bluuebunny/crossref_metadata_2025 huggingface dataset:
Photon Recycling in Double Heterostructures. III. Variational Calculations
Authors: Enders P.
Published: July 2007

The influence of photon recycling onto the minority carrier distribution in double heterostructures is investigated by means of variational calculations based on the unified formulation of the construction of variational principles by Gerjouy, Rau, and Spruch. The time‐independent variational treatment by von Roos is examinated and shown to be actually one for the effective carrier lifetime. This approach is applied to finite samples and numerical results for dependence of the influence of photon recycling upon the sample thickness are presented.
Effect of Back‐Surface Reflection on the Electroreflectance Spectra of GaAs
Authors: Behn U. , Röppischer H.
Published: July 2007

A detailed study of the influence of back‐surface reflection on electroreflectance spectra arising in an additional low‐energy peak is performed. Spectra with and without back reflection are measured on GaAs samples with various doping concentrations. First quantitative calculations on the basis of band‐to‐band related electroabsorption (Franz‐Keldysh effect) including field inhomogeneity reproduce the characteristic features and dependences of the experimental spectra. A new method for estimating the characteristic energy E0 of the exponential absorption tail of semiconductors is suggested.
Analysis of the Structural Phase Transition in Mixed Alkali Halide Crystals
Authors: Shanker J. , Sharma S. C. , Kumar M.
Published: July 2007

An analysis of structural transition in CsClKCl and CsClRbCl mixed crystals is presented by studying the lattice stability in terms of interionic potentials. The potential parameters are determined by fitting the experimental values of lattice energies in standard observed structure viz. CsCl structure for CsCl and CsBr crystals, and NaCl structure for RbCl and KCl crystals. It is found that CsClKCl mixed crystals remain stable in CsCl structure only for KCl less than 25%, and are transformed to NaCl structure when the proportion of KCl becomes equal to or more than 25%. For CsClRbCl mixed crystals, the transition from CsCl to NaCl structure is predicted when the RbCl component becomes equal to or more than 50%. These predictions are found to be in good agreement with experimental results. The lattice theory of structural stability is also applied to predict the transition temperatures for the mixed crystals viz. CsClKCl, CsClRbCl and CsClCsBr at which they transform from CsCl to NaCl structure.
Invariant Harmonic Oscillator Functions III. The Cubic Groups T and Th3)
Authors: Wöhlecke M. , Schöpp J. , Scherz U. , Jovanović A.
Published: July 2007

Two recently introduced methods, suitable to calculate symmetry adapted harmonic oscillator functions of excited states, are applied to the cubic point groups T and Th. Expressions for computational purposes and results for three‐dimensional excitation are presented.
Effect of Size Quantization on Field Emission from Ultrathin Films of Degenerate Wide‐Gap Semiconductors
Authors: Majumdar C. , Bose M. K. , Maity A. B. , Chakravarti A. N.
Published: July 2007

An attempt is made to investigate the effects of size quantization on the field emission from ultrathin films of degenerate wide‐gap semiconductors. It is found, taking n‐type GaAs as an example, that the presence of size quantization increases the field emission by several orders of magnitude as compared to that from bulk specimens of the same semiconductor. Under such quantization, the field emission may also show oscillatory behavior with decreasing film thickness, and is further found to be strongly dependent on the field strength and the carrier concentration.
X‐Ray Absorption Spectroscopic Studies of Chalcopyrite Mineral
Authors: Hemachandran K. , Chetal A. R. , Joshi G.
Published: July 2007

The X‐ray K‐absorption edge of Cu in chalcopyrite mineral is investigated using a 40 cm Cauchois‐type bent crystal X‐ray spectrograph. The study confirms the electronic configuration of chalcopyrite mineral as Cu1+Fe3+S22−. The near‐edge structures (XANES) B and C observed in the K‐absorption edge of Cu in the mineral are explained on the basis of molecular orbital theory and band structure.
Approximation of Electron Energy Bands by Cubic Splines
Authors: Neumann J. , Smrčka L.
Published: July 2007

Cubic spline functions are used to interpolate between the band energy eigenvalues evaluated on the regular cubic mesh of points in the irreducible part of the Brillouin zone (IBZ) making use of the knowledge of normal gradients of eigenenergies at the IBZ faces following from the crystal symmetry. The resulting approximate function has the full symmetry of the energy band and is represented within each cube by three‐dimensional Hermite splines which join together smoothly with continuity up to second derivative accross the cubes boundaries.
Phase Transition and Bipolaron Formation in Quasi‐One‐Dimensional Conductor β‐AgxV2O5
Authors: Onoda M. , Nagasawa H.
Published: July 2007

The electronic states of V4+ ions in β‐Ag0.40V2O5 are investigated by NMR and EPR. The structural phase transition is observed between 170 and 210 K. The 51V Knight shift results show that the spin‐singlet ground state of V4+ ion pairs is realized as bipolaron.
Flexibility Options in Valency‐Mixing Jahn‐Teller Systems
Authors: Weber C. , Wagner M. , Sigmund E.
Published: July 2007

In a previous study we have presented a novel species of a Jahn‐Teller system, which goes a good way to describe the unusual ESR behaviour in the system SmB6:Er3+. In the present study the “minimal” model is extended in the two most suggestive directions (additional states of the valency‐mixing surrounding and coupling dependence on nuclear motion). These models reduce the original ESR anisotropy of a crystal field calculation by a factor of five and come very close to the experiment.
Neutral Bound Excitons in a High Magnetic Field
Authors: Dujardin F. , Stébé B. , Munschy G.
Published: July 2007

