bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of conduction and interface states of laterally wet-oxidized AlGaAs with oxidation time
Authors: Chen J. F. , Hsiao R. S. , Hung W. K. , Wang J. S. , Chi J. Y. , Yu H. C. , Su Y. K.
Published: February 2006

The conduction and interface states of laterally wet-oxidized GaAs-AlGaAs-GaAs structures after various oxidation times are investigated. Effective current blocking is achieved after 150min oxidation and the conduction of current through the oxidized AlGaAs layer is controlled by the Poole-Frenkel mechanism, from which a relative dielectric constant of 7.07 is obtained. At an oxidation time of 15min, capacitance-voltage spectra exhibit capacitance dispersion over frequency, implying the presence of an interface state. The intensity of the dispersion increases with increasing the oxidation time and admittance spectroscopy reveals a significant interface state at ∼0.28eV at 45min. Further increasing the oxidation time to 150min broadens the interface state to a set of continuous interface states from 0.19–0.31eV with decreasing densities from 3×1011to0.9×1011eV−1cm−2 and generates fixed charges of about 9.1×1011cm−2 in the oxidized layer. By comparison to a similar trap in a relaxed InGaAs∕GaAs, the interface state is tentatively assigned to the interaction of residual As with dislocations.
Application of radial x-ray diffraction to determine the hydrostatic equation of state and strength of TiB2 up to 60GPa
Authors: Amulele George M. , Manghnani Murli H. , Somayazulu Maddury
Published: February 2006

Room temperature investigations of the shear strength of hexagonal TiB2 have been performed in order to determine the hydrostatic equation of state of the material up to 60GPa using radial x-ray diffraction in a diamond anvil cell. We have analyzed the deformation mechanisms under pressure by analyzing the (001) and (100) peaks in the powder diffraction data, and we have deduced the hydrostatic equation of state of TiB2. The uniaxial stresses in the (100), (001), and (101) diffraction planes show a large pressure dependence, indicating a significantly large anisotropy in the material. The stress in the (001) plane shows the largest increase with pressure and reaches a maximum value before the other planes, indicating an initial activation of slip in the (001) plane at the onset of plastic deformation. Compared to gold, the averaged uniaxial stress component in TiB2 is almost 27 times as large at the maximum loading pressure, 60GPa, achieved in the experiment.
Linewidth dependence of grain structure and stress in damascene Cu lines
Authors: Paik Jong-Min , Park Il-Mok , Joo Young-Chang , Park Ki-Chul
Published: February 2006

Damascene Cu interconnects show significant differences in both their microstructural and stress behavior as compared to those of Al interconnects patterned using the etching process. Thermal stresses build up during the successive thermal cycles due to the differences in the coefficients of thermal expansion of the component materials. Other than these thermal stresses, growth stresses originating from grain growth develop in damascene Cu interconnects as well. In this study, the linewidth dependence of the stress in damascene Cu was examined experimentally, as well as by numerical simulation. The stresses of damascene Cu with widths ranging from 0.13to2μm were measured using x-ray diffraction, and the measured hydrostatic stress was found to increase with increasing linewidth, in contrast to the typical behavior of Al interconnects. Microstructure analysis using transmission electron microscopy revealed that the grain sizes increased with increasing line dimensions. The increase in stress in the interconnect with increasing dimensions is attributed to the larger grain size, which induces higher growth stress in addition to the thermal stress. The contribution of the growth and thermal stresses of the damascene lines were quantified based on the grain size data utilizing finite element analysis. In this way, the linewidth dependence of the hydrostatic stress of damascene Cu was clearly explained. Finally, the effect of growth stress on the stress-related reliability is discussed.
Dimension dependence of the thermomechanical noise of microcantilevers
Authors: Álvarez M. , Tamayo J. , Plaza J. A. , Zinoviev K. , Domínguez C. , Lechuga L. M.
Published: February 2006

Thermomechanical noise determines the lowest detection limits of microcantilever-based devices for measuring forces and surface stress variations. In this work, arrays of 334-nm-thick single-crystalline silicon microcantilevers with dissimilar lengths and widths from 50to500μm and 20to200μm, respectively, have been fabricated to calculate the minimal detectable force and surface stress on the basis of the measurement of the spring constant, resonance frequency, and quality factor. The calculated minimal detectable force and surface stress are of the orders of 10−15NHz−1∕2 and 10−7Nm−1Hz−1∕2, respectively, and both follow a nonintuitive dependence on the dimensions. The minimal detectable force decreases as the cantilevers are shorter and narrower, whereas the minimal detectable surface stress decreases by making the cantilevers shorter and wider. Theoretical expressions of the minimal detectable force and surface stress are provided as a function of the material properties, cantilever dimensions, and quality factor, which allow us to interpret the results. Both force and surface stress noises follow the same dependence on the quality factor and material properties, however, exhibit striking differences in the dimension dependences. The force and surface stress noises enhance with the quality factor. If the quality factor is kept constant, the force noise enhances as the cantilever is longer and wider, whereas the surface stress noise enhances by making the cantilever shorter and wider. The observed increase of the force noise with the length is attributed to the strong decrease of the quality factor. The results imply that the design of cantilevers for surface stress measurements in general should be different than for atomic force microscopy probes.
Velocity measurement of flow through a model three-dimensional porous medium
Authors: Agelinchaab M. , Tachie M. F. , Ruth D. W.
Published: February 2006

