bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition state spectroscopy via infrared excitation of Li⋯HF and Li⋯DF van der Waals precursors
Authors: Paniagua Miguel , Aguado Alfredo , Lara Manuel , Roncero Octavio
Published: July 2002

The photoinitiated reactions after infrared excitation from the LiHF and LiDF complexes in the reactant valley are studied as an extension of a recent communication by Paniagua et al. [J. Chem. Phys. 109, 2971 (1998)]. For LiHF two broad bands, associated to Δv=1 and 2 transitions, are obtained at which the probability of forming LiF products is very high, >90%. For LiDF the Δv=1 band consists of several narrow resonances, and some of them are supported by the barrier separating reactant and product valleys. Even at these resonances the reaction probability is relatively high, starting at a value about 30% and increasing rapidly to >90% with increasing energy. This implies the tunneling through the barrier. The reason for the high efficiency in the photoinitiated reaction is that the main excitation corresponds to the HF (or DF) stretch within the complex, which is the “active” mode for the reaction in agreement with the presence of a late barrier. These results are very different from those obtained in Li+HF or Li+DF collisions at the same total energies, the reaction probabilities being much lower in these latter since the excitation of the HF (DF) mode is unlikely to occur during the collision.
Equation of state and critical behavior of polymer models: A quantitative comparison between Wertheim’s thermodynamic perturbation theory and computer simulations
Authors: González MacDowell L. , Müller M. , Vega C. , Binder K.
Published: July 2002

We present an application of Wertheim’s thermodynamic perturbation theory (TPT1) to a simple coarse grained model made of flexibly bonded Lennard-Jones monomers. We use both the reference hypernetted chain (RHNC) and mean spherical approximation (MSA) integral equation theories to describe the properties of the reference fluid. The equation of state, the density dependence of the excess chemical potential, and the critical points of the liquid–vapor transition are compared with simulation results and good agreement is found. The RHNC version is somewhat more accurate, while the MSA version has the advantage of being almost analytic. We analyze the scaling behavior of the critical point of chain fluids according to TPT1 and find it to reproduce the mean field exponents: The critical monomer density is predicted to vanish as n−1/2 upon increasing the chain length n while the critical temperature is predicted to reach an asymptotic finite temperature that is attained as n−1/2. The predicted asymptotic finite critical temperature obtained from the RHNC and MSA versions of TPT1 is found to be in good agreement with the Θ point of our polymer model as obtained from the temperature dependence of the single chain conformations.
Theory of magnetoelastic vibrations in spin glass
Authors: Akhiezer I. A. , Belozorov D. P. , Spol’nik Z. A.
Published: July 2002

The spectra of magnetoelastic vibrations in spin glass are determined in the absence and in the presence of an external magnetic field. Various cases of magnetoacoustic resonance are considered.
A flow visualization study of the effects of buoyancy on Taylor vortices
Authors: Ball K. S. , Farouk B.
Published: July 2002

A flow visualization study, using smoke injected into the annular gap between concentric vertical cylinders, has been completed to determine the effects of buoyancy on the development and structure of Taylor vortices. The experimental facility consists of a heated, rotating inner cylinder enclosed by a transparent, stationary outer cylinder. Stationary horizontal endplates are used to seal the annulus. The axisymmetric Taylor vortex flow becomes distorted as buoyancy is introduced into the system. With increasing buoyancy, the flow undergoes a transition to a spiral form, after which another axisymmetric cellular pattern emerges. Finally, the natural convection flow pattern is established.
Vortex ring dynamics at a free surface
Authors: Bernal L. P. , Kwon J. T.
Published: July 2002

The results of a flow visualization study of the evolution of vortex rings near a free surface are presented. The vortex rings were formed underwater with their axis parallel to the free surface one ring diameter below the surface. It is shown that vortex lines in the ring open during the interaction with the surface. The resulting flow field consists of vortex lines, beginning and terminating at the free surface. Data are reported on several features of the vortex ring evolution, which show a large reduction of the propagation speed and an oscillation of the vortex eccentricity as it propagates downstream after the interaction.
On the three-dimensional instability of strained vortices
Authors: Waleffe Fabian
Published: July 2002

The three-dimensional (3-D) instability of a two-dimensional (2-D) flow with elliptical streamlines has been proposed as a generic mechanism for the breakdown of many 2-D flows. A physical interpretation for the mechanism is presented together with an analytical treatment of the problem. It is shown that the stability of an elliptical flow is governed by an Ince equation. An analytical representation for a localized solution is given and establishes a direct link with previous computations and experiments.
Velocity component and diameter distribution characteristics of droplets within two interacting electrohydrodynamic sprays
Authors: Dunn Patrick F. , Snarski Stephen R.
Published: July 2002

The droplet axial and lateral velocity distributions, diameter distributions, and velocity-component–diameter correlations in the interaction region of two sprays of electrically charged, micrometer-sized droplets are presented and discussed. These results reveal the occurrence of interspray droplet mixing and a correlation between velocity component and diameter within the mixing region. They further support that interspray droplet mixing and the evolution toward a spatially uniform combined spray are enhanced with increasing spray charge density and decreasing interneedle spacing.
Bragg scattering of electromagnetic waves by microwave-produced plasma layers
Authors: Kuo S. P. , Zhang Y. S.
Published: July 2002

