It was noted that the images could be explained by taking account of angular deviation effects upon beam propagation. They were visible because of the almost plane-wave character of the sources. In particular, it was shown how changes in the direct image width of a dislocation, as a function of the sample-film distance, could permit the determination of the sign and modulus of the Burgers vector. The experimental results of monochromatic beam topography were compared with simulated images that had been calculated by assuming plane-wave illumination. Satisfactory agreement was found. The usefulness of the weak-beam technique for enhancing spatial resolution was demonstrated, and a criterion was presented for the selection of experimental conditions. These depended upon the required spatial resolution, the signal-to-noise ratio and the exposure time.

F.Zontone, L.Mancini, R.Barrett, J.Baruchel, J.Härtwig, Y.Epelboin: Journal of Synchrotron Radiation, 1996, 3[4], 173-84