bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles
Authors: Eastman J. A. , Choi S. U. S. , Li S. , Yu W. , Thompson L. J.
Published: July 2002

It is shown that a “nanofluid” consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure ethylene glycol or ethylene glycol containing the same volume fraction of dispersed oxide nanoparticles. The effective thermal conductivity of ethylene glycol is shown to be increased by up to 40% for a nanofluid consisting of ethylene glycol containing approximately 0.3 vol % Cu nanoparticles of mean diameter <10 nm. The results are anomalous based on previous theoretical calculations that had predicted a strong effect of particle shape on effective nanofluid thermal conductivity, but no effect of either particle size or particle thermal conductivity.
Laser-triggered ion acceleration and table top isotope production
Authors: Nemoto K. , Maksimchuk A. , Banerjee S. , Flippo K. , Mourou G. , Umstadter D. , Bychenkov V. Yu.
Published: July 2002

We have observed deuterons accelerated to energies of about 2 MeV in the interaction of relativistically intense 10 TW, 400 fs laser pulse with a thin layer of deuterated polystyrene deposited on Mylar film. These high-energy deuterons were directed to the boron sample, where they produced ∼105 atoms of positron active isotope C11 from the reaction B10(d,n)11C. The activation results suggest that deuterons were accelerated from the front surface of the target.
Phase-coherent light scattering spectroscopy. I. General principle and polarized dynamic light scattering
Authors: Tanaka Hajime , Takagi Shinsaku
Published: July 2002

Conventional light scattering methods measure light scattered by spontaneously excited fluctuations and provide its power spectrum. Since modes are thermally excited, their phases are random and do not have any physical meaning. Different from the basic principle of these conventional methods, we recently proposed a new method of light scattering providing “complex” spectra instead of power spectra. We call this new method the “(phase-)coherent light scattering method.” It is based on a new measurement principle: Coherent modes having phase information are generated resonantly by an optically induced scanning interference pattern. By a phase-sensitive detection of the light scattered by the optically generated coherent modes, complex resonance spectra of these modes can be measured. This principle is applicable to any modes in condensed matter, including thermal and concentration diffusion modes, rotational modes, propagating sound modes (longitudinal and transverse phonons), and surface modes (ripplons and Rayleigh waves). Here we present the basic principle of our new method and the theoretical background of polarized dynamic light scattering.
Pump-probe thermal lens near-infrared spectroscopy and Z-scan study of zinc (tris) thiourea sulfate
Authors: Gupte Sonal S. , Marcano O. A. , Pradhan Ranjit D. , Desai C. F. , Melikechi Noureddine
Published: July 2002

We demonstrate a novel use of the pump-probe thermal lens spectroscopy and Z-scan techniques for the measurement of the small absorption coefficient in a semiorganic, nonlinear optical crystal zinc (tris) thiourea sulphate. We measure the absorption spectrum and the absolute values of the absorption of the crystal in the near-infrared region (700–980 nm). A maximum absorption coefficient of ∼0.04 cm-1 is reported.
Gain mechanism in GaN Schottky ultraviolet detectors
Authors: Katz O. , Garber V. , Meyler B. , Bahir G. , Salzman J.
Published: July 2002

Schottky barrier GaN ultraviolet detectors, both in vertical and in lateral configuration, as well as in a metal–semiconductor–metal geometry were implemented. All devices exhibit a high gain at both reverse and forward bias. The photoresponse in the forward bias is in the positive current direction. We attribute the gain to trapping of minority carriers at the semiconductor–metal interface. The excellent agreement between the calculated responsivity and the experiment indicates that the model is valid for all device structures under study, and represents a unified description of gain mechanism in GaN Schottky detectors.
Fourier transform microwave spectroscopy of the Σ+2 ground states of YbX (X=F, Cl, Br): Characterization of hyperfine effects and determination of the molecular geometries
Authors: Dickinson C. S. , Coxon J. A. , Walker N. R. , Gerry M. C. L.
Published: July 2002

The pure rotational spectra of low lying v=0 and 1 vibrational levels of the Σ+2 ground states of several isotopomers of YbF, YbCl, and YbBr were recorded using a pulsed jet cavity Fourier transform microwave spectrometer. Through least squares fits, parameters describing rotational, fine, and hyperfine effects (such as Fermi-contact, dipole–dipole coupling, and nuclear spin-rotation coupling) are presented. Trends in this halide series show an increasing amount of unpaired spin-density on the halide nucleus with increasing halide atomic number, which is consistent with results obtained in previous studies of the calcium analogs. Effective equilibrium bond lengths for 174YbF and 174Yb35Cl have been determined to be 2.016 514(1) Å and 2.488 285(1) Å, respectively. The spectra of the two major bromine isotopomers, 79Yb174Br and 81Yb174Br, were studied only in the v=0 level, and the derived values of r0 are 2.647 364 5(2) Å and 2.647 347 6(2) Å, respectively. The uncertainties in the equilibrium bond lengths of YbF and YbCl are discussed in terms of the measurement accuracies of the spectra and of the Born–Oppenheimer approximation.
Stability of return thermocapillary flows under gravity modulation
Authors: Suresh V. , Homsy G. M.
Published: July 2002

