bluuebunny/crossref_metadata_2025 huggingface dataset:
Accounting for the response of dynamically loaded annealed manganin gauges
Authors: Rosenberg Z. , Charest J.
Published: July 2002

The piezoresistive response of annealed manganin stress gauges is analyzed in terms of an elastoplastic model which was used to describe the behavior of nonannealed gauges. It is shown that the measured resistance changes can be accurately accounted for if we choose the right values for the yield strength of the annealed gauge and its variation with shock stress. This good agreement between predicted and measured values enhances our confidence in the analytical model which was used recently to explain various features of the response of piezoresistance gauges to shock loading.
Theory of thin-film orientation by ion bombardment during deposition
Authors: Bradley R. Mark , Harper James M. E. , Smith David A.
Published: July 2002

We study the development of orientational order in thin films grown with off-normal incidence ion bombardment during deposition. The overall orientational order in our model results from the dependence of the sputtering yield on grain orientation. We demonstrate that the degree of orientational order at the surface of a thick film grows slowly with increasing ion flux until, at a critical value of the flux, it begins to rise more steeply and then saturates at its maximum value. The time needed to approach the thick-film limit displays a peak as the ion flux is varied. We compare our work with the experimental results of Yu et al. [Appl. Phys. Lett. 47, 932 (1985)] and use our results to show how the deposition technique can be optimized.
Bounds on the conductivity of a suspension of random impenetrable spheres
Authors: Beasley J. D. , Torquato S.
Published: July 2002

We compare the general Beran bounds on the effective electrical conductivity of a two-phase composite to the bounds derived by Torquato for the specific model of spheres distributed throughout a matrix phase. For the case of impenetrable spheres, these bounds are shown to be identical and to depend on the microstructure through the sphere volume fraction φ2 and a three-point parameter ζ2, which is an integral over a three-point correlation function. We evaluate ζ2 exactly through third order in φ2 for distributions of impenetrable spheres. This expansion is compared to the analogous results of Felderhof and of Torquato and Lado, all of whom employed the superposition approximation for the three-particle distribution function involved in ζ2. The results indicate that the exact ζ2 will be greater than the value calculated under the superposition approximation. For reasons of mathematical analogy, the results obtained here apply as well to the determination of the thermal conductivity, dielectric constant, and magnetic permeability of composite media and the diffusion coefficient of porous media.
Measurements of the lifetime of the ruby R1 line under high pressure
Authors: Sato-Sorensen Yosiko
Published: July 2002

The lifetime τ of the R1 fluorescence line, 2E(Ē)→4A2 of ruby (Al2O3:Cr3+) has been measured under high-pressure conditions (up to 42.7 GPa) using a modulation fluorometry technique. This study shows that τ increases linearly with pressure and that this increase is primarily caused by a rapid decrease in the transition probability of the radiative transition. The present measurements agree qualitatively with the theoretically predicted decrease in the oscillator strength at high pressure.
Influence of ac contact impedance on high-frequency, low-temperature, or fast-transient junction measurements in semiconductors
Authors: Shiau Jeng-Jye , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

The behavior of a semiconductor contact is usually represented by the specific contact resistance determined by a dc measurement. A copper-gold contact on p-type cadmium telluride is used to illustrate the influence of the ac contact impedance on standard semiconductor measurements such as capacitance versus voltage, admittance spectroscopy, and deep-level transient spectroscopy. These experimental results show that a semiconductor contact with negligible dc voltage drop may have a significant influence on high-frequency, low-temperature, or fast-transient measurements. Knowledge of the contact capacitance as well as the contact resistance is necessary to predict the influence of the contact.
Space-charge-limited current and capacitance in double-junction diodes
Authors: Grinberg A. A. , Luryi Serge
Published: July 2002

An analytical theory is given for the space-charge-limited current in n-i-n or p-i-p diodes. The exact I-V characteristic is obtained in a parametric form. In the limit of high currents or for a large width of the intrinsic (i) base region the characteristics reduce to a Mott–Gurney form. In the low-current limit a linear I-V characteristic is obtained. The space-charge barrier presents a conceptually different case from a conventional barrier current in that the position of the barrier moves depending on the biasing condition. It is this motion which is responsible for the linear regime—which extends over a substantial range (∼10kT/e) of the applied voltage. The distribution of the electrostatic potential and of the quasi-Fermi level in the base, as well as the position of the potential maximum (the virtual cathode), are shown for different current levels. The differential capacitance of the double-junction diode is calculated and shown to be strongly dependent on the applied bias.
Structural properties of GaAs on (001) oriented Si and Ge substrates
Authors: Neumann D. A. , Zabel H. , Fischer R. , Morkoç H.
Published: July 2002

A detailed x-ray scattering study of GaAs grown by molecular beam epitaxy on (001) oriented Si and Ge substrates is reported. It is shown that the broadening of the GaAs Bragg peaks can be understood in terms of residual strains for samples 2 μm thick. For a sample 0.2 μm thick, domain size broadening effects corresponding to the total thickness of the GaAs film must also be included in order to explain the peak widths. In none of the samples was any evidence of antiphase domain broadening observed and we are thus able to place a minimum of 4000 Å on the size of any possible antiphase domains. We also find that the GaAs lattice is incommensurate with the Si substrate and that the GaAs is tetragonally distorted at room temperature. This distortion is explained by the difference in the thermal expansion of GaAs and Si.
Stresses in TaSix films sputter deposited on polycrystalline silicon
Authors: Teal V. L. , Murarka S. P.
Published: July 2002

