bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge trapping in alumina and its impact on the operation of metal-alumina-nitride-oxide-silicon memories: Experiments and simulations
Authors: Padovani Andrea , Larcher Luca , Della Marca Vincenzo , Pavan Paolo , Park Hokyung , Bersuker Gennadi
Published: July 2011

We investigate the electron/hole trapping phenomena in alumina blocking oxide and their impact on the program/erase operations and retention of TaN/Al2O3/Si3N4/SiO2/Si (TANOS) memory devices. For this purpose, we perform simulations using a physical model that reproduces the charge injection/trapping in TANOS devices, which is extended in order to account for the charge trapping phenomena in the blocking layer. We derive the electrical characteristics of both electron and hole traps in Al2O3 by reproducing the measured program, erase, and retention transients. Our results show that the amount of electron charge trapped in the alumina during a program operation strongly depends on the stack composition and program voltages and can account for up to 25% of the total threshold voltage shift, whereas hole trapping during erase is negligible. Finally, we investigate the degradation of retention caused by the electron trapping in the alumina blocking layer, which is shown to result in an accelerated charge loss.
Enhancement of thermal conductivity and volumetric behavior of FexOy nanofluids
Authors: Pastoriza-Gallego M. J. , Lugo L. , Legido J. L. , Piñeiro M. M.
Published: July 2011

Homogeneous and stable magnetic nanofluids containing iron oxide nanoparticles, α-Fe2O3 (hematite) and Fe3O4 (magnetite) in ethylene glycol, were prepared at concentrations up to 25% in mass fraction. Commercial Hexagonal Scalenohedral-shaped α-Fe2O3 nanoparticles were selected while Fe3O4 nanoparticles were synthesized using a coprecipitation method. The products were characterized by transmission and scanning electron microscopy and x-ray diffraction. The thermal conductivity of both nanofluids was measured as a function of volume fraction and temperature. The results illustrate that the enhanced thermal conductivity of the nanofluids increases with volume fraction but is temperature independent. The experimental results show that both types of nanoparticles in this base fluid present no significant aggregation. These experimental values were also compared with theoretical models. Moreover, the density of these nanofluids was measured as a function of volume fraction, temperature, and pressure. The volumetric behavior of nanofluids containing hematite is closer to the ideal behavior than those using magnetite.
Self-sustained fracture waves in a lead oxide-silica glass
Authors: Chaudhri M. Munawar
Published: July 2011

Using high-speed framing photography operating at 500000 frames per second, it has been shown that in Prince Rupert’s drops of a lead oxide-silica glass containing 24% by weight of lead oxide, the fracture waves propagate at a stable and self-sustained manner at a speed of (1300 ± 100) m s−1. This fracture wave speed is close to the terminal crack speed in the glass. These results, along with those from Prince Rupert’s drops of soda-lime glass reported by us earlier, confirm that the speed of a self-sustained fracture wave in a glass is controlled by the terminal speed of individual cracks in the glass.
Theoretical conversion efficiency of a two-junction III-V nanowire on Si solar cell
Authors: LaPierre R. R.
Published: July 2011

The continuity and Poisson equations are solved numerically to obtain J-V characteristics and photoconversion efficiency of a two-junction solar cell. The cell consists of a top junction comprised of nanowires with bandgap of 1.7 eV grown on a bottom junction comprised of a Si substrate. The lattice relaxation possible in nanowires permits lattice-mismatched III-V material growth on Si, thereby achieving the optimum bandgaps in a two-junction cell. The model indicates a limiting efficiency of 42.3% under a concentration of 500 Suns (AM1.5 D spectrum). This limiting efficiency is similar to that calculated for the planar lattice-matched triple-junction Ge/InGaAs/InGaP cell. Methods of fabricating the nanowire/Si cell are discussed including requirements for nanowire sidewall surface passivation. The model indicated that passivation of the nanowire sidewall surfaces that produces a surface recombination velocity of 3000 cm·s−1 and surface trap density of 1012 cm−2 should be sufficient to yield high efficiency solar cells.
Power consumption, discharge capacitance and light emission as measures for thrust production of dielectric barrier discharge plasma actuators
Authors: Kriegseis J. , Grundmann S. , Tropea C.
Published: July 2011

A new procedure of determining the time resolved capacitance of a plasma actuator during operation is introduced, representing a simple diagnostic tool that provides insight into the phenomenological behavior of plasma actuators. The procedure is demonstrated by presenting example correlations between consumed electrical energy, size of the plasma region, and the operating voltage. It is shown that the capacitance of a plasma actuator is considerably increased by the presence of the plasma; hence a system that has previously been impedance matched can be considerably de-tuned when varying the operating voltage of the actuator. Such information is fundamental for any attempts to increase the energy efficiency of plasma-actuator systems. A combined analysis of the capacitance, light emission, size of the plasma region, force production, and power consumption is presented.
Nitrogen and copper doping in MgxZn1−xO films and their impact on p-type conductivity
Authors: Mohanta S. K. , Nakamura A. , Temmyo J.
Published: July 2011

