Volume 44, Nº 12 (2018)

Using the methods of the field emission microscopy, the condensation of Si on the W surface at various temperatures T of the substrate and numbers n of monatomic layers of the deposited condensate is studied. At low temperatures of T ~ 600 K, a low-temperature Si monolayer with the structure of pure W is formed on the surface, whereas another structure of a high-temperature monolayer, namely, surface silicide, is formed at T ≥ 1000 K. The low-temperature monolayer and surface silicide also differ in their orienting effect when constructing the Si layers. In the case of condensation on a low-temperature monolayer, crystallites of Si are formed starting already from the third monolayer at n ≥ 3, whereas the Si crystallites grow during the condensation on surface silicide starting from n ≥ 300 monolayers.

The potential of the interaction between a C₆₀ fullerene molecule and a single-walled carbon nanotube is calculated. Using this potential, the equilibrium distance and binding energy as functions of the nanotube radius and the location of the molecule (inside and outside of the nanotube) are calculated. The minimum size of a nanotube inside which a fullerene molecule can be placed is determined. The results obtained are in good agreement with the experimental data.

In this paper, we calculated the impedance characteristics of a two-element antenna array with a chiral metamaterial substrate. A system of singular integral equations with Cauchy-type singularity with respect to the unknown longitudinal distributions of the surface current density is obtained. The input impedance dependences on the normalized arm length for various substrate types, as well as various values of the chirality parameter of the substrate, are presented.

The preparation and sonoluminescence of Cr(CO)₆ nanodispersed suspensions in water, 83% H₂SO₄, and 74% H₃PO₄ are described for the first time. In the spectra of single- and multibubble sonoluminescence of these suspensions, chromium atom lines are found that are analogous to the corresponding lines in the sonoluminescence spectra of true Cr(CO)₆ solutions in dodecane. Sonoluminescence of nanodispersed suspensions of metal carbonyl, by which the electronic temperature reached in the bubbles under sonolysis (from 6500 to 16 000 K in water and acids) was measured, expands the scope of the sonochemical model of injection of nanodroplets of low volatile compounds into cavitation bubbles due to the inclusion of injection of suspensions of insoluble substances into it.

The structural and electrical physical properties of barium titanate zirconate thin films on pure sapphire substrates and sapphire substrates with a platinum sublayer are investigated. The nature of substrate is shown to have a considerable effect on the crystal structure, phase composition, and electrical parameters of the prepared thin films. Capacitive elements fabricated using barium zirconate titanate films display high nonlinearity at low dielectric losses, as measured at a frequency of 2 GHz.

The variability of the heart rate of people depending on their age was analyzed for the first time using numerical characteristics of recurrence plots. The results are comparable with the data obtained by multifractal analysis. It is noted that the method of recurrence plots has a significant advantage since it requires a much smaller number of time counts and, therefore, can be used for rapid diagnostics in extreme situations.

To determine the effect of a metal substrate on the electronic state of quasi-free-standing graphene, a simple model taking into account the presence of the double electric layer on the metal surface is proposed. The arising electrostatic field shifts the Dirac point of graphene, which leads to its doping. An analytical expression for the charge of graphene atoms is obtained. Numerical estimations are made for (111) faces of Cu, Ag, Au, and Pt. The agreement of the obtained estimations with the available results of numerical calculations is discussed.

The explosive mode of operation of an electrochemical actuator is studied. In this mode of operation, we observe explosion of microbubbles containing the oxygen–hydrogen gas mixture that forms in the working chamber of the actuator during electrochemical water splitting by high-frequency pulses of alternating polarity. We demonstrate that shock wave emission occurs as a result of implosion of the void formed due to the microbubble explosion, rather than the explosion of the microbubble itself. Using the experimentally measured variation in the bubble wall velocity with the distance from the explosion center, we estimate the pressure amplitude at the shock front. The dynamic of microbubble collapse is established using time-resolved photography.

The ionic resistance of the membrane electrode assembly (MEA) of O₂/H₂ fuel cells is studied in situ in a broad range of MEA compositions by using electrochemical impedance spectroscopy and polarization measurements. The MEAs are composed of platinum on carbon, carbon nanotubes, and Nafion, a proton- conducting polymer. We investigate atypical growth of the MEA resistance with the increasing Nafion content and spatial nonuniformity in the MEA ionic resistivity. A mechanism underlying this phenomenon is proposed.

