bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and texture dependence of the dielectric anomalies and dc conductivity of Bi3TiNbO9 ferroelectric ceramics
Authors: Moure A. , Pardo L.
Published: April 2005

Ceramics of composition Bi3TiNbO9 (BTN) and perovskite-layered structure (Aurivillius type) [B. Aurivillius, Ark. Kemi 1, 463 (1949)] were processed by natural sintering and hot pressing from amorphous precursors. Precursors were obtained by mechanochemical activation of stoichiometric mixtures of oxides. These materials are in general interesting for their use as high-temperature piezoelectrics. Among them, BTN possesses the highest ferroparaelectric phase-transition temperature (>900°C). The transition temperature establishes the working limit of the ceramic and the electric properties, especially the dc conductivity, affect on its polarizability. In this work, dielectric studies of BTN ceramics with controlled texture and microstructure have been made at 1, 100KHz, and 1MHZ and in the temperature range from 200°C up to the ferroparaelectric transition temperature. Values of ε′∼250 at 200°C are achieved in ceramics hot pressed at temperatures as low as 700°C for 1h.
Characterization of a radio frequency carbon nanotube growth plasma by ultraviolet absorption and optical emission spectroscopy
Authors: Cruden Brett A. , Meyyappan M.
Published: April 2005

Radio frequency driven methane/hydrogen plasmas for carbon nanotube growth at pressures between 0.5 and 20Torr, bias power from 0to110W, and inductive coil power from 0to200W are characterized via optical diagnostics. Ultraviolet absorption spectroscopy is used for quantitative determination of CH3 radical density for these systems, giving densities on the order of 1013cm−3, accounting for approximately 0.1% of the plasma neutral content. Emission data are also analyzed to extract neutral gas temperatures from the H2 spectrum and electron densities and temperatures and approximate atomic H densities in the system. Neutral temperature is estimated between 700 and 1100K, though the lower electrode is heated to 1273K. Electron temperature is estimated to be between 2.5 and 3.5eV in the high-energy (>12eV) portion of the electron energy distribution, and the data suggest an overall non-Maxwellian distribution of electrons. The dissociation of hydrogen is estimated at around 0.1%. Dependencies on power and pressure are explored, indicating more efficient ionization, dissociation, and electron heating at lower pressure and higher power. The absence of any dependency on coil power suggests the plasma is operating in a noninductive mode for these conditions.
Mechanism of the Smart Cut™ layer transfer in silicon by hydrogen and helium coimplantation in the medium dose range
Authors: Nguyen Phuong , Cayrefourcq I. , Bourdelle K. K. , Boussagol A. , Guiot E. , Ben Mohamed N. , Sousbie N. , Akatsu T.
Published: April 2005

We investigate the mechanism of the Si layer transfer in the Smart Cut™ technology for H and He coimplantation in the dose range of (2.5–5)×1016cm−2. Using infrared spectroscopy and cross-section transmission electron microscopy we study the microstructure of defects formed in Si in the as-implanted state. With H preimplant we observe significant enhancement of damage production as compared to the case where He is implanted first. At higher coimplant doses a buried nonuniform amorphouslike layer is formed. The structure of the layer resembles “swiss cheese” with highly damaged but still crystalline pockets embedded into amorphous material. The effect of coimplantation parameters on the thickness and crystal quality of transferred layer is discussed in the framework of a simple phenomenological model.
Effect of columnar structures on resistivity behavior of epitaxial La0.8MnO3 thin films
Authors: Wang C. C. , Wang H. , Zhu J.
Published: April 2005

We report here studies on the effect of columnar structure on the resistivity behavior of self-doped La0.8MnO3 thin film with single phase and c-axis epitaxy fabricated by pulsed laser deposition. The film exhibits an abnormal resistivity behavior similar to that found in lanthanum-deficient LaMnO3 thin films with mixed (110)∕(001) grains or polycrystalline pellets, where the resistivity peak remains almost the same temperature under external fields. This behavior is not expected based on the double exchange theory and is found to result from grain-boundary effect due to the columnar structure in this epitaxial film.
A joint experimental and numerical study of mechanisms associated to instability of partial cavitation on two-dimensional hydrofoil
Authors: Leroux Jean-Baptiste , Coutier-Delgosha Olivier , Astolfi Jacques André
Published: April 2005

The present work was carried out in the scope of a numerical-experimental collaborative research program, whose main objective is to understand the mechanisms of instabilities in partial cavitating flow. Experiments were conducted in the configuration of a rectangular foil located in a cavitation tunnel. Partial cavitation was investigated by multipoint wall-pressure measurements together with lift and drag measurements and numerical videos. The computations were conducted on two-dimensional hydrofoil section and are based on a single fluid model of cavitation: the liquid/vapor mixture is considered as a homogeneous fluid whose composition is regulated by a barotropic state law. The algorithm of resolution is derived from the SIMPLE approach, modified to take into account the high compressibility of the medium. Several physical features were pointed out by this joint approach. Particularly two distinct cavity self-oscillation dynamics characterized by two different frequencies (dynamics 1 and dynamics 2) were obtained experimentally and numerically at the angles of incidence of 6° and 8°. In both cases, the reentrant jet was found to be mainly responsible for the cavity breakdown. Dynamics 2 corresponds to the “classical” cavity breakdown and resulting cloud cavitation. A more complex flow pattern was evidenced for dynamics 1. In this case the growth/breakdown cycle of the cavity was observed at a lower Strouhal number (∼0.07∕0.09) than dynamics 2 (∼0.3). Moreover, the mechanism is composed of two successive steps: (i) an interaction between the reentrant jet and the cavity interface in the closure region leading to the periodic shedding of secondary cavitation clouds before the main cloud detachment occurs, and (ii) a shock wave induced by the collapse of the main cloud, which influences the growth of the residual cavity.
Influence of the a-SiGe:H thickness on the conduction mechanisms of n-amorphous-SiGe:H∕p-crystalline-Si heterojunction diodes
Authors: Rosales-Quintero P. , Torres-Jacome A. , Murphy-Arteaga R. , De la Hidalga Wade F. J. , Marsal L. F. , Cabré R. , Pallarès J.
Published: April 2005

