bluuebunny/crossref_metadata_2025 huggingface dataset:
Point Contact Andreev Reflection from Erbium: The role of external magnetic field and the sign of the spin polarization
Authors: Stamenov P.
Published: March 2012

Point Contact Andreev Reflection has established itself as a technique of choice for the measurement of Fermi level spin polarization in a variety of metallic and degenerate semiconducting materials. So far, the methodology has been limited to determination of the absolute value of the spin polarization in zero or small magnetic field. Here an experimental account is presented of the existence of magnetic field and current antisymmetric effects in the PCAR spectra of some Nb/Er contacts. This is hoped to bridge the gap to the neighboring Tedrow-Meservey technique and help in the determination of correct sign and magnitude of the polarization in new and novel materials. The spin polarization of erbium has been determined to be P = +0.58(2).
Structural and magnetic study of SmTAl single crystals (T=Pd and Ni)
Authors: Prchal Jiří , Rusňák Martin , Pospíšil Jiří , Dönni Andreas , Valeš Václav , Matěj Zdeněk , Sechovský Vladimír
Published: March 2012

Some of the RTX (R – rare earth, T – transition metal, X – p-metal element) including SmNiAl and SmPdAl, compounds crystallizing in the hexagonal ZrNiAl-type of structure exhibit a discontinuity in the temperature or composition dependence of the lattice parameters (a and c). This phenomenon is connected with some “forbidden” c/a ratio values. Single crystals of SmNiAl and SmPdAl have been studied and found to undergo a second order structure phase transition in the vicinity of 500 K, characterized by a change of the temperature dependence of the c/a ratio. The transition is seen also in the change of the temperature dependence of the magnetic susceptibility near to 500 K. The second order type of the transition induces appearance of c/a falling into the forbidden range of values. The enhanced thermal movement at high temperatures causes possibility of the forbidden values. The low temperature specific heat, resistivity and magnetization data point to antiferromagnetism in SmPdAl and SmNiAl with TN = 15.3 and 20.3 K, respectively. Various features of the specific magnetism of the Sm3+ ion, like strongly reduced magnetic moments, magnetocrystalline anisotropy, exotic (non-Curie-Weiss) temperature dependence of the paramagnetic susceptibility are presented and discussed.
Columnar grain growth of FePt(L1) thin films
Authors: Yang En , Ho Hoan , Laughlin David E. , Zhu Jian-Gang
Published: March 2012

An experimental approach for obtaining perpendicular FePt-SiOx thin films with a large height to diameter ratio FePt(L10) columnar grains is presented in this work. The microstructure for FePt-SiOx composite thin films as a function of oxide volume fraction, substrate temperature, and film thickness is studied by plan view and cross section TEM. The relations between processing, microstructure, epitaxial texture, and magnetic properties are discussed. By tuning the thickness of the magnetic layer and the volume fraction of oxide in the film at a sputtering temperature of 410 °C, a 16 nm thick perpendicular FePt film with ∼8 nm diameter of FePt grains was obtained. The height to diameter ratio of the FePt grains was as large as 2. Ordering at lower temperature can be achieved by introducing a Ag sacrificial layer.
Enhancement in coercivity of Pulsed Laser Deposition-fabricated Fe-Pt thick film magnets by reducing droplets
Authors: Nakano M. , Urakawa D. , Yanai T. , Fukunaga H.
Published: March 2012

A high-speed Pulsed Laser Deposition method with the deposition rate of several ten microns per hour followed by a post-annealing process enabled us to obtain isotropic Fe-Pt thick film magnets with the L10 order phase. In the study, we investigated the relationship between droplets and coercivity of the post-annealing films. It was found that the reduction in the numbers of droplets enabled us to increase the coercivity although the average deposition rate decreased from 40 to 15 μm per hour. In the samples with Ra less than 0.5 μm, the coercivity exceeded 450 kA/m at the annealing temperature of 673 K. A SEM-EDX analysis of droplets revealed that they tended to have iron-rich or platinum-rich compositions compared with the average one of Fe50Pt50.
Resonant surface magnetoplasmons in two-dimensional magnetoplasmonic crystals excited in Faraday configuration
Authors: Chetvertukhin A. V. , Baryshev A. V. , Uchida H. , Inoue M. , Fedyanin A. A.
Published: March 2012

The resonant excitation of surface magnetoplasmons in Faraday configuration is studied via spectroscopy of the longitudinal magneto-optical Kerr effect (LKE) in two-dimensional nickel-based magnetoplasmonic crystals. The fulfillment of phase matching conditions for surface plasmon-polaritons using both reciprocal vectors of the magnetoplasmonic crystal allows tuning of the LKE enhancement in the wide spectral range.
Design of permanent magnet eddy current brake for a small scaled electromagnetic launch model
Authors: Zhou Shigui , Yu Haitao , Hu Minqiang , Huang Lei
Published: March 2012

A variable pole-pitch double-sided permanent magnet (PM) linear eddy current brake (LECB) is proposed for a small scaled electromagnetic launch model. A two-dimensional (2D) analytical steady state model is presented for the double-sided PM-LECB, and the expression for the braking force is derived. Based on the analytical model, the material and eddy current skin effect of the conducting plate are analyzed. Moreover, a variable pole-pitch double-sided PM-LECB is proposed for the effective braking of the moving plate. In addition, the braking force is predicted by finite element (FE) analysis, and the simulated results are in good agreement with the analytical model. Finally, a prototype is presented to test the braking profile for validation of the proposed design.
Magnetic anisotropy and magnetization reversal in Co/Cu multilayers nanowires
Authors: Ahmad Naeem , Chen J. Y. , Shi D. W. , Iqbal Javed , Han Xiufeng
Published: March 2012

