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

A direct measurement of the ejected electron yield (${\ensuremath{\gamma}}_{i}$) for ${\mathrm{A}}^{+}$ incident on flashed and ${\mathrm{H}}_{2}$-, ${\mathrm{N}}_{2}$- and ${\mathrm{O}}_{2}$-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 ${\ensuremath{\gamma}}_{i}$ for ${\mathrm{A}}^{+}$ ions, with the effect increasing with decreasing ion energy. For both Ta and Pt the ${\mathrm{O}}_{2}$ treatment was found to be the most effective in reducing ${\ensuremath{\gamma}}_{i}$ while the ${\mathrm{H}}_{2}$ treatment was found to be the least effective. ${\ensuremath{\gamma}}_{i}$ for nitrogen ions on ${\mathrm{N}}_{2}$-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.