Activation and measurement of nonevaporable getter films

An experimental setup for studying the pumping and capacity properties of nonevaporable getter (NEG)-coated films has been designed and built in the ASTeC Vacuum Science Laboratory at Daresbury Laboratory. The measurement system is based on the dynamic expansion method with a gas injection system that is capable of injecting the residual gases present in a typical UHV system, such as H(2), CO, CO(2), and CH(4). The test particle Monte Carlo model was used for accurate evaluation of NEG film sticking probability from the pressure reading during gas injection. The experimental measurements with NEG-coated samples have shown that the NEG film can be poisoned during the NEG film activation (and/or regeneration) by molecules of CO and CO(2) desorbed from uncoated parts of the vacuum chamber. The effect of NEG film poisoning was reduced by lowering the temperature of the uncoated parts of the vacuum chamber during the NEG film activation and, as a result, a new activation procedure was developed for vacuum systems containing NEG-coated parts.