Nº 4 (2025)

Despite the large number of already published articles on the topic of ferroelectric properties of Hf_0.5Zr_0.5O₂ (HZO), this material still attracts enormous attention of the scientific community due to the prospects for creating competitive non-volatile HZO-based memory devices compatible with modern silicon technology. Among the difficulties on the way to creating industrial technology for such devices is the instability of the residual polarization of the ferroelectric during multiple switching by an external electric field. In particular, at the initial stages of such “cycling”, as a rule, a significant increase in residual polarization is observed (the so-called “wake-up” effect), and then, after a certain number of cycles, its decrease (the so-called “fatigue” effect). The question of what processes lead to such instability remains debatable. Using the previously developed methodology for analyzing the phase composition of ultrathin HZO layers by the NEXAFS synchrotron radiation method, it is shown that in capacitors based on TiN/HZO/TiN structures, the “wake-up” effect observed during the first 10⁵ switching cycles is explained by an increase in the relative content of the polar orthorhombic phase in HZO due to a decrease in the content of the “parasitic” tetragonal phase. The obtained results confirm the electric field-stimulated structural phase transition in films as one of the mechanisms explaining the evolution of the functional properties of ferroelectric memory elements based on HZO throughout their service life.

A crystallographic theory of martensitic transformations has been developed, which adequately describes their real mechanisms. A mathematical description of real processes occurring during martensitic transformation has been obtained as a product of four matrices: P₁ = R₁PB₁Г, where Г is the shear deformation of the austenite lattice, В₁ is its additional “pure” deformation, the main axes of which coincide with the shear direction, with the normal to the shear plane and, accordingly, with the transverse direction, Р is the deformation of martensite with an invariant lattice, R₁ is a slight rotation of the martensite plate to obtain an invariant plane (relaxation rotation). All four processes occur almost simultaneously, but in the specified sequence. Crystallographic analysis of eight alloys based on the theory allowed obtaining a number of important results. A relaxation rotation has been detected during martensitic transformations. A relationship has been found between the relaxation rotation and martensite texture dispersion. The mechanism of packet structure formation during polymorphic transformation in a zirconium single crystal has been established. The real mechanisms of deformation during martensitic transformations in these alloys have been established.

The process of of non-stationary diffusion of nonequilibrium minority charge carriers is considered by mathematical modeling methods, which is realized after the termination of the effect of an electronic probe on a homogeneous semiconductor target. For a low-energy (up to 10 keV) electron probe, a mathematical model of two-dimensional diffusion of charge carriers in a homogeneous semiconductor material is proposed, taking into account the dynamics of changes in target temperature after the termination of electron irradiation of the probe. When calculating the dependence on the coordinates of the density of nonequilibrium minority charge carriers generated by an electron probe, a mathematical model of energy loss by primary electrons was used, taking into account the separate contribution of electrons that experienced small-angle scattering and absorbed into the target and the contribution of backscattered electrons that experienced a small number of scattering at large angles and left the target. The differential equation of thermal conductivity is solved approximately using the projection method. The quantitative description of the temperature dependences of the effective lifetime and the diffusion coefficient of the generated charge carriers was carried out taking into account the available results of experimental electron probe studies of cathodoluminescence of homogeneous monocrystalline gallium nitride. Model calculations have been performed for the diffusion of excitons in homogeneous monocrystalline gallium nitride in the presence of two independent recombination channels of nonequilibrium charge carriers.

Studies have been carried out of the influence of a high-power ion beam of nanosecond duration on the atmospheric oxidation of polycrystalline magnesium. A decrease in the magnesium oxide phase was detected with increasing beam current density, which is probably due to the intensification of the processes of gas-dynamic expansion of the surface. Subsequent exposure of unirradiated and irradiated samples to a powerful ion beam at a temperature of 240°C in air led to a slowdown in the growth of the oxide phase in the irradiated samples. In this case, the greatest effect was observed for samples irradiated by a beam with a current density of 150 A/cm². The role of chemical processes, mechanical stresses and structural changes occurring in the beam-modified zone and influencing the oxidation process is discussed. The observed nonmonotonic dependences of the ratios of oxygen and carbon concentrations to magnesium for different heating times are explained by the formation of not only magnesium oxide, but also probably magnesium hydroxide and carbonate. It has been shown that the effect of increasing the oxidation resistance of magnesium irradiated with a powerful ion beam can also be influenced by an increase in the concentration of carbon during its penetration into the surface layer.

