bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of viscous fingering in miscible displacements with nonmonotonic viscosity profiles
Authors: Manickam O. , Homsy G. M.
Published: July 2002

The nonlinear evolution of viscous fingering instabilities in miscible displacement flows in porous media with nonmonotonic viscosity profiles is investigated. The flow is accurately simulated using a Hartley transform based spectral method. A flow with nonmonotonic viscosity profile has an unstable region followed downstream by a stable region. Instabilities first begin in the unstable region and then grow and penetrate the stable region. The striking contrast between viscous fingering in flows with monotonic and nonmonotonic viscosity profiles is the direction of fluid penetration. The nonmonotonicity in the viscosity profile gives rise to a new phenomena of ‘‘reverse’’ fingering in which the displaced fluid fingers through the displacing fluid more readily than vice versa. A forward and a reverse mixing lengths are defined to characterize the growth of the mixing zone in the two directions. At large times, both the forward and reverse mixing lengths grow linearly in time. A model nonmonotonic viscosity profile is used to parametrically study the asymptotic mixing rates. The parametric study shows that for a given end point and maximum viscosities the growth rate of the mixing zone varies nonmonotonically with the length of the stable barrier in the viscosity profile. A physical mechanism is put forth to explain the observed phenomena of reverse fingering and its dependence on the parameters of the problem. Finally, a finger is isolated and its evolution is studied to understand the differences in the mechanisms that control the growth of a finger in flows with monotonic and nonmonotonic viscosity profiles.
Wetting effects on the spreading of a liquid droplet colliding with a flat surface: Experiment and modeling
Authors: Fukai J. , Shiiba Y. , Yamamoto T. , Miyatake O. , Poulikakos D. , Megaridis C. M. , Zhao Z.
Published: July 2002

In this paper an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented. The theoretical model accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact-angle hysteresis. Experiments with impingement surfaces of different wettability were performed. The study showed that the maximum splat radius decreased as the value of the advancing contact angle increased. The effect of impact velocity on droplet spreading was more pronounced when the wetting was limited. The experimental results were compared to the numerical predictions in terms of droplet deformation, splat radius, and splat height. The theoretical model predicted well the deformation of the impacting droplet, not only in the spreading phase, but also during recoiling and oscillation. The wettability of the substrate upon which the droplet impinges was found to affect significantly all phases of the spreading process, including the formation and development of a ring structure around the splat.
Numerical simulations of Richtmyer–Meshkov instabilities in finite-thickness fluid layers
Authors: Mikaelian Karnig O.
Published: July 2002

Direct numerical simulations of Richtmyer–Meshkov instabilities in shocked fluid layers are reported and compared with analytic theory. To investigate new phenomena such as freeze-out, interface coupling, and feedthrough, several new configurations are simulated on a two-dimensional hydrocode. The basic system is an A/B/A combination, where A is air and B is a finite-thickness layer of freon, SF6, or helium. The middle layer B has perturbations either on its upstream or downstream side, or on both sides, in which case the perturbations may be in phase (sinuous) or out of phase (varicose). The evolution of such perturbations under a Mach 1.5 shock is calculated, including the effect of a reshock. Recently reported gas curtain experiments [J. M. Budzinski et al., Phys. Fluids 6, 3510 (1994)] are also simulated and the code results are found to agree very well with the experiments. A new gas curtain configuration is also considered, involving an initially sinuous SF6 or helium layer and a new pattern, opposite mushrooms, is predicted to emerge. Upon reshock a relatively simple sinuous gas curtain is found to evolve into a highly complex pattern of nested mushrooms.
Stabilization of thin liquid films by internal heat generation
Authors: Oron Alexander , Peles Yoav
Published: July 2002

Stability properties of a thin liquid film subject to internal heat generation are studied within the framework of the long-wave theory. A strongly nonlinear evolution equation for the film interface is derived, studied, and solved numerically. Linear stability analysis is performed by a further reduction of the evolution equation. Internal heat generation is found to stabilize the film interface. The film is linearly stable if the intensity of internal heat generation is sufficiently strong. Within the range of linear instability the nonlinear evolution of the film results in the film rupture.
Surface tension force on a partly submerged body
Authors: Keller Joseph B.
Published: July 2002

The vertical component of the surface tension force on a body partly submerged in a liquid is shown to equal the weight of liquid displaced by the meniscus. It is upward if the meniscus is depressed and downward if the meniscus is elevated. Previously this was known for vertical axially symmetric bodies and for two-dimensional vertical plates. The vertical component of the pressure force on the body is shown to equal the weight of liquid which would fill the volume bounded by the wetted surface of the body, a vertical cylinder through the waterline, and the original horizontal free surface.
Modulational instability of Langmuir wave packets
Authors: Popel S. I. , Tsytovich V. N. , Vladimirov S. V.
Published: July 2002

The broad spectra of random waves in unmagnetized plasmas are considered. A universal nonlinear formalism is developed for description of the nonlinear effects (modulational instability, etc.) in which random plasma waves take part. The integral equations for perturbations of wave field correlation functions are obtained. In a description of the modulational instability of random wave packets these equations play the same role as the set of coupled equations for the fields of modulational perturbations in the case of a single monochromatic pump wave. On the basis of these integral dispersion equations the modulational instability of broad wave spectra is investigated for the one-dimensional situation (when directions of propagation of the random waves coincide with that of the modulational perturbations) and for isotropic wave turbulence.
Nonlinear evolution of the toroidal Alfvén instability using a gyrofluid model*
Authors: Spong D. A. , Carreras B. A. , Hedrick C. L.
Published: July 2002

