In this work we have measured the frequency response of a heterodyne receiver based on a mixer at the Superconductor-Insulator-Superconductor (SIS) tunnel junction for the frequency range 211–275 GHz. The measurement was done with a Fourier spectrometer using two methods of reading the detector signal: by direct current and by the power of the intermediate frequency output signal. The reason for studying these methods is that intermediate frequency (IF) measurements give a better signal-to-noise ratio than direct current (DC) measurements. It is found that the spectrograms obtained by these methods are different up to the degree of squaring, also for IF measurements the appearance of artefacts in the microwave range, which coincide with the bandwidth of the IF system, is found. Modelling of the spectrometer operation for both methods is carried out, explaining the reason of 'artefacts' occurrence at measurements in the intermediate frequency reading mode and describing the nature and size of the convolution of the receiver spectrum in comparison with direct current measurements.

On the basis of furfuryl glycidyl ether, the product derived from furfural, diol chain extenders have been synthesized. Using these chain extenders and bismaleimide as a crosslinker polyurethanes with thermally induced self-healing effect have been prepared by the reversible Diels–Alder reaction. The structure of the synthesized polymers is studied by IR spectroscopy. Thermal and physicomechanical properties of the materials are also investigated. Differential scanning calorimetry measurements revealed the cyclic nature of direct and retro-Diels–Alder reactions. Visual assessment of the self-healing ability of the material is carried out using scanning electron microscopy. Quantitative evaluation (the self-healing efficiency of the Young’s modulus and strength) is performed by means of dynamometric analysis of initial and recovered polymer samples. It has been demonstrated that the content of dynamic bonds affects the properties of polyurethanes, as well as the efficiency of self-healing.

An epoxy polysulfone binder modified with an active diluent, furfuryl glycidyl ether (FGE), is studied. The addition of FGE significantly improves the technological parameters of the high-viscosity binder. The processing temperature of modified binders varies in the range of 80 to 120°C depending on the FGE concentration. The phase decomposition of the binder during its preparation is not observed, but occurred during curing. The glass transition temperature of matrices based on the obtained binder remains at a high level: 100–107°С. The type of phase structure formed during the curing of the hybrid binder depends on the concentration of FGE and polysulfone PSK-1.

The physical-mechanical properties of epoxy matrices modified with polyethersulfone (PES) and unidirectional glass- and carbon-fiber-reinforced plastics (GFRP and CFRP) based on them were investigated. The fracture toughness of epoxy matrices modified with 20 wt% PES, increased by 4.3 times. The delamination energy of GFRP and CFRP with this content of PES in the matrix increases by 50 and 65%, respectively. A correlation between the fracture toughness of modified matrices and the delamination toughness of GFRP and CFRP was established, and the influence of structure of the matrices on the fracture toughness of the reinforced plastics was demonstrated. A significant increase in the fracture toughness of the matrices and reinforced plastics was also observed during the formation of extended phases enriched with PES.

We present an analysis of a waveguide structure for a 211–275 GHz sideband separating (2SB) mixer based on superconductor–insulator–superconductor (SIS) tunnel junctions. A general analytical model describing the quality of the sideband rejection ratio (SRR) is developed. It shows a crucial influence of reflections from single-ended mixers, reference frequency (RF) load, and the RF hybrid on the SRR level. Due to the intrinsic asymmetry of the 2SB waveguide structure, the reflections strongly affect both the balance of the observed signal and the balance of the local oscillator (LO) pumping signal. The model is verified and confirmed by 3-D electromagnetic simulations showing good qualitative and quantitative agreement. The developed theory gives a practical tool to design 2SB waveguide mixers with a required SRR level. Based on the presented theory, the waveguide structure of the 211–275 GHz 2SB SIS mixer is designed. It is predicted a degradation of the SRR level from 26 dB to about 18 dB due to reflections. The developed model explains some experimental data measured for 2SB SIS mixers developed earlier.

Iron-containing composites with nanoparticles are synthesized by the method of thermal decomposition of pentacarbonyl and iron formate in a polyethylene melt. The synthesized nanoparticles are characterized by transmission electron microscopy (TEM), X-ray phase analysis, and Mössbauer spectroscopy. The size of nanoparticles synthesized from iron pentacarbonyl and iron formate is 5.3 and 11.5 nm, respectively. It follows from the diffraction patterns that the particles have a complex composition. Composite materials are obtained based on iron nanoparticles and high-density polyethylene (HDPE). According to dynamic mechanical analysis, the elastic modulus of HDPE filled with particles obtained from iron pentacarbonyl is higher than for matrices containing iron formate. The biocidity test showed that the particle-modified matrix inhibits the growth of microorganisms more effectively than pure polyethylene.

