bluuebunny/crossref_metadata_2025 huggingface dataset:
Roughness of molecularly thin perfluoropolyether polymer films
Authors: Toney Michael F. , Mate C. Mathew , Leach K. Amanda
Published: July 2002

X-ray reflectivity has been used to measure the roughness of perfluoropolyether (PFPE) polymer films on silicon substrates and carbon overcoats. For PFPE on smooth silicon, we find that the rms roughness of the PFPE–air interface increases slowly from about 2 to 4 Å as PFPE thickness increases from 5 to 33 Å. This increase is consistent with capillary waves roughening the polymer film, but inconsistent with current theories for the dewetting of polymer films. For PFPE on the rougher surface of amorphous hydrogenated carbon, we find that the PFPE polymer smoothes the surface with the rms roughness decreasing from 9 to 4 Å. We also discuss the implications of these results on the limits of disk drive technology.
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Structure and vibrations from density functional theory, Franck–Condon factors, and the pulsed-field ionization zero-electron-kinetic energy spectrum
Authors: Calaminici Patrizia , Köster Andreas M. , Carrington Tucker , Roy Pierre–Nicholas , Russo Nino , Salahub Dennis R.
Published: July 2002

Density functional calculations of neutral and cationic vanadium trimers are presented. The all-electron calculations employed a gradient-corrected exchange-correlation functional and a newly developed vanadium basis set optimized for gradient-corrected density functional calculations. For both neutral and charged systems, different isomers were studied in order to determine the lowest energy structures. A vibrational analysis was performed in order to characterize these isomers. We found an equilateral triangle A1′2 ground state for V3 and an equilateral triangle A2′3 ground state for V3+. The experimental pulsed-field ionization zero-electron-kinetic energy spectrum was simulated by calculating multidimensional Franck–Condon factors, using the geometries and harmonic frequencies of the calculated minima of V3 and V3+. The excellent agreement between the experimental and theoretical spectra allows the unequivocal determination of the ground state structure of V3. This work provides a final answer to the controversy in the literature about the ground state structure of V3 and yields deeper insight into the electronic structure of the neutral and cationic systems.
Local structure of uncapped and Si-capped Ge/Si(100) self-assembled quantum dots
Authors: Kolobov Alexander V. , Oyanagi Hiroyuki , Brunner Karl , Schittenhelm Peter , Abstreiter Gerhard , Tanaka Kazunobu
Published: July 2002

Local structure of uncapped and Si-capped Ge quantum dots on Si(100) has been probed by extended x-ray absorption fine structure and x-ray absorption near-edge structure spectroscopy. It is found that the uncapped Ge dots are partially oxidized and partially alloyed with Si. The amount of Ge present in the Ge phase is found to be about 20–30%. In the Si-capped sample, Ge is found to be dissolved in silicon, the fraction of Ge atoms existing as a Ge phase being less than 10%.
Electronic and chemical passivation of hexagonal 6H–SiC surfaces by hydrogen termination
Authors: Sieber N. , Mantel B. F. , Seyller Th. , Ristein J. , Ley L. , Heller T. , Batchelor D. R. , Schmeißer D.
Published: July 2002

Hydrogenation of 6H–SiC (0001) and (0001̄) is achieved by high-temperature hydrogen treatment. Both surfaces show a low-energy electron diffraction pattern representative of unreconstructed surfaces of extremely high crystallographic order. On SiC(0001), hydrogenation is confirmed by the observation of sharp Si–H stretching modes. The absence of surface band bending for n- and p-type samples is indicative of electronically passivated surfaces with densities of charged surface states in the gap of below 7×1010 cm−2 for p-type and 1.7×1012 cm−2 for n- type samples, respectively. Even after two days in air, the surfaces show no sign of surface oxide in x-ray photoelectron spectroscopy.
Modeling grain size and dislocation density effects on harmonics of the magnetic induction
Authors: Sablik M. J. , Stegemann D. , Krys A.
Published: July 2002

Microstructural attributes of steels affect hysteretic magnetic properties because the microstructure affects domain wall movement and pinning. Two important features are grain size and dislocation density. The consensus experimentally is that the coercivity tends to be linearly related to the inverse of the average grain diameter and to the square root of the dislocation density. In this article, these experimental tendencies are utilized in formulating the dependence of the hysteresis parameters of the Jiles–Atherton model as a function of grain size and dislocation density. The results are then used in computing the first and third harmonics of the magnetic induction as a function of grain size and dislocation density. This is done via an adaptation of a hysteresis model formulated by Jiles for higher excitation frequencies. The results indicate that the harmonic amplitudes decrease monotonically with inverse grain size and the square root of dislocation density. Since increasing inverse grain size and dislocation density are correlated with increasing tensile strength, the results are consistent with experimental results for the decrease of the harmonic amplitudes with increasing tensile strength in automotive steels. Also, the harmonic amplitudes decrease with increasing excitation frequency, consistent with experiment.
Nitrogen incorporation effects in Fe(001) thin films
Authors: Menéndez J. L. , Armelles G. , Cebollada A. , Briones F. , Peiró F. , Güell F. , Cornet A. , Fernández Gubieda M. L. , Gutiérrez J. , Meyer C.
Published: July 2002

