bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular dynamics study of the effects of voids and pressure in defect-nucleated melting simulations
Authors: Agrawal Paras M. , Rice Betsy M. , Thompson Donald L.
Published: May 2003

The defect-nucleated melting of Ar has been simulated by the gradual heating of lattices that contain voids using isobaric molecular dynamics. The criterion given by Solca et al. [Chem. Phys. 224, 253 (1997)] has been used to determine the melting point from the transition temperature versus void size curve. A crystal containing a single void created by the removal of an atom and its nearest (n−1) neighboring atoms was found to give almost the same melting temperature as a crystal containing n randomly distributed single-atom voids. The melting temperature is insensitive to the shape of the void. The critical void size, beyond which there is a sudden drop in the melting temperature, decreases with pressure. At various values of pressures ranging from 0.094 to 531.6 kbar the melting points are found to be in good agreement with the experimental results and with thermodynamic results using the same exp-6 potential. The results are consistent with the Lindemann criterion of melting and in better agreement with the Lindemann criterion than are the thermodynamic results.
Comment on “Submillimeter spectroscopic study of concentrated electrolyte solutions as high density plasma” [J. Chem. Phys. 116, 5701 (2002)]
Authors: Gaiduk V. I. , Vij J. K.
Published: May 2003

The authors of the title article: (1) contrary to their findings did not fully comprehend that in our paper [Phys. Chem. Chem. Phys., 3, 523 (2001)], the estimated contribution of ions oscillating between the two “reflecting walls” (which model water surroundings) is very small and (2) the negative result of their experiment, that plasma oscillations are not excited in the concentrated electrolyte solutions, could have also been foreseen from the known experimental data.
Spectra of the very large anisotropic scales in turbulent channels
Authors: del Álamo Juan C. , Jiménez Javier
Published: May 2003

The spectra of numerically simulated channels at Reτ=180 and Reτ=550 in very large boxes are described and analyzed. They support a model in which the u-structures can be decomposed in two components. The first one is formed by structures of size λx≳5 h, λz≈2 h, which span most of the channel height, and penetrate into the buffer layer. The second one has maximum intensity in the near-wall region, where it is highly anisotropic and scales in inner units. It widens, lengthens, and becomes more isotropic in the outer layer, where it scales with h. The cospectrum exhibits an analogous quasi-isotropic range, whose width grows linearly with wall distance. At the present Reynolds numbers, nothing can be said about a possible streamwise similarity, due to limited scale separation. An extensive set of statistics from the simulations is downloadable from ftp://torroja.dmt.upm.es/channels.
On the measurement of “tack” for adhesives
Authors: Tirumkudulu Mahesh , Russel William B. , Huang T. J.
Published: May 2003

One of the tests for determining the bond strength of adhesives involves measuring the force or the work required to pull apart two surfaces separated by a thin film of adhesive. The pull-off force is measured via the bending of a cantilever that connects one of the surfaces to a motor controlled vertical traverse. Although such tests are routinely performed, little attention has been paid to the understanding of force measurements and their relation to the dynamics of the instrument. Specifically, the measured force versus gap profile for the pull-off process is different from that measured when the same adhesive is compressed between two approaching surfaces. Through experiments on Newtonian liquids and a simple analysis involving lubrication analysis of thin liquid films, we show that the hysteresis in measurements results from a combination of an instrument-related instability and the nucleation and collapse of cavitation bubbles in the flow field.
Hydrodynamic effects on phase separation of binary mixtures with reversible chemical reaction
Authors: Huo Yanli , Jiang Xiuli , Zhang Hongdong , Yang Yuliang
Published: May 2003

The hydrodynamic effect on the phase separation dynamics of chemically reacting binary mixtures is investigated based on the extended model H. Our simulation results reveal that many interesting patterns are obtained under different chemical reaction rates due to the coupling of hydrodynamics and chemical reaction. For the case of high reaction rate, when the average order parameter at equilibrium is equal to zero, spiral structures appear due to the delicate coupling between the hydrodynamic flow and chemical reaction regardless of the value of initial order parameter. When the chemical reaction rate is low, the pattern observed under the critical quench seems like the result of double phase separation. On the other hand, under the off-critical quench, at the same low chemical reaction rate, phase inversion behavior is observed, and it is aggravated under the hydrodynamic flow. Moreover, the domain growth kinetics under both critical and off-critical quenches is investigated.
Discrete electron forces in a nanoparticle-tunnel junction system
Authors: Suganuma Y. , Trudeau P.-E. , Dhirani A.-A. , Leathem B. , Shieh B.
Published: May 2003

According to the “orthodox” model for single electron tunneling, sudden changes in current–voltage characteristics of nanoparticle (NP)-tunnel junction (TJ) systems [“Coulomb blockade” (CB) and “Coulomb staircase” (CS) phenomena] arise fundamentally due to charge quantization. We have embedded NPs (∼2.5 nm in diameter) in the TJ of a hybrid scanning tunneling-atomic force microscope and have simultaneously measured current and forces generated in the system. We discuss an application to micromechanical switching actuated by single electrons. We also show that CB and CS phenomena are in fact associated with steplike changes in force, directly confirming the discrete charge nature of the phenomena.
O–D bond dissociation from the 3s state of deuterated hydroxymethyl radical (CH2OD)
Authors: Feng Lin , Demyanenko Andrey V. , Reisler Hanna
Published: May 2003

