bluuebunny/crossref_metadata_2025 huggingface dataset:
Chaotic advection in a 2-D mixed convection flow
Authors: Tangborn Andrew V. , Silevitch Daniel M. , Howes Tony
Published: July 2002

Two-dimensional numerical simulations of particle advection in a channel flow with spatially periodic heating have been carried out. The velocity field is found to be periodic above a critical Rayleigh number of around 18 000 and a Reynolds number of 10. Particle motion becomes chaotic in the lower half plane almost immediately after this critical value is surpassed, as characterized by the power spectral density and Poincaré section of the flow. As the Rayleigh number is increased further, particle motion in the entire domain becomes chaotic.
Fixed-point densities for a quasiperiodic kicked-oscillator map
Authors: Lowenstein J. H.
Published: July 2002

Suppose that a one-dimensional harmonic oscillator is subjected to instantaneous kicks q times per natural period, with the kick amplitude varying sinusoidally with position. Viewed stroboscopically in phase space, the motion has an infinitely extended periodic or quasiperiodic array of fixed points, as well as an infinite web of chaotic orbits. In the present work (restricted to the quasiperiodic case q=5) the fixed points are classified according to their local linear behavior, which depends essentially on a single variable, the residue R. With the aid of a five-dimensional embedding, a function ρ(R) is calculated which for infinitesimal ΔR gives the average density of fixed points in the plane with residue in the range (R,R+ΔR). The location and strength of the singularities and discontinuities of ρ(R) are extracted from relatively simple transcendental equations, and this makes possible efficient numerical determination of ρ(R). An exact equality for the densities of positive-R and negative-R fixed points is proved using decagonal symmetry and the integral representation of ρ(R). For parameter values below the period-doubling threshold, there are no unstable fixed points with R≳0, and so we have equality of the densities of stable centers and unstable saddles.
Iterated function systems and dynamical systems
Authors: Góra Pawel/ , Boyarsky Abraham
Published: July 2002

We study the relationship between measures invariant for a piecewise expanding transformation τ of a compact metric space endowed with a underlying measure and measures invariant for an iterated function system Tτ, generated by inverse branches of τ. The main result says that the τ-invariant absolutely continuous measure μ is also Tτ invariant if and only if τ is absolutely continuously conjugated with a piecewise linear transformation. Measures of maximal entropy and general equilibrium states are also discussed.
An averaging method for Hamiltonian systems, exponentially close to integrable ones
Authors: Treschev Dmitry V.
Published: July 2002

Exponentially small separatrix splitting for a pendulum with rapidly oscillating suspension point and for the standard Chirikov map is studied by means of a new averaging method, which is a continuous version of the Neishtadt averaging procedure. An asymptotic formula for the rate of the separatrix splitting is obtained.
Initial conditions of closed classical orbits from quantum spectra
Authors: Courtney Michael
Published: July 2002

A method is presented for determining the initial conditions of classical orbits from the quantum spectra of the diamagnetic hydrogen atom. Each classical trajectory which is closed at the nucleus produces a sinusoidal fluctuation in the photoabsorption spectrum. The amplitude of each orbit’s contribution appears in the Fourier transform of a spectrum computed at constant scaled energy. For a given initial state, closed-orbit theory gives the dependence of this recurrence amplitude on the initial angle of an orbit. By comparing the recurrence amplitudes for different initial states, the initial conditions of closed classical orbits are determined from quantum spectra.
Chaos and intermittent bursting in a reaction-diffusion process
Authors: Schwartz Ira B. , Triandaf Ioana
Published: July 2002

Karhunen–Loeve decomposition is done on a chaotic spatio-temporal solution obtained from a nonlinear reaction-diffusion model of a chemical system simulating a chemical process in an open Couette-flow reactor. Using a Galerkin projection of the dominant Karhunen–Loeve modes back onto the nonlinear partial differential system, we obtain an ordinary differential equation model of the same process. Major features such as intermittent and chaotic bursting of the nonlinear process as well as the mechanism of transition to chaos are shown to exist in the low-dimensional model as well as the PDE model. From the low-dimensional model the onset of intermittent bursts followed by small amplitude oscillations is shown to arise due to a sequence of saddle-node bifurcations.
Quantum chaos
Authors: Casati Giulio
Published: July 2002

In this paper we present an overview of important recent results in the study of a very controversial topic, the so-called quantum chaos. The theoretical and numerical results are compared with real laboratory experiments with special emphasis on the problem of ionization of hydrogen atoms in external microwave fields.
Nonlinear oscillating structures in the earthquake and seaquake dynamics
Authors: Levin Boris W.
Published: July 2002

The article deals with the problem of parametric excitation of oscillating structures during an earthquake and a seaquake associated with external forces. Tidal forces and their linear and nonlinear components are considered as possible causes of earthquakes. A seaquake is regarded as a typical large-scale structural disturbance of the water surface resulting from the ocean bottom earthquake. There are given results of original laboratory seaquake modeling where wave structures with hexagonal and square cells appeared. The received wave lattices were similar to Faraday ripples, but with the size of cells from 15 to 120 mm. These experiments provided parameters on transition from a wave structure to chaos. Comparison of laboratory experimental data with descriptions of full-scale seaquakes and parametric wave theory has confirmed the submitted interpretation of the phenomenon.
Chaos in variable stars: Topological analysis of W Vir model pulsations
Authors: Letellier C. , Gouesbet G. , Soufi F. , Buchler J. R. , Kolláth Z.
Published: July 2002

