bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystalline, electronic, and magnetic structures of θ-Fe3C, χ-Fe5C2, and η-Fe2C from first principle calculation
Authors: Faraoun H. I. , Zhang Y. D. , Esling C. , Aourag H.
Published: May 2006

First principle calculations have been performed to study the crystalline, electronic, and magnetic structures of three iron-carbide systems: θ-Fe3C, χ-Fe5C2, and η-Fe2C. The Kohn-Sham equations were solved by applying the full-potential linearized augmented plane wave method. The generalized gradient approximation in the Perdew-Wang formalism was used to the exchange and correlation energy functional. The internal positions of atoms within the unit cell were optimized and the ground state properties such as lattice parameter and bulk modulus were calculated. The results are compared with experimental data when available. Comparison of the two metastable systems χ-Fe5C2 and η-Fe2C shows that the last one has lower formation energy; this is corroborated by the formation sequence observed during tempering. The electronic structures of the three carbides were then studied and the magnetic moments calculated by means of electronic spin-resolved density of state calculations at their equilibrium lattice constants and optimized internal parameters.
Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations
Authors: Hamaya K. , Taniyama T. , Yamazaki Y.
Published: May 2006

We study magnetization reversal processes of in-plane magnetized (Ga,Mn)As epilayers with different hole concentrations in out-of-plane magnetic fields using magnetotransport measurements. A clear difference in the magnetization process is found in two separate samples with hole concentrations of 1020 and 1021cm−3 as the magnetization rotates from the out-of-plane saturation to the in-plane remanence. Magnetization switching process from the in-plane remanence to the out-of-plane direction, on the other hand, shows no hole concentration dependence, where the switching process occurs via domain wall propagation. We show that the balance of ⟨100⟩ cubic magnetocrystalline anisotropy and uniaxial [110] anisotropy gives an understanding of the difference in the out-of-plane magnetization processes of (Ga,Mn)As epilayers.
Thermoelectric properties of sintered clathrate compounds Sr8GaxGe46−x with various carrier concentrations
Authors: Fujita Isao , Kishimoto Kengo , Sato Masaya , Anno Hiroaki , Koyanagi Tsuyoshi
Published: May 2006

Polycrystalline samples of Sr8GaxGe46−x clathrates with varied nominal Ga contents were prepared by powder metallurgy to produce n-type samples with carrier concentration n of 1.8×1020–1.1×1021cm−3. Their thermoelectric properties were measured in the temperature range from 300to900K. Their Seebeck coefficient and electrical conductivity were found to be typical for a heavily doped semiconductor, and varied systematically with their carrier concentration. The maximum value of the figure-of-merit ZT was 0.62 at 800K for n=5.6×1020cm−3. Other following properties were also measured or estimated, and their relationships with the thermoelectric properties are discussed. The band gap of the samples was estimated to be 0.4–0.5eV; their effective mass was an almost constant value of 3.1me at room temperature, and this value decreases with increasing temperature; and their electron Hall mobilities were 8–13cm2V−1s−1 at room temperature, increasing slightly with decreasing carrier concentration.
Densification of silica glass induced by 0.8 and 1.5μm intense femtosecond laser pulses
Authors: Saliminia A. , Nguyen N T. , Chin S L. , Vallée R
Published: May 2006

We investigate the physical mechanisms responsible for waveguide formation in silica glass induced by 1kHz intense femtosecond laser pulses from a Ti-sapphire laser at 0.8μm as well as from a femtosecond optical parametric amplifier at 1.5μm. It is demonstrated that the densification taking place at the irradiated region is the principal cause for refractive index change in the waveguides written with both 0.8 and 1.5μm pulses. The birefringence induced by the stress arising from such densification and its behavior against thermal annealing are also studied.
Revisiting the hexane-water interface via molecular dynamics simulations using nonadditive alkane-water potentials
Authors: Patel Sandeep A. , Brooks Charles L.
Published: May 2006

We present results addressing properties of a polarizable force field for hexane based on the fluctuating charge (FQ) formalism and developed in conjunction with the Chemistry at Harvard Molecular Mechanics (CHARMM) potential function. Properties of bulk neat hexane, its liquid-vapor interface, and its interface with a polarizable water model (TIP4P-FQ) are discussed. The FQ model is compared to a recently modified alkane model, C27r, also based on the CHARMM potential energy function. With respect to bulk properties, both models predict bulk density within 1%; the FQ model predicts the liquid vaporization enthalpy within 2%, while the C27r force field underestimates the property by roughly 20% (and in this sense reflects the quality of the C27r force field across the spectrum of linear and branched alkanes). The FQ hexane model realistically captures the dielectric properties of the bulk in terms of a dielectric constant of 1.94, in excellent agreement with experimental values in the range of 1.9–2.02. This behavior is also in conformity with a recent polarizable alkane model based on Drude oscillators. Furthermore, the bulk dielectric is essentially captured in the infinite frequency, or optical, dielectric contribution. The FQ model is in this respect a more realistic force field for modeling lipid bilayer interiors for which most current state-of-the-art force fields do not accurately capture the dielectric environment. The molecular polarizability of the FQ model is 11.79Å3, in good agreement with the range of experimental and ab initio values. In contrast to FQ models of polar solvents such as alcohols and water, there was no need to scale gas-phase polarizabilities in order to avoid polarization catastrophes in the pure bulk. In terms of the liquid-vapor and liquid-liquid interfaces, the FQ model displays a rich orientational structure of alkane and water in the respective interfacial systems, in general conforming with earlier simulation studies of such interfaces. The FQ force field shows a marked deviation in the interfacial dipole potentials computed from the charge densities averaged over simulation trajectories. At the liquid-vapor interface, the FQ model predicts a potential drop of −178.71mV in contrast to the C27r estimate of −433.80mV. For the hexane-water interface, the FQ force field predicts a dipole potential drop of −379.40mV in contrast to the C27r value of −105.42mV. Although the surface dipole potential predicted by the FQ model is roughly 3.5 times that predicted by the C27r potential, it is consistent with reported experimental potentials across solvated lipid bilayers in the range of 400–600mV.
Phase equilibrium and metastability of liquid benzene at high pressures
Authors: Azreg-Aïnou M. , Hüseynov A. , İbrahimoğlu B.
Published: May 2006

