bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of field-dependent photogeneration on holographic contrast in photorefractive polymers
Authors: Khand K. , Binks D. J. , West D. P.
Published: July 2002

The field-dependence of the charge photogeneration efficiency reduces the holographic contrast in an organic photorefractive composite. In this article, the Braun model for field-dependent photogeneration efficiency is incorporated into the standard model of photorefractivity. Using this formalism, the effect on the space-charge field, and thereby holographic index contrast, is calculated directly without the need for empirically found parameters. The dependence of the space-charge field on experimental geometry is also analyzed. A powerful description of the effective space-charge field is thus derived and is experimentally verified. This analysis is then used to compare the observed holographic contrast to that predicted from transmission ellipsometry measurements.
Acoustic imaging by second harmonic of phase-conjugate wave in inhomogeneous medium
Authors: Pyl’nov Yu. , Pernod P. , Preobrazhensky V.
Published: July 2002

Application of the supercritical magnetoelastic wave phase conjugation to harmonic imaging in acoustic C-scan microscopy is demonstrated. Second-harmonic generation by phase-conjugate wave is used for improvement of resolution of an imaging system. Possibility to compensate phase aberrations introduced in harmonic image by inhomogeneity of propagation medium is shown experimentally and explained theoretically.
A unified framework for Lie and covariant differentiation (with application to tensor fields)
Authors: Hurley D. J. , Vandyck M. A.
Published: July 2002

A unified framework is provided in which Lie and covariant differentiation may be considered as special cases of a new operation, called “D differentiation.” The present article develops D differentiation of tensor fields, whereas the extension to spinor fields, called “D̃ differentiation,” is presented in a companion article. The concept of “generalized curvature” of D differentiation is introduced, and a bundle formulation of D differentiation is obtained.
Infrared response of multiple-component free-carrier plasma in heavily doped p-type GaAs
Authors: Zangooie S. , Schubert M. , Thompson D. W. , Woollam J. A.
Published: July 2002

Spectroscopic ellipsometry is used to measure the dielectric function of heavily doped p-type GaAs for wave numbers from 100 to 2000 cm−1. Due to partial filling of the heavy- and light-hole valence bands, heavy holes as well as light holes form a multiple-component plasma coupled with longitudinal optical phonons. Line-shape analysis of the infrared response allows differentiating between light- and heavy-hole contributions to the carrier plasma, and the results observed suggest nonparabolicity effects of the heavy- and light-hole valence bands in GaAs.
Short-wavelength intersubband transitions down to 1.6 μm in ZnSe/BeTe type-II superlattices
Authors: Akimoto R. , Kinpara Y. , Akita K. , Sasaki F. , Kobayashi S.
Published: July 2002

We report photoinduced electron intersubband absorption in ZnSe/BeTe type-II superlattices. The wavelength of the intersubband transition as short as 1.6 μm, covering the 1.55 μm optical communication wavelengths within its absorption band width (∼250 nm), is achieved in the ZnSe/BeTe SLs with 4.5 ML-thick ZnSe layers. The intensity in photoinduced intersubband absorption increases sublinearly with pump intensity, reflecting the characteristic recombination processes of electron-hole pairs in a heterostructure with type-II band alignment.
Interface instabilities during displacements of two miscible fluids in a vertical pipe
Authors: Scoffoni J. , Lajeunesse E. , Homsy G. M.
Published: July 2002

We study experimentally the downward vertical displacement of one miscible fluid by another in a vertical pipe at sufficiently high velocities for diffusive effects to be negligible. For certain viscosity ratios and flow rates, the interface between the two fluids can destabilize. We determine the dimensionless flow rate Uc above which the instability is triggered and its dependence on the viscous ratio M, resulting in a stability map Uc=Uc(M). Two different instability modes have been observed: an asymmetric “corkscrew” mode and an axisymmetric one. We remark that the latter is always eventually disturbed by “corkscrew” type instabilities. We speculate that these instabilities are driven by the viscosity stratification and are analogous to those already observed in core annular flows of immiscible fluids.
A versatile matrix-based solution for the two plasmon decay instability
Authors: Machacek A. C. , Wark J. S.
Published: July 2002

A Floquet-based solution of the equations governing the two plasmon decay (TPD) instability which is valid over a range of plasma densities is presented. The capability to include a large number of modes allows the validity of conventional fluid-based analytic solutions at densities differing from quarter-critical to be assessed. The conventional assumptions are upheld in the absence of a magnetic field, however, it is shown that the extra modes have a significant effect once a static magnetic field is present in the plasma.
Comparison of Josephson vortex flow transistors with different gate line configurations
Authors: Schuler J. , Weiss S. , Bauch T. , Marx A. , Koelle D. , Gross R.
Published: July 2002

We performed numerical simulations and experiments on Josephson vortex flow transistors based on parallel arrays of YBa2Cu3O7–δ grain boundary junctions with a cross gate line allowing us to operate the same devices in two different modes named the Josephson fluxon transistor (JFT) and Josephson fluxon–antifluxon transistor (JFAT). The simulations yield a general expression for the current gain versus number of junctions and normalized loop inductance and predict higher current gain for the JFAT. The experiments are in good agreement with simulations and show improved coupling between gate line and junctions for the JFAT as compared to the JFT.
Characterization of RuO2 electrodes on Zr silicate and ZrO2 dielectrics
Authors: Zhong Huicai , Heuss Greg , Misra Veena , Luan Hongfa , Lee Choong-Ho , Kwong Dim-Lee
Published: July 2002

