bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermolecular energy transfer in binary systems of dye polymers
Authors: Liu Lin-I , Barashkov Nikolay N. , Palsule Chintamani P. , Gangopadhyay Shubhra , Borst Walter L.
Published: July 2002

We present results and physical interpretations for the energy transfer mechanisms in two-component dye polymer systems. The data consist of fluorescence emission spectra and decays. Two dyes were embedded in an epoxypolymer base, and only they participated in the energy transfer. Following pulsed laser excitation of the donor dye, energy transfer took place to the accept dye. The possible transfer paths considered here were nonradiative and radiative transfer. The latter involves two steps, emission and absorption of a photon, and therefore is relatively slow, while nonradiative transfer is a fast single step resulting from direct Coulomb interactions. A predominantly nonradiative transfer is desirable for applications, for instance in wavelength shifters in high energy particle detection. We studied the concentration effects of the dyes on the energy transfer and obtained the relative quantum efficiencies of various wavelength shifters from the fluorescence emission spectra. For low acceptor concentrations, radiative transfer was found to dominate, while nonradiative transfer became dominant at increasing dye concentrations. The fluorescence decays were analyzed with a sum-of-exponentials method and with Förster kinetics. The sum of exponential model yielded mean decay times of the dye polymers useful for a general classification. The decay times decreased as desired with increasing acceptor concentration. The samples, in which nonradiative energy transfer dominated, were analyzed with Förster kinetics. As a result, the natural decay times of the donor and acceptor dyes and the critical radii for nonradiative energy transfer were obtained from a global best fit.
Ultrafast charge division imaging detector
Authors: Liu Alan , Woo Brian , Odom Robert W.
Published: July 2002

We have developed position computing electronics having less than 60 ns dead times for resistive anode encoders, a form of charge division imaging detector. These electronics are at least a factor of 5 faster than anything available commercially and are based on using a fast, self-resetting charge integrator and subrange digital division techniques. Our primary application for this detector is secondary ion mass spectrometry (SIMS)/ions imaging and we demonstrate that SIMS imaging applications using these ultrafast electronics can readily be performed at ion intensities above 106 cps. This article discusses the overall electronics design and presents experimental data on dead-time measurements, detector lateral resolution, and SIMS imaging.
Low degradation and fast annealing effects of amorphous silicon multilayer processed through alternate hydrogen dilution
Authors: Jun Kyung Hoon , Ouwens Jeroen Daey , Schropp Ruud E. I. , Lee Jeong Yong , Choi Jae Hyung , Lee Ho Seong , Lim Koeng Su
Published: July 2002

Alternately hydrogen diluted a-Si:H multilayers are shown to be a promising concept for the fabrication of stable a-Si:H solar cells or other a-Si:H based devices. The alternately hydrogen diluted amorphous silicon multilayers were obtained by toggling both the H2/SiH4 dilution ratio and the total flow rate of the gases under continuous UV light irradiation into the reaction chamber of a photochemical vapor deposition system. The films were characterized by Fourier transformed infrared spectroscopy, spectroscopic ellipsometry, cross-sectional transmission electron microscopy, and atomic force microscopy. We applied these multilayers as the active layer of p–i–n type thin film solar cells. The multilayer solar cells are compared to solar cells incorporating a-Si:H made from pure SiH4 gas and to solar cells incorporating a-Si:H made at a constant hydrogen dilution ratio containing nearly the same hydrogen amount as the multilayer. We report on the light-soaking and annealing behavior of the solar cells. The multilayer solar cell has an exceptionally high recovery rate at low temperatures, which makes the solar cell degradation behavior highly sensitive to the cell temperature during degradation. Following the relation, DH∝1/τ, where DH and τ are the diffusion coefficient for hydrogen and time constant for annealing, respectively, the layered structure in the multilayer possibly elevates DH, which accounts for rapid stabilization and annealing.
Kinetic foundation of extended irreversible thermodynamics
Authors: Chen M.
Published: July 2002

In this paper we investigate the kinetic foundation of extended irreversible thermodynamics via the moment method. First we consider the construct of the 1-particle distribution function f in terms of its moments by maximizing the entropy density function. We then project f from its L2 space onto the local thermodynamic variables z=(z1,…,zN) in the thermodynamic base space B̂N. Thus instead of the Boltzmann equation we consider a set of evolution equations of z in B̂N. Second, we formulate the laws of thermodynamics governing the variable z in B̂N. These laws exhibit an intrinsic geometric structure of thermodynamics in the setting of contact geometry. Finally, as an illustration, we discuss the evolution equations for the bulk pressure Pb, heat flux Q, and the symmetric traceless tensor π⇊ corresponding to the viscous and heat conduction irreversible processes. These equations can be formulated as an abstract inhomogeneous hyperbolic evolution equation. By employing the C0 semigroup technique, we discuss the solution of the evolution equation and its asymptotic behavior. We show that thermodynamic stability condition of the system implies asymptotic dynamical stability of the solution and vice versa.
Variable temperature, variable-gap Otto prism coupler for use in a vacuum environment
Authors: Cairns G. F. , O’Prey S. M. , Dawson P.
Published: July 2002