The paper reports an experimental investigation of flow through model porous medium adjacent to open flow in a two-dimensional channel. The model consists of circular cylindrical rods installed vertically on the bottom wall of the channel in regular square arrays. The channel height was kept constant but the ratio of rod height to channel height was varied to simulate different filling fractions. Various combinations of rod diameter and rod spacing were chosen to achieve solid volume fractions (ϕ) in the range 0.01⩽ϕ⩽0.50. A viscous fluid having a refractive index similar to that of the rods was selected as the working fluid. Particle image velocimetry was used to conduct detailed velocity measurements between the rods and in the open flow between the top edges of the rods and the top wall of the channel. From these measurements, values of the slip velocity at the interface between the rods and the open flow were determined. It was found that values of the slip velocity normalized by the maximum velocity in the open flow depend on solid volume fraction, rod spacing, and fraction of channel filled by rods. The slip velocity made dimensionless by the shear rate at the interface were higher for the larger filling fraction but independent of solid volume fraction and rod spacing.
Probing mechanistic photochemistry of glyoxal in the gas phase by ab initio calculations of potential-energy surfaces and adiabatic and nonadiabatic rates
Authors: Li Quan-Song , Zhang Feng , Fang Wei-Hai , Yu Jian-Guo
Published: February 2006

In the present work, the wavelength-dependent mechanistic photochemistry of glyoxal in the gas phase has been explored by ab initio calculations of potential-energy surfaces, surface crossing points, and adiabatic and nonadiabatic rates. The CHOCHO molecules in S1 by photoexcitation at 393-440 nm mainly decay to the ground state via internal conversion, which is followed by molecular eliminations to form CO, H2CO,H2, and HCOH. Upon photodissociation of CHOCHO at 350-390 nm, intersystem crossing to T1 followed by the C–C bond cleavage is the dominant process in this wavelength range, which is responsible for the formation of the CHO radicals. The C–C and C–H bond cleavages along the S1 pathway are energetically accessible upon photodissociation of CHOCHO at 290-310 nm, which can compete with the S1→T1 intersystem crossing process. The present study predicts that the C–H bond cleavage on the S1 surface is probably a new photolysis pathway at high excitation energy, which has not been observed experimentally. In addition, the trans-cis isomerization is predicted to occur more easily in the ground state than in the excited states.
A general framework for non-Boltzmann Monte Carlo sampling
Authors: Abreu Charlles R. A. , Escobedo Fernando A.
Published: February 2006

Non-Boltzmann sampling (NBS) methods have been extensively employed in recent years, mainly due to their ability to enhance ergodicity in simulations of complex systems. In addition, they make possible reliable computation of equilibrium properties (ensemble averages, free-energy differences, and potentials of mean force) over continuous ranges of thermodynamic conditions. In this work, we put forward a general and systematic framework for NBS methods that allows a single set of equations and procedures to be applied to diverse systems. Moreover, we show how to exploit simulation data most effectively by obtaining continuous profiles of any mechanical properties, including structural quantities not directly related to the ensemble parameters. Finally, we demonstrate the usefulness of the developed formulation by applying it to spin systems, Lennard-Jones fluids, and a model protein molecule (both in isolation and in the proximity of a flat wall).
Trapping artifacts in quasi-steady-state photoluminescence and photoconductance lifetime measurements on silicon wafers
Authors: Bardos R. A. , Trupke T. , Schubert M. C. , Roth T.
Published: February 2006

Photoluminescence and photoconductance lifetime measurements on multicrystalline silicon wafers are presented. It is demonstrated experimentally that the large overestimation of the lifetime at low carrier concentrations due to trapping that is observed in photoconductance measurements is not found in photoluminescence data. This is explained theoretically by the dependence of photoluminescence and photoconductance on the product and the sum, respectively, of the minority and majority carrier densities. Based on this analysis, it is shown that photoluminescence lifetime measurements are not significantly affected by minority carrier trapping in most practical cases while implied current-voltage curves obtained from photoluminescence are completely unaffected.
Catalytical growth of carbon nanotubes/fibers from nanocatalysts prepared by laser pulverization of nickel sulfate
Authors: Shi J. , Lu Y. F. , Tan K. F. , Wang X. W.
Published: February 2006

Dispersed nickel sulfate (NiSO4) microclusters on Si substrates were fragmented by pulsed excimer laser irradiation to serve as catalysts for carbon nanotube/nanofiber (CNT/CNF) growth. At proper fluences, NiSO4 clusters were pulverized into nanoparticles. The sizes of clusters/nanoparticles were found to be dependent on laser fluence and laser pulse number. By increasing the laser fluence from 100to300mJ∕cm2, the size of disintegrated particles decreased drastically from several micrometers to several nanometers. It was found that laser-induced disintegration of as-dispersed NiSO4 clusters was mainly due to physical fragmentation by transient thermal expansion/contraction. Thermal melting of nanoparticles in a multipulse regime was also suggested. Hot-filament chemical vapor deposition (HFCVD) was used for growth of CNTs from the pulsed-laser treated catalysts. For samples irradiated at 100 and 200mJ∕cm2, CNFs were dominant products. These CNFs grew radially out of big NiSO4 clusters, forming dendritic CNF bunches. For samples irradiated at 300mJ∕cm2, dense multiwalled carbon nanotubes (MWCNFs) with uniform diameters were obtained. It is suggested that elemental Ni was formed through thermal decomposition of NiSO4 clusters/nanoparticles during HFCVD. The size and the shape of the Ni aggregation, which were determined by the initial size of NiSO4 clusters/nanoparticles, might affect the preference in the synthesis of CNTs or CNFs.
Pressure-induced exfoliation of inorganic fullerene-like WS2 particles in a Hertzian contact
Authors: Joly-Pottuz L. , Martin J. M. , Dassenoy F. , Belin M. , Montagnac G. , Reynard B. , Fleischer N.
Published: February 2006

