SEM-EDS Analysis: Composition and Methodology

SEM-EDS analysis is one of the most widely used material-characterisation techniques in scientific research, manufacturing, engineering, geology, pharmaceuticals and environmental analysis. It combines detailed surface imaging with elemental composition analysis, allowing researchers to observe the physical features of a sample and determine the chemical elements present in selected areas.

SEM means Scanning Electron Microscopy, while EDS means Energy-Dispersive X-ray Spectroscopy. The technique may also be written as SEM-EDX because EDS and EDX are commonly used to describe the same elemental-analysis method.

SEM produces highly magnified images of a sample’s surface. EDS, on the other hand, detects characteristic X-rays generated when the electron beam interacts with atoms in the sample. Together, they provide complementary information about surface morphology, microstructure and elemental composition.

Researchers and industries that require SEM-EDS testing can explore available laboratory tests and analytical services on Allanalysis or connect with verified laboratories offering material characterisation.

What Is SEM Analysis?

Scanning Electron Microscopy is an imaging technique that uses a focused beam of electrons rather than visible light.

During analysis, the electron beam moves across the sample surface in a controlled scanning pattern. When the electrons interact with the sample, they produce several signals. Detectors collect these signals and convert them into images.

The two commonly used imaging signals are secondary electrons and backscattered electrons.

Secondary-electron images provide detailed information about surface texture and topography. They are useful for studying cracks, pores, particles, fibres, coatings and surface defects.

Backscattered-electron images are influenced by the average atomic number of the material. Areas containing heavier elements generally appear brighter than areas containing lighter elements. This contrast can help reveal different phases or regions within a sample.

SEM can provide much greater depth of field and magnification than conventional optical microscopy. It is therefore valuable for examining features that are too small to be studied clearly with an ordinary microscope.

The Allanalysis guide on common applications of SEM in material science explains how the technique is used for particle analysis, fracture investigation, contamination studies and material verification.

What Is EDS Analysis?

Energy-Dispersive X-ray Spectroscopy is an analytical technique used to identify the elements present in a sample.

When the SEM electron beam strikes an atom, it can remove an electron from one of the atom’s inner energy shells. An electron from a higher shell then moves into the vacant position. The difference in energy is released as an X-ray.

Because each chemical element produces characteristic X-ray energies, the detector can use the emitted X-rays to identify the elements in the analysed region.

The result is usually displayed as an EDS spectrum. The horizontal axis represents X-ray energy, while the vertical axis represents the number or intensity of X-rays detected.

Each major peak in the spectrum is associated with a particular element. The stronger the peak, the greater the contribution of that element to the detected signal, although proper quantification requires software corrections and careful interpretation.

Thermo Fisher Scientific explains that EDS adds chemical-composition data to electron-microscopy images, allowing researchers to obtain both morphological and elemental information from a sample.

Composition Information Obtained From SEM-EDS

SEM-EDS can provide qualitative, semi-quantitative and, under carefully controlled conditions, quantitative elemental information.

Qualitative Elemental Analysis

Qualitative analysis identifies which elements are present in the selected area.

For example, an unknown particle may contain iron, oxygen and silicon. This information can help determine whether it is likely to be an iron oxide, mineral particle, corrosion product or external contaminant.

Semi-Quantitative Analysis

Semi-quantitative analysis estimates the relative amounts of the detected elements.

The results are commonly reported as:

• Weight percentage.

• Atomic percentage.

• Normalised elemental percentage.

Weight percentage describes the contribution of each element based on mass, while atomic percentage describes the relative number of atoms.

These values must be interpreted carefully because surface condition, sample geometry, coating material, peak overlap and analytical settings can influence the result.

Elemental Mapping

Elemental mapping displays where particular elements are located across a selected area.

Each pixel or group of pixels is associated with an EDS spectrum. The software then creates maps showing the distribution of chosen elements.

