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The method of THz radiation modulation based on the semiconductor-metal phase transition in vanadium dioxide (VO₂) is explored. Thermal heating of the VO₂ film on the silicon substrate above the metallic state temperature results in ~80% reduction of THz radiation transmission. For two-electrode VO₂ film structures with a millimeter-sized interelectrode gap, heating the film by electric current leads to ~42% transmission reduction only. At the same time, due to heating of the VO₂ film substrate, a slow (seconds-running) cooling process and the reverse transition of the film to the semiconductor state occur. To increase the modulation frequency up to hundreds of kHz, it is proposed to create a structured system of separated micron-sized VO₂-elements instead of a continuous film, which allows for much faster cooling of such elements confirmed experimentally.

In this work, we study the temperature- and electrically-induced phase transition in thin vanadium dioxide films by spectral and microellipsometry methods. It is shown that the resistance of the vanadium dioxide film changes dramatically, by more than three orders of magnitude, at a temperature of about 67 °C, which is associated with the semiconductor-metal phase transition. Using the developed numerical algorithm for solving the inverse ellipsometry problem, the spectral dependences of the refractive n(λ) and absorption k(λ) indices for the semiconductor and metallic phases of vanadium dioxide are calculated from experimentally determined parameters Ψ and Δ. In the ultraviolet and visible regions of the spectrum, the changes in n and k are found to be insignificant upon heating, whereas in the near-infrared range there is a sharp redistribution of the optical response associated with the phase transition in vanadium dioxide. It is shown that the greatest changes in the refractive and absorption indices occur at a wavelength of 1100 nm and range from 2.94 to 1.57 and from 0.91 to 1.95, respectively. A reversible change in the parameters Ψ and Δ is detected by microellipsometry during the electrically initiated formation of a thin conductive filament in vanadium dioxide between two contact pads. The results obtained demonstrate the promise of vanadium dioxide for use in tunable optical and optoelectronic devices in the near and middle infrared ranges.

This work presents the design and experimental investigation of a prototype heat flux sensor based on a thin YBaCuO film deposited by pulsed laser deposition onto single-crystal Al₂O₃(1̅102) substrates. A technologically simple approach is proposed for producing oriented YBCO films without expensive miscut substrates, enabling the realization of the transverse thermoelectric effect. Comprehensive studies of the morphology, phase composition, and thermoelectric properties of the films deposited at various substrate temperatures are carried out. The sensor prototype fabricated from the film grown at 700 °C demonstrates the maximum sensitivity of 177 μV∙cm²/W, comparable to that of reference water-cooled sensors.

The work is aimed at numerical simulation of electromagnetic characteristics of multiresonant metamaterials, consisting of microresonators made of vanadium dioxide and silicon designed to operate in the infrared range. The dependence of the spectral response on the metamaterial geometric parameters and reflection coefficient contrast during the semiconductor-metal transition in vanadium dioxide is analyzed. It is shown that the electromagnetic response in the infrared range is determined by the Mie resonances, as well as by the plasmon and quasi-guided resonances. Hybrid metamaterials on silicon substrates can ensure higher reflection coefficient switching contrast in a wider spectrum compared to similar structures on quartz substrates. Spectral dependencies of the switching power threshold for metamaterials on quartz and silicon substrates are determined.

Cleaning the surface of InSb from oxides is an important step in epitaxial growth and post-growth technological processes, since the oxide layer leads to the formation of defects in epitaxial layers and degradation of device parameters. It is shown that cleaning the InSb surface from oxides by annealing in an indium flux reduces the maximum annealing temperature and surface roughness compared to thermal annealing in vacuum: the root mean square roughness of the InSb surface is found to be 1.2 nm after cleaning by annealing in vacuum at 400 °C and 0.9 nm after cleaning by annealing in an indium flux at 355 °C followed by annealing in vacuum at 380 °C. The lower surface roughness of the InSb substrates after the cleaning step improves the crystal quality of the grown epitaxial layers. Based on the in-situ monitoring of oxide desorption by high energy electron diffraction, it is shown that the antimony flux slows down the indium oxide desorption process, which leads to the necessity of increasing the maximum annealing temperature.

In this paper, we present the results of a study of Al_xGa_1-xN layers with different Al contents grown by ammonia molecular beam epitaxy on Al₂O₃ substrates using scanning electron microscopy and transmission electron microscopy. It is shown that the inversion domains from the AlN buffer layers do not grow to the film surface during further growth of Al_xGa_1-xN layers with Al contents x ≤ 0.2. In the Al_xGa_1-xN layers with 0.2 ≤ x ≤ 0.5, plateau-shaped defects extending to a height of more than 200 nm form above the inversion domains; at x ≥ 0.5, plateau-shaped defects extend through the entire Al_xGa_1-xN layers.

A numerical solution of the direct scattering problem for the one-dimensional Helmholtz equation is considered. Within the framework of the transfer matrix method, an implicit difference scheme for the transfer matrix of the second order of approximation accuracy is obtained by the integral method. Based on the duplication strategy, the convolution theorem, and the fast Fourier transform, an algorithm for the accelerated solution of the Helmholtz equation is presented, which asymptotically requires only O(Nlog²N) arithmetic operations. Numerical modeling of the scattering problem is performed using the example of an exponential smooth layer whose solution is known. Numerical simulation has confirmed the accuracy and high speed of the proposed algorithm, which is necessary in practical applications for optical and acoustic sensing of media in applied optics and acoustics.

The subwavelength scattering of a plane electromagnetic wave normally incident onto an array of parallel cylinders is considered. If the wavelength is much longer than the lattice period, then a quasi-static approximation can be used. The solution for the electric field potential is presented as a series of the Laplace operator eigenfunctions. To find the coefficients of the series, a conformal mapping that drastically simplifies the boundary conditions is used. The result of solving the Laplace equation by the conformal mapping method is compared to the calculation of the wave problem in the COMSOL^® Multiphysics. The quantitative difference between the electric field intensities obtained is less than 1% at a wavelength 60 times greater than the grating period.

Image registration methods are widely used in processing satellite images of the Earth. This solves the problem of establishing the correspondence of images of the same landmark obtained from different distances, different angles, under different lighting conditions, at different times of the year, etc. This article presents a method for assessing the potential accuracy of localization of area and linear landmarks of significant sizes, which can be considered flat given the altitude of the orbit from which the survey is made. The accuracy of localization is determined depending on the shape of the vector reference image, its size, accuracy, and the accuracy of localization of the boundaries of the observed image of the object. It is shown that, under favorable conditions, it is possible to obtain subpixel accuracy of localization of area and linear objects of significant sizes.

The problem of creating a control system for angular movements of a quadcopter that takes into account the transient process of traction motors is considered. Motion equations are obtained for a two-dimensional model of an apparatus mounted on a gyroscopic stand. This model takes into account the displacement of the vehicle rotation center relative to the center of mass and the transient process of the engines in the form of a first-order device reaction. A regulator based on the structural synthesis method is proposed, which ensures quadcopter setting in a given orientation. The algorithm effectiveness is confirmed by the results of HIL modeling, taking into account the noise and time delays of the real device.