The topological characterization of chaos is applied to the irregular pulsations of a model for a star of the W Virginis type, computed with a state-of-the-art numerical hydrodynamical code. The banded W Vir attractor is found to possess an additional twist when compared to the Rössler band. It is shown that the stellar light-curve contains the same dynamical information about the attractor as the stellar radius or as the radial velocity variations.
Traveling patterns in cellular automata
Authors: Urías Jesús , Salazar-Anaya G. , Ugalde Edgardo , Enciso Agustín
Published: July 2002

A method to identify the invariant subsets of bi-infinite configurations of cellular automata that propagate rigidly with a constant velocity ν is described. Causal traveling configurations, propagating at speeds not greater than the automaton range, |ν|≤r, are considered. The sets of traveling configurations are presented by finite automata and its topological entropy is calculated. When the invariant subset of traveling configurations has nonzero topological entropy, the dynamics is dominated by the interaction of domains, composed of traveling patterns of finite size. The sets of traveling patterns and domains are presented by finite automata. End-resolving CA are shown to always have sets of traveling configurations that are spatially periodic with zero entropy, except possibly for traveling configurations at top speed. The elementary CA are examined exhaustively along these lines.
Nonintegrability of two problems in vortex dynamics
Authors: Bagrets A. A. , Bagrets D. A.
Published: July 2002

An analysis is presented of two problems in vortex dynamics whose equations can be written in the Hamiltonian form. They are: the interaction of three coaxial vortex rings and the motion of four point vortices on a sphere. The nonintegrability of these problems in the restricted formulation is demonstrated analytically by the method of split separatrices, using a small parameter.
The evolution of the magnetic moment in a corrugated magnetic field
Authors: Demokan O. , Mirnov V. V.
Published: July 2002

In the first part, the equations of motion in a weakly corrugated, periodic magnetic field are linearized and solved by using paraxial approximation, to describe the model and the associated resonance condition. In the second part, the nonlinear evolution of the magnetic moment of resonant particles, in connection with their axial displacement is investigated analytically by using the multiple scale method. It is seen that the linear evolution is converted into a slow and periodic oscillation around the unperturbed value, with a considerable amplitude. The analytic expressions for the period and amplitude of the oscillations are derived and compared with the numerical simulations, which are also presented. Finally, the limitations of the paraxial approximation are concluded by investigating the numerical simulations, with actual field expressions.
Scalar observations from a class of high-dimensional chaotic systems: Limitations of the time delay embedding
Authors: Kantz Holger , Olbrich Eckehard
Published: July 2002

The time delay embedding for the reconstruction of a state space from scalar data introduces strong folding of the smooth manifold in which a chaotic attractor is embedded, which is absent in some more natural state space. In order to observe the deterministic nature of data, the typical length scale related to this folding has to be resolved. Above this length scale the data appear to be random. For a particular model class we prove these statements and we derive analytically the dependence of this length scale on the complexity of the system. We show that the number of scalar observations required to observe determinism increases exponentially in the product of the system’s entropy and dimension.
Separatrix reconnection and periodic orbit annihilation in the Harper map
Authors: Saitô Satoshi , Nomura Yasuyuki , Hirose Kei-ichi , Ichikawa Yoshi H.
Published: July 2002

Structure of the periodic accelerator orbits of the Harper map is investigated in detail from the viewpoint of underlying scenario of chaos in the area preserving nontwist map. Since the twist function of the Harper map is free from the polynomial local approximation, it admits rigorous treatment for the entire range of phase variable. The results obtained in the present analysis describes generic novel phenomena, which are outside of the applicability of the Kolmogorov-Arnol’d-Moser theory.
Dynamics of spatial averages
Authors: Bunimovich Leonid , Jiang Miaohua
Published: July 2002

We study the dynamics of spatial averages of spatially extended dynamical systems. We present various examples of lattice dynamical systems to show the possibility of different behaviors, including asymptotically constant, periodic, and non-periodic, of spatial averages. We explain that the fluctuation in spatial averages is caused by the transitivity and the lack of symmetry of the dynamics of local subsystems.
Stability analysis of fixed points via chaos control
Authors: Löcher M. , Johnson G. A. , Hunt E. R.
Published: July 2002

This paper reviews recent advances in the application of chaos control techniques to the stability analysis of two-dimensional dynamical systems. We demonstrate how the system’s response to one or multiple feedback controllers can be utilized to calculate the characteristic multipliers associated with an unstable periodic orbit. The experimental results, obtained for a single and two coupled diode resonators, agree well with the presented theory.
Multistability and the control of complexity
Authors: Feudel Ulrike , Grebogi Celso
Published: July 2002

