bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of exchange field in CoFe∕IrMn by Os∕Cu buffer layer
Authors: Peng Tai-Yen , Chen San-Yuan , Lo C. K. , Yao Y. D.
Published: April 2007

Enhancement of exchange field (Hex) and thermal stability of the textured CoFe∕IrMn with Os∕Cu buffer layer and Os diffusion barrier layer were studied. As revealed by x-ray Diffraction (XRD), an Os (0002) surface mesh was observed to form on Cu (100)/Si (100). The growth of CoFe (111)/IrMn (111) on such a template is parallel to the Os (0002). With the Os∕Cu buffer layer, the CoFe∕IrMn presents an enhancement of 70Oe on Hex larger than that without Os∕Cu. The Hex of the textured sample was 230Oe at room temperature and it was increased to 330Oe after 250°C annealing. When the temperature reached 350°C, Hex vanished. The increment of the temperature at which the textured and the nontextured sample obtaining their maximum Hex and the vanishing temperature of Hex were 50 and 75°C, respectively. Furthermore, the CoFe∕Os (d)∕IrMn slowed down the Hex degradation. The sample with d=0.3nm obtained its maximum Hex at 250°C and vanished when it reached 400°C. The combination of CoFe∕IrMn with Os∕Cu buffer layer and Os barrier layer made the Hex higher and also better thermal stability.
One-megajoule, wetted-foam target-design performance for the National Ignition Facility
Authors: Collins T. J. B. , Marozas J. A. , Betti R. , Harding D. R. , McKenty P. W. , Radha P. B. , Skupsky S. , Goncharov V. N. , Knauer J. P. , McCrory R. L.
Published: April 2007

Wetted-foam, direct-drive target designs are a path to high-gain experiments on the National Ignition Facility (NIF) [J. Paisner et al., Laser Focus World 30, 75 (1994)]. Wetted-foam designs [S. Skupsky et al., in Inertial Fusion Sciences and Applications 2001, edited by K. Tanaka, D. D. Meyerhofer, and J. Meyer-ter-Vehn (Elsevier, Paris, 2002)] take advantage of the increased laser absorption provided by the higher-atomic-number elements in a target ablator composed of plastic foam saturated with deuterium-tritium (DT). The increased laser coupling allows more fuel to be driven with the same incident laser energy, resulting in increased hydrodynamic stability and target gain. A stability analysis of a 1-MJ design was performed using the two-dimensional hydrodynamic code DRACO [P. B. Radha et al., Phys. Plasmas 12, 032702 (2005)]. Simulations examining the effect of the expected levels of laser nonuniformities (single-beam and multiple-beam) and target nonuniformities (surface and ice roughness) have been performed. A nonuniformity-budget analysis has been constructed and suggests that two-dimensional (2D) smoothing by spectral dispersion (SSD) [S. Skupsky et al., J. Appl. Phys. 66, 3456 (1989)] is needed to reduce single-beam nonuniformities to levels sufficient for ignition to proceed. Two integrated 2D simulations with 0.75-μm initial ice roughness, multiple-beam nonuniformity, surface roughness, and imprint were completed, one with 2D SSD smoothing and one with 1D SSD. The former ignited and produced a gain of 32, while the latter failed to ignite. A third integrated 2D simulation with 1-μm initial ice roughness and an ice power-law spectral index of 1 was also completed and produced a gain of 27.
Probing multiferroicity and spin-spin interactions via angular dependent dielectric measurements on Y-doped HoMnO3 in high magnetic fields
Authors: Vasic R. , Zhou H. D. , Brooks J. S. , Wiebe C. R.
Published: April 2007

Dielectric measurements are used to characterize magnetic phase transitions in the doped ferroelectric oxides Ho1−xYxMnO3 (x=0.4). The focus of this experiment is on the effects of the magnetic field direction on the reentrant T-B-θ phase diagram below the Néel temperature. The Ho sublattice plays a major role in all magnetic phase transitions for Y doping (x=0.4), consistent with previous results (x=0,0.6,0.8). Two successive Mn spin rotations in the ab plane in the antiferromagnetic state are driven by the interaction with the Ho subsystem, although the Ho ordering peak in data is not pronounced. The dielectric response is a very sensitive probe for fine analysis of all aspects of spin-spin interactions in diluted Ho1−xYxMnO3. The magnetic field anisotropy study is an important step towards the understanding of magnetic and electric phase competition in the diluted 4f system by the nonmagnetic yttrium (Y) ion.
Coercivity enhancement of melt spun FePt ribbons by Au addition
Authors: Chang C. W. , Chang H. W. , Chiu C. H. , Chang W. C.
Published: April 2007

The effect of Au content on the magnetic properties and microstructure of melt spun (FePt)100−xAux (x=0–40) ribbons have been investigated. X-ray diffraction and thermal magnetic analysis results indicate that Au-rich phase coexists with ordered L10-FePt(Au) phase in ternary FePtAu ribbons after an isothermal annealing. Meanwhile, the Curie temperature of L10-FePt(Au) phase in annealed (FePt)100−xAux (x=0–40) ribbons is almost unchanged, revealing that higher volume fraction of Au addition does not modify the composition of the L10-FePt(Au) phase. All the Au containing ribbons exhibit a completely isolated L10-FePt(Au) granular structure, and the grain size is effectively decreased with the increase of Au content. As a result, the intrinsic coercivity (Hci) of the ribbons increases substantially from 2.1kOe for binary FePt to 19.5kOe for (FePt)60Au40.
Effects of Cu doping on the microstructure and magnetic properties of CoPt nanowires
Authors: Min Ji Hyun , An Boo Hyun , Cho Ji Ung , Ji Hye Min , Noh Su Jung , Kim Young Keun , Liu Hong Ling , Wu Jun Hua , Ko Young-Dong , Chung Jin-Seok
Published: April 2007