The influence of a constant magnetic field on the energy of the ground state of an exciton bound to a neutral shallow impurity is studied in the high field limit. The Schrödinger equation is solved using the adiabatic approximation and considering the Coulomb potential as a perturbation with respect to the fundamental Landau level. The total energy is calculated by means of a combination of four Gaussian type variational wave functions. The results show that the magnetic field enhances the Coulomb interaction and allow to estimate the transition energies.
A Curved‐Wave Theory for EXAFS with Effective Scattering Amplitudes
Authors: Fritzsche V. , Rennert P.
Published: July 2007

The modified small‐scattering‐centre approximation (MSSCA) is applied to the multiple‐scattering theory of EXAFS. In the MSSCA the incoming spherical electron waves are approximated in the range of the scattering potential by an isotropic spherical wave. The scattering of these isotropic spherical waves can be described by effective scattering amplitudes, which are easy to evaluate. This method is a much better description than the plane‐wave approximation routinely used in EXAFS analysis. In comparison with the plane‐wave approximation the effort is some what increased by the distance dependence of the effective scattering amplitudes. The strength of the MSSCA is that it yields simple expressions for the multiple‐scattering contributions, which improve the accuracy especially for scattering pathways involving forward scattering events considerably.
On the Inconsistencies of Axially Symmetric Force Models for Noncubic Solids
Authors: Ramamurthy V.
Published: July 2007

The origin of the elastic inconsistency of a modified axially symmetric force model, proposed by Lehman, Wolfram, and De Wames, for noncubic solids and the circumstances under which its phonon frequencies become imaginary are analysed by making use of this model in the lattice dynamical study of face centred tetragonal indium. It is shown that the arbitrary differences in the tangential force constants along x and z directions destroy the compatibility between off‐diagonal and diagonal matrix elements, relatively stronger off‐diagonal elements give rise to imaginary frequencies at certain wave vectors along nonsymmetry directions while the failure of this model to comply with the rotational invariance conditions manifests itself as the elastic inconsistency. The distortions introduced by the deficiencies of this model into the phonon dispersion curves of f.c.t. indium, consequences of imposing additional invariance conditions on this model as well as its apparent equivalence with central and general tensor force models, are discussed.
Quantum Tunneling at First‐Order Phase Transitions in a Uniaxial Antiferromagnet with External Magnetic Field
Authors: Klamut J. , Prystasz W.
Published: July 2007

The formation of a new phase at or close to absolute zero cannot be due to thermal fluctuations and must be ascribed to a quantum mechanism. This means that the formation of the new phase can be reduced to tunneling movement of the system under the energy barrier separating the initial metastable state and the stable one. The probabilities of the transitions between the antiferromagnetic (AF) and ferromagnetic (F) states are obtained for the uniaxial two‐sublattice antiferromagnet by using quasiclassical approxamation (WKB fomalism).
Structural Stability and Phonon Dispersion of Arsenic
Authors: Shimamura S. , Shindo K. , Morita A.
Published: July 2007

The stability of the A7 crystal structure of As is studied using the third‐order pseudopotential expansion method. On the basis of model potentials fitted to the atomic energy levels in As4+, phonon frequencies of As in the A7 structure are calculated. It is shown that s–p hybridization plays a predominant role in stabilizing the A7 structure to the internal strain. An analysis of phonon dispersion curves of As in terms of the present method and additive short‐range force constants suggests that there are considerably strong covalent forces between neighboring atoms in As.
Chemical Processes on Semiconductor Electrode Interfaces and Distribution of Charge Transfer on the Orbital Energy Scale
Authors: Lorenz W. , Katterle T.
Published: July 2007

After a look at the significance of total‐to‐orbital‐energy relations and of the tight‐binding scheme (in the sense of an independent‐particle model) for treating systems with a band gap, the orbital energy distribution of many‐electron partial charge transfer in chemical bond formation processes on semiconductor surfaces is discussed. Difference densities of states are evaluated for chemi‐sorption of water or its dissociation products, as well as for their displacement by an electrochemical model reactant (halide) on GaAs(111) surfaces.
Interaction of Semiconductors with a Strong Resonance Electromagnetic Field
Authors: Kruglov V. I.
Published: July 2007

A procedure is developed of constructing an effective Hamiltonian, which makes it possible to reduce the nonstationary problem of interaction between a semiconductor and a strong resonance electromagnetic field to a corresponding problem of equilibrium statistical mechanics. Criteria are obtained when the proposed approach is valid. A corresponding effective Hamiltonian has been found taking into account the electron and hole acceleration by the field as well as different relaxation processes, which permits the investigation of both, the energy spectrum of a semiconductor in a strong field and its thermodynamical properties.
Nonadiabatic Electron–Phonon Interaction. Matrix Continued Fraction Treatments and Reduction of High‐Dimensional Problems
Authors: Scheuing A. , Reineker P. , Durst C. , Sigmund E.
Published: July 2007

An electronic two‐level system interacting with two different vibrational modes via displacive and transitive couplings is investigated. The eigensolutions are determined using a matrix continued fraction method including infinite matrices. The approximations used in the numerical evaluation are discussed. As another example for the applicability of the continued fraction method it is shown that the E–e‐Jahn‐Teller Hamiltonian proves to be a specialized case, whose eigenvalue problem may be solved using ordinary continued fractions. Finally, the eigenvalue problem of the extended Hubbard Hamiltonian of a dimer with linear local electron–phonon coupling is reduced to the evaluation of a matrix continued fraction with three‐dimensional matrices.
Quasi‐Resonance in Hydrostatically Compressed Isotopic Mixed Crystals of Deuteronaphthalene
Authors: Gaidai S. I. , Meletov K. P. , Shchanov M. F.
Published: July 2007

