bluuebunny/crossref_metadata_2025 huggingface dataset:
35Cl NQR Spin‐Spin Relaxation Mechanism in Mg(D2O)6SnCl6 and Ni(H2O)6SnCl6 Crystals
Authors: Horiuchi K.
Published: July 2007

The temperature dependence of the 35Cl NQR spin‐spin relaxation times T2Q in Mg(D2O)6SnCl6 and Ni(H2O)6SnCl6 is measured. T2Q of the former compound is determined mainly by the magnetic dipolar field at the chlorine nucleus produced by the intramolecular nuclei, the tin nucleus, and five other chlorine nuclei in the [SnCl6]2‐ ion. T2Q of the latter compound is governed mainly by the local magnetic field at the chlorine site produced by the intramolecular nuclei and unpaired electrons in the Ni2+ ions. The correlation time for electron‐spin flips due to the exchange interaction among neighbouring unpaired electrons is evaluated from T2Q. A general behaviour of halogen NQR T2Q in diamagnetic and paramagnetic insulators is summarized.
A Method of Data Processing for X‐Ray L‐Edge Absorption
Authors: Wang Wen‐Cai , Chen Yu , Hu Tian‐Dou
Published: July 2007

A method of data processing for the rare earth (RE) L‐edge X‐ray absorption spectrum in materials is presented. Mathematical analyses show that if the L‐edge is decomposed into a Lorentzian line and an arctan curve, their second derivatives are very different and the former represents a symmetric negative peak at the same location as the original Lorentzian peak. The white line (WL) in the RE L‐edge can be separated without decomposition of the edge. This method simplifies the data processing and reduces some artificial factors in data processing. The RE L‐edges in some fluorides and glasses are analyzed by this method and the ordinary method. The changes in the WL intensities at the L‐edges of various materials, which are obtained by two data processing, are consistent to each other.
Structural Properties of II–VI Heterostructures for Blue‐Green Lasers
Authors: Petruzzello J. , Herko S. P. , Gaines J. M. , Marshall T.
Published: July 2007

The structural characteristics of II–VI separate confinement heterostructure lasers containing Zn1−xMgxSySe1−y quaternary cladding layers, ZnSySe1−y guiding layers, and Zn1–zCdzSe quantum well active layers are investigated with transmission electron microscopy. The dislocation density in these lasers is dramatically reduced because the entire structure is pseudomorphic to the GaAs substrate. The pseudomorphic structures, however, contain stacking faults that cause degradation and shorten the lifetimes of laser devices. The optical degradation of a pseudomorphic laser structure is investigated with photoluminescence imaging and correlated with the propagation of dislocations in the active layer from existing defects as seen by transmission electron microscopy.
ZnSe‐Based MOVPE and MBE Grown LEDs
Authors: Stanzl H. , Reisinger T. , Wolf K. , Kastner M. , Hahn B. , Gebhardt W.
Published: July 2007

The properties of ZnSe‐based heterostructures on (001) GaAs substrates grown by metalorganic vapor phase epitaxy (MOVPE) are compared with those grown by molecular beam epitaxy (MBE). The structural and optical properties are examined with high‐resolution X‐ray diffraction (HRXRD) and photoluminescence (PL). Furthermore the results of C–V measurements of p‐ZnSe layers doped with nitrogen are discussed and I–V characteristics and electroluminescence (EL) spectra of LEDs grown with both techniques are presented. ZnSe/Zn(SSe) MQWs are prepared with MOVPE and (ZnCd)Se/ZnSe MQWs with MBE to improve the optical efficiency of the diodes.
Blue‐Green Ternary and Quaternary Lasers. Technological Problems and Theoretical Investigations
Authors: Jakobs A. , Schüll K. , Behr Th. , Jobst B. , Hommel D.
Published: July 2007

To overcome the constraints imposed by lattice mismatch on the design of ternary laser structures asymmetric and pseudomorphic waveguides are proposed. The latter structures are shown to give high luminescence efficiency indicative for a low defect density and a high differential quantum efficiency. The measured far‐field patterns agree well with theoretical predictions. Several possibilities to reduce carrier leakage out of the active zone are reviewed and investigated by computer simulations. Gain measurements based on the modulation depth of the Fabry‐Perot modes are also presented.
Exciton scattering with bare electrons
Authors: Koch M. , Bastian G. , Hellmann R. , Feldmann J. , Göbel E. O. , Dawson P.
Published: July 2007

