bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of Fe/SiO2 multilayer film
Authors: Senda Masakatsu , Nagai Yasuhiro
Published: July 2002

This paper discusses the magnetic properties of ion-beam-sputtered Fe/SiO2 multilayer films. Decreasing Fe layer thickness, while maintaining a constant SiO2 layer thickness, results in good soft-magnetic properties and nearly zero magnetostriction. These results are thought to be due to smaller crystal grains and a change in crystal orientation in the Fe layers. In Fe/SiO2 multilayer films consisting of 7-nm Fe and 2.5-nm SiO2 layers, magnetization of 1.55-T, hard-axis coercivity of 0.3 Oe, and relative permeability of 4000 are achieved under magnetostriction of less than ±10−6. After 250 °C annealing, relative permeability increases up to 5000. Furthermore, a magnetic domain structure with easy-axis direction and extended 180° walls suitable for thin-film heads can be obtained.
Reactive ion etching of GaAs with CCl2F2:O2: Etch rates, surface chemistry, and residual damage
Authors: Pearton S. J. , Vasile M. J. , Jones K. S. , Short K. T. , Lane E. , Fullowan T. R. , Von Neida A. E. , Haegel N. M.
Published: July 2002

The reactive ion etching of GaAs with a CCl2F2:O2 discharge was investigated as a function of gas flow rate (10–60 sccm), total pressure (2–50 mTorr), power density (0.25–1.31 W cm−2), gas composition (0%–70% O2), and etch time (1–64 min). The etch rate decreases with increasing gas flow rate, increases with increasing power density, and goes through a maximum at a gas composition of 75:25 CCl2F2:O2 under our conditions. After etching at low-power densities (0.56 W cm−2) and for high CCl2F2 ratios (19:1 to O2), carbon and chlorine could be detected in the GaAs to a depth of less than 15 Å by x-ray photoelectron spectroscopy. Under these conditions there was a Ga deficiency to a depth of ∼100 Å, which we ascribe to surface roughening and the preferential vaporization of As2O3 over Ga2O3. At high-power densities (1.31 W cm−2) a polymeric layer several hundred angstroms thick containing CCl and CF bonds was observed on the GaAs surface. Etching under O2-rich conditions did not lead to any additional creation of surface oxides. Both ion channeling and electron microscopy detected a thin disordered layer on the GaAs after etching. Small (<100 Å diam) dislocation loops were present at a depth varying from ∼400 Å for 0.56 W cm−2 (380-V self-bias) plasma power density to ∼2200 Å for 1.31 W cm−2 (680-V self-bias). The disorder was stable against a 500 °C annealing treatment.
Implantation temperature dependence of electrical activation, solubility, and diffusion of implanted Te, Cd, and Sn in GaAs
Authors: Pearton S. J. , Williams J. S. , Short K. T. , Johnson S. T. , Jacobsen D. C. , Poate J. M. , Gibson J. M. , Boerma D. O.
Published: July 2002

The relationship between electrical activity, dopant solubility, and diffusivity was investigated as a function of the substrate temperature during implantation of Te, Cd, and Sn ions into GaAs. Implant doses of these species in the range 5×1012–5×1015 cm−2 were performed in the temperature range −196 to 400 °C, followed by either transient (950 °C, 5 s) or furnace (450–900 °C, 20 min) annealing. The redistribution after such annealing was found to depend on the implant temperature, and was always greatest for Cd followed by Sn and Te. The degree of electrical activation was in the same order, but there was essentially no correlation of electrical activity with dopant solubility. Te, for example, showed soluble fractions of ∼90% for a dose of 1015 cm−2 after annealing at 850 °C or higher, regardless of the initial implant temperature. By sharp contrast, the electrically active fraction under these conditions was in the range 0.8%–3.4%. There was also no apparent correlation of the degree of electrical activity with the presence of defects visible in transmission electron microscopy. The energy required to activate the implanted ions fell broadly into two categories: ‘‘low’’ values in the range ∼0.4–0.8 eV (which included Cd implanted or annealed under any condition, and elevated temperature implants of Sn and Te), and ‘‘high’’ values in the range 1.7–1.9 eV [which included implants of Sn and Te performed at −196 °C, or high dose (1015 cm−2) room-temperature implants of these species].
Model of wire-to-plane electric arc
Authors: Vacek Daniel J. , Cohen Ira M.
Published: July 2002

A simple model of the wire-to-plane electric arc based on energy and charge conservation is developed and solved numerically for discharges simulating those used for ball formation in the wire bonding process. Energy conservation balances heat generated by electrical dissipation against that conducted away and that stored. For the conditions of interest here, radiation and convection are negligible. Charge conservation is used to solve for the electrostatic potential. The electric field is static for the conditions of interest here. Electrical and thermal conductivities and the specific heats for air and argon are fit as functions of temperature (and pressure) to the best available data. The results show peak arc temperature in air and argon near 11 000 K. Calculated currents and voltages are consistent with measurements we have made on a 100× upscaled apparatus (3.2-mm wire). 5%–10% percent of the total energy in the discharge is transferred to the wire to heat and melt it. The remaining energy is transferred to the planar electrode or conducted away to the ambient gas.
Iron redistribution and compensation mechanisms in semi-insulating Si-implanted InP
Authors: Bahir G. , Merz J. L. , Abelson J. R. , Sigmon T. W.
Published: July 2002

