Secondary electron emission from Au by medium energy atomic and molecular ions

Number distributions of secondary electrons emitted from a Au metal surface have been measured for atomic and molecular ions of H+, He+, C+, N+, O+, H+2, H+3, HeH+, CO+ and O+2 in the energy range 0.3-2.0 MeV. The emission statistics obtained are described fairly well by a Polya function. The Polya parameter b, determining the distribution shape, is found to decrease monotonously with increasing emission yield γ, revealing a surprising relationship of bγ∼1 over the different projectile species and impact energies. This finding supports certainly the electron cascading model. Also we find a strong negative molecular effect for heavier molecular ions, showing a significant reduction of γ compared to the estimated values using constituent atomic projectile data