bluuebunny/crossref_metadata_2025 huggingface dataset:
Structures in BCN Ruijsenaars–Schneider models
Authors: Avan J. , Rollet G.
Published: July 2002

We construct the classical r-matrix structure for the Lax formulation of BCN Ruijsenaars–Schneider systems proposed in Commun. Math. Phys., 115, 127 (1988). The r-matrix structure takes a quadratic form similar to the AN Ruijsenaars–Schneider Poisson bracket behavior, although the dynamical dependence is more complicated. Commuting Hamiltonians stemming from the BCN Ruijsenaars–Schneider Lax matrix are shown to be linear combinations of particular Koornwinder–van Diejen “external fields” Ruijsenaars–Schneider models, for specific values of the exponential one-body couplings. Uniqueness of such commuting Hamiltonians is established once the first of them and the general analytic structure are given.
On the structure of degenerate solutions of the Einstein conformally invariant scalar system
Authors: Delgado J. Estevez , Zannias T.
Published: July 2002

We address the question of the existence and construction of nontrivial, regular solutions of the Einstein–conformally invariant massless scalar field equations, i.e., solutions (g,Φ) satisfying (1−αΦ2)Rμν=α(4∇μΦ∇νΦ−2Φ∇μ∇νΦ−gμν∇σΦ∇σΦ), ∇μ∇μΦ=0, and additionally geometry and the scalar field are regular across the degeneracy region defined as the zeros of (1−αΦ2). Under the assumptions (1) the solution (g,Φ) is minimally of class C3 and admits a hypersurface orthogonal, timelike Killing vector field ξ, and (2) relative to the three spacelike hypersurfaces perpendicular to the Killing field, the degeneracy region constitute regular two-surfaces, and the induced positive definite three metric possesses a degenerate Ricci, we show that the conformal system admits nontrivial, regular across the degeneracy region solutions and we demonstrate that any such solution necessarily admits an additional local G(3) group of isometries possessing two-dimensional orbits of constant Gaussian curvature coinciding with the Φ=cons- equipotential two surfaces. Those solutions exhibit similar properties as the Levi–Civita–Ehlers–Kundt class of static solutions of Einstein’s vacuum equations. We investigate this coincidence and in particular we probe the origin of the additional local G(3) group of isometries exhibited by both classes of solutions. From the partial differential equations point of view, both systems, i.e., conformal system as well as the vacuum system, degenerate or become singular, the conformal system along solutions subject to αΦ2=1 within the static region, the vacuum along solutions subject to V=(−ξ⋅ξ)1/2→0+. We demonstrate that as a consequence of the singular nature of the dynamical equations, among all solutions possessing degenerate Ricci in the open vicinity of αΦ2=1, respectively, V→0+, the only regular across degeneracy region solutions are those characterized by a vanishing York–Cotton tensor and, furthermore, such solutions necessarily admit an additional local G(3) group of isometries possessing two-dimensional orbits of constant Gaussian curvature.
Excitation of right- and left-circularly polarized photoluminescence in silicon-based luminescent materials
Authors: Yamamoto Naokatsu , Hosako Iwao , Akiba Makoto , Ohtani Naoki , Takai Hiroshi
Published: July 2002

Silicon-based luminescent materials have been investigated widely for use in advanced optoelectronic integrated circuits and display devices. We tested the application of such materials and investigated their basic characteristics. In this study, luminescent silicon was produced by photochemical etching. The polarization of the photoluminescence under a right and left circularly polarized laser (Ar+ laser, 488 nm) irradiation was observed at 20–290 K. We found that the right- and left-circularly polarized photoluminescence intensities were intensified under right- and left-circular excitation, respectively. Information on the circular polarization of the laser excitation is apparently preserved in silicon-based luminescent material. This tendency was observed at room temperature. Additionally, a luminescence mechanism is studied by the spin dynamics of the photon-electron interaction.
Modeling light scattering from mesoporous silicon
Authors: Abouelsaood Ahmed A.
Published: July 2002

Porous silicon (PS) made from highly doped material is modeled as a uniaxial effective medium consisting of two components: hollow cylindrical silicon shells and free cylindrical pores. The complex refractive index is calculated in the coherent potential approximation leading to a very good agreement with the experimental refractive index data. Light scattering in porous silicon is estimated using the vector radiative transfer theory. It is found that the diffuse reflectance of a porous layer at its interface with air agrees with the available experimental measurements of light scattering from p+ porous silicon at a wavelength λ=457 nm. It is also found that, at longer wavelengths, the diffuse reflectance can be much higher, and increases with the porous layer thickness, reaching a maximum value of almost 10% for very thick layers. As for the scattered light transmitted or reflected through a PS/Si interface, a qualitative agreement is obtained between the model and the available measurements of the spectral photoconductivity of a silicon wafer with a front-surface porous film and the optical transmittance of a silicon wafer with a back-surface porous film.
Calculations of nonlinear spectra of liquid Xe. I. Third-order Raman response
Authors: Cao Jianshu , Wu Jianlan , Yang Shilong
Published: July 2002

