High-precision SIMS oxygen, sulfur and iron stable isotope analyses of geological materials: accuracy, surface topography and crystal orientation

• Published in: Surface and interface analysis 2011-01, Vol.43 (1-2), p.427-431
• Main Authors: Kita, N. T., Huberty, J. M., Kozdon, R., Beard, B. L., Valley, J. W.
• Format: Article
• Language: English
• Subjects: Atomic, molecular, and ion beam impact and interactions with surfaces; Beams (radiation); Condensed matter: electronic structure, electrical, magnetic, and optical properties; crystal orientation; Crystal structure; Electron and ion emission by liquids and solids; impact phenomena; Exact sciences and technology; geology; Impact phenomena (including electron spectra and sputtering); isotope ratio; Isotopes; Magnetite; Mathematical analysis; Minerals; Physics; Secondary Ion Mass spectrometer; Secondary ion mass spectrometry; Sulfur
• ISSN: 0142-2421; 1096-9918; 1096-9918
• DOI: 10.1002/sia.3424

A high‐precision SIMS analysis technique has been established for oxygen, sulfur, and iron isotope ratios and applied to a wide range of geoscience research areas using a Cameca IMS‐1280 at the Wisconsin Secondary Ion Mass Spectrometer Laboratory (WiscSIMS). Precision and accuracy of 0.3‰is achieved routinely for the measurement of 18O/16O ratio using multicollection Faraday Cup (FC) detectors and primary Cs+ beam size of 10 µm. Smaller beam sizes of 3 µm to < 1 µm yield precisions of 0.7–2‰using a multicollection Electron Multiplier (EM) in pulse‐counting mode for 18O. We evaluate small SIMS analytical biases at the level of a few ‰or less using standard minerals with homogeneous oxygen isotope ratios: (i) topography of samples related to polishing relief of grains and location of analysis in a sample holder; and (ii) crystal orientation effects in magnetite (Fe3O4). The latter effect has not been detected for oxygen isotope ratio measurements in other minerals including a variety of silicate, oxide, and carbonate minerals at WiscSIMS. However, similar analytical biases that are correlated with crystal orientation have been identified from Fe isotope analyses in magnetite and S isotope analysis in sphalerite (ZnS), and many minerals have not yet been evaluated. The total range of analytical bias among randomly oriented magnetite grains becomes smaller by reducing the sputtering energy of the primary ions (from 20 to 10 keV), which may help reduce crystal orientation effects. Copyright © 2010 John Wiley & Sons, Ltd.