Vol 69, No 3 (2024)

The features of the Bragg diffraction of coherent synchrotron radiation on the atomic lattice of a single crystal in the Laue geometry are studied theoretically, provided that the radiation beam is limited by a relatively large slit placed in front of the crystal. The method of numerical simulation is used and dependences of the intensity distribution are obtained for various thicknesses of the crystal. It is shown that the slit edges introduce inhomogeneous intensity distortions inside the Bormann triangles with an angle of 2θ_B, where θ_B is the Bragg angle. In the area where the triangles intersect, the intensity distribution is similar to that for diffraction by a slit in air at a certain (large) distance. An equation for the correspondence between the distance and the thickness of the crystal is obtained, which describes well the results of numerical calculations.

The Curie principle, which establishes a relationship between the symmetries of a cause and its effect, was originally developed for finite bodies (crystals), but Pierre Curie himself noted the possibility of its application to extended media. This direction was initiated by the works of A. V. Shubnikov (crystalline media) and I.I. Shafranovsky (mother solution), and it requires further development. The systems of limiting symmetries for finite bodies and extended media are compared. The former is partially correlated with the symmetry system of crystallographic point groups. For the latter, in addition to the known data from Curie and Shubnikov, the introduction of new types of limiting symmetries is theoretically justified, and a general systematization is proposed.

The effect of a traveling magnetic field on the parameters of Te-doped GaAs single crystals in the carrier density range of 5 × 10¹⁷–2 × 10¹⁸ cm^–3 has been studied. A traveling magnetic field was induced in a melt by a graphite inductor located in the setup chamber around the main heater. It is shown that a high-frequency magnetic field slightly reduces the dislocation density in the crystals without changing the shape of the dislocation distribution over their cross sections. The magnetic field affects the impurity distribution along the crystal axis, almost doubling the distance between the striation bands from 9 µm in the absence of magnetic field to 17 µm in a field with a frequency of 300 Hz.

A thin amorphous film of fluoroplast (polytetrafluoroethylene) was obtained and studied by the electron diffraction structure analysis methods. The previously developed method of constructing the radial distribution function of atoms by the electron diffraction patterns from amorphous structures is applied, based on the determination of the normalization coefficient by varying the thermal parameter. The possibility of applying and necessary adaptations of this technique for the studied polytetrafluoroethylene samples are shown, taking into account its not quite usual amorphous structure due to the rigid spiral conformation of polymer chains …–CF₂–…, which does not allow us to speak about the complete absence of the long-range order of the arrangement of atoms along the direction of the spiral axis. The measurements were carried out using the developed registration system on the electron diffraction camera EMR-102.

The crystal structure of the metallocarboxypeptidase T from Thermoactinomyces vulgaris complex with L-phenylactate was obtained with a resolution of 1.73 Å. Unlike pancreatic carboxypeptidase A, which binds one L-phenylactate molecule, in complex with CPT, the ligand occupies both S1 and S1ʹ sites of the active center simultaneously. In this case, conformational changes occur that differ from the changes caused by the alternate occupation of the S1 and S1ʹ sites by BOC-leucine and benzylsuccinic acid. These changes concern the residues E277, E59, L254, G192, S127 and Y218 and reach a span of 0.77 Å. A conclusion is made about the possible role of these residues in the recognition and catalysis of substrates by carboxypeptidase T.

The spectra of transmission coefficients and absorption indices of monodomain and polydomain LaBGeO₅ samples were measured. It is shown that for a more accurate measurement of the rotation of the plane of polarization of light, it is necessary to use the transmission coefficient spectra not only for parallel and crossed polarizers, but also at other angles between them. The obtained values of p for both samples are described quite well by a single variance using the Drude formula. This is consistent with the fact that the value of p should not change with monodomenization of the crystal at a given symmetry (P3₁ in the ferroelectric phase and P3₁21 in the paraelectric phase). It is shown that the generation of the second harmonic of the Cherenkov type is observed only in a polydomain sample, while the radiation of the second harmonic is not polarized. The domain structure of the samples was observed by scanning electron microscopy and piezoelectric force microscopy. For a polydomain sample, the presence of a labyrinthine domain structure was shown, for a monodomain sample, no contrast changes were observed within the scanning area.

Within the framework of a crystal-physical model, the maximum values of mobility and concentration of charge carriers in fluoride superionic conductors belonging to the structural types of fluorite (CaF₂, SrF₂, BaF₂, PbF₂) and tysonite (LaF₃) were calculated. It has been shown that the upper limit of ionic conductivity, mobility and charge carrier concentration in the crystalline state of fluoride superionics is 4 ± 1 S/cm, (5 ± 1) × 10^–3 cm²/(сВ) и (5 ± 2) × 10²¹ cm^–3 (10 ± 4% of the total fluoride ions), respectively.