A set of parallel plasma layers is generated by two intersecting microwave pulses in a chamber containing dry air at a pressure comparable to the upper atmosphere. The dependencies of breakdown conditions on the pressure and pulse length are examined. The results are shown to be consistent with the appearance of tail erosion of the microwave pulse caused by air breakdown. A Bragg scattering experiment, using the plasma layers as a Bragg reflector, is then performed. Both time domain and frequency domain measurements of wave scattering are conducted. The experimental results are found to agree very well with the theory.
A free-electron laser with a rotating quadrupole wiggler
Authors: Levush B. , Antonsen T. M. , Manheimer Wallace M. , Sprangle P.
Published: July 2002

A new rotating quadrupole wiggler configuration for free-electron lasers is proposed. The stability analyses of the particle trajectories in a continuously rotating quadrupole magnetic field and self-fields of a solid beam are performed. The resulting orbit equations are solved exactly and it is shown that high-current beams can be confined. To analyze the potential of this wiggler for free-electron lasers, a set of nonlinear orbit equations is derived which averages over the fast time variation in both the wiggler and radiation fields. By integrating these equations, the linearized single particle gain of the free-electron laser is calculated. It is shown that, at comparable wiggler strengths, the rotating quadrupole wiggler and conventional wiggler give similar gains.
A similarity solution for the axisymmetric viscous-gravity jet
Authors: Wilson Dennis E.
Published: July 2002

A local similarity solution to the viscous-gravity jet valid for large Reynolds number flows is given. The jet is divided into an inner core where axial gradients are small relative to the outer annular region. A similarity transformation is found for the outer region, reducing the resulting differential equations to a two-point boundary value problem. This solution is matched to the inner solution through the boundary conditions. This approach effectively eliminates the mathematical difficulties associated with the unknown free surface and the stress singularity at the exit.
Local flow properties at a viscous free surface
Authors: Lugt Hans J.
Published: July 2002

A local analysis has been made about a point at the free surface of an incompressible viscous fluid flow at steady state by means of series expansions of the Navier–Stokes equations. Dividing streamlines, curvature effects, and the role of vorticity have been studied. A single dividing streamline is always perpendicular to the free surface. This means, in particular, that all steady vortices with one end of their axes attached to a free surface are perpendicular to it. Double dividing streamlines of two-dimensional viscous fluid flows at a free surface always have an angle of 90° between them, whereas double dividing streamlines of inviscid irrotational motion on a free or solid surface are separated by an angle of 60°. For an interface between two immiscible viscous fluids a novel ‘‘refraction law’’ for dividing streamlines has been derived.
Equilibrium shapes of nonaxisymmetric liquid bridges of arbitrary volume in gravitational fields and their potential energy
Authors: Laverón-Simavilla Ana , Perales José M.
Published: July 2002

Bifurcation diagrams of nonaxisymmetric liquid bridges subject to a lateral gravitational force and to both lateral and axial gravitational forces are found by solving the Young–Laplace equation for the interface by a finite difference method. The potential energy of the equilibrium shapes is also calculated. The results obtained show that the slenderness of the bridge determines whether the breaking of the liquid bridge subject to a lateral gravitational force leads to equal or unequal drops. The stability limits calculated are compared with the ones obtained using asymptotic techniques around the cylinder, the agreement being extremely good for a wide range of the parameters.
Bifurcation phenomena in confined thermosolutal convection with lateral heating: Commencement of the double-diffusive region
Authors: Tsitverblit N.
Published: July 2002

As has recently been reported by Tsitverblit and Kit [Phys. Fluids A 5, 1062 (1993)], a vertical rectangular enclosure containing stably stratified brine and differentially heated from its side walls is characterized by complex steady bifurcation phenomena. In the present work, the structure of steady solutions in the enclosure has been studied in detail for several values of the salinity Rayleigh number, RaS, fixed near the commencement of the double-diffusive region. It was found that when the thermal Rayleigh number, RaT, is either very small or sufficiently large, the steady solution is unique while in an intermediate region of this parameter, there exists a great variety of the multiple steady flows, being the result of nondegenerate hysteresis points and isolas of asymmetric solutions forming as RaS is increased. In particular, at the maximal value of RaS considered there have been observed symmetric and asymmetric one-, two-, three-, four-, and five-cell flows. Despite the multiplicity of the flow patterns, a critical interval of the buoyancy ratio has been distinguished, above and below which the generic characteristics of the steady solutions were found to resemble the respective features of the ‘‘successive’’ and ‘‘simultaneous’’ regimes of layer formation whose existence was established in previous studies. Although the set of the steady solutions has been found to contain no linearly stable multicell flows, the perturbation was so long retained in the close proximity of the unstable steady solutions that such flows could be easily observable in the experiment. In spite of the appreciably different range of the Rayleigh numbers, the physically meaningful parameters suggested in previous studies were found to be represented in the present results.
Combined effect of disk inequality and axial gravity on axisymmetric liquid bridge stability
Authors: Slobozhanin Lev A. , Alexander J. Iwan D.
Published: July 2002

