Development of capability in the SEM-CL of carbonates

Bouch, J.E.. 2006 Development of capability in the SEM-CL of carbonates. Nottingham, UK, British Geological Survey, 25pp. (IR/06/111) (Unpublished)

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This report describes investigations into methodologies that can be applied to overcome imaging problems associated with carbonate minerals on scanning electron microscope-based cathodoluminescence (SEM-CL) systems. The problem arises due to the persistent nature of luminescence from carbonate minerals, which causes ghosting or streaking across SEM-CL images. Two methodologies were tested: • The first methodology (Lee 2000) applied very long image acquisition times that, in certain situations proved capable of producing excellent images at higher resolution than is possible using optical-based CL systems. However, the image acquisition times are too slow (c. 40 minutes per image) to be useful in most day-to-day situations. • The second methodology (Reed and Milliken 2003) uses an optical filter to remove the portion of the CL spectrum responsible for the persistent luminescence (in this case in the yellow to red portion of the visible light spectrum). This enabled capture of SEM-CL images at far faster acquisition times (c. 5 minutes per image) than was possible without the filter. However, the resulting ‘filtered’ images suffer from relatively poor contrast and zoning apparent in these images did not always match zoning observed in optical Cl or unfiltered SEM-CL images. Poor image contrast was observed in the filtered images because the luminescence in the studied carbonates is predominantly due to activation by substitution of Mn, which predominantly occurs in the orange to red portion of the visible spectrum. Therefore, this type of luminescence was effectively excluded by the filter. Consequently the measured signals from the detector reflect the much less intense intrinsic luminescence of the carbonate or luminescence activated by other substituted cations (e.g. rare earth elements) or thermally activated luminescence. Although filtered SEM-CL carbonate imaging met with variable levels of success, the filtered imaging approach will prove useful in the SEM-CL analysis of quartz in mixed quartz-carbonate-bearing lithologies such as carbonate-cemented sandstones, which have previously been hindered by the persistence of the luminescence from the carbonates.

Item Type: Publication - Report
Programmes: BGS Programmes > Laboratory Operations
Funders/Sponsors: NERC
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
Additional Keywords: Scanning electron microscopy, Carbonates
NORA Subject Terms: Earth Sciences
Date made live: 08 Jun 2009 08:59 +0 (UTC)

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