Scientific Herald of Uzhhorod University.Series Physics

The influence of laser radiation on the structure and optical properties of amorphous films in arsenic–antimony–sulphur system

Tue, 31 Dec 2019 00:00:00 +0200

Purpose. As40−xSbxS60 amorphous films are suitable for creation of highly efficient, diffraction gratings, optical diffraction elements, optical compact-disks and sensors, waveguides, elements for infrared and nonlinear optics. This paper is devoted to investigation of Raman spectra of glasses and films and transmission spectra of films in As-Sb-S system with the Sb content up to 12 at % and their changes under laser radiation.

Methods. Raman and optical spectroscopy, atomic forse microscopy. The transmission spectra were studied in 400-750 nm range at room temperature using a diffraction monochromator “MDR-23”. The spectral resolution was no worse than 10-3 eV.

Results and discussion: Increased concentration of antimony in the composition of As40−xSbxS60 (0≤x≤12) amorphous films and laser irradiation (λ=530 nm) of them result in the shift of their absorption edge to the longwave range. In this case the pseudogap width Eg decreases, whereas the index n increases. Under the same conditions of irradiation, the largest changes in optical parameters occur in the As36Sb4S60 film. Changes in the optical characteristics of films are caused by photostructural transformations taking place in them under the laser irradiation.

The nanoheterogenous structure of the studied films was established. The structural matrix of As40−xSbxS60 films is built from As(Sb)S3 pyramidal units connected by bridging S atoms. No molecular fragments with Sb-Sb bonds in the structure of films were detected. However, the large amount of structural groups with homopolar As-As (As4S4, As4S3) and S-S bonds (Sn) are present in the structure of films. The laser irradiation of As40−xSbxS60 films leads to the breaking and switching of As-As and S-S bonds in As4S4, As4S3, and Sn type structural fragments. Accompanied with the formation of structural units with heteropolar bonds As-S (AsS3). These structural transformations are related with the decreasing content of molecular fragments possessing homopolar bonds in films matrix.

Conclusions. Transmission and Raman spectra of as-prepared and irradiated As40−xSbxS60 amorphous films were investigated. The nanoheterogenous structure of the studied films was confirmed by Raman spectra. It was established that the growth of the Sb content in composition of films and irradiation induced the absorption edge shift to the longwave region, Eg decreased and n increased. The largest changed in optical parameters of as-prepared and irradiated films occur in the As36Sb4S60 film. These changes are caused by the photostructural transformations, which are accompanied by decreasing in the number of structural groups with homopolar bonds in films matrix.

Pressure effect on the adiabatic potential in the crystals with D²_3d space symmetry and strong electron-phonon interaction

Л. Ю. Хархаліс, К. Є. Глухов, Т. Я. Бабука — Tue, 31 Dec 2019 00:00:00 +0200

Purpose. The CuInP2S6 and CuInP2Se6 crystals are characterized by an order-disorder phase transition mechanism, which is caused by electron-phonon interaction and the Jan-Teller cooperative effect. Vibronic instability is related to the electronic configuration of copper d10 in octahedral symmetry, and the disorder in the paraelectric phases can be explained by the jumping movements of Cu ions. It is of interest to study the conditions of this instability at the pressure. The main aim of our paper is to carry out the investigation of the matrix of the vibronic potential energy and the adiabatic potentials at the pressure.

Methods. Adiabatic potentials concept based on the group -theoretical analysis and Pikus’ method of invariants.

Results. For the case of hydrostatic pressure for crystals with D3d symmetry, an adiabatic potential depending on the components of the strain tensor and the coordinates of normal vibrations active in the Jahn-Teller effect has been obtained. We carried out the numerical simulations of the pressure effect on the shape of the adiabatic potentials From our qualitative analysis follows that the changing of the adiabatic potential depth (EJT ) and the value of the minimum displacement ρ0 takes place. Especially the shape of the adiabatic potential energy is changed at the shift strain εxy.

Conclusions. Using the symmetry methods, we constructed the matrix of the vibronic potential energy and found the adiabatic potentials. It is shown that in a consequence of the phase transition the splitting of the equivalent minima (disorder) of the adiabatic potential on the group of the nonequivalent minima (order) is occurred. The shape of these adiabatic potentials shows that in their concept one can confirm about the order-disorder phase transition and also to consider the pressure influence on these potentials.

Effect of temperature on the reflective index dispersion of As_XS_1−X glasses

І. Й. Росола, О. І. Чобаль, В. М. Різак — Tue, 31 Dec 2019 00:00:00 +0200

Purpose. The purpose of this research was to prepare AsXS1−X glasses and to study concentration and temperature dependences of their refractive index.