We studied the effects of copper doping on the microstructure and magnetic properties of CoPt nanowires fabricated in anodized aluminium oxide (AAO) nanotemplates by electrodeposition. The morphological observation indicates well-formed CoPt and CoPtCu nanowires, while the structural analysis shows that fcc-Co3Pt phase exists prior to annealing and is retained in the doped nanowires, with minor hcp-CoPt phase postannealing. The doping causes shrinkage of the lattice spacing prior to annealing due to the insertion of smaller copper atoms. Compared to the undoped CoPt nanowires, the magnetic measurements reveal significant enhancement in the magnetic properties of the CoPtCu nanowire postannealing, resulting in the more rapid increase in the coercivity with annealing temperature.
Magnetic behavior of mixture of magnetic ionic liquid [bmim]FeCl4 and water
Authors: Lee Sang Hyun , Ha Sung Ho , Ha Seung-Seok , Jin Hong-Beom , You Chun-Yeol , Koo Yoon-Mo
Published: April 2007

The magnetic response of the mixture of 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]FeCl4) and water was investigated. The [bmim]FeCl4 rich phase in the mixture forming two phases was easily separated under an external magnetic field. The homogeneous mixtures of [bmim]FeCl4 and water were also attracted to the direction of the magnetic field. Under a gradually varied magnetic field, the concentration of the mixture varied as a function of the magnetic field strength. We confirmed the possibility of a magnetic recovery system using the mixtures of [bmim]FeCl4 and water.
Electrical detection of spin currents: The spin-current induced Hall effect (invited)
Authors: Valenzuela S. O. , Tinkham M.
Published: April 2007

We demonstrate electrical detection of spin currents in metallic nanostructures. In a conductor with nonzero spin-orbit coupling, a spin current is predicted in a direction perpendicular to the applied electric field, giving rise to a spin Hall effect, where electrons with opposite spin orientations accumulate at opposite edges of the sample. Conversely, when a spin current is present, a charge imbalance is expected, following the Onsager reciprocal relations between spin and charge currents. We report direct electronic measurements of this effect in a lateral geometry by using a ferromagnetic electrode in combination with a tunnel barrier to inject a spin-polarized current in a paramagnetic conductor. We observe a laterally induced voltage in the latter that results from the conversion of the injected spin current into charge imbalance owing to the spin-orbit coupling. Such a voltage is proportional to the component of the injected spins that is perpendicular to the plane defined by the spin-current direction and the voltage probes. By using this technique in CoFe–Al2O3–Al devices, we determine the spin Hall conductivity of aluminum.
Fundamentals and applications of a plasma-processing system based on electron-beam ionization
Authors: Leonhardt D. , Walton S. G. , Fernsler R. F.
Published: April 2007

Plasmas generated from moderate energy (2–5keV) electron beams (e-beam) have unique, attractive characteristics that are ideal for materials processing applications. These plasmas possess low electron temperatures (<0.5eV), variable plasma densities (109–1012cm−3) with an improved control of plasma species generation, and perhaps most importantly, a direct scalability to processing areas exceeding one square meter. These characteristics are due to the plasma ionization being driven by the e-beam instead of an external electromagnetic field as used in conventional processing plasma sources. Theoretical and experimental system details are discussed in terms of plasma operating conditions applied to three different surface modification approaches: metal nitriding, negative ion etching, and polymer surface energy tailoring.
Field statistics and correlation functions for stochastically growing waves
Authors: Cairns Iver H. , Konkolewicz D. L. , Robinson P. A.
Published: April 2007

Bursty waves are common in laboratory and space plasmas. This paper simulates the generation of bursty waves using stochastic differential equations, calculating the field statistics and correlation functions with and without thermal effects, linear instability, nonlinear processes, intrinsic spatiotemporal inhomogeneities (clumps), and different sampling techniques. Driven thermal waves are shown to have field statistics that agree very well with an analytic prediction (typically power-law above a low field peak near the thermal level, but whose peak can be moved to high fields with appropriate fine tuning of parameters) and are robust against changes in sampling and inclusion of clumping effects. Purely stochastically growing waves, expected to have the log normal statistics observed in multiple applications, only do so under stringent conditions and inclusion of spatiotemporal clumping effects. These conditions have similar forms to ones derived previously using analytic arguments. Deviations from a log normal can be due to sampling and clumping effects, rather than due to the nonlinear and convolution effects inferred previously. Correlation functions are predicted and observed to have an exponential decrease at small lags, with time constant equal to the inverse effective growth rate, provided stochastic effects are relatively small and sufficient averaging is possible. Extraction of the wave, stochastic, and clump parameters from observed field statistics and correlation functions appears viable. An evolutionary transition must exist between driven thermal waves and stochastically driven waves, since their field statistics have different functional forms, dependencies, and sensitivity to clump effects, but still requires identification.
Quantum Monte Carlo study of first-row atoms using transcorrelated variational Monte Carlo trial functions
Authors: Prasad Rajendra , Umezawa Naoto , Domin Dominik , Salomon-Ferrer Romelia , Lester William A.
Published: April 2007

