bluuebunny/crossref_metadata_2025 huggingface dataset:
The site of the redox‐linked proton pump in eukaryotic cytochrome c oxidases
Authors: Holm David E. , Godette Gerald , Bonaventura Joseph , Bonaventura Celia , Peterson Jim
Published: July 2002

The electronic spectra of fully oxidized derivatives of some cytochrome c oxidase preparations are distinctly pH dependent. In general, the observed spectral shifts are greater in the case of pulsed derivatives compared to resting preparations and also, greater for preparations of the enzyme from shark skeletal muscle compared to beef heart. The low temperature near‐infrared magnetic circular dichroism spectrum of the fully oxidized shark enzyme is not pH dependent in the experimental range, indicating the sensitivity of the visible region electronic spectrum to variation in pH to be due principally to changes at the heme a
3‐CuB chromophore. The results are discussed in relation to proposed mechanisms of proton translocation in cytochrome c oxidase.
Identification of the Zn2+ binding region in calreticulin
Authors: Baksh Shairaz , Spamer Cornelia , Heilmann Claus , Michalak Marek
Published: July 2002

Calreticulin binds Zn2+ with the relatively high affinity/low capacity. To determine the location of the Zn2+ binding site in calreticulin different domains of the protein were expressed in E. coli, using the glutathione S‐transferase fusion protein system, and their Zn2+‐dependent interaction with Zn2+‐IDA‐agarose were determined. Three distinct domains were used in this study: the N + P‐domain (the first 290 residues); the N‐domain (residues 1–182) and the proline‐rich P‐domain (residues 180–273). The N + P‐domain bound to the Zn2+‐IDA‐agarose and were eluted with an increasing concentration of imidazole. The N‐domain also bound 65Zn2+ as measured by the overlay method. The P‐domain did not interact with the Zn2+‐IDA‐agarose and it did not bind any detectable amount of Zn2+. Chemical modification of calreticulin with diethyl pyrocarbonate indicated that five out of seven histidines were protected in the presence of Zn2+ but they were modified by diethyl pyrocarbonate in the absence of Zn2+ suggesting that these residues may be involved in Zn2+ binding to calreticulin. We conclude that Zn2+ binding sites in calreticulin are localized to the N‐domain of the protein, region that is not involved in Ca2+ binding to calreticulin.
Desmin degradation and Ca2+−dependent proteolysis during myoblast fusion
Authors: Elamrani Najat , Brustis Jean Jacques , Dourdin Nathalie , Balcerzak Denis , Poussard Sylvie , Cottin Patrick , Ducastaing André
Published: July 2002

Summary— It has already been reported that, in vitro, intermediate filaments such as desmin and vimentin are very susceptible to proteolysis by calpains (Ca2+‐activated cysteine proteinases). On the other hand, desmin and m‐calpain are both present at the onset of myoblast fusion and throughout this phenomenon. Based on these observations, the aim of this study was to demonstrate, with cultured rat myoblasts, that the amount of desmin decreased significantly as multinucleated myotubes were formed. Using immunoblot analysis, it has been shown that the desmin concentration decreased 41% as myoblasts fuse. Moreover, under conditions which stimulate myoblast fusion, desmin concentration was reduced by 21% compared to the control culture. Under our experimental conditions, which lead to a reduced desmin level, the amount of m‐calpain was increased about three‐fold. These results suggested that m‐calpain could be involved in myoblast fusion via desmin cleavage. This hypothesis was confirmed by the results obtained after calpeptin treatment. In the presence of this cell‐penetrating inhibitor of calpains, desmin seems not to be degraded. Taking into account the observations obtained after different hydrolysis assays and as compared to those observed on cultured cells, it seems conceivable that m‐calpain would be able to initiate desmin cleavage leading to the formation of proteolytic fragments which should be immediately degraded.
Should Individual Investors Avoid the Stock Market Outside of January?
Authors: Mann Steven V. , Solberg Donald P.
Published: July 2002

Recent studies suggest that there is no rewardfor bearing risk outside of January, implying that individuals should invest in common stocks only in January. The purpose of this study is to demonstrate that this conclusion isfar too strong given existing empirical evidence. Our results suggest that inferences drawnffom the evidence can be altered greatly through small changes in the way the empirical question is addressed. There is suficient evidence to doubt the conclusion that individuals are not compensated for the risk of participating in the stock market outside of January.
Effective Credit Costs in Retail Financial Markets
Authors: Plath D. Anthony , Nunnally, Jr. Bennie H.
Published: July 2002

This study examines reported credit cost information in the automobile sales market to deter- mine if vehicle leasing really is cheaper than installment borrowing. In addition, the study evaluates the accuracy of credit cost data furnished to consumers by commercial banks, vehicle leasingjrms, and automobile dealers to gauge whether any systematic differences exist in the accuracy of reported credit cost information. Results of the study suggest that the cost of leasing is significantly different from borrowing, yet neither financing alternative is unilaterally cheaper than the other. In addition, suppliers of credit in consumerjnance markets routinely and signif?cantly understate effective credit costs reported to consumers.
The Individual Investor in the Market
Authors: Peevey Robert M. , Uselton Gene C. , Moroney John R.
Published: July 2002

Do the actions of investors drive the market toward efficiency or do investors utilize fads and other information unrelated to the true value of the security to drive the market away from eficiency? Investors have been forced to examine a multitude of challenges to the eficient markets hypothesis in recent years. One of the most formidable of the challenges is the “excessive market price volatility” argument. We examine this argument, as presented in the “variance bounds” literature, and conclude that, although markets may be ineficient, the “variance bounds” literature has not proved the case conclusively.
What Strategies Are Experienced Estate Planners Recommending?
Authors: Prestopino Chris J.
Published: July 2002

