Oxygen-free palladium/titanium coating, a novel nonevaporable getter coating with an activation temperature of 133 °C

A novel nonevaporable getter (NEG) coating was developed with an activation temperature as low as 133 °C, that is, a palladium/titanium coating with extremely low oxygen concentration (oxygen-free Pd/Ti coating). The substrate was coated with Ti and then overcoated with Pd using sublimation under ultrahigh vacuum conditions. The morphology and surface elemental composition of the Pd/Ti thin film were investigated with electron microscopes and x-ray photoelectron spectroscopy, respectively. The thicknesses of Ti and Pd films were approximately 1.3 μm and 50 nm, and the Ti film was completely overcoated by the Pd film. Ti and oxygen were found to be negligible on the oxygen-free Pd/Ti surface. The oxygen-free Pd/Ti coating was applied to the formed bellows. The bellows was successively baked at 133 °C for 12 h, 176 °C for 3.5 h, and 200 °C for 3.5 h. After sealing off a turbomolecular pump from the vacuum system containing the bellows, the pressure reached values of 4.6 × 10⁻⁶, 1.7 × 10⁻⁷, and 6.1 × 10⁻⁸ Pa, respectively. The pumping speeds of the bellows were estimated to be 0.028, 0.23, and 0.23 l s⁻¹, respectively. These results demonstrate that oxygen-free Pd/Ti deposition can be used as a new NEG coating for vacuum systems with a baking temperature of 133 °C or higher.