The Mechanism of Self-Sustained Electron Emission from Magnesium Oxide

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Abstract
Thin films of magnesium oxide, under the influence of an electric field, have been observed to emit extremely large secondary emission currents when bombarded with electrons. This current has been found to be exponentially dependent upon the electric field in the oxide film, and under certain conditions, to persist for many hours after the bombarding current has been cut off. Experiments have shown that the enhanced emission is due to the fact that the surface acquires a positive charge during bombardment, thereby creating an intense field in the thin film. Electrons released in the film by internal ionization are then accelerated by the field and cause further ionization, so that eventually an electron avalanche ensues. It has been found that there are two components of the enhanced electron emission. The first component is a true field-enhanced secondary emission effect similar to that described in previous work. The second component is a self-sustained electron emission. This self-sustained electron emission is produced by the same type of avalanche effect, except that the internal ionization of the dielectric is initiated by electrons produced from within the material rather than by electrons bombarding the material from an external source.

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