The field of surface polariton physics really took off with the prism coupling techniques developed by Kretschmann and Raether, and by Otto. This article reports on the construction and operation of a rotatable, in vacuo, variable temperature, Otto coupler with a coupling gap that can be varied by remote control. The specific design attributes of the system offer additional advantages to those of standard Otto systems of (i) temperature variation (ambient to 85 K), and (ii) the use of a valuable, additional reference point, namely the gap-independent reflectance at the Brewster angle at any given, fixed temperature. The instrument is placed firmly in a historical context of developments in the field. The efficacy of the coupler is demonstrated by sample attenuated total reflectance results on films of platinum, niobium, and yttrium barium copper oxide and on aluminum/gallium arsenide (Al/GaAs) Schottky diode structures.
A fast high-voltage amplifier for driving piezoelectric positioners
Authors: Colclough M. S.
Published: July 2002

A dc-coupled high-voltage amplifier suitable for driving piezoelectric positioners in both linear and stepping modes is described. The amplifier provides a bipolar output of up to 200 V and 340 mA, and has a maximum slew rate of 300 V/μs.
A multipurpose apparatus for studying the interaction of low energy ions with solid state surface
Authors: Terzić I. , Bundaleski N. , Rakočević Z. , Oklobdžija N. , Elazar J.
Published: July 2002

A new concept of a multipurpose device for the investigation of a low energy in beam interactions with solid state surfaces is realized in an apparatus for surface analysis by means of low energy ion scattering (LEIS), direct recoil spectrometry (DRS), mass spectrometry of recoil ions (MRSI), and secondary-ion mass spectrometry (SIMS). This device provides broad alkali ion beams, homogeneous and much more intense than in standard commercial realizations available, as well as various high quality intense gas ion beams. A long tube with a magnetic quadrupole triplet is introduced. This construction disjoins the high vacuum from the ultrahigh vacuum (UHV) parts of the system and makes possible low cost differential pumping. The use of an UHV broad alkali ion beam in SIMS experiments should importantly decrease crater effect problems without use of rastering and electrical gating systems. In order to demonstrate the possibilities and the advantages of the proposed concept, we present the results of experimental analysis of primary ion beam characteristics, as well as LEIS and DRS experimental results obtained by use of gas ion beams scattered from silver polycrystalline surfaces. This design concept results in a simple and low cost device with operating characteristics comparable to those of high quality devices of similar type.
Computer optimization for high-resolution time-of-flight mass spectrometer
Authors: Even U. , Dick Bernhard
Published: July 2002

We describe the theoretical computation, and provide construction details, of a high-resolution time-of-flight mass spectrometer that can replace reflectrons in many applications.
Development of a high-resolution x-ray imaging system with a charge-coupled-device detector coupled with crystal x-ray magnifiers
Authors: Sato K. , Hasegawa Y. , Kondo K. , Miyazaki K. , Matsushita T. , Amemiya Y.
Published: July 2002

A high-spatial-resolution x-ray imaging system for microscopic use has been developed, which utilizes a charge-coupled-device (CCD) detector as an imaging device. The spatial resolution of the x-ray CCD detector with Gd2O2S:Tb is 8.0 μm in terms of the full width at half-maximum of the line-spread function with a conversion gain of 0.58 e-h/xph. In order to obtain a higher spatial resolution, x-ray magnifiers based on asymmetric Si(111) Bragg reflections are placed in front of the x-ray CCD detector. The spatial resolution of this imaging system has been improved to 1.2 μm.
Vibration–rotation transfer in molecular super rotors
Authors: McCaffery Anthony J.
Published: July 2002

The collisional behavior of (X)6Li2 molecules in very high rotational levels of v=0 is considered. Highly efficient vibration–rotation transfer is predicted in these “super rotors” particularly when the conditions for quasiresonant transfer are fulfilled. This requires simultaneous near-resonance in energy and in angular momentum. Values of Δj for which quasiresonant vibration–rotation transfer (QRT) occurs become smaller as initial rotor state increases and transfer is likely to become particularly fast for Δj=2, predicted to occur when ji=130. This behavior is contrasted with the inefficiency of pure rotational transfer within the v=0 level for fast-rotating molecules. QRT will take place for quite cold collisions and thus will provide competition for the spinning-up process used to create the super rotors.
Potential energy surfaces of supercooled water: Intrabasin and interbasin structures explored by quenching, normal mode excitation, and basin hopping
Authors: Tanaka Hideki
Published: July 2002

We investigate the potential energy surfaces of supercooled water, both intrabasin structures and distributions of the potential energy basins in configuration space by the steepest descent quenching and the normal mode excitation. The paths from liquid configurations to the corresponding local energy minima and the root mean square distance exhibit different characters below and above the temperature 213 K where the thermodynamics and structural properties change abruptly. The root mean square distance in the temperature range (298 K to 173 K) is larger than the corresponding harmonic oscillator system and it drastically increases above 223 K. The complexity also increases along the steepest descent path by increasing the number of inflection points. In order to investigate the other potential energy basins distributed in the vicinity of the (central) basin that the molecular dynamics trajectory visits, the distributions of these basins are examined by the normal mode excitation. The number of distinct basins increases with increasing temperature in the same volume of configuration space. The minimum potential energy of the adjacent basin at low temperature is almost always higher than the minimum potential energy of the central basin while that of the adjacent basin at high temperature is comparable to the central basin. The locations of the other basin centers are mostly orthogonal to the normal mode excitation. The potential energy surfaces are also examined by the basin hopping technique to seek for lower energy configurations started with a random and high energy molecular arrangement. It is found that energetically more stable molecules aggregate rather heterogeneously in the intermediate energy levels, which are hardly observed in the simulation, while the stable molecules distribute homogeneously in the lowest energy levels.
Epitaxial Sc1−xTixN(001): Optical and electronic transport properties
Authors: Gall D. , Petrov I. , Greene J. E.
Published: July 2002