We report on nitrogen (N) and copper (Cu) doping in MgxZn1−xO films grown via remote-plasma-enhanced metalorganic chemical vapor deposition and their impact on p-type conduction. The MgxZn1−xO films showed a transformation of conductivity from n-type to p-type with increasing Mg content (x), which occurred at x = 0.078 with N2 carrier gas and x = 0.106 with H2 carrier gas. A comparison of the temperature dependent photoluminescence and the Hall effect measurement data revealed that the transformation of the conduction type with the increasing Mg content of MgxZn1−xO films is due to a conduction band up shift that causes the enhancement of the activation energy of donor states and the reduction of n-type residual electron concentrations. The p-type conductivity of MgxZn1−xO films with a low value of Mg content with N2 carrier gas was due to the contribution from the (N)O acceptor. Though N doped MgxZn1−xO (MgxZn1−xO:N) films showed p-type conductivity for x > 0.078, the N and Cu co-doped MgxZn1−xO (MgxZn1−xO:Cu,N) films showed n-type conduction with larger electron concentrations. Despite being a good acceptor, Cu doped MgxZn1−xO films had an n-type conductivity that was due to the contribution from shallow donors such as Cui and CusZni. Moreover, the reduction of the Mg content of MgxZn1−xO:Cu,N films led to an increase in the residual electron concentrations and contributed to the n-type conductivity.
Giant magnetodielectric effect in Terfenol-D/PZT magnetoelectric laminate composite
Authors: Yao Y. P. , Hou Y. , Dong S. N. , Li X. G.
Published: July 2011

The magnetic field dependence of the dielectric permittivity of Terfenol-D/PbZrxTi1-xO3 magnetoelectric composites in the temperature range from 200 K to 340 K was investigated systematically. It was found that there is a large magnetodielectric effect up to 15% around the electromechanical resonance frequency in a magnetic field of 5 kOe at room temperature. Nonmonotonic variations of dielectric permittivity with magnetic fields are associated with the mechanical energy loss due to magnetic domain wall motion in the magnetostrictive layer Terfenol-D. A numerical modeling is proposed and agrees well with the experimental data. The results are of significance in the development of magnetic-field-tuned electronic devices at room temperature.
Processing, texture quality, and piezoelectric properties of <001>C textured (1-x)Pb(Mg1/3Nb2/3)TiO3 - xPbTiO3 ceramics
Authors: Poterala Stephen F. , Trolier-McKinstry Susan , Meyer Richard J. , Messing Gary L.
Published: July 2011

This paper describes the link between texture quality and electromechanical properties for <001>C textured, 0.03(Na1/2Bi1/2)TiO3 - 0.97[0.715Pb(Mg1/3Nb2/3)TiO3 - 0.285PbTiO3] (0.03NBT-0.97[PMN-28.5PT]) ceramics with and without Mn-doping. Here, the subscript C denotes pseudocubic indices. Textured ceramics were prepared by templated grain growth of PMN-25PT on platelet-shaped 0.4(Na1/2Bi1/2)TiO3-0.6PbTiO3 (NBT-0.6PT) templates. Texture fractions of f = 0.92 (for undoped (1-x)Pb(Mg1/3Nb2/3)TiO3-xPbTiO3 (PMN-PT)) and f = 0.49 (for Mn-doped PMN-PT) were determined by fitting 002C XRD pole figures to the March-Dollase model, which was modified to account for symmetry-related 200C and 020C reflections. Using resonance methods, the elastic constants cij, sij, piezoelectric constants dij, eij, gij, hij, dielectric constants ɛij, and coupling coefficients kij of textured PMN-PT ceramics were characterized. It was found that the properties of textured PMN-PT approach the single crystal values along the texture axis (<001>C, also the poling axis), but not in transverse directions. In particular, the elastic compliance sE11 (perpendicular to <001>C) approaches an average of the single crystal sE11 and sE11(45°) coefficients, resulting in anomalous -sE12/sE11 ratios of − 0.01 and 0.04 in pure and Mn-doped textured PMN-PT, respectively. The 33-mode properties as measured by resonance-antiresonance methods were d33 = 852 pC/N, k33 = 0.83, ε33 = 3500, and mechanical quality factor Qm = 94 for undoped textured ceramics and d33 = 515, k33 = 0.76, ε33 = 2200, and Qm = 714 for Mn-doped textured ceramics.
Phase-corrected surface hopping: Correcting the phase evolution of the electronic wavefunction
Authors: Shenvi Neil , Subotnik Joseph E. , Yang Weitao
Published: July 2011

In this paper, we show that a remarkably simple correction can be made to the equation of motion which governs the evolution of the electronic wavefunction over some prescribed nuclear trajectory in the fewest-switches surface hopping algorithm. This corrected electronic equation of motion can then be used in conjunction with traditional or modified surface hopping methods to calculate nonadiabatic effects in large systems. Although the correction adds no computational cost to the algorithm, it leads to a dramatic improvement in scattering probabilities for all model problems studied thus far. We show that this correction can be applied to one of Tully's original one-dimensional model problems or to a more sophisticated two-dimensional example and yields substantially greater accuracy than the traditional approach.
Isochoric thermal conductivity of solid n-alkanes: Hexane C6H14
Authors: Konstantinov V. A. , Revyakin V. P. , Sagan V. V.
Published: July 2011

The isochoric thermal conductivity of solid n-hexane C6H14 is studied using three samples with different densities for temperatures ranging from 100 K to the onset of melting. In all cases, the isochoric thermal conductivity varies more weakly than Λ∝1/T. The present results are compared with the thermal conductivities of other representatives of the n-alkanes. The contributions of low-frequency phonons and “diffuse modes” to the thermal conductivity are calculated.
Comparison of enveloping distribution sampling and thermodynamic integration to calculate binding free energies of phenylethanolamine N-methyltransferase inhibitors
Authors: Riniker Sereina , Christ Clara D. , Hansen Niels , Mark Alan E. , Nair Pramod C. , van Gunsteren Wilfred F.
Published: July 2011

