Vol 45, No 7 (2019)

The structural properties of ferroelectric barium titanate–stannate films on sapphire substrates and microwave characteristics of related planar capacitive elements have been investigated. The gas-medium composition during the film deposition has been established to affect significantly the crystal structure, phase composition, and electric characteristics of the films. The low dielectric loss and high controllability of planar capacitive elements based on barium titanate–stannate films in the frequency range of 2–60 GHz are demonstrated for the first time.

The possibility of reducing the threshold of the effect of dynamic light scattering in liquid-crystal cells has been demonstrated. The threshold lowering is favored by using electrodes with metal–insulator–semiconductor microstructures containing gold nanoparticles. The increase in the efficiency of the electrodes leads to a higher cell conductivity and weaker light intensity at low voltages.

The results of experiments and simulations of the transport of heat and particles in the Globus-M spherical tokamak are presented. Investigations were carried out in the ohmic mode in hydrogen and deuterium plasma. It is shown that in the phase of current growth under the same initial conditions, as long as the condition is met at which the minimum of the safety factor exceeds unity, two scenarios of discharge development are possible: with an electron temperature dive or with an electron density peak. After the safety factor reaches the value of 1, the differences are no longer observed. Modeling of transport processes using the ASTRA code showed that the dive of the electron temperature and density is a consequence of the decrease in the transport of heat and particles in the plasma core (i.e., the presence of internal transport barriers).

The relationship is substantiated between the amplitude-frequency and phase-frequency performances of forced oscillations of a nonlinear fractional oscillator and the orders of fractional derivatives in its model equation. Using computer simulation, it is shown that the orders of fractional derivatives are related with the quality factor of an oscillatory system. A decrease in the superior order (“fractional” inertia) leads to a decrease in the quality factor, while a decrease in the inferior order (“fractional” friction) leads to an increase in the quality factor. We have compared numerical calculations of the amplitude-frequency and phase-frequency performances for a linear fractional oscillator with the calculation results obtained using analytical formulas of other authors. The analysis has shown a good agreement between these calculations, confirming the correctness of the numerical calculations presented.

The current–voltage characteristics of light-emitting diodes based on InGaAs/GaAs heterostructures with an injector made of (In, Fe)Sb diluted magnetic semiconductor are studied. The current–voltage characteristics of the (In, Fe)Sb/n-GaAs and (In, Fe)Sb/p-GaAs structures are analyzed. The band diagrams of heterojunctions are constructed. It is shown that the investigated structures have the same current transfer mechanism as in the structures with a Schottky barrier.

The dynamics of a two-dimensional ensemble of nonlocally coupled van der Pol oscillators is studied by numerical simulation. The possibility of realization of regular spiral and target waves is established. The emergence of a new type of chimera structure realized on the basis of target waves with nonlocal coupling is shown.

The mechanism of generation of electron bunches upon the interaction of a laser pulse with a semibounded plasma having a diffuse boundary with vacuum in the form of a transition layer is studied.

We have studied the resistive switching in memristive structures based on 40-nm-thick yttria-stabilized zirconia (YSZ) films exposed to 6-keV Si⁺ ion irradiation to a total dose of 5.4 × 10¹⁵ cm^–2. It is established that the ion irradiation leads to increased stability of the parameters of resistive switching in YSZ based memristive structures. This effect is related to the fact that the diameter of conducting filaments in irradiated structures is limited by lateral dimensions of the region of atomic displacement cascades (i.e., the region occupied by point defects produced by bombarding ions). The oxidation of ion-modified filaments during resistive switching proceeds more effectively and leads to increasing resistance in the high-resistance state of memristive structures.

Methods of equilibrium chemical thermodynamics have been used to simulate laws of the influence of geometric factors (pore shape and volume) on the phase equilibria is stratifying polymer solutions in porous matrices. Using the example of the phase separation in a liquid polybutadiene–polystyrene system, it is established that deformation of the porous matrix determining the geometric characteristics of pores can be used to control the mutual solubilities of components and the volumes and thermodynamic stability of coexisting equilibrium phases. Significant deformations of the matrix lead to suppression of the phase separation in pores and make any solution compositions possible (up to equimolar mixtures).

The task of accelerating a thin plane impactor in a cylindrical channel with high-pressure gas (in particular, detonation products of acetylene–oxygen fuel mixture) encounters the well-known problem of “falling paper sheet” since the impactor motion in the channel is also unstable with respect to lateral (radial) displacements. This displacement can lead to breakage of the symmetry of flight, skewness of the impactor, and a sharp decrease in the achieved velocity. It has been experimentally established that the impactor orientation can be retained by limitation of its lateral shifts with the aid of several thin filaments of a polymer thread (fishing line) arranged uniformly on the inner channel surface along the cylinder generatrix.

A three-layer heterostructure consisting of AlN (∼0.72 μm thick), AlGaN (∼ 1.82 μm thick), and GaN (∼2.2 μm thick) layers has been grown by hydride–chloride vapor phase epitaxy (HVPE) method on a Si substrate with a SiC buffer nanolayer. The heterostructure was studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and other techniques. The results showed that SiC/Si substrates can be used for growing films of III–V semiconductor compounds by HVPE at a high rate (~66 μm/h) free of cracks and with small residual elastic stresses (~160 MPa).

Plates of boron carbide B₄C were used as refractory targets for determination of energy and fluences of protons collectively accelerated in a Luce diode accelerator by control of ⁷Be and ¹³N gamma radioactivity induced by nuclear reactions ¹⁰B(p, α)⁷Be and ¹²C(p, γ)¹³N, respectively. The Luce diode exploited a cylindrical tungsten rod as a cathode and a polyethylene washer as an anode, producing pulsed electron beams with durations and currents of up to 100 ns and 30 kA at voltages of 250 kV. The technique allows controlling proton energies within the range of 500–1500 keV and fluences of up to 5 × 10¹³ protons per cm² per pulse.

The morphology and electrical properties of doped semi-insulating gallium nitride (GaN) epilayers have been studied. It was found that doping-induced improvement of the insulating properties of GaN epilayers with increased level of doping with carbon or iron is limited by the accompanying deterioration of surface morphology. The character of impurity-related morphology development is different for the two dopants. It is established that the co-doping with carbon and iron allows planarity of the GaN surface to be retained along with a significant improvement of insulating properties of epilayers.

Experimental data on the formation of thermocapillary structures and the rupture of a heated liquid film flowing down on a vertical wall have been analyzed and generalized. It is established that the interaction of waves and thermocapillary structures of type A leads to an increase in the critical heat flux (CHF) corresponding to the film rupture as compared to the CHF values known from literature for type B structures.

Design and manufacturing technology of high-power microwave Schottky photodiodes with microstripe leads have been developed based on an InAlAs/InGaAs heterostructure. The operating frequency of photodiodes with a mesa diameter of 15 μm is above 25 GHz and a maximum output microwave power at 20 GHz exceeds 50 mW, which allows these photodiodes to be employed in analog fiber-optic microwave signal transmission lines, as well as for the microwave signal generation and processing by optical methods in remote sensing and measuring microwave technology.