bluuebunny/crossref_metadata_2025 huggingface dataset:
Co‐located ACE‐FTS and Odin/SMR stratospheric‐mesospheric CO 2004 measurements and comparison with a GCM
Authors: Jin J. J. , Semeniuk K. , Jonsson A. I. , Beagley S. R. , McConnell J. C. , Boone C. D. , Walker K. A. , Bernath P. F. , Rinsland C. P. , Dupuy E. , Ricaud P. , De La Noë J. , Urban J. , Murtagh D.
Published: May 2005

This paper presents a comparison of co‐located and near simultaneous CO measurements from January to May, 2004 and from the Arctic to southern polar regions using the ACE‐FTS, in solar occultation mode, and the Odin/SMR, which measures atmospheric emission. We find that there is excellent agreement between the two instruments at the locations investigated over 4 orders of magnitude from the lower stratosphere to the lower thermosphere. There is also good agreement with the CMAM model simulation from 20 km to 90 km in sub‐tropical and tropical latitudes but poorer agreement in the upper stratosphere and lower mesosphere in winter polar regions. For the Arctic in March 2004 this can be attributed, at least partly, to the unique dynamical processes in the stratosphere in the winter of 2003–2004. Clearly CO measurements from these instruments will provide a useful tool for testing model transport from the troposphere to the thermosphere.
ACE‐FTS measurements across the edge of the winter 2004 Arctic vortex
Authors: Nassar Ray , Bernath Peter F. , Boone Chris D. , Manney Gloria L. , McLeod Sean D. , Rinsland Curtis P. , Skelton Randall , Walker Kaley A.
Published: May 2005

Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) solar occultation measurements have been used to create volume mixing ratio (VMR) profiles of H2O, CH4, and N2O inside and outside the 2004 Arctic vortex. Using derived meteorological quantities such as potential vorticity, we have classified 450 occultations (from February and March 2004 spanning 0 to 79.8°N) as vortex, vortex edge, or extravortex. We plot [CH4] versus [N2O] correlations to display the distinct patterns observed for measurements of different air masses and use these correlations to further classify the extravortex occultations as tropical, subtropical, or midlatitude. Using comparisons between high latitude profiles of [N2O], [CH4], and [H2O] inside and outside the Arctic vortex, we estimate upper stratospheric and lower mesospheric descent rates and find that descent in the winter 2004 Arctic vortex was rapid, with evidence of descent at higher altitudes than in past years.
Ion cyclotron waves in the Saturnian magnetosphere associated with Cassini's engine exhaust
Authors: Russell C. T. , Leisner J. S. , Khurana K. K. , Dougherty M. K. , Blanco‐Cano X. , Fox J. L.
Published: May 2005

Five hours after the orbit insertion maneuver that placed Cassini into orbit about Saturn, a long (90 minute) burst of ion cyclotron waves were seen, very different than any waves on the inbound leg of the orbit or on succeeding orbits. The ion cyclotron waves were left‐hand elliptically polarized and propagating at a moderately large angle to the local magnetic field. The waves had a noticeable compressional component consistent with their off angle propagation. The frequency band of the signals was moderately broad and consistent with the singly ionized components of the engine exhaust gases: CO2, N2, CO, and H2O. While H2O waves are seen elsewhere, and associated with the E ring, these waves were stronger and propagated at a much larger angle to the magnetic field. It appears that the engine exhaust products became ionized by solar EUV and electron impact and then accelerated by the magnetospheric electric field associated with co‐rotation. This acceleration produced a ring‐beam in velocity space much like that produced by Io pickup ions in the jovian magnetosphere.
Relationship between the Jovian magnetospheric plasma density and Io torus emission
Authors: Nozawa H. , Misawa H. , Takahashi S. , Morioka A. , Okano S. , Sood R.
Published: May 2005

Ground‐based observations of [SII] 673.1 nm emissions from the Io plasma torus (IPT) showed a year‐to‐year decrease between 1997 and 2000. This phenomenon suggests that the electron and ion densities in the IPT decreased during the period, since an excitation source of the [SII] 673.1 nm emissions is an electron impact. Using Galileo plasma wave subsystem (PWS) data, local electron density in the magnetosphere (30–60 RJ) was investigated. The electron density in the middle and outer magnetosphere also showed a long‐term decrease between 1997 and 2000. This concurrent long‐term variation in the magnetospheric electron density with the IPT emissions verifies that the IPT gives influence to the magnetospheric plasma environment, as has been suggested since the Voyager era. Relative amplitudes of variations in the [SII] intensity and electron density were, however, different from each other.
Simulation of extraction of high current uranium beams
Authors: Xiang W. , Spädtke P. , Hollinger R. , Galonska M. , Heymach F.
Published: May 2005

To generate uranium ion beam with high current and high brightness to fill up the heavy ion synchrotron SIS to its space charge limit, the behavior of the uranium ion beam in the extraction system and the postacceleration system for a high current metal vapor vacuum arc ion source has been investigated using the KOBRA3-INP code. The beam trajectory and space charge map in the extraction system as well as space profiles and the emittance diagrams of the ion beam along the beam line are presented. The influences of degree of the space charge compensation on the characteristics of the extracted ion beam are discussed. The results show that the ion beam has to be space charge compensated from the screening electrode to the entrance of the acceleration gap; otherwise the transport would not be possible. Simulation also quantitatively supports the experimental results under the assumption of the full space charge compensation in the drift sections.
Space charge lenses for particle beams
Authors: Pozimski J. , Meusel O.
Published: May 2005