Spectra of absorption and luminescence of two isotopic mixed crystals (IMC) of deuteronaphthalene for the 0.1% C10H8 guest in C10D8 host and for the 0.1% C10H8 guest in C10H2D6 host are measured in the range of the lowest singlet exciton transition at T = 4.2 under hydrostatic pressure up to 2 GPa. The dependence of the binding energy E and of the localization amplitude |a0|2 of the exciton on the impurity is determined in a wide range of values, involving the cross region. The dependences are verified quantitatively by the Rashba theory of quasiresonance.
Effect of Orbit–Lattice Interaction on Mössbauer Quadrupole Splitting of Iron(II) in Fe(p‐CH3C6H4SO3)2
Authors: Sinha T. P. , Choudhary S. N. , Srivastava K. K. P.
Published: July 2007

The effect of vibronic coupling between low lying electronic states on the temperature dependence of the Mössbauer quadrupole splitting of Fe(II) in Fe(p‐CH3C6H4SO3)2 is theoretically analysed over 9 to 291 K. This results in a better agreement between theoretical and experimental data than hitherto obtained from the static crystal field scheme. It shows that the orbit–lattice interaction is important for ferrous ions and its effect should be duely included in the interpretation of Mössbauer observables as a function of temperature.
Two‐Particle Monte‐Carlo Method for Warm Electrons in a High‐Frequency Electric Field
Authors: Kancleris Ž. , Matulis A.
Published: July 2007

A two‐particle Monte‐Carlo method for the numerical simulation of the nonhomogeneous kinetic equations useful for the treatment of warm electron properties in the case of ac fields is given. The method is based on the solution of the Green function equation by the Monte‐Carlo technique. The electric field time dependence is taken into account by the simulation of the motion of particles with variable weights. Making use of the proposed method the frequency dependence of the non‐linearity coefficient for p‐Ge is calculated.
Random Motion Studied by Time Delayed Mössbauer Spectroscopy
Authors: Vapirev E. I. , Bourin K. I. , Christoskov I. D. , Tsankov L. T. , Kamenov P. S.
Published: July 2007

The time dependence of resonantly filtered radiation is studied in the case of source or absorber nuclei moving randomly. Experiments are performed for liquid absorber and the results are compared with theory.
4f Optical Absorption Model in Rare‐Earth Semiconducting Compounds
Authors: Parlebas J. C. , Chetouane K. , Hugel J.
Published: July 2007

The effect is explored of a local attractive 4f hole potential Ufd on the contribution to the optical absorption from electronic 4f → 5d transitions in SmS‐type compounds. After formulating the problem of the imaginary part of the dielectric function in a general manner, a simple numerical study of a two band model is presented to illustrate the essential Ufd effect and to make some qualitative contact with available data on the metallic and semiconducting phases of SmS.
First Principles Prediction of Static Structural Properties of Aluminum from Pressures and Total Energies
Authors: Rodríguez C. O. , Cappannini O. M. , y Blancá E. L. Peltzer , Casali R. A.
Published: July 2007

Ground state structural properties (equilibrium lattice constant, bulk modulus and its pressure derivative) of aluminum are obtained using an ab‐initio selfconsistent calculation of pressures and total energies. First principles non‐local pseudopotentials and Wigner's interpolation formula for exchange and correlation are used within the local density functional formalism. Values obtained are in good agreement (errors less than 6%) with experimental ones. These results are obtained for the first time for Al from a direct first principles pseudopotential calculation of pressure–volume relation. A comparison is made with results from alternative schemes.
X‐Ray Induced Relaxation Band Due to Higher Aggregates in KCl:Pb
Authors: Mukherjee M. L. , Capelletti R.
Published: July 2007

Although aggregation of impurity centres in doped alkali halides upon X‐irradiation is proposed earlier, direct evidence of such centres having dipole moment is reported here for the first time by the method of ionic thermocurrents (ITC). The norma Idipolar relaxation band in KCl: Pb is located around 224 K, while sometimes a small band at about 160 K is found in the ITC spectrum of heavily doped systems. Exposure to X‐rays increases this band around 160 K at the cost of the 224 K dipolar band. Optical absorption in the A‐band of KCl:Pb, along with ITC measurements indicates that higher aggregates of I–V dipoles are easily formed in heavily doped systems. Formation and growth of the 160 K ITC band upon X‐ray irradiation are explained from the fact that the effect of X‐irradiation is to increase the rate of aggregation of I–V dipoles, through temporary electron trapping by lead ions.
EPR and Optical Absorption of Cr3+ in CsCl and CsBr
Authors: Elbers G. , Remme S. , Lehmann G.
Published: July 2007

EPR spectra of Cr3+ in CsCl and CsBr single crystals grown from aqueous solutions are studied at 293 and 20 K. In both cases two tetragonal centers with zero‐field splittings in ratios near 2:1 and several centers of orthorhombic and monoclinic site symmetries, respectively, are found. Their relative concentrations vary with growth conditions in CsCl. The structures of these centers can be understood assuming incorporation on interstitial sites similar to those for divalent transition‐metal ions. Application of the superposition model suggests coordination by mixed ligands, the tetragonal centers most likely are [CrX4/2H2OY] complexes with X = Cl or Br and Y = H2O or OH− and Cl− or Br−, respectively. Analysis of the optical absorption spectra also supports these models.
Lattice Dynamics of Al and Pb
Authors: Thakur V. K. , Singh T. N.
Published: July 2007

