Том 61, № 3 (2016)
- Жылы: 2016
- Мақалалар: 26
- URL: https://journals.rcsi.science/1063-7842/issue/view/12315
Theoretical and Mathematical Physics
Analysis of the stability of states of semiconductor superlattice in the presence of tilted magnetic field
Аннотация
A method to calculate the spectrum of the Lyapunov exponents for a periodic semiconductor nanostructure (superlattice) described in the framework of a semiclassical approach is proposed. The analysis of the stability of a stationary state in such a system is performed for autonomous dynamics and in the presence of a tilted magnetic field. The method of the Lyapunov exponents is used to study the effect of the tilted magnetic field on the stability of the stationary state and the characteristics of subterahertz oscillation regimes.
Calculation of the effective thermal conductivity of powders formed by spherical particles in a gaseous atmosphere
Аннотация
We describe a method for calculating the effective thermal conductivity of powders formed by spherical particles with a size exceeding 1 μm in a gaseous atmosphere in wide ranges of temperatures and pressures. We take into account the structural factor of the powder medium, adsorption of gas on the surface of solid spheres, the temperature dependences of the thermal conductivities of the powder components, and the formation of melt necks between the spheres after the attainment of the melting point. In the case of complete melting of the spheres, we propose a model for thermal conductivity of the melt with gas inclusions. The results of calculation of the effective thermal conductivity are in good agreement with experimental data.
Electrodynamics of circular dichroism and its application in the construction of a circular polaroid
Аннотация
Electrodynamic principles of circular dichroism are developed using a concept of conducting circular structures in matter. A simplified representation of material equations for an optically active medium is obtained in the absence of a transition to the complex domain. A dependence of the absorption coefficient of a circular polarization as a component of the linearly polarized radiation on material parameters is found. Such parameters are analyzed to reveal a possibility of construction of a circular polaroid.
Atomic and Molecular Physics
Elementary processes during collisions of ions with tryptophan molecules
Аннотация
The relative cross sections of elementary processes occurring in single collisions of tryptophan molecules in the gaseous phase with He2+ ions with energy 4 keV/u are measured using time-of-flight mass spectrometry for studying the mechanism of radiation damage of amino acid molecules. The fragmentation channels for intermediate singly and doubly charged tryptophan molecular ions formed during one-electron capture, two-electron capture, and electron capture with ionization are investigated. Significant difference is observed in the mass spectra of fragmentation of intermediate doubly charged ions formed during the capture with ionization and double capture, which is associated with different energies of excitation of {C11H12N2O2}2+* ions.
Gases and Liquids
Radiative gas dynamics of the Fire-II superorbital space vehicle
Аннотация
The rates of convective and radiative heating of the Fire-II reentry vehicle are calculated, and the results are compared with experimental flight data. The computational model is based on solving a complete set of equations for (i) the radiative gas dynamics of a physically and chemically nonequilibrium viscous heatconducting gas and (ii) radiative transfer in 2D axisymmetric statement. The spectral optical parameters of high-temperature gases are calculated using ab initio quasi-classical and quantum-mechanical methods. The transfer of selective thermal radiation in terms of atomic lines is calculated using the line-by-line method on a specially generated computational grid that is nonuniform in radiation wavelength.
Electromagnetic radiation due to nonlinear oscillations of a charged drop
Аннотация
The nonlinear oscillations of a spherical charged drop are asymptotically analyzed under the conditions of a multimode initial deformation of its equilibrium shape. It is found that if the spectrum of initially excited modes contains two adjacent modes, the translation mode of oscillations is excited among others. In this case, the center of the drop’s charge oscillates about the equilibrium position, generating a dipole electromagnetic radiation. It is shown that the intensity of this radiation is many orders of magnitude higher than the intensity of the drop’s radiation, which arises in calculations of the first order of smallness and is related to the drop’s charged surface oscillations.