Space charge lenses provide strong cylinder symmetric focusing for low-energy high-perveance particle beams using a stable space charge cloud. They need drastically reduced magnetic and electrostatic field strength compared with conventional systems and are superior for a degree of lens filling above 17%. They can theoretically provide linear transformation in phase space and reduce beam aberrations and space charge forces. The density distribution of the enclosed space charge is given by the transverse and longitudinal enclosures of the cloud. By the use of self-consistent simulations of the space charge cloud, the focusing properties of space charge lenses in the presented design can be forecasted with sufficient quality. The presented simulations show that the theoretical values can be reached locally. The results of our investigations on the beam transport in a high-current test injector equipped with space charge lenses, including emittance measurements, will be presented and discussed. They show that significant improvements of lens operation have been reached by the reduction of the residual gas pressure and a careful design of the external fields using numerical simulation techniques to calculate the local density distributions. Comparisons of the experimental results with the beam transport simulations show good agreement concerning both focusing strength and linearity of phase space transformation. For the lens design used, the observed degree of lens filling is at least 38% of the theoretical value and more than twice the threshold value.
Kinetic pathway to double-gyroid structure
Authors: Imai M. , Sakai K. , Kikuchi M. , Nakaya K. , Saeki A. , Teramoto T.
Published: May 2005

We have investigated the structural development during order-order transitions to the double-gyroid (DG) phase of nonionic surfactant/water systems based on two-dimensional small-angle x-ray scattering patterns from highly oriented ordered mesophases. The lamellar (L) to DG transition proceeds through two intermediate structures, a fluctuating perforated layer structure having ABAB stacking and a hexagonal perforated lamellar structure with ABCABC stacking (HPLABC). For a hexagonally packed cylinder (H) to DG transition, we also observed the HPLABC structure as the intermediate phase, thus the HPLABC is an entrance structure for the DG phase. The hexagonal perforated lamellar (HPL) structure consists of hexagonally packed holes surrounded by the planar tripods, and the transition from HPL structure to the DG phase proceeds by rotation of the dihedral angle of connected tripods. A geometrical consideration shows that large deformations of HPL planes are necessary to form the DG structure from the HPLABC structure, whereas the transition from a HPL structure with ABAB stacking (HPLAB) to the DG structure is straightforward. In spite of the topological constraints, the HPLABC structure is observed in the kinetic pathway to the DG structure.
The influence of substrate anisotropy on laser-focused atom deposition studied by two-dimensional Monte Carlo simulation
Authors: Nita Florin , Pimpinelli Alberto
Published: May 2005

We study the role of the surface diffusion anisotropy in the fabrication of nanostructures by laser-focused (“cold”) atom lithography, and on the stability of nanostructures using two-dimensional kinetic Monte Carlo simulations. The simulations were performed using one- and two-directional standing-wave fields (using two different wave profiles) and two different diffusion models (limited and total diffusion model) on anisotropic surfaces, such as (110) surfaces of face-centered-cubic crystals, or reconstructed surfaces such as Si(100). The simulations were made with and without Schwoebel barriers. Our diffusion-deposition models reproduce qualitatively experimental results.
Vibrational Raman optical activity as a mean for revealing the helicity of oligosilanes: A quantum chemical investigation
Authors: Liégeois Vincent , Quinet Olivier , Champagne Benoît
Published: May 2005

Using theoretical simulations based on Hartree–Fock and density-functional theory calculations, the simulated vibrational Raman optical activity spectra of helical conformers of heptasilane are shown to present signatures sensitive to the helicity. These signatures are associated with collective wagging, twisting, and rocking motions. These simulated spectra have been obtained by combining analytical and numerical differentiation procedures to evaluate the geometry derivatives of the optical tensors entering into the expressions of the vibrational Raman optical activity intensities. From an investigation of basis set and electron correlation effects, it is shown that, like for local vibrations, diffuse functions are compulsory for evaluating the vibrational Raman optical activity intensities of collective vibrational motions.
Electrical damage induced by reactive ion-beam etching of lead-zirconate-titanate thin films
Authors: Soyer C. , Cattan E. , Rèmiens D.
Published: May 2005

