bluuebunny/crossref_metadata_2025 huggingface dataset:
The local electronic structure of α-Li3N
Authors: Fister T. T. , Seidler G. T. , Shirley E. L. , Vila F. D. , Rehr J. J. , Nagle K. P. , Linehan J. C. , Cross J. O.
Published: July 2008

New theoretical and experimental investigations of the occupied and unoccupied local electronic densities of states (DOS) are reported for α-Li3N. Band-structure and density-functional theory calculations confirm the absence of covalent bonding character. However, real-space full-multiple-scattering (RSFMS) calculations of the occupied local DOS find less extreme nominal valences than have previously been proposed. Nonresonant inelastic x-ray scattering, RSFMS calculations, and calculations based on the Bethe–Salpeter equation are used to characterize the unoccupied electronic final states local to both the Li and N sites. There is a good agreement between experiment and theory. Throughout the Li 1s near-edge region, both experiment and theory find strong similarities in the s-and p-type components of the unoccupied local final DOS projected onto an orbital angular momentum basis (l-DOS). An unexpected, significant correspondence exists between the near-edge spectra for the Li 1s and N 1s initial states. We argue that both spectra are sampling essentially the same final DOS due to the combination of long core-hole lifetimes, long photoelectron lifetimes, and the fact that orbital angular momentum is the same for all relevant initial states. Such considerations may be generally applicable for low atomic number compounds.
Quantitative time- and frequency-domain analysis of the two-pulse COSY revamped by asymmetric Z-gradient echo detection NMR experiment: Theoretical and experimental aspects, time-zero data truncation artifacts, and radiation damping
Authors: Kirsch Stefan , Hull William E.
Published: July 2008

The two-pulse COSY revamped by asymmetric Z-gradient echo detection (CRAZED) NMR experiment has the basic form 90°−Gδ−trec−β−nGδ−trec-FID, with a phase-encoding gradient pulse G of length δ applied during the evolution time τ for transverse magnetization, readout pulse β, rephasing gradient nGδ, and recovery time trec prior to acquisition of the free-induction decay. Based on the classical treatment of the spatially modulated dipolar demagnetizing field and without invoking intermolecular multiple-quantum coherence, a new formulation of the first-order approximation for the theoretical solution of the nonlinear Bloch equations has been developed. The nth-order CRAZED signal can be expressed as a simple product of a scaling function Cn(β,τ) and a signal amplitude function An(t), where the domain t begins immediately after the β pulse. Using a single-quantum coherence model, a generalized rf phase shift function has also been developed, which explains all known phase behavior, including nth-order echo selection by phase cycling. Details of the derivations are provided in two appendices as supplementary material. For n>1, An(t) increases from zero to a maximum value at t=tmax before decaying and can be expressed as a series of n exponential decays with antisymmetric binomial coefficients. Fourier transform gives an antisymmetric binomial series of Lorentzians, where the composite lineshape exhibits negative wings, zero integral, and a linewidth that decreases with n. Analytical functions are presented for tmax and An(tmax) and for estimating the maximal percent error incurred for An(tmax) when using the first-order model. The preacquisition delay Δ=δ+trec results in the loss of the data points for t=0 to Δ. Conventional Fourier transformation produces time-zero truncation artifacts (reduced negative wing amplitude, nonzero integral, and reduced effective T2∗), which can be avoided by time-domain fitting after right shifting the data by Δ. A doped water sample (9.93 mM NiSO4, 10 mm sample tube) was used to study the behavior of the CRAZED signal for n=1–4 with β=90° at 7 T (300 MHz H1 frequency) as a function of Δ, with and without radiation damping. Pulse-acquire experiments were used to determine the relaxation times (T1=61.8 ms and T2∗=29.7 ms), and the radiation damping time constant Trd=18.5 ms. When experimental CRAZED data sets were right shifted by Δ, excellent least-squares fits to the first-order model function were obtained for all n using a minimal set of free variables. Without radiation damping the fitted T2∗values (29.7–30.2 ms) agreed with the reference value. With radiation damping the fitted effective T2∗ values were 16.2 ms for a 90° pulse-acquire experiment and 18.8–20.2 ms for the CRAZED experiment with n=1–4 and signal amplitudes spanning a range of 105.
The consequence of lateral composition modulation on the anisotropic emission for transitions to the heavy hole subbands in InGaAs quantum wells
Authors: Czaban J. A. , Thompson D. A.
Published: July 2008

The lateral composition modulation that is present in InGaAs quantum wells (QWs) produces an asymmetry in the plane of the QW with two regions where transition to the heavy hole (HH) can occur. Polarization resolved photoluminescence shows that transitions between the conduction band to HH subbands in both the In-rich and Ga-rich regions produce anisotropic features. Also, changing the relative separation of the light hole and HH subbands has little impact on the separation of the anisotropic features of the photoluminescence curves.
Anelasticity of FexO at high pressure
Authors: Kantor A. , Kantor I. , Kurnosov A. , Dubrovinsky L. , Krisch M. , Bossak A. , Jacobsen S.
Published: July 2008

A combined single-crystal inelastic x-ray scattering (IXS) and x-ray diffraction (XRD) study of synthetic wüstite Fe0.95O at elevated pressure revealed an increasing difference in the bulk modulus determined from static XRD and dynamic IXS measurements upon compression. We explain this observation by anelastic relaxation in the studied material and propose a model for the quantitative description of such a physical phenomenon. The analysis of available data provides evidence for a reasonably good agreement for bulk moduli and a systematic difference for their pressure derivatives between static and dynamic measurements.
Absolute instability of light jets emerging from circular injector tubes
Authors: Coenen W. , Sevilla A. , Sánchez A. L.
Published: July 2008

