Electronic energy loss of light ions transmitted through nanometer films of Al has been studied at very low ion velocities. For hydrogen, the electronic stopping power S is found to be perfectly proportional to velocity, as expected for a free electron gas. For He, the same is anticipated, but S shows a transition between two distinct regimes, in both of which S is velocity proportional-however, with remarkably different slopes. This finding can be explained as a consequence of charge exchange in close encounters between He and Al atoms, which represents an additional energy loss channel.

The electronic stopping cross sections (SCS) of Ta and Gd for slow protons have been investigated experimentally. The data are compared to the results for Pt and Au, to learn how electronic stopping in transition and rare earth metals correlates with features of the electronic band structures. The extraordinarily high SCS observed for protons in Ta and Gd cannot be understood in terms of a free electron gas model, but are related to the high densities of both occupied and unoccupied electronic states in these metals.

A comparative study of Auger neutralization (AN) of He ions at noble metal surfaces is presented in order to reveal how the electronic structure of the sample influences this charge exchange process. Comparison of calculated ion fractions to experimental data obtained in low energy ion scattering (LEIS) shows that good agreement is achieved only if the relevant aspects of the He-metal interaction are properly taken into consideration. For instance AN depends sensitively on the distance-dependent position of the projectile level, which varies significantly when considering different target materials.

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In recent energy loss measurements, band structure effects in electronic stopping have been observed for materials with finite excitation thresholds, for example, noble metals such as Cu and Au. To further investigate the influence of the position of the d band relative to the Fermi edge, electronic stopping of hydrogen and helium ions in Ag and Pt was determined. For Ag, the electronic stopping power exhibits a velocity dependence similar to Cu and Au. No particular effect due to the comparatively large d-band offset in Ag is found. In the case of Pt, the electronic stopping power is virtually velocity proportional for H + ions and exhibits a distinct velocity dependence for He + ions. For hydrogen the results are compatible with modeling the conduction band as a free electron gas with an energy-dependent effective number of electrons. For He + , however, the observed effects point towards an additional energy loss mechanism, e.g., by charge-exchange processes.