Nanoparticles are potential additives for the improvement of lubricant properties, because of the structural modifications they undergo under high pressures in mechanical contacts. The behavior of inorganic fullerene-like WS2 nanoparticles (IF-WS2) under high isotropic pressures of up to 20GPa generated in a diamond anvil cell was studied and compared to the response of the lamellar 2H phase of WS2. The same materials were then subjected to static uniaxial pressures in a Hertzian contact in the GPa range. The evolution of the particles as a function of pressure was studied by in situ Raman spectroscopy and transmission electron microscopy at the end of the test. Data analysis shows that IF-WS2 particles resist high hydrostatic pressures well, but they are totally exfoliated by uniaxial compression in a Hertzian contact under low pressure. These results explain the excellent tribological properties at ambient temperature of IF-WS2 nanolubricant that have previously been attributed to the nested nanospheres during the friction process but whose origin had not been clearly identified.
The influence of acceptor anneal temperature on the performance of InGaN/GaN quantum well light-emitting diodes
Authors: Thomson J. D. , Pope I. A. , Smowton P. M. , Blood P. , Lynch R. J. , Hill G. , Wang T. , Parbrook P.
Published: February 2006

Temperature-dependent measurements of the pulsed light-current characteristics of InGaN light-emitting diodes that were thermally annealed at different temperatures have been investigated. A distinct light output, at a fixed current density, with operating temperature arises where the light output increases as the operating temperature is reduced from 300 K, reaches a maximum, and then decreases with subsequent reductions of the operating temperature. We observe that light-emitting diodes thermally annealed at higher temperatures, which is believed to increase the number of electrically activated acceptors in the p layers, have a lower light output below 300 K and the maximum light output shifts to higher operating temperatures. Measured absorption and emission spectra show that the thermal anneal process has not affected the structure of the quantum wells within these samples. The light output, for a fixed current density, has been simulated as a function of operating temperature, and we find that by changing the concentration of acceptor atoms, compensating donor atoms, and the hole mobility in the p layers, the trends observed experimentally can be reproduced. On the basis of the simulations we find that the distinct behavior of the light output with operating temperature is due to the combination of Shockley-Reed-Hall recombination, at operating temperatures around 300 K, and electron drift leakage, at operating temperature below 300 K, and the increase of the acceptor concentration results in an increased electron drift leakage due to the change of the concomitant hole mobility. The simulations support the view that the experimental observations can be explained through changes of the acceptor concentration in the p layers when the thermal anneal temperature is increased.
Identification of the free boundary of a space-charge region with the aid of a Laplacian potential
Authors: Donolato C.
Published: February 2006

The possibility of identifying the free boundary of the space-charge region around a conductor, without going through the solution of the related Poisson’s problem, is discussed in the depletion approximation. The use of Green’s second theorem leads to an integral identity that involves this boundary and a Laplacian potential for the same configuration. The identity is applied to a spherical and a right-angle concave conductor. For the sphere, the method yields the exact solution; in the wedge case, with some additional conditions, an approximate boundary identification is obtained, which is in good agreement with published numerical results.
Backward branch of surface dust cyclotron wave in a semi-bounded magnetized dusty plasma
Authors: Chang Won-Seok , Chang Dong-Man , Jung Iyoung Michelle , Jung Young-Dae
Published: February 2006

The surface dust cyclotron waves are investigated in semi-bounded magnetized dusty plasmas. The dispersion relation is obtained by the plasma dielectric function with the specular reflection boundary condition. The result shows the existence of the low-frequency backward wave branch in the surface dust cyclotron wave. The frequency of the wave is found to be decreased with the dust Debye wave number. It is also found that there is a minimum position of the scaled group velocity in the small-wave-number region. It is interesting to note that the group velocity increases below the minimum position and, however, decreases above the minimum position with increasing the dust Debye wave number.
Plasmon resonant absorption and third-order optical nonlinearity in Ag–Ti cosputtered composite films
Authors: Han Jun-Bo , Chen Dai-Jian , Ding Sha , Zhou Hui-Jun , Han Yi-Bo , Xiong Gui-Guang , Wang Qu-Quan
Published: February 2006