The effect of using the transcorrelated variational Monte Carlo (TC-VMC) approach to construct a trial function for fixed node diffusion Monte Carlo (DMC) energy calculations has been investigated for the first-row atoms, Li to Ne. The computed energies are compared with fixed node DMC energies obtained using trial functions constructed from Hartree-Fock and density functional levels of theory. Despite major VMC energy improvement with TC-VMC trial functions, no improvement in DMC energy was observed using these trial functions for the first-row atoms studied. The implications of these results on the nodes of the trial wave functions are discussed.
The influence of subgap features in the electromodulation and built-in voltage measurements of polyfluorene blue light-emitting diodes with anodic charge injection layers
Authors: Bodrozic Vladimir , Roberts M. , Phillips N. , Burroughes J. H. , Mian Shabbir , Cacialli Franco
Published: April 2007

We report on electroabsorption (EA) and built-in voltage (VBI) measurements of polymer light-emitting diodes with the general structure ITO/PEDOT:PSS/emitting polymer/LiF∕Ca∕Al where ITO is indium tin oxide, PEDOT:PSS is poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate), and the emitting polymer is either poly(9,9-dioctylfluorene), poly(9, 9-dioctyl-fluorene-alt-bis-N,N′-(4-butyl-phenyl)-bis-N,N′-phenyl-1, 4-phenylenediamine), or poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)-diphenylamine). We find that the EA nulling voltage, i.e., the dc bias at which the EA signal vanishes, depends on the frequency of the ac voltage and on the incident photon wavelength. Such dependence poses a problem for accurate measurement of the built-in voltage (VBI), which is the voltage generated between the electrodes upon equilibration of the Fermi levels through the heterostructure. We find that the EA signal is mixed with a smaller intensity signal which can be ascribed to excited state absorption (ESA). We propose a method for separating the excited state absorption signal and producing accurate VBI measurements. We also demonstrate that in our devices the ESA contribution to the electromodulated (ΔT∕T) signal is negligible with respect to the accuracy with which VBI can be determined from the nulling voltage of ΔT∕T and can thus be safely ignored.
Nonlinear dc electric-field dependence of the dielectric permittivity and cluster polarization of Sr1−xMnxTiO3 ceramics
Authors: Tkach Alexander , Vilarinho Paula M. , Kholkin Andrei L.
Published: April 2007

The dc electric-field dependence of the dielectric constant ε′(E) in Sr1−xMnxTiO3 (x=0.005−0.02) ceramics is studied in the temperature range from 10 to 125 K, i.e., around the ε′(T) peak temperature Tmax. Results are analyzed using equations derived analytically from the implicit equations of the Landau-Ginzburg-Devonshire (LGD) theory. Corrections due to cluster contribution attributed to the reorientation of random-field-induced polar nanometer-scale regions turn out to be important, if not decisive, for a reliable description of ε′(E). So, it is found that a combined equation including the Langevin-type cluster term, i.e., εL′(E)=P02L3∕(2kBTε0[cosh(P0L3E∕2kBT)]2) is the most suited to describe the dc electric-field dependence of the dielectric constant around Tmax. Based on the fitting of the ε′(E) data, the cluster polarization P0 reaches values as high as ∼0.4 μC∕cm2 with the cluster size L of 11±4.5 nm. Thus, the existence in the Sr1−xMnxTiO3 system of polar clusters with nanometer-scale size is consistent with ε′(E) data and their contribution to the permittivity at E=0 and temperatures close to Tm is estimated to be up to 30%. In addition, besides inducing the peak in ε(T), the formation of polar nanoregions is beneficial to the high relative electric-field tunability of the dielectric constant nr=[ε′(0)−ε′(E)]∕ε′(0)∼70% as well as high communication quality factor K=[ε′(0)∕ε′(E)−1]2∕[ε′(0)∕ε′(E)tan δ(0)tan δ(E)]∼10 000 under 20 kV∕cm at 10 kHz.
Surface kinetics and thermal instability of N-face InN grown by plasma-assisted molecular beam epitaxy
Authors: Koblmüller G. , Gallinat C. S. , Speck J. S.
Published: April 2007

The role of thermal instability and In surface coverages on the growth kinetics has been investigated for N-face InN films grown by plasma-assisted molecular beam epitaxy. Film thickness analysis using scanning electron microscopy combined with In desorption measurements by quadrupole mass spectrometry demonstrated significant thermal decomposition starting at ∼560°C and inhibiting growth completely beyond ∼635°C. Within this temperature region two decomposition pathways were identified: a low-temperature regime characterized by In droplet accumulation and a high-temperature regime with direct desorption from bulk InN. A growth diagram has been constructed, exhibiting three characteristic growth structures for different In∕N flux ratios and growth temperatures: a dry no-adlayer terminated surface under N-rich conditions, an In adlayer terminated surface, and a surface, consisting of an In adlayer and droplets under In-rich conditions. Smooth step-flow growth terraces were observed in films grown under In-rich and surprisingly also under N-rich conditions at temperatures of thermal decomposition. Such high adatom diffusivity resulted from the autosurfactant action of the In adlayer, with a saturated coverage of 1 ML as determined from the reflection high energy electron diffraction patterns during the consumption of adsorbed In by active nitrogen.
Extension of compressible ideal-gas rapid distortion theory to general mean velocity gradients
Authors: Yu Huidan , Girimaji Sharath S.
Published: April 2007

