bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation in polycrystalline thin films using a preconditioned finite element method
Authors: Suess D. , Tsiantos V. , Schrefl T. , Scholz W. , Fidler J.
Published: July 2002

The dynamic response of a 80 nm×400 nm×25 nm Co film with and without polycrystalline grains is calculated. The numerical method combines a finite element scheme for space discretization with a preconditioned backward differentiation method for the time integration of the Landau–Lifshitz–Gilbert equation. The use of proper preconditioning techniques for the backward differentiation formulas increases its efficiency by a factor of 40. The speed up factor compared to the Adams method is more than three orders of magnitude. In the polycrystalline thin film the nucleation of reversed domains occurs throughout the sample at grain boundaries and sharp edges. For the single crystalline film reversal starts at particle ends. Surface roughness does not significantly change the reversal mode but reduces the switching time by 40%.
Magnetoresistance study in thin zig zag NiFe wires
Authors: Tsai J. L. , Lee S. F. , Yao Y. D. , Yu C. , Liou S. H.
Published: July 2002

Thickness dependence on the domain wall resistivity of zig zag thin permalloy wires was studied from 10 to 300 K. The maximum domain wall resistivity was obtained in wire with 100-nm-film thickness. The multidomain state resistivity was 14.29 μΩ cm, while single-domain state resistivity was 14.36 μΩ cm at 10 K. The ratio of domain wall magnetoresistance was measured to be 0.034%, 0.112%, and 0.258%, and the magnetic field where the domain wall started to switch was measured as −70, −40, and +80 Oe for wires with thicknesses of 20, 40, and 100 nm, respectively, at 250 K. Domain wall resistivity was nearly independent of temperature for wire with 40-nm-film thickness but varied significantly with temperature for 100-nm-thick wire between 10 and 300 K.
Z type Ba hexagonal ferrites with tailored microwave properties
Authors: Lubitz P. , Rachford F. J.
Published: July 2002

The microwave properties of Z type Ba hexagonal ferrites with uniaxial anisotropy can be controlled over a wide range by choice of an appropriate mixture of Zn, Ni, and Co as divalent species. Using unmagnetized powders of these ferrites, the microwave permeability spectra were taken in a swept frequency mode in the temperature range 200–550 K. From these data, the product γHa was derived. SQUID magnetometry was used to measure the magnetization and anisotropy separately. Pure Zn or Co Z type ferrites were found to have temperature dependences of γHa similar to those of other hexagonal ferrites containing Zn or Co, i.e., nearly flat for Zn and strongly increasing with T for Co. Ni–Z ferrite is notably different: the combination γHa, which determines the frequency of maximum absorption, is found to decrease rapidly with increasing temperature near 300 K. Magnetometry indicates that this temperature dependence γHa is caused mostly by variation of Ha with temperature. The temperature dependence of γHa for Ni–Z suggests a strategy to compensate the strong and opposing temperature dependence of γHa induced by Co ions, which are used to reduce Ha. By independently varying the mix of Zn, Co, and Ni in these ferrites, a useful range of microwave resonance frequencies, γHa, were obtained without undesirable temperature dependence near 300 K. This strategy may allow use of these materials as self-biased microwave components or for absorbing microwave energy in the 5–20 GHz range.
Effect of rare earth content on microstructure and magnetic properties of SmCo and NdFeB thin films
Authors: Neu V. , Hannemann U. , Fähler S. , Holzapfel B. , Schultz L.
Published: July 2002

Thin films of highly anisotropic rare earth intermetallic compounds increasingly come into the focus of interest for application in magnetic miniature devices. We prepared hard magnetic SmCo and NdFeB films by pulsed laser deposition and investigated the influence of rare-earth content on phase formation, microstructure, and magnetic properties. The phase evolution with rare earth content, as observed by x-ray diffraction, shows a distinct difference for the two systems. For SmCo a disordered SmCo7 structure is found at low Sm content and a change in the lattice constants is observed for a Sm-rich sample. Simultaneously, the coercive field improves whereas the magnetic in-plane texture found for Sm-poor films vanishes for higher Sm content. For NdFeB the increase in Nd content leads to an additional Nd phase because of the small homogeneity range. Contrary to the bulk, coercivity is reduced, which can be attributed to a significant increase of grain size and roughness.
Magnetic tunnel junctions utilizing diamond-like carbon tunnel barriers
Authors: Cadieu F. J. , Chen Li , Li Biao
Published: July 2002

We have devised a method whereby thin particulate-free diamond-like carbon films can be made with good adhesion onto even room-temperature substrates. The method employs a filtered ionized carbon beam created by the vacuum impact of a high-energy, approximately 1 J per pulse, 248 nm excimer laser onto a carbon target. The resultant deposition beam can be steered and deflected by magnetic and electric fields to paint a specific substrate area. An important aspect of this deposition method is that the resultant films are particulate free and formed only as the result of atomic species impact. The vast majority of magnetic tunnel junctions utilizing thin metallic magnetic films have employed a thin oxidized layer of aluminum to form the tunnel barrier. This has presented reproducibility problems because the indicated optimal barrier thickness is only approximately 13 Å thick. Magnetic tunnel junctions utilizing Co and permalloy films made by evaporation and sputtering have been fabricated with an intervening diamond-like carbon tunnel barrier. The diamond-like carbon thickness profile has been tapered so that seven junctions with different barrier thickness can be formed at once. Magnetoresistive (MR) measurements made between successive permalloy strip ends include contributions from two junctions and from the permalloy and Co strips that act as current leads to the junctions. Magnetic tunnel junctions with thicker carbon barriers exhibit MR effects that are dominated by that of the permalloy strips. Since these tunnel barriers are formed without the need for oxygen, complete tunnel junctions can be formed with all high-vacuum processing.
Basis set limit binding energies of dimers derived from basis set convergence of monomer energies
Authors: Park Sun Yong , Lee Jae Shin
Published: July 2002