The relative binding free energy between two ligands to a specific protein can be obtained using various computational methods. The more accurate and also computationally more demanding techniques are the so-called free energy methods which use conformational sampling from molecular dynamics or Monte Carlo simulations to generate thermodynamic averages. Two such widely applied methods are the thermodynamic integration (TI) and the recently introduced enveloping distribution sampling (EDS) methods. In both cases relative binding free energies are obtained through the alchemical perturbations of one ligand into another in water and inside the binding pocket of the protein. TI requires many separate simulations and the specification of a pathway along which the system is perturbed from one ligand to another. Using the EDS approach, only a single automatically derived reference state enveloping both end states needs to be sampled. In addition, the choice of an optimal pathway in TI calculations is not trivial and a poor choice may lead to poor convergence along the pathway. Given this, EDS is expected to be a valuable and computationally efficient alternative to TI. In this study, the performances of these two methods are compared using the binding of ten tetrahydroisoquinoline derivatives to phenylethanolamine N-transferase as an example. The ligands involve a diverse set of functional groups leading to a wide range of free energy differences. In addition, two different schemes to determine automatically the EDS reference state parameters and two different topology approaches are compared.
Composition and temperature-induced structural evolution in La, Sm, and Dy substituted BiFeO3 epitaxial thin films at morphotropic phase boundaries
Authors: Kan Daisuke , Cheng Ching-Jung , Nagarajan Valanoor , Takeuchi Ichiro
Published: July 2011

Detailed structural investigations on the substitution-induced structural phase transition from the rhombohedral phase to an orthorhombic phase in (Bi,RE)FeO3 epitaxial thin films (RE = La, Sm, and Dy) grown on (100) SrTiO3 substrates are presented. X ray diffraction reveals that the unit cell dimensions of the orthorhombic phase are strongly dependent on the type of the RE dopant. For RE = La3+ ion, which has an ionic size comparable to the Bi3+ ion, the unit cell is found to be a0 × a0 × 2a0, where a0 is the pseudo-cubic lattice parameter. This is in contrast with the √2a0 × √2a0 × 2a0 unit cell for the case of smaller ionic radius RE (= Sm and Dy) elements. While clear double-hysteresis loops in the polarization versus electric-field curves due to field-induced transitions are observed for smaller ionic radius RE (= Sm and Dy), no signature of the double hysteresis loops is observed for the RE = La case across the structural boundary. We have also performed systematic tracking of the structural phases as functions of the RE composition and temperature, based on which we propose a phase diagram. This work reveals that the ionic size of the RE element plays a critical role in the evolution of the structural and functional properties of RE-substituted BiFeO3 thin film materials systems.
Structural origin underlying poor glass forming ability of Al metallic glass
Authors: Li F. , Liu X. J. , Hou H. Y. , Chen G. , Chen G. L.
Published: July 2011

We performed molecular dynamics simulations to study the glass formation and local atomic structure of rapidly quenched Al. Both potential energy and structural parameters indicate that the glass transition temperature of amorphous Al is as low as 300 K, which may lead to the poor thermal stability of the amorphous Al as it is prone to crystallize even at room temperature. Voronoi polyhedra analysis reveals that the most popular polyhedron is the deformed body-centered cubic (bcc) cluster characterized by the index < 0, 3, 6, 4 > in the amorphous Al, while the icosahedron with the index < 0, 0, 12, 0 > is always predominant in bulk metallic glass formers with excellent glass forming ability (GFA). Moreover, these deformed-bcc short-range orders can make up medium-range orders via the linkage of vertex-, edge-, face-, intercrossed-shared atoms, which are believed to more easily transform into face-centered cubic (fcc) Al nanocrystal compared with the icosahedral clusters in terms of the symmetrical similarity between bcc and fcc structures. This finding could unveil the structural origin of poor GFA of Al-based alloys.
Study of RgS− and RgS (Rg = Ne, Ar, and Kr) via slow photoelectron velocity-map imaging spectroscopy and ab initio calculations
Authors: Garand Etienne , Neumark Daniel M.
Published: July 2011

High-resolution photoelectron spectra of RgS− (Rg = Ne, Ar, and Kr) were obtained using slow electron velocity-map imaging (SEVI). The SEVI spectra reveal well-resolved vibrational transitions between multiple spin-orbit states of RgS− and RgS, both of which are open-shell species. Detailed assignments are made by comparison with theoretical simulations based on high level ab initio calculations and a atoms-in-molecule model that accounts for spin-orbit coupling in the anion and neutral. Several RgS− and RgS vibrational frequencies and excited-state term energies are accurately determined from the analysis of the experimental spectra and are found to be in excellent agreement with the calculated values.
Communication: Interfacial water structure revealed by ultrafast two-dimensional surface vibrational spectroscopy
Authors: Zhang Zhen , Piatkowski Lukasz , Bakker Huib J. , Bonn Mischa
Published: July 2011

Knowledge of the interfacial water structure is essential for a basic understanding of the many environmental, technological, and biophysical systems in which aqueous interfaces appear. Using ultrafast two-dimensional surface-specific vibrational spectroscopy we show that the structure of heavy water at the water-air interface displays short-lived heterogeneity and is very different from that at the water-lipid interface.
Technique for high axial shielding factor performance of large-scale, thin, open-ended, cylindrical Metglas magnetic shields
Authors: Malkowski S. , Adhikari R. , Hona B. , Mattie C. , Woods D. , Yan H. , Plaster B.
Published: July 2011