Responses from 124 experienced estate planning attorneys in 33 states reveal the frequency with which their 1991 clients undertook over forty estate planning techniques commonly promoted in practitioner literature. Nearly 83 percent of their clients had a net worth of at least $600,000, implying the need for careful consideration of these strategies. Among the most popular techniques implemented include the durable power of attorney for property, durable power of attorney for health care, living will, credit shelter bypass plan, standard QTIP trust, revocable living trust, and nonsimple will. Among the least popular techniques include flower bonds, private annuity, grantor retained unitrust, large custodial gif, and grantor retained annuity trust.
Localization of riboproteins in a trypanosomatid mitochondrion
Authors: Tittawella Ivor , Baranov Vladimir
Published: July 2002

There is growing evidence in support of mitochondrial translation in trypanosomes but mitoribosomes have never been characterized or localized in these parasites. On RNA–protein blots we identified several proteins from the trypanosomatid Crithidia fasciculata which bound the parasite's 12S and 9S mitochondrial ribosomal RNAs. Two of these proteins had significant amino acid sequence homology to riboproteins S8 and S21 across phyla. Immunoelectron microscopy revealed that antibodies raised against the two proteins react with matrix components in the C. fasciculata mitochondrion. Our data thus provide, we believe for the first time, evidence for the presence of riboproteins within a trypanosomatid mitochondrion, bound, possibly, to the 12S and 9S RNAs. The proteins were immunologically related to two cytosolic riboproteins which were also of identical size, suggesting the interesting possibility that the same set of riboproteins is shared between the cytosol and the mitochondrion in this parasite.
Partially structured state of the functional VH domain of the mouse anti‐ferritin antibody F11
Authors: Martsev Sergey P , Dubnovitsky Anatoly P , Stremovsky Oleg A , Chumanevich Alexander A , Tsybovsky Yaroslav I , Kravchuk Zinaida I , Deyev Sergey M
Published: July 2002

An antibody combining site generally involves the two variable domains, VH from the heavy and VL from the light chain. We expressed the individual VH domain of the mouse anti‐human ferritin monoclonal antibody F11. The loss of affinity was not dramatic (K
a=4.0×107 M−1 versus 8.6×108 M−1 for the parent antibody) and comparable to that previously observed for other VHs. However, the functional VH domain adopted a partially structured state with a significant amount of distorted secondary and compact yet greatly destabilized tertiary structures, as demonstrated by spectroscopic and calorimetric probes. These data provide the first description for a functional antibody domain that meets all the criteria of a partially structured state.
Catalytic cysteine residues of ER‐60 protease
Authors: Okudo Hirokazu , Urade Reiko , Moriyama Tatsuya , Kito Makoto
Published: July 2002

ER‐60 protease contains two CGHC motifs that appear to include an active site cysteine residue(s). Its proteolytic activity was lost with a double mutation of the C‐terminal cysteines of the two motifs to alanine, but not with a single mutation of the C‐terminal cysteine of either of the motifs to alanine. This suggests that these C‐terminal cysteines independently constitute the catalytic active site. A mutation of both histidine residues in the two CGHC motifs to serine did not abolish the proteolytic activity, suggesting these histidine residues in the CGHC motifs do not constitute the catalytic dyad of ER‐60 protease.
Fine Affinity Discrimination by Yeast Surface Display and Flow Cytometry
Authors: Van Antwerp Jennifer J. , Wittrup K. Dane
Published: July 2002

Yeast surface display is a eucaryotic system for the directed evolution of protein binding and stability. For antibody affinity maturation, achievable single‐pass enrichment factors are a critical variable. Both reliable recovery of rare clones (yield) and effective differentiation between clones of only slightly improved affinity (purity) are paramount. To validate yeast display's purification potential, trial sorting experiments were performed. The D1.3 (anti‐hen egg lysozyme) single chain variable fragment antibody and a 2‐fold higher affinity mutant (M3) were each displayed on the surface of Saccharomyces cerevisiae. M3‐displaying cells were mixed into the D1.3‐displaying cells at a ratio of 1:1000. Cells were fluorescently labeled according to antigen equilibrium binding and then sorted using a flow cytometer. Single‐pass enrichment of M3‐displaying cells was 125‐fold (± 65‐fold). This level of performance is achievable because of the precision and reproducibility of optimal labeling conditions. This work further demonstrates the capability of yeast display for very fine discrimination between mutant clones of similar affinity. Because large improvements in affinity typically result from combinations of small changes, this capability to identify subtle improvements is essential for rapid affinity maturation.
Geographic and seasonal variability of resistance to insecticides in Cacopsylla pyri L. (Hom., Psyllidae)
Authors: Buès R. , Boudinhon L. , Toubon J. F. , D’Arcier F. Faivre
Published: July 2002

Pear psylla (Cacopsylla pyri L.) resistance to insecticides was studied in adults using the topical application method. In the Avignon population, the winter forms tested (diapausing generation) showed a greater tolerance to insecticide than the summer forms. High resistance rates, ranging from 25‐ to 180‐fold, were observed for three organo‐phosphorous insecticides. Resistance rates were seven times lower for pyrethrinoids and amitraz and practically nil for carbamates. Inter‐population resistance rates, for an identical period, were different for the three organo‐phosphorous insecticides and for deltamethrin in two localities. However, it was difficult to make comparisons in time due to seasonal variations.