The experimentally observed dispersion curve, specific heat, and Debye characteristic temperatures of the complex polyvalent aluminium and lead are reproduced using the phenomenological model developed earlier for the study of lattice dynamics of f.c.c. noble and transition metals. The model is employed to calculate the compressibilities of Al and Pb. The agreement between calculated and experimental results is satisfactory.
On the Dynamical Scaling Behaviour in Nucleation and Growth Kinetics
Authors: Lorenz B.
Published: July 2007

A one‐dimensional model for nucleation and growth is investigated with respect to the validity of scaling relations for spatial correlation functions. On the basis of the rigorous solution for the grain‐size and cluster‐size distribution functions the corresponding autocorrelation functions for grains and clusters are calculated. Scaling relations are detected only in the late time behaviour of the cluster autocorrelation function.
On the Luminescence at the Surface and in the Surface Space Charge Region
Authors: Vakulenko A. V. , Vardanyan R. A. , Hovakimyan L. B.
Published: July 2007

The radiative transitions of excess electrons to the levels, associated with the semiconductor surface states and deep impurity states in the surface space charge region are investigated. Expressions for the corresponding cross‐sections of the spontaneous light emission are obtained. It is shown, that the luminescence spectral lines, corresponding to the surface and impurity states, can be identified by their polarization dependences.
Electronic Structure of Disordered Alloys. Effect of Off‐Diagonal Disorder
Authors: Dahmani L. , Brezini A. , Sebbani M. , Deppolier C.
Published: July 2007

A method is presented for calculating the density of electronic states on a Bethe lattice. A random binary alloy A1−cBc is considered. Extensive results are presented and compared with other theories. In particular off‐diagonal disorder is taken into account.
Binding Energy of Excitons in a Polar Crystal Slab
Authors: Gu Shi‐Wei , Shen Meng‐Yan
Published: July 2007

Based on previous results, we calculate the ground state energy, the first excited state energy, and the binding energy of an exciton in a polar crystal slab. We find that the polaron effect increases the binding energy of the slab exciton, but decreases the energy difference between the first excited state energy and the ground state energy.
Mobility Edges for Interacting Electrons Based on Hubbard's Alloy Analogy
Authors: Kolley E. , Kolley W.
Published: July 2007

With respect to localization the interacting electron system in disordered alloys AcB1−c is studied within the random Hubbard model by means of the alloy analogy approximation. The dc conductivity affected by localization is calculated, at T = 0 and d = 3, in the framework of a four (two genuine, two fictitious)‐component CPA (coherent potential approximation). Extensive numerical results are presented for an open mobility‐edge trajectory, conductivities, and a phase diagram on the disorder‐interaction plane, typifying the discrete probability distribution. Significant differences to results of other approaches based upon continuous, rectangular or Gaussian randomness are pointed out.
Spin–Orbit and Crystal‐Field Matrices of d4,6 Configuration and Application to RbFeCl3
Authors: Wei‐Li Shuen , Min‐Guang Zhao
Published: July 2007

The spin–orbit and crystal‐field matrices of d4,6 configuration with C3v symmetry are derived based on the weak‐field scheme. Utilizing these matrices obtained and the approximate SCF d‐orbit of Fe2+ proposed by Zhao, the zero‐field splitting, optical absorption bands, and the Zeeman dependences are calculated for RbFeCl3. The calculation results agree well with experimental findings.
The Temperature Dependence of the Resistivity of Liquid Copper
Authors: Chaïb C. , Gasser J. G.
Published: July 2007

The high melting point of copper (1083 °C) explains why the resistivity of the pure liquid is not well known. Important differences exist between the scarce old data. In this paper new accurate measurements are presented and the temperature dependence of the resistivity is discussed in the framework of Ziman's formalism in terms of structure factor and form factor. Both, experimental (obtained by neutron scattering experiments) and calculated (following a hard sphere description) structure factors are used. The form factor is deduced from model pseudo‐potentials which take into account the d band like the Moriarty (1972) potential or from the t matrix expressed in terms of phase shifts. The different calculations lead to a fairly good agreement.
Magnetovolume Effects in MnAs. Role of Space Spin Correlations
Authors: Gribanov I. F. , Zavadskii E. A.
Published: July 2007

The results of experimental separation of the various contributions to the MnAs volume magnetostriction in a wide range of temperatures are presented. This separation is made by determination of different magnetovolume constants from forced volume magnetostriction and susceptibility measurements using a phenomenological theory, in which both itinerant electron and local moment characters are taken into account. It is shown that the main contribution to the spontaneous magnetovolume effect in the ferromagnetic region and to the discontinuous volume change at the Curie temperature is the exchange striction. The band contribution connected with the change of the local moment magnitude in these cases is small. It is obtained that there are strong spin‐spin correlations near and above the Curie point, so the molecular field approximation often used for the description of the MnAs magnetic behavior is inadequate in this temperature region. The results obtained are used to estimate the temperature variation of the local magnetic moment magnitude in MnAs.
Magnetic Field‐Induced Transitions in the Mo4 Cluster Compounds GaMo4S8 and GaMo4Se8 Showing Heavy Fermion Behaviour
Authors: Rastogi A. K. , Wohlfarth E. P.
Published: July 2007