The Co/Cu multilayer nanowires fabricated in an array using anodized aluminum oxide (AAO) template by electrodeposition method, have been investigated. It has been observed that the magnetization reversal mode and magnetic anisotropy depend upon the Co and Cu layer thicknesses. Magnetization reversal occurs by curling mode at around Co = 400 nm and Cu = 10 nm, while for Co = 30 nm and Cu = 60 nm, magnetization reversal occurs by nucleation mode. A change of magnetic anisotropy from out of plane to in plane is observed when thickness of Cu layer tCu = 60 nm and that of Co tCo = 30 nm. Magnetic anisotropy is lost when thickness of the Co layer tCo = 400 nm and that of Cu tCu= 10 nm. Magnetic properties have been explained by the competition among shape anisotropy, magnetostatic interactions and magnetocrystalline anisotropy. Magnetic properties can be tuned accordingly depending upon the thickness of the Co and Cu nanodisks.
Memory effects in Heisenberg spin glasses: Spontaneous restoration of the original spin configuration rather than preservation in a frozen state
Authors: Mamiya Hiroaki , Nimori Shigeki
Published: March 2012

Universality of spin configuration restoration is studied in Heisenberg spin glasses: a dilute magnetic semiconductor Cd55Mn45Te as well as a dilute magnetic alloy Cu97Mn3. Reversions of the relaxations of magnetization were observed in both systems undergoing positive/negative temperature cycling under a constant magnetic field. Because the magnetization mirrors evolution of the spin configuration, these reversions indicate that the spin configurations are spontaneously restored to the initially stabilized states when the temperature is returned to the original. Whereas such spin restoration does not occur if the spin glasses are simply frozen, it is possible in the alternative ghost domain scenario of the droplet picture. This finding thus provides fresh insight into the nature of glassy systems.
Analysis of mid-range electric power transfer based on an equivalent circuit model
Authors: Sasada Ichiro
Published: March 2012

This study analyzes the steady state behavior of wireless power transfer through the magnetic coupling between two LC-resonators that consist of a loop coil (diameter = 0.2 m) and a terminating capacitor based on an equivalent circuit model. Parameters considered include the quality factor Q of resonators and the distances between coils, which govern the strength of the magnetic coupling and the frequency of the sinusoidal power source (24 ∼ 28 kHz range). The efficiency and amount of power transferred are calculated under the optimum load for the distance of transfer. The analysis proves that with a moderately high Q of 227, the efficiency can reach above 85% at the distance equal to the radius of the resonant coil, when the load is optimized. An important finding from the analysis is that there is a value for the frequency where the optimum load is almost unchanged, even when the distance between two resonators changes.
Ziz-zag interface and strain-influenced ferromagnetism in epitaxial Mn3O4/La0.7Sr0.3MnO3 thin films grown on SrTiO3 (100) substrates
Authors: Mukherjee Devajyoti , Bingham Nicholas , Phan Manh-Huong , Srikanth Hariharan , Mukherjee Pritish , Witanachchi Sarath
Published: March 2012

Epitaxial Mn3O4/La0.7Sr0.3MnO3 (Mn3O4/LSMO) bilayer thin films were grown on single crystal SrTiO3 (STO) (100) substrates, with Mn3O4 as the top layer, using pulsed laser deposition technique. X-ray diffraction revealed the single crystalline nature and epitaxial relationship between the layers, as well as increased lattice distortion of LSMO in the bilayer structure relative to a single layer film of LSMO. Cross-sectional high resolution transmission electron microscope images showed atomically sharp interfaces, but in contrast to the almost flat interface between LSMO and STO substrate, the Mn3O4 and LSMO interface showed a zig-zag structure. Magnetic measurements indicated that the high temperature in situ deposition of a Mn3O4 layer on top of the LSMO film significantly reduced the magnetization of the LSMO film, probably due to the formed ziz-zag interface between LSMO and Mn3O4.
Analysis and control of the Hanle effect in metal–oxide–semiconductor inversion channels
Authors: Takamura Yota , Sugahara Satoshi
Published: March 2012

The authors theoretically analyzed the output characteristics of a proposed Hanle-effect spin transistor based on a spin-MOSFET. The device can easily create oscillating Hanle-effect signals by applying an accelerating bias voltage. The behavior of the magnetic field interval of the oscillatory Hanle-effect signals for a sufficiently high accelerating bias is well correlated with the universality of the effective electron mobility in the Si MOS inversion channel, which is useful for revealing spin transport dynamics in the MOS inversion channel.
A study on modeling of the writing process and two-dimensional neural network equalization for two-dimensional magnetic recording
Authors: Yamashita Masato , Okamoto Yoshihiro , Nakamura Yasuaki , Osawa Hisashi , Miura Kenji , Greaves S. , Aoi H. , Kanai Y. , Muraoka Hiroaki
Published: March 2012

A simple writing process considering magnetic clusters due to exchange coupling between grains is studied for two-dimensional magnetic recording. The bit error rate (BER) performance of a low-density parity-check coding and iterative decoding system with a two-dimensional neural network equalizer (2D-NNE) that can diminish the influences of jitter-like medium noise and inter-track interference is obtained using a read/write channel model based on the proposed writing process, and it is compared with those for one- and two-dimensional finite impulse response equalizers (FIREs). It is clarified that the BER performance for the 2D-NNE is far superior to those for the FIREs.
Influence of magnetic viscosity on the first order reversal curves of antiferromagnetically coupled perpendicular recording media
Authors: Piramanayagam S. N. , Ranjbar M.
Published: March 2012

