bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Absorbate Geometries from Angle‐Resolved X‐Ray Photoelectron Spectra. Nitrogen on Fe(111)
Authors: Chassé A. , Rennert P. 
Published: July 2007

AbstractThe angular dependence of the X‐ray photoelectron intensity of excited deep core levels is used to investigate the structural properties of several molecular and atomic states for chemisorbed nitrogen on the Fe(111) surface. The N1s photoelectron intensity is calculated within the small scattering center approximation and the single scattering model for several angular variations and geometrical arrangements. It is shown that the angular anisotropies can be used to explain the surface geometries of the nitrogen–iron system.
Correlation between X‐Ray Chemical Shift and Partial Charge in Some Minerals
Authors: Hemachandran K. , Chetal A. R. 
Published: July 2007

AbstractThe K‐absorption spectra of arsenic in the minerals orpiment, realger, smaltite, and arsenopyrite are investigated using a Cauchois‐type bent‐crystal X‐ray spectrograph. The chemical shift of the edges is determined and correlated with the partial charge, calculated using Sanderson's method. A theoretical justification is given for the relation observed between the shift and partial charge.
2kF Distortion of the Impurity Distribution in the Peierls‐CDW State
Authors: Bâldea I. 
Published: July 2007

AbstractA self‐consistent approach is developed to investigate the possibility that the impurity distribution embedded in a one‐dimensional system becomes distorted with the wavevector 2kF (kF Fermi wave vector) as a result of the Peierls‐CDW (charge density wave) distortion. The properties of the double distorted state are obtained for both, T = 0 and T ≠ 0 (e.g. enhancement of both, the gap in the electron spectrum and the CDW effective mass). The conditions to have a state with 2kF‐double distortion are derived. The interplay between the 2kF‐regularity in the impurity distribution and the disorder effect usually associated with the latest is also discussed.
Lattice Thermal Conductivity of Deformed Lithium Fluoride Crystals at Low Temperatures
Authors: Kumar A. , Srivastava B. K. , Ansari M. A. 
Published: July 2007

AbstractStatic dislocation scattering processes result in an additional phonon scattering term because of the simultaneous presence of the impurity–phonon scattering processes. The additional term of the inverse of relaxation time is calculated by using the perturbation and is found to be proportional to the square of the phonon frequency. Excellent agreement is obtained between theory and experimental results of the phonon conductivity of the plastically deformed LiF crystals.
Magnetoelastic Model of the Temperature‐Induced Metamagnetism for Lattices with Axial Symmetry
Authors: Pawlicki P. 
Published: July 2007

AbstractA new model of the temperature‐induced metamagnetic phase transitions is considered for the class of the two‐sublattice magnets with axial symmetry. The model Hamiltonian contains the usual Ising term as well as the coupling of the uniform strain with both exchange interaction and single ion anisotropy. Within the MFA all these couplings are found to be necessary to produce the metamagnetic phase change. The results are compared with experiment.
Plasmon Excitations in Thin Metal Films. Transition from Three‐Dimensional to Two‐Dimensional Behaviour
Authors: Teich W. G. , Mahler G. 
Published: July 2007

AbstractDensity oscillations are studied within the infinite‐barrier model. Intersubband and intrasubband modes are characterized with respect to their frequency, spatial amplitude field, and collective nature. Special attention is paid to particular limiting cases in terms of the length scales defined by slab thickness and excitation wavelengths.
Comparison between Monte Carlo and Davydov Approaches to Hot‐Carrier Transport in Semiconductors
Authors: Reggiani L. , Brunetti Rossella , Normantas E. 
Published: July 2007

AbstractHot‐electron transport in a simple model semiconductor is investigated in the presence of acoustic phonon scattering. Analytical calculations, based on the Davydov distribution function, are compared with Monte Carlo results to demonstrate the limitations of the analytical approach. By displaying the results in a universal form, it is found that the quasi elastic approximation required to fully justify the Davydov approach, is controlled by the condition τ/τ∈ < 10−3, τ and τ∈ being the momentum and the energy relaxation times, respectively.
Lattice Theory of Fourth‐Order Elastic Constants of Primitive Lattices. Application
Authors: Kumar K. , Goyal S. C. 
Published: July 2007

