Atomic oxygen surface recombination in glow discharge plasmas

Surfaces interact with either active discharges or their afterglow in most plasma processes, via heterogeneous surface kinetics. These processes can affect both plasma and surface properties. In particular, in oxygen-containing discharges, the adsorption and recombination of atomic oxygen on reactor surfaces determine the gas composition, the availability of O for important volume reactions (e.g.: CO₂ + O → CO + O₂; CO + O + M → CO₂ + M) and eventually the flux of reactive oxygen species (ROS) towards target surfaces. The wall loss frequencies of O atoms have been measured in the positive column of O₂ and CO₂ glow discharges in a Pyrex tube (borosilicate glass), for several pressures, currents and wall temperatures. However, the surface mechanisms determining recombination are not fully known yet. In this work the LoKI global model is employed to self-consistently simulate the volume kinetics in the plasma and the surface kinetics of O atoms in the conditions of the experiments. The simulation results are compared with experimental measurements, describing the experimental dependence of the atomic oxygen recombination probability on pressure, current, gas temperature and wall temperature. Moreover, the newly developed model allows to identify the most important recombination mechanisms for each condition.