Work-Function Distribution Studies of Pressed Matrix Cathodes

Abstract

The work-function distribution of commercial pressed matrix cathodes has been investigated from room temperature to 1300°K. The measurements were obtained by probing the surface with a beam of electrons in the retarding field region. The beam, which was of the order of 2 μ in diameter, sampled the work function of 30 000 regions of the surface during the 3 sec. required for one scan. The results show that the emitter exhibits a very patchy behavior at low temperatures, while a relatively uniform temperature insensitive region exists from ∼900° to 1400°K. Above this temperature, activation and poisoning effects are dominant. Patch field distribution measurements show that surface fields as high as 1500 V/cm exist in the patchy state, whereas a well activated pressed matrix cathode would have surface fields only of the order of 100 V/cm. The measurement of thermionically emitted electrons is in good agreement with results obtained by the incident electron beam. These data as well as work-function and conductivity measurements from various microregions are discussed in terms of a thin semiconductor surface layer.