bluuebunny/crossref_metadata_2025 huggingface dataset:
Spontaneous remission of double pulsatile umbilical venous flow in twin‐twin transfusion syndrome: a case report
Authors: Gramellini D. , Ludovici G. , Paita Y. , Merialdi A. , Vadora E.
Published: July 2002

Double umbilical pulsatile venous flow is a rare event generally associated with fetal right heart failure. We observed, at 21 weeks' gestation, this venous flow pattern in a case of twin‐twin transfusion syndrome occurring in the recipient twin affected by severe hydrops.

In spite of a spontaneous remission of fetal hydrops at 30 weeks, the fetus died suddenly in utero, 2 weeks later.

We hypothesized that this unexpected event was related to reversed acute twin‐twin transfusion, and concluded that fetal hydrops remission in twin‐twin transfusion syndrome must not be considered as a reassuring prognostic index but as an indication of the need for continuing biophysical monitoring. Copyright © 1995 International Society of Ultrasound in Obstetrics and Gynecology
Longitudinal spherical aberration and mass of bi‐aspheric aphakic rigid contact lenses
Authors: El‐Nashar Nabil F.
Published: July 2002

The purpose of this study is to calculate the longitudinal spherical aberration and thickness, and consequently the mass of aphakic corneal contact lenses in air to determine optimum lens designs. The longitudinal spherical aberration has been calculated by the ray tracing method through the aspheric surfaces. The volume of the lens was computed by solving integrations of rotationally symmetric bodies. The results show that longitudinal spherical aberration can be made zero in ellipsoid–ellipsoid designs for back vertex powers ranging from +8 to +20 dioptres (for a 4 mm marginal axial ray height). A reduction in mass of about 23% was obtained when the anterior surface became ellipsoid and posterior surface spherical for back vertex power +20 dioptres.
RAPD Analysis and Taxonomic Reconsideration of the Ceropegia aristolochioides Complex (Apocynaceae‐Ceropegieae)
Authors: Meve U. , Masinde P. S. , Sentner U. , Liede S.
Published: July 2002

Abstract: Flower morphology, karyology and taxonomy of the polymorphic Ceropegia aristolochioides are reviewed. Ten different samples from Africa and Arabia, representing the main morphotypes, were analysed using RAPDs. The dendrogram resulting from cluster analysis is compared with the current taxonomy. Only two subspecies within C. aristolochioides should be recognized, despite considerable differences in floral morphology within both. It is proposed to confine the typical subspecies to tropical Africa and to consider C. aristolochioides ssp. albertina and Ceropegia seticorona as synonyms. C. aristolochioides ssp. deflersiana, easily distinguished by hairy carpels, is restricted to the SW Arabian Peninsula. The formal recognition of varieties within each subspecies, which might be considered with regard to the highly diverse flower morphology, is rejected.
Efficient generation of 480 fs electrical pulses on transmission lines by photoconductive switching in metalorganic chemical vapor deposited CdTe
Authors: Nuss Martin C. , Kisker D. W. , Smith P. R. , Harvey T. E.
Published: July 2002

We have generated electrical pulses of only 480 fs duration by photoconductive switching in CdTe grown by ultraviolet-enhanced metalorganic chemical vapor deposition (MOCVD). In addition to the extremely fast switching times, MOCVD CdTe also exhibits a high mobility of 180 cm2/V s and can be grown on almost any substrate, making it ideal for integration into existing circuits and devices.
Defect chemical explanation for the effect of air anneal on CdS/CuInSe2 solar cell performance
Authors: Cahen David , Noufi Rommel
Published: July 2002

We formulate a consistent defect chemical model of the effect of air/O2 anneals on CdS/CuInSe2 devices. The model centers on O-induced neutralization of (near) surface donor states in CuInSe2 grains. The simplest identification of these states is with ionized Se vacancies, due to coordinatively unsaturated In on grain surfaces and boundaries.
Structure of CdTe-Cd1−xMnxTe multiple quantum wells grown on (001) InSb substrates by molecular beam epitaxy
Authors: Williams G. M. , Cullis A. G. , Whitehouse C. R. , Ashenford D. E. , Lunn B.
Published: July 2002

Molecular beam epitaxy has been used to prepare multiple quantum well structures of CdTe/Cd1−xMnxTe on (001) InSb substrates. The growth of such a system on InSb allows the use of particularly low growth temperatures, hence minimizing interdiffusion effects. This study presents the first transmission electron microscope investigation of this multilayer system grown on InSb. The work clearly demonstrates that multiple quantum wells of high structural quality can be grown reproducibly over a wide range of layer thicknesses. The importance of efficient substrate surface cleaning prior to growth is demonstrated. In order to grow high structural quality multilayers, the choice of buffer layer is also important and a possible explanation for this observation is given.
Carbon in GaAs: Implantation and isolation characteristics
Authors: Pearton S. J. , Abernathy C. R.
Published: July 2002

Carbon was implanted into GaAs at doses between 1013 and 5×1014 cm−2, either by itself or with Ga coimplantation at room temperature or 200 °C. Activation percentages as high as 40% were obtained for C+Ga implants at 5×1014 cm−2 compared to <3% for C implantation only. The peak activation occurs for an annealing temperature of 800 °C for 10 s, while above this the net activation decreases, apparently due to site switching. The C shows fairly minimal redistribution during anneals up to 1000 °C in contrast to other acceptor dopants in GaAs. The formation of highly resistive (>106 Ω/⧠) layers in C-doped (p∼2×1020 cm−3) GaAs is possible by using oxygen bombardment doses above 5×1014 cm−2. Under these conditions the evolution of the implanted layer resistivity with annealing temperature can be described by the usual trap-related compensation mechanism.
Use of cation-stabilized conditions to improve compatibility of CdTe and HgTe molecular beam epitaxy
Authors: Arias José , Singh Jasprit
Published: July 2002