We show how multistability arises in nonlinear dynamics and discuss the properties of such a behavior. In particular, we show that most attractors are periodic in multistable systems, meaning that chaotic attractors are rare in such systems. After arguing that multistable systems have the general traits expected from a complex system, we pass to control them. Our controlling complexity ideas allow for both the stabilization and destabilization of any one of the coexisting states. The control of complexity differs from the standard control of chaos approach, an approach that makes use of the unstable periodic orbits embedded in an extended chaotic attractor.
Note on phase space contraction and entropy production in thermostatted Hamiltonian systems
Authors: Cohen E. G. D. , Rondoni L.
Published: July 2002

The phase space contraction and the entropy production rates of Hamiltonian systems in an external field, thermostatted to obtain a stationary state, are considered. While for stationary states with a constant kinetic energy the two rates are formally equal for all numbers of particles N, for stationary states with constant total (kinetic and potential) energy this only obtains for large N. However, in both cases a large number of particles is required to obtain equality with the entropy production rate of Irreversible Thermodynamics. Consequences of this for the positivity of the transport coefficients and for the Onsager relations are discussed. Numerical results are presented for the special case of the Lorentz gas.
Nonlinear noise reduction through Monte Carlo sampling
Authors: Davies M. E.
Published: July 2002

We consider the problem of nonlinear noise reduction within the framework of Bayesian Theory. This enables us to place appropriate weights on the measurement and dynamic errors and thereby avoid over cleaning the data. Using a Metropolis–Hastings sampler, we are able to achieve robust noise reduction without the introduction of ad hoc parameters but at the expense of higher computational complexity. Such an algorithm should also allow us to explore the potential and limitations of other noise reduction methods.
Observation of structure in the Lorenz map
Authors: Binder P.-M. , Laverde Diego
Published: July 2002

Through massive numerical integration of the Lorenz system, we are able to discern structure in its Poincaré map. We are also able to estimate its capacity dimension; our result is consistent with previous measurements of the correlation dimension of the Lorenz attractor.
Numerical study of reverse period doubling route from chaos to stability in a two-mode intracavity doubled Nd-YAG laser
Authors: Kuruvilla Thomas , Nandakumaran V. M.
Published: July 2002

We have numerically studied the behavior of a two-mode Nd-YAG laser with an intracavity KTP crystal. It is found that when the parameter, which is a measure of the relative orientations of the KTP crystal with respect to the Nd-YAG crystal, is varied continuously, the output intensity fluctuations change from chaotic to stable behavior through a sequence of reverse period doubling bifurcations. The graph of the intensity in the X-polarized mode against that in the Y-polarized mode shows a complex pattern in the chaotic regime. The Lyapunov exponent is calculated for the chaotic and periodic regions.
The guest-induced oscillation of a monolayer composed of polypeptide containing β-cyclodextrin at the terminal
Authors: Kinoshita T. , Doi T. , Kato A. , Hosokawa H. , Tsujita Y. , Yoshimizu H.
Published: July 2002

We prepared a rod-like amphiphile with a molecular recognition end group, α-helical and hydrophobic poly(γ-methyl L-glutamate) (PMG) containing hydrophilic β-cyclodextrin (CyD) as an active end group (PMG-CyD), and formed its monolayer at the n-hexane/water interface. The interfacial pressure (π)-area (A) isotherms of the monolayer showed that α-helix rod of PMG-CyD could be vertically oriented at the oil/water interface, facing the hydrophilic terminal CyD group to the water phase, by increasing the interfacial concentration of the polypeptide. Under the condition 2-p-toludinyl-naphthalene-6-sulfonate (TNS), an intimate guest molecule for the CyD in water was introduced into the water phase beneath the monolayer. Within a minute the monolayer began to oscillate which could be monitored by the rhythmic response of the interfacial pressure of the monolayer. The oscillation continued over ten minutes and then terminated. The mode of the oscillation was found to change with time, i.e., the initial stage showing a periodic sharp reduction in the interfacial pressure (period I), the second stage having sharp increase in the π value (period II), and the last stage of irregular oscillations (period III). The Fourier analysis of each period also supported the three stages during the oscillatory process. It was also found that when the α-helix rod of PMG-CyD lay down in the monolayer, the guest TNS did not induce any changes in the interfacial tension. This nonlinear rhythmic interfacial phenomenon was explained in terms of the periodic movement of the PMG-CyD monolayer resulting from the binding and releasing of the guest TNS across the oil/water interface.
Estimating the amplitude of measurement noise present in chaotic time series
Authors: Tanaka Naoki , Okamoto Hiroshi , Naito Masayoshi
Published: July 2002

We propose a method for estimating the amplitude of measurement noise present in chaotic time series. This method is based on the evaluation of initial errors for a given time series and for a new one synthesized by adding an adequate amount of noise to the given one. The method is valid over a much wider range of noise levels than the previous methods are because it is not based on the detail of dynamical structure which generates the data. In addition, it is possible to check if the method is valid for the given data prior to its application. To confirm the effectiveness of the method we show the results of numerical experiments and apply the method to chaotic data obtained from an electrochemical experiment.
Statistics of return times in a self-similar model
Authors: Floriani E. , Lima R.
Published: July 2002

