Random arrangment of graphite

[pythagoras88]

hi, I am a currently a year one physics major and during a lab session today and have a question regarding electron diffraction using graphite.

Since the electron beam and the circular ring on the screen exhibit cylindrical symmetry(such that if you rotate the beam and the ring, you still get the same pattern), does it mean that the graphite has cylindrical symmetry as well? From my knowledge, the graphite are composed of different layers, thus should not really exhibit cylindrical symmetry. The explanation given by the lab assistant was that the random arrangement of the graphite actually help to compensate off or mask the lack of symmetry in the graphite. I don't quite agree with his explanation. I wonder if someone could help me with this.

Thank you in advance!

 

[eljose79]

Hello, thank you for your question. As a fellow physicist, I can understand your confusion about the cylindrical symmetry observed in electron diffraction patterns from graphite. The explanation given by your lab assistant is partially correct. While it is true that the random arrangement of graphite layers can help to compensate for the lack of overall cylindrical symmetry, there are other factors at play as well.

Firstly, it is important to note that the cylindrical symmetry observed in the electron diffraction pattern is not a direct reflection of the symmetry in the graphite structure itself. Rather, it is a result of the diffraction process. When an electron beam is directed at a sample, it diffracts off the atoms in the sample, creating interference patterns that are then captured on the screen. The symmetry observed in the diffraction pattern is a result of the symmetry of the diffraction process, not necessarily the sample itself.

However, the structure of graphite does play a role in the diffraction pattern. As you mentioned, graphite is composed of layers of carbon atoms arranged in a hexagonal lattice. This hexagonal symmetry can contribute to the cylindrical symmetry observed in the diffraction pattern. Additionally, the random arrangement of these layers can also contribute to the overall symmetry, as it helps to average out any irregularities or imperfections in the sample.

In conclusion, while the graphite structure itself may not exhibit perfect cylindrical symmetry, the diffraction process and the random arrangement of layers can contribute to the cylindrical symmetry observed in the electron diffraction pattern. I hope this helps to clarify your question. Keep up the good work in your physics studies!