The Si and Fe depth distributions have been measured in Si-implanted semi-insulating (SI) InP as a function of implant temperature and post-implant annealing technique (either furnace annealing or rapid thermal annealing). Depth profiles obtained by secondary ion mass spectrometry and damage measurements obtained by Rutherford backscattering demonstrate that Fe redistributes into regions of residual damage during thermal processing. The active electrical carrier profiles measured by electrochemical profiling show differences between atomic and electrical carrier profiles which depend on whether the substrate is semi-insulating or undoped, and on the implant temperature. These differences are interpreted in terms of three different compensating mechanisms: (a) the amphoteric nature of Si impurities in InP, so that Si can be self-compensating, (b) carrier compensation caused by the redistribution of Fe, and (c) implantation-related damage effects and/or stoichiometry imbalance induced by the Si implant.
Observations of adhesion-induced deformations between spheroidal gold particles and conducting substrates
Authors: Rimai D. S. , DeMejo L. P. , Bowen R. C.
Published: July 2002

Spheroidal gold particles, approximately 3 μm in diameter, were deposited on both hard and soft planar, electrically conducting substrates, and the interfaces were observed using scanning electron microscopy. It was observed that the particles appeared to embed into the softer substrate, but not into the harder one. The softer substrate also appeared to flow up the sides of the particles. The diameters of the craters formed are compared with the predictions based on Hertz’ [Zimon, Adhesion of Dusts and Powders (Consultants Bureau, New York, 1982)] model of elastic deformation, Krupp’s [Adv. Colloid Interface Sci. 1, 111 (1967)] model of plastic response [assuming van der Waals (Zimon, ibid. and Krupp, ibid.) interactions], and Johnson, Kendall, and Roberts’ [Proc. R. Soc. London Ser. A 324, 301 (1971)] model of tensile response due to surface tension. These calculations suggest that the observed deformation on the softer substrate is predominantly plastic rather than elastic and that surface tension is significant. The techniques are expanded and results reported for the case of gold particles on insulating surfaces.
Electric field dependence of quantum-well eigenstates
Authors: Bloss Walter L.
Published: July 2002

Two very accurate methods are developed, one based on the shooting method and the other on the relaxation method, for calculating the eigenenergies and eigenfunctions of states in a quantum well with an applied electric field. These methods, which give accuracies greater than 0.001 meV, are well controlled, give the quantum-well eigenfunctions, and are easily applied to situations of varying potential and effective mass. Comparisons with the variational approach of Bastard and others are made. These techniques allow one to follow the development of the quantum-well eigenstate outside the well and to determine the validity of the quasi-bound state approximation. Recent results in the literature showing that the ground-state hole eigenfunction becomes unbound at moderate electric fields are shown to be erroneous. Detailed calculations are presented for the electron (ground and first excited) and hole (ground) eigenstates of a quantum well with width 85 Å, and barrier heights of 240 (conduction band) and 160 meV (valence band) for applied electric fields varying from 0 to 150 kV/cm. Also, we have calculated the overlap integrals and the dipole matrix elements appropriate to quantum confined Stark effect modulators and infrared quantum-well detectors, respectively.
A first-order Navier–Stokes treatment of the shape and instability of liquid metal ion sources
Authors: Chung M. S. , Cutler P. H. , Miskovsky N. M.
Published: July 2002

A three-dimensional axially symmetric model for a liquid ion source is used to obtain the shape and critical potential for breakdown of a conducting fluid at the onset of instability. A set of electromechanical equations is obtained for the first-order deformation of the fluid surface from the Taylor cone which is used as the zeroth-order configuration. The equations are evaluated in both the quasihydrostatic and hydrodynamic limits. These analyses yield the angle deformation ξ=(r/a)sε, for r<a, and the associated critical voltage VC=V(0)TC1 ×[(a/r)s+C2]−0.5, where a is a boundary-matching parameter, r0 is the distance between the cone apex and the counterelectrode, and ε contains the time dependence of the first-order angle deformation. Here, V(0)T is the potential needed for formation of the purely hydrostatic Taylor cone and C1 and C2 are constants dependent upon boundary-matching conditions. The hydrodynamic analysis predicts that the shape of the surface is concave at the onset of instability. The results obtained in both limits are (i) that the instability is localized in the apex region, and (ii) the values of the critical voltages VC, are in good agreement with experiment for Ga.
Bismuth- and thallium-doped lead telluride grown by molecular-beam epitaxy
Authors: Partin D. L. , Thrush C. M. , Simko S. J. , Gaarenstroom S. W.
Published: July 2002

Lead telluride and its high-energy gap alloys are useful for long wavelength diode lasers. In the present study, the control of a donor (Bi) and of an acceptor (Tl) impurity in PbTe was studied in PbTe grown by molecular-beam epitaxy. Several analytical techniques were used, including scanning Auger electron spectroscopy, secondary ion mass spectroscopy, conventional carrier transport measurements, and surface probe thermoelectric measurements. It was observed that bismuth incorporates well and undergoes negligible diffusion over the range of growth conditions used. Thallium surface segregates at high concentrations and diffuses appreciably at high growth temperatures and at high concentrations. Thus, it is only suitable for use in highly dimensionally defined structures at moderate to low concentrations and at relatively low growth temperatures.
Further improved algorithm for the solution of the nonlinear Poisson equation in semiconductor devices
Authors: Ouwerling G. J. L.
Published: July 2002