Rates of synergism by S,S,S‐tributyl phosphorotrithioate (DEF) and piperonyl butoxide (PBO) were low when applied 4 h before the insecticide (0.3‐ to 3.3‐fold), except for deltamethrin with PBO (>60‐fold). The presence of mixed‐function oxidases in winter forms is discussed with regard to bibliographical data concerning another psylla species from North America (Psylla pyricola Foerster).
The Renin‐Angiotensin System in the Bovine Utero‐Placental Unit
Authors: Nielsen AH , Schauser KH , Winther H , Dantzer V , Poulsen K
Published: July 2002

Contents

Renin, angiotensin converting enzyme, and angiotensin II receptors are expressed in the bovine utero‐placental unit, indicating the presence of a local renin‐angiotensin system (RAS). Angiotensin II receptors of type AT1 and AT2 as well as non‐AT1/non‐AT2 binding sites were identified. The expression of both renin and the angiotensin II receptor types in the bovine utero‐placental unit differs from that in humans. This fact is probably related to differences in placental architecture. The RAS in the bovine utero‐placental unit might be important for growth processes in the endometrium and for placentation. It might also participate in the regulation of the utero‐placental blood flow and secretion of hormones. Disturbances in the utero‐placental RAS might cause a reduced utero‐placental blood flow, intrauterine growth retarda_tion and intrauterine death.
Quality assurance audit in an Australasian phase III trial of accelerated radiotherapy for head and neck cancer (TROG 91.01)
Authors: Hamilton C , Poulsen M , Walker Q , Krawitz H , Hindley A , Spry N , Peters L , Lamb D , Denham J , Steigler A
Published: July 2002

The Trans‐Tasman Radiation Oncology Group (TROG) initiated a randomized trial, testing accelerated (twice daily) radiotherapy against conventional radiotherapy for stage III and stage IV squamous cell carcinoma of the head and neck in 1991. In 1996, the Trial Management Committee arranged for a technical audit of 76 cases from 11 institutions, conducted by investigators from interstate institutions. A 10% unacceptable protocol violation rate was detected, which compares favourably with initial Radiation Therapy Oncology Group (RTOG) experience in the late 1970s. Infrastructural deficits with poor quality of documentation, incomplete retrieval of films and document return have been demonstrated in some cases. The Trans‐Tasman Radiation Oncology Group is actively pursuing procedural and resourcing issues in order to redress this and is actively expanding its Quality Assurance (QA) Programme with an intercentre dosimetry study. Ultimately, comprehensive clinical and technical QA site visits are planned.
Photobias effect in laser-controlled etching of InP
Authors: Willner A. E. , Podlesnik D. V. , Gilgen H. H. , Osgood R. M.
Published: July 2002

We have investigated laser-assisted photochemical etching of InP in aqueous solutions without external electric fields. The process produces highly directional, high-aspect features with smooth vertical walls. Additionally, we demonstrate that the laser etching rate may be controlled externally by the application of a secondary light source.
Effects of low-frequency modulation on rf discharge chemical vapor deposition
Authors: Watanabe Y. , Shiratani M. , Kubo Y. , Ogawa I. , Ogi S.
Published: July 2002

Low-frequency square-wave modulation of a rf discharge in silane diluted with a rare gas brought about an improvement in the deposition rate of amorphous hydrogenated silicon films and in the film quality as well as a drastic suppression of powder concentration in the discharge space. These results can be explained by a SiH3 density in the modulated discharge that is high compared to that without modulation, because of the electron density enhancement resulting from the modulation and also because the lifetime of SiH3 radicals is much longer than those of SiHn radicals (n=0–2).
Magnetic flux noise in thin-film rings of YBa2Cu3O7−δ
Authors: Ferrari M. J. , Johnson Mark , Wellstood Frederick C. , Clarke John , Rosenthal P. A. , Hammond R. H. , Beasley M. R.
Published: July 2002

The low-frequency magnetic flux noise in thin-film rings of YBa2Cu3O7−δ (YBCO) is measured over the temperature range 1.3–125 K by means of a dc superconducting quantum interference device (SQUID) maintained at liquid-helium temperatures. Below the transition temperature Tc of the YBCO, the spectral density of the noise scales as 1/f, where f is the frequency, and generally increases with increasing temperature. The magnitude of the noise depends strongly on the microstructure of the film, and is lowest for a sample which is predominantly oriented with its c axis perpendicular to the substrate. These results imply that SQUID’s and flux transformers of YBCO must be fabricated from highly oriented films to produce good resolution at low frequencies.
Tunneling escape time of electrons from a quantum well under the influence of an electric field
Authors: Norris T. B. , Song X. J. , Schaff W. J. , Eastman L. F. , Wicks G. , Mourou G. A.
Published: July 2002

We have performed time-resolved photoluminescence on GaAs/AlxGa1−xAs single quantum well structures with an electric field applied perpendicular to the well plane. The quantum wells are coupled to the GaAs continuum through a thin barrier; the escape time of the electrons in the well was measured by time-resolved photoluminescence. The dependence of the decay time on applied bias was found to agree very well with a simple semiclassical model.
All-optical switching in nonlinear X junctions
Authors: Sabini J. P. , Finlayson N. , Stegeman G. I.
Published: July 2002

All-optical switching in nonlinear X junctions with Kerr and saturable nonlinearities is analyzed using the beam propagation method. We establish that switching is possible in the nonlinear X junction, and compare its nonlinear phase shift requirements with that of other all-optical devices.
NH3 as a photosensitizer in the epitaxial growth of Ge on GaAs by laser photochemical vapor deposition
Authors: Kiely C. J. , Tavitian V. , Jones C. , Eden J. G.
Published: July 2002

