Electron Ejection by Slow Positive Ions Incident on Flashed and Gas-Covered Metallic Surfaces

A direct measurement of the ejected electron yield (γᵢ) for A⁺ incident on flashed and H₂-, N₂- and O₂-treated Ta and Pt and for the singly-charged hydrogen, nitrogen, and oxygen ions incident on Ta and Pt after treatment with the respective parent gas has been made for the kinetic energy range of 2 to 150 ev. The gas treatment for Pt consisted of an exposure to the molecular gas at a pressure of a few mm of Hg, while the treatment for Ta consisted of an exposure plus a glow discharge in which the Ta surface served as the cathode. In general, gas treatment of Ta and Pt was found to produce large decreases in γᵢ for A⁺ ions, with the effect increasing with decreasing ion energy. For both Ta and Pt the O₂ treatment was found to be the most effective in reducing γᵢ while the H₂ treatment was found to be the least effective. γᵢ for nitrogen ions on N₂-treated Ta and Pt showed a unique behavior at low ion energy in that it was found to increase with decreasing ion energy. This behavior was not observed for the other ions in this study.