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

The geometrical diffraction model is used to simulate superscrew dislocatio n images both on characteristic radiation and synchrotron radiation topogra phs. It is revealed that, due to the finite spectrum width, characteristic radiation diffraction occurring in the deformed lattice of a dislocation al so 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 di slocation images increase drastically with increasing sample-to-film distan ces, making the characteristic radiation images recorded at short sample-to -film distances much smaller than the synchrotron radiation images recorded at large distances.