bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular cloning and functional expression of a novel potassium channel β‐subunit from human atrium
Authors: Majumder Kumud , De Biasi Mariella , Wang Zhiguo , Wible Barbara A.
Published: July 2002

We report the cloning and functional expression of a novel K+ channel β‐subunit from human atrium, hKvβ3. hKvβ3 is highly homologous to the two β‐subunits cloned from rat brain, Kvβ1 and Kvβ2, but has an essentially unique stretch of 79 N‐terminal residues. Upon expression in Xenopus oocytes, hKvβ3 accelerates the inactivation of co‐injected hKv1.4 currents and induces fast inactivation of non‐inactivating co‐injected hKv1.5 currents. By contrast, hKvβ3 had no effect on hKv1.1, hKv1.2, or hKv2.1 currents. Thus, hKvβ3 represents a third type of K+ channel β‐subunit which modulates the kinetics of a unique subset of channels in the Kv1 subfamily.
In vitro dissociation and self‐assembly of three chaperonin 60s: the role of ATP
Authors: Lissin Nikolai M.
Published: July 2002

A comparative study has investigated the in vitro dissociation and self‐assembly of chaperonin 60 14‐mers isolated from E. coli (GroEL), yeast mitochondria and pea chloroplasts. In all cases Mg2+ inhibits, and low temperature stimulates, the urea‐induced dissociation. ATP or ADP in the presence of Mg2+ enhance the dissociation of the chaperonins. Re‐assembly of the 14‐mers from their monomers shows different efficiencies between the three proteins. In all cases, however, self‐assembly is stimulated by Mg‐adenine nucleotides. Surprisingly, effective self‐assembly of GroEL is promoted by 20% glycerol in the absence of ATP. The role of Mg‐adenine nucleotides in the dissociation and assembly of the chaperonins is discussed.
The active site of the cyanide‐resistant oxidase from plant mitochondria contains a binuclear iron center
Authors: Siedow James N. , Umbach Ann L. , Moore Anthony L.
Published: July 2002

The cyanide‐resistant, alternative oxidase of plant mitochondria catalyzes the four‐electron reduction of oxygen to water, but the nature of the catalytic center associated with this oxidase has yet to be elucidated. We have identified conserved amino acids, including two copies of the iron‐binding motif Glu‐X‐X‐His, in the carboxy‐terminal hydrophilic domain of the alternative oxidase that suggest the presence of a hydroxo‐bridged binuclear iron center, analogous to that found in the enzyme methane monooxygenase. Using the known three‐dimensional structures of other binuclear iron proteins, we have developed a structural model for the proposed catalytic site of the alternative oxidase based on these amino acid sequence similarities.
Purification, and phosphorylation in vivo and in vitro, of phosphoenolpyruvate carboxykinase from cucumber cotyledons
Authors: Walker Robert P , Leegood Richard C
Published: July 2002

Phosphoenolpyruvate carboxykinase (PEPCK) with a subunit molecular mass of 74 kDa has been purified 450‐fold to homogeneity from the cotyledons of cucumber (Cucumis sativusL.). This is the first purification of the native form of the enzyme from any plant tissue. Incubation of the purified enzyme with [γ‐32P]ATP and either phosphoenolpyruvate‐carboxylase kinase or mammalian cAMP‐dependent protein kinase led to labelling of the enzyme in a part of the molecule separate from the active site. This was reversed by incubation with protein phosphatase 2A. Cotyledons of cucumber seedlings were also supplied with32Pi. Homogenates of such cotyledons contained a heavily labelled polypeptide which was confirmed as PEPCK by immunoprecipitation. Labelling of PEPCK by32Piin darkened cotyledons was reversed by illumination.
Processing of proendothelin‐1 by human furin convertase
Authors: Denault Jean-Bernard , Claing Audrey , D'Orléans-Juste Pedro , Sawamura Tatsuya , Kido Tsuneo , Masaki Tomoh , Leduc Richard
Published: July 2002

