Electron diffraction from modulated structures. I. Theory

The theory of high-energy electron diffraction from modulated structures is discussed. A perturbation theory is used in which the change of potential caused by the modulation is treated as being weak in comparison with that of the average structure. An expression for the single scattering diffraction amplitude is derived and analysed in terms of its symmetry. The large thickness limit of this expression is also considered. It is shown that it takes a simple form, enabling information about the nature of a modulated structure to be obtained from diffraction experiments. Double diffraction is also briefly discussed to show that such effects are experimentally distinguishable from single diffraction.