We present a numerical study of the spatiotemporal, inviscid linear instability of light jets emerging from round tubes for values of the Reynolds number, Rej=ρjQ∕(πaμj)⪢1, where Q is the volumetric flow rate, ρj and μj are, respectively, the jet density and viscosity, and a is the injection tube radius. The analysis focuses on the influence of the injector length lt on the stability characteristics of the resulting jet, whose base velocity profile at the exit is computed in terms of the dimensionless tube length Lt=lt∕(Reja) by integrating the boundary-layer equations along the injector. Both axisymmetric (m=0) and helical (∣m∣=1) modes of instability are investigated for different values of the jet-to-ambient density ratio S=ρj∕ρ∞<1. For short tubes Lt⪡1 the base velocity profile at the tube exit is uniform except in a thin surrounding boundary layer. Correspondingly, the stability analysis reproduces previous results of uniform velocity jets, according to which the jet becomes absolutely unstable to axisymmetric modes for a critical density ratio Sc≃0.66 and to helical modes for Sc≃0.35. For tubes of increasing length the analysis reveals that both modes exhibit absolutely unstable regions for all values of Lt and small enough values of the density ratio. In the case of the helical mode, we find that Sc increases monotonically with Lt, reaching its maximum value Sc≃0.5 as the exit velocity approaches the Poiseuille profile for Lt⪢1. Concerning the axisymmetric mode, its associated value of Sc achieves a maximum value Sc≃0.9 for Lt≃0.04 and then decreases to approach Sc≃0.7 for Lt⪢1. The absolute growth rates in this limiting case of near-Poiseuille jet profiles are, however, extremely small for m=0, in agreement with the fact that axisymmetric disturbances of a jet with parabolic profile are neutrally stable. As a result, for S<0.5 the absolute growth rate of the helical mode becomes larger than that of the axisymmetric mode for sufficiently large values of Lt, suggesting that the helical mode may prevail in the instability development of very light jets issuing from long injectors.
On the mechanism of charge transport in pentacene
Authors: v. Laarhoven H. A. , Flipse C. F. J. , Koeberg M. , Bonn M. , Hendry E. , Orlandi G. , Jurchescu O. D. , Palstra T. T. M. , Troisi A.
Published: July 2008

Terahertz transient conductivity measurements are performed on pentacene single crystals, which directly demonstrate a strong coupling of charge carriers to low frequency molecular motions with energies centered around 1.1 THz. We present evidence that the strong coupling to low frequency motions is the factor limiting the conductivity in these organic semiconductors. Our observations explain the apparent paradox of the “bandlike” temperature dependence of the conductivity beyond the validity limit of the band model.
Mixed quantum-classical equilibrium: Surface hopping
Authors: Schmidt J. R. , Parandekar Priya V. , Tully John C.
Published: July 2008

We re-examine the analysis of the equilibrium limits of the fewest switches surface hopping algorithm for mixed quantum-classical dynamics. In contrast with previously reported results, we show that surface hopping does not, in general, exactly yield Boltzmann equilibrium, but that in practice the observed deviations are quite small. We also demonstrate that surface hopping does approach the exact equilibrium distribution in both the limits of small adiabatic splitting and/or strong nonadiabatic coupling. We verify these analytical results with numerical simulations for a simple two-level quantum system connected to a bath of classical particles.
Osmotic pressure and polymer size in semidilute polymer solutions under good-solvent conditions
Authors: Pelissetto Andrea
Published: July 2008

We consider the lattice Domb–Joyce model at a value of the coupling for which scaling corrections approximately vanish and determine the universal scaling functions associated with the osmotic pressure and the polymer size for semidilute polymer solutions (c/c∗≤10, where c is the concentration of the solution and c∗ is the overlap concentration) in good-solvent conditions. Our result for the osmotic pressure agrees with previous renormalization-group calculations (the relative difference is less than 1%) but differs significantly from previous numerical determinations in which polymers were modeled as lattice self-avoiding walks. We show that for c/c∗≳6 simulations of lattice self-avoiding walks give results that are affected by strong scaling corrections even for chain lengths as large as 1000: The self-avoiding walk model is therefore unsuitable for the determination of universal properties of polymer solutions deep in the semidilute regime.
The near-field scanning thermal microscope
Authors: Wischnath Uli F. , Welker Joachim , Munzel Marco , Kittel Achim
Published: July 2008

We report on the design, characterization, and performance of a near-field scanning thermal microscope capable to detect thermal heat currents mediated by evanescent thermal electromagnetic fields close to the surface of a sample. The instrument operates in ultrahigh vacuum and retains its scanning tunneling microscope functionality, so that its miniature, micropipette-based thermocouple sensor can be positioned with high accuracy. Heat currents on the order of 10−7W are registered in z spectroscopy at distances from the sample ranging from 1 to about 30nm. In addition, the device provides detailed thermographic images of a sample’s surface.
Ferroelectric polarization and piezoelectric properties of layer-structured K0.5Bi4.5Ti4O15 single crystals
Authors: Noguchi Yuji , Suzuki Muneyasu , Kitanaka Yuuki , Teranishi Shunsuke , Miyayama Masaru
Published: July 2008

