bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Plastic Deformation upon Optical Absorption of KCl:Eu2+ Crystals
Authors: Czapelski M. , Suszyńska M.
Published: July 2007

The effect is studied of plastic deformation (by uniaxial compression) on the optical absorption spectrum of europium doped KCl crystals. The main effect of the stress applied is to decrease the value of the absorption coefficient characteristic of the high energy absorption band. The stress induced effect is quantitatively explained on the basis of elastic interactions between impurity–vacancy dipoles and edge dislocations moving in one pair of orthogonal slip planes.
Dynamic Conductivity Singularities of a Many‐Valley Semiconductor in a Quantizing Magnetic Field
Authors: Magarill L. I. , Savvinykh S. K.
Published: July 2007

The absorption of linear‐polarized electromagnetic waves in many‐valley n‐Ge type semiconductors in a quantizing magnetic field is considered. A low‐temperature region where the main scattering mechanism is the elastic collision of electrons on point defects is studied. Short‐range impurity centres (“isoelectronic ecntres”) are considered within a zero‐range potential model. The theory is developed for the case of low impurity concentration, and the absorption is expressed in terms of an one‐centre scattering operator. The parameters of the problem are intervalley and intravalley scattering lengths. Main attention is paid to the study of the frequency dependence of the absorption coefficient near resonance peaks due to transitions between Landau levels of different valleys and also due to those from localized impurity states to continuous spectrum. Formulae are derived to describe the shape of resonance peaks and their field and orientation dependences.
GMR Effect on Conversion Electron Polarization
Authors: Mitin A. V. , Popov E. A.
Published: July 2007

(γ;e) conversion scattering under the GMR conditions is considered. To solve this problem the density matrix method is used. It is shown that the process is accompanied by the time oscillations of conversion electron (CE) flux. The oscillation frequencies are multiple to the frequency of rf magnetic field. CE polarization is analysed on the example 57Fe nuclei in iron. The possibility of application of these results for spin polarization study of the inner atomic shells is shown.
Displacement of the Fermi Level Due to Impurities in a Random Distribution
Authors: Yoshida K.
Published: July 2007

The displacement of the Fermi level, ΔEF, on alloying, when impurity atoms are in a random distribution, is investigated in terms of a cellular structure where spherical cells, each containing an impurity atom at its center, have various sizes. This model is a simple extension of Friedel's model in which all the cells have an equal size. An appropriate distribution function of cell sizes is estimated by the aid of a computer simulation. For a random distribution of impurity atoms, ΔEFp is found to depend more linearly on the impurity concentration than expected from Friedel's model. A comparison is made with experimental data reported in literature for copper alloys.
Electron Spin Resonance Study of Ni2+ Centers in AgCl(Cu, Ni)
Authors: van Robbroeck L. , Bouwen A. , Schoemaker D.
Published: July 2007

Single AgCl crystals doped with Cu2+ and Ni2+ were studied by means of electron spin resonance. As grown crystals contain three different Ni2+ centers which reduce to Ni+ defects under illumination at 50 K with blue light. Six Ni+ defects were found with tetragonal, orthorhombic, and cubic symmetry. At 101 K the orthorhombic centers transform to the tetragonal defects. The latter become thermally unstable at 135 K and induce the decay of the Cu2+ centers.
A Fast Computational Method to Obtain Spin‐Hamiltonian Parameters of S and I = 5/2 Ions
Authors: Korkmaz M. , Aktas B.
Published: July 2007

When the crystal field term is not weak enough, the perturbation method is not convenient to obtain the ESR spin‐Hamiltonian parameters for ions with S > l/2. To overcome this difficulty the matrix diagonalization technique which is a rather lengthy and time consuming process, is generally used in the literature. A fast computational method is proposed based partly on diagonalization and partly on perturbation techniques to calculate these parameters quickly and accurately.
On the Theory of Scattering by Short‐Range Pointials
Authors: Iskra V. D.
Published: July 2007

A convenient technique of handling δ‐like potentials is developed using a factorization device. Results are applied to study the temperature dependence of the mobility limited by scattering of the charge carriers by a set of randomly spaced centers with short‐range potentials. Born's approximation is avoided and resonance scattering is shown to be of some importance in a certain temperature range.
Photoconductivity of Corundum Irradiated with High Energy Electrons at Excitation of F and F+ Centres
Authors: Atabekyan R. R. , Vinetskii V. L. , Gevorkyan V. A. , Godenko L. P. , Ezoyan R. K.
Published: July 2007

The photoconductivity excited in the region of absorption of colour centres in irradiated corundum by high energy electrons is investigated. A theory of photoconductivity is constructed determined by electron jumps between spatially separated F+ centres. With reasonable values of parameters one may achieve a satisfactory quantitative agreement of theoretical and experimental values of the photocurrent.
Mössbauer radiation dynamical diffraction in crystals being subjected to the action of external variable fields
Authors: Baryshevskii V. G. , Skadorov V. V.
Published: July 2007

A dynamical theory is developed of the Mossbauer radiation diffraction by crystals being subjected to an variable external field action. Equations describing the dynamical diffraction by nonstationary crystals are obtained. It is shown that the resonant interaction between Mössbauer radiation and shift field induced in the crystal by a variable external field giving rise to an effective conversion of the incident wave into a wave with changed frequency.
Band structure of TIGaSe2 ternary layered crystals
Authors: Abdullaeva S. G. , Mamedov N. T.
Published: July 2007

