bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscous attractor for the Galton board
Authors: Hoover W. G. , Moran B.
Published: July 2002

We analyze the Galton Board [or periodic ‘‘Lorentz Gas’’] with a point mass scattered by elastic disks of diameter σ, using a constant driving field g and a constant-viscosity linear drag force −p/τ, where p is the point–mass momentum. This combination leads to a nonequilibrium steady state which depends only upon the dimensionless ratio gτ2/σ. The long-time-averaged trajectory leads to multifractal phase-space structures closely resembling those we found earlier using isokinetic equations of motion derived from Gauss’ Principle of Least Constraint. A highly damped [small τ] creeping-flow limit describes our results for gτ2/σ less than about 0.2. The lightly damped Green–Kubo linear-response limit for the model provides an accurate description of the dissipative dynamics for gτ2/σ greater than about 2.0.
Instability criteria for steady flows of a perfect fluid
Authors: Friedlander Susan , Vishik Misha M.
Published: July 2002

An instability criterion based on the positivity of a Lyapunov-type exponent is used to study the stability of the Euler equations governing the motion of an inviscid incompressible fluid. It is proved that any flow with exponential stretching of the fluid particles is unstable. In the case of an arbitrary axisymmetric steady integrable flow, a sufficient condition for instability is exhibited in terms of the curvature and the geodesic torsion of a stream line and the helicity of the flow.
Control of dynamical systems behavior by parametric perturbations: An analytic approach
Authors: Loskutov Alexander Yu. , Shishmarev Andrew I.
Published: July 2002

The problem of parametric suppression of deterministic chaos is considered. It is proved that certain parametric perturbations of a one-dimensional map with chaotic dynamics can lead to a transition of that map into a regime of regular behavior.
Chemical turbulence and standing waves in a surface reaction model: The influence of global coupling and wave instabilities
Authors: Bär M. , Hildebrand M. , Eiswirth M. , Falcke M. , Engel H. , Neufeld M.
Published: July 2002

Among heterogeneously catalyzed chemical reactions, the CO oxidation on the Pt(110) surface under vacuum conditions offers probably the greatest wealth of spontaneous formation of spatial patterns. Spirals, fronts, and solitary pulses were detected at low surface temperatures (T<500 K), in line with the standard phenomenology of bistable, excitable, and oscillatory reaction-diffusion systems. At high temperatures (T≳540 K), more surprising features like chemical turbulence and standing waves appeared in the experiments. Herein, we study a realistic reaction-diffusion model of this system, with respect to the latter phenomena. In particular, we deal both with the influence of global coupling through the gas phase on the oscillatory reaction and the possibility of wave instabilities under excitable conditions. Gas-phase coupling is shown to either synchronize the oscillations or to yield turbulence and standing structures. The latter findings are closely related to clustering in networks of coupled oscillators and indicate a dominance of the global gas-phase coupling over local coupling via surface diffusion. In the excitable regime wave instabilities in one and two dimensions have been discovered. In one dimension, pulses become unstable due to a vanishing of the refractory zone. In two dimensions, turbulence can also emerge due to spiral breakup, which results from a violation of the dispersion relation.
How organisms do the right thing: The attractor hypothesis
Authors: Emlen John M. , Freeman D. Carl , Mills April , Graham John H.
Published: July 2002

Neo-Darwinian theory is highly successful at explaining the emergence of adaptive traits over successive generations. However, there are reasons to doubt its efficacy in explaining the observed, impressively detailed adaptive responses of organisms to day-to-day changes in their surroundings. Also, the theory lacks a clear mechanism to account for both plasticity and canalization. In effect, there is a growing sentiment that the neo-Darwinian paradigm is incomplete, that something more than genetic structure, mutation, genetic drift, and the action of natural selection is required to explain organismal behavior. In this paper we extend the view of organisms as complex self-organizing entities by arguing that basic physical laws, coupled with the acquisitive nature of organisms, makes adaptation all but tautological. That is, much adaptation is an unavoidable emergent property of organisms’ complexity and, to some a significant degree, occurs quite independently of genomic changes wrought by natural selection. For reasons that will become obvious, we refer to this assertion as the attractor hypothesis. The arguments also clarify the concept of “adaptation.” Adaptation across generations, by natural selection, equates to the (game theoretic) maximization of fitness (the success with which one individual produces more individuals), while self-organizing based adaptation, within generations, equates to energetic efficiency and the matching of intake and biosynthesis to need. Finally, we discuss implications of the attractor hypothesis for a wide variety of genetical and physiological phenomena, including genetic architecture, directed mutation, genetic imprinting, paramutation, hormesis, plasticity, optimality theory, genotype-phenotype linkage and puncuated equilibrium, and present suggestions for tests of the hypothesis.
Diffusion and scaling in escapes from two-degrees-of-freedom Hamiltonian systems
Authors: Kandrup Henry E. , Siopis Christos , Contopoulos G. , Dvorak Rudolf
Published: July 2002