The homogeneity condition in compressible flows requires that mean velocity gradient and mean thermodynamic variables must be spatially invariant. This has restricted the use of rapid distortion theory (RDT) for compressible flows to a small set of mean-velocity gradients. By introducing an appropriate body force, we show that the homogeneity condition can be satisfied for a large class of compressible turbulence. We proceed to derive RDT spectral covariance equations of all relevant moments and recover the limiting behavior at vanishing and infinite (pressure-release) Mach numbers for homogeneous shear, plain-strain, axisymmetric expansion, and contraction cases.
Analysis of the electron and ion fluxes to the wall of a hot-filament discharge device
Authors: Wang Xu , Knappmiller Scott , Robertson Scott , Sternovsky Zoltan
Published: April 2007

The current densities of ions and electrons to the wall of a hot-filament discharge device are examined both experimentally and theoretically. The ion current to the wall as a function of neutral gas pressure is found theoretically from a model of the sheath and presheath that includes charge-exchange collisions of the ions with neutrals. The electron current is found from a model based upon the energy distributions of secondary electrons from ionization of the neutral gas and of secondary electrons from the wall. In a hot-filament discharge device with argon plasma (density (0.2–4.5)×109cm−3, electron temperature 0.14–0.21eV, and pressure 0.3–12mTorr), a gridded energy analyzer is placed behind a slit in the wall and the current collected is recorded as a function of the retarding potential. The dependence of the collector current on the grid bias potential identifies the electrons in the 10–65eV range as being mostly secondaries from ionization and those in the 0–10eV range as being mostly secondaries from the wall. Ions are collected at the most negative grid bias voltages. The measured ion currents are within about 40% of values calculated from a model with charge exchange collisions of ions, and at the highest pressure differ by about a factor of 3 from the collisionless value, indicating that the Bohm ion current should be corrected for collisions when the charge exchange mean free path is less than about 0.2 of the plasma radius.
Influence of redeposition on the plasma etching dynamics
Authors: Stafford L. , Margot J. , Delprat S. , Chaker M. , Pearton S. J.
Published: April 2007

This work reports on measurements of the degree of redeposition of sputtered species during the etching of platinum (Pt), barium-strontium-titanate (BST), strontium-bismuth-tantalate (SBT), and photoresist (PR) in a high-density argon plasma. While PR exhibits a redeposition-free behavior, the degree of redeposition of Pt, BST, and SBT species increases from 10% to 95% as the argon pressure increases from 0.5to10mTorr. These results are in good agreement with the predictions of a simple model accounting for the backscattering of sputtered species following their interaction with the gas phase. Based on these results and using other experimental data reported in the literature, it is further demonstrated that, depending on the plasma etching conditions, redeposition effects can induce misinterpretation of the etch rate data.
Mechanisms of GaAsN growth: Surface and step-edge diffusion
Authors: Reason M. , Rudawski N. G. , McKay H. A. , Weng X. , Ye W. , Goldman R. S.
Published: April 2007

We have investigated the mechanisms of GaAs1−xNx film growth by plasma-assisted molecular-beam epitaxy. A comparison of in situ reflection high-energy electron diffraction and scanning tunneling microscopy (STM), with ex situ atomic force microscopy, reveals a temperature-dependent interplay between surface and step-edge diffusion. At low temperatures, layer-by-layer growth is observed, presumably due to limited adatom surface mobility. As the temperature increases, the interplay between surface and step-edge diffusion leads to multilayer growth. For sufficiently high temperatures, adatoms overcome the step-edge diffusion barrier, resulting in layer-by-layer growth once again. The temperature range for multilayer growth is influenced by the Ga flux and may be narrowed by using As2. Using in situ STM, we quantified the activation energies for Ga surface diffusion, Ed, and step-edge diffusion, Ee, during layer-by-layer GaAsN growth. We estimate Ed=0.75 and 0.96 eV for growth using As4 and As2, respectively. Thus, the narrowing of the multilayer growth temperature range is likely due to the decrease in Ga surface diffusion length through the use of As2 in lieu of As4. Furthermore, we estimate Ee=80 meV, larger than what has been reported for GaAs growth.
Direct experimental verification of the sound-induced tunable resonance on a flexible electrorheological layer
Authors: Tang Hong , Lee Seung-Yop
Published: April 2007

The tunable behaviors of low-frequency sound waves transmitted through a flexible electrorheological (ER) layer with plastic-aluminum electrodes are investigated. It shows that, within 80–210 Hz, the sound-pressure level (SPL) decreases with the electric field E, while within 210–300 Hz, the SPL increases with E. The vibration displacement of the ER layer surface is directly measured via a laser Doppler vibrometer. It reveals that two resonance modes exist on the ER layer and all the modes are tunable via the electric field. Around the first resonant frequency of 100 Hz, the vibration displacement decreases with the increase of E, while around the second resonant frequency of about 180 Hz, the vibration displacement increases with E. The consistently varying characteristics with respect to the electric field imply an intrinsic relation between the vibration of the ER layer and the sound transmission. The relation is further qualitatively explained by the vibration-radiation model. The tunable resonance effect in the ER layer would be useful in constructing tunable phononic crystals and other acoustic devices.
Maintenance of a stable current profile in a reversed field pinch
Authors: Boozer Allen H.
Published: April 2007

Externally produced magnetic fields could be used to maintain the reversed field pinch (RFP) plasma confinement configuration in a stable current, j‖∕B, profile. This would be accomplished by the creation of stochastic magnetic field regions in the vicinity of rational surfaces on which the safety factor q is the reciprocal of an integer N. External coils simultaneously excite the poloidal mode number unity and toroidal mode number N and N−1 helical fields from N=Nmax on down in a peristaltic manner, where Nmax is given by the maximal value of q in the RFP plasma. The time scale for turning off and on the N and N−1 pairs of coils is given by τw≡(μo∕η)w2, where w=a∕2Nmax is a typical island half-width required for island overlap, which implies local magnetic stochasticity, and a is the minor radius of the plasma. The total time scale for a complete current spreading cycle is Nmaxτw=(μ0∕η)a2∕4Nmax, which is a factor of Nmax≈10 faster than the time scale for the overall relaxation of the j‖∕B profile.
Minimum free energy pathways and free energy profiles for conformational transitions based on atomistic molecular dynamics simulations
Authors: van der Vaart Arjan , Karplus Martin
Published: April 2007