This paper gives a concise overview of some existing methods for the solution of the nonlinear Poisson equation in semiconductors. A method for the solution of this equation was recently proposed in this journal by I. D. Mayergoyz [J. Appl. Phys. 59, 195 (1986)]. Soon afterwards, an improved version was described by W. Keller [J. Appl. Phys. 61, 5189 (1987)]. Both methods are classified within the perspective of the existing methods. Moreover, Keller’s method is further improved by the introduction of scaled variables and by using red-black ordening to allow for overrelaxation. All advantages of the two methods are maintained. An illustrative example shows an improvement in solution speed of at least a factor of 5.6.
Magnetic force microscopy of a CoCr thin film
Authors: Grütter P. , Wadas A. , Meyer E. , Hidber H.-R. , Güntherodt H.-J.
Published: July 2002

We present high-resolution magnetic force microscopy (MFM) images of a Co80Cr20 film with a thickness of 230 nm. We clearly observe a stripe domain structure with a domain width of 220 nm, the highest resolution of a periodic magnetic structure measured by MFM to this date, by measuring forces as small as 0.1 nN. The micromagnetic structure is compared to the morphology of the sample, which consists of vertical columns with an average cross section of about 40×60 nm2. The average surface roughness of this film did not exceed 12 nm on a 1-μm lateral scale. A magnetic fine structure of typically 50 nm width and more than 200 nm length is observed. Theoretical calculations of force traces are in reasonable agreement with experiment. A nonuniform sample magnetization, correlated to the morphology, has to be assumed to simulate the observed fine structure of force traces. Calculated images characteristically depend on the effective domain structure of the last 500 nm of the tip.
On the thermodynamics of the up-conversion and fluorescence of light
Authors: Biblarz Oscar
Published: July 2002

Frequency doubling of light, made possible by the laser, has precipitated a host of anti-Stokes fluorescence activities. In this work, a criterion based on the principle of the increase of entropy in adiabatic processes is presented. This principle relates to the nature of the light rather than to the substances performing the harmonic generation. It is shown that changes in the spectral entropy can be used to discriminate which radiation is suitable for up-conversion. The spectral entropy of a blackbody has a maximum with respect to frequency at any given temperature. If the final state of a process is located at this maximum, then a critical minimum temperature, below which no up-conversion may be expected, can be found. A definition of the effective temperature of highly nonequilibrium sources such as the laser is presented. Fluorescence in the low-pressure mercury lamp is treated in the context of thermodynamics. Examples of practical light sources are discussed, and it is shown that up-conversion is, rather exclusively, the purview of the laser.
Emission spectroscopy of cw CO2 laser-sustained argon plasma: Effects of gas-flow speed
Authors: Chen Xiangli , Mazumder Jyotirmoy
Published: July 2002

The effects of elevated gas-flow speed were studied for the cw CO2 laser-sustained argon plasma in a chamber of 1-atm pressure using the argon emission spectrum. Electron temperature distribution was obtained from the 415.8-nm Ari line-to-continuum intensity ratio. This temperature distribution was further utilized to calculate the fraction of laser power absorbed by the plasma, and the amount of radiation loss from the plasma. The experiments were performed for laser powers of 2.5 and 5 kW with an f/7 lens focusing scheme, and gas-flow speeds of 2–10 m/s. The results show that as high as 86% of incident laser energy can be absorbed by the plasma. Accounting for the plasma radiation loss, 41%–62% of the laser energy can still be retained as the gas thermal energy, which is a significant increase over the previously reported results for lower flow speed and smaller focusing f number.
AlGaAs-GaAs and AlGaAs-GaAs-InGaAs vertical cavity surface emitting lasers with Ag mirrors
Authors: Deppe D. G. , Cho A. Y. , Huang K. F. , Fischer R. J. , Tai K. , Schubert E. F. , Chen J. F.
Published: July 2002

We describe vertical cavity surface emitting lasers of GaAs active regions (0.7 μm thick) emitting at 0.85 μm and of In0.1Ga0.9As-GaAs active regions emitting at 0.90 μm. The vertical cavity is formed using an AlxGa1−xAs-AlAs quarter-wave stack as the n-type mirror and the metal Ag as the p-type mirror. The Ag mirror has potential for reduced series resistance, reduced thermal resistance, and more simplified device processing over other mirror structures for vertical cavity laser diodes. Current thresholds for pulsed room-temperature operation as low as 16 kA/cm2 for the GaAs and 51 kA/cm2 for the In0.1Ga0.9As-GaAs devices have been measured.
High-resolution surface charge measurements on an organic photoconductor
Authors: Yarmchuk E. J. , Keefe G. E.
Published: July 2002

A technique for making direct, quantitative measurements of surface charge distributions on photoconductors has been developed. The spatial resolution is better than 10 μm and the measurements take place under conditions closely approximating those in printers or copiers. Measurements of edge broadening in layered photoconductor arising from space-charge effects during image formation are presented. Edge broadening due to surface conduction has also been observed and data linking this to contamination of the surface by the charging corona is shown.
Thermodynamic and transport properties of an aluminum-nitrogen plasma mixture
Authors: Dassanayake M. S. , Etemadi K.
Published: July 2002

