bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoluminescence Governed by Simultaneous Thermal Stimulation of Electrons and Holes
Authors: Chen R. , Mathur V. K. , Rhodes Joanne F. , Brown M. D. , McKeever S. W. , Bull R. K. 
Published: July 2007

AbstractThe possibility of a simultaneous thermal release of electrons and holes in the thermoluminescence (TL) process was suggested in the early stages of the development of this discipline. However, most investigators utilized a model in which carriers of only one kind are thermally released from their “traps”. In this model these carriers then radiatively recombine with carriers of opposite charge in “luminescence centers”. This paper presents the results of a theoretical investigation into a more complex model, which allows the thermal release of electrons and holes in the same temperature range. The solution of a set of four simultaneous differential equations is required in this investigation. The equations are not amenable to analytical solution, so the equations are solved numerically for given values of the model parameters. Conclusions are drawn about the shapes of the TL curves, and the expected stability of the corresponding traps at given temperatures, and the apparent effective parameters namely, the activation energy, the frequency factor, and the order of kinetics, are obtained using the “general order” formalism. In all cases examined, there is a good three parameter fit to the TL peak generated by the examined model. This shows that even a rather general TL peak can be described quite accurately by the three parameter model. The activation energy determined using the three parameter analysis is found to agree rather well with the input activation energy of trapped electrons which is used in the original peak generation for the particular cases examined. In cases where the activation energy for holes is small, the glow peaks occur at relatively low temperatures, and are characterized by a very high effective frequency factor in the three parameter analysis. Furthermore, several cases are studied in which the calculated kinetics order is found to be less than 1.0.
Decay Kinetics and Polarization of the AT Emission of Pb2+ Centres of Different Structure in KBr:PbBr2
Authors: Egemberdiev Zh. , Nagirnyi V. , Soovik T. , Zazubovich S. 
Published: July 2007

AbstractThree types of Pbc [001] centres) are found in a KBr:PbBr2 crystal. The luminescence of all these centres is caused by electronic transitions from tetragonal minima of the adiabatic potential energy surface (APES) of the triplet excited state of the Pb2+ ion. A comparison of the spectral, polarization and kinetic characteristics of their emission is performed. The position and structure of the defect associated with the Pb2+ ion are shown to have strong influence on the luminescence properties of KBr:PbBr22+v dipole and interstitial bromine atom associates (Hz(Pb2+) centres) as well as a Pb2+ ion associated with the next‐nearest‐neighbouring cation vacancy (Pb2+v− crystal.
Charge Transfer and Electron‐Molecular Vibration Coupling in Tetramerized Quasi‐lD Semiconductors
Authors: Yartsev V. M. 
Published: July 2007

AbstractElectron‐molecular vibration coupling in tetramerized organic ion‐radical semiconductors is considered. Eigenvalues and eigenfunctions of the molecular tetramer with two electrons are calculated in terms of extended Hubbard model parameters. The energy inequivalence of the monomer sites is introduced explicitly. The complex frequency dependent conductivity of the tetramerized compounds is found to produce a number of sharp maxima due to indirect excitation of the totally symmetric (ag) internal molecular modes of vibrations. These peaks are shown to have a fine structure if the charge density is not shared equally by the constituent molecules. The calculated reflectance is compared with the measured one for TEA (TCNQ)2 single crystals.
The Effect of Many‐Electron Correlation on Photothresholds of Semiconductors and Valence Band Discontinuities at Heterojunctions
Authors: Bechstedt F. , Enderlein R. , Heinrich O. 
Published: July 2007

AbstractPhotothresholds of semiconductors are known to deviate by 3 to 4 eV from the predictions of one‐electron band theory. It is shown that these discrepancies are due to many‐electron correlation effects, in particular, to electronic relaxation. The corrections to photothresholds due to electronic relaxation are calculated by means of Green's function technique applying the linear shielded potential approximation to the exchange‐correlation self‐energy. Within the uncertainties of LCAO theories the calculated photothresholds of group IV, III‐V, and II‐VI semiconductors agree with experimental data. A simple physical picture of the correlation effect is provided. Relaxation corrections to valence band discontinuities from one‐electron band theories are also calculated.
Relativistic Theory of Photoemission from Solids. I. Key Aspects of the Model
Authors: Thörner G. , Borstel G. 
Published: July 2007

