bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced oxidation of silicon using a collimated hyperthermal ozone beam
Authors: Nishiguchi T. , Morikawa Y. , Miyamoto M. , Nonaka H. , Ichimura S.
Published: July 2002

Silicon was oxidized by a collimated hyperthermal ozone beam produced by pulsed-laser ablation of solid ozone to increase the controllability of the silicon dioxide film thickness and to achieve low-temperature oxidation. The oxidation rate could be accurately controlled by the number of laser shots to which the number of supplied ozone molecules was proportional. Ozone molecules with a translational energy of around 1 eV obtained by laser ablation produced an initially rapid oxidized region with no temperature dependence in which a 0.6 nm silicon dioxide film could be synthesized at room temperature with only 200 laser shots. Higher-efficiency oxidation was also achieved in comparison with that by using a spray of ozone with thermal energy.
Liquid-crystal photoalignment using low-molecular-weight photo-cross-linkable composites
Authors: Yaroshchuk O. , Cada L. G. , Sonpatki M. , Chien L.-C.
Published: July 2002

A liquid-crystal (LC) photoalignment method, based on the use of low-molecular-weight photo-cross-linkable (LMWPC) composites is proposed. The basic idea of this method is that cross linking or both cross linking and polymerization of LMWPC composites are realized immediately on the substrate simultaneously with the photoalignment or as a stage of the backing process. Providing the advantages of a conventional photoalignment method, the use of LMWPC composites simplifies the synthesis and alignment procedure, makes possible wide range control of pretilt angles, and enhances the thermal stability of the LC alignment. The abilities of this method are demonstrated using a series of cinnamate-containing monomers.
Systematic convergence in the dynamical hybrid approach for complex systems: A numerically exact methodology
Authors: Wang Haobin , Thoss Michael , Miller William H.
Published: July 2002

An efficient method, the self-consistent hybrid method, is proposed for accurately simulating time-dependent quantum dynamics in complex systems. The method is based on an iterative convergence procedure for a dynamical hybrid approach. In this approach, the overall system is first partitioned into a “core” and a “reservoir” (an initial guess). The former is treated via an accurate quantum mechanical method, namely, the time-dependent multiconfiguration self-consistent field or multiconfiguration time-dependent Hartree approach, and the latter is treated via a more approximate method, e.g., classical mechanics, semiclassical initial value representations, quantum perturbation theories, etc. Next, the number of “core” degrees of freedom, as well as other variational parameters, is systematically increased to achieve numerical convergence for the overall quantum dynamics. The method is applied to two examples of quantum dissipative dynamics in the condensed phase: the spin-boson problem and the electronic resonance decay in the presence of a vibrational bath. It is demonstrated that the method provides a practical way of obtaining accurate quantum dynamical results for complex systems.
Laser emission under resonant pump in the emitting level of concentrated Nd:YAG ceramics
Authors: Lupei V. , Lupei A. , Pavel N. , Taira T. , Shoji I. , Ikesue A.
Published: July 2002

The possibility of using the thermally activated optical absorption bands for a resonant pump in the emitting level of highly doped Nd laser materials is discussed. This potential is demonstrated by the continuous wave 1064 nm laser emission under 885 nm pump in concentrated (up to 6.8 at. %) Nd:YAG ceramics.
Improvements in tunability of (Ba0.5Sr0.5)TiO3 thin films by use of metalorganic chemical vapor deposited (Ba,Sr)RuO3 interfacial layers
Authors: Jeon Young-Ah , Choi Eun-Suck , Seo Tae-Suck , Yoon Soon-Gil
Published: July 2002

The conducting oxide (Ba,Sr)RuO3 (BSR), which offers an appropriate match in structure with (Ba,Sr)TiO3 (BST), was investigated as an interfacial layer to obtain a high tunability and high dielectric constant in BST films. The (100)-textured BST films deposited onto BSR interfacial layers showed smoother smaller grain size than those without BSR layers. The tunability and dielectric constant of the BST films increased with increasing BSR seed layer thickness and showed ∼70% tunability and a dielectric constant of 1300 at interfacial layer of 150 Å. The tunability and dielectric constant of BST films increased nearly two times and two and a half times, respectively, as much as that of BST films without BSR interfacial layers. The higher tunability and dielectric constant have been attributed to the suppression of low-dielectric layer formation and the reduced thermal stress by lattice mismatch.
Double quantum dots as a high sensitive submillimeter-wave detector
Authors: Astafiev O. , Komiyama S. , Kutsuwa T.
Published: July 2002

A single-electron transistor (SET) consisting of parallel double quantum dots fabricated in a GaAs/AlxGa1−xAs heterostructure crystal is demonstrated and it serves as an extremely high sensitive detector of submillimeter waves (SMMWs). One of the double dots is ionized by a SMMW via Kohn-mode plasma excitation, which affects the SET conductance through the other quantum dot, yielding the photoresponse. The noise equivalent power of the detector for wavelengths of about 0.6 mm is estimated to reach the order of 10−17 W/Hz at 70 mK.
Dynamics of anisotropy on decaying homogeneous turbulence subjected to system rotation
Authors: Morinishi Y. , Nakabayashi K. , Ren S. Q.
Published: July 2002