The band structure in the high‐symmetry points of the TIGaSe2, Brillouin zone is calculated by the pseudopotential method. The top of the valence band is found to be located at the Γ point. The bottom of the conduction band is located at the line Γ–Y and the additional extremum of this band – at the point Γ of the Brillouin zone of TlGaSe2. The data obtained are compared with the results of previous band calculations and optical absorption data of TlGaSe2.
Solution of the spin‐hamiltonian with orthorhombic HF and g‐tensors (S = 1/2). II. Application to VO2+ centres in oxide glasses
Authors: Seth V. P. , Yadav A. , Bansal R. S.
Published: July 2007

A theory developed previously is used in the analysis of ESR spectra of VO2+ in ternary borate glasses. The theoretical optical basicity of these glasses is calculated. It is found that |P| and |A′‖| are larger and K is smaller in those glasses for which the optical basicity is large.
Photocarrier kinetics in IrBr‐doped AgBr
Authors: Spoonhower J. P. , Deri R. J.
Published: July 2007

The kinetics of photogenerated carriers in AgBr crystals doped with trivalent iridium are investigated by photoconductivity measurements. The temperature dependence of the photoelectron lifetime is highly dependent on the level of iridium doping. Experiments show that photoelectron‐iridium reaction cross‐sections have a weak dependence on the number of vacancies bound to the iridium site. Estimates of the cross sections for electron capture a t IrBr centers with one and two associated vacancies are deduced.
Low‐symmetry doped Cu(II) complexes in (gly)2CaCl2 · 4 H2O single crystal: EPR studies
Authors: Hoffmann S. K. , Goslar J. , Szczepaniak L. S.
Published: July 2007

EPR results for copper(II) ions doped in (gly)2CaCl2 · 4H2O single crystals are reported. The copper(II) complex formed in the chromophore CuN2Cl4 displays rhombic crystal field symmetry with an unusual spin‐Hamiltonian parameter sequence: gx = 2.115, gy = 2.034, gz = 2.308, and Ax = 40.1, Ay = 113.4, Az = −73.0 × 10−4 cm−1. The g‐factors are related to the ground state wave function α |ad−bd〉 with α2 = 0.86, a = 0.9835, and b = 0.181, and the untypical hyperfine splitting parameters result from the very low value of the Fermi contact parameter of χ = 0.087.
Resonant excitation of helicon waves by two microwave beams in a solid state plasma
Authors: Maheshwari K. P. , Tarey G.
Published: July 2007

An investigation is made of resonant excitation of helicon waves at the difference frequency of two microwave beams propagating in a magneto‐active solid state plasma viz. n‐InSb. The two beams propagating obliquely with the magnetostatic field interact in the semiconductor to give rise to a nonlinear ponderomotive force at the difference frequency which resonantly excites helicon waves if the dispersion relation corresponding to helicon waves is satisfied. The results show that microwave beams of power densities 1 MW cm−2 can excite helicon waves of power density 0.98 kW cm−2 when ωc/ω = 25. The power carried by helicon waves depends on the direction of propagation of the pumps relative to magnetostatic field. For the parameters under consideration the power gets optimised at an angle θ = 63.4°. Helicon waves are not excited if the pumps propagate parallel or perpendicular to the magnetic field. The increase in magnetic field increases the power density of the excited helicon wave.
Nature of the centres of positron annihilation in intensively irradiated alkali halides
Authors: Annenkov Yu. M. , Nurmagambetov S. B. , Chormonov A. B.
Published: July 2007

The positron capture centres are identified in high irradiated (in the temperature range of 300 to 520 K) KBr. The dependences of the intensity of the annihilated 2γ radiation on the temperature of proton irradiation and that of a following pulse heating of crystals are studied. The spectra of optical absorption of the crystals are measured under identical conditions. The volume rates of a positron capture into the basic radiative defects are calculated. The divacancies are shown to be the basic centres of positron captnre in the investigated temperature range in the high irradiated alkali halides.
Magnetostatic interactions of moving vertical bloch lines in a domain wall
Authors: Kosiński R. A. , Strzeszewski J.
Published: July 2007

The propagation of a pair of vertical Bloch lines in a moving domain wall, used in a Bloch line memory, is simulated numerically using a full implicit method and taking into account non‐local magnetostatic interactions. Results concerning the influence of the magnetostatic interactions on the motion of vertical Bloch lines along the domain wall, in particular the process of their collision, are discussed.
Nature of deep luminescence centres in CdSe and CdSexTe1–x
Authors: Ermolovich I. B. , Milenin V. V.
Published: July 2007

Both, the dependences of the luminescence intensities of the bands with λm = 920 and 1160nm at 77 K in CdSe and the corresponding bands in CdSexTe1–x (x = 0 to 1) on temperature and the dependences of band intensities on excitation level measured at low temperatures and at the temperatures from the ranges of band quenching are investigated. Obtained data enable conclusion to be made about both band quenching mechanisms: the “external” mechanism is valid for the 920 nm bands and the “internal” one is valid for the 1160nm bands. The parameters of electron‐phonon interactions at radiative carrier capture on investigated centres are obtained and the configuration coordinate models for both types of centres are constructed. Different mechanisms are shown to be caused by the differences of chemical nature and geometrical configuration of the 920 and 1160 nm centres. It is shown also that the process of the nearest anion altering of the emission centre causes the change of its interaction with lattice.
Twofold coordinated Si and Ge atoms and “hydrogen” paramagnetic centers in amorphous SiO2 and GeO2
Authors: Radtsig V. A. , Bobyshev A. A.
Published: July 2007