AbstractThe key aspects known to be important in photoemission: matrix elements, scattering of the outgoing wave, band structure, and surface effects are formulated within a relativistic singleparticle theory with the objective of developing a workable relativistic model for photoemission from magnetic and nonmagnetic solids.
On the Theory of Ion‐Induced Electron Emission
Authors: Rösler M. , Brauer W. 
Published: July 2007

AbstractA microscopic theory of H ion‐induced electron emission is developed in close analogy to the theory of secondary electron emission and applied to polycrystalline aluminum. The formation of excited electrons by screened Coulomb interaction with H+ ions of primary energy E0 between 20 and 800 keV is considered. Both, elastic and inelastic collisions of these electrons are taken into account. As far as possible the results calculated are compared with recent experimental data. Energy and angular distributions of ejected electrons prove to be in accordance with measurements. The calculated electronic yield γ shows a maximum in the primary energy dependence at E0 ≈ 55 keV with a maximum value γmax = 1.1. With increasing primary energy there are larger deviations from the measured yield values.
Magnetic Field Dependence of the Spin Polarization of the F Center
Authors: Iwahana K. 
Published: July 2007

AbstractA simple model for the magnetic field dependence of the spin polarization of the F center is developed, in which the spin mixing due to the hyperfine interaction both in the ground state and in the relaxed excited state is taken into account. It is shown that the spin mixing due to the hyperfine interaction plays an essential role in the interpretation of the spin polarization at low fields less than 0.5 T. Quantitative fitting of the experimental data of the magnetic field dependence of the spin polarization is performed for KBr and RbBr.
Effective Medium Approach for the Residual Resistivity of Alloys Containing Guinier‐Preston Zones
Authors: Gläser U. H. , Löffler H. 
Published: July 2007

AbstractDifferent models for describing the residual resistivity of alloys with precipitates are briefly reviewed. The microscopic theories are able to reproduce the initial increase in the resistivity appearing during the ageing in some alloys forming Guinier‐Preston zones but fail in the largezone limit, whereas just the opposite situation is known for the macroscopic effective medium theories. The classical Maxwell‐Garnett theory for inhomogeneous materials is extended to particle sizes comparable or smaller than the electron mean free path. Regarding only the inner part of a GP zone as a macroscopic inclusion and treating the outer part microscopically as a part of the matrix one obtains a model for the resistivity containing only two essential parameters: The extra resistivity due to coherent scattering and the mean free path of the electrons inside the zones. The values of the parameters are derived from the electronic structure of the alloy. The model is found to be in a good agreement with experimental data for an Al‐5 at% Zn alloy.
The Peculiarities of the Electronic Structure of BaTiO3 in the ATiO3 (A = Ca, Sr, Ba) Series
Authors: Nemoshkalenko V. V. , Timoshevskii A. N. 
Published: July 2007

AbstractThe electronic structure of ATiO3 (A = Ca, Sr, Ba) titanates is studied by the APW and Xα‐SW methods. The degree of participation of atom A states in formation of the valence band and the conduction band is shown to grow in this order. The results are confirmed by X‐ray emission and XPS experimental data. The peculiarity of the electronic structure of BaTiO3 is the presence of Ba 5p, 5d, 4f levels in the vicinity of the valence band and the bottom of the conduction band. Due to this fact in the investigated series of the compounds the Ti‐O interaction is weakened in BaTiO3.
F‐Centres in KCl–Tl Crystals
Authors: Nagli L. E. 
Published: July 2007

AbstractThe infrared emission and photostimulated luminescence under excitation in F‐absorption band are investigated in KCl–Tl crystals coloured by X‐ray or by KrF‐laser pulses at 12 or at 290 K. Basing on the concentration, temperature, kinetic, and spectral dependences of these emissions, it is proposed that the main part of the F‐centres is created at distances smaller than 12a from Tl+ and Tl2+ ions.
Electron–Phonon Scattering and Low‐Temperature Thermal Conductivity of Niobium and Tantalum Single Crystals
Authors: Wasserbäch W. 
Published: July 2007

AbstractThe thermal conduction of niobium and tantalum single crystals of different impurity contents is measured below 20 K. The investigation of the lattice thermal conductivity as limited by the interaction of phonons with electrons demonstrates that both, longitudinal and transverse phonon modes are scattered strongly.
The Study of Tl 〈110〉 Centres in NaCl and RbCl
Authors: Nistor S. V. , Schoemaker D. , Ursu I. , Yang B. R. 
Published: July 2007