The effect of gravity modulation on the stability of a time-harmonic parallel flow in a slot geometry is studied. A constant temperature gradient applied along the length of a slot with a flat free interface at the top drives a steady thermocapillary return flow. A vertical time-harmonic gravity modulation drives a time-periodic buoyant return flow. The relative strength of the two components is characterized by the Marangoni number Ma and the Rayleigh number Ra, respectively. There is potential for Rayleigh–Bénard, shear, and hydrothermal wave instabilities. The linear stability for two-dimensional rolls is studied and the stability boundaries are obtained by Floquet theory. Stability diagrams in the Ra–Ma plane are obtained for fixed modulation frequency and various Prandtl numbers and a disturbance kinetic-energy analysis is used to determine the instability mechanism. Buoyant and hydrothermal instabilities are found at small Ma and small Ra, respectively, whereas shear instabilities are found not to be important in the parameter regime studied. The two active mechanisms are found to either reinforce or oppose each other in different parameter regimes. This leads to regions of stability in the Ra–Ma plane where flows are stable due to the combined effect of buoyancy and thermocapillarity whereas a purely buoyant or a purely thermocapillary flow at the same Ra or Ma would be unstable. These results are contrasted with those obtained by Nield [J. Fluid Mech. 19, 341 (1964)] in the case of steady gravity, for which thermocapillarity and buoyancy reinforce each other.
Nearly 100% internal phosphorescence efficiency in an organic light-emitting device
Authors: Adachi Chihaya , Baldo Marc A. , Thompson Mark E. , Forrest Stephen R.
Published: July 2002

We demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy)2Ir(acac)] doped into 3-phenyl-4(1′-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0±1.0)% and luminous power efficiency of (60±5) lm/W are achieved. The calculated internal quantum efficiency of (87±7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of (ppy)2Ir(acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)2Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer.
Accurate quantum dynamics of electronically nonadiabatic chemical reactions in the DH2+ system
Authors: Kamisaka Hideyuki , Bian Wensheng , Nobusada Katsuyuki , Nakamura Hiroki
Published: July 2002

Three-dimensional accurate quantum dynamics calculations are carried out for the DH2+ system for J=0 (J, total angular momentum quantum number) by the hyperspherical coordinate approach with use of the new potential energy surfaces constructed based on the recent ab initio quantum chemical calculations. Not only electronically nonadiabatic reactions, i.e., reactive charge transfer processes, but also electronically adiabatic reactions and electronically nonadiabatic nonreactive processes are investigated. Because of the deep well on the electronically adiabatic ground surface, there appear a large number of resonances and the electronically adiabatic reactions are mostly statistical. Nonadiabatic transitions along the potential crossing seam cause deviations from the statistical behavior and some interesting dynamical features are found.
Role of Ga flux in dislocation reduction in GaN films grown on SiC(0001)
Authors: Lee C. D. , Sagar Ashutosh , Feenstra R. M. , Inoki C. K. , Kuan T. S. , Sarney W. L. , Salamanca-Riba L.
Published: July 2002

GaN films are grown by plasma-assisted molecular-beam epitaxy on SiC substrates. The width of the x-ray rocking curve for the (101̄2) reflection exhibits a distinct minimum for Ga/N flux ratios which are only slightly greater than unity. Correlated with this minimum, the surface morphology is somewhat rough, with a hill and valley topography. Based on transmission electron micrographs, the reduction in rocking curve width is attributed to enhanced annihilation of edge dislocations due to their tendency to cluster at topographic valleys.
Development of transferable interaction models for water. II. Accurate energetics of the first few water clusters from first principles
Authors: Xantheas Sotiris S. , Burnham Christian J. , Harrison Robert J.
Published: July 2002

We report accurate energetics for the water trimer through pentamer global ring minima and four low-lying hexamer isomers (cage, prism, book, cyclic S6) from first principles electronic structure calculations. The family of augmented correlation-consistent orbital basis sets of double through quintuple zeta quality was used in order to estimate complete basis set (CBS) limits for the cluster total association energies at the second order perturbation (MP2) level of theory. These are −15.8 kcal/mol (trimer), −27.6 kcal/mol (tetramer), −36.3 kcal/mol (pentamer), −45.9 kcal/mol (prism hexamer), −45.8 kcal/mol (cage hexamer), −45.6 kcal/mol (book hexamer), and −44.8 kcal/mol (ring S6 hexamer). Effects of higher correlation, estimated at the coupled cluster plus single and double with a perturbative estimate of the triple excitations [CCSD(T)] level of theory, as well as inclusion of estimates for core–valence correlation suggest that these estimates are accurate to within 0.2 kcal/mol.
Empirical correction to density functional theory for van der Waals interactions
Authors: Wu Qin , Yang Weitao
Published: July 2002