Measurement of first order reversal curves (FORC) is emerging as a common characterization method to understand the exchange and magnetostatic interactions in magnetic films. In this paper, the FORC of the top and bottom layers of an antiferromagnetically coupled (AFC) perpendicular recording media is studied. The AFC media shows four peaks in the FORC contours, as against a single peak observed in the FORC of typical magnetic samples. Moreover, it is also pointed out that the FORC contours may be affected by time-dependent magnetization effects.
Chemical vapor deposition of polycrystalline Fe3O4 thin films by using the cyclohexadiene iron tricarbonyl liquid precursor
Authors: Mantovan R. , Vangelista S. , Cocco S. , Lamperti A. , Salicio O.
Published: March 2012

Magnetite (Fe3O4) thin films are synthesized by chemical vapor deposition (CVD) with the cyclohexadiene iron tricarbonyl Fe(C6H8)(CO)3 liquid precursor. The growth of pure, polycrystalline, and stoichiometric Fe3O4 films is confirmed by X-ray diffraction, Raman spectroscopy, time-of-flight secondary ion mass spectrometry, and conversion electron Mössbauer spectroscopy. At 297 K, the resistivity for 24.8 nm (100 nm) Fe3O4 thin film is 17 × 10−3 Ω cm (4.2 × 10−3 Ωcm), indicating the good electrical quality of the as-deposited layers. Magnetoresistance (MR) up to −2.2% is measured at 297 K at 1.1 T, corresponding to 15% electron spin polarization. A gradual increase of MR is observed at low temperature. In particular, the observed MR = −4.4% at 120 K (at 0.8 T) is attributed to an intrinsic enhancement of the electrons spin polarization up to 21.5%.
Effect of high temperature annealing on ion-irradiation induced magnetization in FeRh thin films
Authors: Tohki A. , Aikoh K. , Iwase A. , Yoneda K. , Kosugi S. , Kume K. , Batchuluun T. , Ishigami R. , Matsui T.
Published: March 2012

Low temperature ferromagnetic FeRh with B2-type crystal structure was successfully synthesized by annealing of the excessively irradiated FeRh thin film samples having nonmagnetic A1-type crystal structure. The B2 phase transformed from the A1 phase by this process contained some amount of lattice defects, such as anti-site defects and vacancies, which made the magnetic spins of the sample aligned. These results imply that the combination of the process of the ion-beam irradiation and annealing of the film samples makes the magnetic state systematically controlled.
Transition metal diffusion in diluted magnetic Si and GaAs prepared by pulsed laser processing
Authors: Bürger Danilo , Seeger Michael , Zhou Shengqiang , Skorupa Wolfgang , Schmidt Heidemarie
Published: March 2012

Starting from a random or ordered distribution of 0.8%, 1.6%, 3.7%, and 12.5% dopants over the lattice sites of a simple cubic grid, we estimate the fraction of unclustered dopants after pulsed laser processing of different host:dopant systems. Initial clustering events are simulated with a greedy algorithm implemented in a Monte Carlo study. The greedy algorithm gives adequate results for dopants with low diffusivity and low solubility. The absolute initial dopant concentration and declustering strongly influence the kinetics of clustering. Particularly, we consider transition metal doped Si and GaAs after pulsed laser annealing, which are of interest for spintronics applications. An uncritical integral diffusion of Mn in GaAs:Mn and a tendency of Mn to form silicides in Si:Mn are simulated. These results are in good agreement with experimental observations.
Calculation of longitudinal polarizability and second hyperpolarizability of polyacetylene with the coupled perturbed Hartree-Fock/Kohn-Sham scheme: Where it is shown how finite oligomer chains tend to the infinite periodic polymer
Authors: Lacivita Valentina , Rèrat Michel , Orlando Roberto , Ferrero Mauro , Dovesi Roberto
Published: March 2012

The longitudinal polarizability, αxx, and second hyperpolarizability, γxxxx, of polyacetylene are evaluated by using the coupled perturbed Hartree-Fock/Kohn-Sham (HF/KS) scheme as implemented in the periodic CRYSTAL code and a split valence type basis set. Four different density functionals, namely local density approximation (LDA) (pure local), Perdew-Becke-Ernzerhof (PBE) (gradient corrected), PBE0, and B3LYP (hybrid), and the Hartree-Fock Hamiltonian are compared. It is shown that very tight computational conditions must be used to obtain well converged results, especially for γxxxx, that is, very sensitive to the number of $\vec{k}$k⃗ points in reciprocal space when the band gap is small (as for LDA and PBE), and to the extension of summations of the exact exchange series (HF and hybrids). The band gap in LDA is only 0.01 eV: at least 300 $\vec{k}$k⃗ points are required to obtain well converged total energy and equilibrium geometry, and 1200 for well converged optical properties. Also, the exchange series convergence is related to the band gap. The PBE0 band gap is as small as 1.4 eV and the exchange summation must extend to about 130 Å from the origin cell. Total energy, band gap, equilibrium geometry, polarizability, and second hyperpolarizability of oligomers −(C2H2)m−, with m up to 50 (202 atoms), and of the polymer have been compared. It turns out that oligomers of that length provide an extremely poor representation of the infinite chain polarizability and hyperpolarizability when the gap is smaller than 0.2 eV (that is, for LDA and PBE). Huge differences are observed on αxx and γxxxx of the polymer when different functionals are used, that is in connection to the well-known density functional theory (DFT) overshoot, reported in the literature about short oligomers: for the infinite model the ratio between LDA (or PBE) and HF becomes even more dramatic (about 500 for αxx and 1010 for γxxxx). On the basis of previous systematic comparisons of results obtained with various approaches including DFT, HF, Moller-Plesset (MP2) and coupled cluster for finite chains, we can argue that, for the infinite chain, the present HF results are the most reliable.
Spin-bias driven field effect transistor
Authors: Ma M. J. , Jalil M. B. A. , Siu Z. B.
Published: March 2012

