AVS 53rd International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuM

Paper VT-TuM2
Use of Getter-Catalyst Thin Films for Enhancing Ion Pump Vacuum Performances

Tuesday, November 14, 2006, 8:20 am, Room 2000

Session: Vacuum Generation and Measurement
Presenter: M. Mura, Varian Vacuum Technologies, Italy
Authors: M. Mura, Varian Vacuum Technologies, Italy
C. Paolini, Varian Vacuum Technologies, Italy
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Extreme High Vacuum can be achieved only by combined pumping systems: on the basis of this scenario, the idea is to reach this pressure range with a unitary system, easy to use and with long lifetime, based on an ion pump specially designed for this purpose and provided with an additional internal NEG-Catalyst thin film coating. The conceived pump is designed with a new anode geometry and a magnetic circuit optimized in order to reduce boundary effects, moreover its shape is tailored for internal NEG+Pd coating produced by means of magnetron sputtering. Since the main drawback in the use of NEG films is their limited lifetime due to the progressive accumulation of contaminants (e.g. nitrogen, oxygen, etc.), with consequent reduction of adsorption performances, the idea is to protect the NEG, depositing on it an overlayer of a noble metal, such as palladium, which acts as a catalyst for the adsorption of hydrogen and allows its diffusion towards the NEG. In this way it is possible to pump large amounts of hydrogen, also in presence of not negligible pressures of other gases, with a very high sticking factor. The consequent loss of pumping for other getterable gases (with the exception of CO) is not an issue in the UHV pressure range, where hydrogen is typically the main residual gas, since the ion pump works fine to pump them all. The sorption of both hydrogen and CO is fully thermally reversible, resulting in a theoretically endless lifetime of the film. The performances of the combined pump, in terms of base pressure and hydrogen pumping speed, will be presented through the evidence of the experimental data collected.