The magnetization versus field curves of GaMo4X8 (X = S, Se) show magnetic field induced transitions at 5 and 1 kOe at 4.2 K, respectively. The critical fields at different temperatures are obtained from differential susceptibility measurements. Field cooled specimens are also investigated. A provisional magnetic phase diagram is constructred. The transition is ascribed to crystal anisotropy effects.
Aggregation Kinetics of Divalent Impurity–Vacancy Dipoles in Alkali‐Halide Matrix. I. Theoretical Approach
Authors: Poźzniak J. , Berg G. , Galbatar T.
Published: July 2007

Approximate solutions of the equations describing the kinetics of reversible agregation reactions of the divalent‐impurity–vacancy dipoles in alkali halide crystals are obtained in which the dimers and trimers are assumed to be the only aggregation products. Using the solutions obtained a method is elaborated permitting to calculate the rate constants of individual reactions on the basis of the knowledge of the time evolution of the dipole concentration.
Volume of Mixing in Binary Liquid Alloys
Authors: Khanna K. N. , Pal C. , Singh P.
Published: July 2007

The thermodynamic properties of liquid metal alloys are computed using the hard sphere mixture theory. It is shown that the volume of mixing plays an important role in describing the thermodynamic properties of binary alloys. The temperature dependence of the volume of mixing is also briefly discussed.
Pressure Effect on the Melting Point of Noble Metals
Authors: Soma T. , Suzuki S. , Kagaya H.‐Matsuo
Published: July 2007

The temperature dependence of the mean‐square displacement for noble metals is quantitatively calculated by using the treatment for the lattice dynamics by Kulshreshta et al. The Debye temperature at higher and lower temperatures is also estimated using Debye's model. Then, using the volume dependence of the mean‐square displacement the pressure effect on the melting point of Ag and Au is studied by Lindeman's melting law, and the melting curve obtained increases as function of the compressed volume.
Recursion Method for the Density of States of Bond‐Diluted Central‐Force Elastic Triangular Lattices
Authors: Böttger H. , Freyberg A. , Wegener D.
Published: July 2007

The vibrational density of states of two‐dimensional bond‐diluted triangular lattices with nearest‐neighbour central forces is calculated with the aid of the recursion method by means of termination of the continued fraction by a constant parameter and by embedding the system into an effective medium. Unlike the effective‐medium theory, the recursion method provides a rather peaky structure of the density of states, especially for systems near the rigidity threshold.
On Field Emission from Ultrathin Films of Semiconductors with Effects of Image Forces
Authors: Bose M. K. , Majumdar C. , Maity A. B. , Chakravarti A. N.
Published: July 2007

An attempt is made to investigate the effects of size quantization on field emission from ultrathin films of degenerate wide‐gap semiconductors, taking the image force into consideration. It is noted, taking n‐type GaAs as an example, that size quantization enhances the field emission by several orders of magnitude as compared to that of bulk specimens. Such quantization also leads to oscillatory behavior of the emission with changing film thickness and to a significant dependence of the emission on field strength and carrier concentration.
An Improved Virtual Mode Theory of ATR Experiments on Surface Polaritons. Application to Long‐Range Surface Plasmon‐Polaritons in Asymmetric Layer Structures
Authors: Wendler L. , Haupt R.
Published: July 2007

The damping properties of surface polaritons, especially long‐range surface plasmon‐polaritons (LRSP) in asymmetric layer structures are analyzed taking into account the presence of a coupling prism. Both, the response treatment to calculate attenuated‐total‐reflection (ATR) spectra and the virtual mode treatment are used. Two different types of virtual modes are analyzed. One of them describes the propagation properties of the surface polariton in the presence of both intrinsic and radiative damping. The other type describes a surface polariton with a driving field and hence this mode allows to find out the optimum conditions for the ATR experiment. These two modes are investigated in detail and the results of the numerical calculation are presented in graphical form. The results for the ATR configuration show that in asymmetric embedded silver layers the propagation length exceeds the value for the symmetric embedded one significantly.
Calculated Electronic Structures and Chemical Bonding in Sc and Y Carbides
Authors: Zhukov V. P. , Gubanov V. A. , Jepsen O. , Christensen N. E. , Andersen O. K.
Published: July 2007

The energy band structures of ScCx and YCx for x = 1.0, 0.75, and 0.5 are calculated self‐consistently by the LMTO method. From the total energies, the theoretical values of the lattice constants and the energies of vacancy formation are determined. It is shown that in YCx for x > 0.7 the metalloid vacancies are stabilized energetically and it is suggested that vacancies in YCx for x < 0.7 and in ScCx for all x are formed when the compounds are synthesized at high temperature and they persist at low temperatures as a result of quenching. Furthermore the changes in the energy band structures are studied and cohesive properties of these compounds when carbon is substituted by oxygen or nitrogen.
Effects of Spin Fluctuations on the Magnetism of (Fe1−xCox)Si
Authors: Inoue J. , Hattori T. , Shimizu M.
Published: July 2007

Curie temperature and temperature dependence of the spin susceptibility for (Fe1−xCox)Si are calculated by taking into account the effect of spin fluctuations in the Gaussian approximation. Saturation magnetization and the low‐temperature specific heat coefficients are calculated making use of the rigid band approximation. Qualitative agreement between the theoretical and experimental results is obtained.
The Role of Gadolinium in the Magnetocrystalline Anisotropy of (Y1−xGdx)2Co17 Pseudobinaries
Authors: Kąkol Z. , Figiel H. , Apusta Cz.
Published: July 2007

