Convergent beam electron microdiffraction from small crystals

Diffraction spots in convergent beam electron diffraction patterns obtained with a coherent incident beam show a characteristic fine structure when the incident beam is close to a small crystal or the edge of a larger crystal. The fine structure may take the form of a splitting of the spot into two or more sharp spots or else a bright annulus with a dark spot in the middle. It is shown that this fine structure results from coherent interference effects for an asymmetrically placed crystal and reflects the sensitivity of the relative phases of the diffraction pattern amplitudes to the absolute position of the diffracting object.