The basis set limit electronic binding energies of He2, (HF)2, and (H2O)2 at the MP2 and CCSD(T) level (coupled cluster single and double excitations with perturbative triples correction) were estimated through the extrapolation of two successive energies of the dimer with correlation-consistent aug-cc-pVXZ (X=D(2),T(3),Q(4),5,6) basis sets by 1/Xp, where the convergence power p was derived from the basis set convergence behavior of the monomer (He, HF, and H2O) energies toward the known corresponding basis set limits. It is shown that the convergence behaviors of the correlation energy of the monomer and dimer with correlation-consistent basis sets closely resemble each other in these weakly bound systems, which is well demonstrated by the excellent agreement of the estimated basis set limit binding energies on this premise with the reference values in all cases. By contrast, the accuracy of a simple two-point 1/X3 extrapolation scheme in estimating the binding energies of these complexes is shown to depend on the correlation level, basis set quality, and kind of interatomic or molecular interactions present in the system. For the extrapolation of correlation energies of the dimer with aug-cc-pVDZ and aug-cc-pVTZ basis set by 1/Xp with the convergence power p determined from the basis set convergence behavior of the monomer correlation energies, the estimated MP2 binding energies for He2, (HF)2, and (H2O)2 are 19.5 μEh(21.4), 7.00 mEh(7.04), and 7.79 mEh(7.82), with the values in parentheses representing the exact basis set limit binding energies. The corresponding CCSD(T) binding energies for He2, (HF)2, and (H2O)2 are 30.8 μEh(33.8), 7.19 mEh(7.21), and 7.86 mEh(7.88), respectively.
Stacking faults in Co–Cr–Pt perpendicular magnetic recording media
Authors: Takahashi Yoshio , Tanahashi Kiwamu , Hosoe Yuzuru
Published: July 2002

The stacking fault density and its spatial distribution in Co–Cr–Pt films used for perpendicular magnetic recording media have been studied with high-resolution transmission electron microscopy. The stacking fault density increased as the temperature for film fabrication increased. In addition, the number of stacking faults was large in the initial region of film growth, regardless of the fabrication temperature, due to interfacial stress with the underlayer. By comparing the structural properties in terms of stacking faults and grain size with the magnetic properties, we found that stacking faults strongly affect the anisotropy constant and the coercivity of perpendicular media.
Laser beam induced currents in polycrystalline silicon thin films prepared by interference laser crystallization
Authors: Rezek B. , Nebel C. E. , Stutzmann M.
Published: July 2002

Polycrystalline silicon layers are prepared by interference laser crystallization (ILC) in the superlateral growth regime. To characterize their microscopic photoelectrical properties, light beam induced current (LBIC) is used, employing a focused laser beam for local generation of photocarriers in the layers with spatial resolution of ≈0.4 μm. The results are correlated with surface morphology obtained by atomic force microscopy. In the single pulse ILC, the temperature profiles are optimized by changing the proportion of interfering beam intensities. The typical grains are of triangular shape, with a length of 1.5 μm and width <0.5 μm. The photocurrent response is dominated by variations in the sample thickness. In the multiple pulse ILC, thin films with grains of quadratic shape and of size exceeding 5 μm are obtained by shifting the sample through an interference pattern, thus taking advantage of lateral epitaxial regrowth. Here, by use of a lock–in, LBIC can detect position and local electronic properties of individual grain boundaries. Grain boundaries are clearly identified by 180° shifts of the photocurrent phase close to maxima of photocurrent amplitude. The photocurrent is attributed to local fields at grain boundaries. These fields extend about 1.4 μm into the grains. The barrier height at the boundary is about 110 mV.
Room temperature operation of a high output current magnetic tunnel transistor
Authors: van Dijken Sebastiaan , Jiang Xin , Parkin Stuart S. P.
Published: July 2002

The structure and properties of a magnetic tunnel transistor with high current output at room temperature are presented. The transistor marries a two-terminal magnetic tunnel junction with an Al2O3 tunnel barrier and a GaAs collector. The output current depends on the spin-dependent transport of hot electrons in the base layer of the transistor, which is formed from a single ultrathin ferromagnetic film. At a bias voltage of 1.4 V across the tunnel barrier, output currents larger than 1 μA and magnetocurrent changes of 64% are obtained at room temperature.
Plasticity of electromigration-induced hillocking and its effect on the critical length
Authors: Proost Joris , Delaey Luc , D’Haen Jan , Maex Karen
Published: July 2002

