SciMed Education
Introduction to Energy Dispersive
X-ray Spectroscopy
What is Energy Dispersive Spectroscopy (EDS)?
How Characteristic X-rays are Formed
The formation of characteristic X-rays is a key principle in EDS. When an electron beam in an electron microscope strikes a sample, electrons from the beam may undergo inelastic scattering. This process knocks an inner-shell electron from an atom in the sample (typically from the K, L, or M shells). This creates a vacancy in the inner electron shell, which is then filled by an electron from a higher-energy shell.
During this transition, excess energy is released in the form of an X-ray photon. The energy of this photon is characteristic of the element from which it originated, as it depends on the energy difference between the atomic shells. Each element has unique energy levels for its electron shells, so the emitted X-rays have distinct energy peaks that can be detected, allowing for the identification of the element.
Additionally, the distribution of these X-rays depends on the energy of the electron beam. At higher accelerating voltages, electrons penetrate more deeply into the material, scattering across a larger area. As a result, the X-ray signal is more spread out, providing information about the elemental composition deeper within the sample.
The EDS Detector
Modern EDS systems primarily use Silicon Drift Detectors (SDDs), which have largely replaced older Si(Li) detectors. SDDs offer higher efficiency and faster processing speeds, making them ideal for high-performance analysis. These detectors provide energy resolution typically between 120-130 eV at the Mn Kα (5.9 keV) peak.
When an X-ray enters the detector, it interacts with the silicon atoms in the detector, creating electron-hole pairs in the depletion region. The number of electron-hole pairs generated is directly proportional to the energy of the X-ray.
Under an applied electric field, these charge pairs are collected and processed into an electrical signal. This signal is then amplified and digitized to determine the energy of the original X-ray, which then identifies the emitting element.
To allow X-rays to pass through while protecting the detector, a thin window is used. Most detectors use a beryllium window, which is opaque to low-energy X-rays (less than 1 keV). This can limit the detection of light elements such as boron, carbon, oxygen, and nitrogen. Currently, researchers are developing windowless or ultra-thin window detectors, which improve the detection of these light elements. The efficiency of X-ray capture is also affected by the geometry of the detector and its alignment within the scanning electron microscope (SEM) chamber.
EDS Applications in Industry
Materials Science and Metallurgy
In materials science and metallurgy, EDS plays a crucial role in analysing and characterising materials at the microscopic level. Here are some key applications:
Phase Composition Analysis: EDS helps identify phase compositions in alloys. Alloys, which consist of multiple elements, derive their mechanical properties, corrosion resistance, and performance from the specific balance of these elements. EDS provides precise elemental analysis, ensuring that metal formulations are correct for industrial applications.
Failure Analysis: Metals and alloys used in high-stress environments, such as aerospace or construction, may fail due to fatigue, stress corrosion cracking, or intergranular corrosion. EDS allows for the examination of elemental distribution in the damaged areas, helping engineers understand the causes of failure and implement preventive measures.
Trace Contaminants Detection: Even trace contaminants can drastically affect the performance of materials in high-precision applications. EDS enables the detection of impurities, allowing manufacturers to refine their processes and improve material quality.
Semiconductor and Nanotechnology Research
In the semiconductor industry, EDS is indispensable for impurity analysis in semiconductor devices:
Impurity Analysis: Modern electronics require ultra-pure materials. Even minute impurities can degrade the performance of semiconductor devices. EDS allows engineers to detect and identify unwanted elements within these materials, ensuring the quality and performance of devices.
Thin Films and Multilayer Structures: EDS is also crucial in the analysis of thin films and multilayer structures in semiconductors and photovoltaics. By providing detailed compositional analysis at different depths, EDS ensures that these thin layers have the correct elemental distribution, preventing defects that could impair their functionality.
Nanoparticle Quality Control: Nano- and microparticles such as those used in battery cathodes must meet strict purity standards. EDS verifies the elemental composition of nanoparticles, ensuring they conform to these standards and are safe for use in sensitive applications.
Geology and Environmental Science
In geology, EDS is widely used for mineral analysis, providing insights into the composition of geological samples. Here are some key uses:
Mineral Exploration and Petrology: EDS helps geologists identify the elemental makeup of rocks and minerals, aiding in resource extraction and land-use decisions. By detecting valuable or hazardous elements, such as gold or arsenic, EDS informs mining operations and exploration.
Environmental Contaminant Detection: EDS plays a significant role in environmental science, particularly in identifying pollutants in soil and water samples. Heavy metals like lead, mercury, and arsenic can be detected, which is crucial for pollution assessment, remediation efforts, and regulatory compliance
Forensics
Gunshot Residue (GSR) Analysis: When a firearm is discharged, it releases tiny particles containing elements like lead, barium, and antimony. EDS helps forensic scientists identify these particles on a suspect’s clothing or nearby surfaces, providing evidence in criminal investigations.
Archaeology
EDS is also applied in archaeology for analysing ancient materials and artifacts:
Pigment Identification: EDS is used to determine the elemental composition of pigments in ancient paintings and artifacts. This aids in the authentication of artworks and helps researchers uncover historical painting techniques and materials.
Elemental Fingerprinting of Artifacts: EDS assists in verifying the origins of historical items like coins, manuscripts, and ceramics. By comparing the elemental signatures of artifacts with reference materials, archaeologists can establish the provenance of objects, helping to authenticate them.
Biomedical and Pharmaceuticals
EDS plays an important role in biomedical research and the pharmaceutical industry:
Trace Element Analysis in Tissues: In biomedical research, EDS is used to analyse biological tissues for trace elements, such as metals in organs. This helps researchers understand disease mechanisms, nutritional deficiencies, and toxicology.
Biomineralisation Studies: EDS helps in analysing biomineralisation, the process by which organisms form minerals. This is critical in fields like orthopaedics and regenerative medicine, where understanding the composition of bone or cartilage is key to developing better treatments and implants.
Pharmaceutical Quality Control: In the pharmaceutical industry, ensuring the consistency of ingredients in drugs is critical for efficacy and safety. EDS is used for process and quality control in pill manufacturing to verify the composition of tablets and capsules, detect contaminants, and assess the integrity of coatings.
What to do next?
If you require more information, such as detailed application notes or a conversation with a member of our team, please contact us using the methods provided below. Alternatively, you can explore SciMed’s SEM Range.
Contact Us Today
We take great pleasure in assisting you and ensuring you get a prompt response to your questions
Live chat opening hours Mon – Fri 9:15 to 16:30 (UK Time)