The photodissociation of the deuterated hydroxymethyl radical CH2OD is investigated on the lowest excited state, the 3s Rydberg state, in the wavelength region 365–318 nm where the D atom is the only significant product. The translational energy distribution and kinetic energy-dependent anisotropy parameter of the D channel are determined by the core-sampling time-of-flight technique at 352.5 nm. The negative recoil anisotropy parameter βeff=−0.7±0.1 is consistent with the perpendicular nature of the transition from the ground state. The fraction of the available energy partitioned into the translational degree of freedom is 0.69. Ground state products CH2O (1 1A1)+D constitute the main photodissociation channel, and no significant H product is detected at these wavelengths. Comparison with the conical intersection calculations of Hoffman and Yarkony suggests that O–D bond rupture involves crossing from the 3s potential energy surface to a repulsive region of the ground state surface at a large O–D bond distance. Isomerization of CH2OD to CH2DO is not competitive with the fast O–D dissociation.
Control of aeolian tones radiated from a circular cylinder in a uniform flow
Authors: Inoue Osamu , Mori Masaaki , Hatakeyama Nozomu
Published: May 2003

Effects of artificial forcing on the generation and propagation mechanisms of the sound generated by a circular cylinder in a uniform flow are investigated by direct solution of the two-dimensional, unsteady, compressible Navier–Stokes equations. Two types of forcing are considered: rotation of the cylinder at a constant angular velocity and periodic blowing/suction from the (nonrotating) cylinder surface. For the case of a rotating cylinder, results show that the sound generation can be controlled by controlling the periodic shedding of (Kármán) vortices from the cylinder surface into its wake. On the other hand, results for the case of periodic blowing/suction show that the generation and propagation of the sound can be effectively controlled without drastic changes of the vortex shedding. It is found in this case that the interactions among the lift dipole (which is generated by the vortex shedding), the drag dipole and the monopole (both of which are generated by the periodic blowing/suction) play a principal role in the control process of the generation and propagation of the sound.
Ponomarenko dynamo with time-periodic flow
Authors: Normand Christiane
Published: May 2003

The Ponomarenko dynamo theory is revisited to take into account time-dependent flows. Our purpose is to investigate how a small departure from a steady flow can modify the onset of dynamo action. We consider a typical helical flow when the velocity components are modulated in time at the same frequency and with a small modulation amplitude of the order ε. Using ε as an expansion parameter we calculated the shift in the critical magnetic Reynolds number and the shift in frequency at dynamo onset. We found that modulation can either lower or enhance the threshold of dynamo action depending on ε1, the relative amplitude of modulation of the azimuthal and axial velocity components. More specifically, in-phase modulation with 0.7⩽ε1⩽1 delays the onset of dynamo action, while in a larger range including out-of-phase modulation, −1⩽ε1<0.7, low-frequency forcing promotes dynamo action.
Pulsed-laser-deposited ultraviolet-emitting SrS:Te thin films
Authors: Fitz-Gerald J. M. , Hoekstra J. , Rack P. D. , Fowlkes J. D.
Published: May 2003

SrS has an indirect band gap of ∼4.32 eV, however, when it is doped with tellurium, ultraviolet emission occurs at 360 nm and 400 nm due to recombination from bound exciton states. In this letter, we discuss the ultraviolet emission of pulsed-laser-deposited thin films of SrS:Te grown at room temperature on Si. The deposited film thickness ranged from 0.1–1.5 μm, with optimized films grown at ∼0.5 μm. Te doping was incorporated by both ion implantation and conventional diffusion of deposited Te films. The characteristics of the ultraviolet emission will be discussed and correlated to the microstructural, chemical, and optical properties of the films.
Localizations of junction points of ABC 3-miktoarm star terpolymers
Authors: He Xuehao , Huang Lei , Liang Haojun , Pan Caiyuan
Published: May 2003

Microdomain structures of ABC 3-miktoarm star terpolymers in three-dimensional space were investigated by dynamic density functional theory (DDFT). Analysis of DDFT demonstrates that the junction points are restricted to lie on the periodically spaced parallel lines formed by the mutual intersections of different domains at the strong segregation between distinct blocks. With the improvement of compatibility of one component with the two other components, the localization of junction points is changed to the tendency of distribution over intermaterial dividing surface between the domains.
A temperature-dependent nudged-elastic-band algorithm
Authors: Crehuet Ramon , Field Martin J.
Published: May 2003

In this paper we present a method to introduce temperature corrections to a minimum-energy reaction path. The method is based on the maximization of the flux for the Smoluchowski equation and it is implemented using a nudged-elastic-band algorithm. We present the results of applying the algorithm to transitions in three systems—the three-well potential, the alanine dipeptide, and a molecular ratchet—and also remark on some points related to the location of temperature-dependent paths and the nature of the transition state.
Dense granular flow around an immersed cylinder
Authors: Chehata D. , Zenit R. , Wassgren C. R.
Published: May 2003

