Energy dispersive X-ray spectroscopy (EDS) is an analytical technique used to identify the elemental composition of materials.
EDS works by exciting a sample with a focused beam of electrons, causing the emission of X-rays that are characteristic of the elements present in the sample.
The Working Principle of Eds
EDS relies on the principle that each element has a unique atomic structure, allowing a unique set of peaks on its electromagnetic emission spectrum.2
Step 1: Interaction of Electron Beam with Sample
In EDS, a beam of electrons is focused onto the sample being analyzed. The energetic electrons collide with the sample atoms, ejecting inner shell electrons and creating electron vacancies.3
Step 2: Excitation of X-rays
The vacancies are filled by electrons from higher energy levels dropping into the lower energy levels. To conserve energy, X-rays are emitted with energies characteristic of the difference between the two electronic levels involved.
Step 3: Detection of X-rays
The X-rays emitted by the sample are detected and measured by an energy-dispersive spectrometer. The spectrometer uses a solid-state semiconductor detector, usually made of Si(Li) or high-purity germanium.4
Step 4: Energy-dispersive detection
As X-rays strike the detector, they generate charge pulses proportional to the energy of the X-rays. The voltages of the pulses are amplified and sorted on a multichannel analyzer, producing an EDS spectrum with peaks corresponding to the energy levels for the elements present.5
Notable Advantages of Energy Dispersive X-Ray Spectroscopy (EDS)
Compared to wavelength dispersive X-ray spectroscopy (WDS), EDS offers some key advantages:
Simultaneous detection of all elements
EDS detects all elements simultaneously, while WDS scans through wavelengths sequentially. This allows faster elemental analysis.6
Minimal sample preparation
EDS can be performed with no special sample preparation, unlike WDS which requires standards. This enables rapid analysis.
Qualitative and quantitative analysis
EDS can provide both qualitative identification of elemental composition and quantitative compositional information.7
Applications of EDS
Some major applications of EDS include:
Scanning Electron Microscopy
EDS is commonly coupled with SEM, allowing microscopic examination of a sample and determination of elemental composition at micro-scale points or areas.
EDS can rapidly analyze and differentiate particles based on elemental compositions in applications like air quality monitoring.
In forensic studies, EDS can detect trace evidence by identifying the elemental fingerprints of materials like glass, soil, or dust.
EDS aids in quality control and failure analysis in materials science by verifying the elemental composition of alloys, ceramics, or other compounds.
EDS is applied in geosciences for determining mineral compositions and chemistry in fields like petrology and mineral exploration.
Limitations of EDS
Despite its utility, EDS has some limitations:
Qualitative analysis only
EDS is not very effective for detecting elements with atomic numbers below 4, i.e. H, He, Li.8
EDS spectra can have overlapping peaks that are difficult to deconvolute, limiting unambiguous elemental identification.
In EDS, irregular sample geometry and composition can affect absorption and fluorescence, impacting quantitative accuracy.9
Detection limits for EDS are relatively high, ranging from 0.1 to a few wt%. Trace elemental analysis requires more sensitive techniques.
Relationship of EDS with Scanning Electron Microscopy (SEM)
EDS is very commonly coupled with scanning electron microscopy (SEM), which provides high-resolution images of a sample’s surface topography and morphology. When EDS is combined with SEM, it enables correlating elemental composition to specific microstructural features and areas on the sample.
Some key advantages of using EDS with SEM include:
- SEM’s high magnification allows EDS analysis of very small features and inclusions.
- SEM imaging enables precise targeting of specific points or regions for EDS analysis.
- SEM provides contextual information about sample heterogeneity that aids EDS interpretation.
- SEM-EDS can perform rapid elemental mapping over sample surfaces.
- In-situ SEM-EDS can monitor dynamic processes like oxidation, corrosion, or crystallization.
The correlative capabilities of SEM imaging and EDS chemical characterization make SEM-EDS a very powerful tandem technique for advanced sample analysis.
EDS of Periodic Table Elements
EDS can detect all elements from boron (atomic number 5) to uranium (atomic number 92) in the periodic table, though it is not as effective in detecting low atomic number elements below sodium (atomic number 11).
For high atomic number elements, EDS is highly sensitive and can detect elements at levels as low as 0.1% by weight. Heavy elements like lead, gold, and uranium produce very prominent, intense EDS peaks as shown in Figure 1.
Light elements like carbon, nitrogen, and oxygen produce weaker EDS signals that may overlap. Detection limits for these light elements can be in the 1-5% range.
Elements like sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, potassium, calcium, titanium, manganese, iron, cobalt, nickel, copper, zinc, gallium, and arsenic are considered medium atomic number elements. EDS can easily detect these elements above 0.1-0.5% levels.
Probable Future Developments in EDS
Some key developments that can improve EDS capabilities include:
- Improved resolution with newer silicon drift and annular detectors.10
- Novel quantification methods to account for matrix effects.
- Correlative EDS with other analytical microscopy techniques for comprehensive characterization.
- Machine learning for automated analysis of complex EDS data.
- Portable, miniaturized EDS solutions.
Frequently Asked Questions
What type of samples can be analyzed with EDS?
EDS can analyze almost any solid, inorganic sample as long as it is compatible with high vacuum conditions and electron beam irradiation required of SEM. Organic materials can also be analyzed with appropriate sample preparation.
What information does EDS provide?
EDS provides both qualitative (which elements are present) and quantitative (how much of each element is present) information about the elemental composition of a sample.
How is EDS used with SEM?
SEM provides high-resolution images of the sample while EDS coupled to SEM provides elemental analysis at precise points or areas on the sample selected on SEM images.
What sample preparation is required for EDS?
Minimal sample preparation is needed for EDS compared to other techniques. Samples just need to be solid, dry, vacuum-compatible, and small enough to fit in the SEM specimen chamber.
What are the advantages of EDS over WDS?
Compared to WDS, EDS offers simultaneous multi-element analysis, minimal sample preparation, qualitative and quantitative capabilities, and ease of use.