Single crystalline Sc1−xTixN layers, with compositions spanning the entire range (0⩽x⩽1), were grown on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition at 750 °C. Optical transmission and reflectivity spectra are well described by a Drude–Lorentz model. The optical carrier density N* increases linearly from 1.0×1021 for ScN to 4.6×1022 cm−3 for TiN while the room-temperature electrical resistivity ρ300K varies by more than 2 orders of magnitude, from 2×10−3 Ω cm for ScN to 13 μΩ cm for TiN. ρ300K agrees well with optically determined resistivity values for alloys with compositions up to x=0.66, corresponding to the onset of electron filling in the second and third conduction bands. We calculated ScN and TiN band structures by ab initio density functional methods and used the results to simulate the field responses of free carriers in the Sc1−xTixN layers. From this, we determined, in combination with the measured temperature dependence of the resistivity, the low-temperature carrier relaxation time τ(x). The composition dependence of τ is dominated by alloy scattering and agrees well with our measured optical results. Hall experiments were used to obtain the effective carrier density Neff(x) which increases linearly with x up to x=0.4. Neff(x) is relatively flat for alloy compositions between x=0.4 and 0.7, due to anisotropies in the conduction band, and exhibits a steep increase at x>0.7 as higher lying conduction bands begin to be occupied. Our simulated Sc1−xTixN electronic transport properties are in good agreement with experiment. Interband optical absorption results can also be understood based upon the calculated band structures.
Petrov type D Einstein space–times of embedding class two
Authors: Hodgkinson D. E.
Published: July 2002

A space–time is of embedding class 2 if its curvature tensor can be written in terms of two symmetric tensors aαβ and bαβ which satisfy the Gauss, Codazzi, and Ricci equations. For an Einstein space–time the Ricci tensor is proportional to the metric tensor. Using the Petrov classification of the curvature tensor and canonical forms of aαβ and bαβ, this paper produces a list of the embedding class 2 Petrov type D Einstein space–times. After a summary of the basic equations and the previous work on embedding class 2 space–times, the field equations for Einstein space–times are expressed in a canonical form and the type D Petrov conditions applied. The resulting equations are solved and give two sets of metrics. The first are known metrics which are products of two 2-spaces of constant curvature and the second set is a generalization of the Kottler solution. The form of the second set of solutions depends upon whether the metric depends upon one or two of the four coordinates.
Numerical test of the Percus–Yevick approximation for continuum media of adhesive sphere model at percolation threshold
Authors: Lee Sang Bub
Published: July 2002

We test accuracies of the Percus–Yevick (PY) approximation for percolation thresholds and long-range correlated probability functions for continuum media of the adhesive sphere model. We clarify the universality of the continuum percolation of such a model and estimate the percolation thresholds for selected values of the adhesiveness parameter τ. We then calculate the pair-connectedness function and the two-point cluster function at percolation point and compare them with the analytical predictions by the PY approximation. We find that the PY approximation yields the pecolation points overestimated for τ>0.161 and underestimated for τ<0.161. The analytical calculations of the probability functions exhibit fairly good agreement with the Monte Carlo data for τ=0.161. However, for other values of τ, the analytical results show marked deviations from the Monte Carlo data.
High order relativistic corrections to Keplerian motion
Authors: Fernández-Jambrina L. , Hoenselaers C.
Published: July 2002

The first terms of the general solution for an asymptotically flat stationary axisymmetric vacuum spacetime endowed with an equatorial symmetry plane are calculated from the corresponding Ernst potential up to seventh order in the radial pseudospherical coordinate. The metric is used to determine the influence of high order multipoles in the perihelion precession of an equatorial orbit and in the node line precession of a nonequatorial orbit with respect to a geodesic circle. Both results are written in terms of invariant quantities such as the Geroch–Hansen multipoles and the energy and angular momentum of the orbit.
Adiabatic positron affinity of LiH
Authors: Strasburger Krzysztof
Published: July 2002

The equilibrium geometry of the positronic molecule e+LiH has been found, using the explicitly correlated Gaussian functions in the variational calculations. The value of the adiabatic positron affinity of lithium hydride has been calculated. The influence of the geometry relaxation on the properties of the system has also been shortly discussed.
Near-field scattering from red pigment particles: Absorption and spectral dependence
Authors: McNeil L. E. , Hanuska A. R. , French R. H.
Published: July 2002