Nitrogen incorporates into Fe thin films during reactively sputtered TiN capping layer deposition. The influence that this nitrogen incorporation has both on the structure and magnetic properties is discussed for a series of Fe(001) thin films grown at different temperatures. A higher nitrogen content is accompanied by distortion in the Fe lattice and by reduction in the Fe magnetization saturation as well as in the effective anisotropy constant, K. The reduction of K brings as a consequence lowering in the coercive field with respect to equivalent Fe films with no nitrogen present.
Anisotropic self-diffusion in the nematic phase of a thermotropic liquid crystal by H1-spin-echo nuclear magnetic resonance
Authors: Dvinskikh S. V. , Furó I.
Published: July 2002

The orientation-dependent molecular diffusion in the nematic liquid crystal 4-pentyl-4′-cyanobiphenyl is measured to high accuracy. The applied nuclear magnetic resonance method combines multiple-pulse homonuclear dipolar decoupling with pulsed-field-gradient stimulated echo and slice selection. The obtained temperature dependencies of the principal diffusion coefficients are not described by a simple Arrhenius relationship but reflect the decrease of the molecular orientational order close to the nematic-to-isotropic phase transition. The geometric average of the principal diffusion coefficients is continuous with the diffusion coefficient in the isotropic phase. The results are best described in terms of the affine transformation model of diffusion in hard-ellipsoid nematics.
Molecular-beam-deposited yttrium-oxide dielectrics in aluminum-gated metal–oxide–semiconductor field-effect transistors: Effective electron mobility
Authors: Ragnarsson L.-Å. , Guha S. , Copel M. , Cartier E. , Bojarczuk N. A. , Karasinski J.
Published: July 2002

We report on high effective mobilities in yttrium-oxide-based n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) with aluminum gates. The yttrium oxide was grown in ultrahigh vacuum using a reactive atomic-beam-deposition system. Medium-energy ion-scattering studies indicate an oxide with an approximate composition of Y2O3 on top of a thin layer of interfacial SiO2. The thickness of this interfacial oxide as well as the effective mobility are found to be dependent on the postgrowth anneal conditions. Optimum conditions result in mobilities approaching that of SiO2-based MOSFETs at higher fields with peak mobilities at approximately 210 cm2/V s.
Structure and thermodynamic stability of the OsC and OsC2 molecules by theoretical calculations and by Knudsen cell mass spectrometry
Authors: Meloni G. , Thomson L. M. , Gingerich K. A.
Published: July 2002

Knudsen cell mass spectrometric equilibrium measurements together with theoretical computations have been employed to gain structural and thermodynamic information of the OsC and OsC2 molecules. Several levels of theory have been applied to determine the structures, molecular parameters, and physico-chemical properties of OsC(g) and OsC2(g), and their singly charged ions. Complete active space self-consistent field (CASSCF) calculations were performed on the apparent Σ3– ground state and first Δ3 excited state of OsC. From the analyzed gaseous equilibria and the thermal functions calculated from the computed molecular parameters, the following atomization enthalpies, ΔaH0o(OsC,g) and ΔaH0o(OsC2,g), and enthalpies of formation, ΔfH298.15o(OsC,g) and ΔfH298.15o(OsC2,g), in kJ mol−1, have been obtained: OsC, 605.6±14.0 and 895.4±14.0; OsC2, 1154.6±18.0 and 1059.5±18.0. The results have been compared with those for the other platinum metal carbides and oxides.
Effect of growth interruptions on the light emission and indium clustering of InGaN/GaN multiple quantum wells
Authors: Cho H. K. , Lee J. Y. , Sharma N. , Humphreys C. J. , Yang G. M. , Kim C. S. , Song J. H. , Yu P. W.
Published: July 2002

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InxGa1−xN well and GaN barrier by metalorganic chemical vapor deposition were investigated using photoluminescence (PL), high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The integrated PL intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blueshift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher-intensity and lower-energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.
Muonium diffusion in solid CO2
Authors: Eshchenko D. G. , Storchak V. G. , Brewer J. H. , Cottrell S. P. , Cox S. F. J. , Karlsson E. , Waeppling R.
Published: July 2002

The quantum diffusion of interstitial muonium atoms in solid CO2 is studied in the temperature range from 5 to 200 K using the technique of muonium spin rotation and relaxation. Muonium exhibits coherent bandlike dynamics between 140 and 160 K. At low temperature Mu undergoes strong localization.
Water-saturated Si(100)-(2×1): Kinetic Monte Carlo simulations of thermal oxygen incorporation
Authors: Estève A. , Chabal Y. J. , Raghavachari Krishnan , Weldon M. K. , Queeney K. T. , Djafari Rouhani M.
Published: July 2002

An atomic scale model of thermal oxidation of Si(100) has been developed based on a kinetic Monte Carlo approach. This method makes it possible to analyze the effects of elementary mechanistic steps of oxidation on macroscopic surfaces. The initial thermal decomposition of chemisorbed hydroxyl groups resulting from water adsorption on Si(100)-(2×1) is investigated by utilizing extensive IR data and ab initio calculations.
Optical spectroscopy of tungsten carbide (WC)
Authors: Sickafoose Shane M. , Smith Adam W. , Morse Michael D.
Published: July 2002

