bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation of crystallites in piezoelectric poly(vinylidene fluoride)
Authors: Kupferberg Lenn C.
Published: July 2002

The distribution of the orientation of the b and c axes of crystallites in the piezoelectric polymer, poly(vinylidene fluoride), is inferred from the distribution (with varying sample orientation) of diffracted x-ray intensity of the (111) and (001) reflections. Measurements of drawn and poled samples are reported, and results from these measurements as well as those for rolled material are analyzed. The c axes of the crystallites are narrowly distributed about the drawing (or rolling) direction. The b axes are broadly disturbed in the plane perpendicular to the drawing (rolling) direction. The effects of drawing, rolling, poling, and thermal aging upon the distribution of crystallite orientations are discussed. The distribution of dipole orientations and the resulting net polarizations are calculated, using fast Fourier transforms to deconvolve the diffraction data. A model is proposed, for the distribution of the b axes, and is found to fit the data well in most cases. The correlation between the alignment of crystallographic axes and the piezoelectric constants is discussed. Possible improvement in the net polarization of the polymer of a factor of 2 is suggested.
An x-ray diffraction line profile analysis on the microstructure of cold-worked face-centered-cubic Cu-Mn-Si alloys: Effects of Mn and Si as solutes
Authors: Pradhan S. K. , De M.
Published: July 2002

In continuation of our earlier investigations on the microstructures of cold-worked Cu-(Sn,Ni,Mn)-Zn ternary alloys by x-ray diffraction line profile analysis [J. Appl. Phys. 54, 6652 (1983); ibid. 48, 3560 (1977); ibid. 56, 1213 (1984)] the present work with Cu-Mn-Si alloy system in the fcc phase has been undertaken to elucidate the effects of Mn and Si, when present together, on the cold-worked substructure of this system. From detailed analyses of peak shift, peak asymmetry, and Fourier line shapes, quantitative estimates of the related microstructural parameters, namely, intrinsic (α′), extrinsic (α″), and twin fault (β) probabilities, domain sizes, rms strain, dislocation density, and stacking fault energy (for pure Cu), have been made. The results indicate, as in the earlier cases, increased presence of intrinsic stacking faults (α′)—primarily responsible for the observed peak shift and domain size broadening with relatively small presence of extrinsic faults (α″) and complete absence or very small presence of deformation twins (β) responsible for the observed asymmetry in the profiles. Unlike earlier observations, the presence of transitional solute Mn along with nontransitional Si as another solute appears to have a pronounced effect on the stacking fault probability of the present Cu-base alloys in the fcc phase.
Fabrication of dry-etched cavity GaAs/AlGaAs multiquantum-well lasers with high spatial uniformity
Authors: Yamada Tomoyuki , Yuasa Tonao , Asakawa Kiyoshi , Shimazu Mitsuru , Ishii Makoto , Uchida Mamoru
Published: July 2002

In order to obtain dry-etched lasers with high spatial uniformity, the relation between the etching profile and the laser structure is investigated in detail for two types of GaAs/AlGaAs multiquantum-well lasers, with and without selective Zn diffusion, with reactive-ion-beam-etched facets. It is found that a laser structure with an abrupt step on the surface locally roughens the facets during etching through the generation of etching residues on the etched bottom. Such an abrupt step on a wafer can be typically introduced by the conventional selective Zn-diffusion process including surface chemical treatment. The etched lasers fabricated with the selective Zn-diffusion process show a wide distribution in the threshold current. In contrast, the lasers without the selective diffusion process realize a narrow distribution in the theshold current.
A theoretical model of lateral photoeffects in amorphous materials
Authors: Chen Inan
Published: July 2002

A recent observation of the lateral photoeffect in multilayers of amorphous silicon and titanium has renewed the interest in this phenomenon. In this communication, a theoretical model of the effect is developed for a quantitative understanding of the effect and to assess the potential of its applications in large area electronic devices. The model has been specifically developed for the case of lateral photoeffect in amorphous materials. In addition to reproducing the observed unique features of the effect, the model quantitatively specifies the requirements on the transport parameters, in particular the carrier diffusion lengths, for the observation of a significant lateral photoeffect in macroscopic scale.
Some properties of bulk Y-Ba-Cu-O compounds containing SiO2
Authors: Qiu C. X. , Shih I.
Published: July 2002

Bulk Y-Ba-Cu-O samples containing Si with nominal compositions of Y:Ba:Cu:Si=1:2:3:x (x=0.2, 0.4, and 0.6) have been prepared by adding SiO2 to the source materials. After a relatively short heat treatment, the resistance transition characteristics of the samples were found to improve as the SiO2 content was increased. Results from ac susceptibility measurements also showed improved values as the SiO2 content was increased. However, as the solid-state reaction was carried out at a lower temperature but for a longer time, the sample resistance increased and the superconductivity was found to degrade.
Two-beam laser recrystallization of polycrystalline silicon on an insulating substrate
Authors: Dasgupta Samhita , Jackson Howard E. , Boyd Joseph T.
Published: July 2002

