Showing papers in "Technical Physics Letters in 2017"
TL;DR: In this paper, a molecular-beam-epitaxy technology was used to fabricate heterostructures for quantum-cascade lasers of the wavelength range of 7-8 μm with an active region comprising 50 cascades based on a heterojunction of In0.53Ga0.47As/Al0.48In0.52As solid solutions.
Abstract: It is shown that molecular-beam-epitaxy technology can be used to fabricate heterostructures for quantum-cascade lasers of the wavelength range of 7–8 μm with an active region comprising 50 cascades based on a heterojunction of In0.53Ga0.47As/Al0.48In0.52As solid solutions. The optical emission is obtained using a quantum-cascade design operating on the principle of two-phonon resonance scattering. The properties of heterostructures were studied by the methods of X-ray diffraction and transmission electron microscopy, which showed their high quality with respect to the identical compositions and thicknesses of all 50 cascades. Stripe-geometry lasers made of these heterostructures exhibited lasing with a threshold current density below 1.6 kA/cm2 at a temperature of 78 K.
29 citations
TL;DR: In this paper, the characteristics of signal registration of nuclear-magnetic resonance in a weak magnetic field from a small volume of an investigated medium have been considered, and a new developed design of a magnetic system for a compact nuclearmagnetic spectrometer, and also in the NMR-signal registration method allows significant extension of the possibility to use the phenomenon of nuclear magnetic resonance for the study of condensed medium in an express mode.
Abstract: The characteristics of signal registration of nuclear-magnetic resonance in a weak magnetic field from a small volume of an investigated medium have been considered. The consideration of the characteristics revealed in a new developed design of a magnetic system for a compact nuclear-magnetic spectrometer, and also in the NMR-signal registration method allows significant extension of the possibility to use the phenomenon of nuclear-magnetic resonance for the study of condensed medium in an express mode. The experimental results of different media studies have been presented.
27 citations
TL;DR: In this article, the compaction behavior in Al2O3 ceramics with a pore space volume in the range from 35 to 60% and with the following three types of hierarchical pore structure: coarse porosity, fine porosity and intermediate interblock porosity comprised of elongated microchannels formed as a result of zonal isolation during sintering.
Abstract: The compaction behavior is studied in Al2O3 ceramics with a pore space volume in the range from 35 to 60% and with the following three types of hierarchical pore structure: coarse porosity with a size of 80 to 100 μm, fine porosity with a size of 14 to 15 μm, and intermediate interblock porosity comprised of elongated (110–120 μm) porous microchannels formed as a result of zonal isolation during sintering. It is shown that the obtained hierarchical porous structure causes the formation of a hierarchical deformation structure in the volume of ceramics and leads to a decrease in the extent of destruction processes from the macroscopic scale in the case of unimodal ceramics to the microscale destruction comparable with the sizes of the blocks formed during sintering.
23 citations
TL;DR: In this paper, specific features of the formation of dark I-V characteristics of α-Si: H/Si heterojunction solar cells are investigated taking account the ratio between silicon doping level N d and excess concentration Δn of electron-hole pairs.
Abstract: Specific features of the formation of dark I–V characteristics of α-Si: H/Si heterojunction solar cells are investigated taking account the ratio between silicon doping level N
d and excess concentration Δn of electron–hole pairs. It is demonstrated that, at Δn ≥ Nd, the I–V characteristic is fundamentally different from the characteristic of a classical Shockley diode due the effect of the backside surface (additional drop of the applied voltage). The results of analysis are used to describe the experimental I–V characteristics reported in studies on α-Si: H/Si heterojunction solar cells. Numerical values of the ideality factors of the dark I–V characteristics are obtained by comparing the experimental and calculated curves.
23 citations
TL;DR: In this paper, the I-V and radiative characteristics of multilayer quantum-cascade GaAs/AlGaAs heterostructures with a double metal waveguide were investigated.
Abstract: I–V and radiative characteristics of multilayer quantum-cascade GaAs/AlGaAs heterostructures with a double metal waveguide are investigated The I–V characteristics typical of the quantum-cascade lasers are seen The observed threshold-intensity growth and narrow radiation spectrum are characteristic of laser generation The measured radiation frequency was found to be about 3 THz, which coincides with the calculated value Thus, fully domestic terahertz quantum-cascade lasers are demonstrated for the first time
22 citations
TL;DR: In this article, the dimensions of elements of a structure formed by particles of a colloidal solution of magnetite under the action of a magnetic field were determined by diffraction on the infinitely long dielectric cylinder.
