Role of d electrons in electronic stopping of slow light ions

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.