Journal of the Belarusian State University. Physics
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Effect of thermal cycling and ultraviolet irradiation on epoxy polymers: the role of graphene filler
To evaluate the influence of near-Earth orbit factors on the structural features of epoxy polymer with graphene filler the effect of combined thermal cycling and ultraviolet irradiation under vacuum conditions (pressure 2 ⋅ 10– 4 Pa, temperature range from 15 to 160 °C; 4 and 10 thermal exposure cycles) on epoxy polymers based on ED-20 resin and amine hardener «Etal-45M» was studied. Two types of cured polymer samples (an unmodified polymer and a composite containing 1 wt. % graphene nanoplatelets) are considered. Optical and infrared spectroscopy in reflection mode was applied to record spectra from both the face (irradiated) and back surface of samples. A combined analysis of spectral and morphological data allowed to identify characteristic markers of polymer degradation, densification and structural modification induced by thermal cycling and ultraviolet irradiation. It was found that the unmodified polymer exhibits signs of degradation at the early stage of thermal cycling (4 cycles), whereas prolonged treatment (10 cycles) results in post-curing and structural stabilisation. The introduction of graphene enhances structural stability at the early stage, but with increasing number of cycles it initiates destructive processes on the surface of the sample due to interfacial interactions and localised absorption of ultraviolet radiation. The obtained results can be applied to the development of polymer composites for aerospace applications and to the assessing their durability.
Copyright (c) 2026 Journal of the Belarusian State University. Physics https://creativecommons.org/licenses/by-nc/4.0
Synthesis and properties of Ag/TiO2/Ti heterostructures
Ag/TiO2/Ti heterostructure was fabricated by electrochemical deposition method from a silver nitrate solution onto a titanium substrate with a thin titanium dioxide layer obtained via two-step chemical-thermal oxidation. Scanning electron microscopy analysis revealed that silver forms on the surface of the nanostructured titanium dioxide film predominantly as disordered complex tree-like structures (dendrites) with average dimensions of 1 × 8 μm, in this case, the formation of grains with a tendency toward clustering (cluster sizes up to 3.5 μm) was also observed. The metallic nature of the silver structures was confirmed by X-ray diffraction analysis. The photocatalytic activity of the Ag/TiO2/Ti heterostructure was determined with respect to the test contaminant rhodamine B in an aqueous solution (concentration 10 mg/L) upon exposure to ultraviolet radiation (wavelength 365 nm). The plasmonic activity of heterostructures with a lower detection threshold for the dye methylene blue at a concentration of 10–6 mmol/L when activated by a green laser (wavelength 532 nm) is shown. The obtained heterostructures, which combine photocatalytic and plasmonic properties, can be used to develop flow-through water purification and disinfection systems, as well as to create multifunctional substrates for real-time monitoring of organic pollutant degradation and for tracking photochemical reactions on the surface of such heterostructures.
Spectral and generation properties of new coumarins – benzopyrylium derivatives
The spectral and generation parameters of coumarins, benzopyrylium derivatives, in ethanol and acetonitrile under coherent excitation were studied. It was found that the absorption spectra of the investigated compounds contain several maxima and the structuredness of the spectra is associated with their bichromophoric structure. It is shown that these organic dyes are bichromophoric compounds. It is noted that the nature of the substituents in positions 6 and 7 of the coumarin base and positions 6′ and 7′ of the benzopyrylium core determines their spectral-luminescent and lasing properties. It is demonstrated that the presence of substituents in certain positions of the coumarin base and the benzopyrylium core changes the conformation of the molecule and, accordingly, the dipole moments and oscillator strengths of the transition. The generation ability of coumarins of this class manifests itself only in the presence of the strongest donor substituents (for example, Et2N and OH) in position 7, and sufficiently strong acceptors in positions 6′ and 7′. Lasing was obtained in the spectral region of 730 –740 nm on dyes – benzopyrylium derivatives.
Copyright (c) 2022 Journal of the Belarusian State University. Physics
Formation of epitaxial 3C-SiC layers on Si by rapid vacuum thermal processing
The results of a study of the structure and phase composition of epitaxial layers of silicon carbide (SiC) formed on silicon substrate with orientation (100) under rapid vacuum thermal processing are presented. Planar-view transmission electron microscopy investigation revealed the formation of epitaxial layers of cubic polytype SiC (3C-SiC) on silicon in the process of carbidisation at 1100 °C during 30 s, using a gas mixture of propane (10 %) and argon (90 %) as a carbon source. The formation of a monocrystalline 3C-SiC with polycrystalline inclusions and twins on all possible planes {111} was found. A rather narrow band of 793 cm–1 transverse optical phonon mode SiC on Raman spectra confirms the formation of a cubic polytype SiC. It is noted that the presence of a 180 cm–1 spectral line and a 793 cm–1 half-width band on Raman spectra indicate the presence of deformation defects in SiC.
