bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Structure of the GeZnSe, GeGaAs, and GeAlAs(110) Interfaces and Superlattices
Authors: Kumar A. , Singh I. 
Published: July 2007

AbstractThe semi‐empirical tight binding method with sp3 s* basis is used for the electronic structure of GeZnSe, GeGaAs, and GeAlAs (110) superlattices. As the work of Vogl et al. shows, the inclusion of an excited s state s* in the basis set describes the lower part of the conduction band very well. Interface band structure, layer density of states, and charge transfer at the interfaces are given. Various interface states are differentiated between bound interface states and resonance states.
Nonequilibrium Thermalized Stage of Noble Metals
Authors: Heiner E. 
Published: July 2007

AbstractStarting from first principles of quantum statistics a system of differential equations is derived by use of a time dependent projector technique. It describes the evolution of electron‐ and phonon temperatures in noble metal layers in the macroscopic thermalized (hydrodynamic) stage. Within numerical model calculations for gold results are obtained for the relaxation time which are in satisfying agreement with experimental measurements.
Magnetoresistance Behavior in Orthorhombic Crystals
Authors: Haritonidis J. H. , Kyriakos D. S. 
Published: July 2007

AbstractThe action of a magnetic field on any crystalline material is to induce an anisotropy in the electric resistivity even in the case of isotropic materials. In anisotropic crystals the natural anisotropy and the one imposed by the field act competitively. Thus the magnetoresistance behavior is peculiar because of the continuous change of the principal resistivity directions. A study of this behavior in orthorhombic crystals is made, based on the weak‐field phenomenological theory.
Orientational Vibrations of Two‐Dimensional Dipole Lattice on Support
Authors: Goichuk I. A. , Kukhtin V. V. , Petrov E. G. 
Published: July 2007

AbstractThe ground and metastable energy states are defined for a dipole system on a rectangular lattice. The latter appears when the ratio of lattice parameters becomes equal to 1.043. The spectrum of dipole vibrations is calculated with (and without) taking into account the mechanical coupling of dipoles with support for the 2D model of a lipid monolayer.
A Model for Lattice Dynamics of Lanthanides
Authors: Kushwaha S. S. , Dikshit M. P. , Srivastava S. K. 
Published: July 2007

AbstractA simple model is proposed for studying the lattice dynamics of h.c.p. rare earth metals. The interaction between core‐core and (f, d)shells–(f, d)shells via conduction electrons is considered through a screened‐Coulomb potential. The direct Coulomb interaction between cores and (f, d)shell electrons is essentially short‐range and is, therefore, described through a non‐central type interaction extending upto the third neighbours.
Collective Excitations in Liquid Cesium Using a Theory of Phonons in Amorphous Solids
Authors: Rani M. , Pratap A. , Saxena N. S. 
Published: July 2007

AbstractA theory of phonons in amorphous solids as developed by Takeno and Goda using a self‐consistent method, is applied for the numerical calculations of the collective excitations in the longitudinal and the transverse modes in liquid cesium at its melting temperature. The pair potential used for these calculations is the model potential obtained from Ashcroft's pseudopotential with Singwi's dielectric screening procedure for liquid cesium. An independent estimation of these collective excitations is done using the Hubbard and Beeby approach. Besides, an effort is also made to calculate the phonon lifetimes in the large wave vector transfer region where the collective excitations are observable. Results of the phonon dispersion obtained from these two methods are compared and good agreement is observed.
Anharmonic Properties of IV–VI Compound Semiconductors
Authors: Singh R. K. , Gupta D. C. , Sanyal S. P. 
Published: July 2007

AbstractThe anharmonic properties of IV–VI compound semiconductors are analysed by means of a theoretical model in which the charge transfer effects, arising from the deformation of electron shells leading to three‐body interactions, are included explicitly in the crystal potential energy. The agreement between the experimental and the theoretical results on anharmonic elastic properties is reasonably good in almost all the cases under consideration. The charge transfer effects show appreciable influence on the third‐order elastic constants and the pressure derivatives of the second‐order elastic constants of IV–VI semiconductors.
Dynamical Properties of the Molecular Crystals with Electrostatic Interaction Taken into Account. Low Pressure Ice Phases (Ih and Ic)
Authors: Belosludov V. R. , Lavrentiev M. Yu. , Syskin S. A. 
Published: July 2007

