No 6 (2024)

The attenuation of vortex motion on the surface of shallow and deep water is investigated. The vortex flow was formed by two mutually perpendicular waves excited by plungers at a frequency of 6 Hz (wavelength λ = 5.6 cm) on the surface of water measuring 70 × 70 cm and depth h. After reaching a stationary state in the vortex system, the wave pumping was switched off, and the attenuation of the surface flow was recorded. On the surface of shallow water, λ/2π ≈ h, when the characteristic size of the vortices L exceeds the depth of the liquid, L >> h, the time dependence of the energy of the vortex flow Е(t) is described by an exponential function at all pumping levels, and the dependence of the enstrophy Ф(t) = Ω²(t) has an exponential dependence only in the range of wave vectors 0–0.3 см^–1. On the surface of deep water λ/2π < h, L ≈ h dependence Е(t) and Ф(t) are far from exponential in all ranges of wave numbers. At high pumping levels, the dependencies Е(t) and Ф(t) are nonmonotonic, which can be attributed to the influence of volumetric flows.

In the present work NiO and NiO–SiO₂ were investigated by X-ray diffraction and radial atomic pair distribution methods. By X-ray diffraction method, it was determined that the NiO particle sizes have coherent scattering region of more than 100 nm, while the NiO–SiO₂ sample has a particle size of about 2–3 nm. At the same time, full-profile Rietveld simulation does not describe the effects observed on diffraction: the asymmetry of peaks, the appearance of an additional shoulder of peak 111 in the area of small angles, so the radial atomic pair distribution method was used to analyze the structure. During the simulation of the experimental atomic pair distribution curve, 3 different models were used: pure NiO, a mixture of NiO and Ni₂SiO₄, and a modified NiO model with Si embedded in the lattice. The latter model was created based on the assumption of silicon incorporation into the NiO structure, which can be evidenced by X-ray diffraction data. According to the results of radial atomic pair distribution modeling it is the latter model that gives the best description of the observed effects: significantly increased unit cell parameter, compared to the sample without SiO₂ addition, as well as decreased metal cation–oxygen distances in the structure, while cation–cation distances are increased.

Based on the analysis of the angular distributions of particles passing through thin gold films, the parameters of the potential that best describes the experiment are obtained. The resulting potential differs from the potential describing collisions in the gaseous phase by a noticeable change in the screening constant. The influence of the collision energy, the choice of potential, and the model of electron bremsstrahlung on the depth distribution of implanted particles is analyzed.

This paper presents the main experimental results of measuring the density of beryllium bronze BrB-2, aged in the constant magnetic field and in its absence, using the hydrostatic weighing method. The temperature and time dependences of the density of beryllium bronze BrB-2 during the decomposition of a supersaturated solid solution in a constant magnetic field of strength 557.2 kA/m were studied, at aging temperatures of 250, 300, 350 and 400°C and aging duration from 0 to 1 hour, and a comparative comparison analysis of their behavior with the corresponding microhardness dependencies was carried out. The correlation was discovered between the temperature and time dependences of the density and microhardness of beryllium bronze BrB-2, so at an aging temperature of 350°C a sharp maximum in the density of the alloy is observed, and similarly, at the same point the absolute maximum microhardness is achieved. In addition, it was found that the application of a constant magnetic field to the aging process under all heat treatment modes always leads to an increase in the density and microhardness of beryllium bronze BrB-2 compared to the density of the alloy aged in its absence. A physical interpretation is given to the observed facts and patterns. In the future, it is planned to find a correlating function between two independent measured characteristics density and microhardness, which is important for solid state physics and materials science from a scientific and practical point of view.

The velocity effect was studied in the synthesis of nanopores with a noncircular cross section by etching tracks of swift heavy ions in olivine. The developed atomistic model for the etching of olivine irradiated with swift heavy ions predicts the possibility of synthesizing nanopores with a noncircular cross section in it. The model consists of connected blocks that describe the sequential stages of track formation and etching. The TREKIS Monte Carlo model describes the initial electronic and lattice excitations in the nanoscale vicinity of the trajectory of an incident ion. These results are used as initial conditions for molecular dynamics simulation of structural changes along the ion trajectory. The obtained atomic coordinates after cooling of the structurally damaged area serve as the initial data for the original atomistic model of track etching in olivine. The results of the model application show that it is possible to control the cross section of these pores by changing the orientation of the crystal relative to the direction of irradiation. The presented simulation results for Xe ions demonstrate that the size of the resulting pores depends on the velocity of the incident ion, and not only on its linear energy loss.

In this work we provide a step-by-step description of the technique for manufacturing various van der Waals heterostructures. First, we discuss the procedure to obtain monolayer and few-layer flakes from layered materials, in particular from graphite and hexagonal boron nitride. Next, we consider different approaches to the assembly depending on the required final device. Further, we describe in detail the procedure for making ohmic contacts and give the parameters for plasma chemistry and metal deposition. We observe the field effect in transport measurements but a number of features – a strong shift of the charge neutral point from the zero-gate voltage, a large resistance away from the charge neutral point, and low mobility – indicate a problem with the quality of the resulting devices. Nevertheless, one of the fabricated devices demonstrates reasonable quality – the maximum mobility is estimated at 15000 cm²V^–1s^–1, the magnetic field dependences demonstrate the quantum Hall effect, which is standard for high-quality graphene. Unexpectedly, scanning electron microscope images of the resulting devices reveal a large amount of contamination on the surface of the flakes, which may explain the corresponding quality of our devices. Preliminary results of flakes cleaning with chemical compounds and thermal treatment are given.

It is shown that when a MOS (metal–oxide–semiconductor) structure is simultaneously exposed to radiation and high-field injection of electrons, part of the radiation-induced positive charge can be erased when interacting with injected electrons, and the density of surface states can increase. These phenomena must be taken into account when operating MOS radiation sensors in high-field charge injection modes. High-field injection modes used for post-radiation erase of positive charge in MOS sensors are analyzed. It has been established that to annihilate one hole (radiation-induced positive charge), it is necessary to inject (0.5–2) × 10⁴ electrons into the gate dielectric; the magnitude of the electric field has almost no effect on the process of erasing the radiation-induced charge.