A novel two-laser technique has been investigated for recrystallizing polycrystalline silicon deposited on an insulating substrate. An Ar+ laser and a CO2 laser have been scanned simultaneously to perform the recrystallization of unpatterned samples and samples patterned with antireflection stripes. The use of the two beams enabled recrystallization without the use of a substrate heater, and resulted in grain widths a factor of 2 larger than those obtained with the more conventional technique using an Ar+ laser only. A Raman microprobe analysis revealed that the stress in the two-beam recrystallized material was about an order of magnitude less than found in Ar+ laser recrystallized material. The polarization dependence of the Raman scattered light indicated that the orientation of the recrystallized material between antireflection stripes was in a 〈100〉 orientation.
Deposition of a Si monolayer on sapphire using an ArF excimer laser for Si epitaxial growth
Authors: Ishida M. , Tanaka H. , Sawada K. , Namiki A. , Nakamura T. , Ohtake N.
Published: July 2002

Si monolayer deposition on sapphire substrates was investigated by in situ x-ray photoelectron spectroscopy (XPS). Si deposition was carried out using direct photolysis of Si2H6 by irradiation of 193 nm ArF excimer laser light (1–2 W/cm2 , 70 Hz) at room temperature in a high-vacuum chamber. At first, decomposed Si atoms bound strongly with O atoms on sapphire until the entire sapphire surface was covered, then SiSi bonds were formed. From the growth mode analysis of the early stage of Si deposition, it can be seen that the growth mode of the deposited layer is a layer-by-layer mode (the Frank–Van der Merwe-type growth). The thickness of the deposited Si layers can be controlled on an atomic scale. As these features are suitable for Si-on-sapphire (SOS) epitaxial growth with predeposited layers, SOS epitaxial growth was demonstrated and the SOS films were characterized by replica electron microscopy and fabricating a metal-oxide-semiconductor field-effect transistor.
Thermal decomposition mechanism of triple carbonate (Ba,Sr,Ca)CO3
Authors: Takamori Takeshi , Boland John J.
Published: July 2002

The thermal decomposition mechanism of the triple carbonate (Ba,Sr,Ca)CO3 is shown to proceed in a single step from the carbonates to the corresponding oxides under the condition where the decomposition itself is rate limiting. When the decomposition occurs under a high local CO2 pressure, it appears to proceed in two steps due to a subsequent recombination reaction between the CO2 and the oxides. The carbonates initially decompose into an x-ray amorphous oxide which upon further heat treatment yields a solid solution oxide (Ba,Sr,Ca)O. The exact nature of this x-ray amorphous oxide is uncertain but hydration experiments support it being either a microcrystalline or structurally disordered solid solution.
Space-charge behavior near implanted contacts on infrared detectors
Authors: Haegel Nancy M.
Published: July 2002

A phenomenological model for the steady-state distribution of electric field and potential near an implanted contact on a low-temperature infrared detector is presented. The model assumes a linear distribution of trapped space charge and calculates the resulting electric field gradient and potential barrier that are established. The change in these distributions for changes in incident photon flux, applied electric field, or compensating donor concentration is determined. An increase in photon flux under constant applied electric field results in no change in the space-charge distribution for low-field situations. A change in field for constant flux conditions, by contrast, results in a change in potential barrier width and height. These results indicate that transient phenomena should be strongly dependent on operating conditions and may explain why a wide range of apparently unrelated transient phenomena are observed in practice.
Influence of surface defects on the characteristics of high electron mobility transistors grown by molecular-beam epitaxy
Authors: Nakamura Tomohiro , Nanbu Kazuo , Ishikawa Tomonori , Kondo Kazuo
Published: July 2002

Surface defects on layers grown by molecular-beam epitaxy were classified, and their effect on high electron mobility transistor characteristics was studied. The defects originating from the Ga source consist of cores and hillocks. These defects had a strong influence only when their cores were located in the gate region. They decreased the transconductance and K value significantly and shifted the threshold voltage to the negative direction. This indicates the cores are highly conductive. The other defects, originating from substrate surface contamination, slightly decreased the K value and transconductance while increasing the deviation in the threshold voltage.
The influence of water on the annealing behavior of midgap traps at the silicon oxide-silicon interface
Authors: Burte Edmund P. , Matthies Pamela
Published: July 2002

The annealing of interface traps in silicon oxide-silicon structures has been studied using forming gas with three levels of water concentration. The samples were annealed at 450 °C without gate and, for comparison, with an aluminum gate present on top of the silicon oxide layer. The density of interface traps at the midgap was lower with the higher level of water concentration in the atmosphere of the tube.
Self-aligned Si-Zn diffusion into GaAs and AlGaAs
Authors: Zou W. X. , Corzine S. , Vawter G. A. , Merz J. L. , Coldren L. A. , Hu E. L.
Published: July 2002

A practical technology for self-aligned Si-Zn diffusion into GaAs and AlGaAs has been developed. It is found that the use of a Si film alone for self-aligned Si-Zn diffusion is subject to serious problems of morphology degradation and doping contamination during the process of the Si diffusion. A procedure combining the use of a SiO2 film as an encapsulant with a sputtered Si film as source for Si diffusion and mask for Zn diffusion is investigated in detail. Optimum thicknesses of the Si and SiO2 films are determined to be 180 and 550 Å, respectively.
Diffusion studies of the Si δ-doped GaAs by capacitance-voltage measurement
Authors: Chiu T. H. , Cunningham J. E. , Tell B. , Schubert E. F.
Published: July 2002