AbstractThe lattice theory of fourth‐order elastic constants for primitive lattices recently derived by Goyal and Kumar is applied to obtain the relations for the FOE constants of CsCl structure type solids within the framework of the Lundqvist many‐body potential. The derived relations of FOEC are used to compute the numerical values of the FOE constants and the second‐order pressure derivatives of the SOE constants of cesium halide solids.
Theoretical Analysis of the Effective Electron Mass in n‐Channel Inversion Layers on Ternary Chalcopyrite Semiconductors
Authors: Mondal M. , Ghatak K. P. 
Published: July 2007

AbstractAn attempt is made to derive expressions of the effective electron masses in n‐channel inversion layers on ternary chalcopyrite semiconductors, taking n‐channel inversion layers on CdGeAs2 as examples, under both the weak and strong electric field limits. It is found, on the basis of newly derived 2D electron energy spectra for both the limits by considering the various types of band‐anisotropies, that the effective electron masses at the Fermi level depend on the electric sub‐band index due to the combined influence of the crystal field splitting, the anisotropic spin—orbit splitting parameter, and the band non‐parabolicity. The anisotropy parameters enhances the numerical values of the effective Fermi level masses for both the limits for relatively low values of the surface fields. Besides, the corresponding results for the isotropic three band Kane model are also obtained from the expressions derived.
3d‐Like Electron Localization and Charge Transfer in Hydrogenated V‐Fe Alloys
Authors: Ostrasz A. , Szuszkiewicz M. 
Published: July 2007

AbstractThe influence of hydrogen absorption on the electronic structure of V1−yFey, alloys is studied. The results of the Mössbauer effect and X‐ray diffraction measurements as well as the positron annihilation data allows to determine the mean number of 3d‐like electrons localized at Fe atoms in V1−yFeyHx alloys. The problem of hydrogen participation in charge transfer in these alloys is also discussed.
Optical Absorption Spectrum of Cr3+ Ions Doped in NH4Cl Single Crystals
Authors: Rao J. Lakshmana 
Published: July 2007

AbstractOptical absorption spectrum of Cr3+ ions doped in NH4Cl single crystals is studied in the temperature range from 300 to 143 K. From the observed spectrum it is concluded that Cr3+ ions enter interstitially into NH4Cl lattice and the site symmetry of the Cr3+ ions are lowered from octahedral to tetragonal. The crystal field and the tetragonal parameters are evaluated.
Lattice Dynamics Study of Polycrystalline 57CoO by Mössbauer Spectroscopy
Authors: Fontcuberta J. 
Published: July 2007

AbstractThe Mössbauer emission spectra of 57Co1−xO recorded in the temperature range from 293 to 1273 K for samples synthesized under various oxygen‐pressure conditions, are used to determine the Debye temperature θD of these oxides. It is found that θD decreases when the non‐stoichiom‐etric parameter x increases. In the highest temperature range, anharmonic contributions to the vibrational spectrum of the solid are observed.
Analysis of Cohesive and Anharmonic Properties of Alkaline Earth Fluoride Crystals
Authors: Singh R. K. , Rao Chandrika N. 
Published: July 2007

AbstractThe cohesive and anharmonic properties of alkaline earth fluoride crystals are described using the model parameters determined for the computer simulation study by de Leeuw using the two‐body interaction potential devised by Benson and Dempsey. It is found that this potential gives better prediction of these properties when the hardness parameters (ϱij, i,j = +, −) are taken different for different ion pairs. The results obtained from this potential on cohesive energy and second and third‐order elastic constants are in better agreement with their corresponding experimental data than those achieved by earlier workers from similar or other potentials.
Physisorption and Chemisorption Effects on Atom—Adsorbate van der Waals Potentials. Application to He and He* Scattering from Adsorbed CO
Authors: Lovrić D. , Gumhalter B. 
Published: July 2007

