Vol 42, No 3 (2016)

An experimental technique for the determination of electric conductivity and temperature of plasma is presented. The technique is based on comparing the signals that are produced by a pulsed magnetic field in the circuits of two probes located within the studied plasma and outside of it. The proposed technique for the measurement of plasma parameters was tested experimentally in the context of measuring the electric conductivity and temperature of plasma flux formed in cathode spots of a high-current pulsed vacuum arc with a magnesium cathode.

The variation of the emission frequency of a quantum cascade laser of the 3.2 THz range within a single radiation pulse was studied using high-resolution Fourier spectroscopy. A significant (108 MHz) increase in frequency in the first 4 μs of a pulse was found. This increase is attributed to a change in the electron part of permittivity of the laser active region coinciding with a rise in the emission intensity. The frequency dropped by 81 MHz in the following 40 μs of a radiation pulse due to a change in the lattice part of permittivity occurring as the laser active region was heated during a radiation pulse.

We propose a technique for identifying the type of resonance excitation by ac magnetic or electric fields in conducting chiral elements by reflection of electromagnetic waves in the standing- and travelingwave modes. The technique was tested experimentally in the microwave range and confirmed numerically. We demonstrate the possibility of broadband matching of composite radar absorbing materials with the use of a lattice of resonance elements excited by magnetic field of the wave rather instead of the traditional quarter- wavelength effects.

The process of evaporation of an inhomogeneous (containing a graphite particle) water drop moving through a high-temperature (about 1100 K) gas medium has been experimentally studied using highspeed (no less than 10⁵ fps) video recording tools, the PIV scanning optical method, and Tema Automotive software. The influences of the ratio of water and inclusion masses, shape of inclusion (by the example of cylindrical disk, cube, and parallelepiped), and its surface area on the integral characteristics of liquid evaporation when heterogeneous drops are passed through a channel (length 1 m, inner diameter 0.2 m) with high-temperature gases are established.

Results of an experimental investigation of transformation of water projectiles (spherical “balls” with a volume of 50–1000 mL) in the course of their free fall (from a height of 3 m) within a high-temperature (about 1100 K) gaseous medium (with the application of the standardized fire) are represented. Investigations are carried out for projectiles of water, its solutions with NaCl, and suspensions with carbon particles. Conditions and characteristics of disruption of projectiles are determined as they move through high-temperature gases. The transformation deceleration of the projectile was revealed because of its “compression” in the high-temperature zone (in comparison with moderate temperatures).

The dependence of the sensitivity of photodetectors based on A^III–B^V photodiodes on accidental variations of the temperature of its elements is analyzed. It is shown that the temperature drift of the bias level in input circuits of op-amps strongly contributes to the resulting photodetector noise up to frequencies on the order of 1 MHz. To reach the limiting sensitivities of the sensors, it is necessary to stabilize the temperature of not only the photodiode chip, but also the integrated circuit of the first amplifier stage. For most of applications, the required stabilization accuracy does not exceed ±0.1°C. As a result of the analysis, prototype high-sensitivity medium-wavelength (2–5 μm) sensors were developed that operate without forced cooling and have a detection threshold of tens of nanowatts at a detection bandwidth of 0–1 MHz.

X-ray and UV photoelectron spectroscopic data are used to demonstrate that, when pulsed laser light with a photon energy of 6.4 eV acts on the surface of nonstoichiometric molybdenum oxide MoO_x (x < 2), methanol is effectively formed from adsorbed molecules of carbon dioxide and water. The processes in which CO₂ and H₂O molecules are adsorbed on substrate surface defects and their bonds are activated, enhanced under the effect of photons, should be regarded as the key factors.

Ceramics of (1–x)La_0.7Sr_0.3MnO₃/x(GeO₂) and (1–x)La_0.7Sr_0.3MnO₃/x(Li₄P₂O₇) compositions with x = 0.1–0.3 have been synthesized that possess high absolute values of isotropic negative magnetoresistance MR at room temperature. In a composite containing 20 mass % GeO₂ as the barrier component, the negative magnetoresistance reaches MR = 15% in a magnetic field of 18 kOe, while an analogous composite with Li₄P₂O₇ under identical conditions has MR = 16%.

