Measurement of stress/strain in single-crystal samples using diffraction

Diffraction profiles from an Si-single-crystal strip deformed in cantilever bending are presented as a function of tip displacement and incident-beam energy. Data obtained with slit-based diffracted-beam optics contain a secondary peak in addition to the primary 004 reflection for all energies when the bending strain is finite. This secondary peak can be identified as a `mirage' peak, predicted by dynamical diffraction theory to occur in weakly deformed single-crystal samples. The integrated intensity of this mirage peak increases with increasing energy and tip displacement and exceeds the primary peak intensity at higher values. The mirage peak disappears when a monochromator is used in the diffracted-beam path. Data that show the effect of these mirage peaks on X-ray diffraction strain analysis are presented, and it is shown that a diffracted-beam monochromator may be used to eliminate these errors.