We propose a spin field effect transistor driven by spin biases which are externally generated in the source and drain electrodes. We employed the Keldysh non-equilibrium Green’s function formalism to evaluate the charge and spin currents through the transistor, and verify the operation of the transistor as predicted by a semiclassical model. Our calculations show that in the “off” state, both the charge and spin currents are suppressed. In the “on” state, the device allows only the spin current to pass through but not charge current, thus potentially improving the energy efficiency of the device.
Dielectric spectra broadening as the signature of dipole-matrix interaction. II. Water in ionic solutions
Authors: Levy Evgeniya , Puzenko Alexander , Kaatze Udo , Ishai Paul Ben , Feldman Yuri
Published: March 2012

In this, the second part of our series on the dielectric spectrum symmetrical broadening of water, we consider ionic aqueous solutions. If in Part I, dipole-dipole interaction was the dominant feature, now ion-dipole interplay is shown to be the critical element in the dipole-matrix interaction. We present the results of high-frequency dielectric measurements of different concentrations of NaCl/KCl aqueous solutions. We observed Cole-Cole broadening of the main relaxation peak of the solvent in the both electrolytes. The 3D trajectory approach (described in detail in Part I) is applied in order to highlight the differences between the dynamics and structure of solutions of salts on one hand and dipolar solutes on the other hand.
Non-empirical improvement of PBE and its hybrid PBE0 for general description of molecular properties
Authors: del Campo Jorge M. , Gázquez José L. , Trickey S. B. , Vela Alberto
Published: March 2012

Imposition of the constraint that, for the hydrogen atom, the exchange energy cancels the Coulomb repulsion energy yields a non-empirical re-parameterization of the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) exchange-correlation energy functional, and of the related PBE hybrid (PBE0). The re-parameterization, which leads to an increase of the gradient contribution to the exchange energy with respect to the original PBE functional, is tested through the calculation of heats of formation, ionization potentials, electron affinities, proton affinities, binding energies of weakly interacting systems, barrier heights for hydrogen and non-hydrogen transfer reactions, bond distances, and harmonic frequencies, for some well known test sets designed to validate energy functionals. The results for the re-parameterized PBE GGA, called PBEmol, give substantial improvement over the original PBE in the prediction of the heats of formation, while retaining the quality of the original PBE functional for description of all the other properties considered. The results for the hybrids indicate that, although the PBE0 functional provides a rather good description of these properties, the predictions of the re-parameterized functional, called PBEmolβ0, are, except in the case of the ionization potentials, modestly better. Also, the results for PBEmolβ0 are comparable to those of B3LYP. In particular, the mean absolute error for the bond distance test set is 17% lower than the corresponding error for B3LYP. The re-parameterization for the pure GGA (PBEmol) differs from that for the hybrid (PBEmolβ0), illustrating that improvement at the GGA level of complexity does not necessarily provide the best GGA for use in a hybrid.
Electrostatic vortex structures in a rotating magnetized electron-positron plasma with stationary ions
Authors: Mahmood S. , Kanwal Savera , Haque Q.
Published: March 2012

Nonlinear electrostatic vortex structures in the rotating magnetized electron-positron-ion plasmas are investigated. The electrons and positrons are considered to be dynamic while ions are taken to be stationary to neutralize only plasma background. In linear limit, the dispersion relation for electrostatic wave in a rotating electron-positron-ion plasma is discussed for both local and nonlocal cases. It is also found that conditions for the existence of dipolar vortex structures are modified in the presence of stationary ions in a magnetized rotating electron-positron plasma.
Enhancement of the Jahn-Teller distortion by magnetization in manganites
Authors: Chu Y. Y. , Wu H. H. , Liu S. C. , Lin Hsiu-Hau , Matsuno J. , Takagi H. , Huang J. H. , van den Brink J. , Chen C. T. , Huang D. J.
Published: March 2012

Using measurements of resonant x-ray scattering from a LaMnO3/SrMnO3 superlattice grown on SrTiO3(001), we present experimental evidence for the enhancement of the Jahn-Teller distortion by magnetic ordering in manganites. With a specially tuned periodicity of the superlattice, scattering due to the Jahn-Teller (JT) distortion is separated from charge and magnetic scattering. The measured JT distortion is markedly enhanced upon the emergence of magnetization and strongly correlated with the spin ordering in the superlattice. Such strong correlation reveals the nature of electron-electron interaction for orbital ordering in manganites.
Super-Poincarè algebras, space-times, and supergravities. II
Authors: Santi A. , Spiro A.
Published: March 2012

The presentation of supergravity theories of our previous paper “Super-Poincarè algebras, space-times, and supergravities. I” is re-formulated in the language of Berezin-Leites-Kostant theory of supermanifolds. It is also shown that the equations of Cremmer, Julia, and Scherk's theory of 11D-supergravity are equivalent to manifestly covariant equations on a supermanifold.
Magnetoelectric effect of three-phase core-shell-matrix particulate multiferroic composites
Authors: Kuo Hsin-Yi , Wu Tzu-Sheng
Published: March 2012