Stress in thin TaSix films sputtered on polycrystalline silicon was studied as a function of temperature. A dual laser-beam apparatus was used to measure wafer curvature in situ. Stress was studied in the TaSi2/undoped polysilicon structure, in TaSi2 on polysilicon doped with either phosphorus, arsenic, or boron, and in films with a deposited Si/Ta ratio of more than 2. Several observations of stress-temperature behavior in TaSi2 were made. Tensile stress in TaSi2/undoped polysilicon increases to 1.2×1010 dyn/cm2 at 450 °C during the postdeposition anneal, decreases to near 0 at 900 °C, and linearly increases as temperature is subsequently lowered. Both doping and stoichiometry affected the stress-temperature behavior. N-type dopants decreased tensile stress and boron did not. Raising the Si/Ta ratio increased tensile stress at high temperatures. The stress-temperature measurements were combined with results from other characterization techniques to draw conclusions about the influence of temperature on the film. TaSi2 compound formation was found to occur at less than 400 °C in these films.
Mechanisms of spark propagation in ambient air at the surface of a charged dielectric. II. Theoretical modeling
Authors: Larigaldie S.
Published: July 2002

Experimental investigations on linear surface discharges in air at atmospheric pressure have shown three main regions displayed at the advancing tip of these discharges. Theoretical models of the evolution of the ionized medium along these three succeeding regions are now established. They show how the matching between the coronalike head of the negative gliding spark and the thermalized leader channel occurs via a turbulent plasma region of small dimensions, where the energy of the electrical field is transferred into ionization within a duration of about 10 ns.
Scattering of silicon inversion layer electrons by metal/oxide interface roughness
Authors: Li Jia , Ma T.-P.
Published: July 2002

The roughness at the metal/gate oxide interface of metal-oxide-semiconductor field-effect transistor (MOSFET) has been modeled. The mobility of electrons inside the channel of the MOSFET, limited by the scattering resulting from this roughness, has been calculated. The magnitude of this scattering mechanism is a strong function of the oxide thickness. For a MOSFET with very thin gate oxide (<100 Å), this limiting mobility may become comparable to the total mobility, and the scattering of electrons by the remote interface roughness can no longer be ignored.
Theory of induced spatial incoherence
Authors: Lehmberg R. H. , Schmitt A. J. , Bodner S. E.
Published: July 2002

This paper describes theoretical and experimental investigations of induced spatial incoherence (ISI), a technique for achieving the smooth and controllable target beam profiles required for direct-drive laser fusion. In conventional ISI, a broadband laser beam (coherence time tc=1/Δν≪tpulse) is sliced into an array of mutually incoherent beamlets by echelon structures that impose successive time delay increments Δt>tc. A focusing lens then overlaps those beamlets onto the target, which is usually located at the far field. Here, we evaluate the ideal target beam profiles for practical ISI focusing configurations, and examine the perturbing effects of transient interference, laser aberration, and plasma filamentation. Analytic and numerical calculations show that nonuniformities due to interference among the beamlets are smoothed by both thermal diffusion and temporal averaging. Under laser-plasma conditions of interest to inertial confinement fusion (ICF), average ablation pressure nonuniformities ∼1% should be readily attainable. We also investigate a partial ISI scheme, which allows widely spaced beamlets to remain mutually coherent; the resulting high spatial frequency interference structure can be effectively smoothed by thermal diffusion alone. A perturbation analysis shows that the average target profile 〈I(x)〉 remains relatively insensitive to laser beam aberration when the scale length of that aberration is larger than the initial beamlet width. This aberration will tend to broaden and smooth 〈I(x)〉, rather than introduce any small-scale structure. The broadening is largely controllable because it depends only upon spatial averages

of the aberrated quantities over the entire laser aperture; the uncontrollable perturbations can be reduced to ∼1% in practical cases. Filamentation in the underdense plasma has been studied numerically using a 2D propagation/hydro code selfoct, which includes both ponderomotive and thermal effects. For 0.25-μm light, this code predicts that ISI should suppress filamentation in plasmas of interest to ICF. We review recent planar target experiments carried out at the Naval Research Laboratory using 1.054- and 0.527-μm light, which show that the combination of ISI and shorter wavelength substantially reduces all evidence of plasma instabilities. Finally, we review a promising alternative technique for achieving ISI in KrF lasers without using echelons.
Temporal evolution of beam emittance from a field-emission electron gun
Authors: Bekefi G. , Hartemann F. , Kirkpatrick D. A.
Published: July 2002

The temporal evolution of the beam emittance and beam brightness from a field-emission electron gun (1.3 MV, 0.5 kA, 30 ns) has been measured with nanosecond time resolution by using a novel Čerenkov-electro-optic diagnostic. Observations show that guns provided with velvet-backed cathodes behave differently than, and are superior to, the more conventional graphite cathodes.
Atomic chlorine concentration measurements in a plasma etching reactor. I. A comparison of infrared absorption and optical emission actinometry
Authors: Richards Albert D. , Thompson Brian E. , Allen Kenneth D. , Sawin Herbert H.
Published: July 2002