An efficient method for the calculation of minimum free energy pathways and free energy profiles for conformational transitions is presented. Short restricted perturbation-targeted molecular dynamics trajectories are used to generate an approximate free energy surface. Approximate reaction pathways for the conformational change are constructed from one-dimensional line segments on this surface using a Monte Carlo optimization. Accurate free energy profiles are then determined along the pathways by means of one-dimensional adaptive umbrella sampling simulations. The method is illustrated by its application to the alanine “dipeptide.” Due to the low computational cost and memory demands, the method is expected to be useful for the treatment of large biomolecular systems.
Spontaneous breaking of classical PT symmetry
Authors: Bender Carl M. , Darg Daniel W.
Published: April 2007

The classical trajectories of the family of complex PT-symmetric Hamiltonians H=p2+x2(ix)ϵ (ϵ⩾0) form closed orbits. All such complex orbits that have been studied in the past are PT symmetric (left-right symmetric). The periods of these orbits exhibit an unusual dependence on the parameter ϵ. There are regions in ϵ of smooth behavior interspersed with regions of rapid variation. It is demonstrated that the onset of rapid variation is associated with strange new kinds of classical trajectories that have never been seen previously. These rare kinds of trajectories are not PT symmetric and occur only for special rational values of ϵ.
On the glass temperature under extreme pressures
Authors: Drozd-Rzoska A. , Rzoska S. J. , Paluch M. , Imre A. R. , Roland C. M.
Published: April 2007

The application of a modified Simon-Glatzel-type relation [Z. Anorg. Allg. Chem. 178, 309 (1929)] for the pressure evolution of the glass temperature is presented, namely, Tg(P)=Tg0[1+ΔP∕(π+Pg0)]1∕bexp[−(ΔP∕c)], where (Tg0,Pg0) are the reference temperature and pressure, ΔP=P−Pg0, −π is the negative pressure asymptote, b is the power exponent, and c is the damping pressure coefficient. The discussion is based on the experimental Tg(P) data for magmatic silicate melt albite, polymeric liquid crystal P8, and glycerol. The latter data are taken from Cook et al. [J. Chem. Phys. 100, 5178 (1994)] and from the authors’ dielectric relaxation time (τ(P)) measurements, which employs the novel pressure counterpart of the Vogel-Fulcher-Tammann equation: τ(P)=τ0Pexp[DPΔP∕(P0−P)], where ΔP=P−PSL (PSL is the stability limit hidden under negative pressure), P0 is the estimation of the ideal glass pressure, and DP is the isothermal fragility strength coefficient. Results obtained suggest the hypothetical maximum of the Tg(P) curve, which can be estimated due to the application of the supporting derivative-based analysis. A hypothetical common description of glass formers characterized by dTg∕dP>0 and dTg∕dP<0 coefficients is suggested. Finally, the hypothetical link between molecular and colloidal glass formers is recalled.
Spectroscopic study of high energy excited deuterium atoms in a hollow cathode glow discharge
Authors: Majstorović G. Lj. , Šišović N. M. , Konjević N.
Published: April 2007

The presented results are concerned with the shape of the Balmer alpha line emitted from a low pressure dc glow discharge with stainless steel (SS) and titanium (Ti) hollow cathode (HC) with D2 or Ar∕D2∕H2 gas mixture. The analysis indicates that the line profile represents a convolution of three Gaussian profiles resulting from different collision excitation processes. The average energy of excited deuterium atoms determined from the width of the broadest Gaussian is about 86eV in both HCs. In Ar∕D2∕H2 gas mixtures, the energies are in the range from 33eVto47eV, but with much larger contribution of this Gaussian to the Balmer alpha profile. In discharges with hydrogen isotopes, the energy derived from the medium-width Gaussian is in the range from 4eVto6eV, while in gas mixtures it is between 1eV and 2eV. The width of the narrowest Gaussian slightly exceeds the instrumental broadening and it is always below 0.5eV.
Dielectric relaxation behavior of colloidal suspensions of palladium nanoparticle chains dispersed in PVP/EG solution
Authors: Chen Zhen , Zhao Kong-Shuang , Guo Lin , Feng Cai-Hong
Published: April 2007

Dielectric measurements were carried out on colloidal suspensions of palladium nanoparticle chains dispersed in poly(vinyl pyrrolidone)/ethylene glycol (PVP/EG) solution with different particle volume fractions, and dielectric relaxation with relaxation time distribution and small relaxation amplitude was observed in the frequency range from 105to107Hz. By means of the method based on logarithmic derivative of the dielectric constant and a numerical Kramers-Kronig transform method, two dielectric relaxations were confirmed and dielectric parameters were determined from the dielectric spectra. The dielectric parameters showed a strong dependence on the volume fraction of palladium nanoparticle chain. Through analyzing limiting conductivity at low frequency, the authors found the conductance percolation phenomenon of the suspensions, and the threshold volume fraction is about 0.18. It was concluded from analyzing the dielectric parameters that the high frequency dielectric relaxation results from interfacial polarization and the low frequency dielectric relaxation is a consequence of counterion polarization. They also found that the dispersion state of the palladium nanoparticle chain in PVP/EG solution is dependent on the particle volume fraction, and this may shed some light on a better application of this kind of materials.
Ab initiolifetimes in the interatomic Coulombic decay of neon clusters computed with propagators
Authors: Vaval Nayana , Cederbaum Lorenz S.
Published: April 2007