The regional nanosatellite constellation modelling formation by a piggyback launch from different spaceports
The roadmap for constructing a regional nanosatellite constellation using the piggyback launch according to Chinese provider information has developed. For nanosatellite constellation formation to a specific purpose, it is necessary to analyse existing constellation operated similar tasks. Therefore, the software module for the Spire Global constellation orbital construction analysis was developed. The construction of Spire Global nanosatellites constellation based on orbital parameters database in the two-line element set format, satellite constellation databases and the developer site was analysed. A launch from the International Space Station and a piggyback launch were used for constellation formation. Nanosatellite deployment schemes, orbital parameters and flight parameters are investigated launches from the Taiyuan and Jiuquan Satellite Launch Centers with orbit inclination about 90°, that best correspond to the passes over Minsk (ϕ = 53°54′27″ N, λ = 27°33′52″ E) are analysed. The method of nanosatellite orbit preflight prediction at a passing launch has been developed. It involves a finding the nanosatellite state vector in the first flight day and at the time of constellation mission operate start. The launch time, satellite launch center coordinates, launch vehicle type, orbit inclination and altitude (period) are used in the method. In addition, the launch history and the satellite motion dynamics analysis on similar orbits is carried out. It was found that five launches are enough to organise a regional nanosatellite constellation with average radio visibility interruption time of at least 36 min with a maximum value of 85 min.
Uni- and multivariate calibration of tempe­rature from the neodymium fluorescence spectra in nanocrystals of yttrium-gadolinium oxide and yttrium-gadolinium garnet
The use of neodymium-doped nanocrystalline powders of yttrium-gadolinium oxide and yttrium gadolinium garnet to increase the sensitivity of local fluorescent optical temperature sensors is considered. Based on the temperature dependences of the neodymium fluorescence spectra in this powders, univariate (using fluorescence intensity ratio from thermally coupled energy levels of the activator) and multivariate (using the partial least squares method) calibration models are developed. When using the spectral range 860 – 950 nm falling into the first biological transparency window (700 – 980 nm), both calibration models have a standard deviation of about 10 % and are comparable in accuracy. The spectral variables selection by searching combination moving window in the multivariate model made it possible to reduce the root mean square error for yttrium-gadolinium oxide by more than 12 times (from 9.8 to 0.8 °C), and for yttrium-gadolinium garnet by more than 2 times(from 8.7 to 4.0 °С). The result obtained indicatesthe proposed neodymium-doped nanocrystalline powders and multivariate methods of calibration can be used to localise areas with febrile temperatures for biological and medical purposes.
Structure formation and peculiarities of crystallisation of lead-free tin – zinc alloys obtained by rapid solidification
The results of the study of the microstructure of lead-free alloys of the tin – zinc system obtained by rapid solidification at a cooling rate of at least 105 K/s are presented. In tin and zinc alloys with concentrations of 1.2–2.0 wt. % Zn and 1.5 wt. % Sn, respectively, during rapidly cooling of the melt, the alloying element is captured. The formed solid solutions are supersaturated and at room temperature disintegrate according to the mechanism of formation and growth of nuclei of a new phase. The average size of zinc and tin precipitates after holding the foil for two days does not exceed 0.5 μm. Melts of compositions Sn – 4.4–15.0 wt. % Zn after rapidly cooling are supercooled and supersaturated by two components and experience spinodal decomposition (stratification) followed by the formation of supersaturated solid solutions based on tin and zinc, which disintegrate at room temperature. The average size of zinc precipitates in non-equilibrium eutectic does not exceed 2 μm. In rapid solidificated foils of alloys containing 50–80 wt. % Zn, a two-phase structure is formed from solid solutions based on tin and zinc. The average size of tin precipitates does not exceed 1 μm. As the crystallisation front moves away from the contact surface of the foil with the surface of the mold, the tin particles become larger and the specific surface of the interphase boundary decreases.