The rectification of electromagnetic waves to direct currents is a crucial process for energy harvesting, beyond-5G wireless communications, ultra-fast science, and observational astronomy. As the radiation frequency is raised to the sub-terahertz (THz) domain, ac-to-dc conversion by conventional electronics becomes challenging and requires alternative rectification protocols. Here we address this challenge by tunnel field-effect transistors made of bilayer graphene (BLG). Taking advantage of BLG's electrically tunable band structure, we create a lateral tunnel junction and couple it to an antenna exposed to THz radiation. The incoming radiation is then down-converted by the tunnel junction nonlinearity, resulting in high-responsivity (> 4 kV/W) and low-noise (0.2 pW/√(Hz)) detection. We demonstrate how switching from intraband Ohmic to interband tunneling regime can raise detectors' responsivity by few orders of magnitude, in agreement with the developed theory. Our work demonstrates a potential application of tunnel transistors for THz detection and reveals BLG as a promising platform therefor.

The change in viscosity of an epoxy oligomer modified with polyethersulfone is investigated. The range of temperatures of binder processing with the maximum effect of modification is determined. The concentration dependence of the crack resistance of the epoxy-polyethersulfone matrix and a glass composite based on it is determined. The morphology of the crack surface is investigated. The reason for the reduced effect modifying the binder with a thermoplastic has on the rise in the crack resistance of glass fiber reinforced plastics fiberglass in comparison with the unreinforced matrix is established.

In the 20th century, microelectronics was revolutionized by silicon—its semiconducting properties finally made it possible to reduce the size of electronic components to a few nanometers. The ability to control the semiconducting properties of Si on the nanometer scale promises a breakthrough in the development of Si-based technologies. In this paper, we present the results of our experimental studies of the photovoltaic effect in Ag2S QD/Si heterostructures in the short-wave infrared range. At room temperature, the Ag2S/Si heterostructures offer a noise-equivalent power of 1.1 × 10−10 W/√Hz. The spectral analysis of the photoresponse of the Ag2S/Si heterostructures has made it possible to identify two main mechanisms behind it: the absorption of IR radiation by defects in the crystalline structure of the Ag2S QDs or by quantum QD-induced surface states in Si. This study has demonstrated an effective and low-cost way to create a sensitive room temperature SWIR photodetector which would be compatible with the Si complementary metal oxide semiconductor technology.

In the 20th century, microelectronics was revolutionized by silicon-its semiconducting properties finally made it possible to reduce the size of electronic components to a few nanometers. The ability to control the semiconducting properties of Si on the nanometer scale promises a breakthrough in the development of Si-based technologies. In this paper, we present the results of our experimental studies of the photovoltaic effect in Ag2S QD/Si heterostructures in the short-wave infrared range. At room temperature, the Ag2S/Si heterostructures offer a noise-equivalent power of 1.1 × 10-10 W/√Hz. The spectral analysis of the photoresponse of the Ag2S/Si heterostructures has made it possible to identify two main mechanisms behind it: the absorption of IR radiation by defects in the crystalline structure of the Ag2S QDs or by quantum QD-induced surface states in Si. This study has demonstrated an effective and low-cost way to create a sensitive room temperature SWIR photodetector which would be compatible with the Si complementary metal oxide semiconductor technology.

We present an elegant and effective technology of extending the photoresponse of Si towards the IR range. Our approach is based on the use of Ag2S quantum dots planted on the surface of Si to create impurity states in Si band gap. Given the variety of available QDs and the ease of extending the photoresponse of Si towards the IR range, our findings open a path towards the future study and development of Si detectors for technological applications. The current research at the interface of physics and chemistry is also of fundamental importance to the development of Si optoelectronics of the IR range.

