bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and physical properties of ternary organic conductors of TCNQ, iodine, and double‐charged unsymmetrical cations: PET and PESe
Authors: Abashev G. G. , Russkikh V. S. , Koshta A. , Lapinski A. , Król S. , Pukacki W. , Graja A. 
Published: July 2007

AbstractTernary organic salts of TCNQ, iodine, and double‐charged unsymmetrical cations containing sulfur or selenium are investigated. The crystal structure of the salts is determined; their dc electrical conductivity, ESR, and IR spectral properties are studied. The physical properties of the investigated salts are found as typical for Q‐ID organic semiconductors.Nous avons étudié les sels ternaires du TCNQ, du iode et des cations double chargés, dissymétriques, comprenant le soufre ou le sélénium. La structure crystalline des sels examinés a été déterminée. La conductivité électrique en courant continu, la résonance électronique de spins et les propriétés spectrales en infrarouge ont été étudiés. Nous avons montré que les propriétés physiques des sels examinés sont typiques des semiconducteurs organiques de bas dimensionalité.
Temperature dependence of the electrical resistivity of Y3Co11B4 and Gd3Co11B4 compounds
Authors: Kowalczyk A. , Ivanov V. 
Published: July 2007

AbstractThe temperature dependence of the electrical resistivity Q of R3Co11B4 (R = Y and Gd) in the temperature range from 4.2 to 370 K is presented. These compounds crystallize in the Ce3Co11B4‐type structure. The unit cell of the structure contains 18 atoms. The rare earth atoms are distributed in two different crystallographic sites, the Co atoms in three different positions, and boron is located in one type of site. In the low‐temperature region Q is proportional to T2. This quadratic dependence is caused by electron‐spin wave scattering. The experimental results are compared with transport properties of other rare earth‐transition metal compounds.
Photon avalanche in Tm doped CdF2
Authors: Bouffard M. , Jouart J. P. , Mary G. 
Published: July 2007

AbstractThe spectroscopic and dynamic studies of the Tm3+ doped cadmium fluoride show the existence of a 450 nm emission (1D2 → 3F4 transition), excited around 650 nm (3H4 → 1D2 transition) by a tunable laser. The presence of a power threshold for the density of excitation allows to establish that the upconversion mechanism is the photon‐avalanche process.
X‐ray diffraction study of gallium nitride grown by MOCVD
Authors: Metzger Th. , Angerer H. , Ambacher O. , Stutzmann M. , Born E. 
Published: July 2007

AbstractAn X‐ray diffraction study of gallium nitride grown on the c‐plane (0001) and r‐plane (0112) of sapphire substrates by metal organic chemical vapour deposition using triethylgallium and ammonia was performed. By measuring asymmetric reflections with a ω‐2θ two‐circle diffractometer, lattice constants of α‐GaN could be resolved for both substrate orientations and the epitaxial relationships could be confirmed. Additionally, the existence of β‐GaN on the r‐plane sapphire substrate could be determined. Pole figure measurements show different qualities of in‐plane orientation of the α‐GaN layers for the two substrate orientations.
Bond distribution and structure of amorphous germanium‐nitrogen alloys
Authors: Zanatta A. R. , Chambouleyron I. 
Published: July 2007

AbstractThe Ge 3d core levels of sub‐stoichiometric amorphous germanium‐nitrogen (a‐GeN) alloys are studied by X‐ray photoelectron spectroscopy (XPS). The nitrogen concentration in the samples, as determined from nuclear reaction analysis (NRA), is allowed to vary from zero to ∼ 3 × 1022 atoms cm−3. For the whole series of samples both, the chemical shift and the bonding distribution are studied as a function of the nitrogen concentration in the alloys. The chemical shift per Ge‐N bond is also investigated using different methods to deconvolute core level energy spectra, and found to be approximately (0.5 ± 0.1) eV. Furthermore, the present study shows that the GeN bond distribution, as obtained from the analysis of Ge 3d core level data, is in relatively good agreement with the random bonding model (RBM).
A study of interlayer coupling in Fe/Cu multilayers by spin wave resonance
Authors: Jin Q. Y. , Xu Y. B. , Zhou S. M. , Lu M. , Zhai H. R. , Shen Y. H. 
Published: July 2007

