Electron Diffraction: Polycrystalline vs Monocrystal

In summary, in this conversation, it is discussed that in an experiment, a graphite with a polycrystalline structure produces two intense rings, while a monocrystal would produce a pattern of bright spots. This is because a polycrystalline material is made up of multiple monocrystals at different angles, while a monocrystal would only have one crystal orientation. The rings are formed by the maxima from each crystal being at the same angle to the incident beam. This is similar to the formation of a rainbow. If the material was a monocrystal, it would only have one ring, formed by one family of planes. Different orientations of planes would produce additional rings. This can be seen in Laue
  • #1
M. next
382
0
In this experiment, the graphite is a polycrystalline structure. That's is why we observe two intense rings. What will happen if it was a monocrystal? And why?

Thank you.
 
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  • #2
a monocrystal would give a pattern of bright spots. Imagine those spots drawn on a piece of paper then rotated quickly...you would see rings... a polycrystalline material is lots of monocrystals at different angles.
 
  • #3
So if they were at different angles, I would see many rings? And if it were a monocrystal I would only see one ring? If so, why? I don't get the relation between arrangement of families of planes with rings.
 
  • #4
The rings are there because the maxima from each crystal are at the same angle to the incident beam, whichever way the crystals are orientated. This is the same argument that applies to the formation of a rainbow - same angle gives the appearance of a circle.
This argument is a bit over-simplified because the crystalites can be in any orientation but, as the fringes on a flat screen are equally spaced near the axis, the different orders will still coincide to give rings - but only over a limited range of angles. Off axis, the fringes will not reinforce and the pattern will degrade.
 
  • #5
M. next said:
What will happen if it was a monocrystal?

Google "Laue diffraction".
 
  • #6
So one ring is formed by one family of planes? And another from a different oriented set of planes and so on? Is this the case?
 

1. What is the difference between polycrystalline and monocrystal in electron diffraction?

The main difference between polycrystalline and monocrystal structures is the arrangement of atoms. In polycrystalline materials, the atoms are arranged in random orientations, whereas in monocrystals, the atoms are arranged in a repeating pattern. This difference affects the way electrons interact with the material during diffraction.

2. How does electron diffraction work?

Electron diffraction is a technique used to study the structure of a material by shooting a beam of electrons at it. When the electrons hit the material, they scatter in different directions depending on the arrangement of atoms in the material. This scattering pattern is then analyzed to determine the structure of the material.

3. Why is polycrystalline electron diffraction more complex than monocrystal?

Polycrystalline electron diffraction is more complex because the random orientation of atoms in the material creates a more varied scattering pattern compared to the regular pattern seen in monocrystals. This makes it more challenging to interpret and analyze the diffraction pattern for polycrystalline materials.

4. What are the advantages of using polycrystalline samples in electron diffraction?

One advantage of using polycrystalline samples in electron diffraction is that they are more readily available and easier to produce compared to monocrystals. This makes them a more practical option for large-scale studies. Additionally, polycrystalline samples can provide information about the average structure and properties of a material, rather than just a single crystal structure.

5. Can electron diffraction be used to determine the atomic structure of a material?

Yes, electron diffraction can be used to determine the atomic structure of a material. By analyzing the diffraction pattern, scientists can determine the positions of atoms within the material and the distances between them. This information can then be used to create a detailed model of the atomic structure of the material.

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