When film coatings are made of pigment particles embedded in a transparent resin, the optical characteristics of the resulting film are determined not only by the bulk optical properties of the constituent materials, but also by the spatial distribution of the light scattered from small particles. If the particles are separated by distances comparable to their diameter, as is the case for high particle concentrations or agglomerated systems, the near-field interactions between the radiation fields of the particles can strongly influence the resulting far-field intensity distribution. In this work we have used full-field finite-element solutions of Maxwell’s equations to calculate the near- and far-field scattering patterns for single 500 nm quinacridone spheres and for pairs of particles. We find that the scattered intensity forms a forward-directed plume that extends far beyond the particle surface, especially at short wavelengths and where the absorption is large. This results in near-field interactions between pairs of particles that can either increase or decrease the scattering (both the total scattering and the fraction of the scattered light that is directed into the backward hemisphere), depending on the orientation of the particle pair relative to the direction of the incident light. In some cases, particularly if the particles are aligned along the incident direction, the two spheres can produce a far-field scattering distribution that is approximately that of a single, larger (sometimes much larger) sphere. If the particles are aligned perpendicular to the incident direction, the strength of the scattering per particle volume is roughly the same as for a single particle, but the scattering is more forward directed. These interaction effects occur even though the surface-to-surface separation of the particles is larger than the distance for which a single particle shows significant scattered intensity. These near-field and far-field phenomena are beyond the limitations of single-scattering and independent multiple-scattering approaches, and the near-field interactions can have a significant effect on the scattering of light from films containing such particles, especially if they tend to form oriented clusters.
Nano-oxidation of silicon nitride films with an atomic force microscope: Chemical mapping, kinetics, and applications
Authors: Chien F. S.-S. , Chou Y. C. , Chen T. T. , Hsieh W.-F. , Chao T.-S. , Gwo S.
Published: July 2002

We demonstrate that local oxidation of silicon nitride films deposited on conductive substrates with a conductive-probe atomic force microscope (AFM) is a very promising approach for nanofabrication. Scanning Auger microscopy and spectroscopy are employed to verify the chemical changes after AFM-induced oxidation. Furthermore, the growth kinetics are found to have a logarithmic relationship of oxide height versus pulse duration [h∝ln(t/t0)]. In contrast to rather slow thermal oxidation process, AFM-induced oxidation on silicon nitride has an anomalously high initial oxidation rate (∼30 000 nm/s at 10 V) and a small onset time t0 (∼10 μs). As for the applications in ultrahigh-density recording, an oxide dot array (∼100 Gbit/in.2) produced by this process is demonstrated. The nitride film patterned by AFM can be utilized as an etching mask to fabricate “subtractive” silicon nanostructures, due to the large etching selectivity of Si3N4:SiO2:Si in various etchants. With this method, which is entirely compatible with the existing microelectronic processes, synthesis of ultrahigh packing density and ordered nanostructures could become readily achievable.
Modeling the effect of interactions in granular magnetic films
Authors: Liu Alfred D. , Bertram H. Neal
Published: July 2002

The effect of interactions on the blocking temperature of granular magnetic films is modeled using a variable time step Monte Carlo method. Both magnetostatic and exchange interactions are considered in the calculation of field cooled magnetization curves. Cubic grains with 28 Å side lengths are randomly packed within a larger cubic volume. Each grain has a random crystalline easy axis. For the parameters simulated, magnetostatic interactions do not have an effect on the blocking temperature, and exchange interactions cause average blocking temperatures to increase.
Effects of pressure on the trapping site structures and absorption spectra of Li in solid H2: A path integral Monte Carlo study
Authors: Ma Y. M. , Cui T. , Zou G. T.
Published: July 2002

Simulation studies for single atomic lithium in solid hydrogen using the path integral Monte Carlo (PIMC) method with a constant pressure ensemble are reported. The pressure dependencies of the absorption spectra of Li in solid H2 for various trapping sites are extensively investigated at T=5 K and different pressures in the range from 0 to 4.8 GPa. The local structure around the Li atom cannot be rearranged with respect to the presence of pressure. Effects of pressure on the trapping site structures refer only to the decrease in the Li–H2 and H2–H2 separations. The general pressure-induced effects on Li atomic absorption spectra associate with an increase in half-width and a centroid spectral shift (CSS), which experiences a blue shift below a turning pressure (Pt) and a red shift above Pt. For higher symmetrical trapping site structures, the peak splitting of the highly symmetrical triplet absorption pattern is mainly ascribed to the perturbation of the H2 molecules around the Li atom. For lower symmetrical trapping site structures, application of pressure also results in a change in absorption line shape from a low symmetrical triplet feature to a doublet plus singlet pattern, in which the doublet to singlet splitting increases remarkably with the increasing of pressure, while the perturbation of the H2 around the dopant largely determines the peak splitting for the “doublet.” We demonstrate that the pressure provides a powerful means to probe the properties, which cannot be observed at zero pressure.
Epitaxial growth of CoSi2 film by Co/a-Si/Ti/Si(100) multilayer solid state reaction
Authors: Qu Xin-Ping , Ru Guo-Ping , Han Yong-Zhao , Xu Bei-Lei , Li Bing-Zong , Wang Ning , Chu Paul K.
Published: July 2002

Epitaxial growth of CoSi2 by solid state reaction of Co/a-Si/Ti/Si(100) is investigated. A Ti/a-Si composite interlayer is used to modify the diffusion barrier and influence the epitaxial growth process. The epitaxial quality of the CoSi2 is improved compared to the film grown by Co/Ti/Si reaction. A multielement amorphous layer is formed by a solid-state amorphization reaction at the initial stage of the multilayer reaction. This layer acts as a diffusion barrier, which controls the atomic interdiffusion of Co and Si while limiting the supply of Co atoms. CoSi2 grows as the first phase and the growth interface of the epitaxial CoSi2 is at both the CoSi2/Si and CoSi2/CoSi interfaces. Investigation of the growth kinetics shows that the activation energy of CoSi2 formation is larger than that without an amorphous Si layer.
Spatial domain realization of the cavity ring-down technique in a plane Fabry–Perot cavity
Authors: Lee Jae Yong , Lee Hai-Woong , Hahn Jae Won
Published: July 2002