Polycrystalline films of organo-inorganic perovskite semiconductors are promising as a foundation for creating functional optical metasurfaces. The requirements for film structural perfection, thickness uniformity, and defect-free characteristics are much more stringent compared to perovskite films for photovoltaics. This work presents the results of searching for optimal conditions for one-step synthesis of lead methylammonium bromide films using centrifugation, and describes the successful fabrication of subwavelength optical gratings from these films through focused ion beam processing. The measured spectra of light transmission through the gratings demonstrated their excellent optical quality and confirmed the possibility of creating semiconductor photon metasurfaces with submicrometer periodicity and high-Q dielectric resonances.

Structural dynamics of multilayer of dimyristoyl-phosphatidylserine formed on the surface of silica sol with 5 nm nanoparticles size has been investigated by X-ray reflectometry and grazing-incidence diffraction at 71 keV photon energy. Combined model-based and modelless analysis of reflectometry data revealed the structure consisting of a surface monolayer and a stack of lamellar bilayers sandwiched between water layers, with a spatial period of ~ 150 Å. With increase in temperature above the chain-melting point the surface monolayer is observed to transition from a surface crystal phase with minimal area-per-lipid value of (40 ± 1) Ų to a disordered liquid phase with estimated area-per-lipid value of (52 ± 2) Ų. Under low temperatures both monolayer and bilayer slabs contain 5 to 8 H₂O molecules bound to lipid PS-fragment; however, above the melting point the amount of contained water rises to about 14 molecules per bilayer headgroup.

The paper reports an analysis of surface morphology variation and cavity band formation in silicon single crystal induced by ion implantation and post-implantation annealing in different regimes. Critical implantation doses required to promote surface erosion are determined for samples subjected to post-implantation annealing and in absence of post-implantation treatment. For instance, implantation with helium ions to fluences below 3 × 10¹⁷ He⁺/cm² without post-implantation annealing does not affect the surface morphology; while annealing of samples implanted with fluences of 2 × 10¹⁷ He⁺/cm² and higher promotes flaking.

The influence of the structure of copper powder particles on the catalytic activity of the CeO₂/Cu catalyst was studied using the methods of X-Ray diffraction, electron microscopy, electron diffraction, energy dispersive X-Ray analysis, as well as programmed temperature reduction of CO (CO-TPR). Nanocomposites were obtained by mechanochemical synthesis using copper particles differing in size and morphology: micron-sized dendrites and nanoparticles. It was shown that the activity of the catalyst obtained from nanosized copper is two times higher, which is due to the presence of Cu_xO clusters located on the atomic steps of cerium oxide nanocrystals. This arrangement of clusters apparently ensures that the activating centers are not blocked. Thus, the surface structure of cerium oxide particles formed when using nanosized copper powder is a key factor responsible for the catalytic activity.

In ternary fluoropolymers Viton GFLT 600S and Viton GFLT 200S, more types of nanoformations with the size of 3–80 nm are found than in double SCF-26 and SCF-32, while their prehistory changes according to the X-ray diffraction analysis data in the region of large angles. This process is more influenced by the chemical structure of the junctions in the macromolecules than by the molecular weight. The complex and unequal character of change of dynamic viscosity of fluoropolymers with temperature increase is caused by multiple phase transitions. It is shown that fluorocarbon rubber SKF-32 does not transition to the viscous-fluid state up to ~190°C in contrast to three fluoropolymers due to intermolecular nanoformations of 5 nm in size, the strength of which is significantly higher than nanoformations of 3–4 nm in the latter. It was found that the rotational mobility of the TEMPO radical is determined not so much by the intermolecular distances in the disordered part of the copolymers as by the flexibility of the passing chains connecting the ordered formations into a single system.

The presented work presents the structural and morphological characterization and the results of studies of luminescent, photocatalytic properties of ZnO tetrapods synthesized by the method of high-temperature pyrolysis. It has been shown that the morphology and structural parameters of ZnO tetrapods are determined by the location in the synthesis zone (correlated with the distance from the air inflow window). All samples were characterized by pseudo-three-dimensional morphology of tetrapods. A correlation was found between luminescent properties and photocatalytic activity of tetrapods. The highest photodegradation rates of methylene blue under ultraviolet radiation were demonstrated by ZnO tetrapods grown in the zones closest and farthest from the window (rate constants 54 × 10^–3 min^–1 and 50 × 10^–3 min^–1, respectively).