Single crystals of ferroelectric K0.5Bi4.5Ti4O15 with a Bi-layered structure were grown by the flux method, and the properties of polarization hysteresis, piezoelectric strain, and leakage current were investigated along the polar a axis at 25°C. K0.5Bi4.5Ti4O15 crystals exhibited a large remanent polarization of 31μC∕cm2, which suggests that K0.5Bi4.5Ti4O15 has the largest spontaneous polarization among Bi layer-structured ferroelectrics with four TiO6 layers in the perovskite blocks. Strain measurements showed that the piezoelectric strain constant was 31pm∕V.
Jacobi’s last multiplier and Lagrangians for multidimensional systems
Authors: Nucci M. C. , Leach P. G. L.
Published: July 2008

We demonstrate that the formalism for the calculation of Jacobi’s last multiplier for a one degree of freedom system extends naturally to systems of more than one degree of freedom thereby extending results of Whittaker dating from more than a century ago and Rao [Proceedings of the Benares Mathematical Society 2, 53 (1940)] dating from almost 70 years ago. We illustrate the theory with an application taken from the theory of coupled oscillators. We indicate how many Lagrangians can be obtained for such a system.
Effects of substrate bias on the preferred orientation, phase transition and mechanical properties for NbN films grown by direct current reactive magnetron sputtering
Authors: Wen M. , Hu C. Q. , Wang C. , An T. , Su Y. D. , Meng Q. N. , Zheng W. T.
Published: July 2008

NbN films are deposited using direct current reactive magnetron sputtering in discharge of a mixture of N2 and Ar gas, and the effects of substrate bias (Vb) on the preferred orientation, phase transition, and mechanical properties for NbN films are explored by x-ray diffraction, selective area electron diffraction, and nanoindentation measurements. It is found that Vb has a significant influence on the stress in NbN films, leading to a pronounced change in the preferred orientation, phase structure, and hardness. As the substrate is at voltage floating, the stress is tensile. In contrast, as negative Vb is applied, the stress becomes compressive, and increases with increasing the absolute value of negative Vb. It is observed that a phase transition from δ (face-centered cubic) to δ′ (hexagonal) for NbN films occurs as Vb is in the range of −80to−120V, which can be attributed to a decrease in the strain energy for NbN films. In order to explore the relationship between the stress and phase transition as well as preferred orientation, density-functional theory based on first principles is used to calculate the elastic constants and shear modulus for NbN with a structure of δ or δ′. The calculated results show that the shear modulus for δ′-NbN is larger than that for δ-NbN, whereas the bulk modulus for δ′-NbN is almost equal to that for δ-NbN, resulting in a difference in hardness for δ- or δ′-NbN single crystal.
Generation of high flux, highly coherent extreme ultraviolet radiation in a gas cell
Authors: Van Dao Lap , Teichmann Sven , Davis Jeff , Hannaford Peter
Published: July 2008

We report the generation of extreme ultraviolet radiation with high photon flux (1010–1012 photon/cm2 s), high spatial coherence (up to 0.95), and good spatial beam profile by high-order harmonic generation in various noble gases (argon, neon, and helium) in a gas cell. The photon flux was determined using an extreme ultraviolet spectrometer equipped with a charge-coupled device camera and the spatial coherence was determined from Young double-slit interference fringes. The high-order harmonic emission is confined to just a few orders because of the small phase mismatch in the cut-off region that allows macroscopic phase matching to be satisfied for just a few harmonics in this region. The efficiency and spatial beam profile are studied as a function of gas pressure and geometrical configuration.
Voltage and temperature dependence of high-field magnetoresistance in arrays of magnetic nanoparticles
Authors: Tan Reasmey P. , Carrey Julian , Respaud Marc
Published: July 2008

Huge values of high-field magnetoresistance have been recently reported in large arrays of ferromagnetic CoFe nanoparticles embedded in an organic insulating matrix in the Coulomb blockade regime. The magnetoresistance displays two characteristic behaviors: a scaling with the magnetic field/temperature ratio and an unusual exponential decrease with increasing voltage. To describe all these features, we propose a model where the electronic charges tunnel from one nanoparticle to another through a paramagnetic impurity. It is assumed that the noncollinearity between the magnetic moment of the ferromagnetic nanoparticles and the paramagnetic moment induces an effective tunnel barrier, the height of which depends on the relative angle of the paramagnetic moment with respect to the ferromagnetic one. A systematic study of the magnetoresistance behavior as a function of the effective tunnel barrier parameters and applied bias voltage is carried out. Finally, we show that by using Fowler–Nordheim current expressions, i.e., in the hypothesis of small energy barriers, the main features of the magnetoresistance are well reproduced with realistic parameters.
Hydrogen-inclusion-induced variation of critical current in Nb–AlOx–Nb Josephson junctions
Authors: Hinode Kenji , Satoh Tetsuro , Nagasawa Shuichi , Hidaka Mutsuo
Published: July 2008

