bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous effects in silicon solar cell irradiated by 1-MeV protons
Authors: Kachare R. , Anspaugh B. E.
Published: July 2002

Several silicon solar cells having thicknesses of approximately 63 μm, with and without back-surface fields (BSF), were irradiated with 1-MeV protons having fluences between 1010 and 1012 protons/cm2. The irradiations were performed using both normal and isotropic incidence on the rear surfaces of the cells. It was observed that after irradiation with fluences greater than 1011 protons/cm2, all BSF cells degraded at a faster rate than cells without BSF. The irradiation results are analyzed using a model in which irradiation-induced defects in the BSF region are taken into account. A number of other possibilities for BSF cell degradation are considered. Tentatively, it is concluded that an increase in defect density due to the formation of aluminum and proton complexes in BSF cells is responsible for the higher-power loss in the BSF cells compared to the non-BSF cells.
Phosphorous coimplantation effect on threshold voltage uniformity of GaAs transistors
Authors: Hyuga Fumiaki , Yamazaki Hajime , Ishida Satoru , Kato Naoki
Published: July 2002

Phosphorous coimplantation effect on electrical uniformity of Si-implanted GaAs active layer is investigated for undoped as-grown, undoped ingot-annealed, and In-doped substrates. Pairs of field-effect transistors, fabricated with and without P coimplantation, are placed on whole 3-in.-diam substrates at a 200-μm interval. Threshold voltage measurements reveal that a concentration of 1018 /cm3 coimplanted P reduces the standard deviation in threshold voltage for undoped as-grown substrates to 1/2.5. Undoped ingot-annealed substrates achieve the same uniformity of threshold voltage as In-doped substrates, which showed the best data. Moreover, this method reduces the variation in the mean threshold voltage among substrates by one-half. These results indicate that P coimplantation successfully suppresses the change of As to Ga vacancy concentration ratio.
Phonon-assisted recombination in GaAs/AlGaAs multiple-quantum-well structures
Authors: Dai H. H. , Choi M. S. , Gundersen M. A. , Lee H. C. , Dapkus P. D. , Myles Charles W.
Published: July 2002

The photoluminescence spectra of GaAs/AlGaAs multiple-quantum-well structures with varying thicknesses have been studied as a function of excitation intensity and polarization. An intense sideband luminescence with a narrow linewidth is observed at 36 meV below the band-to-band transition in all samples. These results, along with additional investigations detailed in this paper, support the conclusion that for the samples studied in these experiments this emission is a stimulated phonon-assisted recombination.
Thermal conductivity of La3−xRxS4 where R=Sm, Eu, and Yb
Authors: Kokos G. B. , Gschneidner K. A. , Cook B. A. , Beaudry B. J.
Published: July 2002

The thermal diffusivity values of La2.7Sm0.3S4 , La2.3Sm0.7S4 , La2.7Eu0.3S4 , La2.2Eu0.8S4 , La2.8Yb0.2S4 , and La2.3Yb0.7S4 were measured by the flash diffusivity method from 400 to 1000 °C. The values ranged from 0.007 to 0.018 cm2 /s. The thermal conductivities of the six ternary rare-earth sulfides were calculated from the thermal diffusivity data and ranged from 10.7 to 31.6 mW/cm °C. Of the alloys measured, La2.2Eu0.8S4 had the highest thermoelectric figure of merit at 1000 °C (0.52×10−3 °C−1). All of the samples had an oxysulfide present at the grain boundaries which degraded their high-temperature performance.
Terraced substrate inner stripe semiconductor lasers by one-step liquid-phase epitaxy
Authors: Du Guotong , Ma Xiaoyu , Zou Zheng , Zhang Xiaobo , Gao Dingsan
Published: July 2002

A new (GaAl)As/GaAs laser with low threshold current and a single mode is developed. By making use of selective growth properties of liquid-phase epitaxy over a nonplanar substrate, the growth of all layers and an inner stripe for a current channel are completed by one-step liquid-phase epitaxy. This allows for a very simple fabrication process.
Influence of thermal annealing on the optical absorption and dark conductivity of amorphous gallium sulfide thin films
Authors: Micocci G. , Rella R. , Tepore A.
Published: July 2002

The influence of thermal annealing on the optical absorption and dark conductivity of evaporated GaS thin films below the onset of crystallization is investigated. Annealing is performed at different temperatures and for different periods of time. The experimental results are tentatively interpreted in terms of variations in the density of localized states due to a progressive decrease of the unsaturated bonds during thermal annealing.
Melt-spun Nd2(CoxFe1−x)14B systems: Optimization of the hard magnetic properties
Authors: Fuerst C. D. , Herbst J. F.
Published: July 2002

By appropriate variation of starting composition we demonstrate that melt-spun materials comprised primarily of Nd2(CoxFe1−x)14B and having optimum energy products can be prepared. Twelve cobalt concentrations spanning the entire cobalt substitution range have been investigated. We report ambient as well as elevated temperature magnetic properties. A spin reorientation characterized by a change of easy magnetization direction from the c axis to the basal plane of the Nd2Fe14B structure occurs at a temperature Ts for x≳0.65. In that concentration range the technological properties are limited by Ts rather than the Curie temperature Tc.
Rapid thermal annealing of YBaCuO thin films deposited on SiO2 substrates
Authors: Ma Q. Y. , Yang E. S. , Chang Chin-An
Published: July 2002

