EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Spin exchange and chemi-ionization during collisions of polarized metastable helium atoms with ground-state cesium atoms

The kinetics of the optical orientation of atoms in a helium-cesium gas-discharge plasma are considered, and kinetic equations describing the optical orientation of atoms in the case of two simultaneously occurring processes, viz., an elastic process (spin exchange) and an inelastic process (chemi-ionization), are derived. The rate constants of these processes are determined experimentally: C _se=(2.8±0.8)×10⁻⁹ cm³s⁻¹, C _ci=(1.0±0.3)×10⁻⁹ cm³s⁻¹. Zh. Tekh. Fiz. 69, 36–40 (September 1999)     

Addition and spin exchange rate constants by longitudinal field μSR: The Mu+NO reaction

The addition reaction Mu+NO+M→MuNO+M and the spin exchange reaction Mu(↑) +MO(↓)→Mu(↓)+NO(↑) have been measured by longitudinal field μSR at room temperature in the presence of up to 58 atm of N₂ as inert collider. The pressure dependence of the longitudinal relaxation rate due to the addition reaction (λ_c) demostrates that the system is still in the low pressure regime in this pressure range. The corresponding termolecular rate constant has been determined ask _0,Mu =(1.10±0.25)×10⁻³² cm⁶ molecules⁻² s⁻¹, almost 4 times smaller than the corresponding H atom reactionk _0,H=3.90×10⁻³² cm⁶ molecules⁻² s⁻¹ [I.M. Campbell et al., J. Chem. Soc. Faraday Trans. 1.71 (1975) 2097]. The average value of the spin exchange rate constants in the 2.5–58 atm pressure range,k _SE=(3.16±0.06)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, is in good agreement with previous values obtained by transverse field μSR [D.G. Fleming et al., J. Chem. Phys. 73 (1980) 2751].     

Thin TiO2 grown by metal–organic chemical vapor deposition on (NH4)2S x -treated InP

The electrical characteristics of thin TiO₂ films prepared by metal–organic chemical vapor deposition grown on a p-type InP substrate were studied. For a TiO₂ film of 4.7 nm on InP without and with ammonium sulfide treatment, the leakage currents are 8.8×10⁻² and 1.1×10⁻⁴ A/cm² at +2 V bias and 1.6×10⁻¹ and 8.3×10⁻⁴ A/cm² at −2 V bias. The lower leakage currents of TiO₂ with ammonium sulfide treatment arise from the improvement of interface quality. The dielectric constant and effective oxide charge number density are 33 and 2.5×10¹³ cm², respectively. The lowest mid-gap interface state density is around 7.6×10¹¹ cm⁻² eV⁻¹. The equivalent oxide thickness is 0.52 nm. The breakdown electric field increases with decreasing thickness in the range of 2.5 to 7.6 nm and reaches 9.3 MV/cm at 2.5 nm.     

EPR and Optical Absorption Studies of Cu2+-Doped Bis(l-Asparaginato)Mg(II)

The electron paramagnetic resonance study of Cu²⁺-doped bis(l-asparaginato)Mg(II) is performed at room temperature. Two magnetically non-equivalent sites for Cu²⁺ are observed. The spin-Hamiltonian parameters evaluated by fitting spectra to the crystalline field of rhombic symmetry are as follows: g _x  = 2.0420 ± 0.0002, g _y  = 2.0808 ± 0.0002, g _z  = 2.3600 ± 0.0002, A _x  = (99 ± 2) × 10⁻⁴ cm⁻¹, A _y  = (108 ± 2) × 10⁻⁴ cm⁻¹, A _z  = (140 ± 2) × 10⁻⁴ cm⁻¹. The ground state wave function of Cu²⁺ is also determined. The g-anisotropy is estimated and compared with the experimental value. Further, with the help of optical study the nature of bonding of a metal ion with different ligands in the complex is discussed.     

Search for direct CP violating charge asymmetries in K±→π±π+π- and K±→π±π0π0 decays

A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes A_g=(g⁺-g^-)/(g⁺+g^-) in K^±→π^±π⁺π^- and K^±→π^±π⁰π⁰ decays by the NA48/2 experiment at CERN SPS is presented. A new technique of asymmetry measurement involving simultaneous K⁺ and K^- beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be A^c _g=(-1.5±2.2)×10^-4 with 3.11×10⁹K^±→π^±π⁺π^- decays, and Aⁿ _g=(1.8±1.8)×10^-4 with 9.13×10⁷K^±→π^±π⁰π⁰ decays. The precision of the results is limited mainly by the size of the data sample.     

Improved electrical properties of HfTiO/GeO x N y gate dielectric Ge MOS capacitors by using wet–NO Ge-surface pretreatment

Reactive cosputtering is employed to prepare high-permittivity HfTiO gate dielectric on n-Ge substrate. Effects of Ge-surface pretreatment on the interface and gate leakage properties of the dielectric are investigated. Excellent performances of Al/HfTiO/GeO _x N _y /n-Ge MOS capacitor with wet–NO surface pretreatment have been achieved with a interface-state density of 2.1×10¹¹ eV⁻¹ cm⁻², equivalent oxide charge of −7.67×10¹¹ cm⁻² and gate leakage current density of 4.97×10⁻⁵ A/cm² at V _g =1 V.     