We have fabricated, electrically characterized and simulated n-type hydrogenated amorphous silicon germanium alloys on p-type crystalline-silicon heterojunction diodes with three different a-SiGe:H layer thicknesses: 37, 86, and 200nm. The capacitance–voltage results confirm the existence of abrupt heterojunctions. The conduction and valence-band discontinuities of the heterojunctions and the electron affinity of the n-type a-SiGe:H films were obtained. The conduction mechanisms were determined by analyzing the temperature dependence of the current–voltage characteristics. The results show that at low forward bias (V<0.45V) the diodes with thinner amorphous layers (37 and 86nm) are dominated by recombination in the a-SiGe:H depletion region, whereas the thicker diode (200nm) is dominated by multistep tunneling through depletion region. In addition, at high forward bias (V>0.45V) the space-charge limited effect becomes the main transport mechanism in all the measured devices. The increase in the amorphous layer thickness also causes an increase in the leakage reverse current. Numerical simulations support the proposed transport mechanisms.
Magnetic reversal of double-layer patterned nanosquares
Authors: Zhang J. X. , Chen L. Q.
Published: April 2005

The magnetic reversal process of double-layer patterned nanosquares was studied by means of micromagnetic simulations. Different types of hysteresis loops were observed, depending on the thickness ratio of the two layers and the interlayer distance. Antiparallel state was induced by different mechanisms, either through the differential magnetostatic fields or through the differential coercitivies of the two layers. It is revealed that the interlayer magnetostatic interaction is the key factor that determines the reversal behavior. In this study, we constructed a diagram for the dependence of the types of hysteresis loops on thickness ratios and interlayer distances. The switching dynamics for the double-layer patterned nanosquares were also investigated.
Self-organized metal networks at ion-etched Cu∕Si and Ag∕Si interfaces
Authors: Stepanova M. , Dew S. K. , Karpuzov D. S.
Published: April 2005

We report self-organized metal nanopatterns on Si substrates produced by ion beam etching. We have deposited thin layers of metal such as Cu or Ag on Si substrates and then etched the deposited layers by a 1–5keV Ar+ ion beam at room temperature. At the stage when the metal-Si interface is reached, we have observed networks of metal clusters on the Si substrate with the characteristic size of 30–60nm for Cu and 100–200nm for Ag. The Cu patterns are sensitive to the ion energy. At 1keV energy, we observe a well-defined Cu network, whereas at 3–5keV energy, the Cu pattern becomes fuzzy without clear boundaries. To systematize and explain our results, we have suggested a kinetic model that combines ion etching and coarsening of the metal clusters on Si substrates. From our kinetic Monte Carlo simulations, we have found that the cooperative effect of coarsening and etching has a regime when the size of metal clusters can be approximated by the expression a(4D∕aR)1∕3, where D is the surface diffusivity of metal adatoms on the Si substrate, R is the etch rate, and a is the interatomic distance. Our synergistic model of coarsening and sputtering explains the observed difference in Cu and Ag cluster sizes and predicts the fuzzy Cu patterns at elevated ion energies.
Cavity resonators of metal-coated dielectric nanorods
Authors: Diao J. J. , Huang Shuogang , Reeves M. E.
Published: April 2005

Metallic nanoparticles bridge the length scale between atoms and crystals, exhibiting mesoscopic properties unique to their size. Thus, they have generated much interest for their potential applications as chemical or biological sensors and particularly as waveguides for light in nanoscale structures. [Y. W. C. Cao, R. C. Jin, and C. A. Mirkin, Science297, 1536 (2002); H. J. Lezec et al., Science297, 820 (2002); S. A. Maier, P. G. Kik, and H. A. Atwater, Appl. Phys. Lett.81, 1714 (2002); J. M. Oliva and S. K. Gray, Chem. Phys. Lett.379, 325 (2003)]. One important direction of research into the properties of individual metal nanoparticles involves the controlled variation of their geometry, which can yield new and tunable optical properties that simple spherical configurations do not possess. [T. S. Ahmadi, Z. L. Wang, T. C. Green, A. Henglein, and M. A. Ei-Sayed, Science272, 1924 (1996)]. A prime example of this is the core-shell nanostructure that has a central material surrounded by differing cladding layer.
Density functional calculations of molecular parity-violating effects within the zeroth-order regular approximation
Authors: Berger Robert , van Wüllen Christoph
Published: April 2005

