Poverhnostʹ. Rentgenovskie, sinhrotronnye i nejtronnye issledovaniâ

The effect of volume capture of fast charged particles in a curved single crystal has been studied. The transverse energy losses, the hanging effect, and the criterion for volume capture of fast charged particles have been investigated. Possible mechanisms of volume capture are considered: transverse energy losses due to crystal excitation by a fast charged particle (proton, lepton); multiple scattering of particles in a curved crystal; elastic scattering and diffraction of particles in a curved crystal. It is shown that in the hanging region, the ratio of the velocities of transverse and longitudinal energy losses of fast charged particles increases significantly compared to the ratio of longitudinal and transverse energies and is equal in order of magnitude to the ratio of the off-diagonal elements of the inverse dielectric susceptibility matrix to the diagonal ones. It is established that the effect of volume capture of fast protons (leptons) is due to diffraction in a curved crystal, as well as the effects of damping of the off-diagonal elements of the particle density matrix. The proposed diffraction mechanism is based on taking into account quantum coherent scattering of a fast proton (lepton) in a curved crystal.

Images of the distribution of microfocus bremsstrahlung from a new source based on an 18 MeV betatron, which has passed a 0.4 mm thick steel plate with a 1.2 mm wide sharp edge, are presented. The photographs demonstrate an anomaly in the interaction between the microfocus bremsstrahlung and the plate tip in the form of a narrow dark stripe along the tip image, which indicates an increase in the radiation intensity in this area. The dark stripe provides a contrast in the tip image, which, together with the high sharpness due to the microfocus of the source, allows the tip position to be visualized with high precision. The dark stripe in the images was not observed when using radiation from 450 and 45 keV X-ray tubes with foci of 400 and 100 µm. The absorption of radiation ensures a smooth change in the blackening of the sharp edge and blurring of the tip in the image due to the size of the radiation source. The observed effect with microfocus radiation of the new source is determined by the scattering of radiation by the tip with the possible participation of wave effects, which needs to be further investigated.

The results of the study on the radiation resistance of optical properties of ZrO₂ micropowder modified with MgO nanoparticles after electron irradiation (E = 30 keV, Φ = 2 × 10¹⁶ cm^–2) are presented. It has been found that modification with MgO nanoparticles does not lead to the formation of new types of radiation defects; however, the number of formed radiation defects decreases with an increase in MgO content. When modified, radiation resistance increases by 1.7 times compared to unmodified samples.

A comparative analysis in situ of diffuse reflection spectra in the range from 200 to 2500 nm and their changes after irradiation of coatings based on polymethylphenylsiloxane resin and pigment powders of two-layer hollow particles ZnO/SiO₂ and SiO₂/ZnO was carried out. Irradiation was performed with light from a xenon arc lamp simulating the solar radiation spectrum, with an intensity of 3 e.s.i. (equivalent of solar irradiation, 1 e.s.i. = 0.139 W/cm²). The photostability of the studied coatings based on two-layer hollow ZnO/SiO₂ and SiO₂/ZnO particles was estimated relative to coatings based on ZnO polycrystals from an analysis of the difference diffuse reflectance spectra obtained by subtracting the spectra of unirradiated and irradiated samples. It has been found that the intensity of the induced absorption bands in coatings based on ZnO/SiO₂ and SiO₂/ZnO hollow particles is lower than in coatings based on ZnO microparticles, and the radiation resistance when assessing changes in solar absorptance (Δα_S) is twice as high. The increase in photostability is probably determined by the different nature of defect accumulation: for bulk microparticles, radiation defects can accumulate inside the grains, while in hollow particles, the accumulation of defects can occur only within the thin shell of the sphere.