Ag/Cu/BaO/Y2O3/Ag layered structures have been formed using electron-beam evaporation on SiO2 substrates, and post-annealed by rapid thermal annealing at different temperatures. After a 960 °C 15-s anneal, the film showed a superconducting onset temperature of 93 K and a zero resistance at 79 K. With a lower-temperature anneal, the film exhibited metallic behavior. On the other hand, for a higher-temperature anneal, silicon was found to diffuse into the film as observed by Auger depth profiling. The Si out-diffusion degraded the superconducting properties of the film.
The source term in energy deposition calculations
Authors: Penetrante B. M. , Bardsley J. N.
Published: July 2002

A discrete-loss energy deposition model is used to study the functional dependence of the W value (mean energy expended per electron-ion pair) on the beam energy and ionization fraction. Two types of secondary electron source terms are considered: one in which energetic electrons are completely stopped by the medium, the other in which a continuous beam passes through the plasma. We show that the W value, and hence the energy-loss modes, strongly depend on the type of source term used.
Preparation and properties of Pb-doped Bi-Sr-Ca-Cu-O superconductors
Authors: Lee H. K. , Lee K. W. , Park K. , Huang N. M. , Oh O. K. , Kim J. S. , Yoo K. H. , Kim Y. B. , Kim C. S. , Cho Y. K. , Park J. C. , Suck S. I.
Published: July 2002

Electrical and magnetic properties of the superconducting oxides with nominal composition (Bi0.7 Pb0.3 )2Sr2Ca2 Cu3 Ox prepared from polymeric precursors have been investigated. Superconducting transition with zero-resistance temperature at T=108 K was achieved for a sample sintered at 840 °C under a low oxygen pressure. The critical current density at 77 K in a zero magnetic field is ∼400 A/cm2 , which is much higher than that of the Pb-free sample. Variations of the superconducting transition temperature, the critical current density, and magnetic properties with heat treatment time are discussed in connection with the structural properties.
Cavity perturbation measurement of plasma density in complex geometry rf discharges
Authors: Moroney R. M. , Lichtenberg A. J. , Lieberman M. A.
Published: July 2002

A noninvasive microwave diagnostic is used to determine the plasma density in a complex geometry rf discharge chamber. Data have been obtained using several cavity modes and a wide range of pressures and powers. The measured peak densities are approximately a factor of 2 lower than those obtained from Langmuir probe measurements.
A prototypical model of a dislocation source capable of generating shear band structures in crystalline solids during shock or impact
Authors: Coffey C. S.
Published: July 2002

The response of crystalline solids to high rate loading by shock or impact is often determined by the formation of shear band structures and the subsequent response of these localized structures to the applied stress. The discrete nature of these shear bands suggests that a single source, or at most a very few dislocation sources, may be responsible for creating the dislocations that form the shear bands. Here this is postulated to be the case, and a simple prototypical oscillator type source is established. The maximum dislocation generation rate of the source is shown to be of the order of 1011 dislocations per second for high shear stress loads.
Edge effect in near-intrinsic germanium observed with a novel method for resistivity measurements
Authors: van Haaren J. A. M. M. , Rikken G. L. J. A. , van Gelder A. P. , van Kempen H. , Wyder P.
Published: July 2002

We report the observation of edge effects in the magnetoconductance of macroscopic samples of near-intrinsic germanium near room temperature as a model system for an ambipolar conductor. We used a novel method for resistivity measurements, which allows for a check of the consistency of a description with a single resistivity tensor for the whole sample. Such a description was found to fail near the magnetic field strengths with a vanishing Hall coefficient. The inconsistency is attributed to the spatial variation of the density of charge carriers, which is caused by the unbalance of the influxes of carriers to the sample’s edge and their recombination/generation via traps in the edge region.
Propagation of electromagnetic waves of crossroads with a reflector inside a tunnel
Authors: Murakami Yasushi , Chiba Jiro
Published: July 2002

We analyzed the wave propagation characteristics of the crossroad inside a tunnel, using the boundary-element method. To simplify, the tunnel structure is assumed to be two-dimensional and the side walls to be lossy dielectrics. We could improve the radio communication characteristics between two cross tunnels by a tetragonal reflector placed at the center of the crossroad. The diagonal length of the proper reflector is about 10%–20% of the tunnel width.
X-ray photoelectron spectroscopy of Si/Pt and Pt/Si layers on GaAs
Authors: Kuroda Tsukasa , Iwakuro Hiroaki
Published: July 2002

The difference in the chemical reactions between Si/Pt/GaAs and Pt/Si/GaAs systems have been investigated using x-ray photoelectron spectroscopy. For the Si/Pt/GaAs system, annealing at 450 °C leads to out-diffusion of Ga and As atoms to the surface of the deposited film. On the other hand, for the Pt/Si/GaAs system, no Ga and As atoms out-diffuse to the surface. This indicates that the interface at GaAs is more stable for the Pt/Si/GaAs system than for the Si/Pt/GaAs system. The difference in these interfacial reactions is due to the difference in chemical states of Pt atoms when Pt atoms come in contact with GaAs.
Microwave absorption of aligned crystalline grains of YBa2Cu3O7−x
Authors: Poirier M. , Quirion G. , Quirion B. , D’Orazio F. , Thiel J. P. , Halperin W. P. , Poeppelmeier K. R.
Published: July 2002

