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The article studies the propagation of electromagnetic waves in metal-dielectric systems based on opals. We revealed anomalous transmission and absorption of light by hybrid plasmon- photonic layered heterostructures associated with the excitation of surface plasmon polaritons propagating along the metal-dielectric interface. The position of maxima in the reflection spectra of nanocomposites, obtained by filling the opal matrix with metal by the electrothermodiffusion method, is explained by the Bragg diffraction, and the asymmetric form of the spectral curves is attributed to the Fano resonance.

The paper studies multilayer graphenes in the form of free-standing films. The authors provide data about the morphology and electrical properties of films treated with plasma of various chemical composition. It is shown that it is possible to control the electrical properties of the surface and electron work function without significantly affecting its morphology. The obtained samples, combining mechanical flexibility with unreactiveness and high electrical conductivity, are promising for application in flexible charge storage devices.

Abstract The electrical and optical properties of nanocomposite materials fabricated by the dispersion of iodine in porous dielectric matrices of zeolites, zeolite-like aluminum phosphates, opals, asbestos, and porous aluminum oxide are studied. It is demonstrated that the physical properties of the produced nanocomposites depend significantly on the structure of a matrix.

An experimental study of the optical properties of two types of metal–dielectric composites based on opal matrices has been carried out: (1) layered structures, obtained by successive deposition of metal and dielectric films on a monolayer of opal globules, where anomalous transmission and absorption of light was found due to the excitation of surface plasmon polaritons of various types; (2) “massive” opal samples, into which the metal was introduced by the method of electrothermal diffusion, where an asymmetric shape of Bragg resonance curves was observed, due to the Fano resonance.

The results of investigating charge-transfer processes in thin layers of a vitreous system (As2Se3)100 – xBix are presented. A power-law dependence of the conductivity on the frequency and a decrease in the exponent s with increasing temperature are found. Charge transfer is a thermally activated process with two regions in the temperature dependence of the conductivity with the activation energies E1 = 0.12 ± 0.01 eV and E2 = 0.23 ± 0.01 eV, respectively. The results are explained in terms of the correlated barrier hopping (CBH) model of hopping conductivity in disordered systems. The main microparameters of the system are calculated: the density of localized states (N), the hopping length (Rω), and the largest height of the potential barrier (WM).

We propose a concept for reservoir computing on oscillators using the high-order synchronization effect. The reservoir output is presented in the form of oscillator synchronization metrics: fractional high-order synchronization value and synchronization efficiency, expressed as a percentage. Using two coupled relaxation oscillators built on VO2 switches, we created an oscillator reservoir that allows simulating the XOR operation. The reservoir can operate as with static input data (power currents, coupling forces), as with dynamic data in the form of spike sequences. Having a small number of oscillators and significant non-linearity, the reservoir expresses a wide range of dynamic states. The proposed computing concept can be implemented on oscillators of diverse nature., 8 pages, 7 figures

The results of the study of the charge transfer processes in the thin layers of a Ge28.5Рb15S56.5 vitreous system are presented. The power-law dependence of the conductivity on frequency and a decrease in the value of the exponent s with increasing temperature are found. The charge transfer is a thermally activated process and two areas on the temperature dependence of conductivity are present. The activation energies of these areas are Е1 = 0.20 ± 0.01 and Е2 = 0.50 ± 0.01 eV, respectively. The obtained results are explained within the scope of the correlated barrier hopping (CBH) model of the hopping conductivity in disordered systems. The main microparameters of the system, namely, the density of the localized state (N), hopping length (Rω), and the maximal value of the height of the potential barrier (WM), are calculated.

Optical properties of novel metal–dielectric nanocomposite materials based on opal matrices have been investigated. The position of optical resonances of nanocomposites, obtained by embedding of silver into the opal matrix by the electrothermodiffusion method, is explained by the Bragg diffraction, and an asymmetric form of resonance curves is attributed to the Fano resonance. An anomalous transmission and absorption of light by hybrid plasmon-photonic layered heterostructures, which is apparently associated with excitation of surface plasmon-polaritons, propagating along “metal–dielectric” interfaces, was revealed.