The dynamics of the anisotropy of the Reynolds stress tensor and its behavior in decaying homogeneous turbulence subjected to system rotation are investigated in this study. Theoretical analysis shows that the anisotropy can be split into two parts: polarization and directional anisotropies. The former can be further separated into a linear part and a nonlinear part. The corresponding linear solution of the polarization anisotropy is derived in this paper. This solution is found to be equivalent to the linear solution of the anisotropy. While proposing a method to introduce the polarization anisotropy into an isotropic turbulence, direct numerical simulation (DNS) of the rotating turbulence with or without the initial anisotropy is carried out. The linear solution of the anisotropy agrees very well with the DNS result, showing that the evolution of the polarization anisotropy is mainly dominated by the linear effect of the system rotation. With an immediate rotation rate, the coupling effect between the system rotation and nonlinear interactions causes an energy transfer from the region near the pole to the region near the equator in wave space. This type of transfer causes an anisotropic distribution of the kinetic energy between the pole and equator, which relates closely to the directional anisotropy and the two-dimensionalization. In addition, we find that the presence of the initial polarization anisotropy does not affect the evolution of the directional anisotropy, while the presence of the initial directional anisotropy greatly influences the evolution of the polarization anisotropy.
Energetics and cooperativity in three-center hydrogen bonding interactions. I. Diacetamide-X dimers (X=HCN, CH3OH)
Authors: Parra Rubén D. , Furukawa Makoto , Gong Bing , Zeng X. C.
Published: July 2002

High level ab initio calculations are carried out on diacetamide–X (DA–X) dimers, X=HCN, CH3OH. The dimers are used as model systems to investigate the energetics and cooperative phenomomena in intermolecular three-center hydrogen-bond (H-bond) interactions relative to two-center H-bond interactions. The trans–trans conformer of diacetamide is chosen as a suitable model for intermolecular three-center H bonding where one H atom is interacting with two acceptor atoms. The proton–acceptor atoms are rigidly held in the same molecule. For both model systems, it is found that the calculated interaction energy per H bond is appreciably smaller in the three-center than in the two-center H-bond dimers, suggesting possibly a general characteristic of intermolecular three-center H bonds, namely, a negative cooperativity. More importantly, it is found that frequency shifts, intensity factors, bond lengths, and H1 nuclear magnetic resonance chemical shifts all support the energetic calculations in that the intermolecular three-center H-bond dimers exhibit marked negative cooperative effects. Despite the negative cooperativity, the three-center DA–HCN dimer is actually energetically favorable over the two-center counterpart, whereas the three-center DA–CH3OH dimer is energetically unfavorable over the two-center counterpart.
Connections between coupled cluster and generalized valence bond theories
Authors: Van Voorhis Troy , Head-Gordon Martin
Published: July 2002

We explore the fundamental connections between certain approximate coupled cluster (CC) and generalized valence bond (GVB) wave functions. We show that the GVB restricted configuration interaction (GVB-RCI) wave function can be associated with a compact CC expansion in the valence space. However, careful analysis reveals that a standard CC expansion contains terms that are not contained in the GVB-RCI wave function. The offending terms violate an effective pairwise exclusion principle (PEP) that is present in the RCI expansion, but is not enforced in the CC analog. These terms do not affect the size separability of either method. Variational calculations show noticeable improvements to the CC wave function when the PEP is enforced, with the most significant improvements coming near the dissociation limit. We modify the standard CC amplitude equations by removing the PEP violating terms and demonstrate remarkably improved results for the dissociation of N2 and the double dissociation of H2O.
Opal-like photonic crystal with diamond lattice
Authors: Garcı́a-Santamarı́a F. , López C. , Meseguer F. , López-Tejeira F. , Sánchez-Dehesa J. , Miyazaki H. T.
Published: July 2002

A method to fabricate a diamond structure with a complete photonic bandgap in the near infrared is proposed. The procedure starts by building an opal with body-centered-cubic symmetry composed of two types (organic and inorganic) of microspheres by means of a microrobotic technique. Then, the organic particles may be selectively removed to obtain a diamond structure of inorganic particles. This method can be extended to make diamond inverse opals of silicon with full gap to midgap ratios as large as 13% for moderate filling fractions.
Measurement of plasma diamagnetism in the SINP tokamak by a flux loop system inside the vacuum vessel
Authors: Saha S. K. , Kumar R. , Hui A. K.
Published: July 2002

Plasma diamagnetism has been measured in the SINP tokamak by a toroidal flux loop placed inside the vacuum vessel. The flux due to the strong toroidal field has been compensated for by a coplaner annular loop which encircles but does not contain the plasma column. The influence of the eddy currents in the vacuum vessel and the conducting shell in these loops has been calculated analytically by a circuit model using the theory of linear networks and compensated accordingly. This method has been shown to yield an almost exact compensation for toroidal flux (∼0.01%) as well as pickups from other fields. Typical results with plasma shots have been presented.
Design, construction, and performance of a low-cost deposition system for thin film multilayers
Authors: Lukoschus K. , Kraschinski S. , Herzog S. , Bensch W.
Published: July 2002

