bluuebunny/crossref_metadata_2025_split huggingface dataset:
A search for defect configurational changes in the post‐breakdown metastability of semi‐insulating GaAs
Authors: Luo Y. L. , Fung S. , Beling C. D. , Ling C. C. , Li S. 
Published: January 2004

AbstractRecently room temperature electrically induced metastability in semi‐insulating (SI)‐GaAS has been reported in which the normally high resistivity state of SI‐GaAs converts into a low resistivity state when breakdown electric fields are applied to the metal/SI‐GaAs/metal systems. In this brief report, the methods of photo‐quenching and positron annihilation lifetime spectroscopy have been employed to see whether the high field breakdown and subsequent metastability has its origins in some configurational change of a native defect in the sample. Our results indicate that rather than being due to an atomic configurational change the observed metastability is most likely of purely electronic origin. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonequilibrium kinetics in spin‐crossover compounds
Authors: Gudyma Yu. , Semenko O. 
Published: January 2004

AbstractWe provide a detailed theoretical analysis of the non‐linear kinetics in spin‐crossover with the application of the nonequilibrium potential conception. The probability stationary density of a spin‐crossover system in the presence of a weak external noise of thermal origin and the mean first passage time of the potential barrier were obtained. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman scattering spectra of La3Ga5SiO14 (LGS) crystals
Authors: Lu G. W. , Li C. X. , Wang W. C. , Wang Z. H. , Wang Z. M. , Yuan D. R. , Xia H. R. 
Published: January 2004

AbstractBased on the space group theory, the normal vibration modes of La3Ga5SiO14 (LGS) crystal were predicted, and the Raman scattering intensities of non‐polar and polar modes were calculated respectively. The lattice vibration and structure of LGS crystal were investigated by Raman spectroscopy and density‐functional theory (DFT). The DFT calculations were made on SiO4, GaO4, GaO6, La3Ga4O12 and La3Ga3SiO12 clusters, which model the atomic cluster in LGS crystal. Excellent agreement has been achieved between vibrational frequencies predicted by the theory and those observed in experiments. The layer structure of LGS crystal is identified, and its excellent piezoelectric properties are mainly attributed to the large polarizability anisotropy of La3Ga4O12 and La3Ga3SiO12 clusters, which results from the strong interaction between Ga(Si)O4 tetrahedras of LGS crystal. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ionic disorder and Yaffet–Kittel angle in nanoparticles of ZnFe2O4 prepared by sol‐gel method
Authors: Wang Li , Zhou Qingguo , Li Fashen 
Published: January 2004

AbstractZnFe2O4 nanoparticles have been prepared by sol‐gel methods. Mössbauer spectra from 4.2 K to RT showed their magnetic ordering took place at much higher temperature than that of bulk zinc ferrite. Mössbauer measurements that cover the temperature range 4.2 K to room temperature were acquired in zero field and an applied magnetic field of 5 T. The large increase of TN for nanoparticles can be attributed mainly to the redistribution of Fe and Zn cations on the A and B sites. Nanoparticles with smaller size have bigger θYK (Yaffet–Kittel angle). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mössbauer Study of ZnxCu1−xFe1.2Cr0.8O4
Authors: An D. H. , Kang K. U. , Lee B. G. , Lim J. B. , Jang S. U. , Baek K. S. , Choi E. J. , Oak H. N. 
Published: January 2004

AbstractZnxCu1−xFe1.2Cr0.8O4 (x = 0.0, 0.2, 0.4, 0.6) have been studied by Mössbauer spectroscopy, SQUID magnetometry, and X‐ray diffraction. The crystals are found to have a cubic spinel structure, and the lattice constant a0 increases linearly with increasing Zn concentration x. The iron ions are in ferric states and occupy both the tetrahedral (A) and octahedral (B) sites; the fraction of the iron irons at the A‐sites is 0.70 for x = 0 and decreases to 0.40 for x = 0.6. As the Zn concentration increases, both Néel temperature and magnetic hyperfine field decrease monotonically. While spin orderings are collinear for low Zn concentrations (x > 0.2), the spin canting emerges for x > 0.2 and increases with increasing Zn concentration; the canting angle at liquid helium temperature reaches up to 37° for x = 0.6. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic diffuse scattering of X‐rays in fcc 4He
Authors: Venkataraman C. T. , Schwoerer‐Böhning M. , Simmons R. O. 
Published: January 2004

