Advanced Chemical Analysis
Figure 2 : Historic Mocs meteorite. (a) Photograph of the sample (65 mm × 50 mm). (b) Overview X-ray map at 6 kV, 10 pA, input count rate 3 kcps, and 800 × 600 pixels was acquired for 2800 s. X-ray map was overlaid with the secondary electron (SE) image revealing lead contamination from the historical polishing process. (c) Pb M-line (Mα 2.343 keV) and S K-line (Kα 2.307 keV) were deconvoluted during measurement using a physical background subtraction and a least square fi t with stored line profi les. (d) A higher magnifi cation composite map showing only the elements C, O, Pb, and S of the rectangular region of interest in (b) overlaid with the SE micrograph. This shows that lead and soot were deposited on the sample surface that may consist of sulfi des (orange areas = red + yellow) and oxides (blue shows the O content). (e) Image detail of the outlined area in (d), without S, documenting that carbon features < 300 nm in size (green fi laments) can be made visible under high-vacuum conditions using low kV and ultra-low probe current. Sample courtesy of Natural History Museum, Vienna, Dept. of Mineralogy and Petrography. Sample NHMW-H9898 was a donation from industrial magnate Sigmund Sachsel. Special thanks to Ludovic Ferriere for taking the sample to the Bruker Nano laboratories for analysis and the resulting discussion.
probe currents, and the acquisition of high-resolution element mappings of large sample areas or of single nanoparticles with sizes down to a few nm. Non-destructive sample analysis with high spatial resolution can be very difficult to accomplish
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using conventional EDS detectors because sample surface charging, electron beam damage, and shadowing eff ects are common problems in scanning electron microscopy (SEM) that complicate X-ray acquisition.
www.microscopy-today.com • 2017 March
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