A new type of intrinsic structure defects in amorphous SiO, and GeO, – twofold coordinated silicon magnified image and germanium magnified image – is identified. In the reaction with H(D)atoms they convert to paramagnetic centers magnified image. The electron structure, geometry, and chemical properties of these centers are analyzed.
The origin of the minority impurity states in heavily doped semiconductors
Authors: Domanevskii D. S. , Krasovskii V. V. , Prokopenya M. V. , Vilkotskii V. A. , Zhokhovets S. V.
Published: July 2007

The influence is examined of growth conditions of heavily doped n‐type semiconductors on the width and energy position of Gaussian‐shape impurity band where non‐equilibrium holes are localized. The energy levels of the impurity band are shown to be caused by associations of oppositely charged crystal imperfections (so‐called associates) including several shallow donor impurity atoms and a deep structural defect. The reason of Gaussian broadening of these states is a random spatial arrangement of associated imperfections about each other within a given associate.
Lattice dynamics and ionic conductivity of PbF2:6%LiF superionic crystals
Authors: Kosacki I. , Hibner K. , Litvinchuk A. P. , Valakh M. Ya.
Published: July 2007

Temperature studies of lattice dynamics and ionic conductivity, within the temperature range of 100 to 700 K, are performed for PbF2 and PbF2:6% LiF superionic crystals. The doped crystals exhibit a decreased activation energy of the conductivity. A decrease, by about 70 degrees, in the temperature at which the ionic conductivity changes and Raman spectra anomalies occur is observed. It is found that at temperatures significantly lower than that of the superionic state transition, the Raman line form is determined by processes of phonon scattering at thermally excited defects.
The effects of electron excitation energy transfer to the impurity centre in LiH crystals
Authors: Cholakh S. O. , Pustovarov V. A. , Shulgin B. V.
Published: July 2007

Possible mechanisms of electron excitation energy transfer to the impurity centres in LiH crystals are considered in the case of LiH :Mg and LiH :Na crystals. Along with the electron‐hole mechanism, the exciton mechanism of energy transfer is of considerable efficiency. The main role in this process belongs to unrelaxed excitons. The free path value of excitons in LiH is estimated to be about 3 × 103 nm at 4.2 K. Optical manifestation of energy transfer is observed both, in the impurity centre luminescence and in the formation of Frenkel radiation defects as a result of nonradiative decay of near‐impurity excitons.
The lorenz number of some AgCr alloys
Authors: Ducastel R. , Pitsi G.
Published: July 2007

The temperature dependence of the Lorenz number L of five coldworked AgCr Kondo alloys is measured between 1.5 and 14 K by combining the results of thermal and electrical conductivity measurements. The results are compared with data obtained on other Kondo systems. Inelastic electron‐dislocation scattering is proposed for explaining the value of L (T → 0) lower than the classical Sommerfeld value L0.
Non‐linear conduction in networks of random potential barriers
Authors: Fishchuk I. I.
Published: July 2007

The dc conductivity in high electrical fields for the cubic network of the random macroscopic barriers with non‐linear I–U characteristics is calculated. For not a very large spread of the heights of the potential barriers the differential conductivity decreases with increasing electrical field just after Ohmic region. This result is obtained using both, the effective medium and the cumulant approximations. In the ohmic region the cumulant approximation result for the dependence of the conductivity on the degree of barriers height spreading is in better agreement with computer results than the effective medium approximation result.
A novel self‐consistent theory of the electronic structure of inversion layers in InSb MIS structures
Authors: Zöllner J.‐P. , Übensee H. , Paasch G. , Fiedler T. , Gobsch G.
Published: July 2007

Field effect devices on the basis of InSb are increasingly used in semiconductor technique. Due to the non‐parabolicity of the band structure of the conduction band the theoretical description of such devices is more complicated than for other materials. A simple method for the self‐consistent quantum mechanical calculation of the electronic structure of inversion layers in materials with a Kane conduction band is presented which is well suited for the application in semiconductor technique. The method is based on an extension of a modified local density approximation for interface problems. The efficiency of this simple method is shown for the example of InSb by compzring with experiments and with results of earlier laborious self‐consistent calculations using wave functions. The necessity is proved to take into account the deviation from the parabolic band structure in the self‐consistent calculations.
Single crystal growth and investigation of optical and ESR absorption spectra of zirconium‐doped YAG
Authors: Asatryan H. R. , Kuzanyan A. S. , Petrosyan A. G. , Petrosyan A. K. , Sharoyan E. G.
Published: July 2007

Single crystals of yttrium aluminium garnet doped with zirconium ions (Y3Al5O12:Zr, YAG:Zr) are grown from the melt and their optical and ESR absorption spectra are investigated. It is established that the color centers and paramagnetic centers have an identical nature being caused by Zr3+ ions in dodechahedrical sites of the garnet lattice. The experimental results are interpreted in the approximation of crystal field and molecular orbital theories.
Quantum properties of the two‐dimensional electron gas in the n‐inversion layers of InSb grain boundaries under high hydrostatic pressure
Authors: Herrmann R. , Kraak W. , Nachtwei G. , Schurig Th.
Published: July 2007

