Photoconductivity of Cu x Ag1−x Cd2InTe4

Summary The prominent photoelectric parameters of the semiconducting solid solutions Cu _x Ag_1−x Cd₂InTe₄ are reported. From the spectral dependence of photoconductivity at room temperature and at 77 K the energy gaps and their thermal coefficients are obtained. The detectivityD ^*, the photocurrent gainG and the carrier lifetime are measured and the carrier mobility is deduced. In order to improve theD ^* characteristics, the analysis of its parameters is also performed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Orientation ordering of N<Subscript>2</Subscript> molecules in vertically aligned CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanotubes

Arrays of vertically aligned nitrogen-doped carbon (CN _x ) nanotubes have been synthesized by decomposition of aerosol mixture of acetonitrile and ferrocene at 850°C. Nitrogen concentration in the outer shells of the CN _x nanotubes was found from X-ray photoelectron spectroscopy (XPS) data to reach ∼6%. The XPS N 1s spectra and N 1s near-edge X-ray absorption fine structure (NEXAFS) spectra identified three chemical forms of nitrogen in the CN _x nanotube arrays: pyridine-like, graphitic, and molecular nitrogen. The π ^* resonance of molecular nitrogen showed clear polarization dependence that indicates predominant orientation of N₂ molecules along the nanotubes axis. The estimated range of the polar angle distribution of the N₂ molecules orientation in the CN _x nanotube array amounts to 15°.     

Strontium diffusion in Sr3−3x La2x □x(VO4)2 solid solutions

Layer-by-layer radiometric analysis in the temperature range 800–950 °C was used to measure the diffusion coefficients of ⁹⁰Sr, ⁴⁵Ca, ¹³³Ba radionuclides in Sr_3−3x La_2x □_x(VO₄)₂ (x=0,0.1,0.15,0.2,0.25) solid solutions. It was established that D _Ca ^* >D _Sr ^* >D _Ba ^* . An increase in the concentrations of vacancies (□) in the strontium sublattice leads to increased coefficients of diffusion of rare-earth metal cations. The activation energies for radionuclide diffusion were determined. It was shown that M²⁺ cations migrate via Sr(2) positions. Fiz. Tverd. Tela (St. Petersburg) 40, 223–226 (February 1998)     

Theoretical investigation of some hexagonal ferrite ac data

An almost new method has been confirmed for experimentalists to have a first insight into the solid under study, by investigating the Cole–Cole diagrams of both the electric modulus M^* and the permittivity ε^* at different temperatures. All points of M^* function at different temperatures of the investigated hexagonal ferrite data have been collected in one semicircular master curve for each composition. This indicates that the studied compositions belong to a category of solids having what we have referred to as an “electric stiffness” as the dominating property, which is the reciprocal to an “electric compliance”—this would be the dominating property if the permittivity ε^* points could be collected in a master curve. In the present work, it has been found that the Cole–Cole diagrams of M^* have given some detailed information that are not obviously displayed in the conductivity representation.Moreover, a fitting of the investigated experimental data of the hexagonal ferrites—BaZn_2-xMg_xFe₁₆O₂₇, where (x=0.0,0.4,0.8,1.2,1.6 and 2)—with Dyre's macroscopic model of ac conductivity has been performed.An indirect method of fitting of the investigated data with the percolation path approximation (PPA) final equation of Dyre's macroscopic model has shown quite satisfactory results especially at relatively low frequencies . Whereas for the effective medium approximation (EMA) final equation of Dyre's macroscopic model the fitting has failed in hexagonal ferrites on contrary with a limited success found in a previous work with spinel ferrites. This is attributed to the more complex structure of hexagonal ferrites than that of spinel ferrites which makes the EMA no more suitable.     

Universal behavior of CePd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Rh<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> ferromagnet at the quantum critical point

The heavy-fermion metal CePd_1−x Rh _x can be tuned from ferromagnetism at x = 0 to the nonmagnetic state at some critical concentration x _c . The non-Fermi liquid behavior (NFL) at x ≃ x _c is recognized by the power-law dependence of the specific heat C(T) given by the electronic contribution susceptibility X(T) and volume expansion coefficient α(T) at low temperatures: C/T ∝ X(T) ∝ α(T)/T∝ 1/ √T. We also demonstrate that the behavior of the normalized effective mass M _N ^* observed in CePd_1−x Rh _x at x ≃ 0.8 agrees with that of M _N ^* observed in paramagnetic CeRu₂Si₂ and conclude that these alloys exhibit the universal NFL thermodynamic behavior at their quantum critical points. We show that the NFL behavior of CePd_1−x Rh _x can be accounted for within the frameworks of the quasiparticle picture and fermion condensation quantum phase transition, while this alloy exhibits a universal thermodynamic NFL behavior that is independent of the characteristic features of the given alloy such as its lattice structure, magnetic ground state, dimension, etc. The text was submitted by the authors in English.     

