The oxidation of evaporated barium films (getters)

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Abstract
Mott's theory of the oxidation of metals is summarized and expressed in terms comparable with the throughput, capacity, and speed of pumping, which are measured in the present work on barium getters. It has been found that there is a critical temperature, about 40° C for barium, below which a thin protective film of oxide is formed. Above 40° C, barium films oxidize right through, and so in this case, the capacity of getters for oxygen depends upon the amount of metal used. The feature of the mechanism which limits the speed of pumping of oxygen has been found, and hence the speed has been increased in various ways. The theory of Mott concerns only the growth of an oxide film that is already at least a monolayer thick. In the present study it has been found that the first monolayer spreads from nucleation centres in the barium surface.