A (quasirelativistic) two-component density functional theory (DFT) approach to the computation of parity-violating energy differences between enantiomers is presented which is based on the zeroth-order regular approximation (ZORA). This approach is employed herein to compute parity-violating energy differences between several P and M conformations of dihydrogen dichalcogenides (H2X2 with X=O, S, Se, Te, Po), of which some compounds have recently been suggested as potential molecular candidates for the first experimental measurement of parity-violating effects in chiral molecules. The DFT ZORA results obtained in this work with “pure” density functionals are anticipated to deviate by well less than 1% from data that would be computed within related (relativistic) four-component Dirac–Kohn–Sham–Coulomb schemes. In our implementation of the ZORA slightly larger relative deviations are expected for hybrid functionals, depending on the amount of “exact” exchange. For B3LYP (20% exact exchange) differences are estimated to amount to at most 3% in hydrogen peroxide, 2% in disulfane, and 1% or less for the heavier homologs. Thus, the present two-component approach is expected to perform excellently when compared to four-component density functional schemes while being at the same time computationally more efficient. The ZORA approach will therefore be of particular interest for the prediction of parity-violating vibrational frequency shifts, for instance, in isotopomers of H2Se2 and H2Te2.
Monoenergetic electron beam optimization in the bubble regime
Authors: Malka V. , Faure J. , Glinec Y. , Pukhov A. , Rousseau J.-P.
Published: April 2005

Within the last decade, laser-plasma based accelerators have been able to deliver electron beams with Maxwellian energy distributions characterized by effective temperatures in the range of 1–20MeV. Changing the interaction parameters, the electron beam quality was improved. Especially, matching the interaction length to the dephasing length was crucial to produce an extremely high quality electron beam with a quasimonoenergetic distribution at 170MeV. The optimization of these distributions is presented, as well as comparisons with three-dimensional particle-in-cell code simulations.
Resonant heating of a cluster plasma by intense laser light
Authors: Antonsen Thomas M. , Taguchi Toshihiro , Gupta Ayush , Palastro John , Milchberg Howard M.
Published: April 2005

Gases of atomic clusters are interaction media for laser pulse propagation with properties useful for applications such as extreme ultraviolet (EUV) and x-ray microscopy, harmonic generation, EUV lithography, and laser plasma acceleration. To understand cluster heating and expansion, a series of two- and three-dimensional electrostatic particle in cell simulations of the explosion of argon clusters of diameter in the range 20nm–53nm have been preformed. The studies show that heating is dominated by a nonlinear, resonant absorption process that gives rise to a size-dependent intensity threshold for strong absorption and that controls the dielectric properties of the cluster. Electrons are first accelerated out from the cluster and then driven back into it by the combined effects of the laser field and the electrostatic field produced by the laser-driven charge separation. Above the intensity threshold for strong heating there is a dramatic increase in the production of energetic particles and harmonic radiation. The dielectric properties of a gas of clusters are determined by the ensemble average cluster polarizability. Individual electrons contribute to the polarizability differently depending on whether they are in the core of the cluster or in the outer edge. Consequently, there can be large fluctuations in polarizability during the heating of a cluster.
Magnetohydrodynamics equilibria with toroidal and poloidal flow
Authors: Guazzotto L. , Betti R.
Published: April 2005

In the present work, the effects of flow on tokamak equilibria are investigated, focusing in particular on the effects of poloidal flows. It is shown that discountinuous transonic equilibria with a pedestal structure can be obtained for relatively low values of the poloidal velocity. Equilibria with poloidal flow of the order of the poloidal Alfvén speed are shown to develop inverted Shafranov shift. Since the rotation is damped by the neoclassical poloidal viscosity, a quasi-omnigenous solution for equilibria with large rotation is also derived in order to minimize the flow damping. In this solution, the magnetic field is construed to be a function of the poloidal magnetic flux Ψ up to a small correction by an appropriate choice of the flow profiles. All numerical results are obtained with the code FLOW [L. Guazzotto, R. Betti, J. Manickam, and S. Kaye, Phys. Plasmas 11, 604 (2004)].
Cauchy problems of the gauged sigma model
Authors: Huh Hyungjin
Published: April 2005

We study the gauged sigma model. In R1+1 the existence of the global smooth solution will be proved. Furthermore we show that the global weak solutions exist in Rn+1 (n=2,3).
Predissociation mechanism for the lowest Πu1 states of N2
Authors: Lewis B. R. , Gibson S. T. , Zhang W. , Lefebvre-Brion H. , Robbe J.-M.
Published: April 2005

Separate coupled-channel Schrödinger-equation (CSE) models of the interacting Πu1 (b,c,o) and Πu3 (C,C′) states of N2 are combined, through the inclusion of spin-orbit interactions, to produce a five-channel CSE model of the N2 predissociation. Comparison of the model calculations with an experimental database, consisting principally of detailed new measurements of the vibrational and isotopic dependence of the Πu1 linewidths and lifetimes, provides convincing evidence that the predissociation of the lowest Πu1 levels in N2 is primarily an indirect process, involving spin-orbit coupling between the bΠu1- and CΠu3-state levels, the latter levels themselves heavily predissociated electrostatically by the C′Πu3 continuum. The well-known large width of the b(v=3) level in N214 is caused by an accidental degeneracy with C(v=9). This CSE model provides the first quantitative explanation of the predissociation mechanism for the dipole-accessible Πu1 states of N2, and is thus likely to prove useful in the construction of realistic radiative-transfer and photochemical models for nitrogen-rich planetary atmospheres.
Quantitative determination of tensile stress creation during island coalescence using selective-area growth
Authors: Hearne S. J. , Seel S. C. , Floro J. A. , Dyck C. W. , Fan W. , Brueck S. R. J.
Published: April 2005