The rutile stoichiometric phase of RuO2, deposited via reactive sputtering, was evaluated as a gate electrode on chemical vapor deposited ZrO2 and Zr silicate for Si–p-type metal–oxide–semiconductor (PMOS) devices. Thermal and chemical stability of the electrodes was studied at annealing temperatures of 400, 600, and 800 °C in N2. X-ray diffraction was measured to study grain structure and interface reactions. The resistivity of RuO2 films was 65.0 μΩ cm after 800 °C annealing. Electrical properties were evaluated on MOS capacitors, which indicated that the work function of RuO2 was ∼5.1 eV, compatible with PMOS devices. Post-RuO2 gate annealing up to 800 °C, resulted in only a 1.4 Å equivalent oxide thickness (Tox-eq) change and 0.2 V flatband voltage change for Zr silicate and a 4 Å Tox-eq change for ZrO2 dielectrics. Tantalum electrodes were also studied on ZrO2 as a comparison of the stability of RuO2 electrodes.
Factors Affecting Sorption of Organic Compounds in Natural Sorbent/Water Systems and Sorption Coefficients for Selected Pollutants. A Review
Authors: Delle Site Alessandro
Published: July 2002

Factors affecting sorption of organic pollutants by natural sorbents (soils, sediments, clays, humic materials, and dissolved organic matters) and sorption coefficients for selected pollutants are reviewed on the basis of the literature results and interpretations; with 681 references examined. The most significant aspects of the sorption process are discussed: sorption isotherms and sorption kinetics; effects of sorbent physico-chemical characteristics (pH, cation exchange capacity, ionic strength, surface area, etc.); effect of the temperature; sorption of volatile compounds; effect of the presence of a cosolvent; association with dissolved organic matter; effect of the sorbent concentration; “hysteresis” or nonsingularity in the sorption–desorption process, and its implications in the transport of these contaminants through soil columns. The experimental and prediction methods adopted for the determination and estimation of the sorption coefficients are also described. Literature sorption coefficients for selected hydrophobic, polar, and ionizable compounds are collected. The compounds taken into consideration belong to the following classes: monoaromatic hydrocarbons, polycyclic aromatic hydrocarbons, chlorinated alkyl and aryl compounds, phenol and chlorinated phenols, polychlorobiphenyls, dioxins, and pesticides. The respective sorption coefficients (log Kd) and organic carbon-referenced sorption coefficients (log Koc) are tabulated together with the most relevant characteristics of the respective sorbent, the measurement temperature, and the experimental methods. The log Koc values are averaged and compared with other experimental and estimated literature data. Differences of sorption coefficients on soils and sediments and effect of pH on sorption coefficients for ionizable compounds are evidentiated.
Equation of state and structure of binary mixtures of hard d-dimensional hyperspheres
Authors: González-Melchor M. , Alejandre J. , López de Haro M.
Published: July 2002

Computer simulations have been performed on binary fluid mixtures of hard hyperspheres in four and five dimensions. The equation of state and the radial distribution function have been obtained for a variety of compositions and size ratios. The simulation results for the excess compressibility factor and the contact values of the cross radial distribution functions in both dimensions are described rather accurately by a recent theoretical proposal for these quantities up to a reduced density where some features arise which are reminiscent of a fluid–solid phase transition.
Digital signal processor-based dc superconducting quantum interference device controller
Authors: Hahn Inseob , Weilert Mark
Published: July 2002

We report on the design and evaluation of a convenient digital signal processor-based (DSP) controller for a dc superconducting quantum interference device (SQUID). Program algorithms for the DSP conveniently replace major functions of an analog flux-locked loop: current bias, modulation signal, demodulation, filtering, integration, feedback, and reset. For the controller described here, the entire system was built using commercially available electronics and sensor units with the addition of a simple operational amplifier circuit for the required gain. The noise level of the nonoptimized dc SQUID controller system at 1 Hz was ∼50μΦ0/Hz. Application of the system was demonstrated as a readout system for a low-temperature magnetic susceptibility thermometer that required flux counting.
Electrical properties of Co-doped β -FeSi2 crystals
Authors: Brehme S. , Behr G. , Heinrich A.
Published: July 2002

β- FeSi 2 crystals were grown from high-purity starting materials by chemical vapor transport. The crystals were in situ n-type doped adding Co to the source material. Electrical properties have been investigated by temperature-dependent resistivity and Hall effect measurements. Above 100 K, we observed conventional conduction band transport. The Co doping was found to create a shallow donor level at Ec—0.053 eV. Hall mobilities up to 50 cm2/Vs were observed. At lower temperatures defect band conduction dominates the electrical transport and negative magnetoresistance is observed. The main contribution to the Hall voltage observed at low temperatures arises from the anomalous Hall effect.
Tribocharging phenomena in hard disk amorphous carbon coatings with and without perfluoropolyether lubricants
Authors: van den Oetelaar R. J. A. , Xu L. , Ogletree D. F. , Salmeron M. , Tang H. , Gui J.
Published: July 2002