AbstractThe dynamical polarizability of an atomic or molecular species may undergo significant changes upon physical and chemical adsorption onto a metallic substrate. The physical effect derives from the presence of the polarizable substrate surface which gives rise to a modification of all the polarization induced or van der Waals potentials acting between the adsorbate and the nearby atoms or molecules in the gas phase. The chemical effect, viz. chemisorption, may give rise to the broadening of adsorbate valence orbitals into resonances which will be occupied up to the substrate Fermi level. Provided the electronic density of the localized resonance states at the Fermi level is non‐vanishing, chemisorption will open a new channel of intra‐adsorbate dynamic polarizability. Both effects (i.e. the physical and the chemical one) will enhance the total van der Waals potentials encountered in the thermal energy atom scattering and Penning spectroscopy of adsorbates. Calculations are made of these effects on the adsorbate—gas phase atom van der Waals potentials and their influence on the thermal energy atom scattering (TEAS) cross sections and the effective Penning deexcitation energies discussed for the case of He and He* collisions with adsorbed CO.
A Pseudopotential Band Structure Calculation of Bismuth, Antimony, and Their Alloys
Authors: Rose J. , Schuchardt R. 
Published: July 2007

AbstractA semiempirical pseudopotential band structure calculation with account of spin—orbit‐interaction is performed for Bi, Sb, and Bi1−xSbx alloys considering the alloy potential in the framework of VCA. The parameter of Fermi surfaces are evaluated on the basis of the calculated energies. The resulting Fermi surfaces of the pure elements correspond better to experimental data than those of previous work. The composition dependences as well of gap and overlap as the Fermi surface dimensions agree qualitatively with the measured dependences.
Short‐Range Order and Superconductivity in Binary Alloys Containing V, Nb, and Ta
Authors: Khwaja Farid A. , Brouers F. 
Published: July 2007

AbstractThe problem of superconductivity in V, Nb, and Ta binary solid solutions is discussed in the light of interatomic pair interaction and density of states. Using a tight‐binding recursion method for degenerate d‐bands the superconducting transition temperatures are calculated for equiconcentration VNb, VTa, and NbTa alloys. The theoretical predictions about the existence of clustering of similar atoms in NbTa and ordering in VTa and VNb alloys is confirmed by measuring the values of Cowley's short‐range order parameter αi for these systems. The measured data show negative values of α1 on the first coordination sphere for VNb and VTa alloys and positive values for NbTa.
2D NMR Study near the Ferroelectric Phase Transition of TSCC
Authors: Engelke F. , Michel D. , Windsch W. , Petersson J. 
Published: July 2007

AbstractDeuterium nuclear magnetic resonance (2D NMR) investigations are performed in order to get information about structural changes of the hydrogen bonds for deuterated crystals of trissarcosine calcium chloride (TSCC) near the ferroelectric phase transition at Tc = 130 K. The electric field gradient (efg) tensors at the deuterium sites in the hydrogen bonds are determined at room temperature by measuring the angular dependence of the spectra for rotations around the three crystallographic axes. Near the phase transition (Tc − T = 5 K) the positions of the 2D NMR lines change in an interval of about 10 kHz. These changes can be explained through a rotation of the efg tensor by an angle of about 4° at 125 K. The interpretation is in agreement with results from 1H ENDOR and 13C ENDOR measurements of TSCC crystals doped with Mn2+ according to which a static rotation of sarcosine molecules occurs at the phase transition giving rise also to the spontaneous polarization.
Mn 3d states in photoelectron spectra from Cd1−xMnxTe
Authors: Mašek J. , Velický B. 
Published: July 2007

AbstractA parametrized tight‐binding model is used to describe the electronic structure of semimagnetic Cd1–xMnxTe. The density of states and the spectral density are calculated by using the coherent potential approximation. The features connected with the presence of the Mn 3d states are identified and the controversial results of angle‐resolved and integrated photoemission from Cd1–xMnxTe are then explained.
Electronic structure of the Cd vacancy in CdTe
Authors: Meijer P. H. E. , Pecheur P. , Toussaint G. 
Published: July 2007

AbstractBy means of a tight binding parametrization of the band structure of cadmium telluride, in conjunction with the Green's function method the density of states of the perfect crystal is determined. Various parametrizations for this compound are compared. Next, the energy levels for the Cd vacancy are calculated taking into account the change in the wave functions around the missing atom as well as the various possibilities for the charged state at this site. Spin–orbit coupling is not taken into account, nor the possible neighbor relaxation around the vacancy.
“Dissolution” of 4f–4f transitions in phonon sidebands (ZnS:Tm3+)
Authors: Boyn R. , Zimmermann H. 
Published: July 2007