We investigate here the anisotropic magnetic and electric properties of aligned crystalline grains of YBa2Cu3O7−x. The microwave absorption is indeed consistent with the expected temperature behaviors of the resistivity in the normal state along the c axis and in the a-b plane. In the superconducting state, both the absorptions in pure rf electric and magnetic fields are high compared to the conventional superconductors; for the magnetic case activation energies are deduced and the dispersion is related to the diamagnetic susceptibility. These results are discussed qualitatively in relation to similar data obtained on single crystals and ceramic samples.
Analysis of domain structure by calculating magnetostatic energy for magnetic thin film
Authors: Saka Chiaki , Shiiki Kazuo , Shinagawa Kiminari
Published: July 2002

A method of calculating magnetostatic energy is studied by a two-dimensional approximation. This is required in order to analyze the domain structure of a magnetic thin film. The energy Es is calculated as the product of demagnetization field Hd and magnetization M. Since Hd varies widely within a domain, Es must be calculated in a number of subdivided regions in which Hd is assumed to be uniform, and their summation is calculated. Good precision can be achieved by subdividing a domain along possible charged surfaces. The closure domain structure of a rectangular film whose triangular domain has an extra wall is thus analyzed. Although the total energy of the film is increased by the addition of an extra wall, the local energy of the triangular domain has a negative minimum value when the magnetization direction is inclined. The calculated magnetization direction corresponding to the minimum energy agrees with the observation by scanning electron microscopy. Thus, it becomes clear that this domain structure can be determined in a quasi-stable condition by precisely calculating the magnetostatic energy.
Laser-induced grating spectroscopy of cadmium telluride
Authors: Petrovic Mark S. , Suchocki Andrzej , Powell Richard C. , Cantwell Gene , Aldridge Jeff
Published: July 2002

Laser-induced transient gratings produced by two-photon absorption of picosecond pulses at 1.064 μm were used to examine the room-temperature nonlinear optical responses of CdTe crystals with different types of conductivity. Pulse-probe degenerate four-wave mixing measurements of grating dynamics on subnanosecond time scales were used to measure the ambipolar diffusion coefficient (Da) of charge carriers in the crystals. The value of Da =3.0 cm2 s−1 which was obtained is in very good agreement with theoretical estimates. A long-lived contribution to the signal consistent with a trapped charge photorefractive effect was observed at large grating spacings for n-type conductivity, and is tentatively attributed to a larger trap density in this sample. Measurements of the relative scattering efficiencies of successive diffracted orders in the Raman–Nath regime allowed for calculation of the laser-induced change in the index of refraction, due to the creation of free carriers. The value of Δn=4×10−4 which was obtained is in good agreement with theoretical estimates.
Mechanics of the silica cap during zone melting of Si films
Authors: Dutartre D.
Published: July 2002

Zone melting recrystallization of polycrystalline silicon films on oxidized wafers, performed using linear strip heaters, is an easy way of obtaining good quality silicon-on-insulator films. After recrystallization, the top silicon surface has undulations which are very detrimental when applications in very-large-scale integration circuits are being considered. In this paper, which is the first quantitative study of this mass transport, the silica viscosity derived from experiments at 1685 K has been estimated at 2–3.4×108 decapoises, and the silicon undulations are found to vary as the inverse of the cap thickness. We therefore demonstrate that the mechanical resistance of the silica cap is the mechanism which limits the silicon mass transport during zone melting, and his cap behavior is in good agreement with the classical properties of silica at 1685 K.
Gold diffusion in chemical-vapor-deposited amorphous silicon
Authors: Calcagno L. , Campisano S. U. , Coffa S.
Published: July 2002

The diffusion coefficient of gold implanted into chemical-vapor-deposited (CVD) amorphous silicon has been measured in the temperature range 400–800 °C by Rutherford backscattering spectrometry. In this temperature range the diffusion coefficient varies in the range 10−15 –10−10 cm2 /s and exhibits an activation energy of 1.5±0.1 eV. The diffusion coefficient in amorphous CVD silicon correlates well to the diffusion in ion-implanted amorphous silicon and to the high-temperature diffusion in highly dislocated silicon crystal.
Magnetic ordering in a dilute triangular X
Y antiferromagnet
Authors: Harrison A. , Mason T. E.
Published: July 2002

We consider the effect of dilution with nonmagnetic sites on the sublattice magnetization 〈Ms〉 and the staggered chirality 〈κ〉 in a triangular lattice of XY spins coupled only by nearest-neighbor antiferromagnetic exchange. We argue that the condition for 〈Ms〉 and 〈κ〉 to percolate is more stringent than that for simple connectivity. A single bond is insufficient to convey the necessary information from one part of the percolating cluster to another. Two sets of connections are necessary but not sufficient to ensure connectivity. Consequently, the percolation threshold will be higher than 0.5, the value for ordinary percolation on site dilution of a triangular lattice. The results of Monte Carlo simulations are presented, demonstrating the dependence of the internal energy, heat capacity, and 〈κ〉 on temperature and lattice coverage.
Effect of bias sputtering on stability of amorphous Tb32Fe68 compositionally modulated thin films
Authors: Choe G. , Walser R. M.
Published: July 2002