Resonant two-photon ionization spectroscopy has been used to study the diatomic transition-metal carbide, WC. A low-resolution scan revealed a five-member vibrational progression beginning with the 0-0 band at 17 585 cm−1. Analysis of this progression yielded a vibrational frequency of ωe′(184W12C)=752.6(4.9) cm−1 and a bond length of re′(184W12C)=1.747(4) Å. Several unassigned bands were also rotationally resolved and analyzed. All of the observed bands are Ω′=2←Ω″=1 transitions, confirming the predicted ground state of Δ13 arising from a 14σ28π415σ24δ116σ1 configuration. The measured line positions in these bands were simultaneously fitted to provide B0″=0.509 66(10) cm−1 for W12184C, corresponding to r0″(184W12C)=1.713 5(2) Å. These values are corrected for spin-uncoupling effects in the ground state and represent our best estimate of the true bond length of WC. Dispersed fluorescence studies provide the ground-state vibrational constants of ωe=983(4) cm−1 and ωexe=11(1) cm−1, and have also permitted the low-lying [1.2] 3Δ2 and [4.75] states to be located and characterized. These results on WC are discussed in relation to the isovalent molecule MoC and other transition-metal carbides.
Dresden EBIT: Results and perspectives
Authors: Kentsch U. , Landgraf S. , Zschornack G. , Grossmann F. , Ovsyannikov V. P. , Ullmann F.
Published: July 2002

The Dresden electron-beam ion trap (EBIT) is a long-term stable room-temperature EBIT working without any cryogenic techniques. Spectroscopic investigations have shown that in the Dresden EBIT bare nuclei at least up to nickel can be produced as well as helium-like ions from elements such as krypton or germanium and neon-like ions from elements such as xenon or iridium. The output of quantum radiation from highly charged ions trapped in the Dresden EBIT is high enough that wavelength-dispersive spectroscopic investigations are possible. Up to now, two devices (Dresden EBIT I and Dresden EBIT II) have been built up. Results derived on Dresden EBIT II demonstrate that it is possible to produce the described apparatus in any number. Thus, it opens up a way also for small laboratories to employ highly charged ions in their investigations.
Self-similarity theory of stationary coagulation
Authors: Pushkin D. O. , Aref H.
Published: July 2002

A theory of stationary particle size distributions in coagulating systems with particle injection at small sizes is constructed. The size distributions have the form of power laws. Under rather general assumptions, the exponent in the power law is shown to depend only on the degree of homogeneity of the coagulation kernel. The results obtained depend on detailed and quite sensitive estimates of various integral quantities governing the overall kinetics. The theory provides a unifying framework for a number of isolated results reported previously in the literature. In particular, it provides a more rigorous foundation for the scaling arguments of Hunt, which were based largely on dimensional considerations.
Near-field photoluminescence spectroscopy of InGaN films grown by molecular-beam epitaxy
Authors: Kim Jeongyong , Samiee Kevan , White Jeffrey O. , Myoung Jae-Min , Kim Kyekyoon
Published: July 2002

The spatial and spectral distribution of photoluminescence from InGaN films grown by plasma-assisted molecular-beam epitaxy are studied by near-field scanning optical microscopy. The luminescence intensity is low in the vicinity of pits in the surface that are believed to be associated with dislocations. For 20% In, the emission is random on a submicron length scale, but clumps into micron-sized regions at 27% In. The clustering is quantified by calculating the image entropy. Near-field spectra indicate that the regions of high intensity are not due to a local increase in In. Spatial variations in the luminescence wavelength indicate that composition fluctuations are enhanced with increasing In.
Watergel—a new form of water condensed in liquid He4
Authors: Kokotin A. M. , Mezhov-Deglin L. P.
Published: July 2002

The semitransparent layer (cloud) of impurity condensate formed on the interface between superfluid He II and the vapor during condensation of gaseous He4 containing impurity water vapor in a cell filled with superfluid helium at a temperature T⩽1.5 K is transformed over time into an oval iceberg with an average diameter of ∼9 mm, suspended on the walls of the glass cell under the surface of the liquid. Within the liquid helium, icebergs can exist at temperatures above Tλ as well. At a vapor pressure P=150 torr over the surface of normal liquid He I the temperature Td at which intense decomposition of the icebergs occurs is 2.5 K. When the pressure is increased to 760 torr the temperature Td increases to 4 K. In an atmosphere of gaseous He4 the “dry” icebergs extracted from He II at T∼1.4 K decompose on heating above 1.8 K. The decomposition of the icebergs is accompanied by the formation of a fine powder (apparently amorphous ice) on the bottom of the cell; the volume of this powder is nearly two orders of magnitude less than the volume of the initial icebergs, i.e., the total water content in an iceberg is ⩽1020 molecules/cm3. This estimate agrees with an estimate of the difference of the density of an iceberg and the density of the surrounding liquid ρL (the ratio Δρ/ρL<0.1) from the results of observations of oscillations of the sample when thermoacoustic vibrations arise in a cell filled with liquid He I. In considering the structure of the icebergs it can be assumed that in helium vapor over the surface of He II the H2O impurity molecules agglomerate into clusters, so that the core of the impurity–helium water condensate in He II (a gel dispersion system) is formed by water nanoclusters surrounded by one or two layers of solidified helium, and the superfluid He II filling the pores between particles serves as the dispersion medium of the watergel.
Cyclotron frequency coupled enhancement of Kerr rotation in low refractive index-dielectric/magneto-optic bilayer thin-film structures
Authors: De A. , Puri A.
Published: July 2002