Discrete shear Alfvén modes such as the TAE (toroidal Alfvén eigenmode) are susceptible to destabilization by energetic alpha populations and neutral beams; this can lead to enhanced fast ion losses and degraded heating efficiencies. A gyrofluid model with Landau closure has been developed for understanding both the linear and nonlinear phases of these instabilities. The linear wave–particle resonances necessary to excite Alfvén instabilities are included in a coupled set of fluid equations. This model is used to analyze several nonlinear saturation mechanisms that arise from mode coupling effects. The effects of shear flow velocity generation (through the Reynolds stress) and localized current generation (leading to modifications in the q profile) are specifically examined.
Theory of electron multipactor in crossed fields
Authors: Riyopoulos Spilios , Chernin David , Dialetis Demos
Published: July 2002

A general theory of multipactor in orthogonal electric and magnetic fields is given. The model consists of two parallel plates of known secondary emission properties, across which a time varying voltage is applied, and between which a constant magnetic field is applied. Expressions are derived for the resonant phases at which the RF-driven cascades occur; these reduce to previously derived expressions in the limit of the vanishing magnetic field. In addition, this work obtains the conditions governing the stability of the motion about those phases, as well as a dynamic constraint from imposing the restriction that each impact on a plate is the first impact that is allowed by the equations of motion. Chaotic effects from the random ejection velocities of the secondaries are addressed for the first time. It is proven that the phase focusing effect from the radio frequency (RF) interaction will overcome the dispersive effect from the random emission, provided that the mean square emission velocity is sufficiently small; in that case stability of the multipactor is determined by the stability of an ‘‘ideal’’ multipactor with zero emission velocity. That reduces the multipactor parameter space to only two control parameters: the normalized RF electric and DC magnetic field strengths. The multipactor prone region is mapped over the entire parameter space by applying both dynamic and secondary yield criteria; previous studies have been limited to specific cases. Finally a simplified model is adopted to address collective effects and multipactor saturation from the space charge buildup. In addition to the mutual electron repulsion, we find that the previously neglected interaction of the electron sheath with the induced image charge on the plates is important to saturation.
Phase angle diffusion of newborn ions in the self-consistently generated fields in solar wind plasmas
Authors: Cao J. B. , Mazelle C. , Zhou G. C.
Published: July 2002

The phase angle diffusion, pitch angle diffusion, and energy diffusion of newborn ions in the self-consistently generated fields in solar wind plasmas are studied by means of a one-dimensional electromagnetic hybrid code. For newborn ions, the time for phase angle diffusing to 2π is a little shorter than the time for pitch angle scattering to a relatively thin complete shell, and it is much shorter than the energy scattering time for broadening of the shell toward a thermal distribution. The speed of phase angle diffusion increases monotonously with the injection velocity, but it does not change in the same way with the injection rate. The phase angle diffusion of heavier injected ions is slower than that of lighter injected ions. The complete pickup process of newborn ions should consist of four stages: (1) the creation of the newborn ions and macroperpendicular pickup due to the motional electric field; (2) phase angle diffusion; (3) pitch angle diffusion; and (4) energy diffusion.
The past, present, and future of Z pinches
Authors: Haines M. G. , Lebedev S. V. , Chittenden J. P. , Beg F. N. , Bland S. N. , Dangor A. E.
Published: July 2002

The Z pinch is enjoying a renaissance as the world’s most powerful yet efficient soft x-ray source which can energize large volume hohlraums for indirectly driven inertial confinement fusion. It has the advantages of being efficient and having high energy and power density. Its early history will be traced from the 18th century to the present day. The most notable feature of the Z pinch is its instability. The various regimes of stability analysis will be reviewed, including resistive and finite ion Larmor radius effects. Work in the last 10 years on single fibres, especially of cryogenic deuterium, gave neutrons that were of the same origin, namely, beam–plasma interactions, as reported by Kurchatov. The renaissance has come about through the implosion of arrays of fine wires. Research at Sandia National Laboratory has shown that by using more and finer wires, the x-ray radiation emitted at stagnation increased in power and decreased in pulse width. The understanding of these results has been advanced considerably by theory, simulation and smaller-scale, well diagnosed experiments showing the early uncorrelated m=0 instabilities on each wire, the inward jetting of plasma to the axis, the global Rayleigh–Taylor instability and the mitigating effect of nested arrays.
Molecular beam epitaxial growth of In1−xGaxAs1−ySby lattice matched to GaSb
Authors: Tsang W. T. , Chiu T. H. , Kisker D. W. , Ditzenberger J. A.
Published: July 2002

We have succeeded in growing epitaxial layers and multilayer heterostructures of In1−xGaxAs1−ySby quaternary and InAs0.92Sb0.08 ternary alloys lattice matched to GaSb by molecular beam epitaxy. High quality epilayers with lattice mismatch Δa/a∼8×10−4, excellent morphology, and efficient photoluminescence were grown. The surface reconstructions during growth of these quaternary and ternary alloys were also investigated using in situ reflection high-energy electron diffraction.
Observation of discrete resistance levels in large area graded gap diodes at low temperatures
Authors: Judd T. , Couch N. R. , Beton P. H. , Kelly M. J. , Kerr T. M. , Pepper M.
Published: July 2002