Endothelin‐1 (ET‐1) is the most potent vasoactive peptide known to date. The peptide is initially synthesized as an inactive precursor (proET‐1) which undergoes proteolysis at specific pairs of basic amino acids to yield bigET‐1. Production of ET‐1 then proceeds by cleavage of bigET‐1 by the endothelin converting enzyme (ECE). Here, we demonstrate that the in vitro cleavage of proET‐1 by furin, a mammalian convertase involved in precursor processing, produced bigET‐1. Upon further processing, bigET‐1 was converted to biologically active ET‐1. Furthermore, we demonstrate that the furin inhibitor, decanoyl‐Arg‐ValLys‐Arg chloromethylketone, abolished production of ET‐1 in endothelial cells.
Ala335 is essential for high‐affinity cAMP‐binding of both sites A and B of cAMP‐dependent protein kinase type I
Authors: Zorn Michaele , Fladmark Kari E. , Øgreid Dagfinn , Jastorff Bernd , Døskeland Stein O. , Dostmann Wolfgang R.G.
Published: July 2002

A single amino acid substitution (Ala335 Asp) in cAMP binding site B of the regulatory subunit of cAMP‐dependent protein kinase type I was sufficient to abolish high affinity cAMP binding for both cAMP binding sites A and B. Furthermore, the Ala335 Asp mutation increased the activation constant for cAMP of the mutant holoenzyme 30‐fold and also enhanced the rate of holoenzyme formation. Thus, the substitution was responsible for the dominant negative phenotype of the enzyme. Activation of mutant holoenzyme with site‐selective cAMP analogs indicated that the enzyme dissociated through binding to site A only. Our results provide evidence that Ala335 is an essential residue for high affinity cAMP binding of both sites as well as for the functional integrity of the enzyme.
The association of pp125FAK, pp60Src, CDC42Hs and Rap1B with the cytoskeleton of aggregated platelets is a reversible process regulated by calcium
Authors: Dash Debabrata , Aepfelbacher Martin , Siess Wolfgang
Published: July 2002

The integrin α

IIb

β
3‐mediated redistribution of the tyrosine kinases pp125FAK and pp60
Src
and the small GTP‐binding proteins CDC42Hs and Rap1B from the membrane skeleton to the cytoskeleton was found to be reversible: upon prolonged platelet aggregation (up to 15 min) induced by the thrombin‐receptor activating peptide (TRAP) these signalling proteins dissociated from the cytoskeleton and reappeared in the membrane skeleton. Addition of the extracellular Ca2+ chelator EGTA and the intracellular Ca2+ chelator BAPTA/AM 30 s after TRAP allowed platelet aggregation and the association of pp125FAK, pp60
Src
, CDC42Hs and Rap1B with the cytoskeleton, but prevented their dissociation from the cytoskeleton. The results indicate that the prolonged elevation of cytosolic Ca2+ in stimulated platelets leads to the dissociation of signalling proteins from the cytoskeleton.
From structure to function: possible biological roles of a new widespread protein family binding hydrophobic ligands and displaying a nucleotide binding site
Authors: Schoentgen Françoise , Jollès Pierre
Published: July 2002