We investigated the effect of bias sputtering on the oxidation resistance of amorphous Tb32Fe68 compositionally modulated films (CMFs). The columnar morphologies of aged, unbiased films were more diffused than those of as-deposited films. On the other hand, the morphologies of the −70 V bias sputtered, aged film were as dense and featureless as those of as-deposited films. The substrate bias also influenced the magnetic and magneto-optical characteristics of aged films. The Kerr rotation obtained from the film surface was significantly increased by the formation of a transparent, nonmagnetic oxide layer, and by optical interference between this layer and the unoxidized amorphous matrix. The coercivity of the amorphous matrix in unbiased films increased markedly with aging time. These changes are attributed to compositional changes enhanced by the easy diffusion path of oxygen in the columnar void structure. In contrast, the coercivity of −70 V bias sputtered films was unchanged with aging, and exhibited the B-H loops of exchange coupled double layers. The results indicated that the intrinsic stability of Tb-Fe CMFs was strongly influenced by the film microstructure and was improved by the application of substrate bias during deposition.
Spin-glass properties of a planar antiferromagnet
Authors: Coey J. M. D. , Ballet O. , Bakas T. , Mangin P.
Published: July 2002

Small-angle neutron scattering is used to define the magnetic state of a powder sample of minnesotaite at points around its hysteresis loop. The silicate [idealized formula [Si4] {Fe2+3}O10(OH)2] has a planar antiferromagentic ground state giving a magnetic 00 (1)/(2) reflection, but this state is destroyed to the profit of a ferromagnetic state (001 reflection) in those grains where the component of the applied field exceeds Hs =0.7 T at 4.2 K, never to be re-established in an isothermal cycle. Likewise, the planar antiferromagnetic ground state is destroyed, and the susceptibility peak eliminated, on field cooling. The existence of spin-glass magnetic properties in a material that does not have a highly degenerate, frustrated ground state derives from the irreversibility of the antiferromagnetic→ferromagnetic transition.
Magnetic properties of the Sm-Gd alloy system
Authors: Rives Carol J. , Anderson Elmer E. , Arajs Sigurds
Published: July 2002

Preliminary results are reported for a magnetic study of the Sm-Gd alloy system. For Gd-rich alloys, the results show a ferromagnetic transition with Curie temperature decreasing to approximately 255 K for 30% Sm. For the Sm-rich end of the alloy range, the Sm-type antiferromagnetic transitions are seen. The ferromagnetic influence of Gd clearly exists down to Gd concentrations of 20%, where a ferromagnetic-like transition is seen with a Curie temperature of 180 K. In one sample of 60% Sm–40% Gd, we have seen evidence of different magnetic regions, one of which is a Gd ferromagnet with a Tc of approximately 290 K.
Improved thermal stability of Mo-modified γ-Fe2O3 particles
Authors: Hsu J. H. , Kuo P. C. , Hsu C. W.
Published: July 2002

Acicular α-(FeO)OH particles were synthesized using the chemical coprecipitation method with the reaction system of Fe2Cl2-NaOH. The Mo-modified γ-Fe2O3 particles are obtained by adding the proper amount of sodium molybdate to the solution of geothite, followed by the processes of dehydration, reduction, and oxidation. The thermal stability was investigated by thermal differential analysis. It was found that the transition temperature of γ-Fe2O3→α-Fe2O3 increases from 544 °C for the unmodified particles to 720 °C for particles containing 4% by weight of molybdenum. The improved thermal stability has the advantage that the temperature for the oxidation of Fe3O4 particles can be considerably increased without the risk of forming nonmagnetic α-Fe2O3 particles. The magnetization (σs) and coercivity (Hc) of the magnetic acicular γ-Fe2O3 have been determined from room temperature to 200 °C with a vibrating sample magnetometer. The results indicate that both σs and Hc at room temperature decrease with increasing Mo content. The dependence of Hc can be approximately described by the linear equation Hc=Hc,0(1−AT) over that temperature range. The temperature coefficient A decreases with Mo content until the Mo content reaches 4 wt. %. The origin of improved thermal stability is discussed.
Remanent-magnetization decay in CoCr films
Authors: Skorjanec J. , Cottles V. , Close J. , Iverson P. , Edwards J. , Dahlberg E. Dan
Published: July 2002

The decay of the remanent magnetization of several thin films of CoCr has been studied using the extraordinary Hall effect as a probe of the component of the magnetization perpendicular to the plane of the films. Consistent with previous measurements of CoCr, the remanent magnetization decays quasilogarithmically with time after the removal of a saturating magnetic field. In the present work the effect of a magnetically soft keeper layer on the decay of the magnetization has been investigated. It is found that the keeper layer does not affect the remanent magnetization nor does it decrease the decay rate of the perpendicular magnetization. This result indicates that the soft keeper layer is not effective at screening the demagnetization field on a length scale relevant to the decay-producing fields.
A random phase approximation theory of nuclear relaxation in CuO2 planes
Authors: Bulut N. , Hone D. W. , Scalapino D. J. , Bickers N. E.
Published: July 2002