The critical current density (Jc) of Nb–AlOx–Nb Josephson-junction (JJ) arrays was found to depend on their wiring structure. The Jc values of all JJs wired with a niobium electrode covered with a palladium layer increased by about 20%, while the Jc values of those with electrodes without palladium coverage stayed unchanged (except for that of the two junctions directly connected to the pads of an electrical probe covered with palladium.) To explain this Jc increase, we propose a “hydrogen mechanism,” that is, the hydrogen inclusion into niobium electrodes occurs during fabrication, and its desorption occurs after fabrication. Hydrogen atoms incorporated in the electrodes are thought to influence the mechanical and the electronical properties of niobium, resulting in the deviation of critical current density. Hydrogen desorption analysis and measurements on niobium-film properties verified the occurrence of hydrogen incorporation into the niobium films during the fabrication process for superconducting JJ circuits. The incorporation and desorption processes were confirmed to proceed, even in air, if the niobium film is covered with palladium. As hydrogen diffuses quickly in niobium but stops in aluminum or aluminum oxide, differences in hydrogen concentration can happen within a circuit consisting of electrically connected multiple junctions. This hydrogen concentration difference can explain the observation that two junctions with increased Jc exist in the serial junction array without palladium coverage.
Linear growth kinetics of nanometric silicides in Co/amorphous-Si and Co/CoSi/amorphous-Si thin films
Authors: Cserháti C. , Balogh Z. , Csik A. , Langer G. A. , Erdélyi Z. , Glodán Gy. , Katona G. L. , Beke D. L. , Zizak I. , Darowski N. , Dudzik E. , Feyerherm R.
Published: July 2008

Evolution of the reaction zone on the nanoscale has been studied in bi- and multilayered Co/a-Si as well as in trilayered Co/a-CoSi/a-Si and Co/CoSi/a-Si thin film diffusion couples. The kinetics of the phase boundary movement during solid state reaction has been followed with special interest of the initial stage of the diffusion, i.e. effects happening on the nanoscale (short time, short distance). The interfacial reactions have been investigated in situ by synchrotron radiation. The formed phases were also characterized by transmission electron microscopy and resistance measurements. The effect of phase nucleation and shift of phase boundaries have been separated in order to determine the “pure” growth kinetics of the crystalline CoSi and Co2Si product phases at the very early stages. Deviations have been found from the traditional diffusion controlled parabolic phase growth. Computer simulations based on a kinetic mean field model illustrated that the diffusion asymmetry (large difference in diffusion coefficients of the materials in contact) may offer a plausible explanations for this.
Interlaboratory comparison of positron annihilation lifetime measurements for synthetic fused silica and polycarbonate
Authors: Ito Kenji , Oka Toshitaka , Kobayashi Yoshinori , Shirai Yasuharu , Wada Ken’ichiro , Matsumoto Masataka , Fujinami Masanori , Hirade Tetsuya , Honda Yoshihide , Hosomi Hiroyuki , Nagai Yasuyoshi , Inoue Koji , Saito Haruo , Sakaki Koji , Sato Kiminori , Shimazu Akira , Uedono Akira
Published: July 2008

Interlaboratory comparison of positron annihilation lifetime measurements using synthetic fused silica and polycarbonate was conducted with the participation of 12 laboratories. By regulating procedures for the measurement and data analysis the uncertainties of the positron lifetimes obtained at different laboratories were significantly reduced in comparison with those reported in the past.
Surface anchoring effects on spectral broadening of cholesteric liquid crystal films
Authors: Fan B. , Vartak S. , Eakin J. N. , Faris S. M.
Published: July 2008

This paper describes the spectral broadening of cholesteric liquid crystal film prepared from a blend comprising a cross-linkable liquid crystal polymer and a non-cross-linkable low-molecular-weight liquid crystal. The spectral broadening arises from the formation of gradient pitch across the film thickness. It is shown that both phase-separation and in situ swelling during photopolymerization are important mechanisms for the resulting film structure. The surface anchoring is important to achieve high wavelength- and polarization-selective reflectance.
Phase transition and phase stability in [110]-, [001]-, and [111]-oriented 0.68Pb(Mg1/3Nb2/3)O3−0.32PbTiO3 single crystal under electric field
Authors: Li Zhenrong , Xu Zhuo , Yao Xi , Cheng Z.-Y.
Published: July 2008

The phase transition and the phase stability in 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PMN-0.32PT) single crystals under different electric fields were investigated over a temperature range from −20 to 200 °C using the dielectric property. Crystals with different orientations were used in the research. First, it is found that the intermediate monoclinic or orthorhombic phases are involved in the phase transition from the rhombohedral to tetragonal phase and that the appearance and stability of the intermediate phases as well as the phase path are strongly dependent on factors, such as the history of the sample and the direction and strength of the electric field. The transition behavior from the rhombohedral to tetragonal phase for the samples during the field-heating process is much more complex than that during the field-cooling process. Second, for the ferroelectric-to-paraelectric phase transition, it is found that the dielectric-constant peak actually reflects two processes: one is the ferroelectric relaxor process and the other is the tetragonal to cubic phase transition. The electric field shifts both transitions toward high temperature at different rates, which results in a “λ-like” dielectric-constant peak in [111]-oriented samples. The results indicate that the polar regions in the ferroelectric relaxors should have a spontaneous polarization along the [111] direction. Finally, the temperature–electric field (T-E) phase diagrams for crystals under electric field along different directions. It is also found that the piezoelectric activities are strongly related to the appearance of the intermediate phases.
Ultraviolet photoelectron spectroscopy and inverse photoemission spectroscopy of [6,6]-phenyl-C61-butyric acid methyl ester in gas and solid phases
Authors: Akaike Kouki , Kanai Kaname , Yoshida Hiroyuki , Tsutsumi Jun’ya , Nishi Toshio , Sato Naoki , Ouchi Yukio , Seki Kazuhiko
Published: July 2008

