3D DuMond diagrams of multi-crystal Bragg-case synchrotron topography. II. Curved sample

The dimensional features of multi-crystal synchrotron X-ray topographs are explained by 3D DuMond diagrams for a flat double-crystal monochromator and a curved sample. Symmetric Bragg-case reflections are assumed for all crystals. s-s and s-p geometries are considered, where the diffraction plane of the sample is parallel and perpendicular, respectively, to the vertical diffraction plane of the monochromator (s polarization). It is shown that the shape of the sample image is closely connected to the shape of the volume shared by the diffraction domains of monochromator and sample in the 3D DuMond diagram. In particular, for the s-p set-up, the image shape depends on the curvature value and sign. An experiment is reported for this latter crystal geometry to determine lattice mismatch, its lateral homogeneity and curvature value and sign in a sample made of epilayer and substrate.