This work is mainly an investigation of some of the liquid-to-solid properties of pure benzene on a restricted domain of high pressures (20.6⩽P⩽102.9MPa). Newly obtained equilibrium experimental data and recently developed analytical equation of state are exploited and compared with each other and with previous experimental data. Curves fitted to the pressure, volume discontinuity, and enthalpy change at liquid-to-solid equilibrium points are provided. Concerning the metastable liquid benzene, both experimental and theoretical data for the minimum nucleation temperatures (limits of liquid metastability) are provided and correlated to each other.
Optimal control landscapes for quantum observables
Authors: Rabitz Herschel , Hsieh Michael , Rosenthal Carey
Published: May 2006

The optimal control of quantum systems provides the means to achieve the best outcome from redirecting dynamical behavior. Quantum systems for optimal control are characterized by an evolving density matrix and a Hermitian operator associated with the observable of interest. The optimal control landscape is the observable as a functional of the control field. The features of interest over this control landscape consist of the extremum values and their topological character. For controllable finite dimensional quantum systems with no constraints placed on the controls, it is shown that there is only a finite number of distinct values for the extrema, dependent on the spectral degeneracy of the initial and target density matrices. The consequences of these findings for the practical discovery of effective quantum controls in the laboratory is discussed.
Drift resonance in high density non-neutral plasmas
Authors: Kaup D. J.
Published: May 2006

Theoretical studies of the operation of crossed-field electron vacuum devices such as magnetrons and crossed-field amplifiers (CFA) have usually centered on their initial growth, taking this as an indication of their operating modes. In such an analysis one solves the equations for the density profile, the operating frequency, the growth rate, and other features of these devices. What one really obtains then are only the conditions for the device to turn on. The dominant interaction in this stage is a Rayleigh-type instability which initiates a quasilinear diffusion process whereby the electron density profile redistributes itself into a profile which will be in equilibrium with the ponderomotive-like forces produced by the growing rf fields. Eventually the rf fields will saturate and an operating device will settle into a stationary operating regime. This stage of a device’s operation is called the “saturation stage.” This latter stage involves a different set of physical interactions from the initiation stage. No longer is there a growth rate; rather the rf amplitudes have saturated and as a result, the ponderomotive-like forces have also vanished along with the quasilinear diffusion. In this saturation stage, we find that new rf modes appear. In fact, there are a total of five rf modes, two of which are the usual slow modes of the initiation stage, and three of which have fast oscillations in the vertical direction. One fast mode corresponds to a drift plasma oscillation while the other two fast modes are drift cyclotron modes. In this paper, we will describe how the drift plasma oscillation interacts and couples with the slow rf modes at the diocotron resonance.
Viscoelasticity of suspensions of magnetic particles in a polymer: Effect of confinement and external field
Authors: Auernhammer Günter K. , Collin Dominique , Martinoty Philippe
Published: May 2006

We study the suspensions of magnetic particles, the precursor state of magnetic gels and elastomers. We use magnetic particles with a permanent magnetization which is high enough to overcome thermal energy and low enough to guarantee a long live time of the sample. These particles form a space-filling structure at very low volume fractions (≈0.5vol%), which modifies the viscoelastic response of the matrix significantly. In confined geometry the particles form clusters of a size that depends on the sample thickness. Even small external fields induce a strong anisotropy in the mechanical and optical properties of the suspension. The action of the applied magnetic field induces a gel-like response in one direction but leaves the other directions liquidlike. The viscosity is a very sensitive mechanical test for the anisotropy of the material. Light scattering data confirm our mechanical results.
Ab initio potential-energy surface and rovibrational states of the HCN–HCl complex
Authors: van der Avoird Ad , Bondo Pedersen Thomas , Dhont Guillaume S. F. , Fernández Berta , Koch Henrik
Published: May 2006