Reflection high-energy electron diffraction (RHEED) dynamic studies are used to reveal the strong differences in growth kinetics of CdTe and HgTe grown by molecular beam epitaxy. These differences arise from the stronger CdTe bond compared to the HgTe bond. Surface migration activation barriers for Cd and Hg migration on (100) Te-stabilized surfaces were estimated from the RHEED dynamic studies to be 0.72 and 0.45 eV, respectively. These differences result in a large disparity in the ideal growth temperature for two-dimensional layer-by-layer growth of the two material systems. However, by altering the growth conditions (i.e., going from anion stabilized to cation stabilized), the disparity in temperatures is shown to vanish. Consequences for this important heterostructure system are discussed.
Etching characteristics of Si1−xGex alloy in ammoniac wet cleaning
Authors: Koyama Kazuhisa , Hiroi Masayuki , Tatsumi Toru , Hirayama Hiroyuki
Published: July 2002

Etching characteristics of Si1−xGex alloys in ammoniac wet cleaning (RCA cleaning) were examined. The etching rate of Si1−xGex became larger with increasing Ge ratio (X). Temperature dependence of the etching rate was studied and the etching rate was large at high temperatures. However, no obvious difference was observed in the temperature dependence of Si1−xGex etching rate at different Ge ratio (X). A surface morhology degradation after RCA cleaning was observed at high Ge ratio (X). A stoichiometry change of Si1−xGex surface after RCA cleaning was observed by x-ray photoelectron spectroscopy (XPS). The etching rate increase and the surface morphology degradation are thought to be due to the rapid etching of Ge atoms at the top surface layer.
Control of misoriented grains and pinholes in CoSi2 grown on Si(001)
Authors: Jimenez J. R. , Hsiung L. M. , Rajan K. , Schowalter L. J. , Hashimoto Shin , Thompson R. D. , Iyer S. S.
Published: July 2002

Two types of growth conditions have been obtained that consistently overcome the formation of epitaxially misoriented grains in CoSi2/Si(001). One is by co-deposition of Co and Si at Co-rich ratios at a substrate temperature of ∼500 °C. This method yields films of low resistivity (16 μΩ cm) and low ion channeling minimum yield (χmin≊2%), but the misfit dislocation densities are of the order of 105 cm−1. The second way uses a template method of growth after an epitaxial Si buffer layer. Films grown this way have somewhat higher resistivities than those grown by the first method, but have lower misfit dislocation densities. The strain relief mechanism in these films also appears to be different from that of co-deposited films. Pinhole densities in films grown by both methods are below our detection limit of 103 cm−2.
Atomic step resolution in scanning tunneling microscope imaging of H2SO4 covered Si(100) surfaces
Authors: Houbertz R. , Memmert U. , Behm R. J.
Published: July 2002

Stable, high-resolution scanning tunneling microscopy imaging of Si surfaces in an electrochemical environment, under potentiostatic control, is demonstrated. Atomic scale structures such as monoatomic steps are resolved on H2SO4 covered Si(100) surfaces. In this environment, contamination and reoxidation are quantitatively inhibited, making this method applicable for imaging of technical Si surfaces.
Influence of trap filling on photocurrent transients in polycrystalline TiO2
Authors: Schwarzburg K. , Willig F.
Published: July 2002

Electron injection from optically excited dye molecules into the depletion layer of polycrystalline n-TiO2 electrodes is measured as photocurrent. The characteristic shape of the photocurrent transients has a point of inflection and is controlled by the complete filling of deep traps. The rate equations for the Shockley–Read trapping process are solved numerically for the case of high injection levels, and the shape of the transients is simulated.
High-power, very low threshold, GaInP/AlGaInP visible diode lasers
Authors: Serreze H. B. , Chen Y. C. , Waters R. G.
Published: July 2002

Visible light (665 nm) laser diodes employing a strained-layer, single quantum well, graded index separate confinement heterostructure were fabricated from epitaxial wafers grown by metalorganic chemical vapor deposition. Threshold current densities for single element, uncoated, broad-area diodes operated cw as low as 425 A/cm2, cw power outputs of 340 mW per facet, and pulsed outputs (100 μs pulse width) of slightly under 1 W per facet were achieved. These power output values are believed to be the highest reported to date for visible light diode lasers, and this cw threshold current density is believed to be, by far, the lowest.
In situ spectroscopic ellipsometry study of the electron cyclotron resonance plasma oxidation of silicon and interfacial damage
Authors: Hu Y. Z. , Joseph J. , Irene E. A.
Published: July 2002

The growth of SiO2 films on Si and the evolution of interfacial damage resulting from electron cyclotron resonance plasma oxidation was studied using in situ during process spectroscopic ellipsometry. Accelerated growth under positive substrate bias indicates that negative atomic species dominate the growth above an oxide thickness of 4 nm. Below this thickness bias appears less important. The interfacial damage is different in both nature and extent from that caused by ions with higher energies. It appears that the damage layer is composed of SiO2 with a-Si and is due to the oxidation reaction rather than the ions from the plasma.
Complex third-order phase conjugation nonlinearity of polymeric thin films
Authors: Nunzi Jean Michel , Charra Fabrice
Published: July 2002

