EFFECT OF SURFACE-TREATMENT ON THE ADSORPTION-KINETICS OF WATER-VAPORIN A VACUUM CHAMBER

Adsorption kinetics of water vapor in a vacuum chamber can be characte rised by the sticking probability, s, the mean sojourn time, tau, and the amount adsorbed, sigma, of water molecules on the surface in the c hamber. 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 irradiatio n of water vapor condensed on the cold surface. On the surface of a st ainless steel chamber polished electrolytically, s was about 0.01 duri ng the pumping at room temperature, and increased to about 0.1 after t he degassing at 250 degrees 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 th oroughly. Change of s on those surfaces caused by the exposure with hu mid nitrogen or air was also observed. Copyright (C) 1996 Elsevier Sci ence Ltd.