This paper studies the magnetoelectricity of a core-shell-matrix three-phase particulate composite made of piezoelectric (PE) and piezomagnetic (PM) phases. We propose a micromechanical model, the two-level recursive scheme in conjunction with Mori-Tanaka’s method, to investigate the effective magnetoelectric coupling coefficients of the composite. We compare this micromechanical solution with those predicted by finite element analysis, which provides the benchmark results for a periodic array of inclusions. Both the magnitudes and trends between them are in good agreement. Based on this micromechanical approach, we show that, for the case of PE/PM/PM (core/shell/matrix) multiferroic composite, with a coating appropriate for the inhomogeneity, the effective magnetoelectric coupling can be enhanced many-fold as compared to the noncoated counterpart. Further, useful design principles are proposed for engineering magnetoelectric composites.
Piezoelectricity in zincblende polar semiconductor nanowires: A theoretical study
Authors: Sen Banani , Stroscio Michael , Dutta Mitra
Published: March 2012

A systematic evaluation of the piezoelectrically induced electric polarization vector and the associated potential on the application of mechanical strain to charge-free semiconductor nanowires with zincblende crystal structure is reported. It is found that the bending mode which is easier to realize in practice over stable compressional modes generates maximum piezo energy for these zincblende semiconductor nanowires. Also zincblende ZnO nanowires are found to be superior over zincblende AlN and GaN wires for piezo energy harvesting.
Semi-infinite boundary conditions for the simulation of interfaces: The Ar/CO2(s) model revisited
Authors: de Gregorio Rocio , Benet Jorge , Katcho Nebil A. , Blas Felipe J. , MacDowell Luis G.
Published: March 2012

We propose a method to account for the long tail corrections of dispersive forces in inhomogeneous systems. This method deals separately with the two interfaces that are usually present in a simulation setup, effectively establishing semi-infinite boundary conditions that are appropriate for the study of the interface between two infinite bulk phases. Using the wandering interface method, we calculate surface free energies of vapor–liquid, wall–liquid, and wall–vapor interfaces for a model of Lennard–Jones argon adsorbed on solid carbon dioxide. The results are employed as input to Young's equation, and the wetting temperature located. This estimate is compared with predictions from the method of effective interface potentials and good agreement is found. Our results show that truncating Ar–Ar interactions at two and a half molecular diameters results in a dramatic decrease of the wetting temperature of about 40%.
Calorimetric and relaxation properties of xylitol-water mixtures
Authors: Elamin Khalid , Sjöström Johan , Jansson Helén , Swenson Jan
Published: March 2012

We present the first broadband dielectric spectroscopy (BDS) and differential scanning calorimetry study of supercooled xylitol-water mixtures in the whole concentration range and in wide frequency (10−2–106 Hz) and temperature (120–365 K) ranges. The calorimetric glass transition, Tg, decreases from 247 K for pure xylitol to about 181 K at a water concentration of approximately 37 wt. %. At water concentrations in the range 29–35 wt. % a plentiful calorimetric behaviour is observed. In addition to the glass transition, almost simultaneous crystallization and melting events occurring around 230–240 K. At higher water concentrations ice is formed during cooling and the glass transition temperature increases to a steady value of about 200 K for all higher water concentrations. This Tg corresponds to an unfrozen xylitol-water solution containing 20 wt. % water. In addition to the true glass transition we also observed a glass transition-like feature at 220 K for all the ice containing samples. However, this feature is more likely due to ice dissolution [A. Inaba and O. Andersson, Thermochim. Acta, 461, 44 (2007)]. In the case of the BDS measurements the presence of water clearly has an effect on both the cooperative α-relaxation and the secondary β-relaxation. The α-relaxation shows a non-Arrhenius temperature dependence and becomes faster with increasing concentration of water. The fragility of the solutions, determined by the temperature dependence of the α-relaxation close to the dynamic glass transition, decreases with increasing water content up to about 26 wt. % water, where ice starts to form. This decrease in fragility with increasing water content is most likely caused by the increasing density of hydrogen bonds, forming a network-like structure in the deeply supercooled regime. The intensity of the secondary β-relaxation of xylitol decreases noticeably already at a water content of 2 wt. %, and at a water content above 5 wt. % it has been replaced by a considerably stronger water (w) relaxation at about the same frequency. However, the similarities in time scale and activation energy between the w-relaxation and the β-relaxation of xylitol at water contents below 13 wt. % suggest that the w-relaxation is governed, in some way, by the β-relaxation of xylitol, since clusters of water molecules are rare at these water concentrations. At higher water concentrations the intensity and relaxation rate of the w-relaxation increase rapidly with increasing water content (up to the concentration where ice starts to form), most likely due to a rapid increase of small water clusters where an increasing number of water molecules interacting with other water molecules.
Signatures of fragile-to-strong transition in a binary metallic glass-forming liquid
Authors: Lad K. N. , Jakse N. , Pasturel A.
Published: March 2012

