Evaluation of oxygen-free silver/palladium/titanium (Ag/Pd/Ti) nonevaporable getter (NEG) coating

Nonevaporable getter (NEG) pumps are widely used for maintaining a clean ultra-high vacuum (UHV) of 1 x 10^-7 Pa or less because of their high pumping speeds for H₂ and active gases in the UHV region. Recently, we have developed a novel NEG consisting of an oxygen-free thin film of Ti covered with a thin film of Pd (oxygen-free Pd/Ti) with an activation temperature of 133degC. After activation by baking at 150degC for 6 hours, a NEG pump using oxygen-free Pd/Ti evacuates H₂ and CO efficiently at room temperature, and its pumping speeds for H₂ and CO do not decrease even after repeated cycles of activation and exposure to the air. In the present paper we report on evaluation of a vacuum vessel coated with oxygen-free silver/palladium/titanium (oxygen-free Ag/Pd/Ti) by partial pressure measurements using a quadrupole mass spectrometer. After activation by baking at 150degC for 3 hours, the partial pressure of CO was suppressed in comparison with the case of an oxygen-free Pd/Ti coated vessel. The partial pressures of H₂ and H₂O, however, were increased in comparison with the case of an oxygen-free Pd/Ti coated vessel. (author)