We describe a simple method for measuring magnitude and argument of degenerate four-wave-mixing nonlinearities in polymer thin films. It is based on an analysis of phase conjugation response of films interfering with their glass substrate. In evaporated polycrystalline polydiacetylene blue layers, picosecond two-photon resonant nonlinearity is a function of pump intensity. It increases and undergoes a 30° argument variation between 0.2 and 1 GW/cm2.
Phase-noise and shot-noise limited operations of low coherence optical time domain reflectometry
Authors: Takada K. , Himeno A. , Yukimatsu K.
Published: July 2002

This letter shows theoretically and experimentally that Fresnel end reflection of the waveguide under test degrades the sensitivity of low coherence optical time domain reflectometry (OTDR). Optical mixing of end reflection and reference light in the OTDR produces the phase noise in proportion to end reflectivity. With the balanced detection technique, the excess photon noise is subdued and the phase noise becomes the dominant source of sensitivity degradation. At 3.2% end reflection and 300 μA mean photocurrent, the noise floor due to the phase noise is −138 dB/Hz. By reducing the fiber end reflection with matching oil, a shot-noise limited sensitivity of −140 dB at a 3 Hz bandwidth has been demonstrated at submillimeter resolution.
Comparison of the facet heating behavior between AlGaAs single quantum-well lasers and double-heterojunction lasers
Authors: Tang W. C. , Rosen H. J. , Vettiger P. , Webb D. J.
Published: July 2002

The facet heating behavior of AlGaAs double-heterojunction (DH) lasers was measured as a function of injection current using Raman microprobe spectroscopy. The result from the DH lasers is compared to AlGaAs ridge-waveguided single quantum-well (SQW) lasers. A clear discontinuity in the facet temperature rise was found below and above the lasing threshold for the DH lasers, indicating a substantial contribution to facet heating by the photon flux. This is in contrast to the facet heating behavior of SQW lasers in which photon flux has been shown to play only a minor role. The data suggest a large difference in the facet absorption of the lasing photons between the two types of lasers. This is further supported by the effect of argon laser probe beam induced facet heating on the diode laser’s output power.
InSb/In1−xAlxSb strained-layer superlattices grown by magnetron sputter epitaxy
Authors: Webb James B. , Yousefi G. H. , Rousina R.
Published: July 2002

The growth of strained-layer superlattices of InSb/In0.6Al0.4Sb prepared by magnetron sputter epitaxy is reported for the first time. Individually controlled magnetron sputter sources of InSb, Al, and Sb were used to deposit 20-period superlattices with periods ranging from 76 –154 Å. Layer thicknesses determined from x-ray and cross-sectional transmission electron microscopy (TEM) analysis were in close agreement with those predicted on the basis of the growth-rate/deposition-time product, indicating a high degree of deposition control. X-ray and electron-channeling patterns showed excellent crystallinity. The absence of surface features in the InSb cap layer indicated the layers to be under tensile stress due to the 2.1% lattice mismatch between InSb and InSb/In0.6Al0.4Sb.
Tip artifacts of microfabricated force sensors for atomic force microscopy
Authors: Grütter P. , Zimmermann-Edling W. , Brodbeck D.
Published: July 2002

It is demonstrated that due to inevitable intrinsic imperfections in the microfabrication process of atomic force microscopy (AFM) tips, images of rough surfaces can be totally dominated by tip artifacts. These images reflect the mesoscopic tip shape as concluded from a comparison of AFM and scanning electron microscopy images of the tip and sample. These tip artifacts have been found on a scale of 20–600 nm, showing the necessity of characterizing the tip shape in order to make reliable sample-specific statements.
Modeling a collisional, capacitive sheath for surface modification applications in radio-frequency discharges
Authors: Börnig Karla
Published: July 2002

Starting from previous analytical theories of the plasma sheath of an (rf) excited molecular discharge, we introduce an extension of these theories for the whole pressure range from the collision-free up to the collision-dominated sheath, including the region between these extremes. Collisions of the ions are taken into account via a viscous drag fluid model, leading to a set of integral equations. They are solved numerically using a fast-converging iteration scheme. The time-average potential distribution, electric field, sheath length, and ion and electron distribution within the sheath are obtained.
Morphological model of reflection high-energy electron-diffraction intensity oscillations during epitaxial growth on GaAs(001)
Authors: Shitara T. , Vvedensky D. D. , Wilby M. R. , Zhang J. , Neave J. H. , Joyce B. A.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) measurements have been carried out on vicinal GaAs(001) surfaces which are misoriented by 2° and 3° toward the [010] direction. The misorientation-angle dependence and the Ga-flux dependence of the growth-mode transitions for a fixed As/Ga ratio of approximately 2.5 have been reproduced by Monte Carlo simulations of a solid-on-solid model. The surface step-density evolutions generated by the simulations are remarkably similar in profile to the measured RHEED oscillations, and show approximately the same relative change of amplitude with temperature for the chosen diffraction conditions.
Initial stages of native oxide growth on hydrogen passivated Si(111) surfaces studied by scanning tunneling microscopy
Authors: Neuwald U. , Hessel H. E. , Feltz A. , Memmert U. , Behm R. J.
Published: July 2002