Atomic chlorine concentrations in Cl2 and CF3Cl plasmas have been measured using both infrared absorption spectroscopy and optical emission actinometry. These measurements were made over a range of plasma conditions including plasma excitation frequencies of 72 kHz–13.5 MHz, power inputs of 10–100 W, and pressures of 200–800 mTorr. In Cl2 plasmas, the technique of optical emission actinometry misrepresents atomic chlorine concentration changes by nearly an order of magnitude. The errors in the actinometry technique are believed to result from excited state Cl production by electron impact dissociation of Cl2. A simple model for Cl emission is in good agreement with the experimental observations. In CF3Cl discharges, the technique of optical emission actinometry is shown to accurately represent variations in atomic chlorine concentration with changing process conditions.
Threshold voltage of luminescence and electrical tree inception in low-density polyethylene
Authors: Bamji S. S. , Bulinski A. T. , Densley R. J.
Published: July 2002

The characteristics of luminescence observed during the initiation of an electrical tree have been studied for polyethylene subjected to high electrical stresses. Use of a light detection system which is at least three orders-of-magnitude more sensitive than conventional partial discharge detectors shows that luminescence occurs during tree initiation and this luminescence is not due to partial discharges. Applying a constant high voltage to the polymer or interrupting the voltage several times does not change the behavior of luminescence. The light starts at about the same voltage and its intensity returns to the same value as before the interruption. This behavior is contrary to that observed for partial discharges. The luminescence inception voltage is the threshold voltage at which the polymer starts to degrade. Thus, it is important that the insulation of electrical equipment be protected from transient overvoltages which exceed the threshold level.
A structural and electrical comparison of thin SiO2 films grown on silicon by plasma anodization and rapid thermal processing to furnace oxidation
Authors: Nelson S. A. , Hallen H. D. , Buhrman R. A.
Published: July 2002

We have used capacitance-voltage (C-V) techniques and x-ray photoelectron spectroscopy (XPS) to study for the first time the electrical and structural properties of thin SiO2 films grown on silicon by plasma anodization and rapid thermal processes (RTO) and then compared them to furnace oxides. We have compared the SiO4 tetrahedral ring structure and the suboxide content of the ∼3-nm-thick interfacial region of these oxides and have found significant structural differences. By correlating these differences with measured electrical differences, we have identified the structural causes of some of the electrical characteristics of the plasma and RTO oxides. In plasma oxides we see larger amounts of silicon dangling bonds, Pb centers, at the Si-SiO2 interface and have identified these dangling bonds as the source of a localized peak of interface states found at 0.3 eV above the silicon valence band. Low-temperature rapid thermal annealing of the plasma oxides relieves localized compressive interfacial strain, apparently by allowing the completion of oxidation at the interface, and reduces the amount of dangling bonds. However, this strain relief simultaneously increases the average SiO4 ring structure at the interface. A larger interfacial SiO4 ring structure is also seen in rapid thermal oxides and has been attributed to the very rapid cooling which takes place at the end of the rapid thermal process. Post-growth thermal processing has been shown to reduce the average ring structure by relieving localized tensile interfacial stress, but this stress relief is accompanied by the appearance of a peak of interface states at about 0.8 eV above the valence band which is attributed to Si–O bonds broken during the anneal. Long furnace anneals of rapid thermal oxides remove these states and give interface state densities comparable to those of furnace oxides.
An experimental study of a parallel-plate radio-frequency discharge: Measurements of the radiation temperature and electron density
Authors: Hebner G. A. , Verdeyen J. T. , Kushner M. J.
Published: July 2002

Microwave diagnostic techniques have been used to measure the radiation temperature and electron density in parallel-plate capacitively coupled radio-frequency (2.5 MHz) discharges. Evidence is presented for the existence and importance of an energetic electron beam, produced by the large cathode sheath voltage, which sustains and excites the plasma. The measured radiation temperature of the bulk electrons is 500 K for helium and 800 K for argon. An upper limit on the radiation temperature is obtained for N2 (1200 K) and CF4 (3000 K) discharges. Measurements of the electron density in helium as a function of electrode spacing show a peak in the electron density that is consistent with the theory of ionization by beam electrons. The electric fields required to carry the rf current by drift in the bulk of the glow are low and consistent with the measured radiation temperature. The implications of these measurements on the nature of the rf plasma-sustaining mechanism. The voltage distribution, and the electron energy distribution are discussed.
Reactions of Zr thin films with SiO2 substrates
Authors: Wang S. Q. , Mayer J. W.
Published: July 2002

The reactions between Zr thin films and SiO2 substrates in the temperature range of 650–950 °C in vacuum have been studied by Rutherford backscattering spectrometry and glancing angle x-ray diffraction. A Zr-rich silicide, Zr5Si4, formed next to the SiO2 substrate and a surface layer of Zr oxide appeared on top of the Zr-rich silicide. The reaction was characterized by an activation energy, Ea =2.8 ±0.2 eV.
Brillouin scattering study of equation of state of single component liquids
Authors: Bohidar Himadri B.
Published: July 2002