We have investigated the low-temperature properties of a GaAs n-i-n diode where the intrinsic region consists of a linearly graded gap of AlGaAs, and is surrounded by lightly doped GaAs regions. The current-voltage (I-V) characteristics are strongly asymmetric and are dominated by the graded cap. Unstable I-V characteristics are obtained in forward bias. Random switching is seen between resistance levels. This is ascribed to single electron events at traps near the abrupt heterojunction of the graded gap—the first such observation in a large area device.
Stoichiometry dependence of electrical activation efficiency in Si implanted layers of undoped, semi-insulating GaAs
Authors: Sato Takashi , Nakajima Masato , Fukuda Tsuguo , Ishida Koichi
Published: July 2002

Stoichiometry dependences of the electrical activation efficiency in Si implanted layers have been investigated for undoped, semi-insulating (SI) liquid encapsulated Czochralski (LEC) GaAs grown from melts of different compositions. The absolute value of lattice parameter was used as a measure for deviation from stoichiometry in GaAs. Irrespective of the annealing procedures, the electrical activation efficiency tends to increase and saturate to a maximum value as the crystals become As-rich, i.e., the lattice parameter increases from 0.565358 to 0.565364 nm. These results demonstrate that the precise control of stoichiometry greatly improves the reproducibility of LEC growth of undoped SI GaAs suitable for GaAs integrated circuits.
Role of boron in electrical properties of semi-insulating GaAs grown by the liquid encapsulated Czochralski method
Authors: Osaka Jiro , Hyuga Fumiaki , Kobayashi Takashi , Yamada Yutaka , Orito Fumio
Published: July 2002

The effects of the predominant residual impurity boron on the electrical properties of In-doped, dislocation-free, semi-insulating GaAs crystals are investigated. Crystals are grown from various arsenic-rich melts using the vertical magnetic field applied, fully encapsulated Czochralski technique. It is found that carrier and neutral EL2 concentrations in as-grown crystal and sheet carrier concentration in the Si-implanted active layer decrease as the boron concentration increases. The effect of boron decreases as the melt composition becomes more arsenic rich. The results suggest that boron decreases the Ga vacancy concentration.
Low-loss single-mode GaAs/AlGaAs optical waveguides grown by organometallic vapor phase epitaxy
Authors: Kapon E. , Bhat R.
Published: July 2002

We report the fabrication and the characterization of low-loss, single-mode GaAs/AlGaAs ridge waveguides. The waveguides were grown by organometallic vapor phase epitaxy and were characterized at 1.52 μm wavelength. Their propagation losses were evaluated by measuring the finesse of the Fabry–Perot waveguide resonators formed by cleaving two opposite ends of these waveguides. Losses as low as 0.15 dB/cm were measured for single-mode waveguides, which is the lowest value reported to date for single-mode semiconductor waveguides. Such low-loss waveguides should be useful in guided-wave components for integrated optoelectronics.
Dependence of resonant tunneling current on Al mole fractions in AlxGa1−xAs-GaAs-AlxGa1−xAs double barrier structures
Authors: Tsuchiya Masahiro , Sakaki Hiroyuki
Published: July 2002

Electron transport in AlxGa1−xAs-GaAs-AlxGa1−xAs double barrier tunneling structures is studied as a function of Al content x in the barrier for the case where the thickness of the barrier is 11 atomic layers and that of the GaAs well layer is 7 nm. It is shown that the density JRT of resonant tunneling current varies systematically from 7.0×102 to 3.5×104 A cm−2 as x is varied from 1.0 to 0.43. These data are found to be quantitatively explained by the theoretical calculation, in which the band discontinuity at Γ valley is taken as the barrier height. This result indicates that the electron tunneling through the double barrier structure is dominated by the barrier height of Γ minimum even when the subsidiary minima have lower energies (0.45≤x≤1.0).
Transmission electron microscopy and photoluminescence study of silicon and boron ion implanted GaAs/GaAlAs quantum wells
Authors: Arakawa Y. , Smith J. S. , Yariv A. , Otsuka N. , Choi C. , Gu B. P. , Venkatesan T.
Published: July 2002

Transmission electron microscopy (TEM) and photoluminescence (PL) data are presented on GaAs/Ga0.25Al0.75As quantum well (QW) structures grown by molecular beam epitaxy which were implanted with B ions and Si ions, respectively, to a dose of 1015 cm−2. TEM observations reveal that significant intermixing of the layers occurs in Si implanted QW structures at a depth well beyond the projected range of the implanted ion after 1 h thermal annealing at 850 °C. A subsequent 2-h annealing causes mixing near the surface, while the unmixed region still remains at a distance twice the projection range. In contrast, intermixing was not observed in annealed B implanted QW structures, which suggests a strong dependence of alloy mixing effects on the impurity. PL data support these results.
Molecular beam epitaxial growth and characterization of the dilute magnetic semiconductor Zn1−xFexSe
Authors: Jonker B. T. , Krebs J. J. , Qadri S. B. , Prinz G. A.
Published: July 2002

We report the growth by molecular beam epitaxy of the dilute magnetic semiconductor Zn1−xFexSe on GaAs(100) substrates. The epilayers were characterized in situ by reflection high-energy electron diffraction and Auger electron spectroscopy, and by x-ray θ-2θ and rocking curve measurements. We obtain the variation of lattice parameter and optical band gap for 0≤x≤0.22. Both increase linearly with Fe concentration in this range, but the increase is much less than that reported for Zn1−xMnxSe.
Laser projection patterned aluminum metallization for integrated circuit applications
Authors: Blonder G. E. , Higashi G. S. , Fleming C. G.
Published: July 2002

