Volume 43, Nº 10 (2017)

Hard aluminum–magnesium boride (BAM) films were fabricated onto Corning® Gorilla® Glass by radio-frequency magnetron sputtering of a single stoichiometric AlMgB₁₄ target. BAM films exhibit a Vickers hardness from 10 to 30 GPa and a Young’s modulus from 80 to 160 GPa depending on applied loading forces. Deposited hard coating increases the critical load at which glass substrate cracks. The adhesion energy of BAM films on Gorilla® Glass is 6.4 J/m².

The influence of ligands—organic molecules on the quantum dot (QD) surface—on the optical properties of thin-layer condensates of lead sulfide QDs and the photoconductivity of diode structures based on them has been investigated. A decrease in the ligand length by a factor of 4 is shown to reduce significantly the luminescence-decay time and increase exponentially the conductivity.

A spherical distributed Bragg reflector (SDBR) for near-infrared applications is elaborated via plasma-enhanced chemical-vapor deposition. It consists of the alternating quarter-wave layers of amorphous hydrogenized silicon carbide (a-Si_1–xC_x: H) and amorphous silicon oxide (a-SiO₂) deposited onto a glass microsphere. The reflection spectra of the SDBR are measured at different points of its surface. In all cases, the Bragg-reflection bands, as well as the wavelength range of their overlap, are detected, evidencing the presence of a complete photonic band gap in the SDBR obtained.

The phenomenon of explosive synchronization in a network of generalized Kuramoto oscillators is considered. It has been shown that this process results from self-similarity observed after the loss of stability by synchronous clusters of different dimensions. The appearance of self-similarity can be revealed when studying the processes of destruction in the synchronous state of a network. It has been demonstrated that a system passes through a sequence of self-similar configurations of interacting oscillators after the abrupt destruction of a synchronous regime.

An electrothermal method of nondestructive inspection of conducting materials is proposed and tested experimentally. This method is based on filming the IR emission of the surface induced in a sheet sample excited by a millisecond current pulse. Subsequent computer processing of the nonstationary thermalfield patterns reveals millimeter and submillimeter defects and provides an opportunity to estimate their geometrical parameters and the temperature-diffusivity coefficient of the material.

A study by secondary-ion mass spectrometry of InAs_xP_ySb_1–x–y/InAs heterostructures (x > 0.55) grown by vapor-phase epitaxy for lattice-mismatched with substrates samples revealed a noticeable and extended (~800 nm) exponential variation of the As and P content (y up to 0.12) across the layer thickness. The lattice mismatch calculated from the experimentally determined distribution of the As and P components was the strongest at the interface between the epitaxial layer and the substrate and decreased away from the heterointerface into the epitaxial layer.

The influence exerted by random dopant-concentration fluctuations on the current–voltage characteristics of the current flowing through a semiconductor superlattice has been studied. It was shown that the characteristics of the current flowing through the superlattice noticeably vary with the amplitude of fluctuations of nanostructure parameters. It was possible to find for a small sample the probability-density distribution of the integrated absolute values of the difference of currents at various amplitudes of the dopantconcentration fluctuations.

Spin-polarized current in thin-film tunnel mesa-structures formed by epitaxial cuprate superconducting (YBa₂Cu₃O_7–δ) and manganite (LaMnO₃) films and an upper superconducting Au–Nb bilayer is studied experimentally. Intrinsic narrow-band generation in the microwave range is reported. Its frequency is tuned by the bias voltage and an external magnetic field.

Some results of studying a planar “open” discharge with generation of counterpropagating electron beams at high voltages and appreciable working gas pressures up to atmospheric one are presented. The possibility of its functioning in helium at a voltage above 100 kV is demonstrated, and an increase in the working voltage does not prevent fast breakdown with characteristic switching times of ~1 ns. A specific feature of this type of discharge is the existence of a gas-pressure region, where the discharge-development delay time nonmonotonically depends on the voltage due to the competition between emission processes leading to breakdown.

The cathode attachment of a high-current vacuum arc on the fall of a current pulse was studied. Contacts generating an axial magnetic field were used. The revealed transformation of the attachment shape near zero current was explained quantitatively in a way that was in satisfactory agreement with experimental results.

A theoretical explanation of the phenomenon of spontaneous emergence of density waves experimentally observed recently in bilayered systems of miscible liquids placed in a narrow vertical gap of the Hele–Shaw cell in the gravitational field is provided. Upper and lower layers represent aqueous solutions of acids and bases, respectively, whose contact leads to the beginning of a neutralization reaction. The process is accompanied by a strong dependence of the reagent’s diffusion coefficients on their concentrations, giving rise to the generation of local density pockets, in which convection develops. The cavities collapse under certain conditions, causing a density jump, which moves faster than typical perturbations in a medium and takes the form of a shock wave. A mathematical model of the phenomenon is proposed, which can be formally reduced to equations of motion of a compressible gas under certain assumptions. Numerical calculations are given and compared with the experimental data.

Al₂O₃ nanocrystalline coatings are obtained for the first time by anodic thermal evaporation of aluminum in an arc discharge in an oxygen–argon mixture at a temperature of 600°C on stainless-steel substrates with a Cr₂O₃ sublayer. The effect of the surface state of the samples and ion energy on the phase composition, microstructure, and properties of the coating is assessed. The α-Al₂O₃ phase is formed in the range of the bias potential of 25–200 V, with the growth of which the microcrystallite size decreases from 60 to 15 nm and the hardness of the coating increases from 8 to 20 GPa.