Vol 44, No 11 (2018)

A complex systematic study of the effect of various parameters of the CVD diamond growth in a microwave plasma (MPCVD diamonds), such as substrate temperature, the chemical composition of a gas mixture, etc., on dielectric losses in two frequency bands (25–30 and 250–350 GHz) for more than ten samples of various series is carried out. A correlation between the values of the losses in these two frequency bands is identified.

In this paper, we simulated the dependence of the effect of reducing the drain-induced barrier lowering on the thickness of a buried oxide layer in a finned (vertical) metal-oxide-semiconductor field effect transistor (FinFET) based on silicon-on-insulator technology. Three shapes of the fin with the rectangle, trapezoid, and triangle cross sections were considered. The drain-induced barrier lowering effect significantly depends on both the fin shape and the thickness of the buried oxide layer. The smallest drain-induced barrier lowering effect occurs when the thickness of the buried oxide layer is small for the fin of a triangular shape. This behavior of the drain-induced barrier lowering effect is strongly correlated with the behavior of the parasitic capacitance between a gate and a source.

Heat transfer in a heated film of distilled water under the action of external artificial perturbations with “the most dangerous wavelength” and variation in the Reynolds number from 300 to 500 has been studied. It has been shown that the action of artificial perturbations with an increase in the heat flux density leads to a change in the rivulet-wave structure of the flow, increase in wave amplitudes, and, finally, heat transfer enhancement.

A simple structural model is proposed for the zigzag interface formed by contacting two-dimensional graphene-like compounds AB and CD (both free and formed on a metal). For the graphene–hexagonal boron nitride system, analytical expressions for the electron spectrum, density of states, and atom occupation numbers at the interface are obtained. The results of calculating the densities of states and occupation numbers within two alternative approximations are in good agreement.

Amorphous films of two varieties of zinc stannate (ZnSnO₃ and Zn₂SnO₄) have been considered that were fabricated by radio-frequency sputtering of ceramic compound targets containing ZnO and SnO₂ in 1: 1 and 2: 1 ratios. The elemental and phase compositions of the films and their optical and electrical parameters were determined. The transparency of the films in the visible spectral range is on average 87%. Zinc stannate amorphous films have a high electrical conductivity in contrast to amorphous ZnO and SnO₂. This phenomenon, which makes it possible to use zinc stannate amorphous films in transparent and flexible electronics, is explained.

The behavior of a superelastic Cu−14.2% Al−4%Ni single crystal in the case of high reversible strains under a longitudinal bending force was investigated. The effect of strain confinement along the crystal length was revealed and studied. The highest reversible strains (up to 10%) were shown to be confined within the central part of the bent crystal.

The influence exerted by the heat removal conditions on the extent of overheating of photovoltaic converters of high-power (>10³ W/cm²) laser light has been studied. The temperature of the p–n junction of photovoltaic cells was measured by recording the instantaneous values of the open-circuit voltage generated by laser light. The effect of cooling in high-efficiency photovoltaic cells (efficiency = 55%) via removal of a substantial part of absorbed optical power by the photocurrent into the external load was demonstrated. It was shown that, at laser radiation power of 2.5 W, the overheating of a photocell with an area of 1.7 × 10^–3 cm² relative to the copper heatsink temperature is 48°C in the no-load conditions and 30°C in operation with the optimal load.

The results of studying the emissive ability, structure, and elemental composition of the surface of an impregnated cathode with a fine-grained tungsten matrix with addition of polyhedral multilayer carbon nanostructures of the fulleroid type (0.2−0.7 wt %), impregnated with barium-calcium aluminate with addition of sulfoadduct of carbon nanoclusters (0.1−0.2 wt %), are presented. The tests in diode prototypes showed that these cathodes provide a current density of 20 A/cm².

The photoconductivity of condensates of lead-sulfide quantum dots (QDs)—QD solids—with various organic ligands is studied. It is demonstrated that the QD solid photoconductivity increases exponentially with a reduction in length of ligand molecules and does not depend on their chemical structures, since it is governed by hopping transport of charge carriers. In contrast, the photocurrent in photovoltaic ITO/PEDOT: PSS/PbS/ZnO/Al elements depends on the ligand structure, since this structure sets the positions of QD energy levels and thus affects the efficiency of charge carrier transfer to electrodes. The difference between mechanisms of generation of photoconductivity and photovoltaic currents is discussed.

Carbon fibers are prepared during the conversion of acetylene and propane–butane mixture in a jet of the helium and argon plasma without using catalysts. The synthesis is carried out in a plasma jet reactor. The synthesis products are studied by electron microscopy, synchronous thermal analysis and energy dispersive X-ray spectroscopy. The effect of the synthesis parameters on the structure and properties of the carbon fibers prepared in the volume is established. When the propane–butane mixture is decomposed in an inert medium, conditions are found for the synthesis of cylindrical carbon nanofibers of a tortuous shape with a diameter of up to 20 nm and a length-to-diameter ratio of up to 1000. The decomposition of acetylene at 350 Torr produces nanofibers formed by a chain of straight cylinders with a diameter of up to 20 nm, and cylindrical fibers are synthesized in the form of spirals of up to 200 nm in diameter at 150 Torr.

A method is presented for reconstructing ensembles of nonlinear oscillators coupled with each other by nonlinear time-delay feedbacks. The method allows one, using time series, to reconstruct nonlinear functions of all elements of the ensemble, as well as the architecture of couplings between oscillators and the parameters of all sigmoid coupling functions, including the time delay.

It is established that simple color centers of the F⁺ and F type (anion vacancies with one or two electrons, respectively) in anion-deficient corundum (α-Al₂O_3–δ) crystals can be transformed into complex centers (including divacancy centers of the F₂ type) using a special thermo-optical treatment. A fine structure of the photoluminescence bands of complex centers of both the known and unknown natures was recorded in these crystals at helium temperatures in the near-IR range. A comparison with the photoluminescence bands in neutron-irradiated α-Al₂O₃ samples with the initial stoichiometric composition reveals their complete similarity, which indicates the possibility of nonradiative formation of complex centers in α-Al₂O₃.

In this paper, we have proposed to use accelerated flame propagation in the channel to generate directed flows of microparticles for effectively spraying them onto the substrate surface in the pulsed regime. Using mathematical modeling, we showed the basic possibility of practical using this approach and quantitatively estimated the effectiveness of the proposed procedure when gaseous mixtures based on hydrogen are used.

A new approach to selective laser cladding using conical laser beams has been elaborated. The initial round laser beam is divided into two or more circular beams with regulated distribution of the laser power between them. The circular beams are converted into conical beams that are focused separately on the surface and on different areas of the deposited material for their efficient heating. The delivery of laser energy into the powder stream is very effective because it provides a complete uniform absorption of laser energy in a dense powder stream (10⁴–10⁶ cm^–3). Under wire deposition, substrate heating reduces residual stresses due to temperature gradients and compensates for heat loss from the deposition zone by thermal conduction. The required power density for melt contact formation is significantly reduced.