AbstractFor the example of the 1G4 → 3H6 emission spectra of two Tm3+ centers in ZnS crystals (measured by means of dye‐laser site‐selective excitation at helium temperature) it is shown that lines arising from transitions to higher Stark levels of a given manifold may “dissolve” in the phonon sideband of the transitions to lower Stark levels. This phenomenon, which involves a transfer of intensity from lines to sidebands, is discussed quantitatively by applying Fano's general theory of continuum–discrete level interaction, as formulated by Shibatani and Toyozawa, to this vibronic problem. On this basis the large sideband‐intensities observed may be understood for the present systems. Furthermore, the dissolution effect can, at least partly, explain the general observation that transitions to higher Stark levels tend to have smaller apparent intensities than those to the lowest Stark levels.
NMR powder spectrum simulation for nuclei with I > 1/2
Authors: Goc R. , Fiat D. 
Published: July 2007

AbstractA program to calculate powder NMR spectra for nuclei with spin I > 1/2 is written. The spin Hamiltonian used includes Zeeman term, isotropic dipolar broadening, anisotropic chemical shift, and quadrupolar interaction with asymmetric field gradient treated up to second‐order term of perturbation theory. Two sites with different sets of parameters determining the shape of the spectrum can be included in calculation. The approach to the problem is entirely numerical without deriving analytical formulas for the lineshape.
Molecular dynamics in [(CH3)4N]2 CdI4. A proton magnetic relaxation study
Authors: Venu K. , Sastry V. S. S. , Ramakrishna J. 
Published: July 2007

AbstractProton spin–lattice relaxation experiments (at Larmor frequencies 10, 20, and 30 MHz), and second moment measurements are carried out on [(CH3)4N]2 CdI4 in the temperature range 77 to 400 K. The results are interpreted based on a molecular dynamical model of randomly reorienting methyl groups and isotropically tumbling tetramethyl ammonium group. The relaxation data show contributions from spin–rotation interaction at high temperatures and presence of inequivalent methyl groups. The correlation times and associated activation energies, connected with this model, are calculated from the data. The structure in the absorption line and in the free‐induction decay signal at 77 K indicates the possibility of tunnelling motion of the methyl groups.
Interference spectra of semiconducting slabs at excitonic resonances studied by Stahl's coherent wave approach to band gap electrodynamics
Authors: Czajkowski G. , Schillak P. 
Published: July 2007

AbstractInterference structures observed in reflection and transmission spectra of thin semiconducting slabs in the excitonic region of the spectrum are investigated within the framework of Stahl's coherent wave theory of electrodynamic processes near the semiconductor band edge. The theoretical spectra agree well with those experimentally observed. An adjustable damping parameter is used. From the best fit the exciton collision time is determined.
Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U4+–ThCl4 System
Authors: Krupa J. C. , Malek C. Khan , Delamoye P. , Moine B. , Pedrini C. 
Published: July 2007

AbstractThe second order phase transition in β‐ThCl4 (Tc = 70 K) leads to an incommensurate tetragonal structure modulated along the fourfold symmetry axis. This is due to the freezing of an optical soft mode which induces a modulation of the chlorine ion positions in a plan perpendicular to this axis. Consequently in neighbouring unit cells the crystal field strength acting on the U4+ ion is slightly different. Then the line shape in the optical spectra shows a continuous variation which reflects the shift of the energy as the symmetry changes. Selective excitation of the resulting different classes of sites, S4, D2, and various C2p ermits one to establish a correlation between absorption and emission profiles of U4+ ions. The green and the red observed fluorescences of U4+ in ThCl4 are assigned in the different symmetries and the energy level mapped out as a function of a phase angle φl related to the distortion according to the Delamoye and Currat model.
Pair‐correlation functions of liquid noble metals through Born‐Green‐Yvonne theory
Authors: Bhattacharya T. , Ghosh A. K. 
Published: July 2007

AbstractBorn‐Green‐Yvonne (BGY) equation is numerically solved to calculate pair‐correlation functions for liquid Cu, Ag, and Au utilizing the resonant model potential of Lam et al., and an experimental potential for Cu given by Rautioaho. A comparison of results with the earlier calculations of the authors based on the Percus‐Yevick (PY) equation helps to conclude that the BGY equation is at least as good as the PY equation as far as calculation of pair‐correlation functions of liquid noble metals is concerned.
Calculating the energy parameters for the CV and OPF methods
Authors: Gusev A. I. , Rempel A. A. 
Published: July 2007

