Showing papers by "Uzhhorod National University published in 2006"
TL;DR: In this article, the effect of different types of disordering on the optical absorption processes and specific features of compositional changes in the absorption edge spectra under S→Se and Br→I anion substitution in the mixed crystals are investigated.
74 citations
TL;DR: In this paper, the authors hypothesize that some new observed features in the Raman spectra of these glasses are related to transformations of As 4 S 4 molecules possible through the m-As 4S 4 intermediate.
Abstract: Light-induced structural changes of g-As 40 S 60 and g-As 45 S 55 were probed by macro FT-Raman and photon-energy dependent micro-Raman spectroscopy. We hypothesize that some new observed features in the Raman spectra of these glasses are related to transformations of As 4 S 4 molecules possible through the m-As 4 S 4 intermediate. At the same time, other processes, connected mainly with the layers, composed of pyramidal AsS 3 structural units, take place. These new observed Raman modes and their possible interconnection to changes of the glassy structure are discussed.
18 citations
TL;DR: In this paper, the authors proposed a model to explain the mechanism of Se diffusion in As2S3, which suggests that diffusion takes place through the wrong bonds, and the proposed model was supported by the XPS data.
Abstract: Photoinduced interdiffusion was observed with above band gap light in nanolayered Se/As2S3 films. It is discussed in terms of the optical parameters such as band gap, Urbach edge (E-e) [F. Urbach, Phys. Rev. 92, 1324 (1953)], and B-1/2 (Tauc's parameter) [J. Tauc , Phys. Status Solidi 15, 627 (1966)]. Experimental data of B-1/2 and E-e for as-prepared samples do not show clear correlation implied by the Mott-Davis model [N. F. Mott and E. A. Davis, Electronic Process in Non-crystalline Materials (Clarendon, Oxford 1979), p. 287]. It is also shown that the optical parameters can be changed with a change in the Se sublayer thickness. Variations of these optical parameters as a function of modulation period and photoinduced interdiffusion were discussed in terms of the quantum confinement effect and changes in the valence and conduction bands. We proposed a model to explain the mechanism of Se diffusion in As2S3, which suggests that diffusion takes place through the wrong bonds. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical alternations in the bonding. The proposed model was supported by the XPS data.
10 citations
TL;DR: In this article, the authors used analytic methods to analyze the discrete spectrum for the problem (Z1eZ2)2 in the united-atom limit (R ≪ 1) and obtain asymptotic expansions for the quantum defect and energy terms of the system.
Abstract: We use analytic methods to analyze the discrete spectrum for the problem (Z1eZ2)2 in the united-atom limit (R ≪ 1) and obtain asymptotic expansions for the quantum defect and energy terms of the system (Z1eZ2)2 at small intercenter distances R up to terms of the order O(R6). We investigate the effect of the dimensionality factor on the energy spectrum of the hydrogen molecular ion H2+.
10 citations
TL;DR: In this paper, the spectral and electric characteristics of atmospheric-pressure high-frequency barrier discharge plasma based on mixtures of mercury diiodide with neon and admixtures of argon, xenon, and nitrogen are analyzed.
Abstract: The spectral and electric characteristics of atmospheric-pressure high-frequency barrier discharge plasma based on mixtures of mercury diiodide with neon and admixtures of argon, xenon, and nitrogen are analyzed. A repetition rate of sinusoidal voltage pulses of about 100 kHz is used both to produce the gas discharge plasma and to excite the components of the working mixture. The radiation of the discharge in the range 200–900 nm is analyzed with a high resolution. It is found that, in the range 400–900 nm, the system of bands of excimer molecules HgI(B → X) emits 85% of the barrier discharge radiation. It is established that the radiation intensity of HgI(B → X) molecules is maximal in the mixture HgI2/Xe/Ne = 0.6/10/90 kPa. In this mixture, UV radiation of molecules XeI(B → X) and XeI(B → A) is observed. The regular features of the spectral and electric characteristics of the gas discharge plasma are discussed. An atmospheric-pressure high-frequency barrier discharge in mixtures of mercury diiodide with gases is of interest for use in a selective (Δλ = 438–446 nm) excilamp with a cylindrical working aperture.
