Vol 43, No 3 (2017)
- Year: 2017
- Articles: 24
- URL: https://journals.rcsi.science/1063-7850/issue/view/12679
Article
Optical spectroscopy of arrays of Ag–Au nanoparticles obtained by vacuum-thermal evaporation
Abstract
The possibility of creating irregular arrays of bimetallic Ag–Au nanoparticles is investigated. The ability to manipulate their optical properties based on the simple engineering processes of thermal spraying followed by low-temperature annealing is demonstrated.
A CuBr laser with high efficiency in the double-pumping-pulse mode
Abstract
The results of examination of characteristics of a CuBr laser operated in the double-pumping-pulse mode with a lasing pulse repetition rate of 50 Hz are presented. The potential to enhance the laser efficiency by choosing the optimum voltages of dissociation and excitation pulses and time delay values is discussed. It is confirmed that a more than twofold increase in the laser efficiency may be achieved through optimization and matched injection of the excitation-pulse energy into the active medium plasma. A laser efficiency as high as 2.6% (with respect to an excitation pulse) with an average power of 16 mW, an energy of 0.32 mJ, a halfamplitude laser pulse duration of 40 ns, and a time delay of 150 μs is demonstrated. The maximum average radiation power is 37 mW with an energy of 0.7 mJ and a laser efficiency of 0.7% at an energy density of 24 (2.7) mJ/cm3 of a dissociation (excitation) pumping pulse.
Characteristics of the effect of low-current gas discharge on a strong shock wave
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.
Effect of a thin a-SiOx: H film on plasmonic properties of gold nanoparticles
Abstract
Data on the optical properties of a nanocomposite material constituted by gold nanoparticles covered with a thin film of amorphous hydrogenated silicon suboxide have been obtained for the first time. The thin film was deposited by gas-jet electron-beam plasma chemical-vapor deposition. As gold particles situated on the surface of quartz glass are covered with a thin a-SiOx: H film, their plasmonic resonance peak is shifted to longer wavelengths. The calculations made in the study demonstrated a good agreement with the experiment.
Specifics of electron–ion heat exchange under intense photoexcitation of dielectrics with ultrashort laser pulses
Abstract
The rate of energy exchange between overheated electrons and the lattice of a dielectric exposed to an ultrashort laser pulse is analyzed in the case of electron scattering by the deformation potential of acoustical phonons and the polarization potential of optical phonons. The temperature and concentration dependences of the emerging heat flux are determined, and analytical approximating expressions are proposed. Estimates for silica are given.
Photo- and thermoinduced color centers in TiO2 ceramics
Abstract
Using a cryostat chamber developed for a spectrophotometer equipped with an integrating sphere, we have studied color centers (CCs) in photochromic titanium dioxide ceramics induced by radiation in the UV and visible spectral ranges. The channel of CC formation and annihilation during reductive-oxidation treatment is revealed, and the effect of thermoinduced growth of CC absorption has been found.
Ferromagnetic resonance of a magnetostatically stabilized domain wall in a nanowire–nanoparticle planar system
Abstract
The results of micromagnetic simulation of induced high-frequency magnetization oscillations in a planar ferromagnetic system composed of a magnetostatically coupled nanowire and nanoparticle are reported. The possibility of transformation of the spectrum of this system by introducing a domain wall stabilized with the magnetic field of the nanoparticle into the nanowire is discussed. The dependences of the frequency and amplitude of resonant oscillations of the domain wall on the geometric parameters of the system are analyzed.
Elastic and photoelastic characteristics of graphene-like compounds
Abstract
The central and noncentral harmonic force constants of the Keating model, proposed previously for describing elastic graphene constant, are obtained for 13 graphene-like IV–IV and III–V compounds. It is shown that the relative role of the noncentral forces decreases with an increase in the compound ionicity. For graphene, the anharmonic central-interaction constant is estimated and the dependences of the secondorder elastic constants on the two-dimensional pressure are calculated. Values of the photoelastic constants are determined.