«Uncanny valley» effect in holographic image transmission
The quality of computer-synthesised images is continuously improving, increasing in the volume of files representing them. It is noticed that passing from simple schematic images to increasingly complex ones, their perception goes through different stages. If initially the complication of the image and its approximation to the real image of a person makes a favourable impression, then there comes a moment of fright and rejection. Masahiro Mori called it the «uncanny valley» effect. Since then, all new technologies for presenting human images have been tested in order to avoid this effect. This effect should be treated especially carefully when compressing and then restoring complex images. This paper shows the position relative to the «uncanny valley» of the reconstructed 3D images, reconstructed by a hologram synthesised and transmitted with compression over the communication channel in accordance with patent RU2707582C1.
Analysis of the reciprocal lattice of crystals with non-primitive Bravais cells
The aim of the work was proof the independence of the reciprocal lattice of a crystal from the choice of a cell in its direct lattice. The object of analysis was the dependence of the position of reciprocal lattice cell sites and direct lattice parameters based on quadratic formulas, as well as the structural amplitudes («weights» of reciprocal lattice sites) for crystals with non-primitive cells. The following tasks were solved: choice of a Bravais rapper with a P-type cell in a crystal with I-, F- and C-type cells; construction of direct and reciprocal metric tensors for centered cells of a direct lattice and for P-type cells of crystal lattices; establishment of the transition rule from the HKL indices of the nodes of the reciprocal lattice with the selected P-cell to the hkl indices of the same nodes for non-primitive cells based on quadratic formulas; determining a connection between HKL and hkl indices using metric tensors; analysis of the results obtained by two different methods (based on quadratic formulas and using metric tensors); proof, that in the reciprocal lattice of crystals with non-primitive cells, the nodes that correspond to «fading» reflections are actually absent in the reciprocal lattice. The research results are addressed to specialists in the field of crystal physics and represent a rigorous proof that fills a gap in the mathematical apparatus of the kinetic theory of scattering by crystals with non-primitive Bravais cells. It allows eliminating redundant statements about the «extinction» of part of the reflexes that are not recorded on X-rays due to their real absence from scientific circulation.
Equivalent circuits of FeCoZr-alloy nanoparticles deposited into Al2O3 and PZT dielectric matrices nanogranular composite films
The paper presents equivalent substitution circuits (ESCs) describing nanogranular composite films (Fe0.45Cо0.45Zr0.10)x(Al2O3)1 – x and (Fe0.45Cо0.45Zr0.10)x(PZT)1 – x with a concentration of metal-containing granules in the range 0.3 < х < 0.8. Films of 2–7 μm thick were obtained by ion-beam sputtering of composite targets in pure argon or in Ar – O2 mixture, followed by stepwise (with a step of 25 K) isochronous (15 min) annealing in air in the temperature range of 398 – 873 K. Deposition of nanocomposites in an oxygen-containing atmosphere or subsequent annealing in air led to the formation of nanoparticles with a core – shell structure consisting of Fe0.45Cо0.45Zr0.10 metallic alloy cores coated with shells of native iron and cobalt oxides (FeO, Fe3O4, Fe2O3, CoO). It has been established that when such shells contain semiconductor-type iron oxides (like FeO and Fe3O4) the frequency dependences of the total impedance Z (f, T) of nanocomposites can be described using ESCs containing two resonant RCL-circuits, that is accompanied by a positive phase shift of the current relative to the applied bias voltage (the so-called negative capacitance effect). The prevailing of dielectric-like oxides (Fe2O3) in shells around metallic cores leads to ESCs either with one resonant RCL-circuit or without it at all. This results in disappearing of the negative capacitance effect when usual capacitive-like behaviour of nanocomposite behaviour is observed. It is shown that if we construct ESCs for nanocomposites with different ratios of the metallic (FeCoZr) and dielectric (Al2O3, PZT) components, it is possible to describe the Z (f, T) dependences for every circuit elements (R, C, L) corresponding both to individual phase components in nanocomposites including intrinsic semiconductor- or dielectric-like iron and cobalt oxides in shells around metallic cores.