The microscopic interactions and dynamics probed by third-order Raman spectroscopy in an atomic liquid (Xe) are explored within the Drude oscillator model, both numerically and analytically. Many-body polarization effects reduce the coefficient of the effective dipole–induced-dipole tensor. The isotropic part of the effective dipole–induced-dipole tensor arises primarily from the three-body interaction and is short-ranged. With an isotropic sample, the Raman response in any polarization geometry can be rigorously decomposed into an isotropic component and an anisotropic component, which primarily measure the strength and evolution of the two-body and three-body interactions, respectively. An interesting result from our analysis is the derivation of the standard mode-coupling equation for the intermediate scattering function and the mode-coupling equation for the bilinear density mode using Gaussian factorization of the memory kernel and the mean spherical approximation of the direct correlation function. The initial moment expansion along with the Gaussian factorization scheme allows us to predict the temporal profile of the Raman response function with reasonable accuracy. Furthermore, the Kirkwood superposition scheme approximates the Raman correlation function with pair distribution functions and time correlation functions and allows us to predict the ratio of the pair, three-particle, and four-particle contributions. These results, though obtained for Xe, are generally helpful in interpreting third-order spectroscopies of other liquids.
Effects of Mn addition on interfacial segregation kinetics of sulfur and magnetic induction in 3% silicon steel
Authors: Heo N. H. , Choi Y. S. , Cho S. S. , Chai K. H. , Kim S. B. , Lee W. S.
Published: July 2002

In the manganese-free 3% silicon steel, the trough in magnetic induction corresponded to the convex profile in segregation concentration of sulfur. This is due to the surface-energy induced selective growth of grains from (110) to (111) or higher index plane in the increasing order of segregated sulfur. The manganese-added steel showed a minimum in segregation concentration at the initial stage of final annealing, and a maximum with further annealing. Such a segregation behavior in the manganese-added strip may result from the precipitation and subsequent dissolution of MnS with final annealing time. A lower maximum of segregation concentration in the manganese-added strip is due to the faster H2S reaction rate under hydrogen atmosphere than the evaporation rate of sulfur under vacuum. Final magnetic induction of 1.9 T was obtained from the manganese-free strip through the selective growth of {110}〈001〉 Goss grains, while the other strip showed a much lower value of 1.71 T due to the main texture component close to {100}〈011〉.
Multitime correlation functions for single molecule kinetics with fluctuating bottlenecks
Authors: Barsegov Valeri , Chernyak Vladimir , Mukamel Shaul
Published: July 2002

Stochastic trajectories in single molecule kinetics coupled to several Gaussian Markovian coordinates are analyzed using a generating function obtained by solving the multidimensional Smoluchowski equation. Multitime correlation functions are computed and used to identify direct signatures of non-Poissonian kinetics resulting from coupling to slow coordinates. Effects of various degrees of correlation between collective coordinates with multiple time scales are studied.
Magnetization reversal in exchange biased Co/CoO probed with anisotropic magnetoresistance
Authors: Gredig Thomas , Krivorotov Ilya N. , Dahlberg E. Dan
Published: July 2002

The magnetization reversal in exchange coupled polycrystalline Co/CoO bilayers has been investigated as a function of CoO thickness using anisotropic magnetoresistance as a probe. The anisotropic magnetoresistance (AMR) was measured during the magnetization reversal and it was used to determine the orientation of the magnetization. For thin CoO layers large training effects were present; ergo the first hysteresis loop after field cooling was not the same as the second. The magnitude of the observed training was found to decrease with increasing CoO thickness. In the samples where substantial training was observed, the first magnetization reversal was dominated by nucleation of reversed domains. For the reversal from the antiparallel state back to the parallel direction, the AMR is consistent with a rotation process. In thicker CoO films where the training was less, the asymmetry was drastically reduced. A simple model that couples the antiferromagnetic grains to the ferromagnetic layer simulates qualitatively the observed magnetoresistance.
Epitaxial Fe films on GaAs(001): Does the substrate surface reconstruction affect the uniaxial magnetic anisotropy?
Authors: Moosbühler R. , Bensch F. , Dumm M. , Bayreuther G.
Published: July 2002

The in-plane magnetic anisotropy of Fe films epitaxially grown on GaAs(001), in addition to a thickness-dependent four-fold contribution has a uniaxial component originating from the Fe/GaAs interface. This has been observed in several previous investigations. The orientation of the uniaxial easy axis (e.a.), however, was found to be along the [110] direction in most studies, but also an e.a. parallel to [−110] was reported in a few cases. It has been suggested that different reconstructions of the GaAs surface prior to Fe deposition could be responsible for this discrepancy. In the present contribution, it is shown that in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature the uniaxial anisotropy always has its easy axis along [110] with practically the same magnitude. In particular, the surface reconstruction of the GaAs substrate — either (4×2) or (2×6) — has no effect on the resulting uniaxial magnetic anisotropy. This [together with recent results related to the phase transition of Fe/GaAs(001)] suggests that the same atomic configuration is formed at the Fe/GaAs(001) interface in both cases connected with the segregation of a certain amount of As (and Ga) to the surface.
Tilted media by micromagnetic simulation: A possibility for the extension of longitudinal magnetic recording?
Authors: Hee C. H. , Zou Y. Y. , Wang J. P.
Published: July 2002