Non-steady-state photo-EMF in nanostructured GaN and polypyrrole within porous matrices

We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=442 nm, I ₀=0.045–0.19 W/cm², T=293 K) and σ=(3.5–4.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=532 nm, I ₀=2.3 W/cm², T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L _D=0.18 μm.     

Diffusion study of nitrogen implanted into <Emphasis Type="Italic">α</Emphasis>-Hf using the nuclear resonance technique

The diffusion of nitrogen in α-Hf was studied in the temperature range of (823–1123) K using the ion implantation and nuclear resonance techniques. The measurements show that the diffusion coefficients follow the Arrhenius behavior D(T)=D ₀exp (−Q/RT) with D ₀=(5.5±2.1)×10⁻⁷ m²/s and Q=(228±1) kJ/mol. A comparison of the present results with the previous one is done.     

Diffusion of deuterium in tantalum from internal friction measurements (Gorsky effect)

The long-range diffusion of deuterium in tantalum has been investigated as a function of temperature by means of the anelastic process due to redistribution of deuterium impurities between compressed and dilated regions of the sample, under an applied stress alternating at about 4 Hz. The diffusion coefficient was found to obey an Arrhenius-type law in the temperature range 200–390 K; a deviation was observed at lower temperatures. The diffusion parameters in the exponential region areD _0D=(3.3±1.5)×10⁻⁴ cm²/s, andW _D=(0.176±0.008) eV.     

Searches for gamma-quanta from local sources by a wide-angle imaging telescope

Summary A new Cherenkov imaging telescope SHALON equipped with a very high-definition camera (144 pixels, imaging 7.2⁰×7.2⁰) takes data since 1993 at a mountain altitude of 3338 m. We discuss some results of the observations of the indicated gamma-ray sources and the discrimination methods between gamma-rays and protons. Selection of showers produced by gamma-quanta from a background of showers produced by protons has been made according to the following criteria: 1) alpha<20⁰; 2) length/width>1.6 for γ; 3) Cherenkov light intensity in pixels with max light to the light in the light pixels near around is >0.2 for γ and <0.6 for p; 4) Cherenkov light intensity in pixels with max light to all light in imaging excluding in centre is >0.8 for γ and <0.8 for p; 5) distance for γ is <3.5 pixels.I _Crab=(0.95±0.18)·10⁻¹² cm⁻²c⁻¹.I _Mark421=(0.98±0.36)·10⁻¹² cm⁻²c⁻¹. Paper presented at the Special Session on ground-based gamma-ray astronomy of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Integral energy spectrum of primary cosmic rays at high energies

The integral energy spectrum of primary cosmic rays has been obtained. In the energy range (2.4×10³−1.1×10⁵ GeV), the spectrum of all nuclei is consistent with a power law of indexγ=1.55±0.06 and the flux of all nuclei is:N(⩾E ₀)⋍(5.1±1.8)×10⁻¹×E ₀ ^−1.55 particles/cm² sterad. sec., whereE ₀ is in GeV. The spectrum of primaryα-particles in the energy range (4.4×10³−4.8×10⁴) GeV is also consistent with a power law of indexγ=1.71±0.12 and the flux is:N(⩾E ₀)=(4.2±1.4)×10⁻¹×E ₀ ^−1.71 , particles per cm² sterad. sec, whereE ₀ is in GeV.     

Effect of plasticizer on safranine-T-dye-based solid-state photo electrochemical cell

Effect of plasticizers on electrical and photovoltaic properties of safranine-T-dye-based solid-state photo electrochemical cell (PEC) is studied. Ethylene carbonate (EC) and propylene carbonate (PC) are used as plasticizers. Dark current–voltage characteristic and different photovoltaic parameters such as open-circuit voltage, short-circuit current, and power conversion efficiency are measured. To understand the effect of plasticizers on charge transport process, we analyze the dark current–voltage characteristics to estimate the trap energy. From detail analysis of dark I–V, it has been observed that there is a crossover voltage called transition voltage where the conduction mechanism changes. Above this voltage, the dark current is a space charge limited current (SCLC) in the presence of exponentially distributed traps. Below transition voltage, current is ohmic for the cell without plasticizers and dark current is an SCLC in presence of discrete traps for the cell with plasticizers. From our analysis, it is shown that the transition voltage reduces due to the presence of plasticizers but the characteristic trap energy (E_T) is not changed significantly. From photovoltaic measurements, it is observed that in presence of EC and PC power conversion efficiency of the device increase from 7.319 × 10⁻⁴% to 14.64 × 10⁻⁴% under illumination with polychromatic light of 100 mW/cm². It is expected that the power conversion efficiency depend on transition voltage. Due to the presence of plasticizers, the barrier potentials of the devices reduce which results lowering of transition voltage. Lowering of it assists the migration of charge carriers and as a result power conversion efficiency enhances.     