Using triethylgallium and arsine, high-quality GaAs can be grown at a relatively low substrate temperature of 500 °C by chemical beam epitaxy. Such a low temperature has the advantage of a negligible Si diffusion effect. Capacitance-voltage (C-V) measurements of the Si δ-doped GaAs show extremely narrow profile widths of 22 Å at 300 K and 18 Å at 77 K, indicating a very high degree of Si spatial localization has been achieved. The subsequent annealing experiments reveal that significant Si segregation and diffusion exist at a high growth temperature of ∼600 °C, usually employed in conventional molecular-beam epitaxy. The C-V widths of the annealed δ-doped structures also provide an excellent measure to determine the Si diffusion constant in GaAs.
A thermionic energy converter with polycrystalline molybdenum electrodes
Authors: Gubbels G. H. M. , Wolff L. R. , Metselaar R.
Published: July 2002

A research diode with polycrystalline molybdenum electrodes is described. Voltage-current characteristics are presented as a function of the cesium reservoir temperature. A power density of 4 W/cm2 is obtained at an emitter temperature of 1400 °C. The influence of the temperatures of the emitter, collector, and cesium reservoir and of the interelectrode distance is experimentally investigated. Physical explanations for the various effects are given. The work function of the polycrystalline molybdenum emitter in a cesium atmosphere is evaluated as 2.5–2.7 eV depending on the reduced emitter temperature (i.e., the emitter temperature divided by the cesium reservoir temperature). A barrier index Vb =2.0 eV and a cesium plasma drop Vd =0.4 eV are found.
Gain suppression in semiconductor lasers: The influence of dynamic carrier temperature changes
Authors: Gomatam Badri N. , DeFonzo Alfred P.
Published: July 2002

An analytic expression for the gain suppression coefficient of semiconductor laser in terms of carrier temperature and other material parameters is presented. The expression is derived from a density matrix formulation of gain in diode lasers based on a dynamic carrier heating model. We find that in the single mode approximation the theoretical estimate of the gain suppression coefficient is of the order 10−23 m3 in agreement with experimental values. This supports recent direct experimental demonstrations that dynamic carrier heating, rather than spectral hole burning provides the dominant contribution to nonlinear gain in semiconductor lasers.
Effect of substrate materials in the growth of ZnSe on GaAs and GaP substrates
Authors: Imai Tetsuji , Fuke Shunro , Izawa Makoto , Kuwahara Kazuhiro
Published: July 2002

ZnSe layers were grown on GaP and GaAs substrates by hydrogen-transport vapor-phase epitaxy. The influences of the substrate materials upon the growth rate and the lattice parameter of the ZnSe layers were studied. The ZnSe lattice parameter normal to the heterointerface was measured by using x-ray diffraction. In the case of the growth on the (100) plane, a larger growth rate and better crystallinity on GaAs were obtained compared with growth on GaP. This strongly suggests that misfit strain together with dislocation formation is quite harmful to the growth of high-quality heteroepitaxial layers. The layers were considered to be strained compressively in the normal direction to the heterointerface by thermal stress.
rf suppression of E×B drift driven ion-cyclotron modes in a plasma
Authors: Praburam G. , Jain V. K.
Published: July 2002

Ion-cyclotron instabilities driven unstable by E×B drift in a low-pressure beam produced plasma are shown to be stablilized by lower hybrid pump waves under certain parameter conditions. Suppression is due to a ponderomotive force which shifts the frequency towards the cyclotron harmonics, thus increasing ion-cyclotron damping.
Observation of radiation defects generated in edge defined film fed growth silicon ribbons under 400 kV irradiation in the high-resolution electron microscope
Authors: Katcki Jerzy , Ast Dieter
Published: July 2002

Irradiation of edge defined film fed growth silicon in the 400 kV HREM generates two kinds of radiation defects. The first ones are {113} planar faults which appear both as single defects and in more complicated arrangements (‘‘snaking ribbons,’’ crossing defects). When a {113} defect encounters a twin boundary at an angle close to 80° the defect penetrates the boundary and continuous on the mirror symmetric {113} plane. Defects generated inside a twin band at an inclination of 30° are not able to penetrate the boundary. This difference can be explained by considering the size of the residual defects left in the boundary. The second type of defects are {111} defects which appear as single defects or in groups. The {111} defects are nucleated exclusively on the outside of twin bands but in wider twins they also form inside. This finding can be explained by considering the interaction between the interstitial, which is an extended defect and the twin boundary, which is a planar defect in which higher-order nearest-neighbor distances are reduced.
Implantation tailoring of electrically active dopant profiles in GaAs
Authors: Short K. T. , Pearton S. J. , Wu C. S.
Published: July 2002

A common problem with fabricating n-type layers in semi-insulating GaAs by ion implantation is the variation in the net activation efficiency on the substrate side of the implanted dopant profile. We compare two methods for modifying these doping profile tails in order to achieve uniform activation properties of implanted layers over large wafer areas. The two methods are compensation of an n-type doping profile by a buried damage layer (oxygen or helium implants) or by coimplantation of an acceptor species (beryllium). Experimental results are shown both for n-only and n+-n profile modifications. The use of Be to form a buried p-type layer has several advantages over the damage-induced compensation.
Channel length dependence of the 1/f noise in silicon metal-oxide-semiconductor field-effect transistors. II. Verification of the acceleration 1/f noise process
Authors: Peng Q. , Birbas A. N. , van der Ziel A. , van Rheenen A. D. , Amberiadis K.
Published: July 2002

