I am learning about electron diffraction in a transmission electron microscope and was wondering about following topic:

A single crystalline material will exhibit a diffraction pattern with discrete spots or disks while an amorphous material will show speckle contained within rings. Both are the result of Bragg diffraction with coherent illumination.

But, how would these diffraction patterns look like if the illumination were fully incoherent? Surely they can't look the same but what exactly would change?

Thanks for ideas and answers!

  • 1
    $\begingroup$ In a TEM there is, on average, one electron in the column at a time. Further, what do you mean by 'coherence' to describe the electrons? $\endgroup$
    – Jon Custer
    Mar 31 at 15:45
  • $\begingroup$ Here is my understanding of electron coherence in a TEM: The electron beam consists of a flux of electrons, each with a similar energy and being emitted from nearly the same point of origin. The individual electrons are mutually incoherent with each other because each of them has a unique phase. But the electrons, or better the indivudial electron waves, are coherent with themselves and show self-interference in e.g. biprism experiments. Now, a diffraction pattern is the sum of many self-interference occasions between beam electron and sample. The random phases average out. [1/2] $\endgroup$ Mar 31 at 15:58
  • $\begingroup$ And now I wonder how the diffraction patterns in both cases would change if even this self-interefernce and coherence of the individual electrons would not apply?Perhaps it isn't even possible to realize this. [2/2] $\endgroup$ Mar 31 at 16:03
  • $\begingroup$ Yes, an individual electron is coherent with itself. That is all that is needed to get a diffraction pattern. $\endgroup$
    – Jon Custer
    Mar 31 at 16:04


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