A four-dimensional intermolecular potential-energy surface has been calculated for the HCN–HCl complex, with the use of the coupled cluster method with single and double excitations and noniterative inclusion of triples. Data for more than 13 000 geometries were represented by an angular expansion in terms of coupled spherical harmonics; the dependence of the expansion coefficients on the intermolecular distance R was described by the reproducing kernel Hilbert space method. The global minimum with De=1565cm−1 and Re=7.47a0 has a linear HCN–HCl hydrogen-bonded structure with HCl as the donor. A secondary hydrogen-bonded equilibrium structure with De=564cm−1 and Re=8.21a0 has a T-shaped geometry with HCN as the donor and the acceptor HCl molecule nearly perpendicular to the intermolecular axis. This potential surface was used in a variational approach to compute a series of bound states of the isotopomers HCN–HCl35, DCN–HCl35, and HCN–HCl37 for total angular momentum J=0,1,2 and spectroscopic parities e, f. The results could be analyzed in terms of the approximate quantum numbers of a linear polyatomic molecule with two coupled bend modes, plus a quantum number for the intermolecular stretch vibration. They are in good agreement with the recent high resolution spectrum of Larsen et al. [Phys. Chem. Chem. Phys. 7, 1953 (2005)] in the region of 330cm−1 corresponding to the HCl libration. The (partly anomalous) effects of isotopic substitutions on the properties of the complex were explained with the aid of the calculations.
Nearby-fluids equilibria. I. Formalism and transition to single-fluid magnetohydrodynamics
Authors: Steinhauer Loren C. , Ishida Akio
Published: May 2006

The nearby-fluids model is an improvement of the basic two-fluid flowing equilibrium system developed elsewhere [L.C. Steinhauer, Phys. Plasmas 6, 2734 (1999)]. The two-fluid system is a singular perturbation problem in which the usually small ion-inertia length (ion skin depth) gives rise to a small parameter. This has frustrated attempts to find practical equilibria. The nearby-fluids ordering assumes that the ion and electron flow surfaces are close to (“nearby”) each other but do not coincide exactly. This eliminates the singularity and “softens” the stiff differential equations, thus facilitating numerical solution. Previous treatments of two-fluid equilibria did not find a smooth transition to the single-fluid magnetodynamics (MHD) model in the small ion-inertia-length limit. This difficulty is only partly eliminated by recognizing that the electric field is ordered “large” in MHD. A small but nonzero ion-inertia length produces several important effects, including the appearance of a transition layer between the “closed” and “open” field regions of a field-reversed configuration plasma.
Nearby-fluids equilibria. II. Zonal flows in a high-β, self-organized plasma experiment
Authors: Steinhauer L. C. , Guo H. Y.
Published: May 2006

The field and flow structure observed in a high-β field reversed configuration (FRC) produced in the translation, confinement, and sustainment (TCS) experiment are modeled using the newly developed nearby-fluids equilibrium model. These results are the first evidence that experimental FRCs have complex flows, that is nonrigid rotational flow and poloidal flow, both with maximum speeds nearly half the Alfvén speed. The interpretive approach is an innovative “backwards” method using the nearby-fluids platform for two-fluid equilibria. The most remarkable outcome is the prediction of a poloidal flow structure with significant zonal features. The poloidal flow has never been directly measured in FRCs; thus this discovery results from applying the flowing equilibrium model as an interpretive tool. The poloidal flows explain the unusual toroidal field structure observed in TCS. Zonal features in the rotational flow are also inferred from the unfolding of chord-integrated measurements. The results also indicated that a broad core of the FRC is very close to a minimum energy state.
Developing a coarse-grained force field for the diblock copolymer poly(styrene-b-butadiene) from atomistic simulation
Authors: Li Xuejin , Kou Dazhi , Rao Shuling , Liang Haojun
Published: May 2006

We have developed a coarse-grained force field for the poly(styrene-b-butadiene) diblock copolymer. We describe the computational methods and discuss how they were applied to develop a coarse-grained force field for this diblock copolymer from the atomistic simulation. The new force field contains three different bonds, four angles, five dihedral angles, and three nonbonded terms. We successfully tested this coarse-grained model against the chain properties, including static and dynamic properties, derived from the atomistic simulation; the results suggest that the coarse-grained force field is an effective model.
Threshold photoelectron spectroscopy of ozone
Authors: Couto H. , Mocellin A. , Moreira C. D. , Gomes M. P. , Naves de Brito A. , Lopes M. C. A.
Published: May 2006

Threshold photoelectron spectrum of ozone is presented for the first time at a resolution of 21–38meV using synchrotron radiation in the energy region of 12–21eV. The ionization energies of the first ionized states were determined and an interpretation of the O3 spectrum with respect to its first three ionic states, 1A12, 1B22, and 1A22, is presented. Above 16eV the enhancement of the intensities of the 2B12, 3A12, and 4B22 band systems due to the contribution of indirect processes was observed, not accessible by conventional photoelectron spectroscopy. It was also resolved and assigned the extensive vibrational structures of ozone. Between 15.5 and 18.5eV the main band contours are similar to those found in conventional photoelectron spectroscopy, except that our threshold photoelectron spectrum reveals extensive additional vibrational structures. The band 2B12 was found to present an irregular vibrational spacing ΔE, with a minimum value of 80meV at ∼16.47eV.
Observation of low-temperature object by phase-contrast x-ray imaging: Nondestructive imaging of air clathrate hydrates at 233K
Authors: Takeya Satoshi , Honda Kazumasa , Yoneyama Akio , Hirai Yasuharu , Okuyama Junichi , Hondoh Takeo , Hyodo Kazuyuki , Takeda Tohoru
Published: May 2006

