Vol 45, No 2 (2019)

The effect of the time delay of thermal coupling on the synchronization of two VO₂-oscillators has been studied for the first time. A modification of the methods for determining high order synchronization parameters has been proposed. The dependence of these parameters on the magnitude of the time delay and distance between the oscillators in the presence of internal noise has been studied. The results will contribute to the development of technology for creating three-dimensional neural networks.

Using the example of DNA water solutions, a manifestation of the light polarization plane rotation effect has been shown (in comparison with a number of dyes). Numerical values of the rotation angle have been established that significantly exceed those for water solutions of dyes and sugar traditionally used in saccharimeters and polarimeters. Therefore, another optical effect in biostructuring optical materials has been identified and confirmed.

The results of the simulation of plasma fluxes onto the surface of rotating substrates during the combustion of a vacuum arc of the Cr–Ti–Mo cathode system are presented. The structure and composition of the arc-PVD Ti_0.15Cr_0.74Mo_0.11N_0.84 coatings are experimentally studied. The numerical simulation results of the coating structures based on experimental data were analyzed. The possibility of the simulation of the structure of multilayer, multicomponent coatings and the concentration distribution of chemical elements and its components is shown by calculating the plasma fluxes using the Monte Carlo method.

A model of internal friction at a grain boundary containing equidistant parallel cylindrical pores is presented. Variable shear stress induces a mutual displacement of the interfacial regions matched at the segments between pores depending on their position. The values of scattered energy at each segment and total internal friction are determined. The temperature dependence of the internal friction has a form of a wide peak.

It was found that in a hydrogen-methane mixture in microwave plasma reactor for diamond deposition, there is a threshold pressure after which the contraction of microwave discharge occurs. The results of measurements of gas temperature and spatial distributions of optical emission intensity of discharge are presented. The mechanism of discharge contraction is discussed.

The ferroelectric domain structure has been investigated in bismuth-ferrite rhombohedral phase films prepared on the rhombohedral plane of sapphire by solid-phase epitaxy. The piezoelectric modulus has been estimated to be d₃₃ ~ 2 pm/V. In films of the Bi₂₅FeO₃₉–BiFeO₃ and Bi₂Fe₄O₉–BiFeO₃ systems on sapphire, the magnetoelectric-switching effect has been observed in bismuth ferrite crystallites without deposition of exchange-coupled layers. The values of the magnetic moment in bismuth ferrite microcrystallites have been estimated.

The resilience of nanoclusters surrounded by a perfect crystal matrix has been studied via the molecular dynamics approaches. Clusters with sizes of up to 10 nm are found to be unstable and dissolve in the matrix.

The elastic properties of a flat graphene layer calculated using the classical empirical Tersoff, Brenner, AIREBO, PPBE-G, and LCBOP potentials have been compared. It is shown that, although the popular Brenner and AIREBO potentials have been developed formally taking into account the elastic properties of graphene, they give significant discrepancies in the values of Young’s modulus and Poisson’s ratio. Among the potentials under consideration, the LCBOP potential yields the values of these parameters that are closest to experimental data and results of ab initio calculations in the limit of zero elongation. For the quantitative simulation of mechanical phenomena in graphene-based systems, the potential parameters should be fitted to reproduce elastic properties of graphene completely taking into account system deformations and dependences of these constants on the elongation.

The acceleration of a plasmoid, for the formation of which a conical spiral expanding in the direction of the expected plasma acceleration is used, in a rapidly increasing magnetic field of complex geometry has been considered. An algorithm for calculating the longitudinal magnetic field in the approximation of replacing a spiral line with a system of rings of variable radius has been presented. A mathematical model that is based on the interaction of the plasmoid magnetic moment with gradient of the longitudinal magnetic field decay has been proposed to analyze the efficiency of the acceleration. The possibility of deuterons reaching an average speed exceeding 10⁶ m/s has been shown.