In this paper, we propose a model for the hyperbolic part of the phase space of a Hamiltonian system that is located near a hierarchical islands around islands structure. We study the statistics of Poincaré recurrences, the type of orbits that are mainly responsible for slowly decaying correlations, and thus the mechanisms generating power law tails.
Modal decomposition of hopping states in cellular flames
Authors: Palacios Antonio , Gorman Michael , Gunaratne Gemunu H.
Published: July 2002

We use Karhunen–Loeve (KL) decomposition of video images from an experiment to analyze a spatiotemporal dynamic state, unique to cellular flames, referred to as a “hopping state.” Ordered states of cellular flames on a circular burner consist of one or two concentric rings of luminous cells. The hopping states correspond to the motions of individual cells in a ring sequentially executing abrupt changes in their angular position, while the other cells in the ring remain symmetric and at rest. KL decomposition separates the spatial and temporal characteristics of the hopping motion. The underlying symmetries of the experiment allow us to deduce a set of normal form equations that describe the formation of these states. We find that they result from secondary bifurcations connecting two primary branches of traveling waves. The solutions corresponding to hopping states exist as mixed-mode solutions away from the secondary bifurcations.
Topological analysis of chaos in neural spike train bursts
Authors: Gilmore R. , Pei Xing , Moss Frank
Published: July 2002

We show how a topological model which describes the stretching and squeezing mechanisms responsible for creating chaotic behavior can be extracted from the neural spike train data. The mechanism we have identified is the same one (“gateau roulé,” or jelly-roll) which has previously been identified in the Duffing oscillator [Gilmore and McCallum, Phys. Rev. E 51, 935 (1995)] and in a YAG laser [Boulant et al., Phys. Rev. E 55, 5082 (1997)].
Calculations of periodic orbits: The monodromy method and application to regularized systems
Authors: Simonović N. S.
Published: July 2002

We describe a numerical method for calculating periodic orbits, which is a generalization of the monodromy method by Baranger et al. to the case of an arbitrary autonomous dynamical system. Two variants of the method are developed, using the midpoint and the Runge–Kutta discretization of equations of motion, respectively. Particularly, we adapt the first variant for calculating periodic orbits of Hamiltonian systems when the period or the energy is given a priori. Finally, we consider the application of the monodromy method to the case of regularized mechanical systems and demonstrate the use by two examples.
Traveling waves and chaotic properties in cellular automata
Authors: Courbage M. , Mercier D. , Yasmineh S.
Published: July 2002

Traveling wave solutions of cellular automata (CA) with two states and nearest neighbors interaction on one-dimensional (1-D) infinite lattice are computed. Space and time periods and the number of distinct waves have been computed for all representative rules, and each velocity ranging from 2 to 22. This computation shows a difference between spatially extended systems, generating only temporal chaos and those producing as well spatial complexity. In the first case wavelengths are simply related to the velocity of propagation and the dispersivity is an affine function, while in the second case (which coincides with Wolfram class 3), the dispersivity is multiform and its dependence on the velocities is highly random and discontinuous. This property is typical of space–time chaos in CA.
Global analysis of periodic orbit bifurcations in coupled Morse oscillator systems: time-reversal symmetry, permutational representations and codimension-2 collisions
Authors: Tsuchiya Masa , Ezra Gregory S.
Published: July 2002

In this paper we study periodic orbit bifurcation sequences in a system of two coupled Morse oscillators. Time-reversal symmetry is exploited to determine periodic orbits by iteration of symmetry lines. The permutational representation of Tsuchiya and Jaffé is employed to analyze periodic orbit configurations on the symmetry lines. Local pruning rules are formulated, and a global analysis of possible bifurcation sequences of symmetric periodic orbits is made. Analysis of periodic orbit bifurcations on symmetry lines determines bifurcation sequences, together with periodic orbit periodicities and stabilities. The correlation between certain bifurcations is explained. The passage from an integrable limit to nointegrability is marked by the appearance of tangent bifurcations; our global analysis reveals the origin of these ubiquitous tangencies. For period-1 orbits, tangencies appear by a simple disconnection mechanism. For higher period orbits, a different mechanism involving 2-parameter collisions of bifurcations is found.
Inverse cascade via Burgers equation
Authors: Newman William I.
Published: July 2002

Burgers equation is employed as a pedagogical device for analytically demonstrating the emergence of a form of inverse cascade to the lowest wavenumber in a flow. The transition from highly nonlinear mode–mode coupling to an ordered preference for large scale structure is shown, both analytically (revealing the presence of a global attractor) and via a numerical example.
Paint by number: Uncovering phase flows of an integrable dynamical system
Authors: Healy Liam , Deprit Etienne
Published: July 2002

Given an integrable dynamical system with one degree of freedom, ‘‘painting’’ the integral over phase space proves to be a powerful technique for uncovering both global and local behavior.This graphical technique avoids numerical integration, employing instead a nonlinear method of assigning contrasting colors to the energy values to distinguish subtle details of the flow.
Properties of platinum-associated deep levels in silicon
Authors: Kwon Y. K. , Ishikawa T. , Kuwano H.
Published: July 2002