Classical molecular dynamics investigations of the evolution of the microscopic structure and atomic dynamics are found to provide signatures of fragile-to-strong transition in a Cu-Zr bulk metallic glass forming alloy. Present study reveals that (i) the alloy exhibits a non-monotonic decoupling of the self-diffusion coefficient D and the relaxation time τ as observed in case of supercooled water despite the difference in the intermolecular interactions compared to this system, (ii) the temperature dependence of D and τ suggests a crossover from non-Arrhenius to Arrhenius behavior near mode-coupling transition temperature TC, and (iii) the alloy exhibits a crossover from Stokes-Einstein ((D ∼ (τ/T)−1) to fractional Stokes-Einstein (D ∝ (τ/T)−ζ) with exponent ζ ≈ 0.6. A weak first-order transition, associated with the fragile-to-strong transition, has also been observed in the undercooled region. These findings are in accordance with the growing idea of fragile-to-strong crossover having larger generality than the traditional classification of the glass-forming liquids as fragile and strong.
Terahertz time domain attenuated total reflection spectroscopy with an integrated prism system
Authors: Nakanishi Atsushi , Kawada Yoichi , Yasuda Takashi , Akiyama Koichiro , Takahashi Hironori
Published: March 2012

We demonstrated attenuated total reflection (ATR) spectroscopy with an integrated prism system that included a terahertz emitter, a terahertz receiver, and an ATR prism. The ATR prism had two internal off-axis parabolic mirrors for, respectively, collimating and focusing the terahertz waves. The Fresnel loss at each interface was reduced, and the total propagation efficiency was 3.36 times larger than when using a non-integrated prism system. The refractive index of water samples calculated from the experimental data showed good agreement with values reported in the literature.
Theoretical study of the surface waves in semi-bounded quantum collisional plasmas
Authors: Khorashadizadeh S. M. , Taheri Boroujeni S. , Rastbood E. , Niknam A. R.
Published: March 2012

The propagation of surface waves on a semi-bounded quantum plasma is investigated taking into account the collisional effects. The quantum hydrodynamic model includes Bohm’s quantum force, Fermi-Dirac statistical, and collisional corrections are used to derive the dispersion relation of these waves. It is shown that the collisions play a significant role on the decay of surface wave amplitude. Furthermore, the surface waves can be unstable in the presence of collisional effects. It is also indicated that the growth rate of the surface wave instability increases with the increase of collisional and quantum effects, especially in the high wavenumber region.
Experimental study of initial condition dependence on Richtmyer-Meshkov instability in the presence of reshock
Authors: Balasubramanian S. , Orlicz G. C. , Prestridge K. P. , Balakumar B. J.
Published: March 2012

We present an experimental study on the dependence of initial condition parameters, namely, the amplitude δ and wavenumber κ (κ = 2π/λ, where λ is the wavelength) of perturbations, on turbulence and mixing in shock-accelerated Richtmyer-Meshkov (R-M) unstable fluid layers. A single mode, membrane-free varicose heavy gas curtain (air-SF6-air) at a shock Mach number M = 1.2 was used in our experiments. The density (concentration) and velocity fields for this initial configuration were measured using planar laser -induced fluorescence (PLIF) and particle image velocimetry (PIV). In order to understand the effects of multi-mode initial conditions on shock-accelerated mixing, the evolving fluid interface formed during the incident shock (M = 1.2) was shocked again by a reflected shock wave at various times using a movable wall, thus enabling us to change both δ and κ simultaneously. A dimensionless length-scale defined as η = κδ is proposed to parametrically link the initial condition dependence to late-time mixing. It was observed experimentally that high wavenumber (short wavelength) modes enhance the mixing and transition to turbulence in these flows. Statistics such as power spectral density, density self-correlation, turbulent kinetic energy, and the rms of velocity fluctuations were measured using simultaneous PLIF-PIV to quantify the amount of mixing for varying values of η. The results indicate a dependence of initial condition parameters on mixing at late times. The results of this study present an opportunity to predict and “design” late-time turbulent mixing that has applications in inertial confinement fusion and general fluid mixing processes.
Highly precise and compact ultrahigh vacuum rotary feedthrough
Authors: Aiura Y. , Kitano K.
Published: March 2012

The precision and rigidity of compact ultrahigh vacuum (UHV) rotary feedthroughs were substantially improved by preparing and installing an optimal crossed roller bearing with mounting holes. Since there are mounting holes on both the outer and inner races, the bearing can be mounted directly to rotary and stationary stages without any fixing plates and housing. As a result, it is possible to increase the thickness of the bearing or the size of the rolling elements in the bearing without increasing the distance between the rotating and fixing International Conflat flanges of the UHV rotary feedthrough. Larger rolling elements enhance the rigidity of the UHV rotary feedthrough. Moreover, owing to the structure having integrated inner and outer races and mounting holes, the performance is almost entirely unaffected by the installation of the bearing, allowing for a precise optical encoder to be installed in the compact UHV rotary feedthrough. Using position feedback via a worm gear system driven by a stepper motor and a precise rotary encoder, the actual angle of the compact UHV rotary feedthrough can be controlled with extremely high precision.
Effect of sintering conditions on mixed ionic-electronic conducting properties of silver sulfide nanoparticles
Authors: Yin Shong , Terabe Kazuya , Toney Michael F. , Subramanian Vivek
Published: March 2012

The process dependence of the mixed ionic-electronic conductivity of sintered octadecylamine-encapsulated silver sulfide nanoparticle thin films has been studied and correlated with the film structure. Although grain growth begins around 120 °C, there is no significant electrical conductivity until 350 °C and mixed conductivity until 400 °C, when the nanoparticle encapsulant evaporates. Higher temperatures decompose the silver sulfide. In lateral structures, no filaments form until sintering at 400 °C. The process dependence of mixed ionic electronic conducting properties may provide a method for engineering materials for use in electrochemical metallization resistive random access memories.
Diffusion in one-dimensional channels with zero-mean time-periodic tilting forces
Authors: Muñoz-Gutiérrez E. , Alvarez-Ramirez J. , Dagdug L. , Espinosa-Paredes G.
Published: March 2012

