Kossel pattern

The X-rays generated when an electron beam strikes a crystal also can be diffracted by the specimen in which they are produced. If a photograph is made of this diffracdon pattern (the Kossel pattern) using a special camera, localized crystallographic information can be gleaned. 

K-M and Kossel patterns are extremely sensitive to crystal orientation, and are therefore particularly useful for tilting a crystal into a precise orientation. However, their most important use is in obtaining three-dimensional crystal symmetry information, including the complete determination of the point group and space group of a crystal. Extensive reviews of... 

G.44 Shuji Taira, ed. X-Ray Studies on Mechanical Behavior of Materials (Kyoto Society of Materials Science, Japan, 1974). A collaborative account by twenty-seven Japanese investigators of x-ray studies of phenomena affecting the strength of materials. X-ray stress measurements are described, as well as texture determination, line-broadening studies, microbeam methods, pseudo-Kossel patterns, small angle scattering, and x-ray topography. 

In a single crystal, the excited X rays are Bragg diffracted at the lattice plane, and their isotropic angular characteristics show defect and excess Kossel lines of apex angle 90°-0b. which can be used for accurate measurement of lattice parameters and strains when the Kossel pattern is recorded on a photographic emulsion. 

In 1939 Kossel and Mollenstedt demonstrated the possibility of obtaining CBED patterns from crystals with more information than obtained from the more conventional focused patterns for special beam directions. Later, in 1940, it was demonstrated that the intensity of a reflection is a function of the excitation error, and the thickness, t, of a plane parallel crystal slab [3]. Lately, more advances in CBED became possible with the introduction of field emission guns and scanning TEM (STEM) techniques. Thus, the STEM instrument has electron optics similar to CBED for obtaining diffraction results from areas as small... 

Figure 7.10. Interference patterns for Kossel lines intersecting at right angles. Left experiment. Right theory (from Miller et al. [69]).

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