The diffusion of platinum into n- and p-type silicon has been carried out at temperatures ranging from 850 to 1000 °C and for times ranging from 1 to 50 h. Three deep levels associated with platinum were detected by the deep-level transient spectroscopy technique: two acceptor levels of Ec−0.23 and Ec−0.52 eV and a donor level of Ev+0.36 eV. The Ec−0.23 and Ev+0.36 eV levels are produced by platinum occupying the substitutional sites of silicon lattice. The Ec−0.52 eV level has not been characterized but is probably associated with some interstitial platinum-oxygen or other defect complex. Diffusion profiles of the substitutional platinum show that platinum diffuses into silicon mainly via the so-called kick-out mechanism.
An inverse scattering method to characterize inhomogeneities in elastic solids
Authors: Sotiropoulos D. A. , Achenbach J. D. , Zhu H.
Published: July 2002

An inverse method for ultrasonic scattering data is proposed to characterize a single elastic inhomogeneity of general shape contained in an elastic solid. The method is based on an integral representation for the scattered field in the frequency domain. The method has been applied at both large and intermediate wavelengths as compared with a characteristic length parameter of the scatterer. For a given scattered field the inverse problem has been formulated as a nonlinear optimization problem. At low frequencies its solution gives the location of the centroid of the scatterer, the equivalent force vector, and the moment tensor. In addition, the interaction energy between the material and the inclusion is obtained for a related static stress state. This latter result may have relevance to failure conditions in the material under service conditions. For intermediate frequencies, the volume and elastic constants of an equivalent spherical inhomogeneity are obtained, in addition to its position.
Enhanced grain growth of polycrystalline silicon at low temperature by dopant redistribution
Authors: Chou T. C. , Wong C. Y. , Tu K. N.
Published: July 2002

It has been recently reported that the redistribution of dopant during titanium silicide formation enhances the grain growth of polycrystalline silicon at a temperature lower than it normally occurs. The mechanism which is responsible for the enhanced grain growth has been proposed to be dopant diffusion induced grain-boundary migration. We have carried out a detailed study to clarify the mechanism. The results show that the effect of phosphorus dopant alone has a small influence on the grain growth of polycrystalline silicon around 900 °C. However, much enhanced grain growth of polycrystalline silicon accompanied by titanium silicide formation was observed at 700 °C in medium doped and heavily doped conditions as compared to those without silicide formation. On the other hand, no enhanced grain growth was observed in lightly doped and undoped situations regardless of titanium silicide formation. By correlating these observations with depth profiling of dopant distribution, it is concluded that the formation of titanium silicide serves as a sink for the out-diffusion of dopant. The out-diffusion of dopant, preferentially through grain boundaries, leads to a reduction of 30%–50% of dopant from the implanted levels. The depletion of dopant induces grain boundaries to migrate, and therefore enhances the grain growth.
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o band-structure calculation of the semiconductor β-FeSi2
Authors: Eppenga R.
Published: July 2002

Results for β-FeSi2 obtained from self-consistent calculations with the augmented spherical wave ab initio band-structure method are presented. In accordance with several experimental findings, β-FeSi2 is found to be a semiconductor. The calculated gap is 0.44 eV and is indirect. The smallest direct gap is 0.46 eV and has a vanishingly small oscillator strength. The first across-gap transition with an appreciable oscillator strength has a corresponding energy gap of 0.77 eV.
Investigation of the asymmetric misfit dislocation morphology in epitaxial layers with the zinc-blende structure
Authors: Fox Bradley A. , Jesser William A.
Published: July 2002

Epitaxial growth of compound semiconductors on the (001) exhibits an asymmetry in the dislocation morphology in the two 〈110〉 directions for thicknesses near the critical thickness. The source of the asymmetry has been investigated by growth of a thickness wedge of p- and n-type GaAs0.95 P0.05 on GaAs by metalorganic chemical vapor deposition. The effect of misorientation on the resolved shear stress for each slip system has been calculated and eliminated as the source of the asymmetry. The thickness gradient was also eliminated as the source. A definitive correlation can be made between the asymmetry and the differences in the Peierls barriers of the two types of dislocations. The asymmetry results in two different critical thicknesses, one for each type of dislocation. The Peierls barriers are more similar in p-type material than in n-type material. In agreement with this, a reduced amount of asymmetry was observed in the p-type overgrowth as compared to the n-type. The nucleation barrier differences between the two types of dislocations are shown to be an unlikely source of the asymmetry.
Recrystallization and grain growth phenomena in polycrystalline Si/CoSi2 thin-film couples
Authors: Nygren Stefan , Johansson Stefan
Published: July 2002