We demonstrate the projection patterning of Al by laser activated metalorganic chemical vapor deposition. The laser activated deposition technique, which selects surface over gas phase reactions, is found to be compatible with standard photolithographic patterning and shows promise for simplifying integrated circuit fabrication. Two applications are highlighted: metal-oxide field-effect transistor metallization and Al interconnect fabrication.
Ridge waveguide injection laser with a GaInAs strained-layer quantum well (λ=1 μm)
Authors: Fischer S. E. , Fekete D. , Feak G. B. , Ballantyne J. M.
Published: July 2002

Ridge waveguide lasers emitting near 1 μm have been made on a GaAs substrate using a single GaInAs strained-layer quantum well in a GaAs/AlGaAs graded-index separate confinement heterostructure. The epitaxial layers were grown by low-pressure metalorganic chemical vapor deposition, and the ridge waveguide was fabricated by chemically assisted ion beam etching. The lasers have threshold currents near 17 mA with fundamental lateral mode operation to five times this value. These are the first reported strained-layer current-injection lasers to run cw at room temperature; they operate, without bonding, to greater than 24 mW/facet (100 mA dc), and have 18 mW/facet (80 mA dc) lifetimes in excess of 144 h.
Theoretical study of a nonlinear prism output coupler
Authors: Arlot P. , Vitrant G.
Published: July 2002

We study a nonlinear output coupler. The nonlinear medium is the substrate which exhibits Kerr effect. New effects are predicted, which have no equivalent in the linear case: nonexponential decay of the guided field, increase of the intensity of the output radiated field, variation of the output angle along the waveguide, strong modification of the output beam intensity distribution.
Effect of compositionally graded and superlattice buffer layers on the device performance of graded barrier quantum well heterostructure laser diodes
Authors: Givens M. E. , Mawst L. J. , Zmudzinski C. A. , Emanuel M. A. , Coleman J. J.
Published: July 2002

The device performance of graded barrier quantum well laser diodes with various buffer layer structures grown by metalorganic chemical vapor deposition has been studied. Devices having four structures (a GaAs buffer layer only, a compositionally graded buffer layer, a superlattice buffer layer, or both a graded and a superlattice buffer layer) have been characterized. In contrast with similar studies involving laser devices grown by molecular beam epitaxy, little variation in device performance is observed. These data indicate that the quality of AlGaAs-GaAs heterostructures for optical devices may be dependent on the details of the method used for the epitaxial growth of the layers.
Yb-doped InP grown by metalorganic chemical vapor deposition
Authors: Uwai Kunihiko , Nakagome Hiroshi , Takahei Kenichiro
Published: July 2002

Rare-earth ion Yb is doped into InP at concentrations ranging from 1×1015 to 3×1018 cm−3 by metalorganic chemical vapor deposition (MOCVD) using Yb(C5H5)3. Uniform depth profiles revealed by secondary ion mass spectroscopy indicate that controlled rare-earth doping can be achieved by MOCVD. The grown layers show distinct photoluminescence (PL) spectra at 1.2 eV originating from intra-4f-shell transitions in Yb as well as near-band-edge emissions at 1.4 eV. In contrast to Yb-ion-implanted InP [H. Ennen, J. Schneider, G. Pomrenke, and A. Axman, Appl. Phys. Lett. 43, 943(1983)], PL spectra of MOCVD-grown layers below 30 K suggest the absence of Yb ions associated with other impurities or defects. This shows that MOCVD-grown Yb-doped InP is of higher quality than the Yb-ion-implanted InP.
New phases in the superconducting Y:Ba:Cu:O system
Authors: Eaglesham D. J. , Humphreys C. J. , Alford N. McN. , Clegg W. J. , Harmer M. A. , Birchall J. D.
Published: July 2002

An electron diffraction and microscopy study is presented of a variety of phases in the Y:Ba:Cu:O system in which superconductivity occurs. The superconducting phase is demonstrated by convergent beam electron diffraction to be centrosymmetric with space group Pmmm, in contrast to a previous determination of Pmm2. This discrepancy arises from local symmetry-breaking defects. In addition to this phase and a cubic BaCuO2 phase, we characterize two other phases. One is the Y-rich orthorhombic phase: Pnma with a=13.5 Å, b=6.3 Å, and c=7.6 Å. The second occurs by a phase transition of the superconducting Pmmm phase to P4/mmm with a=3.85 Å, c=11.7 Å. The superconducting phase may now be described as either an ordered array of oxygen vacancies in the perovskite structure, or an ordered array of oxygen interstitials in the new tetragonal phase, which may explain how the material can lose oxygen reversibly.
Oxide trapping under spatially variable oxide electric field in the metal-oxide-silicon structure
Authors: Avni E. , Shappir J.
Published: July 2002

An improved trapping-detrapping model is presented describing the effect of electron injection into the oxide of metal-oxide-silicon devices. The model covers both hot-electron and tunneling injection. It takes into account the spatial variation of the oxide electric field due to the trapped charge as well as the effect of this variation on the trapping-detrapping processes. The calculated results agree well with previously reported experimental results such as the field-dependent steady-state flatband voltage and the trapped charge centroid.
High-speed and high-power 1.3-μm InGaAsP buried crescent injection lasers with semi-insulating current blocking layers
Authors: Cheng W. H. , Su C. B. , Buehring K. D. , Huang S. Y. , Pooladdej J. , Wolf D. , Perrachione D. , Renner D. , Hess K. L. , Zehr S. W.
Published: July 2002

The fabrication and performance of high-speed and high-power 1.3-μm InGaAsP buried crescent lasers with semi-insulating current blocking layers are reported. A modulation bandwidth of 11 GHz and acw output power of 42 mW/facet have been achieved. An approximate circuit model of the semi-insulating buried crescent laser, which describes the effect of dc bias on parasitic capacitance at high-speed operation, is also presented.
Dual implantation of Be+ and F+ in GaAs and AlxGa1−xAs
Authors: Adachi Sadao
Published: July 2002