Ion-beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) thin films with x equal to 0.54 grown on Pt∕TiOx∕SiO2∕Si substrates has been performed using pure Ar gas and a varying CHF3∕Ar gas mixing ratio. The etch rate dependence on the process parameters (gas composition, current density, and acceleration voltage) has been investigated. PZT etch rate under 40% CHF3 in Ar can reach 100nm∕min with an acceleration voltage of 900 V and a current density of 0.7mA∕cm2 (in comparison to 35nm∕min in pure Ar). A selectivity ratio of 8 has been obtained between PZT and photoresist (1.3 in pure Ar). We have evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases less under a gas mixture than under a pure argon beam, and that the preferential etching observed at the grain boundaries under a pure argon beam disappears when we increase the proportion of CHF3 in the gas mixture. For some etching parameters (current density, acceleration voltage, and gas mixing ratio), we have observed electrical damage. C(V) and hysteresis loops P(E) measurements before and after etching have demonstrated these degradations. We have noted a large decrease of the permittivity after the etching process, independently of the current density and the acceleration voltage. The ferroelectric damage was illustrated by a large increase of the average coercive field after etching in pure argon. The presence of CHF3 in the plasma partially reduces the damage.
Cyclization of Rouse chains at long- and short-time scales
Authors: Yeung Chuck , Friedman Barry
Published: May 2005

We have investigated cyclization of a Rouse chain at long and short times by a Langevin dynamics simulation method. We measure S(t), the fraction of nonreacted chains, for polymerizations ranging from Z=5 to Z=800 and capture distances ranging from a=0.1b to a=8b where b is the bond length. Comparison is made with two theoretical approaches. The first is a decoupling approximation used by Wilemski and Fixman to close the relevant master equation [J. Chem. Phys. 58, 4009 (1973); 60, 866 (1974)]. The second approach is the renormalization group arguments of Friedman and O’Shaughnessy [Phys. Rev. Lett 60, 64 (1988); J. Phys. II 1, 471 (1991)]. We find that at long times S(t) decays as a single exponential with rate k∞. The scaled decay rate K=k∞τR appears to approach a constant value independent of the capture distance for very large chains consistent with the predictions of both the renormalization group (RG) and Wilemski–Fixman closure approximation. We extract K*, the long chain limit of K, from the fixed point a=a* where K is independent of Z. K* is larger than both the RG and closure predictions but much closer to the RG result. More convincing evidence for the RG analysis is obtained by comparing the short-time decay of S(t) to long-time results. The RG analysis predicts that dS∕dt should decay as a power law at early times and that the exponent in the power law is related to K by a simple expression with no free parameters. Our simulations find remarkable agreement with this parameter-free prediction even for relatively short chains. We discuss possible experimental consequences of our result.
Soluble stochastic dynamics of quasi-one-dimensional single-file fluid self-diffusion
Authors: Mon K. K. , Percus J. K.
Published: May 2005

We solve a model of random-walk stochastic dynamics for hard single-file fluids in the experimentally important quasi-one-dimensional regime. This is a nontrivial extension of exact solution beyond one dimension. We point out that quasi-one-dimensional single-file self-diffusion of one-component hard fluids of diameter a under stochastic forces is equivalent at long time to a one-dimensional hard-rod fluid with the same linear density but a different diameter, aeff. This effective diameter is controlled by the details of the relative dynamics between the transverse and longitudinal directions. There are two regimes of limiting behavior. For very fast transverse motion, the system is likely (but we cannot prove rigorously) to be equivalent to the soluble-oriented hard-rectangle or cylinder systems, with aeff=a. With very slow transverse motion, the self-diffusion dynamics is described by an equivalent soluble one-dimensional mixture of fluids with aeff=aave, the average longitudinal separation between nearest-neighbor particles at contact. We have explored our theoretical predictions with Monte Carlo simulations.
Effect of attractive interactions on the structure of polymer melts confined between surfaces: A density-functional approach
Authors: Goel Teena , Patra Chandra N. , Ghosh Swapan K. , Mukherjee Tulsi
Published: May 2005

A density-functional theory is presented to study the structure of polymers, having attractive interactions, confined between attractive surfaces. The theory treats the ideal-gas free-energy functional exactly and uses weighted density approximation for the hard-chain contribution to the excess free-energy functional. The bulk interactions of freely jointed hard spheres are obtained from generalized Flory equation of state and the attractive interactions are calculated using the direct correlation function obtained from the polymer reference interaction site model theory along with the mean spherical approximation closure. The theoretical predictions are found to be in quite good agreement with the Monte Carlo simulation results for varying densities, chain lengths, and different interaction potentials. The results confirm important implications of using different approximations for the hard-sphere and attractive interactions.
Relaxation of hot atoms following H2 dissociation on a Pd(111) surface
Authors: Pineau N. , Busnengo H. F. , Rayez J. C. , Salin A.
Published: May 2005

We study the relaxation of hot H atoms produced by dissociation of H2 molecules on the Pd(111) surface. Ab initio density-functional theory calculations and the “corrugation reducing procedure” are used to determine the interaction potential for a H atom in front of a rigid surface as well as its modification under surface-atom vibrations. A slab of 80Pd atoms is used to model the surface together with “generalized Langevin oscillators” to account for energy dissipation to the bulk. We show that the energy relaxation is fast, about 75% of the available energy being lost by the hot atoms after 0.5ps. As a consequence, the hot atoms do not travel more than a few angstroms along the surface before being trapped into the potential well located over the hollow site.
Mechanism of enhanced positronium formation in low-temperature polymers
Authors: He Chunqing , Shantarovich V. P. , Suzuki Takenori , Stepanov S. V. , Suzuki Ryoichi , Matsuo Masaru
Published: May 2005