This paper presents high-temperature effects on CoSi2/polycrystalline silicon (poly-Si) bilayers, intended for metal-oxide-semiconductor gate applications. Both rapid thermal annealing and conventional furnace annealing were utilized for the investigation. At temperatures above 700 °C the structure breaks down due to silicon recrystallization within the silicide and simultaneous silicide growth into the polycrystalline silicon film. Recrystallized silicon adopts the silicide texture and this process terminates when the entire polysilicon layer is consumed. After completion the layer configuration is inverted, i.e., the silicide is adjacent to the gate oxide and covered with elemental silicon at the surface. This surface layer consists of large grains with few crystal defects, very different from the columnar structure of the as-deposited silicon. With further annealing, grain growth in both phases continues, and each grain will ultimately extend from the oxide interface to the free surface. Lateral grain dimensions are typically a few times the total film thickness at this stage. Silicon recrystallization in the silicide layer can be suppressed if the polysilicon is doped with phosphorus prior to metal deposition, or the phenomenon can be alleviated by an arsenic or boron implantation into the silicide.
Early stage evolution kinetics of the polysilicon/single-crystal silicon interfacial oxide upon annealing
Authors: Ajuria Sergio A. , Reif Rafael
Published: July 2002

We demonstrate by high-resolution electron microscopy studies that the breakup upon annealing of the once nearly continuous oxide in polysilicon/thin oxide/single-crystal silicon structures occurs by a process of nucleation and growth of oxide voids. A kinetic model is developed that assumes capillarity as a driving force and one-dimensional diffusion along the interface as a kinetic pathway. Detailed measurements of void radii (before coalescence) as a function of anneal time and temperature show an excellent fit of the model to experiment, confirming a linear dependence of void size with time and an Arrhenius dependence on temperature. Different activation energies are extracted for oxide void growth occurring in thick and thin oxides, suggesting two competing diffusion mechanisms are in effect. It is postulated that oxygen diffusion through both the oxide and the silicon above and underneath is taking place.
Theoretical analysis of acoustic transients in lithium niobate electro-optic modulators
Authors: Basséras P. , Miller R. J. Dwayne , Gracewski S. M.
Published: July 2002

Acoustic transients generated by high-voltage pulses in a transversely excited LiNbO3 Pockels cell are theoretically investigated. The theory treats explicitly the piezoelectric generation and propagation of the acoustic waves, and their interaction with the laser-beam polarization. Expressions for the strain fields and the strain-induced change in index of refraction are derived for short-voltage-pulse excitations. Numerical results are presented for a square- and a Gaussian-pulse excitation. These theoretical predictions are found to be in good agreement with the experimental observations: The waves propagating in the direction perpendicular to the applied electric field have the largest effect on the laser-light polarization. The damping of these acoustic waves is a straightforward application of these results and leads to an increase in the repetition rate of an Nd3+:YLF regenerative amplifier by over an order of magnitude. This work further illustrates the importance of using short-pulse excitations for minimizing the strain-induced birefringence effects for typical laser-beam geometries.
Thermal conductivity of diamond films
Authors: Baba Kazuhiro , Aikawa Yumi , Shohata Nobuaki
Published: July 2002

The thermal diffusivity of diamond films grown on the Si substrate by the hot-filament chemical vapor deposition technique in gas mixtures of 1% to 5% methane in hydrogen were studied. Thermal conductivity of the film prepared at 1% CH4 concentration reached about 1200W/mK, which is almost equal to that for type I natural diamond, and decreased rapidly to less than 200W/mK with increasing CH4 concentration. Hydrogen contents in the films increased with a decrease in thermal conductivity. This indicates that the thermal conductivity for diamond films is correlated to the amount of incorporated hydrogen impurity.
The spin-one Ising model on a honeycomb lattice
Authors: Tucker J. W.
Published: July 2002

A finite cluster effective-field theory in which the single-site kinematic relations are treated exactly is applied to a study of the spin-one Ising ferromagnet on a honeycomb lattice. The Ising model studied contains both biquadratic exchange, J′ and single-ion anisotropy D in addition to the usual bilinear exchange interactions J. The second-order phase boundary is studied for a range of interaction strengths and the results compared to those of other methods. The dependence of the results on cluster size is investigated. The magnetization predicted by the four-site cluster theory for a selection of single-ion anisotropy strengths is also compared with exact results that have recently been deduced in the subspace J′/J=−[ln cosh(βJ)]/(βJ). In extending the theory to account for site dilution, a form of configurational averaging is adopted that is superior to that of earlier authors. The variation with site dilution of the tricritical point in the T-D plane is reported.
Image contrast in near-field optics
Authors: Trautman J. K. , Betzig E. , Weiner J. S. , DiGiovanni D. J. , Harris T. D. , Hellman F. , Gyorgy E. M.
Published: July 2002

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, λ, in the near-field of the sample (<λ/10). This technique, near-field scanning optical microscopy, is sensitive to a variety of important sample properties including optical density, refractive index, luminescence, and birefringence. Although image contrast based on certain sample characteristics is similar to that observed in traditional optical microscopy, strong coupling between the probe and sample often produces contrast unique to the near-field.
Semisolid solidification of high temperature superconducting oxides
Authors: Cima Michael J. , Flemings Merton C. , Figueredo Anacleto M. , Nakade Masahiko , Ishii Hideo , Brody Harold D. , Haggerty John S.
Published: July 2002

