Dynamical Interaction of Electron Waves in a Perfect Single Crystal

Electron diffraction from a perfect single crystal shows the influence of many-beam interaction. Investigations with a single crystal wedge allow a direct analysis of the Bloch-waves which are displayed into their partial waves. The strength of the dynamical interactions in a MgO crystal wedge was investigated by comparing the photographic record of a section through the dispersion surface with many-beam calculations. For a direction of the incident beam near the [110] zone axis the interaction of at least 50 beams has to be taken into account. Using a 50-beam calculation the structure potential V1U was determined to 1.80 volts ± 3 % . The influence of many-beam interactions on the absorption and the extinction fringe profiles in electron micrographs is discussed. Analysis of extinction fringes on the basis of a 50-beam approximation allowed the determination of the mean absorbing potential F 0 i m of MgO to 0.7 volts ± 1 0 % .