We investigate the motion of overdamped Brownian particles in a one-dimensional channel under a zero-mean time-periodic tilting force F(t). By introducing a simple harmonic signal, strong enhancement of diffusion is possible for relatively large values of the Peclet number. Direct numerical simulations over the corresponding Fokker-Planck equation show that the diffusion enhancement is induced by a type of nonlinear resonance effect involving the tilting force and the density gradient.
Shape fluctuation-induced dynamic hysteresis
Authors: Das Moupriya , Mondal Debasish , Ray Deb Shankar
Published: March 2012

We consider a system of Brownian particles confined in a two-dimensional bilobal enclosure whose walls are driven in time periodically by an external perturbation. The response of the particles under shape modulation is characterized by a relaxational delay which results in a non-vanishing area of the response function—field loop, response function being the integrated probability of residence of the particles in any of the lobes. This phenomenon is an entropic analogue of dynamical hysteresis, which vanishes in the quasi-static limit. The hysteresis loop area depends on temperature, strength of modulating field, and the geometrical parameters of the enclosure and exhibits a turnover as a function of frequency of the field.
Bernstein-Greene-Kruskal waves in relativistic cold plasma
Authors: Singh Verma Prabal , Sengupta Sudip , Kaw Predhiman
Published: March 2012

We construct the longitudinal traveling wave solution [Akhiezer and Polovin, Sov. Phys. JETP 3, 696 (1956)] from the exact space and time dependent solution of relativistic cold electron fluid equations [Infeld and Rowlands, Phys. Rev. Lett. 62, 1122 (1989)]. Ions are assumed to be static. We also suggest an alternative derivation of the Akhiezer Polovin solution after making the standard traveling wave Ansatz.
Post growth annealing study on long wavelength infrared InAs/GaSb superlattices
Authors: Haugan H. J. , Brown G. J. , Elhamri S. , Pacley S. , Olson B. V. , Boggess T. F.
Published: March 2012

The impact of post growth annealing on the electrical properties of a long wavelength infrared type-II superlattice (SL) was explored. Quarters of a single SL wafer were annealed at 440 °C, 480 °C, and 515 °C, respectively for 30 min. Changes in the electrical properties were followed using spectral photoconductivity, temperature dependent Hall effect, and time-resolved pump-probe measurements. The bandgap energy remained at ∼107 meV for each anneal, and the photoresponse spectra showed a 25% improvement. The carrier lifetime increased from 12 to ∼15 ns with annealing. The electron mobility was nearly constant for the 440 °C and 480 °C anneals, and increased from ∼4500 to 6300 cm2/Vs for the 515 °C anneal.
Integrated photonic structures for light trapping in thin-film Si solar cells
Authors: Sheng Xing , Johnson Steven G. , Broderick Lirong Z. , Michel Jurgen , Kimerling Lionel C.
Published: March 2012

We explore the mechanisms for an efficient light trapping structure for thin-film silicon solar cells. The design combines a distributed Bragg reflector (DBR) and periodic gratings. Using photonic band theories and numerical simulations, we discover that light can be scattered into the DBR by gratings, with an unusual way of light trapping different from metal reflectors and photonic crystals. We further investigate the influence of DBR on generated photocurrent in different device configurations. These results would provide new design rules for photonic structures in thin-film solar cells.
On a measure of distance for quantum strategies
Authors: Gutoski Gus
Published: March 2012

The present paper studies an operator norm that captures the distinguishability of quantum strategies in the same sense that the trace norm captures the distinguishability of quantum states or the diamond norm captures the distinguishability of quantum channels. Characterizations of its unit ball and dual norm are established via strong duality of a semidefinite optimization problem. A full, formal proof of strong duality is presented for the semidefinite optimization problem in question. This norm and its properties are employed to generalize a state discrimination result of Gutoski and Watrous [In Proceedings of the 22nd Symposium on Theoretical Aspects of Computer Science (STACS’05), Lecture Notes in Computer Science, Vol. 3404 (Springer, 2005), pp. 605–616. The generalized result states that for any two convex sets S0, S1 of strategies there exists a fixed interactive measurement scheme that successfully distinguishes any choice of S0 ∈ S0 from any choice of S1 ∈ S1 with bias proportional to the minimal distance between the sets S0 and S1 as measured by this norm. A similar discrimination result for channels then follows as a special case.
Superficial magnetic imaging by an xy-scanner of three magnetoresistive channels
Authors: Cano M. E. , Pacheco A. H. , Cordova T. , Mazon E. E. , Barrera A.
Published: March 2012

A scanning system developed for planar magnetic surfaces composed of a moving line of three magnetoresistive ultrasensitive transducers, complemented by a signal conditioning circuit is presented. After the calibration of the sensors, it was used to determine magnetized surface images with different shapes to evaluate the sensitivity of the device, and the images are represented in gray levels on a scale from 0 to 255 intensities, to get a visual representation of the magnetic field strength. The device is shown to be sensitive enough to detect gradients homogeneities and discontinuities in the magnetic field maps and images of magnetic susceptibility.
Phonon transport in Si nanowires with elastically dissimilar barriers
Authors: Hyun Oh Jung , Jang Moon-Gyu , Shin Mincheol , Lee Seok-Hee
Published: March 2012