AbstractSpin wave resonances related to interlayer exchange are observed in the FMR measurements in Fe/Cu multilayers with the Cu spacer layer thickness dCu < 28 Å. The spin wave is demonstrated to propagate through the whole multilayers and the phase change of the spin wave is shared by both Fe and Cu sublayers. The phase change across the Cu atomic layer is found to decrease with the increase of Cu sublayer thickness.
From solar cell research to a photovoltaics industry
Authors: Hill R. 
Published: July 2007

AbstractKarl Böer was a pioneer in research on thin film solar cells, and a committed builder of bridges between academic research and industrial applications. Amongst his many achievements was the founding of the Institute of Energy Conversion at the University of Delaware and a company SES Inc., to exploit the fruits of the research at the IEC. He also built, in the early 1970's, what was probably the world's first building with an integrated PV roof. The paper outlines the paths by which research on solar cells has led to significant advances in commercial products, and seeks to identify some common themes in this successful transfer of technology from R&D laboratories to industry. This is then extended to consider the routes by which R&D in general may be transferred into industry to create new or improved commercial products.
Recent developments in amorphous silicon‐based solar cells
Authors: Beneking C. , Rech B. , Fölsch J. , Wagner H. 
Published: July 2007

AbstractTwo examples of recent advances in the field of thin‐film, amorphous hydrogenated silicon (a‐Si:H) pin solar cells are described: the improved understanding and control of the p/i interface, and the improvement of wide‐bandgap a‐Si: H material deposited at low substrate temperature as absorber layer for cells with high stabilized open‐circuit voltage. Stacked a‐Si: H/a‐Si: H cells incorporating these concepts exhibit less than 10% (relative) efficiency degradation and show stabilized efficiencies as high as 9 to 10% (modules 8 to 9%). The use of low‐gap a‐Si:H and its alloys like a‐SiGe:H as bottom cell absorber materials in multi‐bandgap stacked cells offers additional possibilities. The combination of a‐Si: H based top cells with thin‐film crystalline silicon‐based bottom cells appears as a promising new trend. It offers the perspective to pass significantly beyond the present landmark of 10% module efficiency reached by the technology utilizing exclusively amorphous siliconbased absorber layers, while keeping its advantages of potentially low‐cost production.
Growth of bulk ZnSe crystals — recent developments
Authors: Siche D. , Hartmann H. , Böttcher K. , Krause E. 
Published: July 2007

AbstractStarting with a historical review and a general comparison of growth methods, the paper deals with the seeded vapour growth of substrate‐quality ZnSe crystals. Under optimized growth conditions, in contrast to the growth from the melt, in SPVT and SCVT (seeded physical and chemical vapour transport) twin‐free single crystals are prepared. The dislocation density decreases down to ≈104 cm−2 in growth direction away from the seed transition region. SPVT‐grown crystals are the better ones with respect to optical properties showing exciton luminescence and decreasing deep level emission. For the application in homoepitaxy, the SCVT‐grown crystals with lowest defect densities seem to be superior.
Tailoring of Si doping layers in GaAs during molecular beam epitaxy
Authors: Däweritz L. , Kostial H. , Ramsteiner M. , Klann R. , Schützendübe P. , Stahrenberg K. , Behrend J. , Hey R. , Maier M. , Ploog K. 
Published: July 2007

AbstractFor Si δ‐like doping of GaAs lateral ordering processes and segregation in growth direction have been investigated in real time by monitoring longe‐range and short‐range ordering effects using reflection high‐energy electron diffraction (RHEED) and reflectance anisotropy spectroscopy (RAS). When Si is supplied in pulses to GaAs(001) distinct ordering processes occur which are promoted by misorientation steps on the vicinal surface. The incorporation of Si atoms on Ga sites in a single plane can be completed to a high degree. The depth profile of the electron concentration is closely related to Si segregation during GaAs overgrowth. In the case of a doping layer of extremely high coverage it shows a minimum at the centre of the doping spike. For samples grown on vicinal GaAs(001) surfaces under conditions favourable for wire‐like Si incorporation a considerable enhancement of the exciton photoluminescence (PL) intensity and decay time has been found.
High‐density effects, stimulated emission, and electrooptical properties of ZnCdSe/ZnSe single quantum wells and laser diodes
Authors: Grempel H. , Diessel A. , Ebeling W. , Gutowski J. , Schüll K. , Jobst B. , Hommel D. , Pereira M. F. , Henneberger K. 
Published: July 2007

