Vol 45, No 4 (2019)

In this paper, we experimentally studied pulsed electron beams with a high local density. The conditions in which the energy density cumulation is observed during the interaction of electrons with the anode are shown to develop in vacuum and gas diodes at nanosecond and subnanosecond durations of a beam current pulse and a decrease in the interelectrode gap. The average electron energy in filamentation and self-focusing of an electron beam in a vacuum diode of an accelerator at a current of ~2 kA and a no-load voltage of ~400 kV was established to be 50–100 keV while the energy density was 10⁹–10¹⁰ J/cm³. It is confirmed that the beam current density in a gas diode can exceed 1 kA/cm². It is hypothesized that superdense electron beams in vacuum and gas diodes are formed as a result of avalanche multiplication of runaway electrons in the cathode–anode gap plasma.

Plasmonic nanoparticles have become a popularly accepted research tool in optoelectronics, photonics, and biomedical applications. The relatively recently appearing semiconductor plasmonic nanoparticles, as opposed to metal ones, are characterized by infrared plasmonic optical transitions and their application has a great future. In this work, the possibility of conversion of semiconductor (excitonic) fluorescence nanocrystals, i.e., quantum dots of the CuInS₂ composition, to plasmonic nanoparticles by postsynthetic treatment without changes in the chemical composition of inorganic part of the nanocrystals was demonstrated for the first time ever.

An approach of the epitaxial jointing of the GdBa₂Cu₃O_{7 – δ}-based tapes using the YBa₂Cu₃O_{7 – δ} layer is proposed. The structural and electrical characteristics of the formed joint have been investigated. Using the scanning transmission electron microscopy, the cross section of the joined region has been studied, partial melting of the YBa₂Cu₃O_{7 – δ} layer has been observed, and the solid-phase diffusion with the formation of the (Gd, Y)Ba₂Cu₃O_{7 – δ}, Y₂BaCuO₅, BaCuO₂, and CuO phases has been established. It is shown that the current-carrying capability of the superconducting joint is over 30% of the initial tape current.

It has been established that the loss of superconductivity in high-temperature superconductor wires at alternating current overloading is accompanied by changing the phase difference sign between current and voltage. In a second-generation stabilized HTSC wire with overloading, oscillations of the amplitudes of the alternating current and voltage have been observed due to variations in the size of the normal zone in the superconducting layer. A change in the phase difference sign can be used for the timely registration of the normal zone formation in the current-carrying elements of superconducting electrical equipment.

We demonstrate that it is technologically possible to obtain graphite-like films which can be used for the creation of a thermoelectric generator. The proposed technology ensures uniformity and rather small thickness of these films and allows them to be formed on a diamond-like film substrate with deposited contacts at acceptable interface. Measurements show that the electron-phonon drag effect in this system ensures thermo-emf values about 100 times as large as those provided by the diffusion process. Arrangement of the graphite-like material on a diamond-like film substrate also favors increase in the thermo-emf, which is a manifestation of the electron–ballistic phonon drag. It is established that conditions necessary for the creation of a thermoelectric generator can be achieved based on the proposed carbon nanostructures.

A technique for in situ fabrication of aluminum-based Ohmic contacts to EuO by molecular-beam epitaxy is proposed. These contacts have a linear current–voltage curve and a contact resistance of 0.55 Ω mm and are stable in air. This suggests that the proposed technique holds promise for spintronic applications.

We propose a method for simulating optoacoustic signals initiated by a laser pulse in an absorbing medium with elastic radiation scattering and carry out corresponding calculations. It is shown that the use of the method of spherical harmonics allows obtaining an analytical expression for the optoacoustic signal. The deviation of the absorption profile from the Bouguer type near the sample surface leads to a strong influence of the medium parameters on the position of the signal maximum. The growth of the albedo of onefold scattering leads to a decrease in the effective signal growth constant and its amplitude.