Plasma
Experimental study of cyclic action of plasma on tungsten
Аннотация
We report on experimental results on multiple action of hydrogen, deuterium, and helium plasmas produced by a plasma gun and the Globus-M tokamak on tungsten. The surface temperature in the course of irradiation is measured with a bichromatic pyrometer with a time resolution of ⩾1 μs. The morphology of the surface layer is investigated and X-ray structure analysis of tungsten exposed to multiple radiations by the plasma under various conditions is carried out. A slight decrease in the lattice parameter in the sample subjected to the maximal number of irradiation cycles is detected. It is shown that the morphology of the tungsten surface irradiated by the hydrogen plasma from the gun and by the deuterium plasma from the Globus-M tokamak changes (the structure becomes smoother). The characteristic depth of the layer in which impurities have been accumulated exceeds 0.5 μm. This depth was the largest for the sample exposed to 1000 shots from the gun and 2370 shots from the tokamak. It is shown that the helium jet from the plasma gun makes it possible to simulate the action of helium ions on the International Thermonuclear Experimental Reactor (ITER) diverter, producing a layer of submicrometer particles (bubbles).
Solid State
Influence of hydrostatic pressure on the ductility of copper as a function of its initial state
Аннотация
The influence of hydrostatic pressure in the interval 0-250 MPa on the deformation properties of copper versus its initial state is studied. After liquid nitrogen storage, the torsion strain to fracture is found to increase when the pressure rises to 200 MPa. As the pressure rises further and reaches 250 MPa, the torsion strain to fracture drops. Preliminary torsion to a strain of 5% in opposition to torsion under pressure makes the pressure dependence of the ultimate strain linear. If the prestrain equals 25%, a rise in the pressure to 150MPa increases the ductility of the material. A further increase in the pressure to 250 MPa changes the ductility insignificantly.
Relation between the synthesis conditions and the fine structure of fiber carbon
Аннотация
The fine structure of carbon fibers synthesized under various technological conditions is studied. It is found that the material of the fibers is heterogeneous and its component composition is determined by thermomechanical treatment conditions and the presence of a boron addition and depends on the angle of coherent-domain orientation φ with respect to the fiber axis. The detected dependences of the component composition of the fibers on the heat-treatment temperature and time and the angle of coherent-domain orientation with respect to the fiber axis suggest that the transition of the carbon material of the fibers into a more equilibrium state is likely to proceed through a number of metastable states.
Dissipative processes under the shock compression of glass
Аннотация
New experimental data on the behavior of the K8 and TF1 glasses under shock-wave loading conditions are obtained. It is found that the propagation of shock waves is close to the self-similar one in the maximum compression stress range 4-12 GPa. Deviations from a general deformation diagram, which are related to viscous dissipation, take place when the final state of compression is approached. The parameter region in which failure waves form in glass is found not to be limited to the elastic compression stress range, as was thought earlier. The failure front velocity increases with the shock compression stress. Outside the region covered by a failure wave, the glasses demonstrate a high tensile dynamic strength (6-7 GPa) in the case of elastic compression, and this strength is still very high after transition through the elastic limit in a compression wave.
Hysteresis in the behavior of a long periodically modulated Josephson junction in a magnetic field for not small values of the pinning parameter
Аннотация
The magnetization curve for a long periodically modulated Josephson junction is calculated using the approach based on analysis of the continuous change in the configuration in the direction of the decrease in the Gibbs potential upon cyclic variation of the external magnetic field for not small values of pinning parameter I. It is shown that unlike in the case of small I, when the hysteresis loop is a part of a certain universal curve, the segments of the loops corresponding to a decrease in h in the first and second quadrants (and symmetric to them) pass below the universal loop, the degree of deviation increasing with pinning parameter I. The properties of the hysteresis loops are considered for various amplitudes of the magnetic field variation on the basis of analysis of vortex configurations.
Physical Science of Materials
Formation of nanodiamond films from aqueous suspensions during spin coating
Аннотация
The formation of multifunctional ordered arrays of detonation diamond particles is studied during self-assembling in spin coating of films of evaporating microdroplets. It is shown that the most homogeneous layer of diamond particles on a crystalline silicon substrate forms at a rate of substrate rotation of 8000 min–1, whereas a relation between the distribution of particles and the radius is clearly detected at rates of about 2000 min–1. As the rate of substrate rotation increases from 2500 to 8000 min–1, the density of the coating of a silicon substrate with diamond nanoparticles decreases approximately threefold. A model is proposed to estimate the increase in the number of individual diamond “points” with the substrate rotation frequency.
Structural modification of TiAlN coatings by preliminary Ti Ion bombardment of a steel substrate
Аннотация
The TiAlN coatings deposited onto steel 12Cr18Ni9Ti substrates before and after preliminary treatment by Ti ion beams are studied by X-ray diffraction, transmission electron microscopy, atomic force microscopy, and nanoindentation. The modification of the surface layer of a substrate is shown to change the structure and the preferred orientation of the coatings. The mechanical properties of the TiAlN coatings are found to depend substantially on the ion bombardment time.
