Determination of 16O and 18O sensitivity factors and charge-exchange processes in low-energy ion scattering

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 O-18-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 O-18/O-16 sensitivity ratio indicates an 18% higher sensitivity for the heavier O isotope. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758699]