Том 63, № 6 (2018)
- Год: 2018
- Статей: 25
- URL: https://journals.rcsi.science/1063-7842/issue/view/12552
Theoretical and Mathematical Physics
Simulation of Properties of Images with Atomic Resolution in a Scanning Probe Microscope
Аннотация
A method for simulation of images in a scanning probe microscope (SPM) using simultaneous wavelet transform and median filtering is proposed. The wavelet transform with the fourth-order Daubechies kernel is used. Such a transform makes it possible to select details of different scales in the SPM image and, hence, study fractal properties of surfaces. Simulation is used to show that ultrahigh (atomic) resolution is possible in SPM provided that the size of the contact region in the probe–sample system is significantly greater than atomic size and the lattice atoms are randomly distributed. Contrast inversion in the SPM images in the multiscan mode is interpreted.
Gases and Liquids
On the Hydrothermodynamics of the Icing of a Wing Profile in the Air-Crystalline Flow
Аннотация
An experimental and theoretical complex was created to study the physical processes accompanying the interaction of the air flow carrying ice crystals with the heated surface of the streamlined body. An effective coefficient of phase transformations (evaporation and transition—through melting and solidifying in a liquid film—into barrier ice) of the mass of crystals bombarding a dry or moistened heated surface taking into account their partial entrainment with flowing air has been found. The physical and mathematical model of hydrothermodynamics of a liquid film is developed, the numerical data for the thickness, velocity, and temperature, complementing the results of the experiment, are obtained.
Plasma
Short Thermionic-Cathode Discharge in Alkaline-Earth Metal Vapor
Аннотация
A short (without a positive column) Knudsen thermionic discharge initiated in barium and strontium vapor has been investigated. It has been shown that the behavior of these discharges and their formation mechanism, effective heating of the plasma electrons by a cathode electron beam, are, in general, similar to the discharge in cesium.
Streamers at the Subnanosecond Breakdown of Argon and Nitrogen in Nonuniform Electric Field at Both Polarities
Аннотация
An ICCD camera was used to study plasma glow at the stage of the streamer (ionization wave) formation in the tip–plane gap with a length of 3 mm filled with argon or nitrogen at a pressure of 12.5–400 kPa. Positive and negative nanosecond voltage pulses were applied across the gap. Images of streamer were obtained at different time at its propagation along the gap. A streak-camera equipped with a spectrometer was used to measure time evolution of the radiation intensity of nitrogen molecules at a wavelength of 337.1 nm in several regions along the gap at the negative polarity. Average streamer velocity (1.8 cm/ns) was estimated from experimental data at atmospheric pressure of nitrogen. Amplitude–time characteristics of voltage, discharge current and the current of runaway electron beam behind the aluminum-foil anode with a thickness of 10 μm were measured. Reasons for a diffuse discharge under the given experimental conditions were discussed.
Microstructure of a Spark Discharge in Air in a Point–Plane Gap
Аннотация
A microchannel structure of a spark discharge initiated in atmospheric-pressure air in a point–plane gap has been discovered by shadow photography. The structure has been observed since the onset of the discharge glow. The evolution of the microstructure over times from several nanoseconds to several tens of nanoseconds has been traced. Specifically, the development of microchannels from the point into the discharge gap, expansion of the microchannels, and their interaction have been observed. A correlation has been found between the microstructure of the spark channel in the discharge gap and its autograph on the surface of the plane electrode.
Filling of a Plane Slit Volume with a Glow Discharge in a Transverse Magnetic Field and Its Effect on the Discharge Contraction
Аннотация
We consider a dc glow discharge in a plane slit volume with electrodes in the slit plane in a magnetic field transverse to the current, which has been studied experimentally. As in the experiment, the discharge is artificially confined at one of the dielectric boundaries of the volume and propagates to the opposite dielectric boundary until it is stabilized. It is shown using a 2D calculation of the nonstationary process that the discharge in a magnetic field occupies a noticeably larger volume (with a lower current density at the electrodes) than in zero magnetic field. The effect of the magnetic field is also manifested in that it hampers the contraction of the discharge, substantially elevating the threshold current of the diffuse discharge. The discharge contraction is calculated in the approximation of a homogeneous positive column along the current right to the attainment of the stationary state. In calculations with a magnetic field, hysteresis appears in transitions from the diffuse to the contracted state and back.