We propose and demonstrate a spatial version of the cavity ring-down concept in which a photon flux decay is displayed along the spatial coordinate at the exit of a plane Fabry–Perot cavity. The photon decay signals are simulated based on a simple theoretical model combining ray optics and diffraction involved in the spatial ring-down generation, which are found to be in good accordance with the results of a proof-of-principle expermient.
Ultraviolet-visible photodissociation spectra of Vn+Xe (n=5–8) cluster complex cations
Authors: Antonietti J. M. , Châtelain A. , Fedrigo S.
Published: July 2002

Photodissociation spectra of vanadium cluster ion-xenon atom complexes Vn+Xe (n=5–8) have been measured between 290 and 670 nm. Spectra have been obtained by recording the depletion signal induced on the mass-selected cluster current intensity by the absorption of a photon. Due to the weak interaction between the ionic cluster and the rare-gas atom, photodissociation spectra are regarded as the absorption spectra of the vanadium cluster cations themselves. The absorption bands are broad, but several peaks can be resolved for the smallest sizes. The influence of the rare-gas atom on the electronic structure of the vanadium cluster cation is probed by performing the measurements on krypton instead of on xenon complexes. The features of the spectra do not change, but a blueshift of 0.12 eV is observed from krypton to xenon.
Alloy-like Co environment in Co/Pd multilayer films having perpendicular magnetic anisotropy
Authors: Kim Sang-Koog , Shin Sung-Chul
Published: July 2002

Short-range atomic structures including the chemical environment and interatomic distance along the in- and out-of-plane directions in [Co (1 ML)/Pd(3 ML)]13 multilayer films (ML notes monolayer) are studied using polarized Co K-edge extended x-ray absorption fine structure. The chemical Co environment is found to be isotropic. The alloy-like character is dominant at interfaces in typical Co/Pd multilayers and yields perpendicular magnetic anisotropy (PMA) through the strain anisotropy of Co atoms. The broken symmetry, generally considered as of PMA origin, is not definitely necessary to result in PMA in Co/Pd multilayers.
Coalescence reactions in (C70)mIrx clusters
Authors: Branz W. , Malinowski N. , Martin T. P.
Published: July 2002

A mass spectrometric investigation of the photofragmentation behavior of mixed clusters composed of C70 molecules and iridium atoms (C70)mIrx (m=2, 3; x>2) reveals that coalesced fullerenes C138−2n and C206−2n (n=0, 1, 2,…) are the predominant reaction products at high laser intensities. More detailed tandem time-of-flight experiments on mass selected (C70)2Irx indicate that the efficiency of the coalescence reaction increases with increasing iridium content in the precursor cluster. Most probably the formation of strongly bound IrC molecules plays an important role for the reaction mechanism. For comparison, the fragmentation behavior of preselected (C70)2Co5 is also investigated.
Ionized physical vapor deposition of Cu using a mixture of rare gases
Authors: Rauf Shahid , Ventzek Peter L. G.
Published: July 2002

Ionized physical vapor deposition of Cu in a mixture of three rare gases (He–Ar–Xe) is explored in this article. Results indicate that total Cu flux to the wafer, ionization fraction of Cu at the wafer, and ratio of total effective ion flux to total Cu flux increase with increasing Xe concentration in the gas mixture. This is because of enhancement of electron density and Xe+ ions having a larger sputter yield on Cu than other ions. Increase in He concentration decreases the ionization fraction due to a lower electron density. However, Cu flux to the wafer increases because He is less effective in thermalizing the hot sputtered neutrals. One major consequence of these trends is that one can independently control total Cu flux to the wafer (corresponding to deposition rate) and ionization fraction (a major factor controlling the deposition profile) over a wide range by means of the buffer gas composition.
Chaotic and irreversible properties of quantum scattering systems
Authors: van Winter Clasine
Published: July 2002

Recent results for a free particle are generalized to N-particle quantum systems. Chaotic and irreversible behavior occurs in scattering states that belong to a certain Hilbert space K2 with a preferred time direction pointing to the future. At positive times the time evolution of positive observables exhibits quantum analogs of sensitive dependence on initial conditions, topological transitivity, and existence of a dense set of periodic points. A mixture of states in K2 can be described in terms of a density operator with thermodynamical entropy that increases to its least upper bound when the time tends to infinity.
Thermohydrodynamic characteristics of the cascaded arc plasma generator with a large ratio of radius and pipe length
Authors: Shimada K. , Iwabuchi M. , Matsuda N.
Published: July 2002

Numerical analysis was performed on the laminar thermal plasma flow of a constricted cascaded arc plasma generator with a larger ratio of radius and pipe length compared to previously used arc plasma generators. The numerical results concerning plasma temperature and velocity were compared with the experimental data measured using the probes methods. The effects of the mass flow rate of the plasma gas and the supplied current on plasma temperature, velocity, and current at a cross section of the plasma torch are clarified. These effects on plasma temperature and current density are estimated to be small when using a numerical model employing a single flow and a single temperature without taking into account the effects of the collision and dispersion of plasma gas particles. Except for the large mass flow rate of plasma gas, the numerical results for the plasma velocity are almost identical in magnitude to the experimental data.
Simultaneous measurement of the surface and bulk magnetization in thin magnetic films
Authors: Teplin Charles W. , Rogers Charles T.
Published: July 2002

