Electrical phenomena occurring at the surface of electrically stressed metal cathodes. III. Current voltage characteristics of electroluminescent (k-spot) regions on broad area cathodes

For pt.II see ibid., vol.12, p.2247 (1979). Studies of the I-V characteristics of electroluminescent (k-spot) regions on OFHC copper cathodes are reported. Two types of electron-emitting site have been identified. For an a-site the I-V characteristic can be satisfactorily analysed in terms of the Fowler-Nordheim equation. DC breakdown occurs for currents in the range 10 -5 to 10 -4 A and destroys the emission site. For a b-site a similar analysis gives meaningless results, the emission being current-controlled and following a negative resistance characteristic for currents >10 -5 A. The b-sites are not destroyed by breakdown unless the current limiting resistor is removed. The emission sites are attributed to conducting filaments wholly or partially penetrating through impurities in the cathode surface.