In this article, we have studied the potential of tilted media to extend the longitudinal recording density via micromagnetic simulation. The magnetization reversal mechanism is systematically analyzed to determine the angular dependence of coercivity of this media. Such a characteristic determines the recording performance for different recording directions. A sharp transition is observed for the good recording direction. In contrast, large transition noise is observed for the bad recording direction. Tilted media have the advantage similar to the perpendicular media for extreme high recording density, resulting from the use of high Ku and low demagnetization field at the transition. Most importantly, the magnetization in the tilted configuration can be reversed effectively with a longitudinal ring head.
Advanced synthetic ferrimagnetic media (invited)
Authors: Inomata A. , Acharya B. R. , Abarra E. N. , Ajan A. , Hasegawa D. , Okamoto I.
Published: July 2002

The exchange coupling field (Hex) in two-layer synthetic ferrimagnetic media (SFM) is enhanced to extend the areal density capability of earlier structures. The thermal stability of SFM is improved by employing high magnetic anisotropy stabilizing layers without significantly affecting the required write fields. However, this necessitates larger Hex values than were earlier realized, to preserve the antiparallel layer magnetic configuration at remanence. Hex is improved by inserting thin high Co content hcp layers, called “E-layers,” between the Ru layer and the magnetic layers. Large Hex values from 1 to 4 kOe are obtained depending on the E-layer composition and thickness. As the intergranular coupling is affected by the Co-rich E-layers, a method is provided that improves Hex to values >1 kOe without degrading read-write properties.
Time-domain ferromagnetic resonance in epitaxial thin films
Authors: Engebretson D. M. , Berezovsky J. , Park J. P. , Chen L. C. , Palmstrøm C. J. , Crowell P. A.
Published: July 2002

Time-resolved ferromagnetic resonance is used to study magnetic relaxation in epitaxial Fe1−xCox films grown on vicinal GaAs(100) surfaces. The magnetic free energy of these films is determined by a combination of a four-fold volume anisotropy and a two-fold anisotropy due to surface bonding and morphology. The response following a high bandwidth (∼10 GHz) magnetic field pulse is measured using the polar Kerr effect. Samples with transverse dimensions much larger than the spatial extent of the field pulse show simple free induction decays. The measured precession frequencies are in good agreement with a coherent rotation model in the case of films grown on (100) surfaces with little or no (<2°) miscut. The magnetic response of 20 μm diameter disks is more complicated, particularly for static fields along the hard direction. Long-lived features appear in the response, and single precession frequencies are no longer observed. Micromagnetic simulations indicate the critical role played by the combination of the anisotropy and demagnetizing fields in the patterned structures.
Preparation and magnetic properties of melt-spun Nd2Fe14(BC)/α-Fe nanocomposite magnets
Authors: Wang Z. C. , Davies H. A. , Zhou S. Z. , Zhang M. C. , Qiao Y.
Published: July 2002

Phase evolution and magnetic properties of melt-spun Nd8Fe86B6−xCx (x=0, 2, 4, 5, 6) alloy ribbons have been investigated. Increasing the C content was found to decrease the glass-forming tendency of as-spun ribbons. For samples with low C content (x⩽4), the best magnetic properties were achieved by directly quenching at an optimum roll speed, by which a uniform exchange coupled nanocomposite Nd2Fe14(BC)/α-Fe structure was developed. Moreover, within this composition range, C substitution did not significantly affect the microstructure of the optimally quenched ribbons. However, for the samples with higher C content (x>4), the composite 2:14:1/α-Fe structure can only be obtained by a phase transformation from the mixture of 2:17:Cx+2:14:1+α-Fe phases during annealing treatment. Moreover, the resultant 2:14:1/α-Fe composite structure was irregular, with a coarse grain size, which strongly degraded the exchange interaction between hard and soft magnetic phases. For optimally processed samples, replacement of up to 4 at. % of B by C significantly increased the coercivity with only nominal reduction in remanence, in contrast to the alloys with x>4, for which drastic deterioration of both coercivity and remanence occurred.
Effects of some additives on the magnetic properties of single stage hot deformed NdFeB magnets
Authors: Li Ying , Kim Y. B. , Yoon T. S. , Jin D. Z. , Suhr D. S. , Kim C. O.
Published: July 2002

The effects of the eight kinds of additives, such as Al, BN, C, MoS2, Si, Zn, oleic acid, and diethylene glycol on the magnetic properties of the single stage hot deformed NdFeB magnets had been investigated in this work. Among these additives, it was observed that MoS2 and Al were more effective in increasing remanence and maximum energy product, and Zn in increasing coercivity considerably.
Temperature dependence of tunneling magnetoresistance: Double-barrier versus single-barrier junctions
Authors: Lee J. H. , Lee K. I. , Lee W. L. , Shin K.-H. , Lee J. S. , Rhie K. , Lee B. C.
Published: July 2002

The temperature dependence of tunneling magnetoresistance (TMR) is studied for spin valve type double-barrier tunnel junctions. Normalized TMR values for double-barrier tunnel junctions (DBTJs) and single-barrier junctions (SBTJs) are plotted as functions of temperature and it is found that the DBTJ shows stronger temperature dependence of TMR than the SBTJ. The strong temperature dependence of TMR for the DBTJ is explained in terms of temperature dependence of the spin polarization of the middle magnetic layer and decrease of the spin coherence length with increasing temperature.
Enhancement of exchange coupling for antiferromagnetically coupled media
Authors: Yamanaka H. , Inaba N. , Koda T. , Fujita E. , Matsunuma S.
Published: July 2002