Metglas 2705M is a low-cost commercially available, high-permeability cobalt-based magnetic alloy, provided as a 5.08-cm wide and 20.3-μm thick ribbon foil. We present an optimized construction technique for single-shell, large-scale (human-size), thin, open-ended cylindrical Metglas magnetic shields. The measured dc axial and transverse magnetic shielding factors of our 0.61-m diameter and 1.83-m long shields in the Earth's magnetic field were 267 and 1500, for material thicknesses of only 122 μm (i.e., 6 foil layers). The axial shielding performance of our single-shell Metglas magnetic shields, obtained without the use of magnetic shaking techniques, is comparable to the performance of significantly thicker, multiple-shell, open-ended Metglas magnetic shields in comparable-magnitude, low-frequency applied external fields reported previously in the literature.
Calibration of a Thomson parabola ion spectrometer and Fujifilm imaging plate detectors for protons, deuterons, and alpha particles
Authors: Freeman C. G. , Fiksel G. , Stoeckl C. , Sinenian N. , Canfield M. J. , Graeper G. B. , Lombardo A. T. , Stillman C. R. , Padalino S. J. , Mileham C. , Sangster T. C. , Frenje J. A.
Published: July 2011

A Thomson parabola ion spectrometer has been designed for use at the Multiterawatt (MTW) laser facility at the Laboratory for Laser Energetics (LLE) at the University of Rochester. This device uses parallel electric and magnetic fields to deflect particles of a given mass-to-charge ratio onto parabolic curves on the detector plane. Once calibrated, the position of the ions on the detector plane can be used to determine the particle energy. The position dispersion of both the electric and magnetic fields of the Thomson parabola was measured using monoenergetic proton and alpha particle beams from the SUNY Geneseo 1.7 MV tandem Pelletron accelerator. The sensitivity of Fujifilm BAS-TR imaging plates, used as a detector in the Thomson parabola, was also measured as a function of the incident particle energy over the range from 0.6 MeV to 3.4 MeV for protons and deuterons and from 0.9 MeV to 5.4 MeV for alpha particles. The device was used to measure the energy spectrum of laser-produced protons at MTW.
Suprathermal plasma analyzer for the measurement of low-energy electron distribution in the ionosphere
Authors: Shimoyama M. , Oyama K.-I. , Abe T. , Yau A. W.
Published: July 2011

It is commonly believed that an energy transfer from thermal to suprathermal electrons (<several eV) greatly affects the energy budget of the ionosphere. However, observation of electron energy spectrum in this energy range is quite limited because of technical difficulties of measurement. We have developed an instrument to measure electron energy distribution from thermal to suprathermal energy continuously with high-energy resolution of about 0.15 eV. The measurement principle is based on the combination of a retarding potential analyzer with a channel electron multiplier (CEM) and the Druyvesteyn method, which derives energy distribution from the current-voltage characteristics. The capability of detecting plasma space potential enables absolute calibration of electron energy. The instrument with a small vacuum pump, which is required for the CEM to work in low-vacuum region, was first successfully tested by a sounding rocket S-310-37 in the ionospheric E region. The instrument is expected to provide new opportunities to measure energy distribution of thermal and non-thermal electrons in low-density plasma, where a Langmuir probe cannot measure electron temperature because of low plasma density.
Phase transition line of solid molecular nitrogen into the cubic gauche-polymeric phase
Authors: Yakub L. N.
Published: July 2011

The coexistence line of two high-pressure phases of solid nitrogen, molecular and polymeric cubic gauche (CG), has been predicted using two separate equations of state. The phase transition parameters, latent heat, volume, and entropy jumps, were calculated. At low temperatures, the predicted volume jump ΔV(P) is in agreement with recent experimental data; at elevated temperatures the P(T)-curve approaches the pressure maximum on the melting line.
Role of distortion in the hcp vs fcc competition in rare-gas solids
Authors: Krainyukova N. V.
Published: July 2011

As a prototype of an initial or intermediate structure between hcp and fcc lattices we consider a distorted bcc crystal. We calculate the temperature and pressure dependences of the lattice parameters for the heavier rare gas solids Ar, Kr, Xe in a quasiharmonic approximation with Aziz potentials, and confirm earlier predictions that the hcp structure predominates over fcc in the bulk within wide ranges of P and T. The situation is different for confined clusters with up to 105 atoms, where, owing to the specific surface energetics and terminations, structures with five-fold symmetry made up of fcc fragments are dominant. As a next step we consider the free relaxation of differently distorted bcc clusters, and show that two types (monoclinic and orthorhombic) of initial distortion are a driving force for the final hcp vs fcc configurations. Possible energy relationships between the initial and final structures are obtained and analyzed.
On the SO(10, 2) dynamical symmetry group of the MICZ-Kepler problem in a nine-dimensional space
Authors: Le Van-Hoang , Phan Thanh-Tu , Truong Cat-Tuong
Published: July 2011

We propose an effective algebraic method to investigate the dynamical symmetry of a 9-dimensional MICZ-Kepler problem by using the connection between this problem and a 16-dimensional isotropic harmonic oscillator. The dynamical symmetry group of the considered problem is found as SO(10,2). Explicit forms of all group elements are given. We also obtain all group elements in the algebraic representation of annihilation and creation operators that are very useful for concrete calculations.
Potential and electron density calculated for freely expanding plasma by an electron beam
Authors: Ho C. Y. , Wen M. Y. , Tsai Y. H. , Ma C.
Published: July 2011