A cryochamber and a liquid cell that are designed for nondestructive three dimensional observations and arranged in a two-crystal x-ray interferometer expand the use of phase-contrast x-ray imaging that could only be performed at room temperature in previous studies to a new temperature range of 190K to room temperature. The methyl acetate in the liquid cell prevents undesirable sample outline contrasts and enables internal observations. Both a nondestructive observation and a highly accurate absolute density of the materials under low-temperature conditions can be obtained with a single measurement using this new technique. A three dimensional x-ray computed tomography (x-ray CT) of the air clathrate hydrate in the hexagonal ice drilled from Dome Fuji in Antarctica is shown, and the density of the air hydrate is estimated to be 0.937(3)g∕cm3 at 233K.
Spherically shaped active transducer based on proton-irradiated vinylidene fluoride-trifluoroethylene 70∕30mol% copolymer
Authors: Lau S. T. , Chan H. L. W. , Choy C. L. , Cheung W. Y. , Wong S. P.
Published: May 2006

Spherically shaped active transducers using proton-irradiated vinylidene fluoride-trifluoroethylene 70∕30mol% copolymer films as the active elements are described. The copolymer films prepared by hot compression molding were irradiated with a high energy proton over a broad dose range (20–250Mrad). The electrostrictive and piezoelectric responses of the copolymer have been characterized before subsequent transducer fabrication. The performances of the focused transducers constructed with a 4mm aperture size and epoxy backing were evaluated under dc bias voltages. The transducers with focal lengths of 17.4–19.0mm and a center frequency of 19MHz display a broad bandwidth up to 94%. Besides, the transmitting output of the transducers increases with the dc bias voltage. For the copolymer active element irradiated at a proton dose of 107Mrad, the transducer shows the highest transmitting voltage response of 1.34kPa∕V.
MgO epitaxy on GaN (0002) surfaces by molecular beam epitaxy
Authors: Craft H. S. , Ihlefeld J. F. , Losego M. D. , Collazo R. , Sitar Z. , Maria J-P.
Published: May 2006

We report on the epitaxial deposition of magnesium oxide films with [111] crystallographic orientation on (0002) GaN by molecular beam epitaxy. Specifically, we use an adsorption controlled growth mechanism to initiate the growth process. Electron diffraction shows a spotty intense pattern without intensity fluctuations during growth and evidence of in-plane twinning. X-ray diffraction reveals the films to be epitaxial with full width at half maximum values of 0.3°, 0.5°, and 1° in 2θ, ϕ, and χ circles, respectively. Wet etching of the GaN surface with a HCl:HF mixture prior to growth is critical for achieving high crystalline quality. Epitaxial growth is observed between room temperature and 650°C, with negligible changes in crystalline quality with increased temperature. Atomic force microscopy analysis shows grainy surfaces with feature sizes near 10nm and rms roughness values of 1.4Å over 1μm2 areas. X-ray diffraction analysis suggests MgO film stability up to 850°C in ex situ air annealing.
Percolating ion transport in binary mixtures with high dielectric loss
Authors: Brohede U. , Strømme M.
Published: May 2006

We investigate the ion transport percolation properties of a binary system of an ion conductor (NaCl) and an insulator (ethyl cellulose) for which the ac component of the conductivity is non-negligible over the entire measured frequency range. We find that the dc conductivity, extracted from a well-defined range of frequencies, can be described by a low percolation threshold, ϕc=0.06 three-dimensional conducting network. The low ϕc was explained by the water-layer-assisted ion conduction in micrometer-sized ethyl cellulose channels between NaCl grains. The present findings provide valuable knowledge for the analysis and design of a broad class of ion conducting functional materials.
Analysis of electromigration statistics for Cu interconnects
Authors: Hauschildt M. , Gall M. , Thrasher S. , Justison P. , Michaelson L. , Hernandez R. , Kawasaki H. , Ho P. S.
Published: May 2006

Electromigration failure statistics and the origin of the lognormal standard deviation for copper interconnects were investigated by analyzing the statistics of electromigration lifetimes and void size distributions at various stages during testing. A statistical correlation between electromigration lifetimes and void evolution was established. Using simulation to fit the experimental data, the parameters influencing the electromigration lifetime statistics were identified as variations in void sizes, geometrical and experimental factors of the electromigration experiment, and kinetic aspects of the mass transport process, such as differences in the interface diffusivity between the lines.
Three-axis optical force plate for studies in small animal locomotor mechanics
Authors: Hsieh S. Tonia
Published: May 2006

The use of force plates to measure whole-body locomotor mechanics is a well-established technique. However, commercially available force plates are not sensitive enough for use on small-bodied vertebrates or invertebrates. The standard design for single- and multiple-axis, high-sensitivity force plates built by individual research groups uses semiconductor foil strain gauges to measure deflections; yet foil strain gauges are highly temperature and position sensitive, resulting in a drifting base line and nonlinear responses. I present here a design for a three-axis optical force plate that was successfully calibrated to measure forces as small as 1.5mN and is capable of determining the position of center of pressure with a mean error of 0.07cm along the X axis and 0.13cm along the Y axis. Using optical sensors instead of foil strain gauges to measure deflection, this force plate is not subject to temperature-related drift and is more robust against slight positioning inaccuracies. This force plate was used to measure forces produced by amphibious fishes weighing less than 2g as they jumped off the force platform.
Energy calibration of superconducting transition edge sensors for x-ray detection using pulse analysis
Authors: Hollerith C. , Simmnacher B. , Weiland R. , Feilitzsch F. v. , Isaila C. , Jochum J. , Potzel W. , Höhne J. , Phelan K. , Wernicke D. , May T.
Published: May 2006