Abstract: We have studied the dimensions of elements of a structure formed by particles of a colloidal solution of magnetite under the action of a magnetic field. The pattern observed in a thin layer of this fluid illuminated by a focused laser beam was characteristic of diffraction on the infinitely long dielectric cylinder that was used for determining the dimensions of separate aggregates. The obtained results proved to be well consistent with the values determined by means of optical microscopy.
21 citations
TL;DR: In this paper, Doppler backscattering (DBS) has been applied for the study of Alfven oscillations in the tokamak plasma for the first time, and the oscillations of the plasma rotation velocity at the Alfven frequency have been registered using DBS during the studies on the Globus-M spherical tokak.
Abstract: The method of Doppler backscattering (DBS) has been applied for the study of Alfven oscillations in the tokamak plasma for the first time. The oscillations of the plasma rotation velocity at the Alfven frequency have been able to be registered using DBS during the studies on the Globus-M spherical tokamak. The area of the development of Alfven instability has been determined. The measurement of the amplitude of rotation velocity oscillations has allowed the estimation of the absolute values of the amplitudes of the oscillations of the electric and magnetic fields of Alfven oscillations in the region of their existence in the plasma-discharge volume in tokamak.
18 citations
TL;DR: In this article, the secondary ion mass-spectroscopy technique was used to study the results of hydration of borosilicate, aluminosilicate and soda-lime silicate glasses in 1H2 18O water vapor containing 97% of the isotope 18O.
Abstract: The secondary ion mass-spectroscopy technique was used to study the results of hydration of borosilicate, aluminosilicate, and soda-lime silicate glasses in 1H2
18O water vapor containing 97% of the isotope 18O. It is shown that hydration of the surface of the soda-lime silicate glass occurs as a result of the ion-exchange reaction with alkali metals. In the case of borosilicate and aluminosilicate glasses, water molecules decompose on the glass surface, with the observed formation of hydrogenated layer in the glass being the result of a solid-state chemical reaction—presumably, with the formation of hydroxides from aluminum and boron oxides.
16 citations
TL;DR: In this paper, the authors experimentally studied how the Prandtl number of a nanofluid depends on the concentration, size, and material of nanoparticles, and found that the number increases with the size of the nanoparticles and decreases with increasing particle diameter.
Abstract: We have experimentally studied how the Prandtl number (Pr) of a nanofluid depends on the concentration, size, and material of nanoparticles. The nanofluids were prepared using distilled water and nanoparticles of silica, alumina, titania, and zirconia. The volume concentration of particles was varied from 1 to 8% and their diameters changed from 10 to 150 nm. It is established that Pr values of nanofluids increase with the concentration of nanoparticles. The Prandtl number also significantly depends on the size of nanoparticles and decreases with increasing particle diameter.
16 citations
TL;DR: In this article, the mechanisms of evaporation of silicon from the surface of silicon carbide (SiC) grown by atomic substitution are studied, and a method for growing epitaxial SiC films with a homogeneous composition and a low density of silicon vacancies from a gas mixture of carbon monoxide and trichlorosilane is proposed.
Abstract: The mechanisms of evaporation of silicon from the surface of silicon carbide (SiC) grown by atomic substitution are studied. It is assumed that the emergence of elastic deformations at the stage of cooling of the sample with a SiC film is one of the causes of Si evaporation. It is demonstrated theoretically that elastic stresses induce the mechanochemical Gorsky effect in the SiC layer. This effect initiates redistribution of Si and C atoms in the SiC layer, which results in violation of the stoichiometry of films and asymmetry of their composition over the SiC-layer thickness. A method for growing epitaxial SiC films with a homogeneous composition and a low density of silicon vacancies from a gas mixture of carbon monoxide and trichlorosilane is proposed.
15 citations
TL;DR: In this article, an instrumental model of a neuron based on a phase-locked loop with a bandpass filter in the control loop is proposed, and the main constructive elements of the system are described.
Abstract: An instrumental model of a neuron based on a phase-locked loop with a bandpass filter in the control loop is proposed. The main constructive elements of the system are described. The existence of different dynamic modes that are qualitatively similar to the spiking and bursting neuron dynamics has been experimentally demonstrated.