A systematic study of the 1/f noise dependence on the channel length in p- and n-channel silicon MOSFETs (metal-oxide-semiconductor field-effect transistors) is presented. Devices made by the same procedure on the same chip were used. In this way, the nonuniformity of noise sources, which strongly depend on the fabrication procedure (like 1/f noise produced by surface trapping), was avoided. Hooge’s parameter αH was used as a measure of the magnitude of the 1/f noise in the device. The αH was found to vary as the square of the channel length in p MOSFETs and in the most of the n MOSFETs. Existing theories and known noise mechanisms do not explain this dependence. The incorporation of a recent theory involving the acceleration 1/f noise in semiconductors, developed by van der Ziel, explains the experimental data very well. The αH was found to be independent upon the electric field and the extraction of an effective time constant was used for comparison between theory and experiment.
Transport properties of hexagonal and tetragonal MoSi2 thin films
Authors: de Vries J. W. C. , van Ommen A. H.
Published: July 2002

The electrical resistivity and the Hall coefficient of thin polycrystalline MoSi2 films were measured as a function of temperature from 4.2 to 300 K. The transverse and longitudinal magnetoresistances have been determined at temperatures between 2 and 50 K at fields up to 10 T. Samples of both the high-temperature tetragonal MoSi2 phase and the low-temperature hexagonal phase have been prepared. The Hall coefficient of tetragonal MoSi2 changes sign with temperature, which means that this compound is a multiband conductor, and thus no reliable value for the carrier concentration can be derived from Hall measurements alone. Magnetoresistance data have therefore been analyzed with a simple two-band model in order to determine the dominant carrier type in both MoSi2 structures. In tetragonal MoSi2, electrons and holes are present in equal concentrations, whereas in hexagonal MoSi2 holes are the dominating type of carrier.
Influence of stress on high coercive force of γFe2O3-Fe3O4 thin films
Authors: Langlet M. , Joubert J. C.
Published: July 2002

Strongly coercive films of γFe2O3-Fe3O4 solid solution [xFe8/3O4-(1−x)Fe3O4] have been deposited using a new pyrolysis technique. The magnetic and crystallographic properties of nonoxidized Fe3O4 (x=0) and completely oxidized γFe2O3 (x=1) films are shown to be closely related to the planar stress present in the films. An x-ray method is proposed for the study of the iron oxide film stress. The different results are applied to understand the origin of the strong coercive force of partially oxidized solid solution films.
Mean electronic resonant wavelength of liquid crystals
Authors: Wu Shin-Tson
Published: July 2002

Mean electronic resonant wavelength of some single substance liquid crystals obtained by ultraviolet transmission spectrum and by wavelength dependent birefringence agrees very well. Both ground and higher state π→π* electronic transitions are found to make a major contribution to the observed birefringence of those liquid crystals containing delocalized π electrons. The role of the σ→σ* electronic transitions may or may not be significant, depending on the liquid crystal composition.
High-power laser beam guidance in periodic system of lenses with holes
Authors: Zakowicz Wladyslaw , Bledowski Aleksander
Published: July 2002

A periodic system of lenses with central holes can confine and guide laser beams with small diffraction losses. In the fundamental mode an intensive part of the laser beam can be concentrated in the holes and the system may be used for high-power beams.
Normal emittance measurements by a transient temperature technique
Authors: Tiernan Robert J. , Saunders James E.
Published: July 2002

Normal spectral emittance measurements from 5000 to 400 cm−1, and normal total emittance measurements, were made for sapphire and polycrystalline aluminas using Fourier-transform infrared spectroscopy. Samples were dropped from a furnace into the nitrogen ambient of the spectrometer to the position where the internal global source is normally focused. Radiance was measured as the alumina cooled to derived emittances from 900 to 1450 K. The temperatures were determined from radiance measurements at 1027 cm−1 where alumina has zero reflectivity and transmittance. Standard deviations of total normal emittance measurements averaged over three drops were ≤0.3% of the averages.
Degradation behaviors of buried heterostructure InGaAsP/InP distributed feedback lasers grown by liquid-phase epitaxy
Authors: Fukuda M. , Suzuki M. , Motosugi G. , Ikegami T. , Yoshida J.
Published: July 2002

Some degradation modes of 1.3 and 1.55 μm buried heterostructure distributed feedback (DFB) lasers grown by liquid-phase epitaxy are clarified. A degradation mode induced by the inhomogeneous optical-field distribution along the laser cavity is found to exist in DFB lasers. In most DFB lasers, the interface degradation between first growth-step (double heterostructure) layers and second growth-step (burying) layers occurs in the same manner as Fabry–Perot lasers.
Ultraviolet photoionization in CO2 TEA lasers
Authors: Scott S. J. , Smith A. L. S.
Published: July 2002

The factors affecting spark ultraviolet (UV) emission and transmission, photoionization, and photoelectron loss mechanisms in CO2 TEA laser gas mixtures have been investigated and compared with the results of other workers. We found two different sources of UV radiation: N2 and an unidentified emitter, postulated to be associated with ionized electrode material; C (from CO and CO2) appeared to have little effect. UV emission was directly proportional to the amount of stored electrical energy in the spark-discharge circuit and to the cube of the peak current produced by the discharge of this energy. The uniformity of preionization produced by two kinds of spark-free space and notched surface guided was examined and the free-space spark was found to be superior. Photoionization was found to be due to the presence of low ionization potential (IP) alkenes in unseeded and fresh gas mixtures and also to NO and NO2 in sealed devices—these were formed as a result of spark plasma reactions. The nature of the photoionization process in NO and C3H6 (an alkene) was investigated; both were ionized in a single-step process. The absorption coefficient for ionizing radiation in CO2 was measured in a gas mixture containing 9% N2 and a N2 free mixture and values of 1.3 and 1.9 cm−1 atm−1 were obtained. It is thought that this may be due to changes in the spark UV emission spectrum when N2 is present. The loss of photoelectrons by third body attachment to NO, NO2, and O2 was monitored and only the attachment to O2 was found to be significant. However, the oxides of N can play a dominant role in the subsequent negative ion reactions on a millisecond timescale.
Electroreflectance and wavelength-modulated reflectivity measurements of Zn1−xMnxTe mixed crystals
Authors: Stankiewicz Jolanta
Published: July 2002