The viability of ammonia as a sensitizer for the growth of epitaxial Ge on GaAs (100) by laser photochemical vapor deposition (LPVD) has been investigated. Specifically, NH3/GeH4/He (0.8/55.0/95 sccm, 5.5 Torr total pressure) mixtures have been irradiated by an excimer laser beam (ArF, 193 nm) in parallel geometry and for substrate temperatures (Ts) in the range 25≤Ts<400 °C. As evidenced by a more than an order of magnitude acceleration in the Ge film growth rate (factor of ∼33 improvement at 305 °C), even trace amounts of NH3 added to the gas stream efficiently couple the laser radiation to the Ge precursor (GeH4) without incorporating significant concentrations of N and H into the film. Auger, secondary-ion mass spectrometry (SIMS), and x-ray photoelectron spectroscopy analyses of the films show the nitrogen content to be negligible (<1%). Also, the slight amount of hydrogen detected by SIMS appears to arise from hydrocarbon contaminants rather than from the ammonia. Transmission electron microscopy studies demonstrate that films grown at Ts≥300 °C are epitaxial with an amorphous overlayer. Embedded within the amorphous matrix are Ge microcrystals which are textured, having their 〈112〉 axes parallel to the substrate normal. The beneficial effect of NH3 on the growth rate of LPVD Ge films is attributed to the photolytic production of hydrogen atoms which efficiently decompose GeH4 by hydrogen abstraction collisions.
Observation of nonlinear optical rectification at 10.6 μm in compositionally asymmetrical AlGaAs multiquantum wells
Authors: Rosencher E. , Bois P. , Nagle J. , Costard E. , Delaitre S.
Published: July 2002

We report the first experimental evidence of a nonlinear optical effect due to intersubband transitions in compositionally asymmetrical multiquantum wells. The effect is detected as an optical rectification signal appearing at the structure terminals when irradiated by a continuous 10.6 μm CO2 laser. The net electro-optical coefficient of the structure is found to be 7.2 nm/V which is more than three orders of magnitude higher than for bulk GaAs. The results are in good agreement with theoretical predictions.
Efficient coupling of a semiconductor laser to an optical fiber by means of a tapered waveguide on silicon
Authors: Shani Y. , Henry C. H. , Kistler R. C. , Orlowsky K. J. , Ackerman D. A.
Published: July 2002

A Si3N4 core waveguide, matched to a laser mode, is adiabatically tapered into a SiO2:P core waveguide, matched to a fiber mode. When used to couple the light from a semiconductor laser into an optical fiber, a loss of 3.1 dB is obtained, compared to a loss of 4.5 dB obtained with a lensed fiber.
Three-photon absorption in CaF2 at 248.5 nm
Authors: Tomie T. , Okuda I. , Yano M.
Published: July 2002

Nonlinear absorption at 248.5 nm is studied with an 8 ps pulse. Two-photon absorption in fused silica and three-photon absorption in CaF2 are observed. Absorption coefficients are 8×10−11 cm/W and 2×10−21 cm3 /W2 for fused silica and CaF2 , respectively.
Low-temperature silicon cleaning via hydrogen passivation and conditions for epitaxy
Authors: Iyer S. S. , Arienzo M. , de Frésart E.
Published: July 2002

In low-temperature epitaxial Si deposition methods such as molecular beam epitaxy (MBE), pre-epitaxial substrate preparation usually incorporates a high temperature (≳800 °C) step. Elimination of this step is essential to wider applicability of these epitaxial methods. We show that Si(100) wafers exposed to HF vapors in a laboratory ambience are bulk terminated and that such termination is stable in air for several tens of minutes, and in vacuum for several hours. It is possible to obtain good epitaxy, as determined by surface diffraction and transistor characteristics, provided epitaxy is commenced on these bulk-terminated surfaces. We also give evidence that under certain conditions, bulk-terminated surfaces are maintained in low-temperature epitaxy using the method of ultrahigh vacuum chemical vapor deposition.
Strongly directional emission from AlGaAs/GaAs light-emitting diodes
Authors: Köck A. , Gornik E. , Hauser M. , Beinstingl W.
Published: July 2002

We show for the first time that strongly directional emission of defined polarization can be achieved from conventional AlGaAs/GaAs double-heterostructure surface-emitting light-emitting diodes (LEDs) via coupling to surface plasmons. By microstructuring the surface, we have fabricated LEDs with a beam divergence of less than 4° and an increased quantum efficiency. It is demonstrated that the surface plasmon excitation and emission mechanism have the potential to improve the performance of LEDs.
X-ray rocking curve measurement of composition and strain in Si-Ge buffer layers grown on Si substrates
Authors: Fatemi M. , Stahlbush R. E.
Published: July 2002

The level of strain and the fraction of Ge in SiGe layers grown on Si can be found rapidly and unambiguously using double-crystal x-ray diffraction and a simple application of the linear elasticity theory combined with Vegard’s law. The method gives excellent results for 0.4-μm-thick buffer layers of SiGe/Si containing 5%–50% germanium. It is shown that lattice relaxation rises abruptly at x(Ge)≥15%, and that some strain remains for x(Ge) as high as 50%.
Epitaxial yttria-stabilized zirconia on (11̄02)sapphire for YBa2Cu3O7−δ thin films
Authors: Wu X. D. , Muenchausen R. E. , Nogar N. S. , Pique A. , Edwards R. , Wilkens B. , Ravi T. S. , Hwang D. M. , Chen C. Y.
Published: July 2002