The magnetotransport properties of conduction electrons in n‐type inversion layers adjacent to the grain boundary in p‐type InSb bicrystals are investigated under high hydrostatic pressure (up to 103 MPa) in magnetic fields up to 15 T. A rapid decrease of the carrier concentration in the inversion layer is observed when hydrostatic pressure is applied. From the quantum oscillations of the magnetoresistivity the characteristic parameters of the electric subbands (subband population nsi, subband energies EF — EI, and the effective cyclotron masses m*i) and their pressure dependences are established. A simple theoretical model taking into account the pressure dependence of the energy band structure of pure InSb is proposed to describe the found experimental‐data. Under high pressures and in high magnetic fields it is verified experimentally that the Hall resistivity gxy is quantized into integer multiples of h/e2.
Structural disorder model pressure‐induced transitions in Sn and semiconducting compounds
Authors: Dixit P. K. , Vaid B. A. , Sharma K. C.
Published: July 2007

The structure disorder model, recently proposed to explain the thermodynamic properties near the transition of first order, is generalized to include the pressure‐induced transitions in tetrahedrally coordinated tin and ANB8—N compounds (with N = 2, 3 ). For Sn the calculated values of the change in thermodynamic quantities during the transition are found to be closer to the experimental values. For ANB8—N compounds, the transition is explained in a satisfactory manner in terms of partial ionic bonds and covalent bonds. The change in compressibility near the transition is found to be in agreement with that obtained from experiments.
Bethe‐Peierls study of magnetic field induced phase transitions
Authors: Paraskevaidis C. E. , Papatriantafillou C. T.
Published: July 2007

Using a Bethe‐Peierls like approach the thermodynamic behavior of a two‐sublattice Ising antiferromagnet is studied focusing on low temperatures and high magnetic fields portion of its phase diagram, where the system undergoes magnetic field‐induced phase transitions. The results for the H‐T phase diagram agree quite well with those from Monte Carlo calculations and show a „peculiar”︁ boundary at low temperatures and high magnetic fields separating the AF from the PM state in which, in a certain narrow range of magnetic field values, the system undergoes an AF to PM phase transition both by increasing or decreasing the temperature at constant magnetic field. The behavior of the system is investigated in this „peculiar”︁ regime by calculating the relevant thermodynamic quantities and a qualitatively symmetric behavior at the two AF to PM transition points with respect to the two directions of temperature variation at constant field is found.
Spectral density method applied to the study of the energy spectrum of the XY model in a transverse field
Authors: Bernardes L. A. B. , Borges O. N. , Ribeiro L. A. Amarante
Published: July 2007

The energy spectrum of the XY model in a transverse field is studied by the spectral density method (SDM), using polar and Gaussian „ansätze”︁. Expressions for the critical temperature and critical transverse field are obtained. It is shown that, within some approximations, the static properties of this model are not modified by including damping effects in the elementary excitations.
The properties of the band spectrum parameters in the band‐inversion region of narrow‐gap Ph1−xSnxTe
Authors: Dmitriev A. I. , Lashkarev G. V. , Orletskii V. B. , Tovstyuk K. D.
Published: July 2007

A calculation technique based on experimental data is proposed for determining the Dimmock model parameters m , P⊥,‖ of narrow‐gap Pbi−xSnxTe alloys. From the six‐band model, a relation is derived to describe the dependence of the current carrier g‐factor on carrier concentration of the alloy composition. The composition dependence of the matrix element of the momentum operator (MOME) P ⊥ as derived earlier by the authors is studied over a wide range of compositions x. The analysis of experimental data reveals an anomalous behaviour of P ⊥ in the region of band inversion. The dependence P ⊥(x) may be approximated by an exponential function. The dependences of effective masses, the g‐factor of electrons and holes, as well as mass anisotropy coefficients, on composition and carrier concentration are analyzed on the assumption that P is a function of composition. The results of the analysis are compared with experiment. It is shown that the disagreement between theory and experiment can be substantially reduced by substituting P ⊥ (x) for P ⊥ = const. Relations are given by which the carrier parameters in Pb1−xSnx Te can be calculated in terms of the Dimmock model.
Angular‐resolved X‐ray photoelectron spectra and electronic structure of SnS2
Authors: Berg U. , Chassé T.
Published: July 2007

Valence band spectra of SnS2 are measured in dependence on the polar electron emission angle. Moreover, the valence band spectra of Sp‐like electrons are calculated on the basis of two different densities of states. The possibilities but also the limits of the ARXPS with reference to a detailed comparison of measurements and calculations are shown.
A kinetic equation for polaritons
Authors: Stolz H.
Published: July 2007

In the framework of the Schwinger‐Keldysh formalism for nonequilibrium many‐particle systems the interaction of radiation with the electron‐hole system is considered. Spectral and kinetical properties of the photon within the system, i.e. the polariton, are investigated including the many‐body effects like phonon interaction, screening, and Pauli blocking. A kinetic equation for incoherent polaritons including the influences of these effects is presented.
Induced field at a dipole near the metal surface in the hydrodynamic approximation
Authors: Bao Tran Thoai Duy
Published: July 2007

The induced field at an oscillating dipole near the metal surface is derived within the hydrodynamic model. Spatial dispersion and diffuseness of the electron density at the surface are included. Numerical calculations for a rs = 2 jellium are carried out, and the image plane position is determined. Results are compared with those of Feibelman and Fuchs et al.
Inelastic scattering of electrons at the InP‐SiO2 interface
Authors: Er‐Wang Mao , Hung‐Rei Zhang , Wei‐Yuan Wang , Liang Ye , Guo‐Ping Faag
Published: July 2007

The negative magnetoresistance effect of the InP–SiO2, interface is investigated. The results indicate that the inelastic interaction of electrons with polar optical phonons plays an important role in the inelastic scattering process of the system.