When passing electrical current through metallic conductor lines in integrated circuits, the resulting drift velocity is generally taken to decrease linearly with the inverse line length, following the work of Blech [I. A. Blech, J. Appl. Phys. 47, 1203 (1976); erratum J. Appl. Phys. 48, 2648 (1977)]. A central parameter in Blech’s theory is the threshold or critical length, defined as the interconnect length at which the electromigration flux completely vanishes due to a counteracting mechanodiffusion flux. We provide experimental evidence from drift experiments on unpassivated, polycrystalline pure Al for a deviation of the length dependence of the drift rate from the Blech equation in near-threshold interconnects. New analytical expressions for the drift velocity in the near-threshold regime, taking into account diffusional creep as the plastic flow mode involved in electromigration-induced hillocking, have been validated by the experimental data. The diffusivities derived from the creep viscosity are in agreement with values measured independently for Al/TiN interfacial diffusion. Corroborating microstructural evidence showed that the hillocks grow by a wedge-shaped tilt of the original line uniformly over its width. The new expressions have a significant impact on the determination of the critical length; extrapolation of the newly predicted parabolic dependence of the drift velocity on line length in the near-threshold regime results in a critical product of 670±120 A/cm, well below the value obtained from the inverse linear extrapolation predicted by Blech.
Ordering stripe structures of nanoscale rods in diblock copolymer scaffolds
Authors: Chen Kang , Ma Yu-qiang
Published: July 2002

We report a simulation on the formation of ordered stripe structures of nanoscale rods driven by symmetric diblock copolymer melts. Due to the preferential adsorption of one species of the diblock onto the mobile rods, the phase ordering process will couple with the movement of rods. We find that the self-assembly of rods on the copolymer scaffold produces the highly ordered nanowires of rods, and copolymer blends in turn form the well-oriented lamellar structure. This is due to the interplay among the micro-phase separating dynamics in the diblock copolymer, the wetting interaction between rods and diblock copolymer, and the nematic ordering dynamics of rods. We examine the influence of the domain size, the wetting strength, and the rod number density on the formation of such a nanoscale structure. Additionally, we indicate that the orientation of the pattern can be well controlled by external fields acting on the rods. The results suggest that our model system may provide a novel and simple way to control and design the ordering nanowire structure.
Magnetic force microscopy observation of antivortex core with perpendicular magnetization in patterned thin film of permalloy
Authors: Shigeto K. , Okuno T. , Mibu K. , Shinjo T. , Ono T.
Published: July 2002

The cross-tie wall is a kind of magnetic domain wall composed of a main straight wall and crossing subwalls and observed in magnetic thin films. This wall contains two kinds of magnetic vortex structures: “circular vortex” and “antivortex.” At the cores of both vortices, the existence of a spot with perpendicular magnetization has been theoretically predicted. We have detected the perpendicular magnetization spots at each vortex core and identified the direction of it by applying magnetic force microscopy imaging to cross-tie walls in patterned rectangular thin permalloy (Ni80Fe20) films. We also fabricated magnetic structures that contain only antivortex by engineering the shape of thin films.
Dynamics of sleep/wake determination—Normal and abnormal
Authors: Mahowald Mark W. , Schenck Carlos H. , O’Connor Kevin A.
Published: July 2002

Virtually all members of the animal kingdom experience a relentless and powerful cycling of states of being: wakefulness, rapid eye movement sleep, and nonrapid eye movement sleep. Each of these states is composed of a number of physiologic variables generated in a variety of neural structures. The predictable oscillations of these states are driven by presumed neural pacemakers which are entrained to the 24 h geophysical environment by the light/dark cycle. Experiments in nature have indicated that wake/sleep rhythm perturbations may occur either involving desynchronization of the basic 24 h wake/sleep cycle within the geophysical 24 h cycle (circadian rhythm disturbances) or involving the rapid oscillation or incomplete declaration of state (such as narcolepsy). The use of phase spaces to describe states of being may be of interest in the description of state determination in both illness and health. Some fascinating clinical and experimental phenomena may represent bifurcations in the sleep/wake control system.
Gas-phase free radical reactions in the glow-discharge deposition of hydrogenated amorphous silicon from silane and disilane
Authors: Kampas Frank J.
Published: July 2002

An analysis of a measurement by Matsuda and co-workers of the lifetimes of the free radicals involved in the glow-discharge deposition of amorphous hydrogenated silicon from silane and disilane at 20-mTorr pressure is consistent with the hypothesis that SiH or SiH2, but not SiH3, is the dominant radical in the deposition from silane at that pressure.
Foldover in YIG
Authors: Seagle D. J. , Charap S. H. , Artman J. O.
Published: July 2002

We have observed distinct and repeatable FMR foldover effects in specimens of pure YIG at modest microwave power levels (1–10 dBm). Our samples were small disks (8.5 μm thick, 300 μm diameter) fabricated by photolithography from a YIG film deposited by LPE on a GGG substrate. The effect was observed at GHz frequencies using a microstrip transmission line and was also detected using X-band cavity and waveguide systems. We demonstrate that the effects that we have seen are not thermal or spin-wave-type foldover but are related to the disk shape anisotropy. In addition to observing foldover in the uniform precession mode, we have also seen foldover in the excitable magnetostatic modes associated with the disk geometry.
Spin- and angle-resolved photoemission study of bcc-Co films grown on (110) GaAs by molecular beam epitaxy
Authors: Prinz G. A. , Kisker E. , Hathaway K. B. , Schröder K. , Walker K.-H.
Published: July 2002