This paper investigates the radial distributions of potential and electron density in free expansion plasma induced by an electron beam irradiating on the plate. The region of plasma production is assumed to be cylindrical, and the plasma expansion is assumed to be from a cylindrical source. Therefore, the one-dimensional model in cylindrical coordinates is employed in order to analyze the radial distributions of the potential and electron density. The Runge–Kutta method and the perturbation method are utilized in order to obtain the numerical and approximate solutions, respectively. The results reveal that the decrease in the initial ion energy makes most of the ions gather near the plasma production region and reduces the distribution of the average positive potential, electron, and ion density along the radial direction. The oscillation of steady-state plasma along the radial direction is also presented in this paper. The ions induce a larger amplitude of oscillation along the radial direction than do electrons because the electrons oscillate around slowly moving ions due to a far smaller electron mass than ion mass. The radial distributions of the positive potential and electron density predicted from this study are compared with the available experimental data.
Multiply resonant high quality photonic crystal nanocavities
Authors: Rivoire Kelley , Buckley Sonia , Vučković Jelena
Published: July 2011

We propose and experimentally demonstrate a photonic crystal nanocavity with multiple resonances that can be tuned nearly independently. The design is composed of two orthogonal intersecting nanobeam cavities. Experimentally, we measure cavity quality factors of 6600 and 1000 for resonances separated by 382 nm; we measure a maximum separation between resonances of 506 nm. These structures are promising for enhancing efficiency in nonlinear optical processes such as sum/difference frequency and stimulated Raman scattering.
Heat conduction across a solid-solid interface: Understanding nanoscale interfacial effects on thermal resistance
Authors: Balasubramanian Ganesh , Puri Ishwar K.
Published: July 2011

Phonons scatter and travel ballistically in systems smaller than the phonon mean free path. At larger lengths, the transport is instead predominantly diffusive. We employ molecular dynamics simulations to describe the length dependence of the thermal conductivity. The simulations show that the interfacial thermal resistance Rk for a Si-Ge superlattice is inversely proportional to its length, but reaches a constant value as the system dimension becomes larger than the phonon mean free path. This nanoscale effect is incorporated into an accurate continuum model by treating the interface as a distinct material with an effective thermal resistance equal to Rk.
Capacitance-voltage characteristics of organic Schottky diode with and without deep traps
Authors: Sharma Akanksha , Kumar Pramod , Singh Budhi , Chaudhuri Sumita Ray , Ghosh Subhasis
Published: July 2011

Capacitance based spectroscopic techniques have been used to characterize defects in organic Schottky diode based on copper phthalocyanine. Deep traps in organic thin films introduced by varying growth conditions have been identified and characterized by voltage and temperature dependence of capacitance. These results are interpreted using a consistent modelling of capacitance of organic Schottky diode with and without deep traps.
Local order of Ca in a CaF2–Al2O3–SiO2 glass by electron energy-loss spectroscopy
Authors: Jiang Nan
Published: July 2011

Local order of Ca in a CaF2–Al2O3–SiO2 glass is studied using electron energy loss spectroscopy technique. The energy shift of ionization threshold in the Ca L2,3 and the differences in the near-edge structure of the Ca M2,3 edge between the glasses with and without F suggest the local ordering of F around Ca in the F-containing aluminosilicate glass. The local order phenomenon requires the clustering of Ca–F. Therefore, the transparent fluorinated calcium aluminosilicate glass is not structurally and compositionally homogeneous at nanometer scale.
On the use of electrostatic force microscopy as a quantitative subsurface characterization technique: A numerical study
Authors: Riedel C. , Alegría A. , Schwartz G. A. , Arinero R. , Colmenero J. , Sáenz J. J.
Published: July 2011

We present a numerical study on the use of electrostatic force microscopy (EFM) as a non invasive subsurface characterization technique. We discuss the ability to resolve a buried object in a dielectric matrix considering two parameters: the detectability (i.e., signal superior to the noise) and the lateral resolution. The effects of the dielectric constant, thickness of the sample, and depth at which the object is buried are quantified. We show that the sensitivity reached in EFM permits to characterize subsurface objects in a dielectric matrix. We demonstrate that both lateral resolution and detectability decreases when the tip object distance increases. On the other hand, these two quantities increase with the dielectric constant of the matrix. A first step toward EFM tomography is proposed for objects creating non correlated signals.
Surface plasmon modes guided by Ga-doped ZnO layers bounded by different dielectrics
Authors: Badalawa Wasanthamala , Matsui Hiroaki , Ikehata Akifumi , Tabata Hitoshi
Published: July 2011

We report two types of surface plasmon (SP) modes guided by a Ga-doped ZnO (ZnO:Ga) layer bounded between air and glass. A symmetric SP (s-) mode having leaky waves was found at an air-ZnO interface by attenuated total reflection measurements and showed a cutoff thickness region from 141 to 107 nm. Consequently, only an asymmetric SP (a-) mode bound at a ZnO-glass interface remained, as confirmed by numerical analyses and finite-difference time-domain simulations. s- and a-modes of the ZnO:Ga layer exhibited a high cutoff thickness and a strongly confined SP field at air-ZnO and ZnO-glass interfaces, respectively.
Magneto-absorption spectra of Bernal graphite
Authors: Ho Yen-Hung , Chiu Yu-Huang , Su Wu-Pei , Lin Ming-Fa
Published: July 2011