The results of studies of technological conditions of formation of LEDs on the basis of an InGaN/GaN micropyramid in the core/shell geometry using a semi-transparent Ni/Au/graphene contact have been presented. The structures have been formed by the method of metalorganic vapor-phase epitaxy. The development of the tranfer conditions of large-area graphene obtained by chemical-vapor deposition has allowed the using of it as a contact for current injection. The fabricated LEDs have demonstrated electroluminescence at a wavelength of 520–540 nm. These sources of radiation are of interest for biomedical applications— in particular, for optogenetics.

The method of transmission electron microscopy is used to study the grain-subgrain structure of the Ti–50.9 at % Ni nanocrystalline alloy after heat treatments at 300–500°C. It is found that the decomposition of the B₂ solid solution of TiNi by the heterogeneous mechanism occurs in the subgrain structure, while the Ti₃Ni₄ particles are not observed in nanograins. The features of the recovery and recrystallization of the alloy and their relationship with the processes of dissolution and precipitation of Ti₃Ni₄ particles are revealed.

Gradual variation of the content y of Group-V components by Δy of up to 0.08 across the thickness (600–850 nm) of an epitaxial layer has been observed for Ga_{1 – x}In_xAs_yP_{1 – y} solid solutions (x = 0.86, y = 0.07–0.42) produced on InP by metal-organic vapor-phase epitaxy under lowered pressure, although the composition of the gas mixture, temperature, and pressure were maintained invariable in the course of the growth process. For different gas mixture compositions, the value of Δy and the manner of its variation were different. An analysis of the data obtained demonstrated that Δy is due to the deformations that appear in a growing layer because of the lattice mismatch with the substrate.

The effect of synchronization of chemical concentration self-oscillations of the Briggs–Rauscher reaction under the periodic external effect of white light was studied. The change in the frequency of concentration oscillations outside the synchronization band was revealed under external exposure to light with a modulation frequency from 0.029 to 0.039 Hz before synchronization and from 0.1 to 0.14 Hz after it. The dependence of the synchronization band on the power is demonstrated, and the limiting values of the external light power at that self-oscillations are “turned off” are found. The synchronization range of concentration oscillations was revealed under external light exposure with a modulation frequency in the range of 0.04–0.1 Hz. When the light flux from a light source exceeds 5000 lm, the self-oscillation process is turned off.

A method of transmitting information with the expansion of the spectrum based on spectral interference between the reference noise and the information noise signal with a delay of different time according to the stream of binary bits is proposed. The occurrence of intrasystem noises with a shift in evaluation of the autocorrelation effect at the output of a two-channel correlation receiver is found. The possibility of noise-resistant transmission of information during spectral modulation as a result of the superposition of completely incoherent ultrawideband noise chaotic signals is shown.

A simulation of the structure and processes of heat and mass transfer in the system of exhaust jets of brake engines of a spacecraft descending in the Martian atmosphere is carried out. It is taken into account that the system of jets is a chemically reacting gaseous medium consisting of the exhaust gases and the Martian atmosphere; it is under conditions of quite high temperatures and is characterized by a developed turbulence. For realistic conditions, the calculation fields of the entire set of parameters of the medium consisting of the system of interacting supersonic exhaust jets of brake engines of a descending spacecraft in the Martian atmosphere are obtained.

The pulsed laser deposition method has been used to fabricate AlInGaPAs/GaAs/Si nanoheterostructures for cascaded photoelectric converters operating at wavelengths in the range of 300–1300 nm. The structural and luminescent structures of AlInGaPAs nanofilms on GaAs and GaAs on Si were studied. The spectral characteristics of photocells in an AlInGaPAs/GaAs/Si triple-cascade photoelectric converter were examined.

It has been experimentally established that the time of switching by triangular pulses in Ti—TiN–ZrO₂(Y)–Zr–Au memristor structures from the state of low resistance to the state of high resistance is inversely proportional to the voltage rise rate, i.e., the bias current through the memristor structure. A mechanism for the influence of a bias current on the switching time of the structure has been proposed.

We present a model of excitation of nonlinear spin oscillations in an antiferromagnet under the action of terahertz pulses of an electromagnetic field. It is shown that, with increasing pumping pulse amplitude, the spin system response increases linearly in the fundamental (resonant) quasi-ferromagnetic mode and quadratically in the second harmonic. We have compared the theoretically obtained dependences of the intensities of the sample response amplitudes for the fundamental mode and the second harmonic with the experimental ones. The comparison demonstrates the applicability of the developed method of analyzing dynamic processes in antiferromagnets occurring under the action of terahertz electromagnetic pulses.

