Energy-dispersive X-ray (EDX) spectroscopy
Compositional analysis technique. The high energy electron beam can eject electrons from inner-shell atomic orbitals. The resulting vacancies are filled by electrons from higher energy shells ; electron energies lost during these transitions are emitted as X-rays. The transitions, and hence X-rays, have energies that are characteristic of the atomic species. Therefore, measuring the X-ray spectrum allows identification of the sample composition, and is typically sensitive down to levels of about 0.5 to 1 atomic percent. Quantification of composition is relatively straightforward for elements heavier than sodium. While lighter elements can be detected, e.g. from boron or carbon upwards, sensitivity to them is low, thus making quantification difficult. In general, spectral analysis must account for possible artefacts such as emission of X-rays from Cu grids or microscope pole pieces induced by back-scattered electrons, and peak overlap from the limited spectral resolution. When combined with STEM, EDX compositional line-scans and maps can be taken.