An empirical method has been designed to account for the van der Waals interactions in practical molecular calculations with density functional theory. For each atom pair separated at a distance R, the method adds to the density functional electronic structure calculations an additional attraction energy EvdW=−fd(R)C6R−6, where fd(R) is the damping function which equals to one at large value of R and zero at small value of R. The coefficients C6 for pair interactions between hydrogen, carbon, nitrogen, and oxygen atoms have been developed in this work by a least-square fitting to the molecular C6 coefficients obtained from the dipole oscillator strength distribution method by Meath and co-workers. Two forms of the damping functions have been studied, with one dropping to zero at short distances much faster than the other. Four density functionals have been examined: Becke’s three parameter hybrid functional with the Lee-Yang-Parr correlation functional, Becke’s 1988 exchange functional with the LYP correlation functional, Becke’s 1988 exchange functional with Perdew and Wang’s 1991 (PW91) correlation functional, and PW91 exchange and correlation functional. The method has been applied to three systems where the van der Waals attractions are known to be important: rare-gas diatomic molecules, stacking of base pairs and polyalanines’ conformation stabilities. The results show that this empirical method, with the damping function dropping to zero smoothly, provides a significant correction to both of the Becke’s hybrid functional and the PW91 exchange and correlation functional. Results are comparable to the corresponding second-order Møller-Plesset calculations in many cases.
Fast x-ray scattering measurements on molten alumina using a 120° curved position sensitive detector
Authors: Hennet Louis , Thiaudière Dominique , Gailhanou Marc , Landron Claude , Coutures Jean-Pierre , Price David L.
Published: July 2002

Fast x-ray scattering measurements on molten alumina were performed on the H10 beam line at the DCI Synchrotron of LURE (Orsay, France). A high-temperature chamber with a levitation device was coupled with the four-circle goniometer of the beam line. A 100 W CO2 laser was used to melt the sample and the temperature was measured using an optical pyrometer operating at 0.85 μm. Usually, measurements of the total structure factor S(Q) on molten materials are performed using a fixed detector scanned over an angular range. In this work, in order to reduce the total scan duration, x-ray scattered intensities were measured with a 120° position sensitive detector (INEL CPS120). We performed several measurements with different acquisition times varying from 10 s to 5 min. In 5 min it was possible to obtain a good determination of S(Q) with a usable signal up to the Q range limit (13 Å−1). The intensity was comparable with a 1 h measurement with a NaI (Tl) scintillator scanned over the 120° 2θ range. On reducing the counting time the statistics are degraded and the data are noisier, especially in the high Q region. Nevertheless, even with 10 s, the S(Q) data remain usable and give good results. Performing the Fourier transformation of S(Q), we obtain similar reliable pair-correlation functions with both 5 min and 10 s acquisition times.
Efficient organic light-emitting diodes with undoped active layers based on silole derivatives
Authors: Murata Hideyuki , Kafafi Zakya H. , Uchida Manabu
Published: July 2002

We report on efficient molecular organic light-emitting diodes (MOLEDs) composed of novel silole derivatives as an electron transporting layer and an emissive layer. The silole derivative, 2,5-bis(2′,2″-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene, used for the electron transport layer exhibits fast electron mobility of 2×10−4 cm2/V s at 0.64 MV/cm measured by the time-of-flight technique. Another silole derivative, 1,2-bis(1-methyl-2,3,4,5-tetraphenyl silacyclopentadienyl)ethane, used for an emissive layer exhibits blue-green fluorescence with an absolute quantum yield of 97±3% in the solid state. The devices using silole derivatives show a very low operating voltage, an external electroluminescence quantum efficiency (ηEL) of 4.8 %, and luminous power efficiency of 9 lm/W at a brightness of 100 cd/m2. This value of ηEL is the best efficiency achieved for MOLED using undoped emissive and carrier transport layers and is close to the theoretical limit for a device using a fluorescent emitter.
Dip-coated films of volatile liquids
Authors: Qu Dan , Ramé Enrique , Garoff Stephen
Published: July 2002

We examine experimentally the hydrodynamics of dip-coated, finite-length films of evaporative fluids, from the film tip through the film body all the way to the connection with the main meniscus. The characteristic film thickness has a power-law dependence on the withdrawing speed similar to that for the thickness of “infinite” films formed by nonvolatile liquids. The film length and cross-sectional area have power-law dependence on the withdrawing speed as well, but the prefactors of the power laws are controlled by the evaporation rate of the fluid. These power laws are consistent with the global mass balance over the film between mass lost by evaporation and mass input by the solid motion. We have also found that the apparent contact angle and the curvature at the film tip both have power-law dependencies on the withdrawing speed that are consistent with those found for the length and the film thickness. Film shape measurements near the film tip reach thicknesses ∼100 Å from the solid; but we did not detect any influence of the inner scale hydrodynamics and van der Waals forces on this shape. We have developed a systematic method for measuring the contributions of gravity, capillary force, viscous force, and vapor recoil on the pressure and flow fields in the film. This exercise reveals detailed information about the flow in evaporative films. The combined effects of evaporation and Marangoni flow on the hydrodynamics are deduced from experimental data, independent of evaporation models.
X-ray beam induced current—a synchrotron radiation based technique for the in situ analysis of recombination properties and chemical nature of metal clusters in silicon
Authors: Vyvenko O. F. , Buonassisi T. , Istratov A. A. , Hieslmair H. , Thompson A. C. , Schindler R. , Weber E. R.
Published: July 2002

