Vol 64, No 2 (2019)
- Year: 2019
- Articles: 27
- URL: https://journals.rcsi.science/1063-7842/issue/view/12627
Theoretical and Mathematical Physics
Localization and Transformation of Nonlinear Excitations in the Vicinity of Interface of Media with Nonlinearities of Different Signs
Abstract
Contact states at the interface of nonlinear media with anharmonicities of different signs are considered. A model that represents a boundary-value problem for the nonlinear Schrödinger equation is proposed. Several types of stationary states that depend on energy and describe local states in the vicinity of the interface, localization of nonlinear waves passing through the interface, and transformation of such waves are obtained for the system under study. Dispersion relations that make it possible to determine the energies of such states are derived. Explicit expressions for the energies of stationary states are obtained in the limiting cases.
Optical Properties of Spiroid C300
Abstract
Calculation results of the electronic spectrum of carbon nanospiroid C300 are presented. The π-electron structure of the spiroid is calculated using the strong coupling method, in which the matrix element of the exchange interaction of neighboring electrons (the resonance integral) is considered as being dependent on the local curvature of the spiroid surface. The optical absorption coefficient is calculated in the framework of the Tautz model and the result is compared with experimental and astrophysical observational data. The calculated and experimental data are in good agreement.
Gases and Liquids
Effect of Variations in the Gas-Dynamic Unloading on the Laser Initiation of the PETN–Aluminum Composite
Abstract
Thresholds of explosive decomposition Hcr under irradiation using the first harmonic of a pulsed neodymium laser (14 ns) are experimentally determined for pentaerythritol tetranitrate (PETN) with aluminum nanoparticles (100 nm) at concentrations ranging from 0.05 to 1 wt %. Amplitudes of optoacoustic signals are measured versus concentrations of impurities in the sample at a fixed laser fluence. The experiments are performed in two regimes. In the first one, the irradiated surface of the sample is covered with a finite-weight glass plate that impedes the gas-dynamic unloading. In the second regime, an external pressure of no less than 107 Pa is applied to the glass plate to prevent the gas-dynamic unloading. The interpretation of the experimental effects is proven by the results of theoretical simulation.
Collisions of Detonation Waves in Bubbly Media
Abstract
The oncoming collisions of detonation waves, generated in bubbly media, is studied in the present paper while determining the critical conditions of collisions initiated in bubbly media, as well as the structure and parameters of detonation waves. The structure and properties of post-detonation waves, which are wave perturbations arising upon collisions of bubbly detonation waves, are also examined.
Plasma
Population of the Metastable A3Σu State of Molecular Nitrogen under Conditions of Plasma Chemical Synthesis of Metal Nitrides
Abstract
The absolute population of the B3Πg state of molecular nitrogen is calculated from the intensity of electron-vibrational bands of the first positive system. The absolute population of the metastable A3Σu state of nitrogen molecules is calculated based on the solution of the balance equation. It is established that the population of the metastable state of molecular nitrogen increases with a decrease in the pressure and increase in the current intensity of the glow discharge. The results of determining the population of the A3Σu state of nitrogen molecules under conditions of simultaneous excitation of glow and vacuum arc discharges are presented.
Erosion Action of a Microstructured Spark Channel on the Surface of a Plane Copper Electrode
Abstract
Using a 3D optical profilometer, an erosion spot on the surface of a plane copper electrode has been studied. The spot arises under the action of the microstructured channel of a spark discharge initiated in atmospheric pressure air in a point–plane gap. It has been found that such spots are aggregations of microcraters. The shapes and sizes of microcraters have been determined.
Solid State
The Influence of Structural Factors on Strength and Electric Conductivity of Bulk Nanostructured Copper Alloys
Abstract
The structural parameters ensuring high strength and low electrical resistance have been analyzed in Cu–Cr alloys exposed to severe plastic deformation (SPD) and aging. Specific resistance and strength characteristics have been modeled for a Cu–0.5 wt % Cr alloy with a nanostructure state caused by SPD. A comparison of modeling data with experimental values reveals the validity of the approach chosen for describing the above states. The formation of nanostructure states with high strength and low electrical resistance is shown to be due to simultaneous effects depending on the treatment conditions of materials.