The stability of an axisymmetric liquid bridge between unequal circular disks in an axial gravity field is examined for all possible values of the liquid volume and disk separation. The parameter defining the disk inequality is K, the ratio between the radii of the smaller and larger disks. Both axisymmetric and nonaxisymmetric perturbations are considered. The parameter space chosen to delimit the stability regions is the Λ-V plane. Here, Λ is the slenderness (ratio of the disk separation to the mean diameter, 2r0, of the two support disks), and V is the relative volume (ratio of the actual liquid volume to the volume of a cylinder with a radius equal to r0). Wide ranges of the Bond number and the ratio K are considered. Emphasis is given to previously unexplored parts of the stability boundaries. In particular, we examine the maximum volume stability limit for bridges of arbitrary Λ and the minimum volume stability limit for small Λ bridges. The maximum volume stability limit was found to have two distinct properties: large values of the critical relative volume at small Λ, and the possibility that stability is lost to axisymmetric perturbations at small values of K. For a set of K, the maximum Bond number beyond which stability of the bridge is no longer possible for any combination of V and Λ is determined. In addition, the maximum value of the actual liquid volume of a stable bridge that can be held between given disks for all possible disk separations was examined for fixed Bond number. It is found that this volume decreases as K decreases and (depending on the sign of the Bond number) tends to the critical volume of a sessile or pendant drop attached to the larger disk.
Lagrangian method for multiple correlations in passive scalar advection
Authors: Frisch U. , Mazzino A. , Noullez A. , Vergassola M.
Published: July 2002

A Lagrangian method is introduced for calculating simultaneous n-point correlations of a passive scalar advected by a random velocity field, with random forcing and finite molecular diffusivity κ. The method, which is here presented in detail, is particularly well suited for studying the κ→0 limit when the velocity field is not smooth. Efficient Monte Carlo simulations based on this method are applied to the Kraichnan model of passive scalar and lead to accurate determinations of the anomalous intermittency corrections in the fourth-order structure function as a function of the scaling exponent ξ of the velocity field in two and three dimensions. Anomalous corrections are found to vanish in the limits ξ→0 and ξ→2, as predicted by perturbation theory.
A velocity transformation for heat and mass transfer
Authors: Nicoud F. , Bradshaw P.
Published: July 2002

The Van Driest transformation for compressible boundary layers with heat transfer is studied in the low-Mach-number limit. The limiting case leads to a bi-logarithmic type of profile for the mean velocity. A (purely mathematical) analogy with incompressible boundary layers having mass transfer at the wall is identified.
Efficiency scaling law for the two-stream amplifier
Authors: Chen Chiping
Published: July 2002

The mechanism of conversion from the kinetic energy of electron beams to electromagnetic wave energy is investigated in the two-stream amplifier. It is shown that the optimal efficiency of the amplifier scales according to ΔV/V for relativistic electron beams and (ΔV/V)2 for nonrelativistic electron beams, where ΔV is the axial velocity difference in the two beams and V is the mean axial beam velocity. This scaling law not only explains intrinsically low efficiencies (≲5%) observed in numerous nonrelativistic two-stream amplifier experiments, but also predicts that the optimal efficiency of a relativistic two-stream amplifier is typically greater than that of a nonrelativistic two-stream amplifier by one order of magnitude.
Effect of crystal stoichiometry on activation efficiency in Si implanted, rapid thermal annealed GaAs
Authors: Von Neida A. R. , Pearton S. J. , Stavola M. , Caruso R.
Published: July 2002

A dramatic dependence on crystal stoichiometry has been observed for the donor activation efficiency of low doses of Si ions implanted into undoped semi-insulating GaAs. Samples from liquid encapsulated Czochralski crystals grown from melts containing As concentrations varying from 47 1/2 to 65 at. % were implanted with 100 keV 29Si ions at a dose of 5×1012 cm−2. Following a rapid, capless annealing cycle (950 °C, 5 s), the surface-depletion corrected activation efficiency ranged from 26 to 91%, with the higher efficiencies for higher As concentrations. In contrast, co-implantation of As and Si into standard (50 at. % As) GaAs resulted in an increase in activation efficiency from 59 to 68% for optimum As doses.
Origin of the band-edge states in [001] thin superlattices of GaAs/AlAs
Authors: Nelson J. S. , Fong C. Y. , Batra Inder P.
Published: July 2002

The self-consistent pseudopotential method is used to investigate the origin of the valence- and conduction-band edge states in thin [001] superlattices of (GaAs)n-(AlAs)n, for n=2, 3, and 4. We find that these superlattices have a staggered band alignment (type II superlattice), with the highest occupied valence-band state (hole) localized in the GaAs region and the lowest unoccupied conduction-band state (electron) localized in the AlAs region. The change in the lowest conduction-band edge states in the GaAs and AlAs region with layer thickness, suggests a transition to a nonstaggered alignment (type I superlattice) at large layer thicknesses. A critical layer thickness is estimated for this transition.
Microcleavage transmission electron microscopy applied to the interfacial structure of multilayers and microstructure of small particles on a substrate
Authors: Lepêtre Y. , Ziegler E. , Schuller Ivan K.
Published: July 2002

We have developed a new technique useful in imaging microstructures such as small particles, multilayers, and superlattices on a substrate. By producing images at various angles with respect to the substrate we have been able to obtain new information on interfacial structure not yet available with other techniques.
Phase transformation kinetics—the role of laser power and pulse width in the phase change cycling of Te alloys
Authors: Rubin K. A. , Barton R. W. , Chen M. , Jipson V. B. , Rugar D.
Published: July 2002

