The surface oxide layer is formed by most metals which are exposed to ambient air. This surface layer prevents any further gas adsorption. Repeated air exposure-activation cycles progressively enrich the film of the getter with oxygen, reducing its performance and shortening its operating life. The palladium coating overcomes this inconvenience. Furthermore palladium coating provide a low electron-stimulated desorption yield even without activation. Palladium coating allows obtaining reversible pumping without a thick passivation layer is formed.
Please see related information here on Non-evaporable getter (NEG) thin film coatings.
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