Scanning polarization force microscopy was used to study changes in surface potential (tribocharging) caused by the contact between a tungsten carbide tip and the amorphous carbon coating of a hard disk, both when bare and when covered with Zdol-TX lubricant. The surface potential change produced by tip contact decays with time at a rate that is strongly dependent on lubricant coverage and on the presence of oxygen and water vapor in the environment. Two different charging mechanisms are proposed. One involves chemical modification of the surface by removal of oxygen bound to the surface. This gives rise to a potential change that decays with time. Another mechanism involves trapping of charge in states within the energy gap of the insulating carbon film. The potential change due to this trapped charge does not decay over periods much greater than 1 h.
Origin of persistent photocurrent in GaN/AlGaN multiquantum wells
Authors: Bonfiglio A. , Traetta G. , Lomascolo M. , Passaseo A. , Cingolani R.
Published: July 2002

We performed systematic photocurrent experiments on GaN/AlGaN multiple quantum wells, both spectrally and temporally resolved. We show that a photopersistence effect is present in our samples even at room temperature. A comparison with photoluminescence (PL) results indicates that a yellow band-like feature is observable in photocurrent spectra which is not seen in PL, indicating the existence of defects which give rise to carrier trapping rather than recombination. A suitable interpretation of results is proposed.
New integrable equations of fourth order and higher degree related to Cosgrove’s equation
Authors: Gordoa Pilar R. , Pickering Andrew
Published: July 2002

We give a general formulation of the algorithm of Fokas and Ablowitz, which then allows us to obtain transformations for nth order ordinary differential equations, to equations of the same order but perhaps of higher degree. Previously this algorithm has been used to obtain transformations for the six second order equations defining new transcendental functions discovered by Painlevé and co-workers, either to other equations in the Painlevé classification or to equations of second order and second degree. As an example of our approach we consider a new fourth order ordinary differential equation due to Cosgrove which is believed to define a new transcendent. We obtain transformations relating this equation to other fourth order ordinary differential equations, of degrees ⩾2. All of these transformations, as well as the corresponding higher degree differential equations, all of which have the Painlevé property, are new.
Thermally stimulated luminescence of SrS:Cu thin films
Authors: Morton D. C. , Forsythe E. W. , Sun S.-S. , Wood M. C. , Ervin M. H. , Kirchner K.
Published: July 2002

SrS:Cu thin films were evaluated using thermally stimulated luminescence (TSL), photoluminescence (PL), electroluminescence (EL), and charge transfer over a temperature range of 10–850 K. The trap states were measured with and without a BaTa2O6 (BTO) overlayer film. From TSL results, the trap state energies were measured in the range of 0.4 eV, with differences due the BTO overlayer. From the PL, EL, and charge transfer measurements, the light emission and charge transfer decrease at a temperature consistent with the 0.4 eV trap level, demonstrating the importance of the trap states to EL devices.
Spectroscopic properties of erbium-doped ultraphosphate glasses for 1.5 μm amplification
Authors: Feng Xian , Tanabe Setsuhisa , Hanada Teiichi
Published: July 2002

The spectroscopic properties of P2O5–Y2O3–Er2O3 and P2O5–Li2O–Al2O3–Y2O3–Er2O3 ultraphosphate glasses have been investigated. The concentration quenching rates of Er3+ in these two systems are lower compared with those in other oxide glasses. The spectral broadening of the measured fluorescence of 83.33P2O5–(16.67−x)Er2O3–xY2O3 (x=0.1 and 16.67) was observed by increasing temperature. Meanwhile, the lifetime of the I13/24 level shows the temperature dependence with increasing temperature, ascribed to the possible thermalization of higher-lying sublevels of the I13/24 level with faster radiative rates and the effect of radiation trapping. At room temperature, the deformation of the emission spectrum line shape has been observed with the increase of Er2O3 concentration due to the reabsorption effect. The 1.5-μm-amplification characteristics of P2O5–Y2O3–Er2O3 ultraphosphate glasses have been predicted from the calculated gain spectra at different pump powers.
Current-driven reversal in annular vertical giant magnetoresistive devices
Authors: Bussmann K. , Prinz G. A. , Bass R. , Zhu J.-G.
Published: July 2002

Experiments are reported that demonstrate the asymmetric switching behavior reported earlier in vertical giant magnetoresistance devices arises from the solid disk geometry of the device that produces a magnetic singularity at the disk center. Annular devices having a 0.1 μm center hole and 0.5 μm outer diameter are shown to switch symmetrically with an Amperian field.
High-frequency asymptotics for Maxwell’s equations in anisotropic media Part I: Linear geometric and diffractive optics
Authors: Garnier Josselin
Published: July 2002

This paper is devoted to the derivation of the equations that govern the propagation of pulses in noncentrosymmetric crystals. The method is based upon high-frequency expansions techniques for Maxwell’s equations. By suitable choices of the scalings we are able to derive two classical models: Geometric optics and diffractive optics (Schrödinger-type equations). In the so-called geometric regime we recover the standard results on the propagation of pulses in crystals (dispersion equation, polarization states, group velocity). In the diffractive regime we exhibit original results and give a closed-form expression for the diffraction operator which reads as an anisotropic operator. Given this expression we identify a critical configuration where the diffraction reduces to a one-dimensional second-order operator instead of the standard transverse Laplacian.
Simulation of the transformation from the C49 to the C54 phase of TiSi2 in blanket films and narrow conductors
Authors: Privitera S. , Spinella C. , La Via F. , Grimaldi M. G. , Rimini E.
Published: July 2002

