Dependence of Secondary Electron Emission Coefficients on z1 in Metal Targets under Bombardment with Bare Projectiles

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Abstract
The secondary electron emission coefficients are measured in targets under bombardment with He2+, C6+, N7+ and O8+ ions at an energy of 6.2 MeV/amu, the backward secondary electron emission coefficients γback being measured for thick Al and Ag targets, and the backward and forward coefficients γback and γfor for an Au foil target. γback/z 2 1 decreases with z 1 in proportion to 1–0.005z 2 1. With the effective charge z * 1, γfor/z *2 1 shows a similar decrease with z 1. These decreases are caused by the decrease in the escape probability of secondary electrons from the surface with increasing z 1, that is, increasing specific electronic energy loss S. This result implies that the surface barrier height U depends on S. A mechanism for the ion-induced increase in U is proposed, and the difference between the way γback and S depend on the energy for N7+ ions is explained by considering this dependence of U on S.