Dual implantation of Be+/F+ ions in GaAs and Al0.3Ga0.7As is performed and studied by means of Hall-effect and secondary ion mass spectrometry analyses. This technique leads to significantly less redistribution of Be implants both in GaAs and Al0.3Ga0.7As and considerably high electrical activity in Al0.3Ga0.7As, as compared with implant of Be+ only. This technique may have the great advantage of being used to fabricate a wide variety of AlxGa1−xAs/GaAs devices.
Monolithic two-dimensional surface-emitting arrays of GaAs/AlGaAs diode lasers
Authors: Donnelly J. P. , Goodhue W. D. , Windhorn T. H. , Bailey R. J. , Lambert S. A.
Published: July 2002

Monolithic two-dimensional arrays with light emission normal to the surface have been obtained by fabricating edge-emitting quantum well GaAs/AlGaAs lasers with deflecting mirrors adjacent to both laser facets. The facets and mirrors were formed by ion beam assisted etching. Proton bombardment between adjoining lasers was used to prevent lasing in the transverse direction. At the highest pulsed current used in these experiments, 10.5 A, the power output of a 22-element array was 1.6 W, which corresponds to a power density of 160 W cm−2. At this level, the power output was still linear with current.
Er-doped InP and GaAs grown by metalorganic chemical vapor deposition
Authors: Uwai Kunihiko , Nakagome Hiroshi , Takahei Kenichiro
Published: July 2002

Erbium is doped into InP and GaAs epitaxial layers for the first time by metalorganic chemical vapor deposition using tris-cyclopentadienyl erbium [Er(C5H5)3]. Uniform doping as high as 1.5×1019 cm−3 across the entire depth of the epitaxial layers is revealed by secondary ion mass spectroscopy. Erbium-related photoluminescence spectra around 1.54 μm from InP:Er and GaAs:Er show remarkable resemblance. At 2 K, in addition to the dominant zero phonon line at 1542 nm for InP:Er and at 1543 nm for GaAs:Er, several other zero phonon lines are observed at longer wavelengths. The Er-related peak is observed at 1539±1 nm even at 300 K for InP:Er, shifting toward the shorter wavelengths by a little as 3 nm with increasing temperature from 2 to 300 K.
InGaAs-InP multiple quantum wells grown by atmospheric pressure metalorganic chemical vapor deposition
Authors: Skolnick M. S. , Taylor L. L. , Bass S. J. , Pitt A. D. , Mowbray D. J. , Cullis A. G. , Chew N. G.
Published: July 2002

The optical and structural properties of multiple quantum wells of InGaAs-InP grown by atmospheric pressure metalorganic chemical vapor deposition are reported. Room-temperature excitons are resolved for well widths from 50 to 200 Å. Below 50 K, exciton linewidths, in absorption, of less than 10 meV are obtained. Absorbances for allowed valence to conduction subband transitions are found to be independent of well width, as expected in the two-dimensional limit. A lower bound for the conduction-band discontinuity of 235±20 meV is obtained.
Deposition of amorphous SiNxH films on InP in the presence of AsH3
Authors: Commère B. , Habrard M. C. , Krawczyk S. K. , Bruyère J. C.
Published: July 2002

Hydrogenated amorphous silicon nitride (a-SiNxH) films have been deposited on InP substrates by the low-temperature (185 °C) plasma enhanced chemical vapor deposition technique in order to realize metal-insulator-semiconductor capacitors. It has been found that the electronic properties of the InP-insulator interface are greatly improved if the insulator deposition is carried out in the presence of AsH3 during the first stage of the process (interface state density in the range of a few 1011 eV−1 cm−2 in the upper part of the gap). The deposited films exhibit very high resistivity (1017 Ω cm) and high breakdown voltage (3×106 V/cm). In similar conditions, no beneficial effect of PH3 during the deposition has been noticed.
Degradation of GaAs lasers grown by metalorganic chemical vapor deposition on Si substrates
Authors: van der Ziel J. P. , Dupuis R. D. , Logan R. A. , Pinzone C. J.
Published: July 2002

Using pulsed current excitation we have studied the rapid degradation of the laser properties of low-threshold-graded refractive-index single quantum well GaAs lasers grown by metalorganic vapor deposition on Si substrates. The degradation results from the growth of nonradiative regions in the active layer, resulting in rapid increase in threshold with time. The stimulated emission is quenched ∼1–5 μs after the start of the current pulse preventing continuous operation at 300 K. The degradation process is similar to that observed in similar lasers grown on GaAs substrates and occurs very rapidly due to the presence of a high density of defects and thermally induced strain.
Combining resonant tunneling diodes for signal processing and multilevel logic
Authors: Lakhani Amir A. , Potter Robert C.
Published: July 2002

A device with multiple negative differential resistances was obtained by combining two AlInAs/InGaAs based resonant tunneling diodes in series. Equal peak currents and large current peak-to-valley ratios were demonstrated at room temperature. Three stable operating points were identified for trilevel logic applications and a multiply-by-three circuit was demonstrated.
Si/Ge0.3Si0.7/Si heterojunction bipolar transistor made with Si molecular beam epitaxy
Authors: Tatsumi Toru , Hirayama Hiroyuki , Aizaki Naoaki
Published: July 2002