Semiempirical tight-binding modelling of III-N-based heterostructures

In this work, we present a second nearest neighbour sp³s^* semi-empirical tight-binding theory to calculate the electronic band structure of heterostructures based on group III-N binary semiconductors and their ternaries. The model Hamiltonian includes the second nearest neighbour (2nn) interactions, the spin–orbit splitting and the nonlinear variations of the atomic energy levels and the bond length with ternary mole fraction. Using this sp³s^* tight-binding approach, we investigated the electronic band structure of Al_1−xGa_xN/GaN and In_1−xGa_xN/GaN heterostructures as a function of composition and interface strain for the entire composition range (0≤x≤1). There is an excellent agreement between the model predictions and experiment for the principal bandgaps at Γ, L and X symmetry points of the Brillouin zone for AlN, GaN and InN binaries and Al_1−xGa_xN and In_1−xGa_xN ternaries. The model predicts that the composition effects on the valence band offsets is linear, but on the conduction band offsets is nonlinear and large when the interface strain and deformation potential is large.     

Electronic excitation and singlet-triplet coupling in uracil tautomers and uracil-water complexes

Electronic spectra of uracil in its diketo (lactam) form and five enol (lactim) tautomeric forms have been investigated by means of combined density functional and configuration interaction methods. We have simulated the effects of hydrogen bonding with a protic solvent by recomputing the spectrum of uracil in the presence of two, four, or six water molecules. Geometries of the electronic ground state and several low-lying excited states have been optimized. Spin-orbit coupling has been determined for correlated wavefunctions employing a non-empirical spin-orbit mean-field approach. In accord with experiment, we find the diketo tautomer to be the most stable one. The calculations confirm that the first absorption band arises from the ¹( π↦π^*) S ₀↦S ₂ excitation. The experimentally observed vibrational structure in this band originates from a breathing mode of the six ring. Complexation with water molecules is seen to cause a significant blue shift of n↦π^* excitations while leaving π↦π^* excitations nearly uninfluenced. Computed radiative lifetimes are presented for the experimentally known weak phosphorescence from the π↦π^* excited T₁ state. Among the uracil lactim tautomers, one is particularly interesting from a spectroscopic point of view. In this tautomer, the π↦π^* excitation gives rise to the S₁ state. Received 18 February 2002 / Received in final form 5 June 2002 Published online 13 September 2002     

A theoretical investigation of the interaction between fluorinated dimethyl ethers and molecular chlorine

Halogen bonds have received a great deal of attention in recent years. In this work, the interaction between fluorinated dimethyl ethers (n_F = 0–4) and molecular chlorine has been investigated by the theoretical methods. The two molecules are bonded together by an O···Cl?Cl halogen bond and the interaction energies calculated at the MP2/aug-cc-pVDZ level range between ?15.5 (n_F = 0) and ?6.1 (n_F = 4) kJ mol^?1. The correlations between interaction energies and proton affinity or ionisation potential of the ethers are discussed. The interaction between the molecules results in a small contraction of the CH bond of ethers and an elongation of the Cl?Cl bond. The data are analysed by a natural bond orbital analysis carried out at the wB97XD/6-311++G(d,p) level. The charge transfer from the ethers to Cl₂ is weak, ranges between 0.044 and 0.008 e and occurs mainly to the external Cl atom. The elongation of the Cl?Cl bond is related to the occupation of the σ^*(Cl?Cl) orbital and to the intermolecular hyperconjugation interaction between LP(O) and σ^*(Cl?Cl) orbitals. The interaction between the ethers and chlorine induces an enhancement of the infrared intensity and Raman scattering activity of the ν(Cl?Cl) vibration.     

