Vol 68, No 1 (2023)

A new method is proposed for determining experimentally the size of a synchrotron radiation beam in the focus of planar compound refractive lenses. The method consists in measuring the angular divergence of radiation after the focus using Bragg diffraction in a perfect crystal during its rotation. This method determines the beam size, which depends only on the focusing properties of the lenses in use, in contrast to other currently applied methods. The efficiency of the proposed approach has been experimentally demonstrated using nanofocusing planar silicon lenses as an example.

The impurity defects in CaMoO4 are simulated by the method of interatomic potentials. The dissolution energies of monovalent, divalent, and trivalent impurities are calculated, their comparative analysis is performed, and the main patterns of change are presented. The most probable localization of defects is determined. In the case of heterovalent impurities, the most energetically favorable mechanism for their charge compensation has been found, both due to intrinsic crystal defects and under conjugate isomorphism. It is shown that the formation of impurity clusters with intrinsic crystal defects and (to a greater extent) the formation of clusters of different-valence impurities may significantly reduce the dissolution energy of impurities. The formation of neutral clusters of univalent impurities with oxygen vacancies not only makes it possible to increase the solubility of impurities but also reduces the probability of the formation of color centers.

New ring silicates Cs4Tm2[Si4O12](OH)2 and Cs4(Tm,Tb)2[Si4O12](OH)2 have been synthesized by the hydrothermal method. A structural analogy is revealed between them and the previously studied silicates K4Sc2(OH)2(Si4O12) and K2Sc[Si2O6]F. Their crystal structures are identified as orthorhombic merohedral twins by the lost element of tetragonal symmetry. The structures of new ring silicates are related to those of fresnoite and tetragonal melilite.

A new coordination compound—derivative of aza-14-crown-4-ether, containing an ethoxycarbonyl subunit, with nickel(II) nitrate, of the [Ni3(NO3)4L4]2(NO3) composition—has been obtained for the first time in the form of single crystals. The presence of nickel atoms in the complex is confirmed by X-ray fluorescence analysis. The complex structure has been studied by precise X-ray diffraction on a laboratory X-ray source. The molecule of this complex is shown to have an intricate geometry and consist of four pairwise symmetric ligand molecules, coordinated by three nickel atoms. Stabilization of the complex molecule is provided by the presence of strong intramolecular hydrogen bonds, involving a crown-ether fragment.

The structures of hydrophobic membrane proteins are studied using matrices, which serve as models of cell membranes and are formed by the appropriate amphiphilic molecules, e.g., by surfactant or lipid molecules. To study the structure of a protein incorporated into an artificial membrane, first of all it is necessary to determine the structure of the membrane. The ELLLIP and ELLMIC algorithms were previously developed to address this issue by small-angle X-ray scattering. These algorithms allow the construction of models of ellipsoidal vesicles based on the atomic structure of a lipid or surfactant monomer. However, the results of modeling depend, to a large extent, on the subjective assessment of the initial values of the structural parameters of the matrices and may be wrong due to the ambiguity in the solution of such problems. Here, we present an independent approach to the determination of the initial sizes of model membranes for their subsequent structural modeling, which is based on the analysis of the pair-distance distribution functions derived directly from the small-angle X-ray scattering curve.

Polycrystalline Cd1–хZnхTe (x = 0.005, 0.03, 0.05) ingots have been obtained by the modified Obreimov–Shubnikov method. The selected single-crystal blocks are studied applying the X-ray diffraction analysis, measurement of electrical characteristics, and magnetometry. The concentration dependence of changes in the magnetic and electrical properties of crystals is investiga11ted. It is established that at Zn concentrations of x = 0.03 and 0.05 ferromagnetic ordering is observed in clusters (inclusions) containing iron and/or nickel at 2 K, which is not observed for Cd1–хZnхTe (x = 0.005) samples.

It is shown that a twinned PT-symmetric gyrotropic structure, composed of semi-infinite media with oppositely directed gyration vectors, lying in the interface plane, exhibits valve properties for surface electromagnetic waves. More specifically, a surface wave can be excited in one direction lying in the interface plane, which is perpendicular to the gyration vectors, and cannot be excited in the opposite direction. This surface electromagnetic wave is linearly polarized, and its characteristic penetration depth is inversely proportional to the small gyration parameter.

Ionizing radiation gives rise to impurity defects in activated crystals due to the transition of impurity ions from the trivalent to divalent state. An approach is proposed for studying the influence of the energy position of R³⁺ ions in the energy-band structure of СaF₂ crystals on the degree of stability of rare-earth ions in the divalent state as a result of the transition of 4fⁿ electronic states of R³⁺ → R²⁺ ions under ionizing irradiation. The processes of direct and reverse photochromism occurring on impurity defects, which are related, respectively, to the coloring of activated crystals under γ irradiation and their bleaching under UV irradiation, have been studied. A mechanism of photochromic transformation taking into account the participation of radiation-induced color centers (CCs) in this process is proposed. The valence transition R³⁺ → R²⁺ is considered in terms of photooxidation reaction. The possibilities and conditions of the ion transformation reaction in dependence of the type of ionizing radiation acting on R³⁺-containing crystals are analyzed based on calculations of the change in the Gibbs energy.