Transition edge sensors (TESs) have been developed to be used as high-resolution x-ray detectors. They show excellent energy resolution and can be used in many applications. TESs are a special kind of calorimeters that can determine small temperature changes after x-ray absorption. Such a temperature change causes a strong resistance change (superconducting to normal-conducting phase transition) that can be measured. The energy calibration of a TES based spectrometer is problematic due to the nonlinear behavior of the detector response. In this article, a method is introduced to calibrate the energy scale of TES spectra. This is accomplished by calculating the energy dependence of the response of the detector operated in electrothermal feedback mode. Using this method a calibration accuracy of a few eV for an x-ray energy of 6keV can be achieved. Examples of energy dispersive x-ray spectroscopy (EDS) measurements demonstrate the high quality of this method for everyday use of TES EDS detectors in material analysis. However, because the method relies only on a few very general assumptions, it should also be useful for other kinds of TES detectors.
Stochastic heating in single and dual frequency capacitive discharges
Authors: Kawamura E. , Lieberman M. A. , Lichtenberg A. J.
Published: May 2006

Two electron heating mechanisms in capacitive discharges are ohmic heating due to electron-neutral collisions and stochastic heating at the plasma edge due to momentum transfer from high voltage moving sheaths. In this work, the stochastic heating and its dependence on various parameters are determined, focusing on dual frequency discharges in which the sheath motion is driven by a combination of high and low frequency sources. Particle-in-cell (PIC) simulations are used in order to investigate the electron heating. For a uniform fixed-ion discharge in which the ions are held fixed in a uniform density profile, there is no stochastic heating, as expected. For a two-step fixed-ion discharge in which the ions are held fixed in a two-step density profile with bulk density nb and sheath density nsh<nb, the stochastic heating is nearly proportional to (1−nsh∕nb)2. For a self-consistent discharge with mobile ions, the stochastic heating is well described by a “hard wall model” provided that the bulk oscillation is taken into account. These results are used to develop a stochastic heating theory for dual frequency discharges, which is compared to PIC simulations, giving good agreement.
Critical Poisson’s ratio for plasticity in Fe–Mo–C–B–Ln bulk amorphous steel
Authors: Gu X. J. , McDermott A. G. , Poon S. Joseph , Shiflet Gary J.
Published: May 2006

Fracture in compression has been investigated in Fe65Mo14C15B6 bulk amorphous steel doped with lanthanides to provide systematic variations of the elastic moduli. An onset of plasticity is observed as Poisson’s ratio approaches 0.32 from below. Combining with previous analysis reported by Lewandowski et al. [Philos. Mag. Lett. 85, 77 (2005)] using single-composition results from different sources, the findings are in support of universal critical Poisson’s ratio for plasticity in metallic glasses. The compositional dependences of elastic moduli are found to be anomalous considering the elastic moduli of the alloying elements. The role of interatomic interactions in designing ductile metallic glasses is suggested.
Control of directional emission in quasistadium microcavity laser diodes with two electrodes
Authors: Choi Muhan , Tanaka Tomoko , Fukushima Takehiro , Harayama Takahisa
Published: May 2006

We fabricated the AlGaAs∕GaAs three quantum well quasistadium laser diodes with two electrodes and succeeded in controlling directional laser emission by applying different currents to each electrode. We showed the ratio of laser emission with two different directions is proportional to the ratio of currents injected into two electrodes. These devices are applicable for beam switching and splitting.
Bragg scattering of surface plasmon polaritons on extraordinary transmission through silver periodic perforated hole arrays
Authors: Tsai Ming-Wei , Chuang Tzu-Hung , Chang Hsu-Yu , Lee Si-Chen
Published: May 2006

Extraordinary optical transmission through a two-dimensional periodic perforated Ag film in the far infrared region was demonstrated. When the squared hole size is close to a half lattice constant a∕2, the split of the degenerate (±1,0) Ag∕Si and (0,±1) Ag∕Si modes into two peaks becomes apparent. Surface plasmon polaritons dispersion relations with variously sized square holes are measured to investigate the different surface charge fields at the periodic metal array. Strong scattering of the forward SPP waves, in the (1,0) Ag∕Si mode, leads to a much lower transmission than that of in the (−1,0) Ag∕Si mode. Experimental results demonstrate that the photonic band gap opens up when the size of the squared hole exceeds a half lattice constant a∕2.
Improved superconducting quantum interference device magnetometer for low cross talk operation
Authors: Granata C. , Vettoliere A. , Russo M.
Published: May 2006