We show by scanning tunneling microscopy (STM) imaging that native oxide growth in moist air on hydrogen terminated Si(111) 1×1 surfaces begins by continuing formation of small oxide nuclei, 10–20 Å in diameter, in the topmost Si layer. Their statistical distribution on the flat terraces points to a homogeneous nucleation process. Oxidation is extremely slow; after about 800 h only one complete monolayer is oxidized. In addition, a small number of three-dimensional oxide nuclei, several layers deep and 50–100 Å in width, are formed at step edges as a minority species, which may be related to surface defects or contaminations.
Bias dependence of responsivity and transport in asymmetric quantum well infrared detectors
Authors: Fraenkel A. , Brandel A. , Bahir G. , Finkman E. , Livescu G. , Asom M. T.
Published: July 2002

A new type of asymmetric stepped GaAs/AlGaAs multiquantum well infrared detector is reported. These asymmetric detectors utilize the usual bound-to-continuum transition. The current responsivity is remarkably asymmetric with regard to the voltage polarity. In contrast with rectangular wells, in which responsivity is saturated in both bias polarities, these wells exhibit saturation only for negative bias. The responsivity increases monotonously with positive electric field. This is attributed to changes induced by the field on the transport properties of the excited electrons. In particular, the bias affects the dwell time spent by the carrier wave packet in the well region. Employing this model, we achieve a very good fit with experimental data.
Buffer-induced modulation of carrier density and mobility in a selectively doped heterostructure
Authors: Reynolds C. L. , Vuong H. H.
Published: July 2002

We report sizable variations in the carrier sheet concentration and consequently the mobility of the two-dimensional electron gas as a function of the thickness of the first GaAs buffer layer deposited on the substrate. The results are interpreted as being related to increased intersubband scattering. Band bending and modulation doping are suggested as the physical mechanisms responsible for the modulation of the carrier density. Preliminary data show the importance of an interaction between the superlattice buffer and Si impurity at the interface.
Complete strain relief of heteroepitaxial GaAs on silicon
Authors: Burns Geoffrey F. , Fonstad Clifton G.
Published: July 2002

High quality strain-free heteroepitaxial GaAs-on-Si has been produced by annealing chemically separated GaAs epitaxial layers grown by molecular beam epitaxy directly on silicon substrates. A process sequence has been developed which retains the GaAs layer in place during chemical separation and post-processing, thus maintaining a monolithic fabrication sequence. Using low temperature photoluminescence, it is shown that the majority of the residual strain is eliminated by chemical separation. Subsequent rapid thermal annealing is found to remove the remaining strain and significantly improve material quality. The presented process sequence forms the basis for monolithic integration of high quality strain-free (Al,Ga)As electrical and optical devices with silicon circuitry.
Superconducting neural circuits using fluxon pulses
Authors: Mizugaki Yoshinao , Nakajima Koji , Sawada Yasuji , Yamashita Tsutomu
Published: July 2002

A superconducting neural circuit is fabricated for the first time by use of a niobium integrated-circuit technology. Fluxon pulses on Josephson transmission lines (JTLs) are used as neural impulses. In this circuit a threshold element (a neuron) is composed of two JTL elements connected through a resistor. The conductance value of the resistor represent a synaptic strength. The fan-in and the fan-out are accomplished by the biased JTL branches. The operation of 2-bit neural based A/D converter is successfully observed. These circuits do not require any hysteretic Josephson junctions, and hence, have a potential to be fabricated with the high-Tc superconductors.
Er:Ca5(PO4)3F saturable-absorber Q switch for the Er:glass laser at 1.53 μm
Authors: Spariosu Kalin , Stultz Robert D. , Birnbaum Milton , Allik Toomas H. , Hutchinson J. Andrew
Published: July 2002

Passive Q switching of an Er:phosphate glass laser using Er:Ca5(PO4)3F (Er:FAP) as a saturable absorber intracavity (IC) load is described for the first time. Q-switched output was obtained consisting of a 6-mJ single pulse of 83 ns full width at half maximum, with a 20% efficiency relative to the corresponding free-running output in the absence of the IC Er:FAP load.
Tactile shear sensing using anisotropically conductive polymer
Authors: Chen L. H. , Jin S. , Tiefel T. H.
Published: July 2002

A new technique for tactile shear sensing using a z-direction-only conductive polymer material is discussed. A thin layer of the material is in situ cured, in the presence of a z-direction magnetic field, on the surface of a circuit board containing a contact-pad array. A small metallic cursor embedded in an overlaid elastomeric skin slides over the z-direction conductive polymer upon shear motion, and its change in position is detected by the occurrence of simple circuit connections between neighboring contact pads. This shear sensor has the advantages of being compliant, transparent, able to accommodate pad height variations, and capable of high-resolution sensing. It may also serve as temperature and pressure sensor because of the characteristic and reversible variation of the z-direction electrical resistance in the conductive polymer upon changes in ambient temperature and contact pressure. The new sensor may be useful for potential applications such as touch-sensitive controllers for computer-related products and robotic skins.
Transient electroluminescence from hole transporting emitting layer in nanosecond region
Authors: Hosokawa Chishio , Tokailin Hiroshi , Higashi Hisahiro , Kusumoto Tadashi
Published: July 2002