A series of Ag/titanium oxide composite films with Ag atom concentration of 28%–82% were prepared by cosputtering technique. The scanning electron microscopy and the x-ray photoelectron spectroscopy studies reveal that metallic Ag nanoparticles with a size of 20–50nm disperse in titanium oxide. The plasmon resonance absorption peak of the embedded Ag nanoparticles shifts to about 860nm at Ag atom concentration of 42%, the nonlinear absorption coefficient βeff and the nonlinear refractive index γ are −1.4×105cm∕GW and 3.8cm2∕GW, respectively, which were measured by the Z-scan technique at 790nm with a peak irradiance of 1.8GW∕cm2. The corresponding third-order susceptibility χ(3) is about 4.7×10−7esu.
Hydrodynamic interactions and orthokinetic collisions of porous aggregates in the Stokes regime
Authors: Bäbler Matthäus Ulrich , Sefcik Jan , Morbidelli Massimo , Bałdyga Jerzy
Published: February 2006

The hydrodynamic interaction of two neutrally buoyant porous aggregates is investigated under creeping flow conditions for the case where the undisturbed velocity of the surrounding flow field is a linear function of position. In this framework, the relative velocity between two aggregates is given by the deformation of the undisturbed flow expressed through the rate of strain and the angular velocity of the flow field, and by two flow-independent hydrodynamic functions, typically referred to as A and B, which account for the disturbance of the flow field due to the presence of the particles [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375 (1972)]. In the present paper, the analysis of the hydrodynamic interaction that is known for the case of two impermeable, solid particles is extended to the case of porous aggregates by applying Brinkman’s equation to describe the flow within the aggregates. A reflection scheme is applied to calculate A and B and the obtained expressions are applied to interpret the orthokinetic aggregation of aggregates in diluted suspensions, where the collision frequency is computed using the method of relative trajectories of a pair of aggregates.
Towards understanding ice nucleation by long chain alcohols
Authors: Ochshorn Eli , Cantrell Will
Published: February 2006

We demonstrate that infrared spectra of water covered by a film of heptadecanol show a continuous spectral shift, from a band characteristic of liquid water to one characteristic of ice, as the temperature is ramped from −10 to −17°C. Experiments with pure water and water covered by films of long chain alkanes showed no such spectral shift. Analysis of the CH2 stretching features in the alcohols’ absorbance bands reveals simultaneous structural changes within the alcohol film. We hypothesize that the spectral shift in the water band is due to an increasing fraction of water molecules participating in icelike clusters and that these clusters are stabilized by the influence of the flexible alcohol film.
The counterpropagating Rossby wave perspective on Kelvin Helmholtz instability as a limiting case of a Rayleigh shear layer with zero width
Authors: Heifetz Eyal , Reuveni Yuval , Gelfgat Alexander , Kit Eliezer , Methven John
Published: February 2006

The Kelvin Helmholtz (KH) problem, with zero stratification, is examined as a limiting case of the Rayleigh model of a single shear layer whose width tends to zero. The transition of the Rayleigh modal dispersion relation to the KH one, as well as the disappearance of the supermodal transient growth in the KH limit, are both rationalized from the counterpropagating Rossby wave perspective.
A high-speed, compressible synthetic jet
Authors: Crittenden Thomas M. , Glezer Ari
Published: February 2006

The operation of a high-speed, compressible synthetic (zero net mass flux) jet is investigated experimentally using a small (nominally 6.5 cm3) piston/cylinder actuator driven by a variable speed motor. The actuator performance is characterized using phase-locked cavity pressure measurements, particle image velocimetry of the jet flow, and Schlieren flow visualization. Cylinder pressure ratios (relative to the ambient) measured over the experimental limits range as high as 8 and as low as 0.2, during the blowing and suction phases, respectively (producing sonic flow velocities at the orifice during both phases). Owing to compressibility effects, the shapes of the time-periodic pressure curves during the blowing and suction cycles are dissimilar (the suction duration is longer) and there is a clear phase shift between the peak piston displacements and the corresponding pressure extrema. It is shown that the performance is primarily affected by the characteristic velocity (defined by the product of the operating frequency and the normalized piston stroke length) and the compression ratio. A simple numerical model of the gas in the cylinder that treats the volume change due to the piston motion as a series of isentropic and adiabatic compressions and expansions and flow through the orifice as inviscid and isentropic is presented and is in good agreement with the measured system performance. The model indicates that the cylinder pressure curve grows to approximate a closed system as the characteristic velocity is increased beyond the experimental range. Finally, it is shown that the duty cycle of the pressure wave form (between blowing and suction) can be modified by increasing the flow area during the suction stroke using self-actuated valves in the cylinder head, resulting in higher peak pressures in blowing.
Vortical structures behind a sphere at subcritical Reynolds numbers
Authors: Yun Giwoong , Kim Dongjoo , Choi Haecheon
Published: February 2006

Large eddy simulations of turbulent flow over a sphere are conducted at subcritical Reynolds numbers (Re=3700 and 104) based on the freestream velocity and sphere diameter. At Re=3700, the separating shear layer persists downstream to form a cylindrical vortex sheet and its instability becomes manifest at x≈2d. The flow right behind the sphere contains only a few vortices. On the other hand, at Re=104, the shear-layer instability occurs right behind the sphere in a form of vortex rings, and the flow becomes turbulent in the near wake. Therefore, at Re=104, the size of the recirculation region is smaller and the wake recovers more quickly than at Re=3700. At both Reynolds numbers, large-scale waviness of vortical structures is observed in the wake and the plane containing the large-scale waviness changes quasirandomly in time. This waviness is more pronounced at Re=104 than at Re=3700. The mechanism responsible for this large-scale waviness of vortical structures is shown to be closely associated with the temporal evolution of vortices generated by the shear-layer instability.
Accounting for mean-flow periodicity in turbulence closures
Authors: Younis Bassam A. , Zhou Ye
Published: February 2006