Methods. The refractive index was measured by a prism method. Plane parallel slabs with thicknesses of ∼1 mm were cut from synthesized bulk samples. The sample prisms had refracting faces with areas of 5 × 10 mm and angles between them of ∼ 10° – 15°. The refracting angles of the prisms were determined on a LOMO G-1.5 goniometer. The temperature was measured with a copper-constantan thermocouple to within ±0.5 K. The error in the refractive index n over the entire observed spectral range was ±2 · 10–4.

Results. The dispersion of the refractive index n(λ) of AsXS1−X glasses was studied in the concentration range from X = 0.20 to X = 0.40 of five samples in the temperature range from 80 to 370 K at wavelengths from 1.0 μm to 2.3 μm. It was found that the refractive index of the studied materials n at a fixed wavelength λ decreases with increasing temperature, dn/dT = −1, 2… − 10, 5 · 10−5 K−1 depending on the composition.

Conclusions. The experimental results of n(λ) of AsXS1−X glasses were described in terms of the Wemple – DiDomenico single effective oscillator model. Based on the experimental results, atomic refractions and the polarizability coefficient of glasses of the AsXS1−X system were calculated, and their temperature behavior and concentration dependence were explained. It was concluded that thermal expansion coefficient makes the main contribution to the value of the temperature dependence of the refractive index.

Ab initio investigations of the electron-phonon interaction in the indium selenides

К. Є. Глухов, Л. Ю. Хархаліс, Т. Я. Бабука, М. В. Лях — Tue, 31 Dec 2019 00:00:00 +0200

Purpose.Nowadays,the indium selenides have attracte dincreasing attention since they arepotential candidates for the applications of their physical properties in many devices. In particular, in the In₄Se₃ semiconductor, it was revealed a high thermoelectric figure of merit that opens its perspectivity for thermoelectrics. In the single layer of InSe, the unusual transport phenomena and optical properties have been observed. For both crystals, these anomalies are connected with the strong electron-phonon coupling owing to the peculiar character of electron states and the irinteraction with phonons. Therefore, for the bulk In₄Se₃ and β-InSe crystals, it is of interest to study the electron-phonon coupling which can play an important role in the physical properties of considered materials. The main aim of our paper is to carryouttheinvestigationoftheevolutionoftheelectron-phonon interaction at the transition from the β-InSe crystal to the In₄Se₃

Methods. The program packet ABINIT with the application of the updated methodology of the density functional perturbation theory (DFPT).

Results. In our work, we calculated the phonon spectra, density of phonon states, the Eliasberg spectral function 2F(ω), and electron-phonon coupling strength. The phonon linewidths Γel−ph for phonon wavevectors along high symmetry directions in the Brillou in zone are obtained too. Conclusion. According to our estimations, the parameters of electron-phonon interaction for In₄Se₃ are higher than for β-InSe that indicates an increase in energy exchange between vibrational and electronic states. This fact is connected with the stronger interaction between the corrugated layers and more complicated chemical bonding topology in In₄Se₃ in comparison with the β-InSe layered crystal. The main contribution in these characteristics is due to the high-frequency optical vibrations which are responsible forthe oscillations in the perpendicular direction to the planes of the layers.

Methods of layer-by-layer deposition of films and characteristics of two-layer structures based on bacteriorhodopsin

І. І. Трикур, М. Ю. Січка, І. Й. Цьома, А. М. Потапчук, В. М. Різак — Tue, 31 Dec 2019 00:00:00 +0200

A modified technique of layer-by-layer deposition of bacteriorhodopsin (BR) films is proposed. This method is a combination of the casting and centrifugation method and involves the application of a pure BR film to the substrate, which is covered with athin layer of sol-gel glass. As a result of using this method we have obtained two-layer film structures based on BR with satisfactory optical quality, which are not destroyed by water and can be used as primary transducers for chemical sensors of aqueous solutions. Surface of the obtained structures сoating the film of pure BR with a thin layer of sol-gel glass leads to the leveling of the film surface and reducing the scattering on its inhomogeneities. The film roughness decreases by an average of 15-20% from 18.5 to 14.0 nm. The maximum height difference decreases byalmost 30% - from 290 nm for pure BR films to 205 nm for BR films coated with a sol-gel glass layer. The study of the spectral characteristics of the obtained films showed that the deposition of a layer of sol-gel glass does not affect the characteristic functional and optical properties of BR.