The effect of laser pulse width and amplitude on the kinetics of laser-induced phase transformations of thin films of Te alloys has been mapped. This map, called a phase transformation kinetics diagram, shows distinct regions of crystallization and amorphization and allows important material parameters to be determined. The observed regions were correlated with results from temperature modeling. The minimum crystallization time was measured to be 50 ns for pure Te and increases to 550 ns for Te80Sn20 and 80 μs for Te90Ge10. A boundary, determined by the critical quench rate, separates the region of melt followed by amorphous quench, from melt followed by crystallization. Three methods of reversible cycling are demonstrated.
Very high relaxation oscillation frequency in dry-etched short cavity GaAs/AlGaAs multiquantum well lasers
Authors: Yuasa Tonao , Yamada Tomoyuki , Asakawa Kiyoshi , Ishii Makoto , Uchida Mamoru
Published: July 2002

Relaxation oscillation frequencies are reported for short cavity GaAs/AlGaAs multiquantum well lasers with dry-etched facets. Decreased electron and photon lifetimes combined with the high differential gain constant of short cavity lasers yield very high relaxation oscillation frequencies. A peak value of 24 GHz was achieved with a 40-μm-long laser, and a linear relationship between frequency and the square root of the output power is observed.
Optical detection of interwell-exciton transfer in In0.53Ga0.47As/InP quantum wells grown by chemical beam epitaxy
Authors: Sauer R. , Harris T. D. , Tsang W. T.
Published: July 2002

We use photoluminescence excitation spectroscopy to show that excitons confined to single quantum wells in In0.53Ga0.47As/InP communicate through thin barriers. The experiments are performed on a sample grown by chemical beam epitaxy with four quantum wells of thicknesses between ∼18 and 60 Å separated by barriers as thin as 30 Å. Exciton transfer between adjacent wells is observed.
Nonradiative carrier recombination processes of n-Hg1−xCdxTe as determined by magnetic quantum oscillations
Authors: Takita K. , Ippōshi T. , Masuda K.
Published: July 2002

A mew method to determine the dominant process of nonradiative carrier recombination is proposed and demonstrated for n-Hg1−xCdxTe (x≂0.2). This method is an application of the magnetic quantum oscillations of high electric field magnetoresistance which were observed successfully in a wide temperature range from 4.2 to 100 K by using a pulse technique and a second derivatives method, where Shockley–Read recombination as well as Auger recombination could be observed as an oscillatory behavior. The dominant origins of the oscillations could be clearly determined from the temperature dependence of the peak positions. Measurement and analysis were performed for a variety of samples with various carrier concentrations n and various electron mobilities μH (n=3×1014–2×1015 cm−3, μH=8×103–3×105 cm2/V s at 4.2 K). A competitive behavior of Shockley–Read and Auger processes and its sample dependence were clearly demonstrated.
Growth and properties of In-doped CdMnTe-CdTe superlattices
Authors: Bicknell R. N. , Giles N. C. , Schetzina J. F.
Published: July 2002

The first successful substitutional doping of dilute magnetic semiconductor superlattices composed of alternating layers of CdMnTe and CdTe is reported. These n-type In-doped multilayer structures were prepared using a new thin-film growth technique, photoassisted molecular beam epitaxy, in which the substrate is illuminated with visible light during the deposition process. The electrical, optical, and structural properties of the CdMnTe-CdTe superlattices are discussed.
Low-temperature film growth of Si by reactive ion beam deposition
Authors: Yamada Hiroshi , Torii Yasuhiro
Published: July 2002

A new low-temperature film formation technique is proposed. It uses ionized species produced by an electron cyclotron resonance-type microwave ion source with reactive gases and controlled in the low ion energy region, less than about 500 eV. Good quality homoepitaxial films on Si(111) are obtained at 600 °C and 100–500 eV ion energy by using SiH4 as a material gas. By increasing the ion energy to 250-300 eV, homoepitaxial growth at 400 °C can be achieved. Polycrystalline Si films on the same type of substrates can also be obtained at 200 °C.
Duplex coatings for the protection of magneto-optic alloys against oxidation and corrosion
Authors: Frankenthal R. P. , van Dover R. B. , Siconolfi D. J.
Published: July 2002

Thin films of Fe or Co and rare-earth metals, such as Tb and Gd, are being developed as high density, mass memory storage media in magneto-optic devices. It is shown that a 10-nm duplex film consisting of a metal that is passivated in air, such as Cr or Al, and a diffusion barrier, such as Nb, will protect these alloys against oxidation and corrosion at temperatures up to at least 200 °C. The duplex film is better than a single passivated metal layer, which may interdiffuse with the alloy, or than a dielectric, which may be reduced by the reactive rare-earth element.
Raman scattering study of folded acoustic phonons in GaAs/InxGa1−xAs strained-layer superlattices
Authors: Lockwood D. J. , Dharma-wardana M. W. C. , Moore W. T. , Devine R. L. S.
Published: July 2002

The excitation of zone-folded longitudinal acoustic phonons in GaAs/InxGa1−xAs strained-layer superlattices is observed by Raman scattering. The Raman data agree well with theory and are consistent with high indium concentrations achieved in the fabrication of these metastable superlattices of good crystalline quality.
Double-crystal x-ray topographic determination of local strain in metal-oxide-semiconductor device structures
Authors: Qadri Syed B. , Ma David , Peckerar Martin
Published: July 2002