The results of the experimental studies and numerical simulation of the switching channel development dynamics in planar structures on the basis of vanadium dioxide are reported. The obtained data on the variation of the temperature in the channel with time and of the current arisen after the pulsed load, and on the times of transition from the high-resistance to the low-resistance state and back are analyzed in order to determine the switching mechanism and to predict the functional characteristics of the switchable vanadium- oxide structures as promising materials for the creation of relaxation generators that can serve as prototypes of neural oscillators. It is shown that the switching behavior is associated with the metal–semiconductor phase transition in vanadium dioxide, which is stimulated by the emission of Joule heat.

The study presents a numerical model of leaky integrate-and-fire neuron created on the basis of VO2 switch. The analogue of the membrane potential in the model is the temperature of the switch channel, and the action potential from neighbouring neurons propagates along the substrate in the form of thermal pulses. We simulated the operation of three neurons and demonstrated that the total effect happens due to interference of thermal waves in the region of the neuron switching channel. The thermal mechanism of the threshold function operates due to the effect of electrical switching, and the magnitude (temperature) of the threshold can vary by external voltage. The neuron circuit does not contain capacitor, making it possible to produce a network with a high density of components, and has the potential for 3D integration due to the thermal mechanism of neurons interaction.

Metal-dielectric nanocomposite optical materials based on colloidal crystals have been prepared by electro-thermo-diffusion or magnetron sputtering of silver. Optical properties of these photonic crystals have been studied by angle-resolved reflectance and transmission spectroscopy. The interpretation of observed spectra has been made taking into account the Bragg diffraction, Fano resonance, Fabry-Perot resonance and surface plasmon-polaritons, which excitations contribute to the optical properties of plasmonic-photonic crystals.

A phenomenological model has been proposed for the formation of the major thermal hysteresis loop of optical parameters upon the semiconductor-metal phase transition in vanadium oxide nanocomposites. It has been demonstrated that the effects associated with the influence of nanocrystallite sizes on the phase transition temperature in an individual nanocrystallite, which is determined by the width of the elementary hysteresis loop and the position of the phase equilibrium temperature on the temperature scale, manifest themselves in the form of pronounced features in the loop shape. In particular, the size effects for VO2 polycrystalline films are observed in the formation of a trapezoidal shape of the optical thermal hysteresis loop with a wide lower base, whereas these effects for nanocomposites based on porous glasses with VO2 nanocrystals are revealed in the form of the optical hysteresis loop with a narrow lower base (wide upper base). The proposed model also explains the symmetric shape of the major hysteresis loop for vanadium oxide nanocomposites based on opals. The size effects in opal nanocomposites with strictly fixed sizes of pores and, therefore, nanocrystallite sizes manifest themselves in the form of well-defined steps in the heating and cooling branches of the major hysteresis loop.

A modified method of gas-phase synthesis of vanadium oxide micro- and nanocrystals was developed. The morphology of the crystals obtained and its dependence on the synthesis conditions are analyzed. The method is shown to permit the growth of rod-shaped crystals rectangular in cross section, whiskers, crystals with a rectangular cavity, and also lamellar crystals and planar ordered textures consisting of oriented rodshaped crystals. The microcrystals synthesized were used to study the mutual reversible transformation of various vanadium oxides using oxidation and reduction reactions.

Vanadium dioxide nanoparticles were synthesized in nanoporous silicate glasses with pore sizes of 7 and 17 nm. The temperature dependences of the optical and electrical properties of the composite obtained were studied near the temperature of the semiconductor-metal phase transition in vanadium dioxide. The non-linear optical response of the nanoparticles to picosecond laser pulses was studied in the visible and near-infrared ranges.

New nanocomposites based on zeolites (NaA-NaNO2, NaA-NaNO3) and opals (o-NaNO2, o-NaNO3) that contain sodium nitrite or sodium nitrate nanoparticles in cages of regular porous matrices are prepared. The nanocomposites are characterized by scanning electron microscopy, diffuse reflectance spectroscopy, and electrical measurements.

The hysteresis loops of reflectivity and capacitance of amorphous and polycrystalline vanadium dioxide films in the range of a semiconductor-metal phase transition were studied. The morphology of these films was studied by an atomic-force microscope. It is established that the small number (2–3) of temperature cycles suppress the phase transition due to possible diffusion of oxygen from VO2 clusters into adjacent clusters consisting of the lowest oxides of the Magnelli series. It is shown that the annealing of an amorphous film of vanadium dioxide in oxygen leads to an additional oxidation of low oxides and the formation of VO2, the formation of a polycrystalline film, and the recovery of the phase transition. The above results and the data obtained by atomic-force microscopy are indicative of the high optical quality of the polycrystalline vanadium dioxide films produced by the annealing of amorphous VO2 films. The results also show that these films can be used in interferometers and optical limiters.