AbstractWithin the atom‐atom potential approximation including electrostatic interaction of charges localized on atoms, the dynamics of the molecular crystals is considered. Formulae determining some elements of the dynamical matrix are corrected and the dynamical properties of Ih and Ic ice phases are calculated. It is shown that taking into account the long‐range Coulomb interaction has an essential influence on vibrational frequencies and gives a possibility to describe the experimental data more precisely.
Monte‐Carlo Simulation of Exoelectron Energy Spectra
Authors: Lanteri H. , Rostaing P. , Bindi R. 
Published: July 2007

AbstractA theoretical model is presented to calculate the energy distribution of exoelectrons. It is based on a Monte‐Carlo simulation method, under the assumption that electron motion is enhanced by the electric field created by surface charge. The computations are carried out in the case of MgO. The variation of the internal field with local modification of the surface charge, i.e. patch field effects, is considered. During the transport process, the electron–phonon interactions as well as the energetic and angular effects of the internal field are taken into account. The influence of the different parameters and particularly the temperature effects are shown.
The Identification of Urbach, Acceptor Impurity, and Phonon‐Assisted Components of the Optical Absorption Band Tail of n‐Type InSb
Authors: Allan G. R. , Mackenzie H. A. , Hunter J. J. , Wherrett B. S. 
Published: July 2007

AbstractNew measurements are presented of the interband absorption edge, in the range 0.01 to 100 cm−1, for uncompensated n‐type InSb obtained using a photo‐Hall technique. A spectral Urbach edge is observed in the range of sample temperature (20 to 77 K) and it is shown that the form of the experimental results derives from a broadening due to the interaction of acceptor impurity states. A phonon‐assisted component is also identified at sample temperatures above 40 K.
Modelling the Role of Electronically Excited States in Laser‐Assisted Phenomena
Authors: Wautelet M. , Gehain E. D. , Quenon P. 
Published: July 2007

AbstractFrom available relations between thermodynamical and microscopic parameters, the role of electronically excited sites on bond breaking and atomic migration is studied. It is demonstrated that, in covalent materials, electronic excitation leads to a decrease of the activation energy for bond breaking and migration, and of the entropy for migration, and to an increase of the entropy for bond breaking. It is also predicted that, under some circumstances, laser excitation might give rise to a decrease of reaction rate above a critical temperature, independent on the photon flux. The shift of the equilibrium position between competing processes is discussed, in the presence of selective excitation. The previous arguments are compared with available experimental data. Hints for future experiments are given.
A Note on the Icosahedral Morphology of Ultrafine Metal Particles
Authors: Nara S. 
Published: July 2007

AbstractA possible interpretation is proposed for the growth morphology of icosahedral ultra fine particles (UFP) of silver, the structure of which are identified as multi‐twin‐particles (MTP) consisting of twenty tetrahedrons having cubic structure accompanied by unavoidable strains or dislocations. It is shown that the stable structure of embryo has the icosahedral symmetry and the twenty triangular facets of icosahedron have the same intra‐planar symmetry with the (111) plane of the cubic close‐packed structure and they provide each a seed for the (111) epitaxial growth of the cubic crystal. It leads consequently to the occurence of the MTP‐icosahedron, near the grain boundaries of which, however, unavoidable lattice strain remains.
Calculation of Electron Velocity in Crystal ab Initio. Role of Relativistic Effects
Authors: Shilkova N. A. , Shirokovskii V. P. 
Published: July 2007

AbstractThe exact formula for the calculation of the electron velocity in the relativistic case is obtained by using the Hellman‐Feynman theorem and the perturbation theory for the matrices. The computation is performed along the symmetrical lines of 1/48th of the b.c.c. Brillouin zone for six energy bands of vanadium. A comparison with the appropriate nonrelativistic velocity values is made.
Self‐Consistent Calculations in the Theory of Mix‐Valence
Authors: Prabhu R. B. , Tangsali R. B. 
Published: July 2007

AbstractSelf‐consistent perturbation theory is employed for the calculation of physical quantities in mixed valence systems. A single impurity U → ∞ Anderson model is considered with and without crystalline field splitting. The main feature of this method is that excitonic and other correlations are included self‐consistently in the theory. In the case of crystalline or magnetic fields coupled non‐linear integral equations are obtained for conduction electron scattering amplitudes. These are solved iteratively by retaining the second order terms in the mixing term in the f‐electron Green function. Thus temperature dependent level shift and width for the f electron are obtained. Calculated are nf, the f level occupancy, the resistivity and thermopower both as functions of temperature, and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline E _{\rm f} $\end{document} the f level position relative to the Fermi level.
A Theory of Higher‐Order Correlations. II. Generalization to the Ising Model with Arbitrary Spin and to the Blume‐Capel Model
Authors: Šamaj L. 
Published: July 2007