We investigate the enhancement of magneto-optic polar Kerr rotation over a broad range of optical frequencies. The Drude model for the dielectric tensor is considered. Resonance-like peaks in the Kerr rotation and ellipticity caused in the vicinity of a plasma edge is extended throughout the visible spectrum by deriving an expression for the cyclotron frequency such that Re(εxx)∼1 at any given incident photon energy and plasma frequency of the material. The Kerr rotation obtained by use of this expression was studied for the case of InSb and further enhancement of Kerr rotation was achieved in the case of LiF/InSb bilayer thin-film structure, grown on a glass substrate. The numerical analysis was carried out using a 2×2 characteristic matrix, which takes into account multiple reflections and interface effects within the medium. In addition the role of various magneto-optic material parameters and layer thicknesses is investigated in determining the optical frequency at which the maximum Kerr rotation occurs, under the present cyclotron frequency condition. Enhanced Kerr rotation greater than 1.5° over a broad range of optical frequencies was obtained. Tables showing optimum figure of merit for repeated LiF/InSb bilayers at 3.1 eV for different plasma frequencies are also provided.
Near field imaging with negative dielectric constant lenses
Authors: Shen J. T. , Platzman P. M.
Published: July 2002

A recent analysis by Pendry [J. B. Pendry, Phys. Rev. Lett. 85, 3966 (2000)] shows that a dielectric slab with a dielectric constant ε=−1 can produce a perfect image in the electrostatic limit (c→∞), independent of the permeability μ, and therefore is a perfect lens. Here we include retardation effects and show how distance and dissipation make the lens no longer perfect. Nevertheless we conclude that very significant improvements over conventional near field imaging may be obtained in the microwave regime.
Stochastic resonance in mammalian neuronal networks
Authors: Gluckman Bruce J. , So Paul , Netoff Theoden I. , Spano Mark L. , Schiff Steven J.
Published: July 2002

We present stochastic resonance observed in the dynamics of neuronal networks from mammalian brain. Both sinusoidal signals and random noise were superimposed into an applied electric field. As the amplitude of the noise component was increased, an optimization (increase then decrease) in the signal-to-noise ratio of the network response to the sinusoidal signal was observed. The relationship between the measures used to characterize the dynamics is discussed. Finally, a computational model of these neuronal networks that includes the neuronal interactions with the electric field is presented to illustrate the physics behind the essential features of the experiment.
Algorithm to solve the time-dependent Schrödinger equation for a charged particle in an inhomogeneous magnetic field: Application to the Aharonov–Bohm effect
Authors: De Raedt Hans , Michielsen Kristel
Published: July 2002

This paper introduces an unconditionally stable, accurate, and efficient algorithm to solve the time-dependent Schrödinger equation for a particle moving in an inhomogeneous magnetic field. The algorithm is used to simulate a fundamental thought experiment of quantum mechanics: the magnetic Aharonov–Bohm effect. The calculations demonstrate that the Aharonov–Bohm prediction of the phase shift holds with great precision, even when the dimensions of the interferometer are comparable to the de Broglie wavelength of the particle.
Parametric curve fitting: An alternative to Lagrange interpolation and splines
Authors: Akyildiz Yilmaz
Published: July 2002

We shall discuss a method for obtaining parametric equations of a smooth curve that passes through a sequence of points, and compare it to cubic splines and to the method of interpolation by quadratic polynomials using the Lagrange formula. A mathematica program automating this method of curve fitting is also provided.
Magnetoelastic processes in steel
Authors: Schneider C. S. , Charlesworth Melanie
Published: July 2002

A magnetoelastic model described previously has been computer programmed to allow averaging over polycrystalline grain orientations and integration of susceptibility to predict magnetization changes. In magnetoelastic (field and stress, H–σ) processes, Brown’s effective field due to stress on 90° domain walls has been extended with the differential susceptibility to describe magnetization changes in σH, σσ̄H, Hσ∼, and HH̄σ∼ processes for coercive fields and stresses: magnetization in the σH process initially exceeds and then drops below that due to H alone. Susceptibility in the σσ̄H process is predicted and was observed to be first higher and then lower than for H alone. Magnetoelastic sensitivity, H(σσ̄)n, was observed to increase with magnetization as predicted by this model and by Bozorth. No Villari reversal was observed.
Refractory amorphous metallic (W0.6Re0.4)76B24 coatings on steel substrates
Authors: Thakoor A. P. , Lamb J. L. , Khanna S. K. , Mehra Madhav , Johnson W. L.
Published: July 2002

Refractory metallic coatings of (W0.6Re0.4)76B24 (WReB) have been deposited onto glass, quartz, and heat-treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As-deposited WReB films are amorphous, as shown by their diffuse x-ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (∼ 1000 °C) crystallization temperature. Adhesion strength of these coatings on heat-treated AISI 52100 steel is in excess of ∼20, 000 psi and they possess high microhardness (∼ 2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin-on-disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 μm thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel.
Surface chemistry of HF passivated silicon: X-ray photoelectron and ion scattering spectroscopy results
Authors: Weinberger B. R. , Peterson G. G. , Eschrich T. C. , Krasinski H. A.
Published: July 2002

X-ray photoelectron spectroscopy and ion scattering spectroscopy studies of HF-treated silicon surfaces are described in an effort to understand the chemical termination leading to the near ideal electrical passivation of such surfaces. Results suggest a fluorine surface density of order a monolayer chemically bonded to silicon with a partial oxygen contamination due to exposure of the HF-treated wafer to air, and a physisorbed hydrocarbon layer on top.
Magnetoresistance of antiferromagnetic metals with localized magnetic moments
Authors: Ali Naushad , Woods S. B.
Published: July 2002

