bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoluminescence, Fluorescence, and Optical Absorption Studies on Europium‐Doped Rubidium chloride
Authors: Sastry S. B. S. , Sapru S. 
Published: July 2007

AbstractThermoluminescence, fluorescence, and optical absorption studies on Rbcl:Eu2+ indicate that Eu2+ ions convert to Eu3+ on irradiation and gain the electron back on thermal or optical treatment. FZ1 centres are formed on bleaching and a glow peak attributable to these centres is identified. Fluorescence measurements give an emission around 3.0 eV and this emission is affected by irradiation and quenching of the sample. The integrated light intensity of these samples is quite high compared to undoped samples which indicates that this material may be a useful TLD phosphor. Spectral distribution of emission under various glow peaks shows emission bands around 1.5, 1.7, 1.9, 2.1, 2.8, and 3.0 eV. The high‐temperature glow peak shows an additional (weak) emission around 4.8 eV. A tentative energy band diagram is suggested showing the various emission processes.
Mobility and Recombination Coefficient of Charge Carriers in Disordered Pentacene
Authors: Maruyama Y. , Bässler H. 
Published: July 2007

AbstractBoth transient and stationary photoconduction of pentacene layers prepared by vapor deposition at 180 K and annealing at 295 K is studied in a surface electrode arrangement. Except at low light intensities photocurrents are recombination controlled. A ratio γ/μ = 1.8 × 10−7 V cm is obtained. The sum of electron and hole mobility monitored in a time interval 5 × 10−5 to 5 × 10−4 s after carrier generation is 10−2 cm2/Vs. It agrees with a value determined previously employing the initial photocurrent pulse method thus proving the reliability of that method to monitor transport properties of disordered solids on a short time scale.
Picosecond Spectroscopy of CdSe at High Excitation
Authors: Collet J. , Pugnet M. , Cornet A. , Brousseau M. , Razbirin B. S. , Mikhailov G. V. 
Published: July 2007

AbstractAt 4.2 K, the time resolved luminescence is studied of CdSe platelets, using two‐photon excitation at 1.064 μm and monopulsed excitation. At first the importance is shown of lattice heating and quasiparticle heating in high excitation experiments in CdSe. Then, the simultaneous kinetics of the A–LO excitonic line and the so‐called P line is studied. In the experiments, the P line cannot at all be interpreted as resulting of radiative exciton–exciton collisions. It is shown that the previously proposed radiative transition from the Γ1 biexciton ground state to the 2p exciton state provides the best understanding of the dynamical behaviour of the P line. A binding energy of 1.4 meV for the biexciton in CdSe is deduced.
Formation of a Complex Charge Carrier Due to the Interaction between a Free Frenkel Exciton and Excess Electron in Molecular Crystals
Authors: Singh J. 
Published: July 2007

AbstractMicroscopic theory of a complex charge carrier formed by the binding of a free exciton and an excess electron is briefly described. The potential of interaction between the exciton and excess electron is shown to be attractive as a function of the dipole moments induced by the excess electron on the molecule that carries the exciton. The complex charge carrier, like exciton, is shown to move throughout the molecular crystal.
Dipole–Dipole Interaction and Short‐Range Order in Amorphous NiP, NiCuP, and NiPB Alloys
Authors: Bakonyi I. , Takács L. , Tompa K. 
Published: July 2007

AbstractThe field‐independent 31P NMR linewidth, δHo, is measured in nonmagnetic amorphous Ni‐based alloys. In addition, the second moment contribution M originating from direct nuclear dipole–dipole interaction is calculated using Van Vleck's theory based on a computer generated DRPHS amorphous model cluster. The calculated second moment M and the experimental second moment M obtained from δHo by Gaussian line shape approximation (i.e., M = (δHo)2/4) agree fairly well for a (Ni0.27Cu0.73)82P18 metallic glass. In the case of amorphous NiP and NiPB alloys M exceeds M by a factor of two or three. This excess second moment seems to indicate the presence of some indirect indirect interactions between nuclear spins.
Phonon‐Polaritons by Two‐Photon Absorption in Solids
Authors: Hassan A. R. 
Published: July 2007

AbstractA semiclassical theory of the two‐photon absorption of phonon polaritons in solids is developed. A four‐band model is introduced for the phonon assisted two‐photon electronic transitions to polariton states. A numerical calculation is performed for Gap. The results show three different absorption peaks. The first peak, at low energy, corresponds to the phonon polariton band due to transitions through the indirect gap. The other two peaks are associated with transitions across the two lowest gaps of Gap.
Electronic States and Fermi Surface Properties of NiH
Authors: Tewari S. , Singru R. M. 
Published: July 2007