GexSi1−x heterobase n-p-n heterojunction bipolar transistor structure has been grown completely by Si molecular beam epitaxy for the first time. A collector-top type design was adopted. The 3000 Å p-type Ge0.3Si0.7 heterobase layer with 5×1019 cm−3 doping level was grown on an emitter layer which was an arsenic highly doped substrate (7×1019 cm−3), followed by a 5000 Å n-type Si collector layer with 7×1017 cm−3 doping level. Low-temperature device processes under 650 °C were used to avoid thermal diffusion of impurities. Common-emitter current gain hFE with a 100-μm-diam emitter was 15 at 2×104 A/cm2 collector current density. Compared with a usual Si-base bipolar transistor of the same size and doping level, an improvement in current gain was observed. Furthermore, GexSi1−x/Si (x=0.1–0.4) p-n junction interfaces were investigated by current-voltage and capacitance-voltage measurements and transmission electron microscopy observation.
Large-area defect-free silicon-on-insulator films by zone-melt recrystallization
Authors: Pandya R. , Martinez A.
Published: July 2002

Large areas of defect-free silicon-on-insulator (SOI) films have been obtained by softening (lowering the viscosity) a layer underlying the silicon film. During zone-melt recrystallization this sublayer provides a stress relief mechanism and relieves mechanical constraints for the growing crystal. Using this technique we have been able to obtain recrystallized silicon films that show significant improvement over the typical material obtained in samples without the soft layer recrystallized under identical conditions. We have reproducibly obtained SOI films that contain large areas that are free of subgrain boundaries as well as other defects such as twin boundaries and threading dislocations.
Reactive ion beam etching of Y-Ba-Cu-O superconductors
Authors: Matsui S. , Takado N. , Tsuge H. , Asakawa K.
Published: July 2002

It has been found that a reactive ion beam etching (RIBE) using Cl2 gas is useful for microfabrication of Y-Ba-Cu-O superconductors. The etching yield enhancement of Y-Ba-Cu-O is observed for Cl2 RIBE. The etching yield of Y-Ba-Cu-O at 400 V accelerating voltage, 2×10−3 Torr Cl2 pressure for Cl2 RIBE is 2, which is twice that for Ar ion beam etching. Y-Ba-Cu-O submicron patterns have been fabricated by focused ion beam lithography and Cl2 RIBE. Moreover, a Y-Ba-Cu-O superconducting line with a 4-μm linewidth has been fabricated by annealing an as-sputtered Y-Ba-Cu-O line pattern.
Metalorganic chemical vapor deposition InGaAs p-i-n photodiodes with extremely low dark current
Authors: Gallant M. , Puetz N. , Zemel A. , Shepherd F. R.
Published: July 2002

Planar, Zn-diffused InP/InGaAs p-i-n photodiodes, which have been fabricated from material grown by metalorganic chemical vapor deposition, have been shown to exhibit extremely low dark current. The typical dark current measured for 100-μm-diam devices was 10 pA at −10 V bias, with some devices having values as low as 3 pA (3.8×10−8 A/cm2). Excellent uniformity of the dark current was found. A low capacitance of 0.45 pF, a responsivity at 1.3 μm of 0.90 A/W, and rise/fall times of less than 150 ps were measured at −5 V bias.
GaAs/AlAs double-barrier resonant tunneling structure on Si with large peak to valley ratio at room temperature
Authors: Kan S. C. , Morkoç H. , Yariv A.
Published: July 2002

We have successfully grown GaAs/AlAs double-barrier resonant tunneling structures on Si substrates by molecular beam epitaxy. At room temperature, a high peak to valley current ratio of 2.9 was observed. At 77 K, the peak to valley current ratio increased to 12.5. We attribute the excellent results to the smooth interfaces and low defect concentrations in GaAs on Si. Only a small deviation in current-voltage characteristics over the wafer was observed indicating a good uniformity of high crystalline quality.
Real-time measurements of plasma/surface interaction by plasma-amplified photoelectron detection
Authors: Selwyn G. S. , Ai B. D. , Singh J.
Published: July 2002

A new method, based on the photoelectric effect, is described for real-time, in situ monitoring of metal or semiconductor surfaces during plasma exposure. As an example of the application of this technique, the effect of both sputter and reactive gas plasma exposure is studied for graphite, silicon, and aluminum surfaces. Results are consistent with the formation of a surface-passivating layer of fluoride on aluminum and penetration of fluorine into the silicon bulk during exposure to the CF4+Ar etching plasma. An application of this technique for endpoint detection monitoring is described.
Improved press forging of Ba2YCu3Ox superconductor
Authors: Grader G. S. , O’Bryan H. M. , Rhodes W. W.
Published: July 2002

An improved press forging technique has yielded ceramic Ba2YCu3Ox with a very high degree of orientation and mechanical integrity. The as-forged samples are dense and tetragonal, and have an oxygen content of ≊6.3. By a partial oxidation of the samples, a superconducting skin 20–100 μm thick is formed on the outer surface. Transport measurements on this skin show a Jc >3000 A/cm2 with an improved field dependence as compared with randomly oriented samples. The restriction of oxidation to the thin outer skin has reduced the microcracking which accompanies the oxidation of tetragonal Ba2YCu3Ox.
Direct optical observation of Bloch lines and their motion in uniaxial garnet films using a polarizing light microscope
Authors: Theile J. , Engemann J.
Published: July 2002