The magnetoresistance (MR) of antiferromagnetic rare-earth hexaborides (ReB6) (Re=Pr, Nd, Gd, and Dy) have been experimentally studied in magnetic fields up to 30 kOe in the temperature range from 4 to 30 K. The MR in general is positive and increases with increasing field for temperature below the Néel temperature (TN) and above TN the MR is negative. A large drop in the MR is observed at the antiferromagnetic to paramagnetic phase transition temperatures. We have also observed an anisotropy in the logitudinal and transverse magnetoresistances of ReB6 compounds except for GdB6. This is thought to be caused by anisotropic conduction electron  f -electron interactions. The experimental results are discussed in light of existing theories.
Control of ion-exchanged waveguide profiles with Ag thin-film sources
Authors: Tervonen A. , Honkanen S. , Leppihalme M.
Published: July 2002

Fabrication of optical ion-exchanged glass waveguides by using thin-film silver ion sources is studied with reference to the use of salt-melt sources. Since the amount of silver in a thin-film source is limited, the process is source controlled, and it is shown that temperature and time as controlling parameters in the process can be replaced by source dimensions. Channel waveguide depth profiles are calculated. When contact film over patterned silver-film-stripe sources is used, silver can be used totally, which results in good uniformity in waveguide depth.
Theory of magnetic surface anisotropy and exchange effects in the Brillouin scattering of light by magnetostatic spin waves (invited)
Authors: Rado G. T. , Hicken R. J.
Published: July 2002

A new theory of the Brillouin shift in the inelastic scattering of light by magnetostatic spin waves is presented. Contrary to previous work, the present calculations do include exchange effects and treat the magnetic surface anisotropy constants Ks and Kss directly rather than via the stratagem of effective volume anisotropies. The experimental data for {110} Fe on W are explained about as well by the present theory as by previous work. A detailed analysis reveals the previously unnoticed fact that the signs of Ks and Kss for (1̄10) Fe on W are opposite to those for (1̄10) Fe on GaAs. Some new spin-wave modes arising from exchange are predicted and shown to occur outside the frequency range which has been investigated experimentally. A quantitative explanation is proposed for the occasional applicability of a theory based on effective volume anisotropies and zero exchange.
Magnetic properties of thin fcc iron films on Cu(001) (invited)
Authors: Stampanoni M. , Vaterlaus A. , Aeschlimann M. , Meier F. , Pescia D.
Published: July 2002

Thin epitaxial iron overlayers and sandwiches on Cu(001) have been investigated by spin-polarized photoemission. The magnetization was measured as a function of perpendicularly applied field and temperature. Up to 14 monolayers (ML) of iron grow epitaxially on Cu(001) in the fcc phase and are ferromagnetic. At 30 K a remanence magnetization perpendicular to the plane of the film is observed for both the Fe/Cu(001) and the Cu/Fe/Cu(001) systems with Fe layers thicker than 2 ML. The coercive field, measured as function of temperature for a 10-ML Fe film, decreases rapidly from 2.7 kOe at 30 K to about 50 Oe at 200 K. The Curie temperature is 300 K for films thicker than 8 ML and increases for thinner films up to 500 K. The transition from fcc to bcc iron occurs at 15 ML. It is recognized by a jump of the Curie temperature to 1000 K and by the disappearance of the remanence magnetization at 30 K. Simultaneous evaporation of Fe and Cu at various rates also results in epitaxial overlayers with characteristic magnetic features. The fcc Fe films are suitable for thermomagnetic recording. Writing and reading has been carried out by a UV excimer laser. Reading was performed by analyzing the sign of the spin polarization of the photoelectrons.
Substrate-driven ordering microstructure in GaxIn1−xP alloys
Authors: Bellon P. , Chevalier J. P. , Augarde E. , André J. P. , Martin G. P.
Published: July 2002

The effect of substrate misorientation on {111} ordering in GaxIn1−xP epilayers grown on (001) GaAs substrates by metalorganic vapor-phase epitaxy has been studied by transmission electron microscopy. Among the four possible variants, only the { 1/2   1/2   1/2 }B are observed, and the substrate misorientation toward (11̄0) can disymmetrize the two B variants to a point such that only one remains. We show that the diffuse intensity observed along (001) originates from a modulation of the degree of order. When the domain size is comparable to the characteristic length of the modulation, domain boundaries and antiphase boundaries contribute to the diffuse scattering, giving rise to the reported wavy diffuse intensity. We propose a few simple rules controlling the growth process at the atomistic level, from which the absence of the { 1/2   1/2   1/2 }A variants, as well as the selection effect of the [11̄0] steps on the two remaining variants may be explained. From existing literature, the validity of these rules seems to be rather general. Finally, considering reports that the ordered structure observed here is not at equilibrium, we suggest that the latter is growth induced. The necessary conditions for such an ordering mechanism to operate are identified.
Dopant diffusion in silicon in the presence of other dopants: A new predictive approach based on modeling boron and phosphorous diffusion in germanium-rich regions of silicon
Authors: Aronowitz Sheldon
Published: July 2002