Transient electroluminescence (EL) for an organic thin film cell with a hole transporting emitting layer was observed by short voltage pulse measurements. For the cell with indium tin oxide/hole transporting emitting layer/Mg:Ag structure, we realized very fast response at a time about 20 ns. This response time has been the fastest in organic EL ever reported. In these measurements, we could observe carrier transit time. We found that this carrier transit time was attributed to that of holes in the emitting layer. The hole mobility in 120-nm-thick emitting layer was obtained to be 1±0.3×10−3 cm2/V s in the electric field region from 1 to 3 MV/cm. Furthermore, we could observe the fast EL decay component with a time constant of 3.0±1.5 ns, which was essentially attributed to the decay of singlet excited states.
High-temperature operation of strained Si0.65Ge0.35/Si(111) p-type multiple-quantum-well light-emitting diode grown by solid source Si molecular-beam epitaxy
Authors: Fukatsu S. , Usami N. , Shiraki Y. , Nishida A. , Nakagawa K.
Published: July 2002

Electroluminescence (EL) was observed at temperatures up to 60 °C in p-type strained Si0.65Ge0.35/Si multiple-quantum-well (MQW) diode structures grown on Si(111) substrates by Si molecular-beam epitaxy. No-phonon line and its transverse optical phonon replica were well-resolved in the room-temperature EL spectrum for the first time. EL spectrum was dominated by a broad alloy band located below the band-edge state by ≊100 meV at lower temperatures, which was taken over by clear band-edge emissions at elevated temperatures. The emission intensity of the alloy band exhibited a saturation behavior with increasing injection current while the band-edge emission was found to develop with a power exponent of 1.4.
Planar double gate quantum wire transistor
Authors: Chou S. Y. , Wang Y.
Published: July 2002

A planar double gate quantum wire transistor (QWT) is proposed and demonstrated. The transistor uses a narrow wire gate placed inside the gap of a split gate to create a single one-dimensional (1D) quantum wire (QW). We demonstrate theoretically and experimentally that the wire gate can create a QW potential with a better confinement and therefore larger subband separations than that in other split-gate QWTs, and that the split gate can adjust the number of electrons inside the QW while keeping the 1D QW potential almost unchanged. Furthermore, we found that, in the double gate QWT, a 1D electron channel can spatially overlap with a 2D electron channel without significant mixing.
Experimental observation of a minority electron mobility enhancement in degenerately doped p-type GaAs
Authors: Harmon E. S. , Lovejoy M. L. , Melloch M. R. , Lundstrom M. S. , de Lyon T. J. , Woodall J. M.
Published: July 2002

The variation of minority electron mobility with doping density in p+-GaAs has been measured with the zero-field time-of-flight technique. The results from a series of nine GaAs films doped between 1×1018 and 8×1019 cm−3 show the mobility decreasing from 1950 cm2 V−1 s−1 at 1×1018 cm−3 to 1370 cm2 V−1 s−1 at 9×1018 cm−3. For the doping range 9×1018–8×1019 cm−3, the decreasing trend in mobility is reversed. The measured mobility of 3710 cm2 V−1 s−1 at 8×1019 cm−3 is about three times higher than the measured value at 9×1018 cm−3. These results confirm and extend recent transistor-based measurements and are in accord with recent theoretical predictions that attribute the increase in minority electron mobility in p+-GaAs to reductions in plasmon and carrier-carrier scattering at high hole densities.
Effect of hydrogen on surface roughening during Si homoepitaxial growth
Authors: Adams D. P. , Yalisove S. M. , Eaglesham D. J.
Published: July 2002

Hydrogen is shown to have a strong influence on the evolution of surface morphology during low temperature (310 °C) Si(100) homoepitaxy. Molecular beam epitaxy growth in the presence of deuterium shows a surface roughness within the epitaxial film that increases rapidly until the Si film exhibits a crystalline to amorphous transition. The rate at which the surface roughens depends critically on the partial pressure of deuterium. Although the kinetics of growth are sensitive to small pressures (4×10−8 Torr) of D, it appears that the breakdown of epitaxy does not result from a ‘‘critical’’ D concentration at the surface. This work suggests that the crystalline to amorphous transition, instead, results from increased roughening during epitaxy.
Optical flip–flop based on two-mode intensity bistability in a cross-coupled bistable laser diode
Authors: Johnson John E. , Tang C. L. , Grande W. J.
Published: July 2002

We present an experimental demonstration of an optical flip–flop based on two-mode intensity bistability in a GaAs/AlGaAs cross-coupled bistable laser diode (XCBLD), in which lasing can be toggled between two orthogonal outputs. Electrically triggered set–reset optical memory operation has been achieved in a folded-cavity device under pulsed bias at 77 K. The XCBLD is monolithically integrable and has extensive applications in optical time-division switching.
Lower-temperature plasma etching of Cu films using infrared radiation
Authors: Hosoi N. , Ohshita Y.
Published: July 2002

The etching of Cu films is achieved at lower temperature (150 °C) with Cl2 plasma by IR light radiation. Anisotropic fine Cu patterns are obtained. The etch rate is 4000 Å/min and there are no microloading effects. It is considered that the etching temperature lowering and the anisotropy are realized by the IR light enhancement of CuClx desorption.
CdTe/MnTe short-period superlattices: Elastic properties
Authors: Abramof E. , Faschinger W. , Sitter H. , Pesek A.
Published: July 2002

We report on the structural characterization of CdTe/MnTe short-period superlattices. The critical thickness of MnTe on CdTe layers was determined by reflection high-energy electron diffraction experiments. Detailed high-resolution x-ray diffraction measurements and the computer simulation of the measured spectra enabled the determination of the zinc blende MnTe elastic properties in the superlattices. The knowledge of these properties allowed the growth of strain balanced CdTe/MnTe superlattices pseudomorphic to a Cd0.96Zn0.04Te buffer. The superlattices exhibited x-ray linewidths of about 100 arcsec.
Radio frequency reactive sputtered iron nitrides using ammonia gas: Structure and magnetic properties
Authors: Xiao John Q. , Chien C. L.
Published: July 2002

