bluuebunny/crossref_metadata_2025 huggingface dataset:
Millions of cantilevers for atomic force microscopy
Authors: Kawakatsu Hideki , Saya Daisuke , Kato Atsushi , Fukushima Kimitake , Toshiyoshi Hiroshi , Fujita Hiroyuki
Published: July 2002

Millions of single-crystal silicon cantilevers were fabricated by anisotropic etching of silicon by KOH. They could be tailored to measure from 500 nm to 100 μm in length and from 30 to 100 nm in thickness. Since the tips and the cantilevers were formed by a combination of crystal-line facets, they had very high uniformity, well-defined shape, and size. The density of the cantilevers was over 1 mil cantilevers per square centimeter. Typical mechanical characteristics of cantilevers measuring a few microns in length were spring constant a few N/m, natural frequency around 10 MHz, Q factor 5 in air, and 104 in vacuum. The natural frequency of cantilevers within the same row differed by 0.01%. Displacement measurement of the cantilever from the back surface of the silicon substrate by an infrared Fizeau interferometer had a visibility of 0.1.
Large-grain polycrystalline silicon films with low intragranular defect density by low-temperature solid-phase crystallization without underlying oxide
Authors: Bo Xiang-Zheng , Yao Nan , Shieh Sean R. , Duffy Thomas S. , Sturm J. C.
Published: July 2002

The solid-phase crystallization of an amorphous silicon film to polycrystalline silicon by a low-temperature (⩽600 °C) furnace anneal has been investigated in a suspended cantilever structure without underlying silicon oxide by transmission electron microscopy and Raman spectroscopy. The grain size of polysilicon increases up to ∼3.0 μm and the density of intragranular defects decreases one order of magnitude in the samples without underlying oxide, compared with those with underlying oxide. The main reasons for the high quality of the suspended structures are thought to be due to the lower stress in the films during crystallization and a reduced grain nucleation rate.
Influence of nitrogen on the magnetovolume effects in La(FexAl1−x)13 compounds
Authors: Irisawa K. , Fujita A. , Fukamichi K. , Yamazaki Y. , Iijima Y.
Published: July 2002

Nitrogen and hydrogen absorptions have been carried out in order to discuss the influence of interstitial atoms on the magnetovolume effects for the La(FexAl1−x)13 (x=0.83 and 0.86) compounds. The average magnetic hyperfine field and the Curie temperature TC of nitrides are lower than that of hydrides. The volume expansion due to the nitrogen absorption is about twice that due to the hydrogen absorption. Comparing the change in TC of the nitrides with that of hydrides and the pressure effect on TC, the hybridization between the Fe 3d and N 2p orbital should be taken into consideration in the lower TC of nitrides.
Measurement of radiation symmetry in Z-pinch-driven hohlraums
Authors: Hanson D. L. , Vesey R. A. , Cuneo M. E. , Porter J. L. , Chandler G. A. , Ruggles L. E. , Simpson W. W. , Torres J. , McGurn J. , Hebron D. , Dropinski S. C. , Hammer J. H. , Bennett G. R. , Seaman H. , Gilliland T. L. , Schroen D. G.
Published: July 2002

The Z-pinch-driven hohlraum (ZPDH) [J. H. Hammer et al., Phys. Plasmas 6, 2129 (1999)] is a promising approach to high yield inertial confinement fusion currently being characterized in experiments on the Sandia Z accelerator [M. E. Cuneo et al., Phys. Plasmas 8, 2257 (2001)]. Simulations show that capsule radiation symmetry, a critical issue in ZPDH design, is governed primarily by hohlraum geometry, dual-pinch power balance, and pinch timing. In initial symmetry studies on Z without the benefit of a laser backlighter, highly-asymmetric pole-hot and equator-hot single Z-pinch hohlraum geometries were diagnosed using solid low density foam burnthrough spheres. These experiments demonstrated effective geometric control and prediction of polar flux symmetry at the level where details of the Z-pinch implosion and other higher order effects are not critical. Radiation flux symmetry achieved in Z double-pinch hohlraum configurations exceeds the measurement sensitivity of this self-backlit foam ball symmetry diagnostic. To diagnose radiation symmetry at the 2%–5% level attainable with present ZPDH designs, high-energy x rays produced by the recently-completed Z-Beamlet laser backlighter are being used for point-projection imaging of thin-wall implosion and symmetry capsules.
Radiative recombination mechanism in GaNxP1−x alloys
Authors: Buyanova I. A. , Rudko G. Yu. , Chen W. M. , Xin H. P. , Tu C. W.
Published: July 2002

Based on the results of temperature-dependent photoluminescence (PL) and absorption measurements, the PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures with N composition up to 4% is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition, these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent redshift of the PL maximum position.
Instabilities of collisionless current sheets: Theory and simulations
Authors: Silin I. , Büchner J. , Zelenyi L.
Published: July 2002

The problem of Harris current sheet stability is investigated. A linear dispersion relation in the long-wavelength limit is derived for instabilities, propagating in the neutral plane at an arbitrary angle to the magnetic field but symmetric across the sheet. The role of electrostatic perturbations is especially investigated. It appears, that for the tearing-mode instability electrostatic effects are negligible. However, for obliquely propagating modes the modulation of the electrostatic potential φ is essential. In order to verify the theoretical results, the limiting cases of tearing and sausage instabilities are compared to the two-dimensional (2D) Vlasov code simulations. For tearing the agreement between theory and simulations is good for all mass ratios. For sausage-modes, the theory predicts fast stabilization for mass ratios mi/me⩾10. This is not observed in simulations due to the diminishing of the wavelength for higher mass ratios, which leads beyond the limit of applicability of the theory developed here.
Phase stabilities of “morphotropic” phases in Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals
Authors: Lu Yu , Jeong D.-Y. , Cheng Z.-Y. , Shrout T. , Zhang Q. M.
Published: July 2002