Solid State
Shape Memory Effects in Cu–Al–Ni Single Crystals and Linear and Rotary Engines on Their Basis
Аннотация
The functional properties of rod-shaped Cu–Al–Ni single-crystal alloy with the shape memory effect (SME) have been studied experimentally. Tensile tests of the samples have been carried out in the conditions imitating the operation of load-bearing elements in linear and rotary SME engines in the cyclic regime. Basic principles of constructing and the operating conditions of engines with load-bearing elements based on these single crystals have been formulated from the results of investigation. Basic relations between the functional properties of the single-crystal alloy and the main parameters of the engines have been established. Such characteristics as the maximal rod stroke in the linear engine and the angle of rotation of the shaft in the rotary engine, the maximal generated force and moment, as well as the effective work done by the engines, have been analyzed.
On a Possibility of the Overgrowth of Diamonds in the Hydrocarbon Atmosphere
Аннотация
The possibility to increase sizes of diamond crystals at least 25 μm by means of their annealing at a temperature of 1450 K in a hydrocarbon atmosphere has been studied. The initial diamond crystals are incorporated in the polyvinyl acetate layer on the surface of a silicon monocrystal and subjected to the annealing in methane atmosphere with low pressure in the presence of an external electric field with intensity up to 0.04 V/μm. Under these conditions the charged ions of methane dissociation products are accelerated and acquire the kinetic energy that is comparable with energy sufficient to form sp3-hybride bonds, which can lead to an increase in the sizes of initial seed crystallites. The obtained substrates of a composite with a typical thickness not higher than 1.2 mm, which contain a joined diamond crystal in the carbon matrix, can be used as thermal conductive and electrical insulating spacers in devices for cooling items of electronic engineering.
Origin of Elastic–Plastic Deformation Invariant
Аннотация
We consider the autowave mechanism of evolution of a localized plastic deformation of crystalline solids of different origins. It is found that localization of the plastic flow is determined by the relation between elastic and plastic phenomena in deforming materials. It is shown that the main parameter of deformation processes is the elastic–plastic deformation invariant, viz., a dimensionless quantity connecting quantitatively the parameters of elastic waves and self-sustained waves (autowaves) of localized plastic deformation. The correctness of this statement is verified for metals, alkali-halide crystals, and rocks. The physical origin of the invariant is explained on the basis of thermodynamic considerations.
Physical Science of Materials
Analysis of the Vacancy System of Restructured Zinc by the Positron Annihilation Method
Аннотация
We have obtained restructured zinc (high-purity zinc prepared by mechanothermal action of various intensity levels) and have analyzed its structure by the positron spectroscopy methods. Bulk vacancytype defects (vacancies and vacancy clusters), as well as the regions with an extended crystal lattice, have been discovered in the restructured samples and analyzed quantitatively. These effects are responsible for the emergence of internal microstresses in the material, which modify its properties.
Radiation-Induced Electrical Conductivity of Nanocomposite Materials
Аннотация
The radiation-induced conductivity of a nanocomposite with the inclusion of spherical nanoparticles as a function of intensity and time of action of gamma-radiation and the concentration and size of inclusions has been studied using the Rose–Fowler–Weisberg model. The energy spectrum of localized states associated with the nanoparticle inclusion has been determined. The numerical experiments have been made for polymethyl methacrylate (PMMA) nanocomposites with inclusion of CdS and α-Al2O3 nanoparticles as well as SrO nanoparticles.
Solid State Electronics
Combined Technology Fabrication of Spin-Valve Magnetoresistive Elements and Micromagnets
Аннотация
We present the research results of the fabrication technology of magnetoresistive (MR) elements based on the multilayer spin-valve magnetoresistive (SVMR) Ta–FeNiCo–CoFe–Cu–CoFe–FeNiCo–FeMn–Та nanostructures and CoNi micromagnets for the construction of digital galvanic interchanges and the magnetic field sensors. The results of experimental studies of test elements based on multilayer SVMR nanostructures with an MR effect from 7 to 8% and films of magnetically hard materials with a coercive force of up to 95 Oe formed on a single silicon die are presented.