Iron nitrides of γ′-Fe4N, ε-Fe2-3N, and ζ-Fe2N have been fabricated using rf sputtering with reactive NH3 gas, which offers significant advantages over the conventional N2 gas. All but ζ-Fe2N nitride films have relative high saturation moments with a large in-plane anisotropy. The Mössbauer results are consistent with structural analyses and those from bulk samples.
Bulk-induced alignment of nematic liquid crystals by photopolymerization
Authors: Jain Sukhmal C. , Kitzerow Heinz-S.
Published: July 2002

A novel technique to produce uniform alignment of nematic liquid crystals is presented. The technique is based on producing an anisotropic polymer network in the bulk nematic liquid crystal by polymerizing a photoresist material. Both uniform planar alignment and homeotropic alignment can be obtained depending on the curing conditions. In the case of planar alignment, the nematic director orientation is governed by the direction of the polarization vector of the linearly polarized ultraviolet light, thus making it possible to produce a defined azimuthal orientation of the nematic director. This technique obviates the need to give any previous treatment to the bounding substrates and as such should be independent of the nature of the substrate.
Effect of spectral broadening and electron-hole scattering on carrier relaxation in GaAs quantum dots
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

Luminescence efficiency in quantum dots has been a matter of some controversy recently. Theoretically, poor efficiency has been predicted owing to the phonon bottleneck in carrier relaxation, while slightly enhanced luminescence has been reported in several experiments. The approach of this letter differs from previous theoretical work in that the scattering rates are computed self-consistently accounting for the spectral broadening of the electronic spectra due to a finite energy level lifetime. Scattering of electrons and holes confined in the dot is found to be responsible for breaking the phonon bottleneck in electron relaxation reducing the relaxation time from several ns to several hundred ps. Results of a Monte Carlo simulation also including confined and interface polar optical phonon and acoustic phonon scattering for a range of quantum dot dimensions and temperatures are presented. These results may provide an explanation of the absence of a significant reduction in quantum dot luminescence compared with that from quantum wells.
Distribution of the critical current density and flux trapping in YBa2Cu3O7−δ ramp-edge Josephson junctions
Authors: Marx A. , Husemann K.-D. , Mayer B. , Nissel T. , Gross R. , Verhoeven M. A. J. , Gerritsma G. J.
Published: July 2002

We have studied the spatial distribution of the critical current density in YBa2Cu3O7−δ ramp edge Josephson junctions using low-temperature scanning electron microscopy. Applying this technique allows the imaging of the critical current density distribution with a spatial resolution of about 1 μm. Our measurements show that the geometry of the ramp-edge junction eases the trapping of magnetic flux quanta in the YBa2Cu3O7−δ layer covering the ramp edge. These trapped flux quanta result in a spatially inhomogeneous magnetic field parallel to the barrier layer, which in turn results in a spatially modulated supercurrent density and an unusual magnetic field dependence of the critical current.
Thermal stability of Ti/Pt/Au nonalloyed ohmic contacts on InN
Authors: Ren F. , Abernathy C. R. , Pearton S. J. , Wisk P. W.
Published: July 2002

Extremely low contact resistance of nonalloyed Ti/Pt/Au metallization on n-type InN is demonstrated. The contacts were annealed at different temperatures up to 420 °C to investigate their thermal stability. A low contact resistivity of 1.8×10−7 Ω cm2 was measured at room temperature using the transmission line method. This was due to the extremely high doping level (5×1020 cm−3) in the InN. After 300 °C annealing, the contact resistivity increased to 2.4×10−7 Ω cm2. For 360 °C annealing, the contact morphology showed some degradation, but the contact resistivity was almost the same as at 300 °C. There was serious degradation of the contacts after 420 °C annealing. The morphology became very rough, and the contact and sheet resistances increased by factors of 3–5 times. This degradation is believed due to the decomposition of the InN film. The contact resistivities between n-type epitaxial GaAs and InN were also investigated, and showed values around 10−4 Ω cm2.
Strain relaxation in InAlSb epilayers grown on InSb substrates
Authors: Maigné P. , Lockwood D. J. , Webb J. B.
Published: July 2002

We report a structural study of partially relaxed, 0.1-μm-thick, In1−xAlxSb (0.15<x<0.64) layers grown by magnetron sputter epitaxy on (100) InSb substrates. X-ray diffraction has been used to measure the extent of strain relief as a function of the Al composition and the results have been compared to the well studied InGaAs/GaAs system. The experimental critical layer thickness is at least five times larger than the critical layer thickness predicted by the mechanical equilibrium model. In addition, a linear relationship was found between the percentage of strain relieved and the normalized thickness of the layers, which suggests that the strain relaxation mechanisms are different for the InAlSb/InSb system. Finally, epitaxial tilting and anisotropy in strain relaxation along 〈011〉 directions, as usually found in III-V heterostructures, have not been observed in these layers.
Photocurrent multiplication in hydrogenated amorphous silicon p-i-n photodiode films
Authors: Sawada Kazuaki , Mochizuki Chihiro , Akata Shinya , Ando Takao
Published: July 2002

