A Quick Guide to EDS Elemental Analysis
Energy Dispersive X-ray Spectroscopy (EDS or EDX) is an indispensable analytical technique employed in
Scanning Electron Microscopes (SEM) for elemental analysis and chemical characterization. This method leverages the interaction of an electron beam with a sample to yield precise information about the sample’s elemental composition. Below we have created a quick guide to understanding the fundamentals and applications of EDS elemental analysis.
Principle of Operation
EDS analyzes characteristic X-rays emitted from samples as a result of irradiation with a high-energy source like an electron beam. These X-rays are generated from atoms within the sample as outer-orbital electrons fill vacancies in inner orbitals created by the interaction with the electron beam. The energy of each generated X-ray is unique to the orbital pair it originated from, so every element has a set of “characteristic” X-rays that can be used to identify it in an unknown substrate. EDS detectors analyze the energy of these X-rays to both identify elements and estimate their abundances in a sample.
Capabilities
EDS is a robust technique that can analyze nearly the entire periodic table - from Beryllium (⁴Be) to Uranium (⁹²U). Modern windowless EDS detectors are even capable of detecting Lithium (³Li). The capabilities of EDS include:
- Qualitative Analysis: EDS can qualitatively determine the presence of elements in a sample. It does this through identifying the characteristic X-ray peaks.
- Semi-Quantitative Analysis: By comparing the relative X-ray peak intensity of every element present in a sample, EDS provides a semi-quantitative assessment of element concentrations.
- Elemental Mapping: EDS mapping is used to visualize the spatial distribution of elements within a sample, revealing compositional heterogeneity.
Advantages
EDS offers several significant advantages, making it a popular choice for elemental analysis:
- Rapid Data Acquisition: EDS can quickly acquire data from a sample, allowing for fast multi-elemental analysis in seconds.
- Non-Destructive: The technique is non-destructive, preserving the integrity of the sample for further analysis.
- Ease of Use: EDS systems are easy to operate. Continuous advancements in EDS software to improve element identification and quantification makes this analysis technique approachable for users of any experience level.
Limitations
Despite its many benefits, EDS has certain limitations:
- Energy Resolution: The energy resolution of EDS (~128-130 eV) is lower than other electron microscopy-based techniques that analyze characteristic X-rays, such as wavelength dispersive spectroscopy (WDS;~10 eV). While this can make it challenging to distinguish X-rays with similar energies, software peak deconvolution has dramatically reduced the effect of energy resolution on data interpretation.
- Detection Limits: With detection limits between 0.1 and 0.5 wt%, EDS is generally used to characterize major elements in a sample. Techniques like WDS may be more suitable for the accurate quantification of trace elements.
Sample Preparation
In general, EDS requires little sample preparation. For element identification or EDS mapping, no additional preparation is required outside of that needed to image the sample via SEM. However, proper sample preparation is crucial for quantitative analysis to obtain accurate results. To acquire these results, samples should be clean, polished flat, and homogenous relative to the interaction volume of the electron beam (nm²-μm²). While non-conductive specimens can easily be characterized by EDS in low vacuum/variable pressure mode, adding a conductive coating, such as carbon, enables a more accurate quantitative analysis in high vacuum.
Data Interpretation
Interpreting
EDS data involves several steps:
- Element Identification: Elements are distinguished by matching the measured characteristic X-ray peaks in the spectrum to a known database.
- Quantification: Elemental composition is quantified by analyzing peak intensities. With standardless EDS, the relative peak intensities of every element present in the sample are compared and normalized to 100%. Alternatively, each peak intensity can be compared to a standard with a known concentration of that element to avoid the need to normalize the data and yield more accurate results. Matrix corrections are used to account for variations in X-ray yield as a function of sample composition and density.
- Elemental Mapping and Line Scans: EDS mapping and line scans provide visual and quantitative information on the distribution of the elements in a sample, aiding in the understanding of material properties and behavior.
Applications
EDS is a versatile tool widely used across various scientific and industrial fields. In materials science, it helps characterize a range of materials including alloys, ceramic composites, geologic specimens, and more. From assessing the composition of minerals in natural samples to assisting with the failure analysis of batteries and semiconductors, EDS is fast, flexible, and powerful.
Choose a Reliable SEM From JEOL USA
Energy Dispersive X-ray Spectroscopy (EDS) is a powerful technique for elemental analysis and chemical characterization within SEMs. Its ability to rapidly identify and map elements makes it invaluable in research and industry applications. Understanding its principles, capabilities, advantages, and limitations ensures effective utilization of this technology for detailed material analysis.