Island coalescence during Volmer–Weber thin film growth is generally accepted to be a source of tensile stress. However, the stochastic nature of unpatterned film nucleation and growth prevents meaningful comparison of stress measurements taken during growth to that predicted by theoretical models. We have overcome this by systematically controlling island geometry using selective growth of Ni films on patterned substrates via electrodeposition. It was determined that the measured power-law dependence of mean stress on island size agreed well with theory. However, our data clearly demonstrates that the majority of the tensile stress associated with coalescence actually occurred after the initial contact of neighboring islands as the film planarizes with additional deposition.
Thickness-dependent stress in plasma-deposited silicon dioxide films
Authors: Au V. , Charles C. , Bulla D. A. P. , Love J. D. , Boswell R. W.
Published: April 2005

Thick silicon dioxide (SiO2) films up to 5 μm have been deposited by helicon activated reactive evaporation (plasma assisted deposition with electron beam evaporation source) as both bilayer and trilayer structures, and the film stress was investigated in the context of optical waveguide fabrication. A model for stress in the SiO2–Si bilayer as a function of film thickness is formulated and interpreted in terms of Volmer–Weber film growth mechanisms. We find that island coalescence begins at a film thickness of less than 165 nm and continues until about 700 nm. Above approximately 1 μm thickness, the film continues growth as a continuous film. The stress in a deposited SiO2 film in an SiO2–Si–SiO2 trilayer structure was investigated by adapting the established Stoney’s equation for a trilayer system, and comparing it with a thermally grown SiO2 trilayer. A constant value of stress is obtained for the deposited SiO2 film for film thickness >1μm which was consistently less than both measured and previously reported values of stress in thermally grown SiO2.
Dam break with Coulomb friction: A model for granular slumping?
Authors: Kerswell R. R.
Published: April 2005

Axisymmetric and two-dimensional dam-break problems are solved under the shallow layer approximation and with basal Coulomb friction in a first attempt to model recent granular slumping experiments [G. Lube, H. E. Huppert, R. S. J. Sparks, and M. A. Hallworth, J. Fluid Mech. 508, 175 (2004); E. Lajeunesse, A. Mangeney-Castelnau, and J. P. Vilotte, Phys. Fluids 16, 2371 (2004); N. J. Balmforth and R. R. Kerswell, J. Fluid Mech. (in press)]. The axisymmetric model predicts a scaling law h0∕h∞∝a for the ratio of initial to final maximum heights which compares well with the slumping data over a wide range of a≔h0∕r0, the initial aspect ratio (h0 and r0 are the initial height and radius). The predicted runout scaling (r∞−r0)∕r0∝a, however, significantly overestimates the data runout which behaves more like a (r∞ being the maximum final radius). This situation may be improved by redefining the runout to take account of the finite granule size but a noticeable discrepancy still remains. The runout scaling prediction in the two-dimensional case mirrors the axisymmetric result, whereas in two dimensions h0∕h∞∝aα with α→23 as a→∞ and a≔h0∕l0 where l0 is the initial base length of the column. The limitations of the model and possible improvements are discussed.
Wilson polynomials and the Lorentz transformation properties of the parity operator
Authors: Bender Carl M. , Meisinger Peter N. , Wang Qinghai
Published: April 2005

The parity operator for a parity-symmetric quantum field theory transforms as an infinite sum of irreducible representations of the homogeneous Lorentz group. These representations are connected with Wilson polynomials.
Clean beams from laser wake-field accelerators via optical injection with a cleanup pulse
Authors: Cary John R. , Giacone R. E. , Nieter C. , Bruhwiler D. L.
Published: April 2005

Multiple colliding-pulse injection schemes have been proposed as means for trapping electrons in the ultrashort acceleration buckets of laser-generated wake fields. The primary goal of this paper is to present a parameter study to determine the beams that can be obtained through collisions of collinear laser pulses in uniform plasma. The parameter study is through fully self-consistent, two-dimensional, particle-in-cell simulations, as previous work used only test-particle computations. To remove the multiple beams that can commonly be generated in colliding pulse injection, we use a cleanup pulse, a trailing laser pulse that absorbs the wake. The wake then no longer exists in the region where the trailing beamlets would be, and so the trailing beamlets no longer form. A series of simulations predicts that with such one can obtain single, short (⩽10fs) beams with a bunch charge of order 10pC, normalized emittance of order 2πμm, and energy spread of the order of 10%. The parameters of the beams are insensitive to the amplitude of the backward pulse above normalized amplitudes of abw≈0.4.
Measurements of intense femtosecond laser pulse propagation in air
Authors: Ting A. , Alexeev I. , Gordon D. , Fischer R. , Kaganovich D. , Jones T. , Briscoe E. , Peñano J. , Hubbard R. , Sprangle P.
Published: April 2005