Es wird der negative Magnetowiderstandseffekt an der InP‐SiO2‐Grenzfläche untersucht. Die Ergebnisse zeigen, daß die inelastische Wechselwirkung der Elektronen mit polaren optischen Phononen eine wesentliche Rolle im inelastischen Streuprozeß des Systems spielt.
The Electronic Energy Bands of AgN02 Crystal at Room Temperature
Authors: El‐Dib A. M. , Hassan H. F.
Published: July 2007

The electronic energy bands of AgNO2 crystals are calculated at room temperature in different directions. The calculations are carried out using a semiempirical LCAO method. The Madelung potentials at different lattice sites are also calculated. The general features of the electronic energy bands of AgNO2 are similar to those of NaNO2 in its ferroelectric phase. The minimum indirect energy gap (Eg) equals to 2.522 eV, and occurs in the R‐T direction.
Energy Band Structure Calculations for Crystals with Spiral Magnetic Structure
Authors: Sandratskii L. M.
Published: July 2007

A generalization is given of three the most universal methods of energy band structure calculations (KKR, APW, and tight binding) in the case of crystals with noncollinear spin configuration. It is shown that the use of generalize dsymmetry allows in many physically interesting cases to deduce a secular equation, which dimension is only two times higher than the dimension of the secular equation for a collinear magnet with the same crystal lattice. The possibilities of the methods are illustrated by a model example.
GME and the Electron or Exciton Initial Condition Term Due to Lattice Relaxation Dimer
Authors: Čápek V.
Published: July 2007

Instantaneous creation of an electron or exciton in a dimer interacting with initially statistically independent unrelaxed lattice phonons leads to an initial condition term in the time‐convolution generalized master equations (GME) for the site occupation probabilities which may be undamped with increasing time till the coherence decay time provided the finite exciton‐lifetime effects are negligible. For the Peier form of the projector diagonalizing the full density matrix in the small polaron representation with the canonical form of the reference phonon density matrix and temperature equal to that of the initially unrelaxed equilibrium harmonic phonons, this term is calculated to the second order in the relevant hopping integral and its magnitude is estimated.
A Reformulation of the LUC‐CNDO Approach to the Properties of Solids. Application to Diamond and Silicon
Authors: Smith P. V. , Szymanski J. E. , Matthew J. A. D.
Published: July 2007

A modified version of the periodic large unit cell (LUC) approach, using the semi‐empirical complete neglect of differential overlap (CNDO) molecular orbital method is applied within the k = 0 approximation to the properties of diamond and silicon. The modified formalism is shown to be capable of producing good results for the properties of the perfect crystal and its capabilities for the study of systems of lower symmetry, such as defects or surfaces, is discussed.
ODMR in Triplet Excited States of ns2 Ions in Alkali Halide Crystals
Authors: Baranov P. G. , Vetrov V. A. , Romanov N. G. , Topa V.
Published: July 2007

Optically detected magnetic resonance (ODMR) is applied for the first time to the investigation of triplet relaxed excited states (RES) of divalent ns2 ions in alkali halide crystals. Four types of ODMR spectra related to the RES of Ge2+ are found. Spectral and angular dependences of ODMR are studied. ODMR data on the RES of monovalent (Ga+) and divalent (Ge2+) ns2 ions are discussed. These results provide the first experimental evidence of the effect of nuclear charge on the wavefunction density distribution for excited states of impurity ions in crystals.
Optical Properties of Metals: Au
Authors: Jungk G. , Röseler A.
Published: July 2007

The dielectric function of Au films is determined ellipsometrically in the wave‐number ranges 700 cm−1 ≦ v ≦ 1900 cm−1 and 2500 cm−1 ≦ v ≦ 3000 cm−1 as well as for 8900 cm−1 ≦ v ≦ 32300 cm−1 (1.1 eV ≦ ħω ≦ 4 eV). The spectra are discussed taking into account intra‐ and interband transitions. An energy‐dependent plasma frequency and damping is found. The sample effects are essentially described within an effective medium approximation assuming the influence of voids. Some peculiarities of the frequency dependence of the damping parameter are likely due to the influence of fractals.
Position and Lifetime of Photoluminescence in Cd1−xMnxTe and Zn1−xMnxTe. Exchange Dependent Effects
Authors: Müller E. , Gebhardt W.
Published: July 2007

Data on position and lifetime of the photoluminescence band in Cd1−xMnxTe and Zn1−xMnxTe are reported for different manganese concentrations x. The luminescence is due to intraatomic transitions within the manganese ions. The blue shift at low temperatures shows the typical behavior of an exchange dependent parameter. The lifetimes are in the microsecond range. At low temperatures the decay is dominated by the radiative lifetime with weak temperature dependence. In Zn1−xMnxTe the lifetime varies with manganese concentration, whereas in Cd1−xMnxTe the concentration dependence is insignificant.
Structural Disorder Model for Amorphous Semiconductors: a‐Se
Authors: Vaid B. A. , Sharma K. C.
Published: July 2007

