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Matter/Electron Waves and the Davisson-Germer Experiment

  1. Feb 5, 2014 #1
    1. The problem statement, all variables and given/known data

    This is a conceptual question that I am not quite sure about. In the Davisson-Germer Experiment (details here), do the electron diffraction peaks that occur only show up if the incident beam of electrons hits the crystal surface perpendicularly?

    2. Relevant equations

    3. The attempt at a solution

    I was really confused when reading this in my textbook when it relates to this question. The book talks a lot about Davisson and Germer's initial intent which was to "attempt to understand the arrangement of atoms on the surface of a nickel sample by elastically scattering a beam of low-speed electrons from a polycrystalline nickel target. (If you are unfamiliar with the story, someone dropped a flask of liquid air on the vacuum system, oxidizing the nickel target. They then realized that the crystalline structures it created scattering of electrons, showing that the electron is also a matter-wave).

    However, in my textbook, they talk about \alpha being the target orientation, and that is 90°. After that brief mention, they do not really speak of it again. Because of this, I am a little unsure as what to believe. Would these peaks arise if the angle was different than 90°?
  2. jcsd
  3. Feb 5, 2014 #2


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    Wikipedia has this 90° in its story too. But they refer to Bragg's law for the angles. There the pictures have angle of incidence = exit angle. I think perpendicular incidence isn't essential, but it gives a nice expression for angles of constructive interference.
  4. Feb 5, 2014 #3
    That is what I thought as well. I thought that the 90 degree angle makes it "easier" - like the simplest case of what actually happens. However, I did not know if there was an actual reason why it does or does not matter.

    Thank you.
  5. Feb 6, 2015 #4
    What is glancing angle?
    I found this definition but I am not getting this.
    the angle between a ray incident on a plane surface and the surface,as of a beam of electrons incident on a crystal;the complement of the angle of incidence.
  6. Feb 6, 2015 #5


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