Monitoring of elastic stresses with optical system for measuring the substrate curvature in growth of III-N heterostructures by molecular-beam epitaxy
Abstract
An original optical system for measuring substrate curvature (OSMSC) is described. The system enables a high-precision analysis of the processes of generation and relaxation of elastic stresses in growth of heterostructures (HSs) based on nitride compounds III-N by plasma-assisted molecular-beam epitaxy (PA-MBE). The application of OSMSC to analyze the growth of GaN/AlN/Si(111) HSs made it possible not only to observe in detail the variation dynamics of elastic stresses in this structure in its metal-enriched growth by low-temperature PA-MBE, but also to develop an HS design eliminating the effect of layer cracking by controlling the compressive stresses.
Features of interaction of an axisymmetric gas jet with a barrier of high-permeability material
Abstract
Complex diagnostics (shadow shooting, smoke imaging, gas analysis) has shown the formation of flows at inleakage of a carbon-dioxide gas jet onto a porous barrier on its surface, inside it, and behind it, as well as the flow circulating between the nozzle and the barrier. The spatial distribution of CO2 concentrations and the scheme of flows at jet interaction with a barrier are presented.
Analysis of spatial resolution of an experiment on verification of the equivalence principle for a neutron by the diffraction method
Abstract
Investigations of the spatial resolution of a setup for verification of the equivalence of inertial and gravitational masses of a neutron by the method of diffraction in a perfect crystal have been performed. Tests were conducted at Bragg angles of 74°–82°. A decrease in spatial resolution at Bragg angles >78° is detected.
2D-printing ink based on ultrasound exfoliated graphite
Abstract
A technique is described for producing 2D-printing ink based on ultrasound exfoliated graphite (UEG). It has been established that the conductivity of a film obtained by microfiltration of such ink is 26.4 S/cm. Data on the morphology, composition, and IR spectra of UEG films are provided and compared with analogous data for reduced graphene-oxide films.
Special features of electromagnetic energy accumulation at regular surface inhomogeneities on a dielectric sphere
Abstract
Evaporation of a water drop with ~1-mm diameter under the action of laser radiation with 10.6-μm wavelength and power-flux density within (4–12) × 105 W/m2 is shown to be determined by the optical properties of regular inhomogeneities occurring on the spherical surface of the liquid.
Synchronization of spin-transfer nano-oscillator by an external source
Abstract
The dynamics of a spin-transfer nano-oscillator (STN) of the point-contact type under the action of a spin wave excited in the ferromagnetic layer by an external source is considered. It is shown that the STN can be synchronized by this external source, and the regions of synchronism capturing and holding in the space of parameters are established. Dependences of the spin-wave amplitude on parameters of the external signal are presented.
The influence of photoelectron processes in a semiconductor substrate on the adsorption of polycationic and polyanionic molecules
Abstract
White-light illumination during the adsorption of polyanionic molecules of glucose oxidase (GOx) enzyme on the surface of p-Si/SiO2/polyethylenimine structure leads to a threefold decrease in the surface concentration of GOx molecules. Same illumination during the GOx adsorption on the n-Si/SiO2/PEI structure leads to a sevenfold increase in the surface concentration of enzyme molecules. Changes in the amount of adsorbed GOx molecules depending on the intensity of irradiation are explained by electron transfer processes and recharging of electronic states at the Si/SiO2 interface and within SiO2 layer.
Change in the mechanism of conductivity in ZrO2-based crystals depending on the content of stabilizing Y2O3 additive
Abstract
The interrelationship between the structure, phase composition, and transport characteristics of solid electrolytes based on ZrO2 has been studied as dependent on the content of stabilizing Y2O3 additive. It is established that twin boundaries do not lead to the appearance of additional mechanism of ionic conductivity acceleration in ZrO2–Y2O3 crystals. The maximum conductivity has been observed in ZrO2–(8–10) mol % Y2O3 crystals containing a t” phase, in which oxygen atoms are displaced from high-symmetry positions characteristic of the cubic phase.