AbstractThe band structure of Nih is calculated using the APW method for two atomic configurations of Ni, A: 3d84s2and B: 3d94s1. The curves for the density of states show that for the configuration B new low‐lying states are formed in Nih which are attributed to the bonding states. The density of states at the Fermi energy,N(EF), is compared with the value determined from the measurements of electronic specific heat. Cross‐sections of Fermi surface and de Haas‐van Alphen frequencies are calculated for two values (11.0 and 10.76) of the number of electrons in the unit cell. The results show that the band structure and Fermi surface of Nih cannot be understood in terms of the protonic (or rigid‐band) model.
Evaluation of Third‐Order Elastic Constants and Pressure Derivatives of Second‐Order Elastic Constants for AgCl–AgBr Mixed Crystals
Authors: Shanker J. , Jain G. D. , Sharma S. K. 
Published: July 2007

AbstractSix third‐order elastic constants and the first pressure derivatives of second‐order elastic constants for AgCl–AgBr mixed crystals with varying compositions are evaluated. Suitable interionic potentials are developed for mixed crystals starting from an analysis of potentials in pure crystals. Long‐range electrostatic forces, the overlap repulsive forces extended up to second neighbours, the van der Waals dipole–dipole and dipole–quadrupole interactions, and three‐body forces are considered. Calculated values of the pressure derivatives of second‐order elastic constants are found to present reasonable agreement with experimental data.
Picosecond Relaxation Processes of High Density Electron–Hole Plasma in CdSe
Authors: Yoshida H. , Saito H. , Shionoya S. 
Published: July 2007

AbstractPicosecond time‐resolved spectra of the spontaneous luminescence from high density electron‐hole plasma in CdSe are measured at 4.2 K with changing excitation photon energy in the vicinity of the bandgap energy by using tunable picosecond pulses. Spectra observed are analyzed, and the electron‐hole concentration and effective carrier temperature of the plasma are obtained as a function of excitation photon energy as well as of the delay time. It is found that both the electron‐hole concentration and effective carrier temperature decrease remarkably for the first 150 ps after pulse excitation, and that thereafter the concentration and temperature remain almost unchanged at ≈3 × 1017 cm−3 and ≈20 K, respectively, until to the very late stage down to the 800 ps delay time. It is concluded that the effective carrier temperature does not fall below ≈20 K in spite of decreasing the excess energy given to the carriers at the instance of pulse excitation by means of changing the excitation photon energy. It is sure that there exists a process which makes the plasma hot. The phonon‐assisted Auger process is suggested as such a process.
On the Theory of Electroreflectance of Metals
Authors: Brodskii A. M. , Daikhin L. I. 
Published: July 2007

AbstractA theory is developed to explain the electroreflectance (ER) of metals in a light energy interval near the photoemission threshold under the assumption that the microscopic mechanism of electromodulation is caused by the dependence of the external photoemission threshold on the field applied. Expressions for electroreflectance are derived containing parameters which depend on the electron structure of surface. The theory is compared with the experiment.
Optical Absorption Study of Nickel Fluoride Thin Films
Authors: Gevers G. , Pichon J. , Barrière A. S. 
Published: July 2007

AbstractAn optical absorption study is made of crystallized thin films of nickel fluoride obtained by sublimation under vacuum. The influence of the structure disorder and of the composition of the samples are investigated by varying the substrate temperature Ts and the residual pressure P during the condensation of the vapors. For well crystallized and quasi stoichiometric thin films, the optical gap is about 9 eV. The spin transitions between the 3d states of Ni2+ ions already reported for single crystals are observed. When P > 10−6 Torr and after an air exposure of the layers, two absorption edges characterizing the presence of NiO appear. For low values of Ts the structural disorder involves a broadening of the fundamental absorption edge. Conversely for high‐temperature values (Ts ≫ 650 K) a lack of fluorine due to a partial dissociation of the compound gives an extra absorption at an energy about 1.75 eV.
The Parity‐Forbidden 4f5 → 4f5 Transition of the Sm3+ Ion in CaF2
Authors: Tsuboi T. 
Published: July 2007