AbstractThe presence of 〈110〉 oriented Tl centres is confirmed in the ESR spectra of heavily doped NaCl:Tl+ and RbCl:Tl+ crystals following X‐irradiation. This identification is supported by an analysis of the spin‐Hamiltonian parameters as well as by the formation and optical bleaching properties, which are similar to the previously reported optical‐absorption and ESR studies on Tl〈110〉 centres in KCl. An analysis of the spin‐Hamiltonian parameters in the frame of a molecular‐orbital model is presented.
Long‐ and Short‐Range Magnetic Interactions in EuO
Authors: Averous M. , Desfours J. P. , Vellas J. R. 
Published: July 2007

AbstractIn Eu‐rich EuO (EuS), the resistivity versus temperature shows an insulator‐metal transition, and in some cases a shoulder and a peak situated above the Curie temperature when T increases. Especially the shoulder temperature range is studied. It is shown that this region has a De Gennes‐Friedel‐type behavior whereas the peak region exhibits a Fisher‐Langer‐type behavior. The long‐range magnetic interactions in the shoulder temperature range are due to the existence of bound magnetic polarons. These interactions are emphasized either by magnetic field or by increasing of the Eu excess, i.e. bound magnetic polaron concentration.
Tensorial Coupling and the Reduced Matrix Elements of One‐ and Two‐Body Operators
Authors: Tuszyński J. A. , Dixon J. M. 
Published: July 2007

AbstractThe reduced matrix elements of products of tensor operators, coupled to form a non‐zero rank, are investigated to emphasize the importance of correctly incorporating all tensorial couplings. It has recently been realized that serious inaccuracies can arise, in some cases, unless the complete many body nature of the full operator and the states involved is properly incorporated. Exact results are presented for one‐ and two‐body operators which include all couplings and compare and contrast them with some approximate methods.
Stimulated Brillouin Scattering of High‐Power Helicon Waves in Longitudinally Magnetized Cubic Piezoelectric Semiconducting Plasmas
Authors: Ghosh S. , Saxena R. B. 
Published: July 2007

AbstractA detailed analytical investigation is made of the stimulated Brillouin scattering of a high‐power helicon pump wave propagating parallel to the applied magnetic field in an n‐type cubic piezoelectric semiconducting plasma belonging to class 43m. A general dispersion relation is obtained by using the hydrodynamic model of a homogeneous, piezoelectric, one‐component (electron) semiconducting plasma, and the threshold value of the pump electric fields and the initial growth rates of both the excited modes (i.e., in the cases of left‐hand and right‐hand circularly polarized modes) well above the threshold are discussed. The analysis is applied to a specific semiconductor, n‐InSb at 77 K, duly irradiated by a high‐power helicon wave for numerical estimations. The laser field intensities used are in the range of 107 to 1011 Wm−2 which is assumed to be less than the damage threshold of the InSb crystal. The order of wave amplitude is experimentally feasible.
On the Temperature Behaviour of DC Conductivity in One‐Dimensional Conductors above Tc
Authors: Dieterich K. , Wagner M. 
Published: July 2007

AbstractAn ab‐initio single particle theory is presented for the temperature behaviour of electrical transport in one‐dimensional conductors. The calculation of the conductivity is based on a Kubo‐Moriformalism. The Kohn mode‐softening near the Peierls temperature is taken into consideration in a new approximation step for the calculation of the relaxation time, which is beyond a mean field calculation. For temperatures sufficiently above Tc the T−1 law of the semiphenomenological earlier calculations is obtained, whereas close to the Peierls temperature a high maximum caused by the Kohn anomaly is found. This conductivity peak depends very sensibly on the quotient of the Debye temperature and the Peierls transition temperature. The calculation permits the suggestion that in the commensurate phase at high pressure single particle excitations provide the dominant conduction path far above Tc.
Temperature Dependence of the Elastic Constants of p+ Silicon
Authors: Khan F. S. , Allen P. B. 
Published: July 2007

