Concerning Single Crystal Reflectivity Curves

Abstract

The extinguished reflectivity curve of a Bragg single crystal reflection represents the basic experimental evidence for the determination of accurate structure factors. In normal measurement procedures of one-dimensional (ID) 'counter' profiles, information on such curves is obscured by the presence of other, more dominant components. It is therefore difficult to separate out these curves so that a realistic correction for extinction can be applied. By considering the 'shape' of a Bragg reflection in the plane of diffraction from the ~w, ~2e viewpoint, procedures have been deduced for practical zero wavelength dispersion measurement of reflectivity curves for virtually any e value and, with these curves, corrections can be applied to produce extinction-free structure factor values. Attention is drawn to the fact that the width of the experimental reflectivity curve (say at half maximum) can provide a valuable criterion to assist in attaining the 'kinematical limit'.