We describe an apparatus for the simultaneous measurement of the transverse and longitudinal linear magneto-optic Kerr effects and the transverse second-harmonic magneto-optic Kerr effect. We have used this system to study low frequency bulk and surface magnetization loops, and high frequency response to 100 ps impulse fields for 70 nm thick Ni80Fe20 films. Magnetization loops show that the surface and bulk magnetization fields in these films respond essentially identically to external fields. Similarly, the dynamic response of the films to 100 ps magnetic field impulses also shows simultaneous rotation of the surface and bulk magnetization. Finally, we use the system to produce 8 μm resolution (at the diffraction limit for our ellipsometric optical geometry) images of the magnetization spatial and temporal response.
Reconstruction of in-plane magnetization distributions from magnetic force microscope images
Authors: Zhao T. , Fujiwara H. , Mankey G. J. , Hou C. , Sun M.
Published: July 2002

A three-step method is proposed for reconstructing the in-plane magnetization distribution from a magnetic force microscope (MFM) image. The magnetization distribution is initialized using some assumptions based on our knowledge about domain structures and MFM contrast mechanisms. Then the high-energy moment configurations, which are initialized based on linear variation assumption, are relaxed by performing a micromagnetic calculation using experimentally measured magnetic parameters. A section of a 360° wall in a NiFe/NiO bilayer has been selected to illustrate the reconstruction procedures. It is shown that the method is effective in revealing the wall structure related to the MFM contrast. This method avoids problems caused by noise and nonunique solutions of the micromagnetic equations.
Influence of microstructure on thermal relaxation in nanocrystalline soft magnetic materials
Authors: LoBue M. , Basso V. , Beatrice C. , Tiberto P. , Bertotti G.
Published: July 2002

The interplay between activation volumes and microstructure is investigated in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 (Finemet) alloys. Experiments are performed beyond the Curie point of the amorphous matrix, where relaxation effects are relevant. Measurements are analyzed within a theoretical framework where hysteresis and relaxation phenomena are jointly described. In highly crystallized samples magnetization processes are characterized by a unique length scale. In poorly crystallized samples the system behavior is controlled by a distribution of characteristic volumes related to structural disorder.
Localized spin flop transition in a ladder structure with nonmagnetic impurities
Authors: Ivanov B. A. , Zaspel C. E. , Merkolov A. Yu.
Published: July 2002

A classical two-leg spin ladder with an antiferromagnetic exchange interaction and easy axis anisotropy in an external magnetic field exhibits a spin flop transition. A single nonmagnetic impurity introduced into this system allows for the formation of a metastable localized spin flop state at a field above the bulk spin flop field. This state will be symmetrically pinned to the impurity. Two neighboring impurities on the same leg will also result in the stabilization of a localized state pinned to the impurities, but in this case the state is not centered on the impurities.
Influence of magnetic domain-wall width and shape on magnetoresistance measurements
Authors: Mangin S. , Bellouard C. , Turban P. , Andrieu S. , Canet F. , Schuhl A. , Barbara B.
Published: July 2002

The influence of magnetic domain walls (DWs) on magnetoresistance in various exchange-bias ferrimagnetic/(ferrimagnetic or ferromagnetic) bilayer systems (Gd68Fe32/Tb55Fe45 and Fe60Gd40/Fe55Sn45) is presented. These systems allow one to create well-defined DWs of various size and shape. The DW morphology is controlled by the applied magnetic field in the film plane. By changing the amplitude of the field, the DW thickness can be controlled, whereas the rotation of the field in plane allows one to create a θ° Bloch DW (90° DW, 180° DW,…). The electrical resistivity of the sample was measured relative to the applied magnetic field (amplitude and direction). The influence of the shape and size of the DW on magnetoresistance was followed. For the two amorphous samples, it made it possible to fit the variation of resistivity relative to the DW thickness and shape using a model based on anisotropic magnetoresistance.
Low-noise GaN Schottky diodes on Si(111) by molecular beam epitaxy
Authors: Deelman Peter W. , Bicknell-Tassius Robert N. , Nikishin Sergey , Kuryatkov Vladimir , Temkin Henryk
Published: July 2002

We report on the achievement of mesa-isolated Schottky diodes fabricated from n-GaN epilayers grown by gas-source molecular beam epitaxy on Si(111) that exhibit extremely low noise and dark current. Silicon dioxide grown by plasma-enhanced chemical vapor deposition provided both surface passivation and electrical isolation, and the Schottky contact was a 10 nm Pd thin film. The dark current of an 86×86 μm2 diode was 2.10×10−8 A/cm2 at −2 V bias, and the zero-bias noise power density at 1 Hz is as low a 9×10−29 A2/Hz.
Yangian construction of a centrally extended Lie algebra of a diffeomorphism group of a torus
Authors: Lipiński Z.
Published: July 2002

