Vol 10, No 3 (2016)

A specialized diffractometer intended for use in studying real-time transient processes in condensed media, which also allows the recording of Bragg diffraction and small-angle neutron scattering spectra, has been created at the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research. Frequently, only the given formulation of the experiment with the continuous recording of information on the process enables us to obtain data required for the correct interpretation of events. One of the crucial parameters of such experiments is the minimal time interval in which sufficient statistics can be acquired. The diffractometer parameters make it possible to measure diffraction and small-angle spectra within minute and even second (for certain types of transition processes) ranges. The possibilities of neutron scattering are discussed as applied to the study of transient processes, the diffractometer design is described, and its main characteristics and the test experiment results are presented.

Mirror polarizers for thermal neutrons are proposed and developed. In contrast to the widespread practice where mirrors are constantly in an external magnetizing field of more than 1 kOe, we have solved the problem of the efficient operation of a polarizer when a weak magnetic field of about 50 Oe is applied perpendicular to its surface.

InAlAs/InGaAs/InAlAs nanoheterostructures with different structures of metamorphic buffer layer and quantum well, which were grown by means of molecular-beam epitaxy on GaAs and InP substrates, are investigated. The laboratory technology of the growth of the given nanoheterostructures with predicted properties is perfected. The potential of an approach based on the comprehensive analysis of experimental data obtained via different techniques, namely, X-ray diffractometry, electron diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and atomic-force microscopy is studied. The metamorphic buffer layer design is improved on the basis of the results of the performed investigations. A method whereby balanced-mismatched superlattices are introduced directly inside the metamorphic buffer layer is proposed. It is established that the technological parameters of the growth of nanoheterostructures affect their structural perfection and electrophysical properties.

This review is devoted to analyzing the results of the thermochemical treatment of titanium-alloy surfaces under plasma action in electrolytes. Plasma electrolytic saturation (PES) with light elements is found to have advantages over alternative methods. Electrolyte compositions by means of which titanium is rapidly saturated with nitrogen, carbon, boron, and oxygen are presented. The treatment modes and characteristics of the modified layers, such as the phase and elemental composition, surface roughness and microhardness, friction coefficient, wear rate, and corrosion resistance, are discussed. Attention is paid to the thermophysical and electrochemical aspects of PES, in particular, to the specifics of titanium heating and its anodic dissolution and oxidation.

The configurations of a vacancy defect on the C(111)–2 × 1 surface, containing atoms with one or two dangling bonds, possessing a high adsorption activity, are calculated. We study the configurations of the vacancy defect at the surface of diamond C(111)–2 × 1 using the semiempirical MNDO method (MOPAC) and the ab initio Hartree–Fock method (PC GAMESS). We calculate the energies of clusters, the orders of atomic bonds, the populations of atomic orbitals, and the localized molecular orbitals.

The ranges of He, Li, Be, B, and C ions in gases and NIKFI-Ya2 nuclear photoemulsion are considered. The general features of the range variations as functions of the energy and ion nuclear charges are discussed. The results of calculations are compared with experimental data and the data of calculations using the SRIM-2013 program.

Gallium nitride is used as an example to show the possibilities of the application of a developed threedimensional mathematical model in the cathodoluminescence studies of direct-gap semiconductor materials using the time-of-flight procedure for obtaining quantitative information on their properties. The values of the diffusion coefficient in gallium nitride are determined from the results of its experimental studies.

The molecular dynamics simulation of the normal incidence of a Cu₃ cluster with an energy of 0.2–1 eV/atom on a Cu(100) substrate at an equilibrium temperature of 500–700 K is performed. This substrate contains a rectilinear step, whose height is one atomic layer. After 20-ps relaxation of the atomic cluster on the substrate, its further thermally activated motion on the surface is simulated using the method of temperature- accelerated molecular dynamics. The Cu₃ cluster mainly demonstrates rotational-translational motion. The time interval between two successive atomic transitions of the cluster is found to be reduced as the distance to the step is decreased.

