Volume and surface loss of O(3P) atoms in O2 RF discharge in quartz tube at intermediate pressures (10-100 Torr)

The O(P-3) atom loss has been studied in O-2 RF plasma in the quartz tube in the intermediate pressure range (10-100 Torr) when the transition from the surface to volume loss is observed. Space-and time-resolved actinometry on Ar and Kr atoms was used to study O(P-3) atom loss. The research has shown that such a transition actually takes place. However, it was revealed that the gas temperature plays a significant role in this. Gas temperature was measured spectroscopically using the O-2(b(1)Sigma(g)+, v = 0) -> O-2(X-3 Sigma(-)(g), v = 0) band emission. It was demonstrated that the gas temperature in the plasma volume was rather high (> 1200 K) due to the high values of the specific input RF power which in turn led to a significant O(P-3) loss rate decrease in the discharge volume. The atomic oxygen loss is limited by the O(P-3) surface recombination as well as by the volume recombination in a thin layer near the wall. It leads to a low integral loss rate and provides a high oxygen dissociation degree. Analysis based on measured [O(P-3)]/N, T-gas, O-3 spatial profiles and surface loss model including recombination with chemisorbed and physisorbed atoms has revealed the importance of both surface and volume losses. High values of the specific input RF power also lead to increase of the gas temperature near the wall and the temperature of the internal tube surface. As a result, the O atom surface loss rate increases and the volume loss rate near the wall decreases, so overall the contributions of both O(P-3) volume and surface recombination are comparable at pressures up to 100 Torr. The O(P-3) loss kinetics at intermediate pressures appears to be a rather complex phenomenon and requires at least 1D or even 2D modeling for its correct description. Using global models under similar conditions may lead to dubious results in a detailed study of kinetic mechanisms and processes, but it can be useful for a simple analysis of experimental results.