AbstractIn II–VI material based laser diode structures, the role of excitonic processes for stimulated emission is still rather controversially discussed. In this paper, the manifestation of biexciton recombination in high‐density luminescence of ZnCdSe/ZnSe quantum wells is investigated by intensity‐ and polarization‐dependent spectroscopy. In spite of their evidence in such spectra, their contribution to stimulated emission in laser diodes with moderately confining wells is not confirmed, instead, indication of strong Coulomb correlation is given when using the new technique of pump‐and‐probe excitation spectroscopy. A strong electrooptic effect yielding saturation is found in laser diodes exactly at their lasing wavelength thus being promising candidates for integrated laser‐modulation devices.
Femtosecond degenerate four‐wave mixing study of exciton coherence in wide‐gap II–VI quantum wells
Authors: Häpl T. , Nickolaus H. , Henneberger F. , Schülzgen A. 
Published: July 2007

AbstractThis paper studies coherent excitons in the presence of alloy disorder by femtosecond degenerate four‐wave mixing on ternary (ZnCd)Se/ZnSe quantum wells. The use of very low excitation densities enables to uncover an impurity‐mediated exciton dephasing time of (16 ± 2) ps and a related homogeneous exciton width of only 80 μeV. At higher densities, the coherence loss speeds up dramatically due to exciton‐exciton interaction. Separating the contributions from inhomogeneous (photon echo) and homogeneous broadening to the spectrally resolved decay transients allows to deduce the energy dependence of the dephasing time across the disorder broadened exciton ensemble. Further, pronounced biexciton resonances are observed in the signal spectrum which exhibit characteristic polarization properties. For cross‐polarized pulses, the biexciton signal shows a striking stimulation when the excitation density is increased.
Photoreflectance studies of (Al, Ga)As/GaAs heterostructures and devices
Authors: Enderlein Rolf 
Published: July 2007

AbstractExperimental and theoretical PR spectra are reported for (AlGa)As/GaAs single heterostructures, (AlGa)As/GaAs quantum well structures as well as MESFET and HEMT structures. The theoretical spectra are calculated by means of a novel technique which combines the two methods previously used for spatially inhomogeneous systems: the transfer matrix method for light propagation between different layers, and perturbation theory for light propagation within each weakly inhomogeneous layer. The electric field distribution is calculated from an integral equation which holds under quite general conditions including incomplete dopant ionizations and carrier degeneracies. In most of the spectra, pronounced interference effects show up. Due to them, PR spectra from quantum wells are sensitive to the well distance from the surface. Besides interference effects, field inhomogeneities like broadening of Franz‐Keldysh oscillations manifest themselves in the reported spectra. A controversy in the literature concerning PR spectra from (AlGa)As/GaAs single heterostructures is solved by means of the novel calculation technique.
Peculiarities of thermomagnetic effects in gapless semiconductors specified by spatial correlations of impurity charges
Authors: Tsidilkovski I. M. 
Published: July 2007

AbstractThe results of measurements of the thermomagnetic Nernst‐Ettingshausen effect (NEE) in the gapless semiconductor HgSe doped with iron are presented. The iron content in the samples varies from 1 × 1018 to 4 × 1020 cm−3 when the temperature varies from 9 to 100 K. A change of sign of the NEE from negative to positive when the iron content increases is observed at low temperatures. It is shown that the unusual dependence of the NEE on iron content in HgSe: Fe crystals at low temperatures, its sign change, and other peculiarities are caused by scattering of electrons on aggregates of charged donors Fe3+. Such an aggregate constitutes a weakly correlated system in the range of low iron concentrations and a strongly correlated Coulomb liquid in the range of high iron concentrations. A new mechanism of inelastic electron scattering on static defects, bivalent iron ions, is proposed, which allows to explain the anomalous decrease of the Lorenz factor with increasing temperature. All observed peculiarities of the thermomagnetic effects are interpreted quantitatively.
Charge transfer in GaP and InP
Authors: Saravanan R. , Israel S. , Srinivasan N. , Mohanlal S. K. 
Published: July 2007

