bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical and experimental study of X‐ray acoustic resonance in perfect silicon crystals
Authors: Entin I. R. 
Published: July 2007

AbstractAn experimental investigation of Borrmann effect resonance suppression by transverse ultrasonic vibrations with wavelengths, approximating the extinction length is carried out. A theory of this phenomenon is developed. It is shown that X‐ray acoustic resonance allows to measure the X‐ray atomic scattering factor with a relative accuracy of ≈ 1%, as well as to investigate the shape of the dispersion surface of X‐ray dynamical diffraction.
The frequency spectra of solid neon and xenon
Authors: Kushwaha M. S. , Kushwaha S. S. 
Published: July 2007

AbstractThe phonon frequencies of normal modes of vibration in solid neon and xenon are calculated at all the irreducible points of the first Brillouin zone with finer subdivisions (1000), using the unpaired‐elastic‐force model (EFM) recently developed. This is used to calculate the phonon densities of states. The calculated frequencies are compared in the highest symmetry directions [100], [110], and [111] with the recent available experimental data. It is observed that the theoretical results show a fairly good agreement with the neutron scattering measurements.
Excitons bound to neutral donor impurities in CuCl
Authors: Sauder T. , Certier M. , Stébé B. 
Published: July 2007

AbstractMagneto‐optical studies as well as theoretical results, allow us to attribute the group of lines v3 (25 533 cm−1 at 4.2 K) of CuCl optical spectra to excitons bound to neutral donors.
A Critical Study of Dynamical Properties of Ionic Crystals
Authors: Gupta H. N. , Upadhyaya R. S. 
Published: July 2007

AbstractThe basic differences among the three most popular extensions of the shell model i. e. the breathing shell model (BSM), the deformable shell model (DSM), and the three‐body force shell model (TSM) are sought out by applying their nearest‐neighbour versions to some representative rocksalt type ionic crystals. The phonon dispersion curves are determined by each model for each of the crystals and compared with the experimental phonons which forms perhaps the best test for this purpose. The same number (eight) of parameters of each model are determined by using the same set of input data. The results and degrees of agreement obtained in each case show clearly the superiority of the “charge‐transfer mechanism” for representing the deformations of electron shells, used in the TSM, over the “breathing” and “deformation mechanism” used in the BSM and DSM, respectively, for the same purpose. The study also shows that the TSM, DSM, and BSM form a series of descending order according to their relative degrees of agreement, obtained in explaining the lattice dynamical behaviour of these crystals.
Analytical theory of crystal growth of two‐component systems I. Basic features and equilibrium properties
Authors: Pfeiffer H. , Haubenreisser W. 
Published: July 2007

AbstractThe basic features of an analytical theory of crystal growth for two‐component systems with atomically rough interfaces are developed in the framework of a multi‐layer SOS‐interface model using the concept of the theory of elementary rate processes. Attachment, detachment, and diffusional processes of the species are taken into account as interfacial elementary rate processes. Rate equations for these elementary rate processes are formulated. The rates are determined in terms of the change of the system free energy due to each specific elementary process using the principle of detailed balance. Especially, the equilibrium properties (interface profile, concentration profiles of the components, phase diagram) are described analytically and evaluated approximately in the continuous Bragg‐Williams approximation (CBWA) for ideal mixtures. The results of the interface model are discussed in comparison with those of the phenomenological theory.
Jahn‐Teller Coupling of Cr2+ Ion with Degenerate Modes in ZnS, ZnSe, and ZnTe Crystals: Microscopic Treatment
Authors: Natadze A. L. , Ryskin A. I. 
Published: July 2007

AbstractThe Jahn‐Teller (JT) interaction energy is calculated for 5T2 and 5E states of the Cr2+ ion in ZnS, ZnSe, and ZnTe crystals. The calculations are made within the framework of a particular microscopic model of the crystal field in the distorted crystal (model of point‐like exchange charges), the multimode interaction is taken into account. For the 5T2 term the energies of interaction with tetragonal and trigonal modes are of the same order of magnitude. This circumstance results in a small height of the barriers that separate various minima of the adiabatic potential and is responsible for the dynamic aspect of the static JT effect in these systems.
On the Dispersion Relation of Carriers in Semimetallic BiSb Alloys
Authors: Jung Th. , Braune W. 
Published: July 2007

