A comparison of conventional and specimen isolation filtering techniques for the SIMS analyses of geologic materials

Abstract Ion microprobe measurements of relative ion intensities and charging potentials of geologic specimens are reported using two forms of kinetic energy filtering, conventional energy filtering (CEF) and specimen isolation (SI) conditions which analyze ∼ 100 eV and ∼ 500 eV ions, respectively. Both techniques give similar M+ and M2+ intensities, but molecular ion intensities are greatly decreased in the SI mode. This increased molecular ion suppression is of greatest importance for heavy element analysis such as in complete rare earth analysis. In the SI mode, with a 3 mm cover plate aperture, samples charge to very similar potentials (530 V ± 10% below the SAV) regardless of the primary beam current or the target structures (e.g. glass, ceramic, or bulk crystal). For either the SI or CEF techniques, the different matrices generally give very similar ion intensities referenced to 28Si+, showing that structural matrix effects can be neglected with either kinetic energy filtering technique. Glass standards can thus be readily used for quantitative analyses of minerals.

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