A fully integrated dc-SQUID (superconducting quantum interference device) magnetometer based on niobium technology including a new feedback coil design is presented. With respect to a standard SQUID design, the new feedback coil design was optimized in order to reduce the mutual inductance between neighbors and to increase the coupling with the pickup coil of the SQUID itself. In such a way, it is possible to reduce cross talk due to both the feedback coil and wires. Experimental results for the characterization of the device and the cross talk measurements are reported. The measurements have been performed in liquid helium using a low noise readout electronics specifically designed for large multichannel SQUID-based instruments. The experimental data show a substantial reduction of cross talk between neighboring sensors with respect to a traditional feedback coil. Furthermore, the new feedback coil system does not introduce any noise degradation.
Ge-modified Si(100) substrates for the growth of 3C-SiC(100)
Authors: Zgheib Ch. , McNeil L. E. , Masri P. , Förster Ch. , Morales F. M. , Stauden Th. , Ambacher O. , Pezoldt J.
Published: May 2006

An alternative route to improve the epitaxial growth of 3C-SiC(100) on Si(100) was developed. It consists in covering the silicon wafers with germanium prior to the carbonization step of the silicon substrate. Transmission electron microscopy and μ-Raman investigations revealed an improvement in the residual strain and crystalline quality of the grown 3C-SiC layers comparable to or better than in the case of 3C-SiC grown on silicon on insulator substrates. These beneficial effects were reached by using a Ge coverage in the range of 0.5–1 monolayer.
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near-infrared electrophosphorescence from organic light-emitting diodes based on copper phthalocyanine
Authors: Cheng Chuan-Hui , Fan Zhao-Qi , Yu Shu-Kun , Jiang Wen-Hai , Wang Xu , Du Guo-Tong , Chang Yu-Chun , Ma Chun-Yu
Published: May 2006

We demonstrated near-infrared organic light-emitting devices employing copper phthalocyanine (CuPc) doped into 4,4′-N,N′-dicarbazole-biphenyl (CBP). Room-temperature electrophos-phorescence was observed at about 1.1μm due to transitions from the first excited triplet state to the singlet ground state (T1-S0) of CuPc. There existed very weak emission of CBP from undoped devices, and at lower doping concentrations (⩽12wt%) the driving voltages of doped devices were higher than that of undoped devices. The results indicated that Förster [Ann. Physik. (Leipzig) 2, 55 (1948)] and Dexter [J. Chem. Phys. 21, 836 (1953)] energy transfers play a minor role in these devices, and direct charge trapping appears to be the dominant mechanism.
Electric field control of magnetization dynamics in ZnMnSe∕ZnBeSe diluted-magnetic-semiconductor heterostructures
Authors: Kneip M. K. , Yakovlev D. R. , Bayer M. , Slobodskyy T. , Schmidt G. , Molenkamp L. W.
Published: May 2006

We show that the magnetization dynamics in diluted magnetic semiconductors can be controlled separately from the static magnetization by means of an electric field. The spin-lattice relaxation (SLR) time of magnetic Mn2+ ions was tuned by two orders of magnitude by a gate voltage applied to n-type modulation-doped (Zn,Mn)Se∕(Zn,Be)Se quantum wells. The effect is based on providing an additional channel for SLR by a two-dimensional electron gas (2DEG). The static magnetization responsible for the giant Zeeman spin splitting of excitons was not influenced by the 2DEG density.
Reversible mechanical bistability of single-walled carbon nanotubes under axial strain
Authors: Chang Tienchong , Hou Juan , Guo Xingming
Published: May 2006

Using Brenner’s second generation reactive empirical bond order potential, we show by molecular dynamics that the single-walled carbon nanotube with a diameter of about 5nm under axial strain possesses excellent reversible mechanical bistability. This feature provides a high potential of using only one single-walled carbon nanotube to realize bistate functions in nanomechanical systems which will benefit from smaller size significantly.
Secondary emission of strain-induced dopant contrast in the source/drain regions of metal-oxide-semiconductor devices
Authors: Hsiao Wen-Chu , Liu Chuan-Pu , Wang Ying-Lang
Published: May 2006

Secondary electron (SE) imaging with scanning electron microscopy has been used for two-dimensional dopant profiling. However, the mechanism of dopant contrast is still not yet understood. Here we propose another significant contribution from interface strain for the source/drain regions in p- and n-type metal-oxide-semiconductor (MOS) devices. The results show that the width of the dopant profile by SE imaging agrees well with the strain profile by dark-field technique with transmission electron microscopy. We demonstrate that the dopant contrast of the p-MOS device by SE imaging is higher than a test wafer by 45%. The enhanced SE signals for both p-MOS and n-MOS devices are caused by band bending through CoSi2-induced strain.
Phase contrast tomography: An alternative approach
Authors: Groso A. , Stampanoni M. , Abela R. , Schneider P. , Linga S. , Müller R.
Published: May 2006

Conventional microtomography is widely used for reconstructing the three-dimensional (3D) distribution of the absorption coefficient of a sample from a set of radiographic projections. The question here is whether the 3D distribution of the phase (refractive index) of a weakly absorbing object can be, alternatively to the combined phase retrieval-backprojection methods presented up to now, directly reconstructed from a single tomographic data set. In this letter a solution to this problem based on a direct filtered backprojection approach, derived from the transport of intensity equation, is investigated numerically and experimentally for monochromatic and polychromatic x rays. The results show that the contrast is increased, while keeping dose minimal and spatial resolution equivalent to the conventional absorption based technique. This method is therefore very promising for imaging of biological specimens.
Improvement of microstructural and optical properties of GaN layer on sapphire by nanoscale lateral epitaxial overgrowth
Authors: Wang Y. D. , Zang K. Y. , Chua S. J. , Tripathy S. , Zhou H. L. , Fonstad C. G.
Published: May 2006