The design, development, and performance of a low-cost deposition system for thin film multilayers are presented. The aim for the construction of the apparatus was to prepare multilayer films of variable composition with a single layer thickness ranging from a few to hundreds of angstroms. To ensure a high flexibility of the film stoichiometries up to five different elements can be deposited independently onto the substrate via electron beam sources or Knudsen cells. The design of the transfer system has been kept very simple although it has a secure load–unload system to provide reliable transport from the antechamber to the deposition chamber and vice versa. The films can be deposited simultaneously onto four substrate platelets. The deposition process is controlled by a computer and all process-parameters are monitored. The shutters of the evaporation cells are activated by a computer providing reproducible deposition processes.
Spectral compression of ultrafast acoustic transients in thin films for enhanced detectability
Authors: Matsuda Youichi , Richardson Christopher J. K. , Spicer James B.
Published: July 2002

Experimental results showing the generation of ultrafast acoustic transients in thin films demonstrate the production and use of an optical pulse train for excitation that enhances signal detectability. Results in an aluminum thin film on a tungsten–carbide substrate show generation and detection of a narrow-band acoustic signal centered at 32.34 GHz. It is shown that the signal-to-noise ratio of the recorded transient is improved by a factor of 1.7 when simple digital bandpass filtering at the center frequency is performed. The physical limitations of this approach are considered in order to assess conditions under which significant bandwidth reduction can be realized.
Coulomb correction effects on bremsstrahlung spectra from non-Maxwellian plasmas
Authors: Jung Young-Dae
Published: July 2002

Coulomb correction effects are investigated on electron–ion bremsstrahlung emission from a non-Maxwellian velocity distribution plasma of the form exp[−(ν/νm)m] where νm2=(3kBTe/Me)Γ(3/m)/Γ(5/m) and 2⩽m⩽5. The bremsstrahlung emission rate is obtained as a function of the photon energy. For soft photon radiations, the Coulomb correction effects on the bremsstrahlung emission rate are found to be more significant for the distribution with m=2, i.e., Maxwellian distribution plasmas. However, for hard photon radiations, the Coulomb correction effects are found to be almost independent of the non-Maxwellian character. Thus, it would be possible to figure out the form of the electron distribution function using hard bremsstrahlung spectra rather than soft bremsstrahlung spectra since the bremsstrahlung emission rate without the Coulomb corrections only depends on the non-Maxwellian character for hard photon radiations.
Switch-free read operation design and measurement of magnetic tunnel junction magnetic random access memory arrays
Authors: Zheng Yuankai , Wang Xiaoyan , You Dan , Wu Yihong
Published: July 2002

A switch-free read operation design and cell measurement method for magnetic tunnel junction magnetic random access memory arrays with a peripheral circuitry is presented. The design effectively reduces the shunting effect and maintains the signal at the original level even for the cases when the lead resistance cannot be neglected. It also allowed us to measure the magnetoresistance curve of each cell independently without the need of a transistor or a diode. Both simulation and experiments showed that this method is useful in the readout operation of the tunnel junction magnetic random access memory as well as in the characterization of its individual cells.
An optical microscope for the study of biopolymer solutions under shear field
Authors: Kim Sanghoon , Willett J. L.
Published: July 2002

Recently, it has been found that some biopolymer solutions show aggregate formation or shear-induced mixing when they are exposed to shear field. An optical microscope was constructed for the study of these behaviors. A phase-contrast microscope is installed to obtain clear images from sample solutions where the refractive index difference of the domains is too small to be observed with common bright field microscopes. A modular type is adopted for the design of microscope for easy adjustment of optical components, alignment, and positioning it to the sample compartment. As a light source, a strobe type flash lamp is employed and its ignition is synchronized with a charge coupled device camera to avoid yielding smeared images. Shear fields are generated by a cone and plate geometry that is directly attached to a microstepper motor with a controllable simple shear rate range of 0.025–2500 s−1. In the case of oscillatory shear, accessible range is 0–120 rad/s. A dual temperature controller allows temperature control of the sample compartment from ambient temperature to 200 °C with ±0.1 °C accuracy. Several starch solutions were used to demonstrate the performance and capability of the instrument.
The influence of interaction details on the thermal diffusion in binary Lennard-Jones liquids
Authors: Bordat Patrice , Reith Dirk , Müller-Plathe Florian
Published: July 2002

There exists a disturbing controversy in the literature about the sign of the Soret effect in binary mixtures of model fluids (Lennard-Jones atoms), whose components differ only in their molecular diameter. For such mixtures, the dependence of the Soret coefficient on the state (liquid versus supercritical), on the system size and on details of handling the range and the cutoff of the Lennard-Jones potential is examined by molecular-dynamics simulations. We establish unambiguously the direction of the Soret effect: Under all circumstances investigated, large particles are driven to the hot region. At supercritical densities, the Soret effect is considerably smaller than in the dense liquid and, furthermore, details of the attractive tail of the Lennard-Jones potential become much more important.
Powered automatic measuring system for Langmuir probe plasma analysis
Authors: Sreenivasulu M. , Patra S. K. , Rao G. Mohan
Published: July 2002

Langmuir probe analysis of a sputtering glow discharge leads to errors in measurements due to contamination of the probe surface by the sputter deposition from the target. An automatic Langmuir probe system using a personal computer has been designed. The design details and performance evaluation of this system are discussed in this article.
The density-potential (Ne-VS/C) relation in the high-latitude prenoon ionosphere
Authors: Adrian M. L.
Published: July 2002