Measurements of the turbulence energy spectrum in the unsteady wakes of bodies in uniform incident streams clearly show the presence of a distinct peak in energy supply that occurs at the Strouhal frequency and whose presence implies a strong and direct interaction between the organized mean-flow unsteadiness and the random turbulence motions. It is argued here that the well-documented failure of conventional turbulence closures in capturing the main features of unsteady flows is largely due to their inability to properly account for the modifications in the energy spectrum wrought by these interactions. We derive a simple modification to the turbulence length-scale determining equation based on analysis of a distorted energy spectrum, and verify the result by computations of vortex shedding behind a square cylinder.
Rayleigh processes in single-phase fluids
Authors: Cramer M. S.
Published: February 2006

In the present study we examine Rayleigh flows of single-phase, nonreacting fluids. When the fluid is of the Bethe-Zel’dovich-Thompson type, it is shown that as many as three sonic points and extrema of the entropy, enthalpy, and heat supply can occur on a fixed Rayleigh line. Exact solutions for van der Waals gases are provided, as is a complete theory of shocked and unshocked flows subjected to strict heating or strict cooling. Further nonclassical results of interest include the occurrence of flow choking in unshocked and shocked strictly cooled flows, the occurrence of as many as three shock waves in cooled or heated flows, and shock splitting in both cooled and heated flows.
Marangoni-induced deformation and rupture of a liquid film on a heated microstructured wall
Authors: Kabova Yu. O. , Alexeev A. , Gambaryan-Roisman T. , Stephan P.
Published: February 2006

Thermocapillary instability is one of the primary causes of a spontaneous rupture of thin films on heated walls. The film rupture may lead to an appearance of uncontrolled dry patches that significantly deteriorate the heat and mass transfer. In the present paper the thermocapillarity-induced film flow on a microstructured wall is studied in the framework of the long-wave theory. When the wall is heated or cooled, the solution predicts a film deformation caused by thermocapillarity. The linear stability analysis shows that the films on heated microstructured walls are less stable to the long-wave disturbances compared to the films on flat walls. The time-dependent film evolution is simulated and the effect of the wall structure on the film thinning and rupture is analyzed. It is shown that the wall topography exerts a profound effect on the dynamics of the film deformation and rupture, as well as on the size and the location of the dry patches. The full-scale direct volume-of-fluid simulations are used to verity the predictions of the long-wave theory. Good agreement is found for the small ratios between the groove depth and period. The agreement is further improved by including the effect of the convection heat transfer into the long-wave model.
Phase formation between lead-free Sn–Ag–Cu solder and Ni(P)∕Au finishes
Authors: Vuorinen V. , Laurila T. , Yu H. , Kivilahti J. K.
Published: February 2006

The interfacial reactions of near-eutectic Sn–Ag–Cu solder with Ni(P)∕Au metal finishes on printed wiring boards as well as in component under bump metallizations have been investigated in this work. With the help of the scanning electron microscopy and transmission electron microscopy it was discovered that the first phase to form was the metastable nanocrystalline ternary NiSnP layer that provided the substrate for the subsequent formation of (Cu,Ni)6Sn5. During cooling or in the subsequent reflows the metastable NiSnP layer partially transformed into the columnar Ni3P. In this transformation Sn atoms and impurities, which do not dissolve into the Ni3P, diffuse towards the remaining NiSnP layer. When the specimens are further annealed in solid state at 170°C the Ni3P phase transforms into Ni5P2 implying that some more Ni has diffused towards the solder. However, when Ni(P)∕Au finishes with a higher P content were used, only the ternary NiSnP layer was observed. Based on the mass balance and available thermodynamic data on the Sn–P–Ni system the evolution of the observed microstructures in the reactions between the solder and Ni(P)∕Au finishes is discussed.
Synthesis and room temperature ferromagnetism of FeCo-codoped ZnO nanowires
Authors: Liu L. Q. , Xiang B. , Zhang X. Z. , Zhang Y. , Yu D. P.
Published: February 2006

FeCo-codoped ZnO nanowires were synthesized by in situ doping with iron and cobalt using a chemical vapor deposition method. Structure and compositional analysis indicated that the as-prepared nanowires were single- crystalline and FeCo codoped. No FeCo clusters and other secondary phases were found in the nanowires. A Curie temperature higher than 300 K was observed from the as-doped nanowires. The room temperature ferromagnetic properties of the synthesized Zn1−x(FeCo)xO nanowire make it useful in future spintronic devices.
Holographically formed Bragg reflection gratings recorded in polymer-dispersed Liquid crystal cells using a He-Ne laser
Authors: Ramsey Robert A. , Sharma Suresh C. , Vaghela Kalpesh
Published: February 2006