Epitaxial yttria-stabilized zirconia (YSZ) films were deposited on (11̄02) sapphire by pulsed laser deposition. The films are formed in a cubic phase with the a axis normal to the substrate surface. Ion beam (2.8 MeV He++) channeling measurements show that the YSZ films are highly crystalline with a channeling minimum yield of 8%. The epitaxial relationship between the film and substrate is further confirmed by a cross-section transmission electron microscopy study. Epitaxial YBa2Cu3O7−δ thin films deposited on YSZ/sapphire have Tc and Jc of up to 89 K and 1×106 A/cm2 at 77 K, respectively.
Ballistic electron transport in macroscopic four-terminal square structures with high mobility
Authors: Hirayama Y. , Saku T. , Tarucha S. , Horikoshi Y.
Published: July 2002

Ballistic electron transport characteristics are studied using macroscopic four-terminal square structures formed in high-mobility wafers (μ=7.8×106 cm2/V s at 1.5 K). Ballistic transport over 200 μm can be detected as a negative peak in resistance around B=0 T when four-terminal resistance is measured as a function of magnetic field. The ballistic mean free path (lb) of electrons is evaluated from the size dependence of the negative peak height. The estimated lb becomes 86 μm, which is approximately equal to a conventional mean free path calculated from carrier density and mobility of the wafer.
Magnetocrystalline anisotropy of (100) face-centered cubic Co structures deposited on Cu/Si(100)
Authors: Chang Chin-An
Published: July 2002

Face-centered cubic (fcc) Co in the (100) orientation has been recently grown using the technique of metal-metal epitaxy on silicon (MMES), with a (100)Cu seed. This enables the determination of the magnetocrystalline anisotropy of fcc Co by measuring its angular dependence of the in-plane magnetization. Using (100)Cu/Co/Cu structures with varying Co thickness between 25 and 500 Å, while keeping the Cu layers at 1000 Å each, an easier magnetization at low field along the [110] edge than that along the [100] one is seen for all the structures studied. The same angular dependence is also observed for the (100)Cu-Co superlattices. Such a crystalline anisotropy is similar to the one observed for bulk Ni crystal and the (100)Cu/Ni/Cu structures. The fcc Co films thus share the same magnetocrystalline anisotropy as fcc Ni, which is different from Fe. The body-centered cubic bulk Fe crystal shows an easier low-field magnetization along the [100] edge than the [110] one; the same has been observed for both the (100) Cr/Fe/Cr and Pd/Fe/Pd structures grown by the MMES technique.
Bi-epitaxial grain boundary junctions in YBa2Cu3O7
Authors: Char K. , Colclough M. S. , Garrison S. M. , Newman N. , Zaharchuk G.
Published: July 2002

We have developed a new way of making grain boundary junctions in YBa2Cu3O7 thin films by controlling the in-plane epitaxy of the deposited film using seed and buffer layers. We produce 45° grain boundaries along photolithographically defined lines. The typical value of the critical current density of the junctions is 103–104 A/cm2 at 4.2 K and 102–103 A/cm2 at 77 K, while the rest of the film has a critical current density of 1–3×106 A/cm2 at 77 K. The current-voltage characteristics of the junctions show resistively shunted junction behavior and we have used them to fabricate dc superconducting quantum interference devices (SQUIDs) which show modulation at temperatures well above 77 K. This is the first planar high Tc Josephson junction technology that appears readily extendable to high Tc integrated circuits.
Varistor property of n-BaTiO3 based current limiters
Authors: Kutty T. R. N. , Ravi V.
Published: July 2002

Highly stable varistor (voltage-limiting) property is observed for ceramics based on donor doped ■Ba1−xSrx■Ti1−yZryO3 (x<0.35, y<0.05), when the ambient temperature (Ta) is above the Curie point (Tc). If Ta<Tc, the same ceramics showed stable current-limiting behavior. The leakage current and the breakdown voltage as well as the nonlinearity coefficient (α=30–50) could be varied with the Tc-shifting components, the grain boundary layer modifiers and the post-sintering annealing. Analyses of the current-voltage relations show that grain boundary layer conduction at Ta<Tc corresponds to tunneling across asymmetric barriers formed under steady-state joule heating. At Ta≳Tc, trap-related conduction gives way to tunneling across symmetric barriers as the field strength increases.
Femtosecond time-resolved free-induction decay of room-temperature excitons in GaAs quantum wells
Authors: Mycek M.-A. , Weiss S. , Bigot J.-Y. , Schmitt-Rink S. , Chemla D. S. , Schaefer W.
Published: July 2002

We directly resolve the femtosecond free-induction decay of excitons in GaAs quantum wells at room temperature by upconverting the diffracted signal from a transient four-wave-mixing experiment. At high laser intensities, we find significant deviations from the temporal evolution of the time-integrated and peak amplitude signals, which we attribute to many-body Coulomb effects.
CH4/H2: A universal reactive ion etch for II-VI semiconductors?
Authors: Foad M. A. , Wilkinson C. D. W. , Dunscomb C. , Williams R. H.
Published: July 2002

A high resolution reactive ion etching process, capable of producing nanostructures less than 50 nm wide in a variety of II-VI semiconductors, is described. Using a mixture of methane and hydrogen, binary II-VI compound, e.g., ZnTe, ZnSe, CdTe, ZnS, CdS, and ternary compounds, e.g., CdMnTe and ZnSSe, have been etched. It would appear that the CH4/H2 gas mixture will play the same role for the II-VI semiconductors as it does for the III-Vs, that of seemingly ubiquitous etching system.
In situ control of As composition in InAsP and InGaAsP grown by gas-source molecular beam epitaxy
Authors: Hou H. Q. , Tu C. W.
Published: July 2002