A double-crystal x-ray topograph was used to determine local strain in metal-oxide-semiconductor (MOS) transistor test chips. The double-crystal machine could sense strains as small as 10−6, with a spatial resolution of a few micrometers. Results indicate that two types of strain are present: local surface strain as well as the more familiar strain due to bulk deformation of the crystal. Both types of strain have been correlated with surface mobility changes in n-channel metal-oxide-semiconductor (nMOS) transistors.
Photoemission oscillations during epitaxial growth
Authors: Eckstein J. N. , Webb C. , Weng S.-L. , Bertness K. A.
Published: July 2002

We report the use of in situ, near-threshold photoemission to study the dynamics of GaAs surfaces during epitaxial crystal growth and, in particular, the observation of oscillations in the photoemitted current. These oscillations are found to depend upon the growth rate in the same manner as do reflecting high-energy electron diffraction intensity oscillations, occurring at the monolayer accumulation rate. We believe that they depend upon a cyclical variation in the step edge density on the growing surface and discuss the mechanism through which the oscillatory current may result from surface states or surface dipoles.
Enhanced Cu-Teflon adhesion by presputtering prior to the Cu deposition
Authors: Chang Chin-An , Baglin J. E. E. , Schrott A. G. , Lin K. C.
Published: July 2002

Adhesion of Cu to Teflon has been studied by depositing Cu to Teflon with and without a presputtering prior to the Cu deposition. Without presputtering, a weak adhesion is observed, with a value of 1 g/mm, which fails the scotch tape test. With a presputtering using 500 eV Ar+ ions, the adhesion rapidly increases, becoming evident after a sputtering of 10 s, and reaches maximal increases of 50 times at longer sputtering times. All the Cu films deposited after presputtering show strong adhesion, and can only be removed by forceful scratching with sharp tools. The presputtering was shown to change both the surface morphology of Teflon, with the deposited Cu following the morphologies created, and the interface chemical bonding between Cu and Teflon as revealed by x-ray photoelectron spectroscopy. Exposure of the presputtered Teflon to air prior to the Cu deposition shows no effect on the strong adhesion obtained. An interface bonding model is suggested for the enhanced adhesion observed.
Carrier transport property in the amorphous silicon/amorphous silicon carbide multilayer studied by the transient grating technique
Authors: Hattori K. , Mori T. , Okamoto H. , Hamakawa Y.
Published: July 2002

The in-plane diffusion coefficient and lifetime of photogenerated carriers in amorphous silicon have been measured by the transient grating technique in amorphous silicon (a-Si)/silicon carbide (a-SiC) multilayered structures, as a function of the a-Si well layer thickness. As the layer thickness is decreased, the diffusion coefficient gradually decreases, while the lifetime drastically increases by more than one order of magnitude than that in thick unlayered a-Si. These behaviors suggest that the carrier transport is determined both by carrier interaction with shallow traps at a-Si/a-SiC interfaces and by quantum-size effect through weakened carrier coupling with deep states.
High-pretilt polyphenylene layers for liquid-crystal displays
Authors: Nehring J. , Amstutz H. , Holmes P. A. , Nevin A.
Published: July 2002

High-pretilt angles (of about 20°), as required for highly multiplexable liquid-crystal displays based on the ‘‘supertwisted birefringence effect,’’ can be obtained by rubbing polyphenylene layers. The aligning properties of such layers depend somewhat on the type of the precursor polymer from which the polyphenylene is made and on the substrate on which it is formed. A 120×240 matrix display prototype with 270° twist and rubbed polyphenylene orientation layers showed a uniform and stable surface alignment over the whole display area.
Influence of an intentional substrate misorientation on deep electron traps in AlGaAs grown by molecular beam epitaxy
Authors: Radulescu D. C. , Schaff W. J. , Wicks G. W. , Calawa A. R. , Eastman L. F.
Published: July 2002

Deep level transient capacitance spectroscopy has been used to investigate deep level electron traps in thick silicon-doped AlGaAs grown by molecular beam epitaxy (MBE) on GaAs substrates intentionally misoriented (tilted) a few degrees from a nominally (001) surface. Of the three dominant traps observed in AlGaAs, the concentrations of two of these are observed to be a direct function of the substrate tilt angle and tilt direction. The concentration of the third dominant trap, which is related to the DX center, is independent of substrate misorientation during MBE. These observations will help in identifying which impurities and/or defects are affected by substrate misorientation during MBE growth in addition to identifying the origin of deep levels in AlGaAs.
Use of thin AlGaAs and InGaAs stop-etch layers for reactive ion etch processing of III-V compound semiconductor devices
Authors: Cooper C. B. , Salimian S. , MacMillan H. F.
Published: July 2002

Reactive ion etching is important for III-V device fabrication. Commonly encountered applications include the need to remove an epitaxial layer selectively from underlying layers and the need for definition of mesas and other structures with carefully controlled dimensions. We present results showing the use of very thin Al0.9Ga0.1As and In0.2Ga0.8As stop-etch layers, which when used in conjunction with a particular etch chemistry can provide highly selective removal of epitaxial layers in GaAs-based III-V compound semiconductors. In addition, we report the selective removal of an Al0.3Ga0.7As layer from underlying GaAs by the use of a thin In0.2Ga0.8As interlayer.
Effect of noble metal buffer layers on superconducting YBa2Cu3O7 thin films
Authors: Chien C. L. , Xiao Gang , Streitz F. H. , Gavrin A. , Cieplak M. Z.
Published: July 2002

