Moscow University Physics Bulletin最新文献

Iron chalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase segregation, where superconducting clusters form at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase segregation. We studied temperature dependences of the photoelectron spectra of Se 3d, Fe 3p, and the valence band at temperatures above and below (T_{c}approx 27) K of the compound (K({}_{0.8})Na({}_{0.2}))({}_{0.8})Fe({}_{1.8})Se({}_{2}) with substitution of alkali metal atoms. A strong temperature dependence was found for both the valence band and the core levels: we observed a significant broadening of the spectra, which monotonically decreased with increasing sample temperature under cyclical temperature change. We believe that this broadening is associated with the appearance of volume charges in the dielectric matrix, leading to the band bending. Moreover, the shape of the potential that arises under the surface of this compound was restored, and an estimate was obtained for the relative amount of the superconducting phase. These results will help to better understand the physical processes occurring in this compound.

In the study, numerical results of simulations for the deposition process of a complex optical coating are presented, utilizing broadband monitoring of this process in the case where the noise level in the measured transmittance coefficient has a nonuniform distribution across the wavelength. The influence on the accuracy of control data at the edges of the measured wavelength range, where the error in the transmittance coefficient is maximal, is investigated. It is shown that the removal of some data at the edges of the range almost does not change the self-compensation factor of the errors in the deposition process, while the average norm of the error vector in the layer thicknesses significantly decreases. Thus, for the first time, it is demonstrated that taking into account the effect of error self-compensation in broadband control opens the possibility of a reasonable choice of the optimal spectral range for practical optical control.

An analysis of the impact of high-energy cosmic radiation protons on the onboard electronics of the spacecraft was performed. It has been shown that protons can cause nuclear reactions with the atomic nuclei of electronics material. Residual nuclei formed as a result of a nuclear reaction have sufficiently high energy to cross the sensitive areas of several bits of electronics, and the high ionizing ability of nuclear fragments makes it possible to generate an excess charge of carriers that exceeds the critical charge for upsets to occur simultaneously in several bits of an electronic device.

Composite films of (Cd({}_{3})As({}_{2}))({}_{100-X})(MnAs)({}_{X}) on silicon and sitall substrates with Mn concentration of 5.8–16.4 at (%) were obtained by vacuum-thermal evaporation. The structural properties of the films were investigated by X-ray phase analysis and scanning electron microscopy. Magneto-optical properties were studied using the transverse Kerr effect (TKE) method in the energy range of 0.5–4.0 eV in magnetic fields up to 3 kOe at temperatures of 20–300 K. In the geometry of the transverse Kerr effect, the spectral, field, and temperature dependences of TKE were obtained. Analysis of experimental data showed that at Mn contents more than 12.9 at (%) the films contain the (alpha^{primeprime})-phase of the topological Dirac semimetal Cd({}_{3})As({}_{2}) in the form of large granules, as well as ferromagnetic MnAs granules. The Curie temperature of the films depends on their Mn content and is lower than that of bulk MnAs samples. At Mn contents in the film of 5.8 and 6.4 at (%), no magneto-optical response was detected, indicating the formation of a superparamagnetic state or a spin glass state at low Mn concentrations. At an Mn content in the film of 9.9 at (%), a significant change in magneto-optical spectra was observed, indicating the formation of MnAs nanoclusters and partial dissolution of Mn in the Cd({}_{3})As({}_{2}) matrix.

The unique protein Dsup of the tardigrade Ramazzottius varieornatus increases resistance to radiation and oxidative stress in various organisms and in human cell culture. According to simulation data, Dsup forms a complex with DNA with an intermolecular distance of ({sim}4) Å, as a result of which DNA is less damaged by reactive oxygen species generated during radiation exposure. However, the stability of the Dsup protein itself under the effect of ionizing radiation remains unclear, which is important for assessing its radioprotective potential and understanding the molecular mechanisms of action of this protein under conditions of high doses of radiation. In this work, the radiation degradation of the Dsup protein after irradiation with (gamma)-quanta using small-angle X-ray scattering (SAXS) and electrophoresis of proteins in polyacrylamide gel under denaturing conditions (SDS-PAGE) was studied for the first time. It was shown that, unlike the control protein bovine serum albumin, the spatial-structural characteristics of the Dsup protein remain almost unchanged even when exposed high doses of radiation (5 and 10 kGy), which indicates its high radiation stability.

Hafnium oxide films HfO({}_{x}) with a thickness of about 40 nm were obtained by electron beam sputtering at different oxygen flow rates in the chamber. The electrophysical properties of the films were studied in air and in a vacuum. It has been shown that the temperature dependences of film conductivity, measured in a vacuum in the temperature range from 20 to 180({}^{circ})C, have an activation character with an activation energy of 0.82(pm) 0.02 eV. It is assumed that in the resulting films, charge transfer is determined by the activation of electrons into the conduction band from the donor level associated with oxygen vacancies. It was found that the conductivity of the films in air changes greatly with varying the oxygen flow, while in a vacuum, the conductivity is practically independent of the oxygen flow. This indicates significant differences in the surface properties of the films obtained at different oxygen flows in the chamber during the deposition process.

The possibilities of engineering energy losses, created in the cascade process of electron-electron scattering during the interaction of multilayer dielectric structures with ionizing radiation, are considered. It is shown that the contribution of surface plasmons associated with layer boundaries to electron energy losses is significant only for nanometer layer thicknesses and increases with increasing electron energy. At the same time, surface states associated with longitudinal optical phonons in ionic crystals significantly change energy losses during electron thermalization and can lead to an increase in the efficiency and rise rate of scintillation in nanostructured systems.

An indirect-drive cryogenic target is necessary for research in the field of laser thermonuclear fusion at a megajoule energy level facility. Solid fuel layer in the target must meet high requirements: a roughness of the inner cryolayer surface must be less than 1 (mu)m, deviations from the sphericity and the concentricity must be less than 1(%). This paper describes the results of the research on meeting these requirements, notably, cryolayer formation and its characterization. Due to the slow crystallization method of the deuterium layer with its simultaneous heating by IR radiation, it is possible to obtain deviations from the sphericity and the concentricity of the inner cryolayer surface within limits of 2(%), the roughness, within limits of 20 (mu)m. Theoretical thermal calculations of the target construction are compared with experiment. The program system was developed using the optical shadow method which makes it possible to measure liquid fuel when filling the shell during the performance of the experiment, to perform the characterization of the solid cryogenic layer parameters, and to evaluate characterization results robustness.

An analysis of both experimental and theoretical data on the study of preferential sputtering of nickel-based and copper-platinum alloys under ion beam bombardment has been carried out. Contrary to existing models, it has been shown that the main factor determining the process of preferential sputtering is the ratio of the surface binding energies of the components.

Proposed as initial activation experiments for photonuclear research with (gamma)-quanta at energies (E_{gamma}leq 40) MeV are those using a source of backward Compton scattered laser radiation on accelerated electrons, which is currently under development. These experiments are crucial both for refining the techniques of tuning and monitoring such (gamma)-beams, and for investigating the excitation of pygmy and giant resonances in nuclei at (E_{gamma}) near the threshold of the ((gamma,n)) reactions, as well as the multiplicity of photoneutrons during the de-excitation of E1 giant resonances at (E_{gamma}) above the threshold of the ((gamma,2n)) reactions.