Bragg reflection gratings are holographically recorded in polymer-dispersed liquid crystal materials by using the 632.8-nm wavelength of the He-Ne laser. Mixtures of the commercially available E8 nematic liquid crystal, pentafunctional monomers, and photooxidant dye methylene blue are employed. We demonstrate that Bragg reflection gratings can be formed in this acrylate photopolymer system with reflection efficiencies of 52% with a peak notch at 1165 nm. We also present results for the switching characteristics of these gratings with switching fields on the order of 6MV∕m and rise times of 62μs.
Determining thermal diffuse scattering of vanadium with x-ray transmission scattering
Authors: Ding Yang , Chow Paul , Mao Ho-Kwang , Ren Yang , Prewitt Charles T.
Published: February 2006

In this work, we have proposed a fitting model to evaluate thermal diffuse scattering in the case of high energy incident x ray with Laue transmission scattering, applicable in future studies on samples at high pressure in a diamond anvil cell. We show that the fitting model including a Voigt function and a lattice contribution can account for the measured data. Phonon dispersion curves extracted in this way are consistent with data collected previously by other methods.
Observation of the subgap optical absorption in polymer-fullerene blend solar cells
Authors: Goris L. , Poruba A. , Hod’ákova L. , Vaněček M. , Haenen K. , Nesládek M. , Wagner P. , Vanderzande D. , De Schepper L. , Manca J. V.
Published: February 2006

This letter reports on highly sensitive optical absorption measurements on organic donor-acceptor solar cells, using Fourier-transform photocurrent spectroscopy (FTPS). The spectra cover an unprecedented dynamic range of eight to nine orders of magnitude making it possible to detect defect and disorder related sub-band gap transitions. Direct measurements on fully encapsulated solar cells with an active layer of poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)]-p-phenylene-vinylene:(6,6)-phenyl-C61-butyric-acid (1:4 weight ratio) enabled a study of the intrinsic defect generation due to UV illumination. Solar cell temperature annealing effects in poly(3-hexylthiophene):PCBM (1:2 weight ratio) cells and the induced morphological changes are related to the changes in the absorption spectrum, as determined with FTPS.
Influence of atomic hydrogen on step stability during homoepitaxial growth on vicinal GaAs surfaces
Authors: Tejedor P. , Crespillo M. L. , Joyce B. A.
Published: February 2006

We have employed a combination of reflection high-energy electron diffraction intensity oscillations and atomic force microscopy to investigate the effect of atomic hydrogen on the step bunching instability that arises during homoepitaxial growth from molecular beams of Ga and As4 on vicinal GaAs(110) surfaces due to the asymmetric incorporation rates of adatoms to upper and lower step edges. We discuss the variations observed in the GaAs growth mode and in the terrace width distribution of the bunched-step morphology in terms of H-induced changes in the reaction pathway and in the kinetics of adatom migration and incorporation at steps.
Plasmon-enhanced molecular fluorescence from an organic film in a tunnel junction
Authors: Liu Hongwen , Ie Yutaka , Yoshinobu Tatsuo , Aso Yoshio , Iwasaki Hiroshi , Nishitani Ryusuke
Published: February 2006

Scanning tunneling microscope (STM)-excited molecular fluorescence from H2TBP porphyrin (H2TBPP) thin films on Au (111), Ag, highly oriented pyrolytic graphite (HOPG), and indium tin oxide (ITO) surfaces has been investigated in air. Molecular fluorescence was observed from the H2TBPP films on Au and Ag, but it was extremely weak or undetectable from films on HOPG and ITO. The maximum intensity of molecular fluorescence from H2TBPP∕Ag is at least 100 times stronger than that from H2TBPP∕HOPG. Strong enhancement of molecular excitation by substrate surface plasmons is suggested for the STM-excited molecular fluorescence from H2TBPP only on the noble metal substrates.
Simulations of collective synchronization in Josephson junction arrays
Authors: Kim K.-T. , Kim M.-S. , Chong Y. , Niemeyer J.
Published: February 2006

We developed a virtual model of a Josephson junction series array based on a rigorous dynamic simulation and investigated coupling effect of Josephson oscillations. Our virtual model for a superconductor-insulator-normal metal-insulator-superconductor junction array reveals that a time-lag junction instability should be avoided for global synchronization in a long array with a large number of junctions. We found that the coupling between the self-generated Josephson oscillations through a microwave transmission line plays an important role in the collective synchronization of the Josephson array.
Piezoelectric and ferroelectric properties of [Bi0.5(Na1−x−yKxLiy)0.5]TiO3 lead-free piezoelectric ceramics
Authors: Lin Dunmin , Xiao Dingquan , Zhu Jianguo , Yu Ping
Published: February 2006

The piezoelectric and ferroelectric properties of [Bi0.5(Na1−x−yKxLiy)0.5]TiO3 (BNKLT-x∕y) lead-free piezoelectric ceramics were studied. The ceramics show excellent piezoelectric and ferroelectric properties, and the optimum properties measured are as follows: piezoelectric constant d33=231pC∕N, planar and thickness electromechanical coupling factors kP=41.0% and kt=50.5%, remanent polarization Pr=40.2μC∕cm2, and coercive field Ec=2.47kV∕mm, respectively. Polarization versus electric (P-E) hysteresis loops of the ceramics are well rectangle shaped, and the dependence of P-E loops on temperature reveals that the depolarization temperature Td of BNKLT-0.15∕0.075 ceramics, which simultaneously have good piezoelectric properties (d33=164pC∕N,kp=36.3%,kt=48.6%) and strong ferroelectricity (Pr=38.8μC∕cm2,Ec=3.73kV∕mm) at room temperature, is about 195 °C.
Static dielectric constant of isolated silicon nanocrystals embedded in a SiO2 thin film
Authors: Ng C. Y. , Chen T. P. , Ding L. , Liu Y. , Tse M. S. , Fung S. , Dong Z. L.
Published: February 2006

