Abstract
The absorption kinetics of water vapour on evaporated Fe and Ti films has been studied by means of quartz-crystal microbalance measurements. The quartz-crystal microbalance technique is uniquely suitable to follow continuously the absorption kinetics at moderate temperatures from ultrahigh vacuum to atmospheric pressures. It is more sensitive to the uptake of oxygen than of hydrogen. The reaction between water vapour and evaporated iron and titanium films of 60 nm thickness has been investigated at 80°C at 1×10 −4 mbar. The partial pressures of the components of the residual gas in the vacuum chamber have been continuously controlled. The absorption kinetics is compared to the initial absorption rate of oxygen from O 2. A fast initial absorption step found with O 2 has not been observed with both metals. In the case of Fe the absorption is strongly delayed, remarkable mass uptake has been observed several minutes, in some cases even hours after water vapour exposure started. For Ti the oxygen absorption begins immediately with the exposure, but the initial absorption rate is smaller than for oxygen gas. The results are compared to those obtained by the volumetric method for H 2O and O 2.
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