It is shown that exciton‐electron scattering is twice as efficient as exciton‐exciton scattering by performing transient four‐wave‐mixing experiments on a mixed type‐I–type‐II GaAs/AlAs double quantum well structure. In addition it is found that the presence of bare electrons in the wide well leads to a quenching of the high‐energetic part of the photoluminescence spectrum. Scattering with electrons releases excitons localized at shallow states and leads to a more complete relaxation of excitons into the energetically lowest quantum well states.
The accurate numerical evaluation of half‐order Fermi‐Dirac Integrals
Authors: Mohankumar N. , Natarajan A.
Published: July 2007

An efficient algorithm for the direct evaluation of Fermi‐Dirac integrals of half orders is presented. The computational scheme consists of a modified trapezoidal rule which exactly corrects for the loss of accuracy caused by the presence of poles of the integrand. The analysis of the scheme leads to useful error bounds which indicate the quadrature scheme to be rapidly convergent. As much as 16 steps of trapezoidal summation along with at most 9 steps of pole correction can provide an accuracy of one part in 1014 for the usual range of values of the argument.
Positron annihilation in narrow‐gap semiconductors
Authors: Bouarissa N. , West R. N. , Aourag H.
Published: July 2007

The valence electron and positron charge densities in InAs and InSb are obtained from wave functions derived in a model pseudopotential band‐structure calculation. It is found that the positron density is maximum in the open interstices and is excluded not only, as usual, from the ion cores but also to a considerable degree from the valence bonds. Electron‐positron momentum densities are calculated for the (001–110) plane. The results are used to analyze the positron effect in narrow‐gap semiconductors.
On the temperature dependence of the optical absorption edge in nickel oxide
Authors: Pattanayak J. , Becker K. D.
Published: July 2007

Results are reported of a high‐temperature investigation (up to 1000 °C) of the optical absorption edge in NiO. An approximately exponential dependence of the absorption coeficient on photon energy is observed. The absorption coeficient is found to be independent of oxygen partial pressure, i.e., of native lattice defects. The temperature dependence of the edge gives evidence of strong exciton‐phonon coupling in NiO.
Model Effective‐Mass Hamiltonians for Abrupt Degraded Heterojunctions
Authors: Brezini A. , Sebbani M. , Marouf S.
Published: July 2007

A class of hermitian effective‐mass Hamiltonians is considered whose kinetic energy term is 1/4 (mαpmβpmγ + mγpmβpmα) with α + β + γ = −1. These Hamiltonians are applied to abrupt degraded interfaces between crystals and the matching conditions across the interface are searched for the effective‐mass wave function Ψ and its spatial derivative Ψ′. For α ≠ γ it is found that the ground‐state energy is negative, i.e. without physical bearing for the considered potential. Consequently, the only viable cases are for α = γ. In a model calculation, β ≈ −1 is estimated, to be the more relevant candidate although the case β = 0 cannot be excluded for typical interfaces.
The Preparation of Amorphous SixGeyOz Alloy Films by Sputtering. Preparation Conditions, Chemical Composition, and Vibrational Properties
Authors: Zacharias M. , Stolze F. , Drüsedau T. , Bock W.
Published: July 2007

Amorphous SixGeyOz, alloy films with x = 0.17 to 0.60, y = 0.19 to 0.68, and z = 0.11 to 0.42 are deposited using reactive dc magnetron sputtering in an Ar/water atmosphere. The alloy concentrations are measured by secondary neutral mass spectrometry (SNMS). The oxygen content strongly decreases with decreasing silicon concentration. The dependence of the alloy composition on the target coverage with germanium pieces is investigated. IR transmission measurements in the range from 400 to 4000 cm−1 show a predominance of the SiOSi asymmetric stretching mode. The minor absorption band due to GeOGe stretching vibrations totally disappears after annealing the film at 800 °C. An increase of the SiOSi absorption mode is detected.
The Iron States in Cd1−xFexTe in the Fundamental Gap Energy Range
Authors: Hołda A. , Rodzik A. , Mielnikow A. A. , Żukowski P. W.
Published: July 2007

The reflectivity, absorption, photoconductivity, and cathodoluminescence spectra for Cd1−xFexTe (0 ≦ x ≦ 0.05) at 300 and 77 K are investigated. The measurements are carried out in the fundamental gap energy range. From the analysis of the experimental results, the energy positions and properties of Fe states in the CdTe matrix in the fundamental gap region are presented and discussed. It is concluded that the increase of the width of the fundamental gap with the change of temperature from 300 to 77 K leads mainly to the rise of the energy distance between the donor‐like iron state 5E and the bottom of the conduction band, whereas the energy distance between the iron state 5E and the top of the valence band remains unchanged. The increase of the fundamental gap value with the decrease of temperature changes the energy positions of the excitation iron state 3T1 with respect to the bottom of the conduction band. Energy positions of iron states in the fundamental gap energy region as well as the increase of the energy width and density of these states with the rise of the iron concentration in Cd1−xFexTe are reflected in the results obtained with the use of different experimental methods.
Preparation and Characterization of Surface‐Modified Luminescent Porous Silicon
Authors: Dubin V. M. , Vieillard C. , Ozanam F. , Chazalviel J.‐N.
Published: July 2007

