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

In summary, selected area diffraction uses X-rays to analyze the crystal structure of a powder sample. By varying the angle of incident radiation, constructive interference occurs at specific angles, resulting in peaks on a diffractogram. These peaks can be used to calculate lattice spacing and miller indices. The resulting pattern, similar to that seen in Debye-Scherrer method, consists of dots and rings, representing the diffracted X-rays from different lattices in the sample.
  • #1
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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  • #2

1. What is selected area diffraction?

Selected area diffraction is a technique used in electron microscopy to analyze the crystal structure of a material. It involves focusing a beam of electrons onto a small area of a sample and measuring the diffraction pattern produced by the electrons interacting with the sample's crystals.

2. How is selected area diffraction different from other diffraction techniques?

Selected area diffraction is different from other diffraction techniques, such as single crystal or powder diffraction, because it allows for the analysis of a specific area of a sample rather than the entire sample. This allows for more precise characterization of small or irregularly shaped samples.

3. What type of information can be obtained from selected area diffraction?

Selected area diffraction can provide information about the crystal structure, crystal orientation, and crystal defects of a material. It can also be used to determine the lattice spacing and identify the type of crystal lattice present in the sample.

4. What are the advantages of using selected area diffraction?

Selected area diffraction has several advantages, including its ability to analyze small or irregularly shaped samples, its high resolution, and its fast data acquisition. It also allows for the analysis of thin films or materials that are difficult to prepare for other diffraction techniques.

5. What are the limitations of selected area diffraction?

Selected area diffraction is limited by the size of the sample that can be analyzed and the quality of the electron beam used. It also requires specialized equipment and training to perform, making it less accessible than other diffraction techniques.

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