Forces on Ion-Bombarded Electrodes in a Low-Pressure Plasma

Abstract

Forces arising on ion‐bombarded electrodes have been measured with a torsion balance immersed in a low‐pressure Hg plasma. The force curves obtained for 22 metals in the range of 20 to 300 ev bombarding energy indicate that Hg⁺‐ions are completely accommodated (α=1) on clean metal surfaces and the forces originate essentially from the ejection of sputtered atoms. On comparing the forces with the sputtering yields, one obtains information on the average ejection velocities of sputtered atoms which are found to be much higher than those of thermally evaporated atoms. Oxide‐covered surfaces exhibit a quite different behavior inasmuch as the accommodation coefficient for Hg⁺‐ions seems to be less than unity.