AbstractA first measurement of the dynamic diffuse scattering (DDS) of X‐rays was made in a fcc 4He crystal. The generally preferred method of studying lattice dynamics is through inelastic neutron scattering (INS). INS experiments, however, require large crystals which, in case of the high pressure fcc phase of helium are difficult to achieve and suffer from some poorly resolved phonon signals. An alternate promising technique uses a beryllium sample cell at cryogenic temperatures and excellent quality single crystals. Diffuse X‐ray scattering measurements on such fcc samples yield information about the elastic constants in solid 4He. Present test results on a crystal at 241(3) MPa and 23.8(1) K are compared with the results from neutron experiments and several theoretical calculations, including a present Hartree‐Fock LCAO model. Various disagreements are found and discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of low‐temperature magnetic relaxations in two systems GdAl2Dx (C15 Laves phase) and Fe3O4 (Inverse spinel)
Authors: Walz F. , Reule H. , Hirscher M. , Kronmüller H. 
Published: January 2004

AbstractMost interestingly, the low‐temperature (T < 45 K) magnetic aftereffect (MAE) spectra occurring in both the cubic C15 Laves phase GdAl2Dx, after deuterium (D) charging, and in stoichiometric, singlecrystalline magnetite (Fe3O4) are of striking similarity – being composed of a plateau‐like relaxation zone (5 K < T < 30 K) and a pronounced Debye‐peak near T ≥ 30 K. Whereas the well‐investigated spectra in magnetite are well understood as resulting from various modes of thermally assisted incoherent tunneling of small polarons, not so much is known, as yet, concerning the respective mechanisms in GdAl2Dx. Guided by the impressive similarity of their spectra, we attempt here an interpretation of the underlying mechanisms in both systems on the basis of well‐corroborated magnetite concepts – i.e., in terms of incoherent tunnelling of specific particles, such as small polarons in Fe3O4 and deuterons in GdAl2Dx. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetry aspects of exciton–exciton interactions and biexciton transitions in wurtzite semiconductor structures
Authors: Tronc P. , Kitaev Yu. E. , Smirnov V. P. , Jacobson M. , Neu G. 
Published: January 2004

AbstractThe inelastic collision of two excitons or the optical decay of a biexciton can induce a transition into an exciton and a photon. From the symmetry point of view, we have studied the states of free and bound biexcitons in bulk GaN with the wurtzite structure and in GaN/AlN heterostructures. Due to the antisymmetry properties arising from the exchange of identical fermions, the ground state of the free Γ biexcitons involving two holes from the same valence band is totally symmetric with respect to the symmetry group of the structure. We established the optical selection rules as well as the possible channels for the processes mentioned above and showed that, whatever is the symmetry of a biexciton, there are at least two channels for its optical recombination. That suggests fast recombination processes. If one (several) phonon(s) is (are) involved in a process, it is always possible to connect by an optical transition any initial state to any final one. An electric field applied parallel to the growth axis lowers the symmetry of superlattices to that of quantum wells. All the results remain valid for any bulk semiconductor with the wurtzite structure and for any wurtzite‐based heterostructure with identical cations or anions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some peculiar properties of the complex magnetic systems
Authors: Kapor D. , Pavkov M. , Manojlović M. , Pantić M. , Škrinjar M. , Stojanović S. 
Published: January 2004

AbstractWe treat two Heisenberg systems with complex magnetic structures: system with three sublattices and superlattice with three‐plane motive, with both ferromagnetic and antiferromagnetic coupling. Within Bloch's spin‐wave approximation they can be represented by a simple bosonic Hamiltonian with anomalous coupling. We show that the energies of the system can be derived by both Green function approach or so called “u–v” transformation. The basic result is that for a particular relation between sublattice spins i.e. S2 = S1 + S3 the system possess two acoustic (gapless) energy branches with linear dispersion law for small wave‐vectors. This leads to peculiar properties. In the Mean Field formalism, we show that the system in this case manifests so called weak ferromagnetism, and for certain system parameters, the three plane superlattice can posses one or even two compensation temperatures. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the NQR detection of nitrogenated substances by multi‐pulse sequences
Authors: Mikhaltsevitch V. T. , Rudakov T. N. 
Published: January 2004

