Vol 12, No 2 (2018)

The interaction between hard gamma quanta and a crystal surface is considered in the case of grazing incidence. It is shown that, under certain conditions, such interaction can be described within the framework of classical wave theory even if the particle energy exceeds 10² GeV.

The main directions of development of the project on the modernization and improvement of the REVERANS reflectometer, which is proposed to be installed at the PIK reactor (REVERANS-2), are described. They include the substitution of magnetic materials in instrument construction and the replacement of the autonomous table for samples; the equipment of the instrument with a polarimeter to measure the polarization components of incident and reflected neutron beams; and replacement of the electronics and mechanisms for moving the platforms. The REVERANS-2 parameters expected after modernization are given.

The time, temperature, and magnetic field dependences of the magnetic moment of thin GaMnSb films containing MnSb clusters are measured using a SQUID (superconducting quantum interference device) magnetometer. It is found that magnetic field-induced magnetization reversal and thermally activated spontaneous magnetization reversal in thin GaMnSb films are interrelated as follows: the maximum of the magnetic-field dependence of the magnetic viscosity coincides with the coercive force for the samples.

The influence of Zn ions implanted in a sapphire single crystal on the kinetics of attainment of the equilibrium state of the surface potential and current characteristics is considered. To consider the influence of the surface state on the dielectric charging process, one of the samples is annealed in an oxygen atmosphere to form ZnO on the surface. The obtained results show a significant increase in the rate of attainment of the equilibrium surface potential after ion implantation. To understand the obtained results, the dependence of the concentration of the doping impurity as a function of the crystal depth is measured. The possible mechanisms affecting a change in achievement of the potential are discussed.

The main parameters of the microstructure of TRIP (TRansformation Induced Plasticity) composites with an austenitic matrix and a ZrO₂ zirconium-dioxide reinforcing phase subjected to plastic deformation of different degrees (compressive uniaxial load) are studied by neutron diffraction and small-angle neutron scattering. A series of composite material samples with different contents of the ZrO₂ ceramic phase (0, 10, 20, 30, and 100 wt %) are prepared by the powder metallurgy method using hot pressing. In the region of plastic deformation at load values above 650 MPa, two phases are observed in the austenitic matrix: cubic α'-martensite and hexagonal ε-martensite. Data on the lattice strains of the observed phases, dislocation density in the austenitic matrix, and characteristic sizes of the martensitic-phase particles are obtained.

The size effect of particles (20–45, 45–56, 56–71, 71–90 μm) of TiC–NiCr n vol % (n = 30, 40, 50) self-propagating high-temperature synthesis (SHS) cermet powders synthesized in the direct combustion mode on the tribological characteristics of detonation coatings is studied. These powders are sprayed in a mode optimized previously using Cr₃C₂–NiCr 21 vol % commercial cermet powder (PraxAir 1375VM, USA) with particle sizes ranging from 20 to 45 μm.

The fluorine-atom profiles over the dielectric-layer thickness, as well as the electrophysical parameters of metal–insulator–semiconductor structures obtained when InAs crystals are anodically oxidized under galvanostatic conditions at two anodizing current densities in an electrolyte containing fluoride ions, are investigated. The features of variations both in the fluorine-atom distribution and in the effective surfacestate charge on the InAs–layer interface, which are observed during layer growth, are discussed.

The results of investigating an Al–Mg alloy (5.8–6.8 wt % Mg) subjected to hydroabrasive action are presented. It is revealed that the cut surface is contaminated with fragments of particles of the abrasive. The cut-surface relief is studied with the help of scanning electron microscopy. The cut-surface microhardness and the cold-hardened layer depth are determined. The structural transformation near the surface is investigated via X-ray diffraction analysis and transmission electron microscopy. The structural state of the alloy near the surface is demonstrated to be extremely inhomogeneous. Plastic deformation leads to the formation of an ultrafine-grained structure with a heightened level of stresses.

The results of long-term tests of Morozov’s stationary plasma thrusters are presented. It is revealed how the surface state and geometry of the discharge chamber’s edges influence the thruster’s parameters. It is shown that, during the ground tests of thrusters with cylindrical geometry of the acceleration channel under initial stage of operation, material sputtered from the discharge chambers’ walls is deposited onto the nearanode segment of the walls. Films of deposited material fail during thruster operation causing fragment formation, which jut out towards the discharge volume and disturb the motion of drifting electrons in the area of their acceleration. As a result the thruster reactive force and specific impulse decrease. The way in which the forming fragments influence thruster performance and operation is examined. It is shown that it decreases under long-term operation and significant channel widening since the ion flux to the wall and the quantity of the sputtered material decrease, and since the profile of the walls changes due to their wear and cleaning effect of the discharge. As a result the thruster’s parameters are restored to a level close to the initial one. It is shown that the dynamics of thruster parameters variation in space and during ground tests is different. This means that it is necessary to simulate more properly the conditions of thruster operation in space when conducting ground development tests. Thrusters with a long lifetime should be designed with widening of the acceleration channel beyond the loop which surrounds the magnetic system so that areas of acceleration and the erosion of walls are located in the widened part of the channel.