Sounding of the Cleft Ion Fountain Energization Region (SCIFER) Thermal Electron Capped Hemisphere Spectrometer (TECHS) data are used to study the plasma density, spacecraft potential relation (Ne-VS/C) in the prenoon topside auroral and cleft ionosphere during a period of low solar activity. The SCIFER TECHS data show a power-law electron temperature dependence on ambient density across the transition from positive to negative spacecraft potential values in the high-latitude ionosphere. The illuminated ionospheric Ne-VS/C relation is numerically modeled by imposing equilibrium of current flowing to/from the conductive surfaces of the payload. This modeling demonstrates a strong dependence of spacecraft potential on electron temperature across a wide range of densities. This electron temperature dependence is especially significant in the negative spacecraft potential regime. SCIFER TECHS observations of the Ne-VS/C relation are used to extend the previous magnetospheric observation-model results to the higher density ionospheric regime.
Spectroscopy and dynamics of calcium dimers deposited on large argon and neon van der Waals clusters
Authors: Gaveau M. A. , Briant M. , Fournier P. R. , Mestdagh J. M. , Visticot J. P.
Published: July 2002

Laser-induced-fluorescence studies of calcium dimer deposited on large argon and neon clusters have been performed. The spectroscopy of the Ca2 A state is slightly perturbed by the cluster surface leading to shifts and broadenings of the order or less than 100 cm−1. An absorption has been evidenced in the 530–550 nm wavelength range that is tentatively assigned to the yet undocumented A ′1Πu state of Ca2 correlating to the Ca(1D)+Ca(1S) asymptotic limit. The excited calcium dimer dynamics are very different in neon and argon clusters. The argon cluster is much more efficient for electronic and vibrational relaxation of the excited dimer. Finally, excitation in the blue of the calcium atomic resonance line leads to a competition between dissociation of the dimer with ejection of an excited calcium atom out of the cluster and the relaxation of the dimer to lower excited levels.
Optical properties of point defects in SiO2 from time-dependent density functional theory
Authors: Raghavachari Krishnan , Ricci Davide , Pacchioni Gianfranco
Published: July 2002

We have studied the optical absorptions of a series of point defects in SiO2 by means of time-dependent density functional response theory (TD-DFT). The structure of the defects has been described with cluster models and atomic orbital basis functions. For each center the lowest singlet→singlet and singlet→triplet (for diamagnetic defects) and doublet→doublet (for paramagnetic defects) transitions have been considered. The results have been compared with accurate ab initio calculations based on explicit treatment of correlation effects and, when possible, with experimental data. Defects with localized wave functions and low excitation energies (<5 eV) are well described by TD-DFT and the predicted transition energies are within a few tenths of an eV from the experimental or ab initio values. For defects which give rise to transition energies higher than 5 eV the TD-DFT values are 10%–20% too low. The comparison of various exchange-correlation functionals show that the hybrid B3LYP method provides more accurate answers than other gradient-corrected DFT approaches.
Design and performance of the infrared beam ports at the Canadian Light Source
Authors: May T. E. , Bosch R. A.
Published: July 2002

The Canadian Light Source is constructing two beamlines for infrared spectroscopy. One will supply mid infrared (2–20 μm) light to a Fourier transform infrared (FTIR) spectrometer and microscope for biological applications. The second will have a vacuum FTIR spectrometer for experiments in the far infrared (beyond 20 μm). Flux and brightness curves for these beam lines are reported. The calculations are made to provide working values for the design, construction, and evaluation of the beamlines. To gauge performance, a comparison is made to other infrared beamlines operating with dipole bending magnets and to a thermal source. Values obtained using standard bend radiation formulas are compared with values obtained using the Synchrotron Radiation Workshop. Issues in the first mirror design are also discussed.
Morphology-dependent resonant laser emission of dye-doped ellipsoidal microcavity
Authors: Juodkazis Saulius , Fujiwara Kunihiko , Takahashi Toshimasa , Matsuo Shigeki , Misawa Hiroaki
Published: July 2002

We report a morphology-dependent resonance (MDR) laser emission of rhodamine-doped ellipsoidal microcavity of the poly(methylmethacrylate) particles. Elliptical particles showed different lasing properties: the lasing threshold, intramode spectral separation, mode intensity, and spectral position, when an excitation is pointed to the different locations on the particle. This differs from the well-understood MDR lasing in spherical microparticles.
Large flexoelectric polarization in ceramic lead magnesium niobate
Authors: Ma Wenhui , Cross L. Eric
Published: July 2002

Flexoelectric coefficient μ12 is greatly enhanced in the relaxor ferroelectric lead magnesium niobate ceramic. Phenomenological analysis suggests the high dielectric permittivity is inadequate to explain the great enhancement. Temperature dependent measurement reveals a close relation between the flexoelectric polarization and the preexisting polar microregions in this relaxor ferroelectrics. It is proposed that the strain gradient might change the Gibbs free energy of the relaxor system and easily reorient the already existing polar microregions, leading to the greatly enhanced flexoelectric effect.
Transient transport experiments in the current-drive experiment upgrade spherical torus
Authors: Munsat T. , Efthimion P. C. , Jones B. , Kaita R. , Majeski R. , Stutman D. , Taylor G.
Published: July 2002

