Some aspects of electron spectroscopic investigations of impregnated tungsten dispenser cathodes

Abstract

Impregnated tungsten dispenser cathodes from various manufacturers and of various impregnant compositions have been examined by several surface analytical techniques. In situ activation of these cathodes in UHV was studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy and energy loss spectroscopy. Previous work on model compounds and structures of barium, oxygen and tungsten has been used to interpret the results, although no generally accepted conclusions could be drawn on the exact chemical states of the various elements present on an activated, operating cathode. The results presented will show that the measurements must be taken at temperature, and will demonstrate a method to overcome charging and other artifacts. In addition, the signature of a good cathode will be shown, which can be synthesized by adding standard barium metal on tungsten and barium on oxygen thin film spectra.