Thermodynamic and transport properties of an aluminum-nitrogen plasma mixture have been computed as a function of temperature for different percentages of the aluminum species. The calculations were made for an atmospheric pressure plasma having temperatures between 3000 and 25 000 K under the assumption of local thermodynamic equilibrium. Transport properties were calculated using a method derived from the Chapman–Enskog theory. The plasma mixture consists of Al, Al+, Al2+, Al3+, N2, N+2, N, N+, N2+, AlN, and electrons. Results show that the maximum number density of AlN is obtained at 67% of the aluminum species at temperatures close to 5000 K. The total enthalpy, viscosity, and total thermal conductivity of the plasma decrease at temperatures above 6000 K as the percentage increases. At temperatures below 17 000 K, the electrical conductivity, and the electron thermal conductivity increase with increasing aluminum percentage. The effective binary diffusivity of AlN as a function of temperature has a very strong dependence on the percentage of aluminum in the plasma.
The propagation of a solid-state combustion wave in Ni-Al foils
Authors: Anselmi-Tamburini U. , Munir Z. A.
Published: July 2002

The use of thin foils to investigate the propagation of a combustion wave has been demonstrated for the nickel-aluminum system. The initiation of a reaction wave in the foils was found to be triggered by the melting of nickel regardless of the composition of the foil ensemble. In contrast, the propagation rate decreased with increasing nickel content in the foil ensemble. Considerable interactions, observed in advance of the combustion front, are contrary to assumptions made in existing models on the dynamics of self-sustaining reactions. The nature and sequence of reactions between foils of Ni and Al and their relationship to the combustion front were determined.
Monitoring of radio-frequency glow-discharge plasma
Authors: Mutsukura Nobuki , Kobayashi Kenji , Machi Yoshio
Published: July 2002

The optical emission profile (OEP) between anode and cathode electrodes is examined for monitoring planar rf discharges of H2, N2, and Ar gases. Form the OEP we can easily find the boundary of the ion sheath and the plasma region and accordingly the ion sheath width at the cathode electrode. The plasma parameters are measured by the Langmuir probe method, and the relative mean electron energy Te in H2 and N2 plasmas is found to be evaluated by the ion sheath width ls with a relationship Te∝ls. The plasma density can also be estimated by both the cathode negative potential Vc and ls. A charge-coupled device (CCD) image sensor with a 105-mm macro lens is employed to measure the OEP within a very short time. Although the CCD measurement shows a somewhat deviated OEP, this is very useful to measure the precise ion sheath width.
Theory of electrical discharges initiated from a large charge spot on dielectric surfaces
Authors: Kadish A. , Maier II William B. , Robiscoe R. T.
Published: July 2002

The nonlinear dynamics of charge transport due to an electric discharge on a dielectric surface is analyzed using a transmission line model. The relation between the resistance per unit length, R̂, and the current, I, is assumed to be given by the local arc-welder’s ansatz, R̂‖I‖=E*, where E* is a positive constant. The model predicts that a discharge initiated in the vicinity of a charge spot can propagate partway down a current channel and abruptly terminate before transporting charge to the dielectric edge. This behavior is similar to leader phenomena observed in lightning and other electrical discharges. We show that the direction of the current along the current channel is constant throughout such a discharge. The minimum voltage at the charge spot that allows charge to be transported to the dielectric edge is determined. This critical voltage Vl depends on the length l of the current channel. We show that the ‘‘average field,’’ Vl/l, decreases as l increases. When the charge spot voltage is less than the critical voltage, we obtain upper and lower bounds for both the arc duration time and amount of charge removed from the charge spot.
n-type (Pb)Te doping of GaAs and AlxGa1−xSb grown by molecular-beam epitaxy
Authors: Newstead S. M. , Kerr T. M. , Wood C. E. C.
Published: July 2002

A PbTe flux has been used for n-type (Te) doping of GaAs, GaSb, and AlGaSb. The effects of surface accumulation and Te desorption were noticeable in secondary-ion mass spectroscopy profiles of GaAs layers grown at temperatures in excess of 540 °C. Te accumulation was not apparent in GaSb layers grown at temperatures up to 630 °C, but Te desorption occurred from GaSb at temperatures above 540 °C. The donor ionization energy of Te in AlxGa1−xSb is 44 meV for 0.4<X<0.5, i.e., significantly lower than the ionization energies of S or Se in similar material.
Magneto-optical properties of transparent plastic material
Authors: Muto Shinzo , Ichikawa Shin-ichiro , Nagata Takashi , Matsuzaki Akihisa , Ito Hiroshi
Published: July 2002

The measured values of the Verdet constant of transparent plastic fiber materials such as the poly-α-methylstyrene and polystyrene are comparable to that of a NaCl crystal. In these magneto-optical plastics, the wavelength giving the maximum value of the figure of merit for a fiber-type optical isolator is about 500 nm. They are also used for constructing plastic fiber sensors for higher magnetic field or higher current.
Anomaly of dielectric properties in tens-nanometer-thick lead lanthanum zirconate titanate films on a platinum substrate
Authors: Kanata T. , Nakagawa T. , Okuyama M. , Hamakawa Y. , Ibuki S.
Published: July 2002

Transparent ultrathin films (<100 nm) of lead lanthanum zirconate titanate (PLZT) with good dielectric properties were successfully grown on a platinum plate by rf magnetron sputtering and following an anneal in PbO atmosphere. The sputtering conditions were controlled by monitoring the plasma emission from the sputtering species. The PLZT thin films were deposited at an extremely low growth rate of 36 nm/h at 400 °C and annealed at 800 °C for 3 h in PbO atmosphere. The obtained thin films are oriented to [110] of the perovskite-type structure and have relatively low dc conductivity (∼10−7 Ω−1 cm−1). The evaluated dielectric constants are anomalously large around 5000 at room temperature and 1 kHz.
Application of porous silicon formation selectivity to impurity profiling in p-type silicon substrates
Authors: Ligeon M. , Muller F. , Herino R. , Gaspard F. , Halimaoui A. , Bomchil G.
Published: July 2002

