By Vvon Engineering Team | Published | Updated
Understand SEM EDS/EDX spectra and elemental mapping, then decide whether you need a new microscope, detector upgrade or sample-analysis service.
Nanotechnology RFQ checklist (TXT)
EDS can identify and estimate elemental composition in an electron microscope, but a software-generated percentage is not automatically a defensible quantitative result. Consider interaction volume, peak overlap, specimen preparation and uncertainty before choosing the detector or interpreting a map.
This article explains the elemental-analysis workflow and interpretation questions around SEM EDS. Use the detector buying guide when preparing hardware, software and integration requirements for a quotation. Related reading: EDS Detector Buying Guide for SEM in Bangladesh.
Start with the SEM make and model, the samples and the elemental information you need. Ask the supplier to confirm the chamber interface, detector geometry, software and acceptance demonstration. The EDS detector buying guide separates those procurement questions from the interpretation discussion below.
Share the microscope model, available port information, specimen types, elements of interest and required maps or reports. Request separate lines for the detector, software, integration, training and support. Browse microscopy and microanalysis equipment or send an EDS project brief.
VVON's catalogue supports equipment procurement. If your immediate need is a test report on a few specimens, establish whether an external laboratory service is the appropriate route before committing to an instrument. For equipment, choose the purchase scope below and prepare representative samples for the supplier discussion.
| Your requirement | Start here | Include in the brief |
|---|---|---|
| A new SEM with elemental analysis | [SEM configuration guide](/choose/scanning-electron-microscope) | Sample types, imaging and mapping requirements, workload and room conditions |
| An EDS upgrade to an existing SEM | [EDS detector buying guide](/insights/eds-detector-buying-guide-sem-bangladesh) | Microscope model, existing detectors/software and required interfaces |
| A combined surface-characterisation laboratory | [AFM versus SEM comparison](/insights/afm-vs-sem-nanoscale-characterisation-bangladesh) | Required topography, imaging, composition and sample-preparation outputs |
The beam knocks electrons out of inner shells of atoms in the sample. As outer electrons fall in to fill those vacancies, they emit X-rays at energies characteristic of the element. An energy dispersive detector collects those X-rays and sorts them by energy, producing a spectrum of counts against energy. Peak positions identify elements. Peak areas, after a good deal of correction, estimate how much of each is present.
Modern silicon-drift EDS detectors generally use thermoelectric cooling rather than liquid nitrogen. Compare detector geometry, energy resolution, throughput and performance on the expected elements and specimens instead of detector area alone.
This is the point that matters most and the one most often missed. The image is formed by signals escaping from very near the surface, which is why an electron image can resolve fine detail. The X-rays used for elemental analysis are generated throughout the volume the beam penetrates, and at ordinary accelerating voltages in a light matrix that volume extends roughly a micrometre in every direction. Your image resolution and your analytical resolution are not the same number, and they are not close.
The consequences show up in every laboratory. A spot placed on a particle a few hundred nanometres across also samples the substrate underneath and the neighbours beside it, so the result is a mixture. A thin film analysed at high voltage returns the substrate composition mixed with the film. A grain boundary phase analysed at the boundary returns the two grains either side of it. None of those spectra are faulty. They are simply not measurements of the thing the operator pointed at.
To excite a characteristic line, the beam energy must exceed the relevant shell ionisation threshold. The overvoltage ratio uses that threshold, not the emitted X-ray energy; an appropriate ratio depends on the analysis. Lower voltage can reduce interaction volume but may remove useful lines or worsen overlap. Thin-film quantification may require standards and a layered-sample model.
Automatic peak identification, in analysis software such as AZtec Suite 6.3, is right most of the time, which is precisely what makes the failures dangerous. The software fits what it can, and a plausible wrong element in a spectrum from an unfamiliar material can travel a long way before anybody questions it. Any identification that changes your conclusion should be confirmed by checking that the full family of lines for that element is present in the right proportions, not just the single strongest peak.
Overlap can defeat automatic identification, particularly where weak peaks sit beside strong ones. Examples include closely spaced Ti/V lines and S K, Mo L or Pb M contributions. Check the full line family, background and fit residuals, and use standards, another excitation condition or WDS when the ambiguity matters.
The correction routines that turn peak areas into weight percentages assume a specimen that is flat, polished, homogeneous within the excited volume, oriented normal to the beam, at a known geometry relative to the detector, and analysed with a stable beam current. A polished cross section can meet those conditions. A powder, a fibre, a fracture surface, a particle on a stub and a rough natural surface cannot.
Check the quantification settings: whether totals are normalised, elements are omitted, oxygen is measured or inferred from stoichiometry, and which matrix correction and standards are used. A normalised total of 100% is not an independent accuracy check.
Report precision consistent with the measurement uncertainty, detection limits and sample variability. Whole percentages may be appropriate for a screening result, while validated quantitative work can justify finer reporting. Retain the spectrum, method and acquisition conditions so that the figures can be assessed.
Elemental maps can show distributions, and spectrum imaging can support quantitative compositional maps with an appropriate method. A raw intensity map is not automatically a concentration map. Inspect the spectrum, background, overlaps, count statistics and geometry, and retain the acquisition conditions. Use suitable drift correction when needed during longer acquisitions.
| What the draft says | What the measurement supports | Better wording |
|---|---|---|
| The particle is pure zinc oxide | A spot on a sub-micron particle also excited the substrate and its neighbours | The particle spectrum is dominated by zinc and oxygen, with a silicon contribution from the substrate |
| Composition quoted to two decimal places | Standardless normalised quantification on a rough surface | Report significant figures consistent with uncertainty, detection limits and the validated method. |
| Sulphur is absent | The detection limit and overlap assessment do not establish complete absence | Sulphur was not detected above the detection limit of this measurement |
| The oxide layer thickness is measured by elemental analysis | The excited volume is larger than the layer | Layer thickness measured from the cross section image; elemental analysis confirms the layer is aluminium and oxygen |
| Carbon content quantified | The sample was carbon coated and the chamber deposits hydrocarbon | Carbon not quantified because of the conductive coating |
| The map shows the element is concentrated at the grain boundary | The boundary is also a topographic step | Map shown alongside the backscattered electron image; boundary enrichment confirmed by line scan across a flat polished section |
None of this reduces the usefulness of the technique. Elemental analysis on an electron microscope answers a huge range of practical questions quickly: which phase is which, what the inclusion is made of, whether the plating is present, where the contaminant came from, which of two suppliers delivered the wrong alloy. It answers them best when the person reading the spectrum knows exactly which volume of material it came from.
Plan your next step
An EDS quotation is more useful when it starts with the samples and the claim your research needs to support. Ask for a detector and software configuration that can be assessed on representative material, alongside confirmation of compatibility with the intended SEM.
Xplore EDS detector: Review the routine microanalysis configuration.
Ultim Extreme Infinity: Review the windowless detector configuration.
Microscopy and microanalysis catalogue: Consider microscope and analytical requirements together.