The electronic structure of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied using ultraviolet photoelectron spectroscopy of vapor and thin film and inverse photoemission spectroscopy of thin film. The threshold ionization energy of PCBM was found to be 7.17±0.04 eV in gas phase and 5.96±0.02 eV in solid phase. The threshold electron affinity was 3.9±0.1 eV in solid phase. These values are 0.4−0.6 eV smaller than C60. The density functional theory calculations gave consistent results with these trends and suggested that the electron donation from the side chain to C60 backbone raised the C60-backbone-derived π orbitals of PCBM. The polarization energy of PCBM is 1.21 eV, which is almost the same as C60 but is about 0.5 eV smaller than the value of typical aromatic hydrocarbons.
High-resolution 17–75keV backlighters for high energy density experiments
Authors: Park H.-S. , Maddox B. R. , Giraldez E. , Hatchett S. P. , Hudson L. T. , Izumi N. , Key M. H. , Le Pape S. , MacKinnon A. J. , MacPhee A. G. , Patel P. K. , Phillips T. W. , Remington B. A. , Seely J. F. , Tommasini R. , Town R. , Workman J. , Brambrink E.
Published: July 2008

17 – 75 keV one- and two-dimensional high-resolution (<10μm) radiography has been developed using high-intensity short pulse lasers. High energy Kα sources are created by fluorescence from hot electrons interacting in the target material after irradiation by lasers with intensity IL>1017W∕cm2. High-resolution point projection one- and two-dimensional radiography has been achieved using microfoil and microwire targets attached to low-Z substrate materials. The microwire size was 10μm×10μm×300μm on a 300μm×300μm×5μm polystyrene substrate. The radiography experiments were performed using the Titan laser at Lawrence Livermore National Laboratory. The results show that the resolution is dominated by the microwire target size and there is very little degradation from the plasma plume, implying that the high-energy x-ray photons are generated mostly within the microwire volume. There are enough Kα photons created with a 300J, 1-ω, 40ps pulse laser from these small volume targets, and that the signal-to-noise ratio is sufficiently high, for single shot radiography experiments. This unique technique will be used on future high energy density experiments at many new high-power laser facilities.
Electric charging and nanostructure formation in polymeric films using combined amplitude-modulated atomic force microscopy-assisted electrostatic nanolithography and electric force microscopy
Authors: Reagan Michael A. , Kashyn Dmytro , Juhl Shane , Vaia Richard A. , Lyuksyutov Sergei F.
Published: July 2008

A hybrid technique, combining lithography which exploits atomic force microscope tip manipulation with modified electric force microscopy was used to study surface electric charging (deposition and evolution) of polymethyl methacryalate and polystyrene films. Upon charging the films past a threshold voltage, two distinct regimes were observed: (1) stable feature formation related to electric breakdown and mass transport resulting in stable film deformation due to the negative surface charging (negative tip bias) and (2) no stable feature formation regime attributed to viscoelastic deformation of polymer surface followed by the surface relaxation in the case of positive surface charging (positive tip bias).
Epitaxy of single crystalline PrO2 films on Si(111)
Authors: Weisemoeller T. , Deiter C. , Bertram F. , Gevers S. , Giussani A. , Zaumseil P. , Schroeder T. , Wollschläger J.
Published: July 2008

A film of praseodymium sesquioxide with hexagonal structure, that has been deposited on Si(111) by molecular beam epitaxy, was annealed in oxygen atmosphere to obtain a PrO2 film for improved heteroepitaxy as buffer dielectric for alternative semiconductor layer integration. The film structure is characterized by x-ray diffraction and x-ray reflectometry. The film is single crystalline with Fm3¯m (fluorite) structure. It is B oriented with respect to Si and has lattice constants close to bulk PrO2. The cubic lattice of the PrO2 film is slightly distorted due to residual oxygen vacancies which increase the diameter of Pr ions.
Morphological evolution of voids by surface drift diffusion driven by the capillary, electromigration, and thermal-stress gradient induced by the steady state heat flow in passivated metallic thin films and flip-chip solder joints. II. Applications
Authors: Ogurtani Tarik Omer , Akyildiz Oncu
Published: July 2008

The void growth and drift motion induced by the combined actions of the phase transformation (evaporation and condensation) and surface drift diffusion driven by the capillary and electromigration forces and thermal-stress gradients are investigated in passivated metallic thin films and flip-chip solder joints via computer simulation using the front-tracking method. As far as the device reliability is concerned, the most critical configuration for solder joint failure occurs even when thermal stresses are low if the void nucleation takes place close to the under bump metallurgy (UBM) where the heat and current flux crowding takes place due to the proximity effect associated with the confinement. The void growth induced by the condensation of excess (athermal) vacancies at the void-matrix dividing surface results in drastic spreading of pre-existing voids along transverse direction of solder joint due to the concurrently occurring heat and current crowding adjacent to the UBM. This accelerated transverse void spreading may eventually cause open-circuit interconnect failure as clearly demonstrated experimentally in literature.
Bottom-contact fullerene C60 thin-film transistors with high field-effect mobilities
Authors: Kitamura Masatoshi , Aomori Shigeru , Na Jong Ho , Arakawa Yasuhiko
Published: July 2008