AbstractThe free hole contribution to the elastic properties of p‐type silicon is investigated. A wide range of doping concentration, from 1017 to 1020 cm−3, and temperature variation, from 100 to 500 K, is considered. Numerical calculations are given for the free hole contribution to the elastic constants. Effects of temperature variation are investigated and numerical results are given for the temperature coefficients of the elastic constants of p+ silicon.
Analysis of the Equation of State of Ammonium Halides
Authors: Agrawal S. C. 
Published: July 2007

AbstractAn analysis of the equation of state is performed for the ammonium halides. The variation of volume with pressure is calculated using interionic potentials including the effect of short range overlap repulsive energy up to next nearest neighbours. The van der Waals dipole‐dipole and dipole‐quadrupole interactions derived from the variational method are also taken into account. The results are discussed and compared with available experimental data.
Structure and Bonding in Cubic IV–VI Crystals. V. Lattice Repulsion. Comparison of Lattice and Vibronic Anharmonicity
Authors: Enders P. 
Published: July 2007

AbstractTwo simple models for the lattice repulsion forces are applied to cubic IV–VI crystals giving semiquantitative results. Nor the lattice nor the vibronic contribution to the anharmonic coefficients of the Landau free energy expansion is negligible in these materials, for what a simple criterion is derived.
Formation of Localized Magnetic Moments in Chromium‐Manganese Alloys
Authors: Aidun R. , Arajs S. , Moyer C. A. 
Published: July 2007

AbstractThe electrical resistivity (ϱ) and magnetic susceptibility (χ) of CrMn alloys containing 2, 8, 10, 13, and 16 at% Mn are studied as a function of temperature (T). Both the ϱ−T and χ−T curves exhibit characteristic anomalies at the Néel temperature (TN). Careful analyses of the χ data by several methods all suggests the existence of a magnetic moment on the Mn impurities below and above TN. These results are discussed briefly from the standpoint of previous investigations and compared with the behavior exhibited by Fe and Co impurity moments in the Cr matrix.
Frequency‐Dependent Conductivity Studies of the Ordered and Disordered Phases of Ag2HgI4 and Cu2HgI4
Authors: Sudharsanan R. , Clayman B. P. 
Published: July 2007

AbstractFar infrared reflection and transmission properties of Cu2HgI4 are measured in the region 10 to 200 cm−1 for both, α‐ and β‐phases. The TO and LO mode frequencies are obtained from a Kramers‐Kronig analysis of the reflection spectra. Frequency‐dependent conductivity is calculated from the values of ε″ in the region 10 to 200 cm−1 for both phases. The conductivity spectra of α‐Ag2HgI4 and α‐Cu2HgI4 are analysed using the Kostadinov and Vu Thi Binh model. It is concluded that the mobile ions (Ag+ and Cu+) have two different sites ofo ccupation during their conduction process. It is suggested that other than regular tetrahedral sites, the mobile ions may occupy interstitial sites, in good agreement with the observations of Kasper and Browall and the Wiedersich and Geller model for the conduction process in these materials.
Phonon‐Dislocation Scattering and Low‐Temperature Lattice Thermal Conductivity of Niobium and Tantalum Single Crystals Deformed at Low Temperatures
Authors: Wasserbäch W. 
Published: July 2007

AbstractThe thermal conduction of niobium and tantalum single crystals plastically deformed in steps at low temperatures is measured between 0.3 and 20 K. The dislocation arrangement is studied by X‐ray topography and transmission electron microscopy. The thermal resistivity Wd due to the plastic deformation deduced in the temperature range 0.3 K < T < 5 K is found to be proportional to about T−3 after weak deformation. Strong deformation gives rise to a thermal resistivity proportional to T−2. The results are consistent with the model of scattering of phonons by the static distortion field of dislocations.
Influence of Cationic Vacancies on the Mobility of Li+ Ions in Some Cation‐Deficient Materials. An NMR Study
Authors: Latie L. , Villeneuve G. , Cros Ch. , Hagenmuller P. 
Published: July 2007

Abstract7Li NMR is carried out between 150 and 450 K in Li‐deficient chlorides with LiCl‐type or the related Suzuki‐type structure. Diffusive motion of Li+ ions is observed and the analysis of experimental data for Li1−2xMgxCl with x = 0.01 shows that the introduction of 1% vacancies into the lattice enhances the Li+ mobility by a factor of 30 at 440 K. By increasing the number of vacancies, the activation energy decreases down to 0.38 eV for ordered Li6VCl8 which contains 12.5% vacancies and even to 0.25 eV for the disordered phase corresponding to the same composition.
Some Photoluminescence Properties of Mn2+ in Magnesium Bromide
Authors: Mićić R. , Drašković B. 
Published: July 2007