Magnetic measurements of (Y1−xGdx)2Co17 oriented powder samples versus temperature in the 78 to 300 K range are made, and the K1 and K2 values are calculated. To explain the differences of the anisotropy energy of Y2Co17 and Gd2Co17 compounds, the dipolar interactions of Gd moments are analysed. The values of the anisotropy energy calculated from dipolar interactions are in very good agreement with experimental values.
Lattice Parameters, Energy Gaps, and Magnetic Properties of the CdxHgyMnzTe Alloy System
Authors: Manhas S. , Khulbe K. C. , Beckett D. J. S. , Lamarche G. , Woolley J. C.
Published: July 2007

Polycrystalline samples of CdxHgyMnzTe alloys (x + y + z = 1) are prepared by the standard melt and anneal technique. Debye‐Scherrer powder X‐ray photographs are used to determine equilibrium conditions in the alloys, to delineate the range of single phase solid solution and to determine values of zinc blende lattice parameter a. It is found that in the zinc blende field the variation of a with composition can be written as a = (0.6481 – 0.0019y – 0.0144z) nm. Optical absorption measurements are made to give room temperature values of energy gap Eg for the single phase alloys and it is found that to a good approximation the composition variation of Eg is given by Eg = (1.46 – 1.62y + 1.33z) eV. Measurements of magnetic susceptibility in the temperature range 4 to 250 K are made to give values of Tg, the spin‐glass transition temperature, and θ, the Curie‐Weiss temperature. Analysis of these data shows that for samples with Eg > 1.5 eV, the results are well explained by the superexchange mechanism previously used in the analysis of the CdxHgyMnzTe etc. results, but that for the cases with Eg ≦ 1.5 eV a Bloembergen‐Rowland type of interaction needs to be included in order to explain the experimental values of Tg and θ.
Correlation between the 1.1 and 1.45 eV Emission Bands and the F+ Optical Absorption Bands in ZnS Crystals
Authors: Matsuura K. , Kishida S. , Fukata Y. , Tsurumi I.
Published: July 2007

Zinc sulfide crystals are fired successively in a Zn liquid at 1184 °C and annealed isochronally. The emission spectra between 700 and 1200 nm and the optical absorption bands ascribed to F+ centres are measured in the specimens. The Zn treatments introduce emission bands with peaks at 1.1 and 1.45 eV, which are reported by other workers. These bands are annealed in company with F+ centers. Therefore it is proposed that these emission bands are due to F+ centers.
Polariton Theory of Infrared Absorption Edges in SiO2, GeO2, and GeO2‐Doped SiO2 Glasses
Authors: Sun Hong , Fang Junxin
Published: July 2007

The infrared absorption edges of SiO2 and GeO2 glasses are calculated using a polariton theory. The glasses are modeled by sets of non‐interacting anharmonic oscillators with vibration frequencies equal to those of the asymmetric stretching motions of T–O–T (T  Si, Ge) bonds. The structural disorders of the glasses are considered by introducing distributions of the vibration freéuencies. The polariton effect as well as the contributions from other vibration modes in the glasses to the infrared absorption edges are studied. Furthermore, by a “mixed crystal” model, mixed up by three different oscillators corresponding to the asymmetric stretching motions of SiOSi, GeOGe, and SiOGe bonds, respectively, the infrared absorption edges in GeO2‐doped SiO2 glasses are calculated using the virtual crystal and superposition approximations to examine which one is closer to the experiments.
Alternative Quasi‐Classical Transport Equations. II. Boltzmann's Equation and the Electron Distribution Function for MIS Systems
Authors: Schnittler Ch. , Scherf S.
Published: July 2007

In Part I of this paper a new quasi‐classical formulation of transport equations in the framework of the local‐density approximation is reported including wave function effects due to the potential barrier near an interface. For practical applications to semiconductor devices the non‐equilibrium distribution function of the charge carriers is to be determined. In Part II this problem will be solved for a MIS field effect transistor as a typical example. For this system Boltzmann's equation is formulated and solved in a more general manner than before. The scattering processes in the bulk are considered together with partly diffuse interface scattering which is introduced by means of special boundary conditions. The transport properties of the MIS field effect transistor will be calculated later in Part III of this paper.
Aggregation Processes in the NaCl:Eu2+, Mn2+ System and Energy Transfer Mechanisms
Authors: Cywiński R. , Fava R. , Manfredi M. , Mugeński E.
Published: July 2007

Energy transfer processes are studied in NaCl:Eu2+, Mn2+ samples, along the annealing treatments that are performed at RT and at 100 °C; the Eu ions and/or Eu aggregates act as donors and Mn ions and/or Mn aggregates act as acceptors. For the samples annealed at RT, a single pair transfer mechanism is evidenced at the early annealing stages, while at late annealing stages a fast energy migration in the donor system followed by a phonon assisted transfer is observed. For the annealing at 100 °C at late aggregation stages the most probable transfer process seems to be connected to a slow energy diffusion in the donor system followed by the transfer to the acceptors. The Mn2+ emission band, that is detectable as a consequence of the EuMn transfer shows a complex behaviour.
Kinetic Theory of the Hydrogen Diffusion in Metals
Authors: Fujita S.
Published: July 2007