Nanoscale lateral epitaxial overgrown (NLEO) GaN layers were investigated for the improvement of microstructural and optical properties of GaN. Nanoporous SiO2 films on the surfaces of GaN/sapphire (0001) were fabricated by inductively coupled plasma etching using anodic alumina templates as etch masks, resulting in an average pore diameter and interpore distance of 60 and 110nm, respectively. GaN was grown over the nanoporous SiO2 layer using metal organic chemical vapor deposition to realize a continuous and smooth film. NLEO GaN was found to result in a significant reduction of threading dislocation density as characterized by transmission electron microscopy and atomic force microscopy. The threading dislocation density was ∼107cm−2 at the surface of NLEO GaN. The narrower band-edge excitonic transition in photoluminescence spectrum shows a better optical quality in the NLEO GaN film.
Dynamical spin separation induced by spin-dependent type-II band alignment in a diluted magnetic double quantum well
Authors: Koyama T. , Kayanuma K. , Souma I. , Murayama A. , Oka Y.
Published: May 2006

Dynamical spin separation is demonstrated in a magnetic double quantum well composed of a diluted magnetic semiconductor well (MW) and a nonmagnetic well (NMW). Excitonic photoluminescence of the type-II transition between an electron in the NMW and a down-spin heavy hole (hh) in the MW is induced with an increase in the magnetic field. A type-I transition involving an up-spin hh inside the NMW is simultaneously observed. Therefore, the hh spins are concluded to be spatially separated, which is sustained by a low hh-spin injection time of 500ps from the NMW to the MW.
White-electrophosphorescent devices based on copper complexes using 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole as chromaticity-tuning layer
Authors: Su Zisheng , Che Guangbo , Li Wenlian , Su Wenming , Li Mingtao , Chu Bei , Li Bin , Zhang Zhiqiang , Hu Zhizhi
Published: May 2006

Efficient white organic light-emitting diodes based on copper complex, [Cu(bis[2-(diphenylphosphino)phenyl]ether)(6,7-dicyanodipyrido[2,2-d:2′,3′-f]quinoxaline)]BF4 [Cu(I) complex], in which the white emission composed of yellow emission from Cu(I) complex doped 4,4′-N,N′-dicarbazole-biphenyl (CBP) layer and blue emission from N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-benzidine)-4,4′-diamine layer, were fabricated. A thin 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (Bu-PBD) layer sandwiched between the two emission layers acts as a chromaticity-tuning layer. The white device with 10nm, 2wt% Cu(I) complex doped CBP layer and 2nm Bu-PBD layer shows CIE coordinates of (0.33,0.36) at applied bias of 10V, a maximum luminance of 2466cd∕m2, and a maximum current efficiency of 6.76cd∕A, corresponding to the power efficiency of 3.85lm∕W. The efficient white emission is attributed to the simultaneous exciton formation in both emission layer. The working mechanism of the thin Bu-PBD layer for achieving white emission was also discussed.
High intermodulation gain in a micromechanical Duffing resonator
Authors: Almog R. , Zaitsev S. , Shtempluck O. , Buks E.
Published: May 2006

In this work we use a micromechanical resonator to experimentally study small signal amplification near the onset of Duffing bistability. The device consists of a PdAu beam serving as a micromechanical resonator excited by an adjacent gate electrode. A large pump signal drives the resonator near the onset of bistability, enabling amplification of small signals in a narrow bandwidth. To first order, the amplification is inversely proportional to the frequency difference between the pump and the signal. We estimate the gain to be about 15dB for our device.
Origin of photocurrent in lateral quantum dots-in-a-well infrared photodetectors
Authors: Höglund L. , Asplund C. , Wang Q. , Almqvist S. , Malm H. , Petrini E. , Andersson J. Y. , Holtz P. O. , Pettersson H.
Published: May 2006