Group-III- and group-V-induced intensity oscillations of reflection high-energy electron diffraction are observed for InAsP in gas-source molecular beam epitaxial growth. The As incorporation rate is found to be dominant, independent of the presence of P when the phosphine flow rate is reasonably low. This observation suggests a simple method of controlling the As composition in InAsP by just controlling the incorporation-rate ratio of As to In when this ratio is less than unity. This successful in situ composition control for InAsP, combined with the in situ composition calibration in GaAsP reported previously, provides a general guideline for controlling the compositions in InGaAsP.
Formation of amorphous aluminum tantalum nitride powders by mechanical alloying
Authors: El-Eskandarany M. Sherif , Aoki K. , Suzuki K.
Published: July 2002

Aluminum tantalum nitride amorphous alloy powders have been synthesized by a high energy ball mill under purified nitrogen gas (N2) flow at room temperature. The alloy powders were characterized by means of transmission electron microscopy, differential thermal analysis, and chemical analysis. An amorphous phase containing 18 at. % N2 was obtained after 65 ks of the milling time. At the final stage of milling (72 ks) the crystallization temperature, Tx, and enthalpy change of crystallization, ΔHx, are 1115 K and −95 kJ mol−1, respectively.
Selectivity in copper chemical vapor deposition
Authors: Cohen Susan L. , Liehr Michael , Kasi Srinandan
Published: July 2002

The fundamental surface chemistry underlying selectivity in copper chemical vapor deposition (CVD) from COD-Cu-hfac and Cu(hfac)2 has been determined. Both electronic and chemistry contributions strongly influence the precursor reactivity on oxide as compared to metal surfaces. These results have important implications regarding the role of surface preparation and cleaning for initiating and maintaining selective deposition.
Two-photon pumped upconverted lasing in dye doped polymer waveguides
Authors: Mukherjee Anadi
Published: July 2002

The first measurements of two-photon pumped upconverted lasing in a waveguide is reported. Nonlinear dependence of the upconversion signal on the square of the input pump intensity and associated spectral narrowing was experimentally observed in dye-doped polymer waveguides. The pump wavelength was 736 nm and the center of the lasing spectrum was 570 nm. The spectra shows excitonlike features at 630 and 654 nm not seen in the absorption spectrum.
Band-gap discontinuity control for InGaAs/InGaAsP multiquantum-well structures by tensile-strained barriers
Authors: Nido Masaaki , Naniwae Koh-ichi , Terakado Tomoji , Suzuki Akira
Published: July 2002

The changes in InGaAsP conduction- and valence-band edge energies due to tensile strain, have been measured by optical methods at 77 K. The measured increases in the conduction- and valence-band edge energies for the 0.5% tensile-strained InGaAsP, compared to the unstrained InGaAsP (1.2 μm band-gap wavelength), are 70 and 38 meV, respectively. The experimentally obtained values are in accordance with calculated values. The results show that the ratio of the conduction- and valence-band discontinuities in InGaAs/InGaAsP multiquantum-well structures can be controlled by the tensile-strained barrier.
Surface-breaking fatigue crack detection using laser ultrasound
Authors: Shan Q. , Dewhurst R. J.
Published: July 2002

Surface-breaking tight fatigue cracks in mild steel have been examined with laser-generated ultrasonic pulses. Before the arrival of transmitted Rayleigh waves arriving at the detector, evidence is presented of a fast skimming longitudinal pulse which is also transmitted through the crack. Additionally, another ultrasonic feature is consistent with a longitudinal wave which is mode converted to a diffracted shear pulse by the tip of the fatigue crack. Such an interaction mechanism can form the basis of laser-based fatigue crack depth measurements.
Interface defects of ultrathin rapid-thermal oxide on silicon
Authors: Stathis J. H. , Buchanan D. A. , Quinlan D. L. , Parsons A. H. , Kotecki D. E.
Published: July 2002

We have used capacitance-voltage and electron paramagnetic resonance to measure interface defects in ultrathin (30 Å) SiO2 prepared by rapid-thermal oxidation. We observe a very narrow interface state peak in the upper portion of the Si band gap, as well as both Pb0 and Pb1 defects in the as-oxidized film. Forming-gas annealing removes the interface state and most of the Pb centers. However, from the energy level and charge state of the interface state peak, we argue that it cannot be reliably ascribed to either Pb0 or Pb1.
Infrared photodetectors with tailorable response due to resonant plasmon absorption in epitaxial silicide particles embedded in silicon
Authors: Fathauer R. W. , Dejewski S. M. , George T. , Jones E. W. , Krabach T. N. , Ksendzov A.
Published: July 2002

Photodiodes with epitaxial CoSi2 particles embedded in a single-crystal silicon matrix show response in the 1–2 μm range with structure which correlates with absorption peaks due to the surface plasmon resonance of the particles. Aspect ratios (height:diameter) of the particles are accurately controlled by molecular beam epitaxy over a range from 1.4:1 to 1:7, allowing the absorption peaks to be tailored from 1.2 to 2.6 μm, respectively. The particle surface plasmon excitation modifies the photoresponse of the devices and allows this response to be tailored through control of the dimensions of the particles. The photodiodes were tested at 77 K, and 4 of 8 devices tested with an absorption peak at 1.7 μm show dark currents less than 2 nA/cm2 at a reverse bias of 1 V. Detectivities for the same devices at 77 K range from 4×109 to 8×109 cm√Hz/W.
Epitaxial growth of Pb(Zr,Ti)O3 films on MgAl2O4 by pulsed laser deposition
Authors: Ling S. H. , Tang Y. S. , Au W. S. , Wong H. K.
Published: July 2002

