Work Functions and Conductivity of Oxide-Coated Cathodes

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Abstract
The thermionic and photoelectric work functions and the temperature variation of coating conductivity have been measured for an oxide cathode. Thermionic and photoelectric currents were measured in both retarding and accelerating fields. The two work functions are found to be different, but not by the amount predicted by applying simple semi‐conductor theory to the data. Photoelectric currents fit a Fowler plot rather well over a limited range of frequencies. The large decrease in work function with applied field, the poor ``saturation'' of thermionic currents typical of oxide cathodes, and the behavior of the photoelectric currents in accelerating fields all suggest that one is dealing with a ``patchy'' surface. Applying ``checkerboard'' patch theory to the experimental data, one finds that most of the data is accounted for by assuming patches about 3×10−4cm on a side differing in work function by about 0.2 volt.