Effect of ionizing radiation on the dielectric characteristics of TlInSe<Subscript>2</Subscript> and TlGaTe<Subscript>2</Subscript> single crystals

The temperature dependences of the electrical conductivity and the permittivity of TlInSe₂ and TlGaTe₂ crystals unirradiated and irradiated with 4-MeV electrons at a doze of 10¹⁶ cm⁻² have been investigated. It has been established that electron irradiation leads to a decrease in the electrical conductivity σ and the permittivity ɛ over the entire temperature range under study (90–320 K). It has been revealed that the TlInSe₂ and TlGaTe₂ single crystals undergo a sequence of phase transitions characteristic of crystals of this type, which manifest themselves as anomalies in the temperature dependences σ = f(T) and ɛ = f(T). Electron irradiation at a doze of 10¹⁶ cm⁻² does not affect the phase transition temperatures of the crystals under investigation.     

The Structure of Electronic States and Optical Properties of Cr<Subscript>80</Subscript>Al<Subscript>20</Subscript> Compound

Ellipsometric studies of the optical properties of the intermetallic Cr₈₀Al₂₀ compound in the spectral range of 0.22–15 μm have been performed. The self-consistent calculation of the electronic structure and density of the electronic states of the material has been carried out. The spectrum of interband light absorption is interpreted on the basis of comparative analysis of theoretical and experimental dispersion dependences of optical conductivity. A number of characteristics of conduction electrons have been determined.     

Ion conduction and space-charge polarization processes in Li<Subscript>2</Subscript>Ge<Subscript>7</Subscript>O<Subscript>15</Subscript> crystals

The electrical properties of a lithium heptagermanate (Li₂Ge₇O₁₅) crystal have been studied in DC and AC measuring fields at temperatures from 500 to 700 K. In a DC field, a substantial decrease of electrical conductivity σ with time has been detected. On the basis of kinetic dependences σ(t), estimates of the charge carrier diffusion coefficient D have been obtained. In the frequency range 10¹–10⁵ Hz, the spectra of complex impedance ρ*(f) have been measured. The analysis of diagrams in the complex plane (ρ″–ρ′) has been performed within the equivalent circuit approach. It has been shown that, in the considered temperature and frequency intervals, the electrical properties of Li₂Ge₇O₁₅ crystals have been determined by the hopping conduction of interstitial lithium ions A _Li and accumulation of charge carriers near the blocking Pt electrodes.     

A statistical analysis of the wavenumbers of triplet rovibronic transitions of the D<Subscript>2</Subscript> molecule: III. Optimum values of level energies

The optimum energy values of the vibrational-rotational levels of all the experimentally studied 35 triplet electronic states of the D2 molecule were found using a one-step optimization procedure only based on the Rydberg-Ritz combination and maximum likelihood principles. The set of energy values for 1050 levels was obtained from 3713 experimental data (3588 old and 125 new data) on the wavenumbers of rovibronic transitions. The energies were counted from the lowest vibrational-rotational level (ν = 0, N = 0) of the (1sσ2sσ)a ³Σ _g ⁺ electronic state. Errors in the empirical determination of optimum level energy values caused only by the limited consistency of the experimental data obtained by different authors, different methods, and in different spectrum regions were found. They are of 0.005–0.1 cm⁻¹ and increase as the vibrational and rotational quantum numbers grow. The possibility of discovery of new not identified earlier band systems was demonstrated. This can be done using the optimum level energies for calculations of the wave-numbers of spectral lines allowed by selection rules followed by the search for these lines in the experimental spectra of D₂.     

Optical properties and electronic structure of YNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The optical properties of hexagonal intermetallic compounds YNi_{5 − x} Cu _x (x = 0, 1, 2) have been investigated by ellipsometry in the spectral range of 0.22–15 μm. It is shown that the replacement of nickel atoms by copper atoms leads to local changes in the optical-conductivity spectra. A new absorption band is found at 3.5–4.5 eV; its intensity depends on the copper content. The plasma and relaxation frequencies of conduction electrons are determined. The electronic structure and interband optical conductivity of these compounds are calculated within the electron density functional theory using the pseudopotential method. The main parameters of the band structure and the total and partial densities of electronic states are determined. Qualitative agreement is obtained between the experimental and theoretical frequency dependences of the optical conductivity.     