Interatomic Coulombic decay (ICD) is a radiationless decay mechanism occurring via electron emission in an inner-valence ionized weakly bound cluster. The ICD has been studied for the neon clusters Nen (n=2,…,5). The decay widths of the neon clusters are calculated using ab initio Green’s function method. The non-Dyson version of Green’s function is employed. This propagator is analytically continued into the complex energy plane with the aid of a complex absorbing potential, and the decaying states are found as resonance states in this plane.
Active-space symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster methods for high accuracy calculations of potential energy surfaces of radicals
Authors: Ohtsuka Yuhki , Piecuch Piotr , Gour Jeffrey R. , Ehara Masahiro , Nakatsuji Hiroshi
Published: April 2007

The electron-attached (EA) and ionized (IP) symmetry-adapted-cluster configuration-interaction (SAC-CI) methods and their equation-of-motion coupled-cluster (EOMCC) analogs provide an elegant framework for studying open-shell systems. As shown in this study, these schemes require the presence of higher-order excitations, such as the four-particle-three-hole (4p-3h) or four-hole–three-particle (4h-3p) terms, in the electron attaching or ionizing operator R in order to produce accurate ground- and excited-state potential energy surfaces of radicals along bond breaking coordinates. The full inclusion of the 4p-3h∕4h-3p excitations in the EA/IP SAC-CI and EOMCC methods leads to schemes which are far too expensive for calculations involving larger radicals and realistic basis sets. In order to reduce the large costs of such schemes without sacrificing accuracy, the active-space EA/IP EOMCC methodology [J. R. Gour et al., J. Chem. Phys. 123, 134113 (2005)] is extended to the EA/IP SAC-CI approaches with 4p-3h∕4h-3p excitations. The resulting methods, which use a physically motivated set of active orbitals to pick out the most important 3p-2h∕3h-2p and 4p-3h∕4h-3p excitations, represent practical computational approaches for high-accuracy calculations of potential energy surfaces of radicals. To illustrate the potential offered by the active-space EA/IP SAC-CI approaches with up to 4p-3h∕4h-3p excitations, the results of benchmark calculations for the potential energy surfaces of the low-lying doublet states of CH and OH are presented and compared with other SAC-CI and EOMCC methods, and full CI results.
Experiments with proteins at low temperature: What do we learn on properties in their functional state?
Authors: Ponkratov V. V. , Wiedersich J. , Friedrich J. , Vanderkooi J. M.
Published: April 2007

The authors compared the spectral response of Zn-substituted horseradish peroxidase in a glycerol/water solvent to hydrostatic pressure at 2K and ambient temperature. The low temperature experiments clearly demonstrate the presence of at least three different conformations with drastically different elastic properties. However, the main conformation, which determines the fluorescence spectrum at ambient temperature, did not show any significant difference between low and high temperature and pressure. The authors conclude that the local compressibility of the heme pocket of the protein depends only very weakly on temperature.
Electron and positron scattering from 1,1-C2H2F2
Authors: Makochekanwa C. , Kato H. , Hoshino M. , Bettega M. H. F. , Lima M. A. P. , Sueoka O. , Tanaka H.
Published: April 2007

1,1-difluoroethylene (1,1-C2H2F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4–1000eV electron and 0.2–1000eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3–49eV and scattering angles 90° and 120° for the two loss energies 0.115 and 0.381eV corresponding to the dominant C–H (ν2 and ν9) stretching and the combined C–F (ν3) stretching and CH2 (ν11) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5to50eV in the static-exchange approximation and from 0.5to20eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B2, B1, and A1 symmetries, respectively. The π* resonance peak at 1.8eV in C2H4 is observed shifted to 2.3eV in 1,1-C2H2F2 and to 2.5eV in C2F4; a phenomenon attributed to the decreasing CC bond length from C2H4 to C2F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1eV, and other less pronounced ones centered at about 5 and 20eV.
Electronic properties of a 3C∕4H SiC polytype heterojunction formed on the Si face
Authors: Chandrashekhar M. V. S. , Thomas Christopher I. , Lu Jie , Spencer M. G.
Published: April 2007

The authors report on the electronic properties of a rectifying Si face 3C∕4H SiC heteropolytype junction on n+ 4H SiC. Capacitance-voltage profiling of the junction at temperatures from 4–300K showed high apparent carrier concentration. A semiclassical model was used to explain the behavior. The model predicted a spontaneous polarization-induced valence band quantum well in the 3C, indicating a polarization charge of 9.7×1012cm−2 for 4H SiC, in good agreement with theory. The formation of a two-dimensional hole gas was predicted. Using a Poisson-Schrödinger solver to analyze the measurements, it was found that large (∼3.5×1012cm−2) mobile hole charge was induced in the n-doped 3C SiC.
Subpicosecond time-resolved Raman studies of electron–longitudinal optical phonon interactions in InN
Authors: Tsen K. T. , Kiang Juliann G. , Ferry D. K. , Lu Hai , Schaff William J. , Lin Hon-Way , Gwo Shangjr
Published: April 2007