The recent success in preparing single-crystal (110) films of metastable bcc-phase Co by molecular beam epitaxy on GaAs has permitted spin- and angle-resolved photoemission studies to be carried out on this material. These studies confirm the theoretical predictions from recent FLAPW calculations of the electronic band structure of bcc-Co and bcc-Fe. The two band structures are essentially the same, except that the Fermi level for Co is shifted relative to that of Fe due to the additional electron per atom. A significant portion of the increased minority electron density occurs in the Γ-Σ-N region of the Brillouin zone investigated here.
Evaluation of III-V semiconductor wafers using nondestructive organic-on-inorganic contact barriers
Authors: Forrest S. R. , Kaplan M. L. , Schmidt P. H. , Gates J. V.
Published: July 2002

We discuss a new technique for measuring the net carrier concentrations, layer thicknesses, and deep level spectra of epitaxial InP and related compounds used in photonic device applications. The technique involves the formation of an organic-on-inorganic (OI) semiconductor contact barrier by vacuum sublimation of the compound: 3, 4, 9, 10-perylenetetracarboxylic dianhydride onto an inorganic semiconductor wafer. The OI barriers are reproducible from wafer to wafer, and can be as high as φBn ≊0.55 V over the entire range of InGaAs (P) compounds lattice matched to InP. High voltages (≳100 V in some cases) can be applied to the small area OI devices (as defined by an ohmic contact pad deposited on the organic film), allowing for deep depletion. Thus, high resolution carrier concentration measurements over extensive distances in all three wafer dimensions are obtained. These data are used to derive both the doping levels and layer thickness contours over the crystal surface. Finally, the OI devices can be removed after wafer evaluation, and the wafer can then undergo processing into conventional devices with no apparent degradation of performance when compared with control wafers that have not undergone OI diode evaluation.
Activation energy and spectroscopy of the growth of germanium films by ultraviolet laser-assisted chemical vapor deposition
Authors: Osmundsen J. F. , Abele C. C. , Eden J. G.
Published: July 2002

Emission and absorption spectroscopic studies of a reactor used to grow germanium thin films by photodissociating GeH4 at 248 nm with an excimer laser are described here. For every Ge or GeH (A→X) transition examined, the dependence of the emission line intensity on pump laser fluence was found to be quadratic, indicating that Ge and GeH have a common precursor which is itself produced by the simultaneous absorption of two 5-eV photons. This conclusion is supported by the known photochemistry of SiH4 and CH4 in the ultraviolet and the laser wavelength and intensity thresholds for the growth of Ge films. The short (∼2 μs) lifetime of GeH2 in the reactor suggests that the immediate precursor to Ge and GeH is the germyl radical, GeH3. The activation energy for Ge film growth in the temperature range 300≤T≤500 K has been measured to be 2.0±0.5 kcal/mole which suggests that the limiting mechanisms for the film growth rate are a gas-phase reaction and surface desorption of residual gases rather than surface diffusion. Radiation trapping on several Ge emission lines and absorption measurements at 422.6 nm indicate that the steady-state Ge number density in the reactor is ∼1012 cm−3 which is sufficient to account for the observed film growth rates. Spatial profiles of the atomic Ge and GeH emission from the reactor have been measured with a resolution of ∼100 μm.
Correlation between 1/f noise and interface state density at the Fermi level in field-effect transistors
Authors: Maes Herman E. , Usmani Sabir H. , Groeseneken Guido
Published: July 2002

New evidence is given for the validity of the number fluctuation model in explaining the 1/f noise behavior of field-effect transistors and for the direct proportionality between the oxide trap density and the interface state density at the Fermi level. This evidence is obtained from the determination of the energy distribution of the interface states in small size metal-nitride-oxide-silicon transistors by the modified charge pumping technique.
Relationship between Hall constant and carrier densities in polycrystalline semiconductor film
Authors: Bennett M. S.
Published: July 2002

A relationship has been derived between Hall constant and carrier densities in terms of two experimentally accessible quantities, the grain size and the intergrain barrier height. It is found that the carrier density as measured by the Hall effect can underestimate the average carrier density in the grain by up to an order of magnitude or more in some cases. These predictions are compared with experimental results.
Electron and hole impact ionization coefficients in (100) and in (111) Si
Authors: Robbins V. M. , Wang T. , Brennan K. F. , Hess K. , Stillman G. E.
Published: July 2002

The impact ionization coefficients for electrons and holes in both (100)- and (111)-oriented Si have been determined from photocurrent measurements performed on reach-through avalanche photodiodes. The results for both orientations are similar, indicating that the ionization coefficients are isotropic. Monte Carlo calculations of the impact ionization coefficients compare favorably with the experimental results.
UV absorption spectroscopy for monitoring hydride vapor-phase epitaxy of InGaAsP alloys
Authors: Karlicek R. F. , Hammarlund B. , Ginocchio J.
Published: July 2002

