I have captured the electron diffraction pattern of a crystalline material and realized that ED shows a pattern characteristic to single crystal structures. However, I noticed that some spots are brighter than the others. I was wondering if there is any scientific explanations for this observation? FYI, the crystalline structure is hexagonal close packed (hcp) with R3c (161) space group. Any help would be greatly appreciated!
Just for reference
Bendersky LA, Gayle FW. Electron Diffraction Using Transmission Electron Microscopy. J Res Natl Inst Stand Technol. 2001 Dec 1;106(6):997-1012. doi: 10.6028/jres.106.051. PMID: 27500060; PMCID: PMC4865294.
Alireza Shirazi Amin
Good Morning Sir,
Each spot is associated with a particular diffracting plane. The intensity of the spots depends on the orientation of the sample with respect to the electron beam. The intensity of the spots is brighter at the Zone axis of the sample considered.
This link could be useful, https://www.coursera.org/lecture/microscopy/3-1-2-beam-electron-diffraction-wn2nV
B. Srikanth Ragunath
Thanks for your contribution. I believe I acquired this image when the electron beam was parallel to the Zone axis. That being said, the Zone axis is located at the center of the image where the electron beam is blocked by the beam stopper. The other sign that confirms that the electron beam is aligned with the Zone axis is that the pattern is symmetric. Still, I don't really understand why some spots are brighter assuming ED is collected at the Zone axis of the crystal.
Harshul Khanna
Thank you so much for sharing the reference with me.
the intensity of each spot depends on the contents of the unit cell.
Look up "Fourier transforms" or "Fourier analysis"" -
It is by measuring the intensity and position of each spot that the contents (electron density and position within the unit cell) of the unit cell can be calculated. This is the classical method of determining the structures of proteins, nucleic acids, and other less complex materials.
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