Using the Shubnikov–de Haas effect, the dependences of electron effective mass m* and transport and quantum momentum relaxation times in Al_0.25Ga_0.75As/In_0.2Ga_0.8As/GaAs pseudomorphic quantum wells with one-sided silicon δ-doping on the electron density in the range of (1.1–2.6) × 1012 cm^–2 have been established. Nonparabolicity coefficient m* in the linear approximation was found to be 0.133m₀/eV. Both the transport and quantum momentum relaxation times depend nonmonotonically on Hall electron density nH, which is related to the competition between growth mechanisms of the Fermi momentum and the increasing contribution of large-angle scattering with increasing donor concentration.

Results of the development and study of an image brightness amplifier on manganese atom transitions for problems of object visualization in active optical systems are presented. The possibility in principle of using the developed active element for visualization of objects and processes in two spectral ranges—visible and near-IR—is shown. Profiles of the active element radiation beam at pulse repetition frequencies of up to 100 kHz have been obtained.

The effect of increasing the tunnel current in a metal–calcium fluoride–silicon structure with addition of a silicon dioxide layer between fluoride and metal (which seems paradoxical at first glance) has been considered. This effect of nonmonotonic change in the tunnel conductivity with an increase in the insulator thickness may occur at a relatively high bias at the structure and is related to the tunnel-barrier deformation, at which electrons are tunneling through its part formed by the oxide. At low biases, the occurrence/ thickening of an additional layer leads to a natural decrease in the current. Similar behavior is possible in principle for some other combinations of materials.

We propose a method of calcium isotope sepration using a countercurrent plasma centrifuge with a hot wall, which separating the fractions by means of vapor deposition at the end faces of the device. The centrifugal force, providing the effect of radial separation, is excited due to acceleration of a weakly ionized calcium plasma by a rotating magnetic field, while the axial circulating flow, which increases the effect of radial separation, is created by a traveling magnetic field. The capabilities of the method are demonstrated by the example of calculation of the separation factor of the plasma centrifuge as a function of the parameter characterizing the circulation intensity.

In this paper, we present the results of the study of a multiplier based on a traveling wave tube with a sheet electron beam and slow-wave double-grating structures. Device configurations with the possibility of obtaining an output power above 60 W at the second harmonic frequency of 190 GHz with an input power of about 10 W at the first harmonic frequency were determined.

The efficiency of broadband filtering of a polychromatic X-ray spectrum by a polycapillary structure in the region of photon energies E > 10 keV was demonstrated. A polycapillary 40.5-mm-long rod made of borosilicate glass and containing 10⁶ parallel hexagonal capillaries was used as a filter. Filtering was performed by introducing a misalignment of 0–4 mrad between the axis of this capillary structure and the primary beam direction. The relative attenuation of spectral density observed at energies ranging from 12 to 23 keV was as high as 17 dB.

A method for nondestructively determining the diffusion coefficient of solvents in thin fibrous material with strongly anisotropic properties is described. The sought-for coefficient is determined in the absence of a real static characteristic of the converter of the diffusant concentration in the solid phase, which substantially increases the productivity of monitoring.

The effect of interaction between a vortex ring and a solid surface is experimentally and theoretically investigated. Analytical formulas are provided that allow describing the pressure pulses arising when the vortex ring passes near the flat surface. The forms of pressure pulses are compared with those recorded in the experiment. The results may be utilized to predict the off-design regimes of a hydraulic turbine; such regimes are characterized by aperiodic high impacts in the hydraulic turbine’s circuit behind the runner.

The electron emission properties of submicron Si, GaAs, InSb, and InAs semiconductor particles and their multigrain structures have been investigated. The effect of the properties of nanoparticles on the field and secondary emissions has been established. A scanning electron microscopy-based method for measuring the secondary emission coefficient of semiconductors has been proposed. The effect of photoexcitation of the multigrain structure of submicron semiconductor particles on their secondary emission properties has been investigated by the vacuum triode method.

The stability of a liquid organic scintillator based on linear alkylbenzene in a volume of 1 m³ was measured. The measurements were performed using an iDREAM reactor antineutrino detector at the National Research Center Kurchatov Institute. No systemic degradation of the scintillator light yield within an observation time of 225 days was observed. These long-term stability measurements of a large-volume liquid organic scintillator based on linear alkylbenzene are the first in Russia.

It is shown that experimentally discovered nanosized bubbles in a water medium arise spontaneously due to the minimization of the Gibbs energy of the gas–liquid disperse system. Increased gas pressure inside the nanobubble gradually equalizes (according to the Henry law) with the atmospheric pressure of the air dissolved in the water. The bubble radius decreases to some extent, and the bubble transits to a stable state.