We present a semiclassical analysis of Dirac electron tunnelling in a graphene monolayer with mass gap through a smooth potential barrier in the ballistic regime. This 1D scattering problem is formulated in terms of a transfer matrix and treated in the WKB approximation. For a skew electron incidence this WKB approximation deals, in general, with four turning points. Between the first and the second, and the third and the fourth, turning points two tunnelling domains are observed. Scattering through a smooth barrier in graphene resembles scattering through a double barrier for the 1D Schrödinger operator, i.e. a Fabry-Perot resonator. The main results of the paper are WKB formulas for the entries of the barrier transfer matrix which explain the mechanism of total transmission through the barrier in a graphene monolayer with mass gap for some resonance values of energy of a skew incident electron. Moreover, we show the existence of modes localized within the barrier and exponentially decaying away from it and its behaviour depending on mass gap. There are two sets of energy eigenlevels, complex with small imaginary part and real, determined by a Bohr-Sommerfeld quantization condition, above and below the cut-off energy. It is shown that total transmission through the barrier takes place when the energy of the incident electron coincides with the real part of one of the complex energy eigenlevels. These facts were confirmed by numerical simulations performed using the finite element method (COMSOL).

The boundary triplets approach is applied to the construction of self-adjoint extensions of the operator having the form S = A⊗I_T + I_A⊗T where the operator A is symmetric and the operator T is bounded and self-adjoint. The formula for the γ-field and the Weyl function corresponding the the boundary triplet Π_S is obtained in terms of the γ-field and the Weyl function corresponding to the boundary triplet Π_A.

This paper is a continuation of a previously reported study of the microstructure transformations in crystalline yttria nanopowder prepared by soft chemistry via precipitation from aqueous acidic nitrates. We have observed the aforementioned transformations over extended periods of time at 900 ^◦C and 1100 ^◦C (isothermal annealing) with the use of X-ray diffraction analysis (full profile analysis of reflections, etc.).

The temperature dependence of output power of microchip laser with intracavity frequency doubling is investigated, where oscillations in the output power are observed. Similar oscillations are observed in the temperature tuning of single pass second harmonic generation in plane parallel nonlinear crystal. It is supposed that in both two cases the oscillations have the same origin. Single pass second harmonic generation is investigated experimentally and theoretically, and it is shown that oscillations are due to multiple beam interference in the nonlinear crystal. Results of the experiments and calculations are presented.

Coherent transmittance and reflectance of multilayers consisting of one-dimensional Fibonacci, Thue-Morse, and periodic sequences of plane-parallel ordered monolayers of spherical alumina and silica particles are inves- tigated in the 0.3 µm to 2 µm spectral range. Consideration is based on the quasicrystalline approximation for individual monolayers and the transfer matrix method for multilayers. Comparison with sequences of the homogeneous plane-parallel layers is made. It is shown that the Fibonacci and Thue-Morse structures provide more possibilities to control light in comparison with the regular ones. These results can be used for the development of optical filters, solar cells, light emitting diodes, displays, etc.

It has been shown that it is possibility to control magnetoresistance by light. The use of light-sensitive banana-shape molecules has been suggested as an engine for varying the thickness or spacer between the magnetic layers. The spacer is filled by a conducting polymer with copper-like conductivity (with inserted bent molecules), ensuring the proper interlayer exchange coupling, which is necessary for transition from a ferromagnetic to an anti-ferromagnetic ordering (and inverse) when the thickness of the spacer changes.

In a number of recent publications, a one-dimensional effective model for quantum transport in a nanotransistor was developed yielding qualitative agreement with the trace of an experimental transistor. To make possible a quantitative comparison, we introduce three phenomenological parameters in our model, the first one describing the overlap between the wave functions in the contacts and in the transistor channel, the second one is the transistor temperature, and the third one is the maximum height of the source-drain barrier. These parameters are adjusted to the traces of three experimental transistors. An accurate fit is obtained if the three adjustable parameters are determined for each gate voltage resulting in three calibration functions. In the threshold- and subthreshold regime the calibration functions are physically interpretable and allow one to extract key data from the transistors, such as their working temperature, their body factor, a linear combination of the flat band voltage and the built-in potential between substrate and source contact, and the quality of the wave function coupling between the contacts and the electron channel.