Optical properties of pyridine funtionalized TbF<Subscript>3</Subscript> nanoparticles

The preparation of pyridine functionalized TbF₃ nanoparticles are described in this report. Synthesized nanoparticles were characterized using the TEM, UV/Vis, FTIR and photoluminescence spectroscopy. TEM micrograph reveals the nanorod shaped, uniform in size with a particles size in the range of 20–30 nm. FTIR spectrum shown characteristic absorption bands of pyridine and a small intensity band at 411 cm⁻¹ corresponding metal nitrogen ν(Tb–N) bonding. Uv-vis spectrum shown the characteristic absorption transitions of Tb³⁺ ion. A strong emission transition at 540 nm (⁵D₄ → ⁷F₅) was observed on excite by visible light at 414 nm.     

Study of the far-infrared and mm-wave conductivity of YBCO in the normal state

Il Nuovo Cimento D - An accurate determination of the optical conductivity σ(ν) of high-T c materials at low frequencies (ν&lt;100 cm−1) is still an open problem. In the...     

Electrical properties,equivalent circuit,and dielectric relaxation studies on [(C<Subscript>3</Subscript>H<Subscript>7</Subscript>)<Subscript>4</Subscript>N]<Subscript>2</Subscript>Cd<Subscript>2</Subscript>Cl<Subscript>6</Subscript> polycrystalline

The Ac electrical conductivity and the dielectric relaxation properties of the [(C₃H₇)₄N]₂Cd₂Cl₆ polycrystalline sample have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 Hz–5 MHz and 361–418 K, respectively. The purpose is to make a difference between the electrical and dielectric properties of the polycrystalline sample and single crystal. Besides, a detailed analysis of the impedance spectrum suggests that the electrical properties of the material are strongly temperature-dependent. Plots of (Z" versus Z') are well fitted to an equivalent circuit model consisting of a series combination of grains and grains boundary elements. Moreover, the temperature dependence of the electrical conductivity in the different phases follows the Arrhenius law and the frequency dependence of σ (ω) follows the Jonscher’s universal dynamic law. Furthermore, the modulus plots can be characterized by full width at half height or in terms of a nonexperiential decay function φ(t) = exp(t/t)^β. Finally, the imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism.     

Anti-stokes luminescence of Zn<Subscript>0.6</Subscript>Cd<Subscript>0.4</Subscript>S solid solutions with adsorbed organic dye molecules and few-atom silver clusters

For microcrystals of Zn_0.6Cd_0.4S with adsorbed molecules of a number of organic dyes, we have observed sensitized anti-Stokes luminescence excited by radiation with wavelengths in the range 610–750 nm and flux density 10¹⁴–10¹⁵ photons/cm²·sec. The positions of the bands in the excitation spectra for such luminescence match those of the absorption spectra for the adsorbed dye molecules, which is evidence in favor of a cooperative mechanism for its appearance. We have shown that enhancement of the anti-Stokes luminescence is possible when silver atoms and few-atom clusters appear on the Zn_0.6Cd_0.4S surface in addition to the dye molecules. We hypothesize that its excitation in the latter case occurs as a result of two-photon optical transitions. These transitions occur sequentially, with transfer of an electron or the electronic excitation energy from the dye molecules to silver atoms and few-atom clusters adsorbed on the surface of Zn_0.6Cd_0.4S, creating deep localized states in the bandgap with photoionization energies 1.80–2.00 eV. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 617–621, September–October, 2007.     

Effect of plasmon-phonon excitations on the coefficient of reflection from the surface of hexagonal silicon carbide

The coefficient R(ν) of reflection from the surface of 6H-SiC single crystals is studied in the case in which the long-wavelength optical vibrations of the lattice are coupled with the electron plasma. It is shown for the first time that the anisotropy of the properties of electrons and phonons in 6H-SiC gives rise to special features in the spectrum of the coupled vibrations and the transparency regions. It is found, in particular, that if the axis of the crystal lies in the polarization plane of the incident radiation (0<θ<90°), for 30 cm⁻¹⩽ν _p⊥<320 cm⁻¹ the spectrum of R(ν) acquires three regions of transparency and opacity, and for ν _p⊥⩾320 cm⁻¹ four such regions, which are absent in an isotropic medium. The width of these regions is found to depend on the electron concentration in the conduction band and on the angle θ. Zh. éksp. Teor. Fiz. 116, 646–654 (August 1999)     

Photoemission study of clean and c(4×2)-2CO-covered Pt (111) using high-harmonic radiation

