Velocity distributions of the negatively charged monatomic secondary ions of copper, silver and gold

Corrected intensity versus inverse velocity plots constructed for the secondary ions of Cu-, Ag- and Au- resulting from either or both Ar+ and Cs+ primary ion bombardment indicate that two processes are active during their formation/survival. This is suggested since two functions are required to reproduce the experimental data. One process (the one predominating at higher emission energies) exhibits an exponential relation between the secondary ion yield and emission velocity while the other (the one observed at lower emission energies) exhibits a much weaker velocity dependence, or in the case of Ag- a negative velocity dependence. These trends are suggestive of competing resonance charge transfer and surface excitation mechanisms