Electrophysical characteristics of power MOSFETs additionally implanted with nitrogen ions
The electrical characteristics of power MOSFETs additionally implanted with nitrogen ions have been studied. Ion implantation of nitrogen was carried out through a protective oxide of 23 nm thickness with energies of 20 and 40 keV and doses of 1 ⋅ 1013‒5 ⋅ 1014 cm–2. Rapid thermal annealing was carried out at temperature of 900 or 1000 °C for 15 s. It has been established that nitridisation of the gate dielectric makes it possible to reduce the noise of the gate leakage currents and their dispersion. In the direct order of heat treatment (first rapid thermal annealing, and then the removal of the protective oxide), for samples prepared with an additional operation of nitrogen ion implantation, there is an increase in the threshold voltage compared to control samples. The capacitance of the gate dielectric in the case of implantation of nitrogen ions in the direct order of heat treatment is less than for control samples. It has been established that in the direct order of rapid thermal annealing, the doses of nitrogen ion implantation do not cause significant changes in the maximum value of the current-voltage slope. At the same time, in all studied cases, there is a shift in the maximum value of the current-voltage slope towards higher gate voltages. In the reverse order of heat treatment (first the removal of the protective oxide, and then rapid thermal annealing), there are no significant differences in the value of the threshold voltage for the samples created with additional nitrogen implantation and the control ones. The maximum value of the current-voltage slope also does not experience significant changes. It is shown that in the voltage range from – 0.15 to 0 V, the drain current of nitrogen-implanted samples manufactured using the direct order of heat treatment is higher than for control samples, and the drain current of nitrogen-implanted samples obtained with the reverse order of heat treatment it is lower compared to control samples. Results are explained by a decrease in the density of surface states at the Si – SiO2 interface in MOS-structures created using an additional operation of nitrogen ion implantation in the direct order of heat treatment.
Thermal and thermoelectric properties of ceramics based on zinc oxide alloyed with iron
In this work, we study the effect of adding iron oxides FeO and Fe2O3 in a ratio of 1 : 9 on the thermal and thermoelectric characteristics of ceramics based on zinc oxide ZnO. The samples themselves were made in two stages based on the ceramic technology of sintering powder mixtures in an open atmosphere. Thermal conductivity studies point to the dominant contribution of lattice thermal conductivity at room temperature. The decrease in thermal conductivity as a result of alloying is due to an increase in phonon scattering at point defects introduced into the ZnO lattice (due to the replacement of zinc ions by iron ions) and at grain boundaries (due to microstructure refinement), as well as an increase in porosity (a decrease in density) and the formation of particles of an additional ZnFe2O4 ferrite phase. Alloying wit iron and the accompanying change in the structure of ceramics (decrease in grain size, increase in porosity, precipitation of the ferrite phase) leads to an increase in the thermoelectric figure of merit ZT by 2 times (due to a decrease in electrical resistivity and thermal conductivity with a relatively small decrease in the thermoelectric coefficient). The results obtained can be used to fabricate ZnO-based ceramics with optimal thermoelectric characteristics.
Influence of high-temperature ion irradiation on nanostructured TiAlN coatings
Nanostructured TiAlN coatings were formed on AISI 304 stainless steel substrates by reactive magnetron sputtering. The studied TiAlN coatings were irradiated with Ar+ ions with an energy of 200 keV in the fluence range from 2.5 ⋅ 1016 to 2.0 ⋅ 1017 ion per 1 cm2 at a temperature of 480 °C. Using energy-dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction phase analysis, the elemental composition, structural-phase state and morphology of the initial and irradiated coatings were studied. Nanoindentation of the obtained structures was carried out according to the method of Oliver and Pharr, the nanohardness (Н) and Young’s modulus (E) were determined, and the impact strength of the coatings under study was calculated as the H/E∗ ratio. The formation of a single-phase structure of the (Ti, Al)N solid solution in the coatings initial state has been detected. The effect of selective sputtering of the lightest component – nitrogen – from the coatings was found. Up to an irradiation fluence of 1.0 ⋅ 1017 ion per 1 cm2, no significant changes were revealed in the structural-phase state of the coatings. When irradiated with a fluence of 2.5 ⋅ 1016 ion per 1 cm2, an improvement in the TiAlN coatings strength properties complex was observed. It has been found that nanostructured TiAlN coatings are radiation-resistant up to an irradiation fluence of 2.0 ⋅ 1017 ion per 1 cm2, at which the onset of segregation of the (Ti, Al)N solid solution as the main phase of the coatings and blistering effect is observed.