Electroreflectance and wavelength-modulated reflectivity data near the fundamental absorption edge of Zn1−xMnxTe solid solutions are presented as a function of temperature and Mn content. From these data the dependence of the energy gap on temperature and composition was determined. The broadening of electroreflectance and wavelength-modulated reflectivity structures is found to depend linearly on [x(1−x)]2 at low temperatures. This indicates that the broadening is produced primarily by the random distribution of Mn and Zn atoms in the lattice.
The effects of gas ambients on the formation of surface and bulk defects in silicon
Authors: Kang J. S. , Schroder D. K.
Published: July 2002

The effects of gas ambients on the density of oxide precipitates and stacking faults have been studied in samples annealed in various gas ambients. It is found that the densities of oxide precipitates and bulk and surface stacking faults in oxynitrided samples are higher than those of samples annealed in oxygen, nitrogen, trichloroethane plus oxygen, and pure ammonia. Also, stacking faults have been observed at the surface of the samples annealed in an ammonia ambient. These observations are contrary to our expectations, and several models are proposed to explain the phenomena.
Photorefractive measurement of photoionization and recombination cross sections in InP:Fe
Authors: Valley George C. , McCahon Stephen W. , Klein Marvin B.
Published: July 2002

The photorefractive effect combined with standard Hall measurements is used to determine photoionization and recombination cross sections and deep-level number densities in a crystal of iron-doped InP. The results are well fit by iron densities [Fe2+]=6×1016 cm−3 and [Fe3+]=2.5×1015 cm−3, photoionization cross sections at 1.06 μm, se= 4×10−18 cm2, and sh= 3.1×10−16 cm2, and recombination cross sections σe= 10−14 cm2 and σh= 3×10−16 cm2. The sign of the photorefractive beam coupling gain implies that holes dominate this process even though the dark conductivity and photoconductivity are dominated by electrons.
Carrier separation effect in single-layered-compensated amorphous silicon
Authors: Jang Jin , Kim Sung Chul , Lee Choochon
Published: July 2002

In this paper we find the microscopic mechanism of persistent photoconductivity in doping-modulated amorphous silicon superlattices is the same as that of compensated amorphous silicon. The carrier separation due to a built-in n-p junction field can explain persistent photoconductivity in compensated amorphous silicon films. This new analysis is favored by experimental results on the persistent photoconductivity in compensated as well as in layered amorphous silicon films.
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u optical reflectance studies in electrochemically intercalated graphite films and characteristics of a color-switching cell utilizing the change of plasma reflection
Authors: Nogami Kou , Ueno Hideki , Yoshino Katsumi
Published: July 2002

Li and K have been electrochemically intercalated into graphite films prepared by pyrolysis of poly(p-phenylene vinylene) films. Sharply defined plasma edges at 1.3 eV for Li intercalation with green luster and 0.8 eV for K intercalation with blue luster were found by in situ optical reflectance measurement. These reflectance spectra are explained by taking both metallic plasma reflection and an interband transition into consideration. A color-switching cell has been constructed utilizing the change of the plasma reflection by electrochemical intercalation, and a response time as short as 50 ms has been obtained in the cell using K intercalation.
Influence of stoichiometry on the electrical activity of impurities in Hg(1−x)Cd(x)Te
Authors: Capper P. , Roberts J. A. , Kenworthy I. , Jones C. L. , Gosney J. J. G. , Ard C. K. , Coates W. G.
Published: July 2002

Elements from groups IB, IIIB, VB, and VIIB have been added to crystals of Hg(1−x)Cd(x)Te grown using the accelerated crucible rotation technique. Assessment on both as-grown and annealed (in Hg vapor) samples was carried out using Hall effect measurements to establish the electrical activity and stability of each dopant. Chemical analysis by atomic absorption spectroscopy and laser scan mass spectrometry determined the total levels of dopants in each crystal. The behavior of dopants in these crystals is compared to that found in Bridgman and epitaxial material and discussed in terms of the stoichiometry of melts and crystals at the growth temperature. It is concluded that group VB and VIIB elements are prevented from occupying Te sites when there is a high Hg vacancy concentration present during growth. Gold, which is inactive in Bridgman material, is found to be an active acceptor in a crystal grown using the accelerated crucible rotation technique. Group IB and IIIB elements are acceptors and donors, respectively, on metal sites irrespective of stoichiometry.
Effects of target temperature on crystallinity and hardness of B+-implanted Fe
Authors: Hirano Motohisa , Miyake Shojiro
Published: July 2002

