Also found in: Acronyms.
the aggregate of X-ray diffraction methods for studying various structural defects in near-perfect crystals. Such defects include mosaic blocks and boundaries of structural elements, stacking faults, dislocations, clusters of impurity atoms, and deformations. When X rays are diffracted by crystals in special X-ray cameras making use of various transmission and reflection methods, X-ray diffraction patterns are obtained. This pattern, which is the diffraction image of the crystal, is called a topogram in X-ray diffraction analysis.
The physical basis for the methods of X-ray topography is the diffraction contrast in the image of different regions of the crystal within a single diffraction spot. This contrast is formed as a result of the differences in the intensities or directions of the rays from different points of the crystal in accordance with the perfection or orientation of the crystal lattice at these points. The effect produced by the change in the path of the rays permits estimates to be made of the dimensions and misorientation of crystal substructure elements, such as fragments and mosaic blocks. The difference in the intensities of beams is used to find stacking faults, dislocations, segregations of impurities, and stresses.
X-ray topography differs from other X-ray techniques for investigating crystals in its high resolving power and sensitivity. In addition, X-ray topography permits the investigation of the three-dimensional distribution of defects in comparatively large near-perfect crystals having dimensions of up to tens of centimeters.
The linear resolution of many methods of X-ray topography ranges from 20 micrometers (μm) to 1 μm, and the angular resolution from 1’ to 0.01”. The sensitivity is determined by the contrast in the intensities of the diffracted rays from correctly and incorrectly oriented crystal regions and from perfect and distorted regions.
The methods of X-ray topography differ in the following respects: range of diffraction angles used; character of defects found, which can be macroscopic defects or lattice defects; de-
gree of imperfection and defectiveness of the crystals; sensitivity; and resolving power. Schematic diagrams of certain methods of X-ray topography are presented in Figures 1–5. The conversion of X-ray images into visible images and the presentation of the images on a television screen permit the defects of crystals to be monitored when the crystals undergo various kinds of treatment during industrial processing or during the investigation of their properties.
REFERENCESIveronova, V. I., and G. P. Revkevich. Teoriia rasseianiia rentgenovskikh luchei. Moscow, 1972.
Umanskii, Ia. S. Rentgenografiia metallov. Moscow, 1967.
Liuttsau, V. G., and Iu. M. Fishman. “Metod difraktsionnoi topografii na osnove skanirovaniia ν shirokom puchke rentgenovskikh luchei.” Kristallografiia, 1969, vol. 14, issue 5, p. 835.
Rovinskii, B. M., V. G. Liuttsau, and A. A. Khanonkin. “Rent-genograficheskie metody issledovaniia strukturnykh nesovershenstv i defektov reshetki ν kristallicheskikh materialakh.” Apparatura i metody rentgenovskogo analiza, 1971, issue 9, pp. 3–35.
Kozaki, S., H. Hashizume, and K. Kohra. “High-resolution Video Display of X-ray Topographs With the Divergent Laue Method.” Japanese Journal of Applied Physics, 1972, vol. 11, no. 10, p. 1514.