Influence of adsorbed gas species on activation process and pumping performance for NEG coating

TiZrV non-evaporable getter (NEG) coating is being developed at KEK for future light source applications. In order to understand influence of adsorbed gases on TiZrV pumping performance, the TiZrV coated films were characterized by thermal desorption spectroscopy, glow discharge optical emission spectroscopy and pumping speed measurement. TiZrV films adsorb active gases, and among these O₂ is pumped 6-7 times as many as CO. After atmospheric exposure, O₂ and H₂O penetrate over 60 nm in TiZrV films at room temperature. In the activation process, H₂ is released and O atoms diffuse into the TiZrV films. The remaining O atoms hinder the activation, resulting in degradation of the pumping speed. (author)