Interband and intersubband transitions of lateral InAs∕In0.15Ga0.85As dots-in-a-well quantum dot infrared photodetectors were studied in order to determine the origin of the photocurrent. The main intersubband transition contributing to the photocurrent (PC) was associated with the quantum dot ground state to the quantum well excited state transition. By a comparison between intersubband PC measurements and the energy level scheme of the structure, as deduced from Fourier transform photoluminescence (FTPL) and FTPL excitation spectroscopies, the main transition contributing to the PC was identified.
Lewis-Base Adducts of Lead(II) Compounds. XIV. Synthetic and Structural Studies of Some 2:1 Adducts of 2,2'-Bipyridine With Lead(II) Oxoanion Salts
Authors: Engelhardt LM , Harrowfield JM , Miyamae H , Patrick JM , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 2: 1 adducts of the N,N′-bidentate aromatic base 2,2′-bipyridine (' bpy ') with lead(II) nitrate and perchlorate. [( bpy )2Pb(NO3)2]2 is triclinic, Pī , a 14.609(6), b 9.400(4), c 8.396(4) Ǻ, α 71.10(3), β 83.53(3), γ 81.72(3)°, Z = 1 dimer; R was 0.037 for No = 3001 independent, 'observed' (I > 3σ(I)) reflections. [( bpy )2Pb(ClO4)2] is monoclinic, P21/c, a 9.8806(6), b 12.198(6), c 19.924(2) Ǻ, β 106.80(1)°, Z = 4, R 0.040 for No 4456. Unlike the two 1,10-phenanthroline (' phen ') systems which are mononuclear with eight-coordinate PbN4O4 environments incorporating a pair of O,O′;- bidentate anions, the bpy systems are centrosymmetric dimers; in each case the coordination environment incorporates a pair of N,N′- bidentate aromatic bases and an O,O′- bidentate anion, but the other anion is not only O,O′- bidentate, but also bridges by a third oxygen atom to the other lead atom so that it is nine-coordinate PbN4O5. Syntheses and room-temperature single-crystal X-ray structure determinations are also recorded for a pair of 2:1 adducts of 2,2?-bipyridine with lead(II) salts of mixed anion stoichiometry , viz. ( bpy )2PbX(ClO4), X = acetate ('ac'), chloride. [( bpy )2Pb(ac)(ClO4)] is triclinic, Pī , a 15.910(6), b 9.067(5), c 8.588(3) Ǻ, α 102.91(4), β 93.64(3), γ 103.41(4)°, Z = 2, R 0.039 for No 5283. [( bpy )2PbCl(ClO4)2 is monoclinic, P 21/c, a 12.923(2), b 8.759(2), c 19.650(2) Ǻ, β 94.776(9)°, Z = 2 dimers (R 0.037 for No 4433). Like the 1:2 oxoanion/phen adducts, the acetate is a discrete molecular species with an eight-coordinate PbN4O4 lead environment, the oxygen array comprising a pair of O,O′- bidentate perchlorate and acetate ligands. The chloride adduct, however, is like the 1:2 oxoanion/bpy adducts, being centrosymmetric binuclear, a pair of μ-chloride ions linking the two lead atoms which have seven-coordinate PbN4(μ- Cl )2O lead environments, the perchlorate species being O-unidentate.
Purification of granulosa cells from human ovarian follicular fluid using granulosa cell aggregates
Authors: Quinn M. C. J. , McGregor S. B. , Stanton J. L. , Hessian P. A. , Gillett W. R. , Green D. P. L.
Published: May 2006

Human follicular fluid can provide a source of human granulosa cells for scientific study. However, removing potentially contaminating cells, such as white and red blood cells, is important for molecular and in vitro studies. We have developed a purification technique for human granulosa cells based on the selection of cellular aggregates. Human granulosa cells from 21 IVF patients were collected. A 50% Percoll gradient was used to remove red blood cells, and granulosa cell aggregates were collected, washed and processed for histology, electron microscopy, flow cytometry analysis, cell culture and RNA extraction. Granulosa cell aggregates were found to be homogeneous and free of white blood cells after histological and electron microscopic analysis. White blood cell contamination, measured by flow cytometry, was found to be between 2 and 4%. Polymerase chain reaction analysis revealed expression of known human granulosa cell genes and a white blood cell marker. Human granulosa cells grown in vitro showed flattened fibroblast-like morphology with lipid droplets consistent with previous reports. Cultured cells expressed the FSH receptor. Selection of human granulosa cell aggregates following centrifugation through a Percoll gradient provides an efficient method of selecting granulosa cells, suitable for both molecular and in vitro studies.
Metabolic regulation of in-vitro-produced bovine embryos. I. Effects of metabolic regulators at different glucose concentrations with embryos produced by semen from different bulls
Authors: De La Torre-Sanchez Jose Fernando , Preis Kimberly , Seidel George E.
Published: May 2006

The toxic and/or beneficial effects of four metabolic regulators on embryo development were evaluated. In-vitro-produced compact morulae were cultured for 3 days in a chemically defined medium + bovine serum albumin (BSA; CDM-2) plus regulators (4991 total embryos). Phenazine ethosulfate (PES), phloretin (PL), pyrroline-5-carboxylate (P5C), and sodium azide (NaN3) were evaluated at four doses each in factorial combinations with four concentrations of glucose: 0, 0.5, 2, and 8 mm. Phenazine ethosulfate at 0.9 μm resulted in poorer development than lower or no PES. Phloretin was, in general, detrimental for embryo development, but most markedly at the highest dose (270 µm). Pyrroline-5-carboxylate had little effect on post-compaction embryos at the doses studied, 9 to 81 μm. Sodium azide at the concentrations used (3, 9, and 27 μm) had little effect on embryo development compared with controls. Concentrations of glucose had little effect on development of embryos. A fifth metabolic regulator, 2,4-dinitrophenol (DNP), was studied at various doses at pre-morula or morula-blastocyst stages cultured in 2 mm glucose. Embryos (2189 total) cultured in 90 µm DNP developed more slowly and were darker than embryos cultured at lower doses. Embryos cultured in 30 µm DNP had a higher blastocyst rate (48.3%) than controls (34.9%). In the last experiment using G1.2/G2.2 media, DNP (30 μm) resulted in a marked decrease in embryonic development when embryos were exposed at the zygote to 8- to 16-cell stages but had little effect when morulae were exposed for 2 days. The dose–response information for these metabolic regulators is crucial for designing future experiments.