Classification of Norway spruce drying states on the basis of reflection spectra
The article is devoted to the development of a method for classifying the reflection spectra of spruce needles of different health categories and assessing the quality of the classification. Such health categories of spruces have been chosen that include the initial stages of drying out, which is essential for early detection of disease foci, but makes it difficult to classify according to visual criteria by means of remote sensing of the Earth. An algorithm for untrained classification and visualisation of spectral data based on correlation and cluster analysis is proposed. The reflection spectra of spruce needles obtained under laboratory conditions were studied and the results were interpreted using the developed software. The analysis of various combinations of parameters within the proposed algorithm, as well as combinations of individual components of the algorithm with known classification methods, made it possible to determine the most effective combination of parameters and classification methods (projection of spectra into the space of principal components, elimination of the influence of the first principal component on spectra, the Ward cluster linking metric and the standardised Euclidean metric for calculating the spectral distance) for detection of different stages of spruce disease. Its use to made it possible to increase the F-score classification quality indicator for the 2nd health category (the most important category for the task of detecting drying in the early stages) up to 70.59 %.
Liquid crystalʼs photoalignment for formation of phase profiles via geometric phase distribution
Basic understandings on the concept of geometric phase, also known as Pancharatnam – Berry phase, and its application to creation of photonic liquid crystal devices as thin-films of photoaligned nematic liquid crystals are presented. The significance of the strong azimuthal anchoring energy and the role of birefringence in liquid crystal photoalignment layer for formation of geometric phase gradients are shown. The dependence of phase retardation of circular polarised light passing through the half-wave phase plate on the azimuthal angle of the plate orientation is explained in details, as it gives ground to formation of geometric phase distribution of optical liquid crystal devices, working in circular polarised light. The effective refractive index is introduced for characterisation of the optical properties of linear periodic liquid crystal’s structure that forms profile of geometric phase surface. The successful implementations of photonic liquid crystal devices (polarisation diffraction grating, annular diffraction grating, q-plate, q-plate with a phase core) are analysed in terms of geometric phase distributions and the corresponding equations of profile of the phase surfaces that ensure functioning of the devices are presented.
Estimation of the contribution of scattered ionising radiation to the dosimeter readings during measurements inside a low-background chamber
The article evaluates the contribution of ionising gamma radiation scattered by structural materials when measuring the dose rate in a low-background chamber. The contribution of scattered radiation to the total dose rate was estimated using Monte Carlo simulations. A model of a low-background camera and a BDKG-05K dosimeter was created in the computer program Fluka. In addition, a model of a point source of 137Cs gamma radiation was placed in the low-background chamber. The fraction of scattered radiation was calculated by comparing the dosimeter readings when measuring the dose rate inside the low-background chamber with the reference model (the dosimeter model is placed together with the source in a vacuum, as a result, scattered radiation is completely absent). The calculation was carried out for two positions of the dosimeter relative to the source (30 and 100 cm). It was found that the contribution of scattered radiation to the dose rate reaches 38 % (distance from the source to the detector is 100 cm). To minimise the contribution of scattered radiation to the readings of the dosimeter, a design in the form of a collimator, inside which the source is located, was considered. Additionally, the work investigated the dependence of the dose rate formed by the scattered radiation on the design features of the collimator. It was found that the use of a collimator makes it possible to reduce the contribution of scattered radiation to 3 %. The aim of the work was to calculate the optimal design of the collimator, in which the contribution of scattered radiation to the total dose rate will be minimal. The results of the work will be used to create a prototype of a low-background camera and an optimised collimator.
Determination of the Bessel light beam cone parameter by Fourier analysis of the diametral distribution of the intensity
Power spectral density (PSD) of the intensity distribution of an ideal Bessel light beam (BLB) expressions are obtained. It is shown that the PSD of the intensity distribution of an ideal BLB is limited and the upper boundary of the PSD is equal to the doubled cone parameter (the product of the wave number and the sine of the half angle of the cone of wave vectors), and the number of zeros in the PSD of an ideal BLB located in the interval from zero frequency to the upper boundary of the spectrum, is equal to the order of the beam. A technique is proposed for estimating the cone parameter of BLBs by analysing the PSD estimates of diametral distributions – one-dimensional intensity distributions obtained in the transverse plane of the beam along a line passing through the beam axis from transverse two-dimensional BLB intensity distributions recorded in the form of digital computer images. The influence of clipping (the end of the distribution at the boundary of the sensitive sensor), Gaussian and cosine modulations of the diametral distribution on the shape of the spectrum and, in case of clipping, the error in the cone parameter estimation using the proposed method is investigated. The technique is tested on the example of the analysis of experimental BLBs of different orders (BLBm, m = 0, 1, 2). The proposed technique can be used to assess the quality parameters of the BLB. The results of the analysis of the influence of cosine modulation on the shape of the PSD can be used to assess the magnitude of the rounding of the apex of the axicon forming the BLB for control the quality of the axicon manufacturing.