A synchrotron radiation based x-ray microprobe analytical technique, x-ray beam induced current (XBIC), is suggested and demonstrated at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The principle of XBIC is similar to that of electron/laser beam induced current with the difference that minority carriers are generated by a focused x-ray beam. XBIC can be combined with any other x-ray microprobe tool, such as the x-ray fluorescence microprobe (μ-XRF), to complement chemical information with data on the recombination activity of impurities and defects. Since the XBIC signal, which carries information about the recombination activity of defects in the sample, and the μ-XRF signal, which contains data on their chemical nature, can be collected simultaneously, this combination offers a unique analytical capability of in situ analysis of the recombination activity of defects and their chemical origin with a high sensitivity and a micron-scale spatial resolution. Examples of an application of this technique to multicrystalline silicon for solar cells are demonstrated.
Correlations between morphology, phase behavior and pair interaction in soft sphere solids
Authors: Liu Jianing , Schöpe Hans Joachim , Palberg Thomas
Published: July 2002

Depending on surface charge Z*, particle radius a, particle number density n, and salt concentration c, aqueous suspensions of charge-stabilized colloidal spheres show a plentiful morphology correlated with both phase behavior and pair interaction. We here use a combination of light scattering and Bragg microscopy to study the solidification process and the resulting crystals for several monodisperse latex samples. We compare the results to predictions of the melting transition in terms of a reduced pair interaction energy and a coupling parameter. Both quantities were systematically computed in dependence on Z*, a, n, and c. For increasing particle number density the crystalline phase is found less stable than predicted. More importantly, transitions from tooth-like to sheet-like morphology and from dominance of heterogeneous wall nucleation to dominance of homogeneous bulk nucleation run parallel to the experimental phase boundary.
Shape effects in plasmon resonance of individual colloidal silver nanoparticles
Authors: Mock J. J. , Barbic M. , Smith D. R. , Schultz D. A. , Schultz S.
Published: July 2002

We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources covering the full range of wavelengths in the visible spectrum.
Density-functional theory of the columnar phase of discotic Gay–Berne molecules
Authors: Coussaert Tamara , Baus Marc
Published: July 2002

We propose a density-functional theory for the study of the phase behavior of discotic molecules interacting via a Gay–Berne potential. The attractions are treated perturbatively in a van der Waals-type manner while the virial series of the repulsions is resummed approximately with the inclusion of the exact second-order Onsager result. On this basis we have studied the isotropic (I)–nematic (N)–columnar (Co) phase behavior for various aspect ratios of the discotic molecules. For small aspect ratios (i.e., large nonsphericities) the phase diagram is found to involve a I–N–Co triple point where the two I–N and N–Co first-order transitions are transformed into a direct I–Co first-order transition. For larger aspect ratios the domain where the N-phase is stable shrinks and disappears above a critical value of the aspect ratio. When compared to the available simulation data it is found that the theory underestimates this critical aspect ratio.
Micromachined droplet ejector arrays for controlled ink-jet printing and deposition
Authors: Perçin Gökhan , Khuri-Yakub Butrus T.
Published: July 2002

In this article, we present a variation on the design of the micromachined flextensional transducer for use to eject liquids. The transducer is constructed by depositing a piezoelectric thin film to a thin, edge clamped, circular annular plate. By placing a fluid behind one face of a vibrating compound plate that has an orifice at its center, we achieve continuous or drop-on-demand ejection of the fluid. We present results of ejection of water and isopropanol. The ejector is harmless to sensitive fluids and can be used to eject fuels, organic polymers, low-k dielectrics, chemical, and biological samples. Micromachined two-dimensional array piezoelectrically actuated flextensional droplet ejectors were realized using planar silicon micromachining techniques. Typical resonant frequency of the micromachined device ranges from 400 kHz to 4.5 MHz. The ejection of water through a 5 μm diameter orifice at 3.5 MHz was demonstrated by using the developed micromachined two-dimensional array ejectors.
Domain structures in KNbO3 crystals and their piezoelectric properties
Authors: Nakamura Kiyoshi , Tokiwa Tsuyoshi , Kawamura Yoshiko
Published: July 2002

The electromechanical coupling factor for the thickness-extensional mode, kt, in KNbO3 crystals has been predicted to be as high as 69% for the 49.5° rotated X-cut about the Y-axis, which is the highest among known piezoelectrics. This paper presents the experimental confirmation of the high coupling factor and elucidates the relationship between the domain structure and the piezoelectric properties in the pseudocubic (001)pc cut, which is close to the maximum kt cut and has a piezoelectric strain constant about 2.9 times that of the Z-cut. Etching of crystals is found to have an outstanding effect on the piezoelectric characteristics. That is, in the case of “as-cut” crystals, the strain versus electric field curves have a large hysteresis and instability due to the occurrence of 60° domains in a high electric field region, whereas etched crystals remain the single domain state and exhibit linear piezoelectric properties even in the high electric field region. It is also demonstrated that the (001)pc cut crystal poled along the 〈001〉pc direction has a polar multidomain structure composed of two kinds of 90° domains, not four kinds of equivalent domains, and that it exhibits almost the same piezoelectric properties as those of single-domain crystals.
Detecting noise in a time series
Authors: Cellucci C. J. , Albano A. M. , Rapp P. E. , Pittenger R. A. , Josiassen R. C.
Published: July 2002

