Evolution of Gases and Ions from Different Anodes Under Electron Bombardment

Abstract

With the aid of a bakeable mass spectrometer a study has been made of the material evolved from Ag, Cu, Ni, Mo, Ta, Ti, and W anodes exposed to oxide cathodes. Chlorine was found to be evolved from all the anodes during the first period of bombardment. No evidence of the dissociation of the thin films of BaO or SrO on the anodes was obtained, suggesting it does not play a significant role in oxide cathode poisoning. It is believed that the Cl evolution may be responsible for the early slump in emission commonly observed at low anode voltages from oxide cathodes. Evolution of O⁺ ions was observed from oxidized Cu, Ni, Mo, Ta, and Ti with efficiencies up to approximately 10⁻⁵ ions/electron for electron energies of 90 ev and current densities of 10 ma/cm². This O⁺ evolution reduced considerably the dc emission capabilities of the oxide cathodes. It was found that heating the anodes from 700° to 1000°C for long periods of time does not always eliminate all evolution products caused by electron bombardment. Hydrogen was observed to be evolved from Ti and O⁺ ions were observed from formerly oxidized Cu, Ni, Mo, and Ta immediately after outgassing at temperatures less than 1000°C.