Nuclear magnetic resonance experiments on the planar CuO2 materials related to high-Tc superconductors suggest that the doped holes are formed from the strongly hybridized Cu(3d)-O(2pσ) orbitals. Within this picture the doped metallic state can be viewed as a strongly interacting quantum liquid, with a dynamic spin susceptibility that reflects the local correlations produced by the Coulomb interactions. It is demonstrated that much of the essential observed behavior is predicted by a simple 2D Hubbard model within the RPA, with a suitable choice of parameters, and the physical implications of these parameters are discussed. The nuclear relaxation rates T−11 at various nuclear sites are calculated. The form factors of the hyperfine interaction act to spatially filter the spin susceptibility. In particular, the O form factor suppresses the antiferromagnetic fluctuations which dominate the relaxation of Cu nuclei, thereby reducing T−11 at O relative to that of Cu, as observed.
Exchange in II-VI-based magnetic semiconductors (invited)
Authors: Larson B. E. , Ehrenreich H.
Published: July 2002

We present a physically oriented survey of exchange constants among Mn local moments, and between Mn moments and sp band electrons in II-VI-based magnetic semiconductors (MS) such as Cd1−xMnxTe. A simple three-site model illustrates the physical principles underlying our quantitative calculations of Mn-Mn exchange based on a semiempirical tight-binding Anderson model. Superexchange interactions, computed perturbatively in the Mn d-sp band hybridization, are the dominant mechanisms of isotropic and anisotropic Mn-Mn exchange. The Dzyaloshinsky–Moriya (DM) anisotropic superexchange constant D has a magnitude of ∼5% of the isotropic superexchange constant J. The DM exchange explains spin resonance linewidths and the nature of short range spin ordering in the magnetically concentrated regime. The contribution of anistropic Mn-sp band exchange is also considered.
Powder metallurgical processing of Tb0.27Dy0.73Fe2−X (0<X≤0.5) by a hydrogen-decrepitation (HD) route
Authors: Jones D. G. R. , Abell J. S. , Harris I. R.
Published: July 2002

The hydrogen absorption/desorption behavior of giant magnetostrictive alloys represented by the general formula Tb0.27Dy0.73Fe2−X (0<X≤0.5) has been investigated to provide background information for the production of powder by the hydrogen-decrepitation (HD) route. X-ray-diffraction studies indicate a range of hydriding behaviors depending upon the particular conditions. Thus, cubic, rhombohedral, and amorphous hydrides have been observed and under certain conditions disproportionation occurs with the production of iron and rare-earth hydrides. Metallographic examination of the latter material reveals the phases produced by this disproportionation. Sintered compacts have been made from the disproportionated material by the HD process and compacts with up to 96% of theoretical density have been achieved after only 1-h sinters. The static magnetostrictive properties of these compacts have been investigated, and compare well with values obtained by other workers on samples produced using conventional powder metallurgical methods. The HD process appears to offer significant advantages over more conventional powder metallurgical routes for the production of compacts of these materials.
Magnetostriction measurements on thin films by a slot-line ferromagnetic resonance technique (abstract)
Authors: Oliver S. A. , Harris V. G. , Vittoria C.
Published: July 2002

We report on a new technique for the determination of the linear magnetostriction constant of thin films. The technique uses the shift in ferromagnetic resonance (FMR) of a magnetostrictive sample upon application of an external stress. A circular thin film is deposited onto a fused quartz plate by ion beam sputter deposition. The plate is mounted in a cantilever configuration, with the film suspended over the junction of a slot-line/coplanar guided structure. The slot line provides a rf magnetic field normal to the film plane, tunable over the frequency range 0.1 GHz<ν<20 GHz. Collinear dc and modulating magnetic fields are applied in the film plane. FMR spectra are obtained by measuring the differential power transmission with respect to modulation field by a phased locked-loop technique. The sample is stressed by deflecting the free end of the cantilever using a micrometer drive. Magnetostriction values are calculated from the measured field shift versus deflection using a model based upon a free-energy expression containing magnetoelastic and magnetic interaction energies. Since this method relies only upon measurement of the FMR field shift, we believe that it is a viable technique for measuring magnetostriction values, especially for very thin films.
Unusual magnetic properties in Cu/Ni multilayered films
Authors: Abdul-Razzaq W.
Published: July 2002

Cu/Ni multilayered films of different layer thicknesses were made by the sputtering technique. In all samples the Cu and Ni layers had the same thickness, and the total thickness of the sample was 5000 Å. Each sample was cooled in zero field to 5 K and the magnetization versus temperature was measured after a magnetic field was applied and kept constant during the experiment. As in spin-glasses, the magnetization of all samples had a peak and was irreversible. In addition, for the 0.1-kOe field, the temperature at which the peak occurred, Tp, decreased as the thickness of the individual layers decreased. This behavior is similar to that of Cu-Mn films, where the spin-glass transition temperature Tg decreases as the spin-glass film thickness decreases [G. G. Kenning, J. Slaughter, and J. Cowen, Phys. Rev. Lett. 59, 2596 (1987)]. The alloying of Cu and Ni at the interfaces probably plays a significant role in causing the spin-glass-like magnetic properties in the Cu/Ni multilayered system.
Comparison of angular coercivity in various magnetic media (abstract)
Authors: Ranjan R. , Gau J.-S. , Amin N.
Published: July 2002

