precession electron diffraction

**PED** (Precession Electron Diffraction) is a **TEM technique that rocks the incident electron beam in a conical precession pattern during diffraction** — averaging over many incident angles to reduce dynamical diffraction effects and produce quasi-kinematical diffraction patterns. **How Does PED Work?** - **Precession**: The beam is tilted and rotated in a cone around the optic axis (precession angle ~1-3°). - **De-Scan**: After the specimen, a complementary de-scan re-centers the transmitted beam on the optical axis. - **Integration**: The recorded pattern is the sum of diffraction patterns from many incident angles. - **Result**: More reflections visible with intensities closer to the kinematical (theoretical) values. **Why It Matters** - **Structure Solution**: PED patterns are close to kinematical -> enables direct structure solution methods from electron diffraction. - **Phase Identification**: Combined with template matching, PED enables automated phase identification. - **ACOM**: Precession + automated template matching = Automated Crystal Orientation Mapping (ACOM-TEM). **PED** is **diffraction without the dynamical headache** — spinning the beam to produce cleaner diffraction patterns that are easier to interpret.