TL;DR: In this paper, the activation energies, capture cross sections, frequency factors, and concentrations of trap levels responsible for these peaks were determined, and the emission intensity and number of components increase with growing aluminum content x.
Abstract: Thermoluminescence of Ca(AlxGa1–x)2S4:Eu2+ (x = 0.1–0.3) solid solutions upon UV irradiation has been studied in the course of linear heating. It is established that the observed thermostimulated emission bands are complex, consisting of several strongly overlapped partial maxima. The activation energies, capture cross sections, frequency factors, and concentrations of trap levels responsible for these peaks are determined. The emission intensity and number of components increase with growing aluminum content x.
TL;DR: In this article, the effect of nonequilibrium plasma medium created by low-current gas discharge on a shock wave (Mach number M = 6.8) was investigated, and the phenomenon of broadening of the shock wave and an increase of its propagation velocity when passing through the region of none-ilibrium gas-discharge plasma was discovered.
Abstract: The effect of nonequilibrium plasma medium created by low-current gas discharge on a shock wave (Mach number M = 6.8) has been investigated. The shock wave is generated in a shock tube with a circular cross section and then passes through the area of the effect in the working chamber having a square cross section. The gas discharge is ignited in the area of the effect before the arrival of the shock wave by applying voltage to special pin electrodes mounted in the upper and lower walls of the working chamber. In the experiment, the phenomenon of broadening of the shock wave and an increase of its propagation velocity when passing through the region of nonequilibrium gas-discharge plasma was discovered.
TL;DR: In this article, the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20-30 μs) in a range of background gas pressures in the discharge chamber from 10−3 to 300 Torr.
Abstract: We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10–3 to 300 Torr. The electron concentration at low pressures (10–3 to 7 Torr) was determined using Starkeffect induced broadening of the Hα atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the Hα line corresponded to a plasma density on the order of 2 × 1016 cm–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 1015 cm–3.
TL;DR: In this paper, the influence of bombardment with accelerated gas-cluster ions on the surface topography of silicon carbide and diamond was studied and the ion-etching rate and efficiency of surface relief smoothing as dependent on the thickness of removed layer were estimated.
Abstract: We have studied the influence of bombardment with accelerated gas-cluster ions on the surface topography of silicon carbide and diamond. Atomic-force microscopy shows that exposure to 10-keV gas-cluster ions at a total dose above 1016 cm–2 leads to smoothing of the surface relief. The ion-etching rate and efficiency of the surface relief smoothing as dependent on the thickness of removed layer have been estimated. Raman-spectroscopy data show that surface irradiation with gas-cluster ions does not introduce defects into the crystalline structure of irradiated material.
TL;DR: In this paper, a comparative study of the microstructure and optical and electrical characteristics of gallium-doped ZnO films synthesized by magnetron sputtering with and without assistance to the growth process by UV radiation has been carried out.
Abstract: A comparative study of the microstructure and optical and electrical characteristics of gallium-doped ZnO films synthesized by magnetron sputtering with and without assistance to the growth process by UV radiation has been carried out. It was found that the UV assistance to the growth process of ZnO-based transparent conducting layers improves their electrical characteristics because of the formation of additional donor centers and the lower carrier scattering at grain boundaries, without any strong inf luence on the layer morphology and on the average optical transmittance in the visible spectral range.
TL;DR: In this paper, a grating was formed in a diamond substrate by implantation with boron ions through a mask, which led to the graphitization of diamond in unmasked regions and resulted in swelling of the irradiated layer.
Abstract: This work is devoted to new method of manufacturing of diffractive optical elements (gratings). A grating was formed in a diamond substrate by implantation with boron ions through a mask. Ion implantation led to the graphitization of diamond in unmasked regions and resulted in swelling of the irradiated layer. The formation of periodic graphitized surface microstructures on the diamond substrate was confirmed by optical, electron, and atomic force microscopy. The efficiency of operation of the obtained diffractive optical element was demonstrated by probing with He–Ne laser radiation.
TL;DR: In this paper, the critical shear stresses under tensile strain of Al0.3CoCrFeNi high-entropy alloy single crystals are independent of crystal orientation, and it is shown that the development of the planar dislocation structure in Al 0.3 CoCrNi single crystals at T = 296 K leads to a decrease in the ratio between the strain-hardening coefficient and shear modulus relative to that the value for Cu single crystals, where the cellular dislocations structure is developed at the similar staking fault energy.