Angular coercivity provides a method for studying magnetization-reversal mechanisms and has stimulated theoretical interests particularly for recording materials.1 This paper reports our experimental results on the angular variation of coercivity in different magnetic media prepared by various means, and compares these data. These include CoNiCr/Cr-type longitudinal media and Ba-ferrite–type particulate longitudinal media for hard-disk applications, and CoNi-type oblique evaporated longitudinal media for video recording. Results from sputtered CoNiCr/Cr media showed a symmetric M-type curve and the peak height decreased with intergranular coupling.2 In addition, the peak position also changed systematically with grain decoupling. M-type curves were also observed when the underlayer Cr thickness was varied, but the peak location remained unchanged. Results from Ba-ferrite media prepared with different packing densities exhibit similar curves as those for CoNiCr/Cr media. However, oriented Ba-ferrite media prepared by having a magnetic field applied at 30° and 60° with respect to the film plane show a very unique behavior. In contrast, CoNi films which were prepared by oblique evaporation in the presence of oxygen showed a canted columnar morphology with an easy axis of magnetization out of the film plane. The resultant angular coercivity featured a shifted M-type unsymmetric curve, and the shift angle increased with the oxygen content in the film. It is noted that at high O2 concentrations the curve deviates significantly from a shifted M-type nature. The microstructures of the aforementioned media will also be discussed.
Domain wall pinning transition in an iron-rich FeCu alloy
Authors: Ng D. , Gaunt P.
Published: July 2002

Specimens of α-phase solid solution of iron-rich FeCu(1.07 at. % Cu) were thermally aged at 700 °C for different time durations. Precipitation and growth of εCu took place during the heat treatments. The specimens were polished and were examined with a transmission electron microscope. The size, density, and shape of the precipitates were determined for different aging conditions. These parameters were fit into the strong and weak domain wall pinning models, allowing values of the coercive field Hc to be predicted. Comparison between the predicted and measured coercive fields shows that weak pinning theory agrees with the observed Hc in low age specimens. For specimens aged over 1700 min, strong pinning theory can provide acceptable calculated Hc values. The pinning index β′ related to the ratio of the domain wall area per pin in the static and dynamic states is also calculated for each specimens. β′ values in low age specimens are found to be <1, which indicates weak pinning. For prolonged age specimens, β′ values are close to or larger than 1, and strong pinning is indicated.
ac Hall measurements on high-T
c superconductors
Authors: How H. , Vittoria C. , Widom A.
Published: July 2002

Hall experiments are carried out normally in bulk materials where a dc current is applied perpendicular to a static magnetic field. Since the dc Hall coefficient is small for type-II superconductors at temperatures well below the transition temperature Tc, the possibility of measuring the Hall coefficient of the superconductor under ac conditions is explored. It is found that the ac Hall coefficient can be readily detected through the measurement of the reflected microwave beam, whose polarization has been rotated 90° away from the incident wave irradiating on the surface of a high-Tc superconducting material biased by a dc magnetic field.
Theory of magnetization and exchange-enhanced susceptibility of Pd-Ni alloys
Authors: Kioussis Nicholas , Garland James W.
Published: July 2002

A recently developed new formalism is used to calculate the temperature-dependent, exchange-enhanced Pauli susceptibility, χP(c,T), of paramagnetic and weakly ferromagnetic Pd-Ni alloys. For the first time both the strong nonlinear effects of local chemical environment and of moment formation are included in the calculation of χP(c,T). Also, the effects of quantum and thermal spin fluctuations are included for the first time in alloy calculations away from the dilute limit. This is done through the use of a semiphenomenological theory consistent with scaling laws and with the results of renormalization-group theory for the single-impurity problem. In order to compare theory with experiment, we analyzed the theoretical results for χP(c,T) in exactly the same way as the experimental results. Two different calculational methods were used, one corresponding to an expansion in powers of the Ni concentration and the other involving the exact embedding of 55-site clusters in a self-consistently determined effective medium. Both methods yielded results superior to those of all previous theories and in good agreement with experiment.
Magnetic response of localized spins coupled to itinerant electrons in an inhomogeneous crystal field
Authors: Iannarella L. , Guimarães A. P. , da Silva X. A.
Published: July 2002

The magnetic behavior at T=0 K of a system consisting of conduction electrons coupled to localized electrons (e.g., 4f electrons), the latter submitted to an inhomogeneous crystal-field distribution, is studied. We consider a simple crystal-field distribution and define an average ionic magnetic moment using the results of the homogeneous case. We obtain a condition for the onset of spontaneous magnetic order and study the magnetic behavior in the paramagnetic and ferromagnetic regions of the phase diagram. The study implies that the inhomogeneity of the crystal field attenuates the quenching effects. The model is interesting to the study of disordered rare-earth intermetallic compounds.
Simultaneous gain and phase-shift enhancements in periodic gain structures
Authors: Yan R. H. , Chuang Z. M. , Corzine S. W. , Coldren L. A.
Published: July 2002

The recently proposed concept of periodic gain, i.e., dividing the active region into segments placed at optical electric-field standing wave maxima, has been shown to greatly reduce the threshold gain requirement of the active media by up to a factor of 2 in high-finesse vertical cavity surface-emitting lasers. The lasing wavelength is determined by the period of the standing wave; however, previous analyses of these structures have failed to show that a similar enhancement effect occurs for the index shift resulting from the active segments as well. In this communication, we show that effects on both gain and index can be rigorously derived from conventional transmission scattering theory.
Electrical inhomogeneity in Ga-rich undoped GaAs crystals: Dependence on melt stoichiometry and dislocation distribution
Authors: Young M. L. , Brown G. T. , Lee D. , Grant I.
Published: July 2002

