Emission mechanism of oxide cathode

The energy levels of single crystal BaO, SrO and CaO measured from thermal electrical conductivity, photoelectric conductivity, photoelectron emission and absorption spectra are so diverse that accurate energy band diagrams cannot be obtained. This suggests that the surface energy levels are more important than the bulk levels. The work function of single crystal BaO film on Ir(100) is single-valued. This is inconsistent with the wide distribution of total work function of carbonate measured by a low energy scanning electron probe, indicating that the semiconductor model cannot be used to accurately describe the oxide cathode. It was found that the coating was richer in oxygen than alkaline earth metal after 2000 hours by Auger electron spectroscopy. However, the capability to emit electrons was not affected. Thus, the oxygen vacancy donor concept is invalidated. The fact that excess barium are electron emission sources can be reconciled with decreasing alkaline earth metals during life by the dynamic surface emission center model. This model suggests that an aggregate of alkaline earth metal oxide molecules with excess absorbed bariumn atoms can effectively emit electrons. This concept can be used to interpret many phenomena observed on oxide cathodes using modern surface analysis techniques.