9 citations
TL;DR: In this article, the emission characteristics of a small short-wavelength (UV) lamp filled with a krypton-bromine mixture and pumped by longitudinal glow discharge at a 100mm distance between electrodes in a quartz tube with an internal diameter of 14 mm.
Abstract: The emission characteristics are reported for a small short-wavelength (UV) lamp filled with a krypton-bromine mixture and pumped by longitudinal glow discharge at a 100-mm distance between electrodes in a quartz tube with an internal diameter of 14 mm. The emission spectrum is formed by the resonance atomic lines of bromine (163.3 and 157.6 nm) and the molecular lines of bromine (Br2) and krypton bromide (KrBr). An increase in the partial pressure of bromine in the working mixture from 50 to 270 Pa is accompanied by a decrease in the intensity of emission lines due to atomic bromine and leads to the formation of VUV-UV continuum based on the molecular bands due to Br2 and KrBr. The operation regime was optimized with respect to the glow discharge current and the gas mixture pressure and composition. The optimum partial pressure of krypton is within 500–800 Pa, and that of bromine vapor is within 100–250 Pa. The average total VUV-UV output radiation power reached 5 W at an efficiency of 8–10%.
5 citations
TL;DR: In this paper, the problem of interpolation of functions of two real variables by two-dimensional continued fractions was investigated, and the problem was shown to be NP-hard, even in the case of continuous functions.
Abstract: We investigate the problem of interpolation of functions of two real variables by two-dimensional continued fractions
5 citations
TL;DR: In this paper, the authors investigated the photoconductivity spectra of Bi-doped nonstoichiometric GeSe layered crystals grown by static sublimation and found two strongly polarized maxima at the photon energies hνmax = 1.35 eV and 1.44 eV due to the V1V → V1c and Δ2v → Δ 1c optical transitions, respectively.
Abstract: The polarization photoconductivity spectra of Bi-doped nonstoichiometric GeSe layered crystals grown by static sublimation were investigated. Two strongly polarized maxima at the photon energies hνmax = 1.35 eV (E ∥ a) and 1.44 eV (E∥ b) due to the V1V → V1c and Δ2v → Δ 1c optical transitions, respectively, were found in the spectra of nominally undoped GeSe crystals near the intrinsic absorption edge at 293 K. In the low-temperature region, an exciton photoconductivity band peaked at hνmax=1.32 eV, which is due to exciton dissociation at the cation vacancies, was revealed. With an increase in excess Se in crystals, a sharp increase in the intensity of the exciton peak in the photoconductivity spectra was observed. It is shown that doping of GeSe crystals with donor Bi impurity is an effective tool of the control of their electrical and photoelectric properties. Although introduction of Bi into germanium monoselenide does not lead to the conductivity conversion from the p to n type, a sharp increase in the resistivity is observed, the crystals become photosensitive, and a strong impurity band peaked at 1.11 eV arises in the photoconductivity spectra.
4 citations
TL;DR: In this article, the authors studied the spectral characteristics of a low-density water vapor plasma in the vacuum ultraviolet (VUV) region of the spectrum, which was formed in a longitudinal glow discharge.
Abstract: We present the results of a study of emission from a low-density water vapor plasma in the vacuum ultraviolet (VUV) region of the spectrum. The plasma was formed in a longitudinal glow discharge. We have studied the spectral characteristics of the plasma and also the dependences of the relative energy characteristics of the hydroxyl (OH) emission band on the discharge current and the helium partial pressure in a He-H2O mixture in the spectral range 130–190 nm.
3 citations
TL;DR: In this paper, the emission characteristics of a glow discharge in bromine vapor have been investigated in the spectral region 130-350 nm, and the currentvoltage characteristics and the emission spectra of the glow discharge with an interelectrode gap of 10 cm and a discharge tube 14 mm in inner diameter have been studied.