The effect of dopant-dopant interaction on diffusion in silicon for a specific set of impurities is modeled. The first step in the modeling process involved quantum chemical calculations. The connection between the atomic scale results and macroscopic behavior was made through the medium for transmission of interactions between dopants. The molecular orbitals of the lattice system comprise that medium; consequently, interactions can be transmitted, with minimal reduction in magnitude, over separations of hundreds of lattice spacings. Macroscopically, additional flux components are generated that modify the conventional expression of Fick’s second law. Detailed simulation of boron and phosphorous diffusion in germanium-rich regions of silicon illustrate the power of this approach to successfully model and predict the complex behavior exhibited by a particular set of interacting dopant species.
The mixing of iron and cobalt during mechanical alloying
Authors: Brüning R. , Samwer K. , Kuhrt C. , Schultz L.
Published: July 2002

At the early stage of mechanical alloying of α-Fe and ε-Co lamellar layers of the initial phases are formed. As the thickness of the layers decreases the interdiffusion of the elements starts and a disordered crystalline Fe-Co solid solution is formed. The progress of the solid state reaction has been monitored by Mössbauer spectroscopy, x-ray diffraction, and measurements of the saturation magnetization. The experimental data allow calculation of the change of fractions of material with different local compositions as the alloying proceeds. The main results are that Co diffuses into the α-Fe while Fe does not diffuse into the ε-Co. In spite of a much lower negative heat of mixing, the reaction proceeds in a similar way to the formation of amorphous NiZr during mechanical alloying.
Magnetic properties of Pd/Co multilayer films studied by Hall effect
Authors: Kim Sangrok , Lee Seong Rae , Chung Jin Duck
Published: July 2002

The magnetic properties and Hall effects of Pd/Co multilayer films fabricated by thermal evaporation have been studied using the Hall hysteresis loop measurement. The polarity of the Hall hysteresis loops of Pd/Co multilayer changed between 4 and 5 monolayers (ML) of Pd. It was speculated that the reason for this phenomena is the change of the position of Fermi level of 3d band in Pd/1Co multilayer from lower half of the band to upper half of the band depending on the Pd thickness. The Hall resistivities as a function of Pd thickness were found to oscillate and the period of oscillation was about 5 ML of Pd. The change of saturation magnetization as a function of Pd thickness reflected the oscillatory behavior up to 7 ML of Pd and the enhanced Co moments were observed in the film with 4 or thicker ML of Pd.
Epitaxial growth of lead phthalocyanine film on KI crystal
Authors: Hoshi Hajime , Fang Shaoli , Maruyama Yusei
Published: July 2002

The molecular-beam epitaxy technique is applied to grow an epitaxial film of lead phthalocyanine (PbPc). The epitaxy found, KI(100)(5×10/7)R45°-PbPc, is a new type with the incommensurate factor 10/7.
Dispersion of surface plasmons in rectangular, sinusoidal, and incoherent silver gratings
Authors: Fischer B. , Fischer T. M. , Knoll W.
Published: July 2002

The dispersion behavior of surface plasmons on silver gratings in the center of the first Brillouin zone is determined by measurements of the reflected light as a function of amplitude and of the profile of the gratings. We studied the dispersion relation of sinusoidal gratings, rectangular gratings, and incoherent gratings. We found a strict relationship between the profile of the grating and the dispersion relation of the surface plasmons. Our experiments showed at small amplitudes a crossing of the dispersion branches without a gap. For higher amplitudes a frequency or a momentum gap occurred depending on whether the profile had higher Fourier components or not. The experimental results are in accordance with numerical simulations.
Soft-magnetic properties of amorphous tapes after dynamic current annealing
Authors: Escobar M. A. , Perron J. C. , Barrué R. , Yavari A. R.
Published: July 2002

The magnetic properties of amorphous FeSiB (2605-S2) and CoFeMoSiB (6025-Vac) tapes have been measured after conventional furnace annealing and dynamic current annealing, which takes place in air and during the winding process of tapes using Joule heating. The measurements showed a significant improvement of the magnetic properties when dynamic annealing temperatures are far below the crystallization temperatures but above the Curie temperature. Magnetic properties and domain patterns are presented and we find that our method of about 10 s of annealing gives a similar magnetic quality to that obtained by classical techniques.
Al-Al2O3-Pd junction hydrogen sensor
Authors: Okuyama K. , Takinami N. , Chiba Y. , Ohshima S. , Kambe S.
Published: July 2002

Al-Al2O3-Pd MIM (metal insulator metal) junctions fabricated on a glass substrate were tested as hydrogen sensors. The I-V (current versus voltage) characteristics of the junctions were measured at room temperature in a vacuum of 10−5 Torr and in H2 gas of 10−2–100 Torr. A significant increase in the current was observed upon introduction of H2 gas. This phenomenon is believed to occur due to the work function lowering of the hydrogen-absorbed Pd top electrode. The rise time was on the order of minutes, while the recovery time when hydrogen was purged was more than 20 h. However, when the junction was placed in an oxidizing ambient such as air, the recovery time was drastically reduced to the order of minutes, indicating that the device is operative as a hydrogen sensor in the atmospheric ambient. Hydrogen adsorption and desorption behavior of the Pd film was also investigated using a Pd coated quartz microbalance, and the results explained the current response of the Pd MIM junction to hydrogen in the presence of oxygen.
Spectroscopic measurements of laser induced plasma during welding with CO2 laser
Authors: Szymański Z. , Kurzyna J.
Published: July 2002

