Enhanced secondary-ion emission under gold-cluster bombardment with energies from keV to MeV per atom

Gold-cluster beams of Auₙ⁺, $n=1--4,$ have been used to measure the secondary-ion emission from organic (biomolecules) and inorganic (CsI) targets over the very large energy range of 4 keV to 10 MeV per atom. The nonlinear enhancement of secondary-ion emission yields with regard to the constituent number in the cluster projectiles is shown to vary with the incident velocity and the type of secondary ions. For complex secondary ions, the yields as a function of the projectile energy per atom present an unexpected maximum around 50--80 keV per atom. The yields increase again above 1 MeV per atom.