A cytosolic 21–23 kDa protein isolated from bovine brain was demonstrated to bind hydrophobic ligands, particularly phosphatidylethanolamine. The protein was encountered in numerous tissues of several species. High expression of the mRNA encoding the 21–23 kDa protein was found in rat testes. Immunohistochemical studies showed the presence of the 21–23 kDa protein in the elongated spermatids and epididymal fluid of rat testis and in brain oligodendrocytes of developing rats. As the bovine, human and rat brain 21–23 kDa proteins had only few sequence homologies with already known proteins, it was concluded that they belong to a new protein family. In order to get additional information on the structural features of the 21–23 kDa protein, we built a molecular model which displayed a nucleotide binding site. The affinity of the bovine brain 21–23 kDa protein towards nucleotides as well as its association with cytosolic proteins and small GTP‐binding proteins were demonstrated. Recently, significant sequence homologies were found with an antigen from Onchocerca volvulus, a fruit fly odorant‐binding protein and the yeast protein TFS1 which is a dosage‐dependant suppressor of CDC25 mutations. A positive regulation of RAS is carried out by CDC25 product which facilitates the GDP/GTP exchange on RAS proteins. These results imply that 21–23 kDa proteins function in oxidoreduction reactions and signal mechanisms during cell growth and maturation.
IL‐13 and IL‐4 share signal transduction elements as well as receptor components in TF‐1 cells
Authors: Lefort Sylvie , Vita Natalio , Reeb Renée , Caput Daniel , Ferrara Pascual
Published: July 2002

IL‐13 and IL‐4 are growth factors for the human erythroleukemia cell line TF‐1. In these cells both cytokines share overlapping binding sites, but the number of sites for IL‐13 is half of that for IL‐4. Two monoclonal antibodies against the extracellular domain of the IL‐4Rα chain completely abolish the binding of IL‐13, although IL‐13 does not bind to this chain. Following receptor triggering, IL‐13 and IL‐4 induce the phosphorylation of a 170 kDa protein, probably the IL‐4‐induced phosphotyrosine substrate. In addition the phosphorylation of the 170 kDa protein results in its tight association with phosphatidylinositol‐3‐kinase.
Oxidized LDL induce hsp70 expression in human smooth muscle cells
Authors: Zhu W.M. , Roma P. , Pirillo A. , Pellegatta F. , Catapano A.L.
Published: July 2002

Heat shock protein 70 (hsp70) has been detected in atherosclerotic lesions, in which endothelial cells and smooth muscle cells are involved. In a previous report we showed that Ox‐LDL, a causal factor in atherosclerosis, could induce hsp70 expression in cultured human endothelial cells [Zhu et al. B.B.R.C 1994, 200: 389]. Here, with immunofluorescence and immunoblotting techniques, we show that Ox‐LDL are capable of inducing hsp70 expression also in human smooth muscle cells, and that this induction is dependent on cell density and on the concentration of Ox‐LDL. The induced expression of hsp70 was higher in human umbilical vein smooth muscle cells than in a human smooth muscle cell line. Conversely, Ox‐LDL was cytotoxic to both types of cells, more so to the human smooth muscle cell line. These observations indicate that Ox‐LDL may be a stress responsible for hsp70 expression in atherosclerotic plaques and the presence of hsp70 in plaques may be a useful marker for continuous oxidative damage in the arterial wall.
Participation of rhop21 in serum‐dependent invasion by rat ascites hepatoma cells
Authors: Yoshioka Kiyoko , Fumio Imamura , Kiyoko Shinkai , Jun Miyoshi , Haruki Ogawa , Mutsuko Mukai , Rika Komagome , Hitoshi Akedo
Published: July 2002

Rat ascites hepatoma cells (MM1 cells) penetrate through a cultured mesothelial cell monolayer (MCL) in the presence of fetal calf serum (FCS), but scarcely do so in its absence. Inactivation of rhop21 of MM1 cells by ADP‐ribosyltransferase C3 resulted in the suppression of this serum effect on the penetration, suggesting that the serum effect was mediated by rhop21. To ascertain this assumption MM1 cells were transfected with an activated (Val14) human rhoA cDNA (Neo/RhoA 1–7). The transfectants penetrated MCL extensively even in the absence of FCS and became largely independent of serum for the penetration. These results suggest that serum‐induced invasion by MM1 cells is mainly mediated by rhop21.
Transfection of cells with basic fibroblast growth factor and Kaposi fibroblast growth factor genes induce resistance to and receptor modulation of tumor necrosis factor
Authors: Aggarwal Bharat B. , Pocsik Eva , Totpal Klara
Published: July 2002

