Energy-dispersive X-ray spectroscopy

Energy-dispersive X-ray spectroscopy (EDS or EDX) identifies and estimates the abundance of elements by measuring the energies and intensities of characteristic X-rays emitted from a specimen.

Characteristic X-ray: An X-ray photon with an energy determined by transitions between an element’s atomic electron shells. Element-specific shell-transition energies form the peaks that EDS uses to identify elements.
Scanning electron microscope: An electron microscope that scans a focused beam across a specimen to form images and collect signals. EDS is commonly paired with scanning electron microscopy to analyze selected regions.
Atomic orbital: A quantum state describing the spatial distribution and energy of an electron in an atom. The energies of occupied and vacant orbitals determine the X-ray transition energies measured by EDS.
Wavelength-dispersive X-ray spectroscopy: An X-ray microanalysis method that separates characteristic X-rays by wavelength using diffraction. Its sharper peak separation contrasts with EDS’s faster, simultaneous energy measurement.
Raymond Castaing: A French physicist who developed electron-probe microanalysis in the 1940s. His electron-probe method established the broader practice of analyzing specimens through electron-induced X-rays.
Electron–matter interaction: The scattering and energy-transfer processes that occur when electrons pass through matter. These interactions create the vacancies and excited atoms that generate an EDS signal.
Transmission electron microscopy: Microscopy that forms images using electrons transmitted through a thin specimen. EDS in a transmission electron microscope can analyze composition at much finer spatial scales.
Electron shell: A group of atomic electron states with similar principal quantum number and characteristic energies. EDS peaks arise when electrons fill vacancies in particular shells.
Energy resolution: A measure of how well a detector distinguishes radiation energies that are close together. Limited detector resolution makes nearby characteristic peaks difficult to separate in EDS.
Electron probe microanalyzer: An instrument that focuses electrons onto a specimen and analyzes emitted X-rays for microchemical composition. It provided the instrument platform on which EDS became a complementary X-ray analysis method.

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