An enhanced positronium (Ps) formation in low-temperature polymers has been widely observed. The additional positronium formation is due to shallow trapped electrons in them. Positron annihilation lifetime spectroscopy was applied to investigate the Ps formation in a series of polymers, such as low-density polyethylene, ethylene-methyl methacrylate copolymers with various methyl methacrylate contents, and pure poly(methyl methacrylate) at low temperature. An analysis of the experimental data based on simple kinetic equations enables one to understand the Ps formation mechanism in polymers during low-temperature positron annihilation experiments as functions of the temperature and elapsed time. Good fittings of the experimental data were obtained. The fitting parameters seemed to show clear physical meanings.
Commutation relations for functions of operators
Authors: Transtrum Mark K. , Van Huele Jean-François S.
Published: May 2005

We derive an expression for the commutator of functions of operators with constant commutations relations in terms of the partial derivatives of these functions. This result extends the well-known commutation relation between one operator and a function of another operator. We discuss the range of applicability of the formula with examples in quantum mechanics.
Transport properties of quantum-classical systems
Authors: Kim Hyojoon , Kapral Raymond
Published: May 2005

Correlation function expressions for calculating transport coefficients for quantum-classical systems are derived. The results are obtained by starting with quantum transport coefficient expressions and replacing the quantum time evolution with quantum-classical Liouville evolution, while retaining the full quantum equilibrium structure through the spectral density function. The method provides a variety of routes for simulating transport coefficients of mixed quantum-classical systems, composed of a quantum subsystem and a classical bath, by selecting different but equivalent time evolution schemes of any operator or the spectral density. The structure of the spectral density is examined for a single harmonic oscillator where exact analytical results can be obtained. The utility of the formulation is illustrated by considering the rate constant of an activated quantum transfer process that can be described by a many-body bath reaction coordinate.
The gas–liquid phase-transition singularities in the framework of the liquid-state integral equation formalism
Authors: Sarkisov Gari , Lomba Enrique
Published: May 2005

The singularities of various liquid-state integral equations derived from the Ornstein–Zernike relation and its temperature derivatives, have been investigated in the liquid–vapor transition region. As a general feature, it has been found that the existence of a nonsolution curve on the vapor side of the phase diagram, on which both the direct and the total correlation functions become complex—with a finite isothermal compressibility—also corresponds to the locus of points where the constant-volume heat capacity diverges, in consonance with a divergence of the temperature derivative of the correlation functions. In contrast, on the liquid side of the phase diagram one finds that a true spinodal (a curve of diverging isothermal compressibilities) is reproduced by the Percus–Yevick and Martynov–Sarkisov integral equations, but now this curve corresponds to states with finite heat capacity. On the other hand, the hypernetted chain approximation exhibits a nonsolution curve with finite compressibilities and heat capacities in which, as temperature is lowered, the former tends to diverge.
The beam position monitor of the BEAR beamline
Authors: Giglia Angelo , Mahne Nicola , Pedio Maddalena , Nannarone Stefano , Pelizzo Maria Guglielmina , Naletto Giampiero , Zambolin Paolo
Published: May 2005

This article describes the photon beam position monitor installed at the BEAR beamline at Elettra, Trieste. The device, based on four Mo photoemitting plates, is installed upstream of the beamline optics. Two modes of operation are possible, including single-plate operation (integral mode) and two-plate operation (differential mode). The integral mode allows beam height determination in the laboratory frame of reference with an overall accuracy of about 0.1mm, while the differential mode features a sensitivity of the order of about 1μm. A quantitative model connecting the device output with beam height was deduced. A satisfactory agreement was found between model predictions and experimental results. The quantitative performance opens the possibility to implement a feedback procedure to stabilize or automatically numerically correct the delivered photon energy.
Spectroscopic and imaging approaches for evaluation of properties of one-dimensional arrays of formulated polymeric materials fabricated in a combinatorial microextruder system
Authors: Potyrailo Radislav A. , Wroczynski Ronald J.
Published: May 2005

We report optical spectroscopic and imaging approaches for the high-throughput nondestructive characterization of formulated polymeric materials fabricated as one-dimensional (1D) polymeric arrays. These materials are fabricated as 1–2 mm diameter fibers or 5–12-mm-wide by 0.3–1-mm-thick films using a combinatorial system that includes a microextruder (total barrel volume of 4.5cm3) and microfeeders. Because our microextruder approach for fabrication of formulated polymeric materials requires ∼200 times less material compared to traditional scale extruders, it provides previously unavailable opportunities for characterization of extruded materials without their pelletization. Property changes in polymeric formulations are induced along the length of the 1D arrays by several approaches that include (1) variation in composition of 1D array during polymer microextrusion, (2) variation in processing conditions during polymer microextrusion, and (3) variation in exposure conditions of a performance test for different spatial regions along the length of the array. Polymeric 1D arrays are analyzed either in-line or off-line. In-line analysis is performed using spectroscopic luminescence emission and reflected light modes. For off-line analysis, 1D fiber and film arrays are coiled as helices and flat coils, respectively. Automated measurements of coiled 1D arrays are performed using modular scanning and imaging systems. The scanning system is based on a portable spectrograph and is coupled to an X-Y translation stage to produce scans of 100μm step size. The imaging system is operated in luminescence emission and reflected light modes. Our fabrication and analysis approaches significantly reduce the amount of material and energy needed and increase the speed of development of formulated polymeric materials by using approaches for characterization of coiled 1D polymeric arrays.
Data management and visualization of x-ray diffraction spectra from thin film ternary composition spreads
Authors: Takeuchi I. , Long C. J. , Famodu O. O. , Murakami M. , Hattrick-Simpers J. , Rubloff G. W. , Stukowski M. , Rajan K.
Published: May 2005

