Experimental spectra from medium energy ion scattering were compared to Monte-Carlo simulations (employing the TRBS code) to obtain information on the scattering potential. The impact of uncertainties in the interatomic potential on quantification of sample properties such as thickness, composition or electronic stopping was investigated for different scattering geometries: backscattering and transmission. For backscattered He ions with tens of keV primary energy the scattering potential was found to overestimate the multiple scattering background in the energy spectra resulting in an uncertainty of < 3 % in quantitative analysis. Light ions transmitted through a sample for equivalent path length in the medium are only affected minorly by changes in the scattering potential. This effect becomes more distinct for heavier primary ions.
The powder of CaF2 has been proposed as a practical reference for the quantitation of Ca and F in LEIS analysis. It is chemically inert, easy to clean and inexpensive. LEIS is extremely surface sensitive. Thus, in contrast to surface analytic techniques such as XPS and SIMS, the surface termination of a sample is clearly reflected in the LEIS results. It is thus unlikely that in LEIS the F/Ca ratio for CaF2 is 2.0. This paper supports the reliability of the CaF2 powder reference by evaluating the calcium and fluorine atomic surface concentrations, roughness factor and shows that the surface termination of the powder is the same as that of CaF2(111). The CaF2 samples are treated by annealing at 725 K and measured at 625 K. The presented spectra are practically free of contamination. Ion scattering by LiF (001), an evaporated Ca layer and a Cu foil are used as basic references for Ca and F. The atomic sensitivity factors (ASF) and the relative sensitivity factors (RSF) have been determined for F, Ca and Cu (3 keV He + , 145 o ). The F/Ca atomic ratio is found to be the same (2.3 ± 0.1) for CaF2(111) and its powder. For the powder the Ca and F signals are reduced by a factor of 0.77 ± 0.03 in comparison with those for the single crystal.
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