The C49–C54 phase transition has been simulated by Monte–Carlo calculations in blanket films and conductors using a unitary model based on transient nucleation and growth which takes into account the temperature dependence of the nucleation parameters. The output of the model has been compared with experimental data from electrical measurements in blanket films and 0.5 μm wide conductors. The comparison allows us to determine the density of available nucleation sites and to interpret the spread of experimental data, observed in the case of lines, as fluctuations in the number of sites and in their random location.
A high-throughput x-ray microtomography system at the Advanced Photon Source
Authors: Wang Yuxin , De Carlo Francesco , Mancini Derrick C. , McNulty Ian , Tieman Brian , Bresnahan John , Foster Ian , Insley Joseph , Lane Peter , von Laszewski Gregor , Kesselman Carl , Su Mei-Hui , Thiebaux Marcus
Published: July 2002

A third-generation synchrotron radiation source provides enough brilliance to acquire complete tomographic data sets at 100 nm or better resolution in a few minutes. To take advantage of such high-brilliance sources at the Advanced Photon Source, we have constructed a pipelined data acquisition and reconstruction system that combines a fast detector system, high-speed data networks, and massively parallel computers to rapidly acquire the projection data and perform the reconstruction and rendering calculations. With the current setup, a data set can be obtained and reconstructed in tens of minutes. A specialized visualization computer makes rendered three-dimensional (3D) images available to the beamline users minutes after the data acquisition is completed. This system is capable of examining a large number of samples at sub-μm 3D resolution or studying the full 3D structure of a dynamically evolving sample on a 10 min temporal scale. In the near future, we expect to increase the spatial resolution to below 100 nm by using zone-plate x-ray focusing optics and to improve the time resolution by the use of a broadband x-ray monochromator and a faster detector system.
Study of ultrathin Al2O3/Si(001) interfaces by using scanning reflection electron microscopy and x-ray photoelectron spectroscopy
Authors: Kundu Manisha , Miyata Noriyuki , Ichikawa Masakazu
Published: July 2002

Al 2 O 3 /Si (001) interfaces were investigated using scanning reflection electron microscopy and x-ray photoelectron spectroscopy. A uniform and stoichiometric ultrathin Al2O3 film of ∼0.6 nm was grown on an atomically flat Si(001)-2×1 surface, and the resulting Al2O3/Si(001) interface was atomically abrupt. Furthermore, an intentional high-pressure oxidation shows that we can grow Si oxide at the Al2O3/Si(001) interface with atomic-scale uniformity as this oxidation proceeds in a layer-by-layer manner. The resulting Si oxide/Si(001) interface was also atomically abrupt. In addition, the rate of oxidation of Si at the Al2O3/Si(001) interface depends strongly on the O2 pressure.
Optical properties of peroxy radicals in silica: Multiconfigurational perturbation theory calculations
Authors: Sousa Carmen , de Graaf Coen , Pacchioni Gianfranco
Published: July 2002

The low-lying electronic transitions in a peroxy radical, ≡Si–O–O•, a fundamental radiation induced point defect in silicon dioxide, have been investigated by means of ab initio multiconfiguration perturbation theory calculations, CASPT2, and cluster models. The accuracy of the computed transition energies and intensities as predicted by the CASPT2 approach has been checked by studying the exited state properties of two molecular analogues, the HOO• and CH3OO• radicals, and of a well-characterized paramagnetic defect in silica, the nonbridging oxygen center, ≡Si–O•, for which unambiguous assignments exist. We found that the peroxy radical gives rise to two optical absorption bands, a very weak one at 0.7 eV and an intense one at 5.49 eV, in agreement with the experimental assignments of Radzig [V. A. Radzig, Chem. Phys. Reports 14, 1206 (1995)].
Diffuse multiself-frequency conversion processes in the blue and green by quasicylindrical ferroelectric domains in Nd3+:Sr0.6Ba0.4(NbO3)2 laser crystal
Authors: Romero J. J. , Jaque D. , Garcı́a Solé J. , Kaminskii A. A.
Published: July 2002

In this letter we demonstrate continuous-wave blue and green diffuse laser light generation from a Nd3+-doped Sr0.6Ba0.4(NbO3)2 crystal located in an end-pumped laser cavity and operating at the F3/24→I11/24 laser channel. The diffuse nature of the visible radiation is attributed to numerous ferroelectric cylindrical domains, which appear in the as-grown crystal. Green radiation is obtained by self-frequency doubling of the infrared radiation, whereas tunable blue radiation is generated by self-frequency sum mixing of infrared and pump radiations. The variety of visible colors is due to the spread in the domain sizes. Finally, we report on the spectral and spatial distribution of this visible radiation.
The dynamics of the reactions H+H2O→OH+H2 and H+D2O→OD+HD at 1.4 eV
Authors: Brouard M. , Burak I. , Joseph D. M. , Markillie G. A. J. , Minayev D. , O’Keeffe P. , Vallance C.
Published: July 2002

