Atom recombination at surfaces on plasmas

摘要

This work deals with the simulation of heterogeneous atomic recombination in plasmas. The system under analysis consists of a single atomic species recombining on a surface covered mostly with physisorption sites and with a small fraction of chemisorption sites. The time-evolution of the fractional coverage of both types of adsorption sites is described using two distinct formulations, a mean-field model for the average surface occupancy and a dynamical Monte-Carlo method, both schemes providing similar results. The recombination probability gamma is calculated from the steady-state surface coverage, and its dependence with the surface temperature and gas pressure is investigated in detail. It is shown that gamma may have a non-monotonic behaviour with the wall temperature. Moreover, as pressure increases recombination may evolve from a first to second order process, and then back to first order. The model is applied to the cases of nitrogen and oxygen recombination in silica.