Fullerene C60 thin-film transistors (TFTs) with bottom-contact structure have been fabricated. The parasitic resistance was extracted using gated-transmission line method. The drain/source electrodes consisted of a single Au layer with no adhesion layer; the channel lengths ranged from 5 to 40 μm. The field-effect mobilities in the saturation regime slightly depended on the channel length, ranging from 2.45 to 3.23 cm2/V s. The mobility of 3.23 cm2/V s was obtained from the TFT with a channel length of 5 μm and is the highest in organic TFTs with bottom-contact structure. The high mobility is due to the low parasitic resistance.
Poly(3-hexylthiophene) thin-film transistors with variable polymer dielectrics for transfer-printed flexible electronics
Authors: Hines D. R. , Southard A. , Fuhrer M. S.
Published: July 2008

The fabrication of high quality organic thin-film transistors onto flexible, plastic substrates has been extended to include the polymeric semiconductor material poly(3-hexlythiophene). The transfer printing method is used to easily assemble these devices onto either polyethylene terephthalate (PET) or polycarbonate (PC) substrates. A PC dielectric layer is used in conjunction with the PC substrate while both poly(methyl methacrylate) and polystyrene dielectric layers are used in conjunction with the PET substrate. In all cases the mobility of the transfer-printed devices, 0.019–0.041 cm2/V s, is significantly higher than that of the unprinted reference devices (SiO2 dielectric layer on a Si substrate), 0.007 cm2/V s. The width-normalized contact resistance is also lower for the transfer-printed devices, 0.18 MΩ cm, as compared to that for the reference devices, 0.56 MΩ cm. For the devices reported, the threshold voltage becomes more positive as the polar component of the surface energy of the polymer dielectric material increases. These results illustrate the simplicity, power, and versatility of the transfer printing method for the fabrication of high quality flexible electronics.
Electron-beam-induced current study of stacking faults and partial dislocations in 4H-SiC Schottky diode
Authors: Chen Bin , Chen Jun , Sekiguchi Takashi , Ohyanagi Takasumi , Matsuhata Hirofumi , Kinoshita Akimasa , Okumura Hajime , Fabbri Filippo
Published: July 2008

Electrical properties of stacking faults and bounding partial dislocations in 4H-SiC Schottky diode were investigated by using electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques. EBIC images show that basal plane dislocation is easily dissociated into two partial dislocations [Si(g) 30° and C(g) 30° partials], with a stacking fault between them. The EBIC contrast of C(g) 30° partial is always several percent higher than that of Si(g) 30° partial. The stacking fault is brighter than the background, having the negative EBIC contrast. CL spectrum shows that a new peak (417nm) appears at stacking fault position. The origin of bright stacking fault in EBIC image is discussed according to its quantum-well state.
Thermally assisted magnetic recording on a bit-patterned medium by using a near-field optical head with a beaked metallic plate
Authors: Matsumoto Takuya , Nakamura Kimio , Nishida Tetsuya , Hieda Hiroyuki , Kikitsu Akira , Naito Katsuyuki , Koda Tetsunori
Published: July 2008

A near-field optical head with a beaked metallic plate was used for writing marks on a Co∕Pd bit-patterned medium with a diameter of 20–25nm and a pitch of 30nm. Magnetic-force-microscope images of the medium show that the magnetizations of single bits were selectively reversed by the head. The light-utilization efficiency (defined as the ratio of the absorbed power in the medium to the incident light power) was estimated from the writing condition used and thermal modeling as about 5%.
A direct approach to study radiative emission from triplet excitations in molecular semiconductors and conjugated polymers
Authors: Singh Jai , Baessler H. , Kugler S.
Published: July 2008

Using the recently discovered time-dependent spin-orbit-photon interaction operator and first order perturbation theory, the rate of spontaneous emission from triplet excitations is derived within the two-level approximation for organic molecular solids and conjugated polymers. The calculated rates and corresponding radiative lifetimes agree very well with the known experimental results. Present results are compared with those obtained through the traditional approach of the second order perturbation theory in some molecular crystals and found to be in better agreement with experiments.
Chemical reversability of the electrical dedoping of conducting polymers: An organic chemically erasable programmable read-only memory
Authors: Chia Perq-Jon , Yeo Yee-Chia , Burroughes Jeremy H. , Friend Richard H. , Ho Peter K.-H.
Published: July 2008

The loss of electronic conductivity of p-doped poly(3,4-ethylenedioxythiophene) at high electrical bias is shown to be chemically reversible upon redoping with iodine vapor. This provides further confirmation that the initial loss of conductivity arises from the injection-induced dedoping mechanism. Repeat “write-erase” cycles are possible, which gives a rudimentary organic chemically erasable programmable read-only memory. Transient measurements show that the write time (i.e., time for loss of conductivity) decreases from thousands of seconds just above the critical electric field of 50kVcm–1 to millisecond well above this value but below the onset of electrochemical destruction.
Effect of magnetic field on domain-wall structures in two antiferromagnetically coupled Co∕Pt multilayers
Authors: Liu Z. Y. , Li N. , Zhang F. , Xu B. , He J. L. , Yu D. L. , Tian Y. J. , Yu G. H.
Published: July 2008

In antiferromagnetically coupled [Pt(5Å)∕Co(4Å)]4∕NiO(11Å)∕[Co(4Å)∕Pt(5Å)]4 multilayer with perpendicular anisotropy, net ferromagnetic stripes are created in demagnetized state between the relatively shifted domain walls in the two Co∕Pt multilayers owing to the competition between magnetostatic and exchange energies. With an external field applied antiparallel to the wall magnetization, involvement of Zeeman energy of net ferromagnetic stripes in the competition makes the net ferromagnetic stripes shrink, and the stripe width varies with field in an inversely proportional way in the low field range.
Temporal characteristics of the S1 and T1 thiophosgene Cl2CS in the gas phase: Comparison of the T1 decay with theoretical predictions
Authors: Fujiwara Takashige , Lim Edward C.
Published: July 2008

