Bohdanov Y. Effects of azimuthal asymmetry of radiation scattering in crystals and new possibilities of diffuse-dynamical diffractometry

In the work, one of the main problems of solid-state physics notably the development of express informative non-destructive methods of structure diagnostics for establishing an interrelation between the structure and properties of the materials for the new technique is solved. For the first time, the effects of asymmetry of azimuthal dependence (AD) of the total integrated intensity of dynamical diffraction (TIIDD) in single crystals with disturbed surface layer (DSL) and inhomogeneously distributed microdefects of different types are demonstrated. Previously, AD TIIDD for imperfect single crystals normalized by AD IIDD for perfect crystals, observed only symmetric with respect to j = 90°. The first effect identified in the dissertation is characterized by the appearance of the maximum AD TIIDD at j ≈ 100°, and the second effect is characterized by the appearance of the maximum AD TIIDD at j ≈ 80°. In the work, the physical nature of these effects of asymmetry of AD TIIDD is discovered and the simplified heuristic models of their formation are created. It is shown, that the first effect of asymmetry is due to the azimuthal angle-dependent amplification of the contribution of the integrated intensity of diffuse X-ray scattering. This amplification is a result of the combined competitive action of dynamical effects of total reflection and extinction due to diffuse scattering and interference absorption, which have different dependences on azimuth angle. This effect is manifested experimentally only with increasing defect sizes. The defect sizes regulate the manifestation and result of the interaction of contributions with different signs of these dynamical effects depending on the azimuthal angle and other diffraction conditions. However, the azimuthal dependence of the effect of total reflection of the diffuse component of TIIDD is the main. It is shown, that the second effect of asymmetry is due to the interference of diffracted rays from kinematical and dynamical scattering layers. This effect has a special azimuthal dependence notably its contribution increases in contrast to the decrease of diffuse scattering contribution on large dislocation loops with decreasing azimuthal angle lower than 90°. As a result, the possibility of selective increase of the structural sensitivity of AD TIIDD of X-rays to the DSL parameters of the crystal with defects is established and realized. In addition, the accuracy of the supplementary determination of the characteristics of the large defects in the dynamical scattering layer is provided. This supplementary determination is carried out already taking into account the calculated parameters of DSL and at the azimuthal angles above 90°, when the contribution of large defects is main. This possibility significantly increases the sensitivity and informativeness of the method of AD TIIDD and non-destructive multi-parameter diagnostics in whole. Particularly, the method of AD TIIDD gives a new convenient parameter φ for control of selectively the manifestation of defects of different types (its changes every ten degrees twice change the width of the total reflection region and up to 40% of IIDD of perfect crystals change the contributions to AD TIIDD from each type of defects separately). For the first time based on the effects of asymmetry of AD TIIDD, the created physical model of formation of these effects and the developed theoretical model of AD TIIDD a generalized diagnostic approach was developed and implemented. This approach is suitable for multiparametrical diagnostics of inhomogeneous distribution of defects by depth in single crystals for the case of smooth profiles of the distribution of defects (each of many types). Thereby the principles and experimental methods for determining the inhomogeneous distribution of microdefects in kinematical scattering crystals were created. The experimental revealed effects of asymmetry of AD TIIDD and established features of their physical nature became the basis for the creation of the physical bases and models of the new diffractometric approach and, in particular, methods with the increased functionality of sensitivity as well as informativeness of multiparametrical phase-variation diagnostics. The main feature is opposite sign of influence of the width of the region of total reflection on Bragg and diffuse components of TIIDD (and accordingly on values of dependent on these components contributions from DSL or large dislocation loops). The influence of the width of the region of total reflection is easily controlled by changes in the azimuthal angle φ. The increasing of mentioned width leads to rising Bragg component (and the contribution from its interference with rays from DSL) and decreases diffuse component.