The flow around a fixed cylinder immersed in a uniform granular flow is studied experimentally. Experiments are performed in a tall vertical chute producing a quasi two-dimensional granular flow. A storage bin at the top of the chute feeds glass particles into the channel while the mean velocity of the flow is controlled by varying the exit width of a hopper located at the channel bottom. Measurements of the drag force acting on a fixed cylinder are made using a strain gauge force measurement system. The flow velocity field is measured through a transparent wall using a particle image velocimetry analysis of high speed video recordings of the flow. Experiments are performed for a range of upstream particle velocities, cylinder diameters, and two sizes of glass particles. For the range of velocities studied, the mean drag force acting on the cylinder is independent of the mean flow velocity, contrary to what is expected from any ordinary fluid. The drag force increases with cylinder diameter and decreases with particle diameter. The drag force scales with the asymptotic static stress state in a tall granular bed. The drag coefficient, defined in terms of a dynamic pressure and an effective cylinder diameter, scales with the flow Froude number based on the hydraulic diameter of the channel. This analysis indicates that the drag acting on the cylinder is strongly affected by the surrounding channel geometry. Although the drag force on the cylinder does not change with the upstream flow velocity, the flow streamlines do change with velocity. A large stagnation zone forms at the leading edge of the cylinder while at the trailing edge an empty wake is observed. The wake size increases with flow velocity. Measurements of the flow vorticity and granular temperature are also presented and discussed.
Stochastic simulations of buoyancy-reversal experiments
Authors: Wunsch Scott
Published: May 2003

Buoyancy reversal occurs when the mixing of two fluids, initially stably stratified, produces a mixture which is more dense than either pure fluid. The resulting instability generates turbulent mixing, and may play an important role in geophysical and astrophysical flows. In this work, a stochastic one-dimensional model is used to simulate these systems. Model validation is accomplished using experimental comparisons. Scalings inferred from the model simulations are used to suggest extrapolations from experimental results to natural systems.
Leidenfrost drops
Authors: Biance Anne-Laure , Clanet Christophe , Quéré David
Published: May 2003

A Leidenfrost drop forms when a volatile liquid is brought in contact with a very hot solid. Then, a vapor film comes in between the solid and the drop, giving to the latter the appearance of a liquid pearl. After a brief description of the shape of a Leidenfrost drop, we show that its size cannot exceed a certain value. Then, we describe the characteristics of the vapor layer on which it floats. We show how it is related to the drop size, and how both vary with time, as evaporation takes place. We finally deduce scaling laws for the lifetime of these drops.
Flow induced patterning at the air–water interface
Authors: Miraghaie R. , Lopez J. M. , Hirsa A. H.
Published: May 2003

Patterns on the air–water interface of a swirling cylinder flow are produced via hydrodynamic symmetry-breaking instability of the bulk flow. The patterns are rotating waves breaking the axisymmetry of the system and are longitudinal at the free surface (i.e., not surface deforming). Qualitative observations and quantitative measurements of velocity and vorticity are provided. Three-dimensional Navier–Stokes computations identify the symmetry-breaking mode responsible for the waves. These waves are then used to pattern Langmuir monolayers at concentrations sufficiently below saturation.
Cavitation luminescence in a water hammer: Upscaling sonoluminescence
Authors: Su C.-K. , Camara C. , Kappus B. , Putterman S. J.
Published: May 2003

Oscillatory acceleration and deceleration of a column of water leads to a pipe hammer as well as cavitation. With a small amount of xenon gas dissolved in the water, we can detect a stream of predominantly ultraviolet subnanosecond flashes of light which are attributed to collapsing bubbles. The observed emission can exceed 108 photons for a single collapse and has a peak power over 0.4 W.
Improvement of n-GaN Schottky diode rectifying characteristics using KOH etching
Authors: Spradlin J. , Dogan S. , Mikkelson M. , Huang D. , He L. , Johnstone D. , Morkoç H. , Molnar R. J.
Published: May 2003

KOH etch was investigated as a means to improve the I–V characteristics of Schottky diodes on n-type GaN grown by molecular-beam epitaxy on sapphire, or on hydride vapor phase epitaxy templates. Atomic force microscopy images and I–V characteristics are presented. After etching as-grown films in molten KOH, Schottky diodes on c-plane GaN had orders of magnitude reduction in reverse leakage current. The best devices had leakage currents less than 10−12 A (10−8 A/cm2) at −5 V, and ideality factors of 1.04. Measurements on several different sample structures indicate a correlation between surface roughness and saturation current, and an improvement in ideality factor when etched in KOH. Phosphoric acid was also investigated, but did not result in significant improvements in I–V characteristics.
Droplet splashing on a thin liquid film
Authors: Josserand Christophe , Zaleski Stéphane
Published: May 2003

We propose a theory predicting the transition between splashing and deposition for impacting drops. This theory agrees with current experimental observations and is supported by numerical simulations. It assumes that the width of the ejected liquid sheet during impact is precisely controlled by a viscous length lν. Numerous predictions follow this theory and they compare well with recent experiments reported by Thoroddsen [J. Fluid Mech. 451, 373 (2002)].
Particle size distribution as key parameter for the flow behavior of ferrofluids
Authors: Thurm Steffen , Odenbach Stefan
Published: May 2003

One of the most promising properties of ferrofluids is the possibility to significantly influence their flow behavior by moderate magnetic fields. An exact understanding of the origin and mechanism of this effect is essential in order to develop future applications in the field of magnetoviscosity. In particular, the influence of the small fraction of larger particles, which can show strong, magnetic field induced interparticle interactions, is in the focus of our interest. Theoretical calculations show that the interaction between larger particles is strong enough to form chain-like structures, which in turn dominate the flow behavior. To investigate this effect more deeply, we change — by a magnetic separation process in a controlled, measurable way — the volume fraction mainly of these larger particles. Thereafter the separated fluid fractions and the original fluid are investigated in magnetization and rheological measurements, which are compared with theoretical calculations.
Magnetic behavior of nanoparticles in patterned thin films
Authors: Escrig J. , Landeros P. , Retamal J. C. , Altbir D. , d’Albuquerque e Castro J.
Published: May 2003

The magnetic behavior of truncated conical nanoparticles in patterned thin films is investigated as a function of their size and shape. Using a scaling technique, phase diagrams giving the relative stability of characteristic internal magnetic structures of the particles are obtained. The role of the uniaxial anisotropy in determining the magnetic properties of such systems is discussed, and a simple method for establishing its strength is proposed.
Midinfrared intersubband absorption in strain-compensated InGaP/InGaAs superlattices on (001) GaAs
Authors: Semtsiv M. P. , Tarasov G. G. , Masselink W. T. , Kissel H. , Woerner M.
Published: May 2003

Intersubband optical transitions in strain-compensated In0.32Ga0.68As–In0.32Ga0.68P superlattices grown using gas-source molecular-beam epitaxy on (001)GaAs are investigated by means of midinfrared absorption and low-temperature photoluminescence. Strong absorption corresponding to the transition from the first to second electronic subband is measured at wavelengths between 5.6 and 10.5 μm. The data indicate that the conduction band offset between the strained In0.32Ga0.68As and the strained In0.32Ga0.68P is 370 meV and the electron effective mass in the strained In0.32Ga0.68As well is 0.060m0. This material system is an interesting GaAs-based candidate for applications in midinfrared intersubband emitters and detectors.
Reversible and bistable terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films
Authors: Kida Noriaki , Tonouchi Masayoshi
Published: May 2003

Reversible and bistable terahertz (THz) radiation by sweeping the temperature has been observed in a dipole-type photoswitching device fabricated on magnetoresistive charge-ordered manganite Pr0.7Ca0.3MnO3 thin film. Based on simultaneous measurements of the photocurrent, we show that this THz functionality of Pr0.7Ca0.3MnO3 arises from the instability of metallic patches embedded with a charge-ordered insulating phase, which is created by the illumination of visible light under an electric field at constant temperature, and that it can also be controlled by a subsequent change of temperature.
Simulation evidence for lateral excitation transfer in a self-assembled quantum-dot array
Authors: Johnson H. T. , Bose R. , Robinson H. D. , Goldberg B. B.
Published: May 2003

Simulations of InAlAs/AlGaAs self-assembled quantum-dot arrays containing as many as 30 individual dots are used to identify a mechanism for lateral excitation transfer through partially delocalized heavy-hole states. Individual hole states exhibit wave-function splitting between several dots in the array, as well as partial confinement in the wetting layer, and have strong overlap with multiple conduction-band electron states in different quantum dots. Electron–hole pair energies involving these partially delocalized hole states correspond well with narrow resonances seen in the experimental photoluminescence excitation spectra taken for similar quantum-dot arrays using low-temperature near-field scanning optical microscopy.
Bleached state transmittance in charge-unbalanced all-solid-state electrochromic devices
Authors: Ahn Kwang-Soon , Nah Yoon-Chae , Park Jin-Young , Sung Yung-Eun , Cho Ki-Yun , Shin Seung-Shik , Park Jung-Ki
Published: May 2003

The bleached state transmittance of a charge-unbalanced, complementary electrochromic (EC) device may show residual coloration due to the presence of residual charges. In this study, EC devices were fabricated with configurations G/ITO/Ni(OH)2/Ta2O5/H+–SPE/Ta2O5/WO3/ITO/G and G/ITO/NiOOH/Ta2O5/H+–SPE/Ta2O5/HWO3/ITO/G (G=glass, H+–SPE=proton-conducting solid polymer electrolytes, and ITO=indium tin oxide). These devices, referred to as EC1 and EC2, were initially fabricated from fully bleached EC layers and from fully colored EC layers, respectively. The change in electrochromic properties as a function of charge capacity ratio (R) for each device was then compared. In comparison to EC2 devices, EC1 devices provided better bleached-state transmittances and higher coloration efficiencies over a wider range of R, and were less sensitive to changes in R value. This may arise because the absorbance caused by the residual charges in the colored state is greater and more sensitive to the charge capacity ratio than that in the bleached state.
Strong in-plane polarized intraband absorption in vertically aligned InGaAs/GaAs quantum dots
Authors: Adawi A. M. , Zibik E. A. , Wilson L. R. , Lemaître A. , Cockburn J. W. , Skolnick M. S. , Hopkinson M. , Hill G. , Liew S. L. , Cullis A. G.
Published: May 2003

We present a midinfrared absorption study of an n–i–n structure containing two planes of strongly coupled In0.5Ga0.5As self-assembled quantum dots. We find that the dominant absorption occurs for light polarized in the growth plane (E//xy), contrasting with uncoupled dots which exhibit stronger absorption for light polarized in the growth direction (E//z) in the same energy range. Results from the coupled dot sample indicate that the confinement length in the growth direction is increased, lowering the energy of the s-like ground state and hybridizing px,y-like excited states and wetting layer states. A significantly increased normal incidence photocurrent signal is measured for the sample containing coupled dots, relative to samples containing up to 30 layers of uncoupled dots, confirming the enhancement of the normal incidence absorption.
Fine-tuning photorefractive properties of monolithic molecular materials
Authors: Hou Zhanjia , You Wei , Yu Luping
Published: May 2003