AbstractAn investigation is made of the descriptive power of the semi‐empirical k · p models and of the deformation models of the band structure of semimetallic BiSb alloys. Using simple k · p models it can be shown that for x > 3 (x in at% Sb) the Fermi surface of the electrons assumes an ellipsoidal shape, whereas for the concentration dependence of the energy gap EgL one obtains a result which appears unrealistic. An application of models of the band structure on the basis of the deformation theory shows that if more than two bands are taken into account it is possible to obtain a concentration dependence of EgL, the essential properties of which are in agreement with the hitherto existing concepts.
Electronic Structure of Sb and Its Dependence on Hydrostatic Pressure
Authors: Pospelov Yu. A. 
Published: July 2007

AbstractHigh‐accuracy computer calculations of the electronic structure of Sb and of its pressure dependence up to 20 kbar are reported. Calculations are performed in the framework of the Falicov‐Lin pseudo‐potential method. Accuracies of calculations of cross sections of the energy surface and of corresponding energy levels are improved up to few per cents and 10−4 to 10−5 Hartrees, respectively. This results in a coincidence between the calculated and observed pressure dependences of the electronic structure of Sb. Basic results of calculations, comparison with experimental data, and a discussion are presented.
A Co‐Ordinated Approach to the Calculation of Lattice Parameter and Heat of Formation for Alkali Halide Solid Solutions
Authors: Maity S. N. , Roy D. , Sengupta S. 
Published: July 2007

AbstractExperimentally observed deviations of the lattice parameter from Vegards' law in alkali halide solid solutions are predicted from the boundary condition on the equation for the heat of formation. This also simultaneously makes the latter consistent with experimental results. The theory uses no experimental information of the solid solution and only the perfect crystal information is sufficient. The model is employed here to calculate the lattice parameter and heat of formation of ten alkali halide solid solutions over the entire concentration range. The agreement with the experimental results is quite satisfactory.
Theory of Planar Channeling of Relativistic Protons in Bent Crystals
Authors: Taratin A. M. , Filimonov Yu. M. , Vyatkin E. G. , Vorobiev S. A. 
Published: July 2007

AbstractDechanneling of relativistic protons in planar channels of bent crystals is examined on the basis of the Fokker‐Planck equation. The dependence of the dechanneling half‐length x1/2 in a curved channel of (110) Si on the particle energy E and the bending radius R is found. It is shown that in the bent crystal the dechanneling lengths are considerably reduced and the proportionality between the x1/2 value and the particle energy E is violated. The optimum conditions for deflection of a proton beam at the definite angle by a bent crystal are considered.
The Interaction of Surface Excitons
Authors: Bobrysheva A. I. , Zyukov V. T. , Beryl S. I. 
Published: July 2007

AbstractThe Fourier transform v(p) of the exciton–exciton interaction energy is derived. The excitons are situated in a semiinfinite polar crystal near the surface. The character of the interaction depends essentially on the symmetry of the spin functions under the permutation of identical particles. On the base of v(p) the shift of the surface excitons level with increasing exciton density nex is obtained. The numerical value is listed for GaAs. The effective Hamiltonian of surface excitons interacting through exchange by virtual surface longitudinal optical phonons is derived.
Some Evidence for the High Density Phase of Excitons in CdS
Authors: Rückmann I. , May V. , Voigt J. 
Published: July 2007

AbstractReflection spectra without and with additional pumping are measured in CdS at 1.8 and 77 K, respectively, starting from very low pump intensities. At low pump intensities a special behaviour of the reflection minimum is found indicating the importance of an exciton dead layer. The experimental spectra up to the highest pump intensities can be fitted very well taking into account spatial dispersion, exciton dead layer, and density dependent excitonic parameters. Polarizability, damping, and layer thickness change continuously in the whole range of excitation intensities. On the other side, the transverse dielectric function of a high density gas of interacting Is excitons is calculated. A comparison between theoretically and experimentally obtained excitonic parameters at different densities shows good agreement. Hence, the importance of many‐exciton interaction for the reflection spectra up to vanishing at highest pump intensities is concluded.
A Comparative Study of Dynamical Behaviour of Ionic Lattices
Authors: Gupta H. N. , Upadhyaya R. S. 
Published: July 2007

