Effect of surface treatment on the adsorption kinetics of water vapor in a vacuum chamber

Abstract

Adsorption kinetics of water vapor in a vacuum chamber can be characterised by the sticking probability, S, the mean sojourn time, τ, and the amount adsorbed, σ, of water molecules on the surface in the chamber. Among them, s can be obtained through the analysis of pressure change in the chamber caused by the pressure pulse with a very short time duration. The pulse was generated by pulsed-laser-beam irradiation of water vapor condensed on the cold surface. On the surface of a stainless steel chamber polished electrolytically, s was about 0.01 during the pumping at room temperature, and increased to about 0.1 after the degassing at 250 °C. When the chamber was coated with TiN s increased by about 0.04 to 0.2 during the pumping at room temperature. Temperature dependence of s was measured on both surfaces degassed thoroughly. Change of s on those surfaces caused by the exposure with humid nitrogen or air was also observed.