The static dielectric constant of isolated silicon nanocrystals (nc-Si) embedded in a SiO2 thin film synthesized by Si+ implantation has been determined from capacitance measurement based on the Maxwell–Garnett effective medium approximation and the stopping and range of ions in matter simulation. For the nc-Si with a mean size of ∼4.5nm, the dielectric constant so determined is 9.8, being consistent with a theoretical prediction. This value is significantly lower than the static dielectric constant (11.9) of bulk crystalline Si, indicating the significance of nc-Si size effect. The information of nc-Si dielectric constant is not only important to the fundamental physics but also useful to the design and modeling of nc-Si-based memory devices.
First-principles study of the anisotropic thermal expansion of wurtzite ZnS
Authors: Wang S. Q.
Published: February 2006

In this letter, a first-principles study of the anisotropic thermal expansion of wurtzite ZnS in the framework of the density-functional theory and the density-functional perturbation theory is reported. The compound in zinc blende structure is also studied for comparison. The curves of the linear and volume thermal expansion coefficients to temperature are presented. The volume thermal expansion coefficient of zinc blende ZnS changes from smaller to larger than that of wurtzite ZnS as temperature increases. The theoretical cross point is at 867 K. The recent experimental observation of phase controlled synthesis of ZnS nanomaterials is explained from the viewpoint of Gibbs free energy.
Stacking and polarization control of wavelength-tunable (1.55μm region) InAs∕InGaAsP∕InP (100) quantum dots
Authors: Anantathanasarn S. , Nötzel R. , van Veldhoven P. J. , van Otten F. W. M. , Eijkemans T. J. , Wolter J. H.
Published: February 2006

Stacking and polarization control of wavelength-tunable InAs quantum dots (QDs) embedded in lattice-matched InGaAsP on InP (100) grown by metalorganic vapor-phase epitaxy is demonstrated. Wavelength control over the 1.55μm region at room temperature is achieved by inserting ultrathin GaAs interlayers underneath the QDs and adjusting the amount of InAs. For widely stacked QDs with a 40nm separation layer, the linear dependence of the emission wavelength on the GaAs interlayer thickness coincides with that of single QD layers revealing the reproduction of identical QD layers. For closely stacked QDs with 4nm separation layer, the emission wavelength as a function of the GaAs interlayer thickness is systematically redshifted and the linewidth is reduced indicating vertical electronic coupling which is proven by the linear polarization of the cleaved-side luminescence changing from in-plane to isotropic.
Globalization in Residential Architecture in Cuenca, Ecuador: Social and Cultural Diversification of Architects and Their Clients
Authors: Klaufus Christien
Published: February 2006

Over the last century, the city and rural surroundings in the canton Cuenca in Ecuador have been physically constructed in a social setting where an elite group of architects, policymakers, and wealthy citizens have made decisions on architecture, urban design, and land use. They introduced international avant-garde influences in urban residential architecture and considered vernacular architecture appropriate in the countryside. However, massive transnational migration of lower-class and middle-class residents and subsequent architectural opulence have transformed both the city and rural villages in the canton, and have affected the elite's monopoly over the production of the built environment. Many established architects criticize the new ostentatious architecture from a professional and ethical point of view, but on the other hand younger architects see new professional opportunities. Whereas the professional debate focuses on opulent architecture in rural areas and on the preservation of the historical inner city, there is no public debate on the changing cityscape, because it is regarded as an issue too sensitive to discuss openly. In this paper I analyze the professional debate and describe how new sociocultural differentiations in Cuenca change the professional stance as well as the social status of architects.
Geographies of Production and the Contexts of Politics: Dis-Location and New Ecologies of Fear in the Veneto Città Diffusa
Authors: Bialasiewicz Luiza
Published: February 2006

Scholars of regionalist mobilisation have focused their attentions largely on the ideal and idealised landscapes that are an integral part of regional mythmaking, noting the ways in which such ‘representative landscapes’ are deployed by regional ideologues to convey belonging and emplace identity. I argue that to understand regionalist mobilisation it is equally important to consider the lived, everyday spaces of the region, spaces within which such regionalist politics are born. In this paper, I focus on the Veneto region in the Italian North East: one of the wealthiest productive areas in Europe but also the site of some of the most reactionary regionalist and localist rhetorics. I explore the links between the transformations in the Veneto's production landscapes over the past decades and the emergence of new political discourses, arguing that it is only through an understanding of the new geographies of production and consumption that structure the Veneto space—a space that is increasingly deterritorialised and decentred, suspended between its rural past and an unaccomplished urbanisation—that we can begin to understand fully the region's increasingly exclusionary identity politics, and the ways in which the globalised Veneto città diffusa that has made its fortunes on the global market and on global migrants is increasingly reacting against both and finding refuge in hyperlocalised myths of belonging.
Parallel Lives? Challenging Discourses of British Muslim Self-Segregation
Authors: Phillips Deborah
Published: February 2006