Thermal hysteresis of the reflectivity of vanadium dioxide films observed upon the metal-semiconductor phase transition is studied. The major hysteresis loop is assumed to form when the phase equilibrium temperature in film grains and the grain size vary and correlate with each other. Within the suggested concept of hysteresis loop formation, it is demonstrated that the major loop may be asymmetric, i.e., broadened (shifted) toward lower temperatures. Unlike hysteresis branches for VO2 bulk single crystal, those for VO2 films are extended along the temperature axis and may exhibit a step if the grain size distribution has several maxima. The validity of the concept is verified experimentally. It is also shown that atomic force microscopy (AFM) data for the grain size distribution can serve to determine the distribution parameters from the phase equilibrium temperatures without constructing a complete set of minor hysteresis loops, as was required before.

Experimental study of the iodine nanoparticles effect on the optical and electrical properties of zeolite - based matrix nanocomposite materials has been carried out. Phase transitions in the nanocomposites under study have been found.

The hopping conductivity and the Seebeck coefficient have been measured in Pb0.78Sn0.22Te with 5 at. % In and supplementary donor doping with Cl. The experimental data obtained are compared with similar results for supplementary acceptor doping with Tl. At temperatures of 150 K and higher, the thermoelectric power changes its sign from positive to negative on the introduction in sufficient amounts of either donors or acceptors. An analysis of the dependence of the thermoelectric power on the content of supplementary donors and acceptors yields the density of localized indium states as a function of energy. The function is essentially nonmonotonic, exhibiting both a density-of-states peak and a minimum between this peak and the conduction band.

The non-empirical self-consistent method of discrete variation is employed to calculate the electronic structure of clusters simulating amorphous Ta2O5, which contains anionic vacancies, hydrogen impurities, and substitutional defects (in anionic (N and F) and cationic (Mo and W) sublattices). The influence of these defects on the electronic structure, as well as interatomic bonds, charge distributions, and dielectric properties of amorphous Ta2O5 is discussed. Eine nichtempirische, selbstkonsistente Methode diskreter Variationen wird zur Berechnung der Elektronenstruktur von Clustern, die die amorphe Struktur von Ta2O5 mit Anionenleerstellen, Wasserstofffremdatomen und substitutionellen Anion-(N und F) und Kation-(Mo and W) Defekten simuliert, angewendet. Der Einflus dieser Defekte auf die Elektronenstruktur und die interatomaren Bindungen, Ladungsverteilungen und dielektrischen Eigenschaften von amorphem Ta2O5 wird diskutiert.

Nonlinear current-voltage characteristics of Ta2O5 and Nb2O5 amorphous oxides are studied in the temperature range from 213 to 363 K. The data give an evidence for the polaron mechanism of charge transport in these materials. A theoretical treatment of data is presented that gives a critical hopping lenght and a critical index. Im Temperaturbereich von 213 bis 363 K werden nichtlineare Strom—Spannungscharakteristiken von amorphen Ta2O5- und Nb2O5-Oxiden untersucht. Die Werte liefern einen Hinweis auf den Pola-ronenmechanismus des Ladungstransports in diesen Materialien. Eine theoretische Behandlung der Daten wird angegeben, die eine kritische Hoppinglange und einen kritischen Index liefert.

The optical and electrical properties of thin film Fabri-Perrout interferometers on the base of VO/sub 2/ and Ag/sub 2/S are studied. The possibility of using of interferometers as optical limiters, femtosecond Q-switchers and materials for holograms recording is shown. The comparative analysis of the physical characteristics of films of the polycrystalline and amorphous vanadium dioxide. The morphology of films is studied on AFM-microscope. The phenomenological mechanisms of a hysteresis loop formation by metal insulator phase transition and superionic conductor - insulator phase transition are discussed.

In the framework of a two-layer model we study dielectrics with an inhomogeneous distribution of current carriers and show that the low drift mobility of current carriers relates directly to a maximum in the tangent of the angle of dielectric losses (tan δ) on a curve which represents a dependence of tan δ on frequency. Experimental data for amorphous Ta2O5, films irradiated by ultraviolet light are in accordance with the theory. The drift mobility is estimated to be equal approximately to 10−15 cm2 V −1 s−1.