Poverhnostʹ. Rentgenovskie, sinhrotronnye i nejtronnye issledovaniâ

The work presents results of studies of coalescence of nematic liquid crystal droplets surrounded by isotropic liquid. With the aid of high-resolution optical microscopy and high-speed video recording coalescence of droplets in thin optical cells has been studied. Cells with planar and homeotropic boundary conditions for the liquid crystal director were used. It is shown that depending on boundary conditions at the cell surface the coalescence process at the initial stage develops in a different manner. In a cell with planar boundary conditions at the initial stage we observe linear dependence of the width of the neck between droplets on time. At subsequent stages the influence of surface leads to slower dynamics. The final stage of coalescence is characterized by exponential relaxation of the droplet to the equilibrium shape. At coalescence of droplets whose diameter exceeds the cell thickness, we observed an intermediate stage with power-law dependence of the neck width on time. The duration of this stage increases with increasing the droplet size. Capillary velocity and characteristic times at different stages of coalescence were determined. Characteristic times for the initial stage increase linearly with increasing the droplet size. For the middle stage the characteristic times increase proportionally to the third power of the droplet radius.

The effect of concentration supercooling on the structure of GaInAsSbP/GaP heterostructures grown by the method of zone recrystallization by a temperature gradient is investigated. The main technological parameters of the growth process are revealed, the value of the initial concentration supercooling of the solution–melt is determined, which is necessary to establish a crystallization regime that prevents thermal degradation of the substrate and eliminates the possibility of capturing microinclusions of the solution–melt. The dependence of the mismatch of the lattice parameters of the GaP substrate and the GaInAsSbP layer on the initial supercooling is found.

The results of the work on the development of an experimental setup for investigating polarized neutron methods at the IR-8 reactor are presented. A scheme for polarizing a monochromatic neutron beam and analyzing it using the Mezei spin flipper has been developed. A reflectometric scheme for measuring thin-film samples has been implemented using a beam of polarized neutrons, and the reflection coefficients of non-magnetic layers have been measured experimentally. The results obtained on the setup confirm the possibility of further implementation of several methods for studying condensed matter, including polarized neutron reflectometry, depolarization, and polarized neutron radiography. These research methods were implemented at the IR-8 reactor for the first time.

Research on the influence of a high intensity (by the order of magnitude of 10²⁴ ion/(m²s)) deuterium ion beam on the surface of anisotropic carbon-based materials — pyrolytic graphite and carbon fiber composite with polyacrylonitrile fiber onion-skin fibers — was conducted in this work. Characteristics of material modification is discussed, and the results are compared to the results obtained in the works conducted by other authors. It is shown that the fragmentation of surface-level graphene layers during irradiation by high intensity deuterium ion flux and the corresponding compressive stress leads to the bending of the exfoliated surface layers and the formation of the hill system-like structure. Further irradiation leads to a reverse process of the formation of graphene layers oriented parallel to surface on the slopes of the hills, and crystals with the similarly oriented layers on the top of the hills. During the irradiation of onion-skin type carbon fibers from the side, folds perpendicular to the axis of the fiber were formed on them when the ions implanted into the surface induced compressive stress that led to fragmentation and bending of the surface layers, and the degree of structural destruction of the lattice was sufficient enough for the re-emission of ions to occur. Folds that are parallel of the axis of the fiber were formed in cases where maximum stress was formed at a certain depth of the material due to high ion path length, and the degree of destruction was insufficient for the re-emission of ions. In this particular case, the surface deformation mechanism is similar to that of blistering. Ion irradiation of the fibers’ ends led to them protruding from the composite matrix and recrystallization of exposed parts, with the graphene layers of crystals oriented perpendicular to the axis of the fiber. The results of this work allow to conclude that irradiation of the carbon-based structures leads to transformation into a formation that is perpendicular to the original independently of the original’s orientation or the direction of the ion beam.

