For studies involving selected area electron diffraction, there is a "rotation" of the image
when switching from the selected area bright field mode to the diffraction mode. Often times
there is a great need to know precisely, the amount of this rotation, in order to make proper
interpretation of results.
The easiest way to do this is to photograph first the image of the crystal being characterized
and then record on a different (or as a double exposure on the same) plate or film, the
diffraction pattern. A good test sample must have crystals of well defined faces
(for the known orientation) and also, a sharp well defined diffraction pattern,
and at the same time, the crystal must be "robust" enough so that it is not quickly
degraded by the beam.
Some years ago it was discovered that molybdenum trioxide is the ideal kind of
specimen for this kind of application. For those wanting to either make their
own or else use the production of such a sample as part of a class room exercise,
we have made available the details for making this sample in your own laboratory.
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