Matter/Electron Waves and the Davisson-Germer Experiment

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Homework Help Overview

This discussion revolves around the Davisson-Germer Experiment, specifically focusing on the conditions under which electron diffraction peaks occur in relation to the angle of incidence of the electron beam on the crystal surface.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand whether the electron diffraction peaks are dependent on the incident beam hitting the crystal surface perpendicularly. They express confusion regarding the textbook's mention of a 90° angle and its implications for the experiment.
  • Some participants reference Bragg's law and suggest that while perpendicular incidence may simplify the analysis, it might not be strictly necessary for diffraction to occur.
  • Another participant questions the definition of "glancing angle" and its relevance to the discussion.

Discussion Status

The conversation is exploring different interpretations of the angle of incidence in the context of electron diffraction. Participants are sharing insights and definitions, but there is no explicit consensus on the necessity of a perpendicular angle for the diffraction peaks to appear.

Contextual Notes

There is a mention of a potential misunderstanding regarding the textbook's treatment of angles and the implications of the experimental setup, as well as a reference to external definitions that may not be fully understood by all participants.

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Homework Statement



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?

Homework Equations





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°?
 
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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.
 
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.
 
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.
 

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