The picosecond optical-optical double resonance experiment in a supersonic free jet as well as the vapor-phase phosphorescence indicates that the decay of T1 Cl2CS belongs to the intermediate case of the classification scheme for electronic relaxation. The Afast/Aslow pre-exponential ratio in the biexponential T1 decay is much greater under picosecond excitation than under nanosecond excitation. In vapor phase at low pressure, the phosphorescence exhibits a decay time that varies with the coherence width of the laser used for excitation. Both the T1 and the S1 decay times of Cl2CS depend strongly on temperature, indicating that Coriolis coupling plays an important role in mode mixing (intramolecular vibrational redistribution).
Conductivity enhancement of carbon nanotube composites by electrolyte addition
Authors: Li Hui-Ching , Lu Sheng-Yi , Syue Sen-Hong , Hsu Wen-Kuang , Chang Shih-Chin
Published: July 2008

The conductivity of carbon nanotubes and polyvinyl alcohol composites is significantly improved by addition of Fe2(SO4)3. The coordinated cations between nanotubes play a crucial role in lowering intertube hopping magnitude.
Highly stable amorphous-silicon thin-film transistors on clear plastic
Authors: Hekmatshoar Bahman , Cherenack Kunigunde H. , Kattamis Alex Z. , Long Ke , Wagner Sigurd , Sturm James C.
Published: July 2008

Hydrogenated amorphous-silicon (a-Si:H) thin-film transistors (TFTs) have been fabricated on clear plastic with highly stable threshold voltages. When operated at a gate field of 2.5×105V∕cm, the threshold voltage shift extrapolated to only ∼1.2V after ten years. This stability is achieved by a high deposition temperature for the gate silicon nitride insulator which reduces charge trapping and high hydrogen dilution during a-Si:H growth to reduce defect creation in a-Si:H. This gate field of 2.5×105V∕cm is sufficient to drive phosphorescent organic light emitting diodes (OLEDs) at a brightness of 1000Cd∕m2. The half-life of the TFT current is over ten years, slightly longer than the luminescence half-life of high quality green OLEDs.
Ultrafast optical control of coercivity in GaMnAs
Authors: Hall K. C. , Zahn J. P. , Gamouras A. , March S. , Robb J. L. , Liu X. , Furdyna J. K.
Published: July 2008

Femtosecond optical control of the magnetization and coercive field is demonstrated in GaMnAs using time-resolved magneto-optical Kerr effect techniques. These experiments reveal a near-complete, subpicosecond collapse of the hysteresis loop, consistent with femtosecond demagnetization. On longer time scales (∼300ps) an increase in coercivity is observed, attributed to hole-mediated enhancement of the domain wall energy.
The effect of doping the M-barrier in very long-wave type-II InAs∕GaSb heterodiodes
Authors: Hoffman Darin , Nguyen Binh-Minh , Huang Edward Kwei-wei , Delaunay Pierre-Yves , Razeghi Manijeh , Tidrow Meimei Z. , Pellegrino Joe
Published: July 2008

A variation on the standard homodiode type-II superlattice with an M-barrier between the π-region and the n-region is shown to suppress the dark currents. By determining the optimal doping level of the M-superlattice, dark current densities of 4.95mA∕cm2 and quantum efficiencies in excess of 20% have been demonstrated at the moderate reverse bias of 50mV; allowing for near background-limted performance with a Johnson-noise detectivity of 3.11×1010cmHz∕W at 77K for 14.58μm cutoff wavelength for large area diodes without passivation. This is comparable to values for the state-of-the-art HgCdTe photodiodes.
Radiotracer diffusion of cobalt, iron, and chromium in dislocation-free germanium
Authors: Lerner L. , Stolwijk N. A.
Published: July 2008

Diffusion of the transition metals Co, Fe, and Cr into single-crystal germanium is found to be fast processes at temperatures relevant to the fabrication of semiconductor devices. These results were obtained from experiments in which electronic-grade Ge samples were provided with a radioactive surface source and short time annealed in a lamp furnace at temperatures ranging from 600to900°C. Diffusion coefficients were determined from penetration profiles of the radioisotopes Co57, Fe59, and Cr51. The results are interpreted within the framework of interstititial-substitutional diffusion and compared with earlier diffusion data on Ge crystals.
Fabry–Pérot microcavities with controllable resonant wavelengths in periodic dielectric waveguides
Authors: Zhang Yao , Huang Wanwen , Li Baojun
Published: July 2008

Fabry–Pérot microcavities with controllable resonant wavelengths and constant quality factors are constructed by introducing defects in periodic dielectric waveguides. Two-dimensional finite-difference time-domain method is used to simulate the field distributions in the cavities. The simulated electric field profile fits a cosine-Gaussian curve. The quadratic relation between the resonant wavelength and the defect length is theoretically discussed and numerically proved. Simulations show that the resonant wavelength can be simply controlled by shifting cylinders in the defects, and the value of quality factor keeps a constant of about 103.
Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics
Authors: Wu Yun , Li Yinghong , Jia Min , Song Huimin , Guo Zhigang , Zhu Ximing , Pu Yikang
Published: July 2008