Machine learning methods were used to construct a demultiplexer for helical wave front separation into orthogonal modes. The accuracy of wave front demultiplexing into eight modes at a signal-to-noise ratio of –3 dB is about 95% in a broad range of signal carrier frequencies. For nonstationary parameters of signals, the proposed demultiplexer accuracy exceeds that of the classical correlation method.

The optoelectronic two-wave method has been developed and a block scheme of the corresponding optoelectronic device has been proposed for remote monitoring of the content of methane in atmosphere. The optoelectronic device employs light-emitting diodes (LEDs) based on GaAlAsSb/GaInAsSb/GaAlAsSb (3.12 μm) and GaAlAsSb/GaInAsSb/GaAlAsSb (3.39 μm) structures as the sources of reference and probing radiation, respectively.

A new experimental method for nanoscale measurements of the absorption spectra of single nanoobjects has been developed based on scanning near-field optical microspectroscopy (SNOM) and nanospectrophotometry (NSP). The main distinctive feature of the proposed SNOM-NSP technique consists in depositing a sample onto a coverglass followed by its probing in the total internal reflection spectroscopy mode. This approach allows the number of analyzed samples to be significantly increased and provides the possibility of combining measurements with other optical techniques. The proposed SNOM-NSP method has been successfully used for studying single plasmonic nanoparticles and their complexes with Rhodamine 6G dye.

Defects in the semiconductor structure of a photovoltaic converter (PVC) with a p–n junction and antireflection film of porous silicon manufactured using chemical stain etching were studied by the current deep-level transient spectroscopy technique. The influence of the regime of porous silicon film formation on the transformation of deep-level defects and the main PVC characteristics is explained.

BaTiO₃/LaSrMnO₃ (BTO/LSMO) structures with a ferroelectric layer thickness of 10 nm have been formed on r-cut sapphire substrate by means of high-frequency magnetron sputtering. Investigations of the sample structure showed the presence of a crystalline phase, while measurements of electrical properties revealed piezoelectric response of the BTO films. The study of local current–voltage characteristics showed dependence of the sample resistance on the prehistory of voltage application as determined by ferroelectric hysteresis of the BTO layer.

Arrays of GaN nanowires (NWs) and nanotubes (NTs) have been grown by metalorganic vapor phase epitaxy using a gold–nickel film as the catalyst. The simultaneous formation of both NTs and NWs in one process in the presence of various Au–Ni catalyst compositions is explained. It is established that NTs grow on solid catalyst particles, while NWs grow according to the classical vapor–liquid–solid mechanism. The optoelectronic properties of obtained NTs and NWs have been studied using photo- and cathodoluminescence techniques.

We have studied X-ray diffraction (XRD) patterns of calcinates isolated from aortic demilunes of patients with calcific aortic stenosis. It is shown that the observed XRD pattern is formed by spherical formations of hexagonal hydroxyapatite with diameters distributed according to the lognormal law. A model of the structure of these formations is constructed and the possible mechanisms of their nucleation and encapsulation of hydroxyapatite particles in the restricted porous space of the basal membrane of aortic valve demilunes are discussed.

Ammonia molecular-beam epitaxy has been used to grow gallium nitride (GaN) transistor heterostructures on sapphire and silicon substrates. GaN transistors with a 1.2-mm periphery fabricated on substrates of both types exhibited similar high static characteristics: saturation current density above 0.75 A/mm, transconductance above 300 mS/mm, and breakdown voltage above 120 V. Measurements of the small-signal parameters showed that transistors based on silicon substrates possessed high gain in a frequency range up to 5 GHz; the specific output power at 1 GHz amounted to 5 W/mm for transistors on sapphire substrate and 2 W/mm for transistors on silicon substrate.

Growth-related structural defects present on the surface of InAlAs layers grown by molecular beam epitaxy on InP(001) substrates influence the temperature dependences of the current–voltage characteristics of Au/Ti/InAlAs Schottky barriers. It is established that these defects in the form of pits cause the appearance of regions with reduced barrier height. At a surface density of ≥10⁷ cm^–2, these defects significantly influence the parameters of the Schottky barriers at temperatures below 200 K.