A high-resolution multiple-crystal multiple-reflection diffractometer

A high-resolution multiple-reflection diffractometer has been built to study crystals distorted by epitaxy and defects in nearly perfect crystals. The diffractometer combines the merits of the two-crystal four-reflection monochromator (to define a narrow wavelength range with a tailless reflectivity profile) and an analyser crystal to select the angular range diffracted from the sample crystal. The diffractometer is operated in two modes. In the first the sample and analyser rotations are coupled to obtain near-perfect rocking curves from distorted crystals, and in the second mode the two axes are uncoupled to obtain a diffraction space map for studying the diffuse scattering. The simulation of these profiles and maps based on dynamical theory is presented. The former allows complex structures to be analysed and the latter case, by deconvolving the dynamical scattering in these maps, permits a complete interpretation of the kinematic scattering.