X-ray Energy Dispersive Spectroscopy XEDS

8 X-ray Energy Dispersive Spectroscopy (XEDS) of Supported Metal Catalysts 

A typical XEDS spectrum generated from a supported metal catalyst powder specimen is presented in Fig. 3.13(a). In this case, the catalyst consisted of an AlgOg support that was co-impregnated with Au and Pd via an incipient wetness method, and exhibits the elemental peaks characteristic of Au (9.71 keV and 2.12 keV), Pd (2.84 keV), A1 (1.49 keV) and, O (0.52 keV). In addition to these elemental 

Once a thorough qualitative analysis has been done, the analyst may then wish to quantify the various elemental constituents that have been identified. However, great care must be taken to avoid the many pitfalls that can plague this type of quantitative analysis. For a comprehensive discussion of the proper approach to quantitative analysis, see, for example, Joy et alF, and Williams and Carter, and the many references therein. 

Once background removal has been accomplished, the ratio of the integrated intensity of the two characteristic X-ray peaks can then be used to calculate the mass fractions of each element using the Cliff-Lorimer relationship  

These quantitative approaches were developed to analyze individual spectra, but they are equally suited to the analysis of spatially resolved XEDS hyperspectral image datasets as well. STEM-XEDS is a particularly powerful technique, since it results in high spatial resolution concentration maps of the various elements analyzed. However, care must be taken, since specimens with complex geometries, such as the rough surfaces typically encountered in supported metal catalysts, can lead to errors when performing quantitative data analysis. 

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A diagonal scan across the surface of the window was recorded with X-ray energy dispersive spectroscopy (XEDS) in the TEM equipment. The atomic ratios of Si 0 N were found to be 43% 13% 44%, which is not the expected stoichiometry of Si02 and Si3N4 (40% 20% 40%). However, we know from the TEM images and the SIMS data shown below that the thickness of the oxide layer is 7 nm and the total window thickness is about 42 nm from which we would expect atomic ratios of 42% 8% 50%. This is most likely indicative of a native oxide present on the backside of the windows, enriching the O content of the whole film (as seen with SIMS), since the escape depth of the photons is much greater than the window thickness. 

The scientist s way is to use X-ray diffraction (XRD), X-ray energy-dispersive spectrometry (XEDS), wavelength-dispersive spectroscopy (WDS), or comparable techniques for chemical analysis. 

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