7.3. PED Simulation

Precession Electron Diffraction (PED) Simulation

Simulates diffraction patterns obtained by precessing the incident electron beam around the optic axis.

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Overview

In PED the electron beam traces a cone around the optic axis. The diffraction patterns from all beam directions are integrated, offering several advantages over conventional SAED:

• Dynamical effects are averaged out, yielding intensities closer to kinematical values
• Higher-order Laue zone (HOLZ) reflections become more visible
• Better intensity data for structure determination

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Settings

Set the beam mode to Precession in Spot property. Dynamical theory is enabled automatically.

Parameter	Description	Typical
Semi-angle	Precession half-angle (mrad)	10–40
Step	Number of beam directions sampled	36–72
No. of Bloch waves	Bloch waves for dynamical calculation	50–200
Thickness	Specimen thickness (nm)	—

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Calculation method

1. For each sampled beam direction at precession angle α, run a full Bloch-wave calculation
2. Integrate diffraction patterns over all directions
3. Project the result onto the detector

Computation time scales linearly with Step.

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SAED vs PED

Feature	SAED	PED
Beam	Parallel, fixed	Precessing (cone scan)
Dynamical effects	Large	Averaged, smaller
HOLZ reflections	Weak	Stronger
Intensity reliability	May be insufficient for structure analysis	Suitable for structure analysis
Computation time	Short	Long

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See also

• 7. Diffraction simulator
• 7.1. SAED simulation
• 7.2. X ray diffraction