This paper summarizes an investigation of the statistical properties of orbits escaping from three different two-degrees-of-freedom Hamiltonian systems which exhibit global stochasticity. Each time-independent H=H0+εH′, with H0 an integrable Hamiltonian and εH′ a nonintegrable correction, not necessarily small. Despite possessing very different symmetries, ensembles of orbits in all three potentials exhibit similar behavior. For ε below a critical ε0, escapes are impossible energetically. For somewhat higher values, escape is allowed energetically but still many orbits never escape. The escape probability P computed for an arbitrary orbit ensemble decays toward zero exponentially. At or near a critical value ε1>ε0 there is a rather abrupt qualitative change in behavior. Above ε1, P typically exhibits (1) an initial rapid evolution toward a nonzero P0(ε), the value of which is independent of the detailed choice of initial conditions, followed by (2) a much slower subsequent decay toward zero which, in at least one case, is well fit by a power law P(t)∝t−μ, with μ≈0.35–0.40. In all three cases, P0 and the time T required to converge toward P0 scale as powers of ε−ε1, i.e., P0∝(ε−ε1)α and T∝(ε−ε1)β, and T also scales in the linear size r of the region sampled for initial conditions, i.e., T∝r−δ. To within statistical uncertainties, the best fit values of the critical exponents α, β, and δ appear to be the same for all three potentials, namely α≈0.5, β≈0.4, and δ≈0.1, and satisfy α−β−δ≈0. The transitional behavior observed near ε1 is attributed to the breakdown of some especially significant KAM tori or cantori. The power law behavior at late times is interpreted as reflecting intrinsic diffusion of chaotic orbits through cantori surrounding islands of regular orbits.
Nonasymptotic properties of transport and mixing
Authors: Boffetta G. , Celani A. , Cencini M. , Lacorata G. , Vulpiani A.
Published: July 2002

We study relative dispersion of passive scalar in nonideal cases, i.e., in situations in which asymptotic techniques cannot be applied; typically when the characteristic length scale of the Eulerian velocity field is not much smaller than the domain size. Of course, in such a situation usual asymptotic quantities (the diffusion coefficients) do not give any relevant information about the transport mechanisms. On the other hand, we shall show that the Finite Size Lyapunov Exponent, originally introduced for the predictability problem, appears to be rather powerful in approaching the nonasymptotic transport properties. This technique is applied in a series of numerical experiments in simple flows with chaotic behaviors, in experimental data analysis of drifter and to study relative dispersion in fully developed turbulence.
Alternating chaotic and periodic dynamics in Chern–Simons–Higgs theory with scalar magnetic interaction
Authors: Escalona J. , Antillón A. , Torres M. , Jiang Y. , Parmananda P.
Published: July 2002

The dynamical behavior of a Chern–Simons–Higgs system is studied for the spatially homogeneous case. The model, described by interacting gauge and scalar fields includes two parity and time violating terms: the Chern–Simons and the scalar magnetic interaction. For the pure Chern–Simons part of the theory the equations of motion are integrable. In general, however, the model system exhibits an interesting pattern of chaos to order transitions as the scalar magnetic moment is varied. The system dynamics are analyzed using a combination of standard techniques, such as phase space portraits, Lyapunov exponents, and Fourier spectra.
Computer modeling experiments on tetrahedral interstitial-kink interactions with a special reference to induced Snoek peak
Authors: Ogurtani Tarik Ö. , Seeger Alfred K.
Published: July 2002

The energy dissipation per cycle due to the harmonic rigid motion of geometric kinks (built-in) in the atmosphere of light interstitials which are hopping between tetrahedral sites is investigated analytically as well as numerically in terms of discrete Fourier k space plus Laplace transformation technique. In the linear response case a discrete Debye-type relaxation spectrum with six distinct branches is found to represent the anelastic behavior of the system uniquely (the nearest neighbor jumps only) and exactly. It is shown by extensive computer modeling experiments that the induced and dislocation embedded kink-enhanced Snoek peak is composed of six subpeaks, one acoustic and five optical in character. The acoustic part and the optical modes, especially the upper band which is composed of optical modes 6 and 5, are strongly and selectively associated with the isotropic (Cottrell Atmosphere) and the pure shear part (Snoek Cloud) of the elastic dipole tensor of the tetrahedral interstitials, respectively. An extremely accurate and concise analytical expression is deduced which shows that the decoupling procedure of Snoek and Cottrell atmospheres is a reliable approximation.
Power dissipated in low-pressure radio-frequency discharge plasmas
Authors: Popov O. A. , Godyak V. A.
Published: July 2002

The experimental study of capacitive radio-frequency (rf) discharges was performed in mercury vapor at low pressures (10−4–10−2 Torr) and at rf applied voltage below 200 V. It was found that at pressures less than 10−2 Torr, plasma electrons gain rf energy basically through a noncollisional mechanism at the oscillating potential barrier formed in electrode sheaths. The rf power dissipated in this process turned out to be much larger than that received by electrons through their collisions with neutral atoms in the plasma bulk. Experimental results are in good agreement with the theoretical model of low-pressure rf discharges developed earlier by one of the authors.
Supercurrent decay in underdamped Josephson junctions: Nonstationary case
Authors: Barone A. , Cristiano R. , Silvestrini P.
Published: July 2002