AbstractA critical study of all the three extensions of the shell model i.e. the breathing shell model (BSM), the deformable shell model (DSM), and the three‐body force shell model (TSM) is further carried out for cesium chloride type ionic crystals on the similar pattern as reported earlier. These models are applied to study comparatively the dynamical behaviour of cesium chloride (CsCI) and thallous bromide (TIBr). The results so obtained, again confirm the superiority of TSM over DSM and BSM, not only in explaining the phonon dispersion curves but also for interpreting the infrared (IR) and Raman spectral peaks and Debye temperature variations.
On the Influence of the Polariton Effect on Excitonic Molecules
Authors: May V. , Röseler J. 
Published: July 2007

AbstractRenormalization and damping of excitonic molecules due to their coupling to the radiation field is theoretically investigated within a picture of interacting polaritons and excitonic molecules. Numerical results are given for some cubic and wurtzite‐type materials. For CdS the renormalization reaches nearly 20% of the binding energy of the excitonic molecule.
Low‐Temperature Properties of an Anisotropic Heisenberg Ferromagnet
Authors: Škrinjar M. J. , Kapor D. V. , Šetrajčić J. P. 
Published: July 2007

AbstractThe low‐temperature properties of the anisotropic Heisenberg model proposed by Belorizky et al. are discussed in the approximation of small anisotropy J′/J ≪ 1. The closed set of self‐consistent equations for the magnetization and the energy of elementary excitations is obtained by the application of Zubarev's double‐time temperature dependent Green's functions. Magnetization is calculated in the approximation linear in J′/J, up to terms of order T9/2. All the coefficients of the low‐temperature expansion are renormalized (compared to Dyson's results), while a new term proportional to T3 appears due to anisotropy only. Zero‐point deviations are shown to be proportional to (J′/J)2.
Bound Magnetic Polaron in Europium Chalcogenides. Magnetic Properties
Authors: Kuivalainen P. , Sinkkonen J. , Stubb T. 
Published: July 2007

AbstractThe effect of shallow‐donor impurities and the bound magnetic polaron (BMP) formation on the magnetic properties of some Eu chalcogenides is considered. The contribution of the inhomogeneous spin polarization around the donors to the magnetic susceptibility and the total magnetization is calculated. It is shown that due to the donors a maximum of the zero‐field differential susceptibility shifts to a higher temperature as the donor concentration increases. Also the magnetization is non‐zero far above the Curie temperature when the donors are present. The results agree with the experimental data obtained in low‐conducting EuSe samples with various donor concentrations. Moreover, the calculated results indicate that the donors must form clusters with large unperturbed parts of the crystal between the clusters in order to explain the details in the experimental susceptibility.
Optical Absorption Spectrum of Cr3+ Ions Doped in CsCl
Authors: Trappeniers N. J. , Stibbe F. S. , Rao J. L. 
Published: July 2007

AbstractThe optical absorption spectrum of Cr3+ ions doped in CsCl is studied at room and liquid nitrogen temperatures. Assuming tetragonal site symmetry for the Cr3+ ion, the band maxima are successfully fitted with the theoretical energy equations of a d3 configuration immersed in a tetragonal ligand field, including full configuration interaction but neglecting spin—orbit perturbation.
Free‐Carrier Doping and Many‐Body Effects in Crystal Dynamics of Lead Sulphide Semiconductors
Authors: Singh R. K. , Singh K. P. 
Published: July 2007

AbstractThe effects of free‐carrier doping and many‐body interactions are thoroughly investigated on the crystal dynamics of lead sulphide semiconductors. The model used for such investigations is developed by incorporating the doping effect of free‐carriers in the framework of a well known extended three‐body force shell model. The importance of these effects in predicting the phonon dispersion curves, two‐phonon Raman, and infrared spectra of the solid under consideration is briefly discussed.
Reflectivity of Uniaxial Antiferromagnetic and Ferrimagnetic Crystals
Authors: Merten L. , Lehmeyer A. 
Published: July 2007

AbstractFormulae for the reflectivity of uniaxial antiferromagnetic and ferrimagnetic crystals are derived for normal incidence parallel to the optical axis. The formulae show that in general the reflected waves are elliptically polarized. In particular, they can be used to fix the zeros of the off‐diagonal elements of the permeability tensor. Besides, the formulae are suitable to determine the properties of magnons from reflectivity spectra of uniaxial antiferromagnetic and ferrimagnetic crystals.
The FA(II) Center Relaxed Excited State and Models of FA(II)‐Like Defects in Alkali Halide Crystals
Authors: Parfianovich I. A. , Salomatov V. N. 
Published: July 2007