An extreme ultraviolet (EUV) laser light source based on high-harmonic generation is presented. Coherent radiation in the photon energy range hν=20–120 eV is produced in the conversion media argon, neon and helium. High-harmonic radiation in the energy range 20–50 eV is applied to investigate photoemission spectra of Pt (111) and CO/Pt (111). In the photoemission spectra of the clean surface, new secondary electron emission structures are found which influence the cross section analysis of the CO states. When taking these Pt resonances into consideration, the 4σ and 5σ CO shape resonances are found at photon energies of 37 eV and 28 eV, respectively. Additionally, a resonance at hν=31 eV is also observed for the CO 1π state, in contrast to formerly published experimental data. Experimental and theoretical data suggest that this resonance is not connected to the well-known shape resonances in the σ-channel. Based on theoretical approaches, it is identified as an autoionization resonance. Received: 8 April 2002 / Accepted: 22 May 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-251/833-3604, E-mail: kutzner@uni-muenster.de     

Electronic structure of TiO<Subscript>2</Subscript> rutile with oxygen vacancies: Ab initio simulations and comparison with the experiment

The electronic structure of TiO₂ rutile with oxygen vacancies, which is a promising insulator, has been analyzed. The ab initio density functional calculations, as well as the comparative analysis of the results obtained in the σ-GGA spin-polarized generalized approximation and those obtained by the σ-GGA + U method with allowance for Coulomb correlations of d electrons titanium atoms in the Hartree-Fock approximation for the Hubbard model, have been performed. It has been found that the effective electron mass in rutile is anisotropic and there are both light (m _e ^* = (0.6–0.8)m ₀, where m ₀ is the free-electron mass) and heavy (m _e ^* > 1m ₀) electrons, whereas holes in rutile are only heavy (m _e ^* ⩾ 2m ₀). It has been shown that the σ-GGA + U method gives a deep occupied level in the band gap and that an oxygen vacancy in rutile is an electron and hole trap.     

Quantum oscillations of the resistivity and hall coefficient and the quantum limit in Bi<Subscript>0.93</Subscript>Sb<Subscript>0.07</Subscript> alloys in a magnetic field along the trigonal axis

The dependences of the electrical resistivity ρ and the Hall coefficient R on the magnetic field have been measured for single-crystal samples of the n-Bi_0.93Sb_0.07 semiconductor alloys with electron concentrations in the range 1 × 10¹⁶ cm⁻³ < n < 2 × 10¹⁸ cm⁻³. It has been found that the measured dependences exhibit Shubnikov-de Haas quantum oscillations. The magnetic fields corresponding to the maxima of the quantum oscillations of the electrical resistivity are in good agreement with the calculated values of the magnetic fields in which the Landau quantum level with the number N intersects the Fermi level. The quantum oscillations of the Hall coefficient with small numbers are characterized by a significant spin splitting. In a magnetic field directed along the trigonal axis, the quantum oscillations of the resistivity ρ and the Hall coefficient R are associated with electrons of the three-valley semiconductor and are in phase with the magnetic field. In the case of a magnetic field directed parallel to the binary axis, the quantum oscillations associated both with electrons of the secondary ellipsoids in weaker magnetic fields and with electrons of the main ellipsoid in strong magnetic fields (after the overflow of electrons from the secondary ellipsoids to the main ellipsoid) are also in phase. In magnetic fields of the quantum limit ħω _c /2 ≥ E _F, the electrical conductivity increases with an increase in the magnetic field: σ₂₂(H) ∼ H ^k . A theoretical evaluation of the exponent in this expression for a nonparabolic semiconductor leads to values of k close to the experimental values in the range 4 ≤ k ≤ 4.6, which were obtained for samples of the semiconductor alloys with different electron concentrations. A further increase in the magnetic field results in a decrease of the exponent k and in the transition to the inequality σ₂₂(H) ≤ σ₂₁(H).     

Photoelectric characteristics of nanostructured hydrochemically deposited films of the Pb<Subscript>0.975</Subscript>Sn<Subscript>0.025</Subscript>Se substitutional solid solution

The photoelectric characteristics of Pb_0.975Sn_0.025Se solid solution films prepared by the hydrochemical codeposition of PbSe and SnSe with the subsequent heat treatment in air at 573–700 K have been investigated. The thermal and optical band gaps, the temperature coefficient of the optical band gap, the dark resistance, the volt-watt sensitivity, and the range of spectral sensitivity have been determined in the temperature range of 220–300 K. It has been found that, after heat treatment below 573 K, the films of the Pb_0.975Sn_0.025Se solid solutions possess metallic conductivity, while being heat treated at elevated temperatures, they become semiconductors with p-type conductivity. The composition of the solid solution is independent of the heat treatment temperature; it is formed during deposition.     