Brillouin scattering experiments have been performed on a set of ten-single component liquids using a piezoelectric scanned, five-pass Fabry–Perot interferometer. The hypersonic sound velocities (vs) were determined as a function of externally applied pressure (P) from the observed Brillouin shifts. Experiments were performed at room temperature [T=(20±1)°C] and the pressure acting on the liquid samples was varied in the range 1–825 bars in steps of 100 bars each. By making use of modified Tait’s equation of state and assigning a linear pressure dependence to the adiabatic bulk modulus, we have constructed a theoretical model equation to express the pressure dependence of sound velocity as vs(P)=A0+A1P+A2P2. The experimental vs(P) values could be least-squares fitted to this equation within experimental error. From the values of the coefficients Ai’s we have determined the values of Tait parameters and the pressure coefficient of adiabatic bulk modulus. We found that the sound velocity, density, and bulk modulus all increase with pressure, the first two nonlinearly and the latter in a linear manner. These dependencies have been determined explicitly.
Effects of misfit dislocations and thermally induced strain on the film properties of heteroepitaxial GaAs on Si
Authors: Lum R. M. , Klingert J. K. , Bylsma R. B. , Glass A. M. , Macrander A.T. , Harris T. D. , Lamont M. G.
Published: July 2002

GaAs hereroepitaxial films on Si contain a high number of misfit dislocations and large internal stresses due to the lattice and thermal mismatch of the two materials. These greatly affect the structural, optical, and electrical properties of the films. We report a study of these effects in films grown by metalorganic chemical vapor deposition using x-ray diffraction, sample curvature, photoluminescence, and carrier concentration measurements. The x-ray data indicate that the lattice misfit strain is almost entirely relieved by the generation of dislocations, but that the difference in thermal expansion between the film and substrate causes significant tetragonal distortion of the GaAs lattice which results in wafer bowing and, for thicker GaAs layers, film cracking. Wafer bowing was successfully eliminated by growth of GaAs films on both sides of the Si substrate. Photoluminescence spectra of crack-free GaAs layers indicated that the thermally induced strain was distributed in a nonuniform but continuous manner throughout the film. The magnitude of the strain, as determined from x-ray diffraction, wafer curvature, and photoluminescence spectroscopy, was consistently 10% lower than the value calculated from simple thermal relaxation. Finally, for large numbers of misfit defects (>108 cm−2) the electrical properties of the sample were found to be correlated to the mean dislocation density of the GaAs film.
Volume holographic interconnections with maximal capacity and minimal cross talk
Authors: Lee Hyuk , Gu Xiang-guang , Psaltis Demetri
Published: July 2002

Optical interconnections utilizing volume holography are described. Intrinsic cross-talk effects that limit the number of independent interconnections are identified and analyzed by applying coupled-wave analysis. Sampling grids for removing the first-order cross talk are presented, resulting in a system limited by second- and third-order cross talk only.
Thermal fixing of holographic gratings in Bi12SiO20
Authors: Arizmendi L.
Published: July 2002

Fixing of holographic gratings in Bi12SiO20 single crystals has been obtained using a thermal process. The properties of the fixed gratings suggest that the charges responsible have an ionic nature. The study of thermal erasure of the fixed gratings provides a value of 1.44 eV for the activation energy and 0.03 cm2 s−1 for the preexponential factor for diffusion of these charges.
Measurements of mass separation in a vacuum arc centrifuge
Authors: Evans P. J. , Paoloni F. J. , Noorman J. T , Whichello J. V.
Published: July 2002

A vacuum arc centrifuge is described which produces a rapidly rotating metal plasma column by means of the Lorentz force between the arc current and an applied axial magnetic field. Analysis of samples deposited on collector surfaces indicates mass separation of elements that increases with the radius. For the plasma formed from a brass cathode, the mass separation of zinc with respect to copper depends on the configuration of the power supply and applied magnetic field and can exceed 50% at the outer radius of the plasma.
Observation of enhanced x-ray emission from long-pulse-width laser-produced plasmas
Authors: Ze F. , Kania D. R. , Langer S. H. , Kornblum H. , Kauffman R. , Kilkenny J. , Campbell E. M. , Tietbohl G.
Published: July 2002

Experiments investigating the pulse-width dependence of thermal x-ray conversion efficiencies (hν<1.5 keV) in laser-heated gold plasmas are described. The results show that the instantaneous ratio of the emitted x-ray flux to the laser energy deposition rate increases throughout a 4-ns laser pulse. The studies were carried out using single arms of the 10-beam Nova laser facility. The irradiance was ∼4–5×1014 W/cm2 in the target plane as we varied the laser pulses’ FWHM from 2 to 4 ns. The laser pulses were nominally flat-topped and contained between 1 and 2 kJ of (1)/(3) μm light. Time-resolved plasma radiation was monitored with a broadband, streaked x-ray spectrograph that has a roughly 30-ps time resolution and channels that are roughly 100–150 eV wide. One-dimensional numerical models run with the lasnex code produce a conversion efficiency that is nearly constant throughout the laser pulse. We discuss various approximations made in the one-dimensional models and conclude that none of them are a likely explanations for the increase of conversion efficiency with time. A preliminary two-dimensional model of a disk heated by a 3-ns pulse shows that the conversion efficiency increases throughout the pulse. The increase is due to soft x rays emitted from outside the laser spot. Further experiments and modeling will be carried out to assess these two-dimensional effects.
Domain wall relaxation in amorphous ribbons
Authors: Amano E. , Valenzuela R. , Irvine J. T. S. , West A. R.
Published: July 2002