Antiferromagnetically coupled (AFC) media with CoPt or Co interlayers inserted between a Ru layer and CoCrPtB magnetic layers were prepared in order to enhance the exchange coupling and the thermal stability. The exchange coupling field Hex increased from 0.6 to 4.2 kOe by increasing the thickness of the Co interlayer from 0 to 1 nm. The coupling energy J increases with increasing thickness of the interlayer. The coupling energy J of the AFC media with the interlayer are ten times larger (for 1-nm-thick Co interlayer) and five times larger (for 1-nm-thick CoPt interlayer) than that of the medium without the interlayer. Thermal stability factor KuV/kBT for the media with 1-nm-thick Co and 1-nm-thick CoPt interlayers are about 10% larger than that for the medium without the interlayer. The results suggest that the enhancement of the exchange coupling energy induces the increasing of KuV/kBT in the AFC media.
Domain walls in elastically soft crystals
Authors: Cullen J. , Wuttig M.
Published: July 2002

The properties of domain walls in ferromagnets that are elastically soft are considered. The wall energy is comprised of exchange, anisotropy, elastic, and magnetoelastic terms. Results are given for the energy and profile of a model crystal with [100] easy axes and large tetragonal magnetostriction. The wall energy is calculated for Neel walls propagating in [010] and [110] directions. It is shown that the [110] wall has lower energy for all values of magnetostriction. It is argued that these walls should be observable in crystals with magnetoelastic energy large enough to overcome demagnetizing effects. Candidate materials include Fe1−xGax alloys, rare earth–zinc compounds, and certain martensitic materials in their cubic phases.
Analytical model for field-induced strain in ferromagnetic shape-memory alloy polycrystals
Authors: Marioni Miguel A. , O’Handley Robert C. , Allen Samuel M.
Published: July 2002

Single crystals of Ni–Mn–Ga have shown promising properties for actuators with field-induced strains up to 6% [Murray et al., Appl. Phys. Lett. 77, 886 (2000)]. There is interest in achieving large field-induced actuation in textured polycrystals as well as in composites of oriented Ni–Mn–Ga particles in a polymer matrix. A simple analytical model has been developed to predict an upper limit to the field-induced strain achievable in ensembles of particles having specified orientations distributions. It is found that in a uniform distribution of orientations (no texture) the strain can reach at most 21% of the single-crystal strain for a given field. Distributions in which the twin plane normal subtends a fixed angle of 55° with the field direction have upper bounds for the strain of 38%. Similarly, orientation distributions in which the normal to the twin plane is the same for all crystals have an upper bound of 50%.
Effect of aging on magnetic properties of Hiperco® 27, Hiperco® 50, and Hiperco 50 HS® alloys
Authors: Fingers Richard T. , Carr Roger P. , Turgut Zafer
Published: July 2002

We started a long-term aging study that will identify the aging related changes in magnetic, mechanical, and electrical properties of three Fe–Co soft magnetic alloys. We performed the aging at a temperature of 773 K and in two different environmental chambers, argon gas and air, in order to determine the oxidation resistance of these alloy laminates as well. Each aging batch includes creep and yield stress test specimens, rings for ac magnetic measurements and specimens for electrical resistivity and microstructural analysis. Here we report the change in total power losses after 2000 h annealing up to frequencies of 2 kHz for the Hiperco® 27, Hiperco® 50, and Hiperco® 50 HS alloys. We also report the temperature dependence of total power losses between 298 and 773 K for these alloys.
Nanoscale modification of optical properties in Ge-doped SiO2 glass by electron-beam irradiation
Authors: Jiang Nan , Qiu Jianrong , Gaeta Alexander L. , Silcox John
Published: July 2002

In this letter, we demonstrate rapid decomposition in Ge-doped SiO2 glass under high-energy electron irradiation, and comment on possible mechanisms for the interaction of the electron-beam with the glass. Nanometer-scale modifications in Ge-doped SiO2 glasses can be obtained by the redistribution of Ge in the glasses as a result of patterned electron-beam writing.
Effect of cantilever–sample interaction on piezoelectric force microscopy
Authors: Hong Seungbum , Shin Hyunjung , Woo Jungwon , No Kwangsoo
Published: July 2002

We report on the evidence for the cantilever–sample (CS) capacitive force contribution to the piezoelectric force microscopy (PFM). In addition, we present that positioning of the tip near the edge of the sample surface can significantly reduce this spurious contribution for any combinations of tip cantilever and film. As proof of both the existence of CS interaction and its reduction, the domains formed by the application of voltage pulses through the tip are observed by PFM at two different positions, i.e., sample center and edge. In accordance with the model that a piezoresponse consists of a piezoelectric vibration of the film and an electrostatic force induced vibration of cantilever, the domain contrasts are characterized by dot structure in the amplitude and negligible contrast in the phase images when the tip is placed in the center of the sample surface. However, reducing the CS interaction by placing the tip near the sample edge yields domain contrasts showing ring structure in the amplitude and a clear 180° phase shift in the phase images. Accompanying resolution enhancement in phase images results in smaller size of domains (bits) produced by identical voltage pulses as is evidenced from bit size estimation. Additional evidence for reduction of CS interaction is obtained from piezoresponse hysteresis measurement.
Micromagnetic modeling of soft magnetic underlayers for perpendicular recording
Authors: Hoinville Jay R.
Published: July 2002

