Formation of soot particles in Ar/H2/CH4 microwave discharges during nanocrystalline diamond deposition: A modeling approach

Abstract

Homogenous mechanism of soot formation in moderate-pressure Ar/CH 4/H9 microwave discharges was analyzed with the help of kinetics modeling of the thermally non-equilibrium plasmas. Two main reaction mechanisms based on either neutral molecular growth and condensation reaction nucleation process were considered. These mechanisms were incorporated in a numerical model that solves for the plasma species and energy equations under a quasi-uniform plasma assumption. This enabled us to estimate the plasma species density and temperature along with the nucleation rate at different discharge conditions. The results showed that soot particles might form at significant density values by both neutral and ionic mechanisms. Their formation mainly takes place at the discharge edges where the temperature level favors the development of large molecular edifices. Simulations showed that the formation of soot is unlikely to happen in the bulk of the discharge where the gas temperature is high and the large molecular hydrocarbon (HC) cannot form at significant concentrations. © 2006 IUPAC.