Abstract
The absolute yield of positive ions, P +, ejected by 2 keV argon ion bombardment of clean metal surfaces was measured. The secondary ion current was measured for normally ejected ions, and the ion yields were calculated as a function of the secondary ion velocity. Experimental measurements included careful calibration and correction for the instrument transmission as a function of ion energy. Materials chosen for this study were polycristalline Cu, Ag, Cr and Zr, which provided a wide range in ionization potential and cohesive energy. Earlier treatment of the data showed reasonably good conformity to the expression P + ∝ exp[(− A/v) cos θ], indicating a predominance of the electron tunneling mechanism under these conditions. A simple correction of the ion kinetic energy for the binding force to the solid brings the data into much better agreement with the exponential dependence than previously observed, and further supports this model.
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