Vol 42, No 5 (2016)

The dependences of the light sum of peaks of thermoluminescence (TL) at 180 and 300°C on the rate of heating of single crystals of anion-defective alumina after high-dose irradiation are investigated. It is found that these dependences for the peak at 180°C are the same for all studied samples and match the known dependence measured after low-dose irradiation. The curves for the TL peak at 300°C vary significantly from one sample to another. The parameters of thermal TL quenching are calculated for both peaks using the Monte Carlo method. Practical suggestions regarding the use of the obtained results in high-dose dosimetry are provided.

The switching rate in gas-discharge devices (kivotrons) based on an “open” discharge with counterpropagating electron beams is studied experimentally. Structures with a total cathode area of 2 cm² were used. A monotonic reduction in the switching time with an increase in the working gas pressure and in the voltage amplitude at the time of breakdown is demonstrated. The minimum switching time is ~240 ps at a voltage of 17 kV. The maximum current rise rate, which is limited by the discharge circuit inductance, is 3 × 10¹² A/s.

Thermal and thermoelectric processes in anisotropic heat elements located on substrates made of different materials have been numerically simulated. It is shown that, when an invariable heat flux passes through a heat element, the thermophysical properties of the substrate and heat transfer coefficient at its rear surface affect significantly the temperature distribution and the value of generated thermal emf.

A method for deposition of transparent nanosize ZnO-based coatings on the glass surface from solutions containing high-molecular polyvinylpyrrolidone is described. The method can be used to form transparent homogeneous coatings based on ZnO with an increased energy gap width. It does not require any intricate technological equipment.

A method for synthesis of carbon nanostructures in a high-frequency arc discharge in the flow of helium (3–4 L/min) is presented. It is shown that the plasma-chemical synthesis of fullerenes and endohedral metal fullerenes (EMFs) can be controlled by changing helium pressure in the chamber. Temperature and electron concentration along the line normal to the discharge axis decrease upon moving away from the axis to the periphery; the larger the pressure, the sharper is the decrease in these parameters. The optimal helium pressure of 98 kPa was found in obtaining the Gd@C₈₂ EMF which corresponds to the maximal EMF yield of 5 wt %.

Specific features of etching of GaN/AlGaN p–n structures in a KOH-based electrolyte have been studied. It was found that the corrosion process first passes across p layers through vertical channels associated with threading structural defects. Then, the corrosion process occurs in the lateral direction along n layers of the structure, with local hollows and voids thereby formed. The lateral etching is due to the presence of positive piezoelectric charges at boundaries of n-AlGaN and n-GaN layers and positively charged ionized donors in the space-charge region of the p–n junction.

The formation of a hardened layer with low-temperature (400°C)nitriding of grade 12Kh18N10T stainless steel in plasma of a pulse electron beam which is generated under continuous and pulse conditions at equal average current (2.6 A) and electron energy (200 eV) is studied. In spite of intense ion sputtering of the surface during the pulse, both nitriding conditions yielded equal quantities of thickness and hardness of the layer, which indicated that neutral atomic nitrogen plays a main role during nitriding.

The phenomenon of photoinduced refractive index change in active optical fibers with Al₂O₃/P₂O₅/Yb₂O₃/SiO₂ core composition has been observed under the action of UV laser radiation with 193-nm wavelength. It is established that hydrogen treatment of active fibers plays a key role in ensuring a radical (about two orders of magnitude) increase in their photosensitivity. It is shown that intrafiber Bragg gratings with reflection coefficients above 99% can be formed, which are promising mirror reflectors for fiber laser cavities.

We have studied Au/SiO_x/TiN/Ti memristive structures obtained by magnetron sputtering, which exhibit a reproducible resistive switching effect. The influence of the thickness and stoichiometry of SiO_x layer and the area of Au electrode on the parameters of switching has been analyzed. The obtained results show evidence in favor of the filament model of resistive switching in SiO_x films.

The influence of technological parameters of the process of thermal diffusion of titanium in lithium niobate substrates on the polarization-dependent losses of obtained optical waveguide has been theoretically studied. It is established that the anisotropy of refractive index variation leads to different conditions of polarization eigenmode cutoff that can be used for separating extraordinary and quenching ordinary polarization modes. Experiments with titanium-diffused waveguides showed the possibility of extraordinary polarization mode separation above 40 dB in the C-range (1530–1565 nm) of telecommunication wavelengths.

The design, main characteristics, and specific features of a new high-sensitivity magnetometer based on the giant magneto-impedance (GMI) effect in amorphous ferromagnetic microwires are considered. It is shown that, in addition to measuring homogeneous fields, the device is capable of detecting weak local magnetic fields of conduction currents and ion currents involved in corrosion processes. Results of in situ magnetic measurements of corrosion processes in the model system of copper–zinc in a sulfuric acid solution qualitatively agree with the data of direct corrosion tests employing the standard gravimetric method.

It is established that the energy of deposited particles influences the structure, composition, and properties of multilayer nitride coatings consisting of alternating layers of nanocrystalline TiN and amorphous Si₃N₄ phases with inclusions of nanocrystalline hexagonal AlN formed at energies of titanium, aluminum, and silicon ions exceeding ~317 × 10^–19, 267 × 10^–19, and 230 × 10^–19 J, respectively. As the energy of titanium ions bombarding the substrate increases above ~512 × 10^–19 J, the phase transition from disordered TiN_x to Ti₃N₂ and the appearance of 2- to 3-nm-thick sublayers in 15-nm-thick nanocrystalline TiN_x layers take place in the coating. The maximum hardness of such coatings reaches a level of ~54 GPa.

We have studied light-induced resistive switching in metal–insulator–semiconductor structures based on silicon covered with a tunneling-thin SiO₂ layer and nanometer-thick layer of antimony. The role of an insulator was played by yttria-stabilized zirconia.

Single-sheet and multiple beam electron emitters based on thermionic minicathodes for terahertz traveling-wave tubes have been studied. Data are presented for impregnated blade thermionic cathode with dimensions 0.1 × 0.7 mm and a maximum current density of 114 A/cm² in a pulsed mode. A variant of the five-beam electron gun with 0.25-mm-diameter cylindrical minicathodes in cells of a control grid is proposed that provides a current density of 85.5 A/cm² at a grid potential of 900–1000 V.

It is shown that the violation of periodicity in a low-dimensional waveguide microwave photonic crystal, in which the periodic structure is formed by dielectric layers and adjacent metal plates partly overlapping the waveguide cross section and forming capacitive gaps between the plate edge and wide wall of the waveguide, leads to the appearance of a defect (impurity) mode. It is established that the defect mode position on the frequency scale significantly depends on both the thickness of “disturbed” dielectric layer and the capacitive gap width of diaphragms.