Tumor necrosis factor (TNF) has been shown to inhibit the growth of some cell types and stimulate the proliferation of others by a mechanism that is not understood. In the present study, we investigated the effect of transfection of NIH‐3T3 cells with either the basic fibroblast growth factor gene (bFGF) or the kaposi FGF gene (K‐fgf) on the growth‐modulatory effects of TNF. Our results show that transformation of cells with either gene leads to resistance to the growth‐inhibitory effects of TNF. The K‐fgf gene was found to be a more potent inducer of cellular resistance than the bFGF gene. The cellular resistance correlated with the inhibition of TNF‐induced activation of phospholipase A2 and downmodulation of TNF receptors. Overall, our results indicate that both K‐fgf and bFGF play an important role in suppression of antiproliferative effects of TNF.
TNFα receptor expression in rat cardiac myocytes: TNFα inhibition of L‐type Ca2+ current and Ca2+ transients
Authors: Krown Kevin A. , Yasui Kenji , Brooker Madelyne J. , Dubin Adrienne E. , Nguyen Cuong , Harris Greg L. , McDonough Patrick M. , Glembotski Christopher C. , Palade Philip T. , Sabbadini Roger A.
Published: July 2002

Tumor necrosis factor‐α (TNFα) is a potentially powerful anti‐neoplastic agent; however, its therapeutic usefulness is limited by its cardiotoxic and negative inotropic effects. Accordingly, studies were undertaken to gain a better understanding of the mechanisms of TNFα‐mediated cardiodepression. Single cell RT‐PCR, [125I]TNFα ligand binding and Western immunoblotting experiments demonstrated that rat cardiac cells predominantly express type I TNFα receptors (TNFRI or p60). TNFα inhibited cardiac L‐type Ca2+ channel current (I
Ca) and contractile Ca2+ transients. Thus, it is possible that the negative inotropic effects of TNFα are the result of TNFRI‐mediated blockade of cardiac excitation‐contraction coupling.
Efficacy of ipriflavone and 1α vitamin D therapy for the cessation of vertebral bone loss
Authors: Ushiroyama T. , Okamura S. , Ikeda A. , Ueki M.
Published: July 2002

Objective: This study investigated whether a combined regimen of ipriflavone and 1α vitamin D is effective in stopping postmenopausal bone loss. Methods: Ninety‐eight postmenopausal women were recruited and randomly assigned to one of four groups: group 1, ipriflavone alone; group 2, 1α vitamin D alone; group 3, combined regimen of ipriflavone and 1α vitamin D; group 4, no treatment. Vertebral bone mineral density, measured by dual energy X‐ray absorptiometry, serum alkaline phosphatase, calcitonin, parathyroid hormone, osteocalcin, urinary calcium and hydroxyproline were measured before and at the 6th, 12th and 18th month of the study. All comparisons were made using Student's t‐test of means. Result: There was a significant reduction in vertebral bone loss in the patients receiving the combined therapy (mean loss after 18 months 0.33% in the combination group vs. 2.37%, 1.15% and 3.70% in the ipriflavone alone, 1α vitamin D alone, and control groups, respectively; P < 0.001). Conclusion: These findings suggest that the combined regimen could prevent postmenopausal bone loss.
Great grand multiparity — beyond the 10th delivery
Authors: Kaplan B. , Harel L. , Neri A. , Rabinerson D. , Goldman G.A. , Chayen B.
Published: July 2002