The features of radiation-induced positive charge accumulation in the gate dielectric film under high-field injection of electrons at the constant voltage are studied. The conditions are determined, under which the current injection mode can be used to increase the dose sensitivity of MOS (metal–oxide–semiconductor) and RADFET (Radiation sensing Field Effect Transistor) sensors. The model describing physical effects taking place in the gate dielectric and at the MOS structure interfaces under concurrent influence of radiation and high-field injection of electrons at constant voltage are improved. It is shown that the absorbed radiation dose at constant voltage on the sample can be calculated from changes in the current density of high-field electron injection. This dose can increase by several orders of magnitude due to the accumulation of radiation-induced positive charge in the gate dielectric. The influence of radiation intensity on the accumulation of radiation-induced positive charge in the gate dielectric of MOS sensors is determined.

To explain the increased yield of positive particles from the surface of a positively charged dielectric, a computer simulation was performed using the density functional theory. The model system was a fragment of a Teflon molecule (CF₂) in a vacuum. The binding energy of atoms in this system in the neutral state (without removing electrons from the system) was calculated, after which a similar calculation was performed for an ionized fragment of the Teflon molecule (with the removal of one electron from the system of atoms). The calculations showed that the energy of complete dissociation of one fragment of the Teflon molecule in the neutral state is 11.02 eV, which agrees with the experimental data with good accuracy. The binding energy in the ionized fragment of the molecule is 2.86 eV, while the Teflon molecule fragment dissociates into a neutrally charged fluorine atom and a positively charged CF fragment. In calculations taking into account the dipole moment of the Teflon molecule fragment, the binding energy value was equal to — 2.75 eV, the Teflon molecule fragment also dissociated into a neutral fluorine atom and a positively charged CF fragment. The obtained results may be the reason for the increased release of positive particles from the surface of a positively charged massive dielectric.

Recently, there has been rapid development of technologies for creating flexible and stretchable optoelectronic devices. A promising material in terms of fundamental properties is the inorganic halide perovskite CsPbBr₃, whose electroluminescence brightness can reach 45.000 cd/m². However, the most common thin-film technology of perovskite-based devices cannot solve a number of significant problems: ensuring the stability of the perovskite to the environment, creating tensile-resistant contacts, ensuring efficient injection of carriers into the electroluminescent layer, etc. To solve these problems, the authors developed a new device architecture based on a distributed electrode, which uses an array of whisker nanocrystals embedded in the light-emitting layer, thus solving the fundamental problem of the short lifetime of CsPbBr₃ carriers. The device is enclosed in a special silicone polymer — a transparent inert flexible and stretchable matrix that protects the CsPbBr₃ perovskite from environmental conditions and maintains the orientation of the arrays of whisker nanocrystals. 90% transparent single-walled carbon nanotubes, which have a high tensile strength and low electrical resistance, were used as an electrode providing lateral transport of carriers. Thus, a flexible device with high electroluminescence efficiency was obtained.

Using X-ray diffraction analysis, the patterns of changes in the atomic structure in Cu-NbTi composite materials were studied at P = 50 atm, with a moving Poisson rotation speed of 0.5 rpm. and rotation speed n = (0–5) rpm. as a result of the action of batch hydroextrusion on the samples. It was found that the samples contain different-sized structural formations with long-range, mesoscopic and short-range atomic order. It is shown that the non-monotonic change in atomic order, with an increase in the number of revolutions of rotation of the mobile Poisson, is due to the structural phase transition of order-disorder into a state with the formation of different-sized atomic groups with long-range, mesoscopic and short-range atomic order, in which the manifestation of new interatomic interaction forces characterizing the formation of intermetallic clusters of atomic groups. It was found that already in the initial state after compacting the samples, the presence of clusters in the copper matrix phase containing niobium and titanium is observed, which characterizes an increase in heterophase in the sample system under study. The result is a homogeneous finely dispersed material containing uniformly distributed multi-scale fractions of metallic and intermetallic phases in the form of crystalline, mesoscopic and amorphous fractions. This structure exhibits increased strength, which is noticeable in the form of an increase in microhardness from 1.56 GPa to 4.15 GPa.