Superconducting YBa2Cu3O7 thin films have been prepared by using a magnetron sputtering system in the single-source mode. Samples deposited on [100] single-crystal MgO with and without a Au buffer layer all show high transition temperatures (82–87 K). The use of a Au buffer layer significantly improves the superconducting properties, particularly the Meissner effect and critical current density (3.3×106 A/cm2 at T=2 K and 3.5×104 A/cm2 at T=77 K). The Au films remain metallic after high-temperature annealing in an oxygen atmosphere. We propose to use Au buffer layers as current shunts to protect superconducting films and devices.
Generation of blue light by intracavity frequency mixing of the laser and pump radiation of a miniature neodymium:yttrium aluminum garnet laser
Authors: Risk W. P. , Baumert J.-C. , Bjorklund G. C. , Schellenberg F. M. , Lenth W.
Published: July 2002

Potassium titanyl phosphate (KTiOPO4,KTP) has been used to generate blue 459-nm radiation by intracavity sum frequency mixing of the circulating 1064-nm laser radiation of a miniature neodymium:yttrium aluminum garnet laser and the 809-nm radiation used as the pump source. A blue output power of approximately 1 mW cw was obtained using 275 mW of pump power from an infrared dye laser. Gain-switched operation leading to high 459-nm peak powers was demonstrated. Direct rapid modulation of the blue radiation was achieved by modulating the pump. In preliminary experiments a high-power laser diode was used as the pump source for the generation of blue radiation.
I
n s
i
t
u observations of misfit dislocation propagation in GexSi1−x/Si(100) heterostructures
Authors: Hull R. , Bean J. C. , Werder D. J. , Leibenguth R. E.
Published: July 2002

We describe in situ electron microscrope observations of the motion of misfit dislocations in Ge0.3Si0.7/Si(100) heterostructures. A 350 Å Ge0.3Si0.7/Si(100) structure is grown by molecular beam epitaxy at 550 °C. Although this is below the critical thickness for this composition and growth temperature, we observe misfit dislocation nucleation and propagation as a function of in situ annealing temperature in the electron microscope. This confirms the metastable nature of GeSi strained-layer growth. The misfit dislocation density increases continuously with temperature, passing through an accelerated transition at ∼850 °C. We also report preliminary measurements of misfit dislocation velocity, which establish the identical relationship between threading and misfit dislocations in this system.
Changes in the electronic properties of bulk GaAs by thermal annealing
Authors: Asom M. T. , Parsey J. M. , Kimerling L. C. , Sauer R. , Thiel F. A.
Published: July 2002

Bulk GaAs grown by the Bridgman technique changes its electronic properties in response to heat treatment. These changes were studied by deep level transient spectroscopy, photoluminescence, and Hall effect measurements. We report the dependence of the conductivity changes on starting material composition, annealing temperature, and annealing duration. The changes are related to the stability of a shallow acceptor which is present in concentrations ≥1016 cm−3 and reflect the equilibration of native defects introduced during the crystal growth process. The implication of this study is that as-grown GaAs is a metastable material with its ultimate electrical properties being determined by process conditions.
Stress reduction and doping efficiency in B- and Ge-doped silicon molecular beam epitaxy films
Authors: Hirayama Hiroyuki , Tatsumi Toru , Aizaki Naoaki
Published: July 2002

Lattice defects in boron highly doped silicon molecular beam epitaxy films (B:2×1020 cm−3) were reduced by a simultaneous doping of germanium and boron. The defect reduction mechanism was investigated with surface defect observation, x-ray diffraction, and Raman spectroscopy. The growth rate of Si and the doping level of Ge and B were controlled precisely, and the suitable germanium-to-boron ratio was determined. At a germanium-to-boron ratio of 4:1, a drastic decrease of the defect density was observed, and the doping efficiency was improved.
Efficient, high-power (>150 mW) grating surface emitting lasers
Authors: Evans G. A. , Carlson N. W. , Hammer J. M. , Lurie M. , Butler J. K. , Carr L. A. , Hawrylo F. Z. , James E. A. , Kaiser C. J. , Kirk J. B. , Reichert W. F. , Chinn S. R. , Shealy J. R. , Zory P. S.
Published: July 2002

Surface emitting AlGaAs second-order distributed Bragg reflector lasers using a superlattice graded-index separate confinement heterostructure with a single quantum well have been fabricated. The total peak power is emitted coherently from both gratings into a 0.06° full width half-power single lobe far field pattern. Peak powers are in excess of 150 mW. The external differential quantum efficiency is as high as 30%. Under severe current modulation conditions, the stable single longitudinal mode had 20–45 dB wavelength side mode rejection.
Ellipsometric spectra of silicon-on-insulator wafers
Authors: Liang Zhongning , Mo Dang
Published: July 2002

Spectroellipsometry (SE) has been used to investigate the silicon-on-insulator (SOI) structures formed by oxygen ion implanted into silicon and the corresponding annealed samples. A simple equation to estimate the thickness of the SOI structure is presented. Using a multilayer model and the Bruggeman effective medium approximation, we have analyzed the thicknesses and compositions of the SOI structures. Having been compared with the results determined by the Rutherford backscattering, spreading resistance probe, and infrared absorption measurements, our results show that, after high-temperature annealing, the top layer of the SOI structure is close to a perfect single crystal silicon, and the buried SiO2 is in a disorder phase. The thicknesses determined by all these measurements are in good agreement with each other.
Electro-optic phase modulation in GaAs/AlGaAs quantum well waveguides
Authors: Zucker J. E. , Hendrickson T. L. , Burrus C. A.
Published: July 2002