A numerical algorithm is presented for estimating whether, and roughly to what extent, a time series is noise corrupted. Using phase-randomized surrogates constructed from the original signal, metrics are defined which can be used to quantify the noise level. A saturation occurs in these metrics at signal to noise ratios (SNRs) of around 0 dB and below, and also at around 20 dB and above. In between these two regions there is a monotonic transition in the value of the metrics from one region to the other corresponding to changes in the SNR.
The TRIMM parallel processor
Authors: Shoemaker R. L. , Barrett H. H. , Landesman A. , Seacat III R. H. , Taylor B. B.
Published: July 2002

A high-performance parallel processor utilizing 60 Inmos T800 transputers and 60 Mbytes of memory has been designed and constructed. Intended especially for applications in nuclear medicine imaging, the system has several unique features, including a global broadcast address mode via a VME bus interface and nonalgorithmic generation of random numbers in hardware. Initial performance tests demonstrate near-linear speedup for image reconstructions using the simulated annealing algorithm, and a processing speed that is over 60 times that of a VAX 8600.
PANACEA: A model for numerical simulation codes
Authors: Brown Stewart A.
Published: July 2002

An analysis of numerical simulation codes from an abstract point of view suggests some structure common to most if not all codes. PANACEA, a practical application of such an analysis, constitutes a significant tool to facilitate building portable, efficient simulation codes with sharable modules and to provide built-in support for problem generation and visualization of simulation results.
Versatile CAMAC–PC/AT system for data acquisition and control in high-resolution extreme-ultraviolet (EUV) spectroscopy following ion–atom and ion–molecule collisions
Authors: Liu G. , Fuelling S. , Bruch R.
Published: July 2002

This work is related to a recent development of a data acquisition and control system for high-resolution EUV spectroscopy following ion–atom and ion–molecule collisions. The system consists of a personal computer, an IEEE-488 interface board, and a CAMAC system, which includes a GPIB crate controller, a stepping motor controller, and two 32-bit up–down counters. A unique software ‘‘DATACQ’’ for data acquisition and control has been designed and tested to simplify complex spectroscopy applications. As a prototype case, EUV spectra of the Lyman series of He+ following simultaneous ionization and excitation of He by fast H+, H+2, and H+3 impact are presented here.
A massively parallel implementation of the worldline quantum Monte Carlo method
Authors: Somsky W. R. , Gubernatis J. E.
Published: July 2002

The worldline quantum Monte Carlo method is a computational technique for studying the properties of many-electron and quantum-spin systems. In this paper, our efforts in developing an efficient implementation of this method for the massively parallel Connection Machine CM-2 are described. Why one must look beyond the obvious parallelism in the method in order to reduce interprocessor communication and increase processor utilization, and how these goals may be achieved using a plaquette-based data representation are discussed. Performance statistics for the implementation and sample calculations for the spinless fermion model are also presented.
A parallel special-purpose computer dedicated to the simulation of interacting particle systems
Authors: Danese G. , De Lotto I. , Dotti D. , Leporati F.
Published: July 2002

A parallel special-purpose computer for computational physics is presented. It works as an interactive desktop system with a user-friendly interface; its performance is comparable to that of a supercomputer. Its rationale, system hardware, software architecture, and performance are described by presenting a Monte Carlo-Metropolis simulation of an interacting particle system. © 1997 American Institute of Physics.
Discrete variable method for nonintegrable quantum systems
Authors: Schweizer W. , Fassbinder P.
Published: July 2002

We present an effective numerical algorithm based on discrete variable techniques combined with finite elements for solving the non-separable three-dimensional Schrödinger equation. As an example we study the hydrogen atom in strong external magnetic and electric fields, a doorway system in the quest of quantum chaology and for studying atomic properties relevant for astrophysical questions. © 1997 American Institute of Physics.
A tensorial approach to computational continuum mechanics using object-oriented techniques
Authors: Weller H. G. , Tabor G. , Jasak H. , Fureby C.
Published: July 2002

In this article the principles of the field operation and manipulation (FOAM) C++ class library for continuum mechanics are outlined. Our intention is to make it as easy as possible to develop reliable and efficient computational continuum-mechanics codes: this is achieved by making the top-level syntax of the code as close as possible to conventional mathematical notation for tensors and partial differential equations. Object-orientation techniques enable the creation of data types that closely mimic those of continuum mechanics, and the operator overloading possible in C++ allows normal mathematical symbols to be used for the basic operations. As an example, the implementation of various types of turbulence modeling in a FOAM computational-fluid-dynamics code is discussed, and calculations performed on a standard test case, that of flow around a square prism, are presented. To demonstrate the flexibility of the FOAM library, codes for solving structures and magnetohydrodynamics are also presented with appropriate test case results given. © 1998 American Institute of Physics.
Waveguide mode conversion by magnetic linear birefringence of Bi-substituted iron garnet films tilted from (111)
Authors: Ando Koji , Takeda Norio , Okuda Takashi , Koshizuka Naoki
Published: July 2002