Pure Fe is implanted with B+ in a target temperature range of −20–300 °C. The effects of the target temperature on the crystallinity and hardness of the B+ -implanted Fe are investigated. It is found that Fe2 B is formed by using direct B+ implantation into pure Fe at target temperatures ranging from −20 to 300 °C without subsequent annealing. ‘‘Cold-implantation,’’ i.e., implantation at a lower target temperature, reduces crystallinity and increases the hardness of the B+ -implanted Fe. By contrast, increased target temperature produces B+ -implanted Fe with high crystallinity and relatively low hardness. Discussion focuses on how the target temperature during implantation affects the crystallinity of the B+ -implanted Fe from the standpoint of the recrystallization during implantation.
Influence of dislocations and annealing cap on the electrical activation of silicon implanted in semi-insulating GaAs: Implications for field-effect transistors
Authors: Morrow Richard A.
Published: July 2002

Numerous studies have shown that the threshold voltage (Vth) of field-effect transistors fabricated on Czochralski-grown semi-insulating GaAs substrates using silicon ion implantation is sometimes dependent and sometimes independent of proximity to dislocations, according to the processing method used. We present a comprehensive model that reconciles these diverse observations and semiquantitatively describes the dependence of Vth on EL2 concentration, boron concentration, silicon fluence, proximity to a dislocation, and post-implant annealing method. Under conditions holding in most of the cited studies, silicon fluence between 2×1012 cm−2 and 5×1012 cm−2 at 60 keV followed by an anneal with a SiN cap, we find that Vth depends on the substrate concentration of EL2 and on the concentration of the boron-silicon acceptor complex BGaSiAs. We suggest that a nonuniform stress field across a wafer reduces the binding energy of BGaSiAs complexes within 50 μm of a dislocation resulting in a local increase in silicon activation and a more negative Vth. When the post-implant anneal is done under a SiO2 cap we suggest that the infusion of VGa due to the out-diffusion of Ga eliminates the stress field nonuniformities and results in Vth showing no dislocation-proximity effect. Under these latter conditions we find that any variation in local substrate EL2 concentration across the wafer is reflected in a variation of Vth.
Minority-carrier lifetime measurements and defect-structure identification for gallium arsenide grown on sapphire by organometallic vapor phase epitaxy
Authors: Timmons M. L. , Ahrenkiel R. K. , Al-Jassim M. M. , Dunlavy D. J.
Published: July 2002

The minority-carrier lifetime in n-type GaAs-on-sapphire structures has been measured by transient laser-induced photoluminescence. Single- and double-heterojunction structures grown by organometallic vapor phase epitaxy have been examined and yield values of lifetime between 0.1 and 0.4 ns. Transmission and scanning electron microscopic analyses of layers show that the best surfaces and lowest defect densities resulted from isothermal growth at 690 °C. Threading dislocations in the range of 5×107 to 6×108 cm−2 are observed in GaAs grown on (0001)-oriented sapphire substrates.
Magnetostriction of 3d-transition metal/noble metal compositionally modulated multilayer films
Authors: Awano H. , Taniguchi O. , Katayama T. , Inoue F. , Itoh A. , Kawanishi K.
Published: July 2002

Young’s modulus (Ef), magnetostriction (λf), stress (σ), and stress-induced anisotropy (Ks) were measured in Co/Cu, Fe/Cu, Co/Ag, Co/Pd, and Co/Au compositionally modulated multilayer films (CMF) prepared by rf sputtering method. The measured values of Ef are almost equivalent to those of noble metals of Cu, Ag, Pd, and Au, respectively. The values of λf have an order of 10−5–10−6 which is the same order of the values in Co and Fe films. The calculated values of Ks from these results are about 10 to 100 times smaller than the measured values of perpendicular anisotropy (Ku) in the CMFs. Consequently, these results suggest that Ku of transition metal/noble metal CMFs cannot be explained only in terms of the stress-induced anisotropy.
Muon spin relaxation studies on high-T
C superconductors and related antiferromagnets (invited)
Authors: Uemura Y. J.
Published: July 2002

Muon spin rotation and relaxation (μSR) techniques have been applied to high-TC and related systems. In the antiferromagnets La2CuO4−y and YBa2Cu3O6.0–6.4, the muon precession frequency in zero field indicates that the microscopic static ordered moments do not change much despite drastic decrease of the Néel temperature with increasing oxygen content. In the family systems of the new three-dimensional superconductor (BaK)BiO3, no signature of static magnetic order was found by μSR, in sharp contrast to the two-dimensional systems with CuO planes. In the superconducting specimens La1.85Sr0.15CuO4 and YBa2Cu3O6.5–7.0, the magnetic field penetration depth λ was determined from the muon spin relaxation rate σ measured in transverse external magnetic fields. The temperature dependence of λ indicates a predominantly finite energy gap. The systematic variation of λ leads to an approximately linear relation TC∝σ∝1/λ2∝ns/m* between the transition temperature TC and the carrier density ns, which suggests a high-energy scale for the pairing interaction.
Image processing system for magnetic domain observation
Authors: Okuno H. , Murai H. , Sakaki Y.
Published: July 2002

This research presents the design and results of an image processing system for static and dynamic observation of magnetic domains. The technique is based on the use of a polarizing microscope, a CCD camera, a frame memory, and a personal computer. Because it is not necessary to use the processed data for real time control, a system was designed in which the data processing was performed after the acquisition of all data. The static image is obtained by a combination of averaging, subtraction of background noise, and median filtering methods. A dynamic image with 85(V)×96(H) pixels/field is acquired at the sampling rate of 30 fields/s. Using this system, static and dynamic domain images of Supermalloy multilayered core and amorphous ribbon were obtained.
10-kHz amorphous core power transformer
Authors: Lupi S.
Published: July 2002