The photocurrent multiplication of hydrogenated amorphous silicon p-i-n photodiodes was observed in photodiodes that were fabricated on a heavily doped n-type silicon substrate using a high-vacuum plasma enhanced chemical vapor deposition (PECVD) system. By using this improved PECVD system, the breakdown field of the photodiodes was changed from 3×105 V/cm to 1×106 V/cm. It seems that the reason for this increase of the breakdown field was a decrease of localized states in the forbidden gap that was produced by contaminants. The a-Si:H p-i-n photodiodes with low residual stress were fabricated on Si substrates, and the photocurrent multiplication was observed in these photodiodes. The wavelength dependence of incident light and the a-Si:H thickness dependence of intrinsic layer were found and these characteristics were explained by the avalanche multiplication of photogenerated electrons.
Photoinduced modification of the catalytic reaction of titanium oxide and palladium in chemical vapor deposition of Al films
Authors: Hanabusa Mitsugu , Komatsu Atsushi
Published: July 2002

In chemical vapor deposition of Al thin films, using dimethylaluminum hydride, the catalytic reaction of titanium oxide was enhanced by irradiation of the UV light from a deuterium lamp. In contrast, the light suppressed nucleation on another catalytic Pd surface, which became pronounced at low temperatures. A 160-nm emission band of the deuterium lamp was more effective in the observed photoinduced effects than a 240-nm band.
Nonstationary 1/f noise in InP/InGaAs heterojunction bipolar transistors
Authors: Alers G. B. , Martin S. , Hamm R. A. , Feygenson A. , Yadvish R. D.
Published: July 2002

1/f noise for most electronic systems is stationary in that repeated measurements of the noise power will give the same result within statistical uncertainty. In contrast, we have observed highly nonstationary 1/f noise in the output current of a series of InP based heterojunction bipolar transistors (HBTs). We have applied higher order statistics to the non-Gaussian fluctuations of these devices to probe the source of the intrinsic 1/f noise. We find signatures of superimposed Lorentzians making up an otherwise featureless 1/f noise spectrum consistent with generation-recombination-type noise in the base-emitter region of the device. The nonstationarity of these devices scales inversely with the device size as would be expected for an intrinsic mechanism. We suggest that these techniques may be utilized to a greater extent in the future as device sizes are reduced.
Polarity of a (111)-oriented CdTe layer grown on a (100) Si substrate
Authors: Sugiyama Iwao , Nishijima Yoshito
Published: July 2002

Direct epitaxial growth on silicon has advantages when fabricating monolithic integrated infrared focal-plane arrays. We demonstrated that both (111)A and (111)B oriented CdTe layers can be grown on (100) Si substrates by molecular-beam epitaxy. The surface morphology of the (111)A layer was rough, while that of the (111)B layer was smooth. The key determining polarity is the substrate temperature during preadsorption of Te2 flux. We found a polarity transition at 450 to 500 °C, and (111)B layers grow above that temperature.
Novel metalorganic route for fabrication of B
a
T
i
O3 thin ferroelectric films
Authors: Nourbakhsh S. , Vasilyeva I. , Carter J. N.
Published: July 2002

A novel diol based metalorganic route has been developed and employed to deposit BaTiO3 films on Si and Pt coated Si substrates. Differential thermal analysis, thermogravimetric analysis, x-ray photoelectron spectroscopy, and x-ray diffraction collectively indicated that BaTiO3 was formed through the reaction of Ba and Ti oxides at approximately 500 °C. The films were single phase, had no crystallographic texture, and contained no detectable impurities.
Temperature dependent electrically detected magnetic resonance studies on silicon pn diodes
Authors: Christmann P. , Stadler W. , Meyer B. K.
Published: July 2002

We report on electrically detected magnetic resonance (EDMR) studies in silicon pn diodes in the temperature range from 30 to 300 K. In the range from 150 to 300 K the resonance effect is, as usually observed, much larger than expected by spin polarization. From 150 K down to 30 K the spin resonance effect increases by a factor of 25, which is attributed to spin polarization of free electrons and electrons bound to recombination centers. Our investigation suggests that at least two different mechanisms contribute to the EDMR signal.
Transmission electron microscopic study of c -BN films deposited on a Si substrate
Authors: Watanabe Syuichi , Miyake Shojiro , Zhou Weilie , Ikuhara Yuichi , Suzuki Tetsuya , Murakawa Masao
Published: July 2002

Microstructure of c-BN films synthesized by the ion-plating method were observed and characterized by high resolution electron microscopy and microdiffraction. The c-BN films of ∼0.2 μm thickness were deposited on top of ∼0.05 μm of h-BN, which was oriented with its c-axis parallel to the substrate. Lattice image taken along the 〈011〉 direction showed that c-BN film was well crystallized with an interplanar distance ∼2.1 Å, although the grain size was extremely small, from 5 to 20 nm. Further, the microdiffraction pattern along the 〈011〉 direction by focusing the electron beam to ∼20 Å, clearly showed that the small grains consisted of a single crystal of c-BN.
Infrared camera and data-acquisition system in Doublet III
Authors: Petrie T. W. , Scoville J. T.
Published: July 2002

