Vol 61, No 7 (2016)

The formation of space charge in weak electrolytes, specifically in liquid dielectrics, has been considered. An analytical solution is given to a simplified set of Nernst–Planck equations that describe the formation of nonequilibrium recombination layers in weak electrolytes. This approximate analytical solution is compared with computer simulation data for a complete set of Poisson–Nernst–Planck equations. It has been shown that the current passage in weak electrolytes can be described by a single dimensionless parameter that equals the length of a near-electrode recombination layer divided by the width of the interelectrode gap. The formation mechanism and the structure of charged nonequilibrium near-electrode layers in the nonstationary regime have been analyzed for different injection-to-conduction current ratios. It has been found that almost all charge structures encountered in weak dielectrics can be accounted for by the nonequilibrium dissociation–recombination mechanism of space charge formation.

The influence of the V/III flux ratio on the submonolayer growth of GaAs on the GaAs (001) surface is simulated by the Monte Carlo method. Growth is carried out using the method of molecular beam epitaxy at different values of process parameters. The surface density of islands against the V/III flux ratio is calculated. The saturation value of the surface density at 580°C is found to be 2 × 10¹² cm^–2, which is in agreement with the experimental data. The V/III flux ratio influences the island density most strongly at a reduced temperature (550°C) and an elevated growth rate (a monolayer per second), when the arsenic desorption is weak. The fraction of arsenic atoms in the growing film is estimated under different process conditions. It has been shown that, as the surface coverage rises, the influence of the V/III flux ratio on the fraction of arsenic atoms becomes weaker.

A theoretical model of steady-state mixing is considered for a binary gas mixture under conditions of free gravitational convection in a vertical channel with impenetrable walls that connects two flasks. It is shown that the mixing rate in the supercritical regime has a peak and then deceases monotonically with increasing pressure. The experimental results are shown to be in good agreement with theoretical data.

The positive-column plasma of a low- and medium-pressure electronegative glow discharge initiated in the gap between two coaxial cylindrical tubes has been considered (the current is directed along the tube axis). It is assumed that the gas mixture contains halogens, and ion diffusion is not negligibly weak. It is found that the coaxial discharge is characterized by plasma separation into three coaxial regions with different compositions in the direction transverse to the current. It has been shown that the ionization and excitation frequencies of atoms are higher than in the purely cylindrical case, even for a small (0.05–0.15) ratio of the radii of the inner and outer walls. An asymptotic analysis of the continuity equations yields analytic expressions that make it possible to rapidly and easily estimate the geometrical parameters of the spatial distributions of charge particle concentrations, as well as energy parameters of the plasma for the radii ratio that exceed 0.3. The conditions for the applicability of analytic relations and their accuracy are established from a comparison of the results of analytic and numerical calculations.

The effect of alloying by 12–20 at % Hf on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary alloys of the quasi-binary NiTi–NiHf section is studied by transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. The electrical resistivity is measured at various temperatures to determine the critical transformation temperatures. The data on phase composition are used to plot a full diagram for the high-temperature thermoelastic B2 ↔ B19’ martensitic transformations, which occur in the temperature range 320–600 K when the hafnium content increases from 12 to 20 at %. The lattice parameters of the B2 and B19’ phases are measured, and the microstructure of the B19’ martensite is analyzed.

The radiation resistance of glass-cloth laminate, impregnating epoxy and silicone compounds, lavsan, and other materials used in particle accelerators is measured. Irradiation is performed on an ILU-6 electron accelerator to a dose of 30–100 MGy. Recommendations on the application of the insulating materials are made.

The wide structure and chemical-composition spectrum of the main technological material of molecular graphenics—reduced graphene oxide (RGO)—is explained from a quantum-chemical standpoint. The proposed concept is used to consider the results of experimental investigations of a natural analog of RGO, namely, shungite carbon, by high-resolution electron microscopy and nanopoint energy dispersive spectral analysis. The results obtained are used to propose an atomic-microscopic model for the structure of shungite carbon.

Titanium oxide particles are produced using electric-discharge dispersion of titanium in aqueous solution of hydrogen peroxide. Electron vacuum microscopy, X-ray diffraction, and diffuse reflection spectroscopy are used to study the morphology, composition, and optical characteristics of the erosion particles. It has been demonstrated that the particles consist of titanium and titanium oxides with different valences. The edge of the optical absorption is located in the UV spectral range. The band gap is 3.35 eV for indirect transitions and 3.87 eV for direct allowed transitions. The band gap decreases due to the relatively long heating in air at a temperature of 480–550°C, so that powder oxide compositions can be obtained, the optical characteristics of which are similar to optical characteristics of anatase. The erosion products are completely oxidized to rutile after annealing in air at a temperature of 1000°C.

Beta-voltaic cells based on standard silicon solar cells with bilateral coating with beta-radiation sources in the form of ⁶³Ni isotope have been studied experimentally and by numerical simulation. The optimal parameters of the cell, including its thickness, the doping level of the substrate, the depth of the p–n junction on its front side, and the p⁺ layer on the back side, as well as the activity of the source material, have been calculated. The limiting theoretical values of the open-circuit voltage (0.26 V), short-circuiting current (2.1 μA), the output power of the cell (0.39 μW), and the efficiency of the conversion of the radioactive energy onto the electric energy (4.8%) have been determined for a beta-source activity of 40 mCi. The results of numerical analysis have been compared with the experimental data.

