SURFACE AND EMISSION CHARACTERIZATION OF THE IMPREGNATED DISPENSER CATHODE

Several osmium/ruthenium-coated and non-coated commercial impregnated cathodes were investigated using scanning Auger microscopy (SAM), photo electron spectroscopy (PES), mass spectroscopy and field-emission retarding potential (FERP) techniques for work function measurements. The ratio of Ba/BaO evaporating from the surface varied from 1-8 at 1418 K with the largest value corresponding to the lowest work function cathode. Work functions measured by the FERP technique varied from 2.7-1.8 eV and correlated well with the emission current density variation among the various cathodes. Richardson work functions in the range 1.5-1.7 eV were obtained, but showed no correlation with cathode current density. PES and SAM results showed that the surface of an operating cathode consisted of a Ba + O chemical combination on an unoxidized tungsten surface. The ratio of Ba/O was larger on the flats than within the pores intersecting the surface. Large beam size Auger spectroscopy gave near identical surface composition for high and low current density cathodes. © 1979.