Influence of cationic substitution on the electronic-energy structure and optical properties of Cu₂B^IVS₃(B^IV=Si, Ge, Sn) compounds

Д. І. Блецкан, В. В. Вакульчак, Ю. В. Кампов, І. П. Студеняк — Tue, 31 Dec 2019 00:00:00 +0200

Purpose. Ternary Cu2B IVS3 (BIV = Si, Ge, Sn) compounds are promising materials that can be used as absorbing layers of solar cells. Methods. This paper presents the results of calculations of the band structure, the state density distribution of the electron density and such optical functions as real ε1 and imaginary ε2 part of the dielectric permittivity, reflectivity R, absorption coefficient α and refractive index n of Cu2B IVS3 compounds. Results. According to the results of the band structure calculations in the LDA+U approximation, the monoclinic phases Cu2SiS3, Cu2GeS3 and Cu2SnS3 are direct-gap semiconductors with the calculated band gaps of 2.46 eV, 1.5 eV and 0.93 eV, respectively, which agrees well with the experimental values obtained from the analysis of the intrinsic absorption edge. Valence band with for monoclinic phases Cu2B IVS3 consists of four subbands separated by forbidding intervals. The analysis of partial contributions into the density of electronic states allowed to identify the genetic origin of different subbands of the valence band, and also to obtain the formation of a chemical bond in the crystals under investigation. For optimized structures of Cu2SiS3, Cu2GeS3 and Cu2SnS3,the spectra of optical functions in the wide range energy of fundamental absorption were calculated for the first time using a unified technique. The spectra of the optical functions of these crystals are characterized by significant polarization anisotropy and are qualitatively similar to each other. The electron density was calculated and maps of the distribution of charge of valency electrons in the planes along the Cu-S and BIV–S bond lines in various structural units of Cu2B IVS3 crystals were constructed, which made it possible to describe the features of the formation of a chemical bond between atoms forming the corresponding crystal. Conclusions. : As a result of quantum-chemical calculations, it was established that the structure of the energy bands of monoclinic Cu2B IVS3 crystals is qualitatively similar to each other, contain the same number of filled bands (44) and have a characteristic topology in which traced four allowed energy region. According to the calculations in the LDA+U approximation, all three crystals are direct-gap semiconductors, the bandgap of which decreases monotonically with increasing atomic number of the cation BIV (Si→Ge→Sn; 2.46 еV → 1.5 еV → 0.93 еV). It has been established that the monoclinic phases Cu2B IVS3 are semiconductors with a complex system of covalent-ionic interatomic bonds

Mechanical properties of composites based on (Cu_1−xAg_x)₇GeSe₅I mixed crystals

А. В. Бендак, К. В. Скубенич, А. І. Погодін, В. С. Біланич, І. П. Студеняк — Tue, 31 Dec 2019 00:00:00 +0200

Purpose. The purpouse of the present work is to investigate a mechanical properties of composites based on polymer matrix and superionic compounds (Cu1−xAgx)7GeSe5I, to perform a comparative analysis with similar properties of 81 Uzhhorod University Scientific Herald. Series Physics. Issue 46. — 2019 a single crystals and to study changes of structural rigidity, which depend on concetration ratio of polymer and microcrystalline components.

Methods. The сomposites were prepared by pressing a mixture of micropowder and polymer. Investigations of their mechanical properties were performed using microindentation test. An indentation was performed by Vickers indenter. For imprints analysis interferential microscope MII–4 was used.

Results. The dependence of microhardness versus concetration ratio of micropowder and polymer has been analyzed. The relative contributions of elastic and plastic deformation components for Cu7GeSe5I single crystal, composite based on it, and ethylyne-vinyl acetate polymer have been calculated and compared. The decreasing of composites’ microhardness at Cu+→Ag+ isovalent cation substitution has been revealed.

Conclusions. The microhardness numerical values of composites based on polymer and superionic micropowder were calculated. It has been founded, that at concentration of microcrystals increase up to 90 wt.%, the mechanical rigidity crossover ”soft-rigid structure” is observed. It has been shown, that with different component concentration the deformation mechanism changes: elastic in polymer, plastic in composites and elasto-plastic in superionic crystals. The microhardness of composites at Cu+→Ag+ cation substitution, decreases.