Electron–longitudinal optical phonon scattering rate in InN has been directly measured by subpicosecond time-resolved Raman spectroscopy. The experimental results show that for a thick layer of InN grown on GaN, the average total electron–longitudinal optical phonon scattering rate is (5.1±1.0)×1013s−1. This enormous electron–longitudinal optical phonon scattering rate, which is comparable to that observed in GaN, has been attributed to the extremely polar nature of InN.
Organic light-emitting devices integrated with solar cells: High contrast and energy recycling
Authors: Yang Chih-Jen , Cho Ting-Yi , Lin Chun-Liang , Wu Chung-Chih
Published: April 2007

In this letter, the authors report that by integrating organic light-emitting devices (OLEDs) with solar cells, luminous ambient-light reflection as low as 1.4% (even superior to that achieved with polarizers) can be achieved without compromising the electroluminescence efficiency for high-contrast display applications. Furthermore, in such a configuration, the photon energies of the incident ambient light and the portion of OLED emission not getting outside of the device can be recycled into useful electrical power via the photovoltaic action, instead of being totally wasted as in other reported contrast-enhancement techniques. These features, the authors believe, shall make this technique attractive for high-contrast display applications and portable/mobile electronics that are highly power aware.
Enhancement of ferromagnetic properties in BiFeO3 polycrystalline ceramic by La doping
Authors: Lin Yuan-Hua , Jiang Qinghui , Wang Yao , Nan Ce-Wen , Chen Lin , Yu Jian
Published: April 2007

The authors present the structure transformation and magnetic properties of Bi1−xLaxFeO3 (x=0.0–0.15) ceramics prepared by a conventional solid-state reaction processing. Magnetic measurements reveal that remnant magnetization of 15% La-doped BiFeO3 has enhanced about 20 times as compared to pure BiFeO3. It is the structural phase transition (R3c–C222) near x=0.15 that destructs the spin cycloid, and thus enhances the ferromagnetic properties significantly. In these Bi1−xLaxFeO3 ceramic samples, besides the known antiferromagnetic Néel temperature TN1∼615K, another Néel temperature TN2∼260K can be observed due to the trace impurity phase of Bi2Fe4O9 in these ceramic samples.
Asymmetrical twin cantilevers for single molecule detection
Authors: Qazi A. , Nonis D. , Pozzato A. , Tormen M. , Lazzarino M. , Carrato S. , Scoles G.
Published: April 2007

Recently, there has been growing interest in sensors based on frequency shift detection of mechanical resonators, that has led to extremely sensitive diagnostic methods for medicine and biology. Here the authors propose and demonstrate a strategy capable of detecting the presence of a few macromolecules, which uses an asymmetrical cantilever structure of several microns in size, operated at room temperature, and under ordinary vacuum conditions. The idea is to detect the presence of one or more molecules by detecting the mechanical cross-talk induced by the molecular link between a short cantilever and an array of longer cantilevers facing the short one.
Direct evidence of linewidth effect: Ni31Si12 and Ni3Si formation on 25nm Ni fully silicided gates
Authors: Kittl J. A. , Lauwers A. , Demeurisse C. , Vrancken C. , Kubicek S. , Absil P. , Biesemans S.
Published: April 2007

The Ni silicidation of polycrystalline-Si∕SiO2 gates with 25nm linewidth was studied by x-ray diffraction and compared to that of blanket films. The authors found direct evidence of a linewidth effect in Ni full silicidation (FUSI), with formation of Ni-richer silicides at short gate lengths, and attribute it to the excess availability of Ni from regions surrounding the gate. On blanket films, the end silicide phase can be controlled by the deposited Ni (tNi) and polycrystalline-Si (tSi) thicknesses (e.g., tNi∕tSi∼0.55, 1.09, 1.37, and 1.64 for stoichiometric NiSi, Ni2Si, Ni31Si12, and Ni3Si, respectively). In contrast, they demonstrate that on 25nm lines, the resulting films can contain Ni31Si12 and Ni3Si even for deposited tNi∕tSi as low as 0.6. They found, however, that the phase formation sequence and required thermal budgets were similar on 25nm lines (tNi∕tSi∼0.6 and 1.2) to those on blanket films with thicker Ni (tNi∕tSi∼1.7). This suggests that the nucleation and phase formation kinetics of Ni silicides, including Ni31Si12 and Ni3Si, are not significantly affected by the small dimensions. They also demonstrated NiSi FUSI phase control down to 25nm, by controlling the reacted Ni to Si ratio through the reaction thermal budget. These results indicate that Ni FUSI is an attractive option for future nodes.
Reduction of threading dislocation density in GaN grown on strain relaxed nanoporous GaN template
Authors: Hartono H. , Soh C. B. , Chow S. Y. , Chua S. J. , Fitzgerald E. A.
Published: April 2007

Growth of gallium nitride (GaN) on strain relaxed nanoporous GaN template by metal-organic chemical vapor deposition has produced GaN layer with 60% reduction in threading dislocation density (TDD). The porous GaN was annealed at 850°C for 3min in a mixed of nitrogen and ammonia ambient, which annihilated most TDs within the porous region via air-gap formation coupled with surface edge step pinning of dislocations. Enhancement of optical quality was indicated by doubled Raman intensity of E2 phonon peak of annealed porous as compared to as-fabricated porous GaN. Besides, a redshift of 0.7cm−1 in E2 phonon peak of porous GaN with respect to as-grown GaN corresponds to a relaxation of compressive stress by 0.17±0.05GPa. Further overgrowth of GaN on annealed porous GaN template gives high quality GaN with reduction in TDD.
Synthesis and properties of single-crystal β3-Ni3Si nanowires
Authors: Song Yipu , Jin Song
Published: April 2007