We discuss techniques for managing and visualizing x-ray diffraction spectrum data for thin film composition spreads which map large fractions of ternary compositional phase diagrams. An in-house x-ray microdiffractometer is used to obtain spectra from over 500 different compositions on an individual spread. The MATLAB software is used to quickly organize the data and create various plots from which one can quickly grasp different information regarding structural and phase changes across the composition spreads. Such exercises are valuable in rapidly assessing the “overall” picture of the structural evolution across phase diagrams before focusing in on specific composition regions for detailed structural analysis. We have also shown that simple linear correlation analysis of the x-ray diffraction peak information (position, intensity and full width at half maximum) and physical properties such as magnetization can be used to obtain insight about the physical properties.
Specific-heat measurement of single metallic, carbon, and ceramic fibers at very high temperature
Authors: Pradère C. , Goyhénèche J. M. , Batsale J. C. , Dilhaire S. , Pailler R.
Published: May 2005

The main objective of this work is to present a method for measuring the specific heat of single metallic, carbon, and ceramic fibers at very high temperature. The difficulty of the measurement is due to the microscale of the fiber (≈10μm) and the important range of temperature (700–2700K). An experimental device, a modelization of the thermal behavior, and an analytic model have been developed. A discussion on the measurement accuracy yields a global uncertainty lower than 10%. The characterization of a tungsten filament with thermal properties identical to those of the bulk allows the validation of the device and the thermal estimation method. Finally, measurements on carbon and ceramic fibers have been done at very high temperature.
Raman spectroscopy as a tool to study TiC formation during controlled ball milling
Authors: Lohse B. H. , Calka A. , Wexler D.
Published: May 2005

Titanium and carbon elemental powder mixtures with compositions of Ti100−xCx (x=50,40,30) were milled under a helium atmosphere using a magnetoball mill. For Ti50C50 and Ti60C40 powder mixtures, the combined results of external mill temperature monitoring and x-ray diffraction (XRD) analysis indicated that, after a specific incubation period, titanium carbide (TiC) was formed rapidly via a highly exothermic mechanically induced reaction. However, contrary to the current understanding of mechanically induced self-propagating reactions, Raman spectroscopy clearly showed the formation of nonstoichiometric TiC in Ti50C50 and Ti60C40 powders prior to the sudden exothermic event occurring inside the mill. This result has not been reported in previous studies that used only XRD analysis to characterize the as-milled powders. It is now thought that a significant component of the heat generated after the incubation period may be due to a combination of rapid grain growth and/or recrystallization of the preexisting TiC, rather than the direct formation of TiC. When milling Ti70C30, the reaction to form TiC proceeded gradually as milling progressed.
X-ray absorption and photoelectron spectroscopic study of plasma-nitrided SiO2 film
Authors: Song H. J. , Shin H. J. , Chung Youngsu , Lee J. C. , Lee M. K.
Published: May 2005

Plasma-nitrided SiO2 thin film has been analyzed by synchrotron-radiation-based x-ray absorption and photoelectron spectroscopies (XAS and XPS). High-resolution N 1s XAS and N 1s, O 1s, and Si 2p XPS spectral changes were obtained for different annealing temperatures. N 1s XPS and XAS spectra show that at room temperature, besides the main species of N[Si(O−)3−x]3, there exist free moleculelike N2 and HN[Si(O−)3]2, H2NSi(O−)3, and N–Si2O species with surface contaminants. The spectral intensities of the N2 and the HN[Si(O−)3]2, H2NSi(O−)3, and N–Si2O species decrease as the annealing temperature increases, and finally the nitrogen exists dominantly in the form of N[Si(O)3]3 species above 820K, indicating out-diffusion of molecular N2 and structural reconstruction to form a stable structure upon annealing. The Si 2p and O 1s XPS spectra show that Si>4+ 2p peak and O 1s peak appear at 103.7 and 534.0eV, respectively, which are higher binding energies than those of thermally grown oxynitride films with lower coverage on silicon. Upon annealing the sample, these peaks shift towards lower binding energy; ∼0.3eV for Si>4+ and 0.4eV for O 1s. The causes of the peaks appearance at relatively higher binding energy and the peak shift upon annealing are discussed.
Control of crystalline orientation of germanium by lateral graphoepitaxy on SiO2 microstructures
Authors: Koide Takeshi , Minemoto Takashi , Takakura Hideyuki , Hamakawa Yoshihiro , Numai Takahiro
Published: May 2005

