Electron diffraction experiment

In summary: The distances between the planes in the crystal are important, but they're not the only thing that matters. The spacing between the planes also matters.
  • #1
Coffee_
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2
I realize this is a very basic question, but I've been thinking about this for a bit and can't seem to find an answer:

When I did the electron diffraction experiment on graphite, I saw 2 rings on the fluorescent screen. The description of these rings should be given to me by Bragg Law, namely ##2dsin(\frac{\theta}{2})=n\lambda##. I'm inclined to take ##n=1## for the first ring and ##n=2## for the second ring to the analogy of classical optics experiments but then I realize I'm not sure what I'm doing.

I don't know how the planes are oriented in the graphite plate, it could be possible that this second ring is just diffraction happening of a different set of planes and such that ##n=1## for the second ring as well. The other things I'm doubting about is that if I'd received only one ring, how could I tell which ##n## this ring corresponds to.

As you can see from this post I'm pretty confused. I need to understand this for the experiment but I don't really have the time right now to start learning the deep theory behind this phenomenon. I looked around online and all the descriptions are either to shallow or either to complicated. So I'd be very grateful if someone can read this and try to elaborate a little about these ##n##. Again I know the basic derivation of Bragg Law, but I have trouble with fully connecting this law to the rings I see.
 
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  • #2
The area of the graphite that the beam passes through contains many many tiny crystals, with their planes oriented in random directions. Only those crystals whose planes are oriented at a certain angle to the beam can produce the diffraction that generates a particular ring. These crystals have different azimuthal orientations around the beam direction (if you know about spherical coordinates, think about the angles θ and φ), and this gives you the circular ring.
 
  • #3
jtbell said:
The area of the graphite that the beam passes through contains many many tiny crystals, with their planes oriented in random directions. Only those crystals whose planes are oriented at a certain angle to the beam can produce the diffraction that generates a particular ring. These crystals have different azimuthal orientations around the beam direction (if you know about spherical coordinates, think about the angles θ and φ), and this gives you the circular ring.
This would mean that n=1 for the second ring as well right?
 
  • #4
Yes. the two rings are produced by different sets of planes (in the same crystal structure) with different spacings. You're seeing the n=1 diffraction order in both cases.

A Google search on "electron diffraction crystal planes" turned up the following diagram. The red and blue lines show the relevant planes, with spacings d1 and d2.

dhKLG.png
 
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  • #5
jtbell said:
Yes. the two rings are produced by different sets of planes (in the same crystal structure) with different spacings. You're seeing the n=1 diffraction order in both cases.

A Google search on "electron diffraction crystal planes" turned up the following diagram. The red and blue lines show the relevant planes, with spacings d1 and d2.

dhKLG.png

Thanks a lot for your time, it's getting more clear now. Do you mind if another question comes up over the coming days I'll just post it in reply?
 
  • #6
jtbell said:
Yes. the two rings are produced by different sets of planes (in the same crystal structure) with different spacings. You're seeing the n=1 diffraction order in both cases.

Why do I only find d1 and d2 by doing this experiment? At first glance it seems to me that much mroe orientations are possible. One for example would be the distance between the planes. Just looking at the picture I can see two sets of plane that differ from d2 and d1 in distance.
 

1. What is an electron diffraction experiment?

An electron diffraction experiment is a scientific technique used to study the structure and properties of materials at the atomic level. It involves directing a beam of high-energy electrons at a material and observing the resulting diffraction pattern, which can provide information about the arrangement of atoms in the material.

2. How does an electron diffraction experiment work?

In an electron diffraction experiment, a beam of electrons is directed at a material, usually through a thin film or crystal. As the electrons pass through the material, they interact with the atoms and are diffracted, or scattered, in different directions. The resulting diffraction pattern is captured on a detector and can be analyzed to determine the arrangement of atoms in the material.

3. What types of materials can be studied with electron diffraction?

Electron diffraction experiments can be used to study a wide range of materials, including crystals, thin films, and nanoparticles. It is particularly useful for studying materials with a regular, repeating atomic structure, such as metals, semiconductors, and ceramics.

4. Why is electron diffraction important in scientific research?

Electron diffraction is an important tool in scientific research because it allows scientists to study the atomic structure and properties of materials in great detail. It can provide information about the arrangement of atoms, the size and shape of crystals, and the presence of defects or impurities in a material. This information can help researchers understand the behavior and properties of materials, and develop new materials for various applications.

5. What are some real-world applications of electron diffraction?

Electron diffraction has a wide range of applications in various fields, including materials science, chemistry, and physics. It is used to study the structure of metals and alloys, to analyze the composition of materials, and to determine the crystal structure of minerals. It is also used in the development of new materials for electronics, energy storage, and medical devices.

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