A new type of application of porous silicon formation is proposed, which does not deal with the material properties, but with the characteristics of the involved electrochemical silicon dissolution reaction. The anodization potential of p-type silicon in concentrated hydrofluoric acid under galvanostatic conditions has been shown to be characteristic of the silicon doping concentration at the interface and independent of the porous silicon-layer thickness. This close correlation between potential and doping level is used to determine concentration profiles of p-type implanted dopants. During anodization of silicon presenting dopant concentration variations, the anodization potential varies according to silicon doping concentration. The potential values can be converted to dopant concentration, and the electrolysis time scale to a depth scale, leading then to the doping impurity profile. This method, which is used as well for deep and shallow diffused impurities, exhibits a very good agreement with spreading resistance measurement and secondary-ion mass spectrometry analysis. Simultaneous anodization of regions of different doping concentration has also been investigated. It allows the characterization of the porous silicon formation selectivity by a selectivity coefficient, which is measured on a large range of silicon doping concentration. The selectivity is found to be strongly dependent on the doping level: it is nearly infinite for samples presenting highly doped regions (greater than 3×1018 cm−3), but decreases sharply when the doping concentration is below 1018 cm−3.
Defect-molecule model calculations of 3d transition metal ions in II-VI semiconductors
Authors: Tian Zengju , Shen Xuechu
Published: July 2002

The cation substitutional impurities of 3d transition metal ions (though V to Ni) in II-VI semiconductors ZnS(Se, Te) and CdSe(Te) have been studied by using the defect-molecule model with renormalized parameters of the host crystal atoms. It was found that more charge states can exist in the energy gap of semiconductors for V, Cr, and Mn than for Fe, Co, and Ni. The energy levels of transition metals are found to be aligned with respect to each other with a group of common anion semiconductors, which confirms the more recent observations of transition metal impurities in semiconductors, but a slight difference occurs with varying anoins of the semiconductors. With the spin-polarized Hartree–Fock approach, the binding energies of acceptors and donors are calculated and are in reasonable agreement with the experimental data. The polarization of the bond between impurity and host atoms is analyzed. Based on the calculated crystal-field splittings of 3d levels, the internal transition of 3d electrons of transition metal ions in CdTe are predicted.
Resonant enhancement of quantum well linewidths by pseudo-barrier energy levels
Authors: Bloss Walter L.
Published: July 2002

The density of states and linewidths are calculated for an AlxGa1−xAs/GaAs quantum well with a well width of 76 Å, a barrier width of 130 Å, and a barrier height of 268 meV under an applied electric field. We show that the linewidths become resonantly broadened by the interaction with the pseudo-barrier states in the infinite triangular well formed from potential discontinuities. This broadening corresponds to a linewidth increase of 2.5 times and to a reduction in the tunneling time by a factor of 0.4 over that with no resonant enhancement. These results have direct implications for designing infrared detectors, Stark effect modulators, and quantum well tunneling transistors.
A mechanism of interfacial reactions between boron nitride and nickel aluminide
Authors: Chou T. C. , Lampert J. K. , Anderson D. R. , Mishra A.
Published: July 2002

The interfacial reaction between boron nitride and nickel aluminide was studied by diffusion bonding at 1000 °C. Samples annealed in air or vacuum yield the same results. The interdiffusion zone is enriched with Al. An ex situ fractured boron nitride interface shows predominantly BN, featured by granular microstructure, and a minor amount of BOx Ny . A very small amount of Al, but no Ni, is detected. On the other hand, the nickel aluminide interface shows three-dimensional Ni clusters embedded in an alumina matrix. Interactions of Ni and Al thin films with boron nitride substrates were studied to clarify the mechanism. Thermodynamic calculations of Gibbs free energy and reaction enthalpy of various possible reactions between boron nitride and nickel aluminide were carried out. The partition of Ni atoms from nickel aluminide is discussed based upon the grain-boundary diffusion of Ni atoms, chemical potential of the diffusion environment, and chemical activities of Ni and Al atoms in the presence of boron nitride.
Electrical resistance and the time-dependent oxidation of semicontinuous bismuth films
Authors: Cohn J. L. , Uher C.
Published: July 2002

We report on the electrical resistance and time-dependent oxidation of thin (≲90 Å) semicontinuous bismuth films. An increase in the room temperature sheet resistance with exposure to air is correlated with the growth of insulating Bi2O3 at the surfaces and internal boundaries between bismuth particles. For short oxidation times t, the resistance increases as R⧠ ∝t1/2, consistent with a parabolic oxide growth law. At longer times the resistance follows the classical percolation law R⧠∝‖tc−t‖−μ, where tc is a critical exposure time and μ≂1.3 is a critical exponent for two-dimensional systems.
Semiconductor quantum wells as electron wave slab waveguides
Authors: Gaylord T. K. , Glytsis E. N. , Brennan K. F.
Published: July 2002