Based on the optic and dielectric data acquired under different mechanical and electric conditions and temperature, we show that an orthorhombic phase exists near the morphotropic phase boundary (MPB) (on both the rhombohedral and tetragonal sides of MPB). Because of the proximity of the free energy of this phase to the two other morphotropic phases, i.e., the rhombohedral and tetragonal phases, the experimentally observed phases and phase diagrams near MPB depend crucially on the mechanical and electric conditions as well as the sample history.
Wave driven N2–Ar discharge. II. Experiment and comparison with theory
Authors: Henriques J. , Tatarova E. , Dias F. M. , Ferreira C. M.
Published: July 2002

Discharges in N2–Ar mixtures are experimentally investigated by means of optical emission and absorption spectroscopy, probe diagnostic techniques, and radiophysic methods. The experimental results provide insight into the mechanisms of wave-to-plasma power transfer, N2 dissociation, creation of N2+ ions, and excitation of metastable states [N2(A 3Σu+),Ar(3P2)]. These results are analyzed in the framework of the theoretical predictions of a model developed in a companion article.
Efficient light harvesting in a photovoltaic diode composed of a semiconductor conjugated copolymer blend
Authors: Russell David M. , Arias Ana C. , Friend Richard H. , Silva Carlos , Ego Christophe , Grimsdale Andrew C. , Müllen Klaus
Published: July 2002

We explore charge generation and recombination kinetics quantitatively in a model polymeric semiconductor ternary system. Resonance energy transfer from a polyfluorene copolymer backbone to perylene-substituted side chains selectively excites the dye. In a blend with an alkoxy-substituted poly-p-phenylenevinylene, photoinduced charge transfer is observed. A comparison of picosecond time scale and quasisteady-state charge generation efficiencies allows measurement of the fraction of charges that survive rapid geminate recombination. This simple procedure allows the unraveling of the role played by recombination kinetics in the device.
Influence of a knot on the stretching-induced crystallization of a polymer
Authors: Saitta A. Marco , Klein Michael L.
Published: July 2002

The effect of stretching a polymer sample containing a single trefoil knot has been studied by computer simulation molecular dynamics calculations. Under axial load that approximates a fiber extrusion process, the knot is found to nucleate crystallization of the sample, which occurs on the ns time scale. The extension of the strain field associated with the knot has been quantified.
Ionomeric control of interchain interactions, morphology, and the electronic properties of conjugated polymer solutions and films
Authors: Nguyen Thuc-Quyen , Schwartz Benjamin J.
Published: July 2002

It is becoming increasingly clear that the electronic properties of conjugated polymer films are strongly dependent on factors such as the conformation and the degree of aggregation of the polymer strands in the solution from which the film was cast. In this paper, we show how we can take advantage of conjugated ionomers (conjugated polymers that have been functionalized with side groups that can be electrically charged) to control the polymer morphology and degree of interchain interactions in both solutions and the films cast from them. The particular ionomer we study in this work, poly(2,5-bis[N-methyl-N-hexyl amino] phenylene vinylene) (BAMH-PPV), has dialkyl amino side groups that can be controllably charged by protonation with organic acids. In dilute BAMH-PPV solutions, protonation of just a few percent of the amino side groups leads to tight coiling of the polymer backbone, resulting in an enormous blueshift of the polymer’s absorption and photoluminescence (PL) spectra. At higher BAMH-PPV solution concentrations, however, protonation of the side groups leads to redshifted emission, indicative of increased interactions between polymer chromophores that presumably result from counterion-mediated attractive interactions. The results suggest that conjugated polymer chromophores in solution interact by interpenetration of neighboring chains rather than by self-aggregation of the chromophores on a single chain. Scanning force microscopy experiments indicate that the surface topography of BAMH-PPV films varies directly with the degree of side-group protonation in the solution from which the film was cast. In addition, BAMH-PPV films cast from protonated solutions have a redder PL spectrum and a higher degree of exciton–exciton annihilation than films cast from neutral solutions, verifying that memory of the chain conformation and degree of chromophore interaction in solution carries through the spin-coating process. The charge-induced changes in the morphology of BAMH-PPV films also lead to dramatic differences in the performance characteristics of BAMH-PPV-based light-emitting diodes. Overall, we believe that the degree of control over the electronic properties of conjugated ionomers makes them attractive candidates for use in a wide variety of optoelectronic devices.
Band alignment of ZnSe/Zn0.75Mg15Be10Se heterostructures
Authors: Godo K. , Makino H. , Cho M. W. , Chang J. H. , Hong S. K. , Yao T. , Shen M. Y. , Goto T.
Published: July 2002

