X-ray maps

Eigure 4.30 is an example of X-ray mapping of an (In,Ga)As quantum wire structure using a TEM/STEM Philips GM20 equipped with a thermally-assisted field-emitter and a Ge EDXS detector (Tracor Northern) [4.124]. The cross-section STEM bright-... 

Fig. 4.30. Imaging of element distribution by X-ray mapping (a) cross-section STEM bright-...

I. Digital X-ray Mapping. The beam may be controlled by a computer to move within a grid of points on the specimen surface. The beam remains at each point for a pre-set time while an analysis is carried out. With an EDS system, data from several elements may be collected at the same time and a BSE image may also be acquired in the same experiment. Digital X-ray maps may then be displayed for each of the chosen elements in turn. 

NCu was calculated for 55 boundaries from four quantitative X-ray maps, and the probability distribution is shown in Figure 5.26. The mean coverage of this distribution is 2.2 atoms/nm2, and these data illustrate the feasibility of measuring segregation by X-ray mapping in the AEM in the case of fine-grained, thin film materials. 

Williams et al. (2002) have reviewed the current state of AEM X-ray microanalysis, and they suggest ways in which the highest resolution of X-ray mapping may be achieved in the STEM with an EDS spectrometer. Because of their small collection angles and thin specimens, very small numbers of X-ray counts are generated, so the minimum detection limit is typically at best 0.1 wt%. This value is an order of magnitude worse than the 0.01 wt% figure for bulk-specimen in an SEM/EPMA. 

Analysis by the Detection of X-rays or y rays. EPMA is a fully qualitative and quantitative method of non-destructive analysis of micrometre-sized volumes at the surface of materials, with sensitivity at the level of ppm. All elements from Be to U can be analysed, either in the form of point analysis, from line scans and also as X-ray distribution maps. Current software allows the combination of elemental data in the latter, so that, for example, the digital data for those elements that corresponds to a selected phase will produce an X-ray map of the distribution of that phase in a given microstructure. 

X-Ray Mapping and the Use of Back-Scattered Electrons in the SEM, Amray Technical Bulletin 106-274, Amray, Bedford, Mass., 1976, pp. 11-13. 

EPMA is a technique for chemically analysing small selected areas of solid samples, in which X-rays are excited by a focused electron beam. Spatial distribution of specific elements can be recorded as two-dimensional X-ray maps using either energy dispersive spectroscopy (EDS) or... 

Elemental x-ray maps (EDS) indicate the nodules are mainly Ca and S (i.e. gypsum) whereas surrounding rims mainly consist of As, Fe, and Ni (Fig. 5). 

XANES analyses indicated the presence of both As3+ and As5+ species in the stack sample and that about one-third of the total As is trivalent (Paktunc 2008). X-ray mapping supplemented by micro-XANES analyses indicated that As is localized along thin rims around spherical Cu particles. These rims have higher As3+ species ranging from 34 to 40% of the total As. 

Figure 2.16. X-ray map of sUica/zirconia in the Extreme FESEM (after Boyes 2001).

Fig. 1. SEM backscattered electron image, Si X-ray map, Ca X-ray map, and Na X-ray map of alteration in pyrochlore from Vishnevogorskii, Russia. Note the loss of Na and Ca and incorporation of Si along cracks and the dark area near the middle of the backseaUered image.

Electron microprobes can be used in spot mode to measure the chemical compositions of individual minerals. Mineral grains with diameters down to a few microns are routinely measured. The chemical composition of the sample is determined by comparing the measured X-ray intensities with those from standards of known composition. Sample counts must be corrected for matrix effects (absorption and fluorescence). The spatial resolution of the electron microprobe is governed by the interaction volume between the electron beam and the sample (Fig. A.l). An electron probe can also be operated in scanning mode to make X-ray maps of a sample. You will often see false-color images of a sample where three elements are plotted in different colors. Such maps allow rapid identification of specific minerals. EMP analysis has become the standard tool for characterizing the minerals in meteorites and lunar samples. 

An X-ray map of the elements As, Sb, Cu, and Ag, was created for each sample at 500X magnification with a wave dispersive spectrometer (WDS) using Geller dPICT 32 software. The X-ray map was created from 24 individual maps combined for a total mosaic area size of 0.5 mm by 1.0 mm. For WDS analysis, an indium arsenic compound was used as an arsenic standard. Otherwise pure element... 

Figure 3. X-ray map for As, Sb, Cu, and Ag on curse tablet AUD-249. Regions with concentrations of...

Figure 17.18. (A) Carbon contents in an entire microaggregate from an alfisol at Arnot Forest in Upstate New York (500-nm resolution). (B) Detail of the microaggregate (red box in A) (50-nm resolution). (C) X-ray map of B. (D) Cluster map [3 components, 20 clusters, without first component PCA GUI 1.0 developed by Lerotic et al. (2004)]. (E) Individual clusters from D numbers in each cluster map correspond to spectra shown in Figure 17.19 (J. Lehmann, unpublished data 2006, measured as described in Lehmann et al., 2007). See color insert.

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