Crystallography Reports最新文献

The conditions and specific features of the formation of Langmuir monolayers of symmetric and asymmetric diacetylene N-arylcarbamates and the structural organization of Langmuir–Schaefer films based on them have been studied. The photopolymerization of monolayer solid films of two types of molecules was monitored using absorption spectroscopy; it demonstrated the transition of diyne molecules to the state of blue-phase polydiacetylenes. The efficiency of solid-phase topochemical polymerization reaction in a film of symmetric diynes turned out to be five times higher than in the film of asymmetric diyne molecules. The monolayer surface morphology before and after UV irradiation was studied by scanning electron microscopy.

A nondestructive layer-by-layer elemental and phase analysis of the ferromanganese intact crust (aged about 60 million years), extracted from the 1200-m rise of Magellan Mountains of the Pacific Ocean, has been performed using the X-ray fluorescence and X-ray diffraction methods. The crust morphology was studied using scanning electron microscopy. This analysis made it possible to estimate the contributions of various oceanic sources of iron and manganese to the crusting process and propose a mechanism for its formation.

Thin manganese silicide films were obtained on mica by magnetron sputtering from targets of three types. The microstructure and elemental composition of the targets and films were studied by scanning electron microscopy and reflection electron diffraction. The phase composition and structure of the films over depth (cuts) were controlled by scanning and transmission electron microscopy. It has been shown that, when depositing films from poly- and single-crystal targets of higher manganese silicide, in contrast to a target from sintered Мn and Si powders, one can obtain polycrystalline films of higher manganese silicide of the Mn₄Si₇ composition after subsequent 1-h annealing at a temperature of 800 K and a pressure of 10^–3 Pa.

The maximum values of the mobility and concentration of charge carriers in fluoride superionic conductors of the fluorite (CaF₂, SrF₂, BaF₂, and PbF₂) and tysonite (LaF₃) structural types have been calculated within the crystallophysical model. It is shown that the upper limits of the ionic conductivity and carrier mobility and concentration in the crystalline state of fluoride superionics are, respectively, 4 ± 1 S/cm, (5 ± 1) × 10⁻³ cm²/(V s), and (5 ± 2) × 10²¹ cm⁻³ (10 ± 4% of the total amount of fluorine ions).

Characteristics of surface acoustic waves in lithium niobate single crystal/silicon dioxide film structures, which are used to increase the thermal stability of acoustoelectric devices on single-crystal substrates, have been calculated. The simulation has been performed by the finite-element method using the COMSOL software, and the velocity, electromechanical coupling coefficient, and temperature coefficient of frequency in the structures with lithium niobate of different cuts have been calculated. A good agreement is observed between the results obtained and the data in the literature. The obtained parameters are of practical importance for developing various acoustoelectric devices.

The structure dynamics in the temperature range of the melting phase transition of a dimyristoyl-phosphatidylserine multilayer on the surface of a colloidal silica solution with a particle diameter of 5 nm has been investigated by X-ray reflectometry and grazing diffraction of 71-keV photons. The joint model and model-free analysis of the reflectometry data revealed a structure consisting of a surface lipid monolayer and a set of lamellar bilayers sandwiched between water layers, with a period of ~150 Å. With an increase in temperature above the critical value one can observe a surface monolayer transition from a crystalline phase with a minimum area per lipid molecule of 40 ± 1 Å² to a disordered (liquid) phase with a calculated area per molecule of 52 ± 2 Å². At low temperatures, the data indicate that from five to eight H₂O molecules are tightly bound to the PS fragment of the lipid in both the monolayer and the bilayer structures. However, above the transition temperature, approximately 14 water molecules are attached to the headgroups of the bilayer: this is almost twice as many molecules as the eight H₂O molecules-per-headgroup in the surface monolayer.

The kinetic regularities of crystallization (its order and constants) in a model solution of human synovia (inorganic composition) under conditions close to physiological have been investigated. The crystallization constants in a pure solution and in the presence of organic synovia additives with variation in their concentration and supersaturation of the model solution are determined. The following descending order sequence is proposed for the influence of additives on the general and particular kinetic characteristics of crystallization in a model synovial solution: glucose → proline → alanine → glycine → citric acid. It is found that impurities affect to a greater extent the nucleation process rather than growth stages.

The spectra of transmisson coefficients and absorption indices of single-domain and multidomain LaBGeO₅ samples have been measured. It is shown that, to measure more exactly the optical rotation ρ, it is necessary to use the spectra of transmission coefficients not only for the cases of parallel and crossed polarizers but also at other angles between them. The obtained ρ values for both samples are described quite well by only dispersion using the Drude formula. This is in agreement with the fact that the ρ value should not change during transition to the single-domain state of the crystal at a given symmetry (P3₁ in the ferroelectric phase and P3₁21 in the paraelectric phase). It is shown that the Cherenkov-type second harmonic generation (SHG) is observed only in a polydomain sample, while the second-harmonic radiation is not polarized. The domain structure of the samples was observed by scanning electron microscopy and piezoelectric force microscopy. The presence of a labyrinth-like domain structure was shown for the multidomain sample, whereas for a single-domain sample no changes in contrast were observed within the scanned region.

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 temperature-programmed 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 prevents blocking of activating centers. Thus, the surface structure of cerium oxide particles formed when using nanosized copper powder is a key factor responsible for the catalytic activity.

A method for searching for parameters of structural models of weakly ordered thin films based on X-ray diffraction data containing a small number of reflexes is proposed. The developed method makes it possible to reduce the number of possible structural models, despite the small number of interference maxima, determine the parameters of possible elementary cells and index the corresponding peaks on diffractograms. It is shown how the use of a priori data makes it possible to obtain physically adequate solutions. The method of determining structural parameters is demonstrated by analyzing an experimental curve containing only three diffraction peaks (maxima). The corresponding search algorithms are implemented within the framework of the analytical software package BARD (Basic Analysis of xRay Diffraction).