Vol 44, No 10 (2018)

The character of the noise component of an electron beam formed by an explosive-emission cathode has been experimentally investigated. It is shown that its source is a large-scale shot noise related to the manifestation of ectonic structures in the electron beam. The measured quantitative characteristics of ectons are in good agreement with previously obtained data and estimates.

The quality of heteroboundaries and optimal conditions for epitaxial growth are critical parameters for obtaining low leakage currents of heterobarrier varactors in the InGaAs/InAlAs/AlAs material system. Grown by molecular-beam epitaxy, three-barrier heterobarrier varactor structures adjacent to InAlAs/AlAs/InAlAs barrier layers by additional mismatched InGaAs layers subjected to compressive stress show, under optimal epitaxy conditions, extremely low levels of leakage current density (not more than 0.06 A/cm² at a voltage of 5 V and 85°C) with relatively thin AlAs inserts (with a thickness of 2 nm).

The influence of electrical current (in the range 20–150 A) on the thermophysical characteristics of activated thermal cathodes (W + 2% ThO₂) in a freely glowing low-pressure argon arc is investigated. For the first time, the dependences of key cathode parameters, such as the heat flux at the electrode, the voltage equivalent of the heat, the specific erosion, and the distributions of the temperature and work function over the extension length of the cathode from the holder, are obtained. A nonmonotonic dependence of the specific erosion on the electrical current with a minimal level at 50–60 A is noted.

Reflectance spectroscopy has been used to determine the refractive indices of nanoscale In_xAl_yGa_1–x–yAs and In_xAl_1–xAs layers with indium and aluminum concentrations x = 0.21–0.24 and y = 0, 0.1, and 0.2 on specially created Bragg-reflector heterostructures at wavelengths in the range 700–2000 nm. It was demonstrated that the method based on an analysis of the auto- and cross-correlation coefficients of the wavelength derivatives of the dependence of the reflectance of structures of this kind in order to determine the dispersion curves of the materials forming a reflector. It was found that raising the concentration of indium in InGaAs and AlInAs leads to a substantial rise in the refractive index, with a preserved spectral run of the refractive indices, which is characteristic of gallium arsenide and aluminum arsenide.

A glow discharge dusty plasma in a magnetic trap in which the current channel narrows is obtained in moderate magnetic fields up to 3000 G. The results of initial experiments are reported. The formation of stable dusty plasma structures rotating at record-high angular velocities up to 15 rad/s is observed. The dependence of the angular velocity on the strength of the applied magnetic field is measured experimentally. We interpret it quantitatively on the basis of the ion drag force.

The structure and conductivity of hybrid nanocomposite poly(p-xylylene) films containing iron nanoparticles are studied. The films are obtained by the method of polymerization on a surface from the gas phase, and the concentration of the filler is 4 and 11 vol %. According to the analysis of microphotographs of nanostructures obtained by transmission electron microscopy, the particles are distributed evenly (with a size in the nanometer range and a rather narrow distribution). Studies of the frequency dependence of conductivity show that the transport of the charge carriers is realized by the hopping mechanism with a jump length of ~3.5 nm.

Aluminum-oxide ceramic samples have been prepared by additive manufacturing with subsequent sintering. The Hugoniot elastic limit and spall strength of the ceramics are determined by analyzing the full wave profiles of the samples recorded using a laser interferometer upon their shock compression with amplitudes of 6.8 and 13.8 GPa.

Three-dimensional interaction of a shock with lateral low-density gas channel of round, elliptic or rectangular cross-section is numerically studied using Euler’s equations. The structure of formed shock wave precursor is described in detail. Internal shear layer instabilities in three-dimensional flow are shown to develop faster than in axisymmetric case. Moderate amplification of high-pressure jet cumulation effect is noted for elliptic and rectangular channel cases. Dependence of precursor growth rate on cross-section shape is studied. It is found that stretching of cross-section shape significantly increases the duration of linear precursor growth phase.

The microstructure of an ML5 commercial magnesium alloy reinforced by aluminum nitride (AlN) nanoparticles with an average size of 80 nm at an amount of 0.5 wt % has been studied. Comparative data on strength and plasticity of the initial ML15 alloy and AlN-reinforced metal-matrix composite were obtained using Instron 3369 universal testing machine. The influence of material microstructure on the resistance of samples to high-rate deformation and fracture was determined by analysis of the full wave profiles measured using a VISAR laser Doppler velocimeter.

Deformation of NAND memory multichip packages (MCPs) with various thicknesses of substrate and silicon dies have been numerically simulated. The results of calculations are consistent with experimental data and show equivalence of the deformation in single- and multichip packages with the same total thickness of silicon. Analytical relationship between the values of MCP deformation, substrate core thickness, and total thickness of silicon dies is proposed, which agrees quite well with the data of modeling and can be used for preliminary estimation of MCP deformations.

The defect structure of a thick (~15 μm) semipolar gallium nitride (GaN) layer grown by hydride–chloride vapor phase epitaxy on a Si(001) substrate with buffer layers has been studied by transmission electron microscopy. The asymmetry of the defect structure of GaN epilayer has been revealed and analyzed. The influence of this asymmetry on the rate of decrease in the density of threading dislocations in the growing epitaxial layer is discussed.

Transmission electron microscopy data showed evidence of the formation of structural regions corresponding to deformation (dislocated) fragments and dynamically recrystallized grains in α-phase titanium upon torsion at high hydrostatic pressure at room and cryogenic temperatures. It is shown that the previously proposed “two-phase mixture” model is applicable to description of these defect structures.

GaAs Schottky barrier detectors for α particle spectrometry have been tested. Detectors had an input window area of 80 mm² and a working barrier layer thickness of 40–50 μm. The energy resolution (FWHM) measured on 5.499 MeV α line of ²³⁸Pu source amounted to 17.5 keV at a generator peak width of 7.8 keV. In the measurements on a ²²⁶Ra source, detectors showed linear response and nearly 100% charge collection efficiency at reverse bias above 65 V for all energies of α particles emitted from the source. Tests for thermal stability showed that the proposed detectors can be used in alpha-spectrometry of radionuclides at temperatures up to 120°C.

The possible formation of an extended low-energy state of electron beam in a coaxial diode with homogeneous cylindrical anode and moderate magnetic field with inhomogeneous profile is demonstrated for the first time. It is established that, depending on the magnetic field configuration, virtual cathodes (VCs) of two types can be formed: (i) a stationary VC with a localized reflection plane and (ii) a moving VC with a two-stream low-energy state of the electron beam.