The structural disorder model, recently proposed by the authors, for amorphous semiconductors is generalized for Se within the framework of the concept of charged dangling bond (CDB) defects, packing fraction, thermodynamic theory of defects, and the additive approximation near the crystalline to amorphous transition which is interpreted as a point of spontaneous production of CDB defects. The model is able to explain at least qualitatively the data on thermodynamic properties, the structural disorder parameter X representing the ratio 〈U2〉x/〈U2〉0, and the width of the Urbach absorption edge E0(T, X).
Monte Carlo Simulation of Electron–Phonon Scattering in the XUV‐Induced Electron Emission of NaCl
Authors: Ausmees A. , Elango M. , Kikas A. , Pruulmann J.
Published: July 2007

A Monte Carlo simulation of the electron emission induced in NaCl by 60 to 250 eV photons is carried out. The number as well as the initial energy and spatial distribution of conduction electrons, obtained in a previous paper, are used as the input. Electron–phonon scattering events are treated semiclassically. Optical as well as acoustical phonons are taken into account, so that with the increase of electron energy the scattering probability decreases for optical and increases for acoustical phonons. The parameters of the model are adjusted to fit the experimental quantum yield and energy spectra of emitted electrons. It appears that for high‐energy (>2 to 3 eV) electrons the electron–phonon scattering is mainly due to acoustical phonons.
Theory of the Infrared Spectrum of Size‐Quantized Bi Films
Authors: Zaluzny M. , Lukasik A.
Published: July 2007

The influence of the intersubband transitions on p‐polarized infrared spectrum of size‐quantized Bi films with normal along trigonal axes is investigated. The optical conductivity is evaluated using the two‐band model. Results indicate that contrary to Cottey's theory the absorption lines connected with intersubband transitions are very weak.
On the Theory of Partial and Total Internal Reflection of a Plane TM Wave from Symmetrically Realigned Nematic Liquid Crystal Layers
Authors: Hinov H. P.
Published: July 2007

The influence of the leading term in the exact solution of the Maxwell equations on the reflection of a plane TM wave from a symmetrically realigned nematic layer with tangential orientation at the limiting walls and arbitrary anchoring is considered theoretically. The reflectivity coefficient R is obtained and the possibilities for application in the experiments eventually performed are discussed in detail. On the basis of the theoretical results obtained, the case of a symmetrically deformed homoeotropic nematic layer is briefly considered as well.
Force Sum Rules at Surfaces
Authors: Kaschner R. , Ziesche P.
Published: July 2007

Hellmann‐Feynman theorems for partially extended arrangements of atoms are derived and applied to one‐, two‐, and three‐dimensional solids. The derivatives of the bulk energy with respect to the lattice spacings are related to the Hellmann‐Feynman forces in the corresponding semi‐infinite unrelaxed solids. These forces have to alternate going from the surface into the bulk provided that the latter is in equilibrium.
Dynamical Structure of Alpha Helical Proteins
Authors: Ichinose S.
Published: July 2007

Vibrational structures of a vibron soliton are studied in terms of the classical vibron model of the α‐helical protein molecule. It is shown that the dynamical structures of the α‐helical protein molecule are described by three types of internal oscillations of vibron solitons which are governed by a set of coupled nonlinear Schrödinger equations.
A Self‐Consistent Theory of Phonon‐Like Excitations in Structurally Disordered Solids
Authors: Wegener D. , Böttger H.
Published: July 2007

Making use of a Green function technique, on the basis of the model of a “frozen‐in hot crystal” a self‐consistent theory of elementary excitations in structurally disordered solids is developed. The theory provides a Green function which is analytical in the whole frequency range. It is used for evaluating dispersion and damping of phonon‐like excitations in a one‐dimensional structurally disordered model.
Fourth‐Order Thermal Expansion for Cubic Solids. Application to Aluminum, Copper, Germanium, and Silicon
Authors: Delannoy‐Coutris M. , Perrin G.
Published: July 2007

The fourth‐order anharmonic finite‐strain theory leads to a model for the volume dependence of the Grüneisen parameter and simultaneously to a Mie‐Grüneisen equation of state. These relations are used to derive the fourth‐order expressions for the thermal expansion coefficient of cubic crystals. A comparative study of the results with experimental data is given for the temperature dependence of the linear thermal expansion coefficient α of aluminum, copper, germanium, and silicon. It is shown that the theory agrees with experiment even better since the Grüneisen coefficient can be reasonably assumed to be temperature independent. Finally, an estimation of the variation of the thermal expansion coefficient with volumetric compression is given for aluminum, copper, germanium, and silicon using both, the Lagrangian and Eulerian strain measures.
Solitary Excitations in Molecular Chains Due to the Anharmonicity of the Intramolecular Vibrations
Authors: Primatarova M. T.
Published: July 2007

Solitary excitations in molecular chains are theoretically investigated in the presence of intramolecular vibrations of one and the same type and of two different types. In both the cases the solitary bound formations are obtained to exist as a result of the anharmonicity of the intramolecular vibrations. It is found that solitary formations can exist and propagate along the chain also in the case when in addition the chain molecule motions are taken into account. The parameters of the solitary excitations (length, energy) are calculated.
Rate‐Equation Treatment of PAC‐Monitored Defect Reactions in Irradiated Metals
Authors: Golczewski J. , Frank W.
Published: July 2007

