Direct measurement of O-atom adsorption with plasma molecular beam scattering

In order to elucidate the radical recombination process on solid surfaces, which is composed of radical adsorption, associative reaction of adsorbates, and desorption of products, oxygen (O)-atom adsorption on quartz, stainless-steel (SS), and alumina surfaces was directly evaluated with a molecular beam scattering technique using a plasma-driven beam source. O-atoms were generated through the plasma decomposition of oxygen molecules (O2) in a radio frequency discharge tube, and the produced O atomic beam was irradiated onto the target surfaces with different surface temperatures Ts. Time-of-flight distributions of O-atoms and O2 scattered from the surfaces were analyzed to obtain the initial sticking coefficient of O-atom S0, O. It is found that S0, O is monotonically decreased with an increase in Ts regardless of the surface materials employed. The values of S0, O on the quartz are 0.119–0.022 at Ts = 30–800 °C. On the other hand, S0, O on the SS are significantly higher than those on the quartz, and they are 0.503–0.135 at Ts = 30–800 °C. As for the alumina, S0, O at Ts = 30 °C is almost the same as that for the quartz, while S0, O becomes almost 0 at Ts ≧ 600 °C, showing much lower O affinity than the quartz.