The decay of the zero voltage state in the presence of noise is investigated in connection with the general problem of a particle in a metastable state of a one-dimensional potential. A large number of important works have considered this problem on the basis of the analysis developed in the pioneering work by Kramers which stems from the condition of a thermal energy kT, small with respect to the potential barrier U0. This assumption legitimatizes the use of the stationary solutions of the Fokker–Planck equation. In the present work we developed an analysis in terms of the classical first-passage time problem due to Stratonovich whose results do not require the prescription kT≪U0. We confine attention to the case of very small damping which is of great interest in the context of Josephson junctions. Distributions of the switching currents are obtained which possess the correct normalization. Such a requirement cannot be satisfied by Kramers’ results. Discrepancies between the two approaches and the influence of noise conditions and junction parameters are also discussed.
Effects of substrate misorientation on the properties of (Al, Ga)As grown by molecular beam epitaxy
Authors: Tsui R. K. , Curless J. A. , Kramer G. D. , Peffley M. S. , Rode D. L.
Published: July 2002

(Al,Ga)As layers have rough surface morphologies when deposited under certain growth conditions in molecular beam epitaxy (MBE). This leads to poor interfaces between GaAs and (Al,Ga)As and degraded performance in heterojunction devices. We have observed that by misorienting the substrate slightly from (100), in a manner specific to the growth conditions, smooth (Al,Ga)As layers can be grown at 675 °C for an Al mole fraction of 0.15. Similar conditions for nominal (100) result in a rough, textured morphology. The results suggest that the roughness is due to an energetic instability at the growth surface with respect to the formation of features such as terraces and hillocks. To our knowledge, this is the first reported experimental verification of singular instabilities in (Al,Ga)As grown by MBE. Smooth layers obtained by using an optimal misorientation of 2° 45′ from (100) towards (111)A also exhibit superior optical properties as determined from low-temperature photoluminescence measurements. These findings may have major implications for the performance of heterojunction device structures grown by MBE.
Wiggle plane focusing in linear wigglers
Authors: Scharlemann E.T.
Published: July 2002

In a free-electron laser with a long, linear wiggler, the external focusing required to keep the electron beam from dispersing can seriously degrade the performance of the laser. The transverse focusing modulates the longitudinal velocity of each electron, periodically and nonadiabatically changing the phase of the electron with respect to the electromagnetic wave. Phase changes of order unity over a betatron period can strongly detrap or debunch electrons and greatly reduce the gain of a linear wiggler amplifier. The modulation of the electron’s longitudinal velocity can be prevented if focusing in the plane of the electron’s wiggle motion is provided by parabolically curved magnet pole faces. The focusing and resonance effects of curved pole faces are analytically calculated and numerically confirmed. Numerical simulations of linear wiggler amplifiers are presented to illustrate the effect of the curved pole faces on amplifier performance.
Forward I-V plot for nonideal Schottky diodes with high series resistance
Authors: Cibils Roberto M. , Buitrago Román H.
Published: July 2002

In this work we present an extension of Norde’s forward I-V plot. This modified method allows us to obtain reliable values for three different parameters (n, R, and Is) in nonideal Schottky barrier diodes with high series resistance.
Electroless deposition of cadmium stannate, zinc oxide, and aluminum-doped zinc oxide films
Authors: D. Raviendra , Sharma J. K.
Published: July 2002

Transparent conducting films of cadmium stannate (Cd2SnO4), zinc oxide, and aluminum-doped zinc oxide have been made by a simple, economical electroless deposition technique. The as-deposited films of cadmium stannate have a 75% transmittance in the visible, 48% reflectance in the IR, and a band gap of 2.7 eV. Its resistivity is ∼10−1 Ω cm. Vacuum annealing changes the transmittance in the visible range to 82%, the IR reflectance to 62%, and the band gap to 3.1 eV. The corresponding values for the hydrogen-annealed films are 87%, 76%, and 3.2 eV. Annealing lowers the resistivity of the films to ∼10−2 and ∼10−3 Ω cm for vacuum and hydrogen-annealed films, respectively. The undoped zinc oxide films have transmittance in the visible and reflectance in the IR of 80 and 67% respectively. Aluminum doping increases the transmittance to 88% and reflectance to 83%. The optical band gap of undoped and aluminum-doped zinc oxide films are found to be 3.40 and 3.98 eV, respectively. The resistivity is 1.20×10−2 and 6.0×10−2 Ω cm for undoped and aluminum-doped ZnO films. Vacuum annealing reduces the resistivity of the films to 2.5×10−3 and 2.1×10−4 Ω cm for undoped and aluminum-doped ZnO films, respectively.
Laser-generated plasma as soft x-ray source
Authors: Gerritsen H. C. , van Brug H. , Bijkerk F. , van der Wiel M. J.
Published: July 2002

We present some properties of laser-generated plasma emission in the soft x-ray region. Detailed spectral distributions are reported for different target materials (C, Mg, Al, Si, Ti, Fe, Ni, Cu, Mo, Ag, Sn, Ta, Au, Pb, and Bi) in the energy range from 100 to 800 eV. Furthermore, we include measurements of the angular distribution, laser power dependence, and source size of the soft x rays. The efficiency for soft x-ray generation in our energy range peaks at a laser power density of 1012 W/cm2, which can be obtained already with standard laser systems. A comparison is made with other x-ray sources. To demonstrate the unique properties of laser-generated plasmas as soft x-ray source, we report the first single-shot EXAFS measurement in the soft x-ray region.
Structure and crystal growth of atmospheric and low-pressure chemical-vapor-deposited silicon films
Authors: Bisaro R. , Magariño J. , Proust N. , Zellama K.
Published: July 2002