The variations of the fractions of defect‐occupied PAC probe atoms in low‐temperature electron‐irradiated metals during isochronal annealing up to the completion of recovery stage III are computer‐simulated within the framework of a rate‐equation approach. It is taken into account that the Stage‐IE interstitials migrate three‐dimensionally in the one‐interstitial model (OIM) but one‐dimensionally in the two‐interstitial model (TIM). The effect of the thermal conversion o crowdions and the existence of “caged” crowdion–PAC‐atom pairs, which are characteristic of the TIM, are investigated in detail. A comparison with experimental data shows that several observations may be understood in terms of the TIM but not of the OIM.
The Theory of Dynamic Annihilation of Dislocations
Authors: Kusov A. A. , Vladimirov V. I.
Published: July 2007

A mechanism is proposed of the rapid annihilation of mixed dislocations by means of the cross‐slip of the double kink on the screw segment of the dislocation. The maximum annihilation distance R between dislocations as a function of applied stress σ, dislocation friction stress σ0, and angle α between the dislocation line and the Burgers vector b is correctly calculated. The comparison is made of theoretical results with available experimental data and previous rough theoretical estimations. It is shown that the annihilation mechanism is weakly connected with thermal fluctuations and it mainly has a pure force nature.
Dielectric Response of Some Semiconducting TCNQ Salts in the Submillimetre Range
Authors: Gorshunov B. P. , Kozlov G. V. , Volkov A. A. , Petzelt J. , Železný V.
Published: July 2007

The complex permittivity spectra of the semiconducting salts MTPA(TCNQ)2, MTPP(TCNQ)2 and of the semiconducting phases of MEM(TCNQ)2 are measured for the first time in the 8 to 30 cm−1 range and in the temperature interval 5 to 350 K for polarization parallel and perpendicular to the conducting stacks. In the case of parallel polarization the model of interrupted conducting strands is used to assign the spectra, where individual tetramers are taken as the strands. In the case of perpendicular polarization the conductivity spectra can be understood as due to hopping conductivity with a broad distribution of relaxation times.
Finite Mean Free Paths and the Electrical Resistivity of Liquid Simple Metals and Binary Alloys
Authors: Daver F. , Khajil T. M. A. , Tomak M.
Published: July 2007

The finite mean‐free‐path correction to the Ziman formalism of the resistivity for liquid metals and some binary alloys are calculated using the Ferraz‐March approach.
Impurities in Ni3Fe Magnetic Alloys
Authors: Matysina Z. A. , Mekhrabov A. O. , Menshikov A. Z. , Babaev Z. M. , Zaginaichenko S. Yu.
Published: July 2007

An expression for the order–disorder transformation temperature in substitutional alloys of AB3‐type is determined in terms of the classical theory of ordering in alloys with low impurity concentration. The order–disorder transformation temperature is shown to increase at the initial stages of alloying at any relations of ordering energies. The data on theoretical calculations are compared with experimental ones obtained with Ni3Fe alloy doped by different impurities. Much consideration is given to results obtained with Ni3(Fe1−xMnx) alloys. Using neutron diffraction analysis, the lack of Ni24Fe4Mn4 ternary superstructure is shown, and the TK(x) dependence with the extremum at x ≈ 0.4 is obtained from dilatometric and specific heat measurement.
Thermodynamic Features of the System of Packed Antiferroelectric Chains
Authors: Kholopov E. V.
Published: July 2007

The system is considered of Ising‐like chains suffering the antiferroelectric instability. The interaction between the chains is taken into account within the framework of the molecular field approximation. Then summing over states of a single chain is carried out by the method making immediately use of the fact that the unit cell can consist of several atoms. Such an approach may sometimes be more convenient than the transfer‐matrix method. An appropriate phase diagram in an uniform external field is investigated. As a result, the electrical effects essentially must be small so that the corresponding measurements will be difficult in such systems. As an example the TlHF2 structure is discussed.
On the Self‐Consistent Statistical Theory of Anharmonic Effects in Imperfect Crystals
Authors: Zubov V. I. , Rabelo J. N. Teixeira
Published: July 2007

The improved unsymmetrized self‐consistent field method developed in preceding papers is used to study anharmonic effects in imperfect crystals. Various one‐dimensional models of anharmonic crystals with defects are considered: vacancy, free surface, adsorption with taking into account the influence of adatoms on the adsorbent, and substitutional impurities. The formulae for the lattice relaxation near defects, for the effective amplitudes of the anharmonic vibrations of atoms, and for the Helmholtz free energy are obtained. They are expressed in terms of the nearest‐neighbour interaction potentials and their derivatives of several orders at the equilibrium points. A comparison with known results for some harmonic models is made. The decisive role of the anharmonicity in such effects as the temperature dependence of the lattice relaxation and the influence of the imperfections on thermal properties of crystals is emphasized. The possibility of application of the method to three‐dimensional imperfect crystals, as well as of taking into consideration the interactions with next neighbours is noted.
Thermoluminescence of BaFCl:Dy and BaFCl:Cu X‐Irradiated at Room Temperature
Authors: Inabe K. , Utsui Y. , Takeuchi N.
Published: July 2007

Three glow peaks around 320, 370, and 410 K are observed for X‐irradiated BaFCl:Dy and BaFCl:Cu. Optical bleaching effects on both glow peaks and F centers suggest that the thermal decay of F(Cl−) centers is not directly related to the 370 and 410 K peaks. Emission spectra indicate that the luminescence centers of these peaks of BaFCl:Dy can be attributed to Dy3+ ions. On the basis of concluding the luminescence centers to be Dy3+, the glow peak reactions are proposed tentatively.
On the Interband Absorption in Disordered Semiconductors
Authors: Arbuzov Yu. D. , Kolenkin M. Yu.
Published: July 2007