TE-TM mode conversion caused by magnetic linear birefringence (MLB) has been studied in liquid-phase-epitaxially grown (BiGdLu)3 (FeGa)5O12 films. The films were grown on Gd3Ga5O12 substrates of which the face normal is tilted from the (111) axis by the angle θc. The LPE growth on the substrate with θc ≠0 made the magnetization of the film tilt from the film normal, and this enabled the mode converter to work without any applied external field. The theory developed to describe the function of the mode converter agreed well with the experimental results. The MLB coefficient is about −9 rad/cm at a wavelength λ=1.15 μm. The Bi substitution is effective to enhance the MLB effect. A role of the MLB mode converter to realize a simple and compact waveguide optical isolator is discussed.
Compositional and electrical analysis of the multilayers of a CdS/CuInSe2 solar cell
Authors: Noufi Rommel , Dick John
Published: July 2002

The compositional profiles and the electrical properties of the bilayers of CdS and CuInSe2 films in CdS/CuInSe2 solar cells are presented and compared with those of the individual layers alone. The CuInSe2 bilayer shows that the two individual layers have mixed, except for the last-to-deposit 0.2–0.4 μm, which is semi-insulating and copper poor. This bilayer remains p type and highly resistive during the cell processing steps. The CdS bilayer consists of an almost stoichiometric layer close to the junction and a top In-doped low-resistivity layer. The CdS/CuInSe2 may possibly operate as a P-S-N device, where the S layer is defined largely by a semi-insulating CuInSe2 layer.
A study on the effect of dislocation on the magnetic properties of nickel using magnetic NDE methods
Authors: Ranjan R. , Buck O. , Thompson R. B.
Published: July 2002

Dislocations affect the magnetic properties of ferromagnetic materials by pinning the domain walls. The primary mechanism is interaction between the stress fields of dislocation and domain walls. Using magnetic nondestructive methods, namely the acoustic Barkhausen noise (AB), magnetic Barkhausen noise (MB), and the hysteresis curves, we have studied these interactions. The three measurements give different types of information. AB provides information about non-180° type domain wall interaction, MB primarily provides information about 180° domain wall interaction, and the hysteresis curve about both these interactions as well as about rotation of domain walls. The paper presents results obtained on polycrystalline nickel which was first deformed and then annealed at different temperatures in order to achieve different dislocation densities. The results show that AB and hysteresis loss follow the same trend as hardness. MB results, however, change in a more complex fashion which is sensitive to grain recrystallization as well as dislocation structure. Interesting features of these results will be discussed in detail.
Growth of GaAs on SiOx by molecular-beam epitaxy
Authors: Chin Albert , Bhattacharya Pallab K. , Kothiyal G. P.
Published: July 2002

We have investigated the molecular-beam epitaxial growth and photoluminescence properties of GaAs on SiOx. It is seen that material with a grain size of 0.6–0.8 μm can be grown directly on the dielectric. The properties improve further when the layers are short-term annealed with a halogen lamp. Optimum grain sizes of 1.6 μm are obtained when the as-grown material is annealed at 950 °C for 10 s, and very strong luminescence is observed in the same material. Photoconductive detectors made on the overgrown GaAs show large responsivities.
Theoretical investigation of superfluorescent emission from an optically pumped CF4 gas column
Authors: Sinha Sucharita
Published: July 2002

A theoretical study of the superfluorescent emission from an optically pumped CF4 gas column is reported. We have estimated the dependence of the superfluorescent pulse energy on the various operating parameters, such as temperature, pressure, pump rate, and the extent of frequency detuning between the pump radiation and the pumped CF4 transition. The calculated temperature dependence of the superfluorescent pulse energy confirms that at any given pressure, the highest output energy would be achieved at the lowest possible temperature determined by the vapor pressure of the CF4 gas. Our estimate for the dependence of the superfluorescent pulse energy on the temporal profile of the CO2 pump pulse indicates the significance of the narrow gain switched spike over the flat tail of the CO2 pump pulse for efficient pumping of the CF4 molecules. We have also estimated the superfluorescent pulse energy in the double-pass configuration and compared it with that for the single-pass configuration.
High-pressure measurements at moderate temperatures in a diamond anvil cell with a new optical sensor: SrB4O7:Sm2+
Authors: Lacam A. , Chateau C.
Published: July 2002

