Auger electron spectroscopy study of cathode surfaces during activation and poisoning. I. The barium‐on‐oxygen‐on‐tungsten dispenser cathode

摘要

Auger electron spectroscopic analyses of the chemical changes taking place on a commonly used dispenser cathode have been carried out during activation and poisoning by several reactive gases (O2, CO, CO2, H2, N2, Ar). The chemical composition and work‐function changes on the cathode were correlated at various stages of activation and poisoning, both at room temperature and at operating temperature. During activation, a process of considerable cleaning up of unwanted contaminants (chiefly carbon) occurs. Poisoning by reactive gases causes changes in the BaO ratio. A good agreement with the theoretical predictions for barium and oxygen concentrations of ∼1014 atoms/cm2 made by Zalm and our results was found. Over all, our results show that the excess barium adsorption model correctly explains electron emission from the dispenser cathode.