Improved pumping speeds of oxygen-free palladium/titanium nonevaporable getter coatings and suppression of outgassing by baking under oxygen

Oxygen-free palladium/titanium (Pd/Ti) is a new nonevaporable getter material with an activation temperature as low as 133 degrees C. Because pumping speeds of oxygen-free Pd/Ti for H-2 and CO have been reported to be improved by baking under an O-2 atmosphere, the authors investigated oxygen-free Pd/Ti samples heated in an ultrahigh vacuum (UHV) or under an O-2 pressure of 1.3 x 10(-4) Pa by x-ray photoelectron spectroscopy. The authors found that carbon contamination decreased to an extent on heating in UHV, but decreased considerably on heating in O-2. Pressure-curve measurements in an oxygen-free Pd/Ti-coated chamber show that pumping speeds for H-2 and CO were considerably improved after baking the chamber under an O-2 pressure of 1.3 x 10(-4) Pa (O-2 baking) in comparison with baking in UHV. Furthermore, partial-pressure measurements suggested that O-2 baking removes adsorbed carbon and hydrogen, and consequently suppresses the formation of H-2, CO, H2O, and CH4. Catalytic chemical reactions on the Pd surface appear to be responsible for the removal of adsorbed carbon and hydrogen. The pumping speeds of the oxygen-free Pd/Ti-coated chamber for H-2 and CO were measured by using the orifice method and were found to be improved after O-2 baking. O-2 baking is therefore useful for improving pumping speeds for H-2 and CO and for reducing the partial pressures of H-2, CO, H2O, and CH4. (c) 2019 Author(s).