bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phonons of Indium Selenide Single Crystals Studied by Inelastic Electron Tunneling Spectroscopy
Authors: Yamaguchi K. 
Published: July 2007

AbstractInelastic electron tunneling spectroscopy is studied for Pb/InSe/Pb tunnel junctions at liquid helium temperature in the normal state of Pb under an external magnetic field. The insulating barrier of InSe, a layered semiconducting compound, is cleaved from a single crystal along the layer. Inelastic electron tunneling spectra for the junctions show phonon structures of indium selenide as well as those of the lead electrodes.
Quantum Confined Stark Effect in InGaAs/GaAs Quantum Wells under High Electric Fields
Authors: Kavaliauskas J. , Krivaite G. , Galickas A. , Šimkiene I. , Olin U. , Ottosson M. 
Published: July 2007

AbstractPhotocurrent and electroreflectance spectroscopies are combined to study the transformation of the quantum confined Stark effect under high electric fields in shallow InGaAs/GaAs quantum wells. Experimental evidences of exciton quenching and carrier tunneling out of the well are obtained. The coupling between quasibound and continuum states in the strong electric field region results in the increase of absorption below the band gap of the barrier.
Hot‐Electron Magneto‐Transport in Narrow‐Gap Semiconductors in Quantum Magnetic Field
Authors: Weng X. M. , Lei X. L. 
Published: July 2007

AbstractThe longitudinal magneto‐transport in narrow‐gap semiconductor InSb under a quantum magnetic field at 42 K is investigated using the balance equation theory. The nonparabolicity of the energy band and scatterings due to ionized impurities, acoustic and polar optical phonons are taken into account. All the subbands occupied by electrons are included in the calculation. The longitudinal magnetic field reduces the drift velocity and leads to a decrease of the electron temperature. The drift mobility decreases with increasing magnetic field. The drift velocity under the extreme‐quantum‐limit assumption is completely different from that taking into account all possible subbands occupied by electrons.
The Critical Pair‐Breaking Current in Superconductors
Authors: Rezlescu N. , Buzea C. Gh. , Buzea C. , Agop M. 
Published: July 2007

AbstractA new way of estimating the critical pair‐breaking current is developed. The superconducting charge carriers are considered as quantized vortex‐like objects, characterized by Γ — the vortex strength, Γ = h/2m. Taking into account that the charge carriers are confined in the CuO planes, and applying the von Karman theory for vortex streets in high‐temperature superconductors, the critical velocity vc and the critical pair‐breaking current Jc are derived. The results are in good agreement with the experimental data.
Interaction of Vortex Lattice and Surfaces of a Superconducting Cylindrical Shell
Authors: Saif A. G. 
Published: July 2007

AbstractA model of a type‐II superconducting cylindrical shell is established to verify the properties of distorted flux lines using the London theory. The field distributions inside and outside the superconducting region are determined. Moreover, the current density and the forces on the vortex segments are calculated using these field distributions. Finally, the Gibbs free energy of the system is obtained in compact form which can be easily applied to real‐life application. As the shell tends to a rigid cylinder agreement with previous results is achieved.
Atomic Structure Analysis of the (10 1 2) Twin in Zinc by HREM and Energetical Calculations
Authors: Braisaz T. , Ruterana P. , Lebouvier B. , Nouet G. 
Published: July 2007

AbstractThe atomic structure of the (10 1 2) twin boundary in zinc is investigated theoretically by atomistic calculations and experimentally by high resolution electron microscopy. For computer simulations, the atomic interactions are described by a many‐body potential of the Finnis‐Sinclair type and are applied to a h.c.p. structure with a large c/a_ratio (1.856). Using this potential, only one planar atomic structure is found to exist for the (10 1 2) twin. This is in agreement with the previous results for h.c.p. metals with c/a ratio close to the ideal value (1.633). In contrast, two atomic structures are observed experimentally: a planar and symmetric interface similar to the one obtained by calculations, and a microfaceted structure. The microfaceted structure is observed for the first time in the (10 1 2) twin.
Study of Anomalous Excitonic Transport in Cu2O
Authors: Benson E. , Fortin E. , Mysyrowicz A. 
Published: July 2007

