OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 “pink” beam, monochromators equipped with X-ray mirrors are used, which are multilayer structures in the form of alternating pairs of layers made of different materials characterized by different refractive indices (Fig. 9). An important characteristic of a monochromator is related to its reflectivity (Fig. 7). This parameter is described by the Darwin curve or, as it is also called, the rocking curve, which is a function of the angular displacement from the Bragg angles for the main X-ray emission [6, 8]. “White” beam of synchrotron radiation falls on an optical element at some angle θd. According to condition (1), monochromatic radiation of the desired wavelength is “extracted” from it. The rocking curves illustrate the dependence of the reflectivity R at angle θ with some angle offset δθ, whose magnitudes are comparable to angular seconds [8]. The reflectivity curve shows the percentage of reflected radiation in a certain range of angles, i.e., indicates the “quality” of the interference peak. In work [9] the results of the experiment, which demonstrates that the reflectivity curves have different widths at different crystal orientation and radiation energy are presented (Fig. 8). Fig. 8. Reflectivity curve for Si(660), Si(440) and Si(220) at energies of 24, 16 and 8 keV. From [9] The reflectivity of a crystal depends not only on the grazing angle but also on the orientation of the plane (Miller indices). The integral along the rocking curve gives a quantitative estimate of the intensity of monochromatic radiation, and from the values of the angle displacement one can estimate the degree of monochromaticity. Monochromators based on multilayer structures One of the widely used practical solutions related to X-ray monochromatization is based on using multilayer structures [10, 11] that are obtained by successive deposition of thin alternating layers of two heterogeneous materials. With this approach, a heterophase structure of the A-B-A-B... (Fig. 9) is formed. Each pair of the multilayer structure is represented by materials that differ from each other by the X-ray Fig. 7. Reflectivity curve of the monochromator optical element
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