The optical properties and band alignment of ZnSe/ZnMgBeSe heterostructures are investigated. Two sets of ZnSe/ZnMgBeSe multi-quantum-well structures that consist of five or three wells with different well thicknesses and 100-nm-thick ZnMgBeSe barrier layers are grown on GaAs (100) substrates by molecular beam epitaxy. Low-temperature photoluminescence spectra show dominant sharp excitonic emission whose peak position systematically shifts to the higher energy side with decreasing the well thickness. Photoluminescence excitation spectra show optical transitions between excited quantum levels in addition to the ground levels. The standard analysis based on the effective-mass approximation gives the valence band offset of ΔEυ=(0.4±0.1)ΔEg. This is consistent with calculated values based on Harrison’s linear combination of atomic orbitals theory.
Neutron reflection study on soluble and insoluble poly[2-(2’-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene) films
Authors: Webster Graham R. , Mitchell William J. , Burn Paul L. , Thomas Robert K. , Fragneto Giovanna , Markham Jonathan P. J. , Samuel Ifor D. W.
Published: July 2002

Neutron reflection (NR) has been utilized to study the physical structure of the light-emitting polymer poly[2-(2’-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene) (MEHPPV). Films of soluble MEHPPV (S-MEHPPV) and insoluble MEHPPV (I-MEHPPV) prepared via a chloro precursor polymer were investigated. For S-MEHPPV spin-coated films were found to contain two layers, one of low-density and thickness of ≈1360 Å with the second layer being thinner, ≈240 Å, but denser. The thicker layer only covered about 30% of the substrate surface. In contrast, I-MEHPPV formed uniform films across the substrate. We found that during the thermal conversion of the chloro precursor polymer the film thickness was maintained and it was only on cooling that the films contracted. Importantly, the thermal expansion and contraction of I-MEHPPV was reversible. NR showed that thermal annealing of I-MEHPPV had little affect on the films physical structure while for S-MEHPPV only the thinner layer was changed and became more dense. Photoluminescence spectra of S-MEHPPV before and after annealing showed that the densification observed in the neutron reflection measurements was mirrored in the emission properties of the polymer film.
Near-field ultrasonic scattering from surface-breaking cracks
Authors: Blackshire James L. , Sathish Shamachary
Published: July 2002

The near-field scattering of ultrasonic Rayleigh waves from surface-breaking cracks has been studied using scanning heterodyne interferometry. Distinct two-dimensional, localized displacement patterns were observed in the near field of the scattering sites, which provide an effective tool for detecting and characterizing the defects. The observed patterns showed a dramatic increase (2×–4×) in the ultrasonic displacement levels near the crack faces, allowing the cracks to be easily distinguished from background levels. A simple explanation for the increased near-field displacement amplitudes is presented that is based on wave propagation and free-boundary reflection arguments.
Cobalt–benzene cluster anions: Mass spectrometry and negative ion photoelectron spectroscopy
Authors: Gerhards M. , Thomas O. C. , Nilles J. M. , Zheng W.-J. , Bowen K. H.
Published: July 2002

( Cobalt ) n ( benzene ) m − cluster anions, (n,m) were generated by laser vaporization and studied by both mass spectrometry and anion photoelectron spectroscopy. Our assignment of the photoelectron spectrum of the (1,2) cluster anion suggests that it possesses a sandwich structure with the cobalt atom located between two parallel benzene rings, that the ground state of this anion is a singlet, and that the ground state of its corresponding neutral is a doublet. The photoelectron spectra of cobalt-rich cluster anions of the form (n,1) are interpreted as cobalt metal cluster anions which have been solvent-stabilized by their interaction with, in each case, a single benzene molecule. The photoelectron spectra of the benzene-rich cluster anions, (2,3), (2,2), and (3,3), are tentatively interpreted as suggesting extended sandwich structures for these anion complexes.
Observation of coherent oxide precipitates in polycrystalline MgB2
Authors: Klie R. F. , Idrobo J. C. , Browning N. D. , Serquis A. , Zhu Y. T. , Liao X. Z. , Mueller F. M.
Published: July 2002

Here we describe the results of an atomic resolution study of oxygen incorporation into bulk MgB2. We find that ∼20–100 nm sized precipitates are formed by ordered substitution of oxygen atoms onto boron lattice sites, while the basic bulk MgB2 crystal structure and orientation is preserved. The periodicity of the oxygen ordering is dictated by the oxygen concentration in the precipitates and primarily occurs in the (010) plane. The presence of these precipitates correlates well with an improved critical current density and superconducting transition behavior, implying that they act as pinning centers.
Influence of AlN nucleation layer temperature on GaN electronic properties grown on SiC
Authors: Koleske D. D. , Henry R. L. , Twigg M. E. , Culbertson J. C. , Binari S. C. , Wickenden A. E. , Fatemi M.
Published: July 2002

GaN electronic properties are shown to depend on the AlN nucleation layer (NL) growth temperature for GaN films grown on 6H– and 4H–SiC. Using identical GaN growth conditions except AlN NL growth temperature, 300 K electron mobilities of 876, 884, and 932 cm2/Vs were obtained on 6H–SiC, 4H–SiC, and 3.5° off-axis 6H–SiC. An AlN NL temperature of 1080 °C was used for the planar and 3.5° off-axis 6H–SiC, while an AlN NL temperature of 980 °C was used for 4H–SiC. Atomic force microscope images of the AlN NL grown at 1080 °C reveal smaller AlN grains on the 6H–SiC than those on 4H–SiC, suggesting that the AlN morphology influences GaN film formation and subsequent electron mobility. Transmission electron microscope cross section measurements reveal the absence of screw dislocations in the AlN and a low screw dislocation density near the AlN/GaN interface, consistent with the high electron mobilities achieved in these films.
Spiral breakup induced by an electric current in a Belousov–Zhabotinsky medium
Authors: Taboada J. J. , Muñuzuri A. P. , Pérez-Muñuzuri V. , Gómez-Gesteira M. , Pérez-Villar V.
Published: July 2002

