Abstract
The several mathematical formulations of X-ray diffraction theory
facilitate its understanding and use as a materials characterization
technique, since one can opt for the simplest formulation that
adequately describes the case being studied. As synchrotrons advance,
new techniques are developed and there is a need for simple formulations
to describe them. One of these techniques is soft resonant X-ray
diffraction, in which the X-rays suffer large attenuation due to
absorption. In this work, an expression is derived for the X-ray
diffraction profiles of reflections where the linear absorption is far
greater than primary extinction; in other words, the crystal is
superabsorbing. The case is considered of a parallel plate crystal, for
which the diffraction profile of the superabsorbing crystal is computed
as a function of crystal size normal to the diffraction planes. For thin
crystals or those with negligible absorption, the diffraction profile of
a superabsorbing crystal coincides with the result of the kinematical
theory. For thick crystals, the absorption intrinsic profile is
obtained, described by a Lorentzian function and characterized by the
absorption intrinsic width. This absorption intrinsic width is
proportional to the linear absorption coefficient and its expression is
similar to that for the Darwin width, while the absorption intrinsic
profile is a special case of the Laue dynamical theory, and it is
similar to the Ornstein-Zernike Lorentzian. The formulation of X-ray
diffraction of superabsorbing crystals is simple and provides new
perspectives for the soft resonant X-ray diffraction technique.
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