The Emission from Oxide-coated Cathodes in an Accelerating Field

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Abstract
It is shown that the steep rise of current with accelerating field in a diode with an oxide-coated cathode cannot be fully explained either by surface roughness or by patch effect. This leads to a theoretical treatment, based on the existence of a space-charge zone immediately inside the coating The charge in this zone is shown to vary with applied field and with current density, and with certain coating parameters The variation in the charge leads to a variation in work function, and thereby to a dependence of emission on field strength, which is to be combined with the normal Schottky effect The effects of partial space charge on the relationship between field and anode voltage are discussed, and the diode characteristics of oxide cathodes can then be calculated for accelerating fields as a function of the coating parameters The results are shown to be in agreement with experiment, and to confirm values of coating conductivity, electron density and mobility as determined directly by conductivity and Hall effect measurements

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