Control of crystalline orientation of germanium (Ge) on a SiO2 surface was demonstrated by lateral graphoepitaxy. An x-ray diffraction curve with a (400) peak was obtained in a Ge crystal grown on microholes, each of which has a side of 1μm long and four 10-nm-thick SiO2 sidewalls made from thermally oxidized Si {111} planes. Using this Ge crystal on the microholes as a seed crystal, a Ge crystal with a (400) orientation was laterally grown on a 10-nm-thick SiO2 layer, which was a thermally oxidized flat Si (100) surface, by zone melting.
Chemical gating and photoconductivity of CF4 plasma-functionalized single-walled carbon nanotubes with adsorbed butylamine
Authors: Valentini L. , Armentano I. , Mengoni F. , Puglia D. , Pennelli G. , Kenny J. M.
Published: May 2005

In this work we have developed a method to covalently attach butylamine molecules to the sidewall of single-walled carbon nanotubes (SWNTs) starting from fluorinated SWNTs (F-SWNTs) obtained by CF4 plasma treatment at room temperature. Scanning tunneling microscopy images demonstrate that after the sidewall fluorination of SWNTs some bundles with a lower number of single tubes are present. The subsequent amine functionalization of the tubes has been demonstrated by infrared spectroscopy and thermogravimetric measurements. The chemical adsorption of butylamine molecules on F-SWNTs has been also investigated by electrical transport measurements in thin-film transistor geometry. The electrical conductance of SWNTs decreases after adsorption of butylamine. The amine groups in the molecule are electron donating and the observed photoconductivity of amino-functionalized F-SWNTs is presumably due to the injection of electrons from amine groups to SWNTs.
Current-driven magnetization reversal in exchange-biased spin-valve nanopillars
Authors: Hayakawa J. , Takahashi H. , Ito K. , Fujimori M. , Heike S. , Hashizume T. , Ichimura M. , Ikeda S. , Ohno H.
Published: May 2005

We have investigated the current-driven magnetization reversal of exchange-biased spin-valve giant magnetoresistive nanopillars with a magnetically pinned ferromagnetic layer. Current-driven magnetization reversal of a ferromagnetic layer with a smaller MV (M: magnetization, V: volume) value is found to take place even when the layer is pinned by the exchange bias induced by an antiferromagnet. The critical current density Jc of the spin-valve nanopillar with a MnIr layer adjacent to the current-driven free layer is of the same order as that of a Co/Cu/Co nanopillar (∼107A∕cm2).
Spectroscopic ellipsometry characterization of nitrogen-incorporated HfO2 gate dielectrics grown by radio-frequency reactive sputtering
Authors: He G. , Zhang L. D. , Li G. H. , Liu M. , Zhu L. Q. , Pan S. S. , Fang Q.
Published: May 2005

Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2∕(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail.
Rapid ripplon spectroscopy with ms time resolution
Authors: Sakai K. , Honda H. , Hiraoka Y.
Published: May 2005

A new light scattering system for the ripplon spectroscopy with the time resolution better than 1ms was developed. Remarkably improved sensitivity to detect weakly scattered light from the thermal fluctuation in the liquid surface displacement enables the digital detection and spectrum analysis of the ripplon propagation. The dynamic adsorption process of the surfactant molecules onto the surface was observed for aqueous solutions of sodium myristic-acid and the results are interpreted in terms of the physical model of diffusion controlled molecular adsorption.
Measurement of the parallelism error of a double crystal monochromator by the pencil beam interferometer
Authors: Lim Jun , Rah Seungyu
Published: May 2005

For the precise measurement of the parallelism error between the two crystals in a double crystal monochromator, we suggest a new method that utilizes the pencil beam interferometer. The wave front-splitting pencil beam interferometer was modified, and applied to the measurement. The method overcomes the limitations of the precedent methods that using an autocollimator. Moreover, we can measure the parallelism error continuously through the full scan range with a simple setup. Especially, it should be noted that the angular sensitivity of this method is about 0.07arcsec rms.
Gaussian laser beam diameter measurement using a quadrant photodiode
Authors: Ng T. W. , Foo S. L. , Tan H. Y.
Published: May 2005

Gaussian laser beam diameters are typically measured using knife-edges or gratings. Both require precise alignment with the photodiode placed after them from the laser source. In addition, beam diameter measurement in two orthogonal axes is only possible via rotation of the knife-edge or grating. Here, we report a novel measurement method that uses a relatively inexpensive and robust quadrant photodiode to circumvent the alignment requirement as well as allow two axes laser beam diameter measurement without rotation of any component. The theoretical basis of this approach is described and experimental results using it are presented. This method portends possibilities in the design of instrumentation that integrates Gaussian laser beam diameter measurement with laser beam tracking in a compact manner using fewer components.
Advanced setup for high-pressure and low-temperature neutron diffraction at hydrostatic conditions
Authors: Lokshin Konstantin A. , Zhao Yusheng
Published: May 2005