Anomalous Electrical Conductivity and Magnetization in Fe–Cr–Ni Austenite–Martensite Alloys
Abstract
We have measured the temperature dependence of the resistivity and magnetization of a special steel of the Fe–Cr–Ni austenite–martensite class in a wide temperature range (77–1100 K). It is found that at temperatures 77–170 K, the resistivity of the material almost remains unchanged, but upon a further increase in temperature, the resistivity sharply increases, which is probably a result of disordering. In addition, anomalous behavior of resistivity with vanishing spontaneous magnetization is observed at 910 K, which is associated with the ferromagnet–paramagnet phase transition. Comparison of the measured ρ(T) dependence with the analogous dependence for 12Kh18N10T austenite stainless steel has not revealed features typical of Fe–Cr–Ni steel.
Solid-State Flexural–Vibrational Low-Frequency Magnetic Field Sensor Based on the Piezoelectric Effect
Abstract
Optimal geometrical and electrophysical parameters are calculated theoretically; the effective response of a solid-state hybrid “magnet–carbon—piezoelectric” sensor is studied experimentally. Experiments are performed under the action of an external magnetic field of low-frequency flexural resonances (from 1 to 230 Hz). Theoretical calculations have formed the basis for designing an experimental prototype of the instrument. The frequency dependence of the direct piezoelectric response to the applied small-signal varying magnetic action is constructed.
SmS/SiC Heterostructure and Its Associated Thermovoltaic Effect
Abstract
A heterostructure based on single-crystal SiC and a polycrystalline SmS thin film has been studied. In the temperature interval 300–456 K, the thermovoltaic effect has been measured in the structure, the amount of which reaches ~12 mV at 456 K. It has been shown that the amount of this effect correlates with its concentration model developed earlier.
Physical Science of Materials
Resistivity and Tensoresistive Characteristics of TlInSe2–CuInSe2 Solid Solutions
Abstract
The concentration dependences of the resistivities and tensosensitivity factors of Ti1 –xCuxInSe2 alloys from TlInSe2–CuInSe2 system have been studied in concentration interval x = 0–0.1. It has been found that the concentration characteristics are linear in the range of solid solution existence (x = 0–0.025) and rapidly change outside this range.
Self-Organization of Multiscale Structural Groups in a Low-Carbon Wire Subjected to Severe Drawing
Abstract
The peculiarities of the mechanical parameters and atomic structure of wires made of 08G2S steel subjected to severe drawing with a combination of shear and classical circular drawing of different diameters. The split form of interference maximums (211) in X-ray diagrams of samples is evidence for delamination in families of the mentioned planes into contracted and extended groups, which is accompanied by the partial order–disorder phase transition with formation of the amorphized fraction from fragments of nanosized atomic groups of these planes (clusters). The dependence on steel deformation revealed the nature of the change in the symmetry of the distribution of structural groups relative to the angular position of the diffraction maximum from the planes (211). It is established that with increased deformation (ε > 30%) the intensities of coherent and incoherent X-ray CrKα-emissions vary quantitatively, which proves the development of self-organizing processes contributing to the increase in the volume fraction of the order relative to the disorder in 08G2S steel, even subject to severe mechanical loading.