Sprial breakup in the Belousov–Zhabotinsky reaction has been observed under the influence of an externally applied alternating electric current. The dynamic mechanism of this breakup is explained in the framework of this reaction. The dependence of the critical electric current amplitude on the period of the wave and on the excitability of the medium is analyzed. Spiral breakup is shown to provide a limit of validity of electric-field-induced drift of vortices in excitable media. Experimental results are complemented with numerical simulations provided by two- and three-variable Oregonator models.
Separatrices splitting for Birkhoff’s billiard in symmetric convex domain, closed to an ellipse
Authors: Tabanov M. B.
Published: July 2002

An example of a convex domain on the plane with the phenomenon of the transversal intersection of separatrices of the corresponding billiard mapping is presented. This example is constructed as an analytic global symmetric perturbation of an ellipse and we investigate the global symmetric analytic perturbation of the integrable billiard mapping in the ellipse. We establish a theorem on the separatrices splitting of the perturbed billiard mapping and derive the asymptotic formulas for a homoclinic invariant as well as for a ‘‘principal’’ splitting angle of separatrices, arising from the hyperbolic fixed point of the mapping.
The application of transport theory to visualization of 3-D scalar data fields
Authors: Krueger Wolfgang
Published: July 2002

This paper describes a general visualization model for 3-D scalar data fields based on linear transport theory that contains common volume rendering models as special cases and/or approximations. The concept of ‘‘virtual’’ particles for the extraction of information from data fields is introduced. The role of different types of interaction of the data field with those particles such as absorption, scattering, source, and color shift are discussed and demonstrated. Special attention is given to possible tools for the enhancement of interesting data features. Random distortions or noise of the data field are mapped onto the image plane in a well-defined way such that picture processing methods can be used to reconstruct the appearance of the undistorted data set. Random texturing can provide visual insights as to the magnitude and distribution of deviations of related data fields, e.g., originating from analytic models and measurements, or in the noise content of a given data field. Hidden symmetries of a data set can often be identified visually by allowing it to interact with a preselected beam of ‘‘physical’’ particles with the attendant appearance of characteristic structural effects such as channeling.
Effect of damping resistance on voltage versus flux relation of a dc SQUID with large inductance and critical current
Authors: Enpuku K. , Sueoka K. , Yoshida K. , Irie F.
Published: July 2002

The effect of a damping resistance on the relation between a voltage V and a magnetic flux Φ of a dc SQUID is studied theoretically for the case with a large SQUID parameter βL=2LI0/Φ0 , where L is a loop inductance, I0 is a critical current, and Φ0 is the flux quantum. An approximate analytical expression for the V-Φ relation is obtained by replacing the Josephson junctions with ac current generators. It is shown that the V-Φ relation becomes almost independent of the value of βL in the case of large damping. As a result, the conversion efficiency dV/dΦ is not degraded even for large βL , as is not the case with a conventional SQUID without the damping resistance. This result indicates the possibility to use the SQUID with large βL for the improvement of the coupling between the SQUID and the input coil without the degradation of the conversion efficiency. Effect of the capacitance is also studied. It is shown that the effect of the capacitance becomes remarkable for the case of βc≳0.4 , where βc is the McCumber parameter; for example, at βc=1 the conversion efficiency becomes about 30% of that at βc=0 . These analytical results are in good agreement with numerical-simulation ones.
Crystallization characteristics of Fe-Zr metallic glasses from Fe43Zr57 to Fe20Zr80
Authors: Altounian Z. , Volkert C. A. , Strom-Olsen J. O.
Published: July 2002

We present a crystallization study of melt-spun Fe-Zr metallic glasses. Unlike Cu-Zr and Ni-Zr, the immediate crystallization products cannot be understood in terms of the equilibrium crystalline phase diagram: all are metastable or unstable phases. In the composition range Fe25Zr75 to Fe33Zr67, there is evidence that explosive crystallization occurs. The behavior of the activation energy with composition suggests there may be a eutectic at the composition Fe37.5Zr62.5.
Photoluminescence studies of Si implanted with In and/or Tl: The effects of thermal treatment and atomic H
Authors: Thewalt M. L. W. , Steiner T. , Pankove J. I.
Published: July 2002

We report photoluminescence studies of Si implanted with In and/or Tl, followed by various treatments. As-implanted samples and those annealed at 300 °C in vacuum showed many well-known damage-related luminescence lines. Treatment at 300 °C in atomic H eliminated most of these lines, while causing only a broadening of the I3 line. We find that the efficient luminescence previously reported at 77 K in implanted, atomic H annealed Si is due to this perturbed I3 center. The H-related increase in luminescence efficiency results from the passivation of competing recombination channels, and not from the creation of a new center. Samples heated to 1000 °C and cooled slowly show well-resolved acceptor bound exciton lines, while those quenched from 1000 °C show very strong luminescence from the In- and/or Tl-related isoelectronic bound excitons.
Raman microprobe analysis of stress in Ge and GaAs/Ge on SiO2-coated Si substrates
Authors: Nishioka Takashi , Shinoda Yukinobu , Ohmachi Yoshiro
Published: July 2002

Stress and strain in single-crystal Ge and GaAs/Ge films grown on SiO2-coated Si substrates have been investigated through the Raman microprobe analysis. The Ge film is found to be subject to a tensile stress of (3.4–6.1)×109 dyne/cm2 and a strain of (2.4–4.3)×10−3 without distinguished spatial variation within a SiO2 island. The stress agrees well with that evaluated from the GaAs electroluminescence spectral shift with the deformation-potential model. The strain can be attributed dominantly to the thermal expansion difference between the Ge and the substrate Si. A large Raman spectral shift to the lower frequency side and a large linewidth for Ge have been observed in the seeding opening region, which represents Ge lattice disorder in this region.
Experimental requirements for quantitative mapping of midgap flaw concentration in semi-insulating GaAs wafers by measurement of near-infrared transmittance
Authors: Dobrilla P. , Blakemore J. S.
Published: July 2002

The experimental properties are critiqued that relate the midgap flaw concentration in semi-insulating GaAs, and the resulting near-infrared transmittance of a polished wafer. Since quantitative information of such flaw concentrations is desirable even for an optical thickness αt≪1, a highly stable and accurate experimental arrangement is described, which permits a meaningful evaluation even when αt≂0.01. (The transmittance is then almost Tmax, as set by the substantial reflectance losses.) This system permits mapping over a wafer’s area, by translation of the wafer with respect to the optical path. Calibration of absorption into flaw concentration is discussed for the midgap EL2 donor defect, and (in an appendix) for chromium-doped GaAs. Representative wafer maps for EL2 are used as illustrations, some as mosaic grey-scale matrix plots, and others as pseudo-three-dimensional contour plots.
Scattering of linearly polarized light from randomly oriented cylinders and spheroids
Authors: Haracz Richard D. , Cohen Leonard D. , Cohen Ariel
Published: July 2002

The Shifrin perturbation theory is applied to the scattering of light from finite cylinders and spheroids, and a procedure is described for averaging over the possible orientations of the symmetry axes of these various target shapes. The possible axis orientations of very long cylinders is limited by the conical shape of the scattering patterns, and the manner of taking this into account in the averaging process is detailed. It is found that the scattering intensities for the scattering of light from randomly oriented long cylinders, with aspect ratios (length/diameter) less than about 200, show differences compared with infinite cylinders of the same radius and dielectric constant (m=1.5). This is especially true for high and low scattering angles and when the plane of linear polarization is changed by the scattering. Moreover, the scattering intensities for the scattering of light from randomly oriented short cylinders and spheroids, with aspect ratios ranging from 0.1 to 10 and the same volume, show significant differences when the plane of polarization is changed by the scattering.
Effect of space angle on constriction resistance and contact resistance for a point contact
Authors: Sano Y.
Published: July 2002

It can generally be considered that an actual contact makes an angle with the extension of the contact surface because the tip of a contact element is convex in shape (macroscopically) and has surface roughness (microscopically). The effect of this angle on constriction resistance and contact resistance for a point contact is analyzed theoretically by solving Laplace’s equation subject to boundary conditions determined by a modeled morphology of the contact. The analysis leads to the modified formulas for the constriction resistance and the contact resistance, which show that the effect cannot always be neglected and that the contact model with space angle is useful.
Nonlinear electromagnetic waves guided by a single interface
Authors: Stegeman G. I. , Seaton C. T. , Ariyasu J. , Wallis R. F. , Maradudin A. A.
Published: July 2002

Electromagnetic waves guided by the interface between two nonlinear media, and a nonlinear and a linear medium are investigated theoretically and numerically. Both s- and p-polarized waves are analyzed and the guided wave power versus guided wave vector is evaluated for a variety of material conditions. The consequences of two different versions of the uniaxial approximation for the p-polarized case are compared. The power-dependent attenuation is approximately evaluated.
Kinetics of damage production in silicon during self-implantation
Authors: Maszara W. P. , Rozgonyi G. A.
Published: July 2002

We have investigated the damage which results from silicon self-implantation for the range of doses from 2×1014 to 1×1016 cm−2 for temperatures from 82 to 296 K for 150- and 300-keV implants. Cross-sectional transmission electron microscopy (TEM) was used to evaluate the nature of the damaged layer. The experimental results were correlated with computer calculated damage distributions using a Monte Carlo simulation program. The depth of the amorphous-crystalline interface(s) was evaluated as a function of dose and temperature. An experimental deposited-damage energy curve for individual cascade was constructed. Using the curve a critical energy density for amorphization Ec, was calculated for the samples implanted at different temperatures. The energy was found to depend on depth and implant energy, and it increases with temperature. A study of amorphous-crystalline interface morphology shows no dependence on temperature within the range considered. The kinetics of dynamic annealing are discussed in conjunction with the above findings.
Modal field transforming fiber between dissimilar waveguides
Authors: Shigihara Kimio , Shiraishi Kazuo , Kawakami Shojiro
Published: July 2002

A fiber mode matching device between dissimilar optical waveguides is proposed and fabricated. The device has a refractive index profile that varies in the direction of propagation without changing the normalized frequency. We fabricated a single-mode tapered fiber with a rectangular core at one end and a circular core at the other. The modal field transformer is expected to allow highly efficient coupling between dissimilar waveguide devices.
Magnetic properties of melt-spun and as-cast SmCo5−xNix alloys
Authors: Mikhov M. T. , Gong W. , Hadjipanayis G. C.
Published: July 2002

The magnetic properties of as-cast, ribbon, and powder samples of SmCo5−xNix compounds, where x=1, 2, and 3, have been studied at temperatures between 4.2 and 900 K and in magnetic fields up to 75 kOe. Some new evidences for exchange and anisotropy fluctuations are given. Substantially higher coercivities are observed in ribbons and powders reaching the value of Hc=30 kOe for SmCo4Ni and Hc=51 kOe for SmCo3Ni2 at 4.2 K. The corresponding values for as-cast samples are found to be 7 and 18 kOe, respectively. Hysteresis loop measurements show that along with homogeneous domain wall pinning a ‘‘size-effect’’ mechanism contributes to the coercivity of ribbon and powder samples.
Spin dynamics of amorphous Fe90−xNixZr10
Authors: Fernandez-Baca J. A. , Lynn J. W. , Rhyne J. J. , Fish G. E.
Published: July 2002

Neutron inelastic scattering experiments have been performed in order to study the long wavelength spin dynamics of the amorphous Invar system Fe90−xNixZr10 (for x=5,10). Spin waves were observed over the entire range of wave vectors (0.05–0.15 Å−1) and temperatures (0.3–0.9 TC) under study. The spin-wave energies are well described by the quadratic dispersion relation Eq=Dq2+Δ, where Δ is a small gap due primarily to dipolar interactions. The stiffness parameter D renormalizes with temperature as D(T)=D(0) ×[1−A(T/TC)5/2] throughout the temperature range under study. The values of D(0) corresponding to x=5, 10, are 42.1 and 78.0 meV Å2, respectively, with A=0.83. In the temperature range 0.55–0.90 TC the intrinsic spin-wave linewidths Γq can be fitted equally well to the q4 dependence predicted by hydrodynamic spin-wave theory, or to the q5 dependence predicted from the topological disorder in amorphous systems, but they did not show the T2 behavior expected from magnon interactions. These findings suggest that there might be relevant spin-wave broadening mechanisms, perhaps due to the magnetic disorder in the system, in addition to magnon-magnon interactions.
Effects of In impurity on the dynamic behavior of dislocations in GaAs
Authors: Yonenaga Ichiro , Sumino Koji
Published: July 2002

The effects of In impurity on the dynamic behavior of dislocations in GaAs crystals are investigated in comparison with those of Si impurity. Indium, even at a concentration of the order of 1020 cm−3, is found to affect the velocity of moving dislocations only slightly while Si impurity at a concentration of the order of 1018 cm−3 reduces it by one or two orders of magnitude. However, α dislocations are easily immobilized by In atoms while they are at rest by gettering the latter. Immobilization of β dislocations due to In gettering is much weaker than that of α dislocations. An interpretation is given of how such a difference in locking by In impurity comes about between α and β dislocations. The function of Si impurity to lock both α and β dislocations is stronger than that of In impurity on α dislocations. Nevertheless, the locking effect due to Si impurity manifests itself only in the high-temperature range. This seems to be related to the low diffusivity of Si impurity in GaAs crystals.
Hard magnetic properties of Nd-Co-B materials
Authors: Fuerst C. D. , Herbst J. F.
Published: July 2002

A systematic investigation of the magnetic properties of neodymium-cobalt-boron alloys rapidly solidified by melt spinning is reported. Room-temperature coercivities and energy products as large as 10.2 kOe and 5.2 MGOe, respectively, have been observed in ribbons comprised primarily of tetragonal Nd2Co14B. We find that the characteristics of optimum as-quenched samples can be essentially recovered by annealing partially amorphous ribbons melt spun at higher quench rates. Although the Curie temperature of Nd2Co14B is Tc ≂995 K, the easy axis of magnetization changes from the c direction to the basal plane at Ts ≂560 K, and the practical magnetic properties deteriorate as Ts, rather than Tc, is approached.
Neutron diffraction study of Y(Ti,Fe)12
Authors: Yang Ying-chang , Sun Hong , Kong Lin-shu , Yang Ji-lian , Ding Yong-fan , Zhang Bei-sheng , Ye Chun-tang , Jin Lan , Zhou Hui-ming
Published: July 2002

Neutron diffraction experiments on Y(Ti,Fe)12 have been carried out to investigate the crystallographic structure and magnetic properties of these compounds. In the ThMn12-type structure, with a space group of I4/mmm, Fe and Ti atoms are distributed on three nonequivalent crystallographic sites. A preferential site occupation for Fe and Ti is observed. The detailed analysis of crystallographic and magnetic arrangement are reported.
Radio-frequency dielectric measurements at temperatures from 10 to 450 K
Authors: Böhmer R. , Maglione M. , Lunkenheimer P. , Loidl A.
Published: July 2002

A coaxial air line was constructed to connect a radio-frequency impedance analyzer and a temperature-stabilized sample holder. It is suitable for dielectric measurements in the frequency range 1 MHz–1 GHz and at temperatures between 10 and 450 K. The dielectric dispersion of Fe-doped BaTiO3 and Na-doped KCN is presented. The results demonstrate the capability of this setup when investigating materials with high as well as with low dielectric constants.
Phthalocyanine semiconductor sensors for room-temperature ppb level detection of toxic gases
Authors: Temofonte T. A. , Schoch K. F.
Published: July 2002