Monodomain, polycrystalline hexagonal ferrites (BaFe12O19) and amorphous ribbons (Vitrovac 6025) were measured as a function of frequency with rf magnetic fields from 5 Hz to 13 MHz of various amplitudes. Monodomain ferrites showed the features of the spin rotation magnetization mechanism, while amorphous ribbons showed the low-frequency dispersion generally attributed to domain wall relaxation. However, at relatively high applied fields, a third dispersion is resolved at lower frequencies from domain wall relaxation, which can be attributed to magnetic hysteresis. By using some of the complex impedance formalisms, the relaxation character of domain wall bulging is confirmed, while hysteresis dispersion exhibited a complex behavior.
Pressure and temperature dependence of laser-induced fluorescence of Sm:YAG to 100 kbar and 700 °C and an empirical model
Authors: Hess Nancy J. , Schiferl David
Published: July 2002

The inability to measure pressure with accuracy at high temperature has been a hindrance to the development of simultaneous high-temperature, high-pressure experimental techniques. The results of recent laser-induced fluorescence studies at high temperature and high pressure indicate that Sm:YAG is a promising pressure calibrant with very low-temperature sensitivity. The most intense feature in the fluorescence spectrum is a doublet at 16186.5 cm−1. The Sm:YAG doublet exhibits a pressure-induced peak shift comparable to the R1 shift of ruby. However, the temperature-induced shift of the doublet is almost two orders of magnitude less than that observed for the R1 peak. Simultaneous high-pressure-temperature experiments indicate that the pressure and temperature effects on the frequency and line shape can be added linearly. An empirical model based on the linear combination of pressure dependent frequency shift and temperature dependent linewidth and intensity ratio successfully predicts the doublet line shape at simultaneous pressure and temperature. Use of the model facilitates measurement of peak position at high temperature resulting in improved accuracy and repeatability of the pressure determination. Pressure measurements at 400 °C and 40 kbar based on the Sm:YAG doublet peak position agree with the temperature-corrected ruby R1 pressure measurement to within 3 kbar. At 15 kbar and 900 °C the uncertainty in the Sm:YAG fluorescence peak wavelength is 5 cm−1 due to temperature-induced line broadening; this corresponds to an uncertainty in the pressure determination of ±2.5 kbar. The high thermal and chemical stability of YAG materials make Sm:YAG an ideal pressure calibrant for high-temperature applications. In addition the frequency and intensity of the Sm:YAG fluorescence allow simple conversion from experimental setups designed for ruby fluorescence measurement.
Degradation and lifetime studies of high-power single-quantum-well AlGaAs ridge lasers
Authors: Gfeller F. R. , Webb D. J.
Published: July 2002

Degradation studies with over 235 000 device hours have been performed on single-quantum-well AlGaAs lasers with uncoated and half-wavelength Al2O3 -coated facets at stress levels ranging from below threshold up to optical power densities of 23 mW per μm facet width. The effectiveness of facet protection has been investigated with respect to gradual degradation and catastrophic failures. Facet protection is very important for obtaining long lifetimes and improved immunity to sudden catastrophic failures. With facet coatings, degradation rates as low as 0.18%/kh have been measured at 30 mW in single-lateral-mode operation and at 50 °C.
Photoluminescence spectra of p-GaSe doped with Cd
Authors: Shigetomi S. , Ikari T. , Nishimura H.
Published: July 2002

Impurity levels in Cd-doped GaSe have been studied by using photoluminescence (PL) measurements. The PL spectra at 77 K are dominated by three new emission bands at 1.95, 1.75, and 1.62 eV. The PL intensity and the peak energy of the 1.95 and 1.62 eV emission bands are measured as a function of the temperature. It is shown that the 1.95 eV emission band is due to the transition between the conduction band and the acceptor level at 0.18 eV above the valence band. The 1.62 eV emission band is caused by the transition from the donor level at 0.37 eV below the conduction band to the acceptor level at 0.13 eV above the valence band. The PL intensity increases with increasing Cd concentration.
Use of atomic layer epitaxy buffer for the growth of InSb on GaAs by molecular beam epitaxy
Authors: Thompson P. E. , Davis J. L. , Waterman J. , Wagner R. J. , Gammon D. , Gaskill D. K. , Stahlbush R.
Published: July 2002

A 300 Å buffer layer of InSb grown by atomic layer epitaxy at a substrate temperature of 300 °C at the GaAs/InSb interface has been employed to grow epitaxial films of InSb having bulk-like properties. The reduction of the defects in the top InSb film has been observed with cross-sectional transmission electron microscopy and channeling Rutherford backscattering spectroscopy. The optimum substrate temperature for the primary InSb layer growth was 420 °C with an atomic flux ratio of Sb to In of 1.4 and a growth rate of 1 μm/h. The best 5-μm-thick InSb layers had x-ray rocking curve widths of 100 s, 77 K n-type carrier concentrations in the low 1015/cm3 range, and 77 K carrier mobilities greater than 105 cm2/V s. Mesa isolated photodiodes had carrier lifetimes of 20 ns, in comparison to 200 ns observed in bulk InSb having a similar carrier concentration. An unexplained, weak free-electron spin resonance transition has been observed in these films.
Influence of Te concentration on the infrared cathodoluminescence of GaAs:Te wafers
Authors: Méndez B. , Piqueras J.
Published: July 2002