Plasmons, collective oscillations of electron systems, can efficiently couple light and electric current, and thus can be used to create sub-wavelength photodetectors, radiation mixers, and on-chip spectrometers. Despite considerable effort, it has proven challenging to implement plasmonic devices operating at terahertz frequencies. The material capable to meet this challenge is graphene as it supports long-lived electrically tunable plasmons. Here we demonstrate plasmon-assisted resonant detection of terahertz radiation by antenna-coupled graphene transistors that act as both plasmonic Fabry-Perot cavities and rectifying elements. By varying the plasmon velocity using gate voltage, we tune our detectors between multiple resonant modes and exploit this functionality to measure plasmon wavelength and lifetime in bilayer graphene as well as to probe collective modes in its moiré minibands. Our devices offer a convenient tool for further plasmonic research that is often exceedingly difficult under non-ambient conditions (e.g. cryogenic temperatures) and promise a viable route for various photonic applications.

—The influence of homogeneity disorder degree of the thin superconducting NbN film across of Si wafer on characteristics of the Hot Electron Bolometers (HEB) has been investigated. Our experiments have been carried out near the superconducting transition and far below it. The high homogeneity disorder degree of the NbN film has been achieved by preparing the Si substrate surface. The fabricated HEBs all have almost identical R (T) characteristics with a dispersion of Tc and the normal resistance R300 of not more than 0.15K and 2 Ω, respectively. The quality of the devises allows us to demonstrate clearly the influence of non-equilibrium processes in the S’SS’ system on the device performance. Our fabrication technology also allows creating multiplex heterodyne and direct detector matrices based the HEB devices.

We show prospects for using the method of high-resolution terahertz spectroscopy for a continuous analysis of the decomposition products of energy substances in the gas phase (including short-lived ones) in a wide temperature range. The experimental setup, which includes a terahertz spectrometer for studying the thermal decomposition reactions, is described. The results of analysis of the gaseous decomposition products of energy substances by the example of ammonium nitrate heated from room temperature to 167°C are presented.

In this paper, we report on the results of the study of the Ti/Au/n-GaAs planar Schottky diodes (PSD) intended for the wideband detection of terahertz radiation. The two types of the PSD devices were compared having either the dual n/n(+) silicon dopant profile or the triple one with a moderately doped matching sublayer inserted. All the diodes demonstrated no noticeable temperature dependence of ideality factors and barrier heights, whose values covered the ranges of 1.15-1.50 and 0.75-0.85 eV, respectively. We observed the lowering of the flat band barrier height of similar to 80 meV after introducing the matching sublayer into the GaAs sandwich. For both the devices types, the series resistance value as low as 20 Omega was obtained. To extract the total parasitic capacitance, we performed the Y-parameters analysis within the electromagnetic modeling of the PSD's behavior via the finite-element method. The capacitance values of 12-12.2 fF were obtained and further verified by measuring the diodes' response voltages in the frequency range of 400-480 GHz. We also calculated the AC current density distribution within the layered structures similar to those being experimentally studied. It was demonstrated that insertion of the moderately Si-doped matching sublayer might be beneficial for implementation of a PSD intended for the operation within the 'super-THz' frequency range.

We present the results of experimental studies of the basic characteristics and operation features of a terahertz heterodyne detector based on the superconducting NbN HEB mixer and a quantum cascade laser as a local oscillator operating at a frequency of 2.02 THz. The measured noise temperature of such a mixer amounted to 1500 K. The spectral resolution of the detector is determined by the width of the local-oscillator spectral line whose measured value does not exceed 1 MHz. The quantum-cascade laser could be linearly tuned with respect to frequency with the coefficient 7.2 MHz/mA within the limits of the current oscillation bandwidth.

We study characteristics of the laboratory prototype of a terahertz heterodyne receiver with an electron-heating mixer and a heterodyne based on the quantum-cascade laser. The results obtained demonstrate the possibility to use this receiver as a basis for creation of a high-sensitivity terahertz spectrometer, which can be used in many basic and practical applications. A significant advantage of this receiver will be the possibility of placing the mixer and heterodyne in the same cryostat, which will reduce the device dimensions considerably. The obtained experimental results are analyzed, and methods of optimizing the parameters of the receiver are proposed.

We present a physically consistent interpretation of the dc electrical properties of niobiumnitride (NbN)-based superconducting hot-electron bolometer mixers, using concepts of nonequilibrium superconductivity. Through this, we clarify what physical information can be extracted from the resistive transition and the dc current-voltage characteristics, measured at suitably chosen temperatures, and relevant for device characterization and optimization. We point out that the intrinsic spatial variation of the electronic properties of disordered superconductors, such as NbN, leads to a variation from device to device.