OH(OD) quantum state populations, rovibrational quantum state-resolved center-of-mass angular scattering distributions, and H2(HD) coproduct internal energy release distributions have been determined for the hot H atom reactions with H2O and D2O at mean collision energies close to 1.4 eV. The experiments employ pulsed laser photolysis coupled with polarized Doppler-resolved laser induced fluorescence detection of the radical products. The OH(2Π1/2,v′=0,N′=1,A′) and OD(2Π1/2,v′=0,N′=1,A′) angular distributions generated by the two isotopic reactions are quite distinct: that for the reaction with H2O shows intensity over a wide range of center-of-mass scattering angles, and peaks in the sideways direction, while the state-resolved angular distribution for the reaction with D2O displays more scattering in the backward hemisphere. For higher OH(OD) angular momentum states the differences in the angular distributions for the two reactions are less marked, with both systems showing a slight preference for backward scattering. The kinetic energy release distributions are insensitive to OH(OD) quantum state and to isotopic substitution, and reveal that the H2(HD) coproducts are born internally cold at 1.4 eV. OH(OD) quantum state averaged energy disposals in the two reactions are also presented. The new experiments provide detailed mechanistic information about the two reactions and clarify the dominant sources of product OH(OD) rotational excitation. Current theoretical understanding of the reaction is critically assessed.
In situ x-ray microscopic observation of the electromigration in passivated Cu interconnects
Authors: Schneider G. , Hambach D. , Niemann B. , Kaulich B. , Susini J. , Hoffmann N. , Hasse W.
Published: July 2002

X-ray imaging of electromigration in a passivated Cu interconnect was performed with 100-nm spatial resolution. A time sequence of 200 images, recorded with the European Synchrotron Radiation Facility x-ray microscope in 2.2 h at 4 keV photon energy, visualizes the mass flow of Cu at current densities up to 2×107 A/cm2. Due to the high penetration power through matter and the element specific image contrast, x-ray microscopy is a unique tool for time-resolved, quantitative mass transport measurements in interconnects. Model calculations predict that failures in operating microprocessors are detectable with 30 nm resolution by nanotomography.
Time-resolved measurement on ablative acceleration of foil plates driven by pulsed laser beam
Authors: He Hongliang , Kobayashi T. , Sekine T.
Published: July 2002

Coupled with the push-pull type velocity interferometer system for any reflector, an electronic streak camera recording system has been established, which provides subnanosecond time resolution in the detection of interferential fringes. Complete acceleration histories of Al, Au, and Pt foil plates, driven by pulsed laser beam at 30–400 GW/cm2, have been measured by using this system. For the 10-μm-thick Al foil irradiated at 280 GW/cm2, an ablative acceleration up to terminal velocity about 9 km/s within 25 ns has been determined with a velocity uncertainty of ∼1%.
On the determination of orientational configurational temperature from computer simulation
Authors: Chialvo A. A. , Simonson J. M. , Cummings P. T. , Kusalik P. G.
Published: July 2002

A straightforward derivation for the configurational temperature associated with the orientational ΩN portion of the configurational phase space of the molecules in an open system is presented. Explicit relationships are given for determining the configurational temperatures in classical simulations of molecular liquids, such as water, and their forms and their evaluation discussed.
Formation of a nanoquasicrystalline phase in Zr–Cu–Ti–Ni metallic glass
Authors: Louzguine Dmitri V. , Inoue Akihisa
Published: July 2002

Structure changes in Zr–Ti–Ni–Cu metallic glass on heating have been studied by x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. It has been found that the first stage of the devitrification process is related to the precipitation of fine particles of an icosahedral phase from about 3 to 7 nm in size. Direct evidence of the formation of the icosahedral phase has been obtained using nanobeam diffraction in transmission electron microscopy.
Anisotropic GaAs island phase grown on flat GaP: A Stranski–Krastanow-formed corrugated surface
Authors: Ohlsson B. J. , Miller M. S. , Gustafsson A. , Pistol M.-E.
Published: July 2002

A dense phase of GaAs wires forms a corrugated surface in the early stages of strained growth on GaP, assembling from elongated Stranski–Krastanow islands. For a series of samples, the evolution of shape and whisker periodicity has been followed as a function of deposition time. This has been done with the help of atomic-force microscopy together with autocorrelation measurements. Transmission electron microscopy measurements support the results. The lateral wire period and long shapes are not predicted by published models, though we conclude that the island orientation is picked out by facet energy inequivalencies.
A molecular approach to quantum fluids based on a generalized Ornstein–Zernike integral equation
Authors: Shinoda Keiko , Miura Shinichi , Okazaki Susumu
Published: July 2002

In this paper, we present an Ornstein–Zernike-type integral equation applicable to quantum fluids. This integral equation was obtained by averaging fully imaginary-time-dependent reference interaction site model integral equation for the quantum fluids over imaginary time. The resulting integral equation is a scalar integral equation for linear response correlation function. The self-correlation function in the integral equation was determined in a self-consistent manner with the aid of Feynman’s variational perturbation method. Our theoretical treatment is an extension of the theory for an excess electron in the classical solvents [J. Chem. Phys. 81, 1975 (1984)] to that for the fully quantum fluids. Numerical calculations have been performed for the fluid helium-4 assuming Boltzmann statistics. The calculated pair correlation functions are in good agreement with path integral molecular dynamics results. The experimental static structure factors are well described by our theory. It was found that the calculated excess quantum kinetic energy decreases slowly with raising temperature; even at high temperature the quantum effect on the kinetic energy cannot be neglected.
Electrical and structural characterization of metal–oxide–semiconductor capacitors with silicon rich oxide
Authors: Crupi I. , Lombardo S. , Spinella C. , Bongiorno C. , Liao Y. , Gerardi C. , Fazio B. , Vulpio M. , Privitera S.
Published: July 2002