The diffusion coefficient D for hydrogen in a metal normally obeys the Arrhenius law: D = D0 exp (– Ea/kBT), where Ea is the activation energy, which represents the barrier potential for the most favorable interstitial channel. The pre‐exponential factor D0 can be related to the mean straight path l in the crystal by Do = (1/3) gvl, where v is the average migration speed and g a statistical weight of order one. The mean straight path l for a pure crystal can be very long, since the migrating atoms cannot readily be scattered or stopped by the (phonon) motion of the regular lattice. This physical picture, reasonable but not widely recognized, is supported by experimental evidence and theoretical considerations. In particular, the distinct isotope effects for hydrogen diffusion in f.c.c. and b.c.c. metals are explained in terms of quantum mechanical zero‐point energies associated with the crystal channel potentials. A few experimental tests for the theory are suggested.
Influence of Many‐Body Effects on the Cyclotron Resonance Mass of Two‐Dimensional Polarons with Application to GaAsAl1−xGaxAs Heterostructures
Authors: Wu Xiaoguang , Peeters F. M. , Devreese J. T.
Published: July 2007

The influence of many‐body effects on the cyclotron resonance mass of two‐dimensional polarons is investigated. Firstly, the occupation effect is considered, which arises from the Fermi‐Dirac statistics. In the calculation the Landau levels are considered to be perfectly sharp. It is found that (1) the occupation effect reduces the polaron effect, i.e. the cyclotron resonance mass renormalization due to the polaron effect is reduced over the whole magnetic field region, (2) for a fixed electron density the cyclotron resonance mass shows an oscillating behaviour as a function of the magnetic field. The polaron cyclotron resonance mass attains minimal values when the filling factor passes through integer values. Secondly, the effect of static screening on the polaron cyclotron resonance mass is examined. The electron screening is found to reduce further the cyclotron resonance mass renormalization. The effect of the finite width of the two‐dimensional electron layer is included into the present calculations by considering the lowest subband. After taking into account the nonparabolicity of the electron energy band, the calculated cyclotron resonance mass is compared to the recent experimental data for GaAsAl1−xGaxAs heterostructures. Good agreement is found in the high magnetic field region, i.e. for magnetic fields H > 12 T.
A Tight‐Binding Description of Isovalent Impurity Clusters. Application to Te Impurities in II‐VI Compound Semiconductors
Authors: Hanke M. , Hennig D. , Kaschte A.
Published: July 2007

For centres of several Te substitutionals in nearest‐neighbour anion position in the host crystals ZnS, ZnSe, CdS, and CdSe a tight‐binding description is given. The matrix of the Hamiltonian in the sp3‐representation includes all interactions up to the second‐nearest neighbours and is based upon a charge self‐consistent parametrization. All Te centres suitable in a tetrahedrally coordinated five‐atom cluster are considered. Using the Koster‐Slater scattering theory the off‐diagonal matrix elements of the impurity potential have to be included. Thereby the results of the calculation are in a good agreement with experimental data for the energy levels of complex Te impurities in II‐VI semiconductors.
Tunnelling in k‐Space. The Case of Time‐Varying Electric Field
Authors: Dargys A.
Published: July 2007

Intervalence transitions between light and heavy mass subbands due to strong time‐varying electric fields are analyzed within the effective mass framework in two limiting cases, when the spin‐orbit interaction is weak and strong. Explicit formulae for the resonance lineshape, lineshift, and frequency of quantum mechanical Rabi oscillations are presented for one‐ and two‐photon absorption. The relationship between the detuning and the amplitude of Rabi oscillations is found to have exactly the same form, as in two‐level atomic systems. In case of p‐type germanium the Rabi oscillation period becomes comparable to the optical phonon scattering time at an intensity of the CO2‐laser of 5 MW/cm2. The conditions for the observation of Rabi oscillations are especially favourable at small energies of light quanta, when optical phonon emission due to energy conservation is forbidden. By this reason in p‐type semiconductors at strong time‐varying electric fields the non‐linear quantum effects similar to those found in two‐level atomic systems e.g. photon echos, self‐induced transparency etc., are expected to be observable as well.
Soliton Mechanism of Superconductivity in Organic Quasi‐One‐Dimensional Crystals
Authors: Brizhik L. S. , Davydov A. S.
Published: July 2007

The soliton model is used to develop a hypothesis on superconductivity in organic quasi‐onedimensional crystals formed by stacks of plane molecules. The pairing of solitons and the dynamics of motion of many solitons are investigated.
On Continuum Mechanics and Special Relativity
Authors: Günther H.
Published: July 2007

It is shown that the quasi elastic model of Maxwell's equations according to MacCullagh‐Sommerfeld can be defined by a non‐covariant gauge for the four potential Aμ. The quasi elastic displacement vector s then is described by the vector potential A. Lorentz invariance of the mechanical model depends on the gauge invariance of the physically measurable quantities. A theoretical relation to relativistic kink equation can be seen.
Metallic Glasses and Chiral Nematic Liquid Crystals
Authors: Trebin H.‐R. , Longa L. , Salzgeber B.
Published: July 2007

Geometrical frustration exists in both metallic glasses and chiral nematic liquid crystals. Applying results from the Landau‐Ginzburg theory of liquid crystals and from polytope models for the amorphous state, a frustrated free‐energy density for metallic glasses is derived. It is expressed in terms of an order parameter that characterizes the bond orientation of neighbouring atoms.
Computational Anisotropic Elasticity
Authors: Condat M. , Kirchner H. O. K.
Published: July 2007

Various methods for computing the fundamental 6 × 6 matrix of anisotropic elasticity are compared. A new method based on Sylvester's formula is proposed.
On Electron Correlations of σ and π Bonding in Tetravalent Clusters and Solids
Authors: Friedel J.
Published: July 2007