Electron transport has been measured in the Current-Drive Experiment Upgrade (CDX-U) (T. Jones, Ph.D. thesis, Princeton University, 1995) using two separate perturbative techniques. Sawteeth at the q=1 radius (r/a∼0.15) induced outward-propagating heat pulses, providing time-of-flight information leading to a determination of χe as a function of radius. Gas modulation at the plasma edge introduced inward-propagating cold pulses, providing a complementary time-of-flight based χe profile measurement. This work represents the first localized measurement of χe in a spherical torus. Core (r/a<1/3) χe values from the sawtooth study are 1–2 m2/s, and from the gas modulation study are 1–6 m2/s, increasing by an order of magnitude or more outside of the core region. Furthermore, the χe profile exhibits a sharp transition near r/a=1/3. Spectral and profile analyses of the soft x-rays, scanning interferometer, and edge probe data show no evidence of a significant magnetic island causing the high χe region. Comparisons are performed to several theoretical models, with measured χe≈5–10× neoclassical estimates in the core.
Reorientational and translational dynamics of benzene in zeolite NaY as studied by one- and two-dimensional exchange spectroscopy and static-field-gradient nuclear magnetic resonance
Authors: Geil B. , Isfort O. , Boddenberg B. , Favre D. E. , Chmelka B. F. , Fujara F.
Published: July 2002

One- and two-dimensional H2- and C-NMR13 (nuclear magnetic resonance) echo spectroscopy and H1 static field gradient NMR self-diffusion experiments have been used to study the reorientational and translational dynamics of benzene molecules adsorbed on zeolite NaY as a function of loading. Comparison of the data with model calculations establish that the elementary motional process of the guest molecules is consistently identified as a jump process among well defined adsorption sites inside a supercage and/or a jump between nearby supercages. In cases where the zeolite cavities contain high loadings of guest molecules, each molecular jump is accompanied by concomitant relaxation of the local environment. Molecular jump events between adsorption sites correspond to the elementary processes from which long range translational diffusion evolves.
Dispersion relation in plasmas generated by a sheath-helix antenna
Authors: Uhm Han S. , Uhm Sae H. , Chang Hong Y.
Published: July 2002

A theoretical model of the plasmas generated by a sheath-helix antenna is developed for axisymmetric perturbations. The system configuration consists of a cylindrical plasma column inside a dielectric tube of radius Rc. The eigenvalue equation is obtained and the eigenfunction is identified as the Bessel function J0(x) of the first kind of order zero. The radial wave numbers ξ and η for the eigenfunction are described in terms of the rf frequency and plasma density. A full dispersion relation is analytically obtained, including influence of the finite plasma size, antenna effects, the electron inertia, and ion mass contributions. It is shown from the dispersion relation that the radial mode number ξ approaches infinity at the lower-hybrid frequency, exhibiting a resonance condition. Meanwhile, the radial wave number η approaches 3.83/Rc at the lower-hybrid frequency. A cross-sectional view of the light emission in experiment indicates that the helicon-plasma density at the lower-hybrid frequency has a hollow profile. The azimuthal component Eθ(r) of the perturbed electric field observed experimentally is very similar to the theoretical model of J1(3.83r/Rc) at the lower-hybrid frequency. The emission peak coincides with the radial location of the strongest electric-field intensity.
Numerical study of a direct current plasma sheath based on kinetic theory
Authors: Vasenkov Aleksey V. , Shizgal Bernie D.
Published: July 2002

A fully kinetic theory model was developed to study plasma properties of the sheath of a direct current glow discharge. This model includes a direct numerical solution of the Boltzmann equations for electron and ion distribution functions with a self-consistent electric field obtained from the Poisson equation. The calculated profiles of density, drift velocity, temperature, and electric potential were used to show the structure of the plasma sheath. The results of the direct numerical solution were compared with a particle-in-cell Monte Carlo simulation. It was also demonstrated that for a small Debye length to the ion mean-free path ratio, results obtained using the continuum sheath model, which includes two parameters, can be matched to the kinetic theory simulations.
Two-and-one-half-dimensional magnetohydrodynamic simulations of the plasma sheet in the presence of oxygen ions: The plasma sheet oscillation and compressional Pc 5 waves
Authors: Lu Li , Liu Zhen-Xing , Cao Jin-Bin
Published: July 2002

Two-and-one-half-dimensional magnetohydrodynamic simulations of the multicomponent plasma sheet with the velocity curl term in the magnetic equation are represented. The simulation results can be summarized as follows: (1) There is an oscillation of the plasma sheet with the period on the order of 400 s (Pc 5 range); (2) the magnetic equator is a node of the magnetic field disturbance; (3) the magnetic energy integral varies antiphase with the internal energy integral; (4) disturbed waves have a propagating speed on the order of 10 km/s earthward; (5) the abundance of oxygen ions influences amplitude, period, and dissipation of the plasma sheet oscillation. It is suggested that the compressional Pc 5 waves, which are observed in the plasma sheet close to the magnetic equator, may be caused by the plasma sheet oscillation, or may be generated from the resonance of the plasma sheet oscillation with some Pc 5 perturbation waves coming from the outer magnetosphere.
The formation of low-dimensional ionic crystallites in carbon nanotubes
Authors: Wilson Mark
Published: July 2002