We describe a design of the experimental setup for neutron diffraction studies at low temperatures and hydrostatic pressure. The significant benefit of the setup, compared to the previous methods, is that it makes possible the simultaneous collection of neutrons diffracted at the 30°–150° range with no contamination by the primary scattering from the sample surroundings and without cutting out the incident and diffracted beams. The suggested design is most useful for third-generation time-of-flight diffractometers and constant wavelength instruments. Application of the setup expands the capabilities of high-pressure neutron diffraction, allowing time-resolved kinetics and structural studies, multihistogram Rietveld, and pair distribution function and texture analyses. The high efficiency of the setup was proven for the HIPPO diffractometer at Los Alamos Neutron Science Center under pressures up to 10kbar and temperatures from 4to300K.
Current multiplier to improve generator-to-load coupling for pulse-power generators
Authors: Chuvatin Alexandre S. , Rudakov Leonid I. , Weber Bruce V. , Bayol Frédéric , Cadièrgues René
Published: May 2005

The load inductance, Ld, can be several times smaller than that of the pulsed power generator, L0, limiting the energy transfer efficiency. We define a relatively simple circuit modification, which improves the generator-to-load coupling, multiplying the load current in the case of interest, where L0⪢Ld. The suggested circuit modification operates similarly to an N:1 transformer and it can be designed to operate in vacuum with pulsed-power loads at high currents (many megaamperes). The current multiplier requires an additional volume having high self inductance, L, connected through convolutes to the generator and load. In its simplest configuration, N=2, a single convolute is required. The presented analysis shows that the efficiency of the proposed current multiplication scheme can theoretically exceed the values for a typical direct load-to-generator circuit. The modified hardware allows an increase of the load current by the factor of Id∕Ig=NL∕(L+Ld), where Ig represents the generator current and L can be easily made much greater than Ld either with or without the use of magnetic cores. The only uncertainties of this approach are potential convolute losses and the slight increase in load current rise time. Preliminary experimental tests were performed with a scaled down configuration which demonstrated current gain of 1.7 in the frequency range of interest and showed good agreement between analytically predicted and measured currents. The benefit of the scheme is also illustrated by simple circuit simulations for two types of potential applications requiring high power densities in vacuum: isentropic compression studies with Ld=constant loads, and imploding z-pinch research with dynamic [Ld(t)] loads. The proposed device is applicable for improving the characteristics of existing and future pulse power facilities.
Periodically poled LiNbO3: Optical parametric oscillation at wavelengths larger than 4.0μm with strong idler absorption by focused Gaussian beam
Authors: Su Hong , Qin Yi-Qiang , Guo Hong-Chen , Tang Sing-Hai
Published: May 2005

Coupled-wave equations for focused Gaussian beams in an optical superlattice are derived. By solving the coupled equations, we investigate theoretically the optimum design parameters for the middle-infrared wavelength generation under the configuration of a singly resonating optical parametric oscillation with strong idler absorption. A positive dephasing is required due to the Gouy effect for optimal idler generation. For idler wavelengths of up to 5.0μm, the threshold power can be kept at a lower level over a wider range of dephasing. Beyond this, the threshold power increases with the absorption coefficient of the idler wave. This model accurately predicts the current experimental results with weaker idler absorption. Validation with strong idler absorption is also verified.
Velocity-dependent wave forms of piezoelectric elements undergoing collisions with iron particles having velocities ranging from 5to63km∕s
Authors: Miyachi T. , Fujii M. , Hasebe N. , Kobayashi M. N. , Kuraza G. , Nagashima A. , Nakamura Y. , Nogami K. , Iwai T. , Sasaki S. , Muranaga K. , Ohashi H. , Hasegawa S. , Yano H. , Shibata H. , Grün E. , Srama R. , Okada N. , Tou T.
Published: May 2005

A response from piezoelectric lead-zirconate-titanate elements was investigated by bombarding them with hypervelocity iron particles. The observed signal form was clearly dependent on the particle velocity during collisions. The signal form exhibited oscillations for particle velocities less than 6km∕s, whereas it changed drastically into a solitary pulse above 20km∕s. This behavior was exclusively classified based on the velocity. The rise time of the solitary pulse in the output form had a good correlation with the velocity at impact. The change in the form was discussed in terms of elastic and plastic states by regarding Young’s modulus as a criterion between both states. It is proposed that a single piezoelectric element has the potential to detect the velocity of particles in space.
Double-pass acousto-optic modulator system
Authors: Donley E. A. , Heavner T. P. , Levi F. , Tataw M. O. , Jefferts S. R.
Published: May 2005

A practical problem that arises when using acousto-optic modulators (AOMs) to scan the laser frequency is the dependence of the beam diffraction angle on the modulation frequency. Alignment problems with AOM-modulated laser beams can be effectively eliminated by using the AOM in the double-pass configuration, which compensates for beam deflections. On a second pass through the AOM, the beam with its polarization rotated by 90° is deflected back such that it counterpropagates the incident laser beam and it can be separated from the input beam with a polarizing beam splitter. Here we present our design for a compact, stable, double-pass AOM with 75% double-pass diffraction efficiency and a tuning bandwidth of 68 MHz full width at half maximum for light transmitted through a single-mode fiber. The overall efficiency of the system (defined as the optical power out of the single-mode fiber divided by the optical power into the apparatus) is 60%.
Development of an ion-to-electron converter
Authors: Rachev Mikhail , Srama Ralf , Fettig Rainer , Köhler Uwe , Maas Dieter , Grün Eberhard
Published: May 2005