Porous silicon layers are chemically grafted with trimethylsiloxy groups by exposure to hexamethyldisilazane (HMDS) vapors. After treatment, infrared spectroscopy reveals that part of the initially hydrogenated surface is actually modified. Luminescence of the porous layers appears to be little affected by the treatment. On strongly luminescent samples, the photocarriers exhibit the same infrared absorption as in hydrogenated or oxidized porous silicon, evidencing the similar involvement of localized states in the luminescence process. The treated porous silicon layers also exhibit an increased stability against aging in ambient, as compared to hydrogenated porous silicon. Furthermore, the modification can be removed by simple exposure to HF vapor, thereby restoring the initial hydrogenated surface.
Phonons of Indium Selenide Single Crystals Studied by Inelastic Electron Tunneling Spectroscopy
Authors: Yamaguchi K.
Published: July 2007

Inelastic 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

Photocurrent 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

The 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

A 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

A 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

The 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

An 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

Using 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

Measurements 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

Based 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

Big 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

Positron 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

Titanium 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

The 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

The 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

Emission, 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

We 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

The 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

The 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

The 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

In 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

The 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

The 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

The 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

Amplification 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

We 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

We 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

We 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

Quantum (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.
Photoluminescence of a Pseudomorphic Si1−yCy/Si MQW Structure under Pressure
Authors: Liu Z. X. , Goñi A. R. , Brunner K. , Eberl K. , Syassen K.
Published: July 2007

We have measured photoluminescence (PL) spectra of a pseudomorphic Si1−yCy/Si (y = 0.0045) multiple quantum well (MQW) structure under hydrostatic pressure (0 to 8 GPa) and at low temperatures (10 to 70 K). The MQW‐related emission at energies below the Si band gap consists of bound and free exciton zere‐phonon lines and related Si‐Si TO phonon replicas. All MQW‐related PL peaks shift to lower energy with increasing pressure. The dependence of PL‐peak intensities and energies on excitation power density, temperature, and pressure are consistent with a type‐I band alignment throughout the pressure range investigated. Furthermore, the total band offset and the activation energies involved in the decay of the free and bound exciton emission show only a very small change with pressure.
Phase Diagram of InSb at High Pressures and Temperatures
Authors: Mezouar M. , Besson J. M. , Syfosse G. , Itié J. P. , Häusermann D. , Hanfland M.
Published: July 2007

The phase diagram of InSb has been studied by energy‐dispersive X‐ray diffraction with synchrotron radiation at pressures up to 8 GPa and temperatures up to 800 K in a Paris‐Edinburgh cell. At room temperature InSb transforms above 2.5 GPa from the zincblende structure to a sixfoldcoordinated orthorhombic structure with Pmm2 (Cmcm) space group (InSb IV). In previous studies it was proposed that another orthorhombic structure with Immm space group (InSb II) existed at higher temperature. We show that this phase is actually metastable, the InSb IV one being the stable form. The low‐pressure melting curve and the triple point position are confirmed and the high pressure melting curve as well as the phase boundaries between the high pressure phases have been determined precisely. A new pressure‐temperature phase diagram for InSb is established which eliminates contradictions in the previously proposed diagrams of its solid phases.
Nature of the Forbidden Gap in Insulating ABxB′1 − xO3 Crystals
Authors: Raevskii I. P. , Prosandeev S. A. , Osipenko I. A.
Published: July 2007

The electronic structure of a wide variety of ternary ABxB′1−xO3 perovskitetype insulating oxides in ordered phases has been analysed using the tight‐binding method. The cases considered me those in which A is divalent and the tetravalent B in ABO3 is replaced by a mixture with the same total number of valence electrons. Widths of the forbidden gaps obtained prove to be much larger than in perovskites of the ABO3 type with the same B ion. The results of the experimental electric conductivity and photoconductivity measurements are in good agreement with the computation.
Monoclinic Spin Hamiltonian Analysis of EPR Spectra of Mn2+ in BiVO4 Single Crystals
Authors: Yeom T. H. , Rudowicz C. , Choh S. H. , McGavin D. G.
Published: July 2007