Single component photorefractive materials based on small molecules have been synthesized. The sidechains located in the electron-withdrawing group of these molecules were systematically changed in order to investigate their influence. It was demonstrated that the photorefractive performance of these materials could be fine-tuned by changing the length of the sidechain. Excellent optical quality and photorefractive properties were obtained. A large net optical gain of 280 cm−1 at a low external field (38.3 V/μm) and a diffraction efficiency of 82% were observed at 780 nm. The results indicate that an optimum sidechain length exists for this type of molecules.
Thermal effect on the field-dependent refractive index of the magnetic fluid film
Authors: Chen Y. F. , Yang S. Y. , Tse W. S. , Horng H. E. , Hong Chin-Yih , Yang H. C.
Published: May 2003

The field-dependent refractive index (nMF–H curve) of the magnetic fluid film (MFF) is measured at various temperatures to investigate the thermal effect on the refractive index. It was found, at a certain temperature, that the refractive index becomes higher under higher magnetic fields. This nMF–H curve is moved toward the region with lower nMF when the temperature is raised. Since the variation in the refractive index of the MF under external fields is due to the formation of the magnetic columns, the structural patterns are then examined to clarify the origin of the change in the nMF–H curve with the temperature. Under a given field strength, the particles of columns are dispersed into the liquid carrier at a higher temperature. This depresses the phase separation in the MFF under fields, and in turn, reduces the refractive index of the MFF. The observed results also reveal that the temperature exhibits a compensation effect on the refractive index of the MFF with respect to the magnetic field.
A hybrid laser system consisting of a frequency-doubled, narrow-line-width, distributed-feedback dye laser oscillator and a high saturation-fluence Ce:LiCaAlF6 crystal amplifier
Authors: Hoa D. Q. , Hung N. D. , Moroe J. , Takeyasu N. , Imasaka T.
Published: May 2003

A tunable narrow-band picosecond dye laser emitting in the ultraviolet region was amplified using a Ce:LiCaAlF6 crystal pumped by the fourth-harmonic emission of a Nd:Y3Al5O12 laser. The single-pass gain obtained exceeded 2 in the spectral range of 288 to 297 nm.
Observation of magnetic-field-enhanced source current of accumulated p-channel metal-oxide-semiconductor field-effect transistors
Authors: Baron F. A. , Zhang Y. , Wang K. L.
Published: May 2003

Gate-induced drain leakage current in accumulated metal-oxide-semiconductor field-effect transistors is pumped out completely by the body, while the source current should be zero due to the barrier of the p/n junction between the source and the accumulated channel. In this work, we report the observation of the current peaks in the source current versus gate voltage characteristics of p-channel transistors when the devices are biased at the accumulation regime. The source current vanishes when the temperature exceeds 11 K. The source current can be enhanced dramatically as the transistors are exposed to a high magnetic field perpendicular to the channel. We believe the Fermi-edge singularity may be responsible for the resonant source current peaks.
Efficient frequency doubling of a femtosecond pulse with simultaneous group-velocity matching and quasi phase matching in periodically poled, MgO-doped lithium niobate
Authors: Yu Nan Ei , Kurimura Sunao , Kitamura Kenji , Ro Jung Hoon , Cha Myoungsik , Ashihara Satoshi , Shimura Tsutomu , Kuroda Kazuo , Taira Takunori
Published: May 2003

We demonstrate efficient frequency doubling of 95-fs pulses with a small temporal broadening in a 10-mm-long, periodically poled, 5-mol % MgO-doped lithium niobate crystal. Simultaneous group-velocity matching and quasi phase matching were achieved by the off-diagonal nonlinear optical coefficient d32 at telecommunications range.
Effect of length and spacing of vertically aligned carbon nanotubes on field emission properties
Authors: Jo S. H. , Tu Y. , Huang Z. P. , Carnahan D. L. , Wang D. Z. , Ren Z. F.
Published: May 2003

The length and the spacing of carbon nanotube (CNT) films are varied independently to investigate their effect on the field-emission characteristics of the vertically aligned CNT films grown by plasma-enhanced hot filament chemical vapor deposition using pulsed-current electrochemically deposited catalyst particles. It is shown that, in general, the macroscopic electric field Emac,1, defined as the electric field when the emission current density reaches 1 mA/cm2, can be reduced by increasing the length and the spacing of CNTs. However, for the very-high-density CNT films, the increase of length increases Emac,1 slightly, whereas for the very short CNT films, the increase of spacing does not effectively reduce Emac,1.
The vacuum ultraviolet photochemistry of the allyl radical investigated using synchrotron radiation
Authors: Schüßler T. , Deyerl H.-J. , Dümmler S. , Fischer I. , Alcaraz C. , Elhanine M.
Published: May 2003

We report a study on the spectroscopy and the photochemistry of the allyl radical, C3H5, in the vacuum ultraviolet energy range using synchrotron radiation as the light source and a flash pyrolysis source to generate the radical. Mass spectra recorded over a wide energy range show the appearance of C3H3+ as a fragment in the dissociative photoionization of allyl above 10 eV. The threshold photoelectron spectrum of the allyl radical shows a progression of around 52 meV, corresponding to the CCC bending vibration.
Self-assembling of Ge on finite Si(001) areas comparable with the island size
Authors: Vescan L. , Stoica T. , Holländer B. , Nassiopoulou A. , Olzierski A. , Raptis I. , Sutter E.
Published: May 2003

Voids in ultrathin oxide and electron-beam lithography-patterned windows were used to deposit Ge selectively. The number of islands is a function of the total amount of Ge deposited in a void or window. Our results show that islands smaller than the void/window size nucleate mainly near the periphery. This might be due to the tensile strain in the Si substrate near the oxide edge. The interruption of the wetting layer reduces the loss of excitons by lateral diffusion, resulting in considerable increase in optical emission from islands.
Band bending independent of surface passivation in ZnO/CdS/Cu(In,Ga)(S,Se)2 heterojunctions and Cr/Cu(In,Ga)(S,Se)2 Schottky contacts
Authors: Deibel C. , Dyakonov V. , Parisi J.
Published: May 2003

We have employed admittance spectroscopy and deep-level transient spectroscopy in order to investigate the electronic properties of ZnO/CdS/Cu(In,Ga)(S,Se)2 heterojunctions and Cr/Cu(In,Ga)(S,Se)2 Schottky contacts. Our work concentrates on the origin of an energy-distributed defect state commonly found in these systems. The activation energy of the defect state addressed continuously shifts upon air annealing or damp-heat treatment and is a valuable measure of the degree of band bending in Cu(In,Ga)(S,Se)2-based junctions. We demonstrate that the band bending within the Cu(In,Ga)(S,Se)2 layer, reported in the literature to become minimal after air exposure, returns after the formation of either a Schottky contact or a heterojunction. The earlier phenomenon turns out to be independent of a surface passivation due to the CdS bath deposition.
Magnetic anisotropy and thermal stability study on FePt nanoparticle assembly
Authors: Wu X. W. , Guslienko K. Y. , Chantrell R. W. , Weller D.
Published: May 2003

The temperature dependence of the first-order magnetic anisotropy constant has been investigated for off-stoichiometric chemically ordered L10, Fe45Pt55 nanoparticle samples. A representative sample shows an anisotropy energy density of Ku=0.7×107 erg/cm3 and a thermal stability factor of KuV/kBT=77 at room temperature. With decreasing temperature, from room temperature to 5 K, a 50% increase of Ku, accompanied by a 25% increase of the saturation magnetization MS is observed. The temperature dependence of Ku is explained on the basis of the spin-Hamiltonian approach with an Fe effective spin. The estimated median “magnetic” grain size, obtained from time-dependent measurements, decreases by about 15% with decreasing temperature from 298 to 100 K. This magnetic grain size reduction is attributed to the decrease of the superparamagnetic fraction in the FePt nanoparticle sample.
Ultrafast photoinduced anisotropy and optical switching in azobenzene sidechain polymers
Authors: Wang Hui , Huang Yaping , Liu Zhigang , Zhao Fuli , Lin Weizhu , Wang Jian , Liang Zhaoxi
Published: May 2003

Photoinduced anisotropic and optical switching properties have been studied in two kinds of azobenzene sidechain polymers, a disazobenzene sidechain polymer (DAP–PGMA) and a monoazobenzene sidechain polymer P(MMA–co–MAZ). Picosecond optical switching dynamics have been observed in both DAP–PGMA and P(MMA–co–MAZ) films. The rise time of the optical switching in DAP–PGMA film is about 40 ps, which is much faster than that of P(MMA–co–MAZ) film (∼100 ps). DAP–PGMA shows enhanced photoanisotropy and larger birefringence (∼7.04×10−4) than that of P(MMA–co–MAZ) (∼1.34×10−4). The influence of the azobenzene sidechain groups on the photoanisotropic dynamics is discussed.
Fluorine-enhanced boron diffusion in amorphous silicon
Authors: Jacques J. M. , Robertson L. S. , Jones K. S. , Law M. E. , Rendon Mike , Bennett Joe
Published: May 2003

Silicon wafers were preamorphized with 70 keV Si+ at a dose of 1×1015 atoms/cm2, generating a deep amorphous layer of 1800 Å. Implants of 500 eV B+11, with and without 6 keV F+, followed at doses of 1×1015 atoms/cm2 and 2×1015 atoms/cm2, respectively. After annealing at 550 °C, secondary ion mass spectroscopy determined that the diffusivity of boron in amorphous silicon is significantly enhanced in the presence of fluorine. Ellipsometry and cross-sectional transmission electron microscopy indicate the enhanced diffusion only occurs in the amorphous layer. Fluorine increases the boron diffusivity by approximately five orders of magnitude at 550 °C. It is proposed that the ability of fluorine to reduce the dangling bond concentration in amorphous silicon may reduce the formation energy for mobile boron, enhancing its diffusivity.
Analysis of thermal stress in wafer bonding of dissimilar materials for the introduction of an InP-based light emitter into a GaAs-based three-dimensional photonic crystal
Authors: Ogawa Shinpei , Imada Masahiro , Noda Susumu
Published: May 2003