AbstractThe method of Part I is extended to the Ising model with arbitrary spin S and to the Blume‐Capel model with uniaxial anisotropy Δ. The generalization from the case of spin \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document} is straightforward and the formalism does not require some extra complications. The values of the transition temperature for the spin 1 and spin ∞ Ising ferromagnets are to within ≈ 0.6% and ≈ 0.4% of series results, respectively. The results for the Blume‐Capel model are also in a remarkable agreement with high‐temperature series including the region, where MFA fails totally.
Time Dependence of Wave‐Mixing Processes under Pulsed Resonant Excitation in Three‐Level Systems
Authors: Hönerlage B. , Frindi M. , Miletic J. 
Published: July 2007

AbstractA theoretical analysis is given of wave‐mixing processes in three‐level systems excited by nano‐second pulses close to a two‐photon resonance. It is shown that the lifetime of the incoherent quasi‐particle population influences the time dependent generation of the coherent signal.
Applications of a Point Polarizable Ion Model to Suzuki Phase Precipitates in Alkali Halides
Authors: de Andrés A. 
Published: July 2007

AbstractLattice energy and phonon frequencies are calculated for the Suzuki phase (SP) precipitates in several materials. The dependences of the phonon frequencies versus pressure, anion relaxation, and the size of the precipitates are calculated in order to simulate the heat treatments effects on A1g and T2g, 1 modes observed by Raman spectroscopy. The observed changes seem to be due to the variation of some SP parameters and to the confinement of the phonons to an estimated size of the precipitates of about 4.5 nm.
Collective Plasmon Modes in Thin Semiconductor Films Including the Effect of the Image Charges
Authors: Aharonian K. H. , Erknapetian H. L. , Tilley D. R. 
Published: July 2007

AbstractThe dispersion of unretarded plasmons in quantized films in the presence of image charge forces is derived. It is shown that the lowest two‐dimensional plasma frequency increases strongly with decreasing film thickness and is independent of wave vector if the film dielectric constant is much larger than that of the substrate. The possibilities for experimental observation are discussed.
Binding Energies of Neutral Bound Excitons for Intermediate to High Magnetic Fields
Authors: Dujardin F. , Stébé B. , Munschy G. 
Published: July 2007

AbstractThe influence of an external constant magnetic field on the ground state energy of an exciton bound to a neutral shallow acceptor impurity is studied in the effective mass approximation using a variational non‐adiabatic method well‐adapted for intermediate to high magnetic field values. It is shown that the magnetic field enhances significantly the Coulomb interaction for any value of the electron‐to‐hole effective mass ratio. The results permit to discuss the validity of those ones previously obtained in the low and high field limits using respectively perturbation and adiabatic variational methods. They allow the estimation of the transition energy between a neutral acceptor A0 and an (A0, X)‐complex knowing the fundamental exciton transition energy in a magnetic field.
Uniaxial‐Stress Dependence of the NQR Frequency of 35Cl in Paradichlorobenzene
Authors: Zamar R. C. , Brunetti A. H. 
Published: July 2007

AbstractMeasurements of the NQR frequency (NQRF) of the 35Cl nucleus in single crystals of paradichlorobenzene are made as a function of isothermal uniaxial stress along several crystalline directions, in the range of 0 to 0.35 MPa, at a temperature of 0 °C. A linear and directional behaviour is observed. A theory is developed which includes the anharmonicity of the crystalline potential by means of the quasi‐harmonic approach. Starting from the Bayer‐Kushida theory an expression for the NQRF dependence with stress at constant temperature is deduced. Similarly, the first‐and second‐order derivatives with respect to the temperature at constant stress are obtained. In both the cases the derivatives are related with the Grüneisen parameters of the external modes and with the parameters which describe the thermodynamic state of the crystal (isothermal elastic constants and thermal expansion coefficients).
Theory of the Optical Stark Effect in Semiconductors under Ultrashort‐Pulse Excitation
Authors: Lindberg M. , Koch S. W. 
Published: July 2007

