Velocity dependence of the K Auger deexcitation of O⁷⁺ projectiles impinging on solid Cu(111) at 51 and 102 keV

The time evolution of deexcitation of O⁷⁺ ions penetrating the (111) surface of Cu is studied by means of secondary electron spectroscopy. It is found that the filling of the K shell proceeds faster at 102 keV than at 51-keV ion energy, by about 10%. This velocity dependence is determined from a comparison of emission depth profiles, assuming straight-line trajectories for the ions. No further model is needed for the ion deexcitation or the solid-state interactions of the emerging Auger electrons. The model independence is based on three steps: (i) the emission depth profiles for different ion energies and angles are evaluated only in conditions where they are practically equal; (ii) the full K Auger electron spectra with their inelastic parts are obtained using matching pairs of measurements with O⁶⁺ projectiles; and (iii) the observation angles are adjusted to equalize, for both ion energies, the laboratory energies of the Auger electrons at emission as well as their solid-state interactions on their way to the surface. The present method can provide benchmark values for multistep cascade models of highly charged ion deexcitation in solids.