Anomalous secondary electron emission of metallic surfaces exposed to a Glow Discharge plasma

Abstract Secondary electron emission (SEE) yields, γ , of Li, stainless steel (SS) and W surfaces immersed in a He Direct Current Glow Discharge (dc-GD) Plasma have been calculated from the experimental I – V curves as a function of electron mean energy. The data obtained showed that γ Li > γ SS > γ W . Line emission ratios 728/706 of excited He and Langmuir probe measurements provide a clear evidence of the presence of a suprathermal electron tail responsible for the observed SEE. The results show that SEE is well correlated with the anomalous extra current component found in the I – V curves. The resulting value of γ Li is significantly higher than its theoretical value suggesting a possible synergetic effect of the ion bombardment in the SEE of lithium. The effect of Li surface oxidation has also been addressed, leading to a substantial decrease of both, sputtering yield and SEE yield of Li with higher oxygen content.