With the availability of Landau wave functions in real space, we investigate the magneto-optical spectra of ordinary bulk graphite within a tight-binding model. The interlayer interactions significantly affect the structure, frequency and intensity of absorption peaks, as well as their field evolution and the double-peak absorptions. Those unique features of the absorption constitute important characterization of graphite and serve to differentiate the bulk spectra from those of true monolayer and bilayer graphenes.
Temperature dependence of Raman scattering from 4H-SiC with hexagonal defects
Authors: Han R. , Han B. , Wang D. H. , Li C.
Published: July 2011

Noncontact temperature measurements based on Raman scattering were performed on 4H-SiC with hexagonal defects. These measurements show that the four-phonon process makes a greater contribution to the E2(TO) mode than to the E1(TO) mode. The longer lifetimes of E2(TO) and E1(TO) phonons in hexagonal defects demonstrate that there are fewer possible decay channels than in the defect free zone. The absence of electronic Raman peaks in the hexagonal defects suggests that hexagonal defects seriously limit the uniformity of the nitrogen distribution. The intensity of electronic Raman spectra is related to the density of neutral nitrogen atoms.
Investigation of weak interlayer exchange coupling in GaMnAs/GaAs superlattices with insulating nonmagnetic spacers
Authors: Chung Jae-Ho , Song Young-Sang , Yoo Taehee , Chung Sun Jae , Lee Sanghoon , Kirby B. J. , Liu X. , Furdyna J. K.
Published: July 2011

A robust long-range antiferromagnetic coupling between ferromagnetic Ga0.97Mn0.03As layers has previously been realized via insertion of nonmagnetic Be-doped GaAs spacers between the magnetic layers. In this paper we report the observation of weak antiferromagnetic coupling between Ga0.97Mn0.03As layers through undoped GaAs spacers with thicknesses as large as 25 monolayers. The field and the temperature dependences of the sample magnetization suggest that the interlayer coupling in these systems substantially deviates from typical ferromagnetic behavior. Polarized neutron reflectivity measurements reveal antiferromagnetic alignment between Ga0.97Mn0.03As layers when a weak field is applied perpendicular to the magnetic easy axis during cooling below TC. The strength of the observed coupling between the magnetic layers is estimated to be weaker than 0.05 mT.
Ferroelectricity and electromechanical coupling in (1 − x)AgNbO3-xNaNbO3 solid solutions
Authors: Fu Desheng , Arioka Takahiro , Taniguchi Hiroki , Taniyama Tomoyasu , Itoh Mitsuru
Published: July 2011

We observed the evolution of polarization states and electromechanical coupling in (1 − x) AgNbO3-xNaNbO3 solid solutions using dielectric and strain hysteresis loop techniques and show that the polarization evolves from the ferrielectric ordering in AgNbO3 to the ferroelectric ordering in NaNbO3. The crossover between these two states occurs in the solid solution with x ≈ 0.8. A strain level ≈ 0.20% is available in the ceramics of these solid solutions. Such a large electromechanical effect might be interesting for the development of piezoelectric materials.
Polarity-dependent kinetics of ferroelectric switching in epitaxial BiFeO3(111) capacitors
Authors: Kim T. H. , Baek S. H. , Yang S. M. , Kim Y. S. , Jeon B. C. , Lee D. , Chung J.-S. , Eom C. B. , Yoon J.-G. , Noh T. W.
Published: July 2011

We report on the intriguing polarity-dependent kinetics of polarization switching in epitaxial BiFeO3(111) capacitors. Two seemingly incompatible switching kinetics were observed depending on the polarity of the applied switching bias. Under a negative switching bias, the polarization switching process occurs mainly through sideways domain wall motion, but under a positive switching bias, domain nucleation governs the polarization reversal. The modified piezoresponse force microscopy reveals these polarity-dependent ferroelectric domain evolutions. This polarity dependence of ferroelectric switching kinetics is attributed to defect-related local fields that have different distributions near film/electrode interfaces, probably due to structural relaxation in the BiFeO3(111) film.
Switching of the symmetry of magnetic anisotropy in Fe/BaTiO3 heterostructures
Authors: Shirahata Y. , Nozaki T. , Venkataiah G. , Taniguchi H. , Itoh M. , Taniyama T.
Published: July 2011

Switching of the symmetry of magnetic anisotropy is clearly demonstrated in an epitaxial Fe layer on BaTiO3, in association with the interface lattice distortion occurred at the structural phase transition of BaTiO3. The polar plot of the normalized remanent magnetization shows the fourfold symmetry with the magnetization easy axis along [100] of Fe at room temperature, while that at 230 K exhibits the twofold symmetry with the easy axis along [110]. Spatially resolved micro-Raman inspection corroborates the fact that the change in the magnetic symmetry arises from the magnetoelastic coupling at the interface.
Temporal and phase measurements of ultraviolet femtosecond pulses at 200 nm by molecular alignment based frequency resolved optical gating
Authors: Li Hao , Liu Jia , Feng Yahui , Chen Cheng , Pan Haifeng , Wu Jian , Zeng Heping
Published: July 2011