The nonlinear self-focusing of an intense femtosecond pulse propagating in air can be balanced by the plasma defocusing as the laser intensity is increased above the threshold for multiphoton ionization. The resultant laser∕plasma filament can extend many meters, suitable for many applications such as remote atmospheric breakdown, laser induced electrical discharge, and femtosecond laser material interactions. Direct (bore-sight) measurements of filament size and fluence over 4 m showed a preservation of the total energy in the filament during propagation. This indicates the energy lost in creating the central plasma column through multiphoton ionization was continuously being replenished from the surrounding radiation. Electrical measurement of the filament conductivity estimated the plasma density to be 1×1016cm−3 and electrical discharges triggered by a femtosecond laser filament were found to occur at substantially reduced breakdown fields.
Enhancement of nitrogen physisorption in coadsorption with oxygen on free, positively charged silver clusters
Authors: Schmidt M. , Masson A. , Bréchignac C.
Published: April 2005

The coadsorption of molecular nitrogen and oxygen on small cationic silver clusters in the gas phase is experimentally studied. The presence of oxygen enhances the adsorption probabilities of N2. This indicates a partial charge transfer out of the finite free electron reservoir of the small silver particles into the chemisorbed oxygen molecule.
Relations between coordinate and potential scaling in the high-density limit
Authors: Whittingham Takeyce K. , Burke Kieron
Published: April 2005

Exact relations are derived between scaling to the high-density limit of density functional theory and taking Z to infinity for nondegenerate atoms. Görling–Levy perturbation results are deduced for hydrogenic densities. The kinetic contribution to the correlation energy is also studied, and estimates given for its value for neutral atoms. Popular approximate functionals are tested against these benchmarks.
Spectrally- and time-resolved vibrational surface spectroscopy: Ultrafast hydrogen-bonding dynamics at D2O/CaF2 interface
Authors: Bordenyuk Andrey N. , Benderskii Alexander V.
Published: April 2005

Time- and frequency-domain three-wave mixing spectroscopy (IR+visible sum frequency generation) is developed as the lowest-order nonlinear technique that is both surface selective and capable of measuring spectral evolution of vibrational coherences. Using 70 fs infrared and 40 fs visible pulses, we observe ultrafast spectral dynamics of the OD stretch of D2O at the CaF2 surface. Spectral shifts indicative of the hydrogen-bond network rearrangement occur on the 100 fs time scale, within the observation time window determined by the vibrational dephasing. By tuning the IR pulse wavelength to the blue or red side of the OD-stretch transition, we selectively monitor the dynamics of different subensembles in the distribution of the H-bond structures. The blue-side excitation (weaker H-bonding structures) shows monotonic decay and ν(OD) frequency shift to the red on a 100 fs time scale, which is better described by a Gaussian than an exponential frequency correlation function. In contrast, the red-side excitation (stronger H-bonding structures) results in a blue spectral shift and a recursion in the signal at 125±10fs, indicating the presence of an underdamped intermolecular mode of interfacial water.
Direct-drive, cryogenic target implosions on OMEGA
Authors: Marshall F. J. , Craxton R. S. , Delettrez J. A. , Edgell D. H. , Elasky L. M. , Epstein R. , Glebov V. Yu. , Goncharov V. N. , Harding D. R. , Janezic R. , Keck R. L. , Kilkenny J. D. , Knauer J. P. , Loucks S. J. , Lund L. D. , McCrory R. L. , McKenty P. W. , Meyerhofer D. D. , Radha P. B. , Regan S. P. , Sangster T. C. , Seka W. , Smalyuk V. A. , Soures J. M. , Stoeckl C. , Skupsky S. , Frenje J. A. , Li C. K. , Petrasso R. D. , Séguin F. H.
Published: April 2005

Direct-drive spherical implosions of cryogenic, D2-filled capsules are performed on the 60-beam OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)]. The targets are energy scaled from the base line ignition design developed for the National Ignition Facility [W. J. Hogan et al., Nucl. Fusion 41, 567 (2001)]. Thin-walled (∼4μm), ∼860μm diam deuterated polymer shells are permeation filled with D2 gas and cooled to the triple point (∼18.7K). Cryogenic ice layers with a uniformity of ∼2μm rms are formed and maintained. The targets are imploded with high-contrast pulse shapes with full single-beam smoothing (1THz bandwidth, two-dimensional smoothing by spectral dispersion with polarization smoothing) to study the effects of the acceleration- and deceleration-phase Rayleigh–Taylor growth on target performance. Two-dimensional hydrocode simulations show good agreement with the experimental observations. Scattered-light and neutron-burn-history measurements are consistent with predicted absorption and hydrodynamic coupling calculations. Time-resolved and static x-ray images show the progress of the imploding shell, the shape, and temperature of the stagnating core. Particle-based instruments measure the fusion yield and rate, the ion temperature in the core, and the fuel areal density at the time of neutron production. These experiments have produced fuel areal densities of up to ∼100mg∕cm2, primary neutron yields of ∼4×1010, and secondary neutron yields of 1% to 2% of the primary yield. These results validate the hydrocode predictions for the direct-drive ignition-point design, giving increasing confidence in the direct-drive approach to inertial confinement fusion ignition.
Potential energy surface for the CCl4+H→CCl3+ClH reaction: Kinetics and dynamics study
Authors: Rangel C. , Espinosa-García J.
Published: April 2005

