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Cathodoluminescence System


Figure 6 : (a) SEM image of some zircon grains. (b) Panchromatic PMT intensity image (false color) of the same area. (c) Close-up panchromatic PMT image of a single zircon grain (measurements by Martijn Haring). These measurements were taken at 10 kV acceleration voltage, 1 nA current, and a dwell time of 100 μs.


on the conditions under which the rock was formed (chemical composition of the melt, pressure, temperature, presence of water, etc.) and what environments it was exposed to during its lifetime. Zircons. As an example we a show a measurement


on a number of zircon grains in which the CL emission (partly) originates from traces of extrinsic rare-earth-ion color centers [ 16 ]. Figures 6 a and 6 b show an SEM image and a panchromatic CL image, respectively, of the same area. Both figures show zircon grains, but the CL image shows more structure within the grains. As growth conditions change during formation, the zircon is aff ected. Such changes in conditions lead to zonation in the zircon (zones of zircon that are slightly different in composition), and this can be visualized with CL because the method is sensitive to such


small changes [ 16 ]. Figure 6c shows another CL image in which there is strong CL contrast within a single grain; here again the zonation is clearly visible. CL is oſt en used as a prescreening tool for high-resolution secondary-ion-mass spectrometry (SIMS) to image the zonation pattern and identify regions of interest (ROIs) for isotope analysis. These regions can then be interrogated with the more expensive and time-consuming SIMS technique. Such an analysis has been used to date zircons that are more than 4.3 billion years old, the oldest native crustal rock of Earth ever to be dated [ 17 ]. Sandstone . Sandstone is a sedimentary rock consisting of compacted grains of sand (typically quartz). Sandstone is one of the rock types that can contain oil and gas. Studying the origin and geological history of such rocks with CL spectroscopy can therefore play an important role in


Figure 7 : Sandstone analysis. (a) PMT image (5 kV) that is used to identify a ROI (indicated by the white box). (b) SEM image of the ROI from (a). (b) and (c) show false-color RGB images derived from the CL datacube acquired from the area with 80 ms dwell time at 5 kV (c) and 15 kV (d), respectively. The color coding is blue = 390–476 nm, green = 477–563 nm, and red = 564–650 nm. (e) and (f) show spectra taken from the regions indicated in (d) for 5 kV (e) and 15 kV (f).


16 www.microscopy-today.com • 2016 May


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