AbstractTheoretical and practical aspects of using multi‐pulse spin‐locking and the “strong off‐resonant comb” (SORC) sequence for detecting nitrogenated substances by the nuclear quadrupole resonance method were studied. A number of optimum correlations between the parameters of multi‐pulse sequences and the relaxation characteristics of the substances under investigation were determined. The obtained relations were used for the fast detection of α‐trinitrotoluene (TNT). Relaxation parameters and temperature coefficients for twelve 14N lines of the orthorhombic phase of TNT measured at room temperature are also presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
kp‐approach for non‐symmetric short‐range defects: resonant states and alloy bandstructure
Authors: Vasko F. T. 
Published: January 2004

AbstractThe short‐range defect with reduced symmetry is studied in the framework of the kp‐approach taking into account a matrix structure of potential energy in the equations for envelope functions. The case of the narrow‐gap semiconductor, with defects which are non‐symmetric along the [001], [110], or [111] direction, is considered. A resonant state at a single defect is described within the Koster–Slater approximation. The bandstructure modification of the alloy, formed by non‐symmetric impurities, is discussed and a generalized virtual crystal approximation is introduced. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model of a superconducting singular Fermi liquid with a first‐order phase transition
Authors: Gonczarek Ryszard , Krzyzosiak Mateusz 
Published: January 2004

AbstractModel of s‐wave and d‐wave superconductivity in a singular Fermi liquid with a divergent scattering amplitude for particles with the same quasi‐momenta and opposite spins is formulated and presented with regard to a narrow, nearly half‐filled conduction band. The ground state and other eigenstates for the superconducting phase are found. Thermodynamic functions are obtained by the use of the Bogolubov method. The gap equation along with the equation for the chemical potential is derived in a general form and solved in a self‐consistent manner for s‐wave pairing. Above a certain temperature there are two solutions of the gap equation, however only for the greater one the superconducting phase remains stable. It is shown that the system undergoes a first‐order phase transition between the superconducting and the normal phase. The critical temperature and the heat of the transition are found. The temperature dependence of the entropy and the specific heat of the system is also presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two relaxation processes in the inhomogeneous deuterated ferroelectric Rb0.96(ND4)0.04D2AsO4
Authors: Trybuła Z. , Kaszyński J. , Łoś Sz. , Mielcarek S. , Trybuła M. 
Published: January 2004

AbstractThis paper reports the results of the influence of dc electric field on the complex permittivity ε* = ε′ – iε″ in the inhomogeneous deuterated ferroelectric Rb1−x(ND4)xD2AsO4, where x = 0.04 (DRADA with x = 0.04). In this crystal the coexistence of ferroelectric and short‐range ordered (glass) phases takes place at a low temperature below Tc. At Tc = 155 K the transition to the ferroelectric state is reported. Two relaxation processes were observed in the perpendicular orientation to the ferroelectric c‐axis in the temperature range from 3.5 K to 300 K. The influence of a dc electric field on the temperature dependence of the dielectric losses shows clearly two different relaxation processes. At temperatures around 60 K, there is a dispersion related to the embryos of the glass clusters, which coexists with ferroelectric domains. The dispersion around 120 K due to frozen domain wall motion is also observed in the perpendicular direction to the ferroelectric c‐axis along hydrogen bonds. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular‐dynamics simulations of surface and bulk properties of Zn, Cd, and ZnCd systems
Authors: Amirouche Lynda , Erkoç Şakir 
Published: January 2004

AbstractSurface and bulk properties of Zn, Cd, and ZnCd systems have been investigated by performing molecular‐dynamics simulations using a recently developed empirical many‐body potential energy function for these systems, which comprices two‐ and three‐body atomic interactions. Surface reconstruction and multilayer relaxation on clean surfaces, adatom on surface, substitutional atom on surface and bulk materials, and vacancy on surface and bulk materials have been studied extensively. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band structure of a harmonically confined electron with an impenetrable boundary
Authors: Hai W. , Fang X. , Li F. 
Published: January 2004