Atomistic computer simulation models are used to interpret the results of recent high resolution transmission electron microscopy (HRTEM) experiments which have studied the filling of carbon nanotubes by liquid KI. In the HRTEM experiments, the liquid KI fills narrow width nanotubes to form low-dimensional crystallites which display specific distortions in comparison with the idealized bulk fragments. The atomistic origin of these distortions are discussed. Molecular dynamics simulations are then used to directly model the filling of these tubes and an understanding of the filling mechanisms is developed. The dependence of the filling structure on the pore radius and morphology of the carbon nanotube is discussed. Novel crystalline structures, often incorporating specific twisting, is observed for the smaller diameter nanotubes. The physical origins of the observed filling mechanisms are discussed.
Improved extraction of carrier concentration and depletion width from capacitance–voltage characteristics of silicon n+–p-well junction diodes
Authors: Poyai A. , Claeys C. , Simôen E.
Published: July 2002

An accurate method is proposed for the extraction of the carrier concentration profile (pp well) and the depletion width (Wp well) in a p-well region from high-frequency capacitance measurements by accounting for the series resistance and the capacitance of the n+ region. Wp well was calculated from the capacitance in the p-well region (Cp well), while pp well was derived from the slope of the plot 1/Cp well2 versus reverse bias. The pp well extracted was compared with profiles obtained from spreading resistance probe results. The differences between the two techniques are within 15% in the accessible depletion width, which will be discussed in view of the depth resolution anticipated.
Design studies of the APS canted undulator beamline front ends
Authors: Shu Deming , Ramanathan Mohan
Published: July 2002

A great majority of the Advanced Photon Source (APS) users have chosen an undulator as the only source for their insertion device (ID) beamline. Compared with a wiggler source, the undulator source has a much smaller horizontal divergence, providing us with an opportunity to explore the possibility to extract multiple beamlines from a single straight section of the APS storage ring. A one-milliradian deflection between the two beams is the optimal angle permitted given the configuration of the existing hardware (see Ref. 1). Based on the new APS front-end design for undulator-only operation (see Ref. 2), we have studied the feasibility of its modification for a one-milliradian canted double-undulator configuration. In this article, the designs and specifications, as well as the optical and bremsstrahlung ray-tracing analyses of the new APS front ends for canted double-undulator operation are presented. The compatibility of the original APS undulator/wiggler front ends with canted double-undulator operation is also discussed.
Performance of a quadruple reflector circular polarizer in VUV region for angle- and spin-resolved photoemission spectroscopy
Authors: Baek In-Gyu , Hulbert Steven L. , Vescovo Elio
Published: July 2002

A quadruple-reflector circular polarizer has been installed and tested at the U5UA beamline of National Synchrotron Light Source. With an intense and highly linearly polarized vacuum ultraviolet (VUV) undulator light source, the polarizer can produce pure circular polarization in the 20–50 eV photon energy range, enabling angle- and spin-resolved photoemission spectroscopy. The optical conditions for circularly polarized light (CPL) as well as the efficiency of the polarizer have been investigated and compared with calculation. Example valence band magnetic circular dichroism and spin-resolved photoemission spectra taken with CPL demonstrate the advantages of CPL in the VUV energy range.
Studies of intensity noise at the Synchrotron Ultraviolet Radiation Facility III
Authors: Arp U. , Lucatorto T. B. , Harkay K. , Kim K.-J.
Published: July 2002

Suppression of beam instabilities has become an important goal at synchrotron radiation light sources, where highly sensitive applications like metrology, Fourier transform spectroscopy, and microscopy are now in use. We describe measurements connecting beam size and position changes to the onset of the saw-tooth instability and an instability generated by attempts to enlarge the vertical beam size for lifetime improvements.
An overview of the information distribution system at the Advanced Photon Source
Authors: Ramanathan M. , Smith M. , Arnold N. , Lenkszus F. , Laird R. , Evans K. , Anderson J. , Sidorowicz K.
Published: July 2002

The Advanced Photon Source (APS) has been in operational mode for more than 5 yr. Currently there are over 40 beamlines in various phases of operation. The control system of choice at the APS is the Experimental Physics and Industrial Control System (EPICS). We have provided various interfaces to the beamlines from the APS control system. An overview of the various systems will be discussed. The General Control System Information (GCSI) uses dedicated computers as EPICS process variable gateways to provide data from the APS control system to each beamline. The GCSI architecture makes the APS control system secure, yet has the flexibility of providing access control to any data available on the APS control system. In addition, the gateway reduces the load on the APS control system equipment by making only one connection for each process variable accessed by multiple users. Each sector, consisting of a bending magnet and insertion device beamlines, is provided its own gateway, which resides on the local sector network. This scheme has the advantage of providing network security and more reliable operation. To provide real-time accelerator data to beamlines, each sector has been provided a chassis to display the storage ring current and other relevant information. These data are transmitted via a direct fiber link from the APS control system hardware to the beamlines. The beamlines are also provided VME-based hardware and associated EPICS software to retrieve key information provided via this fiber link. Some of the information on this link is beam current, lifetime, injection status, and sector specific information such as shutter status, insertion device gap, and energy, and storage ring and front-end beam position monitor signals. The data rates on this link are typically 10 Hz but can be as high as 272 kHz. This scheme allows the beamlines using EPICS-based software to seamlessly use the data from the APS control system without excessively impacting the system. For high-precision x-ray timing experiments, a new scheme has been designed to distribute the radio-frequency timing signals to the beamlines. Using VME-based hardware and EPICS software, the bunch clock signal is generated at the beamline for use in timing experiments. Data are provided at the radio frequency of 352 MHz. Beamlines have also been provided with hardware and software to generate the bunch clock signal for timing experiments.
A novel method of bending crystals to log spiral shape
Authors: Khelashvili G. , Ivanov I. , Morrison T. I. , Bunker G. , Chapman D.
Published: July 2002

