Abstract
Adsorption and desorption of gases in a vacuum chamber can be characterized by sticking probability, s, mean sojourn time, τ, and amount, σ, of adsorption on the surface in the chamber. The values of s and τ can be obtained through the analysis of pressure changes in the chamber under nonequilibrium conditions. These conditions were realized by means of a pressure pulse generated by pulsed-laser-beam irradiation of the stainless steel surface in the chamber. After laser beam irradiation, ion currents of a quadrupole mass spectrometer were measured for m/q = 2, 18, and 28. The time constant of pressure decrement for water vapor desorbed was much smaller than the value calculated. The difference can be explained by a small s and a large τ on the chamber surface. For a new stainless steel chamber, s of water vapor was constant, at about 9 × 10 −4, when bake-out temperature was lower than 150°C, and increased markedly after bake-out at 250°C.
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