AbstractSynthesis and photoluminescence are reported of two phosphors whose basis lattice is MgBr2 · 6H2O. In the first case Mn2+ ions as impurity are introduced in this basis and in the second case Mn2+ and Zn2+ ions. For both the phosphors it is shown that the absorption‐emission center is a manganese Mn2+ ion. In the first case the Mn2+ ion is located in octahedral coordination, reaching this state through an isomorphic substitution of the Mg2+ ion. In the second case, depending on the relative concentration of Zn2+ ions in comparison to Mn2+ ions, the Mn2+ ion may exist in octahedral, tetrahedral, and quasi‐tetrahedral coordination, causing the appearance of three emission bands in its luminescence spectrum. Zn2+ impurities cause two effects: they influence the change of ligands and the site symmetry of the Mn2+ ion and, simultaneously, distort the symmetry of the complex MnCl2+4. It follows that an adequate choice of concentration of ZnCl2 impurities enables one to manage indirectly the emission of Mn2+ in these phosphors.
Magnetic Symmetry in Several Tetragonal Compounds
Authors: Luchian H. 
Published: July 2007

AbstractAll the non‐helical spin arrangements which can be supposed to arise in the sites 4c and 4e in several tetragonal compounds crystallizing in the space group I4/mmm are proposed using a well known group theoretical method derived from the Landau theory of the second order phase transitions. The investigation is based only on black and white symmetry arguments.
1H‐NMR Spectra of Molecular Groups in a Paramagnetic Matrix
Authors: Birczyński A. , Lalowicz Z. T. 
Published: July 2007

AbstractProton NMR spectra of molecular groups (NH+4, H2O) in a diluted matrix of paramagnetic spins are presented and compared with experiments. The sensitivity of the spectra to the paramagneticantiferromagnetic transition is discussed. Fits to experimental lines for antiferromagnetic ammonium salts (NH4)2IrCl6, (NH4)2RhCl6, and paramagnetic CoCl2 · 6 H2O are shown. The range of effective local magnetic fields is evaluated.
Adequacy of the Nearest‐Neighbour LCAO Model Hamiltonian for the F.C.C. Transition and Noble Metals
Authors: Smith P. V. 
Published: July 2007

AbstractThe value of model Hamiltonians as interpolation schemes for studying the electronic properties of a wide variety of systems is now well known. In particular, the mixed basis schemes of Hodges et al., Mueller, and Smith and Mattheiss are extensively applied in determining theoretical photoemission spectra for the f.c.c. transition metals, and in studying the role of impurities in these systems. Unfortunately, however, such schemes are not suitable for studying strongly localized defects, bulk elastic properties or surfaces because of the extended nature of their plane wave basis functions. A novel approach to calculating such properties involves the use of the Chadi total energy algorithm which is based on a nearest neighbour LCAO model Hamiltonian description of the host metal bandstructure. The main objective of this present paper is thus to assess the adequacy of the empirical tight‐binding method within the nearest‐neighbour approximation, in describing the electronic structure of the f.c.c. transition and noble metals. Using copper as a prototype system, it is shown that such a simple LCAO representation can indeed yield band structures and density of state curves which are comparable in accuracy with those of the mixed basis sets. The employment of this simple LCAO model within the Chadi scheme for the determination of therelaxation of f.c.c. transition and noble metal surfaces is then discussed.
Zero Energy Gap Conditions and Band Inversion in Superlattices
Authors: de Dios Leyva M. , Gondar J. López 
Published: July 2007

AbstractUsing the envelope‐function approximation and the transfer‐matrix method, for k⟂ = 0, the wave functions, the dispersion relation, and the zero energy gap conditions connected with light particles (electrons and light holes) in GaAs‐AlxGa1−xAs and InAs‐GaSb superlattice are obtained. One of the obtained zero energy gap conditions is a direct consequence of the spatial dependence of the energy gap. Also studied, in detail, are the properties of those states for which the lowest conduction band and the highest valence band touch each other. It is established that with increasing magnitude of the conduction band‐valence band edge discontinuity, or of layer thickness, the band inversion phenomenon occurs. Finally, some numerical results for the InAs‐GaSb superlattice are reported.