Structure and crystal growth of undoped, as-deposited, and annealed silicon films prepared by chemical vapor deposition (CVD) and low-pressure chemical vapor deposition (LPCVD) of silane have been studied with use of x-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM). The grain size and a complete texture analysis are performed on CVD films grown at atmospheric pressure and temperature range 600≤Td≤805 °C, LPCVD films grown in the pressure range 0.1≤Pd≤2 Torr and temperature range 500≤Td≤650 °C and annealed amorphous CVD and LPCVD films near Ta=600 °C. We obtain systematically amorphous, strong 〈220〉 polycrystalline, and inhomogeneous partially crystallized films 〈111〉 or 〈311〉 oriented depending on the deposition conditions. The presence of a given texture is explained by a model which takes into account the specific free surface energies of the starting equilibrium forms and the extinction of some crystalline planes by {111} slow growing facets. The appearance of the 〈220〉 texture is explained by a gas phase nucleation of crystal occurring during deposition, whereas the observed 〈311〉 texture of LPCVD films is supposed to be due to a gas-phase nucleation mechanism occurring during the first stages of deposition followed by a solid-phase crystallization mechanism.
Mössbauer spectroscopic study on bonding characteristics of iron in Fe–B and Fe–P amorphous alloys
Authors: Tanaka Katsuhisa , Soga Naohiro , Hirao Kazuyuki , Kimura Kunio
Published: July 2002

An expression for the temperature dependence of recoil-free fraction of iron atoms was derived from the two-band theory proposed previously by the present authors, and it was applied to investigate the bonding characteristics of iron in amorphous Fe83B17, Fe80B20, and Fe80P20 alloys. The characteristic temperatures were found to be θ1=605 K and θ3=230 K for amorphous Fe83B17, θ1=655 K and θ3=185 K for amorphous Fe80B20, and θ1=425 K and θ3=185 K for amorphous Fe80P20. The comparison between these values with those obtained from the specific-heat measurements showed a good agreement for θ1, which is a measure of interatomic bond strength, indicating that metalloid atoms are not connected to each other in these Fe–mettalloid binary amorphous alloys but are bonded to iron atoms. Based on this result, the force constant was estimated for Fe–B, Fe–P, and Fe–Fe bonds. On the other hand, the values of θ3 obtained from the Mössbauer study were significantly different from those obtained from specific-heat measurements.
Zinc-oxide thin-film ammonia gas sensors with high sensitivity and excellent selectivity
Authors: Nanto Hidehito , Minami Tadatsugu , Takata Shinzo
Published: July 2002

A sensor with a high sensitivity and an excellent selectivity for ammonia gas was prepared by using sputtered ZnO thin films. The sensor exhibited an increase of resistance for exposure to ammonia gas whereas it exhibited a decrease of resistance for exposure to many other gases such as inflammable and organic gases. The resistance change and the selectivity of the sensor were enhanced by doping group III metal impurities such as Al, In, and Ga. The lower limit of the detection for ammonia gas was about 1 ppm at a working temperature of 350 °C.
Some characteristics of the hollow anode glow
Authors: Miljević Vujo I.
Published: July 2002

A new type of discharge realized in a diode consisting of a cathode and a special type of hollow anode is presented. The distinctive arrangement of dark and luminous regions between the cathode and anode with a characteristic hollow anode glow has been observed in the discharge. The optical spectrum strongly depends on the discharge current, and can be practically a spark or arc spectrum without any lines of anode or cathode material.
Effect of light attenuation on the responsivity and detectivity of transverse and longitudinal detectors
Authors: Szmulowicz Frank , Bloch Kenneth T. , Madarasz Frank L.
Published: July 2002

It is shown that when account is taken of the attenuation of incident radiation into the bulk of a photoconductor, as a result of the absorption, the expressions for the responsivity and detectivity are modified. An earlier derivation [Infrared Phys. 20, 385 (1980)] attributed the difference in the operation of the detectors in the transverse and longitudinal geometries to carefully defined ‘‘effective’’ quantum efficiencies. Here we show that a more physically motivated view attributes the difference to the different photoconductive gains for the two geometries. It is shown that the appropriate gains for the responsivity and detectivity are not the same.
Addendum to ‘‘Dipole moments of conducting particle chains’’ [J. Appl. Phys. 6
0, 2226 (1986)]
Authors: Jones T. B.
Published: July 2002

In this paper, additional data for the effective dipole moment of chains of conducting particles are presented. A more accurate linear-regression analysis of the data is presented. The theoretical result for a chain of four particles is provided. In addition, an error in the theoretical expression for the moment of a chain of three conducting spheres is corrected.
Velocity-field characteristics of III-V semiconductor alloys: Band structure influences
Authors: Krishnamurthy Srinivasan , Sher A. , Chen A.-B.
Published: July 2002

