Abstract
Angle resolved photoelectron spectroscopy has been employed to investigate the chemistry occuring in osmium-ruthenium coated impregnated dispenser cathodes. This analytical technique allows the selection of acceptance angle of electrons analyzed in an X-ray photoelectron spectrometer, thus providing surface or depth enhancement of the signal. Spectra of the barium MNN Auger peaks and 3d and 4d photoelectron peaks were followed throughout activation. Surface enhancement, particularly of the barium MNN peak, showed a marked increase in the metallic component, confirming the increased concentration of metallic-like barium in the topmost layer. Auger-Photoelectron Energy Separations were also plotted for comparison to previous data on impregnated dispenser cathodes [Lampert et al., Appl. Surface Sci. 8 (1981) 66] and barium model compounds. By using higher resolution conditions, we have resolved the barium metal feature in the M 4N 4,5N 4,5 Auger transition at cathode operating temperatures. Using a digital subtraction technique, we are able to clearly distinguish elements which are predominant in the near-surface region as opposed to those which lie deeper in the cathode.
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