Metal–oxide–semiconductor capacitors in which the gate oxide has been replaced with a silicon rich oxide (SRO) film sandwiched between two thin SiO2 layers are presented and investigated by transmission electron microscopy and electrical measurements. The grain size distribution and the amount of crystallized silicon remaining in SRO after annealing have been studied by transmission electron microscopy, whereas the charge trapping and the charge transport through the dots in the SRO layer have been extensively investigated by electrical measurements. Furthermore, a model, which explains the electrical behavior of such SRO capacitors, is presented and discussed.
Characterization of free-standing hydride vapor phase epitaxy GaN
Authors: Jasinski J. , Swider W. , Liliental-Weber Z. , Visconti P. , Jones K. M. , Reshchikov M. A. , Yun F. , Morkoç H. , Park S. S. , Lee K. Y.
Published: July 2002

A free-standing GaN template grown by hydride vapor phase epitaxy has been characterized by transmission electron microscopy (TEM). The TEM investigation was augmented by x-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy and variable temperature photoluminescence. The density of dislocations near the N face was determined to be, in order, 3±1×107, 4±1×107, and about 1×107 cm−2 by cross-sectional TEM, plan-view TEM, and a defect revealing etch, respectively. The same methods on the Ga face revealed the defect concentration to be, in order, less than 1×107 cm−2 by plan-view TEM, less than 5×106 cm−2 by cross-sectional TEM, and 5×105 cm−2 by defect revealing hot H3PO4 acid, respectively. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (101_4) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth was about 1 meV each at 10 K, and a green band centered at about 2.44 eV was observed.
Selective thermal interdiffusion using patterned SiO2 masks: An alternative approach to buried CdTe/CdMgTe quantum wires
Authors: Welsch M. K. , Schömig H. , Legge M. , Bacher G. , Forchel A. , König B. , Becker C. R. , Ossau W. , Molenkamp L. W.
Published: July 2002

Buried CdTe/CdMgTe quantum wires with a lateral confinement potential of about 290 meV have been realized. Using electron beam lithography, SiO2 stripes are defined on a single quantum well sample and a subsequent 2 h annealing step in a Zn atmosphere results in a surprisingly strong interdiffusion between Cd and Mg atoms under the capped areas, causing a lateral modulation of the band gap. We obtain, e.g., for a nominal wire width of 100 nm, a lateral subband splitting of more than 8 meV, while the extension of the squared exciton wave function of the ground state is reduced to about 20 nm due to the error function-like potential shape.
Structure and dynamics of amorphous silica surfaces
Authors: Roder Alexandra , Kob Walter , Binder Kurt
Published: July 2002

We use molecular dynamics computer simulations to study the equilibrium properties of the surface of amorphous silica. Two types of geometries are investigated: (i) clusters with different diameters (13.5, 19, and 26.5 Å) and (ii) a thin film with thickness 29 Å. We find that the shape of the clusters is independent of temperature and that it becomes more spherical with increasing size. The surface energy is in qualitative agreement with the experimental value for the surface tension. The density distribution function shows a small peak just below the surface, the origin of which is traced back to a local chemical ordering at the surface. Close to the surface the partial radial distribution functions as well as the distributions of the bond–bond angles show features which are not observed in the interior of the systems. By calculating the distribution of the length of the Si–O rings we can show that these additional features are related to the presence of two-membered rings at the surface. The surface density of these structures is around 0.6/nm2, in good agreement with experimental estimates. From the behavior of the mean-squared displacement at low temperatures, we conclude that at the surface the cage of the particles is larger than the one in the bulk. Close to the surface the diffusion constant is somewhat larger than the one in the bulk and with decreasing temperature the relative difference grows. The total vibrational density of states at the surface is similar to the one in the bulk. However, if only the one for the silicon atoms is considered, significant differences are found.
Epitaxial growth and exchange biasing of PdMn/Fe bilayers grown by ion-beam sputtering
Authors: Cheng Ning , Ahn JaePyoung , Krishnan Kannan M.
Published: July 2002

Epitaxial PdMn/Fe bilayer structures, in both a-axis PdMn(100)/Fe(001)/MgO(001) and c-axis PdMn(001)/Fe(001)/MgO(001) orientations, were grown by ion-beam sputtering. The a-axis samples were grown at low temperatures (T<280 °C) while the c-axis films were stabilized at a higher temperature range (T>300 °C). Vibrating sample magnetometry measurements show that the as-grown a-axis samples do not have a measurable exchange bias while c-axis samples have an exchange bias field He∼33 Oe. However, annealing at 230 °C for 40 min results in a measurable exchange (He∼10 Oe) for a-axis samples due to chemical ordering. The possible cause for the difference of He in a-axis and c-axis orientations is also discussed. In addition to the normal structure, inverted structures were obtained epitaxially. The exchange biasing for Fe(001)/PdMn(001)/MgO(001) is as big as 68 Oe.
High-quality InGaN/GaN multiple quantum wells grown on Ga-polarity GaN by plasma-assisted molecular-beam epitaxy
Authors: Shen X. Q. , Ide T. , Shimizu M. , Okumura H.
Published: July 2002