An experimental study of rivulet flow in low-boiling liquid driven by gas flow in a minichannel
Abstract
Flow regimes in a low-boiling dielectric liquid driven by gas flow in a minichannel have been experimentally studied, and a map of regimes involving 11 varieties has been constructed. It is established that a rectilinear rivulet flow is observed in a restricted range of liquid and gas flow rates.
Temperature dependence of the optical absorption spectra of InP/ZnS quantum dots
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 E1 = 2.60 ± 0.02 eV (for the first peak of excitonic absorption in the InP core) and E2 = 4.70 ± 0.02 eV (for processes in the ZnS shell). The experimental curve of E1(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 E1 is determined by the interaction of excitons and longitudinal acoustic phonons with hω = 15 meV.
Studying gas temperature variation upon aerosol injection
Abstract
Variation of the temperature of gaseous combustion products upon pulsed injection of aqueous aerosols (water, NaCl solution, clay suspension) with droplet sizes within 40–400 μm has been experimentally studied at initial gas temperatures from 520 to 910 K. The motion of aerosol droplets in the counterflow of combustion products was visualized by panoramic optical techniques. It is established that the process of gas cooling depends on the degree of aerosol dispersion, NaCl concentration in solution, clay content in suspension, and the conditions of liquid phase injection.
Loading characteristics of a spin-transfer nano-oscillator
Abstract
A family of loading and control characteristics of a spin-transfer nano-oscillator (STNO) at various values of direct current have been constructed by integrating the Landau–Lifshitz–Gilbert–Slonczewski equation. The obtained characteristics are compared to approximated dependences calculated using truncated equations with respect to the first harmonic. An approximate expression is derived for the load resistance ensuring the maximum STNO output power.
Collective dynamics of identical bistable self-sustained oscillators with delayed feedback coupled via a mean field
Abstract
Peculiarities of the collective dynamics of self-sustained oscillators in an ensemble of identical bistable systems with delayed feedback coupled via a mean field have been experimentally studied and numerically simulated. It is established that the ensemble can occur in so-called “chimera” states, whereby some elements exhibit synchronous oscillations, while other oscillators exhibit asynchronous behavior.
The magnetoelectric effect in nickel–GaAs–nickel structures
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.
Controlling the position of a stabilized detonation wave in a supersonic gas mixture flow in a plane channel
Abstract
Stabilization of a detonation wave in a stoichiometric hydrogen–air mixture flowing at a supersonic velocity into a plane symmetric channel with constriction has been studied in the framework of a detailed kinetic mechanism of the chemical interaction. Conditions ensuring the formation of a thrust-producing f low with a stabilized detonation wave in the channel are determined. The inf luence of the inf low Mach number, dustiness of the combustible gas mixture supplied to the channel, and output cross-section size on the position of a stabilized detonation wave in the f low has been analyzed with a view to increasing the efficiency of detonation combustion of the gas mixture. It is established that thrust-producing flow with a stabilized detonation wave can be formed in the channel without any energy consumption.
Peculiarities of high-temperature superelasticity in Ni–Fe–Ga single crystals in compression
Abstract
The high-temperature superelasticity and temperature dependence of the yield stress of 14M and L10 martensite in [001]-oriented single crystals of Ni54Fe19Ga27 (at %) in compression alloy have been studied. As the temperature increases, the sequence of stress-induced martensitic transformations (MTs) changes from L21–14M to L21–L10. The yield stress of L10 martensite weakly depends on the temperature and is 1.7 times lower than that of 14M martensite. The temperature interval of superelasticity in [001]-oriented single crystals of Ni54Fe19Ga27 under compression is determined by the growth of critical stresses with increasing temperature, the coefficient of strain-hardening, and the yield stress of L10 martensite.