We have calculated the velocity-field characteristics of semiconductor alloys based on realistic band structures and have obtained the band structures and alloy-scattering rates from a generalization of the coherent potential approximation method. Although we use proper band structures, we still consider a single electron-temperature model. The results agree surprisingly well with experiments, and suggest that InP-based alloys are good candidates for high-speed devices.
Characteristics of plasma flow from laser irradiated planar thin foil targets
Authors: Dhareshwar L. J. , Naik P. A. , Nandwana P. D. , Pant H. C.
Published: July 2002

Filamentary structures or jetting in the plasma flow generated from laser irradiated thin foil targets have been observed using an optical probe technique. Laser wavelength, pulse duration, and intensity range used in the experiments were 1.06 μm, 5 ns, and 5×1012 W/cm2, respectively. A 0.53-μm-wavelength optical pulse of 50-μJ energy and 1-ns duration was used as an optical probe. Optical shadowgrams showed that the filamentary structures or jets in the plasma flow were strongest in the region about 300 μm away from the target surface, and in time, much later than the peak of the main laser pulse. It was also observed that jetting does not affect the stability of the ablatively accelerated thin foils. Jetting was found to be stronger for targets with a higher atomic number. A time-resolved interferometric study of the plasma produced from targets with high atomic numbers also showed the existence of an abrupt change in fringe shift or plasma density in the region of these jets.
Orientation control of the silicon film on insulator by laser recrystallization
Authors: Sugahara K. , Kusunoki S. , Inoue Y. , Nishimura T. , Akasaka Y.
Published: July 2002

We have studied the influence of the growth direction and the solidification speed on crystal quality of the silicon-on-insulator (SOI) film by laser recrystallization. In a 〈100〉 direction on a {100} Si substrate, lateral epitaxial growth of single-crystal regions from a seed extended as much as 1 mm. It was found that the crystalline orientation of the SOI film changes continuously from {100} toward {110}. These results indicated that the quality of the SOI film is strongly affected by the crystallographic arrangement of the growth front relative to the composition of {111} faceted planes. A new recrystallization method for large area SOI films was developed by stabilizing the growth front.
Clockwise C-V hysteresis phenomena of metal–tantalum-oxide–silicon-oxide–silicon ( p) capacitors due to leakage current through tantalum oxide
Authors: Hwu Jenn-Gwo , Jeng Ming-Jer , Wang Way-Seen , Tu Yuan-Kuang
Published: July 2002

Thermal tantalum oxide with a thickness of 620 Å was studied. The dc leakage resistance and high-frequency (1-MHz) resistance of a metal–tantalum-oxide–silicon capacitor were found to be on the order of 108 and 1 Ω cm2, respectively. The C-V behavior of the capacitor, with its initial states being carefully treated, was reproduced and observed to be dependent on the return voltage and hold time (at return point) of the measurement conditions. And only negative charges were observed to be responsible for the conduction current through tantalum oxide. A model with the considerations of the ac equivalent circuit and low-frequency leakage characteristic of tantalum oxide was proposed for these observations. Theoretical examples, with their parameters being suitably given according to the measured data, were shown, and they explained the experimental observations quite well. It is found that the measurement conditions and effect of the ac resistance of tantalum oxide on the determination of flat-band capacitance are important and should be carefully considered when one is interpreting the interface charges from C-V curves.
Phase transitions and ferroelectric attributes in A5M3F19 compounds with A=Sr, Ba and M=Ti, V, Cr, Fe, Ga
Authors: Ravez J. , Arquis S. , Grannec J. , Simon A. , Abrahams S. C.
Published: July 2002

Phase transitions have been found in ten new materials, Sr5Ti3F19 at 755 K, Sr5V3F19 at 735 K, Sr5Cr3F19 at 953 K, Sr5Fe3F19 at 720 K, Sr5Ga3F19 at 893 K, Ba5Ti3F19 at 1005 K, Ba5V3F19 at 1020 K, Ba5Cr3F19 at 1090 K, Ba5Fe3F19 at 960 K, and Ba5Ga3F19 at 1070 K, by calorimetric and dielectric permittivity measurement on polycrystalline samples. All ten are isomorphous with archetypal Pb5W3O9F10, which satisfies the structural criteria for crystals exhibiting ferroelectricity. The optical birefringence of single-crystal Sr5Fe3F19 decreases anomalously at the phase transition.
Optical investigation of highly strained InGaAs-GaAs multiple quantum wells
Authors: Ji G. , Huang D. , Reddy U. K. , Henderson T. S. , Houdré R. , Morkoç H.
Published: July 2002

Low-temperature optical transmission spectra of several InxGa1−xAs/GaAs strained multiple quantum wells (MQWs) with different well widths and In mole fractions have been measured. The excitonic transitions up to 3C-3H are observed. The notation nc-mH(L) is used to indicate the transitions related to the nth conduction and mth valence heavy (light) hole subbands. Steplike structures corresponding to band-to-band transitions are also observed, which are identified as 1C-1L transitions. The calculated transition energies, taking into account both the strain and the quantum well effects, are in good agreement with the measured values. In these calculations the lattice mismatch between the GaAs buffer and the InGaAs/GaAs MQW is taken into account and the valence-band offset Qv is chosen as an adjustable parameter. By fitting the experimental results to our calculations, we conclude that the light holes are in GaAs barrier region (type II MQW) and the valence-band offset Qv is determined to be 0.30. A possible system in which the transition from type I to type II for light holes might be observed is also discussed.
Silicon surface cleaning by low dose argon-ion bombardment for low-temperature (750 °C) epitaxial silicon deposition. I. Process considerations
Authors: Comfort James H. , Garverick Linda M. , Reif Rafael
Published: July 2002