This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics’ dependence on operating pressure. As the pressure decreases, the N2(CПu3) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445Torr.
Internal and External Dynamics of the Munich Film and TV Industry Cluster, and Limitations to Future Growth
Authors: Bathelt Harald , Gräf Armin
Published: July 2008

This analysis uses the case of a seemingly successful industry cluster (ie the film and TV industry in Munich) to demonstrate that deficits in the structure of social relations can impact a cluster's growth potential. In the period after World War II, Munich grew into a national centre of media industries in Germany due to the introduction of private/commercial TV, national entry barriers, and a supportive institutional infrastructure. The recent advertising crisis and the dissolution of the Kirch Group have, however, reinforced already existing internal dilemmas and contradictions. We suggest that the growth prospects of this industry are limited due to a lack of reflexive, interconnected communication and interaction patterns. In conceptual terms, we apply a model which emphasizes that local interaction or ‘buzz’ in clusters and interaction with external firms and markets through translocal or global ‘pipelines’ create reflexive dynamics. Based on this conception, participatory observation and semistructured interviews were conducted with sixty-five Munich firms, as well as with planners and media experts from the region. The results indicate that the regional, national, and occasional international project networks have had a smaller impact on the Munich film and TV industry than expected. Our investigation provides evidence that the cluster's structure of social relations is relatively weak. Internal networks which could drive creative recombination and innovation are underdeveloped, and linkages with external markets which could provide substantial growth impulses to the region are lacking. We argue that this structural weakness limits the potential for future growth.
Comparison of the life histories of three co-occurring wrasses (Teleostei: Labridae) in coastal waters of south-eastern Australia
Authors: Morton Jason K. , Gladstone William , Hughes Julian M. , Stewart John
Published: July 2008

Labrids are abundant on temperate rocky reefs yet their life histories are poorly known. Three co-occurring Australian labrids (Ophthalmolepis lineolatus, Notolabrus gymnogenis and Pictilabrus laticlavius) exhibited protogynous hermaphroditism typical of labrids. Juveniles reached sexual maturity at 184 mm total length (TL) (2.1 years) in O. lineolatus, 177 mm TL (1.8 years) in N. gymnogenis and <95 mm TL (<0.9 years) in P. laticlavius. Individuals were sexually active initial phase females until changing to a terminal phase male at 295 mm TL (5.2 years) in O. lineolatus, 273 mm TL (4.5 years) in N. gymnogenis and 138 mm TL (2.0 years) in P. laticlavius. The occurrence of males only at greater lengths and older ages suggests that O. lineolatus and N. gymnogenis are monandrous, whereas P. laticlavius appears to be diandrous. Reproduction was asynchronous among species with reproductive activity peaking in January–March for O. lineolatus, April–October for N. gymnogenis and October–December for P. laticlavius. Sectioned otoliths revealed that O. lineolatus and N. gymnogenis grew rapidly to 300 mm TL (6 years) and P. laticlavius to 180 mm TL (3 years). Longevity was at least 13.8, 9.6 and 4.8 years respectively. These life history data will aid management of these frequently harvested species.
First observations of young of the year and juvenile great white sharks (Carcharodon carcharias) scavenging from a whale carcass
Authors: Dicken M. L.
Published: July 2008

Observations of great white sharks (Carcharodon carcharias) scavenging from cetacean carcasses are rare and have only been reported in the scientific literature for large (>3.5 m total length (TL)) individuals. Between 13 October and 25 November 2006, young of the year and juvenile great white sharks were observed scavenging from the carcass of a humpback whale (Megaptera novaeangliae) in Algoa Bay, South Africa. Although more than one shark scavenged from the carcass, simultaneous feeding was not observed. The sharks showed a clear preference for soft tissue at sites along the mouth of the carcass. Protective ocular rotation was rarely observed and none of the sharks exhibited palatoquadrate protrusion while feeding. These observations provide a new insight into the foraging behaviour of young of the year and juvenile great white sharks. The prevalence of small great white sharks (1.5 m TL) and the absence of any individuals greater than 3.65 m TL suggest that Algoa Bay may function as a nursery area for great white sharks in South Africa. This information is crucial not only to improve our understanding of great white shark biology, but also for their long-term management and conservation in South Africa.
Evidence of diadromous movements in a coastal population of southern smelts (Retropinninae: Retropinna) from Victoria, Australia
Authors: Crook David A. , Macdonald Jed I. , Raadik Tarmo A.
Published: July 2008

Understanding the migratory behaviour of fishes is critical to the conservation and management of fish assemblages in coastal rivers. We analysed the otolith chemical signatures of smelt, Retropinna sp., from inland and coastal populations in mainland south-eastern Australia to determine whether individuals within coastal populations of the species were diadromous. Assessments of otolith chemical composition combined with water chemistry data were used to make inferences about the migration histories of individual fish. A proportion of the smelt collected from the freshwater reaches of a coastal river exhibited diadromous movements, with the majority of fish analysed showing evidence of estuarine or marine occupation as larvae/juveniles and a minority inhabiting freshwater throughout their life histories. A broad range in the daily ages of upstream migration into freshwater (15–106 days) and the timing of these migrations suggest that spawning and migration occur over several months during the summer/autumn period. The results of this study suggest that southern smelts are an ecologically variable taxonomic group and that conservation and management actions should take into account the range of migratory behaviours exhibited both within populations and across regions.