We demonstrate that the temporal profile and phase of a weak ultraviolet femtosecond pulse around 200 nm can be measured by molecular alignment based cross-correlation frequency resolved optical gating technique. This technique employs the impulsive alignment of gaseous molecules as gate function and exhibits the advantage of no phase-matching constraint and applicability to pulses at various wavelengths. Simultaneous measurements of near-infrared and ultraviolet pulses are demonstrated. Its agreements with the independent spectral phase interferometry for direct electric field reconstruction and second-order auto-correlation measurements confirm that the molecular alignment gating is a robust technique for ultrashort pulse diagnosis.
Polarized x-ray spectroscopy of quaternary ferromagnetic semiconductor (Ga,Mn)(As,P) thin films
Authors: Wadley P. , Casiraghi A. , Wang M. , Edmonds K. W. , Campion R. P. , Rushforth A. W. , Gallagher B. L. , Staddon C. R. , Wang K. Y. , der Laan G. van , Arenholz E.
Published: July 2011

X-ray magnetic circular dichroism (XMCD) is used to study the magnetic and electronic properties of the quaternary diluted magnetic semiconductor (Ga,Mn)(As,P) as a function of the P concentration y. A clear signature of the variation in strain, from compressive to tensile on increasing y, is observed in the angular dependence of the hybridized d5-like Mn L2,3 XMCD spectra. The ferromagnetic transition temperature and magnetic moment per Mn ion both decrease steadily with increasing y.
Thermoelectric power of graphene as surface charge doping indicator
Authors: Sidorov Anton N. , Sherehiy Andriy , Jayasinghe Ruwantha , Stallard Robert , Benjamin Daniel K. , Yu Qingkai , Liu Zhihong , Wu Wei , Cao Helin , Chen Yong P. , Jiang Zhigang , Sumanasekera Gamini U.
Published: July 2011

We report on simultaneous thermoelectric power and four-probe resistance measurements of chemical vapor deposition grown graphene during a degas process, as well as in exposure to various gases. For all investigated samples, a dramatic change in thermoelectric power was observed and found to be sensitive to the gas molecule charge doping on the surface of graphene. The observed p-type behavior under ambient conditions supports an electrochemical charge transfer mechanism between the graphene and oxygen redox couple, while the n-type behavior under degassed conditions is ascribed to the electron doping caused by the surface states of the SiO2/Si substrate.
Extraction of correct Schottky barrier height of sulfur implanted NiSi/n-Si junctions: Junction doping rather than barrier height lowering
Authors: Chan J. , Martinez N. Y. , Fitzgerald J. J. D. , Walker A. V. , Chapman R. A. , Riley D. , Jain A. , Hinkle C. L. , Vogel E. M.
Published: July 2011

Proper analysis of the Schottky barrier height extraction methods shows that sulfur implantation followed by anneal does not effectively reduce the Schottky barrier height of NiSi/n-Si contacts. Instead, the results for sulfur implanted samples are consistent with enhanced field emission due to an increased doping density of the surface region of the silicon. Sulfur has a large impact on contact resistivity for silicon with low initial doping concentration (<∼1017 cm−3), but little impact for silicon with high initial doping density (>∼1017 cm−3). Internal photoemission measurements show that the Schottky barrier height remains unchanged with sulfur implantation.
Errant Paths: The Poetics and Politics of Walking
Authors: Pinder David
Published: July 2011

Walking has moved into increasing visibility in social, cultural, and geographical studies as well as art and cultural practice in recent times. Walking practices are often mobilised as a means for sensing and learning about spaces, for enabling reflection on the mutual constitution of bodies and landscapes, and for finding meaning within and potentially re-enchanting environments. Through the influence of Michel de Certeau in particular, the idea that walking ‘encunciates’ spaces and is a creative, elusive, and resistive everyday practice, counterpoised to the ‘solar eye’, has become commonplace. This paper focuses on projects by the artist Francis Alÿs that are based on walking in London and other cities, to consider their engagements with the politics of urban space. Attention is paid to walking as his method of unfolding stories, and to its potential to unsettle and bring into question current realities, especially in the context of the regulated, fortified, and surveilled zones of London. Addressing the poetics and politics of his spatial practices, however, reveals the inadequacy of undifferentiated models of creative resistance, nomadism, and subversion beloved of much recent theory, and often endorsed through a partial reading of Certeau. Instead, the openness and ambivalence of these practices suggest a need for a more nuanced approach to the multiple rhythms, trajectories, and narratives that constitute urban spaces as well as to their contested (in)visibilities.
The Representative Claim of Deliberative Planning: The Case of Isawiyah in East Jerusalem
Authors: Ron Amit , Cohen-Blankshtain Galit
Published: July 2011

Both advocates and critics of deliberative planning often study deliberative planning processes as if they are real-life approximations of an ideal situation where the only force is the force of the better argument. However, in the course of the last decade democratic theorists came to develop a complex systemic understanding of the role of deliberation in policy making. In this view, legitimate decision making is not a one-time process but an ongoing pattern of interaction between organized institutions and the public sphere. This paper builds on recent work on political representation to develop a framework for studying deliberative planning as a type of representative claim made within a complex ecology of representative institutions and applies this framework to the case of a deliberative planning initiative in East Jerusalem. We examine the weaknesses and strengths of deliberative planning processes in a political environment that is not hospitable to public participation in planning.
Ultra-fine grinding is not essential for acid sulfate soil tests
Authors: Lyons David J. , McElnea Angus E. , Finch Niki P. , Tallis Claire
Published: July 2011