Abstract: It is established that the critical shear stresses under tensile strain of Al0.3CoCrFeNi high-entropy alloy single crystals are independent of crystal orientation. It is shown that the development of the planar dislocation structure in Al0.3CoCrFeNi single crystals at T = 296 K leads to a decrease in the ratio between the strain-hardening coefficient and shear modulus relative to that the value for Cu single crystals, where the cellular dislocation structure is developed at the similar staking fault energy.
TL;DR: The stationary Penning discharge has been numerically simulated using the diffusion-drift model in the pressure range p = 0.5-5 Torr at emf E of 100 and 200 V as discussed by the authors.
Abstract: The stationary Penning discharge has been numerically simulated using the diffusion–drift model in the pressure range p = 0.5–5 Torr at emf E of 100 and 200 V. The two-dimensional electrodynamic-discharge structure has been investigated in the calculation region between a cylindrical anode and two flat disk cathodes. Configurations of the discharge plasma and averaged azimuthal motion rates of electrons and ions have been obtained. The evolution of the plasma configuration at a change in pressure, emf, and magneticfield induction is discussed.
TL;DR: A new method for the removal of physiological artifacts in the experimental signals of human electroencephalograms (EEGs) has been developed based on decomposition of the signal in terms of empirical modes.
Abstract: A new method for the removal of physiological artifacts in the experimental signals of human electroencephalograms (EEGs) has been developed. The method is based on decomposition of the signal in terms of empirical modes. The algorithm involves EEG signal decomposition in terms of empirical modes, searching for modes with artifacts, removing these modes, and restoration of the EEG signal. The method was tested on experimental data and showed high efficiency in the removal of various physiological artifacts in EEGs.
TL;DR: In this article, the authors used liquid phase sintering to construct a striker based on a porous WNiFeCo alloy, alloyed with tungsten carbide with cobalt (WCCo8) and titanium-tungsten carbonide (TiWC).
Abstract: The complex problem of increasing the penetrating power of strikers based on highly porous tungsten composites is considered by improving their strengthening properties by alloying the hardening components under high-speed collision conditions. Using the method of liquid-phase sintering, we fabricated samples of strikers based on a porous WNiFeCo alloy (tungsten + nickel + iron + cobalt), alloyed with tungsten carbide with cobalt (WCCo8) and titanium-tungsten carbide (TiWC). Dynamic tests of the strikers from the developed alloys were carried out at the collision velocity with a steel barrier of the order of 2800 m/s. The penetration depth of the striker based on a porous WNiFeCo alloy doped with tungsten carbides is 30% higher than the penetration depth of a striker of a monolithic WNiFe-90 alloy (tungsten + nickel + iron with a tungsten content of 90%).
TL;DR: In this article, the processes of formation and evolution of chimera states in the model of a multilayered network of nonlinear elements with complex coupling topology are studied.
Abstract: The processes of formation and evolution of chimera states in the model of a multilayered network of nonlinear elements with complex coupling topology are studied. A two-layered network of nonlocally intralayer-coupled Kuramoto–Sakaguchi phase oscillators is taken as the object of investigation. Different modes implemented in this system upon variation of the degree of interlayer interaction are demonstrated.
TL;DR: Results are presented of photochemical experiments with an IR-laser unit for microsurgery and photodynamic therapy in dentistry and the efficiency of direct generation of singlet oxygen in model organic media in the continuous-wave and pulsed nanosecond modes is examined.
Abstract: Results are presented of photochemical experiments with an IR-laser unit for microsurgery and photodynamic therapy in dentistry. The efficiency of direct generation of singlet oxygen in model organic media in the continuous-wave and pulsed nanosecond modes is examined. The unit can serve both as an independent instrument and as a part of a complex for robot-assisted surgery and dentistry.
TL;DR: In this paper, the effect of epitaxial stresses on the excess-carrier dynamics and the terahertz radiation spectrum of the InyGa1-yAs films have been investigated by optical pump-probe and terAhertz time-domain spectroscopy.
Abstract: The effect of epitaxial stresses on the excess-carrier dynamics and the terahertz radiation spectrum of the InyGa1–yAs films have been investigated by optical pump-probe and terahertz time-domain spectroscopy. It has been demonstrated that a InyGa1–yAs film with a higher mechanical stress has the shorter excesscarrier lifetime and broader terahertz radiation spectrum.