As one of the efforts to enhance the thermoelectric conversion efficiency, phonon transport through elastically dissimilar barriers embedded in Si nanowires is investigated. Using a Green’s function method based on an elastic wave equation, the transmission function is calculated for various barrier materials with different acoustic impedance. It is found that the insertion of silicide (especially PtSi) layers into the Si nanowire substantially suppresses the phonon transmission function and, thus, is promising alternative to enhance the efficiency of thermoelectric devices.
Efficiency droop in AlGaInP and GaInN light-emitting diodes
Authors: Shim Jong-In , Han Dong-Pyo , Kim Hyunsung , Shin Dong-Soo , Lin Guan-Bo , Meyaard David S. , Shan Qifeng , Cho Jaehee , Fred Schubert E. , Shim Hyunwook , Sone Cheolsoo
Published: March 2012

At room temperature, AlGaInP pn-junction light-emitting diodes (LEDs) emitting at 630 nm do not exhibit an efficiency droop. However, upon cooling the AlGaInP LEDs to cryogenic temperatures, they show a pronounced efficiency droop. We attribute the efficiency droop in AlGaInP LEDs to electron-drift-induced reduction in injection efficiency (i.e., carrier leakage out of the active region) mediated by the asymmetry of the pn junction, specifically the disparity between electron and hole concentrations and mobilities, with the concentration disparity exacerbated at low temperatures.
Time-resolved single-shot imaging of femtosecond laser induced filaments using supercontinuum and optical polarigraphy
Authors: Yan Lihe , Wang Xiaofang , Si Jinhai , Matsuo Shigeki , Chen Tao , Tan Wenjiang , Chen Feng , Hou Xun
Published: March 2012

We have developed an ultrafast time-resolved imaging technique for the propagation dynamics of ultrashort laser pulses in transparent media. This method utilizes the optical polarigraphy technique and a chirped supercontinuum as the probe light. The supercontinuum senses the instantaneous birefringence induced by the propagation of an intense pulse, and a polarigraphy image with different color distributions could be obtained. Using this method, we performed a space-time characterization of the filament induced by a femtosecond laser pulse in CS2, indicating that this technique could be used for the single-shot imaging of pulse propagation dynamics.
Shape oscillations of an electrically charged diamagnetically levitated droplet
Authors: Hill R. J. A. , Eaves L.
Published: March 2012

We use diamagnetic levitation to investigate the effect of electrical charge on the normal mode vibration frequencies of charged water droplets with radii 4.5-7.5 mm. This technique allows us to levitate almost spherical droplets, enabling us to directly compare the measured frequencies of the first seven modes with theoretical values calculated by Lord Rayleigh, with which we find good agreement.
Sulfur-doped TiO2 nanocrystalline photoanodes for dye-sensitized solar cells
Authors: Sun Qiang , Zhang Jing , Wang Peiqing , Zheng Jun , Zhang Xunni , Cui Yanzheng , Feng Jiangwei , Zhu Yuejin
Published: March 2012

Sulfur-doped TiO2 is prepared by a mechanical process with ball milling the thiourea with commercial P25 TiO2 nanoparticles and successfully used as photoanode of dye-sensitized solar cells (DSSCs). The x-ray photoelectron spectroscopy results indicate that sulfur-doped TiO2 are locally distorted by incorporating S6+ species into TiO2 and substitutes for some of the lattice titanium (Ti4+); meanwhile, a clear reduction in the band gap energy of the sulfur-doped TiO2 photoanode compared to the band gap value for P25. The linear sweep voltammetry indicate that the edge of the conduction band of sulfur-doped TiO2 move positively toward the vacuum level. A conversion efficient of 6.91% was achieved for a DSSC based on sulfur-doped solar cell, which was 24% higher than that of the un-doped solar cell. The improved performance was ascribed to the improved charge injection from the dye to the sulfur doped TiO2 electrode, as evidence by an improved spectral response in the whole wavelength range.
Inter-channel effects in monosolvated atomic iodide cluster anion detachment: Correlation of the anisotropy parameter with solvent dipole moment
Authors: Mbaiwa Foster , Dao Diep , Holtgrewe Nicholas , Lasinski Joshua , Mabbs Richard
Published: March 2012

Photoelectron imaging results are presented for I−·X cluster anions (X = CO2, C4H5N [pyrrole], (CH3)2CO, CH3NO2). The available detachment channels are labeled according to the neutral iodine atom states produced (channel I ≡ 2P3/2 and channel II ≡ 2P1/2). At photon energies in the vicinity of the channel II threshold these data are compared to previously reported results for I−·X (X = CH3CN, CH3Cl, CH3Br, and H2O). In particular, these results show a strong connection between the dipole moment of the solvent molecule and the behavior of the channel I photoelectron angular distributions in this region, which is consistent with an electronic autodetachment process. The evolution of the channel II:channel I branching ratios in this excitation regime supports this contention.
One step high quality poly(dimethylsiloxane)-hydrocarbon plastics bonding
Authors: Xu Bi-Yi , Yan Xiao-Na , Xu Jing-Juan , Chen Hong-Yuan
Published: March 2012

In this paper, one-step air plasma treatment is successfully used for poly(dimethylsiloxane)(PDMS)-plastic chip bonding. The technique is green, cheap, and requires no other reagent other than air. Hydrocarbon plastics: polystyrene (PS), cyclic olefin copolymer (COC), and polypropylene (PP) have all been successfully bonded to PDMS irreversibly. The corresponding compressed air resistances are measured to be around 500 kPa for PDMS-PS, PDMS-COC, and PDMS-PP hybrid chips. The bondings are also of good quality even after storage under different temperatures and subject to solutions from acid to base.