Crystals bent to logarithmic spirals have been used in applications where large acceptance of divergent x rays from a small source is needed. Small acceptances can be easily handled with cylindrically bent crystal. In cases where larger acceptances are needed differential bending may be adequate. However, the largest acceptance is obtained from a flat crystal plate when bent into the logarithmic spiral shape that allows the crystal to present the same angle of incidence to the beam emanating from a point source. The bending of such crystals generally can be accomplished by forcing the crystal into the required shape with a metal frame. A preliminary theoretical study of crystal shapes that when bent will naturally form logarithmic spiral shapes has been done. This study was done for the case of a cantilever beam with fixed end and a normal force applied to a point at the other end. A fixed thickness-variable width beam was considered. The crystal profile in width (direction perpendicular to the diffraction plane) can be spatially varied to achieve this spiral shape. Equations for both cases will be given.
Highly reproducible laser beam scanning device for an internal source laser desorption microprobe Fourier transform mass spectrometer
Authors: Scott Jill R. , Tremblay Paul L.
Published: July 2002

Traditionally, mass spectrometry has relied on manipulating the sample target to provide scanning capabilities for laser desorption microprobes. This has been problematic for an internal source laser desorption Fourier transform mass spectrometer (LD-FTMS) because of the high magnetic field (7 Tesla) and geometric constraints of the superconducting magnet bore. To overcome these limitations, we have implemented a unique external laser scanning mechanism for an internal source LD-FTMS. This mechanism provides adjustable resolution enhancement so that the spatial resolution at the target is not limited to that of the stepper motors at the light source (∼5 μm/step). The spatial resolution is now limited by the practical optical diffraction limit of the final focusing lens. The scanning mechanism employs a virtual source that is wavelength independent up to the final focusing lens, which can be controlled remotely to account for focal length dependence on wavelength. A binary index provides an automatic alignment feature. The virtual source is located ∼9 ft from the sample; therefore, it is completely outside of the vacuum system and beyond the 50 G line of the fringing magnetic field. To eliminate reproducibility problems associated with vacuum pump vibrations, we have taken advantage of the magnetic field inherent to the FTMS to utilize Lenz’s law for vibrational dampening. The LD-FTMS microprobe has exceptional reproducibility, which enables successive mapping sequences for depth-profiling studies.
High pressure angle-dispersive Brillouin spectroscopy: A technique for determining acoustic velocities and attenuations in liquids and solids
Authors: Koski K. J. , Müller J. , Hochheimer H. D. , Yarger J. L.
Published: July 2002

We report the combination of a high-pressure sample chamber and a stable, nonscanning, angle-dispersive Fabry–Perot interferometer allowing the rapid measurement of inelastic light scattering from acoustic phonon modes in solid and liquid samples at high pressure. The primary components of the apparatus are a (i) narrow frequency gas ion laser, (ii) a solid or air-spaced etalon, (iii) a multichannel charge coupled device detector, and (iv) a large volume, high-pressure cell. The fundamental principle of this spectrometer is based on the angular dispersion of light through an etalon, whereupon the multiple-order frequency dispersed spectrum can be acquired with an array detector. Typical acquisition times are less than 1 s using low to moderate laser power.
Fourier-transform photocurrent spectroscopy of microcrystalline silicon for solar cells
Authors: Vanecek M. , Poruba A.
Published: July 2002

The spectral dependence of the optical absorption coefficient in thin films of hydrogenated microcrystalline silicon is measured over nine orders of magnitude in the subgap, defect-connected region, and in the above-the-band gap region. Transmittance, reflectance, and constant photocurrent method measurements are combined with Fourier-transform photocurrent spectroscopy (FTPS). Results are analyzed and interpreted as due to electron transitions from defects or interband electron transitions, all having direct relevance to the thin-film microcrystalline silicon solar cell performance. FTPS is a fast and sensitive quantitative method for quality assessment of microcrystalline silicon absorber in solar cells and can be used for quality monitoring in solar cell production.
Determination of activation volumes in thin film media
Authors: Antel W. J. , Laidler H. , O’Grady K. , Verdes C. , Chantrell R. W.
Published: July 2002