X‐band EPR spectra of Mn2+ in ferroelastic BiVO4 single crystals at room temperature taken in three orthogonal planes are analyzed using a twestage least‐squares fitting procedure. The absence of site splitting from the spectra shows unequivocally that Mn2+ lies on a site with two‐fold rotation symmetry, whose two fold axis is parallel to the monoclinic crystal axis. The low symmetry effects arising from the monoclinic site symmetry are evidenced by the observed coincidence of the extrema for transitions between different Zeeman levels along the monoclinic axis, and by the 180° rotational symmetry in the monoclinic plane and a small noncoincidence of the turning points in this plane. In the first stage, the spectra are fitted using the monoclinic form of the electronic Zeeman and fine structure terms (of second and fourth degree) appropriate for the crystallographically determined orientation of the monoclinic axis. In the second stage, fitting of the nuclear hyperfine tensor (A) and the nuclear quadrupole tensor (P) is carried out with fixed values of the electronic Zeeman tensor (g) and fine structure terms, i.e. the tensor (D) and the fourth‐degree terms, as obtained in the first stage. The principal axes of g, D, A, and P are found to be non‐coincident in the monoclinic plane, as would be generally expected for a monoclinic site.
X‐Ray and Bulk Magnetic Properties of the NiZn Ferrite System
Authors: Kakatkar S. V. , Kakatkar S. S. , Patil R. S. , Sankpal A. M. , Suryavanshi S. S. , Bhosale D. N. , Sawant S. R.
Published: July 2007

Compositions having the general formula Ni1−xZnxFe2O4 with x = 0.30, 0.35, 0.40, 0.45 have been sintered at 1100, 1150, 1200, and 1240°C to attain different microstructures. The grain size D for a particular composition increases linearly with increasing sintering temperature. The lattice parameter α and magnetization Ms are seen to be invariant with the change in sintering temperature. The coercive force Hc and the remanent ratio R = Mr/Ms are seen to depend on the sintering temperature and hence on D. α and M, are found to increase with the increase of the Zn content, whereas Hc values show a decreasing trend with the Zn content. The compositional, thermal, and microstructural variation of hysteresis parameters like Ms, Hc, and R = Mr/Ms reveal that magnetic grains in the compositions investigated are of multi‐domain type. This result is supported by ac susceptibility data.
A 90 day repeated oral toxicity study on plantamajoside concentrate from Plantago asiatica
Authors: Park Byung‐Gyu , Lee Hyun‐Sun , Jung Sung‐Hoon , Hong Chung‐Oui , Won Hye‐Jin , Park Ho‐Young , Ryu Yung‐Sun , Lee Sung‐Joon , Kim Kyoung‐Heon , Park Kuen‐Woo , Lee Kwang‐Won
Published: July 2007

Plantago asiatica is distributed widely in East Asia. Since ancient times it has been used as a diuretic to treat acute urinary infections, and as an antiinflammatory, antiasthmatic, antioxidant, antibacterial, antihyperlipidemic and antihepatitis drug. The major compound, plantamajoside from P. asiatica, which is used as a marker compound in chemotaxonomic studies, was reported to have antibacterial activity, inhibition activity against cAMP phosphodiesterase and 5‐lipoxygenase and antioxidant activity. However, there are no reports on the safety of plantamajoside. This study assessed the toxic effects of plantamajoside concentrate (PC), the purity of which was above 80%, in rats following administration at dose levels of 0, 500, 1000 and 2000 mg/kg body weight/day for 13 weeks, as recommended by the OECD guidelines. The results showed that there were no differences in body weight, food intake, water consumption, relative organ weight or the hematological and serum biochemical values among the different dosage groups. No death or abnormal clinical signs were observed during the experimental period. Therefore, the results suggested that no observed adverse effect level (NOAEL) of the PC in rats after oral administration is considered to be greater than 2000 mg/kg in rats under the conditions employed in this study. Copyright © 2007 John Wiley & Sons, Ltd.
Robust control of a two‐axis, magnetic suspension, flexible‐beam system based on H∞ optimization theory
Authors: Zhou Tong , Fujita Masayuki , Matsumura Fumio
Published: July 2007

This paper deals with how to use H∞ optimization theory for the controller design of a two‐axis magnetic suspension, flexible‐beam system, which is a simplified model for a flexible magnetic bearing system. Both simulation and experimental results show that the designed system not only has good performance in robustness to the plant's parametric uncertainty and the unmodelled dynamics in the beam's vibration modes, mode shapes, etc., but also has good performance in response characteristics.
Flight controller design for uncertain and nonlinear plants with pilot compensation
Authors: Kobylarz T. , Horowitz I. M. , Houpis C. H.
Published: July 2007