Nanostructure and electrical conductivity of amorphous granulated (Co45Fe45Zr10)x(Al2O3)1–x composite films
Аннотация
The nanostructure of amorphous granulated (Co45Fe45Zr10)x(Al2O3)1–x (0.30 < x < 0.75) composite films 2.2-5.8 μm thick deposited onto a pyroceramic substrate is studied by atomic force microscopy, magnetic force microscopy, and scanning electron microscopy. The average grain size and the metallic-phase content are shown to affect the electrical conductivities of these films.
Solid State Electronics
Powerful diode nanosecond current opening switch made of p-silicon (p-SOS)
Аннотация
The nanosecond semiconductor diode-based opening switch (SOS-diode) capable of switching currents with densities up to several tens of kiloamperes per cubic centimeter represents a p+p’Nn+ silicon structure fabricated by the deep simultaneous diffusion doping (to about 200 μm) of n-Si by Al and B from one side and P from the other. In the SOS mode, first a short pulse of forward current passes through the diode and then a fast-growing pulse of reverse voltage is applied. A resulting pulse of reverse current carries away injected holes and thereby forms a plasma front in the p’ layer, which moves toward the p’N junction. When the hole concentration in the flow exceeds the dopant concentration in the p’ layer, a space charge region arises in this layer, the resistivity of the diode increases sharply, and the current switches to a load connected parallel to the diode. Early results concerning an alternative configuration of the SOS diode are presented. Here, the diode was made by the rapid simultaneous diffusion of B and P from the opposite sides of a p-Si wafer to a depth of 60-80 μm. If a short pulse of forward current is passed through such a p+pn+ structure and a pulse of reverse voltage is then applied, a plasma front arising in the p+ region moves toward the p+p interface through the heavily doped (i.e., low-resistivity) p+ region. Having crossed this interface, the front passes into a low-doped region, where the hole concentration in the flow becomes much higher than the dopant concentration and a space charge region causing the current to pass to the load forms at once. It is shown experimentally that, all other things being the same, the time of current breaking in the p-SOS-diode is roughly twice as short as in the conventional n-SOS-diode, switched currents are considerably lower, and the fabrication technique of p-SOS-diodes is much simpler. Ways of optimizing the design of the semiconductor structure of the p-SOS-diode to further raise the speed are outlined.
Physics of Nanostructures
Physical properties of carbon films obtained by methane pyrolysis in an electric field
Аннотация
A method of synthesizing carbon films on single-crystal silicon substrates by methane pyrolysis in an electrical field is suggested. The pressure and temperature arising in a working chamber when the substrate is exposed to C–4 ions during pyrolysis are measured. Ion bombardment generates nuclei in the form of fibers about 2 μm in diameter providing the growth of a polycrystalline film. The resulting material is examined using electron microscopy and photo- and cathodoluminescence. Synthesized films are a composite material the matrix of which contains nanoclusters of a dissimilar crystalline nature. The effect of considerable two-stage decrease in the resistivity of the film material with increasing temperature from 300 to 1750 K is discovered. This points to the semiconducting properties of thick carbon films.
Acoustics, Acoustoelectronics
Radiophysics
Parametric chaos generator operating on a varactor diode with the instability limitation decay mechanism
Аннотация
Equations are derived for a parametric chaos generator containing three oscillatory circuits and a variable-capacitance diode (varactor) and are reduced to equations for slow amplitudes of parametrically interacting modes. With allowance for quadratic nonlinearity, the problem is reduced to a system of three first-order differential equations for Pikovsky–Rabinovich–Trakhtengerts real amplitudes with a Lorenz-type attractor. In a more accurate description of nonlinearity of the varactor, the equations for slow amplitudes are complex-valued, which leads to the loss of robustness of chaotic dynamics, which is typical of the Lorenz attractor. The results of numerical calculations (portraits of attractors and Lyapunov exponents) in models with different approximation levels are compared.
