Three-dimensional diffraction phenomenon at a 90° Bragg reflection

The experimental observation of a three‐dimensional diffraction phenomenon at a 90° Bragg reflection is reported and discussed. A refined experimental technique for the direct observation and accurate measurement of scattered intensity profiles in the vicinity of a 90° Bragg reflection was proposed and implemented. The detector arrangement allowed the scintillator detection of back‐reflected beams via fluorescence scattering from an in‐beam copper plate. A small hole in the plate allowed free passage of the incident beam. This detector system has allowed a very high ratio, up to five orders of magnitude, of fluorescence back‐reflection peak to the incident beam air scattering background. Three‐dimensional tracking of the reciprocal lattice point of the Si(800) Bragg reflection around the 90° Bragg position was studied over a range of tilt angles in a plane perpendicular to the diffraction plane.