Volume 44, Nº 4 (2018)

The effect of a channel’s symmetry type on its internal dimensions, which would allow the movement of atoms (ions, molecules), has been discussed. Based on the symmetry properties of the Lagrange function for the channel and the properties of the channel itself, its internal dimensions are determined. The particular example of the crystallographic channel of quartz and its dislocations is considered.

The effect of rotation flow emerging under centrifugal casting on the first-order phase transition, i.e., crystallization, has been studied using the example of producing a gradient composite material of AK12 aluminum alloy in a mixture with basalt fibers. It has been shown that a material with a hardened surface can be created. Distribution of admixtures in the main material when there is macroscopic motion has been found.

The possibility of nanocrystal formation in silicon layers subjected to plasma-immersion helium-ion implantation at an energy of 5 keV has been proved for the first time. The effect of the implantation dose on the microstructure of the layers has been studied by X-ray reflectometry, transmission electron microscopy and Raman scattering. It has been established that the formation of silicon nanocrystals with dimensions of 10–20 nm is accompanied by a pronounced dependence on the ion flux and occurs at a dose of 5 × 10¹⁷ cm^–2 with subsequent annealing at 700–800°C. The excessive dose has been shown to cause the destruction of the upper protective sublayer and the degradation of the optical properties of nanocrystals.

A new approach to quantitative analysis of the concentration of boron atoms in diamond using secondary- ion mass spectrometers with time-of-flight mass analyzers is proposed. Along with the known boron-containing lines (B, BC, BC₂), many lines related to cluster secondary ions BC_N have been found in the mass spectrum; their intensity increases by one or two orders of magnitude when Bi₃ probe ions are used. Lines BC₄, BC₆, BC₂, and BC₈ have the highest intensity (in the descending order); when they are summed, the sensitivity increases by an order of magnitude in comparison with the known mode of detecting BC₂. The parameters of the boron δ-layer in single-crystal diamond films grown under optimal conditions have been measured to be unprecedented: the δ-layer width is about 2 nm, and the concentration is 6.4 × 10²⁰ cm^–3 (the boron concentrations for doped and undoped diamonds differ by four orders of magnitude).

We have experimentally studied a two-phase flow in a microchannel with a height of 150 μm and a width of 20 mm. Different liquids have been used, namely, a purified Milli-Q water, an 50% aqueous-ethanol solution, and FC-72. Before and after the experiment, the height of the microchannel was controlled, as well as the wettability of its walls and surface tension of liquids. Using the schlieren method, the main characteristics of two-phase flow in wide ranges of gas- and liquid-flow rates have been revealed. The flow regime-formation mechanism has been found to depend on the properties of the liquid used. The flow regime has been registered when the droplets moving along the microchannel are vertical liquid bridges. It has been shown that, when using FC-72 liquid, a film of liquid is formed on the upper channel wall in the whole range of gas- and liquid-flow rates.

The effect of precession-frequency mismatch between ¹²⁹Xe and ¹³¹Xe xenon-isotope nuclei, which arises under spin-exchange pumping by optically oriented alkali-metal (Cs) atoms and affects the characteristics of measuring and navigation devices based on balanced Schemes with spin-exchange pumping of xenon isotopes, has been investigated. An attempt to explain this effect has been made, and methods for its minimization and elimination have been proposed and experimentally verified.

New data concerning the influence of a probing beam of bismuth ions on the depth resolution in elemental depth profiling by secondary ion mass spectrometry (SIMS) have been obtained on a TOF.SIMS-5 system using the principle of two separate ion beams. It is established that the existing criterion of nondestructive character of the probing beam, on which this principle is based, is insufficient. Additional processes must be taken into account so as to formulate a more adequate criterion. A regime of depth profiling is proposed that allows the depth resolution to be improved at low energies of sputtering ions.

Aerodynamic flow past bodies of various geometrical shapes was studied, and the aerodynamic drag force was reduced through optimization of the body shape using a specially proposed method. The resulting drag force was compared to that for bodies formed by revolution of the profiles of well-known standard series. The study was performed using the Ansys Fluent software for isothermal laminar steady-state flows of incompressible fluid with constant density in a velocity range of 0–10 m/s. It is shown that the aerodynamic drag force for a body with the optimized shape is lower than analogous values for the bodies of revolution with Su-26 and NASA-0006 reference profiles. In comparison to the aerodynamic-drag-force level of 100% for the body of revolution with NASA-0006 profile, the drag force for Su-26 profile at airflow velocity of 10 m/s is 89.4%, while that for the proposed optimized body shape is 89.2%.

We have studied the generation of charge carriers and development of the electromotive force (emf) in uniformly heated n-type Si–Ge films heavily doped with titanium obtained by chemical-vapor deposition on p-type silicon substrates. A maximum emf value of ∼3 mV was observed at temperatures within 500–600 K for dark short-circuit currents ∼0.5–1 μA, the value of which increased with the temperature to reach ∼3 μA at 800 K.

Photovoltaic characteristics of more than 20 types of AlGaAs-based light-emitting diodes operating in the 830- to 970-nm wavelength range have been considered. It is established that Al_xGa_{1 – x}As semiconductor structures employed in these devices can also be used for manufacturing photovoltaic converters of monochromatic radiation with quite high efficiency.

It is established that aerodynamic drag alone is insufficient to induce forced rotation of a bearing-supported axial core in a mechanical vortex device at an input-flow pressure of up to 0.7 MPa. A necessary condition for the onset of core rotation is the excitation of bending and axial precession of the cantilever-supported core. In the absence of a mechanical contact between the core and expansion chamber of the vortex device, the direction of core rotation is the same as that of the airflow vortex. Forced rotation in the counter direction starts under conditions of dynamic bending that leads to the mechanical contact and rolling of the core over the surface of the expansion chamber.

We propose a method for the formation of porous germanium (P-Ge) layers containing silver nanoparticles by means of high-dose implantation of low-energy Ag⁺ ions into single-crystalline germanium (c-Ge). This is demonstrated by implantation of 30-keV Ag⁺ ions into a polished c-Ge plate to a dose of 1.5 × 10¹⁷ ion/cm² at an ion beam-current density of 5 μA/cm². Examination by high-resolution scanning electron microscopy (SEM), atomic-force microscopy (AFM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis, and reflection high-energy electron diffraction (RHEED) showed that the implantation of silver ions into c-Ge surface led to the formation of a P-Ge layer with spongy structure comprising a network of interwoven nanofibers with an average diameter of ∼10–20 nm Ag nanoparticles on the ends of fibers. It is also established that the formation of pores during Ag⁺ ion implantation is accompanied by effective sputtering of the Ge surface.

Qualitatively similar spectral characteristics of plasma-resonance reflection in the region of 15–25 μm were obtained for layers of electrodeposited submicron particles of InSb, InAs, and GaAs and plates of these semiconductors ground with M1-grade diamond powder. The most narrow-bandgap semiconductor InSb (intrinsic absorption edge ∼7 μm) is characterized by an absorption band at 2.1–2.3 μm, which is interpreted in terms of the model of optical excitation of electrons coupled by the Coulomb interaction. The spectra of a multigrain layer of chemically deposited PbS nanoparticles (50–70 nm) exhibited absorption maxima at 7, 10, and 17 μm, which can be explained by electron transitions obeying the energy-quantization rules for quantum dots.