Electrophysics, Electron and Ion Beams, Physics of Accelerators
Compensation of large ion energy spreads by multigap grid reflectors in time-of-flight mass spectrometers
Аннотация
The problem of compensation of the initial ion energy spread by a multigap grid reflector of the time-of-flight mass spectrometer is considered. It is shown mathematically that the problem can be reduced to analysis of properties of catastrophes An under additional conditions of positive geometrical gaps of the reflector. Examples of design of reflectors corresponding to catastrophes A2 and A3 are analyzed. The advantage of a three-gap reflector over a two-gap reflector in the compensation of a large energy spread of ions for the same value of the resolution of the device is demonstrated. The application of the three-gap reflector improves the sensitivity of the time-of-flight mass spectrometer. The results of calculations are confirmed experimentally.
Experimental Instruments and Technique
Supersensitive graphene-based gas sensor
Аннотация
Epitaxial graphene layers are produced with the aid of thermal destruction of the surface of a semi-insulating SiC substrate. Raman spectroscopy and atomic-force microscopy are employed in the study of the film homogeneity. A prototype of the gas sensor based on the films is fabricated. The device is sensitive to the NO2 molecules at a level of 5 ppb (five particles per billion). A possibility of the industrial application of the sensor is discussed.
Short Communications
IR photodetectors operating under background illumination
Аннотация
The spectral dependence of the photoconductivity of silicon with multiply charged manganese nanoclusters is studied at different background currents. The spectral ranges where the IR quenching of the photoconductivity takes place and a shift in the photon energy at which the quenching efficiency as a function of the background current reaches a maximum are determined. The results allow us to design low-level IR photodetectors intended for the interval hν = 0.4–0.8 eV in the presence of fairly high background currents.
Reaction-diffusion-induced explosive crystallization in a metal–selenium nanometer film structure
Аннотация
Experimental data for reaction-diffusion-induced explosive crystallization in a nanodimensional metal (Cu, Ag)/selenium structure are presented. It is found that after the metal layer has completely diffused into the amorphous Se film, the electrical potential rises from 0.14 to 1.21 V in the Cu(30 nm)/Se(140 nm) heterolayer and from 0.01 to 1.17 V in the Ag(30 nm)/Se(140 nm) heterolayer. The metals diffusing into the amorphous Se layer interact with Se, forming nuclei of a new phase (CuSe or Ag2Se). The intense growth of the CuSe and Ag2Se crystallization centers results in a considerable liberation of latent energy in the form of phase transformation heat and in explosive growth of CuSe and Ag2Se nanocrystalline particles. The mean size of CuSe and Ag2Se crystallites equals 25 and 50 nm, respectively.
Dynamics of nanoparticle agglomeration in a magnetic fluid in a varying magnetic field
Аннотация
It is found that the dependence of the magnetic nanoparticle agglomerate length in a magnetic fluid on the applied magnetic field has three characteristic segments: a substantial increase in the agglomerate length with the magnetic field in the range of weak fields, a segment with an insignificant increase in the average length of agglomerates upon an increase in the field, and a sharp increase in the agglomerate length with a further increase in the field. It is shown that the agglomerate length increases in the range of strong magnetic fields due to a decrease in the spacing between adjacent agglomerates down to their complete coalescence. The total number of agglomerates decreases thereby.
Hydrogen permeability of thin condensed Pd–Cu foil: Dependence on temperature and phase composition
Аннотация
The hydrogen permeability of thin (about 4 μm thick) magnetron-sputtered Pd–Cu foil and structural transformations during temperature cycling (heating–cooling process) are studied. It is found that the hydrogen permeability is maximal when the content of the β-phase is 100%. Upon annealing of Pd–Cu alloy in hydrogen, the temperature range where a regular structure exists expands.
Selection and design of the secondary electron channel of the time-of-flight mass spectrometer
Аннотация
Computer simulation is carried out for selecting a compact electron-optical system of the channel for detecting secondary electrons formed during the interaction of xenon atoms or ions with energy of 1-30 keV with Xe atoms. The solid angle of passage of secondary electron beams in a wide range of their initial energies is calculated. The energy spectrum of secondary electrons with various energies is determined by constructing their deceleration curve.
Dynamic magnonic crystal based on a layered ferrite–ferroelectric structure
Аннотация
A dynamic magnonic crystal based on a planar multiferroid ferrite–ferroelectric structure is suggested and studied. A space-periodic electric field applied to the ferroelectric layer converts a regular multi-ferroid waveguide to a periodic structure. An electrodynamic model of a dynamic magnonic crystal is constructed, and its dispersion and transfer characteristics are studied.