Investigation of the mass dependence of self-diffusion coefficients by molecular dynamics calculations: binary and ternary isotopic mixtures of atoms

Extensive molecular dynamics calculations have been used to study for the first time systematically the dependence of the self-diffusion coefficients D_i (i = 1, 2, 3) in binary and ternary atomic isotopic mixtures on the particle mass ratios m*₂ = m ₂/m ₁ and m*₃ = m ₃/m ₁ at different reduced temperatures T* and reduced particle number densities n*, using a Lennard-Jones 12-6 potential and a hard-soft-spheres potential. In addition, the dependence of D_i values of binary mixtures on the mole fraction x ₁ = 1—x ₂ was also investigated for some thermodynamic states. The calculated values of D_i can be represented quantitatively by exponential estimates of the form D_i = D* _i (m*₂)^ex _i in the case of binary mixtures and D_i = D ⁰ _i (m*₂)^{ex _i} (m ₃)^{ext _i} in the case of ternary mixtures. D ⁰ _i are the self-diffusion coefficients in reference mixtures of mass ratios m*₂ = m*₃ = 1. The dependence of the exponents ex _i (m*₂, T*, n*, x ₁) of binary mixtures on m*₂, T*, n*, and x ₁ and the dependence of the exponents ext _i (m*₂, m*₃, n*) of equimolar ternary mixtures at T* = 1.8 on the exponents ex _i of the constituent binary mixtures and on m*₂, m*₃, and n* are discussed.     

Magnetische Monopole und Quarks

We discuss the concept of Schwinger, which starts with the hypothesis of the existence of magnetical monopoles and results in a baryon model with magnetically charged constituents. Especially we analyse the mathematical consistency of such a theory. which admits a connection between some magnetically charged “quarks” and the homogeneous Maxwell-equations ?_v*F^μv(x^u) = 0, which, displaying a lack of symmetry with respect to the inhomogeneous one, ?_vF^μv(x^u) = 4?j^μ, are replaced by ?*j^μv. Here *j^μ(x^μ) means a conserved magnetic current which provides a monopole source for the magnetic field.     

Can trimethylamine-N-oxide act to influence the self-aggregation of tert-butyl alcohol?

We report classical molecular dynamics simulation studies of aqueous solution consisting of water, tert-butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO). In spite of the fact that both TBA and TMAO molecules have very similar geometry with hydrophobic and hydrophilic groups, they behave very differently in aqueous solutions. Our aim is to see the role of TMAO on the self-aggregation (or association) of TBA molecules. We observe that, TMAO acts to postpone the aggregation of TBA molecules (takes place via the hydrophobic ends) to some extent. Addition of 0.10 mole fraction of TMAO shifts the aggregation concentration of TBA from x_tba = 0.025 to x_tba = 0.06. From the excess coordination number, calculation it is noticed that up to x_tba = 0.06, TBA molecules are favourably solvated by TMAO by replacing water molecules from TBA solvation shell but above this concentration, TBA–TMAO interaction decreases. This is further confirmed by water–TMAO interactions which shows a shift above x_tba = 0.06 indicating more preferred interactions between them. We also observe a noticeable increase in the water–water hydrogen bond life time in presence of TBA molecules indicating more structuring of water molecules.     

Vortex pinning in YBa2Cu3O7?x films

Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa₂Cu₃O_7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T _c and magnetic field 0<B<6 T. Below the vortex lattice melting transition B_g(T) but above a threshold field B_p≈8(1-T/T _c ) T, the inductance of vortices increases as B², much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical scaling persists over the region B_g(T<B<B^*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ^*≡ξ(B=B^*)≈450?. The value of ξ^* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at B_g.     

Interionic exchange interaction in A 1−x II MxBVI systems

The superexchange interaction integral J _NN is investigated in semimagnetic semiconductors of the type A _1−x ^II M_xB^VI systems, where the Mn, Fe, and Co ions are considered as the magnetic component M. Calculations are done in the framework of Racah’s many particle theory including the ground orbital states of the M ions in a cubic crystal. The results of these calculations are compared with published experimental data and with data from a study of the temperature dependence of Faraday rotation. The superexchange mechanism can be used to explain the correlation in the critical values x* at which the interionic interaction becomes important for the Cd_1−x Mn_xTe and Cd_1−x Fe_xTe systems. Fiz. Tverd. Tela (St. Petersburg) 39, 344–348 (February 1997)     

μ− SR studies of oxide-superconductorsSR studies of oxide-superconductors

The negative muon spin rotation method (μ⁻ SR) has been applied to studies of electronic states at oxygen sites of oxide superconductors YBa₂Cu₃O₇, Nd_2−x Ce _x CuO_4−δ (x=0.15, oxygen reduced), LiTi₂O₄ and related oxide-insulators La₂CuO_4−δ, CuO, Cu₂O. The paramagnetic shifts of μ⁻ trapped at oxygen nuclei in these polycrystalline powder samples have been measured at 300 K. All the measured shifts are positive. In copper-oxides the paramagnetic shifts are of the order 10⁻³, while in LiTi₂O₄ is very small (8.4±3.34×10⁻⁵). In YBa₂Cu₃O₇, a fast μ⁻ spin relaxation timeT ₂ ^* (∼ 200 ns) has been observed; the reason for this is unknown and further studies are now in progress.     