Australian Standard methods for acid sulfate soils (ASS) require the grinding of soil to <0.075 mm. A ring-mill or similar grinding apparatus is therefore needed. We investigated whether ring-mill grinding is required for accurate and reproducible test results and associated calculations (such as acid–base accounting), or if more conventional fine-grinding (i.e. <0.5 mm) is sufficient to obtain acceptable results. An initial experiment (unreplicated) was conducted on 52 soils comparing ring-mill and fine-grinding treatments, and this information was used to formulate final, more detailed experimental work on five soils from the same dataset. Soils from an ASS survey in coastal central Queensland were chosen to reflect the range of chemical properties found in ASS. Soils were analysed by the Chromium and SPOCAS suite of tests for the two grinding treatments. For those tests that follow a relatively vigorous extraction carried out with heating [such as chromium-reducible S, peroxide-oxidisable S and acid-neutralising capacity by back titration (ANCBT)], results were similar for the two grinding treatments. However, for those tests that follow a relatively mild extraction without heating (such as KCl-extractable S, HCl-extractable S and titratable actual acidity), significantly higher values (P < 0.05) were obtained for ring-mill ground soil. There was no significant difference in calculated net acidity between ring-mill grinding and fine-grinding for soils without excess ANC. For self-neutralising soils, fine-grinding gave significantly lower values of ANC than ring-mill grinding. It is uncertain whether ring-mill grinding gives a true reflection of the ANC available in the natural environment.
Deep drainage rates of Grey Vertosols depend on land use in semi-arid subtropical regions of Queensland, Australia
Authors: Silburn D. M. , Tolmie P. E. , Biggs A. J. W. , Whish J. P. M. , French V.
Published: July 2011

Changes in land use can affect the soil water balance and mobilise primary salinity. This paper examines changes in soil chloride (Cl) and deep drainage under pasture and annual cropping on five gilgaied Grey Vertosols in southern inland Queensland, Australia, comparing them to remnant native vegetation. Transient soil Cl mass-balance (CMB) was used for crop and pasture sites, as it is suitable for determining the long-term, low rates of drainage since clearing some 40–50 years ago. Steady-state CMB was used for native vegetation.
Large masses of salts and Cl were stored under native vegetation (31–103 t/ha of Cl to 3.2 m), and deep drainage was low (0.10–0.27 mm/year). The Cl profiles were generally of a normal shape for matrix flow (e.g. no bypass flow). Soil Cl was lost under cropping (average 65% lost to 1.4 m) and pasture (32%) compared with native vegetation. This lost Cl was not stored within the top 4–5 m of soil, indicating movement of water below 4–5 m. Deep drainage averaged 10 mm/year under cropping for both gilgai mounds and depressions (range 2.7–25 mm/year), and 3.3 and 5.1 mm/year under pasture for mounds and depressions, respectively. Subsoil (depth 1.5–4+ m) was generally dry under native vegetation and wetter under cropping and pasture. Deep drainage over the last 40–50 years was stored in the unsaturated zone (to deeper than 4+ m), indicating a long time lag between land-use change and groundwater response. Steady-state CMB greatly underestimated drainage for crop and pasture sites.
Teenagers’ acquisition of variation
Authors: Schleef Erik , Meyerhoff Miriam , Clark Lynn
Published: July 2011

In recent years, the UK has experienced unparalleled numbers of migrants from Eastern Europe, particularly Poland. Many migrants came with their families. We examined variation in the English spoken by adolescent Polish migrants in Edinburgh and London. We asked: to what extent are teenage Polish migrants acquiring the patterns of variation typical of their local peer group? We compare the results for the well-known variable (ing) in the speech of both Polish migrants and their same age British peers. Our results indicate that the Polish teenagers seem to be sensitive to the overall rates of the non-standard variant in the city they have moved to. Moreover, Polish teenagers also replicate some of the linguistic and social constraints found in the speech of the locally-born teens. In some cases, they partially replicate the constraint patterns found in the locally-born teenagers, and in other cases they introduce novel constraints unattested in the speech of their locally-born peers. The results of our study raise several questions regarding local shared constraints and universal learning tools, potential supra-local constraints and the status of (ing) as a sociolinguistic variable for learners of English. We discuss these in the final section of this paper.
Fluency versus accuracy in advanced spoken learner language
Authors: Brand Christiane , Götz Sandra
Published: July 2011

In this paper we present a possible multi-method approach towards the description of a potential correlation between errors and temporal variables of (dys-)fluency in spoken learner language. Using the German subcorpus of the Louvain International Database of Spoken English Interlanguage (LINDSEI) and the native control corpus Louvain Corpus of Native English Conversation (LOCNEC), we first analysed errors and temporal variables of fluency quantitatively. We detected lexical and grammatical categories which are especially error-prone as well as problematic aspects of fluency for all learners in the LINDSEI subcorpus, e.g. confusion in tense agreement across clauses or an overuse of unfilled pauses. In the ensuing qualitative analysis of five prototypical learners, no trend for a possible correlation of accuracy and fluency could be observed. Fifty native speakers’ ratings of these five learners revealed that the learner with an average performance across the investigated variables received the highest ratings for overall oral proficiency.
Fluency, complexity and informativeness in native and non-native speech
Authors: Osborne John
Published: July 2011

Individual speakers vary considerably in their rate of speech, their syntactic choices, and the organization of information in their discourse. This study, based on a corpus of monologue productions from native and non-native speakers of English and French, examines the relations between temporal fluency, syntactic complexity and informational content. The purpose is to identify which features, or combinations of features, are common to more fluent speakers, and which are more idiosyncratic in nature. While the syntax of fluent speakers is not necessarily more complex than that of less fluent speakers, it is suggested that they are able to deliver content more efficiently through a combination of less hesitant speech and of lexical and syntactic choices that allow them to package information more economically.