The technical and economical problems of applying amorphous magnetic cores in medium-frequency transformers for induction heating applications are discussed. The results obtained on a 10 kHz-1200 kV A unit are presented.
Amorphous Fe-B-Si magnetic films by reactive sputtering from a pure iron source
Authors: Wallace John L.
Published: July 2002

The author has successfully used reactive sputtering to fabricate amorphous magnetic thin films with chemical and physical properties similar to those of Metglas■. The sputtering target was commercially available mild steel. The amount of each metalloid in the deposited thin film was controlled by varying the partial pressures of silane and diborane in the sputtering plasma. Total metalloid concentrations were varied over the range of 0–50 at. %. A sample containing 76% Fe:16.5% B:3% Si:3% C was found to be amorphous and to have good soft magnetic properties. This sample had a well-defined uniaxial anisotropy in the plane of the film with an easy axis coercivity of 4.5 Oe. The rf permeability (μ′) of this 2000-Å-thick sample was greater than 1000 from 0 to 900 MHz.
FeTAB: An Ising-like 1D ferromagnet
Authors: Greeney R. E. , Landee C. P. , Reiff W. M. , Zhang J. H.
Published: July 2002

Continuing the investigation of the series of isostructural 1D magnets (CH3)3NHMX3⋅2H2O (M=Mn, Fe, Co, Ni, Cu, X=Cl, Br), we report on the first powder study of FeTAB,(CH3)3NHFeBr3⋅2H2O. X-ray studies show FeTAB to be isostructural with FeTAC, a good example of a 1D Ising ferromagnet. Low-temperature powder susceptibility data agree with the predicted susceptibility of a ferromagnetic 1D Ising model with an exchange constant of 4.0(1.0) K. Mössbauer spectroscopy has shown the ordering temperature to be near 1.3(1) K. The data imply that the ratio of the interchain to intrachain interactions (J′/J) is at least 10 times greater in FeTAB than in the chloride analog.
Investigations of magnetic hysteresis of barium ferrite using the torsion pendulum method
Authors: Richter H. J. , Hempel K. A.
Published: July 2002

The magnetic stiffness is measured by the torsion pendulum method as a function of the applied field. Measurements are performed on random assemblies of chemically coprecipitated barium ferrite powders. The magnetic stiffness for both minor and major loops of the hysteresis cycle is measured and compared with calculated curves based on the model of coherent rotation. The discrepancies between theory and experiment are partly due to the effect of magnetic interaction.
Magnetic phases of Gd-Sc alloys in the multicritical regime
Authors: Melville R. J. , Palmer S. B. , McIntyre G. J. , Sousa J. B.
Published: July 2002

We have carried out ultrasonic and neutron studies of a range of single-crystal Gd1−x Scx random alloys (x=0.25, 0.28, 0.295, 0.31, 0.32, 0.36) in the vicinity of the multicritical point at x=0.29. The sample richest in Gd shows magnetic behavior similar to the pure element while those richer in Sc display helimagnetism with lock-in effects at low temperature. The sample closest to the multicritical point (x=0.28) shows unusual magnetic behavior at low temperatures.
Thermal expansion and ac initial magnetic susceptibility in RECu intermetallic compounds (abstract)
Authors: Ibarra M. R. , Pavlovic A. S.
Published: July 2002

We have carried out a systematic study of the series RECu cubic intermetallic compounds where RE=Y, Gd, Tb, Dy, and Ho by means of the thermal expansion and ac initial magnetic susceptibility measurements. The measurements clearly show in some of these compounds (RE=Y, Gd, and Tb) very large anomalies associated with a martensitic structural phase transition, from the cubic CICs at room temperature to the tetragonal FeB structure. These anomalies exhibit very large hysteresis effects which make it necessary to reobtain the original CICs crystal structure to anneal the samples up to about 600 K. In the case of TbCu a magnetic-phase transition occurs simultaneously to the structural one; the trigger mechanism which drives this transition has been studied on the basis of the strong influence of the magnetoelastic energy using a single-ion crystal electric-field model within the mean-field approximation. In the case of RE=Dy and Ho only slight anomalies have been observed in the thermal expansion measurements at the region of the magnetic-phase transition and no hysteresis effects were observed. The existence or nonexistence of the spontaneous magnetostriction at the order temperature constitutes a suitable test of the nature of the magnetic structure (collinear or multiaxis) in these systems.
Nonlinear microwave response to scanning fields in high-T
c oxides
Authors: Warden M. , Stalder M. , Stefanicki G. , Portis A. M. , Waldner F.
Published: July 2002

Nonresonant microwave (MW) absorption is observed at the surface of high-Tc superconducting oxides in the presence of a static magnetic field and a scanning field. Nonlinear signals are obtained that show absorption troughs at the endpoints of the field scan superimposed on a hysteretic variation in absorption with field. The model of Portis et al. accounts quantitatively for the detailed shape of the observed signals. It enables the direct measurement of a critical field H*=(4π/c)Jcλ which depends on the critical current Jc and the static field penetration depth λ. In addition, the ratio λMW/λ is deduced from the shape of the troughs, with λMW the penetration depth of the MW fields. Typical values are H*≂5 μT and λMW≂3λ for a sintered YBaCuO sample at 77 K, and nearly the same H* but λMW≂λ at 4.2 K. Since the observed shapes also depend on the previous slow changes of the applied field, these investigations account for the memory effect observed with the usual resonance techniques.
Remanence curves of cobalt ferrite powders obtained by fractionation of a suspension through a silica gel column
Authors: Charles S. W. , Chandrasekhar R. , O’Grady K. , Walker M.
Published: July 2002

