligible.