bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasensitive, wide frequency range magnetoelastic strain gage (abstract)
Authors: Wun-Fogle M. , Savage H. T. , Clark A. E.
Published: July 2002

A new technique for measuring strain with extremely high resolution was developed. This technique relies on the ultrasensitive (high coupling factor) amorphous ribbons prepared by magnetic field annealing.Here certain ribbons (e.g., Metglas 2605SC, 2605S-2) when annealed in a transverse field achieve magnetomechanical coupling factors k33≊0.95.1 In this technique the sensitive ribbon is bonded in place on an aluminum bending member with a highly viscous liquid (η≊107 cP at 298 K). This procedure allows the ribbon to remain in a stress-free environment following an initial relaxation period of approximately 10 min. In this state the ribbon is in a ‘‘blocked’’ (constant strain) condition while at the same time being stress-free. Since the susceptibility of the ribbon is highly strain dependent, a measurement of the susceptibility is a direct measurement of the strain. We define a figure of merit (FM) as (∂χ/∂ε)/χ in analogy with (∂R/∂ε)/R for a conventional strain gage. Values of FM of about 2×105 were obtained. This is three orders of magnitude better than semiconductor strain gages. The main features of this technique are its large dynamic range, high sensitivity and strain resolution, very small temperature dependence, and broad frequency range. In a simple device, we measured strains as low as 3×10−10 and secured a dynamic range of 104. The potential dynamic range exceeds 105. Measurements of FM and dynamic range were made from 0.01 to 1 Hz. We expect no deterioration in operational characteristics far above 1 Hz. Calculations also indicate only a slight temperature dependence of the FM from 0 to 500 K.
Magnetic correlations in an amorphous Gd-Al spin glass
Authors: Spano M. L. , Rhyne J. J. , Pickart S. J. , Hasanain S. K. , Gambino R. J. , McGuire T. R.
Published: July 2002

Small-angle neutron scattering (SANS) as well as magnetization measurements have been made on a sputtered film of Gd43Al57. The low field susceptibility peaks at a freezing temperature Tf of 33 K. This agrees well with the SANS data, which shows a peak in the intensity at this temperature for the lowest Q’s measured. The SANS line shapes are unusual in that they can be fitted with a Lorentzian plus Lorentzian-squared cross section with dissimilar correlation lengths. The Lorentzian correlation length peaks near 35 K at a value of ∼14 Å, while the Lorentzian-squared correlation length exhibits a large, essentially resolution-limited, value up to temperatures several times Tf. These results are consistent with the coexistence of finite static spin clusters with relatively long-range ferromagnetic correlations.
Magnetohydrodynamic aspects in a superconducting pump
Authors: Lalli F. , Veca G. M.
Published: July 2002

The use of a superconducting magnet for a dc pump allows one to reconsider this device as technically valid for some applications. In the present paper, the authors have examined some aspects that are typical of a pumped fluid behavior, using a two-dimensional numerical model. The results thus obtained show the transition, through the pump pipe, from the Poiseuille flow (inlet side) to the Hartmann flow and then to the M-shaped velocity profile flow (between the electrodes). Moreover, the model permits one to evaluate the electromagnetic and fluid dynamic conditions in which the breakaway of flow from the pump walls occurs. The code is based on the numerical integration of the magnetohydrodynamic general equations by a finite-difference method, in laminar flow conditions.
Temperature dependence of 0.5-μm bubble propagation in ion-implanted devices
Authors: Jo Soonchul , Kryder M. H.
Published: July 2002

The temperature dependence of 0.5-μm bubble propagation in ion implanted propagation tracks fabricated with garnet films having nearly isotropic magnetostriction is reported. The propagation track cell size was 2.5×2.5 μm2 and the nominal bubble garnet film composition was {Bi0.4Dy0.7Sm0.2Lu1.5Y0.2} [FeGa]5(O)12. ‘‘Good’’ and ‘‘bad’’ track bias margins of diamond and circular patterns were measured from 0 to 130 °C. The patterns showed good overlapping margin width (at least 13% of mid-bias value) of ‘‘good’’ and ‘‘bad’’ tracks up to 120 °C. The margins shifted down monotonically as temperature increased with a coefficient of roughly −0.27%/°C (at 50 °C). The minimum drive field in general showed a monotonic decrease with temperature increase. The wider overlapping bias margin width (at least 14% of mid-bias value) and the lower minimum drive field (at most 40 Oe) over the temperature range tested were obtained from the diamond patterns. It was also observed that the patterns actually showed slightly higher collapse field for ‘‘bad’’ tracks than ‘‘good’’ tracks depending on the rotation sense of the drive field.
Physical and magnetic characteristics of rigid single layer perpendicular recording media (invited)
Authors: Heiman Neil
Published: July 2002

The results presented will be oriented toward the characteristics of single layer perpendicular recording rigid disk media made in a production environment. The desired physical and magnetic parameters for perpendicular media are considerably different from those for longitudinal media. The impact of these differences on production techniques will be discussed. Data relating the physical, magnetic, and recording characteristics will be presented.
Influence of nitrogen, oxygen, and water on magnetic properties of dc magnetron sputtered GdTbFe films
Authors: Heitmann H. , Spruijt A. M. J. , Willich P. , Wilting H.
Published: July 2002

Amorphous GdTbFe thin films were produced by dc magnetron sputtering in argon atmosphere at varying partial pressures of nitrogen, oxygen, and water. The compensation temperature Tcomp, the Curie temperature TC, and the uniaxial magnetic anisotropy constant Ku decrease strongly with increasing impurity concentration in the films. The influence of nitrogen on Tcomp and Ku is about a factor of 3 less than that of oxygen and water. The strong decrease of Tcomp and Ku is due to the preferred reaction of the impurities with the rare-earth (RE) atoms. This leads to a preferred deactivation of the latter resulting in a decrease of the rare-earth (RE) sublattice magnetization. Moreover, the uniaxial magnetic anisotropy is primarily based on the single ion anisotropy of the Tb atoms. If these are deactivated Ku decreases. At increasing impurity concentrations the selectivity of deactivation decreases and increasing amounts of Fe are affected. Thus, the steepest decrease of Tcomp and Ku is observed at low concentrations. For Tcomp the mean values of the slopes at concentrations below 1 at. % are 35 K per at. % for nitrogen, 85 K per at. % oxygen (Ar/oxygen atmosphere), or 125 K per at. % oxygen (Ar/water atmosphere). Ku is reduced to half its original value at concentrations of 4 at. % nitrogen, 1.2 at. % oxygen (Ar/O2), and 0.9 at. % oxygen (Ar/H2O) in the films. The Curie temperature TC decreases at a rate of about 10 K per at. % impurity. This is due to the diminishing magnetic interactions at increasing impurity incorporation.
Spin anisotropy of ferromagnetic slabs and overlayers (invited)
Authors: Gay J. G. , Richter Roy
Published: July 2002

We calculate the spin anisotropy of ferromagnetic monolayers of Fe, Ni, V, and Co. We find the easy direction of magnetization is perpendicular to the plane of the monolayer for Fe and V, but in the plane for Ni and Co. The result for Fe explains why spin splitting but no spin polarization is observed in recent photoemission experiments on Fe monolayers. For thicker ferromagnetic slabs, the depolarization energy will quickly overwhelm the spin anisotropy and force the moment into the plane of the slab. This is illustrated by calculations for thicker slabs of Fe. Preliminary calculations of the anisotropy of a monolayer of Fe on Ag indicate that the Ag must be treated fully relativistically.
Direct dc magnetization measurements of Fe on Ag (abstract)
Authors: Schultz S. , Youm D. , Starr A. F. , Armstrong J. P.
Published: July 2002

We have made measurements of the temperature and field dependence of the dc magnetization of Fe atoms deposited on polycrystalline Ag substrates in the range 0.1–100 monolayers equivalent mass coverage. Our experimental technique is to couple an ultrahigh vacuum sample preparation and transport chamber to a SQUID dc magnetometer. We shall present an analysis of these data and a comparison of the deduced saturation moment and anisotropy constant with the theoretical and experimental results of the companion papers in this symposium.
Magnetism and valence mixing in Eu systems with contrasting band structures
Authors: DiMarzio D. , Croft M. , Sakai N. , Shafer M. W.
Published: July 2002

Eu compounds at or near the strongly magnetic (J=7/2) Eu2+ valence should enter a mixed valent Eu2+δ (‖δ‖<1) nonmagnetic state at sufficiently high pressures. We have performed high pressure (P≤250 kbars) and low temperature (T≥4.2 or 77 K) resistivity measurements on semiconducting EuO and metallic Eu(AuxPd1−x)2Si2 (0≤x≤1). For EuO our results show a nonlinear gap variation above 130 kbar with a hybridization gap and ferromagnetism (Tc ≥200 K) being maintained out to 250 kbars. In the Eu(Au,Pd)2Si2 system the cooperative valence transition can be traced to higher pressures with increasing Au content. In the pure Au the magnetic order persists out to 250 kbars. A common theme in both systems is the substantial pressure-induced enhancement of the magnetic ordering temperature precursive to the eventual large Eu valence change.
Magnetic to nonmagnetic transition in a highly hybridized f-electron system: U(Ga1−xGex)3
Authors: Zhou L. W. , Jee C. S. , Lin C. L. , Crow J. E. , Bloom S. , Guertin R. P.
Published: July 2002

UGa3 is an antiferromagnetic system with a Néel temperature TN =67 K and UGe3 is a weakly paramagnetic system with a nearly temperature-independent magnetic susceptibility and a slightly enhanced low-temperature electronic specific heat coefficient of 20 mJ/mole K2. The room-temperature lattice constant and the temperature dependence of the magnetic susceptibility, electrical resistivity, and low-temperature specific heat have been measured for the pseudobinary alloy system, U(Ga1−xGex)3. TN is rapidly depressed with increasing x and appears to go to zero at x≂0.18. The magnetic susceptibility remains nearly temperature independent across the series and neither the magnetic susceptibility nor low-temperature specific heat display any significant enhancement in the paramagnetic regime.
Coherence in heavy fermion compounds: Effect of impurities
Authors: Cyrot M.
Published: July 2002

We present a model for heavy fermion compounds where the active atoms (U or Ce) create virtual bound states at the Fermi level. We describe the appearance of coherence between these virtual bound states at low temperatures by the formation of a band whose width is strongly reduced by correlations. We study the effect of normal impurities on the coherence and show that a small concentration can destroy it. This explains the different behaviors of the resistivity. The coupling of this heavy fermion band to the conduction band is responsible for both magnetic and superconducting properties. Impurities affect drastically the magnetic and superconducting states. This is a direct explanation of the well-known experimental effects of normal impurities in these compounds.
High power cw operation over 400 mW on five-stripe phase-locked laser arrays assembled by new junction down mounting
Authors: Seiwa Y. , Aoyagi T. , Hinata S. , Kadowaki T. , Kaneno N. , Ikeda K. , Susaki W.
Published: July 2002

The junction down mounting attached to a Si-submount with Au-Si solder has been shown to be very reliable for lasers by aging tests of 5 mW at 80° C. The thermal resistance of this junction down mounting is 30 K/W smaller than that of a junction up mounting. Output powers as high as cw 80 mW/stripe, corresponding to 400 mW, was realized without saturation with a five-stripe phase-locked laser array with an inner-stripe configuration assembled on this mounting.
Photoacoustic response of condenser microphones
Authors: Diószeghy Tamás
Published: July 2002

The membranes of BK 4166 half-inch and BK 4145 1-in.-diameter condenser microphones were illuminated with a chopped light beam of a 5-mW He-Ne laser and the occurring microphone signal detected as a function of the modulation frequency. The response curves provide new information on the frequency dependence of a background noise light absorption by the microphone membrane produces in photoacoustic cells. The signal from the (1)/(2) -in. microphones was found to decrease monotonically with increasing frequency, and the signal phase had a limiting value of −π/2 rad at high frequencies. The corresponding magnitude curves of the 1-in. microphones showed a sharp minimum in the 200–340-Hz region, and the limiting phase was π rad. A complex thermoacoustic signal generation mechanism is proposed to explain some of these results.
Comment on ‘‘Small-angle neutron scattering evidence for the absence of long-range magnetic order in amorphous Fe91Zr9’’[J. Appl. Phys. 5
7, 3407 (1985)]
Authors: Kaul S. N.
Published: July 2002

Contrary to the claim made by Rhyne and Fish, based on their small-angle neutron scattering data, that amorphous (a-) Fe91Zr9 does not exhibit long-range ferromagnetism at any temperature but instead enters a spin-glass state at temperatures as high as ∼210 K, our recent ac susceptibility data demonstrate that a long-range ferromagnetic order is established in this alloy at Tc≂210 K. A host of other experimental observations on the same or nearby compositions in the a-Fe90±xZr10∓x alloy series, available in the literature, are shown to provide firm support to our inference.
Two-cavity autoacceleration of an intense relativistic electron beam
Authors: Coleman P. D. , Lockner T. R. , Poukey J. W.
Published: July 2002

Three series of experiments have been performed using two 40-Ω coaxial autoacceleration cavities to accelerate an intense relativistic electron beam. First, conventional magnetic transport was used to propagate a 1.8-MeV, 11-kA beam through two 1-m-long cavities. An increase of 700±130 keV in kinetic energy was achieved which represents 80% of the maximum theoretical acceleration for an 11-kA beam passing through two 40-Ω cavities. Multiple accelerated pulses were generated and no adverse interaction between the cavities was observed. In the second experiment, ion focused transport (IFT) was used to successfully propagate a 9-kA beam through the accelerator again achieving multipulse operation with both cavities. An energy increase of 560±30 keV was attained which is 78% of the theoretical maximum. Finally, IFT was used to propagate a ≂25-kA beam through a 1-m-long cavity, then a 0.5-m-long cavity, demonstrating two stages of temporal energy compression. Gap leakage and current transport losses limited the acceleration to 1.25±0.16 MeV which corresponded to an 84% increase in kinetic energy.
Rotational hysteresis of elongated-single-domain particles by chain-of-spheres model
Authors: Ishii Y. , Sato M.
Published: July 2002

The behavior of the magnetization of a chain of spheres contacting each other with an area in a rotating uniform magnetic field is studied. The rotational hysteresis integral Rh for the parallel-rotation mechanism is found to be 0.414 for the aligned and planar randomness, and to be 0.379 for the spherical randomness of orientation in assemblies of the chains of spheres. These values are found to be independent of the number of spheres N and of the contacting area. For the fanning mechanism, Rh is found to increase, reach the maximum value, and decrease abruptly to 0 with an increase in the contacting area. And in this case, Rh varies with N and the contacting area from 0.975 to 4 for the aligned and planar randomness, and from 0.670 to π for the spherical randomness of orientation in assemblies of the chains.
Shock compression of powder compacts of CaF2
Authors: Taniguchi T. , Kondo K. , Sawaoka A.
Published: July 2002

Particle velocity gauges were used to measure the Hugoniots to 30 GPa of CaF2 powder compacts having initial porosities of 15% and 35%. The Hugoniot of the material with 15% porosity is concaved upward over the range to 30 GPa and lies close to the solid Hugoniot in the stress range above 15 GPa. The Hugoniot of the material with 35% porosity becomes an isovolume curve, at about the zero-pressure volume, in the stress range above about 10 GPa. Studies of recovered shock loaded samples indicate that the temperature distributions in the shock-compressed samples were very heterogeneous. It is inferred that the higher stress Hugoniot measurements pertain to a nonequilibrated mixture of the solid and liquid phases of CaF2. In view of this evidence against thermal equilibrium, one may question the validity of the Hugoniot data on the initially porous samples to obtain data on Grüneisen’s ratio at high pressures.
Preparation and structural analysis of a PbSe-SnSe strained-layer superlattice
Authors: Hiroi Z. , Nakayama N. , Bando Y.
Published: July 2002

A new superlattice composed of semiconducting PbSe and SnSe has been grown epitaxially on cleaved NaCl substrates by the vapor deposition method. The samples were characterized by x-ray diffraction and cross-sectional high-resolution transmission electron microscopy. Two materials have different crystal structures; PbSe has the cubic NaCl-type structure, whereas SnSe has the orthorhombic SnS-type structure, which is a distorted NaCl-type structure. The lattice mismatch between them is quite large, about 3%, and their growth planes have different symmetries. Therefore, this superlattice should not be classified as an ordinary superlattice like the GaAs-AlAs system, but as a so-called strained-layer superlattice. As a result of the structural analyses, it has been found that the samples have an ideal structure whose compositional modulation can be described by the step model with no mixed layers at the interface. In addition, we have observed a change of crystal symmetry in the PbSe layers: PbSe adopts the SnS-type structure when the thickness is less than about 30 Å, for coherency strain, but it relaxes back to the NaCl-type structure, with loss of the coherency, when the thickness is larger.
The temperature dependence of the anomalous effective g value of BiTm:YIG
Authors: Mitchell T. B. , Lehmann-Szweykowska A. , Wigen P. E. , Belt R. , Ings J.
Published: July 2002

Bi- and Tm-substituted YIG have shown [V. R. K. Murthy et al., in Digest of INTERMAG Conference (IEEE, New York, 1983)] anomalously low effective g values. The experimentally measured temperature dependence of BiTm:YIG shows that the effective g value decreases with decreasing temperature whereas the simple spin-wave theory predicts the opposite behavior. A recent paper [A. Lehmann-Szweykowska et al., J. Magn. Magn. Mater. 54, 1183 (1986)] predicts that the single ion anisotropy and spin-wave damping also make important contributions to the effective g value. These effects are due to the large crystal field effects of Tm in the garnet crystal host. The ground state of the Tm is J=6, L=5, and S=1. The large orbital angular momentum states enhance the spin-orbit coupling which is related to the crystal field effect. The temperature dependence of the effective g value was measured by FMR (ferromagnetic resonance) on BiTm:YIG. The experimental temperature dependence is fitted to the theoretical model and excellent agreement is obtained.
Anisotropy effects of ion-implanted iron, manganese, and argon on high-purity YIG
Authors: Bush G. G. , Rodrigue G. P. , Legg K. O.
Published: July 2002

The objective of this research was to investigate anisotropy effects of implanted ions in the end-of-path region. Argon, manganese, and iron were implanted with doses of 1×1015 and 2×1016 ions/cm2 at energies of 60–190 keV. The resulting changes in X-band ferromagnetic resonance spectra were used to develop models for the magnetization and uniaxial anisotropy in the implanted surface region. These models indicate a correlation between the location of the peak in the dose profile and a change in the uniaxial anisotropy and magnetization. This effect persists after annealing has removed most of the surface damage and restored the magnetic nature of the damage region. Implantation generates an amorphous surface layer whose magnetic nature can be restored to almost bulk properties by annealing in the case of argon, but not for manganese or iron. The thickness of the amorphous layer as a function of annealing time is also quite dependent on which ion is implanted, the energy of implantation, and the dose level.
Magnetic and structural properties of quasi-two-dimensional metamagnetic [C6H22N4]CuCl6
Authors: DeFotis G. C. , McGhee E. M. , Bernal I. , Losee D. B.
Published: July 2002

Single-crystal susceptibility and magnetization data have been obtained for this unusual Cu(II) metamagnet. The structure has also been determined and is monoclinic, P21/c, with two magnetic ions per unit cell. Structural details strongly suggest an effective lattice dimensionality of two. This is confirmed by the failure of the high-temperature susceptibility to conform to a Curie–Weiss law, and by an excellent fit to the susceptibility data using a high-temperature series expansion for the square-planar, S=1/2, Heisenberg model, with g=2.144 and J/k=20.1 K. The single-crystal susceptibility is markedly anisotropic below the approximately 9.55-K Néel temperature, and is also somewhat anisotropic above it. Metamagnetic transitions are clearly observed along the b easy axis, the transition field being quite small (Hc≊31 G near 0 K) and decreasing with increasing temperature. The interlayer antiferromagnetic exchange is estimated to be only about 0.0094 K.
Magnetic properties of fine iron particles
Authors: Du You-wei , Wu Jian , Lu Huai-xian , Wang Tiang-xiang , Qiu Z.-Q. , Tang H. , Walker J. C.
Published: July 2002

Iron particles were prepared by a gas evaporation method in a nitrogen atmosphere. The particle size, shape, and magnetic properties were influenced by the nitrogen pressure. Particles prepared by this method were relatively stable in air and were not seriously oxidized. The recoilless fraction is low for the oxide layer, so that it cannot be detected at room temperature by Mössbauer spectrum. A superparamagnetic peak associated with the oxide microcrystal layer did not occur in the Mössbauer spectra due to the action of the magnetic field from the iron core and the interaction between iron particles and the low Debye temperature. From the electron micrography, the magnetic reversal process seems to be determined by a chain-of-spheres mechanism but Hc∼T curve cannot coincide with the Ms∼T curve at low temperatures. An increase of Hc may be associated with magnetic anisotropy. It is found that the magnetization versus temperature shows an anomalous increase in M(T) at higher T. We think that this means that the surface oxide layer was not magnetized to saturation even under 40 kOe at 5.5 K as the surface anisotropy is rather large.
Theoretical prediction of remote-field eddy current response for the nondestructive evaluation of metallic tubes
Authors: Palanisamy R.
Published: July 2002

The remote-field eddy current effect refers to low-frequency eddy current nondestructive testing (NDT) phenomenon in tubular conductors in which the behavior of both amplitude and phase of induced magnetic field are in apparent contradiction to the well-known ‘‘skin-effect’’ theory. Near-equal detection sensitivity across the wall thickness, the ability to measure wall thickness, and the absence of lift-off problems are some of the attractive features of this technique. Despite its early recognition and useful application in down-hole inspection of oil-well casing, no development of adequate scientific basis that could explain this phenomenon has been reported in the open literature. Modeling of the remote-field eddy current phenomenon using the axisymmetric finite element computer code is described in this paper. The results presented show that the finite element numerical technique originally developed for the computation of fields in electrical and magnetic devices can be used as well for the modeling of remote-field eddy current NDT problems.
Application of nonequilibrium concentration profiles in particle diffusion under the action of a magnetic force (abstract)
Authors: Janssen J. J. M. , Myron H. W. , Perenboom J. A. A. J.
Published: July 2002

For submicron particles diffusion effects and interparticle interactions cannot be neglected in studies of particle behaviour under the action of a magnetic force. Several authors have studied the case of single wire HGMS, where these effects lead to the phenomenon of dynamic buildup: a concentration gradient is induced, but no actual capture occurs. Applications are in, e.g., magnetohydrodynamic separation1 and susceptibility selective separation.2 These applications are based on the equilibrium situation. We have studied the case of nonequilibrium concentration through a numerical solution of the time-dependent diffusion equation, and have found interesting features, that may lead to new applications. The magnetic force will cause a depletion of (ferro)magnetic particles at one end of the sample cell at a size-dependent speed. Observation of the time evolution of the particle concentration at some distance from the end of the cell will then allow to deduce the particle size distribution.
Electric and magnetic properties of CuFe, CuNi, and CuZn composites after thermal annealing (abstract)
Authors: Yao Y. D.
Published: July 2002

CuFe, CuNi, and CuZn composite samples were fabricated by means of the cold powder metallurgy technique. The temperature-dependent electrical resistivity ρ was studied between 4 and 1100 K. The isothermal irreversible electrical resistivity changes due to thermal annealing was measured between 423 and 1073 K. The coercive field Hc at room temperature is increased for CuFe and is decreased for CuNi after thermal annealing; the saturation magnetization Ms at room temperature is decreased for CuNi composite and does not change for CuFe composite after thermal annealing. These results are explained by both the magnetostriction λ of Fe (λ>0) and Ni (λ<0) and the alloying effect. The results of alloying study during thermal annealing indicate that the solubility between two components is almost negligible for CuFe composites, is limited for CuZn composites, and is nonlimited for CuNi composites; these results are consistent with the metallurgical phase diagrams.
Large Barkhausen discontinuity in (Fe1−xCox)-Si,B amorphous wire (abstract)
Authors: Yamasaki J. , Humphrey F. B. , Manabe T. , Kohri K. , Malmhäll R.
Published: July 2002

The magnetostrictive amorphous wires made by the in-water quenching technique have been shown to exhibit the large Barkhausen discontinuities,1 which make them attractive for sensor application.1 We reported earlier that the reentrant magnetic behavior of these wires is attributable to the magnetostrictive anisotropy caused by the residual stresses quenched in during solidification in the water.23 For further understanding of the magnetoelastic effect in amorphous wires, we measured the magnetic properties including the magnetic domain patterns for the in-water quenched (Fe1−xCox)-Si,B amorphous wires. The large Barkhausen discontinuity was observed only for wires having the positive magnetostriction. We found that the compositional variations of the width of labyrinthine domain and the critical field for reverse domain nucleation agree with those expected from the magnetostriction change with composition.
Spin polarization of secondary electrons from 3d ferromagnetic metals
Authors: Meservey R.
Published: July 2002

Secondary electrons with kinetic energy E>8 eV from Fe, Co, and Ni have recently been shown to reflect the expected spin polarization P of the average of the conduction bands of these metals. However, as the threshold value E=0 is approached, the secondary electron polarization sharply increases for each of these metals. It is pointed out that the values for P at E≊0 for secondary electrons agrees very well with the values of P for tunneling electrons. The tunnel current is contributed mainly by a small number of highly mobile electrons from s-d hybridized bands, rather than by the more localized d electrons which contribute most of the magnetic moment. For these bands the sign and approximate magnitude of P are correctly predicted from the known band structure. Inelastic processes that have been suggested to explain the increase in P at E≊0 for secondary electrons cannot apply to elastic tunneling at EF. It is proposed the values of P of secondary electrons for E≊0 reflect the polarization of the s-d bands which contribute to the tunneling current.
Mid-infrared dispersion of the refractive index and reflectivity for GaAs
Authors: Blakemore J. S.
Published: July 2002

Since the band gap of GaAs is more than 40 times larger than hνTO of the Reststrahlen absorption peak, it would seem natural to assume that dispersion caused by one phenomenon ceases completely before that caused by the other begins. However, that is not rigorously true, and the continuous progression of the refractive index n(hν) is modeled here for situations of room temperature (∼300 K) and low temperatures (<30 K). Attention is paid especially to the consequences for the spectral variation of GaAs reflectivity through the mid-infrared at such temperatures, and the implications for making quantitative deductions about the strengths of weak sub-band-gap absorption processes in this material.
A probabilistic model of brittle crack formation
Authors: Chudnovsky A. , Kunin B.
Published: July 2002

Probability of a brittle crack formation in an elastic solid with fluctuating strength is considered. A set Ω of all possible crack trajectories reflecting the fluctuation of the strength field is introduced. The probability P(X) that crack penetration depth exceeds X is expressed as a functional integral over Ω of a conditional probability of the same event taking place along a particular path. Various techniques are considered to evaluate the integral. Under rather nonrestrictive assumptions we reduce the integral to solving a diffusion-type equation. A new characteristic of fracture process, ‘‘crack diffusion coefficient,’’ is introduced. An illustrative example is then considered where the integration is reduced to solving an ordinary differential equation. The effect of the crack diffusion coefficient and of the magnitude of strength fluctuations (ratio of minimal and mean values of the strength field) on probability density of crack penetration depth is presented. Practical implications of the proposed model are discussed.
Observation of resonant tunneling effects in a three-terminal device
Authors: Kastalsky A. , Marroux O. , Bhat R.
Published: July 2002

We present the results of studying the resonant tunneling into a single quantum well (SQW) in a three-terminal device. The resonant process manifests itself as a peak and negative-resistance effect in lateral current in the SQW, the amplitude and position of the peak being controlled by the third collector, electrode. In addition, a peak of resonant current with a pronounced negative transconductance was simultaneously measured in the collector circuit as a result of real-space hot-electron transfer from the SQW to the collector.
Photoconductive gain of a longitudinal detector with an arbitrary absorption profile
Authors: Szmulowicz Frank , Madarasz Frank L. , Diller Jeffrey
Published: July 2002

It is shown that the photoconductive gain of a longitudinal detector is given by the ratio of the average carrier lifetime to the interelectrode transit time regardless of the absorption profile of the detector. Both corpuscular and macroscopic points of view are considered.
The laser emission of rhodamine 110–coumarin bifluorophoric systems under coaxial flashlamp pumping
Authors: Geng Zhang Fu , Lian Yu Chuang
Published: July 2002

In this paper the experimental results of the laser emission of Rhodamine 110–coumarin bifluorophoric systems under coaxial flashlamp pumping have been reported. When coumarin 7 is used as a sensitizer, the laser output of Rhodamine 110 is increased by 130% over that without a sensitizer.
Inducing rapid epitaxy of polycrystalline silicon films deposited on 〈100〉 silicon by arsenic ion implantation
Authors: Komem Y. , Wong C. Y. , Harrison H. B.
Published: July 2002

Alignment of undoped polycrystalline silicon deposited on 〈100〉 single-crystal silicon is known to occur for temperatures higher than 1000 °C. In this paper we provide evidence of a greatly enhanced epitaxy occurring in the polycrystalline silicon film after arsenic ion implantation, which amorphizes the surface layer of this film, followed by rapid thermal processing. The significantly enhanced epitaxy over that of undoped polycrystalline silicon is attributed to the mechanisms of solid phase epitaxial growth of the amorphized surface layer and alignment and realignment and coalescence, which are thought to be enhanced by arsenic segregation to the film grain boundaries and its interface with the silicon substrate via grain boundary diffusion. During this rapid epitaxy the arsenic atoms distribute themselves throughout the film, presumably with a considerable fraction occupying substitutional sites and electrically active.
Global stability of phase lock near a chaotic crisis in the rf-biased Josephson junction
Authors: Kautz R. L.
Published: July 2002

The global stability of phase lock in the rf-biased Josephson junction is studied through digital simulations. Global stability is determined by calculating the lifetime of the phase-locked state in the presence of thermal noise. This lifetime, the mean time required for thermal noise to induce a 2π phase slip, increases exponentially with inverse temperature in the limit of low temperatures, and the low-temperature asymptote can be parametrized in terms of an activation energy ℰ and an attempt time τ0. The activation energy is a useful measure of global stability for both periodic and chaotic phase-locked states. The behavior of ℰ and τ0 is studied over a range of critical-current densities which take the system from a region of harmonic motion through a period-doubling cascade and into a region of phase-locked chaotic behavior which is ended by a chaotic crisis. At the crisis point, the activation energy goes to zero and the attempt time goes to infinity. The results are used to determine the optimum critical-current density for series-array voltage standards.
A study of the chemical oxide/InP interface by deep-level transient spectroscopy
Authors: Ricard H. , Couturier G. , Chaouki A. , Barriere A. S.
Published: July 2002

Metal-insulator-semiconductor structures prepared by chemical oxidation of the InP surface in HNO3 solutions are studied before and after aging and annealing. One interfacial deep level with an activation energy ΔE=0.4 eV and a capture cross section σ=3.7×10−14 cm2 is observed on a freshly oxidized structure. After aging in air the characteristics of the deep level are ΔE=0.2 eV and σ=6×10−20 cm−2. Annealed aged structures exhibit two interfacial deep levels, one with ΔE=0.4 eV and σ=10−14 cm2 and the other with ΔE=0.2 eV and σ=2.1×10−19 cm2; this latter is located further in the bulk of InP. Some hypotheses are proposed to explain the instability phenomena observed in these devices.
Characteristics of p-GaAs/n-Si heterojunctions grown by molecular-beam epitaxy
Authors: Won T. , Munns G. , Unlu M. S. , Unlu H. , Chyi J. , Morkoç H.
Published: July 2002

We have studied the electrical characteristics of p-GaAs/n-Si heterojunction diodes grown by molecular-beam epitaxy in an effort to investigate the quality of the heterointerface. Both Ga and As prelayers were used to initiate the growth of GaAs epilayers on Si substrates. Current-voltage and capacitance-voltage measurements were made between 300 and 83 K. Ideality factors for heterojunction diodes were as good as n=2.0, despite the 4.1% lattice mismatch between Si and GaAs. At high temperatures the I-V characteristics were dominated by generation-recombination mechanisms that lead to a temperature-independent logarithmic slope with applied bias. By removing a thin layer from the Si surface, the surface leakage current was reduced by more than an order of magnitude. The measured intercept voltages, as determined by capacitance-voltage measurements, have no strong dependence on the type of prelayer used to initiate the growth of the GaAs epilayer on Si substrates. The maximum spread in measured intercept voltages was about 1 V, the absolute value of which depends upon the condition of the interface.
Continuous-wave 25-W Nd3+:glass fiber bundle laser
Authors: Zapata Luis E.
Published: July 2002

For the first time, we have achieved continuous, moderate power operation of a Nd3+:glass fiber bundle laser. The fiber bundle laser consisted of 1450 fibers, each 100 μm in diameter, with 75-μm core phosphate laser glass doped at 8 wt. % Nd2O3. In separate experiments, the laser fiber bundle was energized by either a pulsed xenon flashlamp or a continuous-wave argon arc lamp. A maximum energy of 0.8 J at 4.9-kW peak power was obtained in the pulsed flashlamp experiments whereas a maximum cw power of 25 W was obtained with the arc lamp. Neither the pulsed nor the cw systems were optimized. The beam profile was imaged with low spatial resolution and was found to be lobed. In both experiments, the output was characterized and fitted to a first-order kinetic model. The loss coefficient of 0.00 266 cm−1 was inferred from the model and was found to be 30% higher than measured in the bulk laser material.
Experimental and theoretical studies of an HF chemical laser at low temperatures
Authors: Waichman K. , Chuchem D. , Kalisky Y.
Published: July 2002

The delay time between the initiating pulse and the development of the laser emission pulse for various vibrational transitions in a supersonic HF chemical laser have been measured. The measurements have been performed at various low temperatures by varying the Mach number and stagnation pressure in a supersonic-flow premixed electric-discharge initiated HF laser. The direct measurement of the time development of the lasing P-branch transitions as a function of temperature are compared to a theoretical model which yields information on the F+H2 reaction rates.
Plasma chemical aspects of magnetron ion etching with CF4/O2
Authors: Bright A. A. , Kaushik S. , Oehrlein G. S.
Published: July 2002

Magnetron plasmas are of great current interest for semiconductor manufacturing applications because of their high ion density and low operating pressure. We have studied the properties of a magnetron ion etching system using CF4 and CF4/O2 with respect to the plasma chemistry and the interaction of the plasma with both the etched substrate and the chamber walls. The higher dissociation and ionization rates lead to significant changes in the species present in the plasma as compared to a conventional reactive ion etching (RIE) plasma. The F atom concentration in a CF4 magnetron plasma is much higher than in a RIE plasma. The addition of O2 leads to only a small further enhancement and produces a decrease in the Si etch rate. The highly dissociated species in the magnetron plasma produce less C-F polymer, both on the wafer and on the chamber walls, relative to RIE. Sputtering of Al from the electrode produces a substantial deposit of AlFx on the chamber walls, but not on the wafer.
Electrical conduction and dielectric breakdown in sputter-deposited silicon dioxide films on silicon
Authors: Suyama S. , Okamoto A. , Serikawa T. , Tanigawa H.
Published: July 2002

Silicon dioxide films, 8–100 nm thick, are sputter deposited in an oxygen-argon atmosphere onto a silicon substrate at 200 °C. Electrical conduction and dielectric breakdown in oxygen-argon sputter-deposited film are measured using metal-oxide-semiconductor capacitors and compared with those in thermal dioxide film. Moreover, their mechanisms are investigated. Thin oxygen-argon sputter-deposited film is found to have the same low electrical conduction and high dielectric breakdown as thermal dioxide film. Electrical conduction through oxygen-argon sputter-deposited film shows small temperature dependence and Fowler–Nordheim characteristics. For a wide range of film thickness, the breakdown field in oxygen-argon sputter-deposited film correlates well with that in thermal dioxide film and with the impact ionization/recombination model. Thus, the electrical conduction mechanism through oxygen-argon sputter-deposited silicon dioxide film is Fowler–Nordheim tunneling, and dielectric breakdown is explained by the impact ionization/recombination model.
A two-body model for dielectric relaxation in polar liquids
Authors: Marchesoni Fabio
Published: July 2002

A microscopic two-dipole model for dielectric relaxation is proposed which is invoked to explain the absorption spectra of polar liquids. The permanent electric dipole of the tagged molecule interacts locally with the dipole of the nearest-neighbor cage. The two dipoles are coupled by a nonlinear potential and subject to independent random torques simulating the action of the surroundings. The assumption that the cage momentum of inertia is much larger than that of the tagged molecule leads to an entirely diffusive mechanism for dielectric loss.
Liquid-phase-epitaxial regrowth in the GaInAsP system
Authors: Logan R. A.
Published: July 2002

Using In1−xSnx melts saturated with InP, the P overpressure used to protect InP from thermal decomposition during heat treatment prior to growth can be adjusted and optimized. The achievement of uniform, defect free growth on the difficult to wet {111}In plane of InP is shown to be a sensitive measure of the correct P overpressure. Using simultaneous growth from two independent melts, it is shown that quaternary GaInAsP of any lattice matched composition gives superior growth on InP compared to InP growth under the same conditions. For regrowth on quaternaries, care must be taken in the P source design so that there is no line of sight direct path from the source to the substrate. This would permit spattering of micron size source particles that wet and migrate on the quaternary surface giving large local defects in subsequent growth.
Mössbauer spectroscopy of Sn-doped GaAs grown by metalorganic vapor-phase epitaxy
Authors: Williamson D. L. , Gibart P. , El Jani B. , N’Guessan K.
Published: July 2002

GaAs epitaxial layers, doped with 119Sn-enriched tin, have been grown by metalorganic vapor-phase epitaxy (MOVPE). 119Sn Mössbauer spectroscopy and Hall measurements have been used to characterize the layers. Three tin species are observed in the as-grown material. One of these is identified as the SnGa shallow donor site and another is associated with electrically inactive Sn sites that may be SnGaSnAs pairs or Sn3As2-like clusters or microprecipitates. The free carrier concentrations (Nd−Na) obtained from the Hall data agree quantitatively with the concentrations of SnGa sites from the Mössbauer data for samples prepared with MOVPE Sn/Ga ratios up to 0.02 and Nd−Na <6×1018 cm−3, thereby showing no evidence for compensation up to this doping level. Annealing under arsine creates an acceptor species which is identified as SnGaVGa. High-energy electron irradiation may also produce this compensating acceptor species.
CdTe photoluminescence in HgTe-CdTe superlattices
Authors: Feldman Bernard J. , Wroge M. L. , Leopold D. J.
Published: July 2002

We report photoluminescence in HgTe-CdTe superlattices that originates in the CdTe layers. We see a near-band-gap line at 1.493 eV, which demonstrates that strain and Hg-Cd substitutional diffusion are small in the CdTe layers. In addition, a deep-level line at 0.775 eV, possibly due to recombination along dislocation lines, is observed.
Analytical model of the modulation doped field-effect transistors including electron diffusion and drift velocity saturation
Authors: Grinberg A. A.
Published: July 2002

An analytical modulation doped-field-effect transistors model including field-dependent mobility and diffusion transport of the electrons in the gradual channel approximation is proposed. Current-voltage characteristics are obtained in the parametric form. An explicit form of the I-V characteristic is deduced for a subthreshold region of the device operation. The influence of the velocity saturation and diffusion on the current flow is analyzed. It is shown that diffusion plays an important role in the entire region of I-V characteristic. It follows from the model that in the final stage of current saturation the latter is governed by the process of diffusion, and change of the current does not depend on the value of the saturated velocity.
Models for heavy doping effects in gallium arsenide
Authors: Bennett Herbert S. , Lowney Jeremiah R.
Published: July 2002

Klauder’s self-energy method is used in a self-consistent calculation of the effects due to the interactions between carriers and dopant ions in GaAs at 300 K. The many-body effects due to the interactions among the carriers themselves, exchange, and correlation, are estimated by evaluating expressions similar to those of Abram et al. at 300 K. When densities exceed about 5×1016 cm−3 in n-type GaAs and 1018 cm−3 in p-type GaAs, carrier-dopant ion interactions and carrier-carrier interactions become significant and should be included in calculations of band structure changes and of properties which depend on the density of states such as carrier transport, effective intrinsic carrier concentrations, and coefficients for optical absorption.
Fission fragment pumping of a neon plasma
Authors: Moratz Thomas J. , Kushner Mark J.
Published: July 2002

A method for calculating excitation and ionization rates in a plasma generated by the slowing of fission fragments in a gaseous medium (neon) is presented. The energy distribution of the fission fragments as they slow down, and the excitation and ionization of neon due to collisions with the fission fragments, are discussed. Effective W values for ionization and excitation of neon directly by the fission fragments of uranium (71.6 and 110 eV) are derived. The source function for electrons produced by direct ionization by the fission fragments is discussed and compared to that produced by an e beam. The source function of electrons produced by heavy ions has the lower average energy.
Low interface state density SiO2 deposited at 300 °C by remote plasma-enhanced chemical vapor deposition on reconstructed Si surfaces
Authors: Fountain G. G. , Rudder R. A. , Hattangady S. V. , Markunas R. J. , Lindorme P. S.
Published: July 2002

A 300 °C process has been used to deposit high-quality SiO2 on Si. The process is based on remote plasma-enhanced chemical vapor deposition. In this process excited species from a remote oxygen plasma interact with silane in the deposition zone. A hydrogen plasma is used to clean the silicon surface in situ just prior to deposition. After a 400 °C post-metallization anneal, interface-state densities as low as 3.7×1010 cm−2 eV−1 were measured with a fixed charge density of 2×1011 cm−2. The films exhibited good breakdown integrity, sustaining fields of 9–10 MV cm−1. The Si/SiO2 interface-state density directly correlates with the quality of reflection high-energy electron diffraction patterns from the silicon surface just prior to oxide deposition.