A magnetic ink has been prepared which consists of a colloidal suspension of cobalt particles of ∼10-nm median diameter of the volume fraction. Gel filtration techniques have been used to separate the particles into a number of fractions of different particle size. Isothermal remanent magnetization (IRM) curves have been plotted for each fraction in the dried state. The maximum value of IR/IS (remanence/saturation magnetization) is 0.5 equal to a value for a distribution of uniaxial particles with easy axes randomly oriented. This value is well below the value of 0.8 expected for cobalt ferrite which has cubic crystalline anisotropy. All fractions, except for those containing the largest particles, have values of IR/IS <0.5 due to the presence of superparamagnetic particles. The experimental points on the IRM curves have been fitted to theoretical curves derived from a model by Chantrell et al.7 for a system of uniaxial particles with axes randomly oriented and containing a lognormal distribution of particle volume. Using a value of anisotropy constant K=1.8×105 J m−3 obtained from measurement of the decay of remanence with temperature, satisfactory agreement between particle size determined experimentally and that used in the model has been obtained.
Magnetic viscosity and texture in NdFeB magnets
Authors: Martinez J. C. , Missell F. P.
Published: July 2002

The dependence of the magnetic viscosity on texture can be used to study a model recently proposed by Givord and co-workers to describe the angular dependence of the coercive field in NdFeB magnets. We have measured the magnetic viscosity parameter Sv for samples of Magnequench (MQ) II and III as a function of magnetic field H and temperature T above room temperature. Near room temperature, Sv for MQ II is smaller than for MQ III, while for temperatures above ∼70 °C, the opposite behavior is observed. This temperature dependence is discussed and compared with that observed in sintered NdFeB and NdDyFeB magnets.
Analysis of SmCo 2:17 sintered magnets by electron diffraction (abstract)
Authors: Fidler Josef
Published: July 2002

Precipitation-hardened SmCo 2:17 sintered magnets contain a multiphase, cellular microstructure,1 which is determined by nominal composition and heat treatment parameters. A correlation between microstructure and coercivity has been shown by transmission electron microscopy (TEM).1,2 Magnets with different samarium content were investigated. In magnets with iHc<700 kA/m a high density of basal stacking faults (microtwinning) within the hard magnetic, rhombohedral 2:17 phase was shown. Local changes of crystal lattice parameters are observed in low coercivity magnets. Calculated diffraction patterns of CaCu5-, TbCu7-, Th2Zn17-, and Th2Ni17-crystal structures with different types of atomic occupancies3 are compared with experimental electron diffraction patterns obtained by TEM. Our study revealed that the local composition within the hard magnetic grains influences the precipitation structure which is necessary for achieving magnetic hardness by domain wall pinning.
Variable angle spectroscopic magneto-optics and ellipsometry: Application to DyCo multilayers (abstract)
Authors: Tiwald Thomas E. , McGahan William A. , Shan Z. S. , Massengale Alan M. , Woollam John A.
Published: July 2002

The purpose of this paper is twofold. First, we describe the adaptation of a variable angle spectroscopic ellipsometer (VASE) to magneto-optic measurements covering 3000–8000 Å, and 0 to ±8 kOe. Second, we describe application of VASE to determine Kerr rotation and ellipticity for a series of Dy/Co multilayers prepared by sputter deposition. We report spectroscopic ellipsometric and Kerr effect results for samples exhibiting perpendicular magnetic anisotropy, since these are relevant as magneto-optic recording media.
A new dc current detector using bridge-connected magnetic circuit
Authors: Okanuma S. , Ichinokura O. , Murakami K.
Published: July 2002

This paper describes performance characteristics of a bridge-connected magnetic circuit with single output winding in dc control. The difference between positive and negative amplitudes of output current changes with the dc control current. An application of the bridge-connected magnetic circuit to a dc current detector is presented in this paper.
Characteristic improvement of capacitor motor with ferrite magnetic wedge (abstract)
Authors: Kaga Akio , Hasegawa Seiichi
Published: July 2002

Ferrite materials are easy to saturate rapidly under magnetization. In this study, the materials have been wedged into the stator slot openings of a single-phase capacitor motor to elucidate the wedging effect. As the results of some experimental discussions performed, the characteristics of the motor have been improved remarkably.1 In particular, the rate of efficiency improvement with the wedge has attained about 13% for a light load of 300 W. This is due to the decrease of copper losses caused by the increase of magnetizing reactance and the decrease of higher harmonic losses, namly eddy current loss and tooth pulsation loss. In addition to this, the discussions on the alternating torque characteristic of the motor have been evaluated. According to the results, the alternating torque has been also reduced by the installation of ferrite magnetic wedges. The alternating torque is influenced by various factors. Of all these factors, especially, the backward revolving field components of torque and rotor resistance are reduced greatly by wedging the ferrite materials. All the experiments mentioned above have been carried out in terms of exchanging the capacity of running capacitor. When the condenser capacities are increased, the motor characteristics have been improved more or less, but there is a limit for increasing condenser capacities to improve the motor characteristics.