AbstractWe study finite‐size effects of the spatially bounded quantum systems exemplified by a single‐electron quantum dot with a harmonic potential and an impenetrable boundary. A general solution of the corresponding Schrödinger equation is obtained and the unique special solution for any energy is derived from the normalization and boundary conditions. The classical‐mechanically allowable eigenenergies form the continuous spectrum or piecewise continuous bands with the minimum value being much less than the zero point energy of a free harmonic oscillator. As the increase of the confining size, the band widths reduce and the energies finally close to the discrete level of the free oscillator. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Field‐induced magnetic reorientation of the 2D Heisenberg ferromagnet with S = 1: the influence of an exchange anisotropy
Authors: Ilkovič V. 
Published: January 2004

AbstractThe two‐dimensional (2D) Heisenberg model with spin S = 1, with the exchange anisotropy plus a second‐order uniaxial single‐site anisotropy and an external transverse magnetic field is treated by the Tyablikov (Random Phase Approximation: RPA) decoupling of the exchange interaction term and the Anderson‐Callen decoupling of the anisotropy term. The orientation of the magnetization is determined by the expectation values 〈Sα〉 (α = x, z) of the spin components from which the orientation angle θ is obtained as a function of the temperature and of the transverse magnetic field for various parameters of the exchange anisotropy in the (x,y)‐plane. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin dependent distribution and Fermi surface of the perovskite manganite compound La0.7Sr0.3MnO3 via 2D‐ACAR measurements
Authors: Hamid A. S. , Arima T. 
Published: January 2004

AbstractUsing 2D angular correlation of positron annihilation radiation (ACAR) experiment, we have performed a systematic study of the spin dependent and Fermi surface of the colossal magneto‐resistance CMR La0.7Sr0.3MnO3. The measurements have been carried out using a re‐versal magnetic field direction (parallel and anti‐parallel to the direction of motion of the polarized posi‐trons). The measured spectra have been investigated in the momentum space as well as in the wave vector space. They revealed information about the hybridization effect of Mn(3d eg1) and O(2p) like states. Further, the results showed that the majority spin electrons predominated at the Fermi level. From another perspective, the Fermi surface of La0.7Sr0.3MnO3 revealed a cuboids hole surface centered on R point and a spheroid electron surface centered on Γ point. A comparison with the earlier results showed qualitative agreement. However, the current results could reveal the dimension of the electron surface centered on Γ point that was predicted in the earlier 2D‐ACAR measurements. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bound exciton and donor–acceptor pair recombinations in ZnO
Authors: Meyer B. K. , Alves H. , Hofmann D. M. , Kriegseis W. , Forster D. , Bertram F. , Christen J. , Hoffmann A. , Straßburg M. , Dworzak M. , Haboeck U. , Rodina A. V. 
Published: January 2004

AbstractThe optical properties of excitonic recombinations in bulk, n‐type ZnO are investigated by photoluminescence (PL) and spatially resolved cathodoluminescence (CL) measurements. At liquid helium temperature in undoped crystals the neutral donor bound excitons dominate in the PL spectrum. Two electron satellite transitions (TES) of the donor bound excitons allow to determine the donor binding energies ranging from 46 to 73 meV. These results are in line with the temperature dependent Hall effect measurements. In the as‐grown crystals a shallow donor with an activation energy of 30 meV controls the conductivity. Annealing annihilates this shallow donor which has a bound exciton recombination at 3.3628 eV. Correlated by magnetic resonance experiments we attribute this particular donor to hydrogen. The Al, Ga and In donor bound exciton recombinations are identified based on doping and diffusion experiments and using secondary ion mass spectroscopy. We give a special focus on the recombination around 3.333 eV, i.e. about 50 meV below the free exciton transition. From temperature dependent measurements one obtains a small thermal activation energy for the quenching of the luminescence of 10 ± 2 meV despite the large localization energy of 50 meV. Spatially resolved CL measurements show that the 3.333 eV lines are particularly strong at crystal irregularities and occur only at certain spots hence are not homogeneously distributed within the crystal contrary to the bound exciton recombinations. We attribute them to excitons bound to structural defects (Y‐line defect) very common in II–VI semiconductors. For the bound exciton lines which seem to be correlated with Li and Na doping we offer a different interpretation. Li and Na do not introduce any shallow acceptor level in ZnO which otherwise should show up in donor–acceptor pair recombinations. Nitrogen creates a shallow acceptor level in ZnO. Donor–acceptor pair recombination with the 165 meV deep N‐acceptor is found in nitrogen doped and implanted ZnO samples, respectively. In the best undoped samples excited rotational states of the donor bound excitons can be seen in low temperature PL measurements. At higher temperatures we also see the appearance of the excitons bound to the B‐valence band, which are approximately 4.7 meV higher in energy. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Feature Article: Bound exciton and donor–acceptor pair recombinations in ZnO
Authors: Meyer B. K. , Alves H. , Hofmann D. M. , Kriegseis W. , Forster D. , Bertram F. , Christen J. , Hoffmann A. , Straßburg M. , Dworzak M. , Haboeck U. , Rodina A. V. 
Published: January 2004