TL;DR: In this article, the authors measured the thermally stimulated luminescence of Gd3Ga3Al2O12:Ce3+ ceramics (a nominally pure sample and samples doped with rare-earth ions) in the temperature range of 80-550 K.
Abstract: The curves of thermally stimulated luminescence of Gd3Ga3Al2O12:Ce3+ ceramics (a nominally pure sample and samples doped with rare-earth ions) are measured in the temperature range of 80–550 K. The depth and the frequency factor of electron traps established by Eu and Yb impurities are determined. An energy-level diagram of rare-earth ions in the bandgap of Gd3Ga3Al2O12 is presented.
TL;DR: In this article, the possibility of directly synthesizing nanodispersed crystalline phases of titanium dioxides with rutile and anatase structures in a hypervelocity jet of electroerosion plasma generated by a coaxial magnetoplasma accelerator with titanium electrodes is presented.
Abstract: Experimental investigations of the possibility of directly synthesizing nanodispersed crystalline phases of titanium dioxides with rutile and anatase structures in a hypervelocity jet of electroerosion plasma generated by a coaxial magnetoplasma accelerator with titanium electrodes are presented. A powder product containing nanosized polymorphic phases of titanium dioxide with a spherical shape of particles has been manufactured.
TL;DR: In this paper, a technology for epitaxial growth of thin films of strontium iridate (Sr2IrO4) and related heterostructures with cuprate superconductor was proposed and developed.
Abstract: A technology for epitaxial growth of thin films of strontium iridate (Sr2IrO4) and related heterostructures with cuprate superconductor (Sr2IrO4/YBa2Cu3O7 − δ) has been proposed and developed. It is established that the two-layer structure grows epitaxially and the cuprate superconductor layer has the same critical temperature as that (~91 K) of an autonomous film. Crystallographic parameters of the obtained iridate films are close to tabulated values and the temperature dependence of their electric resistivity is consistent with published data.
TL;DR: In this article, the structure of ablated CeO2 nanoparticles is studied by transmission electron microscopy and X-ray-diffraction analysis, and the semiquantitative elemental composition is determined by electron energy-loss spectroscopy.
Abstract: Cerium-dioxide nanoparticles are prepared by laser ablation, and their structure is studied by transmission electron microscopy and X-ray-diffraction analysis. The semiquantitative elemental composition is determined by electron energy-loss spectroscopy. Based on the spectral data obtained before and after annealing of particles, the significant oxygen-vacancy concentration in the structure of ablated CeO2 nanoparticles is established.
TL;DR: In this article, the optical absorption spectra of InP/ZnS (core/shell) quantum dots have been studied in a broad temperature range of T = 6.5-296 K.
Abstract: The optical-absorption spectra of InP/ZnS (core/shell) quantum dots have been studied in a broad temperature range of T = 6.5–296 K. Using the second-order derivative spectrophotometry technique, the energies of optical transitions at room temperature were found to be E
1 = 2.60 ± 0.02 eV (for the first peak of excitonic absorption in the InP core) and E
2 = 4.70 ± 0.02 eV (for processes in the ZnS shell). The experimental curve of E
1(T) has been approximated for the first time in the framework of a linear model and in terms of the Fan’s formula. It is established that the temperature dependence of E
1 is determined by the interaction of excitons and longitudinal acoustic phonons with hω = 15 meV.
TL;DR: In this article, the magnetoelectric (ME) effect in structures obtained by the electrolytic deposition of nickel onto gallium arsenide substrates has been investigated and it is established that the use of a pre-deposited Ni-Au-Ge-Ni buffer sublayer significantly improves the adhesion of electroplated nickel to substrate.
Abstract: We have experimentally studied the magnetoelectric (ME) effect in structures obtained by the electrolytic deposition of nickel onto gallium arsenide substrates. It is established that the use of a pre-deposited Ni–Au–Ge–Ni buffer sublayer significantly improves the adhesion of electroplated nickel to substrate. The resulting Ni–GaAs–Ni structures are featuring both linear and nonlinear ME effects with respect to the alternating magnetic field. Both these effects exhibit a resonance character, the resonance frequency of the nonlinear ME effect being two times lower than that for the linear effect.