Vol 45, No 5 (2019)

In this paper, we experimentally studied the dynamic properties of autoelectron emission in strong pulsed electric fields of microsecond duration for multipointed cathode arrays based on surface-modified silicon crystals of the hole type. A decrease in the thresholds for the autoemission onset with an increase in the pulse duration is shown to increase the transparency of potential barriers due to an increase in the electron energy. Autoemission parameters are determined by surface dipole moments and embedded surface potentials that are formed during plasma etching of silicon in various chemically active media.

The performance of narrow-band optical filters on the basis of frustrated total internal reflection was analyzed taking into account the Gaussian distribution of the angle of radiation incidence. The spectral characteristics of these optical filters are modelled with and without divergence of the incident beam. It is shown that, when measuring the spectral characteristics of optical filters, the divergence of the incident radiation beam should not be greater than a certain limit value that does not exceed several angular minutes.

The experimental frequency and field dependences of the magnetoelectric effect in three-layer permendur–quartz–permendur structures in the region of electromechanical resonance were studied. It was found that the magnetoelectric voltage coefficient and the Q-factor of these structures in the resonance region are much higher than those of similar structures based on lead zirconate titanate. Anomalous behavior of the field dependences of the magnetoelectric voltage coefficient and the Q-factor was observed in the region of electromechanical resonance. This feature is attributable to the negative ΔE effect.

It is shown that the features of the dynamics of the formation of a self-initiated volume discharge in SF₆-based gas mixtures can be explained using the ecton model of the cathode spot formation and the effect of limiting the current density due to the processes of dissociation of molecular components of the gas mixture.

A theory of generation of a photoacoustic signal in a two-layer transparent sample on an absorbing substrate to a buffer gas of a photoacoustic cell has been developed. We have shown that the frequency dependence of the photoacoustic signal amplitude excited in the absorbing substrate obeys the law ∝ ω^–1, when a free path of photons is less than the thermal diffusion length, and is proportional to ω^–3/2 in the opposite case.

The electric conductivity is experimentally studied in nanofluids based on water and ethylene glycol containing copper and aluminum particles. Other properties, such as heat conductivity and rheological characteristics, were evaluated as well. The electric conductivity of nanofluids is shown to increase almost linearly with a nanoparticle concentration, but, unlike the heat conductivity, a gain in electric conductivity is due to a decrease in particle size. In this respect, the mechanisms of electric conductivity and heat conductivity are assumed to have the fundamentally different nature.

A method is described for introducing Mn clusters into nanoporous carbon. The resulting magnetic properties of composite samples of this kind are demonstrated in the dynamics of their development in the course of time.

Multigraphene films have been for the first time obtained on the surface of quartz glass via carbonization of polyimide Langmuir–Blodgett films. The Raman spectra of the films show bands G and D and a broad band at 2300–3200 cm^–1, which are characteristic of graphite-like films. The transmission electron microscopy demonstrated that the films are constituted by “stacks” of layers spaced by 0.36 nm. The surface resistance of the 5-nm-thick films was 1.2 ± 0.2 kΩ, and the transmittance was 87% at λ = 550 nm. The transmittance was 97% in the IR part of the spectrum and 70–80% in the UV part.

The process of discharge-induced substrate heating at the initial stage of film synthesis by method of high-frequency cathode sputter deposition has been studied. The temperature to which the substrate was heated after the discharge switch-on was determined using the optical interferometry technique. In a working regime of barium strontium titanate film deposition onto a magnesium oxide substrate, the substrate temperature exceeded 1000°C.

New resonator design employing a hairpin stripline conductor with a stub situated on one side of a dielectric substrate and regular stripline conductors (connected to a screen) on the other side. Eigenfrequencies of the first three oscillation modes of this resonator can be made closer to each other, so that the resonances of two modes are involved in the formation of the passband while the third mode resonance forms a minimum of the transmission coefficient adjacent to the passband. A structure comprising four resonators of this type has the characteristic of an eighth-order bandpass filter arranged in a case with 45 × 16 × 6.25-mm internal dimensions possessing   f₀ = 0.52 GHz central frequency with a 14% relative bandwidth. The filter is highly selective due to the attenuation poles being close to the pass band and a wide high-frequency stopband extending above a fivefold   f₀  value at a level of  –100 dB.

A scanning optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of hole burning in the signal of optically detected magnetic resonance (ODMR) on atomic-sized color centers in silicon carbide crystals under conditions of spin level saturation by means of additional high-frequency resonance pumping. An increase in the sensitivity is achieved due to narrowing of the ODMR line and increasing slope of the dependence of signal frequency on the magnetic field.

Study of the anodization of aluminum and tantalum at 1.2 kV in pure (distilled) water showed the possibility of generating electroluminescence (EL) in this system, which excluded the need for introducing any impurities into the initial aqueous medium and simplified interpretation of the observed results. It is established that the products of high-voltage anodization of metals in distilled water and the EL emission accompanying this process are similar to those observed during low-voltage anodization of metals in aqueous electrolyte solutions.

A complex chaotic dynamics in a gyrotron was experimentally observed under conditions of high supercriticality corresponding to 1000–1500-fold excess of the beam current parameter over the starting value. At electron beam currents typical of gyrotron test setups, this excess has been achieved by a transition to excitation of the lowest mode of a cylindrical waveguide. Chaotic generation regimes were observed in a 33 GHz frequency range with a spectral width of 500 MHz and record narrow relative width below 1.5% These results imply considerable progress in comparison to previous experiments with gyrotron type devices and are in good agreement with theoretical analysis based on a system of averaged evolution equations derived with allowance for finiteness of the transit time of electrons via the interaction space.

Investigation of the field-induced desorption of cesium atoms from the surface of rhenium crystal emitter carbon-saturated in benzene vapors showed that, after desorption from the surface, the process continues and there appears a contour of desorption around {10\(\bar {1}\)1} and {1\(\bar {1}\)00} faces that contracts toward the centers of faces with increasing field strength. This previously unreported anomalous behavior of the field-induced desorption is explained by the intercalation of cesium into graphite structures formed on the emitter surface.

Competitive interaction of orthogonally polarized modes in a two-mode laser operating in a regime of wide-band frequency modulation has been numerically simulated. This modulation was implemented by means of the corresponding variation of the laser cavity length. Parameters of the active medium adopted in the numerical model were characteristic of He–Ne lasers with an inhomogeneously broadened gain line. It is established that negative consequences of the mode competition can be significantly reduced at certain values of the modulation frequency and frequency deviation.