Energy Dispersive X-Ray Spectroscopy (EDX)
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Energy dispersive X-ray spectroscopy (EDX) (Author: Dr. Armin Zankel)
Fundamentals of energy dispersive X-ray spectroscopy
Energy dispersive X-ray spectroscopy (EDX, EDXS or EDS) is a chemical analysis method that can detect elements from boron to uranium (atomic numbers 5 to 92). Both qualitative and quantitative analyses are possible. The convenience of this method lies in the fact that chemical information can be obtained from sample surfaces very quickly (e.g. two minutes after setting up a sample site) and generally without causing any damage.
EDX detector on an electron microscope
Figure 1 shows an EDX detector flanged to the sample chamber of an electron microscope (see: electron microscopy).
| Fig. 1: | EDX detector flanged to an electron microscope. (a): EDX detector holder; (b): Liquid nitrogen reservoir for cooling the detector; (c): Electron column of the electron microscope; (d): Sample chamber of the electron microscope |
When electron beams are directed at a sample surface, both X-ray braking radiation and characteristic X-ray radiation are produced. The latter is decisive for chemical analysis. Each chemical element corresponds to characteristic energy values of the measured signals.
EDX in scanning electron microscopy allows for very convenient selection of the sample area (see also: test piece). Investigations can be carried out in small areas or even point measurements. Here, a pixel is selected on the sample site and the electron beam is directed only to that point for EDX analysis. It should be noted that the X-ray signal detected does not originate from a single pixel, but from an interaction volume on the sample surface, which can vary in size depending on the material and the electron energy used (diameter e.g. 200 nm to several micrometres).
The typical EDX spectrum
In polymer research, EDX can be used, for example, for the chemical characterisation of fillers and inclusions. It is not possible to distinguish between different polymers using EDX. In this case, vibrational spectroscopy methods are used. The result of an EDX analysis is a spectrum (Fig. 2) showing the number (counts) of signals (X-ray quanta) as a function of the respective energy (electron volts). The higher the peak at the respective energy, the more of the corresponding material is present in the test piece.
| Fig. 2: | Typical EDX spectrum. The y-axis shows the intensity (counts) of the detected X-ray signals in relation to specific energy values (keV on the x-axis). |
When this method is used for imaging, it is referred to as EDX mapping. The resolution of EDX is lower than that achieved using secondary electrons and backscattered electrons, and is predominantly determined by the material and the electron energy used.
Acknowledgements
The editors of the lexicon would like to thank Dr. Armin Zankel, Institute of Electron Microscopy and Nanoanalysis (FELMI) and Graz Centre for Electron Microscopy (ZFE) for the guest contribution. FELMI is an institute of the Faculty of Mathematics and Physics and Geodesy of the Graz University of Technology.
See also
References
| [1] | Goldstein, J., Newbury, D., Joy, D., Lyman, Ch., Echlin, P., Lifshin, E., Sawyer, L., Michael, J.: Scanning Electron Microscopy and X-Ray Microanalysis. Kluwer Academic / Plenum Publishers (2003) (ISBN 0-306-47292-9) |
| [2] | Reimer, L.: Scanning Electron Microscopy. Springer, Berlin Heidelberg (1998), 2nd Edition, (ISBN 3-540-63976-4) |
| [3] | Michler, G. H.: Electron Microscopy of Polymers. Springer, Berlin Heidelberg (2008) (ISBN 978-3-540-36350-7; see AMK-Library under F 1) |
| [4] | Sawyer, L., Grubb, D., Meyers, G. F.: Polymer Microscopy. Springer, Berlin Heidelberg (2008), 3rd Edition, (ISBN 978-0-387-72627-4) |
| [5] | Zankel, A., Reingruber, H., Schröttner, H.: 3D Elemental mapping in the ESEM. Imaging & Microscopy 2 (2011) 35–37 (Link) (last access on January 1, 2024) |