Electron-Bombardment-Induced Dissociation of Alkaline Earth Oxides

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Abstract
The oxygen evolution induced by electron bombardment of alkaline earth oxides has been directly observed by means of an omegatron mass spectrometer. Threshold energies for the process have been determined as 9.5±0.5 ev, 14.0±0.5 ev, and 16.9±0.5 ev for BaO, SrO, and MgO, respectively. It is found that the efficiency of the process is in all cases proportional to the square of the current density at the target. It is suggested that a two-step electron excitation in the solid is involved. In the case of SrO the use of a radioactive isotope of strontium provided a monitor for the release of the metal from the target. The energy dependence of the evolution of oxygen and strontium suggests that there are two processes, one predominating at low energies and the other at higher energies. An evolution of oxygen at a threshold energy of approximately 5 ev was observed for a variety of targets. The behavior of this evolution suggested that a desorption process was involved.