Results of spectroscopic measurements of laser-induced plasma under welding conditions are presented. Welding was performed with the use of a continuous-wave CO2 laser operating at a power of 2 kW. Argon or helium was used as a shielding gas. The welding metal was stainless steel or titanium. Emission spectra from plasma were measured with a spectrograph and 1254 Silicon Intensified Target detector connected to the optical multichannel analyzer. The plasma electron temperatures were determined from the relative intensities of spectral lines and the electron densities were determined either from Stark broadening of atomic line or the absolute intensity of ionic line. The distributions of the electron temperature and density over the metal surface are presented and the influence of a shielding gas on plasma parameters is demonstrated. The plasma parameters obtained were used to calculate the absorption of a laser beam in the plasma over the metal surface. No significant absorption was found in our experimental conditions.
Hall effect of polycrystalline Co-Pd alloys
Authors: Jen S. U. , Chao B. L. , Liu C. C.
Published: July 2002

Hall-effect measurements were carried out on a series of Co100−xPdx alloys from 4.2 to 255 K. The extraordinary Hall coefficient RS is analyzed. The side-jump mechanism is dominant for Co-Pd alloys with x≤65 at. %; however, when x≳65 at. %, both the side-jump and skew scattering mechanisms are equally effective. The Hall conductivity γH changes its sign around xH=77 at. %. xH is shifted to the right-hand side of the band-gap position xG, as implied from the anisotropic magnetoresistance data and the split-band theory.
Deep center related to hydrogen and carbon in p-type silicon
Authors: Kamiura Yoichi , Tsutsue Makoto , Yamashita Yoshifumi , Hashimoto Fumio , Okuno Kazuhiko
Published: July 2002

We have found a hole trap related to hydrogen and carbon in p-type crystalline silicon after hydrogen and deuterium injection by chemical etching and plasma exposure. It was found from deep-level transient spectroscopy that this center is located at 0.33 eV above the valence band and shows no Poole–Frenkel effect in electric fields lower than 6×103 V/cm. The depth profiling technique using deep-level transient spectroscopy indicated that this center is distributed over the range 1–7 μm from the surface with densities of 1011–1013 cm−3, depending on the hydrogenation method. On the other hand, secondary ions mass spectroscopy revealed that the majority of deuterium injected into silicon exists within a much shallower region less than 60 nm from the surface with higher densities of 1018–1020 cm−3. We have therefore concluded that the majority of injected hydrogen stays in the near-surface region probably in the form of a molecule and larger clusters and only the minority diffuses into the bulk in an atomic form to form an electrically active complex with carbon. We performed annealing experiments to investigate the thermal stability of the complex. It was stable in the dark up to 100 °C, above which it was completely annihilated in first-order kinetics with an activation energy of about 1.7 eV. The illumination of band gap light with and without a reverse bias at room temperature and at 50 °C induced no effect on the stability of the trap. This is contrast to the photoinduced annihilation of a recently observed electron trap related also to hydrogen and carbon and with comparable thermal stability in n-type silicon.

These similarities and differences between the two traps and the comparison of the present results with the recently published theoretical calculations of the total energy of hydrogen configurations in the hydrogen-carbon complex suggest that the previously observed electron trap and the presently observed hole trap arise from two different defects with similar origins and structures and are tentatively ascribed to the electronic states of ‘‘bond-centered’’ and ‘‘anti-bonding of carbon’’ configurations of hydrogen in the hydrogen-carbon complex, respectively.
Electromagnetic properties of Mn–Zn ferrite sintered ceramics
Authors: Nakamura T. , Okano Y.
Published: July 2002

Mn–Zn ferrite ceramics were prepared through the ceramic method starting from metal oxides. The ceramics’ microstructural and electromagnetic properties were then evaluated. It was found that sintering density and ferrite grain size depend on both the sintering temperature and the kinds of the raw materials used. The changes in the microstructure were responsible for variations in magnetization, permeability, and electrical resistivity. The grain boundary resistivity, evaluated from the ac resistivity analysis, was especially affected. Increases in the electrical resistivity were counteracted by increases in the magnetization and permeability. This is also reflected in a trade-off of the hysteresis loss reduction and the lowering of the eddy current loss. This relationship between microstructural and electromagnetic properties can be explained by using the nonmagnetic and insulating grain boundary model.
Magnetization reversal process in TbCo-biased spin valves
Authors: Chapman J. N. , Gillies M. F. , Freitas P. P.
Published: July 2002

The magnetization reversal processes in the free and the pinned layers of TbCo-biased spin valves have been studied in a highly modified transmission electron microscope. Reversal of the free layer in the presence of a field antiparallel to the biasing direction proceeds by a complex domain process with 360° walls forming frequently. In the presence of substantially higher fields, the pinned layer reverses by creep of highly irregular walls through the structure. By studying image grey levels, an estimate of the average orientation of the induction vector in the TbCo layer is made.
Low-temperature photoluminescence of detector grade Cd1−xZnxTe crystal treated by different chemical etchants
Authors: Chen H. , Tong J. , Hu Z. , Shi D. T. , Wu G. H. , Chen K.-T. , George M. A. , Collins W. E. , Burger A. , James R. B. , Stahle C. M. , Bartlett L. M.
Published: July 2002