Stoichiometric MgAl2O4 spinel single crystals were used as the substrates for deposition of lead zirconate titanate (PZT) thin films because of their excellent lattice matching. Epitaxial growth of (001) PZT films with a perovskite structure was achieved by means of the pulsed laser deposition technique but there exists a stringent restriction on the substrate temperature and oxygen pressure. PZT films could also be grown epitaxially on spinel substrates with an odd cut surface indicating that other growth directions can be obtained if the substrates are prepared with suitable orientation.
Stable and efficient green light generation by intracavity frequency doubling of Nd:YVO4 lasers
Authors: Kitaoka Y. , Ohmori S. , Yamamoto K. , Kato M. , Sasaki T.
Published: July 2002

A green light source of 11 mW (maximum) has been obtained by frequency doubling in 3 at. % Nd:YVO4 lasers pumped by a single longitudinal mode laser diode (LD), for a 50 mW incident pumping power, with grating feedback optics. When the temperature of the LD was changed within the range of 23±10 °C, the oscillated wavelength of the LD remained unchanged, and the relative intensity noise of the green light was maintained to less than −140 dB/Hz (at 2.5 MHz).
Ge segregation in SiGe/Si heterostructures and its dependence on deposition technique and growth atmosphere
Authors: Grützmacher D. A. , Sedgwick T. O. , Powell A. , Tejwani M. , Iyer S. S. , Cotte J. , Cardone F.
Published: July 2002

Ge segregation at SiGe/Si heterointerfaces has been studied for films deposited by atmospheric pressure chemical vapor deposition (APCVD), ultrahigh vacuum CVD (UHV/CVD) and molecular beam epitaxy (MBE). Profiles were taken by secondary-ion-mass-spectroscopy (SIMS) of samples grown with these techniques at the same growth temperatures and Ge concentrations. The MBE grown profiles are dominated by segregation of Ge into the Si top layer in the temperature range from 450 to 800 °C. SiGe/Si interfaces deposited by UHV/CVD at elevated temperatures are smeared, but at 515 °C and below the interfaces are abrupt within the resolution of the SIMS. Heterostructures grown by APCVD show abrupt interfaces and no indication of Ge segregation in the investigated temperature range from 600 to 800 °C. Surface passivation by hydrogen appears to be responsible for the suppression of the Ge segregation in CVD processes.
Determination of drift mobility and lifetime for dominant charge carriers in polycrystalline CuInSe2 by photomixing
Authors: Tang Yi , Braunstein R. , von Roedern Bolko
Published: July 2002

Drift mobility and lifetime for the dominant charge carriers in polycrystalline CuInSe2 were determined for the first time by a photomixing technique. Evidence for a continuous distribution of localized states in the band gap near the extended states was provided. The temperature dependence of the photoconductive charge transport was found to be determined by multiple trapping processes.
Crystallographic selective growth of GaAs by atomic layer epitaxy
Authors: Isshiki Hideo , Aoyagi Yoshinobu , Sugano Takuo , Iwai Sohachi , Meguro Takashi
Published: July 2002

We found high crystallographic selectivity in atomic layer epitaxy (ALE) growth of GaAs, in comparison with other epitaxial growth methods. In the temperature dependence of the GaAs growth rate, no GaAs growth on the GaAs (111)A and (110) planes was observed in the high temperature range under the condition of GaAs ALE growth on GaAs (100) plane. Also we discussed the mechanism of GaAs growth selectivity, which was believed to be caused by growth limitation due to As desorption. Due to the self-limiting effect and the high selectivity of ALE growth, trapezoidal-shaped GaAs/AlGaAs quantum wire structures, with 20 nm thickness and 50 nm width, were successfully realized.
Improvement of InP/InGaAs heterointerfaces grown by gas source molecular beam epitaxy
Authors: Anan Takayoshi , Sugou Shigeo , Nishi Kenichi , Ichihashi Toshinari
Published: July 2002

Surface modification of a P2 beam-exposed InGaAs surface and an As2 beam-exposed InP surface was studied in situ using reflection high energy electron diffraction during gas source molecular beam epitaxy. It is revealed that the InP surface remained stable under As2 beam exposure after forming an InAs surface layer a few monolayers thick; the InGaAs surface became rough by P2 beam exposure. This surface roughening originates from substitutions of As to P atoms around Ga atoms. These substitutions result in the fairly reactive nature of the InGaAs surface under P2 beam exposure. From this viewpoint, we have proposed a new switching sequence which excludes surface gallium atoms by depositing one monolayer of In on the InGaAs surface before P2 beam exposure. This sequence drastically improves heterointerface quality, which was confirmed by an increase in photoluminescence intensity in InGaAs/InP short period superlattices.
Low-temperature scanning tunneling microscopy study of nucleation, percolation, and growth of ultrathin Ag films on Si(111)7×7
Authors: Meyer Gerhard , Rieder K. H.
Published: July 2002

We have studied the growth of ultrathin Ag films on Si(111)7×7 between 80–100 K with low-temperature scanning tunneling microscopy. Nucleation of Ag in both halves of the 7×7 is observed. Corner holes and dimer sites are not occupied. Percolation occurs at submonolayer coverage through contact between the nucleated 2D Ag islands. This results in a honeycomb random site percolation problem. Upon completion of the first monolayer, 2D layer-like growth is observed.
Pulse-time-modulated electron cyclotron resonance plasma etching for highly selective, highly anisotropic, and notch-free polycrystalline silicon patterning
Authors: Samukawa Seiji
Published: July 2002