Cathodoluminescence (CL) scanning electron microscopy has been used to investigate the nature and distribution of defects involved in the infrared emission of GaAs:Te wafers. Spectral and CL-contrast changes as a function of doping level have been found. Profiles of infrared CL intensity across the wafers show an inverted U shape.
Magnetic viscosity in perpendicular media
Authors: Lyberatos A. , Chantrell R. W. , Sterringa E. R. , Lodder J. C.
Published: July 2002

The remanent magnetization of fine particle media of perpendicular anisotropy is known to exhibit a time decay of pseudologarithmic form. The viscous properties are to a large extent determined by the magnetostatic particle interaction and the particle size. A mean-field model of a perfectly aligned ensemble of Stoner–Wohlfarth particles is presented that gives a qualitative description of the hysteretic and time-dependent properties of particulate perpendicular media. The time decay of the remanent magnetization of Alumite media after initial magnetic saturation was measured. The decay was found to be logarithmic within the measuring period, and a coefficient of magnetic viscosity was obtained. Although the reversal mechanism for the particles in Alumite media is known to be incoherent, a good qualitative agreement between the theoretical model and the measurements was found by introducing a reduced effective volume acting as a scaling factor that accounts for the discrepancy in reversal mechanisms.
Contactless electrical characterization and realization of p-type ZnSe
Authors: Farrell H. H. , Tamargo M. C. , Gmitter T. J. , Weaver A. L. , Aspnes D. E.
Published: July 2002

ZnSe is a potentially useful optoelectronic material for applications requiring emission in the blue region of the spectrum. However, such applications necessitate the development of p-type material, for which reliable ohmic-contact technology does not exist. To avoid difficulties associated with contact formation while developing p-type material, we combine two contactless methods, reflectance-difference spectroscopy and inductive-coupled radio-frequency loss to determine carrier type and sheet resistance, respectively. Using this information we have prepared conducting p-type ZnSe by doping the material during growth with Li.
Die-upset Nd2Fe14 M magnets (M=B and C)
Authors: Fuerst C. D. , Brewer E. G.
Published: July 2002

Melt-spun Nd-Fe-B ribbons are limited to remanences of about 8 kG by the random orientation of the Nd2Fe14B grains. Hot deformation (die upsetting) causes these grains to reorient with the c axis aligned along the press direction, resulting in a 50% increase in the remanence (12 kG). Previously others have produced magnetically hard melt-spun ribbons containing the isostructural phase Nd2Fe14C which, like the boride ribbons, were isotropic. By adjusting alloy stoichiometry and process variables, it is possible to die upset Nd-Fe-C magnets with properties similar to Nd-Fe-B magnets. As with the boride magnets, the remanences of the die-upset Nd-Fe-C magnets were enhanced about 45% relative to the isotropic precursor. However, the remanences of die-upset carbide magnets were limited to about 10 kG due to the lower saturation magnetization of the Nd2Fe14C phase and higher levels of impurity phases.
Generation and recovery of strain in 28Si-implanted pseudomorphic GeSi films on Si(100)
Authors: Bai G. , Nicolet M.-A.
Published: July 2002

Effects of ion implantation of 320 keV 28Si at room temperature in pseudomorphic metastable GexSi1−x (x≊0.04, 0.09, 0.13) layers ∼170 nm thick grown on Si(100) wafers were characterized by x-ray double-crystal diffractometry and MeV 4He channeling spectrometry. The damage induced by implantation produces additional compressive strain in the GexSi1−x layers, superimposed on the intrinsic compressive strain of the heterostructures. This strain rises with the dose proportionally for doses below several times 1014 28Si/cm2. Furthermore, for a given dose, the strain increases with the Ge content in the layer. Upon thermal processing, the damage anneals out and the strain recovers to the value before implantation. Amorphized samples (doses of greater than 2×1015 28Si/cm2) regrow poorly.
A fracture model for a weak interface in a viscoelastic material (small scale yielding analysis)
Authors: Hui Chung-Yuen , Xu Da-Ben , Kramer Edward J.
Published: July 2002

The problem of adhesion at the interface between two polymers is investigated using a fracture mechanics approach. The effect of viscoelastic deformation of the bulk polymers and the micromechanical behavior of the interface on the fracture toughness of the interface was investigated by analyzing the problem of a steadily growing interface crack under the condition of small scale yielding. This condition assumes that the region of displacement discontinuity across the interface (the adhesive zone) due to loss of adhesion is small compared with typical specimen dimensions. It is found that the amount of inelastic or viscous energy dissipation is strongly coupled to the interface behavior and that the measured interface fracture toughness can be much higher than the intrinsic interface fracture toughness. For sufficiently high crack growth rates, a simple expression is obtained which relates the rate of viscous energy dissipation and the intrinsic interface fracture toughness to the viscoelastic properties of the bulk polymer. The dependence of the stress field inside the adhesive zone and the length of the adhesive zone on the viscoelastic properties of the polymer, the applied loading, the interface micromechanical model and the crack growth rate ȧ is obtained by numerically solving an integral equation. The size of the region of the viscoelastic energy dissipation is found to scale with ȧτr , where τr is the retardation time of the bulk polymer.
Excitation and deexcitation of ac-driven thin-film ZnS electroluminescent devices
Authors: Sohn S. H. , Hamakawa Y.
Published: July 2002