A low-energy argon sputter process has been optimized to successfully remove native oxide from a silicon surface at elevated temperatures without introducing permanent damage. The process relies upon confining all sputtering events to the near-surface region of the silicon and exploits the enhancement of sputter efficiencies observed for silicon and silicon dioxide above 600 °C. The procedure has been implemented as an in situ etch for low-temperature (below 800 °C), very low-pressure (1–10 mTorr), epitaxial silicon deposition in a high vacuum ambient. The reactor and conditions employed are presented along with measures of residual substrate damage as a function of processing conditions, and the process limitations are discussed. A companion paper describes the excellent structural quality of the resultant epitaxial films. The ion energies (100 eV) and fluxes (5×1013 cm−2 s−1) employed represent a significant departure from conventional sputter cleaning processes.
Preparation of superconducting thin films of (La1−xSrx)yCuO4−δ by sputtering
Authors: Koinuma H. , Kawasaki M. , Funabashi M. , Hasegawa T. , Kishio K. , Kitazawa K. , Fueki K. , Nagata S.
Published: July 2002

Superconducting thin films of (La1−xSrx)yCuO4−δ have been prepared by sputtering with careful control of such preparation parameters as target composition, total pressure and composition of gases in the reactor, substrate material and temperature, and annealing conditions. In accordance with the bulk target materials, the superconducting films show K2NiF4-type x-ray diffraction patterns, although this crystal structure was not the sole requisite for the superconductivity of the films. The films prepared thus far have a superconducting transition onset of about 36 K and turn out to be fully superconducting at temperatures below 10 K.
Fundamentals of topographic substrate leveling
Authors: Stillwagon L. E. , Larson R. G.
Published: July 2002

The leveling of 100–500-μm-wide, 1-μm-deep isolated holes and trenches on a silicon substrate by 1–3-μm-thick silicone oil films was observed by measuring film thickness changes at the centers of the features using a noncontact, interferometric technique. The dependence of the leveling time t on feature width w, film viscosity η, and the initial film thickness h0 was investigated and compared to theoretical predictions. Experimental data were obtained for various values of w, η, and h0. Except when the film thickness was about 1 μm, the data for each different type of geometry fell on a single curve when the degree of leveling or planarization was plotted against T≡tγh30/ηw4 where γ is the surface tension of the film. At the same value of T, the degree of planarization of isolated holes was about twice that of isolated trenches. The planarization versus T curves should apply to all Newtonian liquids and may be used to predict the degree of planarization that will be achieved at specified leveling times by materials having specified values of η, h0, and γ. Thus, the curves may be useful in selecting planarizing materials for semiconductor fabrication steps that require substrate topography leveling. Simulations of the leveling process based on capillarity-driven flow were performed and agreed well with the experimental data. The simulations predicted some interesting and unexpected behavior that was observed experimentally. At short times the planarization became worse before improving at longer times and bumps appeared in the film profiles that apparently were a first step in minimizing surface energy. Such simulations may prove to be useful in predicting the difficulty of planarizing various types of topographic geometries and in designing ‘‘dummy topography’’ that will make them easier to planarize.
Spurious inductive coupling of a dc-SQUID to a resonant input circuit
Authors: Castellano Maria Gabriella , Cosmelli Carlo
Published: July 2002

A mutual inductance different from zero exists in most real dc-SQUIDs between the feedback/modulation coil and the input coil. This spurious coupling causes many effects when the input circuit of the SQUID is a high Q resonant circuit. In particular, it affects the Q of the input circuit, decreasing it or making the system unstable. A series of measurements showing these effects were made on the dc-SQUID coupled to the gravitational radiation detector of the Rome group operating at CERN. A model is then presented to explain, in detail, these spurious effects and a comparison is made with the experimental measurements. A way to overcome these unwanted effects by modifying the feedback loop is also presented.
Photoinduced current transient spectroscopy in high-resistivity bulk materials: Instrumentation and methodology
Authors: Tapiero M. , Benjelloun N. , Zielinger J. P. , El Hamd S. , Noguet C.
Published: July 2002

A sensitive photoinduced current transient spectroscopy technique using a computer for data acquisition and processing has been worked out. It enables one to determine separately the signatures and concentrations of deep levels in high-resistivity bulk materials. In a previous paper, possible signal processing has been analyzed from a rather theoretical point of view. In the present report, the instrumentation used as well as the experimental procedure and some practical and complementary aspects will be discussed. For the determination of reliable trap signatures, we have proposed and tested a four-gate data treatment that eliminates, or at least reduces, many of the problems encountered when using the usual double-gate procedure provided some experimental precautions are taken. Yet the double-gate method is useful when one wants to estimate the trap concentrations. A standard experimental procedure is presented that takes into account the temperature dependence of the mobility/free-lifetime product of thermal emitted carriers, and its possible variation during the relaxation of the traps.
Magnetization processes in ferromagnetic cubes
Authors: Schabes Manfred E. , Bertram H. Neal
Published: July 2002