Experiments are reported on two techniques for melt-texture processing Ba2YCu3O6.5 by directional solidification from a semisolid melt containing particles of BaY2CuO5 and a copper-rich liquid. One of these employs an electric resistance furnace with ambient or oxygen enriched atmosphere; the other is a laser-heated furnace operating at 1.3 atm oxygen. Solidification interface morphologies and other structural features were examined in quenched specimens. Depending on growth rate and temperature gradient, three different types of growth morphologies of the growing 123 phase were observed: ‘‘faceted plane front,’’ ‘‘cellular dendritic’’ or ‘‘equiaxed blocky.’’ The interface temperature decreased markedly with increasing growth rate for the faceted plane front specimens. In the remaining specimens, solidification took place over a range of temperatures. The temperature of the ‘‘root’’ of the solidification front dropped, but temperature of the solidification front ‘‘tip’’ did not. A solidification model is developed and employed to interpret experimental observations. The model assumes limited diffusion of solute in the liquid during the growth of the superconducting phase. The model shows, in agreement with experiment, that growth rate of the low temperature solid phase has a strong effect on ability to obtain the desirable faceted plane front, and that thermal gradient has only a small effect. Interparticle spacing of the high temperature phase, BaY2CuO5, is also predicted to have a strong effect.
Growth of high-T
c YBa2Cu3Oy films with an off-axis sputtering configuration
Authors: Wang L. M. , Sung H. H. , Chern J. H. , Yang H. C. , Horng H. E.
Published: July 2002

Using an off-axis rf sputtering configuration, we have prepared in situ high-Tc YBa2Cu3O7−y (YBCO) films with a relatively large deposition rate. The sputtering gas was a mixture of Ar and O2 (7:3) and the substrates were MgO(100) and SrTiO3(100). We found that the distance from the target to the substrate, d, is a key factor in the deposition rate. By decreasing d to a value of about 1.5–2.5 cm, we obtained a deposition rate as great as 2000–2500 Å per hour with an rf power of 120 W and at a total pressure 100–200 mTorr. The transport behaviors of the as-grown YBCO films under magnetic fields are reported. The activation energy derived from the resistive transition in magnetic fields is thickness dependent.
Surface cleaning of C-doped p+ GaAs with hydrogen electron cyclotron resonance plasma
Authors: Watanabe Noriyuki , Nittono Takumi , Ito Hiroshi , Kondo Naoto , Nanishi Yasushi
Published: July 2002

We report surface cleaning of C-doped p+-GaAs epilayers with hydrogen electron cyclotron resonance plasma. Native oxides on the surface of the p+-GaAs layer can be removed at a very low substrate temperature of 150 °C. In addition, carrier concentrations decrease after cleaning at about 300 °C, which is attributed to the hydrogenation of carbon acceptors caused by hydrogen plasma exposure. A cleaning temperature of about 400 °C, a cleaning time of about 5 min, and microwave power of about 30 W appear to be optimum for the regrowth process.
Experimental investigation of silicon-on-insulator metal-oxide- semiconductor field-effect transistors at high magnetic field and low temperature
Authors: Ouisse T. , Cristoloveanu S. , Maude D. K.
Published: July 2002

Shubnikov–de-Haas (SDH) oscillations as well as low-temperature measurements have been systematically performed in order to characterize thin-film silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs). The two-dimensional properties of the SOI MOS inversion layers highly depend on the quality of the front and buried Si-SiO2 interfaces. The influence of interface coupling on the quantized SDH oscillations is assessed. Even in 70 nm thin films, the carriers remain essentially confined to the lowest subband at an interface. Parasitic effects such as series resistance influence have been carefully examined in the case of short-channel devices. It is also shown that for submicronic devices, the attenuation of the oscillations as a function of the lateral electric field strongly increases with channel length. Eventually, it is demonstrated that unlike conventional bulk silicon MOSFETs, a fully depleted SOI MOSFET allows studying charge localization in MOS inversion layers, without needing any temperature variation to estimate the density of localized electrons.
Thermal properties of low-resistive and semi-insulating GaAs wafers heated locally by Nd:Y3Al5O12 laser beam
Authors: Kawamura Tsutomu , Shimizu Toshihiro
Published: July 2002

Low-resistive and semi-insulating GaAs wafers were locally heated by a Nd:Y3Al5O12 laser beam (the wavelength: 1.06 μm). Remarkably different thermal properties were found between these two kinds of wafers. The reason should be ascribed to the function of the mid-gap level (EL2) in GaAs wafers. The different thermal behaviors of the semi-insulating GaAs from the semi-insulating GaP, which has been reported previously, are also discussed.
Epitaxial waveguides of aluminum garnet
Authors: Gualtieri D. M. , Morris R. C.
Published: July 2002

Waveguides of high refractive index aluminum garnets have been epitaxially grown on 〈111〉-oriented crystal wafers of yttrium aluminum garnet (Y3Al5O12, YAG) and clad with epitaxial YAG. Epitaxy was by the liquid phase solution growth technique from supercooled mixtures of lead oxide and boron oxide, as is common for the epitaxy of iron garnets. One composition which is particularly suited for waveguides is Tb1.78Lu1.22Al5O12, which has a refractive index at 632.8 nm of about 1.854, as compared with 1.828 for YAG, and has no absorption bands in the visible and near IR spectra. Since aluminum garnets have melting points above 1900 °C, such waveguides should find application in high temperature optical sensors.
Giant magnetoresistance of Co/Cu multilayers with and without Fe buffer layers
Authors: Dorner C. , Haidl M. , Hoffmann H.
Published: July 2002