An analytical potential energy surface for the gas-phase CCl4+H→CCl3+ClH reaction was constructed with suitable functional forms to represent vibrational modes. This surface is completely symmetric with respect to the permutation of the four chlorine atoms and is calibrated with respect to experimental thermal rate constants available over the temperature range 297–904 K. On this surface, the thermal rate constants were calculated using variational transition-state theory with semiclassical transmission coefficients over a wider temperature range 300–2500 K, therefore obtaining kinetics information at higher temperatures than are experimentally available. This surface was also used to analyze dynamical features, such as tunneling and reaction-path curvature. In the first case, the influence of the tunneling factor is very small since a heavy chlorine atom has to pass through the barrier. In the second, it was found that vibrational excitation of the Cl–H stretching mode can be expected in the exit channel.
Doppler-free two-photon excitation spectroscopy and the Zeeman effects of the S1B1u1(v21=1)←SAg1(v=) band of naphthalene-d8
Authors: Okubo Mitsushi , Wang Jinguo , Baba Masaaki , Misono Masatoshi , Kasahara Shunji , Katô Hajime
Published: April 2005

Doppler-free two-photon excitation spectrum and the Zeeman effect of the S1B1u1(v21=1)←S0Ag1(v=0) transition of naphthalene-d8 have been measured. 908 lines of QQ(Ka)(J)KaKc transition of J=0–41, Ka=0–20 were assigned, and the molecular constants of the S1B1u1(v21=1) state were determined. Perturbations were observed, and those were identified as originating from Coriolis interaction. No perturbation originating from an interaction with a triplet state was observed. The Zeeman splittings for lines of a given J were observed to increase with Kc, and those of the Kc=J levels increased linearly with J. The Zeeman effects are shown to be originating from the magnetic moment of the S1B1u1 state, which is along the c axis and is induced by mixing of the S2B3u1 state to the S1B1u1 state by J-L coupling. Rotationally resolved levels were found not to be mixed with a triplet state from the Zeeman spectra. Accordingly, it is concluded that nonradiative decay of an isolated naphthalene excited to low rovibronic levels in the S1B1u1 state does not occur through the intersystem mixing. This is at variance with generally accepted understanding of the pathways of the nonradiative decay.
Electrical percolation characteristics of Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 thin films during the amorphous to crystalline phase transition
Authors: Kim Dae-Hwang , Merget Florian , Laurenzis Martin , Bolivar Peter Haring , Kurz Heinrich
Published: April 2005

Percolation effects are studied in phase change materials used for optical and electrical nonvolatile memory applications. Simultaneous measurements of the electrical resistivity and optical reflectivity allow experimental assessment of the percolation behavior associated with the mixed amorphous and crystalline phases in this class of chalcogenide materials. Dynamic analysis of the isothermal amorphous to crystalline phase transition in as-deposited amorphous Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 thin films are performed. A significantly earlier onset and saturation for the change of electrical resistivity in comparison to the optically measured phase transition is observed. This behavior reflects a significant influence of percolation on the electrical properties of this class of materials, leading to a nonlinear relationship between crystallization degree and electrical resistivity. This nonlinearity is associated with the formation of highly conducting crystalline paths in a lower conducting amorphous matrix. The influence of percolation on optical properties is found to be negligible. The experimental results are quantitatively compared to Wiener bounds and Bruggeman percolation models. Substantial differences in the crystallization behavior of Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 are observed: while heterogeneous nucleation induced by an interfacial layer resulting in layer-by-layer growth is observed for Ge2Sb2Te5, homogeneous nucleation and formation of prism shaped crystallites dominate in Sn doped Ge2Sb2Te5. The presented data represent the experimental analysis of percolation for the electrical resistivity in this class of materials, indicating the relevance of this effect for the adequate modeling and systematic optimization of future phase change random access memories and cognitive devices.
Solvation free energies of amino acid side chain analogs for common molecular mechanics water models
Authors: Shirts Michael R. , Pande Vijay S.
Published: April 2005

Quantitative free energy computation involves both using a model that is sufficiently faithful to the experimental system under study (accuracy) and establishing statistically meaningful measures of the uncertainties resulting from finite sampling (precision). In order to examine the accuracy of a range of common water models used for protein simulation for their solute∕solvent properties, we calculate the free energy of hydration of 15 amino acid side chain analogs derived from the OPLS-AA parameter set with the TIP3P, TIP4P, SPC, SPC∕E, TIP3P-MOD, and TIP4P-Ew water models. We achieve a high degree of statistical precision in our simulations, obtaining uncertainties for the free energy of hydration of 0.02–0.06kcal∕mol, equivalent to that obtained in experimental hydration free energy measurements of the same molecules. We find that TIP3P-MOD, a model designed to give improved free energy of hydration for methane, gives uniformly the closest match to experiment; we also find that the ability to accurately model pure water properties does not necessarily predict ability to predict solute∕solvent behavior. We also evaluate the free energies of a number of novel modifications of TIP3P designed as a proof of concept that it is possible to obtain much better solute∕solvent free energetic behavior without substantially negatively affecting pure water properties. We decrease the average error to zero while reducing the root mean square error below that of any of the published water models, with measured liquid water properties remaining almost constant with respect to our perturbations. This demonstrates there is still both room for improvement within current fixed-charge biomolecular force fields and significant parameter flexibility to make these improvements. Recent research in computational efficiency of free energy methods allows us to perform simulations on a local cluster that previously required large scale distributed computing, performing four times as much computational work in approximately a tenth of the computer time as a similar study a year ago.
Effect of emission velocity spread of secondary electrons in two-sided multipactor
Authors: Sazontov A. , Buyanova M. , Semenov V. , Rakova E. , Vdovicheva N. , Anderson D. , Lisak M. , Puech J. , Lapierre L.
Published: April 2005

