Field Reversal and Particle Growth in DC Discharge

On the Competition Between the Phenomena Involved in the Aerosol Dynamics in Sputtering Nonequilibrium Plasma

“…INTRODUCTION Although solid particle formation is routinely observed in low pressure DC discharges [1] [2], very little effort has been devoted to the understanding of the processes that lead to their formation. Recently we showed, in the case of graphite cathode argon DC discharge, that particle formation is induced by molecular growth and a subsequent electron attachment of the sputtered carbon species [3].It results in the formation of negatively charged clusters that are trapped in the field reversal of the negative glow and can therefore undergo further growth that end up with solid particle nucleation. This growth mechanism was assessed through a first model that did not take into account the dusty plasma effect, i.e.…”

“…the coupling between the discharge equilibrium and the particle aerosol dynamic was not taken into account. Nevertheless, this first model enabled us showing that field reversal effect in the NG plays a key role as far as particle nucleation in DC sputtering discharge is concerned [3]. Then, in a second step, we used a A.…”

“…Particle production is therefore only possible through negative clusters that can be trapped in the positive plasma potential. For these negative clusters, aggregation from C until C 30 can takes place significantly and particle nucleation can occurs near the field reversal position [3].…”

“…The first module of the discharge model describes the sheath structure and is essentially inspired from the non-local approach proposed by Kolobov and Tsendin and based on the solution of the fast electron momentum [9] Once the sheath dimension and the electric field variation in the sheath are determined we perform a Monte Carlo simulation to determine the evolution of the relative ionization rate in the sheath and the negative glow [3]. Once the absolute ionization rate is determined in the sheath and in the negative glow, the (cold) electron density in the negative glow and the Faraday dark space is determined by solving the 1-D transport equation for the cold electrons as described in [3] The electric field in the NG is determined assuming a Boltzmann equilibrium with the cold electrons. Once the plasma characteristics are estimated from the plasma model, we solve for the cluster continuity equations coupled to three balance equations that govern the particle number density, mass density and average charge [3].…”

“…Once the absolute ionization rate is determined in the sheath and in the negative glow, the (cold) electron density in the negative glow and the Faraday dark space is determined by solving the 1-D transport equation for the cold electrons as described in [3] The electric field in the NG is determined assuming a Boltzmann equilibrium with the cold electrons. Once the plasma characteristics are estimated from the plasma model, we solve for the cluster continuity equations coupled to three balance equations that govern the particle number density, mass density and average charge [3]. This allow us to obtain the cluster densities and the nucleation rate taking into account the cluster losses at the particle surface.…”