AbstractCharge transfer in GaP and InP is analysed using our precise and extensive X‐ray diffraction data. The direction and the amount of charge transfer are inferred by plotting and comparing the structure factors of the components (both observed and calculated). The charge transfer parameters thus obtained are 0.45ē from Ga to P and 0.36ē from In to P.
Investigation of substitutional interactions by means of Zener relaxation
Authors: Blanter M. S. , Kolesnikov E. V. 
Published: July 2007

AbstractA new method based on Zener relaxation is elaborated for the determination of substitutional interactions in metal solid solutions. The method consists in computer simulation of temperatures of internal friction peaks taking into account the different values of effective interchange energies. Then comparison between the calculated spectra and the experimental ones is performed. It is suggested that substitutional interaction affects the atomic arrangement in creating short‐range order and shifts the energy of the substitutional atom and therefore the activation energy of internal friction. Experimental parameters of Zener relaxation are used to study the interaction energies of Cu‐Zn, AuAg, and CuAl alloys. The energies are close to those determined by diffuse scattering of X‐rays or neutrons.
Equation of state, isobaric specific heat, and thermal expansion of solids with polyatomic basis in the Einstein‐Debye approximation
Authors: Cankurtaran M. , Askerov B. M. 
Published: July 2007

AbstractA theoretical study of the thermodynamic properties in the Einstein‐Debye approximation is made for solids with polyatomic basis. Analytical expressions are derived for the equation of state, isobaric specific heat (Cp), and linear thermal expansion coefficient (αP). The temperature dependences of Cp and αp are determined by four characteristic parameters of the solid: the Debye temperature θD, the Einstein temperature θE, and the Grüneisen parameters γ and γ associated with the volume dependences of θD and θE, respectively. It is shown that the difference CP−CV between the calculated isobaric and isochoric specific heat capacities is very small at low temperatures (T ≪ θD) and increases markedly at higher temperatures. In the high‐temperature range (T ≫ θE), CP is almost independent of temperature and is determined by a simple combination of the Grüneisen parameters γ and γ. The results obtained for αP, in the low‐ and high‐temperature limits, are in accord with those found for the asymptotic behavior of CV with temperature.
Effective‐mass Hamiltonian for strained superlattices
Authors: Brezini A. , Sebbani M. , Depollier C. 
Published: July 2007

AbstractFor an abrupt heterojunction between two otherwise homogeneous semiconductors in one dimension, the effective‐mass Hamiltonian

is examined with 2α + β = −1, where m(z), a(z), and Ec(z), are the position dependent effective mass, the local lattice parameter, and the local conduction band edge, respectively. The exact Schrödinger equation is compared with that for the effective‐mass equation in the case of an analytically solvable model. In the asymptotic limit of the energy close to the band edge, the conclusions obtained are shown to be dependent on the parity of the bands.
Activation energy of small polarons and conductivity in LiNbO3 and LiTaO3 crystals
Authors: Wang Qi , Leng Shuyan , Yu Yansheng 
Published: July 2007

AbstractEliminating pyroelectric and other disturbances, with the aid of the curves of bulk and surface current versus temperature, the conductivity character of LiNbO3(LN) and LiTaO3(LT) is studied at different temperatures. The activation energy is obtained, which is needed for bound small polarons in LN and LT crystals to jump across their potential barrier to give rise to hopping conduction.
Phenomenological theory of the surface nucleation field in anisotropic superconductors
Authors: Klein U. 
Published: July 2007

AbstractThe surface nucleation field for anisotropic (conventional) superconductors is calculated for an arbitrary modification of the superconducting transition temperature near the surface. We use, as a phenomenological description, anisotropic Ginzburg‐Landau theory including appropriate surface terms. A uniaxial situation, as in layered high‐Tc compounds, is considered, with the external magnetic field oriented along one of the main crystallographic axes. The resulting nucleation fields are all determined by a single universal curve (and appropriate direction‐dependent scaling factors). Depending on the surface state, both an enhancement and a suppression of the usual third critical field 1.7Hc2 may occur. The results are relevant for layered compounds, in particular for high‐Tc materials, where the surface conditions depend sensitively on the nature of the first layer on top of the surface.
Energy eigenvalues in square and rectangular quantum wires with finite barrier potential
Authors: Gangopadhyay S. , Nag B. R. 
Published: July 2007