We present the first absolute measurements of the electric-field-induced refractive index change in GaAs/AlGaAs quantum well waveguides. Phase and intensity modulation are characterized as a function of wavelength both above and below the n=1 exciton resonances.
Influence of coupling of wells on spontaneous emission line shape in GaAs/GaAlAs multiple quantum wells
Authors: Krahl M. , Christen J. , Bimberg D. , Weimann G. , Schlapp W.
Published: July 2002

The results of a comparative study of the low-temperature luminescence line shape of molecular beam epitaxially grown GaAs/GaAlAs coupled and uncoupled quantum wells (QW’s) are presented. A pronounced spectral narrowing of the emission line with increasing coupling of QW’s is found. A detailed model for spontaneous emission line shapes for real superlattices is established: The superlattice density of states is calculated in the framework of envelope function approximation. Interface roughness yields Gaussian distribution of layer thicknesses resulting in a broadened density of states. The variance of this distribution function is a measure of interface quality. The reduction of the variance with increased coupling is explained by an enhanced excitonic averaging mechanism in superlattices.
Transport measurements of Sb contacts to InP(110)
Authors: Zahn D. R. T. , McLean A. B. , Williams R. H. , Esser N. , Richter W.
Published: July 2002

The electrical properties of antimony contacts to vacuum cleaved n- and p-type InP(110) surfaces were studied using current-voltage and capacitance-voltage techniques. While the Sb/n-InP(110) interface forms an ‘‘ohmic’’ contact, an extremely large Schottky barrier was found at Sb/p-InP(110) contacts.
Limitations of TiSi2 as a source for dopant diffusion
Authors: Probst V. , Schaber H. , Lippens P. , Van den hove L. , De Keersmaecker R.
Published: July 2002

The application of TiSi2 as a dopant diffusion source for boron and arsenic was studied. The TiSi2 layers were formed by the usual salicide process and doped by ion implantation. Diffusion was carried out by various furnace and rapid thermal processing steps. Using secondary ion mass spectrometry, scanning electron microscopy, and x-ray diffraction, clear evidence for compound formation between Ti and the two dopant species is found. This leads to low dopant concentrations at the silicide/silicon interface, very poor efficiency of the diffusion source, and unacceptably high contact resistivities.
Electrical and photovoltaic properties of amorphous chalcogenide thin-film p-n junctions
Authors: Tohge Noboru , Kanda Kimio , Minami Tsutomu
Published: July 2002

Amorphous chalcogenide thin-film p-n junctions have been formed between p-type As2Se3 or Ge20Se80 and n-type Ge20Bi15Se65. The rectifying behavior was observed only for the junctions which were formed by depositing the p-type films on the annealed n-type films. The forward currents in these junctions were found to be space-charge-limited, as in the previously formed p-type film/n-type bulk glass junctions. The photovoltaic properties of the thin-film p-n junctions have been improved, compared with the film/bulk glass junctions, due to the decrease in series resistance of the cells.
Radiation-induced enhancement of minority-carrier lifetimes in metal/SiO2/Si capacitors having oxides grown in O2 with trichloroethane additive
Authors: Wang Xie W. , Wang Yu , Nishioka Yasushiro , da Silva Eronides F. , Ma T. P.
Published: July 2002

It has been found that the minority-carrier lifetimes in metal/SiO2/Si capacitors having oxides grown in O2 with very small amounts (much smaller than typically used) of trichloroethane can be substantially enhanced by x-ray irradiation. The depth profile data showed that, immediately after irradiation, the lifetimes in a region close to the SiO2/Si interface would increase significantly while those in the deeper depletion region remained unchanged. Thereafter, the lifetimes throughout the region profiled (1–2 μm) would continuously change with time, and would eventually stabilize at a level much higher than that prior to irradiation. The time constant for lifetimes to reach steady state is typically 1–2 days at room temperature. These results will be explained in terms of the passivation of the generation-recombination centers in Si by liberated Cl after irradiation.
Simulation of extrinsic bistability of resonant tunneling structures
Authors: Liu H. C.
Published: July 2002

A simple biasing circuit for measuring current-voltage characteristics of resonant tunneling double-barrier structures exhibits extrinsic bistabilities due to oscillations, which we show through large-signal simulations.
Mammalian and chicken I forms of gonadotropin-releasing hormone in the gonads of a protochordate,
Ciona intestinalis
Authors: Di Fiore Maria M. , Rastogi Rakesh K. , Ceciliani Fabrizio , Messi Elio , Botte Virgilio , Botte Lucio , Pinelli Claudia , D'Aniello Biagio , D'Aniello Antimo
Published: July 2002

Two forms of gonadotropin-releasing hormone (GnRH) were isolated from the gonads of the tunicate,
Ciona intestinalis
. The primary structure of the purified peptides was determined by MS and chemical sequence analysis. Both GnRH forms have blocked NH
2
and COOH termini, and their primary structures are identical to mammalian (mGnRH) and chicken I (cGnRH-I) forms reported previously in vertebrates. A total of 1.2 mg of purified cGnRH-I and 0.98 mg of mGnRH was obtained from 100 g of Ciona gonads. The physiological effects of native GnRHs included the induction of synthesis and secretion of sex steroids from ciona gonads and the secretion of luteinizing hormone from rat pituitary. These results suggest that the primary structure and functional roles of mGnRH and cGnRH-I have been highly conserved throughout evolution of chordates.
How to assess the relative importance of different colonization routes of pathogens within hospital settings
Authors: Pelupessy Inti , Bonten Marc J. M. , Diekmann Odo
Published: July 2002