AbstractAn experimental study of excitonic transport in Cu2O is presented. Excitons are detected several mm away from their initial location, via the photovoltaic effect. Results at low exciton densities are well explained by a diffusive motion. However, at high densities, anomalous transport, in the form of excitonic packets propagating at constant speed, is observed. Threshold conditions for the onset of ballistic packet motion are determined as a function of lattice temperature and exciton densities. They are consistent with requirements for Bose‐Einstein condensation of excitons. Double pulse experiments reveal an important attraction of low density probe particles towards a packet. The packet is suggested to correspond to the superfluid component of a quantum degenerate ecxitonic fluid.
Calculation of the Ground State Properties of Diamond and Cubic Boron Nitride
Authors: Bross H. , Bader R. 
Published: July 2007

AbstractUsing the modified augmented plane wave method (MAPW), the ground state properties of cubic boron nitride and diamond are investigated within the framework of the local density approximation (LDA). As is common for LDA, the value of the band gap is underestimated by the one‐particle excited states. Calculation of the total energy as a function of the lattice parameter yields equilibrium lattice constants within 1% of the experimental value. Furthermore, the hydrostatic bulk moduli obtained deviate from the experimental values by about 10% in the case of BN and 4% in the case of diamond. An estimate of the cohesion energy of both materials is obtained from the atomic limit within the MAPW scheme yielding improved values when compared to the difference between crystal and single atom LDA total energies.
Electrical Properties of Nonstoichiometric WO3−y at Temperatures 77 to 300 K
Authors: Molenda J. , Kubik A. 
Published: July 2007

AbstractMeasurements of electrical conductivity, thermoelectric power, and crystallographic structure of tungsten trioxide are presented. It is found that the predominant charge carriers are electrons related to nonstoichiometry in the oxygen sublattice (WO3−y). At y = 0.1 the investigated material undergoes a semiconductor—metal transition of Mott type.
Effects of Electron‐Electron Interaction on the Ferromagnetic State in a Quasi‐One‐Dimensional Organic Polymer Ferromagnet
Authors: Fang Z. , Liu Z. L. , Yao K. L. , Li Z. G. 
Published: July 2007

AbstractBased on a theoretical model proposed for quasi‐one‐dimensional organic polymer ferromagnets, the effects of electron‐electron interaction on the ferromagnetic state are studied. Allowing for full lattice relaxation, the system is optimized by a set of self‐consistent iterative equations. The results of the calculation indicate that larger on‐site electron‐electron repulsive interactions will make the ferromagnetic ground state of the system more stable. It is also found that the inter‐site electron‐electron interaction cause a charge density distribution along the main chain and consequently weakens the stability of the ferromagnetic ground state.
Highly‐Ordered Organic Adsorbates: Commensurate Superstructures, OMBE, and 1D Nanostructures
Authors: Umbach E. , Seidel C. , Taborski J. , Li R. , Soukopp A. 
Published: July 2007

AbstractBig organic molecules deposited by vacuum sublimation on reactive surfaces form highly‐ordered superstructures which are often commensurate to the substrate if covalent, nondissociative bonding occurs. The orientation of the molecules at the interface can be varied depending on reactive groups, substrate surface, and coadsorbates. Deposition of highly‐ordered thin films, or even organic molecular beam epitaxy (OMBE), is difficult but appears possible under certain conditions. Organic nanostructures can be produced by self‐organization of covalentiy‐bound molecules and substrate steps on high‐index surfaces. Experiments with different aromatic molecules like NDCA and PTCDA as well as with oligothiophenes (α4T and EC4T) on various substrates such as Ag(111), Ag(775), Ni(111), and Si(111) are reviewed using a variety of complementary surface sensitive techniques.
Positron annihilation studies on the interaction between hydrogen and defects in nickel
Authors: Wu Y. C. , Itoh Y. , Ito Y. 
Published: July 2007

AbstractPositron annihilation is measured for nickel containing defects carefully controlled by cold‐rolling, by further tempering, and by hydrogen doping. By the cold‐rolling the mean positron lifetime was increased from 123 to 179 ps corresponding to the formation of single vacancies and dislocations. The mean lifetime does not change significantly at further tempering. On hydrogen doping of the cold‐rolled sample a long lifetime component of about 390 ps appears, but a similar long lifetime component does not appear by hydrogen doping of the tempered sample. This suggests that hydrogen forms a composite with a vacancy which then becomes the center of vacancy agglomeration. The S‐parameter of the Doppler broadened annihilation radiation also shows changes completely in accordance with this interpretation.
Deep‐level planar doping of titanium in GaAs
Authors: Krispin P. , Kostial H. 
Published: July 2007