AbstractEnergy eigenvalues have been calculated for square and rectangular quantum wires with finite barrier potential of GaAs/Ga0.63Al0.37As and Ga0.47In0.53As/InP systems, by expressing the wave function in terms of a two‐dimensional Fourier series. Calculated values are compared with those obtained earlier by using the finite element method and by using equivalent circular or elliptic wires. Experimental values of the energy shift of Ga0.47In0.53As/InP wires are also compared with the calculations.
Electrical resistivity and thermoelectric power of (GeTe)1−x(Bi2Te3)x solid solutions (0 ≤x≤ 0.05) in the temperature interval from 80 to 350 K
Authors: Christakudi T. A. , Plachkova S. K. , Christakudis G. Ch. 
Published: July 2007

AbstractElectrical conductivity σ, Hall coefficient RH, and thermoelectric power (Seebeck coefficient) S are measured for (GeTe)1−x(Bi2Te3)x solid solutions with 0≤ × ≤ 0.05 in the temperature range 80 to 350 K. On the basis of these investigations some information on the carrier scattering mechanisms in the alloys is obtained. The electrical resistivity ϱ = 1/σ is analyzed as function of temperature T and composition x in the above‐mentioned temperature interval and resistivity contributions due to acoustic phonon scattering (ϱac) and to scattering by defects (germanium vacancies, impurity atoms, etc.) and alloy scattering are distinguished. From the results it may be shown that the acoustic phonon resistivity increases nearly linearly with temperature. At low temperatures the resistivity due to defects ϱdef is almost constant and slowly increases at temperatures T > 250 K.
Study of phonon eigenfrequencies in ternary transition metal‐metalloid Fe40Ni40B20 glass
Authors: Gupta A. , Bhandari D. , Jain K. C. , Saxena N. S. 
Published: July 2007

AbstractThe study of the ternary Fe40Ni40B20 metal‐metalloid glass has been made through a partial pair‐potential approach. Six partial pair potentials of this ternary glass have been computed using pseudopotential‐based interatomic forces. In particular, the model employed here for the calculation of the potential is in analogy with the three‐partial‐structure‐factor approach of Sietsma and Thijsse with the assumptions that Fe and Ni atoms have identical distributions with respect to like neighbours and hence the partial pair potentials of Fe‐B and Ni‐B are identical. The calculated effective pair potential using the partial pair potentials is then employed to investigate the longitudinal and transverse phonon eigenfrequencies. Further, from the elastic part of the frequency spectrum, elastic and thermal properties have been computed. The computed results for these properties are found to be in good agreement with the available experimental results.
Presence of soft phonons in a model ferroelectric
Authors: Freidkin E. S. , Horton G. K. , Cowley E. R. 
Published: July 2007

AbstractWe investigate the behaviour of a one‐dimensional ferroelectric crystal. The model includes both short‐range and long‐range interactions. We prove that the system undergoes a phase transition from an ordered to a disordered state and confirm the existence of a soft mode for this particular model.
Quasi‐resonance and confining phenomena in symmetrical rectangular quadruple‐barrier structures
Authors: Sano H. , Yamamoto H. , Taniguchi K. 
Published: July 2007

AbstractResonant tunneling is studied theoretically in detail in symmetrical rectangular quadruple‐barrier structures by taking into account the mass difference between the well layer and the barrier layer. The variation of the resonance energy with the outer barrier width is investigated. It is found that the resonance level is rarely affected by a small change of the outer barrier width. Especially, it is derived analytically that the transmission peak is decreased to less than unity when the outer barrier width becomes thinner than a critical value. Furthermore, wave functions of an electron at the resonance energy level are calculated and the confining phenomenon is studied.
An effective potential for high‐temperature superconductivity in cuprates
Authors: Silva P. R. 
Published: July 2007

AbstractAn effective potential is proposed as a means to study the mechanism of pairing of high‐Tc superconductivity in cuprates. The relation between size and energy of bound states evaluated in a first approximation is comparable to recent calculations obtained through quantum electrodynamics in (2 + 1) dimensions. In a second approximation, we consider that pairing occurs at the minimum of this effective potential, the problem being related to the quantum mechanical behavior of a particle described by polar coordinates in a plane. So, according to the present model, the topological constraint determined by the CuO2 planes seems to be most relevant in the understanding of the pairing mechanism.