Single-crystal Ni3Si nanowires were synthesized by a chemical vapor transport method, using iodine as the transport reagent. Structural characterization using powder x-ray diffraction, electron microscopy, and energy dispersive spectroscopy confirms that the nanowires are the monoclinic β3-Ni3Si phase. Four-terminal electrical measurements show that the single-crystal nanowires have a resistivity of 72μΩcm and are capable of supporting a high failure current density about 1.7×107A∕cm2. These unique Ni3Si nanowires are attractive nanoscale building blocks for interconnects and for fully silicided gate application in nanoelectronics.
Butt-end fiber coupling to a surface-emitting Γ-point photonic crystal band edge laser
Authors: Park Yeonsang , Kim Sunghwan , Moon Chaeyoung , Jeon Heonsu , Kim Hyo Jin
Published: April 2007

The authors demonstrate a compact and efficient fiber coupling scheme for a surface-emitting photonic crystal laser by using a cleaved fiber tip connected to a wavelength-division-multiplexing 1×2 fiber coupler. Simultaneous optical excitation and laser light collection are achieved for a 1.55μm InGaAsP graphite-lattice Γ-point band edge laser. On comparing with the conventional microphotoluminescence setup based on an objective lens, their direct butt coupling setup is much simpler and yet offers the fiber-coupled output approximately ten times higher. Finite-difference time-domain simulations confirm that the Γ-point band edge laser exhibits the desired vertical emission property and that the fiber coupling efficiency can be as high as 30%.
Quantum dot structures grown on Al containing quaternary material for infrared photodetection beyond 10μm
Authors: Souza P. L. , Lopes A. J. , Gebhard T. , Unterrainer K. , Pires M. P. , Villas-Boas J. M. , Vieira G. S. , Guimarães P. S. S. , Studart Nelson
Published: April 2007

Different InAs quantum dot structures grown on InGaAlAs lattice matched to InP were investigated for quantum dot infrared photodetectors. Extremely narrow photocurrent peaks were observed, demonstrating great potential for fine wavelength selection. Structures which can detect radiation beyond 10μm were developed. Polarization dependence measurements showed that the structures have a zero-dimensional character and are suitable for detection of normal incident light. On the other hand, structures containing coupled quantum wells showed a hybrid two-dimensional/zero-dimensional behavior.
Optical Properties and van der Waals - London Dispersion Interactions of Polystyrene Determined by Vacuum Ultraviolet Spectroscopy and Spectroscopic Ellipsometry
Authors: French Roger H. , Winey Karen I. , Yang Min K. , Qiu Weiming
Published: April 2007

The interband optical properties of polystyrene in the vacuum ultraviolet (VUV) region have been investigated using combined spectroscopic ellipsometry and VUV spectroscopy. Over the range 1.5–32 eV, the optical properties exhibit electronic transitions we assign to three groupings, E1, E2, and E3, corresponding to a hierarchy of interband transitions of aromatic (π → π*), non-bonding (n → π*, n → σ*), and saturated (σ → σ*) orbitals. In polystyrene there are strong features in the interband transitions arising from the side-chain π bonding of the aromatic ring consisting of a shoulder at 5.8 eV (E1′) and a peak at 6.3 eV (E1), and from the σ bonding of the C–C backbone at 12 eV (E3′) and 17.1 eV (E3). These E3 transitions have characteristic critical point line shapes associated with one-dimensionally delocalized electron states in the polymer backbone. A small shoulder at 9.9 eV (E2) is associated with excitations possibly from residual monomer or impurities. Knowledge of the valence electronic excitations of a material provides the necessary optical properties to calculate the van der Waals–London dispersion interactions using Lifshitz quantum electrodynamics theory and full spectral optical properties. Hamaker constants and the van der Waals–London dispersion component of the surface free energy for polystyrene were determined. These Lifshitz results were compared to the total surface free energy of polystyrene, polarity, and dispersive component of the surface free energy as determined from contact angle measurements with two liquids, and with literature values. The Lifshitz approach, using full spectral Hamaker constants, is a more direct determination of the van der Waals–London dispersion component of the surface free energy of polystyrene than other methods.
Ionic Liquid Promoted Regio- and Stereo-Selective Thiolysis of Epoxides—A Simple and Green Approach to β-Hydroxy- and β-Keto Sulfides
Authors: Ranu Brindaban C. , Mandal Tanmay , Banerjee Subhash , Dey Suvendu S.
Published: April 2007

A variety of epoxides underwent facile cleavage by thiols under the catalysis of 1-methyl-3-butylimidazolium bromide, [bmIm]Br, to produce the corresponding β-hydroxy sulfides with high regio- and stereo-selectivity. On the other hand, a specially designed basic ionic liquid, [bmIm]OH, efficiently catalyzes the thiolysis of α,β-epoxy ketones providing β-keto sulfides through simultaneous retro-aldol cleavages. The reactions are clean, high yielding, and do not require any organic solvent. The catalyst is also recycled.
Synthesis of a Novel Bicyclic Nucleoside with a 3,7-Anhydrooctofuranosyl Skeleton
Authors: Kim Myong Jung , Chun Moon Woo
Published: April 2007

We have developed an efficient route for the synthesis of a novel bicyclic nucleoside using a key intermediate 13, which was prepared from 1,2:5,6-di-O-isopropylidene-α-d-glucose. 1,2-Nucleophilic addition of aldehyde 8 with allyltrimethylsilane and intramolecular Williamson reaction were successfully achieved to synthesize an intermediate with a 3,7-anhydrooctofuranosyl skeleton.