AbstractThe infrared absorption spectra of Sm3+ ions in CaF2 crystals are measured between 15 and 300 K. The temperature independence or dependence of the absorption bands, which are due to electric‐dipole forbidden 4f5 → 4f5 transitions, is interpreted in terms of static or dynamic electron–lattice interaction, respectively.
Polarization Dependence of Three‐Photon Absorption in Solids
Authors: Hassan A. R. , Raouf R. 
Published: July 2007

AbstractThe polarization dependence of three‐photon absorption in solids is developed using the Wigner‐Eckart theorem for finite symmetry groups. The expression for the absorption coefficient is separated into two parts: (i) The geometrical part, which depends on the polarization vectors of the three photons, (ii) the dynamical part, which contains the product of three electron‐photon matrix elements. New information can be gained by studying these two parts. An application to TlCl crystal is given and an experimental method is suggested.
Multiple‐Phonon Resonant Raman Scattering in Zn1–x CdxSe Crystals
Authors: Valakh M. Ya. , Litvinchuk A. P. , Pekar G. S. , Polysskii G. N. 
Published: July 2007

AbstractResonant Raman scattering in bulk Zn1–x CdxSe crystals obtained from the vapour phase by the “free‐growing” method is studied experimentally. The existence of seventh‐order LO‐phonon lines under condition of excitation above the band gap and fourth‐order LO‐phonon lines under condition of excitation below the band gap is observed for mixed semiconductor crystals for the first time. The obtained ratios of intensities of different lines in multiple‐phonon spectra are compared with the results of the theory involving the continuous exciton spectrum as an intermediate state.
Pinning by a Macroscopic Spherical Cavity in a Type II Superconductor
Authors: Shehata L. N. 
Published: July 2007

AbstractThe magnetic field created by a vortex line located near a macroscopic spherical cavity as well as the magnetic field within the superconductor are calculated by solving London equations using the generalized spherical function technique. The interaction energy between the flux line and the cavity and consequently the pinning force are also calculated. It is shown that one possible cause of the pinning is that an attractive image force exists at the superconductor sphere boundary.
Lattice Vibrations Around a Vacancy in B.C.C. Transition Metals
Authors: Masuda K. 
Published: July 2007

AbstractA tight‐binding‐type electronic theory is used to calculate the atomic relaxation and force constants between atoms around a vacancy in b.c.c. transition metals (α‐Fe, Mo, and W). This calculation takes into account the d‐function anisotropy as well as the short‐range repulsive energies. The calculated atomic relaxation and force constants are used to obtain the local vibrational spectra around a vacancy. Finally, the so‐called stage III temperature (at which single vacancies migrate) is estimated from the local vibrational spectra and compared with recent experimental results (both positron annihilation experiments and investigations using a high‐voltage electron microscope).
The Role of Symmetry in Mössbauer Relaxation Spectra
Authors: Cianchi L. , Moretti P. , Mancini M. , Spina G. 
Published: July 2007

AbstractA perturbation procedure for dealing with the relaxation operator for a Mössbauer atom undergoing electronic transitions is presented. When the restrictions imposed by the symmetry are also taken into account, it is found that one can greatly reduce the complexity of the computations. For example in the case of Yb3+ in YES using the present theory the problem of deriving the line shape of the Mössbauer spectrum is reduced to that of inverting a 40 × 40 matrix and not a 80 × 80 matrix as in previous theories.
Charge Order‐Disorder Transition in the Extended Hubbard Model. Finite Bandwidth Effects
Authors: Lorenz B. 
Published: July 2007

AbstractThe charge order‐disorder transition in the extended Hubbard model which takes into account the intra‐ and intersite Coulomb interactions is investigated with respect to finite bandwidth effects. It is shown that above a critical bandwidth the charge order is destroyed even in the ground state in contradiction to the results of the mean field approximation. For finite temperatures the phase diagram is calculated. Depending on the model parameters the transition may be of either first or second order. Especially, a parameter region is found where the transition changes from first to second order with increasing bandwidth.
Theory of Planar Channelling of Relativistic Positrons
Authors: Zimin N. I. , Wedell R. , Greschner O. 
Published: July 2007

AbstractA theory of planar channelling of relativistic positrons taking into account multiple scattering, bremsstrahlung on valence electrons, and spontaneous radiation at channelling is developed. The dependence of the energy losses on the impact parameter leads to a stronger broadening of the angular distribution of channelled particles.
Phase Diagrams of the SiSn and GeSn Systems
Authors: Soma T. , Matsuo H. , Kagaya S. 
Published: July 2007