Laser light emission in dye-doped chiral liquid crystals (CLCs) has been experimentally demonstrated for the homeotropic–planar (hybrid) orientation. A numerical simulation of this structure showed that the helicoid (helix) pitch period in CLC in the hybrid cell and the director distribution depend significantly on the anchoring energy at the homeotropic sample boundary. The anchoring energy plays the role of a factor facilitating the CLC helix unwinding. The lower anchoring energy, the smaller the pitch is and the closer to the natural CLC pitch it is. In this case, the length of the “screw"-type structure near the homeotropic cell boundary decreases. Thus, as the anchoring energy at the hybrid-cell homeotropic boundary decreases, the director distribution in the cell approaches the distribution in the planar (Grandjean) cell. This is confirmed by the laser light emission in the same spectral range as in the planar cell.

The structure of Langmuir lysozyme films on a liquid surface, formed from crystallization solutions with addition of metal chlorides as a precipitant, have been investigated. The thicknesses and densities of the films were determined using the X-ray reflectivity technique, and the concentration distribution profiles of the sulfur atoms present in protein molecules, as well as precipitant ions in the subphase surface region, have been obtained by the X-ray standing waves technique. Based on the experimental results, the dependence of the film structure on the precipitant used, as well as some specific features of application of X-ray reflectivity and X-ray standing waves techniques in the study of Langmuir films of globular proteins on a liquid surface, are analyzed.

The features of mathematical optimization methods are considered and algorithms for their use are proposed to increase the efficiency of finding extreme values in solving optimization problems. The proposed algorithms are universal in nature, which allows them to be applied in various fields of computational mathematics. As an illustration, the solution of the inverse problem of reflectometry in the framework of a box model of an electron density profile for a liquid crystal film of a block dendrimer is given. The structure of the thin-film layer on the aqueous subphase was also determined from the grazing-incidence diffraction data. The proposed algorithms of optimization methods are implemented within the analytical software package BARD (Basic Analisys of xRay Diffraction).

The multiphase alloys with a high Al content and the presence of quasicrystalline phases are promising for aviation and space industry due to their low specific weight, high specific strength, corrosion resistance, and high tribological properties. An Al82Cu7Fe11 alloy ribbon has been obtained by spinning. It is shown by X-ray diffraction analysis that the alloy contains Al (sp. gr. Fm m), Al13Fe4 (sp. gr. С2/m), Al2Cu (sp. gr. I4/mcm), Al23CuFe4 (sp. gr. Cmc21), and decagonal quasicrystals (sp. gr. P105mc). The inhomogeneity of the ribbon surface is revealed by scanning electron microscopy. The presence of Al, Al13Fe4, and decagonal quasicrystals in the ribbon is found by transmission electron microscopy.

The results of studying the growth of para-terphenyl derivative (4,4"-di-tert-butyl-para-terphenyl (tBu-3P-tBu)) crystals are presented. The solubility of this compound in toluene at 20°С has been established by spectrophotometry. Using the techniques of growth from solutions and physical vapor transport,tBu-3P-tBu single crystals up to 1 cm long have been obtained for the first time. Their structure at 85 K has been interpreted in the triclinic system, sp. gr. P1 (Z = 8), using single-crystal X-ray diffraction. Flat rectangular crystals with the best morphological characteristics have been grown from vapor. The developed face of these crystals exhibits elementary growth steps 1.4 nm high, corresponding to molecular monolayers oriented in the (001) plane. The presence of a polymorphic transition at 229.2°C and mesomorphic liquid crystal phase above the melting temperature (255.6°С) is found.

The results of studying painted areas on the surface of the Bronze Age anthropomorphic stela, found in the village of Remontnoye, are presented. The elemental and phase composition of the samples has been studied using X-ray diffraction and electron microscopy. It is established that the red color on the front surface of the stela is due to the red mineral pigment based on hematite, while the dark and green areas are of natural origin, associated with the environmental impact on the sandstone.

The results of developing a software package for automated orientational mapping based on diffraction data are presented. The experimental module of the software is responsible for the communication with a microscope and acquisition of diffraction maps. The analytical module automatically processes and solves diffraction patterns obtained by transmission electron microscopy. The test data analysis has shown the diffraction mapping results to be consistent with the model data.

A promising method of scanning transmission electron microscopy is the use of integrated differential phase contrast. Its advantages include high sensitivity to light elements, almost linear relation between the generated image contrast and atomic numbers of Z atoms contained in a sample, noise suppression, and much more. Using the modeling and mathematical processing, prospects of this technique for studying the crystal structure of materials consisting of light atoms have been analyzed by the example of boron carbide polytypes. It is shown that the sensitivity of the technique makes it possible to distinguish columns of boron atoms from columns consisting of carbon. Recommendations on using this technique for analyzing the structures consisting of light elements are formulated.