Studies have been made of the macroscopic and microscopic electrical inhomogeneity in undoped bulk GaAs single crystals grown from As/As+Ga melt ratios of 0.48–0.45. Microscopic inhomogeneity was characterized by contact resistance line scans and whole wafer anodization, which gives high-resolution two-dimensional images of the low-resistivity p-type regions within the wafers. The resistivity was nonuniform in wafers from 0.48 As/As+Ga crystals, having a W-shaped radial dependence with minima in the 〈110〉 directions and varying by six orders of magnitude across a wafer, whereas it was uniform in low-resistivity wafers from 0.45 As/As+Ga crystals at fractions of melt solidified, g>0.4. Precise correlation of microscopic inhomogeneity with grown-in linear and cellular arrays of dislocations was obtained in nonuniform wafers, but no correlation with slip dislocations was observed. Anodization images show that the carrier concentration is quantitatively in agreement with a uniform acceptor background compensated by EL2 concentration fluctuations of factors of 2–3 at the dislocation networks. Inhomogeneity variation with g and As/As+Ga ratio is consistent with macroscopic and microscopic decrease in EL2 with melt stoichiometry.
Spot-size dependence in thermal nonlinear microcavities
Authors: Godsalve C. , Abraham E.
Published: July 2002

We present a theoretical model of a physically pixellated nonlinear interference filter illuminated by a Gaussian laser beam. The plane-wave model figure of merit of a previous paper is redefined as a function of spot size, pixel dimensions, and the thermal conductivities of the pixel and substrate. We present detailed calculations of switching powers, and actual values are obtained for the cases of glass and polyimide pixels on a sapphire substrate. The theory predicts that switching powers of the order of less than 1 mW can be achieved for the polyimide-sapphire combination and 10 mW for the glass-sapphire combination. An upper limit of the order of 107 gate Hz/cm2 in an array of pixels is projected.
A perturbation approach to mixed boundary-value spherical problems
Authors: Boridy Elie
Published: July 2002

The solution of a special form of dual series equations involving Legendre functions is presented in the framework of the perturbation method. This leads to a series whose structure is much simpler than that of the alternative integral form solution, and numerically much more practical. Several examples of physical problems in the areas of electromagnetics and hydrodynamics, which are represented by these types of dual equations, are discussed.
Electric-field-induced absorption changes in triangular quantum wells grown by pulsed-beam molecular-beam-epitaxy technique
Authors: Law K-K. , Yan R. H. , Gossard A. C. , Merz J. L.
Published: July 2002

We present an observation of electric-field-induced excitonic quenching in GaAs/AlGaAs triangular quantum wells, grown by pulsed-beam molecular-beam-epitaxy technique. We have measured photocurrent spectra for both symmetric and asymmetric triangular quantum wells as a function of electric field. In both cases, at the ground-state exciton energy, we observed significant electroabsorption changes that were associated with the vanishing of sharp exciton resonances when the triangular quantum-well structures were electrically switched to systems with no quantum confinement for one or both types of carriers.
Bounds on the effective properties of polydispersed suspensions of spheres: An evaluation of two relevant morphological parameters
Authors: Thovert J. F. , Kim I. C. , Torquato S. , Acrivos A.
Published: July 2002

Expressions for the two microstructural parameters that appear in the variational third-order bounds [G. W. Milton, Phys. Rev. Lett. 46, 542 (1981)] for the effective conductivity and elastic moduli of composite media are derived analytically to first order in the sphere concentration c for random well-mixed dispersions of impenetrable spheres with an arbitrary size distribution. These relations lead to rigorous bounds on the effective properties which are exactly valid to order c2 for such models. The apparent linear behavior of the microstructural parameters up to moderately high c enables one to apply the bounds beyond second-order in c, however. Employing these results, the effect of polydispersivity on the effective properties is examined. It is worth noting that, under some conditions, polydispersivity can actually lead to a slight decrease of the shear modulus, whereas, for highly conducting particles, polydispersivity always increases the effective conductivity.
Effects of C+ implantation on the interdiffusion and resistivity of Cu/Ni/Au thin films
Authors: Madakson Peter , Karasinski J.
Published: July 2002

The effect of C+ implantation on the interdiffusion of Cu/Au and Cu/Ni/Au thin-film structures was investigated at temperatures ranging from 200 to 600 °C, and for different annealing times at 400 °C. For comparison, unimplanted Cu/Ni/Au and Cu/C/Ni/Au thin-film structures were also studied. The implantation of carbon ions has very little effect on the interdiffusion of Cu and Au at the temperatures investigated. For the Cu/C/Ni/Au structure, very little Cu-Au interdiffusion was observed within the temperature range studied. However, spontaneous delamination of C/Ni/Au from Cu occurred at ≥400 °C. This must be due to the poor adhesion of C to Cu which is made worse at these temperatures by the thermal expansion mismatch. X-ray diffraction analysis revealed the formation of intermetallic CuAu compounds after annealing of the implanted and unimplanted Cu/Au and Cu/Ni/Au structures. The mechanisms of diffusion are considered to be associated with this intermetallic alloying, which results in the generation of vacancies that form the diffusion paths. In the case where alloying does not occur, diffusion is therefore limited by solid solubility.
Optically pumped titanium vapor laser at 551.4 nm
Authors: Hirata K. , Yoshino S. , Ninomiya H.
Published: July 2002

