SEM and EDX analysis: what these instruments actually tell you

Scanning electron microscopy and energy-dispersive X-ray spectroscopy are two of the most frequently requested techniques at Drift Core Lab, and also two of the most frequently misunderstood. Clients sometimes expect SEM to give them a composition result, or EDX to show them a fracture surface. Understanding what each instrument actually does will help you commission the right analysis.

What SEM shows you ¶

A scanning electron microscope produces high-resolution images of a surface by scanning it with a focused beam of electrons. The output is a greyscale image with depth of field and resolution far beyond what an optical microscope can achieve. SEM is used to examine fracture surfaces, surface coatings, particle morphology, and microstructural features such as grain boundaries and inclusions. It does not, by itself, tell you what the material is made of.

What EDX adds ¶

EDX (energy-dispersive X-ray spectroscopy) is an attachment to the SEM that analyses the X-rays emitted when the electron beam strikes the sample. The energy of the emitted X-rays is characteristic of the elements present, so EDX produces an elemental spectrum and, with appropriate standards, a semi-quantitative composition. It is useful for identifying inclusions, corrosion products, and unexpected phases, and for confirming that a material matches its specified alloy grade.

Limitations to be aware of ¶

EDX is semi-quantitative, not fully quantitative. For accurate bulk composition, ICP-OES on a dissolved sample is more reliable. EDX also has limited sensitivity for light elements (below sodium in the periodic table), so it will not reliably detect carbon, nitrogen, or oxygen at low concentrations. For those elements, other techniques are needed. We will tell you if EDX is not the right tool for your specific question.

Typical applications at Drift Core Lab ¶

The most common uses of SEM/EDX at our lab are failure analysis (fracture surface examination and identification of corrosion products or contaminants), incoming material verification (confirming alloy composition against a certificate), and research support (characterising particle size, morphology, and composition in experimental materials). The technique is included in the Failure Analysis Starter package and the Basic Material ID Panel.

If you are not sure whether SEM/EDX is the right technique for your question, describe your sample and your question in an email to lab@driftcorelab.com. We will recommend the appropriate method before you commit to a submission.