Quantization of a loop extended Lie algebra of a diffeomorphism group of a torus with a central extension is considered.
The interactions of ultra-short high-intensity laser pulses with large molecules and clusters: Experimental and computational studies
Authors: Sakabe S. , Nishihara K. , Nakashima N. , Kou J. , Shimizu S. , Zhakhovskii V. , Amitani H. , Sato F.
Published: July 2002

Recent experimental and computational studies on intense short-pulse-laser interactions with small objects such as molecules (C60) and clusters are reviewed. An anisotropic Coulomb explosion of C60 was observed, on irradiation by a high-intensity laser pulse (1×1016 W/cm2). The energy distributions of Cq+ ions (q=1–4) (distributed over 1 keV) generated from the explosion process were characterized, with their dependence on laser polarization. These results are qualitatively explained by classical molecular-dynamics simulation. It was clearly established that the crucial process for the anisotropic Coulomb explosion is not electron impact ionization, but cascade hopping of electrons. An analytical model and three-dimensional particle simulations of intense laser interaction with a cluster of overdense plasma are presented. When the laser intensity is above a critical value, it blows off all electrons from the cluster and forms a non-neutral ion cloud. During the Coulomb explosion of the ion cloud, ions acquire energy. Ion energy spectra are discussed in detail for different densities and sizes of clusters with various laser intensities. It is shown that ultra-fast ions are produced for relatively large clusters, and that the ion energy reaches to three times greater than the maximum electrostatic potential energy of the ion cloud. The laser-driven Coulomb explosion of a cluster may provide a new high-energy ion source.
Formation dynamics of free excitonic magnetic polarons in Cd1−xMnxTe
Authors: Nogaku Mituharu , Pittini Raniero , Sato Toshio , Shen Jinxi , Oka Yasuo
Published: July 2002

Formation processes of magnetic polarons from excitons were studied in Cd1−xMnxTe with the Mn composition x varying from 0.02 to 0.1 by transient photoluminescence spectroscopy. Two kinds of excitonic magnetic polarons were observed. One is the magnetic polaron composed of the free exciton, which is interacting with neighboring Mn-ion spins by the exchange interaction. The other is the magnetic polaron composed of the exciton bound to the neutral donor by aligning the surrounding Mn spins. The donor bound magnetic polarons appear for x=0.02–0.05 with the binding energy of 0.5–1.0 meV. The free excitonic magnetic polarons arise for x=0.02–0.1, where the binding energy of the free excitonic magnetic polaron varies in the range of 3.5-8.0 meV depending on the Mn composition. The stability of the free excitonic magnetic polaron state is confirmed by the appearance of the strong transient photoluminescence in the wide Mn composition range.
Effect of Li doping on the charge ordering state of La0.5Ca0.5MnO3
Authors: Ye S. L. , Song W. H. , Dai J. M. , Wang K. Y. , Wang S. G. , Du J. J. , Sun Y. P.
Published: July 2002

The effect of Li doping on the charge ordering (CO) state in perovskite-type manganates La0.5Ca0.5−xLixMnO3 with x=0, 0.05, 0.1, 0.15, 0.2 is investigated by transport and magnetic property measurements. The resistivity of the samples decreases with the increase of the Li-doped level. As x⩾0.1, the insulator–metal (IM) transition has been induced. Accompanying the variation of transport properties, the sample undergoes the variation from antiferromagnetic order for x<0.05 to ferromagnetic (FM) order for x⩾0.1. The experimental results indicate that the Li doping can destroy the CO state and induce the FM metallic (FMM) phase. These phenomena can be interpreted in terms of the strong competition between the CO state and FM phase induced by the Li+ ions substitution for the Ca2+ ions.
Quantum-mechanical effects on semiclassical electron captures by protons from hydrogenic ions in dense high-temperature plasmas
Authors: Jung Young-Dae
Published: July 2002

Quantum-mechanical effects on the electron captures by protons from hydrogenic ions are investigated in semiclassical dense high-temperature plasmas. An effective pseudopotential model taking into account both the quantum-mechanical effects and the plasma screening effects is applied to describe the projectile–electron interactions in dense high-temperature plasmas. The semiclassical version of the Bohr–Lindhard model has been applied to obtain the electron capture radius and the electron capture probability. The impact parameter method is applied to the motion of the projectile proton in order to visualize the electron capture probability as a function of the impact parameter, thermal de Broglie wavelength, Debye length, and projectile energy. The results show that the quantum-mechanical effect reduces the electron capture cross section. It is also found that the electron capture probability significantly decreases with a slight increase of the quantum-mechanical effect through the thermal de Broglie wavelength.
First principles description of the paramagnetic insulating state of chromia
Authors: Dobin Alexander Yu. , Wentzcovitch Renata M.
Published: July 2002

We have investigated the electronic and structural properties of chromia (Cr2O3), a typical Mott–Hubbard insulator. We considered the T=0 K antiferromagnetic insulating ground state and the paramagnetic insulating state above the Néel temperature (TN). Our treatment of the latter resembles in principle a virtual crystal model of the random spins insulator and describes reasonably well the compressive behavior of chromia above and the structural anomalies across TN.
Giant magnetoresistance effect of Co–TbN macroscopic ferrimagnets
Authors: Kim T. W. , Gambino R. J. , McGuire T. R.
Published: July 2002

