| Charge transfer in ion-surface collisions have been extensively studied, since they play important roles not only in the influence on charge states of scattered particles and as a probe of the electronic structure of the surface, but also in a number of technological applications, such as thin-films growth, reactive ion etching, surface catalysis, stimulated desorption, secondary-ion mass spectroscopy(SIMS), and low-energy ion scattering(LEIS). Moreover, the use of alkali-metal ions provides a more sensitive and quantitative analysis for surface science studies due to the low neutralization probabilities of alkali-metal ions. The neutralization probability is a key factor in quantitative analysis of surface elements. As a result, the knowledge of the neutralization probability of alkali-metal ions on different types of solid surfaces is necessary.We studied the charge transfer process of 0.16-5 keV Na~+ ions scattering on a Au(111) surface. We measured the charge state distribution of scattering particles by a position sensitive detector for the scattering angles of 135° and 53°. These results clearly show some common characteristics for large work function surfaces: The neutral fraction is relatively high, and in non-monotonic variations with the incident energy and exit angle. These common characteristics can not be explained by the jellium model.In this work, we carefully analyze the physical mechanism of neutralization from the theoretical calculations. We find that:(1) In large-incident energy range, high neutral fraction is related to neutralization at very small ion-surface distances;(2) For exit angle dependence, the perpendicular exit velocity and parallel exit velocity corporately affect the final charge state distribution; Moreover, it reveals the dominant role of the parallel velocity effect at grazing exit angles;(3) Considering the parallel velocity effects, theoretical calculations based on BN model are in good agreement with experimental results. |
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