Nickel and lead phthalocyanine (NiPc and PbPc) thin films prepared by vacuum sublimation have been investigated for use as gas sensors. High sensitivity (25 ppb), reversibility, and very fast response time (∼ seconds) have been demonstrated for detection of NO2 at room temperature. The sensor output increases by five to seven orders of magnitude as the gas concentration is increased from ∼2×101 to 6×104 ppb. Measurements of transient response characteristics versus gas concentration exhibited a simple logarithmic dependence. Application of this approach to the detection of other agents is discussed. It appears that the unique electrical properties of these films are a result of the film morphology associated with our specific deposition approach. Detection based on optical sensing of NO2 has also been demonstrated.
Characteristics of dislocations at strained heteroepitaxial InGaAs/GaAs interfaces
Authors: Chang Kevin H. , Bhattacharya Pallab K. , Gibala Ronald
Published: July 2002

The formation, interaction, and propagation of misfit dislocations in molecular-beam epitaxial InGaAs/GaAs heterointerfaces have been studied by transmission electron microscopy. With the lattice mismatch less than 2%, most of the interfacial dislocations are found to be 60° mixed dislocations introduced by glide processes. Sessile edge-type dislocations can also originate from the combination of two 60° mixed dislocations. The ratio of densities of edge dislocations to 60° dislocations was increased during the later part of the elastic strain relaxation. These sessile edge dislocations may be generated in appreciable numbers through a climb process. For large lattice-mismatched systems, the majority of the misfit dislocations are pure edge dislocations and high threading dislocation density is generally found. The interfacial dislocation network is found to contain regions of dislocations with the same Burgers vector that extend over several micrometers. The results support a mechanism that involves misfit dislocation multiplication during the molecular-beam epitaxial growth process.
Evidence for disorder-induced vibrational mode coupling in thin amorphous SiO2 films
Authors: Lange P.
Published: July 2002

Infrared spectroscopy was employed to characterize thermal SiO2 layers down to 15 nm thickness. From these measurements, performed in transmission mode under a 30° angle of incidence, we obtained a multiple resonance structure on the high-energy side of the main Si-O stretching vibration at 1075 cm−1. Aside from a longitudinal optical (LO) mode at 1254 cm−1, we found experimental evidence for two additional vibrations, a transverse optical mode at 1200 cm−1, and an LO mode at 1165 cm−1. These features could be explained by assuming disorder-induced vibrational coupling effects. Beyond that, an ion damage study and a comparison with IR spectra of oxide layers deposited in various chemical vapor deposition processes clearly confirmed the idea of disorder-induced mode coupling.
Magnetic and crystallographic properties of NdCo4M (M=B, Al, and Ga)
Authors: Ido H. , Wallace W. E. , Suzuki T. , Cheng S. F. , Sinha V. K. , Sankar S. G.
Published: July 2002

The magnetic and crystallographic properties have been investigated for NdCo4M (M=B, Al, and Ga). The temperature dependencies of lattice parameters have been determined between 80 and 730 K by x-ray diffraction. NdCo4B crystallizes in the CeCo4B-type structure, whereas NdCo4M (M=Al and Ga) exhibits a CaCu5-type structure. Magnetic properties of NdCo4B show a clear difference from those of its Al and Ga counterparts. All these compounds exhibit planar anisotropy in the low-temperature regime, and the spin-reorientation temperature is found to be ∼280 K for NdCo4Al and NdCo4Ga, whereas NdCo4B is planar up to its Curie temperature. Thermal expansion curves of c axes show an anomalous contraction for NdCo4B and expansion for NdCo4Al and NdCo4Ga only in the temperature region of planar anisotropy.
Spin-wave spectrum for barium ferrite
Authors: Marshall S. P. , Sokoloff J. B.
Published: July 2002

We describe the calculation of the spin-wave spectrum for barium ferrite, a complex exchange-coupled hexagonal ferrimagnetic compound, using a method first used in a similar calculation for yttrium iron garnet (YIG). The exchange integrals are calculated by fitting the Weiss molecular field approximation to the sublattice magnetizations while including single-ion anisotropy. The value for the space-averaged stiffness constant as calculated from the acoustic mode of the spin-wave spectrum is 2.5×10−9 Oe cm2, which compares favorably with values obtained by domain wall resonance, considering the accuracy of such measurements.
High-energy electron beam deposition and plasma velocity distribution in partially ionized N2
Authors: Slinker S. P. , Ali A. W. , Taylor R. D.
Published: July 2002

The electron distribution function is calculated for a plasma created when a high-current, high-energy (∼MeV) electron beam enters nitrogen gas. No spatial dependence is considered for the distribution function and the velocity is expanded in the two-term approximation. Time dependence is retained. Benchmark calculations are presented that compare code output with experimental results of electron deposition studies and swarm studies in nitrogen. Production efficiencies are given. The effect of inner-shell processes is discussed. An example illustrates the importance of the beam-induced electric field on the plasma generation and behavior. It shows that considerable ohmic energy deposition can be involved and that, consequently, production of certain species can be greatly enhanced.
Graphitic network models of ‘‘diamondlike’’ carbon
Authors: Tamor M. A. , Wu C. H.
Published: July 2002

We use simple arguments to fix the range of density of randomly distributed defects over which π electrons in a graphite sheet are strongly localized, but the underlying two-dimensional carbon network remains connected. This ‘‘defeated graphite’’ construct leads to simple structural models of both hydrogenated and unhydrogenated amorphous ‘‘diamondlike’’ carbon, which reproduce many important properties of those materials.
A new method for synthesizing nanocrystalline alloys
Authors: Lu K. , Wang J. T. , Wei W. D.
Published: July 2002