Thermal stresses generated by differences in the thermal expansion coefficients of InP and GaAs are analyzed in an attempt to introduce an InP-based light emitter into GaAs-based three-dimensional photonic crystal. Observations of the GaAs/InGaAsP bonding interface by scanning acoustic microscopy reveal that debonding occurs at approximately 300 °C due to thermal stress. Calculations of thermal stress by a two-dimensional finite element method suggested that thermal stress could be reduced by thinning the substrate, which was confirmed experimentally. Using these results, a three-dimensional photonic crystal with light emitter was successfully fabricated.
Hybridization reduction of the magnetization for N-doped FeCo superlattices
Authors: Kim Miyoung , Freeman A. J.
Published: May 2003

In search of a soft magnetic material exhibiting high magnetization, we investigated the magnetic and structural properties of an (Fe3Co)4Nm superlattice (SL) with (m=2) and without (m=0) N doping via first principles full-potential linearized augmented plane wave calculations in order to examine the possible magnetic enhancement by (i) N addition (which has drawn considerable attention since the first report (in 1972) of a giant magnetic moment for quasistable α″-Fe16N2) and (ii) the lowered dimensionality of the SL. The structural optimization was fully accomplished by total energy and atomic force calculations within the generalized-gradient approximation. Despite the lattice expansion by 9% due to the N insertion, the magnetization of (Fe3Co)4N2 was found to be reduced from the value of the Fe3Co superlattice by the strong hybridization of N with Fe and Co.
A completely flexible organic transistor obtained by a one-mask photolithographic process
Authors: Bonfiglio Annalisa , Mameli Fulvia , Sanna Ornella
Published: May 2003

A one-mask optolithographic process is proposed for obtaining a completely flexible organic thin-film transistor structure. The proposed device consists in a “bottom structure” assembled on a flexible and transparent insulating layer, without any substrate, with source and drain contacts on one side and the gate on the opposite side. The main advantage consists in avoiding the presence of a substrate as the insulator itself is able to support the whole structure. Furthermore, being optically transparent, the insulator is suitable to be employed for the photolithographic realization of the contacts with a one-mask process with no need of mask alignment between source–drain contacts and gate.
Erbium–thulium interaction in broadband infrared luminescent silicon-rich silicon oxide
Authors: Seo Se-Young , Shin Jung H. , Bae Byeong-Soo , Park Namkyoo , Penninkhof J. J. , Polman A.
Published: May 2003

The Er–Tm interaction and its effect on the luminescence from Er–Tm codoped silicon-rich silicon oxide (SRSO) is investigated. Er and Tm ions were implanted into SRSO films, which consist of Si nanocrystals embedded in a SiO2 matrix. A broad luminescence spectrum extending from 1.5 to 2.0 μm was observed under excitation with a single light source due to the simultaneous, nonresonant excitation of both Er3+ and Tm3+ via Si nanocrystals. The absolute Er3+ luminescence intensity, however, is reduced relative to the case without Tm codoping. Comparison of the Er3+ and Tm3+ luminescence intensities, lifetimes, and their pump power dependence suggest that Er–Tm interaction leading to an energy transfer from the Er3+:4I13/2 state to the excited Tm3+:3H4 state is responsible for the reduction in the Er luminescence intensity.
Transport and focusing of highly vibrationally excited NO molecules
Authors: Matsiev Daniel , Chen Jun , Murphy Michael , Wodtke Alec M.
Published: May 2003

We report experiments where hexapole focusing is combined with stimulated emission pumping in a molecular beam, providing control over the molecule’s rovibronic quantum numbers, its laboratory frame velocity and its transverse divergence. Hexapole focusing profiles can be quantitatively reproduced by classical trajectory simulations. These experiments provide new ways of manipulating beams of vibrationally excited molecules including: (1) transverse refocusing and concomitant improved efficiency for transport of the vibrationally excited molecules, (2) relative enrichment of the concentration of the vibrationally excited molecules with respect to the unexcited portion of the beam and, (3) orientation of vibrationally excited molecules.
Improved temperature characteristics of laser diodes with nonidentical multiple quantum wells due to temperature-induced carrier redistribution
Authors: Lin Ching-Fuh , Su Yi-Shin , Yu Di-Ku , Wu Chao-Hsin , Wu Bing-Ruey
Published: May 2003

Laser diodes with nonidentical multiple quantum wells could have the lasing wavelength very insensitive to temperature variation. For temperature varying from 33 to 260 K, the lasing energy changes less than 5 meV, while the band gap energy changes more than 50 meV. The origin is due to the strongly temperature-dependent Fermi–Dirac distribution, which favors carriers in high-energy states at large temperature. The temperature-induced carrier redistribution could even cause negative characteristic temperature for a certain temperature range because the low-energy quantum wells behave like reservoirs to overcome the detrimental influence of temperature.
Interplay between the growth temperature, microstructure, and optical properties of GaInNAs quantum wells
Authors: Chauveau J.-M. , Trampert A. , Ploog K. H. , Pinault M.-A. , Tournié E.
Published: May 2003

We investigated the influence of the growth temperature (Tgr) on the microstructure and on the optical properties of GaInNAs quantum wells (QWs). By comparing the structural information (transmission electron microscopy) with the optical properties (photoluminescence spectroscopy), we demonstrate that high photoluminescence efficiency of GaInNAs QWs is achieved only when the two-dimensional growth mode is preserved, which can be obtained at a low Tgr even for high In content. We also show composition modulations in the GaInNAs QWs, which can lead to the interface roughness.
Bond-breaking bifurcation states in carbon nanotube fracture
Authors: Dumitrică Traian , Belytschko Ted , Yakobson Boris I.
Published: May 2003