Method for studying the photostability of solar cells based on organic-inorganic perovskites using a confocal spectrometer
A method for studying photosensitive structures using the example of studying the photodegradation and dark recovery of organic-inorganic perovskite solar cells is present. The method is based on the use of a confocal spectrometer to measure Raman spectra, photo- and electroluminescence spectra and kinetics, the kinetics of the short-circuit current and the open-circuit voltage under local exposure to monochromatic radiation. Raman spectra make it possible to establish the presence or absence of secondary phases, the formation of which is possible in photosensitive layers under the influence of light. The photoluminescence spectra enable to reveal the single-phase nature of the object under study. Mapping the intensity and position of the center of mass of the photoluminescence band in the plane of the object makes it possible to judge the spatial arrangement of the centers of non-radiative recombination of charge carriers, the distribution of the regions with the highest and lowest efficiency of the extraction of charge carriers by transport-acceptor layers and the spatial homogeneity of the chemical composition. Comparison of the electroluminescence spectra before and after light exposure allows revealing the formation of non-radiative recombination centers in the photoabsorbing layer and at interfaces with the transport layers. Analysis of the kinetics of changes in the parameters of the photoluminescence band obtained by measuring the short-circuit current and the open-circuit voltage makes it possible to establish the dominant photoinduced processes leading to a change in the intensity of the photoluminescence band.
Analytical diagonalisation of the Hamiltonian of the quantum Rabi model in the Coulomb gauge
In the present paper we investigate the approximate analytical diagonalisation of the Hamiltonian of the quantum Rabi model written in the Coulomb gauge and taking into account the gauge invariance of the system. It is shown that the Hamiltonian of the model can be diagonalised with high accuracy on the basis of a unitary operator of the gauge transformation utilising a simple basis set of state vectors. It is essential that the obtained approximate expressions do not depend on the variational parameters and are valid within the whole range of the parameter values. The zeroth-order approximation and uniformly available approximation are derived for the eigenstates of the system, and their comparison with the results of the numerical simulation is elaborated. The second-order correction to the zeroth-order approximation is deduced and its contribution to the energy of the system is estimated. The obtained results could be useful for description of the evolution of the quantum Rabi model as well as for investigation of systems of two-level atoms in the resonant quantum field.
Charging properties of thin gate dielectrics, obtained by the method of rapid thermal processing
The charge properties of thin dielectrics, obtained by rapid thermal processing (RTP), and their interfaces with silicon for MOS transistors are investigated. The production of insulator layers was carried out by a two- or three-stage RTP with photon processing regimes similar for each stage (duration – 12 s, maximum temperature – 1250 °C). After the third stage of RTP in a nitrogen atmosphere of the gate oxides, obtained by a two-stage process in oxygen atmosphere, the defects responsible for local charge centers are partially eliminated. There is also an increase in the relative value of the surface potential by an average of 100 relative units. The elimination of defects is a consequence of the rearrangement of the structure of the dielectric, its interface with silicon, and the diffusion of oxygen and silicon atoms along the interface of the insulator layer. For samples obtained by a two-stage RTP in an oxygen atmosphere and subjected to the third stage of processing in a forming gas, there is an almost complete elimination of local charge centers and an increase in the relative value of the surface potential by an average of 300 relative units. In this case, in addition to the processes occurring during the treatment of SiO2 by the RTP method in an nitrogen atmosphere, the liquidation of charge centers is a consequence of the passivation of defects by hydrogen atoms.
Hydrogen-phase naklep as a result of single isothermal hydride transformations
Hydrogen treatment of metallic materials is a promising area of controlled hydrogen action on metals and alloys in order to impart special properties to them. In this work, the changes in the mechanical properties of palladium during single hydride transformations, which are initiated in the initially non-nakleped palladium hydride, have been experimentally studied. Were investigated wire palladium samples with a purity of 99.98 %, a diameter of 0.5 mm and a length of 165 mm. Samples for research were preliminarily subjected to hydrogen treatment, and then mechanical tests were carried out. The mechanical properties of non-nakleped palladium hydride are presented. Hydrogen-phase naklep of palladium during hydrogen treatment has been studied. It is shown that palladium hydride is a plastic material with low strength characteristics. During the reverse hydride transformation, the hydrogen phase naklep of palladium develops. Experimental facts of the appearance of hydrogen-phase naklep during the interaction of hydrogen with other metals and alloys are discussed.
