卷 62, 编号 12 (2017)

The nonlinear emission of electrons from a metal under the action of a femtosecond moderate-intensity laser pulse (laser shot) has been studied. A theoretical model of the process has been constructed based on the 1D nonstationary Schrödinger equation in the vacuum half-space with given boundary conditions for the electron wavefunction. This equation has been solved using the Laplace transformation. It has been assumed that the states of free electrons in a metal, which are described by the Sommerfeld theory of metals, are insignificantly influenced by the laser field. The energy spectrum of emitted electrons has been obtained, and its dependence on the parameters of the lased shot has been found. The calculated spectrum of nonlinear electron emission from a tungsten nanotip under the action of a 6.5-fs-long laser shot generating a field of 9.26 V/nm agrees with the experimental data.

Contact effects at the interface of linear and nonlinear media are studied. The problem of different stationary states in two-level system with different parameters of the dispersion relation is considered. A model that employs the nonlinear Shrödinger equation is used to show coupled states of solitons, localization of waves on one side of a defect, and transformation of nonlinear wave into linear wave upon transition through interface for the system under study due to variation in energy. Dispersion relations that determine the energies of such states are derived.

Abrupt high-density reverse current interruption has been numerically simulated for switching from forward to reverse bias in a silicon p⁺P₀n⁺ structure (p-SOS diode). It has been shown that the current interruption in this structure occurs as a result of the formation of two dynamic domains of a strong electric field in regions in which the free carrier concentration substantially exceeds the concentration of the doping impurity. The first domain is formed in the n⁺ region at the n⁺P⁰ junction, while the second domain is formed in the P⁰ region at the interface with the p⁺ layer. The second domain expands much faster, and this domain mainly determines the current interruption rate. Good agreement is achieved between the simulation results and the experimental data when the actual electric circuit determining the electron–hole plasma pumping in and out is accurately taken into account.

The problem of the stability of capillary waves on the surface of a charged jet of an ideal incompressible electroconducting liquid, which moves with respect to a material dielectric medium, is considered. There is a tangential discontinuity of the velocity field on the interface between the media. Solutions to the problem in two idealized models have been compared, i.e., when the jet has a finite and infinite length. It has been shown that the instability increments and the wave numbers of the most unstable waves, computed in both models, are linearly related, and velocity of motion of the jet acts as a coefficient of proportionality.

Vacuum-gap breakdown has been studied after high-current arc interruption with a subsequent increase in the transient recovery voltage across a gap. The effects of factors, such as the rate of the rise in the transient voltage, the potential of the shield that surrounds a discharge gap, and the arc burning time, have been determined. It has been revealed that opening the contacts earlier leads to the formation of an anode spot, which is the source of electrode material vapors into the discharge gap after current zero moment. Under the conditions of increasing voltage, this fact results in the breakdown. Too late opening leads to the breakdown of a short gap due to the high electric fields.

The temperature gradient and melting depth of the surface of iron-based alloys under the action of high-temperature pulsed plasma beams have been estimated and compared with the experimental data. It has been shown that the steel surface melts under the action of a pulsed plasma flow at an energy density of 15–20 J/cm²; the heat front propagates to a depth of up to 20 μm, the thickness of the molten layer being less than 10 μm. The characteristic size of the microstructure formed as a result of thermal perturbation is estimated at 17 nm. The formation of new phases with crystallite sizes that vary in the range of 16–270 nm is demonstrated experimentally. It has been shown that the formation of nanosize crystalline structure and modified near-surface region are the main factors responsible for strengthening steels.

The correctness of the known plane single-ended probe method for measuring the anisotropic ion distribution functions in a gas-discharge plasma has been considered. Analysis has been performed for positive probe potentials relative to the plasma with magnitudes on the order of the mean ion energy, which as a rule is much lower than the mean electron energy. We have analyzed the dependence of the collection surface area of a plane probe on its potential in this range. The structure of the near-probe layer has been determined for an isotropic electron distribution function of the Maxwellian or Druvestein type and an anisotropic ion distribution function. These results are used to derive analytic relations for the correction to the second derivative of the probe current with respect to the plane probe potential. It has been shown that, when the ion distribution function is measured in a wide range of conditions in the gas-discharge plasma, when the approximation of a collisionless probe layer is applicable, and the probe does not perturb the plasma, the dependence of the collection surface area of the probe on the potential can be disregarded in this range.