A new method to prepare nanocrystalline alloys was developed by means of crystallization from amorphous alloys. By using this method, a Ni-P alloy with 9 nm crystallites was synthesized. The structures and grain sizes of the alloy were examined by means of x-ray diffraction, transmission electron microscopy, and high resolution electron microscopy. Specific heat capacity and thermal expansion coefficient of the nanocrystalline Ni-P alloy prepared by this method were found to be greater than those of the coarse-grained crystalline alloy by 12.3% and 56.2%, respectively. A new micromechanism for nanometer-sized crystallites formation is discussed.
Influence of preparation methods on morphology of powder particles for sintered NdFeB magnets
Authors: Ohmori K. , Shionoya K.
Published: July 2002

Two methods were used to prepare NdFeB alloy particles for sintered magnets: the reduction-diffusion (R/D) method and the melting and casting (M/C) method. In both materials, the Nd-rich phase appears along grain boundaries, but the grain size of the R/D alloy is much smaller than that of the M/C alloy. The shape of the R/D powder particles is more rounded than that of the M/C powder, and the size distribution of the R/D powder is more uniform than that of the M/C powder. These alloys were jet-milled into powders of 3.3 and 3.6 μm diameter, respectively, and were processed into sintered magnets. The large Nd-rich phase are more numerous in the M/C than in the R/D sintered magnet.
Analysis of the effects of oxygen migration on dislocation motion in silicon
Authors: Maroudas Dimitris , Brown Robert A.
Published: July 2002

A systematic theory is presented for the prediction of oxygen migration near a 60° dislocation and for the resulting retardation of dislocation motion. Quantitative predictions are based on the solution of the macroscopic equation for transport of oxygen in the elastic stress field created by the dislocation. The link between the microscopic dynamics of interstitial oxygen within the diamond lattice and macroscopic transport is established by a constitutive model for the dependence of the drift velocity band diffusivity of oxygen on the elastic interaction of oxygen atoms and dislocations and on temperature. The transport equation is solved numerically assuming that the dislocation core is fully saturated with oxygen. The drag force on the gliding dislocation caused by the surrounding oxygen is computed from linear elasticity theory, combined with the phenomenological model of Alexander and Haasen [Solid State Phys. 22, 27 (1968)] for the dependence on the applied stress of the velocity of a dislocation in pure silicon. The predicted dependence of the dislocation velocity on the applied stress at specific temperatures and oxygen concentrations is in qualitative agreement with the experimental data of Imai and Sumino [Philos. Mag. A 47, 599 (1983)].
Simulation of x-ray diffraction for superlattices with fluctuations from perfect periodicity
Authors: Xiu Lisong , Wu Ziqin
Published: July 2002

An investigation on the effects of the disorder of superlattice periods on x-ray-diffraction patterns is reported. Three kinds of disorder (random fluctuations, systematic deviations, and local deviations) have been considered. The results of the simulations show that their effects are quite different. The systematic deviation widens the superlattice peaks and shifts the positions of the low-angle superlattice peaks. The effect of the systematic deviation on the reduction of peak intensity is more serious than that of random fluctuation. The local deviation makes the superlattice peak weaker and wider or splits it into double peaks. These three kinds of disorder can be distinguished.
The effect of stress-induced voiding on electromigration
Authors: Lytle S. A. , Oates A. S.
Published: July 2002

Stress-induced voids present a serious reliability problem in the integrated-circuit industry for near-micrometer technologies. Reliability degradation has been previously evaluated from the viewpoint of open circuits caused by the mechanism of stress-induced voiding. We present a study of the effect of stress-induced voids on electromigration in 1.25-μm AlSiCu metal runners over a wide range of temperatures and void size/density. Median time to fail decreases with increasing void size and density, except for cases of severe voiding where metal microstructure strongly influences failure. For void sizes ≤25% of the linewidth, failure rates remain low, implying that acceptable reliability may still be achieved for relatively low levels of voiding. Failure rates increase with void size up to 50% of the linewidth and then saturate. These results indicate that provided the time for an open circuit due to stress voiding alone exceeds the operational life of the device, then the primary reliability degradation of stress-voided metallization will result from electromigration.
Performance of the star-shaped flyer in the study of brittle materials: Three dimensional computer simulations and experimental observations
Authors: Espinosa H. D. , Raiser G. , Clifton R. J. , Ortiz M.
Published: July 2002

A three dimensional finite element computer simulation has been performed to assess the effects of release waves in normal impact soft-recovery experiments when a star-shaped flyer plate is used. Their effects on the monitored velocity-time profiles have been identified and their implications in the interpretation of wave spreading and spall signal events highlighted. The calculation shows that the star-shaped flyer plate indeed minimizes the magnitude of edge effects. The major perturbation to the one-dimensional response within the central region of the target plate results from spherical waves emanating from the corners of the star-shaped plate. Experimental evidence of the development of a damage ring located in coincidence with the eight entrant corners of the flyer plate is reported. Microscopy studies performed in the intact recovered samples revealed that this damage ring eliminates undesired boundary release waves within the central region of the specimen. Consequently, the observed damage in compression and tension within this region can be attributed primarily to the conditions arising from a state of uniaxial strain.