AbstractTitanium is incorporated in GaAs by planar doping during growth interruption of molecular beam epitaxy. Deep‐level defects are studied by measuring the capacitance and ac conductance in dependence on bias, frequency, and temperature. We report on the first investigation of the dynamic behavior of deep electronic states at interfaces intentionally doped with electrically active defects. Admittance versus bias spectroscopy at sufficiently low frequencies is proposed as a new method to detect deep levels exclusively at interfaces in homo‐ or heterojunctions. For the planar‐doped titanium sheet, an intrinsic point defect level at 0.35 eV is identified in addition to the Ti2+/Ti3+ acceptor level at 0.24 eV. The incorporation of Ti is accompanied by the formation of native defects. The majority of Ti atoms is found to be electrically inactive.
Melting as a first‐order phase transition in a system of defects
Authors: Karasevskii A. I. , Lubashenko V. V. 
Published: July 2007

AbstractThe self‐consistent quasiharmonic model is used to describe the equilibrium atomic structure of a crystal and the thermodynamical properties of vacancies at high temperature. It is shown that an increase in the amplitude of the thermal atomic vibrations with temperature leads to a considerable reduction of the vacancy formation energy in the high‐temperature region, which results in the generation of a large number of defects near the melting point and, as a consequence, in the significant softening of the acoustic vibration modes of the crystal. The effective attraction between the vacancies through the phonon subsystem of the crystal is found to lead to the first‐order phase transition with a discontinuous change in the defect concentration at the transition point. The melting lines are calculated for the rare gas crystals. The effects of the solid–vapour interface on the kinetics of the solid‐liquid transition are studied.
Quantum confined stark effect and optical absorption in AlxGa1−xAs/GaAs/AlxGa1−xAs
Authors: Panda S. , Panda B. K. , Fung S. , Beling C. D. 
Published: July 2007

AbstractThe effects of the electric field on the electron subband energies and wavefunctions in a single quantum well AlxGa1−xAs/GaAs/AlxGa1−x As have been calculated using an analytic method which takes into account the variation of the effective mass at the barriers. The results are compared with the previous calculations which took the effective mass of GaAs inside and outside the well. The calculated energies and wavefunctions together with the experimental linewidth broadening are used to obtain the inter‐subband optical absorption spectra and the change in the real part of the index of refraction in the well.
RES structure of Bi3+ centres in KCI: Bi, S and CaO:Bi crystals
Authors: Aceves R. , Flores M. Barboza , Maaroos A. , Nagirnyi V. , Salas R. Perez , Tsuboi T. , Zazubovich S. , Zepelin V. 
Published: July 2007

AbstractEmission, excitation, and polarization spectra as well as decay kinetics are studied at 4.2 to 500 K for the luminescence of Bi3+ centres in two crystals (KCl and CaO) with strongly different electron–phonon interaction. It is concluded that three bands at ≈2.5, 3.11, and ≈1.5 eV, observed in the emission spectrum of the KCl: Bi, S crystal belong to the same centre, but arise from states of different origin. The splitting of the 2.5 eV band, caused by the presence of a defect (S2−) near a Bi3+ ion is detected. Besides the well‐known triplet 3.3 and 3.1 eV bands, a new 4.15 eV emission is found in CaO: Bi crystal, which is ascribed to transitions from the singlet excited state of the Bi3+ ion. The structure and the parameters of the relaxed excited states are determined and the models of the corresponding Bi3+ centres are discussed.
Magnetic force microscopy imaging of an ultrathin Au/Co/Au sandwich
Authors: Armand C. , Peyrade J. P. , Mamy R. , Ortega M. D. , Goiran M. , Fert A. R. , Raquet B. , Ousset J. C. 
Published: July 2007

AbstractWe present magnetic force microscopy imaging of an Au(40 nm)/Co(0.8 nm)/Au(8 nm) sandwich with strong perpendicular anisotropy which shows stripe features mixed with bubble‐like structures in the μm range. In addition, interior bubble domain structures, 50 nm in size, appear regularly dispersed.
Electronic properties of Al, Si‐containing solid solutions based on B1‐TiN, TiC determined by LMTO band structure calculations
Authors: Ivanovsky A. L. , Medvedeva N. I. , Shveikin G. P. , Zhukovsky V. M. 
Published: July 2007