AbstractThe phase diagrams of the SiSn and GeSn systems are investigated using the previous electronic theory based on pseudopotentials. The calculated results negate the presence of the Si1−xSnx and Ge1−xSnx solid solutions. The obtained curves near the melting point show reasonable agreement with experimental data.
Absorption Coefficients in the Dynamical Theory of Electron Diffraction for Non‐Column Calculations of Stacking Fault Contrast
Authors: Sheinin S. S. 
Published: July 2007

AbstractA method is described which permits absorption coefficients in the dynamical theory of electron diffraction to be obtained for non‐column approximation calculations of stacking fault contrast. The method is based on the use of the exact form of the dynamical equations which include the wave vector change due to the imaginary part of the lattice potential. The results obtained show that absorption coefficients of the Bloch waves excited at the fault are quite different from the absorption coefficients of the Bloch waves excited at the entrance surface.
Theoretical Study of Single Vacancies in GaSb
Authors: Brescansin L. M. , Fazzio A. 
Published: July 2007

AbstractUsing clusters with 17 atoms the electronic structure of Ga and Sb single vacancies is studied in GaSb, using the MS‐Xα method. For the Ga vacancy an impurity level of t2 symmetry is obtained, occupied with three electrons, and in the case of the Sb vacancy two impurity levels are obtained, one a fully occupied a1 level and a t2 level occupied with one electron.
Magnetic Field Dependent Carrier Mobility in Ferromagnetic Semiconductors
Authors: Patil C. G. , Krishnamurthy B. S. 
Published: July 2007

AbstractThe electron mobility in ferromagnetic semiconductors in an external magnetic field due to the electron—two magnon scattering is calculated below the Curie temperature. The calculated two‐magnon mobility is found to be linearly dependent on the external magnetic field in EuO. This is in agreement with experimental observation. Incorporating ionized and neutral impurity scattering besides the two‐magnon process, the Hall mobility data are analysed and the exchange coupling constant I = 0.17 eV and electron effective mass m* = 0.42m are obtained.
Calculations of Phonon Dynamics in Solid Biphenyl. Mixing Between Interphenyl and Lattice Vibrations
Authors: Natkaniec I. , Bielushkin A. V. , Wasiutyński T. 
Published: July 2007

AbstractThe calculation of the lattice dynamics in the high‐temperature phase of solid biphenyl is performed with the inclusion of low‐lying interphenyl motions. The quasi‐harmonic approximation is applied and use is made of the semiempirical atom—atom potential of the form „6‐exp”︁. On the basis of calculated phonon curves the effect of mixing between external and internal modes is studied. The frequencies of the phonons in the Brillouin zone centre are compared with optical spectroscopic results. The phonon density of states weighted on the hydrogen motions is compared with low‐temperature inelastic incoherent neutron scattering spectra. Comparison of the calculated and measured values shows good agreement.
Infrared Band Assignments in Oxidised Hydrogenated a‐Si Films
Authors: John P. , Odeh I. M. , Thomas M. J. K. , Tricker M. J. , Wilson J. I. B. 
Published: July 2007

AbstractThe infrared transmission spectra of two ‘polysilanes’ of approximate composition (SiH2)x and (SiH)x, prepared by chemical means, have been measured in the range 4000 to 650 cm−1. The appearance of new bands in the infrared spectra during the oxidation of films of these materials by exposure to air is interpreted in terms of changes in the local environment around the silicon‐hydrogen moieties. It is demonstrated that the wave number of the silicon—hydrogen stretching modes of SiH and SiH2, groups vary systematically with the number and electronegativity of the next neighbouring atom. The influence of the inductive effect on the stretching frequencies can be empirically related, following the methodology of Lucovsky, to the Pauling electronegativity sum of the adjacently bound oxygen atoms. The infrared band frequencies exhibited in the oxygenated ‘polysilane’ samples correspond exactly with bands that arise during the exposure of certain undoped and P‐doped hydrogenated a‐Si films to air. Ageing phenomena produced in r.f. discharge a‐Si films are associated with the porosity and oxidation of a hydrogen rich phase in the amorphous material.
Self‐Diffusion of Phosphorus in the Amorphous Alloy Fe40Ni40P14B6
Authors: Valenta P. , Maier K. , Kronmüller H. , Freitag K. 
Published: July 2007