AbstractThe optical Stark effect is computed for femtosecond excitation of the electron–hole‐pair states in semiconductors. The theory is based on the effective Bloch equations for semiconductors and is evaluated for the large detuning, low intensity limit. For the example of CdS, good agreement with recent femtosecond experiments is found. It is shown that the coherent interaction of the pulses and the medium polarization dominates the semiconductor response as long as the pulse duration is of the order of, or less than, the coherence decay time of the medium.
Coherent Nonlinear Response of Excitons in Semiconductors
Authors: Balslev I. , Stahl A. 
Published: July 2007

AbstractThe nonlinear optical response of excitons in semiconductors is studied theoretically, particularly the so‐called nonresonant optical Stark effect. Results from a two‐band density matrix formalism and its reduction to a two‐level approximation are compared. It is found that the two models give similar results except at very high pumping levels. The calculated results agree well with experiments on quantum wells in (AlGa)As–GaAs.
All‐Epitaxial GaAs/AlAs Nonlinear Etalons. Towards Continuous and Parallel Operation
Authors: Kuszelewicz R. , Oudar J. L. , Azoulay R. , Michel J. C. , Brandon J. , Emile O. 
Published: July 2007

AbstractThe fabrication and optical characterization are reported of MOVPE‐grown GaAs bistable étalon with GaAs/AlAs integrated mirrors. A 4 mW threshold power and a 2:1 reflectivity contrast are observed. Quasi‐continuous operation is observed in relation with thermal dissipation improvement when the substrate is removed. Two‐dimensional arrays of individual devices are fabricated and buried with Al0.2Ga0.8As for electrical and optical confinement. A theoretical model is also described which calculates the temperature distribution by an iterative propagator method.
Cavityless Dispersive Bistability and Optical Addressing Using a Nonlinear Prism
Authors: Schülzgen A. , Henneberger F. , Rossmann H. 
Published: July 2007

AbstractA new kind of cavityless dispersive optical bistability is analysed and demonstrated on ZnSe at room temperature. Switching intensities of about 10 W/cm2 are observed. Directing of light beams by all‐optical means is also performed.
Optical Nonlinearity and Bistability in Silicon
Authors: Eichler H. J. , Brand T. , Glotz M. , Smandek B. 
Published: July 2007

AbstractThe large number of nonlinear optical effects observed in silicon is referenced. Special emphasis is given to laser‐induced absorption and refraction due to free‐carrier generation and optical heating produced by Nd: YAG‐lasers at 1.06 μm. Nonlinear silicon etalons exhibit high‐order optical bistability. Switching powers down to 1 mW are obtained with the injection of an additional photocurrent. Two‐wave mixing is discussed as an alternative switching scheme.
ps‐Laser Induced Transmission and Absorption in GaInAsP Epitaxial Layers
Authors: Rückmann I. , Kolenda J. , Henneberger F. , Petrauskas M. 
Published: July 2007

AbstractFor a possible application in optical signal processing in the infrared region the laser‐induced change of transmission and its temporal behaviour are studied (1) in 1.65 μm‐GaInAs using ps‐pulses at 1.06 μm (ħωL > Eg + Δso) and (2) – to realize a more near gap excitation – in 1.16 μm‐GaInAsP (Eg < ħωL < Eg + Δso). A strong induced transmission is found with a fast decay rate due to Auger recombination. The density dependence of the absorption coefficient including band filling and gap renormalization and thereby the transmittivity versus intensity and time are calculated and compared with the experiment. In GaInAsP an induced absorption is observed additionally due to free‐carrier intervalence band absorption.
Resonatorless Optical Bistability near the Excitonic Resonance of ZnSe
Authors: Gribkovskii V. P. , Zimin L. G. , Gaponenko S. V. , Malinovskii I. E. , Kuznetsov P. I. , Yakushcheva G. G. 
Published: July 2007

AbstractMonocrystalline MOCVD‐grown ZnSe films are found to exhibit optical bistability and pulsation regimes at nitrogen temperatures. The peculiarities of nonlinear optical response are associated with the polaritonic mechanism of light propagation.
Time‐Resolved Light‐Induced Grating Spectroscopy in Semiconductors
Authors: Lévy R. , Hönerlage B. , Grun J. B. 
Published: July 2007

