3D DuMond diagrams of multi-crystal Bragg-case synchrotron topography. I. Flat sample

The 3D representation of the DuMond diagram is used to explain the dimensio nal features of X-ray topographs obtained by multi-crystal configuration wi th a synchrotron beam. Symmetric Bragg-case reflections are considered for a flat double-crystal monochromator and a flat sample. Two ways of sample a lignment are taken into account. They are referred to as sigma-sigma and si gma-pi geometries, where the diffraction plane of the sample is parallel an d perpendicular, respectively, to the vertical diffraction plane of the mon ochromator (a polarization). It is shown that the shape of the sample image is closely connected to the shape the diffraction domain common to monochr omator and sample assumes in the 3D DuMond diagram. An experiment is report ed for the less commonly used sigma-pi topography, showing how the lattice mismatch and its lateral homogeneity are determined in samples made by epil ayer and substrate.