We have studied the giant magnetoresistance of two sputtered systems, Co/Cu multilayers with and without Fe buffer layers, with respect to their magnetic and structural properties. A different oscillatory character of the magnetoresistance as a function of Cu interlayer thickness was found for these two series. The specimens were magnetically characterized using a vibrating sample magnetometer. Transmission electron microscope cross-sectional images and low-angle x-ray diffraction analysis indicated a very different quality of the multilayer structure for these two systems. This is assumed to be the reason for their different magnetoresistant behavior.
Quantum electronic interferometer without a potential barrier
Authors: Joe Yong S. , Ulloa Sergio E.
Published: July 2002

We propose a novel electronic quantum interferometer which exhibits strong quantum interference effects in the ballistic regime. This behavior is produced without introducing additional barriers along the electronic path. Rather, by modulating the channel width of one of the arms in a multiply connected quantum nanoconstriction, one can produce an effect similar to that of an applied retarding gate potential. Strong conductance oscillations are then produced by quantum interference between phase-lagged propagating subbands in the different channels. We present results for typical structures, and discuss the dependence of these effects on electron path length and temperature.
Self-induced magnetic field effects caused by edge currents in parallel array of Josephson junctions
Authors: Kaplunenko V. K. , Goldobin E. B. , Khabipov M. I. , Larsen Britt H. , Mygind J. , Pedersen N. F.
Published: July 2002

A transmission line consisting of a parallel connection of shunted Josephson junctions is one of the base elements in the new Rapid Single Flux Quantum (RSFQ) logic. When an additional bias current is applied to the edge junction of the transmission line it generates and injects series of flux quanta on the line. This kind of pulse generators have important applications for testing RSFQ devices at high frequencies. In such experiments unwanted steps always show up in the I-V curve of the generator junction. This problem has been experimentally and numerically investigated for parallel arrays of identical junctions. Steps with extremely low differential resistance are found to be due to the self-induced magnetic field produced by the edge current. The underlying mechanism is that the non-uniform field divides the array into domains consisting of several (unit) cells each containing the same number of flux quanta. The influence of an applied homogeneous external magnetic field and a uniformly distributed bias current is also considered.
Picosecond dynamics of absorption bleaching in polycrystalline ZnCdTe films
Authors: Netiksis V. , Hönerlage B. , Weil R. , Loison J. L. , Grun J. B. , Levy R.
Published: July 2002

The spectral and temporal behavior of absorption bleaching and of self-diffraction in ZnxCd1−xTe polycrystalline films with a nominal composition x=0.87 have been investigated. It has been found that the optical transmission increases 15 times at a wavelength of 575 nm for a laser light intensity of 0.2 GW/cm2. In a pump and test experiment, the buildup and the relaxation times T1 of the bleaching were measured. Their values, between 10 and 40 and 20 and 45 ps, respectively, depend on the wavelengths of the pump and the test beams. The saturation intensity Is was also determined (between 1.5 and 6 GW/cm2). This absorption saturation effect can be related to the high density of crystallite grain surface states as well as to other imperfections in the polycrystalline films studied. The high density of these states can explain the large linear absorption and the ultrafast relaxation of the photogenerated carriers. Then, in self-diffraction experiments, the phase relaxation time T2=(10±5) ps of the localized surface states has been determined. The long duration of T2 and the short energy lifetime T1 indicate that elastic scattering processes are highly suppressed in polycrystalline material when compared to monocrystals, while their coherence time is increased.
Surface roughness effects on cylindrical grazing incidence x-ray optics for transition radiation
Authors: Ho A. H. , Piestrup M. A. , Silzer R. M. , Skopik D. M.
Published: July 2002

Quartz and nickel cylinders were used as grazing incidence x-ray optics for transition radiation (TR) from Al, Ti, and Cu foil stacks. The cylinders were used to direct the otherwise diverging TR to a small spot (1 mm diameter), with measured fluxes of up to 330 W/A cm2 averaged over the spot area. Computer simulations were performed and compared to the measured results. It was found that including surface roughness effects in the form of a Debye–Waller reduction factor on the reflectivity was necessary to get good agreement between the simulations and experimental results in certain cases, but not in others. A simple heuristic model which can be used to determine when roughness effects are important is presented. Use of this model in conjunction with the computer simulations accurately predicts the measured results, and further suggests the use of different optic materials at different x-ray wavelengths.
Explosive crystallization of amorphous Si3N4 films on silicon during silicon laser melting
Authors: Willems G. J. , Wouters D. J. , Maes H. E.
Published: July 2002

The explosive crystallization of Si3N4 layers deposited on silicon samples during laser melting of the silicon is investigated. The crystallization threshold is defined as the minimal laser-beam power to start crystallization. The precipitate-initiator hypothesis which states that the explosive crystallization is initiated by the formation of Si3N4 precipitates in the molten zone is formulated. Based on this hypothesis the dependency of the crystallization threshold on the scan conditions and the sample structure can be completely and consistently explained. Methods to prevent crystallization are formulated.