Effects of thermal diffuse scattering and surface tilt on diffraction and channeling of fast electrons in CdTe

A Bloch-wave model for propagating a fast-electron wave through a noncentrosymmetric crystal for non-normal incidence is discussed, as well as approximations for linearizing the equations. Calculations which simulate {111} systematic row diffraction conditions in CdTe are used to illustrate how the tilt of the surface with respect to the diffracting planes affects the fast-electron wave function in the crystal. The influence of thermal diffuse scattering (TDS) removes possible ambiguity from the interpretation of ``alchemi-type'' experiments [J. C. H. Spence and J. Taft{}, J. Microsc. 130, 147 (1983)] in determining the polarity of noncentrosymmetric crystals. The inclusion of mean and anomalous absorption, using a quantitative Einstein model for TDS, allows direct correlation between theory and experiment for convergent-beam electron diffraction, again allowing direct measurement of crystal polarity.