Work Function Patches on Oxide-coated Cathodes†

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Abstract
Variations in the electron emission from different regions of the surface of sprayed barium oxide cathodes have been observed using electron emission microscopes. A method involving magnetic collimation of the electron flux from the cathode has been applied to measure the Richardson work functions of areas of about 2-5 × 10-5 and to perform a one-dimensional scan of part of the cathode surface. Major emitting areas were found to be separated by distances of from 0-1 to 0-3 mm, of the same order as the separation of irregularities in the cathode surface. The variations in work function on this scale are attributed to the surface roughness of the cathode. A correlation between the logarithm of the emission constant in the Richardson equation and the Richardson work function was found to exist for the small areas investigated.