SAED Simulation¶
SAED (Selected Area Electron Diffraction) simulation calculates electron diffraction patterns with a parallel beam. This is the default mode of the diffraction simulator.
Overview¶
Simulates the diffraction pattern when a parallel electron beam passes through a thin specimen. Spot positions and intensities are calculated from the geometrical relationship between the Ewald sphere and reciprocal lattice points.
Intensity calculation modes¶
Only excitation error¶
Fastest mode. Intensity is estimated solely from the distance (excitation error s) between each reciprocal lattice point and the Ewald sphere. Structure factors are not considered.
Kinematical & excitation error¶
Includes the crystal structure factor |F(g)|.
- Intensity ∝ |F(g)|²
- Extinction rules are correctly reflected
- Suitable for thin specimens or weak diffraction
Dynamical theory¶
Rigorous Bloch-wave (Bethe) method. Electron diffraction only.
- Accurate multi-beam scattering
- Thickness-dependent intensity
- No. of Bloch waves: 50–200 for routine work; 500+ for high accuracy
- Thickness: specimen thickness in nm
Spot appearance¶
Solid sphere¶
Reciprocal lattice points are spheres of radius R. The cross-section with the Ewald sphere is drawn as a circle. Points far from the Ewald sphere are hidden.
Gaussian¶
Points are 3D Gaussians (σ = R). The cross-section appears as a 2D Gaussian. All points are visible with intensity-dependent brightness.
Parameters¶
| Parameter | Description |
|---|---|
| Opacity | Spot transparency (0–1) |
| Radius | Virtual radius R of reciprocal lattice points |
| Brightness | Brightness correction for Gaussian mode |
| Colour scale | Greyscale or Cold-Warm |
| Log scale | Logarithmic intensity display |
| Spot colour | Spot drawing colour |
Spot labels¶
Select from the toolbar:
| Label | Content |
|---|---|
| Index | Miller indices (hkl) |
| d | d-spacing (Å) |
| Distance | Spot-to-spot distance on detector |
| Excit. Err | Excitation error s |
| |Fg| | Absolute structure factor |