X-ray and electron microscope diffraction patterns

jbar18

Hey,

I'm having trouble finding a clear answer anywhere. When you have a x-ray diffraction pattern, do the dark spots correspond to the positions of atoms? Or do they represent the position of atoms in reciprocal space or something like that? It would seem natural to assume that the peaks are the atoms themselves but I keep seeing reciprocal space and Fourier transforms coming up wherever I look and so I don't want to assume anything.

One other thing, is this the same for the bright spots in an electron diffraction pattern?

Thanks

DrDu

Whether the spots are dark or bright depends on the detection technique. I suppose you are referring to spots on photographic film in the case of X-rays and spots on a fluorescent screen in the case of electron diffraction?
In both cases the spots don't belong to the real atoms but to positions in reciprocal space.
That means there is a spot whenever planes formed by the atoms have such an orientation with respect to the incident radiation that the Bragg condition for reflection is fulfilled.

Rajini

Hi,

For electron microscope diffraction patterns (DP), the each bright spot corresponds to the reflection formed by the plan formed by atoms. And the distance between spots are in inverse, i.e. as DrDU said they are recriprocal distance. [some reflections are forbidden in electron microscope DPs!].