Abstract: The emission characteristics of a glow discharge in bromine vapor have been investigated in the spectral region 130–350 nm. The current-voltage characteristics and the emission spectra of the glow discharge with an interelectrode gap of 10 cm and a discharge tube 14 mm in inner diameter have been studied. The emission characteristics have been optimized as functions of the bromine vapor pressure and the power deposited into the plasma. It has been shown that, at a low pressure of the bromine vapor, the emission spectrum of the lamp is determined by the spectral lines of atomic bromine in the range 158–164 nm, which are analogous to the known lines (such as those at 206.2 nm) of atomic iodine in an iodine-containing glow discharge plasma. As the pressure of the bromine vapor increases above 100 Pa, the intensity of these emission lines of the bromine atom decreases and the lamp spectrum is formed by bromine molecular bands in the form of a continuum with sharp boundaries (λ = 165–300 nm).
2 citations
TL;DR: In this paper, the optical constants (the complex refractive index tensor and the geometrical thickness) of thin freshly prepared unannealed films from glassy chalcogenide As-S semiconductors with the stoichiometric formula As2S3 are calculated in the weak absorption region (λ = 0.6328 µm) based on multiangle ellipsometric measurements and taking into account the birefringence of optical waves in such films.
Abstract: The optical constants (the complex refractive index tensor and the geometrical thickness) of thin freshly prepared unannealed films from glassy chalcogenide As-S semiconductors with the stoichiometric formula As2S3 are calculated in the weak absorption region (λ = 0.6328 µm) based on multiangle ellipsometric measurements and taking into account the birefringence of optical waves in such films. The advantage of the approximation of an anisotropic uniaxial film is shown, the values of the ordinary and extraordinary refractive indices are determined, and the difference between them is found to be ∼5 × 10−3.
TL;DR: In this article, an experimental investigation of the output characteristics of an excimer lamp utilizing mixtures of zinc diiodide vapors with inert gases and excited by a barrier discharge (BD) with the repetition rate of sine voltage pulses f ≤ 130 kHz was performed.
Abstract: An experimental investigation is performed of the output characteristics of an excimer lamp utilizing mixtures of zinc diiodide vapors with inert gases and excited by a barrier discharge (BD) with the repetition rate of sine voltage pulses f ≤ 130 kHz. Radiation spectra of BD plasma in the range of 200–900 nm with resolution of 0.05 nm are studied, as well as the time characteristics of voltage and current and the dependence of radiation intensity on the composition of mixtures. The radiation of ZnI(B–X) excimer molecules is revealed with a maximum at λ = 602 nm, as well as of I
2
*
excimer molecules, lines of inert gases, and, in mixtures with xenon, of XeI* excimer molecules. The composition and pressure of gas components of mixture are optimized. It is found that the most intense radiation of ZnI* in binary mixtures is observed when helium or neon is used as buffer gas. The specific average radiation power in the visible range is 23 mW/cm2.
TL;DR: In this paper, the internal friction in GexAs40 − xS60 glasses is investigated in the temperature range 100 K-Tg at infralow frequencies (10−3−10−1 Hz).
Abstract: The internal friction in GexAs40 − xS60 glasses is investigated in the temperature range 100 K-Tg at infralow frequencies (10−3−10−1 Hz). It is shown that the concentration dependence of the internal friction of these materials changes as a result of the transformation of the dominant kinetic unit in dissipative processes of the relaxation and nonrelaxation types. It is established tha the change in the mechanism of internal friction in the GexAs40 − xS60 glasses leads to a jump in the activation energy of the α relaxation and to a local minimum in the frequency factor τ0.
TL;DR: In this article, the optical properties of thin As2S3 chalcogenide glass were determined from the results of multiangle ellipsometric measurements using He-Ne laser radiation (λ = 0.6328 μm).
Abstract: The optical characteristics of thin (∼2-μm-thick) films of As2S3 chalcogenide glass prepared by thermal deposition in vacuum have been determined from the results of multiangle ellipsometric measurements using He-Ne laser radiation (λ = 0.6328 μm), with allowance for weak absorption in this spectral range. Relaxation-induced changes in the optical properties of both freshly prepared (unannealed) and annealed As2S3 films are determined. The possibility of using ellipsometry for the qualitative estimation of the degree of inhomogeneity of the film and its variation in the course of structural transformations during relaxation or under the action of other factors is considered.
