Bloch-Wave Analysis in Electron Diffraction Experiments with a CaF₂ Single-Crystal Wedge

The fine-structure spots in an electron diffraction pattern from a crystal wedge represent the strong partial waves of strongly excited Bloch waves. Diffraction experiments near the [100] and the [110] zone axes of a CaF₂ crystal were carried out in order to determine from a fine-structure profile analysis the low-indexed structure potentials V₁₁₁, V₂₀₀ and V₂₂₀and the absorption coefficients of different Bloch waves. Under these experimental conditions there exist three strong Bloch waves; one is concentrated at the rows of Ca atoms, another along the rows of F atoms and a third is concentrated in the space between the atom rows. The absorption coefficients depend in a characteristic way on the density of atoms along the atom rows. This density is different for the two projections leading to different absorption coefficients. A strong background due to inelastic scattering was observed mainly in one strong reflection which was supposed to be due to phonon excitation.