Elemental maps are useful for studying:

• Coatings and interfaces.

• Mineral phases.

• Corrosion products.

• Contaminant particles.

• Pharmaceutical ingredients.

• Metal alloys.

• Composite materials.

• Inclusions and manufacturing defects.

Point and Area Analysis

Point analysis measures the composition at a specific location. It is useful when the researcher wants to identify an individual particle, inclusion or unusual feature.

Area analysis collects signals from a wider selected region and provides an average composition for that area.

Line-scan analysis can also show how elemental composition changes along a selected path, such as across a coating, weld or material interface.

SEM-EDS Methodology

A typical SEM-EDS methodology involves sample planning, preparation, mounting, instrument setup, image acquisition, spectral collection and data interpretation.

The specific procedure depends on the sample, research objective and available equipment.

Step 1: Define the Analytical Objective

Before preparing the sample, the researcher should clearly define what the analysis is expected to show.

The objective may be to:

• Examine surface morphology.

• Measure particle size and shape.

• Detect contaminants.

• Identify corrosion products.

• Compare treated and untreated samples.

• Determine elemental composition.

• Investigate material failure.

• Examine a coating or interface.

• Characterise an unknown substance.

A clear objective helps the laboratory select suitable preparation procedures, accelerating voltage, magnification and EDS acquisition settings.

Researchers can review other analytical techniques used in academic research before deciding whether SEM-EDS alone will answer the research question.

Step 2: Sample Preparation

Good sample preparation is essential for dependable SEM-EDS results.

The sample must normally be clean, dry, stable under vacuum and small enough to fit inside the microscope chamber.

Solid samples may be cut into manageable sections. Powders can be distributed onto conductive carbon tape attached to an aluminium sample stub. Cross-sectional samples may require embedding, grinding and polishing to expose a flat internal surface.

Biological samples often require fixation, dehydration and controlled drying to preserve their structure.

Samples should not be touched directly on the analytical surface because fingerprints, dust, oils and handling tools may introduce contamination.

For polished cross-sections, the surface should be smooth enough to reduce errors caused by irregular sample geometry. Thermo Fisher notes that cutting, embedding, grinding and polishing are common preparation steps for flat microscopic specimens.

Step 3: Mounting and Conductive Coating

The sample is secured to an SEM stub using carbon tape, adhesive or another suitable mounting material.

Non-conductive samples may accumulate electrical charge when exposed to the electron beam. This charging can produce bright areas, image distortion, streaking or loss of detail.

To reduce charging, the sample may be coated with a thin conductive material such as gold, gold-palladium, platinum or carbon.

The chosen coating depends on the purpose of the analysis. Gold coating can improve image quality but may introduce a gold peak into the EDS spectrum. Carbon coating is often preferred when elemental analysis is important because it creates fewer interfering metallic peaks.

The published Allanalysis SEM-EDS procedure describes samples being dried, mounted on aluminium stubs with carbon tape and coated to improve conductivity.

Step 4: Vacuum and Instrument Setup

After mounting, the sample stub is placed inside the microscope chamber. The chamber is evacuated to create a vacuum.

The vacuum allows the electron beam to travel efficiently and reduces unwanted interactions with air molecules.

The operator selects instrument conditions such as:

• Accelerating voltage.

• Beam current.

• Working distance.

• Aperture size.

• Spot size.

• Detector type.

• Scan speed.

• Magnification.

Higher accelerating voltages can produce more X-rays and analyse a greater depth of material, but they may also reduce surface sensitivity. Lower voltages can improve analysis of shallow features but may not effectively excite all required elemental X-ray lines.

The correct settings depend on the elements, sample thickness, feature size and desired analytical depth.

Step 5: SEM Image Acquisition

The analyst first locates the area of interest at a relatively low magnification.

Magnification is then increased to examine specific features such as particles, pores, fibres, cracks, inclusions or surface deposits.