TL;DR: In this paper, the mechanism of formation of doubly charged ions upon nonlinear ionization of Ba atoms as a result of the simultaneous action of yttrium-aluminum garnet laser radiation and its second harmonic is investigated.
Abstract: The mechanism of formation of doubly charged ions upon nonlinear ionization of Ba atoms as a result of the simultaneous action of yttrium-aluminum garnet laser radiation and its second harmonic is investigated. It is shown that this mechanism is two-electron. The experimental data are compared with the results of the calculation carried out for Gaussian laser beams.
TL;DR: In this article, the time-averaged values of the electron temperature and concentration at distances of 1 and 7 mm from a target have been determined from the emission characteristics of the laser erosion plasma of lead and gallium.
Abstract: Time-averaged values of the electron temperature and concentration at distances of 1 and 7 mm from a target have been determined from the emission characteristics of the laser erosion plasma of lead and gallium. The plasma was produced in a vacuum (3–12 Pa) as the corresponding target was exposed to radiation of a neodymium laser (τ = 20 ns, λ = 1.06 μm, f = 12 Hz, W = 108–109 W/cm2). The energy distribution of excited atomic states has been analyzed. The time dependence of the electron temperature at a distance of 7 mm from the target is presented.
TL;DR: In this paper, the photoluminescence and the intrinsic absorption edge of the (Ga0.1In0.9)2Se3 uniaxial crystal are investigated in the temperature range 77-300 K.
Abstract: The photoluminescence and the intrinsic absorption edge of the (Ga0.1In0.9)2Se3 uniaxial crystal are investigated in the temperature range 77–300 K. Exciton and impurity luminescence bands are revealed at low temperatures and the Urbach tail of the absorption edge is found in the temperature range under study. The temperature dependences of the spectral position and the half-width of the luminescence bands, as well as the optical pseudogap and the energy width of the absorption edge, are studied. The mechanisms of radiative recombination and light absorption and the processes of lattice disordering in the (Ga0.1In0.9)2Se3 crystal are discussed.
Journal Article•
01 Apr 2006-Physics and Chemistry of Glasses-european Journal of Glass Science and Technology Part B
TL;DR: In this paper, the photoluminescence properties of chalcogenide glass multilayers with 12-15 nm modulation lengths prepared by a thermal evaporation technique can be changed by laser irradiation.
Abstract: Optical parameters of chalcogenide glass multilayers with 12-15 nm modulation lengths prepared by a thermal evaporation technique can be changed by laser irradiation. Photoluminescence (PL) studies were carried out on non-irradiated and irradiated multilayered samples of $a-Se/As_2S_3$ and $Bi/As_2S_3$. The $Bi/As_2S_3$ samples show higher luminescence efficiencies compared to $a-Se/As_2S_3$. Broadening of luminescence bands with decrease in Se/Bi layer thickness and with irradiation suggests the former is due to change in interface roughness and defects because of the enhanced structural disorder and the latter is due to initial or photo induced interdiffusion. From the deconvoluted photo (PL) spectrum, it is shown that peak PL intensity, full width at half maximum, and the PL quantum efficiency of particular defects which give rise to PL can be tuned by changing the sub layer thickness or by interdiffusion.
TL;DR: In this paper, the formation of argon fluoride molecules in plasma-dynamic jets of gas-potassium fluoride vapor and argon-sulfur hexafluoride vapor mixtures was investigated.
Abstract: The formation of argon fluoride molecules in plasma-dynamic jets of argon-potassium fluoride vapor and argon-sulfur hexafluoride vapor mixtures is investigated. The intensity of the ArF* luminescence band at 193 nm versus the argon and sulfur hexafluoride flow rates, pump power, and distance from the nozzle is studied.
TL;DR: In this paper, the authors considered the limiting displacement of an atom (a group of atoms), which corresponds to the maximum of the interatomic interaction force, as a process of atomic excitation in liquids and glasses.