A cubic discretization procedure of the micromagnetic energy functional is used to carry out numerical studies of the magnetization process in ferromagnetic cubes. Equilibrium magnetization configurations and their switching behavior are calculated for particle sizes in the range from 100 to 550 Å. In the model calculations the particles are assumed to have uniaxial crystalline anisotropy with an anisotropy constant of 18 500 erg/cm3, a saturation magnetization of 370 emu/cm3, and an exchange constant of 10−6 erg/cm. For particle sizes smaller than 520 Å the remanent state has a flowerlike magnetization configuration. Beyond 520 Å this state is replaced by a vortex structure about the easy axis. For particles smaller than 450 Å switching occurs by approximately uniform rotation of the flower state. The switching fields are larger than the corresponding Stoner–Wohlfarth value. Beyond 450 Å the application of an external field leads to the formation of a vortex configuration. The switching of the vortex configuration involves rotation of the vortex axis at a reduced value of the switching field. The angular dependence of the coercive field is calculated for particle sizes of 200, 400, and 550 Å.
A novel microstructure: Semiconductor-impregnated porous Vycor glass
Authors: Huber C. A. , Huber T. E.
Published: July 2002

Porous Vycor glass has been impregnated with selenium and tellurium by pressure forcing the nonwetting semiconductor melt into the interconnected pores. Dense semiconductor microstructures with a characteristic size of 50 Å can be fabricated by this technique. Measurements are reported which show the composite is suitable for both optical and electrical transport studies, particularly those addressing possible quantum confinement of carriers in this class of materials.
Rolled texture and magnetic properties of 3% silicon steel
Authors: Arai Ken Ichi , Ishiyama Kazushi
Published: July 2002

Conventional grain-oriented silicon steels 0.3 mm thick were cold-rolled to thicknesses from 0.18 to 0.08 mm, and the magnetic properties and grain textures of these sheets were observed before and after annealing. The results indicated that the magnetic induction B8 and the coercive force Hc were 1.8 T and 25 A/m, respectively, for a sheet 0.08 mm thick after primary recrystallization. When a 0.12-mm-thick sheet was annealed for more than 6 h at 1200 °C, the tertiary recrystallization had begun, and the (110)[001] texture occupied the whole surface of the sheet. The magnetic properties of this sheet were as follows : B8=1.97 T, Hc =1.7 A/m, W12.5/50 =0.21 W/kg, and W17/50 =0.43 W/kg under the application of a tensile stress of 4 kg/mm2 .
Time resolved annealing of interface traps at the silicon oxide-silicon interface
Authors: Burte Edmund P.
Published: July 2002

Anneal kinetics of interface traps have been studied using capacitance-voltage measurements. The silicon oxide-silicon samples have been annealed without any gate structure on top of the silicon oxide. An exponential decay of trap density with annealing time has been observed at metal gate-silicon oxide-silicon capacitors built after annealing at temperatures ranging from 250 to 620 °C. A model is proposed to explain the obtained results.
Structural and thermodynamic properties of heavily mechanically deformed Ru and AlRu
Authors: Hellstern E. , Fecht H. J. , Fu Z. , Johnson W. L.
Published: July 2002

We report on high-energy ball milling of Ru and AlRu. The deformation results in a drastic decrease of the crystal size to a nanometer scale and in an increase of atomic-level strain. This is accompanied by a disordering of the crystal lattice as is shown by means of the long-range-order parameter in AlRu. The specific heat increases by more than 15%–20%, indicating large changes in the vibrational and configurational part of the entropy. The stored energy of cold work is up to 6 kJ/mol for AlRu and 10 kJ/mol for Ru. This is almost 40% of the heat of fusion of Ru and exceeds by far the energies stored by other deformation processes.
Pt and PtSix Schottky contacts on n-type β-SiC
Authors: Papanicolaou N. A. , Christou A. , Gipe M. L.
Published: July 2002

Schottky barrier rectifying contacts using e-beam-deposited platinum have been demonstrated on n-type β-SiC. The electrical properties of these contacts were examined as a function of annealing temperature using I-V and C-V measurements. Auger analysis was used to study the metallurgical reactions at the Pt/SiC interface. Short annealing cycles in the 350–800 °C temperature range led to formation of a mixed structure of PtSix and PtC at the interface, evidenced by migration of platinum into the SiC above 350 °C. The barrier height was found to increase from 0.95 to 1.35 eV with increasing annealing temperature. The rectifying characteristics improved following an initial 350 °C anneal and remained relatively stable up to 800 °C.
Thermal relaxation of a laser illuminated field emitter
Authors: Lee M. J. G. , Robins E. S.
Published: July 2002

The time dependence of the total emission current from a field emitter illuminated by a chopped cw laser beam has been measured in conditions where the emission of primary photoelectrons is negligibly small. When the laser beam is switched on, the emission current increases with a characteristic time that is found to be in close agreement with the thermal relaxation time of the field emitter, showing that the laser-induced increase in emission is primarily due to tip heating. The large temperature rise and short thermal relaxation time associated with laser heating make it a widely applicable technique for controlling the temperature of a field emitter.
Theory of the quantum well emission transistor
Authors: Grinberg A. , Kastalsky A.
Published: July 2002