Recently, the first direct optical observation of vertical Bloch lines using a laser scanning microscope has been reported (A. Thiaville, L. Arnaud, F. Boileau, and G. Sauron, EMMA Conference, Salford, Great Britain, 1987, paper AD-19). Here we describe a different way of direct observation that uses a polarizing light microscope. This method has the advantage of lower thermal disturbance of the domain structure and the ability of real-time observation. To obtain one-sided dark-field illumination, the incoming light beam is coupled into the garnet film by means of a glass microprism. On examining the Bi-containing film, the Bloch lines can be directly observed through the eyepiece of the microscope. Movement of Bloch lines caused by in-plane field pulses, and also by asymmetric bias field pulses, is observed.
Superconducting thin films of Bi-Ca-Sr-Cu-O by sequential evaporation
Authors: Mogro-Campero A. , Turner L. G. , Garbauskas M. F. , Green R. W.
Published: July 2002

Thin films of the high-temperature superconductor Bi-Ca-Sr-Cu-O have been produced by sequential evaporation and furnace annealing. Zero-resistance transition temperatures are near 70 K, with an onset temperature of about 85 K, which corresponds to transition temperatures measured on bulk samples of this superconductor. X-ray analysis reveals that the superconducting phase identified by others from single-crystal studies is present in these films, and that the films are highly oriented, with the c axis perpendicular to the MgO substrate.
Determination of the D 0/− level in amorphous Si,Ge:H(F) by time-of-flight charge collection
Authors: Shen D. S. , Conde J. P. , Chu V. , Liu J. Z. , Aljishi S. , Smith Z E. , Maruyama A. , Wagner S.
Published: July 2002

We describe and demonstrate a new method for determining the density of states of the doubly occupied D0/− level in amorphous hydrogenated silicon and its alloys. The total charge collected during an electron time-of-flight measurement is determined as a function of T. T determines the energy E from which electrons are emitted during the measurement. Variation of T (and E) probes the local density of states. We present results for hydrogenated amorphous silicon before and after light soaking, and for amorphous silicon-germanium (a-Si,Ge:H,F) alloys.
Photorefractive gain in GaAs under a dc electric field
Authors: Liu Duncan T. H. , Cheng Li-Jen , Rau Mann-Fu , Wang Faa-Ching
Published: July 2002

We report the first observation of a photorefractive gain coefficient as high as 2.6 cm−1 in the undoped liquid-encapsulated Czochralski-grown GaAs crystals at 1.06 μm under a dc electric field of 13 kV/cm without using the moving grating technique. The absorption coefficient of the crystals used is 1.3 cm−1, showing that a net gain has been achieved. This measured gain coefficient is close to the predicted theoretical value.
Antigen-presenting dendritic cells provide the reducing extracellular microenvironment required for T lymphocyte activation
Authors: Angelini Giovanna , Gardella Stefania , Ardy Massimo , Ciriolo Maria Rosa , Filomeni Giuseppe , Di Trapani Giovanna , Clarke Frank , Sitia Roberto , Rubartelli Anna
Published: July 2002

T lymphocytes are defective in cystine uptake and thus require exogenous thiols for activation and function. Here we show that monocyte-derived human dendritic cells (DCs) release cysteine in the extracellular space. Cysteine generation is increased by lipopolysaccharide and tumor necrosis factor α, and by contact with T cells specifically recognizing soluble or alloantigens. These stimuli also induce thioredoxin (TRX) accumulation in DCs. However, only the contact with antigen-specific T cells triggers TRX secretion by the antigen-presenting cells. Fewer extracellular thiols are recovered after DC–T cell interactions when cystine uptake or TRX activity are inhibited. In addition, glutamate (Glu) and anti-TRX-inactivating antibodies inhibit antigen-dependent T lymphocyte proliferation. These findings indicate that, during antigen presentation, DCs uptake cystine and release cysteine and TRX, thus providing a reducing microenvironment that facilitates immune response.
The nitrite reductase from
Pseudomonas aeruginosa
: Essential role of two active-site histidines in the catalytic and structural properties
Authors: Cutruzzolà Francesca , Brown Kieron , Wilson Emma K. , Bellelli Andrea , Arese Marzia , Tegoni Mariella , Cambillau Christian , Brunori Maurizio
Published: July 2002

Cd
1
nitrite reductase catalyzes the conversion of
nitrite to NO in denitrifying bacteria. Reduction of the substrate
occurs at the d
1
-heme site, which faces on the distal side
some residues thought to be essential for substrate binding and
catalysis. We report the results obtained by mutating to Ala the two
invariant active site histidines, His-327 and His-369, of the enzyme
from
Pseudomonas aeruginosa
. Both mutants have lost
nitrite reductase activity but maintain the ability to reduce
O
2
to water. Nitrite reductase activity is impaired because
of the accumulation of a catalytically inactive form, possibly because
the productive displacement of NO from the ferric d
1
-heme
iron is impaired. Moreover, the two distal His play different roles in
catalysis; His-369 is absolutely essential for the stability of the
Michaelis complex. The structures of both mutants show
(
i
) the new side chain in the active site,
(
ii
) a loss of density of Tyr-10, which slipped away
with the N-terminal arm, and (
iii
) a large topological
change in the whole c-heme domain, which is displaced 20 Å from the
position occupied in the wild-type enzyme. We conclude that the two
invariant His play a crucial role in the activity and the structural
organization of cd
1
nitrite reductase from
P.
aeruginosa
.
Specific association of estrogen receptor β with the cell cycle spindle assembly checkpoint protein, MAD2
Authors: Poelzl Gerhard , Kasai Yasuyo , Mochizuki Naoki , Shaul Philip W. , Brown Myles , Mendelsohn Michael E.
Published: July 2002