The 0.255 Å/kbar linear pressure shift of the intense, narrow, and well-isolated 5D0-7F0 (named 0-0) emission line of SrB4O7:Sm2+ (at 6854.1 Å in ambient conditions) is proposed as a new optical pressure gauge for the diamond anvil cell. The pressure determinations can be made with the same experimental devices as those currently used for the ruby sensor. The good accuracy results from the singlet character and a small linewidth which is no more than 2.5 Å up to 200 kbar in a 4:1 methanol:ethanol mixture, provided the linewidth is ‘‘relaxed’’ through thermal cycles. Such a process can probably be of general interest for this purpose. In nonisostatic media, a similar pressure coefficient and a broadening of ∼0.1 Å/kbar are obtained. This broadening does not greatly disturb the pressure measurements, at least up to 200 kbar. High-pressure determinations up to 400 °C are also shown to be more accurate than with the ruby, owing to the very limited temperature effect on the wavelength (−0.001 Å/°C) and linewidth (∼0.005 Å/°C) of the 0-0 line. The other characteristics of the emission spectrum of SrB4O7:Sm2+ are promising for (a) simultaneous measurements of pressure and temperature (at least up to 400 °C) using this same material and (b) further research on other rare-earth-doped compounds. The possibility of pressure coefficients larger than that of the R1 ruby line is shown by the 0.45 Å/kbar value measured for another emission line of SrB4O7:Sm2+.
The dielectric function of AlSb from 1.4 to 5.8 eV determined by spectroscopic ellipsometry
Authors: Zollner Stefan , Lin Chengtian , Schönherr Erich , Böhringer Alexandra , Cardona Manuel
Published: July 2002

We have prepared AlSb substrates for optical measurements by chemomechanical polishing and etching. The quality of the surface was investigated with optical and electron microscopy and by Raman scattering and ellipsometry. We have measured the pseudodielectric function 〈ε〉(ω) of AlSb in the 1.4–5.8 eV photon-energy region with a spectroscopic ellipsometer. A peak value of 〈ε2〉=24.6 at 4 eV was reached. We list the refractive index, the reflectivity, and the absorption coefficient, and obtain the critical point parameters at 300 K. Finally, we fit the index of refraction of AlSb at low photon energies with a semiempirical model.
Liquid metal ion sources: The shape and size of the ion emitting area
Authors: Cho Guang-Sup , Seo Yoonho , Kang Seung-Oun
Published: July 2002

Using the potential profile around the cone-shaped protrusion at the end of the Taylor cone of the liquid metal ion sources, we investigate the shape and size of the ion emitting region and the ion formation mechanisms analytically. We find that the field evaporation is the main current-generating mechanism. Contribution of the field ionization mechanism is around 0.01 μA, independent of the applied voltage. The ion emitting area is usually confined within a few tens of angstroms from the protrusion apex. The most important parameter that determines the emission current is found to be the apex angle of the protrusion cone. The apex angle near the ignition voltage is close to the Taylor angle. At this voltage, the ions are emitted from the very vicinity of the cone apex. Above the ignition voltage, a sharp protrusion cone develops of which the apex angle decreases as the applied voltage increases. In other words, sharpness of the cone apex is the measure of the field strength responsible for the field evaporation. At currents about 10 μA, the apex half angle becomes about 36°, and the ion emitting region expands to about 20 Å from the apex. At currents above 100 μA, the apex half angle reduces to less than 28°, and the emission region is still confined within 100 Å from the apex. These results are found to be well-fitted to the previously reported microscope pictures taken by G. Benassayag [Ultramicroscopy 16, 1 (1985)].
Microfabrication of three-dimensional boron structures by laser chemical processing
Authors: Johansson Stefan , Schweitz Jan-Åke , Westberg Helena , Boman Mats
Published: July 2002

A method for microfabrication of three-dimensional structures in free space is presented. Laser-assisted chemical vapor deposition is used to grow a material at a point where a laser beam locally heats the substrate. By moving the substrate relative to the laser beam with a micropositioning system, three-dimensional shapes can be created. Helical shapes are generated utilizing three linear translational axes as well as an additional rotational axis. Tilting the substrate to align the growth direction with the laser beam direction facilitates improved process control. The smallest structures that can be grown with this technique are about 1 μm. Amorphous boron fibers and crystalline boron springs have been manufactured as two examples of micromechanical elements. The amorphous boron fibers show excellent mechanical properties: A modulus of elasticity of 420–450 GPa, a fracture strain of 2.7%–3.7%, and a fracture stress of 12–17 GPa. The crystalline boron springs produced so far display only moderate mechanical characteristics. This is because of the irregular fiber surface with protruding grains and amorphous nodules. Nevertheless, a maximum relative resilience of about 9% for a tightly wound spring has been obtained. The crystal structure of the grains examined show a fair agreement with the β-boron phase, even though distinct deviations are observed. Metastable arrangement of the B12 icosahedral units is suggested as a possible explanation. A high density of (100) twins and stacking faults are identified by transmission electron microscopy. By further process and system development it is believed that micromechanical details can be tailored more or less arbitrarily for different applications.
Viscosity and elastic constants of amorphous Si and Ge
Authors: Witvrouw Ann , Spaepen Frans
Published: July 2002

The biaxial modulus and coefficient of thermal expansion of ion-beam-sputtered amorphous Si and Ge thin films were determined from curvature changes induced by differential thermal expansion. Viscous flow was measured by stress relaxation and was found to be Newtonian. The viscosity increased linearly with time as a result of structural relaxation, and its isoconfigurational activation enthalpy was 1.8±0.3 and 2.6±1.3 eV for amorphous Si and Ge, respectively. An atomistic model, based on a chain reaction of broken bond rearrangements, is proposed to describe the observation.
Gold nanoparticles ion implanted in glass with enhanced nonlinear optical properties
Authors: Fukumi Kohei , Chayahara Akiyoshi , Kadono Kohei , Sakaguchi Toru , Horino Yuji , Miya Masaru , Fujii Kanenaga , Hayakawa Junji , Satou Mamoru
Published: July 2002

