Is diffraction through an aperture similar to diffraction by a plane of atoms?

Question

I'm asking because I have a problem asking me what the diffraction pattern would be if instead of spherical atoms I'd have triangular atoms. I can't find anything about this in my X-ray diffraction book, but I can in my optics book, but I'm having trouble justifying this.

I thought that in a plane of atoms the separation between atoms acted as the aperture.

I found these patterns: http://www.bakoma-tex.com/doc/generic/pst-diffraction/pst-diffraction-doce.pdf

I don't know if they could be extended to diffraction through a crystal whose atoms are triangular.

Answer 1

It is the atoms (more precisely, the electrons of the atoms) that contribute to X-ray diffraction. The aperture comparison could work, but you should see the atoms themselves as the apertures.

You can invoke the separation between structure factor (given by the lattice) and form factor (given by the shape of the repeating unit, in your case the atoms). The scattering pattern is then simply the reciprocal lattice multiplied by the modulus squared of the Fourier transform of the atom.

For a triangular object, the form factor will indeed resemble the patterns shown in the document you cite. Multiply by the Bragg peaks of the lattice and you're done.