Transmission spectra of copper, aluminum and chalcopyrite – based thin nanostructured films prepared by gas discharge technique

Tue, 31 Dec 2019 00:00:00 +0200

Purpose. At present, alloys of СuIn(Sb)S2(Se2) from chalcopyrite class are perspective materials for solar cells batteries. This is caused by their high absorption coefficient in a wide spectral region as well as high light resistivity of layer coverings. Laser sputtering permit (allow) to obtain stoichiometric thin films of chalcopyrite but the yield of largearea covering is low, and a process of their fabrication is expansive due to high cost of laser and vacuum technique used. Reasonable, exploiting of simpler gas-discharge techniques of chalcopyrite synthesis for photovoltaic solar cells convertors is actual and important. At the same time, optical characteristics of chalcopyrite layers synthesized from over-constrained plasma are not considered. Results of optical absorption spectra for СuInSe2 layers at glass (quarts) substrate, obtained at different gas ambient pressure of over-constrained nanosecond plasma discharge.

Methods. Methods and technique for thin films-based coper oxides, aluminum and chalcopyrite Nanostructures obtained in air and inert gases are considered in details for ecotone mechanism of sputtering are considered. For these samples optical transmit ion were investigated in 200 – 800 nm range.

Results. Transmission spectra for samples on glass substrates in 200 – 500 and 350 – 800nm, correspondingly, were obtained. Gas ambient – air and argon – at 1 atm pressure for all electrode materials. Layers were obtained by abovementioned technique. We start to register transmition for wave-lengths above 300 nm. For copper-based films sputtered in argon observed maximal transmition. Probably this is nanostructured coper films. Minimal transmition is inherent for aluminum- and chalcopyrite films. The strong absorption of light by chalcopyrite films in the region of 200-800 nm indicates that when the films of chalcopyrite are sprayed with a gas-discharge method, they repeat the stoichiometry of the chalcopyrite electrodes.

Conclusions. Pulsed gas-discharge method for copper film preparation is vividly perspective for transparent electrodes applications. Films of chalcopyrite are characterized by strong absorption in the range of the spectrum of 200 – 800 nm, which is promising for their applications in photovoltaics.

Optical characteristics and parameters of gas discharge plasma on a mixture of cadmium diodide vapor with helium and small addition of nitrogen

А. О. Малініна, Р. В. Грицак, І. І. Аксенюк — Sun, 01 Dec 2019 00:00:00 +0200

Purpose. To investigate the optical characteristics and parameters of the barrier discharge plasma on mixtures of cadmium diiodide vapor and helium with small molecular nitrogen additives at high pump pulse frequencies.

Methods. The creation of a gas-discharge plasma and the excitation of the components of the working mixture were carried out by a pulse-periodic (pulse repetition rate of 18–20 kHz, pulse duration 150 ns) barrier discharge. Barrier discharge plasma parameters were determined numerically based on the electron energy distribution function (EEDF) in discharge. EEDF was determined by solving the kinetic Boltzmann equation in two-terms approximation using the well-known program «Bolsig+». Based on EEDF: mean electron energies, electron mobility, specific power losses of electrical discharge and rate constants of elastic and inelastic scattering of electrons on cadmium diiodide, helium and molecular nitrogen as a function of the reduced electric field were identified.

Results.Emission in the visible spectrum of cadmium monoiodide exciplex molecules and cadmium atoms was detected. The regularities in the changes in the optical characteristics of the plasma are established depending on the repetition rate of the pump pulses, the component and the quantitative composition of the mixtures. Discussions of research results are presented. The research data is of interest for creating exciplex gas-discharge sources of visible radiation with a radiation maximum at a wavelength of λ=650 nm.

Conclusions. A gas-discharge barrier discharge plasma on mixtures of cadmium diiodide vapor, helium, and molecular nitrogen is of interest for creating exciplex gas-discharge sources of visible radiation with a radiation maximum at a wavelength of λ=650 nm, which will be used in biotechnology, agrophysics, scientific researches in quantum electronics, for pumping solid-state and liquid lasers and in medicine.

Description of mass spectrum of Bc-meson family

В. Ю. Лазур, В. В. Рубіш, О. К. Рейтій, С. І. Мигалина — Tue, 26 Nov 2019 00:00:00 +0200

Purpose. Calculation of the spectrum of masses of system ^¯bc consisting of two heavy b and c quarks (B_cmesons family) within the potential models of heavy quarkonium. In particular, to calculate the spin-dependent splitting of the energy S and P levels of a given of heavy mesons family. Investigate the dependence of the energy splitting magnitude on the parameters of the interaction potential between the quarks.

Methods. The spin-dependent splittings of the S and P energy levels caused by spin-spin, spin-orbital and tensor interactions in the framework of the Breit-Fermi quasi-relativistic approximation with the screened quark interaction potential are calculated. Wave functions and matrix elements of spin-spin, spin-orbital and tensor interactions were calculated numerically.

