Abstract
Adsorption and desorption kinetics of gases in a vacuum chamber can be characterized by the sticking probability, s, the mean sojourn time, τ, and the amount, σ, of adsorption. Among them, s can be determined through analysis of the pressure change which is induced in the chamber by a pressure pulse of very short duration. In the present study, the pulse was generated by pulsed-laser-beam irradiation of water condensed on a cold surface. On a stainless steel chamber surface treated by glass bead blasting, s for as received conditions was about 9×10-4, and increased gradually to 0.04 after repeated introduction of atmospheric air and degassing at 250°C. On an electropolished stainless steel surface, s was about 0.01 during pumping at room temperature, and increased to about 0.1 upon degassing at 250°C. On a stainless steel chamber surface coated with TiN, s increased by 0.04 to 0.2 during pumping at room temperature. The temperature dependence of s was measured on the above three surfaces after they had been thoroughly degassed. Changes in s on these surfaces caused by exposure to humid nitrogen or air were also observed. The results are compared with the results of micro-calorimetric measurements of the heat of adsorption for water vapor on various oxides. Finally, a schematic representation of the adsorption and desorption processes of water vapor on a stainless steel surface is proposed.
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