The structure of mixed fluorides Ca1?xSrxF2 and Sr1?xBaxF2 and the luminescence of Eu2+ in these crystals

The structure of the mixed fluorites Ca_1−x Sr_xF₂ and Sr_1−x Ba_xF₂, as well as the structure of the Eu²⁺ impurity center in these crystals, is calculated within the framework of the virtual-crystal method realized in the shell model and pair-potential approximation. The phenomenological dependence of the position of the lower level of the 4f ⁶5d configuration of the Eu²⁺ ion on distance to the Eu²⁺-ligand is derived. The dependences of the Stokes shift and the Huang-Rhys factor on x are calculated for the yellow luminescence in Sr_1−x Ba_xF₂:Eu²⁺. The value of x at which the lower level of the 4f ⁶5d configuration of the Eu²⁺ ion in Sr_1−x Ba_xF₂:Eu²⁺ falls within the conduction band is found. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 5, 2003, pp. 823–826. Original Russian Text Copyright ? 2003 by Nikiforov, Zakharov, Chernyshev, Ugryumov, Kotomanov.     

密度泛函理论方法研究6H-SiC(0001)表面对氧分子和水分子的吸附

本文通过密度泛函方法计算6H-SiC(0001)表面对氧分子和水分子的吸附. 在6H-SiC(0001)表面上吸附的O₂分子自发地解离成O^*,并被吸收在C与Si原子之间的空位上. 吸附的H₂O自发地分解成OH^*和H^*,它们都被吸附在Si原子的顶部,OH^*进一步可逆地转化为O^*和H^*. H^*可以使Si悬键饱和并改变O^*的吸附类型,并进一步稳定6H-SiC(0001)表面并防止其转变为SiO₂.     

Infrared spectra of catalysts and adsorbed molecules

The infrared absorption spectra of water adsorbed on Al₂O₃ and NiO-Al₂O₃ catalysts have been studied in the range 4000–1200 cm^–1. For all the catalysts, broad bands are observed at 3400 and 1640 cm^–1, characteristic of the stretching and bending vibrations of the OH groups in liquid water. The bands observed in the spectrum of alumina prepared from suspension in isopropyl alcohol are produced by water molecules and isopropyl alcohol molecules absorbed on the catalyst surface. The influence of treatment with heavy water and thermal treatment on the position of the infrared absorption bands in the spectrum of alumina is discussed.     

NOx generation in laser-produced plasma in air as a function of dissipated energy

An experimental study on the production of NO_x as a function of dissipated energy in laser-produced plasma in air is presented. A plasma was produced by focusing a (60–180) mJ, 5 ns, 532 nm pulse from a Q-switched Nd:YAG laser. The results show that for laser energy in the range of 13–99 mJ the laser plasma generates 6.7×10¹⁶ NO_x molecules per joule and 4.6×10¹⁶ NO molecules per joule. An order of magnitude estimate of the NO and NO_x production per unit volume of heated gas based on a simple model show that the NO_x and NO production efficiency in air are about 3×10²² and 2×10²² molecules J⁻¹ m⁻³.     

Diffractive photoproduction of D*±(2010) at HERA

Diffractive photoproduction of D^*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb^-1. The D^* mesons were reconstructed in the kinematic range: transverse momentum p_T(D^*) > 1.9 GeV and pseudorapidity |η(D^*)|<1.6, using the decay D^*+→D⁰π⁺ _s followed by D⁰→K^-π⁺(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q² < 1 GeV², in two ranges of the Pomeron fractional momentum x_IP<0.035 and x_IP<0.01. The relative contribution of diffractive events to the inclusive D^*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.     

Effect of Cu–Al double substitution on the electrical properties of Bi4V2O11

Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ, 0.02 ≤ x ≤ 0.08, were synthesized by standard solid-state reaction route. Structural and electrical properties of samples are characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) and alternating current (AC) impedance spectroscopy. The tetragonal γ′ phase structure is preserved to room temperature with compound x = 0.02. The stabilization of β orthorhombic phase is observed for compositions 0.04 ≤ x ≤ 0.05. As the Al content increases, the monoclinic α phase is evidenced for materials 0.06 ≤ x ≤ 0.08. The electrical investigation of Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ system has been performed in the frequency range from 20 Hz to 1 MHz using AC impedance spectroscopy. The impedance spectra indicate the two semicircle arcs associated with the bulk and grain boundary resistances at temperature below ～450 ^○C. The conductivity generally changes when Al is substituted. The highest conductivity at 300 ^○C (σ = 2.55 × 10^?4 S cm^?1) is shown for x = 0.02.