Results. It is found that the energies of the S and P levels and the magnitude of the «fine» and «hyperfine» splitting depend essentially on the mixing constant λ of scalar and vector long-range screening potential and the constant of the strong interaction α_s(whose value is almost unchanged within the B_cmeson family). Increasing the contribution of the Lorentz vector potential to operators of spin-orbital, spin-spin and tensor interactions leads to increase of the magnitude of the corresponding splittings of energy levels. The obtained value of the mixing constant λ = 0.3 indicates that the confined screened potential has a predominantly scalar Lorentz nature (about 70 %), and the Coulomb-like potential of one-gluon exchange is purely a Lorentz vector.

Conclusions. The calculated energy levels of the system ^¯bc can be used for experimental search for B_cmesons.

Asymptotics of a semiclassical type for wave functions of quasimolecules in problems of ion-molecular collisions

М. Я. Євич, М. І. Карбованець — Tue, 31 Dec 2019 00:00:00 +0200

Purpose. To construct an asymptotics of a quasiclassical type for the two-center wave function of the tunneliding electron used for calculating of the two-electron exchange interaction in the problems of ion-molecular collisions with particle rearrangement. Methods. The semiclassical method and the Green’s function formalism have been used for construction of the asymptotically correct two-center wave functions of a homonuclear diatomic molecule and a dipole-bound anion in the vicinity of a perturbing multiply charged ion. Results.We have constructed the semiclassical representation for the two-center one-electronic wave function of the quasimolecular system, which consist of the atomic ion and diatomic homonuclear molecule or dipole-bound anion, in the whole region of configuration space at large separation between colliding particles. Conclusions. An analytical study of the asymptotic properties (at large distances between interacting particles) of the quasimolecular systems that consists of an ion and a homonuclear diatomic molecule or dipole-bound anion has been carried out. The new analytical representations for the two-center one-electronic wave functions of the quasimolecular systems in the whole region of configuration space at large separation between colliding particles has been obtained in the framework of the semiclassical version of the asymptotic approach and the method of Green’s function

Approximation of scattering phases for Argonne v18 potential

В. І. Жаба — Tue, 31 Dec 2019 00:00:00 +0200

Purpose. This article is dedicated to the study of phase shifts for single-channel neutron-proton scattering. The phase shifts, which are obtained in the variable phase approach, are studied. For the approximation of phase shifts, a function — 2019 is used in the form of a known formula for a parabolic-type quadratic function y(x)=a+bx+cx2 , which was proposed by M.A. Dolgopolov, L.A. Minin and V.A. Rabotkin in the study of phase shifts for the Paris potential. It is necessary to find the coefficients a, b, c for y(x) when approximating the np- scattering phases for the Argonne v18 potential. Methods. Approximation is used to find the coefficients of the function y(x). Find the optimal values of the coefficients a, b, c at a minimum value χ 2 . Results. An approximation of the neutron-proton scattering phases obtained by various methods for the phenomenological nucleon-nucleon potential Argonne v18 was made. The calculated coefficients of this function obtained for phase shifts by means of the variable phase approach are compared with the results of the approximation of the scattering phases from the original paper. For illustration graphs are given for phase shifts for four spin states for the np- system ( 1S0, 3P1, 1D2, 3D2). Conclusions. The obtained coefficients for the function y(x) can be used to calculate the values of the scalar scattering amplitude, the full cross-section and the partial scattering amplitude for any phase value within the energy interval for the approximation carried out. In next studies one can obtain and compare the coefficients and parameters of approximation for scattering phases for other modern phenomenological nucleon-nucleon potentials. Keywords: variable phase approach, nucleon-nucleon scattering, approximation, phase shifts, Arg

Reasons for change in artificial space objects own rotation

Wed, 27 Nov 2019 00:00:00 +0200

Purpose. Photometry in conjunction with positional observations is currently the main method of controlling the operation of artificial space objects in orbit with which radio communication is lost. This paper presents an analysis oflong-range photometric observations of low-orbital artificial Earth satellites of various functionality class.

Methods. A methodological approach to determining the dynamic characteristics of the behavior of space objects in orbit using photometric information in the form of light curves is considered. It is based on studies of the characteristics of the object’s own rotation and their causes.

Results. 40 years of experience in such studies has made it possible to evaluate virtually all possible factors affecting its functional dynamics by changes in the light of an object. The paper presents six reasons for the occurrence of a satellite’s own rotation in the Earth’s orbit. They cover both natural factors and the effects of human intervention.

Conclusions. If the size and mass of the destabilized satellites are known, then this satellite can be used as an indicator of the course of physical processes in the Earth’s atmosphere at the height of the satellite’s orbit. The variants of finding the period of own rotation of the object in manual and automatic modes are described.