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  Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopy

Macholdt, D. S., Förster, J.-D., Müller, M., Weber, B., Kappl, M., Kilcoyne, A. L. D., et al. (2019). Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopy. Geoscientific instrumentation, methods and data systems, 8(1), 97-111. doi:10.5194/gi-8-97-2019.

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Macholdt, Dorothea S.1, Author              
Förster, Jan-David2, Author              
Müller, Maren, Author
Weber, Bettina2, Author              
Kappl, Michael, Author
Kilcoyne, A. L. David, Author
Weigand, Markus, Author
Leitner, Jan3, Author              
Jochum, Klaus P.1, Author              
Pöhlker, Christopher2, Author              
Andreae, Meinrat O.2, Author              
Affiliations:
1Climate Geochemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_2237635              
2Multiphase Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826290              
3Particle Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826291              

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 Abstract: The spatial distribution of transition metal valence states is of broad interest in the microanalysis of geological and environmental samples. An example is rock varnish, a natural manganese (Mn)-rich rock coating, whose genesis mechanism remains a subject of scientific debate. We conducted scanning transmission X-ray microscopy with near-edge X-ray absorption fine-structure spectroscopy (STXM-NEXAFS) measurements of the abundance and spatial distribution of different Mn oxidation states within the nano- to micrometer thick varnish crusts. Such microanalytical measurements of thin and hard rock crusts require sample preparation with minimal contamination risk. Focused ion beam (FIB) slicing was used to obtain ∼100–1000 nm thin wedge-shaped slices of the samples for STXM, using standard parameters. However, while this preparation is suitable for investigating element distributions and structures in rock samples, we observed artifactual modifications of the Mn oxidation states at the surfaces of the FIB slices. Our results suggest that the preparation causes a reduction of Mn4+ to Mn2+. We draw attention to this issue, since FIB slicing, scanning electron microscopy (SEM) imaging, and other preparation and visualization techniques operating in the kilo-electron-volt range are well-established in geosciences, but researchers are often unaware of the potential for the reduction of Mn and possibly other elements in the samples.

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Language(s): eng - English
 Dates: 2019
 Publication Status: Published in print
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 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.5194/gi-8-97-2019
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Title: Geoscientific instrumentation, methods and data systems
  Abbreviation : Geosci. Instrum. Meth. Data Syst.
Source Genre: Journal
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Publ. Info: Göttingen : Copernicus Publ.
Pages: - Volume / Issue: 8 (1) Sequence Number: - Start / End Page: 97 - 111 Identifier: ISSN: 2193-0856
CoNE: https://pure.mpg.de/cone/journals/resource/2193-0856