Theoretical formulas accounting for the excitation and deexcitation processes of the alternating current-driven thin-film electroluminescent devices have been obtained, which include both the impact excitation and the energy-transfer mechanisms. The empirical equations for the conduction current duration time and the luminescent decay time related to the tunneling emission of electrons at the interface, the capture of holes in traps, and the light emission of luminescent centers lead to the analytical formulas for the transferred charge ΔQ, the luminance L, and other quantities of physical interest as a function of the electric field. The estimates for ΔQ and L in ZnS:Mn and ZnS:TbF3 devices have been made on the basis of Wolff’s distribution function and found to be in good agreement with the experimental data. From the estimated results, it is found that the energy-transfer mechanism depends on various material parameters and drive conditions, and that it plays a role in improvement of the luminance in the low-electric-field region. In the high-electric-field region of interest, the energy transfer from Cu-related sensitizers to luminescent centers in ZnS:Mn and ZnS:TbF3 devices yields an increase of luminance by a factor of about 1.5 and 3, respectively.
Heavily doped p-GaAs grown by low-pressure organometallic vapor phase epitaxy using liquid CCl4
Authors: Yang L. W. , Wright P. D. , Eu V. , Lu Z. H. , Majerfeld A.
Published: July 2002

A hole concentration greater than 1020 cm−3 in GaAs has been achieved using a liquid CCl4 source for carbon in a low-pressure organometallic vapor phase epitaxy system. The resistivity and hole mobility measured at 300 K for a heavily carbon-doped (1.2×1020 cm−3) Hall sample made from a thin (180 nm) epitaxial layer were 8.0×10−4 Ω cm and 65 cm2/V s, respectively. Carbon-doped samples with excellent surface morphology were achieved using a V/III ratio of 22, and growth pressure and temperature of 80 Torr and 600 °C, respectively. A novel photoluminescence technique, based on band-gap shrinkage of heavily doped p+-GaAs, has been shown to be useful for nondestructive measurement of the hole concentration in submicrometer layers.
Some phenomenological relaxation rate equations based on Bose–Einstein similar kinetics
Authors: Kubát Michael J. , Jansson Jan-Fredrik , Delin Mats , Kubát Josef , Rychwalski Rodney W. , Uggla Sven
Published: July 2002

The possibility of describing transient phenomena associated with flow and consolidation of solids, such as stress relaxation or physical aging, in terms of a kinetic mechanism comprising spontaneous and induced events is discussed. The starting point is the differential equation dṅ/dt=−aṅ[1−(b/a)ṅ], with n denoting the number of relaxed entities and ṅ=dn/dt (a,b are constants, t is time), yielding an ṅ(t) function reminiscent of a Bose–Einstein distribution. The corresponding n(t) relation describes the linear variation of n with log t, and the exponential dependence of ṅ on n, as often found experimentally. Replacing ṅ in the starting equation by the relative rate ṅ/n yields a power-law-type ṅ(n) dependence. A further modification, where the induction term ṅ/n is not linear but raised to a power ≳1, finally produces a generalized version of the stretched exponential. When interpreted formally in terms of a spectrum of relaxation times τ, all three equations produce response functions with discrete τ distributions, provided a≠0.
Limits to ion energy control in high density glow discharges: Measurement of absolute metastable ion concentrations
Authors: Giapis Konstantinos P. , Sadeghi Nader , Margot Joëlle , Gottscho Richard A. , Lee T. C. John
Published: July 2002

Unprecedented demands for uniformity, throughput, anisotropy, and damage control in submicron pattern transfer are spurring development of new, low pressure, high charge density plasma reactors. Wafer biasing, independent of plasma production in these new systems is intended to provide improved ion flux and energy control so that selectivity can be optimized and damage can be minimized. However, as we show here, an inherent property of such discharges is the generation of significant densities of excited, metastable ionic states that can bombard workpiece surfaces with higher translational and internal energy. Absolute metastable ion densities are measured using the technique of self-absorption, while the corresponding velocity distributions and density scaling with pressure and electron density are measured using laser-induced fluorescence. For a low pressure, helicon-wave excited plasma, the metastable ion flux is at least 24% of the total ion flux to device surfaces. Because the metastable ion density scales roughly as the reciprocal of the pressure and as the square of the electron density, the metastable flux is largest in low pressure, high charge density plasmas. This metastable ion energy flux effectively limits ion energy and flux control in these plasma reactors, but the consequences for etching and deposition of thin films depend on the material system and remain an open question.
Dynamic activity of dislocations in gallium phosphide
Authors: Yonenaga Ichiro , Sumino Koji
Published: July 2002

Dynamic activities of α, β, and screw dislocations in a GaP crystal containing sulphur as the main impurity at a concentration of 7×1017 cm−3 are investigated as a function of stress and temperature by means of the etch pit technique. Generation of all types of dislocations from a surface scratch is found to be suppressed at temperatures higher than 500 °C and is interpreted in terms of dislocation locking due to impurities and/or impurity-defect complexes as has been observed in GaAs and InP. α dislocations move faster than β and screw dislocations and their velocities are expressed with the same type of empirical equation as a function of the stress and the temperature as those in other semiconductors. Roughly speaking, dislocations in GaP move at velocities lower than those in GaAs by about two orders of magnitude.
Radially dependent solutions of Boltzmann’s equation in low-temperature plasmas using a modified two-term expansion
Authors: Hartig Michael J. , Kushner Mark J.
Published: July 2002