The structure of rapidly solidified foil of Al – Bi alloys
The results of study of the microstructure and texture of aluminum alloys, containing 0.12 and 0.25 at. % Bi, obtained with high-speed solidification, are presented (melt cooling rate liquid – not less 105 K /s). Texture (111) aluminum is formed in the rapidly solidified foils of investigated alloys and it is conserved under annealing at 523 K during 2 h. The average chord of bismuth sections does not exceed 0.05 µm. As the crystallisation front moves from surface A contacted with crystalliser to the surface B, the average size of dispersed bismuth particles increases. Foils of the alloys dissolve in water at room temperature actively forming hydrogen bubbles in vessel with water, white powder of aluminum oxide in an amorphous state and bismuth precipitations. Isotermical annealing of foils at 573 K for 5 h causes a change in distribution of chords in size groups and increases their average value. After the annealing bismuth particles are localised on low- and high-angle boundaries. The rapidly solidified foils of Al – Bi system can be used to produced hydrogen, aluminum oxide powder and create technical devices using hydrogen.
Recording the dynamic polarisation gratings in pure nematic liquid crystal
We report on experimental realisation of polarisation dynamic gratings recording in pure nematic liquid crystal. This work is devoted to the experimental implementation of writing polarisation dynamic gratings in a pure nematic liquid crystal. The registration mechanism is based on the photorefractive effect in a cell filled with a pure nematic crystal under the action of an applied constant electric field. This phenomenon does not require the presence of photoexcited charge carriers in the liquid crystal and is explained by the extremely high anisotropy of the liquid crystal. The article provides an elementary theoretical model of this process. The dependences of the grating writing process on the spatial frequency of the interference field and the intensity of the recording beams are investigated. It was found that the spatial grating does not coincide with the interference field – the response of the medium is non-local. However, we do not associate this property with that in photorefractive crystals. In our case, a mechanism of purely geometric mismatch is more likely due to the peculiarity of the recording mechanism. One of the fundamental properties of the described processes is their independence from the wavelength of the recording radiation, which confirms the model of the recording mechanism we have chosen.
Determination of the parameters of two-beam laser splitting of silicate glasses using regression and neural network models
The current work takes the results of the numerical experiment implemented in the Ansys finite element analysis program to create the neural network and regression models of two-beam laser splitting of silicate glasses. The regression models of two-beam laser glass cutting have been obtained in the DesignXplorer module of Ansys Workbench using a face-centered version of the central composite design. The processing speed, the parameters of laser beams, the glass plate thickness, and the distance between the laser radiation and the refrigerant affected zones were used as variable factors. The maximum temperatures and thermoelastic tensile stresses in the laser processing area were used as responses. The artificial neural networks have been constructed and trained using the TensorFlow package. The results of determining the maximum temperatures and thermoelastic stresses in the laser treatment area using the neural network and regression models have been compared.
Transport properties of two-component radium – halogen dilute gas media
Based on state-of-the-art ab initio potential energy functions and classical kinetic theory, some transport properties (diffusion, viscosity and thermal conductivity coefficients) of two-component dilute gas media of radium and halogen (F, Cl, Br, I) atoms were predicted as functions of the translation temperature up to 3000 K. Calculations were performed by sequential analytical and (or) numerical computations of deflection angle, cross-section and collision integrals. A detailed methodology for the calculation of the transport properties using the Morse potential was developed. Some numerical difficulties arising due to the singularity of the integrands and discontinuous character of the variable of integration are considered. The dependence of transport properties on isotope mass is also shown. Possible errors introduced by using the model Morse potential function instead of the real potential for the interaction between atoms are estimated. These data can be useful for the planning of the experiments on the direct laser cooling of the monohalides of alkaline earth metals.
Crystal growth and f – f transition intensities analysis of praseodymium ions in yttrium-aluminum orthoborates
A Pr3+ : YAl3(BO3)4 crystal with sizes of 20 × 10 × 10 mm was grown from high-temperature solution and its structural and spectroscopic properties were investigated. The distribution coefficient of praseodymium ranged from 0.6 to 0.8, that yield to the Pr3+ ion concentration of 1.1 ⋅1020 cm–3. Visible and infrared groundstate absorption (3H4) was measurement in dependence on the polarisation. The absorption spectra of the Pr3+ : YAl3(BO3)4 exhibit pronounced polarisation anisotropy. The modified Judd – Offelt theory was applied to evaluate the transitions intensities in absorption and emission, branching ratios and radiative lifetimes of the metastable levels 3P0 and 1D2.