High-quality InGaN/GaN multiple-quantum wells (MQWs) with different In fractions varying from 0.04 to 0.30 have been grown on Ga-polarity GaN by N2 plasma-assisted molecular-beam epitaxy (rf-MBE). High-resolution x-ray diffraction results have indicated that the high interface quality and good reproducibility of the InGaN QW have been achieved. Photoluminescence spectra reveals the superior and intense luminescence properties of InGaN MQWs from ultraviolet (∼388 nm) to green-yellow (∼528 nm) range. We have shown that the Ga-polarity GaN underneath is the key parameter for the successful growth of InGaN MQWs by rf-MBE.
Frictional properties of perfluoropolyether monolayers investigated with quartz resonators
Authors: Laschitsch Alexander , Bailey Larry E. , Tyndall George W. , Frank Curtis W. , Johannsmann Diethelm
Published: July 2002

The high-frequency frictional properties of thin lubricating layers of perfluoropolyethers coated onto the surface of quartz-crystal resonators were probed by measuring the increase in resonance bandwidth when the quartz surface comes into contact with a ceramic sphere. For a lubricant thickness of up to 11 Å, a maximum in bandwidth is observed. The width and the height of the maximum decrease with increasing lubricant thickness. This is attributed to dissipation occurring during intermittent contact between the substrate and the sphere. With a 25 Å lubricant film the sphere discontinuously jumps into contact, after which the movements of the sphere and the quartz are locked.
Control of the well-type radial potential profile in the magnetized plasma flow produced by a dc discharge
Authors: Matsubara Akihiro , Tonegawa Akira , Shibuya Takehisa , Sato Kuninori , Kawamura Kazutaka , Takayama Kazuo
Published: July 2002

The control of the well-type radial potential profile in a dc plasma by applying bias potential, VE, to the end plate is investigated experimentally. The experimental evidence that a plasma space potential, Φp, increases at the circumference of the plasma with the increase of VE is interpreted qualitatively by the experimental results of the current drawn by the segmented end plate, and of the relationship of Φp to VE. For the dc discharge the value of Φp at the center of the plasma is naturally settled on the value somewhat lower than the anode potential, the electron sheath therefore appears in front of the end plate and expands radially as VE is increased. Electrons are drawn from the circumference of the plasma to the end plate, inducing the nonambipolar radial electron flux. Since the cross-field electron mobility is not sufficiently large, the inwardly directed radial electric field becomes stronger. The role of electron sheath formed is crucial in actively controlling the radial potential profile in the dc plasma.
Second order magneto-optic effects in Brillouin scattering from spin waves in magnetic multilayers
Authors: Giovannini L. , Zivieri R. , Nizzoli F. , Gubbiotti G. , Carlotti G.
Published: July 2002

The Brillouin light scattering cross section from a thick magnetic multilayer has been calculated using a theoretical model based on a macroscopic partial waves approach for the calculation of the normal modes. Special attention has been paid to analyzing the effect of inclusion of the second order magneto-optic constant in addition to the first order one (corresponding to Voigt and Faraday effects, respectively). This model has been exploited to analyze the experimental Brillouin spectra measured from a several nm thick Ni/Cu bilayer. Both surface and bulk standing spin waves have been experimentally detected for different incident angles and applied magnetic fields (including field reversal). The measured spectra can be satisfactorily reproduced by our model, allowing the determination of magnetic and magneto-optic parameters of the samples.
Conformally flat anisotropic spheres in general relativity
Authors: Herrera L. , Prisco A. Di , Ospino J. , Fuenmayor E.
Published: July 2002

The condition for the vanishing of the Weyl tensor is integrated in the spherically symmetric case. Then, the resulting expression is used to find new, conformally flat, interior solutions to Einstein equations for locally anisotropic fluids. The slow evolution of these models is contrasted with the evolution of models with similar energy density or radial pressure distribution but nonvanishing Weyl tensor, thereby bringing out the different role played by the Weyl tensor, the local anisotropy of pressure, and the inhomogeneity of the energy density in the collapse of relativistic spheres.
Effect of ion energy on photoresist etching in an inductively coupled, traveling wave driven, large area plasma source
Authors: Takechi K. , Lieberman M. A.
Published: July 2002

We report on the effect of ion energy on photoresist etching in an inductively coupled large area plasma source driven by a 13.56 MHz traveling wave with oxygen gas. To control the ion energy at the substrate surface, the electrode on which the substrate is placed is independently driven by a capacitively coupled 1 MHz power source. The etch rate increases with increasing ion energy for gas pressure ranging from 1 to 100 mTorr. Ion-induced desorption rate constants (etch yields) are shown to be proportional to the square root of the ion energy. An increase in the ion energy leads to etch-uniformity improvement over the processing area of 40 cm×50 cm, particularly at a low gas pressure of 5 mTorr. A modified photoresist etch kinetics model combined with a spatially-varying oxygen discharge model is used to explain these experimental results.
Magnetostriction of DyFe2 and HoFe2: Validity of the single-ion model
Authors: Kuz’min M. D.
Published: July 2002

Analysis of available experimental data on the temperature dependence of the tetragonal magnetostriction constant λ100 in DyFe2 and HoFe2 confirms validity of the single-ion model. The most important contributions to λ100 come from the second- and sixth-order terms, which are of the same order of magnitude. They also are similar in magnitude to the higher-order (n=4,6) terms in the trigonal magnetostriction constant λ111. It is therefore concluded that the origin of the extraordinarily large λ111 in RFe2 (where R is rare earth) is confined to the second-order, or quadrupole term in λ111.
Attenuation of homo- and heteronuclear multiple spin echoes by diffusion
Authors: Ardelean Ioan , Kossel Elke , Kimmich Rainer
Published: July 2002