The interest in Van-der-Waals structures is associated with their unique physical and chemical properties and the prospects for technological applications. In this work, the object of study is highly oriented pyrolytic graphite as a model of such materials. The experimental results of measuring the spectra of angle resolved X-ray photoelectron spectroscopy are presented. The experiments were performed for detection angles of 0°, 60°, 80° and 85° from the surface normal, which made it possible to maximally localize the XPS signal generated by the upper layer of the highly oriented pyrolytic graphite. A technique for reconstructing the differential cross section of inelastic electron energy losses from experimental X-ray photoelectron spectroscopy spectra is presented. According to this technique, the differential cross section of inelastic electron scattering in the highly oriented pyrolytic graphite was reconstructed for each detection angle. The obtained cross sections are compared with those reconstructed for graphene with a different number of layers. The determining influence of collective plasmon electron energy losses on the formation of the energy loss spectrum in heterogeneous Van der Waals structures is indicated.

The valence band of photoelectron spectra of complex samples (multicomponent samples, samples with oxide films, molecules adsorbed on the surface) has a complex structure, which complicates the interpretation of the contributions of various sample components to the spectral structure. A method is considered for interpretation of valence band spectra as a result of calculating the density of electronic states for a physical volume using quantum chemistry — an atomic model that most fully characterizes the sample under study. The optimal position of atoms in a given physical volume of the computational model was found using the iterative Broyden–Fletcher–Goldfarb–Shanno numerical optimization method taking into account the spatial distribution of the potential obtained from quantum chemical calculation. The calculation was performed using code written in Python using the ASE and GPAW libraries (atomic simulation environment and grid-based projector-augmented wave) on the equipment of a supercomputer computing cluster. The data obtained by calculation were compared with the measured photoelectron spectra of various systems, such as Ge(111), GeO₂/Ge(111), C₆₀F₁₈/Ge(111), and C₆₀F₁₈/GeO₂/Ge(111). The analysis made it possible to determine the contributions of various atoms and bonds to the final photoelectron spectrum, estimate the thicknesses of individual layers, and determine the types of bonds between molecules and the substrate.

In this work, nanopowders of the Bi_₁–хBa_хFeO₃ system (x = 0, 0.10, 0.20) were synthesized by the combustion method of nitrate-organic precursors. The effect of doping bismuth ferrite (BiFeO₃) with barium (Ba) ions on the morphology, crystal structure and photocatalytic activity of the material was studied. X-ray diffraction analysis showed that all samples crystallize into a rhombohedrally distorted perovskite structure with the R3c space group. Doping with barium led to a significant decrease in the crystallite sizes, as well as to a distortion of the crystal lattice. In the case of 20% substitution, the formation of BaCO₃ impurity was observed, which was also confirmed by the analysis of the Raman spectra. It is shown that the introduction of barium leads to the formation of a more porous texture and a significant increase in the specific surface area of the material. The original BiFeO₃ demonstrated an extremely low efficiency of methylene blue decomposition relative to photolysis, while doping with barium led to a significant improvement in the photocatalytic characteristics of the material: in the case of 20% Ba substitution, the decomposition of methylene blue reached 99% in 1 hour.

The parameters of electromagnetic radiation that should be generated during guiding of accelerated electrons (extended sliding interaction of accelerated electrons with a dielectric surface) pressed to the surface of a dielectric plate by an external electric field are calculated. The model of the effect (guiding) is proposed based on an analysis of the solution to the Hamilton equation for the motion of electrons in an external electric field and in an electrostatic field created by electrons deposited on the surface of a dielectric plate. Superposition of these fields leads to the fact that during guiding electrons experience transverse vibrations relative to the surface of the plate, i.e. acquire lateral acceleration. And this, as is known, should lead to the generation of electromagnetic radiation, the frequency and intensity of which depend on the electron energy, similar to the radiation of undulators and wigglers. Calculations show that when electrons are guided, radiation should be generated depending on their energy. The maximum of its intensity is in the region from IR to the radio frequency range.

The influence of ultrafine-grained structure and cone-shaped surface morphology on the formation of blisters under irradiation of tungsten with He⁺ ions with energy of 30 keV has been studied. In comparative experiments, ultrafine-grained and fine-grained samples with an average grain size of 300 nm and 7 μm, respectively, with smooth and cone-shaped surface morphology were used. The ultrafine-grained structure in tungsten samples was obtained by severe plastic deformation, and the cone-shaped surface morphology was obtained by high-fluence irradiation with Ar⁺ ions with the energy of 30 keV. It was found that blisters are formed on both fine-grained and ultrafine-grained samples when irradiated with He⁺ ions with a fluence of 10¹⁸ ion/cm². On the fine-grained samples, some of the blisters were with the lids removed, while in the ultrafine-grained samples, all blisters were intact. The thickness of the lids, diameter of the blisters depends on the grain size. The cone-shaped surface morphology on ultrafine-grained tungsten was found to suppress blister formation.