Microscopic Examination of the Silicon Surface Subjected to High-Dose Silver Implantation
Abstract
Low-energy (E = 30 keV) Ag+ ions have been implanted into single-crystalline Si wafers (c-Si) with an implantation dose varying from 1.25 × 1015 to 1.5 × 1017 ions cm–2 and an ion beam current density varying from 2 to 15 μA/cm2. The surface morphology of implanted wafers has been examined using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, and their structure has been studied by means of reflection high-energy electron diffraction and elemental microanalysis. It has been shown that for minimal irradiation doses used in experiments, the surface layer of c-Si experiences amorphization. It has been found that when the implantation dose is in excess of the threshold value (~3.1 × 1015 ions cm–2), Ag nanoparticles uniformly distributed over the Si surface arise in the irradiated Si layer. At a dose exceeding 1017 ions cm–2, a porous Si structure is observed. In this case, the Ag nanoparticle size distribution becomes bimodal with coarse particles localized at the walls of Si pores.
Temperature Dispersion of Dielectric Characteristics of Composite Materials Based on Polyethylene and Na+-Montmorillonite Nanoclays
Abstract
The temperature dispersion of dielectric properties of polyethylene-based composites and nanoclays of the Na+-montmorillonite type is studied. It was found that as a result of the heating–cooling cycle, the dielectric characteristics of samples take on new values, which are preserved for some time. It is assumed that this effect is due to thermally stimulated processes of redistribution of charges at the filler–matrix boundary and their accumulation in deeper traps and, as a consequence, emergence of nonequilibrium states of the medium.
Surface Morphology and Structure of Plasma Coatings
Abstract
Specific features of the structure formation in rapidly quenched high-cobalt alloy coatings formed by plasma sputtering have been investigated. The structural state of the investigated coatings has been identified by the X-ray diffraction technique. The sequence and kinetics of structural transformations occurring in the specified time-temperature heating regimes have been examined using differential thermal analysis. It has been established that heat generation and crystallization temperature depend on the conditions of formation of bulk amorphous coatings.
Polystyrene-Based Composites with Aluminosilicate Inclusions of Different Shapes
Abstract
Samples of composites based on polystyrene with addition of halloysite nanotubes, mica, and montmorillonite aluminosilicates are obtained and the influence of these fillers on viscoelastic, mechanical, and structural properties of composites is studied. It is shown that an addition of up to 5% of mica can increase the rigidity of composites along with maintaining their strength at the level of pure polystyrene and without considerable embrittlement of samples. The addition of halloysite nanotubes and montmorillonite also increases the material stiffness but reduces its strength and elasticity. A significant (up to 50%) increase in the bending elasticity modulus of the composite was achieved by addition of 15% of halloysite nanotubes or 5% of mica.
Solid State Electronics
Thermal Surface Interface for High-Power Arsenide–Gallium Heterostructure FETs
Abstract
Application of heat-conducting coatings for cooling of high-power FETs based on heterostructures with arsenide–gallium substrate is theoretically analyzed. When the basic technology for manufacturing of transistors is employed in the absence of additional efforts aimed at a decrease in the thermal resistance of the substrate, the application of an additional thermal interface that represents a heat-conducting dielectric coating makes it possible to substantially decrease the overheating of the transistor channel. A several-fold decrease in such overheating can be reached using variations in the thickness of the coating and modification of the transistor structure and working regimes.
Simulation of a Detector of Visible and Near-IR Electromagnetic Radiation Based on Artificial Diamond
Abstract
A method for calculation of the I–V characteristic is proposed for a detector of visible and near-IR electromagnetic radiation based on artificial diamond with allowance for vertical flow of electric current. The method can be used when the free-path length of carriers in diamond is less than the scale of variations in the concentration of carriers. The method is used to determine the following detector characteristics: the dependence of current on voltage, distribution of carrier concentration, and electric potential for a particular variant of a photodetector based on polycrystalline diamond film consisting of nanosized single crystals doped with boron.
The Morphology and Electronic Properties of Si Nanoscale Structures on a CaF2 Surface
Abstract
Physics of Nanostructures
Structural and Magnetic Properties of the Al2O3/Ge-p/Al2O3/Co System
Abstract
The Al2O3/Ge-p/Al2O3/Co system with an Al2O3 buffer layer deposited by ion-plasma sputtering has been experimentally investigated. The dependences of the magnetic properties of cobalt on the rate of its deposition by ion-plasma sputtering and rate of deposition of preceding layers have been established. It is shown that the technique used to obtain buffer layers can significantly reduce the surface roughness of the next layers. The obtained buffer layers can be used as artificial substrates for growing heterostructures with tunnel junctions.