A micromagnetic model is used to compute the induced image fields in a perpendicular recording medium from an anisotropic soft magnetic underlayer. We investigate the dependence of the image field strength on the write head field strength, the underlayer saturation magnetization, the total underlayer thickness, and the number of micromagnetic layers composing the underlayer. We also compare micromagnetic image fields to the method of images and show that the image fields from an underlayer can be larger than those predicted by the method of images.
Thermal stability and recording characteristics of TbCo/CoCrPt-hybrid media for perpendicular recording
Authors: Nakagawa H. , Nemoto H. , Honda Y. , Ichihara T. , Tanahashi K. , Hosoe Y.
Published: July 2002

We studied the thermal stability and recording characteristics of a hybrid medium consisting of a granular CoCr-based alloy layer and an exchange-coupled Tb(Fe)Co layer. The addition of a thin Tb(Fe)Co layer to a CoCrPt(B) medium increased the squareness and decreased the nucleation field, resulting in high thermal stability. The strong lateral exchange interaction of the Tb(Fe)Co layer may reduce the thermal decay by effectively increasing the magnetic cluster size and suppressing the reversed domains. By adding a relatively thin TbFeCo layer on a well-segregated CoCrPtB layer, thermal stability can be improved without severely degrading the signal to noise ratio, as compared with using the CoCrPtB medium alone. The hybrid medium has a potential for ultrahigh density recording, although the magnetic domain expansion should be suppressed further by introducing pinning sites into the Tb(Fe)Co layer and by promoting the Cr segregation in the CoCr-based alloy layer.
Coherent control of the CH2Br+I←CH2BrI→CH2I+Br branching photodissociation reaction
Authors: Abrashkevich Dmitri G. , Shapiro Moshe , Brumer Paul
Published: July 2002

Coherent control over branching in the photodissociation of collinear CH2BrI to yield either CH2Br+I or CH2I+Br is examined computationally. Quantum photodissociation calculations, using two excited potentials surfaces, are carried out using a new method incorporating negative imaginary absorbing potentials within the artificial channel method. Extensive control over the I/Br branching ratio is shown to result as experimentally controllable laser amplitudes and phases are varied. Such control is observed for excitation from either initial superpositions of chaotic or regular CH2BrI bound states.
Concentration band dynamics in free-surface Couette flow of a suspension
Authors: Timberlake Brian D. , Morris Jeffrey F.
Published: July 2002

Particle concentration banding has been studied by experiments in the flow driven by the inner cylinder of a partially filled concentric cylinder, or Couette, device. In this geometry, alternating bands of relatively concentrated and dilute particle fraction are observed along the axis. A small ratio of the inner to outer radius was used, with Ri/Ro=0.29, and Ri=0.64 cm, resulting in concentration bands which were confined to the vicinity of the inner cylinder. This work examines the dynamics of band formation and subsequent band motions for a range of filled fractions of the annular region, f, and angles of inclination of the Couette device relative to the horizontal, α. The majority of the experiments were performed at a bulk average particle volume fraction of φ=0.2, although banding was observed over the range of concentrations 0.01⩽φ⩽0.4. The focus of this work is on band dynamics, which have been analyzed by time-lapse video imaging and image analysis. At zero inclination angle, the concentrated bands at f<0.65 are narrow, and fluctuate both in position and in number; the intervening zones are dilute relative to the bands but only slightly less concentrated than the bulk average. At fill fractions above f=0.65 and zero inclination, the number of concentrated bands decreases while the bands become much longer in the axial direction, and the intervening regions are both narrow relative to the concentrated bands and very dilute, φ≈0. This change in banding behavior occurs over a narrow range around f=0.65, which corresponds to suspension just covering the inner cylinder in the absence of flow. For inclination angles in the range 0.4°<α<5.3°, concentrated bands form at regular intervals at the elevated end of the device (shallow depth) and move intact at a nearly constant speed down the cylinder axis.
Two-dimensional self-consistent radiation transport model for plasma display panels
Authors: Lee Hae June , Kim Hyun Chul , Yang Sung Soo , Lee Jae Koo
Published: July 2002

A two-dimensional radiation transport model is coupled with a fluid simulation to incorporate the resonance radiation trapping effect in a plasma display panel cell. Compared with the conventional trapping factor approach, this model has an advantage in describing the spatial evolution of the radiative excited-state density. Compared with a Monte Carlo model, it also takes advantage of its fast computation to couple the radiation transport self-consistently with the time-dependent fluid model. The effect of the spatial evolution of the resonant excited state on the light emission is investigated for the variations of system sizes and the gas mixture ratio, and the results are compared with those of the conventional trapping factor approach. The discrepancy between the two methods increases as the gap size between the dielectrics increases, but does not change significantly for the variation of the gas mixture ratio.
Influence of deposition conditions on Ir/IrO2 oxygen barrier effectiveness
Authors: Pinnow C. U. , Kasko I. , Nagel N. , Poppa S. , Mikolajick T. , Dehm C. , Hösler W. , Bleyl F. , Jahnel F. , Seibt M. , Geyer U. , Samwer K.
Published: July 2002

