Interbranch transient beating of X-ray intensities in deformed crystals.
X-ray dynamical diffraction in a deformed crystal is studied using the interbranch resonance concept. It is shown that appreciable beating of the X-ray intensities may be induced by a lattice distortion that produces interbranch transformations of the local dispersion surface. In X-ray plane-wave topography, this effect may be observed as interference fringes arising around the kinematical image of a defect. It is predicted that such interbranch fringes can be induced by edge dislocations.
On the widths of dislocation images in X-ray topography under low-absorption conditions
Detailed measurements have been made of dislocation image widths in X-ray topographs taken under conditions of low absorption (product of linear absorption coefficient and crystal thickness, μt = 0.15) with a silicon specimen and Mo Kα radiation. These have been compared with two theoretical models, the `diffracting-zone' model involving computation of misorientation gradient contours, and the direct-image `mosaic' model using calculations of effective misorientation contours. Neither model completely explains the image widths. The diffracting-zone model, though theoretically more attractive, gives a very poor correlation, probably because of (a) severe photographic limitations and (b) the uncertainty in the reconstruction of the intermediary image in translation topographs. For a given reflection the direct-image mosaic model gives a reasonably good prediction of image widths measured at half peak height. However, the widths in different reflections are not self-consistent; in particular, images in lower-order reflections are significantly wider than those predicted by the model. This implies that contributions from interbranch scattering (giving an intermediary image component) are more important in lower-order reflections, and that such contributions are proportional to the widths obtained from misorientation (rather than misorientation gradient) contours.
Extinction effect and Borrmann effect of resonant dynamical scattering in the Bragg case.
In the Bragg case, X-ray beams suffer from anomalous absorption due to extinction effects without photo-absorption and are localized in the surface when X-ray total reflection occurs around an exact Bragg angle from a perfect crystal. On the other hand, the Borrmann effect due to anomalous transmission occurs in a thin perfect crystal with photo-absorption under a proper condition. There is a clear distinction between the extinction effect and the Borrmann effect. It is found that it is possible to separate the Borrmann effect from the extinction effect when the real part of the atomic scattering factor is zero. The calculated rocking curves agree well with the measured ones around the Ge K-absorption edge of the Ge 844 reflection.