Ultraviolet (UV) absorption spectroscopy has been used to monitor the concentrations of gas-phase reactants participating in the growth of InGaAsP alloys by hydride vapor-phase epitaxy. Room-temperature absorption spectra for PH3, AsH3, and HCl as well as high-temperature (700°C) spectra of InCl, GaCl, PH3,P2, P4, As2, and As4 are presented. For the group V species, the UV absorption bands of the hydride, dimer, and tetramer exhibit considerable overlap, but can still be used to determine the approximate concentration of each species. GaCl and InCl exhibit extremely intense, sharp absorption bands at 248 and 267 nm, respectively. This technique has been used to study the effect of PH3 pyrolysis on InP growth, and to monitor In/Ga ratio for metal transport from an alloy source. This technique can be implemented on reactor systems without reactor design changes and without disturbing the thermal profile by using ‘‘light pipes’’ to probe concentrations of reactive species during growth.
Radiation-induced transient darkening of optically transparent polymers
Authors: Downey S. W. , Builta L. A. , Carlson R. L. , Czuchlewski S. J. , Moir D. C.
Published: July 2002

Results are presented for the radiation-induced transient darkening of thin organic polymer films normally used as Cerenkov light emissions sources. The radiation source is a 27-MeV, 10-μC, 200-ns electron beam generated by the PHERMEX accelerator. The typical dose for a single pulse is 5 Mrad. At this dose, the broadband time-resolved percent transmission above 520 nm was measured for four common polymers: polyimide (Kapton-H), polyethylene terephthalate (Mylar), cellulose acetate, and high-density polyethylene. Kapton was found to darken the most and polyethylene darkened the least. The recovery time to normal transmission for Kapton was found to be greater than 10–20 μs. The radiation-induced attenuation coefficient is shown to depend on electronic band energy separation. The results show that Kapton is not the material of choice for a Cerenkov light source.
Ion-induced volatilization (IIV): A method for quantitative measurement of the amounts of perfluoropolyether lubricant on a particulate disk surface and in the media porosity
Authors: Coburn J. W. , Winters H. F.
Published: July 2002

A method has been developed which allows the quantitative determination of the amounts of perfluoropolyether lubricant on the top surface and in the bulk porosity of particulate disks used in magnetic storage technology. The method, ion-induced volatilization (IIV), involves subjecting a well-defined area of the lubricated disk surface to a low flux of energetic rare gas ions and monitoring the resulting partial pressure increase (at mass 69) with a quadrupole mass spectrometer. Quantification is achieved by calibrating with lubricated quartz crystal microbalances. The method is generally applicable for any lubricated surface but is specific to perfluoropolyether lubricants which undergo essentially residue-free degradation into volatile products when subjected to energetic particle bombardment.
A model for the laser-stimulated oxidation of silicon
Authors: Quenon P. , Wautelet M. , Dumont M.
Published: July 2002

A model is proposed to describe Si oxidation under low-power irradiation. The proposition is that the oxidation is limited by the dangling bond formation and that this formation is enhanced by localized electronic excited states created by laser photons absorbed at the interface.
Observation of quantum confinement effect away from the zone center in a spectroscopic ellipsometry study of the dielectric function of single Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As square quantum wells
Authors: Vasquez R. P. , Kuroda R. T. , Madhukar A.
Published: July 2002

The dielectric response of molecular-beam epitaxially grown single Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As square quantum wells with thicknesses in the range 14–59 Å is examined via spectroscopic ellipsometry in the energy range 1.6–5.7 eV. Shifts in the E1 transitions are observed and found to be consistent with the shifts calculated within a simple square well model with finite barrier height using appropriate L-point parameters of the bulk materials.
Spectroscopic diagnostics of plasma-chemical-vapor deposition from silane and germane
Authors: Hata Nobuhiro , Matsuda Akihisa , Tanaka Kazunobu
Published: July 2002

Coherent anti-Stokes Raman spectroscopy (CARS), laser-induced fluorescence (LIF), and emission spectroscopy are employed for the diagnostics of radio-frequency discharge plasmas of silane and germane; CARS signal of germane molecule; and LIF signal and ultraviolet emission signal of germanium atom in discharges, as well as signals from nongermanium-related neutral species are measured. The effect of hydrogen dilution on emission signal intensities in the steady-state discharge explains dynamic behaviors of the emission and CARS signal intensities in the closed discharge; these spectroscopic techniques are powerful diagnostic tools for gas-phase processes using mixed gas sources.
Relaxation in systems with exponential or Gaussian distributions of activation energies
Authors: Macdonald J. Ross
Published: July 2002

New expressions are presented, simplified, and discussed for the small-signal-frequency response of systems involving distributions of activation energies with either exponential or Gaussian probability densities. The results involve the possibility of separate but related thermal activation of energy-storage and energy-loss processes, and apply to the response of both dielectric and conductive systems. Response with a Gaussian distribution of activation energies (GDAE) may be either symmetric or asymmetric in log frequency, and typical GDAE responses are compared with those associated with several exponential distributions of activation-energy (EDAE) models, using complex nonlinear least-squares fitting. The GDAE model does not lead to the frequently observed fractional-exponent power-law response in time or frequency as does the EDAE; thus, the GDAE cannot fit any EDAE response well which involves an appreciable range of such behavior, but it is found that, conversely, the general EDAE model can often fit a GDAE response very well over