In the framework of the phenomenological approach, we obtained a non-uniform vortex distribution of magnetization and the associated non-uniform electric polarization in small magnetic particles in the shape of cylinders. The microscopic mechanism of this connection between magnetization and polarization is due to spin-orbit interaction. Within the framework of the phenomenological approach, the emergence of an inhomogeneous magnetic state and the associated appearance of inhomogeneous electric polarization in the volume of small magnetic particles have been studied. The specific form for magnetization and polarization is determined by the shape and size of the cylindrical particles. Using the free energy expression for magnetization, we obtained a nonuniform distribution of magnetization in the form of three-dimensional magnetic vortices. A vortex state occurs only for cylinders with a radius greater than a certain critical value, and for particles with a smaller radius a uniform magnetic state arises. In a vortex state, non-uniform electric polarization occurs, directed in the form of rays from the cylinder axis. The region of existence of such inhomogeneous states has been determined. The change in local electric polarization of small magnetic particles in an external magnetic field is considered. An expression for the magnetoelectric susceptibility is obtained.

The work is aimed at solving the problem of improving the quality control of coatings with a porous structure. The problem arises due to the lack of an effective and nondestructive method for assessing the porosity of microarc oxide coatings. Accurate porosity control is necessary to ensure the reliability and durability of coatings, as well as to prevent their defects. The use of optical image recognition techniques can improve the process of indirect measurement of coating porosity and improve the quality of control without affecting the object. The factors affecting the porosity of the microarc oxide coating, as well as methods for its determination, are systematized. A method for estimating the porosity of oxide coatings of AD31 aluminum alloy samples is proposed based on a recognition program written in the MATLAB R2020a environment, surface morphology images using modern microscopy methods. A statistical analysis of the surface morphology was carried out, which confirmed good agreement between the porosity estimate and the data obtained during image processing using scanning electron microscope software. The relative error of the proposed method does not exceed 10%. The scientific novelty of the work consists in the development of algorithms for a unique nondestructive testing method — recognition of porous structures based on optical data, which contribute to increasing the efficiency of porosity estimation and improving the characteristics of oxide coatings.

Two types of multielectron effects of X-ray photoemission in chalcogenide semiconductors Cu₂SnS₃, Cu(In, Ga)Se₂, CuGaTe₂ have been experimentally studied. The first is interatomic Auger transitions with electron ejection from the inner levels of atoms surrounding copper (Sn, In, Ga), which arise as a result of the decay of the photohole formed on copper atoms during absorption of synchrotron radiation. And the second is the characteristic loss of kinetic energy during direct photoemission from the core–electron levels of tin atoms due to the dynamic Coulomb field of the photohole, the inclusion of which leads to shaking of Sn4d electrons into unoccupied states. The cause of both effects is the extremely non-equilibrium nature of the atom photoionization, which generates an almost instantaneous inclusion of the Coulomb field of the photohole in one of the inner levels of the atom. The surrounding electrons are subjected to a kind of impact and can increase their energy by tens of electron volts. The experiments show that the electrons of the 4d levels are “shaken up” most effectively. Firstly, there are many of them (ten per atom) and, secondly, due to the large centrifugal barrier, these electrons are on the periphery of the atom, as are the unoccupied free states, into which they pass when the photohole field is turned on.

Finite element methods have solved the problem of the influence of the morphology of the interface between coating made of high-speed steel P2M9 and substrate made of structural steel 30HGSA on the distribution of thermoelastic stresses in the coating. It was solved in two stages. At the first stage, the behavior of stresses during cooling from a temperature of 1573 K to a temperature of 293 K. was studied. At the second stage, after cooling, a static tensile load was applied to the coating surface. The morphology of the interface was determined using scanning electron microscopy data. It follows from them that the interface has a curved appearance and, in the first approximation, can be described by a harmonic function. It is shown that at the cooling stage, the undulating interface between the coating and the substrate serves as the most effective barrier to crack formation, redistributing the areas of dangerous tensile forces into the substrate. The application of a tensile static load to the coating after cooling has shown that in the case of a rectilinear interface, when the value of the elastic modulus of the substrate (E_c) is an order of magnitude less than the elastic modulus of the coating (E_s), the coating separation from the substrate is observed. The plastic flow occurs mainly in the coating. The same situation is observed for a curved boundary with the only difference that it prevents separation. If E_s = 10E_c, then for a rectilinear boundary, plastic flow is observed both in the substrate and in the coating, and for a curved boundary, this process occurs mainly in the substrate.