Processes in which the island structure is ordered occur in composite carbon films produced by preliminary population of an amorphous substrate with a detonation-diamond system and subsequent condensation of carbon from the vapor–gas phase. These processes, observed already upon filling of the substrate with diamond-growth centers, are manifested in that there appears a structural periodicity of the islands. It was found that the condensation of carbon on the populated substrate is accompanied by the evolution of the island structure of primary growth centers. This consists in that a hexagonal packing of the islands is formed, with the size of these islands increasing by two orders of magnitude. All these structural features of how a composite diamond-carbon film is formed indicate that self-organization processes occur in the system of diamond islands when carbon atoms are condensed and interact with primary diamond crystals.

This Letter presents the results of a study of the physical properties of micromesh transparent electrodes on a flexible substrate, obtained using a template in the form of silica layers subjected to controlled cracking. For the first time, a combined approach to the control of parameters of a micromesh structure (crack width and cell size) by varying the pH and the thickness of the sol layer is proposed. Using this approach, transparent electrodes with a surface resistance of 4.1 Ω/sq with a transparency of 85.7% were obtained. Micromesh electrodes are characterized by linear optical transmission in the visible and IR ranges, which opens up prospects for their use in optoelectronics.

A method of determining the spatiotemporal dynamics of current in semiconductor heterostructures is proposed that is based on the modulation of external probing radiation transmitted through the crystal. The proposed method has been verified on semiconductor laser thyristors based on AlGaAs/InGaAs/GaAs heterostructures. The results of this experiment qualitatively coincide with the results of previous measurements of the device on-state dynamics.

Hydrogel electrodes transparent in the visible range have been used for the first time to generate periodic sequences of nanosecond pulsed spark discharges with current amplitude up to 400 A at a 250-Hz repetition frequency. Video images of the discharge and craters formed on the surface of hydrogel electrodes are presented.

It is shown that high-current vacuum arcs accompanied by partial melting of the cathode surface and its droplet erosion can generate, in addition to the well-known droplets formed immediately in the cathode spot (first type droplets), a second component of erosion. The liquid part of the cathode surface can emit droplets with significantly different sizes and velocities, which may be called second type droplets. The mechanisms of the formation of first and second type droplets are also substantially different.

Single-mode lasing at room temperature in quantum-cascade lasers (QCLs) with arched cavity design has been demonstrated. The output optical power in single-mode lasing regime at ~7.7-μm lasing wavelength was above 6 mW with a side-mode suppression ratio of up to 25 dB. The QCL heterostructure for the arched cavities was grown by molecular-beam epitaxy (MBE) based on a heterojunction of In_0.53Ga_0.47As/Al_0.48In_0.52As solid alloys, lattice-matched with InP substrate, and InP layers performing the function of waveguide claddings.

Statistical analysis of distribution of the tensile strength of commercial oriented polyamide-6 (PA-6) fibers has been performed in the framework of the Gaussian and Weibull models using a large data array of the results of measurements for a large number (50) of identical samples. Using the example of PA-6, the dualism of strength distribution in oriented high-strength polymers is demonstrated for the first time, which consists in the validity of both the normal Gaussian distribution (characteristic of viscoelastic and plastic materials) and the Weibull distribution (characteristic of brittle materials).

We briefly describe the possible character and peculiarities of dispersion-induced distortions of a rectangular pulse with chaotic carrier modeled using the third-order Chebyshev map of the first kind propagating in a resonantly absorbing gas medium. It is established that, as the pulse goes away from the radiator, its envelope exhibits transformation toward a noiselike shape. In a rather wide region of parameters of the dispersive medium, distortions of the envelope are not accompanied by breakage or principal changes of its autocorrelation and frequency correlation functions.

The evolution of the elemental composition, surface morphology, microstructure, and mechanical properties of Ti_{1 –x–y}Al_xTа_yN coatings deposited by reactive magnetron sputtering has been studied when the ratio of the partial pressure of nitrogen to the total pressure of reactive gas mixture was increased from 0.1 to 0.5. It is established that most significant changes in the relative content of Ti, Al, and Ta in as-deposited coatings take place when this ratio is varied from 0.1 to 0.3. The observed changes in the elemental composition of Ti_{1 –x–y}Al_xTа_yN coatings do not influence their phase composition, but lead to changes in the microstructure and mechanical characteristics.