Silica glass with dispersed colloid Au particles was synthesized by ion implantation. Colloid Au particles were found to grow through an Ostwald ripening mechanism controlled by diffusion in the silica glass. The third-order nonlinear optical susceptibility χ(3) of this glass was found to be proportional to the fourth power of the radius of the colloid particles or the fourth power of the absorption coefficient at the peak of a plasmon band when the total volume of the colloid particles was constant. Furthermore, χ(3) of the glass was inversely proportional to the third power of the total volume of colloid particles when the absorption coefficient of the plasmon band was constant.
Low-temperature photoluminescence of Te-doped GaSb grown by liquid phase electroepitaxy
Authors: Iyer S. , Small L. , Hegde S. M. , Bajaj K. K. , Abul-Fadl A.
Published: July 2002

The results of a low-temperature (4.5 K) photoluminescence study of Te-doped GaSb layers grown by liquid phase electroepitaxy are reported. A doubly ionizable native residual acceptor (A/A−) with shallow and deep levels is observed at 34 and 97 meV, respectively, another native acceptor level for GaSb (B) is seen at 54 meV, and two Te-related acceptor levels (C and D) are found at 68 and 83 meV, respectively. In addition, a few Te-related deep levels are also seen between 114–129 meV at higher Te concentrations. The relative dominance of each of these transitions depends on the degree of Te compensation and the incident excitation intensity. At low excitation intensities, the spectra are dominated by deep impurity levels and with increasing intensity the transitions associated with the shallow acceptors become more prominent. The limited data on the PL integrated intensity dependance on excitation intensity further confirms the nature of these transitions. And finally, we also present preliminary results of our PL studies on Te-doped GaInAsSb alloys.
Ion-beam deposition of hard, amorphous carbon from a fullerene discharge
Authors: Maiken E. B. , Taborek P.
Published: July 2002

The design and operation of an ion source that uses fullerene molecular solid as a feedstock of pure carbon is described. Fullerenes were vacuum sublimed and directed into a discharge plasma, which resulted in dissociation of the fullerenes into molecular carbon fragments. Molecular carbon ions extracted from the discharge impinged energetically upon a substrate and condensed into a thin film of hard, amorphous carbon at growth rates of approximately 1 μm/h. For fixed ion energies of 300 eV, substrate temperature was an important process parameter, affording a means for tuning the physical properties of the films. For deposition temperatures ranging from 250 to 575 K, room-temperature dc resistivity ranged from 105 to 10−2 Ω cm. The more resistive films, deposited at lower temperatures, were infrared transparent and showed no evidence of discrete absorption due to either C-H stretching modes or fullerenes. Broad band tails were observed in the resistive films, with optical gaps of 1.1 eV. The optical gaps of the conductive films were below 0.1 eV. Activation energies of conduction were extracted from the temperature dependance of the film resistivities. Both the resistive and conductive films displayed two activation energies in the range 77 to 650 K, with room temperature the demarcation between low-temperature values of tens of meV and high-temperature values of tenths of an eV. The resistivity and infrared transmission data were interpreted as evidence for the growth of sp2-bonded regions with increased deposition temperature.
Optical nonlinearities of Au/SiO2 composite thin films prepared by a sputtering method
Authors: Tanahashi Ichiro , Manabe Yoshio , Tohda Takao , Sasaki Satoshi , Nakamura Arao
Published: July 2002

Third-order nonlinear optical properties of Au/SiO2 composite thin films have been investigated by means of a degenerate four-wave mixing at room temperature. In the optical-absorption spectra the absorption peak due to the surface plasmon resonance of Au particles is observed at the wavelength around 530 nm. With increasing the mean diameter of Au particles, the absorption at the peak is increased and the full width at half-maximum of the absorption band is decreased from 130 to 80 nm. The third-order nonlinear susceptibility χ(3) exhibits a peak at the wavelength of the absorption peak and the maximum value of χ(3) is obtained to be 2.0×10−7 esu. The size-dependent enhancement of the χ(3) in Au particles with the mean diameter of 3.0–33.7 nm has been also investigated. The value of χ(3)/α (α: absorption coefficient) for the films is increased upon an increase of mean diameter of Au particles. This is explained by the size dependences of the local-field factor and the imaginary part of dielectric constant of the metal particles.
Anomalous broadening of energy distributions in photoemitted electron beams
Authors: Guidi Vincenzo
Published: July 2002

Photoemission is widely used to generate electron beams with an energy spread lower than by thermoemission. However, when a photocathode is illuminated by a multimode laser this feature is lost and an electron beam with several eV of energy spread is produced. We have developed an explanation for this anomalous behavior pointing out its origin in the combined effect of charge relaxation, taking place within the beam, together with the modulation of the laser power imposed by laser modes. The model permits a correct interpretation overall experimental evidences.