AN INVESTIGATION OF CRYSTAL IMPERFECTIONS BY X-RAY DIFFRACTION.

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Abstract
High resolution X-ray topographic methods have been used to study lattice imperfections in many natural and man-made crystals. Individual lattice imperfections can be resolved in specimen thicknesses from a few microns to several millimeters. The topographic resolution obtainable is one micron. The effects on the resolution of X-ray geometry, mechanisms of diffraction contrast, photographic processes and statistical fluctuations are discussed. Lattice imperfections studied include dislocations, inclusions, precipitates, impurity layers, and fault surfaces such as stacking faults and twin boundaries. Both the direction and sense of dislocation Burgers vectors can be determined. Studies performed on natural diamond include the origin of dislocations and the correlation of dislocation outcrops with trigon pits; the correlation of lattice imperfections, ultra-violet absorption and 'spike' reflections in Type I and Type II diamonds; planar defects of stacking-fault type; abrasion of natural and polished faces; and the structure of coated diamonds. Synthetic diamonds have been studied by diffraction topography and microradiography. Configurations of grown-in dislocations and of dislocations deliberately introduced by plastic deformation have been studied in silicon, germanium and indium antimonide. The configuration and origin of dislocations have also been investigated in LiF, MgO, aluminium, A1203, quartz and some organic crystals.

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