AbstractThe results of nonempirical self‐consistent band structure LMTO calculations of the electronic properties of B1‐like solid solutions in Ti‐Al‐N‐C and Ti‐Si‐N‐C systems are given. The regularities of changing the electronic and energy parameters of solid solutions as a fuunction of their composition are discussed. Direct computer modelling of the influence of the possible mechanisms of solid solution formations (according to Al, Si → C, N or Al, Si → Ti substitution types) on their band structure is carried out. The effect of oxygen impurities and nitrogen lattice vacancies on the electronic properties of the considered solid solutions is discussed taking Ti silicidonitride as an example. The results obtained are compared with recent XPS investigations of metastable B1‐TiSixNy(O) films.
CEMS, CXMS, and transmission Mössbauer investigation of the RF isochronal annealing of Fe81B13.5Si3.5C2 glass
Authors: Rogalski M. S. , Bibicu I. 
Published: July 2007

AbstractThe distribution of hyperfine fields in the simultaneously recorded conversion electron, conversion X‐ray, and transmission Mössbauer spectra of Fe81B13.5Si3.5C2 ribbon samples, as‐quenched and upon isochronal rf exposure, is analysed in terms of the atomic short‐range ordering of the amorphous state. Structural relaxation, associated with boron diffusion, is obtained by pulsed isochronal rf annealing of ribbon samples (vrf = 54.8 MHz, τpulse = 0.1 s) using an rf power above a threshold value of Prf = 1 W.
Yttrium coordination shell in yag related structures
Authors: Landron C. , Lefloch S. , Gervais M. , Coutures J. P. , Bazin D. 
Published: July 2007

AbstractThe local order around the yttrium atoms in a series of samples belonging to the Y2O3−Al2O3 system have been characterised by X‐ray absorption at the yttrium K‐edge. Three types of Y‐O bonds were found in the first coordination shell for samples rich in Y2O3. The garnet‐like aluminates have been elaborated by an original solution‐polyacrylamide gel technique.
A compton profile study of polycrystalline rhenium
Authors: Sharma B. K. , Sharma M. D. , Joshi K. B. , Ahuja B. L. , Pandya R. K. 
Published: July 2007

AbstractIn this paper the results of the first study on the Compton profile of polycrystalline rhenium are reported. The measurements have been made using 59.54keV γ‐rays. To interpret the data, the renormalized‐free‐atom (RFA) model has been employed taking several 5d–6sconfigurations. Best agreement between theory and experiment is found for 5d66s1 valence electron configuration. The data show surprisingly good agreement with the relativistic APW Compton profile of the isoelectronic metal technetium. This confirms similar electronic structures for rhenium and technetium metals.
Magnetic properties in XMnCl3 (X = Na, K, Rb, and Cs) single crystals
Authors: Lim Ae Ran , Choh Sung Ho , Jeong Se‐Young 
Published: July 2007

AbstractThe magnetic ordering (Néel) temperatures for XMnCl3 (X= Na, K, Rb, and Cs) single crystals grown by the Czochralski method have been investigated in the paramagnetic and antiferromagnetic regions byemploying a superconducting quantum interference device magnetometer. From these results, the Néel temperatures, are (5.3± 0.2) K for NaMnCl3, (94±3) K for KMnCl3, (99±1) K for RbMnCl3, and (85±5) K for CsMnCl3.
The effect of a strong magnetic field on the impurity photoionization in semiconductors
Authors: Sali A. , Fliyou M. , Loumrhari H. 
Published: July 2007

AbstractThe effect of a magnetic field on the hydrogenic shallow donor impurity is investigated with the use of a variational method. Two different expressions describing the photoionization cross‐section for donor‐conduction band transitions are obtained both in absence and presence of an applied strong magnetic field. The effect of the strong magnetic field is well observed in a semiconducting material of high dielectric constant and low effective mass such as germanium. It has been found that the photoionization cross‐section is strongly affected by the magnetic field.
Influence of the mechanical and chemical thresholds on the microhardness of ternary chalcogenide glasses
Authors: Chitralekha J. , Srinivasan A. , Chattopadhyay K. , Gopal E. S. R. 
Published: July 2007

AbstractThe microhardness of Ge‐Sb‐Se, Si‐As‐Te, and Ge‐As‐Te glasses has been studied as a function of the average coordination number 〈r〉. A step‐like increase is observed in the Vickers hardness number (VHN) above 〈r〉 = 2.30 in Ge‐Sb‐Se glasses, and above 〈r〉 = 2.50 in Si‐As‐Te and Ge‐As‐Te glasses. This behaviour can be interpreted on the basis of the occurrence of a mechanical and chemical threshold in these glassy systems. The applicability of this technique to measure the elasto‐plastic properties of small and brittle samples such as tellurium‐based chalcogenide glasses is highlighted.
Amplification of interface phonons in quantum well systems in two laser fields
Authors: Santos W. P. , Fonseca A. L. A. , Nunes O. A. C. 
Published: July 2007