Abstract: The limiting displacement of an atom (a group of atoms), which corresponds to the maximum of the interatomic interaction force, is treated as a process of atomic excitation in liquids and glasses. The formation, migration, and disappearance of excited atoms are caused by local fluctuations of the configurational entropy. These processes in chalcogenide (and other) glasses are considered small-scale low-energy processes. The parameters of the excited state model as applied to oxygen-free inorganic systems are analyzed.
TL;DR: In this paper, a small-size broadband ultraviolet lamp with an emission spectrum of 206-390 nm, which was excited by a dc glow discharge, was described, and the discharge was ignited in a quartz discharge tube with an inner diameter of 1.4 cm and an anode-cathode spacing of 10 cm.
Abstract: A small-size broadband ultraviolet lamp with an emission spectrum of 206–390 nm, which is excited by a dc glow discharge, is described. The discharge was ignited in a quartz discharge tube with an inner diameter of 1.4 cm and an anode-cathode spacing of 10 cm. The tube was filled with a Kr/Xe/Br2/I2 working mixture, the total pressure being 0.5–2.0 kPa. The lamp’s emission spectrum consisted of a 206.2-nm iodine atomic line 0.1 nm wide at half-height and a continuum in a spectral region of 210–390 nm. The continuum resulted from overlapping of wide emission bands with peaks at 221 nm for XeBr(D-X), 253 nm for XeI(B-X), 282 nm for XeBr(B-X), 289 nm for Br
2
*
, 342 nm for I
2
*
, and 386 nm for IBr*. The total power of the ultraviolet emission was no more than 8–12 W, the power injected into the discharge being 10–100 W. The lamp lifetime in the gas-static mode was 300–400 h.
TL;DR: In this paper, the effect of acidity of the solution, the nature and the concentration of the dye, and the nature of the organic solvent on the formation and extraction of ion pairs of nitrophenols was examined; the optimum conditions were found.
Abstract: The extraction of nitrophenols with polymethine dyes of the common formula R1-(CH=CH)3-R2, indolium and benzothiazolium derivatives was studied. The effect of the acidity of the solution, the nature and the concentration of the dye, and the nature of the organic solvent on the formation and extraction of ion pairs of nitrophenols was examined; the optimum conditions were found. The most important chemical analytical characteristics of the ion pairs were determined. Molar absorptivities of extracts are 11.9 × 104–14.3 × 104 for ion pairs of trinitrophenol and 6.8 × 104–10.1 × 104 for ion pairs of dinitrophenol. A new procedure was developed for the extraction-photometric determination of nitrophenols in a mixture.
TL;DR: In this paper, low-energy (0.4-1.2-eV) electron backscattering was applied for the investigation of residual gas adsorption effect on the concentration and energy positions of surface electron states of Ge(1.1) surface.
TL;DR: In this paper, the main parameters of the erosion lead plasma (the atomic density, the densities of electrons and single-and double-charged ions, the pressure, the mean free path, and the degree of ionization) at distances 1 and 7 mm from the laser target are investigated using emission spectroscopy.
Abstract: The main parameters of the erosion lead plasma (the atomic density, the densities of electrons and single-and double-charged ions, the pressure, the mean free path, and the degree of ionization) at distances 1 and 7 mm from the laser target are investigated using emission spectroscopy. The plasma was produced by using a repetitive neodymium laser with a peak intensity of (3–5) × 108 W/cm2, wavelength of 1.06 µm, pulse duration of 20 ns, and repetition rate of 12 Hz.
TL;DR: In this article, the interaction of electrons with metastable Sr atoms, as a result of which the latter are simultaneously ionized and excited, is investigated experimentally, and the magnitudes of the interaction cross sections (reaching ≈5 × 10−20 m2 for the 52 S 1/2-32 P 3/2 transition in Sr II) and their energy dependences are determined.
Abstract: The interaction of electrons with metastable Sr atoms, as a result of which the latter are simultaneously ionized and excited, is investigated experimentally. The magnitudes of the interaction cross sections (reaching ≈5 × 10−20 m2 for the 52 S 1/2-32 P 3/2 transition in Sr II) and their energy dependences are determined. Possible mechanisms of this interaction are discussed.