This article describes the design aspects of an ion-to-electron converter with a large area detector (approximately 450cm2). This converter was designed for a large area mass analyzer for the detection of cosmic dust particles. The design is based on the MM1 electron multiplier and the simulations were carried out using the software package SIMION 3D for the calculations of the electric field. Several dynode profiles were investigated in order to compare the time resolution and particle transmission. It is shown that the converter properties strongly depend on the dynode profile. Potential manufacturing processes are discussed briefly.
Electromigration effects on compound growth at interfaces
Authors: Orchard H. T. , Greer A. L.
Published: May 2005

Interfacial reactions are important in microelectronic devices and can be accelerated or decelerated by imposing a direct electric current normal to the interface. These effects are analyzed by including electromigration-driven interchange of atomic species in a conventional analysis of reaction layer thickening in a binary system controlled by interdiffusion in the layer and by an interfacial reaction barrier. New types of behavior are predicted. When the electromigration augments interdiffusion, layer growth can accelerate as the layer thickens, in contrast to the usual deceleration. When the electromigration opposes interdiffusion, there is a limiting layer thickness, inversely proportional to the applied current.
Hybrid microwave∕conventionally heated calorimeter
Authors: Binner Jon G. P. , Price Duncan M. , Reading Mike , Vaidhyanathan Bala
Published: May 2005

The design and construction of a calorimeter in which the specimen may be heated by microwave radiation and∕or hot air is described. The apparatus was used to examine the effect of microwave radiation on the melting of benzil (89°C) and the solid-state phase transition of silver iodide (147°C). Reproducibility of transition temperature determinations were within ±1°C. No changes were observed for benzil but silver iodide exhibited an apparent reduction in transition temperature to around 120°C in the presence of microwaves, which increased with the level of microwave irradiation.
Tomography for SST-1 tokamak with pixel method
Authors: Chattopadhyay Asim Kumar , Anand Arun , Rao C. V. S.
Published: May 2005

A soft x-ray tomography code by pixel method has been prepared and tested with simulated data for the five array and seven array system of the SST-1 tokamak. A relatively small number of detectors have been used to obtain a partial view of the highly noncircular plasma in a poloidal plane produced in a machine of limited access like SST-1 by optimizing the pixel size and array positions. Tomographic inversions are done using linear regularization, minimum Fisher information and maximum entropy methods. Singular value decomposition method has been used for the identification of magnetohydrodynamic modes by analyzing inversion results.
Effects of applying stress on the electron field emission properties in amorphous carbon thin films
Authors: Poa C. H. P. , Silva S. R. P. , Lacerda R. G. , Amaratunga G. A. J. , Milne W. I. , Marques F. C.
Published: May 2005

Diamond-like carbon (DLC) films have always had high intrinsic stress due to their metastable structure and the fine balance between film density and bond stability. We show the effects of high intrinsic stress on the electron field emission performance, where a lower electric field for emission is recorded with increasing stress in the DLC films. In addition to examining “as deposited” films with different magnitudes of intrinsic stress, we subject the DLC films to external pressure by physically bending the a-C∕silicon substrates. The result is a phenomenon where electrons are “squeezed” out of the films, and can be applied to the fabrication of stress sensors.
Conductivity measurements of individual poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) nanowires on nanoelectrodes using manipulation with an atomic force microscope
Authors: Samitsu Sadaki , Shimomura Takeshi , Ito Kohzo , Fujimori Masaaki , Heike Seiji , Hashizume Tomihiro
Published: May 2005

We have prepared conducting polymer nanowires of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) with diameters under 10 nm by a molecular combing method, and have measured the conductivity of the individual PEDOT nanowires on platinum nanoelectrodes using manipulation with an atomic force microscope (AFM). The temperature dependence of the conductance was explained well by a quasi-one-dimensional variable range hopping model. The conductivity of two single nanowires was determined to be 0.6 and 0.09S∕cm, which is of the same order as that of PEDOT/PSS films. After all the nanowires crossed over the nanoelectrodes were cut off with AFM manipulation, the current was drastically decreased down to the background level. These results directly indicate that the conductivity was derived from the PEDOT nanowires on the nanoelectrodes.
Heating-compensated constant-temperature tunneling measurements on stacks of Bi2Sr2CaCu2O8+x intrinsic junctions
Authors: Bae Myung-Ho , Choi Jae-Hyun , Lee Hu-Jong
Published: May 2005

In highly anisotropic layered cuprates such as Bi2Sr2CaCu2O8+x tunneling measurements on a stack of intrinsic junctions (IJs) in a high-bias range are often susceptible to self-heating. In this study we monitored the temperature variation of a stack (“sample stack”) of IJs by measuring the resistance change of a nearby stack of IJs, which was strongly thermal coupled to the sample stack. We then adopted a proportional-integral-derivative scheme incorporated with a substrate-holder heater to compensate the temperature variation. This in situ temperature monitoring and controlling technique allows one to get rid of spurious tunneling effects arising from the self-heating.