Physics of Nanostructures
Dielectric Spectroscopy of Strongly Correlated Electronic States of Vanadium Dioxide
Аннотация
The thermal evolution of the conductivity of a VO2 film and database-obtained band gap Eg of film nanocrystallites is traced in the temperature range of –196°C < T < 100°C (77 K < T < 273 K); the level position of donor impurity centers is determined to be Ed = 0.04 eV. It is shown that energy Eg decreases from 0.8 to ∼0 eV with an increase in temperature in the range of 273 K < T < 300 K, which is caused by the narrowing of the energy gap due to correlation effects and considered as the temperature-extended Mott “insulator–metal” electron phase transition with the monoclinic lattice symmetry retained. The subsequent jump in the symmetry from monoclinic to tetragonal with a further increase in temperature is considered as the Peierls structural phase transition, the temperature of which is in the vicinity of 340 K and determined by the size effects, nonstoichiometry of VO2 film nanocrystallites, and degree of their adhesion to the substrate.
Formation Mechanism of Argon Clathrates with Carbon Dendrites
Аннотация
The formation mechanism of argon clathrates with carbon dendrites obtained in the plasma of an atmospheric-pressure gas discharge has been studied. It has been shown that the formation of these clathrates is due to the difference between characteristic times: the lifetime of molecules surrounding argon atoms and the time of C–C bonding. It has been noted that argon clathrates with carbon dendrites can form only if a number of conditions are met: formation of molecular traps in the discharge, provision of a sufficiently low temperature at the center of the arc discharge, and the presence of active carbon particles arising from plasma decomposition of hydrocarbon precursors. Whether or not these conditions are met depends primarily on the composition of the initial hydrocarbon mixture and discharge current density, as follows from experimental data.
Optics
Microturbines Formed with the Aid of Direct Laser Recording on Photoresist
Аннотация
A method for fabrication of mechanical elements (microturbines) that receive torque from vortex optical beams is proposed. Experimental results on fabrication of multiple microturbines are presented. Shapes of the microturbines are measured using an optical microscope, ZYGO white-light interferometer, and electron microscope.
Analysis of Different Contributions into the Magnetooptical Signal of Magnetophotonic Crystal Type Three-Dimensional Structures
Аннотация
Interference of effects of different levels and magnitudes in producing a net magnetooptical response was considered for the first time in structures similar to magnetophotonic crystals at different wavelengths of the incident irradiation in regions far from plasmon resonances. Contributions of interference and diffraction phenomena in maxima of different orders in three-dimensional systems of the magnetophotonic crystal type were studied. Use of the integral response in the analysis of the magnetooptical effects was shown to lead to disappearing of the interference phenomena. The zero-order diffraction maximum reflects adequately the magnetic component of the magnetooptical response. Numerical estimates of the observed diffraction and interference effects are reported.
Acoustics, Acoustoelectronics
Acousto-Optic Diffraction in Paratellurite by a Slow Acoustic Mode. Increase of Diffraction Efficiency of Divergent Light
Аннотация
Peculiarities of anisotropic acousto-optic Bragg diffraction in paratellurite by a slow acoustic wave have been considered. The ranges of frequency-angular dependences have been found, in which effective diffraction occurs, and their practical relevance has been formulated. The numerical values for light radiation with a wavelength of 1.06 μm have been obtained. We have proposed the method of enhancement of a diffraction efficiency of divergent optical radiation, which in turn leads to the increase of the response time of an acousto-optical modulator. The method is based on a multifrequency electric control of the acousto-optical modulator. We have shown experimentally that, as distinct from the single-frequency control, a considerable intensity suppression of the zero diffraction order from 30 to 8% is achieved.
Radiophysics
Effect of Ionosphere on the Excitation of Electromagnetic Field at Extremely Low and Lower Frequencies in the Near-Field Zone
Аннотация
Excitation of electromagnetic fields at extremely low and lower frequencies in the near-field zone of the Earth–ionosphere waveguide is considered. Variations in the field amplitude in the lower part of the extremely low frequency (ELF) range and lower frequencies are experimentally determined under different geophysical conditions in the absence of variations in the ultralow frequency (ULF) range. The effects related to such variations are analyzed with the aid of theoretical calculations that show significant effect of ionosphere in the near-field zone at relatively low terrestrial conduction.