Outlook for nuclear physics research in Belarus
The future nuclear physics research capabilities for scientists from Belarus are discussed. The following branches for the activity: megascience class research platforms created in Russia and the European Union, a new generation of ionizing radiation sources, use of the world nuclear science network for short-term research and, monitoring of nuclear power plants are debated. The purposes of nuclear physics research are suggested to be a balanced combining of the further penetration deep into the matter, to clarify its status and time evolution and, the routine activity associated with clarifying the details of the world, for which sufficiently well-developed models have already been created. Further, the goals of nuclear physics research are specified. They include preventing the loss of knowledge in the field of nuclear physics; conservation of the acceptable qualification and its reproducibility, maintaining the appropriate level of the engineering corps for the perception of the latest knowledge. This article is based on the author’s personal experience in participating in projects of high scientific significance. The route of considering the areas of application of nuclear physics scientists’ efforts is formed according to the principle of maximum return from the highly qualified personnel (PhDs and doctors of science). Ain importance of training undergraduates and graduate students for a scientific career is underlined. Finally, a need to maintain a high level of knowledge in the branch for the expertise upon the request of the government to secure and develop the country is pointed out.
Atomic Nucleus and Elementary Particle Physics
Copyright (c) 2021 Journal of the Belarusian State University. Physics
Improving the efficiency of an industrial silicon solar cell by doping with nickel
The possibility of adjusting the operational parameters of industrial solar cells produced by the company Suniva based on monocrystalline silicon by means of additional diffusion doping with nickel in the temperature range 700–1200 °C has been investigated. It is shown that the optimal temperature of nickel diffusion is Tdiff = 800–850 °C. In this case the value of the maximum power Pmax increases by 20–28 % in relation to the parameters of the original industrial photocell. At diffusion temperatures Tdiff > 1000 °C, a sharp decrease in Pmax occurs, which is associated with an increase in the depth of the p–n-junction due to the distillation of phosphorus atoms during high-temperature diffusion of nickel. The positive effect of diffusion alloying with nickel on the electrophysical parameters of photocells is greatest in the case when the nickel impurity clusters are in the region of the p–n-junction, i. e. with diffusion alloying to the front side of the plate. The action of electrically neutral nickel clusters is less pronounced when they are located in the region of the isotypic p–p+ transition; in case of diffusion alloying with nickel in the opposite side of the plate.
Formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors
The paper presents a study of the formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors. The recording process of holographic gratings at the argon-laser radiation wave length 488 nm and the process of chemical etching that enables the formation of а relief holographic grating are analysed. The optimum conditions for the formation of diffraction gratings in films of arsenic sulfide As2S3 are defined. It is shown that at the 488 nm wave length of an argon laser the optimum exposure comes to ∼5–8 J/cm2. At the recording stage a quasi-phase (relief-phase) grating is formed, with the diffraction efficiency on the order of a few per cent. Etching of the exposed sample with a solution of NaOH alkali in deionised water and isopropanol makes it possible to increase considerably the relief depth and to improve the diffraction efficiency of a thin diffraction grating approximately up to 20 % for the red spectral region, and to approach the maximal value ∼34 % for the near infra-red region. The results of the study considered look promising for the creation of relief holographic gratings which are essential in present-day optical instrument building (production of spectral devices, holographic sights, and the like).
Incoherent ultrarelativistic channeling particle scattering by electrons
The problem of high-energy charged particle motion in the field of atomic strings and planes of oriented crystals, widely applied to control large accelerator beams and generate intense gamma radiation, is addressed. Following the previously developed theory of channeled particles incoherent scattering by crystal atom nuclei, we consider here the same by crystal atom electrons. The theory developed takes into consideration all the effects of momentum transfer between fast particles and electrons of atoms in a crystal in the range from the nuclear radius up to the many inter-atomic distances. The theory also includes the temperature-dependent Debye – Waller factor, as well as both the atomic form factors and scattering function, evaluated with the detail consideration of atomic structure. All the modifications of electron scattering in crystals are reduced to the value of the effective minimum momentum transfer, which by an order of value exceeds that one, related with the Bethe – Bloch mean atomic energy. Substituting this quantity to the expression for the mean square of the scattering angle of a classically moving particle makes it possible to compare the scattering by electrons and nuclei, while its joint use with the Rutherford cross section allows for the correct simulations of the planar channeling of positively charged particles in the thickest crystals, supposed to be used for the beam extraction from high energy accelerators, measurement of electromagnetic characteristics of short-living particles and development of intense narrow-band X-ray and gamma radiation sources based on crystal undulators.