Fullerene nanotubes yield to tension in two basic ways. At high temperature (or in the long time limit) a single bond rotation creates a dislocation-dipole favored thermodynamically under large stress. However, at low temperature (or limited time range) this process remains prohibitively slow until further increase of tension causes direct bond-breaking and brittle crack nucleation. This instability proceeds through the formation of a distinct series of virtual defects that only exist at larger tension and correspond to a set of shallow energy minima. The quantum mechanical computations of the intermediate atomic structures and charge density distributions clearly indicate a certain number of broken bonds.
Nucleotide sequence-based typing of meningococci directly from clinical samples
Authors: Diggle Mathew A. , Bell Carolyn M. , Clarke Stuart C.
Published: May 2003

The unpredictable characteristics of meningococcal disease (MD) make outbreaks complicated to monitor and consequently lead to high levels of public anxiety. Traditional molecular techniques have been utilized in order to understand better the epidemiology of MD, but some have disadvantages such as being highly specialized and labour-intensive, with low reproducibility. Some of these problems have been overcome by using multilocus sequence typing (MLST). This technique exploits the unambiguous nature and electronic portability of nucleotide sequencing data for the characterization of micro-organisms. The need for enhanced surveillance of MD after the introduction of serogroup C conjugate vaccines means that it is important to gain typing information from the infecting organism in the absence of a culture isolate. Here, the application of MLST for the laboratory confirmation and characterization of Neisseria meningitidis directly from clinical samples is described. This involved using a newly designed set of primers that were complementary to nucleotide sequences external to the existing MLST primers already in use for culture-based MLST of meningococci. This combination has produced a highly sensitive procedure to allow the efficient genotypic characterization of meningococci directly from clinical samples.
Evaluation of selective media for the isolation of Brachyspira aalborgi from human faeces
Authors: Brooke C. Josephine , Riley Thomas V. , Hampson David J.
Published: May 2003

The purposes of this study were to identify a solid medium that supports improved growth of the anaerobic intestinal spirochaete Brachyspira aalborgi, to modify this for use as a selective isolation medium and then to test the medium for its effectiveness in isolating B. aalborgi from patients’ faeces. Of the media evaluated, brain heart infusion agar (BHIA) with 10 % bovine blood (BB) was the most effective base–supplement combination for growth, with colonies attaining 1.2 mm in diameter by 21 days. Incubation in an anaerobic jar (94 % H2, 6 % CO2) permitted growth of larger colonies than incubation in an anaerobic chamber (80 % N2, 10 % H2, 10 % CO2). Growth was improved only slightly at 38.5 °C compared with 37 °C. Selection of B. aalborgi from artificially seeded faeces was achieved equally well on eight different solid media containing spectinomycin (400 μg ml−1) alone or in combinations with polymyxin B (5 μg ml−1), colistin (25 μg ml−1) and rifampicin (12.5 μg ml−1). By using BHIA 10 % BB with spectinomycin plus polymyxin B, B. aalborgi was isolated from one of five human faecal samples that were positive for B. aalborgi by PCR amplification. This is the first report of the isolation of B. aalborgi from human faeces.
Crystallization of urine mineral components may depend on the chemical nature of Proteus endotoxin polysaccharides
Authors: Torzewska Agnieszka , Stączek Paweł , Róźalski Antoni
Published: May 2003

Formation of infectious urinary calculi is the most common complication accompanying urinary tract infections by members of the genusProteus. The major factor involved in stone formation is the urease produced by these bacteria, which causes local supersaturation and crystallization of magnesium and calcium phosphates as carbonate apatite [Ca10(PO4)6.CO3] and struvite (MgNH4PO4.6H2O), respectively. This effect may also be enhanced by bacterial polysaccharides. Macromolecules of such kind contain negatively charged residues that are able to bind Ca2+and Mg2+, leading to the accumulation of these ions around bacterial cells and acceleration of the crystallization process. The levels of Ca2+and Mg2+ions bound by wholeProteuscells were measured, as well as the chemical nature of isolated LPS polysaccharides, and the intensity of thein vitrocrystallization process was compared in a synthetic urine. The results suggest that the sugar composition ofProteusLPS may either enhance or inhibit the crystallization of struvite and apatite, depending on its chemical structure and ability to bind cations. This points to the increased importance of endotoxin in urinary tract infections.
Relationship marketing practice in relation to different bank ownerships: a study of banks in Hong Kong
Authors: Gilbert David C. , Choi Karen C.
Published: May 2003

Examines relationship marketing’s (RM) present practices in the banking industry in Hong Kong. Banks in Hong Kong were classified into three categories by reference to their different ownership (Chinese, non‐Chinese and merged). Statistics show that there were differences between RM practices among the different ownership of banks. Non‐Chinese banks were more proactive in applying RM elements and on a more tactical basis. On the other hand, findings suggested that there were no significant differences between different ownerships of a bank toward the perception of guanxi (Chinese personal relationship). However, it was reported that guanxi is more in‐depth and more relevant than RM to Chinese business relationships. The research findings imply that different ownership of a bank may exert a different emphasis on RM practices. Also, the study alerts academic and practitioners that RM practices are not yet fully implemented in the banking industry and it is important to develop a more systematic and comprehensive approach to maintain a bank’s competitive advantage.