a wide frequency range. Recent (KBr)0.5(KCN)0.5 dielectric data covering a range from T=13.7 to 34.7 K are analyzed with the Cole–Cole, EDAE, and GDAE models, and the GDAE is found to yield the best overall fits. The results of the GDAE fits are analyzed in detail to illustrate the application of the GDAE model to real data. Contrary to the conclusions of an earlier analysis of the same data using an idealized, symmetric, and approximate GDAE model, we find that much of the data are better fit by a somewhat asymmetric, exact GDAE model which may involve a temperature-independent, finite-width Gaussian probability density. The present analysis suggests an alternative to the earlier results and suggestions that the width of the probability-density distribution increases with decreasing temperature and that the activation energies or barrier heights themselves depend linearly on temperature. The present data fit yield estimates of the lower limit of the temperature independent distribution of activation energies E0 and of the more or less central activation energy E1, but only set a lower limit for the value of the maximum activation energy of the distribution, E∞. There is some evidence from the fitting that there may be a glasslike transition below about 4 K, but other effects outside the GDAE model may intervene before that temperature region is reached.
Ellipsometric measurements of molecular-beam-epitaxy-grown semiconductor multilayer thicknesses: A comparative study
Authors: Woollam John A. , Snyder Paul G. , McCormick Anthony W. , Rai A. K. , Ingram David , Pronko Peter P.
Published: July 2002

Variable angle of incidence spectroscopic ellipsometry, cross-sectional transmission electron microscopy, and Rutherford backscattering are used to measure heterojunction layer thicknesses in the same AlGaAs/GaAs sample. All three techniques yield the same thickness values within error limits. Two additional samples were implanted with 750-keV Ga ions to fluences of 5×1015 and 1016 cm−2, respectively, and results of diagnostics measurements by the three techniques compared. The three techniques are found to complement each other in providing useful information.
Plasma characteristics and etch uniformity in CF4 magnetron etching using an annular permanent magnet
Authors: Kinoshita Haruhisa , Ishida Toshimasa , Ohno Seigo
Published: July 2002

Etch characteristics of SiO2 and Si obtained by magnetron etching using an annular permanent magnet were analyzed. From these analyses, etch characteristics were found to be classified into three regimes. Remarkable enhancements in SiO2 etch rate, 25–40 times, were observed at constant Vrf by applying magnetic field of 150 G. Ion densities over the cathode were found to be distributed linearly along the E×B drift direction. Such an ion density distribution will be formed by the repeated process (ionization→ion bombardment→electron emission and drift→ionization). Etch distribution can be averaged and flattened to a uniformity of below ±2% by the magnetic field being rotated in 90° steps.
Observation on laser-annealed silicon-on-insulator structures by cross-sectional transmission electron microscopy
Authors: Ogura Atsushi , Terao Hiroshi
Published: July 2002

Silicon-on-insulator (SOI) structures, fabricated by laser annealing, were observed with cross-sectional transmission electron microscopy. The film thickness was found to be almost uniform in SOI fabricated using a nonseeded Si3N4 antireflection film stripe technique, but some small mass transfer could be seen. Most of the crystal was of good quality, and almost no defects were observed, even in portions where stress was expected to be strongly exerted, such as at SOI/SiO2 interfaces or Si3N4 stripe edges. The defects which could be seen, however, were mostly those which had penetrated from the SOI/SiO2 interface to the SOI surface. Although the crystal quality was good, under relatively high laser power, dislocation loops were generated in the Si substrate. A grain boundary, generated from the deformed SOI/SiO2 interface, was also found. Furthermore, high-resolutional lattice image observations carried out for the lateral seeding epitaxy SOI revealed that the abruptness at the SOI/SiO2 interface was rougher than that at the SiO2/Si substrate interface.
A model for dislocation sources in a shock or impact environment
Authors: Coffey C. S.
Published: July 2002

An attempt is made to model the operation of a prototypical dislocation source in a crystalline solid undergoing high rate deformation by shock or impact loading. This effort examines the response of the source to a dynamically applied shear stress, to the influence of other dislocations, and to the influence of dislocation nucleation time and inertial effects. The evolution of a two-wave elastic-plastic structure of a shock wave is predicted. For very large amplitude shocks, this two-wave structure effectively gives way to a single plastic wave. The strain rate of the plastic wave is shown to vary as the second power of the applied shear stress. Some initial predictions are given concerning shear band thickness and the onset of fracture failure during shock or impact.
Picosecond phase conjugation in polydiacetylene gels
Authors: Nunzi J. M. , Grec D.
Published: July 2002

A detailed analysis of picosecond time-resolved phase conjugation at 1.06 μm, in the transparency region of soluble polydiacetylenes is presented. Different grating contributions are isolated. It is shown that in red and blue gel forms, phase conjugation at high pump energies is driven by two-photon absorption degenerate six-wave mixing, superimposed on degenerate four-wave mixing. The third-order nonlinear susceptibility of these polymers is reported: It reaches 10−11 esu (30 times CS2 value) for the pure blue amorphous polymer. Two-photon excited species increase phase conjugation at 1-GW cm−2 pump power by one order of magnitude.
Enhanced and wafer-dependent oxygen diffusion in CZ-Si at 500–700 °C
Authors: Lee S.-Tong , Fellinger Paul , Chen Samuel
Published: July 2002

