Vol 44, No 6 (2018)

The instability of viscous incompressible fluid flows caused in a thin spherical layer by torsional oscillations of the inner sphere in a thin spherical layer with respect to the sate of rest is studied numerically. It has been established that an increase in the frequency of torsional oscillations leads to a change in the mode of the instability, with a transition from secondary flows in the form of Taylor vortices to structures not observed earlier. The revealed instability is observed in the frequency range from 0.61 to 2.45 Hz or, if the wavelengths are taken relative to the layer thickness, from 0.67 to 1.33.

Carrier transport and deep-level recharging in semiconductor avalanche S-diode structures have been investigated. Gallium-arsenide n⁺–π–ν–n structures with the diffusion distribution of deep iron acceptors have been studied. It has been found by solving the continuity and Poisson equations with the use of a commercial software that the electron injection affects the avalanche breakdown voltage and the spacecharge region broadens due to capture of avalanche holes on negative iron ions in the π-region. It is demonstrated by comparing the results of numerical calculation with the experimental data that the S-shaped I–V characteristic of the diffusion avalanche S-diodes cannot be explained within the previously proposed mechanism of capture of avalanche holes on the deep iron levels.

The frequency capture of radiation by an external signal was experimentally studied for the first time for a megawatt-power gyrotron. An external signal from the magnetron at a frequency of 35 GHz entered the working space of the gyrotron through a synthesized two-mirror quasi-optical converter that allowed transforming the input signal into a working mode. This converter has been recently developed and implemented in the Institute of Applied Physics, Russian Academy of Sciences. The radiation spectra were experimentally obtained in modes of frequency capture and frequency beats. The dependence of the frequency capture bandwidth on the power of the external signal was found. Comparison of experimental results with the data of numerical modelling of gyrotron equations with an external signal showed their good agreement.

A theoretical analysis of the mechanism of generation of singlet oxygen in the presence of photoexcited nanoporous silicon is presented. It is demonstrated that the mechanism of generation of singlet oxygen is based on nonradiative energy transfer from nanoporous silicon to an oxygen molecule by the exchange mechanism. An analytical expression of the probability of energy transfer from nanoporous silicon to an oxygen molecule is obtained, and a numerical estimate of this process is given. The numerical estimation is of the order of 10³–10⁴ s^–1, a value that agrees rather well with the experiment.

Results of an investigation of galvanomagnetic properties of Bi₉₅Sb₅ block thin films on substrates with different coefficients of thermal expansion covered with polyimide are presented. The difference between thermal expansions of the film material and the substrate was found to have a strong effect on the films’ galvanomagnetic properties. Analysis of the properties of the films using the two-band model showed that the concentration and mobility of the charge carriers in the Bi₉₅Sb₅ films are related to the coefficient of thermal expansion of the substrate material.

The currents induced by ion-acoustic solitons have been studied in a two-component magnetic–hydrodynamic approximation (MHD model) taking into account the trapped electrons. The solitons have been shown to excite unipolar nonpolar pulses of the ion and electron currents, and the established mechanisms of their excitation are. The spatiotemporal characteristics of the current pulses have been calculated, and the requirements for the spatiotemporal resolution of the experimental equipment necessary for detection of plasma currents induced by solitons have been determined. It has been shown that the solitons are the effective mechanism of plasma current generation.

A kinetic model of crystallization of lysozyme is proposed, and computer calculations of this process are carried out. The conditions for the formation of such crystals are determined. Under these conditions, individual crystals were grown that were suitable for X-ray examination. The developed model enables prediction of the quantity, size, and place of crystal nucleation inside the capillary.

The influence of structures formed during the evaporation and boiling of a liquid (n-dodecane) in thin horizontal layers on heat transfer has been analyzed. Structures shaped with the shapes of funnels and craters are formed at low pressures in liquid layers with thicknesses above the capillary constant under the action of a vapor recoil force. Increasing pressure leads to the onset of bubble boiling. It is established that the formation of these structures in the regime of intense evaporation at low reduced pressures leads to an about 70% increase in the heat-transfer coefficient at analogous layer thicknesses in comparison to the case of bubble boiling.

The problem of current density distribution over the surface of a strip dipole antenna occurring in the free space is reduced to a singular integral equation with the Cauchy singularity. Patterns of current distribution on the antenna surface for various values of the dipole length are presented.

We have studied the influence of graphene additives on the initiation of high-energy cobalt salt by a high-current electron beam of nanosecond duration. The high-energy composite was prepared by ultrasonic mixing of 80 wt% cobalt amminate (NCP) and 20 wt % graphene. It is established that the use of graphene as a sensitizing additive in a high-energy composite decreases the necessary energy parameters of the initiating electron beam and increases the energy characteristics and combustion rate of high-energy materials.

We describe the technology of obtaining highly oriented zinc-oxide (ZnO) films on amorphous substrates at high growth rates (up to 7 nm/s) by means of direct-current magnetron sputtering. It is suggested to optimize the substrate position with respect to magnetron and consider the floating potential to which the substrate is charged in magnetron discharge plasma as one of the main technological parameters. Electrondiffraction study of the structural characteristics of the obtained ZnO films showed that increase in the substrate temperature was accompanied by transformation of the crystallite shape from platelike to columnar.

Iron-oxide films on sapphire substrates were obtained using laser radiation with 1064-nm wavelength and studied by methods of scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission Mössbauer spectroscopy. The obtained Fe₂O₃ films probably occur in a superparamagnetic state and may find application in gas sensors and various magnetic devices.

The structure of nonstoichiometric silicon oxide (SiO_x) has been studied by the methods of highresolution X-ray photoelectron spectroscopy and fundamental optical-absorption spectroscopy. The conductivity of SiO_x (x = 1.4 and 1.6) films has been measured in a wide range of electric fields and temperatures. Experimental data are described in terms of the proposed SiO_x structure model based on the concept of fluctuating chemical composition leading to nanoscale fluctuations in the electric potential. The maximum amplitude of potential fluctuations amounts to 2.6 eV for electrons and 3.8 eV for holes. In the framework of this model, the observed conductivity of SiO_x is described by the Shklovskii–Efros theory of percolation in inhomogeneous media. The characteristic spatial scale of potential fluctuations in SiO_x films is about 3 nm. The electron-percolation energy in SiO_1.4 and SiO_1.6 films is estimated to be 0.5 and 0.8 eV, respectively.

X-ray diffraction (XRD) in asymmetric Bragg geometry was measured and XRD intensity distribution maps in the reciprocal space were constructed for GaN epitaxial layers with various degrees of structural perfection grown on c-sapphire substrates. It is established that equal-intensity lines (isolines) related to a regular system of perpendicular rectilinear threading dislocations are extended in a direction parallel to the surface. For a more chaotic distribution of dislocations with a large fraction of horizontal fragments, these isolines are rotated toward a direction perpendicular to the reciprocal lattice vector, although they still not attain a limiting position characteristic of the ideal mosaic crystal.