A comparative study of the structure and the chemical and phase composition of Ni₄₅Ti₃₂Hf₁₈Cu₅ and Ni₂₅Ti₃₂Hf₁₈Cu₂₅ amorphous alloys obtained by fast-quenching of melt stream by spinning has been carried out by transmission and scanning electron microscopy and X-ray diffraction. The critical temperatures of their devitrification were determined by the data of temperatures measurements of electrical resistance. The features of the formation of ultrafine structure and the phase transformation at the vitrification depending on the regimes of heat treatment and chemical composition of alloy have been established.

The influence of the dislocation mobility on the creep rate in aluminum has been estimated. In a steady state of creep, the dislocation mobility is varied by pinning dislocations using impurity atoms during heating. It has been shown that the change in the creep rate is proportional to the fraction of impurity atoms that migrate from the solid solution of deformed aluminum toward the dislocations.

A method has been developed for measuring the oxygen mass-transport resistance of porous electrodes based on micro- and nanostructures of a Nafion proton-conducting ionomer, Pt/C, and carbon nanowires with the ultrahigh porosity. The method suggests measuring the limit oxygen electroreduction current density at the controlled oxygen flow through an electrochemical system and calculating the oxygen mass transport resistance using the ratio based on the Fick’s law. The method has been used to study the mass-transport loss of a membrane-electrode assembly electrode and electrode material based on a rotating disk electrode and can be applied in the development of new electrodes.

The paper reports on the results of simulations of output characteristics of silicon solar cells based on the amorphous silicon–crystalline silicon heterojunction. In addition, the prospect of utilizing high-efficiency bifacial silicon solar modules for various orientational configurations is evaluated. The evaluations are based on the geographical location of the city of Astana (Kazakhstan) located at 51.2° N and 71.4° E at an altitude of 354 m above the sea level

The composition and structure of nanodimensional Ga_{1 – x}Na_xAs phases produced by implantation of Na⁺ ions into the near-surface area of GaAs have been studied by Auger electron spectroscopy and fast electron diffraction. It has been found that the thickness of the ternary epitaxial layer is 10–12 nm for ion energy E₀ = 20 keV. The composition of the three-layer nanosystems is GaAs–Ga_0.5Na_0.5As–GaAs.

Fiber-coupled semiconductor lasers are studied under pumping with high-power short current pulses. Appropriate parameters of the current pumping make it possible to substantially reduce the output pulse duration to 80 ps for a single-mode laser and 120 ps for a wide-stripe multimode laser at a pump pulse duration of 1 ns and to 40 ps for the single-mode laser at a pump pulse duration of 0.5 ns.

It has been shown that, in the presence of a longitudinal external electric field, the magnitude of the tracking or detracking force that emerges during the acceleration or deceleration of a beam propagating along a preliminarily created ion channel in the ion-focusing regime can be commensurate with the force of the interaction of a relativistic electron beam with the ion plasma channel.

The propagation of plane-polarized microwave radiation in magnetic colloids with magnetite particles and magnetosensitive emulsions based on such particles is experimentally studied. A magnetic field exerted along the propagation direction leads to the rotation of the polarization plane (Faraday effect) provided that the magnetite concentration is higher than a certain critical level. Specific features of the effect in structured magnetic colloids and magnetic emulsions related to structural changes in the presence of magnetic field are revealed.

At present, the experiment on measuring neutron lifetime using a big gravitational trap is being performed at Petersburg Nuclear Physics Institute. It is planned to achieve a measurement precision of 0.2 s, which is four times better than the best existing level of precision. The modified installation is simulated using the Monte Carlo method. It has been shown that the application of the absorber in the installation design increases the number of stored ultracold neutrons in the trap by a factor of approximately three and reduces the duration of the measurement cycle.

The results of experimental investigations of the processes of water droplet evaporation upon heating in a gaseous medium at temperatures of 500–1100 K have been presented. High-speed tools of video recording and panoramic optical methods of particle image velocimetry have been applied. The times of full droplet evaporation and mass evaporation rates have been calculated. The evaporation rates have been compared with those calculated using well-known evaporation models. The temperature ranges in which the mathematical modeling data well correlate with experiments have been determined.