Thermal imaging cameras sensitive to 3–5 μ radiation are routinely used to measure heat flow to the main limiter, to the vacuum vessel wall behind the main limiter, and to the divertor plate limiters. The cameras are equipped to provide either a standard television image, one frame per ∼16.7 ms, or a surface temperature profile on one line of the image with a time resolution of ∼125 μs. In the former mode, we can determine both the location and the intensity of the heating on the main limiter during multimegawatt neutral-beam injection into plasma; in the latter mode, we can measure heat pulses striking the limiter from plasma processes occurring on fast timescales (e.g., Dα spikes of ∼500 μs duration). Data is stored in both video image and digitized forms. In the latter, a ‘‘peak-sample-hold’’ circuit electronically records the maximum signal of each line sweep and stores this data in digitized form on magnetic tape. This facilitates later comparisons of infrared camera data with other diagnostic signals using plotting packages on the DEC-10.
Repeating pneumatic hydrogen pellet injector for plasma fueling
Authors: Combs S. K. , Milora S. L. , Foust C. R. , Foster C. A. , Schuresko D. D.
Published: July 2002

A repeating pneumatic pellet injector has been developed for plasma fueling applications. The repetitive device extends pneumatic injector operation to steady state. The active mechanism consists of an extruder and a gun assembly that are cooled by flowing liquid-helium refrigerant. The extruder provides a continuous supply of solid hydrogen to the gun assembly, where a reciprocating gun barrel forms and chambers cylindrical pellet from the extrusion; pellets are then accelerated with compressed hydrogen gas (pressures up to 125 bar) to velocities ≤1.9 km/s (1.6 km/s for deuterium pellets). The gun assembly design can accommodate different pellet sizes and barrel lengths. Steady-state rates of 2 s−1 have been obtained with 2.1- , 3.4- , and 4.0-mm-diameter pellets. The present apparatus operates at higher firing rates in short bursts; for example, a rate of 6 s−1 for 2 s with the larger pellets. These pellet parameters are in the range applicable for fueling large present-day fusion devices such as the Tokamak Fusion Test Reactor (TFTR). Experimental results are presented, including effects of propellant pressure and barrel length on gun performance.
1-millimeter wave interferometer for the measurement of line integral electron density on TFTR
Authors: Efthimion P. C. , Taylor G. , Ernst W. , Goldman M. , McCarthy M. , Anderson H. , Luhmann N. C.
Published: July 2002

A two-pass interferometer at 285 GHz has been developed to measure the line-integrated electron density on the horizontal midplane of the toroidal fusion test reactor (TFTR). Presently, the interferometer employs a 2-mW solid-state source to supply the launch wave and a 2-mm klystron oscillator and, a harmonic mixer to provide a superheterodyne front end. The transmission system consists of 25 m of C-band rectangular waveguide, adjustable miter bends, and a spherical mirror in the vacuum vessel with a total round trip transmission loss of 21 dB. The interferometer signal to noise is ≳50 dB. Utilization of a feed forward tracking system provides long-term stable operation. The interferometer routinely provides real-time feedback control for the gas injection system and a permissive for neutral beam operation.
FIR interferometer/polarimeter system on ISX-B tokamak
Authors: Ma C. H. , Hutchinson D. P. , Staats P. A. , Vander Sluis K. L.
Published: July 2002

Recent results of simultaneous measurements of electron density and Faraday rotation on all five channels of the FIR interferometer/polarimeter system on ISX-B are presented. The time resolution of the interferometer is typically 1 μs. The standard deviation of the output of the interferometer of a constant phase shift is less than 5×10−2 fringe, corresponding to a line electron density of 5×1011 cm−3. The polarimeter shows a sensitivity of the order of 1 mrad and a time resolution of approximately 1 ms. Data are reported on ohmic as well as neutral-beam-heated plasmas including solid hydrogen pellet injections. It is believed that this is the first successful measurement of Faraday rotation in pellet-injected discharges. Data analysis codes have been developed and the results are being compared with other measurements.
Perpendicular electron cyclotron emission from hot electrons in TMX-U
Authors: James R. A. , Ellis R. F. , Lasnier C. J. , Casper T. A. , Celata C. M.
Published: July 2002

Perpendicular electron cyclotron emission (PECE) from the electron cyclotron resonant heating of hot electrons in TMX-U is measured at 30–40 and 50–75 GHz. This emission is optically thin and is measured at the midplane, fce≂14 GHz, in either end cell. In the west end cell, the emission can be measured at different axial positions thus yielding the temporal history of the hot electron axial profile. These profiles are in excellent agreement with the axial diamagnetic signals. In addition, the PECE signal level correlates well with the diamagnetic signal over a wide range of hot electron densities. Preliminary results from theoretical modeling and comparisons with other diagnostics are also presented.
Tokamak Fusion Test Reactor x-ray imaging diagnostic
Authors: Hill K. W. , von Goeler S. , Bitter M. , Davis W. , Dudek L. , Fredd E. , Johnson L. C. , Kiraly J. , McGuire K. , Montague J. , Moshey E. , Sauthoff N. R. , Young K. M.
Published: July 2002

An array of 64 silicon surface-barrier diodes on a circular arc view Tokamak Fusion Test Reactor (TFTR) plasmas through a slot aperture to provide poloidal imaging of x-ray emission in the 200 eV–15 keV range. Information is inferred on magnetohydrodynamic (MHD) instabilities, disruptions, radiation, impurity transport, electron temperature, and electron thermal conductivity. Spatial resolution is 2.5 cm. Movable absorber foil arrays provide energy selection. Preamplifier–amplifier pairs have gains of 0.05–100 V/μA. Two outputs are provided with (1) 40-, 80-, and 300-Hz and (2) 40-, 80-, and 600-kHz filtering. The signals are digitized at rates up to 500 kHz and stored in 128K (total system) memory. Foils, gains, and filters are selectable from the control room by a computer.