Detailed numerical simulations of the two-sided multipactor have been carried out within a plane-parallel model. The main aim of the simulations is to clarify the uncertainty that still exists in the literature concerning the overlapping of multipactor zones. Three different codes (Monte Carlo, particle-in-cell, and statistical) were used to calculate the multipactor charts within a wide range of parameters such as spread of initial velocities of the secondary electrons and maximum value of the secondary emission yield. It was found that an increase in the spread of initial velocities results in overlapping of the multipactor zones, provided the secondary emission is high enough. In the opposite case, an increase in the spread of initial velocities leads to a suppression of the higher multipactor zones.
Dissipative processes and dust ion-acoustic shocks in a Q machine device
Authors: Popel S. I. , Losseva T. V. , Merlino R. L. , Andreev S. N. , Golub’ A. P.
Published: April 2005

A comparative analysis of the most important dissipative processes occurring during the excitation and propagation of dust ion-acoustic shocks in a Q machine device, among which are the charging of dust grains, the absorption of ions by grains, the transfer of the ion momentum to the grains, and Landau damping, is performed. The relative roles played by dissipative processes in different types of laboratory experiments with complex plasmas are estimated.
Control aspects of holonomic quantum computation
Authors: Lucarelli Dennis
Published: April 2005

A unifying framework for the control of quantum systems with non-Abelian holonomy is presented. It is shown that, from a control theoretic point of view, holonomic quantum computation can be treated as a control system evolving on a principal fiber bundle. An extension of methods developed for these classical systems may be applied to quantum holonomic systems to obtain insight into the control properties of such systems and to construct control algorithms for two established examples of the computing paradigm.
A new action photoelectron spectroscopy for anions
Authors: Wolf Israel , Ronen Shai , Giniger Rina , Cheshnovsky Ori
Published: April 2005

We present a new experimental approach, in which anion photodetachment spectroscopy is recorded with electrons of fixed kinetic energy. This approach circumvents some shortcomings of the zero electron kinetic energy method. Our method is based on a modified magnetic bottle photoelectron spectrometer (MBPES). A tunable laser is used to detach electrons from mass selected anions, drifting collinearly with the 40 cm MBPES drift tube. To avoid Doppler broadening, a low voltage pulse removes the velocity component of anions from the detached electrons. Spectra are recorded by collecting the wavelength dependence of electron-signal at a predetermined TOF window, corresponding to a specific electron-kinetic energy. We call this approach PEACE, denoting photoelectron action spectroscopy at constant kinetic energy. Our best resolution is 0.65 meV for 1.5 meV electrons. We present a PEACE spectrum of HgCl− together with the corresponding simulated theoretical spectrum. The method is similar in resolution and data collection rates to the slow electron velocity map imaging technique recently introduced by Neumark and co-workers.
General theory of acceptor-oxygen-vacancy complex single donor in high-dielectric-constant metallic oxide insulators
Authors: Lau W. S. , Han Taejoon
Published: April 2005

Previously, we showed experimentally that Si∕O-vacancy complex single donors and C∕O-vacancy complex single donors in tantalum oxide films have smaller ionization energies than the first ionization energy of O-vacancy double donors [W. S. Lau, L. L. Leong, T. Han, and N. P. Sandler, Appl. Phys. Lett. 83, 2835 (2003)]. In this letter, a theory based on a larger electron orbit for acceptor O-vacancy complex single donors compared to the O-vacancy double donors is proposed to explain the physics behind our previously reported experimental observation and why Si or C may cause an increase in leakage current in tantalum oxide films.
High-efficiency diffractive x-ray optics from sectioned multilayers
Authors: Kang H. C. , Stephenson G. B. , Liu C. , Conley R. , Macrander A. T. , Maser J. , Bajt S. , Chapman H. N.
Published: April 2005

We investigate the diffraction properties of sectioned multilayers in Laue (transmission) geometry, at hard x-ray energies (9.5 and 19.5keV). Two samples are studied, a W∕Si multilayer of 200×(29nm) periods, and a Mo∕Si multilayer of 2020×(7nm) periods, with cross-section depths ranging from 2to17μm. Reflectivities as high as 70% are observed. This exceeds the theoretical limit for standard zone plates operating in the multibeam regime, demonstrating that all of the intensity can be directed into a single diffraction order in small-period structures.
Imaging with short-wavelength surface plasmon polaritons
Authors: Zayats Anatoly V. , Elliott Jill , Smolyaninov Igor I. , Davis Christopher C.
Published: April 2005

Operation and imaging principles of optical microscope with in-plane image magnification by surface plasmon polaritons are discussed. The influence of realistic experimental geometry and losses in the metal are considered. Using two-dimensional optics of surface polaritons on metal–dielectric interface, subwavelength optical resolution can be achieved with long-wave-vector surface polaritons and applied in far-field optical microscopy and photolithography.
Dopant-segregation-controlled ZnO single-grain-boundary varistors
Authors: Sato Yukio , Yodogawa Masatada , Yamamoto Takahisa , Shibata Naoya , Ikuhara Yuichi
Published: April 2005