Multiple spin echoes arise after “nonlinear” evolution of coherences in the presence of modulated demagnetizing fields. Such modulations can be prepared, for example, with the aid of a sequence of two 90° radio-frequency pulses in the presence of pulsed or steady field gradients. The echo amplitudes are sensitively attenuated by translational diffusion so that diffusivities can be determined on this basis. Homo- and heteronuclear variants of multiple-echo pulse sequences are considered here. A formalism based on the Bloch/Torrey equations is presented that describes the features displayed by the experimental data. The resulting attenuation formula for the homonuclear case generally accounts for all radio-frequency and field gradient pulse intervals occurring in the frame of this “pulsed gradient nonlinear spin echo” technique. Furthermore, an analogous formalism is reported for the heteronuclear case where the two nuclear species may populate different molecules with different diffusivities. It is shown that, apart from the conventional attenuation mechanism due to incomplete refocusing of the coherences, there are three additional processes contributing to homo- and heteronuclear multiple-echo attenuation by diffusion: Leveling of the magnetization helix and hence of the z magnetization grid formed by the second radiofrequency pulse, further leveling of that z magnetization grid by displacements of the dipoles producing the grid, and molecular displacements relative to the spatially modulated demagnetizing field.
Grain charge, scaling laws, and wave modes in dense dusty plasmas with high fugacity
Authors: Rao N. N.
Published: July 2002

Scaling laws for grain charge as a function of fugacity have been derived by self-consistently including contributions due to finite grain size, generalized grain capacitance, and near-neighbor effects. Good agreement between the scaling laws and the numerical solution of exact coupled equations is found over a wide range of dust fugacity from tenuous to dense regimes. The effects of these contributions on wave propagation in dense dusty plasmas is illustrated by considering dust-acoustic and dust-Coulomb waves.
Absorption analysis of a single microparticle by optical force measurement
Authors: Matsuo Yasutaka , Takasaki Hidehisa , Hotta Jun-ichi , Sasaki Keiji
Published: July 2002

A method is proposed for precisely and instantaneously analyzing the optical absorption of a single microparticle. This method is based on the measurement of radiation pressure exerted on a particle, in which the Brownian motion of the particle is observed via total internal reflection microscopy, and then the femto-Newton-order radiation pressure induced by absorption is determined by thermodynamic analysis. On the basis of the Mie–Debye scattering theory, the imaginary part of the refractive index is estimated from the strength of the force using knowledge of the real part and the diameter of the particle. As a preliminary experiment, the concentration of rhodamine B molecules in a poly(methylmethacrylate) particle was estimated.
Mueller calculus and perfect polarization conversion modes in liquid crystal displays
Authors: Tang S. T. , Kwok H. S.
Published: July 2002

We introduce a 4×4 Mueller matrix for describing the polarization states of a liquid crystal cell. Using this Mueller matrix, it is possible to derive conditions whereby a linearly polarized input can be converted to either a perfectly linearly or perfectly circularly polarized output. These are called the perfect polarization conversion (PPC) conditions. These PPC conditions can be used in many different ways. For example, based on these PPC conditions, polarization mode switching schemes can be derived for the analysis of most liquid crystal displays.
Gas dependence of paired luminous rings in capacitive radio-frequency discharges
Authors: Sakawa Youichi , Shoji Tatsuo
Published: July 2002

Paired luminous rings separated by a narrow dark gap have been studied in pulsed capacitive radio-frequency (rf) discharges using seven gases. These paired rings are clearly observed when H2 or D2 is used. The isotope effect between H2 and D2 is observed in the pressure dependence of the emission profile and different generation time of rings. When He, N2, O2, Ar, and Xe are used, only a few pairs of rings are observed. The atomic-mass dependence of the gas pressure, at which a pair of ring emission is excited (P1) at the electrode separation d=6 cm, is measured. The axial electric field E is calculated at P1 for each gas using two methods: One is the energy-balance method and the other is the ionization-coefficient method. In the former method, the energy-balance equation is solved to obtain E so that an electron is accelerated and reaches ionization energy at 3 cm from the initial position. In the latter method, the equation for the ionization coefficient α/P=Aexp(−BP/E) is solved to find E by substituting P=P1 and 1/α=3 cm. The calculated E using two methods agree relatively well with each other in H2, D2, He, N2, and O2. The empirical scaling-law, P1=(8.61±0.40)/A and E=(0.302±0.0057)BP1, has been obtained from the ionization-coefficient method.
Carbon nanotubes as electron source in an x-ray tube
Authors: Sugie H. , Tanemura M. , Filip V. , Iwata K. , Takahashi K. , Okuyama F.
Published: July 2002

Field emitters comprised of aligned carbon nanotubes are shown to be promising as a primary electron source in an x-ray tube working in a nonultrahigh vacuum ambience. At a pressure of 2×10−7 Torr, the nanotube emitters continue to emit electrons for more than 1 h, and yield better resolved x-ray images than do thermionic emitters, independently of whether the sample is biological or nonbiological. The near-uniformity in energy distribution of electrons emitted from carbon nanotubes might be related to the improved image quality in the field-emission mode.