A new method for obtaining spatially resolved electron energy distributions is described and applied to cylindrical bore electric discharges. The method is based on a modified two-term spherical harmonic expansion of Boltzmann’s equation in which energy-resolved drift and diffusion are included, as well as Joule heating or cooling by the ambipolar field. It is found that low-energy electrons may be heated by the large ambipolar electric field gradients near the wall while higher-energy electrons may escape the plasma. Therefore, diffusion cooling and Joule heating in the ambipolar field may simultaneously occur, but for different portions of the electron energy distribution.
Comprehensive analysis of Barkhausen emission spectra using pulse height analysis, frequency spectrum, and pulse wave form analysis
Authors: Sipahi L. B. , Jiles D. C. , Chandler D.
Published: July 2002

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard has been agreed upon for parameterization and representation of Barkhausen signals. It appears from this work that field excitation wave form and frequency should define the inputs, while detection frequency range, pulse height spectrum, frequency spectrum, and emitted pulse wave form analysis should be used to quantify the output.
Structural and Mössbauer studies of the alloy system FeAl1−xNbx
Authors: Mahmood Sami H. , Awawdeh Mufeed A. , Saleh Ahmad S.
Published: July 2002

X-ray diffraction and Mössbauer spectroscopy results of the system FeAl1−xNbx show that the cubic (CsCl) FeAl phase dominates for small values of x, and persists as x increases, but also, the hexagonal (C14) Fe2Nb phase develops. The values of the lattice constants and Mössbauer hyperfine parameters indicate that both phases contain impurities, i.e., the phases are FeAl(Nb) and Fe2Nb(Al). The Debye temperature ΘD for the FeAl phase is derived from the intensity analysis of the diffraction lines and a value of (385±5) K is obtained. This is nearly equal to the Debye temperatures for alloys of Fe and Nb. This result is also supported by the fact that the relative Mössbauer absorption intensities corresponding to the two phases remain constant as the temperature is lowered down to 85 K. The absence of magnetic hyperfine splittings in Mössbauer spectra indicate that both phases of the alloy system remain paramagnetic down to the LN2 temperature.
Effect of microstructural features on media noise in longitudinal recording media
Authors: Nolan T. P. , Sinclair R. , Ranjan R. , Yamashita T.
Published: July 2002

High-resolution transmission-electron microscopy (HRTEM) has been used to analyze CoCrTa, CoCrPt, and CoNiCrPt alloy thin films deposited under similar conditions onto NiP plated Al substrates with a Cr underlayer. Apparent ∼50 nm Co alloy grains observed by bright field TEM are found to be clusters of smaller 10–20 nm grains with a common growth orientation. Subtle differences have also been observed in the stacking fault density, Co alloy fcc phase concentration, lattice mismatch, and grain separation in the films. In particular, HRTEM shows that the CoCrTa film has clear physical separation between the 10 and 20 nm grains, which is not observed in the other media. Despite similar hysteresis loop properties, the signal-to-noise ratio of CoCrTa is 2.3 dB higher than CoCrPt and 4.6 dB higher than CoNiCrPt. Small isolated grains have been shown to improve media noise, as is observed in CoCrTa media.
Ce2Fe17: Mixed valence or 4f band?
Authors: Coey J. M. D. , Allan J. E. M. , Minakov A. A. , Bugaslavsky Yu. V.
Published: July 2002

The Ce2Fe17 compound has a volume that is 4% smaller than expected for a localized 4f1 configuration of cerium. The Ce LIII absorption edge shows two peaks, at 5734 and 5740 eV. There is an extremely large linear term in the low-temperature specific heat, γ=560±100 mJ/mol K2. These results are discussed in terms of 4f0(Ce4+)↔4f1(Ce3+) valence fluctuations or a narrow 4f band at the Fermi level occupied by less than one 4f electron per cerium, where the heat capacity is enhanced by 4f quasiparticle formation.
Ferromagnetic instability in a mean-field slave-boson approach for the Anderson lattice
Authors: Dorin V. , Schlottmann P.
Published: July 2002

We consider a stoichiometric metallic Anderson lattice with orbital degeneracy in the U→∞ limit. A Gutzwiller type of mean-field approximation is formulated in terms of three slave bosons per site in analogy to Kotliar and Ruckenstein’s approach for the Hubbard model. In the orbitally nondegenerate case the paramagnetic solution becomes unstable towards ferromagnetism if the valence is smaller than a critical one. This instability is suppressed with increasing orbital degeneracy.
Electrical characteristics of barium titanate films prepared by laser ablation
Authors: Yeh M. H. , Liu Y. C. , Liu K. S. , Lin I. N. , Lee J. Y. M. , Cheng H. F.
Published: July 2002

The BaTiO3 ferroelectric films of quality suitable for applying as dielectrics in 64 and 256 Mb dynamic random access memory have been successfully synthesized using the laser ablation technique. The dielectric constant and dielectric strength of the films are ε=200 and 1 MV/cm, respectively. The switching characteristics are Qc=0.66 μc/cm2, ts=0.1 ps, and J1=1.57 μA/cm2 at 2.5 V, for charge storage density, writing time, and leakage current density, respectively. The quality of the BaTiO3 films is superior to the Ta2O5 dielectric films and is comparable to the lead-zirconate-titanate ferroelectric films.