Estrogen receptors (ERs) are ligand-activated transcription factors
that regulate gene expression and cell growth. Two ERs now have been
identified: ERα and the more recently discovered ERβ. The
physiological function of ERβ remains unclear, but evidence from
vascular injury studies and from ERβ knockout mice suggests that
ERβ may be involved in the regulation of cellular proliferation. Here
we show a direct and specific interaction between ERβ and the cell
cycle mitotic spindle assembly checkpoint protein, MAD2 (mitosis
arrest-deficient 2). The ERβ-MAD2 interaction was identified by
screening of a yeast two-hybrid system vascular endothelial cell
library with ERβ and confirmed with glutathione
S
-transferase-fusion protein interaction studies. In
contrast, ERα did not interact with MAD2 in either the two-hybrid
system or in the protein–protein interaction experiments. Amino acids
173–208 in the hinge region of ERβ were sufficient to mediate the
interaction with MAD2 in the two-hybrid system and in glutathione
S
-transferase-fusion protein studies. These data
identify a link between ERβ and MAD2 of potential importance to
regulation of the cell cycle and support a function of ERβ distinct
from the established role of ERs as transcription factors.
Thymocyte depletion in
Trypanosoma cruzi
infection is mediated by
trans
-sialidase-induced apoptosis on nurse cells complex
Authors: Mucci Juan , Hidalgo Alejandra , Mocetti Esteban , Argibay Pablo F. , Leguizamón M. Susana , Campetella Oscar
Published: July 2002

Trypanosoma cruzi
, the causative agent of Chagas' disease, induces transient thymic aplasia early after infection—a phenomenon that stills lacks a molecular explanation. The parasite sheds an enzyme known as
trans
-sialidase (TS), which is able to direct transfer-sialyl residues among macromolecules. Because cell-surface sialylation is known to play a central role in the immune system, we tested whether the bloodstream-borne TS is responsible for the thymic alterations recorded during infection. We found that recombinant TS administered to naive mice was able to induce cell-count reduction mediated by apoptosis, mimicking cell subsets distribution and histologic findings observed during the acute phase of the infection. Thymocytes taken after TS treatment showed low response to Con A, although full ability to respond to IL-2 or IL-2 plus Con A was conserved, which resembles findings from infected animals. Alterations were found to revert several days after TS treatment. The administration of TS-neutralizing Abs to
T. cruzi
-infected mice prevented thymus alterations. Results indicate that the primary target for the TS-induced apoptosis is the so-called “nurse cell complex”. Therefore, we report here supporting evidence that TS is the virulence factor from
T. cruzi
responsible for the thymic alterations via apoptosis induction on the nurse cell complex, and that TS-neutralizing Abs elicitation during infection is associated with the reversion to thymic normal parameters.
Local and distant protein structural changes on photoisomerization of the retinal in bacteriorhodopsin
Authors: Kandori Hideki , Kinoshita Norimichi , Yamazaki Yoichi , Maeda Akio , Shichida Yoshinori , Needleman Richard , Lanyi Janos K. , Bizounok Marina , Herzfeld Judith , Raap Jan , Lugtenburg Johan
Published: July 2002

The photoisomerization of the retinal in bacteriorhodopsin is selective and efficient and yields perturbation of the protein structure within femtoseconds. The stored light energy in the primary intermediate is then used for the net translocation of a proton across the membrane in the microsecond to millisecond regime. This study is aimed at identifying how the protein changes on photoisomerization by using the O-H groups of threonines as internal probes. Polarized Fourier-transform IR spectroscopy of [3-
18
O]threonine-labeled and unlabeled bacteriorhodopsin indicates that 3 of the threonines (of a total of 18) change their hydrogen bonding. One is exchangeable in D
2
O, but two are not. A comprehensive mutation study indicates that the residues involved are Thr-89, Thr-17, and Thr-121 (or Thr-90). The perturbation of only three threonine side chains suggests that the structural alteration at this stage of the photocycle is local and specific. Furthermore, the structural change of Thr-17, which is located >11 Å from the retinal chromophore, implicates a specific perturbation channel in the protein that accompanies the retinal motion.
Antitumor activity of cytotoxic T lymphocytes engineered to target vascular endothelial growth factor receptors
Authors: Niederman Thomas M. J. , Ghogawala Zoher , Carter Bob S. , Tompkins Hillary S. , Russell Margaret M. , Mulligan Richard C.
Published: July 2002

The demonstration that angiogenesis is required for the growth of solid tumors has fueled an intense interest in the development of new therapeutic strategies that target the tumor vasculature. Here we report the development of an immune-based antiangiogenic strategy that is based on the generation of T lymphocytes that possess a killing specificity for cells expressing vascular endothelial growth factor receptors (VEGFRs). To target VEGFR-expressing cells, recombinant retroviral vectors were generated that encoded a chimeric T cell receptor comprised of VEGF sequences linked to intracellular signaling sequences derived from the ζ chain of the T cell receptor. After transduction of primary murine CD8 lymphocytes by such vectors, the transduced cells were shown to possess an efficient killing specificity for cells expressing the VEGF receptor, Flk-1, as measured byin vitrocytotoxicity assays. After adoptive transfer into tumor-bearing mice, the genetically modified cytotoxic T lymphocytes strongly inhibited the growth of a variety of syngeneic murine tumors and human tumor xenografts. An increased effect onin vivotumor growth inhibition was seen when this therapy was combined with the systemic administration of TNP-470, a conventional angiogenesis inhibitor. The utilization of the immune system to target angiogenic markers expressed on tumor vasculature may prove to be a powerful means for controlling tumor growth.