Oxygen diffusivity in silicon in the intermediate temperature range 500–650 °C has, for the first time, been directly measured. Oxygen diffusion in this temperature range is enhanced relative to the normal diffusion of interstitial oxygen. The degree of enhancement increases with decreasing temperature, with the enhancement factor reaching >102 at ≤550 °C. The diffusivity at 550–750 °C is found to vary among Si wafers by as much as 10×. Oxygen diffusivity generally decreases with increasing annealing time but does not vary proportionally with oxygen concentration as expected from a molecular oxygen model.
Single ion model for magnetostriction in rare-earth–transition-metal amorphous films
Authors: Suzuki Yoshio , Ohta Norio
Published: July 2002

The mechanism of magnetostriction in rare-earth–transition-metal amorphous films was investigated based on a single ion anisotropy model for rare-earth atoms using a point charge approximation. The theory was compared with the observed magnetostriction in (Gd0.75R0.25)19Co81 films with various rare-earth elements R. The dependence of the observed magnetostriction on substitutional rare-earth elements R is well explained with this model. Screening of an electric field was found to be essential for magnetostriction, and a screening function was determined from the observed magnetostriction. The screening was found to be of the type in which an electric field decreases more rapidly with an increase of distance than a Coulombic interaction.
Magnetic properties of sandwiches and superlattices of fcc Fe(001) grown on Cu(001) substrates
Authors: Dutcher J. R. , Heinrich B. , Cochran J. F. , Steigerwald D. A. , Egelhoff W. F.
Published: July 2002

The magnetic properties of Cu/Fe epitaxial sandwiches and superlattices have been measured using Brillouin light scattering and ferromagnetic resonance. All of the samples are perpendicularly magnetized at room temperature, due to the presence of large uniaxial anisotropies with an easy axis perpendicular to the sample surface. Inclusion of a second-order uniaxial anisotropy term is particularly important for one of the superlattice samples.
Curved electromagnetic missiles
Authors: Myers John M. , Shen Hao-Ming , Wu Tai Tsun , Brandt Howard E.
Published: July 2002

An interesting topic has been the possible behavior of transient fields in the limit of great distances from their sources. Under the physical restriction that the total energy radiated is finite, it has been shown that the energy reaching a distant receiver can decrease with distance much more slowly than the usual r−2. Such cases of slow decrease have been referred to as electromagnetic missiles. All of the wide variety of known missiles propagate in essentially straight lines. It is shown here that such a missile can follow a path that is strongly curved. An example of a curved electromagnetic missile is explicitly constructed and some of its simpler properties are discussed.
Experimental vortex transitional nondestructive read-out Josephson memory cell
Authors: Tahara Shuichi , Ishida Ichiro , Ajisawa Yumi , Wada Yoshifusa
Published: July 2002

A proposal vortex transitional nondestructive read-out Josephson memory cell is successfully fabricated and tested. The memory cell consists of two superconducting loops in which a single flux quantum is stored and a two-junction interferometer gate as a sense gate. The memory cell employs vortex transitions in the superconducting loops for writing and reading data. The vortex transitional memory operation of the cell contributes to improving its sense discrimination and operating margin. The memory cell is activated by two control signals without timing control signals. Memory cell chips have been fabricated using a niobium planarization process. A±21% address signal current margin and a ±33% sense gate current margin have been obtained experimentally. Successful memory operations of a cell driven by two-junction interferometer gates has been demonstrated. The single flux quantum operations of this memory cell makes it an attractive basic element for a high-speed cache memory.
Analysis of ac conduction in disordered solids
Authors: Macdonald James Ross
Published: July 2002

Dyre [J. Appl. Phys. 64, 2456 (1988)] has recently stated that the random free-energy barrier model of ac conduction in disordered solids, solved in the continuous time random-walk approximation with the effects of the maximum jump frequency eliminated, is quantitatively satisfactory in describing hopping conduction for a large number of solids. Here, predictions of this model, equivalent to the long-used box model, which posits a distribution of equally probable activation energies, are examined in depth, both without and with an upper cutoff. It is first demonstrated that the type of log-log plot on which Dyre appears to base his conclusion of quantitative adequacy does not allow adequate discrimination to be made between box-model predictions and those of other models, such as the Kohlrausch–Williams–Watts model, even when exact data are used. The results of numerous complex nonlinear least-squares fits of exact box-model data, and of such data containing substantial proportionally added random errors, to the box model, the WW model, the constant-phase-element model, and the Davidson–Cole [J. Chem. Phys. 19, 1484 (1951)] response model make it clear that when using this fitting technique, one can identify the correct model, discriminate against incorrect ones, and obtain good parameter value estimates for the correct model. Further, when the highest frequency of the data exceeds the maximum jump frequency, its value can be accurately estimated. It is concluded that the case for the quantitative adequacy of the box model remains unproven. Future data fitting using complex nonlinear least squares should, however, allow a best-fit model to be selected unambiguously from those compared.
Interface anisotropy in cobalt-based epitaxial superlattices
Authors: He Hui , Lee C. H. , Lamelas F. J. , Vavra W. , Barlett D. , Clarke Roy
Published: July 2002

We have measured the magnetic anisotropy in a series of Co-Au and Co-Cu superlattices prepared by molecular-beam epitaxy. Significant epitaxial strains give rise to a magnetoelastic contribution and a large crossover thickness (∼19 Å) for perpendicular easy magnetization. The results are discussed in the context of a careful analysis of the interfacial strains and coherence determined by in situ. time-resolved reflection high-energy electron diffraction techniques and x-ray scattering.
Identification and ionization energies of the shallow donor metastable states in GaAs:Si
Authors: Klarenbosch A. v. , Klaassen T. O. , Wenckebach W. Th. , Foxon C. T.
Published: July 2002