The possibility of attaining an superhard state in multilayer vacuum-arc ZrN/CrN coatings with a layer thickness of about 20 nm has been established. It has been shown that the application of a constant negative potential for structural engineering during deposition leads to the formation of solid solutions due to mixing of interfaces. The hardness of these systems exceeds 30 GPa. The application of a pulsed high-voltage bias potential at which the ordering of atoms stimulated by elevated mobility is observed makes it possible to suppress the mixing of the interfaces and to attain elevated hardness (up to 42 GPa) for nanometer layer thicknesses.

The peculiarities of the photoluminescence of compounds CaMoO₄: Eu³⁺ and CaWO₄: Eu³⁺ with the scheelite structure associated with a change in the short- and long-range orders of the crystal lattice upon a change in the activator (Eu³⁺) of the photoluminescence range in the interval 1–4 mol %, in which the photoluminescence of the matrix is preserved in the range 484–557 nm, are investigated using X-ray phase analysis as well as photoluminescence, Raman, and diffuse reflection spectroscopies. The introduction of Eu³⁺ ions leads to the reconstruction of the lattice so that up to 10% of these ions stimulate the formation of centrosymmetric localization upon the substitution of Ca²⁺ ions in the noncentrosymmetric positions. It is found that the spectral radiant emittance of the more effective luminophore CaMoO₄: Eu³⁺ can be adjusted to this parameter for an incandescent lamp for the Eu³⁺ concentration of 1–2 mol %.

The influence of a plane electric field on the phase states of barium titanate thin films under the conditions of forced deformation has been studied. The field dependence of a complete set of material constants has been taken in the region of the c-phase, where polarization losses are absent. The material constants are calculated using equations of the piezoelectric effect derived by linearizing the nonlinear equations of state from the phenomenological; theory for barium titanate. It has been shown that there is a critical value of the field at which the electromechanical coupling coefficient reaches a maximum.

A classical model of the emission of radiation by relativistic electrons in a crystal has been developed using the form of the potential maximally close to its actual form. The dynamics of electrons with energies 20–25 MeV performing channeling in crystals is simulated numerically. The generation of electromagnetic radiation that accompanies this motion has been considered. It has been shown that, in the given electron energy range, this radiation corresponds to the X-ray spectral band with characteristic photon energies of up to 40 keV. The radiation yield is estimated. The requirements to the electron beam parameters are formulated based on the results of the simulation. It has been shown that numerical simulation gives results that correlate with the analytic results obtained earlier and with the experimental data.

Atomic-force microscopy is used to study the supramolecular structure of submicron films of electroactive thermally stable polymer (polydiphenylenephthalide (PDP)). It has been demonstrated that PDP films produced using centrifuging are solid homogeneous films with thicknesses down to several nanometers, which correspond to two or three monomolecular layers. The film volume is structurized at thicknesses greater than 100 nm. The study of the rheological properties of solutions used for film production yields a crossover point that separates the domains of strongly diluted and semidiluted solutions. A transition from the globular structure to the associate structure is observed in films that are produced using solutions with a boundary concentration. A model of the formation of polymer film that involves the presence of associates in the original solution is discussed.

Nondestructive technology has been developed for the extraction of light gases dissolved in ice. The technology has been tested on samples of atmospheric and congealed ice of the 5-G3 bore hole of the Vostok station (East Antarctica) extracted from depths of 3457–3698 m. Down to 3539 m, ice is of an atmospheric origin, while ice deposited deeper is formed by natural water of Vostok Lake frozen on the glacier. Light gases were extracted into samplers (glass flasks) in the course of the 3-day degassing of samples freshly elevated from a bore hole. The samples were analyzed on the FT-1 time-of-flight mass spectrometer 6 months after sampling. Measurements reveal the presence of amounts of helium as well as molecular hydrogen considerably exceeding the atmospheric values. Measured values of gas ratio H²/⁴He = 5.4 ± 1.9 in the samples from depths of 3596–3698 m exceed the atmospheric values by more than an order of magnitude.

The problem of expanding spatial potential in terms of eccentricity e accurate to e² has been formulated and solved for a homogeneous gravitating (or charged with static electric charge) elliptical disk. An original method that makes it possible to obtain the desired result using the superposition of a perturbation layer and a circular disk has been developed. The potential of such a layer has been derived. The first term of the expansion of the potential (zero power of parameter e) coincides with the potential of a homogeneous circular disk and the coefficient of the first power of the parameter e is zero. The main term of the expansion of the potential proportional to e² is analytically derived. The resulting expression makes it possible to determine the potential in the entire space, including the inner region of the disk.

The effect of temperature on the charge of atoms adsorbed on the metal, semiconductor, and graphene substrate is analyzed using simple models. It is shown that the role of temperature in the case of metals is insignificant, while in the case of semiconductors, the temperature can only strongly affect the filling of local states in the bandgap. In the case of adsorption on an undoped graphene monolayer, the role of temperature is decisive when the energy of the adatom level is close to the Dirac point.

We have analyzed the electrocaloric response in ferroelectric materials in nonequilibrium thermal conditions. The temperature dependences of the electrocaloric response during polarization and depolarization of ferroelectric samples based on solid solutions of barium–strontium titanate and lead magnoniobate–titanate are considered. The difference in the electrocaloric responses for polarization and depolarization, which can be as large as 5 mK, has been demonstrated experimentally.