Highly selective, highly anisotropic, and notch-free etching for polycrystalline silicon is achieved in a few tens of μs pulse-time-modulated electron cyclotron resonance plasma. In the pulsed plasma, the selectivity ratio of polycrystalline silicon etching rate to the SiO2 etching rate is drastically improved with high etching rate, as compared with the ratio with a continuous discharge. Furthermore, vertical and notch-free phosphorus-doped polycrystalline silicon etching profiles can be achieved even with 100% over etching. These etching characteristics are achieved by controlling ion energy distributions through the duty ratio, maintaining a high ion current density, generating a collimated ion flux and eliminating surface charging with a pulsed discharge of a few tens of μs.
Statistical noise due to tunneling in superconducting tunnel junction detectors
Authors: Goldie D. J. , Brink P. L. , Patel C. , Booth N. E. , Salmon G. L.
Published: July 2002

We discuss the statistical noise associated with tunneling which is intrinsic to superconducting tunnel junctions. We deduce a simple expression for the noise in the general case where the tunneling probabilities may be dissimilar. The statistical tunneling noise exceeds the Fano-factor limited statistical noise of the quasiparticle creation for most cases.
Electron paramagnetic resonance study of a native acceptor in as-grown ZnGeP2
Authors: Rakowsky M. H. , Kuhn W. K. , Lauderdale W. J. , Halliburton L. E. , Edwards G. J. , Scripsick M. P. , Schunemann P. G. , Pollak T. M. , Ohmer M. C. , Hopkins F. K.
Published: July 2002

Electron paramagnetic resonance (EPR) has been used to investigate an acceptor in as-grown single crystals of ZnGeP2. The spectra are characterized by equally spaced triplets with 1:2:1 intensity ratios representing hyperfine interactions (varying from 35 to 55 G in magnitude) with two equivalent phosphorous nuclei. Their angular dependence shows that there are four crystallographically equivalent orientations of the defect. The principal values of the g matrix are 2.002, 2.021, and 2.074 and the corresponding principal axes, at one of the four sites, are the [011], [1̄00], and [01̄1] directions, respectively. Two possible models are suggested for this acceptor: Either a zinc vacancy (VZn) or a zinc ion on a germanium site (ZnGe). It also is suggested that the acceptor responsible for the EPR signal is the same acceptor, namely AL1, that gives rise to a dominant near-infrared absorption band.
Optical clarity and waveguide performance of thin film perovskites on MgO
Authors: Walker F. J. , McKee R. A. , Yen Huan-wun , Zelmon D. E.
Published: July 2002

The optical clarity of a new class of thin film waveguides, epitaxial perovskites on MgO, has been characterized and found to have optical clarity comparable to in-diffused waveguide structures typically represented by Ti drifted LiNbO3. For the simplest member within this new class, SrTiO3, measurements of the wavelength dependence of optical loss show a monotonic decrease with increasing wavelength between 475 and 705 nm, reaching a value of 1 dB/cm at 705 nm.
Ordering induced by swift ions in semicrystalline polyvinylidene fluoride
Authors: Percolla R. , Calcagno L. , Foti G. , Ciavola G.
Published: July 2002

Thin semicrystalline polyvinylidene fluoride foils are irradiated by swift ions (60 MeV carbon) with a dose in the range 10–300 kGy. After irradiation a change of crystalline structure is observed as detected by x-ray diffraction measurements. Diffraction analysis or irradiated polyvinylidene fluoride shows a structural order along the (020) atomic planes. This effect appears when a threshold dose value of about 100 kGy is reached and saturates at higher dose (≥250 kGy). Differential scanning calorimetry measurements performed in the same dose range do not show any change in the melting enthalpy (56.0 J/g) of the alpha-phase polyvinylidene fluoride.
Digital etching of GaAs using Se molecular beam and atomic hydrogen beam
Authors: Takatani Shinichiro , Kikawa Takeshi
Published: July 2002

A novel digital etching technique for GaAs was investigated. The GaAs surface was first irradiated by a Se molecular beam to form Ga2Se3 on the surface as a result of the Se–As exchange reaction. The surface was then irradiated by an atomic hydrogen (H*) beam to selectively etch the Ga2Se3 layer. These steps were repeated until etched to the desired depth. An etch rate of about 0.2 nm/cycle was obtained at the substrate temperature of 500 °C. The etch rate was nearly independent of the Se and H* irradiation time, suggesting the involvement of a self-limiting mechanism in the etching process.
Two kinds of nitrogen atoms in nitrogen-substituted, highly crystalline graphite prepared by chemical vapor deposition
Authors: Matsui T. , Yudasaka M. , Kikuchi R. , Ohki Y. , Yoshimura S.
Published: July 2002

Nitrogen-substituted graphite thin films were prepared by chemical vapor deposition (CVD) using pyrrole as a starting material. Ni was used as the substrate material whose temperature was kept in the range 700–1000 °C. The interlayer spacing of these films, determined by x-ray diffraction, was close to that of single-crystal graphite. Two XPS peaks were observed in the N 1s spectra at around 398 and 401 eV. The former can be assigned to nitrogen atoms substituting for carbon atoms in the graphite layer and the latter to nitrogen atoms bonded to the layer edge.
Large magnetoresistance in La1−xSrxMnO3 and its dependence on magnetization
Authors: Mahendiran R. , Raychaudhuri A. K. , Chainani A. , Sarma D. D. , Roy S. B.
Published: July 2002

In this letter we report large magnetoresistance (MR) in ceramic samples of La1−xSrxMnO3 (0.1≤x≤0.4) in the temperature range 4.2 K≤T≤350 K in fields up to 6 T. We find that a large negative and isotopic MR exists for the whole composition range studied and the absolute value of resistivity change on application of magnetic field is more for samples with lower x which have higher resistivity. We find that the large MR occurs in the ferromagnetic state only and MR has a close relation with the magnetization M.