We present a theoretical analysis of the physical processes and high-speed performance of the recently proposed quantum well emission transistor employing quantum properties of electrons in a single quantum well (QW). The physical mechanism of device operation is based on an exponentially strong variation of the thermionic emission from the QW to the collector induced by the charge density modulation in the QW by the gate voltage. The calculation is performed for the selected structure optimized for the highest device performance.The most essential part of calculation is related to the effect of collector and gate voltages on the ground-state energy in the QW. A variational approach is used to take into account the presence of electrons in the QW. The analysis presented shows a high potential of this device for high-speed, large current drive applications.
Magnetic field of a direct current in a cylindrical-shaped conductor imbedded in a resistive half-space beneath a conductive surface layer
Authors: Inayat-Hussain A. A.
Published: July 2002

New applications of Fourier series and integral equation methods have yielded results of significance for electrical prospecting. This paper presents the first model calculation in three dimensions of the magnetic field due to a direct current flow in a conductor imbedded in a half-space beneath a conductive surface layer. The conductor is in the shape of a cylinder of semi-infinite length, and the current flow is from a point source in the surface layer. The vertical component of the magnetic field is given here by a Fourier series integral over a function which satisfies a Cauchy singular integral equation. For the two special cases, namely, an outcropping cylinder with no surface layer and a nearly invisible (in the sense of negligible conductivity contrast with its surrounding) cylinder, this integral equation can be solved exactly to yield closed-form expressions for the vertical component of the magnetic field. The exact solution in the first special case is based on a new generalization of the Hankel integral transform (published separately), and it extends the class of exactly solvable singular integral equations. This exact solution has also yielded as useful byproducts two new standard integrals involving Bessel functions. The integral equation approach used here, in contrast to the well-established surface integral equation approach, is suitable for numerical calculations, and typical magnetic field profiles are presented. The magnetic field results given here would be valuable for interpretation in electrical prospecting (based on the measurement of magnetic fields of direct currents), and the mathematical techniques used here would be useful for future calculations in electromagnetism.
Investigation of copper electrodes for mercuric iodide detector applications
Authors: Bao X. J. , Schlesinger T. E. , James R. B. , Stulen R. H. , Ortale C. , van den Berg L.
Published: July 2002

Copper diffusion in mercuric iodide was studied by low-temperature photoluminescence (PL) spectroscopy and Auger electron spectroscopy. A broad radiative emission band at a wavelength of about 6720 Å in the PL spectra was found to be related to Cu incorporation in the crystal. PL spectra obtained from surface doping experiments indicate that Cu is a rapid diffuser in HgI2 bulk material. Auger electron spectroscopy performed as a function of depth from the crystal surface confirms the rapid bulk diffusion process of Cu in HgI2. Fabrication of HgI2 nuclear detectors with Cu electrodes indicates that Cu is not acceptable as an electrode material, which is consistent with the fact that it diffuses easily into the bulk crystal and introduces new radiative recombination centers.
Force measurement using an ac atomic force microscope
Authors: Ducker William A. , Cook Robert F. , Clarke David R.
Published: July 2002

Complete amplitude-displacement-frequency spectra for a lever of an atomic force microscope have been measured and used to determine surface forces in air. Two ac techniques were used to measure the shift in resonant frequency of the Ni lever, as a function of separation from a mica surface. A strong, short-range force was observed for freshly prepared surfaces, implying a van der Waals interaction. A weak, long-range force was observed after exposure of the surfaces for some hours, suggestive of a capillary interaction. The long-range force appeared to contain a nonconservative element which increased on approach to the surface. The results have implications for surface-force determinations by single tip displacement scans, and for imaging with force microscopes.
Influence of illumination conditions on the spectral response of hydrogenated amorphous silicon Schottky barrier structures
Authors: Chatterjie P. , McElheny P. J. , Fonash S. J.
Published: July 2002

It is known experimentally that illumination conditions can significantly affect the spectral response behavior of hydrogenated amorphous silicon (a-Si:H) Schottky barrier detector and solar cell structures. This behavior is examined for the first time using a first-principles numerical analysis to explore the repercussions of the relative intensities and absolute intensities of the bias light and the monochromatic light. It is demonstrated that to avoid the experimental difficulty of an ill-defined spectral response, which can arise when lock-in detection is used, the bias light intensity should be an order of magnitude larger than the monochromatic light intensity. More importantly, the numerical modeling demonstrated that spectral response can fundamentally depend on illumination conditions due to field redistribution and recombination redistribution. It is further shown that these redistributions depend on the homogeneity of the intrinsic absorber layer; that is, the behavior with bias light is found to be different if a thin surface layer is postulated to exist at the front of the intrinsic layer. It is also demonstrated that the spectral response can be greater in the shorter wavelengths for materials with a higher midgap density of states. This result can explain the experimentally observed effects of prolonged light soaking.
Magnetization of anisotropic superconducting grains
Authors: Peterson R. L.
Published: July 2002

A critical-state calculation of the magnetization of hard type-II superconducting grains having anisotropic critical-current densities is given. The analysis shows how the critical-current densities should be deduced from magnetization measurements for various grain morphologies. A universal curve of the magnetization hysteresis versus one of the grain dimensions is presented, showing that the hysteresis does not change linearly with grain size. Applications to single crystals and to bulk materials are made.