卷 42, 编号 4 (2016)

Auger-electron spectroscopy has been used to study in situ the initial stage of graphite oxide (GO) reduction under the action of a low-intensity electron beam that does not lead to heating of the irradiated region. It was found that this stage evolves at a rate that is tens of times the rate of the subsequent reduction. It was shown that the fast stage is associated with the removal of oxygen groups from the GO surface. The effective cross sections of the initial and subsequent stages of GO reduction by 1500 eV electrons were found to be σ_in ~ 0.5 × 10^–16 cm² and σ_av ~ 1.2 × 10^–18 cm², respectively.

The influence of microwave radiation with a power flux density of 80 W/cm² and carrier frequency of 9.4 GHz on the thermal stability of aluminum nanopowder after irradiation in air is studied. It is established that, after irradiation, the chemical activity of aluminum nanopowder increases, the temperature for the beginning of its oxidation decreases by 40°, while the thermal effect of oxidation decreases by 13.5%.

A study of synthetic jets created by dielectric barrier discharge of the symmetric actuator has been carried out. The parameter—specific thrust (thrust-to-power ratio)—is used for the first time. The current–voltage characteristics of the dielectric barrier discharge are obtained at different values of the ballast resistance. The dependence of the thrust-to-power ratio on the supply-voltage frequency is determined experimentally.

An alloy of a mixture of fluorides MgF₂ and AlF₃ with CaF₂ has been obtained in a 3-kW solar furnace. It was supposed that a minor CaF₂ additive compensates for the tensile stresses appearing in thin MgF₂ and AlF₃ films, with their mechanical properties being thereby improved. The results of X-ray phase analysis demonstrated that both components of the mixture are present in the alloy, while the complex oxide CaAl₄O₇, the formation of which is attributed to the melting in air, is only identified in AlF₃: CaF₂ = 95: 5 (wt %). The increase in the transmittance of glass and polyethylene terephthalate upon deposition onto their surface of a thin film of the material synthesized in the study is due to the optical properties of AlF₃ and MgF₂.

Amplifying and quenching of IR luminescence of colloidal Ag₂S quantum dots were revealed to take place when they couple to organic dye molecules of 3,3′-di-(γ-sulfopropyl)-9-ethyl-4,5,4′,5′-dibenzothiacarbocyanine betaine and erytrosine pyridinium salts, respectively. The observed effects are explained as due to the formation of organic–inorganic heterostructures with different mutual arrangement of electronic states of the dyes and the quantum dots.

Experimental studies of the breakdown stage in a kivotron, a high-voltage switching device based on an open discharge with counterpropagating electron beams, are performed. It is demonstrated that a fast stage of the breakdown is provided by photoemission of resonance radiation of fast atoms with large Doppler shift with respect to the line center of thermal atoms. For working pressure p_He ≈ 20 Torr, switching time τ_s ≈ 80 ps is achieved. The estimated minimum switching time is ~35 ps.

A low-noise cryogenic amplifier for the measurement of weak microwave signals at sub-Kelvin temperatures is constructed. The amplifier has five stages based on SiGe bipolar heterostructure transistors and has a gain factor of 35 dB in the frequency band from 100 MHz to 4 GHz at an operating temperature of 800 mK. The parameters of a superconducting quantum bit measured with this amplifier in the ultralow-power mode are presented as an application example. The amplitude–frequency response of the “supercon-ducting qubit–coplanar cavity” structure is demonstrated. The ground state of the qubit is characterized in the quasi-dispersive measurement mode.

We investigate nonequilibrium processes of self-heating induced by electric current in ferromagnetic semiconductors exhibiting colossal magnetoresistance (CMR) in the vicinity of the Curie temperature. The heat balance equation is solved taking into consideration localized states that appear as a result of scattering from magnetic inhomogeneities and are characterized by a percolation threshold proportional to the amplitude of spin fluctuations. The appearance of N-shaped current-voltage characteristics and hysteresis in the dependence of magnetization on electric potential difference, which are caused by the emergence of a “hot” (with respect to internal temperature) semiconductor paramagnetic phase, is revealed in the steady-state regime. The possibility of suppression of the effect of colossal magnetoresistance with increasing potential difference is indicated. The onset of self-oscillation of current and magnetization with decreasing transverse dimensions of the sample is demonstrated.

We present experimental data on the distribution of energy deposition along the discharge chamber of a multichamber lightning protection system at the initial stage of a discharge process modeling a lightning current pulse with 10 kA amplitude. The multichamber system comprised serially connected gas-discharge chambers. The breakdown between electrodes situated on the bottom of a channel in each chamber induces the formation of a shock wave. Subsequent energy evolution during the development of discharge proceeds in the entire volume bounded by the shock wave.

The transition to chaos in a microwave photonic generator has been experimentally studied for the first time, and the generated broadband chaotic microwave signal has been analyzed. The generator represented a ring circuit with the microwave tract containing a low-pass filter and a microwave amplifier. The optical tract comprised a fiber delay line. The possibility of generating chaotic oscillations with uniform spectral power density in a 3–8 GHz range is demonstrated.

The dynamics of heating and vaporization of gold in vacuum under the action of laser pulses of low intensity, when the main ablation products are neutral particles, is investigated by mass spectrometry and numerical modeling. The laser-ablation plume is found to consist of gold atoms and dimers with kinetic energies considerably higher than their thermal energy upon evaporation. Nanostructured gold films are synthesized by depositing the ablation products onto a substrate. Formation mechanisms of the gold nanostructures and possibilities of controlling their sizes are discussed.

The structure of AlN/c-sapphire templates obtained by plasma-activated molecular beam epitaxy (PAMBE) has been studied by X-ray diffractometry techniques. The results show the advantages of using coarse-grained AlN nucleation layers prepared by high-temperature (780°C) adatom-migration-enhanced epitaxy. Using 3.5-nm-thick GaN inserts (obtained by three-dimensional growth under N-rich conditions), it is possible to obtain templates with insignificant residual macrostresses and relatively narrow widths (FWHM) of 0002 and 10\(\bar 1\)5 diffraction reflections.

We describe the method and presents results of a mass-spectrometric investigation of the yield of positive ions formed as a result of the dissociative ionization of a molecular selenium beam by electron impact. Appearance energies of fragment ions have been determined from the ionization efficiency curves. The dynamics of formation of the molecular ions of selenium in a temperature interval of 420–495 K has been studied. The energy dependences of the efficiency of formation of singly charged Se_n⁺ (n = 1–3) and doubly charged Se⁺⁺ ions are analyzed.

We have experimentally discovered random telegraph signal generation in tunneling silicon p⁺–n⁺ junctions with embedded self-assembled GeSi nanoislands. The observed phenomenon is related to blocking of the electron tunneling via individual GeSi nanoislands due to the generation of holes in, and their thermal emission from, the nanoislands.