Investigation of voltage effect on reaction mechanisms in capacitively coupled N_2 discharges

摘要

A systematic investigation of voltage effect on the plasma parameters, especially the species densities and chemical reaction mechanisms, in the capacitive N_2 discharges is performed by employing a two-dimensional self-consistent fluid model. The validity of the numerical model is first demonstrated by the qualitative agreement of the calculated and experimental results. Then, the densities, production mechanisms, and loss mechanisms of species from simulation are examined at various voltages. It is found that all the species densities increase monoton-ically with the voltage, whereas their spatial profiles at lower voltages are quite different from those at higher voltages. The electrons and N_2~+ ions are mainly generated by the electron impact ionization of N_2 gas, while the N~+ ions, whose density is one or two orders of magnitude lower, are mostly formed by the ionization of N atoms. The electron impact dissociation of N_2 gas dominates the generation of N atoms, which are mostly destroyed for the N~+ ion production. As for the excited N_2 levels, the level conversion processes play a very important role in their production and depletion mechanisms, except for the electron impact excitation of the ground state N_2 molecules.