X-ray diffraction phenomena in elastically distorted crystals

Abstract

Diffraction phenomena in diametrically compressed single-crystal plates of silicon were systematically studied by topographic methods of the traverse and section types with Cu, Mo and Ag radiations. Black and white contrasts in the traverse topographs depend on the magnitude of the strain gradient, absorption, the sign and the order of the reflection vector, and the crystallographic orientations of the specimens. The results were interpreted in terms of the diffraction theory for a constant strain gradient. The distribution of the strain gradient was calculated under the assumptions of plane stress and isotropic elastic constants. Qualitative agreement was obtained between the theory and experiments. The behaviour of the contrast, including the departure from Friedel's law, is due to Borrmann absorption in distorted crystals. The quantitative discrepancy is explained by anisotropy of the elastic constants. The departure from a constant strain gradient is detectable by the asymmetry of the intensity distribution in section topographs.