AbstractA method is proposed for calculating the energies ε (with ε being the energy of the m‐configuration of a type s figure), which are parameters of the cluster variation (CV) method and the order parameter functional (OPF) method. An analytic expression is derived which describes the energy ε in terms of power series expansion coefficients of the formation enthalpy of a disordered crystal. It is shown that a necessary condition for ordering is the presence of a nonlinear composition dependence of the formation enthalpy of a disordered crystal.
Lifetime studies on excited (F2+)* and M centers in NaF doped with magnesium
Authors: Bosi L. , Nimis M. 
Published: July 2007

AbstractThe lifetime and the decay properties of the relaxed excited state (RES) of the (F2+)* center in NaF:Mg are investigated: similarities with the F2+ center RES in pure NaF are once more evidenced. Nevertheless, two strange new effects are found: a) the radiative quantum yield is an increasing function of temperature up to 300 K; b) the (F2+)* luminescence can be induced by light excitation in the M center absorption band, in spite of the apparent absence of (F2+)* levels which can absorb in this spectral range. Furthermore, an absence of perturbative effects by magnesium ions on the decay properties of the M centers is ascertained.
Lattice thermal conductivity of solid helium crystals
Authors: Pal S. K. , Kumar A. 
Published: July 2007

AbstractVacancy like excitations are suggested for solid helium which can be scattered due to the vacancy–phonon interaction processes. The phonon conductivity of solid helium is analysed by modifying Callaway's expression for high frequency phonons and for Poiseuille's flow of phonons. An excellent agreement between theory and experiment is obtained when the combination of static and dynamic dislocation scattering processes is considered as an effective dislocation scattering of phonons.
Frequencies of a general damped coupled nonlinear oscillator system
Authors: Bose S. K. , Dubey U. B. 
Published: July 2007

AbstractA system of 2m damped coupled nonlinear oscillators is considered when the nonlinear and coupling terms are of homogeneous even power 4p in position variables. Using a convenient canonical transformation to remove the damping term from the equation of motion and action and angle variables in Hamilton‐Jacobi theory, first order corrected frequencies are obtained. The expression for the corrected frequencies bears all the characteristic features of a damped coupled nonlinear oscillator system.
Electron–phonon interaction in dielectric interface systems
Authors: Jin‐Sheng Pan 
Published: July 2007

AbstractThe integral and differential equations for the polarization eigenmodes of the dielectric interface systems are given by making use of the macroscopic electric field caused by the bulk and interface polarization charges. It is shown that the polarization eigenmodes should be normalized according to the ortho‐normalized relation interpreted in the text. It is also shown that the interaction of the charged particles with SO phonons can be described by Fröhlich‐like coupling constant αSO characterizing the interface system.
The role of supersonic davydov solitons for energy exchange between two joined molecular chains
Authors: Ivić Z. , Satarić M. , Shemsedini Z. , Žakula R. 
Published: July 2007

AbstractThe statistical treatment of the energy transfer from one molecular chain to the other by the mechanism of supersonic Davydov solitons is presented. Two one dimensional molecular chains are considered which have the junction point enabling energy exchange between the chains. The supersonic solitons have the contribution to the energy transfer between joined chains. This contribution is inversely proportional to the soliton velocity.
Estimation of plasmon dispersion‐coefficient and evaluation of the effective mass of electrons in metals
Authors: Misra L. K. , Tripathy D. N. 
Published: July 2007

AbstractUsing an improved version of the Bohm‐Pines effective Hamiltonian for the electron–plasmon system, the correct value is reproduced of the critical wave‐vector, kc, for the plasmons in the random phase approximation (RPA) by minimizing the total energy of the system. The calculated values for the effective mass m* of the electron show a close agreement with the experimental result for sodium and potassium. By introducing an adjustable mass‐parameter, meff, in the theory not only a very good fit of the plasmon frequencies with the experimental data is obtained but also reproduced the observed value of the plasmon dispersion coefficient, α, for metals like Al, In, Na, and K. Further, an explanation for the two branch behaviour of the volume plasmon in Al and In is given. Finally, a qualitative argument is put forth to explain the difference between the calculated values of m* and those of meff.