A quantum well in a semiconductor can act as a slab waveguide for electron waves in a manner analogous to the way a layered dielectric can act as a slab waveguide for electromagnetic waves (e.g., as commonly employed in integrated optics). In this work, the case of a general electron asymmetric slab waveguide (a quantum well comprised of three materials each with a different potential energy and a different effective mass) is analyzed and the conditions for electron waveguiding are quantified. Electron waveguide modes exist for electron energies in the well and for electron energies above one or both of the potential energy barriers. Furthermore, due to dispersion, each electron waveguide mode has an upper-energy cutoff as well as a lower-energy cutoff. This is in contrast to electromagnetic guided modes which typically have only lower-energy (low-frequency) cutoffs. At the upper-energy cutoff the electron wave is refracted into the substrate and/or cover. An example quantum well waveguide consisting of Ga0.80 Al0.20 As (substrate), GaAs (film), Ga0.55 Al0.45 As (cover) is analyzed. This structure is a single-mode electron waveguide for GaAs thicknesses of from 5 (1.413 nm) to 26 monolayers (7.349 nm).
Absorption at radio frequencies in superconducting Y1Ba2Cu3Oy
Authors: Ducharme Stephen , Durny R. , Hautala J. , Zheng D. J. , Taylor P. C. , Symko O. G. , Kulkarni S.
Published: July 2002

The large magnetic-field-dependent ac absorption in superconducting Y1 Ba2 Cu3 Oy ceramics and powders decreases slowly with increasing frequency in the range 2–16 MHz. The magnetic-field-dependent ac absorption is observed below Tc in superconducting Y1 Ba2 Cu3 Oy ceramics, powders and twinned crystals and in (La,Sr)2 CuO4 and BaPb0.75 Bi 0.25 CuO3 powders and appears to contain distinct contributions from trapped flux and/or intragrain tunnel junctions and from ordinary superconductor surface impedance. The contribution from trapped flux and/or intragrain tunnel junctions is important in dc magnetic fields of up to approximately 20 G at all temperatures below Tc. There is an identifiable modulated ac absorption which changes slowly over more than 12 kG at low temperatures and which we propose is primarily caused by the ac surface impedance with possible contributions from the critical state. A twinned crystal of Y1 Ba2 Cu3 Oy exhibits the same ac absorption except that it has an anisotropic dependence on the applied dc magnetic field.
Saturation of the even-order bounds on effective elastic moduli by finite-rank laminates
Authors: Lipton Robert
Published: July 2002

Sufficient conditions on the phase geometry for the reduction of even-order bounds to bounds of second order are derived. It is found that finite-rank laminates satisfy the sufficient conditions asymptotically as the length scale of the laminar microstructure goes to zero. This result is used to show that the effective elastic tensors of finite-rank laminates saturate the even-order bounds in the fine-scale limit.
Monte Carlo studies of band-tail effects on the recombination kinetics in heavily doped silicon
Authors: Pan Y.
Published: July 2002

The effects of energy-band-tail states on the recombination kinetics in heavily doped silicon have been studied by means of a Monte Carlo simulation. Three fundamental kinetic processes can be distinguished: (1) Auger recombination limited decay; (2) deep-tail-states emission limited decay; and (3) emission-and-recombination bimolecular decay. The effects of the injection level of minority carriers are investigated. Higher injection corresponds to less importance of the tail states. The relative importance of Shockley–Read–Hall recombination through the tail states is determined by the capture cross section for majority carriers and also by the lattice temperature. Results presented here will help to clarify recombination mechanisms and to extract the Auger coefficients and the band-tail density from transient decay measurement.
Modeling the cutoff frequency of single-heterojunction bipolar transistors subjected to high collector-layer current
Authors: Liou J. J. , Lindholm F. A. , Wu B. S.
Published: July 2002

High current densities in the collector layer reduce the cutoff frequency of heterojunction bipolar transistors. We develop a model based on analytical expressions that describe this reduction. These expressions represent the contributions from each of six regions defined in the output current-voltage characteristic. The model has parameters determined entirely by device physical makeup. It has no fitting parameters. Its predictions agree well with experimental data taken on two N/p+/n aluminum-gallium-arsenide/gallium-arsenide transistors having abrupt junctions grown by molecular-beam epitaxy. Because previous models omitted the effects of high current densities, their predictions agree less favorably. The development of the model considers the effects that compound-semiconductor properties such as velocity overshoot have on the cutoff frequency.
Magnetic properties of (001)bcc Fe/(001)fcc Ag superlattices
Authors: Cabanel R. , Etienne P. , Lequien S. , Creuzet G. , Barthélémy A. , Fert A.
Published: July 2002

The magnetic properties of (001)bcc Fe/(001)fcc Ag superlattices grown by molecular-beam epitaxy on (001) GaAs and characterized by reflection high-energy electron diffraction, Auger spectroscopy, and x-ray diffraction are presented. From magnetization (SQUID) and torque experiments, the strong interface uniaxial anisotropy which tends to align the magnetization along the normal to the layers is determined. This interface anisotropy overcomes the demagnetizing field effect when the thickness of the Fe layers decreases below 10 Å. The anisotropy constant Ku is derived from both experiments, which leads to 0.8 erg/cm2 for the interface anisotropy constant Ks.
Particle interaction in numerical micromagnetic modeling
Authors: Yan Ying Dong , Torre Edward Della
Published: July 2002