The influence of the deposition temperature during the reactive sputtering process on the microstructure of thin Ir and IrO2 films deposited on oxidized Si substrates was investigated and related to the oxygen barrier effectiveness. For this purpose differential thermal analysis combined with residual gas analysis by mass spectrometry was used for the investigation of the microstructural and chemical behavior of the as-sputtered IrO2 films upon heating. Moreover, in situ stress relaxation analyses up to 900 °C, in and ex situ x-ray diffraction measurements were done for various annealing conditions. The investigated polycrystalline IrO2 films exhibited a large compressive stress and a distorted lattice due to the sputter deposition process. It is demonstrated that a high deposition temperature involves a delayed relaxation of the IrO2 grains which is causing an extrinsic, enhanced defect controlled oxygen mobility for the annealing temperatures below the recrystallization. The well-known low intrinsic oxygen diffusivity was only found in those samples which show—in addition to the recovery process—a recrystallization at low temperatures and thus a formation and growth of a new generation of grains with a lattice spacing as in bulk IrO2. Moreover, the oxygen diffusion in Ir films was investigated and the oxygen was found to penetrate the Ir films very quickly at elevated temperatures. The microstructure of the films was investigated by cross sectional transmission electron microscopy and it is shown that the cold-sputtered columnar IrO2 films protect the underlying layers from oxidation during a 700 °C high temperature oxygen anneal with an optimized Ir/IrO2 oxygen barrier stack.
Reduction of quantum systems with symmetry, continuous and discrete
Authors: Iwai Toshihiro , Hirose Toru
Published: July 2002

Reduction of dynamical systems is closely related with symmetry. The purpose of this article is to show that Fourier analysis both on compact Lie groups and on finite groups serves as a reduction procedure for quantum systems with symmetry on an equal footing. The reduction procedure is applied to systems of many identical particles lying in R3 which admit the action of a rotation group SO(3) and of a symmetric or permutation group.
The Weierstrass representation for surfaces immersed into R8 and CP2 maps
Authors: Grundland A. M. , Zakrzewski W. J.
Published: July 2002

A generalization of the Weierstrass system of equations corresponding to CP2 harmonic maps is presented. This generalization allows us to study two-dimensional surfaces immersed in a flat space R8 with Euclidean metric. We use this system to suggest a possible geometrical interpretation of CP2 harmonic maps.
Importance of structural irregularity on dielectric loss in (1−x)Pb(Mg1/3Nb2/3)O3−(x)PbTiO3 crystals
Authors: Priya Shashank , Viehland D. , Uchino K.
Published: July 2002

The dielectric properties of (1−x)Pb(Mg1/3Nb2/3)O3−(x)PbTiO3 (PMN–PT) crystals have been investigated over a temperature range of 4 to 450 K at various frequencies. At low temperatures, an unusual frequency dependent plateau region in the absorption was observed between 75 and 175 K. At both higher and lower temperatures, the absorption was frequency independent. Analysis of the relaxation time constant revealed power-law divergence, typical of fractal behavior in disordered magnetic systems. The results demonstrate the importance of structural irregularities on the dielectric loss mechanism in poled oriented PMN–PT crystals.
Quantization of chaotic systems
Authors: Tanner Gregor , Wintgen Dieter
Published: July 2002

Starting from the semiclassical dynamical zeta function for chaotic Hamiltonian systems we use a combination of the cycle expansion method and a functional equation to obtain highly excited semiclassical eigenvalues. The power of this method is demonstrated for the anisotropic Kepler problem, a strongly chaotic system with good symbolic dynamics. An application of the transfer matrix approach of Bogomolny is presented leading to a significant reduction of the classical input and to comparable accuracy for the calculated eigenvalues.
A critical review on the dynamics of Jovian atmospheres
Authors: Yano Jun-Ichi
Published: July 2002

Some basic theoretical issues of the Jovian atmospheric dynamics are discussed. Those include the depth of the motions, thermal convection both with deep and shallow configurations, the two-dimensional turbulence theory and its relevance. The refractive index analysis is suggested to interpret the coherent structures like Jupiter’s Great Red Spot in terms of Charney–Drazin constraint based on the observations. A possibility of Jovian data assimilation is proposed as a future direction.
Visualization of the “Sisyphus” attractor
Authors: Mirasso Claudio R. , Mulder Martijn , Spoelder Hans J. W. , Lenstra Daan
Published: July 2002

We have performed numerical simulations for a semiconductor diode laser subjected to optical feedback and operating in a chaotic regime. Exploration and investigation of the resulting large data sets call for the application of visualization techniques. Ideally, this should be realized using virtual reality techniques, but for practical reasons we have opted for a more static approach in the form of a video. Using these techniques we have gained more insight into the dynamical behavior of the laser. Given the rapid development of (graphical) hardware and software, interactive visualization and animation techniques are promising tools to study and understand highly nonlinear problems. © 1997 American Institute of Physics.
Computer-algebra program for constructing exponentially fitted methods for solution of the Schrödinger equation
Authors: Simos T. E.
Published: July 2002

A computer-algebra program, written in Maple, is presented for the production of explicit exponentially fitted methods. By using this program, a family of explicit four-step predictor–corrector exponentially fitted methods is obtained for numerical solution of the Schrödinger equation. The four-step methods considered contain free parameters that allow them to be fitted to exponential functions. These sixth-order methods are very simple and integrate more exponential functions than both the well-known fourth-order Numerov methods and the sixth-order Runge–Kutta methods. Based on this computer-algebra program, a variable-step exponentially fitted method is introduced. Numerical results indicate that the new variable-step method is much more efficient than other well-known methods for numerical solution of the radial Schrödinger equation. © 1998 American Institute of Physics.
Unipotential electrostatic lenses: Paraxial properties and aberrations of focal length and focal point
Authors: Rempfer Gertrude F.
Published: July 2002