Investigation of Rb <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript> atomic lines in strong magnetic fields by fluorescence from a half-wave-thick cell

It has been experimentally demonstrated that the use of the effect of significant narrowing of the fluorescence spectrum from a nanocell that contains a column of atomic Rb vapor with a thickness of L = 0.5λ (where λ = 794 nm is the wavelength of laser radiation, whose frequency is resonant with the atomic transition of the D ₁ line of Rb) and the application of narrowband diode lasers allow the spectral separation and investigation of changes in probabilities of optical atomic transitions between levels of the hyperfine structure of the D ₁ line of ⁸⁷Rb and ⁸⁵Rb atoms in external magnetic fields of 10–2500 Gs (for example, for one of transitions, the probability increases ∼17 times). Small column thicknesses (∼390 nm) allow the application of permanent magnets, which facilitates significantly the creation of strong magnetic fields. Experimental results are in a good agreement with the theoretical values. The advantages of this method over other existing methods are noted. The results obtained show that a magnetometer with a local spatial resolution of ∼390 nm can be created based on a nanocell with the column thickness L = 0.5λ. This result is important for mapping strongly inhomogeneous magnetic fields.     

Structural and electrical properties of pure and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> doped (PVA)<Subscript>0.7</Subscript>(NaI)<Subscript>0.3</Subscript> solid polymer electrolyte

Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)_0.7 and sodium iodide (NaI)_0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric acid disrupt the semi-crystalline nature of (PVA)_0.7(NaI)_0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)_0.7(NaI)_0.3 matrix at room temperature was 10⁻⁵ S cm⁻¹ and this increased to 10⁻³ S cm⁻¹ with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out. The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration Na/SPE/MnO₂. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ.     

Dependence of the optical properties of Fe<Subscript>78</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy on its structural state

The optical properties of Fe₇₈Si₁₀B₁₂ ferromagnetic alloy in amorphous, crystalline, and intermediate structural states have been investigated by ellipsometry in the spectral range of 0.22–18 μm. It is established that alloy crystallization leads to a significant change in the optical constants and the frequency dependences of the dielectric functions calculated based on these optical constants. The structural reconstruction under heat treatment leads to an increase in the intensity and shift of interband absorption bands. The plasma and relaxation frequencies of conduction electrons are determined; their numerical values also depend on the degree of atomic ordering.     

Spectroscopic properties and electronic structure of uranyl complex compounds (Review)

Fundamental problems of the photophysics of uranyl complex compounds are considered. Works on the spectroscopy of uranyl compunds in a wide spectral range from the visible to the vacuum UV region of the spectrum are reviewed. The characteristics of their electronic structure are discussed. It is shown that the optical properties of uranyl compounds are determined by electronic transitions from three occupied molecular orbitals. The highest occupied orbital of the uranyl complex is predominantly ligand in character; the lower-lying occupied orbitals have a significant contribution from uranyl orbitals. Intiation of electronic transitions from shielded valent orbitals increases the probability of nonradiative deactivation of electronic excitation of the uranyl complex. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 818–831, November–December, 1998     

S<Subscript>3</Subscript> symmetry and neutrino masses and mixings

Based on the universal seesaw mass matrix model with the three scalars φ_i, and by assuming S₃ flavor symmetry for the Yukawa interactions, the lepton masses and mixings are investigated systematically. In order to understand the observed neutrino mixing, the charged leptons (e,μ,τ) are regarded as the three objects (e₁,e₂,e₃) of S₃, while the neutrino mass eigenstates are regarded as the irreducible representation (ν_η,ν_σ,ν_π) of S₃, where (ν_π,ν_η) and ν_σ are a doublet and a singlet, respectively, which are composed of the three objects (ν₁,ν₂,ν₃) of S₃.     

A study in depth of f<Subscript>0</Subscript>(1370)

Claims have been made that f₀(1370) does not exist. The five primary sets of data requiring its existence are refitted with suitable Breit–Wigner amplitudes. Major dispersive effects due to the opening of the 4π threshold are included for the first time; the σ→4π amplitude plays a strong role. Crystal Barrel data on p̄p→3π⁰ at rest require f₀(1370) signals of at least 32 and 33 standard deviations (σ) in ¹S₀ and ³P₁ annihilation respectively. Furthermore, they agree within 5 MeV for mass and width. Data on p̄p→ηηπ⁰ agree and require at least a 19σ contribution. This alone is sufficient to demonstrate the existence of f₀(1370). BES II data for J/Ψ→φπ⁺π^- contain a visible f₀(1370) signal >8σ. In all cases, a resonant phase variation is required. Cern–Munich data for ππ elastic scattering are fitted well with the inclusion of some mixing between σ, f₀(1370) and f₀(1500). Values of Γ_2π for f₂(1565), ρ₃(1690), ρ₃(1990) and f₄(2040) are determined. PACS 13.25.Gv; 14.40.Gx; 13.40.Hq