In the most simple possible terms it is stressed why electrons are more weakly correlated in π than in π bonding, and what qualitative effects this remark helps to explain.
A Comparison of Electronic Properties of Clusters and Bulk of Copper and Palladium. Bandwidth, Density of States, Deformation Density
Authors: Fritsche H.‐G.
Published: July 2007

F.c.c. clusters Cu14 and Pd14 are investigated by use of the scattered‐wave‐Xα method. Electronic properties of valence electrons (bandwidth, density of states, deformation density) are compared with that ones of the bulk in order to study their dependence on the periodicity of lattice.
On the Theory of Photoemission from Adsorbate‐Induced Surface States
Authors: Beckmann A.
Published: July 2007

On the basis of a tight‐binding model, the photoemission from adsorbate‐covered transition metal surfaces is investigated. The photoemission current from the bulk states and the adsorbate‐induced surface states is deduced from both poles of the excitation function. The conditions for the existence of surface states for a given overlayer structure are given and compared with the case of a 1 × 1 structure. The connection between the peak widths and the various lifetimes is elucidated.
Diffusion Mechanism in F.C.C. Metals
Authors: Mundy J. N.
Published: July 2007

Curvature in the Arrhenius plot of self‐diffusion in metals is commonly interpreted as resulting from a monovacancy jump process at low temperatures with an increasing contribution from a divacancy jump process at higher temperatures. Recently it has been suggested that the Arrhenius curvature in b.c.c. metals could be attributed to monovacancies with temperature‐dependent activation enthalpies. The grounds why the same model could not be applied to f.c.c. metals are examined with particular emphasis on the diffusion and defect properties of aluminum.
Stress Induced Anisotropic Diffusion of Intrinsic Point Defects towards Dislocations in H.C.P. Crystals
Authors: y‐De Grande N. Smetniansk , Savino E. J. , Tomé C. N.
Published: July 2007

The diffusion equations for vacancies and interstitials in the field of straight edge dislocations are numerically solved for a crystal under irradiation and uniaxially stress. The main dislocation systems in hexagonal closed packed metals are considered. The diffusion model takes into account the full lattice and defect symmetry in the equilibrium and migration configurations. A diffusivity tensor for strained h.c.p. metals is deduced, which depends linearly on the strain field. This tensor allows to solve analytically the steady state defect flux towards a hollow cylinder in a homogeneously strained crystal. The resulting vacancy and interstitial absorption (sink strength) are calculated and compared with the ones obtained numerically when the dislocation field is taken into account. It is shown that both approaches result in a similar dependence of the sink strengths on the homogeneous strain as far as a correct capture radius is adopted for the hollow cylinder. The dependence of the results on the boundary conditions and the defect symmetry considered is discussed. For the numerical calculations defect symmetries consistent with those calculated for magnesium are used.
Investigation of the Resonant Vibration Modes of Radiation Induced Interstitial Atoms in Aluminum by Diffuse Inelastic Neutron Scattering
Authors: Urban R. , Ehrhart P. , Schilling W. , Schober H. R. , Lauter H.
Published: July 2007

Diffuse inelastic neutron scattering measurements are reported which are used, for the first time, to study the dynamics of radiation‐induced self interstitial atoms. Large single crystalline aluminum samples are electron‐irradiated in a specially built facility at T ≦ 20 K to defect concentrations of up to 500 at ppm and subsequently transported in the cold state to the high flux reactor at Grenoble. The measurements are done at T = 6 K on the triple axis spectrometer IN3 and are repeated after annealing at T = 46 K (above stage I) and at T ≈ 300 K (after complete recovery). The irradiated samples show a significant increase of the inelastic scattering intensity at transferred energies between 0.7 and 2 THz. By comparison with the results of computer calculations the different frequencies of the energy loss spectrum can be attributed to the different vibration modes of interstitial atoms. The frequencies of the most significant modes of the self interstitial atom are determined to be ν = 0.75 THz and ν = 1.35 THz for the translation‐(A2u)‐and libration‐(Eg)‐mode, respectively.
H2 Dissociation in Nickel. A Cluster Model
Authors: Vargas P. , Kronmüller H. , Böhm M. C.
Published: July 2007

A cluster formed by 38 Ni atoms and two H atoms is studied by a semiempirical Hartree‐Fock (HF) self‐consistent‐field (SCF) variant based on the INDO (intermediate neglect of differential overlap) approximation. The energy of the system is analyzed as a function of the spatial localization of the two H atoms. The energy minimum in the considered part of the singlet‐type potential surface corresponds to a spatial arrangement where the H atoms occupy nearest‐neighbor octahedral sites in the f.c.c. Ni‐lattice (d(HH) = 0.249 nm). This configuration is ≈ 1 eV below another local minimum which is associated to a “H2” molecule (d(HH) = 0.085 nm) in the host system. The H atoms in the Ni‐lattice can be characterized as overscreened protons.
Muon‐Spin Resonance in Metals. RF‐Field Penetration, Diffusion, and Trapping Effects
Authors: Brandt E. H. , Messer R.
Published: July 2007

The longitudinal spin polarization in a μ+‐spin‐resonance experiment is calculated for positive muons diffusing to traps in a metal foil of finite thickness. General expressions are given for the shape of the resonance lines of freely moving and of trapped muons as a function of foil thickness, rf amplitude, trapping probability, and of the local magnetic fields and relaxation rates Γ1, Γ2 of the free and trapped muons.