An experimental study of electrostatic electron lenses as a function of geometrical and electrical parameters is described. The lenses are of the symmetrical three-electrode unipotential type. The parameters are the thickness of the center electrode and the interelectrode spacing, both relative to the center electrode aperture diameter, and the ratio of lens voltage to cathode voltage. The lens properties are characterized in terms of the focal length and focal distance, and the spherical and chromatic aberrations of these quantities. In general, the principal surfaces of a lens are not plane, and the aberrations of focal length and focal distance are not the same. Expressions are derived relating the focal length and focal distance aberrations to the spherical and chromatic imaging aberration coefficients Cs and Cc, and the magnification aberrations. The advantages of formulating the lens properties in terms of focal length and focal distance and their aberrations, and the usefulness of the data presented here, are illustrated with several examples.
The determination of minority carrier lifetimes in direct band-gap semiconductors by monitoring intensity-modulated luminescence radiation
Authors: von Roos Oldwig
Published: July 2002

When an extrinsic, direct band-gap semiconductor sample is irradiated by photons of an energy higher than the energy of the band gap between valence and conduction bands, excess electron-hole pairs are generated which, while diffusing through the sample, produce luminescence via radiative recombination. If, furthermore, the intensity of the impinging beam of photons is modulated sinusoidally, the luminescence radiation escaping from the sample will be phase shifted with respect to the original photon beam in a characteristic way. It will be shown that by measuring the phase shift at different modulation frequencies, the Shockley-Read-Hall lifetime of minority carriers may be ascertained. The method is nondestructive inasmuch as there is no need to fabricate p-n junctions or Ohmic contacts, nor is it necessary to remove already existing Ohmic contacts or angle lap the surface, etc., procedures often needed when determining lifetimes with the scanning electron microscope (in which case a p-n junction must be present).
Heat conduction in layered, composite materials
Authors: Baker-Jarvis James , Inguva Ramarao
Published: July 2002

A solution to the heat conduction equation for multidimensional composite media, with discontinuities of thermal properties, and having contact resistance at inclusion interfaces is presented. The temperature is expressed as an integral over sources and boundary surfaces in terms of a Green function. The solution is thereby reduced to solving the related eigenfunction problem for the Green function. This solution is also expressed in an alternative form utilizing a technique developed by Ölcer which promotes faster convergence of the eigenfunction expansion in regions of discontinuities. The solution technique is summarized, and numerical results are presented for one-dimensional layered slabs, with and without contact resistance specified at layer interfaces.
Domain observation with spin-polarized secondary electrons (invited)
Authors: Koike Kazuyuki , Hayakawa Kazunobu
Published: July 2002

A new method for observing magnetic domain structures with a scanning electron microscope has been realized in which the image video signal is the spin polarization of secondary electrons. Examples of domain structure images are presented and the potential of this method is discussed.
Role of short-circuiting pathways in reduced ZnO varistors
Authors: Sonder E. , Levinson Lionel M. , Katz W.
Published: July 2002

Electrical measurements and secondary ion mass spectrometry (SIMS) observations have been made to elucidate the mechanisms involved in the degradation of ZnO varistors at elevated temperatures in reducing atmospheres. The electrical measurements indicate that the degradation sensitivity depends to some extent on varistor composition but can be highly variable for different varistors of the same formulation and even within a given varistor sample. The SIMS data indicate that oxygen ions are highly mobile when varistors are heated above 290 °C, and it is proposed that flaws, such as microcracks in the varistors, act as conduits for oxygen at elevated temperatures. A circuit model in which a reduced varistor is characterized by short-circuiting regions around such flaws predicts an electric field versus current density that is similar to that observed in experiments.
Type conversion, contacts, and surface effects in electroplated CdTe films
Authors: Basol Bulent M. , Ou Szutsun Simon , Stafsudd Oscar M.
Published: July 2002

Efficient electroplated CdS/CdTe solar cells can be fabricated by heat treating and type-converting the n-CdTe films deposited on CdS layers. In this paper, various mechanisms which may give rise to the conversion of electroplated CdTe films from n to p type are investigated. It is concluded that Cd-vacancy generation is the main mechanism of type conversion. Possible effects of oxygen on this mechanism are also discussed. Evaporated Au contacts to electroplated p-CdTe films were studied. It was found that the Au contacts depleted the excess Te present on the surface of Br2-methanol etched p-CdTe films. Oxygen was found to affect the electrical characteristics of such contacts.
Precipitation of oxygen at 485 °C: Direct evidence for accelerated diffusion of oxygen in silicon?
Authors: Bergholz W. , Hutchison J. L. , Pirouz P.
Published: July 2002