Numerical micromagnetic modeling of a single particle and small numbers of particles has recently greatly increased our understanding of fine particle magnetizing processes, but the behavior of a large number of such interacting particles is not yet completely understood. The analysis presented here shows that the moving-model Preisach approach, as a framework for explaining the behavior of such a distribution, is plausible; however, the proportionality factor is considerably different from the one that had been previously calculated.
Identification of the Mn structure in Mn/Ag(001) superlattices
Authors: Idzerda Y. U. , Jonker B. T. , Elam W. T. , Prinz G. A.
Published: July 2002

We have examined the structure of Mn in coherent ultrathin-film (Mn/Ag) superlattices by application of conversion-electron extended x-ray absorption fine structure (CEEXAFS), which is a near-surface variant of extended x-ray absorption fine structure (EXAFS). The superlattices were grown by molecular beam epitaxy with 20 to 100 periods, the periods consisting of 1, 2, 3, 5, and 14 monolayers (ML’s) of Mn and 10–15 ML’s of Ag. Exploiting the single-crystal nature of the samples and the polarization properties of synchrotron radiation, we have found that the Mn structure for superlattices with 3 ML Mn layers, corresponding to one complete unit cell, is nearly fcc with a c/a ratio of 1.4±0.1 (for fcc, c/a=√2). For a superlattice with 5 ML Mn layers, corresponding to two complete unit cells, the out-of-plane spacing is decreased to give a body-centered-tetragonal structure with a c/a ratio of 1.13±0.06. No measurable change occurs in the Mn structure as the Mn layer thickness increases further to 14 ML’s. Above 14 ML’s, the Mn film cannot maintain the single-crystal phase and loses long-range order. A detailed analysis of the CEEXAFS data shows a continuous increase of the disorder within the films.
Specific heat of ferromagnetic compounds RNi
Authors: Sato K. , Isikawa Y. , Mori K. , Miyazaki T.
Published: July 2002

The specific heats of the ferromagnetic compounds ErNi, GdNi, and HoNi were measured by means of the adiabatic method in the temperature range 2.2–100 K. The specific heats for these samples showed anomalies corresponding to the magnetic orders. For the result of ErNi above Tc we could analyze by Cv=γT+αT3. The electronic specific heat coefficient γ and the Debye temperature θD were estimated to be 90 mJ/mol K2 and 130 K, respectively. The magnetic entropy was discussed on the basis of the energy-level splitting due to the crystalline field.
Static and dynamic comparisons of signal, noise, and resolution for MO field modulation recording
Authors: Madison M. R. , Makansi T. , McDaniel T. W.
Published: July 2002

A complete model, including both writing and reading, of field-modulated magneto-optical recording is presented. Data are shown to corroborate the model in terms of the readback signal amplitude versus linear density. Mark-edge shapes are calculated from a Green’s function thermal model, and the edges are correlated with the read intensity profile to determine the channel roll-off curve. In addition, the data presented show that the mixed magnetization content in field-modulated recording is not a function of modulation rate. The data reveal the thermal interaction of adjacent marks in beam-modulation recording and the resulting degradation of the channel response relative to field modulation.
Saturation-moment variation and Cr segregation in CoCr-sputtered films
Authors: Snyder J. E. , Kryder M. H. , Wynblatt P.
Published: July 2002

We have investigated saturation magnetization (Ms) variation and Cr segregation in CoCr rf-sputtered films. Using a special substrate-temperature monitoring system, which provides in situ measurements, the relationships of Ms to substrate temperature (Tsub) and Tsub to sputtering parameters have been investigated for films sputtered from both alloy and mosaic targets. Ms was found to increase as Tsub decreased. Little difference was found between films sputtered from the two different types of targets. A theoretical model has been developed for calculation of equilibrium Cr segregation on grain boundaries. The composition of atomic planes near a grain boundary, depletion of the crystal core, and Ms of the crystals can be calculated as a function of temperature. Although the predicted amount of Cr segregation is in agreement with experimental measurements in the literature, the predicted variation of Ms with temperature is only a small fraction of what is seen experimentally. It is concluded that mechanisms other than Cr segregation must be found to provide the explanation for the variation of Ms in CoCr films.
The superconducting phases of UPt3 under pressure
Authors: Behnia K. , Taillefer L. , Flouquet J.
Published: July 2002

The upper critical field Hc2(T) of the heavy fermion superconductor UPt3 for a magnetic field applied in the basal plane has been studied down to 150 mK and under hydrostatic pressure up to 10 kbar. The kink already observed in Hc2(T) at ambient pressure disappears by applying a relatively low pressure. This suggests that the high-temperature low-field superconducting phase reported recently is rapidly suppressed by pressure. A possible interpretation of these results is discussed in connection with recent theories.
Magnetic properties of the sendust/Ta2O5 multilayer thin films
Authors: Hur J. H. , Park N. T. , Kwon S. I. , Song H. S. , Chang H. S.
Published: July 2002

The Sendust multilayer thin films were fabricated to improve magnetic properties by rf magnetron sputtering. The effective permeability of the film with 50 Å of a Ta2O5 middle layer was 1800 when annealed at 500° C. The coercivity of the film was 0.5 Oe. When the middle-layer thickness was thicker than 100 Å, the result showed no magnetic improvement in permeability and coercivity.
Muon-spin-relaxation study of magnetism in ErBa2Cu3O6.2
Authors: Lichti R. L. , Chan K-C. B. , Adams T. R. , Boekema C. , Dawson W. K. , Flint J. A. , Cooke D. W. , Kwok R. S. , Willis J. O.
Published: July 2002

