Electrical phenomena at the surface of electrically stressed metal cathodes. I. Electroluminescence and breakdown phenomena with medium gap spacings (2-8 mm)

Abstract

Spectral intensity measurements have been made of the light emitted from discrete points on the surface of electrically stressed metal cathodes. DC and pulsed breakdown voltage measurements have also been made immediately following surface arcing treatment. These show that the significant differences occur between different electrode materials. It is shown that the phenomena of electroluminescence, electron emission and vacuum breakdown, are all consistent with a model based on the production of conducting filamentary channels, electroformed through surface oxide or oxide type impurities by the action of the applied field.

Electron field emission from copper with various thicknesses of oxide film

“…It has been shown [22] that electroluminescence, electron emission and vacuum breakdown are all consistent with a model based on conducting filamentary channels, switched or electro-formed through surface oxide or oxide-type impurities, with the removal of these 'fc-spots' by conditioning spark discharges leading to the higher breakdown voltage. These electron-emitting sites seem to be located at grain boundaries or at other defects [23], and the emitted current has been shown [24] to follow a Fowler-Nordheim characteristic.…”

“…Furthermore, although it was for a long period generally supposed that field enhancement occurs in the gas phase at the cathode due to microprotrusions on its outer surface, the work of Hurley [22][23][24] in recent years suggests that microprotrusions may extend from the cathode metal substrate but not penetrate out beyond the oxide surface. It has been shown [22] that electroluminescence, electron emission and vacuum breakdown are all consistent with a model based on conducting filamentary channels, switched or electro-formed through surface oxide or oxide-type impurities, with the removal of these 'fc-spots' by conditioning spark discharges leading to the higher breakdown voltage.…”

Switching and other nonlinear phenomena associated with prebreakdown electron emission currents

“…Rather, the electron spectral evidence, coupled with the findings from other complementary investigations (Farral11980,1981, Cox 1975, Hurley and Dooley 1977, Athwal and Latham 1981a, Athwal 1981) indicated that the emission stemmed from a more complex regime involving an insulating micro-inclusion. Alternative qualitative models have been proposed by Hurley (1979) and Latham and his co-workers (Allen and Latham 1975, Allen et a1 1979, Athwal and Latham 1981b which provided plausible interpretations of many of the experimental observations. More recently, however, Latham (1982) has developed these earlier ideas to provide an alternative quantitative interpretation of the linear Fowler-Nordheim plot: the slope is now determined by the physical dimensions and dielectric properties of the insulating inclusion.…”

Physical implications of an effective activation energy for arc erosion on oxidised cathodes

“…Recent investigations of phenomena leading up to and including vacuum breakdown attribute their origin to the effect of surface impurities in the form of oxides or chemically similar inclusions (Hurley 1979a(Hurley , b, 1980. A consensus is apparent that conditions favouring breakdown and arc formation on metallicsurfaces of various materials stressed electrically at negative potential, whether in vacuum or in the presence of an interelectrode medium, can be associated with a sudden change in dielectric properties of the surface impurity.…”