energydispersive

Energy-dispersive techniques refer to methods that separate and measure radiation by its energy. In materials analysis, energy-dispersive X-ray spectroscopy (EDS or EDX) is a microanalytical method used with electron microscopes to determine the elemental composition of a sample.

Principle and detectors. When a specimen is irradiated by an electron beam in a scanning or transmission electron microscope, inner-shell electrons are ejected and characteristic X-ray photons are emitted as atoms relax. An energy-dispersive detector measures the energy of these photons, producing a spectrum of counts versus energy. Peaks in the spectrum correspond to specific elements, allowing qualitative and, with standards and corrections, semi-quantitative assessments of composition. The measurement is commonly performed with detectors based on silicon, such as silicon drift detectors (SDD) or older silicon lithium (Si(Li)) detectors. These detectors cover energies from several hundred eV up to around 20 keV and vary in resolution and throughput.

Data output and interpretation. The primary product is a spectrum indicating which elements are present. With appropriate calibration and ZAF-like corrections, concentrations can be estimated in weight or atomic percent. In addition to point spectra, EDS enables elemental mapping and line scans, revealing the spatial distribution of elements across a sample.

Applications and limitations. EDS is widely employed in geology, materials science, metallurgy, electronics, and forensics, often as a fast complement to wavelength-dispersive X-ray spectroscopy (WDS). Limitations include lower spectral resolution compared with WDS, difficulties detecting light elements (below about atomic number 11) and resolving overlapping peaks. Sample preparation typically requires conductive coating for non-conductive specimens and operation under appropriate vacuum conditions.