SAED

Selected Area Electron Diffraction (SAED) is a technique used in transmission electron microscopy (TEM) to obtain electron diffraction patterns from a defined region of a specimen. A selected-area aperture in the TEM’s diffraction or imaging plane limits the beam to a small area, allowing diffraction data to be collected from that region without averaging over the surrounding material.

SAED patterns provide information about crystal structure, lattice parameters, orientation, and phase composition. For a single-crystal area, the pattern typically shows discrete diffraction spots whose arrangement reflects the crystal’s orientation and symmetry. For polycrystalline or nanocrystalline regions, due to randomly oriented grains, ring patterns emerge that correspond to the material’s possible lattice spacings. By indexing the spots or rings and calibrating with known standards and camera length, researchers can identify phases and estimate lattice parameters. SAED can also yield zone-axis information when the sample is oriented appropriately.

Applications of SAED span materials science and solid-state physics. It is used to identify crystalline phases in metals, ceramics, and semiconductors, determine crystal structures, map orientations in polycrystalline films, and analyze defects or strain in thin specimens. In practice, SAED is often employed alongside imaging, energy-dispersive spectroscopy, and other diffraction techniques in TEM or scanning TEM (STEM) workflows.

Limitations include dynamical scattering, which can complicate interpretation relative to kinematic diffraction models, and the small sample volume that can lead to multi-phase signals if the selected area contains several grains. The technique also requires electron-transparent specimens and careful calibration of imaging and diffraction optics to obtain quantitative results.