A new macroscopic ferrimagnet Co–TbN has TbN precipitates in a Co matrix. The Co–TbN system shows the typical magnetic properties of a macroscopic ferrimagnet which are a magnetic compensation point and negative giant magnetoresistance (GMR). The Co–TbN mixture with 32 mole % TbN exhibits 0.72% GMR in fields up to 8 kOe at room temperature and 9% GMR at 250 K in 40 kOe. In the Co–TbN system, the dependence of GMR with temperature is quite different from that of previously studied GMR materials that have magnetoresistance decreases with increasing temperature. The GMR effect in the Co–TbN system increases with increasing temperature, because of the increase of ferromagnetic alignment of Co and TbN in a field at higher temperature.
Structure and magnetic studies on UNiAlD2.2
Authors: Raj P. , Shashikala K. , Sathyamoorthy A. , Malik S. K. , Yelon W. B.
Published: July 2002

Heavy fermion itinerant antiferromagnetic UNiAl is one of the very few U-containing compounds which absorbs H2/D2 without disproportionation. The present neutron diffraction studies on UNiAlDy (y=2.2) are directed towards resolving controversies with regard to the occupancy of Ni atoms and the associated interstitial sites for (H/D) atoms, as well as the nature of magnetic ordering in the higher hydride phase with y⩾2. The fit to the neutron diffraction data is found to improve considerably if the Ni atoms originally lying in the U-atoms’ plane in UNiAl get shifted to the Ni–Al atoms’ plane in the deuteride. This is in agreement with an earlier neutron diffraction report on a deuteride sample of similar composition [T. Yamamoto et al., J. Alloys Compd. 269, 162 (1998)] and our x-ray structural studies on UNiAlH2.3 [P. Raj et al., Phys. Rev. B 63, 94414 (2001)], but differs from those of Bordallo et al., [H. N. Bordallo et al., Physica B 276–278, 706 (2000)] and of Kolomiets et al. [A. V. Kolomiets et al., J. Appl. Phys. 87, 6815 (2000)]. Our values of the structural parameters including the D-site occupancies are broadly in agreement with the results of Yamamoto et al. The magnetization studies on UNiAlD2.2 show a single antiferromagnetic transition with Néel temperature, TN=95 K.
Magneto-optical properties of semiconductor-based superlattices having GaAs with MnAs nanoclusters
Authors: Shimizu H. , Tanaka M.
Published: July 2002

We have fabricated semiconductor-based magnetic superlattices (SLs) containing GaAs:MnAs granular material in which MnAs nanoclusters are embedded in GaAs, and have characterized their structural, optical, and magneto-optical properties. SLs consisting of GaAs:MnAs and AlAs are shown to have good crystalline quality and excellent compatibility with nonmagnetic GaAs/AlAs heterostructures. The optical transmission properties were improved in the SLs, while keeping the strong magneto-optical properties of GaAs:MnAs. We used these magnetic SLs in a semiconductor-based magnetic microcavity as the central magnetic layer, and its optical transmission was found to have improved compared with our previous multilayer structures.
Comparison of particle confinement in the high confinement mode plasmas with the edge localized mode of the Japan Atomic Energy Research Institute Tokamak-60 Upgrade and the DIII-D tokamak
Authors: Takenaga H. , Mahdavi M. A. , Baker D. R.
Published: July 2002

Particle confinement was compared for the high confinement mode plasmas with the edge localized mode in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [S. Ishida, JT-60 Team, Nucl. Fusion 39, 1211 (1999)] and the DIII-D tokamak [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] considering separate confinement times for particles supplied by neutral beam injection (NBI) (center fueling) and by recycling and gas-puffing (edge fueling). Similar dependence on the NBI power was obtained in JT-60U and DIII-D. The particle confinement time for center fueling in DIII-D was smaller by a factor of 4 in the low density discharges and by a factor of 1.8 in the high density discharges than JT-60U scaling, respectively, suggesting the stronger dependence on the density in DIII-D. The particle confinement time for edge fueling in DIII-D was comparable with JT-60U scaling in the low density discharges. However, it decreased to a much smaller value in the high density discharges.
The effect of the charge density of microemulsion droplets on the bending elasticity of their amphiphilic film
Authors: Farago B. , Gradzielski M.
Published: July 2002

Oil-in-water (O/W) microemulsion droplets have been investigated with respect to the effect of the electric charge density on the bending elasticity of the amphiphilic film. For this an originally uncharged microemulsion system became charged by the substitution of the nonionic by an ionic surfactant (up to 5 mol %). The sum of the bending constants, 2κ+κ̄, has been determined from the polydispersity index p of the droplets and alternatively from the macroscopic interfacial tension γ together with the maximum particle radius Rm. p and Rm were measured by means of small-angle neutron scattering (SANS) experiments in the shell contrast. Neutron spin echo (NSE) has been employed to measure directly the dynamics of the shape fluctuations of the droplets. This method enables a separate determination of κ on its own. It is found that the effect of the increasing charge density leads only to a fairly small increase for the sum of the bending constants 2κ+κ̄. Also the change of the ionic strength for a charged microemulsion system has almost no influence on this sum. NSE measurements show no measurable difference in the dynamics of the charged and uncharged system leading to the conclusion that not only the sum but separately the two bending constants stay within experimental error unchanged. This experimental observation is in contrast to simple electrostatic theories that would predict a much more pronounced influence of the electric charge density on the bending properties of the amphiphilic film.