AbstractIn the second order perturbation theory the FA(II) center is considered as the F center in the field of a defect with excess dipole moment due to off‐center position of a small‐radius impurity cation. In such a model, the properties of the FA(II) center may be explained in terms of the wave‐function of greater spatial distribution for the F‐center relaxed excited state. The F‐center perturbation caused by the defect having its own small electric dipole moment (molecules of the type NO2−, OH−, CN−) is also discussed.
ESR Studies of Manganese Centres in LiH X‐Rayed at Low Temperature
Authors: Ikeya M. 
Published: July 2007

AbstractESR studies of the Mn2+ centre in LiH are made in X‐rayed LiH. No spectrum of the Mn2+‐vacancy complex is detected with ESR before irradiation in LiH though mass spectroscopic analysis indicates the presence of 1 to 10 ppm of Mn2+. The signals at g = 4.56, g = 2.057, and g = 2.0014 are produced by X‐irradiation at 20K. The signals are changed into the spectrum of Mn2+ with g = 1.991, A = 71.5 × 10−4 cm−1 and the axial field D = (450 ± 5) G with [100] symmetry at the temperature above 50K reversibly. The spectra are tentatively ascribed to Mn2+‐H− interstitialhydrogen complex with the thermal motion of H− around Mn2+.
Elastic behaviour of mixed alkali halide crystals of rocksalt structure
Authors: Basu C. , Kanrar A. , Ghosh U. S. 
Published: July 2007

AbstractThe dependence of the elastic constants on the relative concentration of the constituents of mixed alkali halide crystals of rocksalt structure is investigated using the pseudo‐unit cell model for the mixed crystal as illustrated by Chang and Mitra and the deformable shell model for the lattice dynamics as developed by Basu and Sengupta. Expressions are derived for the three independent elastic constants C11, C12, and C44 of the mixed system in terms of the relative concentration of the constituents and certain parameters pertaining to the terminal crystals. The theory thus developed is applied with remarkable success to the case of the mixed crystal KCl–KBr for which detailed experimental data are available.
Effect of ultraviolet irradiation on Se2−‐anion vacancy dipoles in potassium iodide
Authors: Prakash J. 
Published: July 2007

AbstractThe absorption bands due to an isolated Se2−‐anion vacancy dipole in KI are located at 275, 291, 371, and 395 nm. It is observed that the irradiation in the 275 and 291 nm absorption bands results in a photo‐chemical reaction. Irradiation in the 395 nm absorption band in the presence of an electric field creates a situation in which more dipoles are aligned along the electric field direction whereas such an irradiation in the absence of the electric field destroys the preferred orientation of the frozen‐in polarized dipoles. The effect of UV irradiation is studied as a function of electric field strength, irradiation temperature, and irradiation time.
Electron hopping energy influence on the specific heat of phosphorus‐doped silicon
Authors: da Silva A. Ferreira , Fabbri M. , da Cunha Lima I. C. 
Published: July 2007

AbstractThe specific heat of doped semiconductors is shown to be very sensitive on the choice of the model that provides the electron hopping energy. The one‐band model of Matsubara and Toyozawa developed for impurity bands by including the effect of a stronger electron correlation via a Heitler‐London two‐particle wave function is applied in order to calculate the specific heat of Si:P. It shows a reasonable agreement with the experimental data. The results of the AMO‐MT, the highly‐correlated‐electron‐gas, and the inhomogeneity models are shown for comparison.
Thermodynamics of strongly anharmonic crystals
Authors: Malinowska‐Adamska C. , Owsiejczyk M. , Wojtczak L. 
Published: July 2007

AbstractA self‐consistent phonon theory of lattice dynamics based on the thermodynamic double‐time Green's function method is applied to the investigation of the thermal properties of the anharmonic face‐centred and body‐centred cubic crystals with the Morse potential as a model for nearest‐ neighbour central force interaction. The temperature and pressure dependence of the thermodynamic functions of cubic metals in the high and low temperature limits are given and compared with experimental data.
Highly localized donor states in InSb and their pressure dependence
Authors: Kończewicz L. , Trzeciakowski W. 
Published: July 2007