Acoustics, Acoustoelectronics
Acousto-Optic Commutation of Fiber-Optic Channels
Abstract
An acousto-optic commutator of fiber-optic channels based on a ТеО2 two-coordinate deflector has been proposed and realized. The commutator yields switching of optical radiation from a single output waveguide into a two-dimensional input matrix of waveguides, or vice versa, switching from any matrix waveguide into a single output one. The main interrelated parameters have been obtained. It has been established that the commutator has a short response time of 2–10 μs, yields up to several hundreds of switching channels, low insertion losses of 2–5 dB, and a considerable inter-channel isolation from –35 to –60 dB. Experiments were performed for the output matrix containing 19 waveguides. The channel multiplexing operating mode of this commutator has been demonstrated, which is simultaneous transmission of a signal from the output waveguide into a given number of waveguides of the input matrix.
Radiophysics
Slow-Wave System of Double Shifted Impedance Comb
Abstract
Using the partial domain method, surface integral equations are obtained for slow-wave systems of double shifted combs taking dissipation on all metal surfaces into account. The case of aliquot comb periods is considered. The quadratic functionals are proposed as dispersion equations. A method to solve complex dispersion equations in the form of functionals for complex constants of propagation is proposed by means of their joint iterations with integral equations. The results of calculating the dispersion with allowance for dissipation in several structures considered are presented.
Nonlinear Damping and Nonlinear Phase Shift of Intense Spin Waves in Screened Ferrite Films
Abstract
We analyze for the first time nonlinear damping and nonlinear phase shift of intense surface spin waves in screened yttrium–iron garnet films. Nonlinear damping coefficients are determined using the phenomenological model of spin wave propagation in such films. It is found that nonlinear phase shift in screened films is a weak effect as compared with free films and amounts to tens of degrees. At the same time, nonlinear damping in screened films is comparable with the corresponding value for free films. It is shown that for micrometer-thick films, the losses introduced upon an increase of power to 15 dBm become larger by 2–5 dB.
Physical Electronics
Annular Multi-Tip Field Emitters with Metal–Fullerene Protective Coatings
Abstract
A technology of creation of annular silicon field emitters with bilayer metal–fullerene coating has been developed and their performance has been studied. It has been shown that annular emitters with a surface area of about 0.3 cm2 provide a current up to 100–110 mA and stably operate under conditions of technical vacuum (~10–7 Torr).
Anisotropy of the Surface Energy and Work Function of IIB Metals
Abstract
On the basis of electron-statistical method of calculation of the surface energy of metals, a technique for estimating the electron work function of hexagonal and rhombohedral metallic crystals has been developed. This technique relates surface energy to work function and can thus be applied to estimate the surface energy of crystal faces from experimental data for a work function. Computations have been made for cadmium, zinc, and mercury macrocrystals. The temperature and orientation dependences of both quantities have been constructed. Our results are in good agreement with literature experimental data.
Physical Devices and Experimental Methods
Experimental Setup for Neutron Lifetime Measurements with a Large Gravitational Trap at Low Temperatures
Abstract
Currently the most accurate measurements of neutron lifetime are being performed at the Petersburg Nuclear Physics Institute with ultracold neutrons (UCNs) stored in a gravitational trap. A modified setup with a large gravitational trap and cooling to 10–15 K is presented. The results of measurements of temperature dependence of UCN losses in collisions with walls, which were coated with a perfluorinated grease (Fomblin UT 18), at 300–77 K, are detailed. The probable heat inflow to the trap is estimated, and the feasibility of cooling to indicated temperatures in experiments with the modified setup is demonstrated.