The urban disturbances in Bradford, Oldham, and Burnley in 2001 served to underline the contested meanings of black and minority ethnic residential segregation in Britain. Official reports into the disturbances highlighted the depth of ethnic divisions in these northern cities, where, it was contended, British Asian and white people are living “a series of parallel lives”. Central to this assertion is the claim that people of South Asian origin, particularly British Muslims, are failing to be active citizens by withdrawing from interactions with wider British society. This paper examines the discourses surrounding charges of British Muslim isolationism and self-segregation, which have been closely linked to the persistence of inner-city ethnic clustering. The arguments draw on in-depth research with people of Pakistani/Kashmiri and Bangladeshi origin in Bradford and connect to debates about Britishness, whiteness. and the Western portrayal of British Muslims as Other. The findings give voice to British Muslims, enabling us to examine critically the processes involved in the racialisation of space and to challenge the view that British Muslims wish to live separately from others and disengage from British society.
Boundaries and the Meaning of Social Space: A Study of Japanese House Plans
Authors: Ozaki Ritsuko , Lewis John Rees
Published: February 2006

If there was a single best way to design a house to live in, all modern houses would be the same, but they are not: typical modern Japanese houses are not the same as typical modern British ones. As cultural values vary, so do psychological needs; and house form changes accordingly. The basic boundaries in the house are expressions of social classifications which regulate human behaviour, and boundaries are a useful focus when considering the meaning and cultural variation of house design. In the present study, data on spatial boundaries (house plans) are interpreted in the light of the Japanese emphasis on the inside—outside classification, which not only forms a physical demarcation in and around the house but also creates and reinforces psychological boundaries in human relationships. The social boundaries which define and maintain this classification are also evident in phenomenological accounts of Japanese people resident in the United Kingdom.
An Effect of Luminance Contrast on High-Spatial-Frequency Tritanopia
Authors: Logvinenko Alexander D , Hutchinson Sara J
Published: February 2006

Luminance contrast was found to affect high-spatial-frequency tritanopia despite the S-cone coordinates of the stimuli being kept constant. This proves that a traditional account of artificial tritanopias based on the spatial resolution differences between the S-cone channel and the M-and L-cone channels is not applicable here. We suggest that the lack of spatial resolution in one of the post-receptor (rather than receptor) spatio-chromatic channels could be a cause of high-spatial-frequency tritanopia.
The Perception of Moving Subjective Contours by 4-Month-Old Infants
Authors: Kavšnek Michael , Yonas Albert
Published: February 2006

We investigated whether 4-month-old infants are capable of perceiving illusory contours produced by the Kanizsa-square display, first introduced by Prazdny (1983, Perception & Psychophysics34 403–404), which tests whether a viewer perceives the illusory contour in the absence of brightness contrast (illusory brightness). Because the illusory square appears to move across the computer screen and infants are attracted to motion, this display holds their interest. In experiment 1, 4-month-old infants were tested for their ability to distinguish between a continuously moving illusory square and a continuously moving control display in which the pacman elements were rotated so that the perception of subjective contours did not occur. Data analysis revealed a significant preference for the subjective contour display. In experiment 2, habituation-dishabituation was used with 4-month-old infants. They were tested for their ability to discriminate between the illusory Kanizsa square that continuously moved back and forth and an illusory square which changed positions randomly. Although the infants did not show differences in dishabituation as a function of the habituation display, they looked significantly longer at the continuously moving display.
Effects of Endogenous Spatial Attention on the Detection and Discrimination of Spatial Frequencies
Authors: Srinivasan Narayanan , Brown James M
Published: February 2006

Two experiments were designed to explore the relationship between visual attention and spatial-frequency processing using a cuing paradigm. In both experiments, the targets were a sharp-edged line segment with high spatial frequencies present and a blurred line segment with only low spatial frequencies present. In each trial an endogenous cue appeared at fixation indicating the probable location, left or right, in which a stimulus would appear. In experiment 1, a typical cuing effect was found with simple reaction times (RTs) for detecting the stimuli being faster when they appeared at a cued (ie attended) compared to an uncued (ie unattended) location. In experiment 2, choice RTs were measured, with participants indicating whether the sharp-edged line segment or the blurred line segment was presented in each trial. In this case, when it was necessary to process the spatial-frequency content of the stimuli, RTs were significantly faster at the attended location only for the sharp-edged line segment. For the blurred line segment without high spatial frequencies, RTs did not differ for attended and unattended locations. The results indicate that endogenous spatial attention interacts differently with high-spatial-frequency and low-spatial-frequency selective mechanisms depending on whether the task is to detect a stimulus or identify it on the basis of its spatial-frequency content.
Can You Do This? Extremely Difficult Interbodypart Coordination Tasks and Implications for Central Limitations on Control of Coordination
Authors: Altschuler Eric Lewin , Ramachandran Vilayanur S
Published: February 2006

We have recently noticed our own inability to perform a number of interbodypart coordination tasks. The inability to perform these tasks indicates an intriguing central processing limitation on movement control, and study of these tasks should be helpful in understanding the neural mechanisms of motor control.