AbstractSome experimental results are given of the pressure dependence of Hall and Shubnikov‐de Haas effects in InSb doped with S and Se. For T = 4.2, 300, and 519 K a decrease of the free‐carrier concentration is observed due to the filling of the resonant impurity states lying highly in the conduction band. Interpreting the data with the simple Koster‐Slater model good agreement of the theory with experiment is obtained. More accurate conclusions could be drawn from such fits if the density of states in the conduction band and its dependence on pressure and temperature were better known.
Theoretical investigation of resonant magnon‐phonon interaction in FeF2 in high magnetic field
Authors: Bancewicz M. , Stasch A. 
Published: July 2007

AbstractThe experimental verification of van Vleck's model for FeF2 by using neutron and Raman spectroscopy and applying strong magnetic fields is discussed theoretically. The possibility of measuring the k‐dependence of the magnon‐acoustical phonon interaction parameter using the magnetic field‐induced splitting of antiferromagnon branches is analyzed. It is shown that for a field in the 0 to 200 kG range this effect can be observed by neutron spectroscopy for values of k from an area covering about 40% of the Brillouin zone. Moreover, the calculations of the magnon‐acoustical phonon interaction parameter proposed for H = 0 by Lovesey are extended to the case of coupling between magnons and optical phonons of Eg and B1g symmetry as well as to high magnetic fields. The values of the Eg phonon‐one magnon and B1g phonon‐two magnon coupling parameter, calculated on the basis of the van Vleck model, amount to 9.9 and 6.3 cm−1, respectively. It is also shown that in a magnetic field of the order of 100 kG two magnon‐B1g phonon hybridization can occur manifesting itself as a splitting of the Raman line.
Defect states in amorphous silicon
Authors: Ishii N. , Kumeda M. , Shimizu T. 
Published: July 2007

AbstractThe nature of defects in amorphous silicon is calculated by using several methods for clusters with varying size. The wave function of the dangling bond state has an approximately exponential decay with a decay length of about 0.2 nm. The correlation energy of electrons and the hyperfine structure constant with 29Si for the dangling bond state are evaluated. The correlation energy and the g‐values are calculated both for a weak bond and for a two‐fold coordinated defect and are compared with experiments.
A localized orbital description of Ge and α‐Sn
Authors: Smith P. V. 
Published: July 2007

AbstractIn previous work an accurate description of the band structure and the valence electron pseudocharge density of Si is given in terms of a small set of well localized basis functions comprising only ten states of s, p, d, and f symmetry per atomic site. Now this work is extended to the case of Ge and α‐Sn and it is shown that this localized orbital approach also provides an excellent representation of the electronic structure of these other diamond elemental semiconductors. Moreover, the resulting basis functions are again very well localized about their respective lattice sites. The implications of this work in relation to semiconductor impurity problems are also briefly discussed.
The influence of the surface barrier on the trajectory of sputtered particles
Authors: Abdel‐Malik T. G. , Aly A. A. , Abdeen A. M. , Motaweh H. A. 
Published: July 2007

AbstractThe parameters of a spherical surface barrier with refraction for the particles sputtered from Cu single crystals are computer calculated. Use is made of the method of straightforward simulation of the surface atom ejection in the field of the near‐surface block of atoms. The interactions of the atoms are described by a Morse potential.
Excitation of magnetoacoustic waves by two microwave beams in InSb
Authors: Maheshwari K. P. , Tarey Ganesh 
Published: July 2007

AbstractAn investigation is made of the resonant excitation of magnetoacoustic wave at the difference frequency of two microwave beams propagating in a magnetoactive solid state plasma viz. n‐InSb. Due to the interaction of the two waves in the semiconductor the ponderomotive force at the difference frequency becomes finite and generates a magnetoacoustic wave if the dispersion relation corresponding to magnetoacoustic wave is satisfied. The analysis shows that there is a finite probability of excitation of an acoustic wave alongwith the magnetoacoustic wave. The excited acoustic and magnetoacoustic waves couple at magnetic fields when the thermal pressure is equivalent to the magnetic pressure. The propagation characteristics of the coupled wave are also studied. The results show that microwave beams of power densities 1 MW cm−2 excite magnetoacoustic wave of power density 0.04 kW cm−2 when ωc/ω = 0.1. The increase in magnetic field increases the power density of the excited magnetoacoustic wave whereas it tends to reduce the refractive index and attenuation constant of the coupled wave.