AbstractIn amorphous and crystallized Fe40Ni40P14B6 alloys the self‐diffusion coefficient of phosphorus is investigated using radiotracer and a microsectioning technique. Diffusion coefficients of 4 × 10−19 to 5 × 10−17 cm2 s−1 are determined in the temperature range between 553 and 823 K. They do not obey an Arrhenius law.
On the Defect Structure of Zinc‐Doped Zinc Oxide
Authors: Neumann G. 
Published: July 2007

AbstractThe reinterpretation of the EPR investigations of electron irradiated and doped zinc oxide reveal that the EPR signal with the g‐factor near 1.96 has to be attributed to the conduction electron. Oxygen vacancies with the EPR signal near 1.99 solely can be created by electron irradiation or strong mechanical damaging. These results are exclusively compatible with the assumption that zinc oxide contains excess zinc in the form of zinc interstitials.
On the Theory of Radiation of Non‐Relativistic Electrons Grazing into Metal Targets
Authors: Gevorgian L. A. , Korkhmazian N. A. 
Published: July 2007

AbstractIt is shown, that the experimentally observed abnormally high radiation intensity caused by electrons grazing into the metal is a mixture of the undulator radiation resulting from the roughness of metal surface and the transition radiation. Close to the radiation spectrum peak the undulator radiation predominates over the transition radiation contrary to the far‐from‐the peak region.
Etude du gradient de champ électrique dans la muscovite par spectrométrie Mössbauer du fer
Authors: Bonnin D. , Muller S. 
Published: July 2007

AbstractLa spectrométrie Mössbauer est utilisée pour l'étude du Fe2+ dans la couche octaédrique des micas. Dans le cas qui nous occupe, il s'agit d'un monocristal de muscovite. l'analyse des spectres en fonction des angles entre la direction des γ incidents et les axes cristallographiques permet de trouver les directions principales du gradient de champ électrique. Les axes du feuillet ne sont pas équivalents, les spectres sont symétriques par rapport au plan a, c* et non symétriques par rapport au plan b, c*. Nous montrons que la direction principale du gradient de champ électrique est proche du plan a, b du cristal et fait un angle de 45° avec l'axe b. Les directions du gradient de champ électrique trouvées sont comparées à la symétrie locale du site M2 et aux valeurs trouvées par le calcul dans un modèle à charges ponctuelles.
Size‐Dependent Electric Conductivity in Semiconducting thin Wires
Authors: Arora V. K. 
Published: July 2007

AbstractA quantum theory for electric conductivity in a thin rectangular‐shaped wire is developed taking into account the wave character of an electron. It is shown that the quasi‐one‐dimensional (QOD) gas behaves somewhat like the strictly‐one‐dimensional (SOD) gas when the wire is ultra‐thin, so that the spacing between the quantized levels is quite large, and all the electrons are assumed to be in the lowest quantized level. In the ultra‐thin limit (UTL), the ratio of longitudinal resistivity to bulk resistivity is shown to be proportional to λD2/A, where λD = h/(2m*kBT)1/2 is the de‐Broglie wavelength of an electron of effective mass m* at temperature T, and A is the area of the cross‐section of the wire. The transverse resistivity ratio depends strongly on the scattering parameters and is inversely proportional to the area for wires of square cross‐section.
Electron Momentum Distribution and Compton Profiles of Ag
Authors: Kanherem D. G. , Singru R. M. , Harthoorn R. 
Published: July 2007

AbstractA band structure calculation of the electron momentum distribution for Compton scattering in Ag is made employing Hubbard's approximate scheme. Plots are shown of the contributions of the individual bands to the total momentum distribution along the 〈100〉, 〈110〉, and 〈111〉 directions. The graphs of the total momentum density in the form of isodenses in the (100) and (110) planes are also presented. The results are used to calculate the anisotropy in the Compton profiles viz. J110 — J100, J100 — J111, and J110 — J111 in Ag.
Variational Hartree‐Fock Calculations of the Ground State Energy of Metallic Hydrogen
Authors: Tua P. F. , Mahan G. D. 
Published: July 2007

AbstractThe ground state energy of metallic hydrogen is calculated by a variational method in the Hartree‐Fock approximation. The periodic wave functions are taken to be a linear combination of Slatertype orbitals and k‐dependent and the exchange energy is treated exactly. Then it is shown that the inclusion of correlation effects, in the same approximation of the Kohn‐Sham equation, does not modify the result appreciably. The introduction of additional parameters confirms the previous results except those obtained by density functional method.