The emergence of antibiotic resistance among nosocomial pathogens has reemphasized the need for effective infection control strategies. The spread of resistant pathogens within hospital settings proceeds along various routes of transmission and is characterized by large fluctuations in prevalence, which are typical for small populations. Identification of the most important route of colonization (exogenous by cross-transmission or endogenous caused by the selective pressure of antibiotics) is important for the design of optimal infection control strategies. Such identification can be based on a combination of epidemiological surveillance and costly and laborious as well as time-consuming methods of genotyping. Furthermore, analysis of the effects of interventions is hampered by the natural fluctuations in prevalence. To overcome these problems, we introduce a mathematical algorithm based on a Markov chain description. The input is longitudinal prevalence data only. The output is estimates of the key parameters characterizing the two colonization routes. The algorithm is tested on two longitudinal surveillance data sets of intensive care patients. The quality of the estimates is determined by comparing them to accurate estimates based on additional information obtained by genotyping. The results warrant optimism that this algorithm may help to quantify transmission dynamics and can be used to evaluate the effects of infection control interventions more carefully.
Monoclonal antibodies reveal receptor specificity among G-protein-coupled receptor kinases.
Authors: Oppermann M , Diversé-Pierluissi M , Drazner M H , Dyer S L , Freedman N J , Peppel K C , Lefkowitz R J
Published: July 2002

Guanine nucleotide-binding regulatory protein (G protein)-coupled receptor kinases (GRKs) constitute a family of serine/threonine kinases that play a major role in the agonist-induced phosphorylation and desensitization of G-protein-coupled receptors. Herein we describe the generation of monoclonal antibodies (mAbs) that specifically react with GRK2 and GRK3 or with GRK4, GRK5, and GRK6. They are used in several different receptor systems to identify the kinases that are responsible for receptor phosphorylation and desensitization. The ability of these reagents to inhibit GRK- mediated receptor phosphorylation is demonstrated in permeabilized 293 cells that overexpress individual GRKs and the type 1A angiotensin II receptor. We also use this approach to identify the endogenous GRKs that are responsible for the agonist-induced phosphorylation of epitope-tagged beta2- adrenergic receptors (beta2ARs) overexpressed in rabbit ventricular myocytes that are infected with a recombinant adenovirus. In these myocytes, anti-GRK2/3 mAbs inhibit isoproterenol-induced receptor phosphorylation by 77%, while GRK4-6-specific mAbs have no effect. Consistent with the operation of a betaAR kinase-mediated mechanism, GRK2 is identified by immunoblot analysis as well as in a functional assay as the predominant GRK expressed in these cells. Microinjection of GRK2/3-specific mAbs into chicken sensory neurons, which have been shown to express a GRK3-like protein, abolishes desensitization of the alpha2AR-mediated calcium current inhibition. The intracellular inhibition of endogenous GRKs by mAbs represents a novel approach to the study of receptor specificities among GRKs that should be widely applicable to many G-protein-coupled receptors.
P
1
,
P
4
-Dithio-
P
2
,
P
3
-monochloromethylene diadenosine 5′,5‴-
P
1
,
P
4
-tetraphosphate: A novel antiplatelet agent
Authors: Chan Samuel W. , Gallo Steven J. , Kim Byung K. , Guo Mao J. , Blackburn G. Michael , Zamecnik Paul C.
Published: July 2002

We have previously demonstrated in a series of searches for antithrombotic agents that diadenosine 5′,5‴-
P
1
,
P
4
-tetraphosphate (AppppA) and its analogues are competitive inhibitors of ADP-induced platelet aggregation. Among various analogues, the
P
2
,
P
3
-monochloromethylene analog of AppppA (AppCHClppA) is superior to unmodified AppppA in its antiplatelet and antithrombotic effects. In this communication, we compare the antiplatelet potency of five newly synthesized agents with that of AppCHClppA. The five new agents include four diadenosine polyphosphate analogues [Ap
s
pCHClpp
s
A (p
s
indicates a thiophosphate), dAppCHClppdA, dAp
s
pCHClpp
s
dA, and AppCHClpCHClppA], and an adenosine tetraphosphate analogue (AppCHClpCHClp). When tested for their inhibitory effects on platelet aggregation by ADP, the most promising agent among them was Ap
s
pCHClpp
s
A. Both molecular and functional integrity of this compound proved to be stable in blood at 37°C for at least 3 h. It also showed an excellent heat stability. This agent inhibits a number of aspects of ADP-induced platelet activation—e.g., release reaction, cytoplasmic calcium mobilization, thromboxane production, fibrinogen binding sites, and platelet factor 3 activity. Moreover, platelet aggregation induced by agonists other than ADP—e.g., arachidonic acid, collagen, and epinephrine—was inhibited partially by Ap
s
pCHClpp
s
A. It is concluded that (
i
) Ap
s
pCHClpp
s
A is a promising antiplatelet agent; (
ii
) it is resistant to blood phosphodiesterases and stable to heat treatment; (
iii
) platelet aggregation induced by collagen, epinephrine, or arachidonic acid is also inhibited in part by this agent; and (
iv
) specificity of the inhibitory effects is presented by unmodified adenosine moieties of the agent. Resistance to phosphodiesterases raises the possibility of oral administration.