The activation volume of reversal νact is a critical parameter in the characterization of thin film media since it determines the smallest unit of a magnetic material that can be reversed in a single step and hence defines the minimum bit size. In the recent past, there have been reports in the literature of a number of methods to determine the activation volume and it has become apparent that these methods provide inconsistent results. In this work, we describe both a theoretical and experimental comparison between the two principle methods used to determine the fluctuation field and hence the activation volume in thin film media. We have examined a thin film medium and find that inconsistencies between the methods do occur. These can be attributed to the reversible component of magnetization. We show that measurements of the fluctuation field, which is the fundamental quantity, determined from measurements of the ratio of the magnetic viscosity to the irreversible susceptibility are consistent with measurements undertaken following a waiting time approach for the aligned case. However, measurement gives rise to an erroneous value for the fluctuation field and hence the activation volume unless the data are corrected for reversible changes in the magnetization which occur. Both experimental data and theoretical calculations are provided to demonstrate this effect.
Perpendicular magnetic anisotropy in CoPt3(111) films grown on a low energy surface at room temperature
Authors: Albrecht M. , Maret M. , Maier A. , Treubel F. , Riedlinger B. , Mazur U. , Schatz G. , Anders S.
Published: July 2002

Epitaxial (111)-oriented CoPt3 films were deposited on WSe2(0001) substrates at room temperature using molecular beam epitaxy. We observed strong growth induced uniaxial perpendicular magnetic anisotropy which has a maximum of 3.2×106 erg/cm3 and coercivity of about 200 Oe for films with thicknesses <6 nm. At a thickness larger than 6 nm the easy magnetization axis progressively rotates into the plane of the film as the film thickness is increased. The magnetic domain structure in films with perpendicular magnetic anisotropy was investigated by photoemission electron microscopy revealing a characteristic thickness dependence near the reorientation transition.
Barrier dependence of magnetoresistance enhancement in nano-oxide added spin valves
Authors: Li Kebin , Wu Yihong , Qiu Jinjun , Chong Towchong
Published: July 2002

The effects of different types of nano-oxides on the properties of spin valves have been studied. The nano-oxides that have been investigated in this study include NiFe–O, Al–O, CoFe–O, Ta–O, and Cu–O. From the point of view of overall properties (magnetoresistance ratio, change of sheet resistance, exchange coupling field, and interlayer coupling field), CoFe–O turned out to be the most desirable oxide when being used as the bottom oxide for top spin valves. As a capping layer for bottom spin valves, however, it was found that Al–O is the best choice among those investigated. Under optimum conditions, IrMn-based dual spin valves with a magnetoresistance ratio up to 21.8% has been successfully fabricated by incorporating oxide layers in both pinned ferromagnetic layers.
Seedlayer and underlayer effects on the crystallographic orientation and magnetic recording performance of glass media
Authors: Zheng Min , Choe Geon , Johnson Kenneth E.
Published: July 2002

Seedlayer and underlayer effects on crystallographic orientation and recording performance were studied for CoCrPtB media sputtered on glass substrates. For this study, the seedlayers are XAl (X=Ni, Co, Ti, and Ru) and the underlayers are CrY (Y=V, Mo, W, and Ti). It was found that not only different seedlayers, but also different combinations of seedlayer and underlayer, led to different magnetic performance. NiAl and CoAl seedlayers orient the Co c axis to (10.0) and TiAl and RuAl seedlayers produce (11.0) Co orientation. For the NiAl and CoAl seedlayer, CrV and CrW underlayers develop less out-of-plane c-axis orientation and higher coercivity and coercive squareness while CrTi and CrMo underlayers work better for TiAl and RuAl seedlayers, respectively. Media with RuAl seedlayers have better parametric performance than media with NiAl and CoAl seedlayers. The detailed relationship between seedlayer and underlayer types and crystal orientation and recording performance is discussed.
High frequency performance of laminated soft magnetic films (NiFe, FeAlN, and amorphous CoFeBSi) in external fields
Authors: Rieger Gotthard , Rupp Guenther , Gieres Guenther , Losehand Reinhard , Hartung Wolfgang , Maass Wolfram , Ocker Wolfgang
Published: July 2002

Thin film multilayers of different compositions (NiFe, FeAlN, and amorphous CoFeSiB) were prepared by sputter deposition. The ultrahigh frequency performance was studied using rf fields perpendicular to the in-plane easy axis. By applying external bias fields either along or perpendicular to the easy axis (perpendicular to the rf field excitation), the cutoff frequency of the different alloys can be shifted significantly to higher frequencies (>1 GHz) according to theory. On the other hand, it is possible from these measurements to identify different phenomenological damping of the material systems due to structural effects. Although FeAlN exhibits the highest saturation magnetization compared to NiFe and CoFeBSi, it shows a higher damping which is explained by nonideal structure.
A linear actuator with 3 Å closed-loop control resolution and 50 mm travel range (abstract)
Authors: Shu Deming , Han Yufeng , Toellner Thomas S. , Alp Esen E.
Published: July 2002

We have designed and constructed a novel linear actuator with 3 Å closed-loop control resolution and 50 mm travel range. Two major ultraprecision motion control techniques have been applied to this actuator: (i) a novel laser Doppler encoder system with multiple-reflection optics [D. Shu et al., Proc. SPIE 3429, 284 (1998)]; and (ii) a specially designed high-stiffness weak-link mechanism with stacked thin metal sheets having sub-Angstrom driving sensitivity with excellent stability [D. Shu et al., Nucl. Instrum. Methods Phys. Res. A 467–468, 771 (2001). In this paper, we present recent test results of this actuator with an atomic force microprobe. Applications of this new technique to synchrotron radiation instrumentation are also discussed.