Energy Dispersive X-Ray Spectroscopy

Because all elements have characteristic X-ray energy “fingerprints” those energies can be used both to identify and quantify elements in unknown samples. One technique for doing this is “energy-dispersive x-ray spectroscopy” or EDS. This technique is used routinely on MATCO’s scanning electron microscopes. A similar technique (WDS) is used on electron microprobes, only there the wavelengths of the x-rays are measured, rather than their energies.

EDS techniques allow rapid determination of elemental compositions of areas down into the micron range. The beam of energetic electrons in the scanning electron microscope penetrates several micrometers into the sample surface, so that the EDS results are an average of the compositions of the top layer of the sample, not its absolute surface. Refer to the section on Auger Spectroscopy for a brief discussion of true surface analysis.

Quantification of EDS results, rather than simple identification of the elemental constituents, can be done by a theoretical calculation (using the well known ZAF corrections) or it can be done more precisely using appropriate standards. The only way to get more than semi-quantitative results is to use polished samples such as metallurgical cross-sections. Rough surfaces such as usually used in the SEM make it difficult to get highly precise quantitative results from EDS spectra.