The imaginary part of the interband dielectric function ϵ2(ω) of disordered semiconductors is calculated in the case of a Gaussian random field. The corrections to the semiclassical expression for ϵ2(ω) are obtained. The limits of validity of the semiclassical approximation are found.
Nonlinear Propagation of Nanosecond Laser Pulses through Polycrystalline CuCl Layers
Authors: Bigot J. Y. , Frindi M. , Fidorra F. , Levy R. , Hönerlage B.
Published: July 2007

A temporal and spectral analysis is made of high intensity nanosecond laser pulses when propagating through polycrystalline CuCl samples of different thickness. The spectral region investigated is around the two‐photon resonance of the biexciton. The dynamical behaviour of the nonlinear transmission is studied when varying the laser incident intensity, its photon energy, and the sample thickness. It is shown that the experimental results can be explained, when calculating the transient dielectric function. The importance of the dynamics of excitons and biexcitons is stressed.
LO‐Phonon Modes Bound to Neutral Impurities in Polar Semiconductors. I. General Theory
Authors: Monecke J. , Cordts W. , Irmer G. , Bairamov B. H. , Toporov V. V.
Published: July 2007

The influence of the Fröhlich interaction between charge carriers bound at impurities and LO‐phonons in polar semiconductors is considered within second‐order perturbation theory taking into account the possibility of degenerate unperturbed electronic ground states. From the general theory presented here changes of the bare electronic excitation energies (bound polaron excitations), Jahn‐Teller like splittings of degenerate ground states and the formation of bound to neutral impurities phonons (dielectric modes) can be obtained. The application of the general theory to special cases and experimental results will be published in a forthcoming paper.
Further Calculations of the F+‐Center Wave Function for Lithium Niobate
Authors: Ho Fat Duen
Published: July 2007

This work is a continuous effort of the F+‐center calculation for lithium niobate. The simplified semicontinuum model developed previously by this author is again used. The polarization effect is taken into account. Although the major procedures follow those developed before, there is one departure in the 2p‐energy‐eigenvalue calculation. It is assumed that the Franck‐Condon principle applies, and that the ions do not move during the absorption process. The transition energies computed here are rather compatible with those values calculated by using the point‐ion‐lattice model. All results are found to be in good agreement with the experimentally observed value.
Localization Effect of Electrons in the InP–SiO2 Interface
Authors: Er‐wang Mao , Hung‐rei Zhang , Wei‐yuan Wang , Liang Ye , Guo‐ping Fang
Published: July 2007

A research on the conductivity of the InP‐SiO2 interface reveals a localization effect related to long‐range fluctuations of the surface potential. The investigation of the negative magnetoresistance effect shows that the inelastic scattering interactions of electron–electron and electron–polar optic phonon play an important role in the InP interface and obviously affect the negative magnetoresistance. Interaction between electrons is decisively important in activated localization conductance and Mott's mobility edge model is the limit of the model obtained by neglecting the interaction.
IR Spectroscopy and Structure of RF Magnetron Sputtered a‐SiC:H Films
Authors: Rübel H. , Schröder B. , Fuhs W. , Krauskopf J. , Rupp T. , Bethge K.
Published: July 2007

Amorphous hydrogenated silicon carbide (a‐SiC:H) films are prepared by magnetron sputtering of crystalline silicon in an argon—hydrogen—methane atmosphere. The specific absorption modes (wagging, rocking, deformation, stretching) of the SiC, (CHm)nC/Si(n = 1, 2, 3; m = 2, 3), and SiHm−(m = 1,2) groups are assigned and analyzed. The composition of the films is determined by nuclear reaction techniques. Structural, electrical, and optical properties of the films show characteristic changes near an alloy composition of a‐Si1−xCx:H, x = 0.5 which indicate the transition to a structure with threefold coordinated carbon. For x ⪆ 0.75 in the infrared absorption spectra an absorption band is identified which arises from graphitic constituents.
Effect of Pressure on the Luminescence of Trapped Excitons in Xe Crystals
Authors: Kink R. , Kalder K. , Lôhmus A. , Niedrais H.
Published: July 2007

At 115 to 130 K, where the concentration of vacancies in solid Xe is in thermodynamical equilibrium, the intensities of two luminescence bands at 7.2 (A) and 7.6 eV (B) are investigated for Xe crystals under 70 at pressure or without any excess pressure. The decrease of the band A intensity compared to that of the band B is in reasonable agreement with the decrease of the vacancy concentration under an excess pressure. The results confirm an earlier suggestion that the band A originates from excitons trapped at vacancies, whereas the band B is due to self‐trapped excitons.
Electronic Structure and Optical Properties of Polycrystalline Cubic Semiconductors
Authors: Gavrilenko V. I.
Published: July 2007

An analysis of the electronic energy structure (EES) in ideal cubic semiconductors shows that the values of direct energy gaps E′0 and E′1 are determined by an interatomic interaction primarily in the nearest coordination sphere. This is the reason of their relative stability to external effects (mechanical and electric fields, atomic structure distortions, etc.) which may be observed in the experiments. A method for calculating the EES in polycrystalline cubic semiconductors with regard to the main factors (atomic structure distortions, internal mechanical and electric fields) characterizing the grain boundary effect is proposed. The EES of polycrystalline silicon in dependence on an average size of microcrystallites is calculated. The main conclusions of this study are confirmed by the experimental data available in literature.