A physical model and mathematical calculations of the maximum partial depths of origin of sputtered particles versus mass, energy, and the angle of incidence of ions bombarding a one-component amorphous target are presented. Calculations reveal that the maximum depth of origin of secondary particles depends on the primary-ion incidence angle, which attains the highest value at angles of 30°–60° relative to the normal to the sample surface. When the primary beam and the target material have identical parameters, the maximum depths of origin of light secondary particles exceed those of heavy ones. Secondary particles exhibit the isotope effect. For light elements (Li, Be, and B), a heavier isotope has a larger maximum depth of origin than a lighter one. In the case of heavy elements (e.g., Mo), a lighter isotope has a greater maximum depth of origin than a heavier one.

The features of the dissolution and nucleation of dispersed precipitates in alloys and their possible structural changes under ion irradiation are considered. The analytical calculation of nucleation is performed with allowance for dissolution and the growth of dispersed particles. The calculation results are in good agreement with experimental data.

The method of thermally stimulated electron emission is applied in order to investigate ionization processes and defect formation in Si/SiO₂ structures under the impact of high-energy α particles. The implantation of Si/SiO₂ films with Li⁺, Na⁺, and K⁺ alkali-metal ions is found to contribute to the formation of active emission L centers in the modified oxide layer, which provides sensitivity to α radiation. The parameters of the emission centers are identified and analyzed. It is shown than Si/SiO₂: Li heterostructures could be used to detect α radiation.

The features of linear simulators with beam-plasma discharge are examined. A description of five discharge modes is provided. They can be implemented in such devices, depending on working-gas pressure, operating parameters of the electron gun and collecting electrode: vacuum beam transport, diffuse discharge, beam-plasma discharge, vacuum arc and self-oscillating modes. We describe how to use these modes in combination with diagnostics methods and sample holders, which allow studies of thermal and plasma loading, thermal cycling, sputtering, redeposition, gas capture, cleaning of deposited layers, development of instabilities, and ion etching.

We investigate the sputtering of single-crystal and polycrystalline films of Pb_1–xEu_xTe (x = 0.02–0.10) in high-frequency inductively coupled argon plasma. Layers of Pb_1–xEu_xTe are grown via molecular beam epitaxy on barium-fluoride substrates of the (111) orientation at 340 and 200°C. For single-crystal films, the dependence of the sputtering rate on the europium concentration is found. For polycrystalline layers, a decrease in the sputtering rate is observed. This is caused by the effect of europium oxidation at the surface of the polycrystallites.

Multiple scattering at grazing angles of incidence is shown to affect the value of inelastic energy loss determined from the position of the quasi-single scattering peak on the energy scale.

The results of studying the structure and properties of composite ceramic coatings produced by microarc oxidation (MAO) on zirconium alloy E110 are presented. To form the coatings, a suspension electrolyte is used with the addition of aluminum-hydroxide nanopowder. It is shown that the addition of the nanopowder results in a substantial increase in the growth rate and thickness of the coating compared with coatings obtained in the same amount of time without the addition of nanopowder to the electrolyte. A decrease in the porosity of coatings with increasing time of microarc oxidation is also revealed. It is found that samples with MAO coatings have a greater resistance to corrosion in an autoclave as compared to uncoated samples.

We demonstrate the possibility of fabricating high-efficiency semiconductor hydrogen detectors based on tangsten-oxide thin films deposited onto silicon-carbide crystals by reactive pulsed-laser deposition. The obtained WO₃/SiC structures ensure a noticeable voltage shift ΔU on the reverse branch of the I−V characteristics without commonly used catalyst layers of platinum-group metals. The ΔU value reached 2.1 V at a detected hydrogen concentration of 0.2% in air at 350°C. The response times to hydrogen inlet and recovery of the WO₃/SiC structure after hydrogen outlet are found to be much shorter than those for the Pt/WO₃/SiC structure. The high performances of the fabricated WO₃/SiC sensor are due to the layered structure of the orthorhombic phase of tungsten oxide, which consists of loosely packed microcrystalline plates containing nanocrystals smaller than 100 nm.

The cross section of the electric dipole absorption of a small conducting cylindrical particle located in the field of a plane electromagnetic wave is calculated in terms of the classical kinetic theory of electrical conductivity. The boundary conditions of the nonequilibrium charge-carrier distribution function are specified using the Soffer model taking into account the dependence of the specular reflectance on the surfaceroughness parameter and the angle of electron (hole) incidence on the particle’s internal surface. The results of calculating the cross sections of the electromagnetic-radiation absorption of metal and semiconductor particles are presented. The obtained results are compared with theoretical calculations for the model of diffusespecular Fuchs boundary conditions.