AbstractThe article [1] features the current state of knowledge on the optical properties of excitonic and donor–acceptor pair recombination in bulk n‐ZnO, as revealed by recent photo‐ and cathodoluminescence measurements.The cover picture is a photograph showing an unusual look at the green luminescence of rod‐shaped ZnO crystals under ultraviolet excitation.The first author, Bruno K. Meyer, is professor of physics at the Justus Liebig University of Giessen. His scientific interests include synthesis of semiconductor oxides by chemical vapour deposition and magnetron sputtering, in particular with respect to doping issues, materials science of electro‐ and thermochromic materials, recombination phenomena and defect characterization by magnetic resonance.This issue also contains an Editor's Choice on “Evolution of molecular ordering and phase transitions in C60/C70 solid solutions” by Gabriela Rueda‐Morales and Jaime Ortiz‐López [2].
Effect of equity ownership on the survival of international joint ventures
Authors: Dhanaraj Charles , Beamish Paul W. 
Published: January 2004

AbstractThis note extends transaction cost analysis of international joint ventures (IJVs) to include explicitly the effect of equity. It challenges the common practice of treating all foreign investments with between 5 percent and 95 percent equity as IJVs. A fine‐grained analysis of the role of foreign equity ownership on the survival of 12,984 overseas subsidiaries confirms a declining, nonlinear, and asymmetrical relationship between equity and mortality in overseas subsidiaries. While investments involving small ownership levels (<20%) have very high mortality rates, those with high ownership levels (>80%) have mortality rates comparable to that of wholly owned subsidiaries. Implications for research, practice, and policy are discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Strategic benefits to firms issuing private equity placements
Authors: Folta Timothy B. , Janney Jay. J. 
Published: January 2004

AbstractFor young technology firms, acquiring resources can often be costly due to the information asymmetry and uncertainty that exist surrounding the new technology. We contend that firms able to issue private equity can better manage their ability to mobilize three kinds of resources: capital, research partners, and commercial partners. We investigate the existence of long‐term, strategic benefits to private placements, and a number of factors may determine the long‐term effectiveness of this governance form. Overall, the empirical analyses demonstrates that private placements provide long‐term benefits to firms by reducing hazards associated with information asymmetry. Copyright © 2003 John Wiley & Sons, Ltd.
An empirical test of heuristics and biases affecting real option valuation
Authors: Miller Kent D. , Shapira Zur 
Published: January 2004

AbstractThis study applies insights from behavioral decision theory to explain how managers value call and put options. Behavioral decision theory points to important deviations from the assumptions of normative option pricing models in finance. We used a questionnaire to collect option pricing data to test our behavioral hypotheses. The evidence indicates specific biases affecting subjective valuations of options: (1) buyers and sellers price options below their expected values; (2) buyers' prices are consistently below sellers' prices; (3) irrelevant outcomes decrease option values; (4) discount rates vary with the option time horizon; and (5) changes in option values do not fully reflect increases in exercise prices. We discuss the implications of these findings for the management of real options and suggest directions for developing descriptive real option theory. Copyright © 2003 John Wiley & Sons, Ltd.