Images may be recorded using secondary-electron or backscattered-electron detectors.

Secondary-electron imaging is particularly useful for surface detail. Backscattered imaging helps distinguish regions with different average atomic compositions.

SEM images should include a clear scale bar, magnification information and relevant acquisition details.

The Allanalysis article on how SEM reveals surface defects explains how surface imaging can reveal fractures, pores, corrosion and manufacturing defects that may not be visible through ordinary inspection.

Step 6: EDS Spectrum Collection

Once a suitable area is identified, the EDS detector collects emitted X-rays.

The analyst may perform point analysis, selected-area analysis, line scanning or elemental mapping.

A sufficient number of X-ray counts must be collected to obtain a useful spectrum. Longer acquisition times usually improve counting statistics, although they may increase the possibility of beam damage or sample drift.

The software identifies peaks and assigns them to likely elements. The analyst must then review the assignments because automatic identification can sometimes confuse overlapping peaks.

Energy-dispersive spectrometry measures X-ray photons across an energy range and is used with excitation sources such as electron beams. NIST also notes that EDS spectra may contain artefacts, including peak broadening, escape peaks and coincidence peaks.

Step 7: Quantification and Interpretation

Quantitative software calculates estimated elemental concentrations after correcting for physical effects within the sample.

Common corrections account for:

• Atomic-number effects.

• X-ray absorption.

• Secondary fluorescence.

• Detector response.

• Background radiation.

• Peak overlap.

Results may be presented as weight percentage or atomic percentage.

Interpretation should compare the spectrum with the SEM image, sample history, expected composition and other analytical evidence.

For high-accuracy composition measurements, reference materials, standards and well-controlled operating conditions may be required. NIST provides specialised tools such as DTSA-II for simulating, planning and quantifying EDS measurements using established correction algorithms.

Applications of SEM-EDS Analysis

SEM-EDS is used across many fields.

In materials engineering, it identifies phases, inclusions and contaminants in metals, ceramics, polymers and composites.

In geology, it helps characterise minerals and determine the elemental composition of rock particles.

In environmental science, it can examine dust, soil particles, ash and industrial residues.

In manufacturing, it supports quality control, product comparison and failure analysis.

In pharmaceuticals, SEM can examine particle shape and surface structure, while EDS may detect inorganic elements or unexpected contaminants.

In construction, it can investigate cement products, corrosion, aggregates and material deterioration.

The article on quality control through analytical testing provides additional examples of how SEM-EDS supports product verification and failure investigation.

Limitations of SEM-EDS

Although SEM-EDS is powerful, it has important limitations.

EDS provides elemental rather than molecular information. It may show that carbon and oxygen are present, but it does not necessarily identify the exact compound containing those elements.

Light elements can be more difficult to analyse accurately, depending on the detector and operating conditions.

Hydrogen and helium are generally not detected through conventional SEM-EDS.

Overlapping X-ray peaks can lead to incorrect elemental identification.

The detected composition may include signals from the coating, mounting tape, sample holder or material beneath a thin specimen.

EDS also analyses a small region. Results from one point should not automatically be treated as representative of an entire sample.

For trace elements, detection limits depend on the element, matrix, detector and measurement conditions. NIST reports that fluorescence and detector construction materials can increase detection limits for certain elements, including carbon, aluminium and silicon.

Conclusion

SEM-EDS analysis combines detailed electron-microscope imaging with elemental-composition testing.

SEM reveals surface morphology, texture, particle shape, cracks, pores and material phases. EDS identifies the chemical elements present and can show how those elements are distributed across the sample.

A reliable methodology requires a clearly defined objective, proper sample preparation, appropriate mounting, suitable microscope settings, careful spectral collection and professional interpretation.

Although SEM-EDS does not directly identify every chemical compound and may have limitations in trace analysis, it remains an important technique for research, manufacturing, geology, environmental testing, pharmaceuticals, construction and material-failure investigations.

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