Secondary Electron Emission from Metal Targets under Heavy Ion Bombardment

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Abstract
The secondary electron emission coefficients γ for in-situ vacuum-deposited Al, Cu, Ag and Au targets were measured under bombardment with He2+, C4+, C6+, N4+, N5+, N7+, O5+ and O8+ ions in the energy region of 4.5–8 MeV/amu. The ratio between γ and the electronic stopping power S increases with the incident energy. The energy dependence of γ is insensitive to the variation of the projectile charge state. The square of the effective charge Z 2 eff(z 1, c; Z 2) of a projectile with atomic number Z 1 and electric charge c in the thin surface region of the target with atomic number Z 2 is obtained. Z 2 eff(z 1, c; Z2) expresses the projectile charge state dependence of γ, and is equal to (z 2 1+c 2)/2+(z 1-c)+α(z 1-c)Z 2/3 2. α is a numerical factor and is 0.16 for N4+ ions.