Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

When doing electron diffraction on graphite (a popular experiment for students at universities) always diffraction at these two planes with distances $d_1$ and $d_2$ are observed:

enter image description here

But a plane parallel to the ones with distance $d_2$ can also be formed with a distance of the atom spacing $s$. When looking through crystal diffraction databases there's also no data about diffraction on these "$s$" planes.

Why is it not possible that electrons or X-Rays scatter at the planes with distance $s$ or some multiple of it?

share|cite|improve this question
up vote 3 down vote accepted

You can make two parallel planes a distance $s$ apart in the way you describe, but you need an infinite stack of them $s$ apart to get diffraction.

The reason there are no such stacks even though the distance between sites is $s$, is because the honeycomb is actually a triangular tiling, where the corners of the triangle are every other atom. So the vector which connects the two adjacent is not actually a symmetry of the crystal (i.e. it is not a Bravais lattice vector).

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.