We have used the atomic force microscopy and Hall effect measurements to study the influence of In_0.52Al_0.48As transition layer design on the electron mobility in the InAlAs/InGaAs/GaAs channel of a highelectron- mobility transistor (HEMT) with the metamorphic buffer. The optimum buffer layer favors suppression of the misfit dislocation threading into upper layers of the HEMT heterostructure and prevents development of the surface microrelief.

Thin films of Cu₂Zn_1–xMn_xSnS₄ (0 ≤ x ≤ 1) solid solutions have been obtained for the first time by the spray pyrolysis of aqueous salt solutions (copper, zinc, manganese, and tin chlorides and thiourea) at a temperature of T_S = 563 K. The films possess specific electric conductivities within σ ≈ 35–422 Ω^–1 cm^–1 and optical bandgap width E_g^op that increases with the manganese content from 1.54 eV (x = 0) to 2.25 eV (x = 1). Electrical and optical properties of the obtained films have been studied and analyzed based on a model of polycrystalline materials with grain boundaries. The energy barriers Eb between grains have been determined. The dependence of the bandgap of Cu₂Zn_1–xMn_xSnS₄ (0 ≤ x ≤ 1) solid solutions on the composition has been established using the results of measurements of the optical transmission and absorption coefficients.

We propose a method of controlling an ensemble of mobile agents with variable coupling topology that is based on the principles of phase synchronization in a system of regular and chaotic oscillators. Results of modeling of the controlled motion of mobile agents in systems with serial, parallel, and strictly preset motion are presented.

We have studied the charging of copper microparticles in electron flow. It is established that the parameters of secondary electron emission from microparticles can significantly differ from those for metal films and volume targets. Conditions are determined under which negative charging of micron-sized copper particles in electron flow takes place. In the case of spherical microparticles, secondary emission is significantly increased as a result of the oblique incidence of primary electrons. A general approach is proposed that can be used to estimate the electron energy necessary for charging microparticles to high negative potentials.

Temperature dependences of the photovoltaic characteristics of (p)a-Si/(i)a-Si:H/(n)c-Si singlecrystalline- silicon based heterojunction-with-intrinsic-thin-layer (HIT) solar cells have been measured in a temperature range of 80–420 K. The open-circuit voltage (V_OC), fill factor (FF) of the current–voltage (I–U) characteristic, and maximum output power (P_max) reach limiting values in the interval of 200–250 K on the background of monotonic growth in the short-circuit current (I_SC) in a temperature range of 80–400 K. At temperatures below this interval, the V_OC, FF, and P_max values exhibit a decrease. It is theoretically justified that a decrease in the photovoltaic energy conversion characteristics of solar cells observed on heating from 250 to 400 K is related to exponential growth in the intrinsic conductivity. At temperatures below 200 K, the I–U curve shape exhibits a change that is accompanied by a drop in V_OC. Possible factors that account for the decrease in V_OC, FF, and P_max are considered.

We have studied the characteristics of a pulsed gas-discharge laser on iron bromide vapor generating radiation with a wavelength of 452.9 nm at a pulse repetition frequency (PRF) of 5–30 kHz. The maximum output power amounted to 10 mW at a PRF within 5–15 kHz for a voltage of 20–25 kV applied to electrodes of the discharge tube. Addition of HBr to the medium produced leveling of the radial profile of emission. Initial weak lasing at a wavelength of 868.9 nm was observed for the first time, which ceased with buildup of the main 452.9-nm line.

Experiments with stainless steel (304L grade) samples exposed to microsecond pulses of high-current low-energy (10–30 keV) electron beam have been performed to determine dependences of the morphology, average diameter, and density of irradiation-induced microcraters on the beam energy density. A mechanism is proposed, according to which the crater formation is caused by radial spreading of the melt from the site of localization of a MnS inclusion under the action of the surface tension gradient caused by overheating of the inclusion. Estimations of the dimensions of microcraters are in satisfactory agreement with experimental data.