Be K-shell Auger-electron emission in slow-ion--surface collisions

We have observed beryllium K-shell Auger electrons from clean Be surfaces bombarded by 2.5--10-keV Ne, Ar, and Kr ions at 450 incidence. The electron spectra show a broad structure similar, although not identical, to that observed under electron impact, which was assigned to the KVV transition from excited Be decaying in the bulk of the solid. A small sharp line is identified to result from the decay in vacuum of neutral Be(1s2s22p) sputtered from the solid. The Auger yields can be scaled when plotted against the maximum energy transfer in a projectile-Be collision, indicating that excitations occur mainly from symmetric collisions between target atoms. This is supported by Monte Carlo simulations of the atomic collision cascade in the solid. We have applied these simulations to evaluate the relative role of symmetric and asymmetric collisions in early measurements of Be K x-ray yields, at higher energies. By comparing experimental and simulated results, we obtained information about the variations of the fluorescence yields and outer-shell occupation numbers with projectile energy