AbstractAmplification of interface optical phonons in quantum well systems in the presence of two laser fields, namely a weak laser field and an intense laser field, is reported here. The rate of change of the phonon population due to the scattering of the free quasi‐two‐dimensional electrons in the presence of the two laser fields is calculated from which the amplification coefficient is derived. It was found that interface optical phonons propagating parallel to the direction of polarization of the two radiation fields may become unstable over a relatively wide band of phonon wavenumbers. An application is made for a nondegenerate semiconductor GaAs/AlAs quantum well system.
Magnetic properties of quasi‐2D antiferromagnets
Authors: Pratap A. , Tripathi Ajay , Tripathi R. S. 
Published: July 2007

AbstractWe have studied the magnetic dynamics of quasi‐2D high‐Tc antiferromagnets within nonlinear spin‐wave approximation. The Green function method within the random phase approximation (RPA) is used to obtain the expressions for various magnetic properties such as staggered magnetization, specific heat, parallel and perpendicular susceptibilities. These properties have been analyzed by introducing an effective ratio (r2 = J⊥/J|) of interplanar to planar antiferromanetic (AFM) coupling strengths. The magnetic properties are found to be dependent on the renormalization factor (1 + α), r2, and temperature T, and it is shown that the magnon‐magnon interaction plays a significant role in modifying the crossover temperature and other magnetic properties. Its effect in 2D is more pronounced than in 3D antiferromagnets. The various properties are estimated numerically and compared with the existing results.
Cryogenic Pressure and Lifetime Studies of a Defect Related Emission in Heavily Silicon Doped GaAs
Authors: Holtz M. , Sauncy T. , Dallas T. , Seon M. , Palsule C. P. , Gangopadhyay S. , Massie S. 
Published: July 2007

AbstractWe have used cryogenic high pressure measurements and lifetime studies to investigate a defect related emission at 1.269eV in silicon doped GaAs. The pressure measurements prove that the 1.269 eV photon energy is relative to the conduction band. This implies a deep defect level ≈︁ 0.30 eV above the valence band and an electron capture process from near the conduction band into the defect. The defect level moves up in the bandgap at a rate of (23 ± 3) meV/GPa. Between 20 K and room temperature the defect emission lifetime remains constant at (9.63 ± 0.25) ns, while the intensity decreases over this same range. We explain this surprising result using an intradefect emission process. These results are consistent with a vacancy related defect level, possibly stemming from a gallium vacancy‐silicon at gallium (second‐nearest‐neighbor) defect complex.
Study of Transport, Phase, and Spin Relaxation Times of 2D Electrons by Means of Pressure
Authors: Knap W. , Zduniak A. , Dmowski L. H. , Contreras S. , Dyakonov M. I. 
Published: July 2007

AbstractWe report magnetoconductivity experiments carried out on pseudomorphic AlGaAs/InGaAs/GaAs quantum wells in a wide range of magnetic fields (0.1 to 80 kG). Pressure‐illumination cycles were used for tuning the free electron density. Measurements of the Shubnikov‐de Haas and Hall effects allowed us to determine the transport and quantum relaxation times. Corrections to the magnetoconductivity due to weak localization and weak antilocalization were determined and used to calculate the phase and spin relaxation times. We analyzed phase, spin, quantum, and transport relaxation rates as a function of electron density which allowed for a characterization of the dominant scattering processes.
Study of Quantum and Classical Scattering Times in Pseudomorphic AlGaAs/InGaAs/GaAs by Means of Pressure
Authors: Dmowski L. H. , Zduniak A. , Litwin‐Staszewska E. , Contreras S. , Knap W. , Robert J. L. 
Published: July 2007

AbstractQuantum (single particle) and classical (transport) scattering times have been measured and analyzed as a function of density of the two‐dimensional electron gas (2DEG) in pseudomorphic AlGaAs/InGaAs/GaAs heterostructures. Hydrostatic pressure was used to decrease and infrared LED light pulses to increase the 2DEG density. Our experimental results allow us to distinguish two different persistent photoionization mechanisms induced by the light pulses, which have quite different effects on the two kinds of scattering times. We have also found evidence that a modification of the spatial correlation of charges on remote donors in the barrier (by means of pressure and/or illumination by light pulses) affects the quantum lifetime much more than the transport scattering time.