Applicability of real-space methods to diffraction strain measurements in single crystals

It is shown through rigorous dynamical diffraction modeling that the ray tracing methods employed in kinematical diffraction analysis of strain become invalid for weakly deformed crystals that scatter in the dynamical limit. For an Si crystal illuminated by 12 keV X-rays, the kinematical formalisms should not be used if the strain gradient along the diffraction vector is smaller than 10^-5 µm^-1.