A ZnO single-grain-boundary varistor was designed using a bicrystal. Pr and Co dopant cosegregation at the boundary, key to obtain high varistic property, is optimized by controlling grain-boundary misorientation and, hence, grain-boundary atomic structure. Thus obtained single grain boundary exhibited sufficiently high varistic property. The present result opens up the possibility of single-grain-boundary varistors required for future nanoscale electronic devices.
Adjustable spin torque in magnetic tunnel junctions with two fixed layers
Authors: Fuchs G. D. , Krivorotov I. N. , Braganca P. M. , Emley N. C. , Garcia A. G. F. , Ralph D. C. , Buhrman R. A.
Published: April 2005

We have fabricated nanoscale magnetic tunnel junctions (MTJs) with an additional fixed magnetic layer added above the magnetic free layer of a standard MTJ structure. This acts as a second source of spin-polarized electrons that, depending on the relative alignment of the two fixed layers, either augments or diminishes the net spin torque exerted on the free layer. The compound structure allows a quantitative comparison of spin torque from tunneling electrons and from electrons passing through metallic spacer layers, as well as analysis of Joule self-heating effects. This has significance for current-switched magnetic random access memory, where spin torque is exploited and, for magnetic sensing, where it is detrimental.
Tuning and tailoring of broadband quantum-well infrared photodetector responsivity spectrum
Authors: Bandara S. V. , Gunapala S. D. , Liu J. K. , Rafol S. B. , Hill C. J. , Ting D. Z.-Y. , Mumolo J. M. , Trinh T. Q. , Fastenau J. M. , Liu A. W. K.
Published: April 2005

The spectral response of quantum-well infrared photodetectors (QWIPs) based on the III-V material system are tailorable to narrow or broad bandwidths within mid- and long-wavelength infrared bands. Typical broad-band QWIPs show considerable spectral shape change with bias voltage, particularly near the cut-off wavelength region. Two alternatives to the typical broadband QWIP design have been demonstrated. These designs consist of two multiquantum-well (QW) stacks or alternatively placed QWs and produce nearly fixed spectrums within the operating bias voltages. Flexibility in many design parameters of these detectors allows for tuning and tailoring the spectral shape according to application requirements, specifically for spectral imaging instruments.
Flexible top-emitting electroluminescent devices on polyethylene terephthalate substrates
Authors: Li Yanqing , Tan Li-Wei , Hao Xiao-Tao , Ong Kian Soo , Zhu Furong , Hung Liang-Sun
Published: April 2005

An aluminum-laminated polyethylene terephthalate (Al-PET) is used as the substrate for flexible organic light-emitting devices (OLEDs). The efficient flexible electroluminescent devices have a top-emitting OLED architecture. An acrylic layer is formed on the Al-PET surface to improve the surface morphology and also the adhesion between the substrate and the anode. Poly(styrene sulfonate)-doped poly(3,4-ethylene dioxythiophene) was used as hole transporting layer. The light-emitting polymer used is a phenyl-substituted poly(p-phenylenevinylene). Bilayer anodes of Ag∕CFX and Ag/indium-tin oxide and a semitransparent top cathode were used for the flexible polymer OLEDs. For a flexible polymer OLED with a 110-nm-thick light-emitting polymer, it exhibited superior electrical and optical characteristics with a luminous efficiency of 4.56cd∕A at an operating voltage of 7.5V.
Direct observation of a frozen junction in polymer light-emitting electrochemical cells
Authors: Dane Justin , Tracy Corey , Gao Jun
Published: April 2005

Doping propagation in polymer light-emitting electrochemical cells (LECs) has been studied based on the direct imaging of extremely large planar LECs at various temperatures and driving voltages. In situ electrochemical p doping, manifested as strong photoluminescence quenching in the polymer film, propagates at a nearly constant rate from anode toward cathode until it encounters an n-doped region to form a p-n junction. The propagation rate is found to be proportional to the applied bias at a fixed temperature. At a fixed bias, the propagation rate has a superexponential dependence on temperature. Below the glass transition temperature (Tg), the propagation rate becomes negligible, and a frozen junction has been confirmed by direct imaging of the doping profiles.
Fabrication and physical properties of Pb∕Cu multilayered superconducting nanowires
Authors: de Menten de Horne François , Piraux Luc , Michotte Sébastien
Published: April 2005

Using nanoporous media as templates for electrodeposition, we have fabricated multilayered Pb∕Cu nanowires 50nm in diameter and 20μm long with Cu layer thicknesses as low as 10nm. This was achieved by using a single-bath technique and a precise selection of the copper deposition potential to limit the redissolution of lead when the potential is raised to electrodeposit the more noble metal. Such superconductor∕normal multilayered nanowires show interesting magnetoresistance properties at a low magnetic field that may be related to the proximity effect, which can therefore be investigated in a quasi-one-dimensional geometry.
Fabrication of inverted opal ZnO photonic crystals by atomic layer deposition
Authors: Scharrer M. , Wu X. , Yamilov A. , Cao H. , Chang R. P. H.
Published: April 2005

We have fabricated three-dimensional optically active ZnO photonic crystals by infiltrating polystyrene opal templates using a low-temperature atomic layer deposition process. The polystyrene is removed by firing the samples at elevated temperatures, and reactive ion etching is used to remove the top layer of ZnO and expose the (111) photonic crystal surface. The resulting structures have high filling fractions, possess photonic band gaps in the near-UV to visible spectrum, and exhibit efficient photoluminescence.