OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 refractive index as well as by the atomic mass Z. The thickness of A (tA) material layers, characterized by low transmissivity (high Z values), is usually smaller if compared to the thickness of B (tB) material that has higher transmissivity [3]. The period of a multilayer structure is the value Λ = tA + tB. An example of a heavy element used to produce multilayer X-ray mirrors is tungsten and a light element is carbon. Typically, thin layers are grown using the magnetron sputtering method. The scattering of X-rays at the interfaces between two sublayers also, as in crystals, leads to forming diffraction maxima. The Wolf – Bragg law for multilayer materials can be written in the following form: 2 sin , n Λ ⋅ θ = λ (7) where the integer n = 1, 2, ... is the order of the reflection maximum. It should be emphasized that in this case the period Λ = tA + tB is not the distance between atomic planes in the crystal. Taking into account the circumstances, multilayer materials can be considered as “artificial crystals” [3]. An example of an artificially created heterophase material is a multilayer Ru/B4C type structure used as the material of an X-ray mirror at the BM5 beam line at ESRF (France, Grenoble) equipped with a bending magnet [12]. Seventy equally thick Ru and B4C layers were formed on a silicon substrate. The period of the Λ multilayer structure was 4.0 nm. The simulation results indicated the roughness of the interfacial surface at 0.3 nm. The monochromatic beam increases the image contrast by reducing artifacts and also provides access to more sophisticated contrast techniques. At the same time, the manifestation of contrast is facilitated by an increasing number of photons which can be provided by using mirror monochromators [13]. Compared to crystal monochromators, multilayer monochromators have a number of other advantages. In particular, it is possible to form a periodic structure with the distance between layers much larger than 1 nm, which allows increasing the wavelength range of reflected photons. Thus, the bandwidth of the multilayer material ΔЕ/Е is one or two orders of magnitude greater than the bandwidth of the monochromator. Consequently, multilayer mirrors reflect a larger part of the spectrum, which leads to an increasing integral intensity of radiation [14]. For this reason, multilayer mirrors and two-mirror monochromators are widely used to form “pink” beams. Various combinations of materials can be used to obtain multilayer structures. In some cases, such pairs of substances as W/Si, Mo/Si, Pd/B4C, W/B4C, Mo/B4C, Ru/B4C are preferred. Other systems including Ni/C, Cr/Sc, Cr/Be, La/B4C, etc. may be used. [9, 14, 15, 16] reflect the examples of studying multilayer structures. When selecting bilayer types for multilayer monochromators, it is important to take into account other factors arising during manufacturing and operating the equipment. One of it is the level of thermal load Fig. 9. Schematic of a multilayer X-ray mirror represented by pairs of layers of materials A and B characterized by refractive indices n1 and n2
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