Low-temperature photoluminescence (PL) spectra of detector grade Cd1−xZnxTe (x=0.1) have been measured to obtain information about shallow level defect concentration introduced during mechanical polishing and chemical etching processes. We present here a comparative PL study of Cd0.9Zn0.1Te crystals treated by different chemical solutions used for nuclear detector surface treatment. The results show that the 5% Br–MeOH+2%Br–20% lactic acid in ethylene glycol treatment combines the advantages of bromine and lactic acid for chemical etching and results in the best surface condition, as evidenced by the largest I(D0,X)/Idef intensity ratio and the narrowest full width at half-maximum of the main peak (D0,X). Changes in the surface morphology were also analyzed by atomic force microscopy and correlated with the PL results. Current–voltage (I–V) curves and the room-temperature 55Fe spectral response of the sample etched by the best treatment are also presented and discussed.
Characterization of laser-driven shocks of high intensity using piezoelectric polymers
Authors: de Rességuier T. , Couturier S. , Boustie M. , David J. , Niérat G. , Bauer F.
Published: July 2002

Piezoelectric elements made of polyvinylidene-fluoride-trifluoroethylene copolymer P(VDF/TrFE) have been used to measure the pressure induced on the rear surface of metallic foils irradiated by infra-red laser pulses of 1.5 ns duration, with intensities up to 3 TW/cm2. The application of such piezoelectric materials under those conditions is new, and a special effort has been made for their improvement and characterization under plate impact loading. Then, the laser experiments have been carried out. First, peak pressures of 0.5–7.5 GPa transmitted in the copolymer have been derived from the peak voltage measured at each shot, using simple assumptions. Next, a more accurate analysis of the data, involving computer simulations, has provided the pressure profiles characterizing the laser shocks driven on the front surface of the targets, over a wide range of laser intensities. Peak pressures of 7–60 GPa on the irradiated surface have been inferred from that analysis. The results have been compared to values obtained from a classical scaling law on one hand, and to predictions of a laser-matter interaction simulation code on the other hand. An overall coherence has been obtained, despite some discrepancies that have been discussed.
Long-range exchange coupling between a ferromagnet and an antiferromagnet across a nonmagnetic spacer layer
Authors: Gökemeijer N. J. , Ambrose T. , Chien C. L. , Wang N. , Fung K. K.
Published: July 2002

The antiferromagnet/ferromagnet exchange coupling giving rise to a shifted hysteresis loop has usually been considered an interfacial effect. We show evidence that this exchange coupling between an antiferromagnet (CoO) and a ferromagnet (Ni81Fe19) is long range in nature. Exchange coupling has been observed in tri-layer films consisting of a nonmagnetic noble metal (Ag, Au, and Cu) spacer layer sandwiched between 300 Å CoO and 300 Å NiFe. The strength of the coupling decreases with increasing spacer layer thickness and vanishes at about 55 Å. This suggests that the antiferromagnetic/ferromagnetic exchange coupling is beyond an interfacial effect, and that conduction electrons may be involved in the mediation of the coupling.
Application of nanocrystalline soft magnetic Fe–M–B (M=Zr, Nb) alloys to choke coils
Authors: Naitoh Y. , Bitoh T. , Hatanai T. , Makino A. , Inoue A.
Published: July 2002

We have developed a choke coil made of new nanocrystalline soft magnetic Fe–M–B (M=Zr, Nb) alloys (“NANOPERM™ ” material) which exhibit high saturation magnetic induction (Bs), above 1.5 T, excellent soft magnetic properties and zero magnetostriction. A choke coil made of NANOPERM™ material exhibits good dc bias characteristics of inductance because of the high Bs. Furthermore, the choke coil made from NANOPERM™ material showed 1/3rd the temperature rise shown by a core made from Fe–Si–B amorphous alloy. The low core loss and high Bs of NANOPERM™ material allow the reduction of the core size. It is concluded that NANOPERM™ is suitable as a core material for choke coils.
Formation of regular step arrays on Si(111)7×7
Authors: Lin J.-L. , Petrovykh D. Y. , Viernow J. , Men F. K. , Seo D. J. , Himpsel F. J.
Published: July 2002

Highly regular arrays of steps are produced on vicinal Si(111)7×7 surfaces. A tilt of the surface normal from (111) toward (1̄1̄2) produces single steps (0.3 nm high and typically 15 nm apart). The opposite tilt toward (112̄) produces bunched steps with adjustable height (1–5 nm) and a spacing of 70 nm. Preparation criteria for straight edges and regular spacings are determined, taking into account the miscut angle (azimuthal and polar), annealing sequence, current direction, and applied stress.
Pyroelectric properties of polymer dispersed ferroelectric liquid crystals
Authors: Bartolino R. , Scaramuzza N. , Barna E. S. , Ionescu A. Th. , Beresnev L. A. , Blinov L. M.
Published: July 2002

A polymer dispersed ferroelectric liquid crystal (PDFLC) is a novel material combining properties of a polymer (flexibility, elasticity) and ferroelectric liquid crystal (low voltage, fast electro-optical switching). Another interesting field of application of PDFLC is the detection of low intensity radiation using the pyroelectric response of the material. A PDFLC material containing a ferroelectric liquid crystal (FLC) with very high spontaneous polarization (close to 200 nC/cm2 at room temperature) was prepared to study its pyroelectric properties. The matrix was pure polymer poly-butadiene-styrene which can be mixed with liquid crystals in volatile solvents. The pyroelectric response and the spontaneous polarization were measured over a wide temperature range of the smectic C* phase and compared with the corresponding quantities of the pure FLC. Figures of merit of pyroelectric PDFLC films were estimated and compared with those known for conventional ferroelectrics.