The output characteristics of an optically pumped titanium vapor laser on various buffer gas species and pressures have been measured, and the role of buffer gas on the laser output is accordingly discussed. He, Ne, Ar, and Kr are used as buffer gases. The optimum condition for the maximum output energy is 4 Torr of He with 10 μs delay time.
Brillouin scattering in FeSi/X/FeSi double-layer films, X=ZnO and SiO2
Authors: Otake Toru , Haneda Yoichi , Yoshihara Akira , Shimada Yutaka , Fujimura Tadao
Published: July 2002

Thermally-excited spin waves in double-layer films of FeSi/X/FeSi (where X=ZnO and SiO2) have been studied by Brillouin scattering. The thickness of the FeSi (2.6 wt. % of Si) layers is fixed at 1100±30 Å. Scattering from the Damon-Eshbach-type surface wave and the standing spin waves has been observed. The standing spin-wave structure of a 28-Å-thick SiO2 spacer is modified by interlayer exchange coupling, but not that of a 5-Å-thick ZnO spacer. The general trend of magnon frequencies as functions of the external magnetic field, the surface wave vector, and spacer thickness can be explained by the theory developed by Grünberg [J. Appl. Phys. 51, 4338 (1980)]. The Damon-Eshbach-type surface mode exhibits a systematic deviation from that theory at small surface-wave vectors.
Influence of temperature distribution along the junction plane on the lateral mode in AlGaAs phased array lasers
Authors: Sagawa M. , Kajimura T. , Todoroki S. , Sekine Y.
Published: July 2002

It is experimentally shown for the first time that far field lobe broadening, which is a multilateral mode operation under continuous wave operation in phased array lasers that emit diffraction limit beams under pulsed conditions mainly originates from temperature distribution along the junction plane. Spectrally resolved near field measurements show that pulse width, where broadening occurs, corresponds well to the one where temperature influence appears. Moreover, measurement of temperature distribution by the near field measurements and laser Raman spectroscopy show that a considerable temperature difference does exist between the center and edge elements in the array.
Anodic oxidation of AlGaAs and detection of the AlGaAs-GaAs heterojunction interface
Authors: Fischer C. W. , Teare S. W.
Published: July 2002

This paper presents the results of a study of the anodic oxidation of n-type AlGaAs and AlGaAs/GaAs heterojunctions in acid-glycol-water electrolytes. Anodic oxides with thickness up to 300 nm may easily be grown under constant-current conditions if external illumination is used. Real-time derivative spectra of the anodic voltage-time data show structure that is dependent upon the thickness of the AlGaAs epitaxial layer, its doping density, and possibly band-gap energy differences. The derivative results clearly show that epitaxial layer thickness and thickness variations are readily measured. The oxide growth constant and material consumption rate are found to be 1.52 and 1.08 nm/V, respectively. Optical dispersion in the wavelength range from the near UV to the IR range is also measured and fitted to Sellmeier’s equation. Composition of the AlGaAs is measured using Rutherford backscattering, which reveals an As-rich oxide.
Vertical amorphous silicon thin-film transistors
Authors: Shaw John G. , Hack Mike
Published: July 2002

A vertical amorphous silicon thin-film transistor that has a very short channel length that is determined by deposition, not lithography, is described. These transistors have a field-effect mobility of approximately 0.5 cm2 /V s, an effective channel length of 1.5 μm, and a dynamic range of over five orders of magnitude. A method for suppressing excessive leakage currents and improving the saturation of the output characteristics by a novel current-blocking technique is shown. A two-dimensional computer program is used to analyze these devices and guide their design and optimization. Unlike a conventional thin-film transistor, the current path is primarily parallel to the electric field created by an insulated gate electrode. These vertical transistors are easy to fabricate, compatible with large-area processing techniques, and have suitable terminal characteristics for use in practical circuits.
Damping effects of magnetic fluids of various saturation magnetization (abstract)
Authors: Chagnon Mark
Published: July 2002

Magnetic fluids have been widely accepted for use in loudspeaker voice coil gaps as viscous dampers and liquid coolants. When applied properly to a voice coil in manufacturing of the loudspeaker, dramatic improvement in frequency response and power handling is observed. Over the past decade, a great deal of study has been given to the effects of damping as a function of fluid viscosity. It is known that the apparent viscosity of a magnetic fluid increases as a function of applied magnetic field, and that the viscosity versus field relationship approximate that of the magnetization versus applied field. At applied magnetic field strength sufficient to cause magnetic saturation of the fluid, no further increase in viscosity with increased magnetic field is observed. In order to provide a better understanding of the second order magnetoviscous damping effects in magnetic fluids used in voice coils and to provide a better loudspeaker design criterion using magnetic fluids, we have studied the effect on damping of several magnetic fluids of the same O field viscosity and of varying saturation magnetization. Magnetic fluids with saturation magnetization ranging from 50 to 450 G and 100 cps viscosity at O applied field were injected into the voice coil gap of a standard midrange loudspeaker. The frequency response over the entire dynamic range of the speaker was measured. The changes in frequency response versus fluid magnetization are reported.