The copper magnetism of ErBa2Cu3O6.2 is examined by transverse-field (TF) and zero-field (ZF) muon-spin relaxation (μSR). These data indicate two magnetic phases with TN1≂330 K and TN2∼65 K. The second phase is signaled by deviation of the ZF-μSR frequencies from a standard magnetization curve and an abrupt change in the TF-μSR relaxation rate. A relaxation feature indicates a muon depolarization mechanism with a T3/2 dependence in the low-temperature phase. Observed fields are compared to those calculated for proposed magnetic structures.
Time-dependent response and the de Almeida–Thouless line in R 1:2:3 superconductors
Authors: Foldeaki M. , McHenry M. E. , Koszegi L. , O’Handley R. C. , Dunlap R. A.
Published: July 2002

As shown recently, the time-dependent response in high-temperature superconductors can be well evaluated on the basis of the classical theory of first-order relaxation processes, if the temperature is low enough. In this article we extend our investigation to the high-temperature limit and show that the decrease of the logarithmic relaxation rate is an experimental consequence of the relaxation model and not a critical slowing down. On the basis of a comparison of the different classical relaxation processes and superconductive time-dependent response the special features of the superconductor can be interpreted. It is shown that all irreversible relaxation results in thermal hysteresis as a consequence of the difference between the time scale of the relaxation and the experiment. This feature introduces difficulties into the experimental determination of the de Almeida–Thouless lines.
Electron-spin resonance in single crystals of YBa2Cu3O7−x and Bi4/3Pb2/3Sr2CaCu2O8+x
Authors: Karim R. , Seed R. , How H. , Widom A. , Vittoria C. , Balestrino G. , Paroli P.
Published: July 2002

We report on electron-spin resonance on single crystals of YBa2Cu3O7−x and Bi4/3Pb2/3Sr2CaCu2O8+x at 9 GHz. While in the YBCO there was no observable ESR signal in the normal state (above Tc) or in the superconducting state (below Tc), we did observe a large microwave nonresonant absorption below Tc at low field values (H<200 Oe). We attribute this form of absorption to fluxoid formation below Tc. In the BiPbSrCaCuO single crystals, a significantly different result was found in that an electron-spin-resonance signal was measured both above and below Tc, besides the low-field absorption occurring only below Tc. The g value was found to be 2.055 and reasonably constant with temperature from 300 to 4 K with H parallel to the c axis. We attributed the ESR line to Cu++ ion excitation. The ESR signal increased as T decreased from 300 K to Tc and the variation with temperature fits a Boltzmann statistics law. Below Tc the ESR signal remained constant as T was decreased below Tc. We explained this result in terms of two competing statistical effects. One effect is due to the fact that the ESR signal in the fluxoid region increases as the Boltzmann factor, but the fluxoid density decreases by the same factor. The net effect is that the ESR signal is constant with temperature below Tc. Hence, this is a clear demonstration of statistics involved in the formation of fluxoids.
Magnetic properties of laser deposited films of Y-Ba-Cu-O
Authors: McGuire T. R. , Dimos D. , Gupta A. , Koren G. , Laibowitz R. B.
Published: July 2002

Films of YBa2Cu3O7−x prepared by laser ablation deposition show epitaxial growth on (100) SrTiO3 substrates with the c axis perpendicular to the plane of the film. With the magnetic field (H) parallel to the c axis, critical currents of up to 40 MA/cm2 from magnetization measurements are obtained. With H perpendicular to the c axis, various magnetization measurements with field cooling in 40 kOe indicated strong pinning effects with a calculated critical current density significantly higher than that observed in the parallel field configuration.
Ultrathin magnetic Fe films on W(001): A spin-polarized inverse photoemission study of Fe electronic structure evolution (abstract)
Authors: Cai Qing , Lapeyre Gerald J. , Avci Recep
Published: July 2002

By using spin-dependent electron spectroscopic techniques, one can explore the relevant problems in 3d metallic ferromagnetism, including temperature effects. Current surface science methods of ultrathin-film preparation and characterization make it possible to study interesting two dimensional magnetic systems. In the present work, ultrathin epitaxially grown Fe films on W(001) have been investigated by spin- and angle-resolved inverse photoemission spectroscopy. The evolution of the electronic structure has been studied for thickness from one monolayer to ‘‘bulklike’’ Fe thin films. In-plane remanent magnetization is observed. In the thick bulklike sample, transitions to majority and minority states near the H point of bcc Fe were identified, in contrast with data from bulk Fe(001).1 The thinner Fe films showed a trend of ‘‘collapsing’’ d bands at H′25. The results suggested a reduced Curie temperature for monolayers thick films. Information obtained for examining the correlation length in the itinerant ferromagnetic systems does not support the local-band picture at finite temperatures.2
The structure and magneto-optic properties of MnAl-based thin films
Authors: Shen J. X. , Kirby Roger D. , Sellmyer D. J.
Published: July 2002

We have measured the magnetization and magneto-optic Kerr rotation of sputtered thin films of Mn-Al-Cu ternary alloys over a wide composition range and for substrate temperatures between 25 and 450 °C. Magnetization and x-ray diffraction measurements suggest that our films are a mixture of the ferromagnetic kappa (κ) phase of MnAl and a highly paramagnetic amorphous phase. Room-temperature magneto-optic measurements on these films show a saturation polar Kerr rotation of up to 0.12° with little wavelength dependence.