Quantitative analysis in low-energy ion scattering (LEIS) requires an understanding of the charge-exchange processes to estimate the elemental sensitivity factors. In this work, the neutralization of He scattered by 18O-exchanged silica at energies between 0.6 and 7 keV was studied. The process is dominated by Auger neutralization for E i 0.8 keV. An additional mechanism starts above the reionization threshold. This collision-induced neutralization becomes the dominant mechanism for E i > 2 keV. The ion fractions P were determined for Si and O using the characteristic velocity method to quantify the surface density. The 18O/ 16O sensitivity ratio indicates an 18 higher sensitivity for the heavier O isotope.
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