Vol 43, No 9 (2017)

The preparation of composite transparent electrodes of poly(3, 4-ethylenedioxythiophene) polystyrene sulfonate/single-wall carbon nanotubes by the spray method is described. The influence of the successive treatment of each functional layer in acid media with different activities on the optical and electric film characteristics is considered. The composite with the surface resistance of 89 Ω/sq at the transparency of 85.3% (550 nm) on a polymer substrate is obtained.

The possibility of detecting H₂ by registering the thermal electromotive force signal, which arises between the surfaces of 6H-SiC plates with a thickness of 400 μm, is established. The working surface of the plates is modified by deposition of a WO_x film and catalytic Pt. An ohmic contact (Ni/Pt) is created on the rear surface of the plate, and this surface is maintained at a stabilized temperature of 350°C. The temperature gradient through the plate thickness arises due to the cooling of the working surface with the air medium. The delivery of H₂ into this medium up to a concentration of 2% gives rise to a 15-fold increase in the electric signal, which considerably exceeds the Pt/WO_x/SiC/Ni/Pt system’s response registered in the usual way by measuring the current–voltage dependence. In this case, an additional power source for the registration of the thermal electromotive force is not required.

The complex problem of increasing the penetrating power of strikers based on highly porous tungsten composites is considered by improving their strengthening properties by alloying the hardening components under high-speed collision conditions. Using the method of liquid-phase sintering, we fabricated samples of strikers based on a porous WNiFeCo alloy (tungsten + nickel + iron + cobalt), alloyed with tungsten carbide with cobalt (WCCo8) and titanium-tungsten carbide (TiWC). Dynamic tests of the strikers from the developed alloys were carried out at the collision velocity with a steel barrier of the order of 2800 m/s. The penetration depth of the striker based on a porous WNiFeCo alloy doped with tungsten carbides is 30% higher than the penetration depth of a striker of a monolithic WNiFe-90 alloy (tungsten + nickel + iron with a tungsten content of 90%).

Within the theoretical model of a high-pressure hybrid nanosecond discharge with runaway electrons, a strong dependence of the electron beam amplitude, duration, and energy spectrum on the conditions of the preliminary ionization of a gas in the discharge gap is demonstrated. The conditions with uniform and nonuniform distributions of initial electrons in a coaxial diode filled with sulfur hexafluoride at atmospheric pressure are simulated. It is shown that the amplitude and current pulse profile of the electron beam substantially change upon the variation of the initial distribution of the electrons in the discharge gap.

The emission directionality of self-catalytic GaAs nanowires in an AlGaAs shell, produced by molecular-beam epitaxy with a varied level of beryllium doping, is studied. It is shown that an undoped sample possesses pronounced waveguide properties along the growth direction. With increasing doping level, the intensity of the emission directed perpendicular to the lateral nanowire walls grows.

A prototype of a new flaw detector for remote noncontact diagnostics of soft solids is proposed. The operating principle of the flaw detector is based on the features of the nonlinear interaction of two ultrasonic waves in the test material with defects. Ultrasonic waves in the test material are excited remotely by ultrasonic beams focused in air. It is demonstrated experimentally that with the help of the proposed flaw detector, subsurface defects with dimensions much smaller than the wavelength of the probing ultrasound can be remotely detected and localized.

We propose a new type of potentiometric gas sensor operating on the basis of the thermovoltaic effect in uniformly heated (without temperature gradients) ZnO/ZnO–Fe sandwich structures obtained by the sol–gel method. It is established that a significant contribution to the gas responsivity of sensors is related to the thickness of the upper doped layer of the structure.

The possibility of generating ultrashort microwave pulses in the sub-THz and THz range using the mechanism of cyclotron superradiance (SR) from electron bunches moving over helical trajectories in a homogeneous magnetic field is demonstrated in the framework of averaged model description of the electron–wave interaction and by particle-in-cell (PIC) numerical simulations. In a significantly oversized waveguide tract, selective excitation of the working mode is ensured for an electron bunch propagating at a velocity close to the group velocity of the SR pulse.

The dependence of the transverse section of an electron beam on the distance between plates and on the accelerating potential difference is determined for a chevron unit of a microelectronic position-sensitive detector (MPSD) with two microchannel plates. The geometry of the MPSD chevron unit is designed and optimized.

We present a new interferometric method that can be used for studying the dynamics of photoinduced processes in biologically important molecules at ultrahigh temporal resolution. The method is based upon the detection of changes in the refractive index of a substance excited by pulsed radiation of a femtosecond laser, which are measured by the pump-and-probe technique using time-delayed pulses of the same laser. The high sensitivity and stability of the interferometer allow this method to be used for monitoring variation of the concentration of short-lived excited states of biomolecules in solution. The proposed method has been verified by application to indole solutions in propylene glycol. The upper estimate of the lifetime of photoexcited indole molecules in solution amounted to about 40 ps.

The influence of the initial conditions on specific features of the formation and development of a cathode-directed ionization wave between two flat electrodes in helium at atmospheric pressure was studied at nanosecond time resolution using an FER2-1 high-speed photoelectron monitor. Results of numerical simulations based on a two-dimensional axisymmetric diffusion–drift model are in satisfactory agreement with experimental data.

Temporal behavior of the intensity of Ba I emission lines (413.24 and 553.55 nm) in plasma of optical breakdown induced by femtosecond laser pulses (800 nm, 45 fs, 0.82 mJ) on the surface of BaCl₂ aqueous solution was experimentally studied as dependent on delay time t_d relative to the breakdown onset. The maximum intensity of the Ba I (413.24 nm) line was observed at t_d = 20 ns, while the intensity of the Ba I (553.55 nm) line reached a maximum at t_d = 40 ns. At t_d = 10 ns, the intensity of the Ba I (413.24 nm) line was almost three times as large as that of Ba I (553.55 nm) line (despite the about two orders of magnitude lower probability of spontaneous transition for the former line), which is explained by the recombination cascade. It is established that, in the subsystem of 5d6p³D⁰ and 6s6p¹P⁰ levels, the Boltzmann distribution is not valid and the local thermodynamic equilibrium is absent.

The phenomenon of transformation of the spectrum of magnetic noise in a Metglas/PZT/Metglas magnetoelectric (ME) planar composite structure has been experimentally discovered and investigated. It is established that a narrowband noise with central frequency f_N leads to the linear generation of electric noise voltage at the noise frequency and the nonlinear generation of noise voltage in the vicinity of zero frequency and in the region of 2f_N. The experiment is well explained by the theory of magnetic-field mixing in ME composites with nonlinear field dependence of the ferromagnetic-layer magnetostriction.