Dependence of the direct dislocation image on sample-to-film distance in X-ray topography

The geometrical diffraction model is used to simulate superscrew dislocation images both on characteristic radiation and synchrotron radiation topographs. It is revealed that, due to the finite spectrum width, characteristic radiation diffraction occurring in the deformed lattice of a dislocation also belongs to polychromatic diffraction. The contrast formation mechanisms of characteristic radiation topography are thus almost identical to that of synchrotron white-beam topography. As a general rule, the dimensions of dislocation images increase drastically with increasing sample-to-film distances, making the characteristic radiation images recorded at short sample-to-film distances much smaller than the synchrotron radiation images recorded at large distances.