Nonlinear quantitative feedback theory (QFT) is used to design a flight control system for the nonlinear model of the YF‐16 aircraft (A/C) with C* as the controlled output. The resulting closed loop stability augmentation system (SAS), Pe(S), becomes part of the outer loop containing the pilot. The Neal‐Smith pilot model for a compensatory tracking task is used to develop a technique which allows the designer to synthesize compensation in the outer loop, which includes a free compensator Fp(S). The latter is chosen to minimize pilot workload, increase system bandwidth, and improve handling qualities ratings as per the Neal–Smith criteria, for the tracking task. The available pilot compensation abilities are then available for further increasing of system bandwidth to improve overall capabilities. This approach can be used at the early stages of flight control design, thus saving time and money over the current practice. Simulations in the time and frequency domains demonstrate that the desired performance is attained.
Robust output feedback stabilization of uncertain dynamic systems with bounded controllers
Authors: Hui Stefen , Żak Stanislaw H.
Published: July 2007

We propose a new class of infinitely many bounded output feedback controllers for uncertain dynamic systems with bounded uncertainties. No statistical information about the uncertainties is assumed. A variable structure systems approach is employed in the synthesis of the proposed output feedback controllers. The role of the system zeros in the output feedback stabilization using the variable structure approach is discussed. We show that the proposed controllers guarantee the practical stability of the closed‐loop system and give estimates of the regions of practical stability.
H∞ controller design for boilers
Authors: Pellegrinetti Gordon , Bentsman Joseph
Published: July 2007

This paper examines the ability of the H∞ design methodology to provide a solution to a gas‐ or oil‐fired boiler control problem, and addresses the nontrivial application issues of the H∞ design. The H∞ methodology is applied to an experimentally verified heating‐cogeneration boiler model which exhibits nonlinearities, instability, time delays, non‐minimum phase behaviour, and coloured noise disturbances with sensor noise in the frequency range of the significant plant dynamics. The design shows that, to satisfy performance criteria, a high order controller is needed. The paper also demonstrates a trade‐off between the reduction of controller order and the loss of controller performance.
Robust stability of large‐scale systems which contain time‐invariant lur'e‐type uncertainties in subsystems and norm‐bounded uncertainties in interconnections
Authors: Saeki Masami , Araki Mituhiko
Published: July 2007

In this paper a new frequency‐domain condition for the robust stability of a class of large‐scale systems is derived. It is assumed that each subsystem contains one time‐invariant nonlinearity satisfying a sector condition, and that the interconnecting functions are linearly bounded by the norms of the scalar outputs of subsystems. In deriving the above such Lur'e‐type Lyapunov functions of subsystems are constructed so that their weighted sum is a Lyapunov function of the overall system. This condition is potential to give a sharper result than the circle‐condition‐type result which was obtained previously. Furthermore, a method to estimate the domain of attraction using the above Lyapunov function is also given when the sector condition is satisfied only locally.
Bedeutung der Vakuumtechnik in der Metallpulver‐Technologie
Authors: Hohmann Michael , Ertl Manfred
Published: July 2007

Powder‐Technology has developed into a significant and still increasing market. There is a demand for high quality meaning highest purity and spherical particle shape of the powder. In order to reach this aim metal alloys are melted under vacuum and atomized with intertgas. To improve the chemical purity the produced powder is treated under vacuum for instance by the static or dynamic degassing process.
Schmelzen und Behandeln von Metallen und Legierungen im Vakuum
Authors: Choudhury Alok
Published: July 2007

The growing demands for better quality of metallic materials can only be met by the application of vacuum during the production of these metals and alloys and their field of application.
Vakuumgerechte Werkstoffe und Verbindungstechnik
Authors: Mühlhoff Martin
Published: July 2007

Detachable connections are used in cases where the operating time is not too long, or the arrangement of the vacuum equipment is required to be variable. Using detachable connections also allows access to the inner section of the vacuum equipment (for the purpose of service, maintenance, insertion of samples, etc.). Valves and vibration dampers e.g. are mainly flanged‐on.

In general, these connections are more expensive than nondetachable ones (welding, soldering, melting, glueing) and provide almost the same high level of reliability of He‐tight, fittings, as far as leakages are concerned.
Zur Entwicklung der Oberflächenphysik
Authors: Jahrreiss Heribert
Published: July 2007

With special emphasis on the crucial influence of vacuum physics and its techniques, a survey of the development of solid surface physics from its rudimentary beginnings in the early 1960s to its present state is given. Research aims and basic methods, as well as shifts in the areas of interest, are treated in chronological order. Comparing the development of surface physics with that of older fields of physics, the question of predicting its future development is then posed.