The results of studying the energy spectrum of electrons and holes localized in second-type Ge/Si heterostructures with Ge quantum dots are presented. In such structures, holes are localized at Ge quantum dots, and electrons, in three-dimensional quantum wells, which form in Si at the Ge—Si interface because of inhomogeneous deformations that appear as a result of the difference between the Ge and Si lattice constants. It is shown that changes in the deformations in the assembly of quantum dots as a result of a variation in their spatial arrangement significantly changes the binding energy of electrons, the position of their localization at quantum dots, the binding energy and wave-function symmetry of holes at double quantum dots (artificial molecules), and the exchange interaction of electrons and holes in the exciton composition. A practically important result of the presented data is the development of approaches to increase the luminescence quantum efficiency and the absorption coefficient in assemblies of quantum dots.

Thin films of Zn_{1 – x}Co_xO_y (х = 0–0.3) with a temperature of the ferromagnetic transition of ТС > 300 K are obtained from ZnO–Co₃O₄ ceramic targets. The electron concentration in the films is found to decrease exponentially with increasing cobalt content. It is revealed that the magnetization of the films obtained under oxygen deficiency conditions varies in a nonmonotonous way as the cobalt concentration increases. This is caused by the oxidation of metallic nanoclusters of cobalt due to an increase in the oxygen content in the targets. Investigation of the transmission spectra of Zn_{1 – x}Co_xO_y films revealed extrema in the visible region of the spectrum and near the edge of the fundamental absorption band, associated with electron states introduced by cobalt.

Measurements of the direct magnetoelectric effect with respect to voltage are performed for threelayer structures of multiferroic composites. In the region of 83.6 kHz, corresponding to the resonance frequency, an anomalous increase in the magnetoelectric effect is observed for all samples. The maximum effect value is 22 mV/(cm Oe) for a Ni–PZT–Pt sample with a nickel layer 1.8 μm in thickness, which is a good indicator, considering that the bias field was zero. The anomalies of the magnetoelectric effect are of a nonlinear nature, as they depend on the thickness and technology of deposition of the magnetostrictive layers.

The post-discharge processes in the electrical supply circuit of a technological system with a pulsed glow discharge used for the ion-plasma treatment of materials are analyzed, in which a direct current glow discharge is maintained in the pauses between the treatment pulses. The variants of connecting a pulse generator through a separating capacitor or a separating diode are considered and the formulas for determining the time parameters of the recovery process of the direct-current discharge after the end of the treatment pulses are obtained. Recommendations for organizing the electric mode for fast recovery of the direct-current discharge are given, as well as for preventing arc discharge at the negative electrode and extinguishing the arc if it appears.

The problems of the radiation resistance of diodes for different purposes, created on the basis of lightly doped epitaxial n-4H-SiC layers with Schottky barriers and ion-doped p‒n- and n‒p junctions, are considered. The effect of irradiation with high-energy particles in a wide range of energies and masses—from electrons to Bi heavy ions—on the electrical and optical characteristics of 4H-SiC-based devices is studied. The general regularities of radiation-defect formation under irradiation with different high-energy particles are shown. The high radiation resistance of 4H-SiC is confirmed, and the possibility of increasing its radiation durability and endurance with high energies of irradiating particles and at operating temperatures of up to 400–500°C is shown.

The results of experimental studies of the diffusion layer at the interface between a nickel electrolyte film and a copper substrate are presented. Studies have shown that in the transition layer, diffusion of the deposited metal into the substrate material occurs. The depth of the diffusion layer and, consequently, the concentration of interstitial nickel atoms strongly depend on the electrocrystallization conditions: 2 μm in the constant-current mode and 4 μm under laser-assisted deposition. The diffusion coefficient of nickel adatoms in polycrystalline copper is 8.3 × 10^–16 m²/s in the constant-current deposition mode and 3.3 × 10^–13 m²/s under laser-assisted deposition.

Images of crystal imperfections are experimentally studied depending on their location with the use of special perfect silicon single crystals, whose surface layers are deformed by rough mechanical treatment (grinding). A new X-ray diffraction method based on the interpretation of a section topogram is proposed for studying crystal imperfections. It is shown that thin lines in the topogram are produced by kinematic scattering, and its central band is a result of dynamic scattering, i.e., this method provides the simultaneous observation of both kinematic and dynamic X-ray scattering from the same crystal.