AbstractDegenerate light‐induced grating spectroscopy experiments in semiconductors which are excited close to electronic resonances are discussed. Under these conditions, the finite lifetime of the quasiparticle states becomes important and governs the time dependence of the generated signal.
Transient Gratings in Metrology of Semiconductor Parameters and Optoelectronic Devices
Authors: Jarašiunas K. , Vaitkus J. 
Published: July 2007

AbstractThe origin of optical nonlinearity and its magnitude is investigated in different semiconductors and structures, as CdSe, GaAs, InSb, Si (pure, ion‐implanted, heavily doped or amorphous), MQWS. The usefulness of the transient grating technique is shown to study peculiarities of the non‐equilibrium processes in strong electric fields, at high excitation levels or to reveal the presence and transformation of defects. Some novel possibilities for the deflection of a laser beam and its modulation are demonstrated.
Thermoelectric Power of Dilute Magnetic Alloys in the Presence of CEF and Exchange Scattering
Authors: Kumar S. , Ahluwalia P. K. , Sharma K. C. 
Published: July 2007

AbstractSelf energy in third order and the thermo‐electric power, Q, of a metal containing magnetic impurities with crystal field split energy levels are calculated. The effect of exchange inelastic scattering on the thermo‐electric power is studied in the limit ω, T ≪ δ. The most dominant term in Q is found to be of the type sech2 (δ/2T) T ln T.
Internal Structure of Two‐Dimensional Domain Walls in Finite Bulk Crystals
Authors: Hartmann U. 
Published: July 2007

AbstractThe two‐dimensional structure of a 180° Bloch‐type interdomain boundary in the near‐surface region of bulk crystals of finite thickness is derived by an approximate analytic solution of the constitutive micromagnetic equations. The symmetrical equilibrium wall structure is characterized by an extensive flux closure internal to the crystal and a compressed charge distribution on the crystal surface. It is found that the magnetostatic energy term is the principal stabilizing factor that prevents a 180° Bloch wall, even in non‐magnetostrictive materials, from structural decomposition into two adjacent 90° walls.
The Selective Trapping of Arsenic Interstitial Atoms by Impurities in Gallium Arsenide
Authors: Collins J. D. , Gledhill G. A. , Murray R. , Nandhra P. S. , Newman R. C. 
Published: July 2007

AbstractCarbon doped GaAs is irradiated either with fast neutrons (1 MeV) or2 electrons (2 MeV). Complexes previously labelled C(1) are produced and the fine structure of the two LVM lines is discussed. A comparison is made with the BGaAsi complex and it is concluded that the C(1) centre is a CAsAsi defect. The defect dissociates at about 150 °C.
Vibrational Spectra of Fibonacci Chains with Defects
Authors: Böttger H. , Bradl I. , Kasner G. 
Published: July 2007

AbstractUsing different methods the effect of defects on the vibrational spectrum of Fibonacci chains is studied. Mistakes can strongly affect high‐frequency vibrational modes. Replacements of every A(B) segment by two A(B) segments extend the low‐frequency band‐like behaviour up to higher frequencies and enlarge the gaps and narrow the bands in the high‐frequency part of the spectrum.
Electron Paramagnetic Resonance Study of Copper(II) Ions in Single Crystals of Thallium Magnesium Sulphate Hexahydrate
Authors: Krishna R. M. , Rao J. L. , Chand Prem , Lakshman S. V. J. 
Published: July 2007

AbstractEPR investigations of the copper(II) ion is carried out in its paramagnetically dilute form in thallium magnesium sulphate hexahydrate (Tl2Mg(SO4)2 · 6 H2O) at 300 and 77 K at X‐band. Cu2+ ions are found to substitute for divalent cations exhibiting two symmetry related equivalent complexes. The g‐ and A‐tensors are found to be axially symmetric upto liquid nitrogen temperature (LNT) and are temperature dependent. The ground state is suggested to be mainly a d orbital. The molecular orbital coefficients are evaluated and indicate a moderate covalency of Cu2+ ion.
General Properties of Highly Excited Direct Semiconductors in the Athermal Stage
Authors: Heiner E. 
Published: July 2007

AbstractStarting from first principles and prolonging a series of three previous papers some general and global properties of highly excited direct semiconductors are considered. The evolution of the lengths of the state vectors is considered and some properties are discussed. Furthermore the evolution of the total electron production rate and of the total energy are investigated. Thereby new terms are derived which describe the energy storage due to nonlinearities in the evolution equations. Finally, some aspects of ultrashort pulse duration are considered.