Nanoparticles based on ZrO₂ in the form of spheres, cylinders and agglomerates in the form of hollow microspheres were obtained. It is shown that the main factor influencing on the formation of nanostructures based on zirconium dioxide under hydrothermal conditions is the chemical prehistory of the starting materials. The possibility of varying the synthetic parameters to obtain a zirconia-based material with high porosity and specific surface area was shown.

Polycrystalline Pb_1−xSn_xTe (0.0 ≤ x ≤ 1.0) telluride alloys were synthesized by the direct fusion technique. Thin films of these materials were prepared by a hot wall deposition method on glass substrates at T_sub =230–330 ^◦C and in a vacuum of about 10⁻⁵ Torr. The microstructure of the films was characterized by XRD, SEM, EDX and AES. The films showed a natural cubic structure. The thin films’ microstructure consisted of densely packed grains with dimensions of 50–300 nm and crystallite growth direction is perpendicular to substrate plane. The as-grown Pb_1−xSn_xTe films showed p-type conductivity. Thermoelectric measurements of the films showed high values for the room-temperature Seebeck coefficient ranging, from 20 to 400 µV·K⁻¹, for SnTe to PbTe thin films, respectively. The conductivity of the films was in the range of 3·10¹–1·10⁴ Ω⁻¹·cm⁻¹.

The subject of this study is the formation of the phase composition and structure in nanoscaled CoSbx (30 nm) (1.82 6 x 6 4.16) films deposited by molecular-beam epitaxy on substrates of oxidized monocrystalline silicon at 200˚C and the following thermal treatment in vacuum from 300–700˚C. It is established that after deposition, the films are polycrystalline without texture. With increased Sb content, the formation of the phase composition in the films takes place in such a sequence as is provided by the phase diagram for the bulk state of the Co–Sb system. With annealing in vacuum at temperatures above 450–500˚C, sublimation occurs not only for the crystalline Sb phase, but for the antimonides as well. This is reflected in the phase composition change by the following chemical reactions: CoSb₂ 600˚C → Sb↑ = CoSb, CoSb₃ 600˚C −→ Sb↑= CoSb₂, CoSb₃+ Sb↑ 600˚C → CoSb₃ and leads to increases in the amounts of the CoSb and CoSb₂ phases and decreases in the amounts of CoSb3. CoSbx(30 nm) (1.826x64.16) films are found to be thermostable up to ≈350˚C.

Fullerene C₆₀ / epoxy polymers nanocomposites with different C₆₀ loadings (0.01-0.12 wt.%) have been prepared. Mechanical testing shows that compared with the neat epoxy, the mechanical and toughening properties of the composites are greatly improved. The addition of fullerene C₆₀ increased the modulus of the epoxy (up to 20 %), but the glass transition temperature was unaffected. The measured impact strength was also increased, from 38 to 115 kJ/m² with the addition of 0.12 wt.% of fullerene C₆₀. The toughening mechanism has been discussed. Dielectric spectroscopy was used to investigate the influence of nanoparticles on the relaxation processes in the polymer matrix.

Magnetoelectric composites of 0.6(Ni_0.7Zn_0.3Fe₂O₄) / 0.4((Na, Li, Sr)NbO₃ + MnO₂) are prepared by conventional ceramic technology. The effect of composite sintering temperature on their phase composition and structure is studied. It is stated that the composites obtained are two phase systems (perovskite and spinel). It is established that modulation of spinel structure is shown more accurately at low sintering temperatures (1180˚C), while modulation of perovskite structure is shown at high temperatures (1220˚C). The discovered modulations of perovskite and spinel structures are assumed be connected with extended defects such as crystallographic shear planes. Increasing composite sintering temperature (T_sint.  1200˚C) was shown to lead to the disappearance of an impurity phase and the change of perovskite phase composition.

The formation mechanism of GdFeO₃ nanoparticles by varying of the hydrothermal conditions has been investigated. The mean size of coherent scattering regions of GdFeO₃ was determined to be equal to 53, 68 and 73 nm. The observed regularities allowed us to assume the oriented attachment of nanocrystals.