Prolonged annealing of Czochralski silicon at 485°C leads to the formation of a number of defects which is accompanied by a reduction in the concentration of oxygen interstitials in the matrix. High-resolution electron microscopy has been used to investigate the structure of these defects which are basically of three types: (1) ribbonlike, (2) looplike defects which result in local lattice strains and hence are also visible in conventional transmission electron microscopy, and (3) dark regions visible in high-resolution micrographs with no lattice strains. Based on image characteristics and a comparison of the reduction in interstitial oxygen, from infrared spectroscopy, with the sizes of the ribbons, estimated from high-resolution micrographs, it is proposed that the ribbonlike defects are, in fact, the coesite phase which forms at prolonged anneals of the same material at the higher temperatures of 630–650°C. Using a simple model for the diffusion of oxygen to ribbons, the diffusivity of oxygen in silicon is estimated to be enhanced by nearly four orders of magnitude at 485°C! It is proposed that the looplike defects are extrinsic Frank loops which act as sinks for the interstitial silicon ejected during the oxygen precipitation. The fading away of the dark regions under electron irradiation in the microscope suggests that they are agglomerates of point defects.
Electron-hole pair creation at a Ge(100) surface by ground-state neutral Xe atoms
Authors: Amirav A. , Lambert W. R. , Cardillo M. J. , Trevor P. L. , Luke P. N. , Haller E. E.
Published: July 2002

We have directly measured the excitation of electron-hole pairs at a crystal surface by ground-state neutral atoms. Utilizing seeded molecular beam techniques we have scattered hyperthermal (1–6 eV) Xe atoms from the (100) face of a Ge p-i-n diode and recorded the current transient induced due to the scattering process. We find the product of the excitation and collection probability to be ∼10−4 over a range of kinetic energies 2<EXe(eV)<6. The excitation of electron-hole pairs constitutes a small portion of the massive energy loss (ΔE/E∼70%) of the Xe atom to the crystal.
Properties of AlxGa1−xAs (xAl≂0.3) grown by molecular-beam epitaxy on misoriented substrates
Authors: Tsui R. K. , Curless J. A. , Kramer G. D. , Peffley M. S. , Wicks G. W.
Published: July 2002

The effects of substrate misorientation on the morphological and optical properties of AlxGa1−xAs (xAl≂0.3) grown by molecular-beam epitaxy (MBE) have been studied. The substrate temperatures and V/III beam-flux ratios used were such that layers grown on nominally (100) substrates typically exhibited rough morphologies and poor 4.2 K PL characteristics. By intentionally misorienting the substrate slightly from (100), smooth layers can be grown at 620 and 650 °C at typical MBE growth rates (≂1 μm/h). These smooth layers also exhibited sharp, exciton-related emission peaks at 4.2 K with half-widths as narrow as 5 meV. Since rough surfaces may lead to poor interfaces between GaAs and (Al,Ga)As and in turn to degraded performance in heterojunction devices, the present results may have significant implications for the performance of such structures grown by MBE.
Numerical calculation of the temperature distribution and evolution of the field-ion emitter under pulsed and continuous-wave laser irradiation
Authors: Liu H. F. , Liu H. M. , Tsong T. T.
Published: July 2002

The temperature distribution and evolution of metal field-ion emitters under pulsed and continuous-wave (cw) laser irradiation are obtained numerically using implicit alternating direction method. For the cw laser irradiation, the temperature distribution in the emitter reaches a steady-state value after approximately 2 μs of laser heating. The peak temperature of the tip apex reached depends almost linearly on the incident energy flux of the laser beam, and also on the cone angle of the emitter. For the fast laser pulse, both the waveform and the spatial intensity variation of the laser beam are considered. The numerical result is found to differ only slightly from that obtained by assuming a square shape of the laser pulse. The feasibility and advantages of using a laser beam as a means of heating the emitter in the study of single atom surface diffusion and adatom-adatom interaction, laser-induced silicide interface formation, and other studies with the Atom Probes and Field Ion Microscope are also discussed.
Thermal-wave nondestructive evaluation of a carbon-epoxy composite using mirage effect
Authors: Inglehart L. J. , Lepoutre F. , Charbonnier F.
Published: July 2002

We report new results obtained for thermal-wave nondestructive evaluation applied to composite material using the mirage effect. We have thermally characterized a composite of woven carbon fibers and epoxy consisting of both opaque and transparent parts. We have measured the thermal diffusivity in the different regions of the composite. An anisotropy was found in the thermal diffusivity of the fibers and an effective diffusivity of the epoxy was calculated. From these experimental values we have been able to determine the thickness of the epoxy which coats, in many parts, the fibers. Subsurface cuts made perpendicular to the fibers were easily detected.
Comparisons between a gas-phase model of silane chemical vapor deposition and laser-diagnostic measurements
Authors: Breiland William G. , Coltrin Michael E. , Ho Pauline
Published: July 2002

Theoretical modeling and experimental measurements have been used to study gas-phase chemistry in the chemical vapor deposition (CVD) of silicon from silane. Pulsed laser Raman spectroscopy was used to obtain temperature profiles and to obtain absolute density profiles of silane during deposition at atmospheric and 6-Torr total pressures for temperatures ranging from 500 to 800 °C. Laser-excited fluorescence was used to obtain relative density profiles of Si2 during deposition at 740 °C in helium with 0–12 Torr added hydrogen. These measurements are compared to predictions from the theoretical model of Coltrin, Kee, and Miller. The predictions agree qualitatively with experiment. These studies indicate that fluid mechanics and gas-phase chemical kinetics are important considerations in understanding the chemical vapor deposition process.