TL;DR: A broadband ultraviolet-vacuum-ultraviolet lamp, which emits at wavelengths of 150-300 nm, and its output characteristics are described in this article, where the lamp is excited by a longitudinal glow discharge, initiated in a quartz tube with an inner diameter of 1.4 cm and an interelectrode distance of 10 cm.
Abstract: A broadband ultraviolet-vacuum-ultraviolet lamp, which emits at wavelengths of 150–300 nm, and its output characteristics are described. The lamp is excited by a longitudinal glow discharge, which is initiated in a quartz tube with an inner diameter of 1.4 cm and an interelectrode distance of 10 cm. The tube is filled with a He/Br2 working mixture at a total pressure of 0.2–1.0 kPa. The lamp emission spectrum consists of a 163.3-nm spectral line of bromine atoms and continuum in the spectral region 165–300 nm. A continuum is formed as a result of an overlap of broad emission bands of bromine molecules. The total emission power of the lamp reaches 4–5 W at an electric power of up to 60 W. The lamp’s efficiency is 5–10%, and its service life in the gas-static mode is 300–400 h.
TL;DR: In this paper, the emission characteristics of a transverse volume discharge in a He: HCl = 10: 1 mixture at a total pressure of 1-8 kPa were investigated.
Abstract: The emission characteristics of a transverse volume discharge in a He: HCl = 10: 1 mixture at a total pressure of 1–8 kPa were investigated. The plasma volume was 18 × 2.2 × 1 cm3, the interelectrode distance was d=2.2 cm, and the charging voltage of the main storage capacitor was 5–10 kV. The emission characteristics of the discharge were studied in the spectral range of 500–1000 nm. This type of discharge can be used in pulsed dry-etching plasmochemical reactors. The density of atomic chlorine radicals in the plasma was optimized in terms of the pressure of the initial working He-HCl mixture by measuring the relative radiation intensity of the Cl 837(5)-nm spectral line. The density of molecular radicals can be monitored indirectly by recording radiation from the excited chlorine-free decomposition products of HCl molecules (the Hα 656-nm line).
TL;DR: It has been found that pH of water essentially influences the quantitative indices of plankton Ciliatadevelopment in the water bodies of the Dnieper reservoirs.
Abstract: A total of 227 taxa of free-living Ciliata was found in floodplain water bodies of the Dnieper reservoirs in 1982–1985. It has been found that pH of water essentially influences the quantitative indices of plankton Ciliata development. The highest quantitative indices of Ciliata development were observed in summertime in the water bodies of the first group. To specify the classification of the studied water bodies, the discriminant analysis of the quantitative indices of development of microinvertebrates of 6 groups was used. Nematoda and Rotatoria dominated in terms of the quantitative indices of their development. Among protozoo- and microzoobenthos, Ciliata predominated in terms of their functional significance. Ciliata, and Copepoda predominated in terms of their functional significance in periphyton.
TL;DR: In this paper, the effect of light Mn doping on the dielectric properties of Li2BrO7 was analyzed in terms of the Debye model of relaxations, and the energy characteristics of the relaxation processes and the ion hopping lengths were determined in the materials under study.
Abstract: Dielectric relaxation in Mn-doped single-crystal and glassy Li2B4O7 was studied. The effect of light Mn doping on the dielectric properties of Li2BrO7 was revealed. The experimental results are analyzed in terms of the Debye model of dielectric relaxation. The energy characteristics of the relaxation processes and the ion hopping lengths are determined in the materials under study.
TL;DR: The electrical properties and emission characteristics of plasma formed in a transverse volume discharge in helium-propane (He-C6H14) mixtures at a total pressure of 3-15 kPa have been studied in this paper.
Abstract: The electrical properties and emission characteristics of plasma formed in a transverse volume discharge in helium-propane (He-C6H14) mixtures at a total pressure of 3–15 kPa have been studied. The spatial parameters, plasma emission spectra, and current and voltage oscillograms of the discharge, as well as the yield of carbon-containing products of propane decomposition at various pressures and compositions of the He-C6H14 gas mixture, have been determined.