Transitions from the 1s0 ground state to the shallow donor metastable states in n-GaAs have been investigated at a temperature of T=4.2 K, magnetic fields up to 6 T, and for far-infrared transition energies between 50 and 300 cm−1. The final states of these transitions have been identified and characterized by high-field quantum numbers. The magnetic-field dependence of the ionization energies of some of these metastable states have been determined.
Study of sublattice orientation of GaAs on Ge
Authors: Strite S. , Biswas D. , Adomi K. , Morkoç H.
Published: July 2002

High crystalline quality GaAs/Ge/GaAs heterostructures have been grown on both straight and slightly misoriented GaAs(100) substrates by molecular beam epitaxy. High-energy electron diffraction was used to study the sublattice rotation of GaAs on epitaxial Ge dependent on the use of a Ga or As prelayer. On straight (100) substrates, a Ga prelayer was observed to rotate the GaAs surface reconstruction by π/2 while an As prelayer preserved the GaAs orientation observed prior to Ge deposition. No rotation of the surface was observed on substrates tilted 4° towards [011]. We present a growth model to explain these results.
Spatial distribution of defects in high-purity silica glasses
Authors: Tohmon Ryoichi , Ikeda Akihiro , Shimogaichi Yasushi , Munekuni Shuji , Ohki Yoshimichi , Nagasawa Kaya , Hama Yoshimasa
Published: July 2002

The spatial distribution of defects and impurities in a variety of high-purity silica glass manufactured by different methods are studied. The defects investigated include those found in the as-manufactured glass (oxygen vacancy and peroxy linkage), as well as those induced by ionizing radiation or ultraviolet light (E′ center and oxygen hole centers). A significant difference is observed in the distribution between silica manufactured by different methods. Furthermore, the defects induced by ionizing radiation or ultraviolet light have a spatial distribution relative to the geometry of the as-manufactured boule, suggesting that these defects arise primarily from the activation of preexisting precursors.
Neutron diffraction and transmission electron microscopy study of hydrogen-induced phase transformations in Zr3Al
Authors: Meng W. J. , Faber J. , Okamoto P. R. , Rehn L. E. , Kestel B. J. , Hitterman R. L.
Published: July 2002

Hydrogen-induced phase transformations of the equilibrium intermetallic compound Zr3 Al have been studied by in situ elastic neutron scattering, x-ray diffraction, and transmission electron microscopy (TEM). TEM observations reveal two distinct modes of amorphous phase formation in Zr3 Al upon hydrogenation, namely, heterogeneous nucleation at preexisting grain boundaries, and homogeneous nucleation within single-crystal grains. In situ neutron diffraction reveals a phase separation between a hydrogen (deuterium) poor and a hydrogen (deuterium) rich crystalline phase. Rietveld profile refinement of the neutron diffraction data indicates predominant hydrogen (deuterium) occupation of the octahedral interstitial sites in the crystalline matrix that have only Zr nearest-neighbor atoms. The two different modes of amorphous phase nucleation are directly related to the degree of hydrogen dissolution in the host crystalline matrix.
Measured electrical conductivities of carbon-fiber composite materials: Effects on nuclear magnetic resonance imaging
Authors: Lind Arthur C. , Fry Charles G. , Sotak Christopher H.
Published: July 2002

Various techniques were used to measure the anisotropic electrical conductivity of carbon-fiber/epoxy resin composites. The conductivity of these materials, irrespective of the direction, is large enough to consider the composite to be a good conductor for all frequencies normally used in nuclear magnetic resonance (NMR). Thus, a simple analysis based on the skin depth can be used to determine the rf magnetic fields in the composite. The rf magnetic fields decrease exponentially with distance into the material. This attenuation is severe enough to prevent detection of NMR signals from nuclei located much deeper into the material than the skin depth. For rf penetrating into the face of a cross-ply composite panel, the attenuation is dominated by the conductivity along the carbon fibers. We found this effective conductivity to be 25 000 S/m, which allowed NMR imaging to depths <2 mm. In some cases images were obtained at greater depths in regions where broken fibers existed. For penetration into the edge of a cross-ply composite, the attenuation is dominated by the fiber-to-fiber conductivities between adjacent plies. We found this conductivity to be 125 S/m, allowing NMR images to be obtained within an ∼1-cm-wide strip around the edge of the composite. Thus, NMR imaging is most likely not a viable technique for the nondestructive evaluation of large carbon-fiber composites, but NMR might be applicable to imaging samples having conductive regions smaller than the skin depth, and for mapping rf magnetic fields within slightly conductive materials.
Oxidation-induced substrate strain in advanced silicon integrated-circuit fabrication
Authors: Stiffler S. R.
Published: July 2002

A simple model for the generation of substrate strain is developed and applied to the fabrication of advanced silicon integrated-circuit structures. These structures consist of SiO2-filled isolation trenches residing in a silicon substrate and strain is generated at elevated temperature by thermal oxidation. The high-stress behavior of the viscosity of SiO2 is considered and leads to self-limiting behavior. During the initial stages of oxidation, the strain rises rapidly and then asymptotically approaches an equilibrium level determined by the oxidation conditions and the trench geometry.