EPR of trivalent iron ions in a LiCaAlF6 crystal

The orientational dependences of the EPR spectra of Fe³⁺-doped LiCaAlF₆ single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail. The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B ₂₀=40.072×10⁻⁴ cm⁻¹, B ₄₀=−5.799×10⁻⁴ cm⁻¹, B ₄₃=−4.281×10⁻⁴ cm⁻¹, A _s=24.33±1, A _p=6.13±1, g _∥=g _⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F⁻). Fiz. Tverd. Tela (St. Petersburg) 39, 488–490 (March 1997)     

Calibration of the 67 keV mössbauer resonance of73Ge

Using the first-principles scalar-relativistic LMTO method, we have calculated the electronic structure of crystalline Ge and rutile-structured GeO₂. By comparing the calculated electron contact densities with experimental isomer shifts of the 67 keV transition of⁷³Ge in these materials, we obtain a value for the relative change in the nuclear radius of ΔR/R=(7.4±0.7)×10⁻⁴. The results of the present work are compared with previous attempts to calibrate this isomeric transition.     

State selective step-wise photoionization of NO with mass spectroscopic ion detection

State and isotope selective two-step photoionization of NO with mass spectroscopic ion detection has been demonstrated and investigated. Using saturation condition the photoionization cross section for a single rotational level of the intermediate state, No(A ²Σ⁺, ν′=0), has been measured: σ_i=(7.0±0.9) X 10⁻¹⁹ cm². The charge transfer¹⁵NO⁺+¹⁴NO→¹⁵NO+¹⁴NO⁺ has been observed and investigated, yielding a cross section of the order of 13×10⁻¹⁶ cm², consistent with recent measurements at about 1 eV.     

Investigation of temperature-dependent electrical properties of p-VOPc/n-si heterojunction under dark conditions

An organic/inorganic heterojunction p-VOPc/n-Si was fabricated and its electrical properties were investigated. Temperature-dependent dark current–voltage (I–V) characteristics of the heterojunction exhibited rectification behaviour with a rectification ratio of 405 at ±1 V and room temperature. The current–voltage characteristics of the cell showed ohmic conduction at low voltages followed by a space charge-limited current (SCLC) conduction dominated by an exponential trap distribution at higher voltages. At room temperature, the series and shunt resistances were found to be approximately 1.4 and 100 kΩ, respectively. Diode ideality factor n was found to be 3.2 at room temperature and dropped to 1.9 at 363 K. Room temperature mobility of vanadyl phthalocyanine (VOPc) was extracted from the I–V characteristics in the SCLC region and was found approximately 15.5 × 10⁻³ cm² V⁻¹ s⁻¹. The effective barrier height, Ф_B, was estimated as 0.77 eV. The effect of temperature, on various heterojunction parameters was recorded under dark conditions and at temperatures ranging from 300 to 363 K.     

K*0 and φ meson production in proton–nucleus interactions at ?s=41.6\textGeV\sqrt{s}=41.6\text{GeV}

The inclusive production cross sections of the strange vector mesons K^*0, K̄^*0, and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to p_T = 3.5 GeV/c. The atomic number dependence is parametrised as σ_pA=σ_pN*A^α, where σ_pN is the proton–nucleon cross section. Within the phase space accessible, α(K^*0)=0.86±0.03, α(K̄^*0)=0.87±0.03, and α(φ)=0.96±0.02. The total proton–nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are σ_pN→K*0=(5.06±0.54) mb, σ_pN→K̄*0=(4.02±0.45) mb, and σ_pN→φ=(1.17±0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K^± mesons, the measured values of α for φ mesons coincide with those of K⁺ mesons for all transverse momenta, while the enhancement for K^*0/K̄^*0 mesons is smaller.     

z-Scan characterization of zwitterionic chromophores for optoelectronic switching

Single beam z-scan measurements have been made on films containing amorphous polycarbonate and the zwitterionic chromophore, PYR-3, that has a very high second order nonlinear optical (NLO) figure of merit. The third order NLO figure of merit is ≈1.6 at 1030 nm and is comparable to that found in organic compounds optimized for high n ₂ values. The two-photon absorption coefficient is 2.1×10⁻¹² m/W, which is very low and advantageous for NLO device applications. The third order NLO refractive index is −1.4×10⁻¹⁸ m²/W.     

Anisotropy of nonlinear absorption in Co<Superscript>2+</Superscript>:MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> crystal

Anisotropy of the nonlinear absorption of Co²⁺ ions in MgAl₂O₄ single crystal at the wavelengths of 1.35 and 1.54 μm has been experimentally demonstrated. The experimental data are analyzed in the framework of a phenomenological model when the Co²⁺ ions are described as three sets of linear dipoles oriented along the crystallographic axes. Ground-state and excited state absorption cross-sections at 1.35 and 1.54 μm are evaluated to be σ_gsa=(4.0±0.3)×10^-19, σ_esa=(3.6±0.4)×10^-20 cm² and σ_gsa=(5.1±0.3)×10^-19, σ_esa=(4.6±0.4)×10^-20 cm², respectively. PACS 42.55.Rz; 71.20.Be