Electrophysics, Electron and Ion Beams, Physics of Accelerators
High-Efficiency Electron Source with a Hollow Cathode in Technologies of Thin Film Deposition and Surface Treatment under Forevacuum Pressures
Аннотация
It is shown that low-energy beams with a high efficiency in a wide range of beam currents can be obtained in electron sources with a hollow cathode in the forevacuum pressure range. By varying the geometrical parameters of the electrode system and electromagnetic optics of the electron source, we succeeded in reaching the efficiency at a level of 0.9 for an accelerating potential of 1 kV and beam currents from 100 to 300 mA. The parameters affecting most strongly the efficiency and stability of operation of the electron source with a hollow cathode have been determined.
Physical Electronics
Stability of Field Emission from a Single Carbon Nanotube
Аннотация
It has been found experimentally that the field emission current passing through a single multiwall carbon nanotube heats it up and generates a thermionic component. The nanotube is heated by the Joule heat that releases on its series resistance, through which the current passes. From the solution to the heat conduction equation, the overheating temperature of the emitting end has been estimated. Conditions for field emission stability and for the onset of thermal field emission have been found.
The Influence of Film Thickness on Annealing-Induced Grain Growth in Pt Films
Аннотация
Pt films with thickness h = 20–100 nm deposited on oxidized с-Si(100) substrate have been subjected to vacuum annealing at 500°C for 1 h, which resulted in recrystallization and growth of grains. Simultaneously with the normal growth of grains, abnormal grain growth has been observed, as a result of which the grains have separated in normal and secondary grains. For h = 20–40 nm, the secondary grains become much larger than the normal ones and the grain lateral size distribution therefore becomes bimodal. It has been shown that the abnormal grain growth rate increases with decreasing h, whereas the normal grain growth rate is independent of h. From the Pt(111) and Pt(222) X-ray diffraction peaks analysis it follows that the mean size D of coherently diffracting domains increases as a result of annealing. In the annealed films, D sublinearly grows with h, whereas in the as-prepared films, D grows linearly.
Biomedical Physics
The Complex Nature of Thermal Phase Transitions in Albumin Solutions
Аннотация
Dielectric and optical methods were used to reveal the complex nature of globule–coil–coil associate phase transitions in solutions of human serum albumin. The impedancemetric and nephelometric curves of temperature dependences of the parameters of the phase transitions in albumin that was introduced into the standard saline were obtained. Impedancemetry revealed a two-stage mechanism of the globule–coil phase transition, and nephelometry established a two-stage mechanism of the coil–coil associate phase transition. The concentration dependences of the critical indices and temperatures were determined for both phase transitions.
Experimental Instruments and Technique
A Method of Video Goniography to Study the Morphology of the Lateral Surface of Profiled Monocrystals and the Device for Its Implementation
Аннотация
The method of video goniography and the device for its implementation has been described. The results of the study of the morphology of the lateral surface of profiled monocrystalline sapphire rods, which were grown by Stepanov’s method, of three main crystallographic orientations c{0001}, a{112̅0}, and m{101̅0} have been presented.
Short Communications
On the Question of the Source of the Apokamp
Аннотация
The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage pulse-periodic discharge under conditions where the electrodes have a capacitive decoupling with the ground. The aim of this work is the identification of distinctive properties of the offshoot in comparison with the apokamp. The differences in the spectra of the offshoot and plasma jet (apokamp) were detected experimentally in air under normal conditions. The results of the previous studies, according to which the apokamp is a wave of ionization, were confirmed. The launch of a helium plasma jet from the offshoot of the pulse-periodic discharge in a mode of the apokamp forming was demonstrated experimentally. It was shown that the offshoot of high-voltage pulsed discharge in the mode with the apokamp is a medium that is strongly heated and conducting electric current.
Influence of Dopant Incomplete Ionization on the Capacitance of a Reverse-Biased 4H-SiC p+−i−n+ Diode
Аннотация
The transient process in an RC circuit with a reverse-biased 4H-SiC p+−i−n+ diode serving as a capacitor has been numerically simulated using the SILVACO TCAD software environment. The model experiment has shown that the charge time of an optimally designed 4H-SiC p+−i−n+ capacitor with dopant incomplete ionization is roughly an order of magnitude shorter than in the hypothetical case of complete ionization. The potential effect of the dopant ionization dynamics on the transient process has been found.