What are the patterns and formations seen in selected area diffraction?

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SUMMARY

The discussion focuses on the patterns obtained from selected area diffraction (SAD) in transmission electron microscopy (TEM). Participants clarify that the dots and rings observed in SAD are analogous to the peaks in X-ray powder diffraction, where constructive interference occurs at specific angles. The formation of these patterns is explained through the interaction of electrons with the crystal lattice, similar to the Debye-Scherrer method used in X-ray diffraction. Understanding these concepts is crucial for interpreting diffraction patterns and calculating lattice spacings and Miller indices.

PREREQUISITES
  • Understanding of transmission electron microscopy (TEM)
  • Knowledge of X-ray powder diffraction techniques
  • Familiarity with lattice structures and Miller indices
  • Basic principles of constructive interference in wave physics
NEXT STEPS
  • Study the principles of selected area diffraction (SAD) in detail
  • Learn about the Debye-Scherrer method and its applications in X-ray diffraction
  • Explore the calculation of lattice spacing and Miller indices from diffraction patterns
  • Investigate the role of electron diffraction in material characterization
USEFUL FOR

This discussion is beneficial for materials scientists, electron microscopists, and researchers involved in crystallography and diffraction analysis.

Milchy
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Can anyone explain me the pattern that is obtained from selected area diffraction? What does it show? What are the dots? What are the rings? (example: http://www.microscopy.cz/html/images/2605_1_d0f65ce7_fig2.png)
I know that during X-ray powder diffraction, radiation is shined at the powder at varying incident angles. At certain theta angles the radiation diffracts from different lattices in the powder to form constructive interference, which shows up as peaks in the diffractogram. From the peaks you can calculate the latice spacing and miller indices.However, I am unable to understand/visually picture how the dots/rings are obtained from this TEM/diffraction method. Could someone explain me with some basic visual concepts using a unit cell and interacting/diffracting electrons and this shape formations?
 
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