Objective: To investigate the perinatal outcome and obstetric complications of women delivering for the 10th time or more. Methods: Four hundred twenty women of great grand multiparity were analyzed in a modern health care setting and compared with our general population of obstetric patients, with regard to past history, maternal age, gestational age, mode of delivery, fetal outcome and intercurrent medical/obstetric problems. Results: The study group showed significantly lower rates of low birth weight infants and instrumental delivery. No significant difference was seen in the incidence of cesarean section, pathologic fetal presentation, maternal hypertension, gestational diabetes, hemorrhage, or perinatal morbidity or mortality. There was a slightly higher incidence of twin births compared with the general population. Conclusion: It is probable that women capable of reaching their 10th delivery are basically healthy. If offered adequate perinatal care, they are not a high‐risk group during subsequent deliveries.
A membrane‐permeant ester of phosphatidylinositol 3,4,5‐trisphosphate (PIP3) is an activator of human neutrophil migration
Authors: Niggli Verena
Published: July 2002

Activity of phosphatidylinositol (PI) 3‐kinase is required for optimal migration of human neutrophils [Niggli and Keller (1999) Eur. J. Pharmacol. 335, 43–52]. We have tested the direct effect of a product of PI 3‐kinase, phosphatidylinositol 3,4,5‐trisphosphate (PIP3), on neutrophil migration. To this end, a membrane‐permeant ester of PIP3, dilauroyl phosphatidylinositol 3,4,5‐trisphosphate‐heptakis‐(acetooxymethyl)ester (PIP3/AM) was used. PIP3/AM (ED50: 10–17 μM) induced development of polarity and accumulation of F‐actin in the leading lamellae in up to 70% of the cells. These cells exhibited stimulated random migration, comparable to that observed in uniform concentrations of chemotactic peptide. Evidence is provided for a role of Rho‐kinase and for activation of PI 3‐kinase in a positive feedback loop in PIP3/AM‐induced motility.
Temperature‐sensitive Arabidopsis mutant defective in 1‐deoxy‐d‐xylulose 5‐phosphate synthase within the plastid non‐mevalonate pathway of isoprenoid biosynthesis
Authors: Araki Naohiro , Kusumi Kensuke , Masamoto Kazumori , Niwa Yasuo , Iba Koh
Published: July 2002

The temperature‐sensitive mutant of Arabidopsis, chs5, developed chlorotic leaves at restrictive temperatures (15°C), but almost normal green leaves at permissive temperatures (22°C). At the restrictive temperature, the chs5 mutation blocked the accumulation of chlorophylls and carotenoids. A temperature‐shift analysis revealed that the manifestation of the chlorotic phenotype occurred in young leaf tissues, but did not in mature leaf tissues. Genetic and sequence analysis demonstrated that the chs5 mutation was caused by a single‐base change in the coding region of a recently identified CLA1 gene. The CLA1 gene exhibited a high sequence similarity to the genes encoding 1‐deoxy‐d‐xylulose 5‐phosphate synthase (DXS) localized to the non‐mevalonate pathway, which was recently discovered in bacteria and higher plants. In addition, the application of 1‐deoxy‐d‐xylulose, the free sugar of 1‐deoxy‐d‐xylulose 5‐phosphate, rescues the defect in the chs5 mutant. These results indicated that the chlorotic phenotype of the chs5 mutant was caused by a defect in DXS activity and that DXS functions preferentially at an early stage of leaf cell development. A transiently expressed green fluorescent protein fused with the CLA1 transit peptide was localized within the chloroplasts in the green cultured cells of tobacco, which suggests that the putative localization of the non‐mevalonate pathway is in plastids.
Seasonal distribution of the long‐nosed bat (Leptonycteris curasoae) in North America: does a generalized migration pattern really exist?
Authors: Rojas‐Martínez Alberto , Valiente‐Banuet Alfonso , Del Coro Arizmendi Maríía , Alcántara‐Eguren Ariel , Arita Hééctor T.
Published: July 2002

AimThis paper examines the migration of the tropical nectarivorous batLeptonycteris curasoaeconsidered as a latitudinal migrant that breeds in south‐west United States and northern Mexico in spring and migrates southward during fall. We tested the hypothesis that the latitudinal migration occurs only locally given by the local availability of bat resources, leading to migratory movements in zones with seasonal scarcity of resources and to resident bat populations where resources are available throughout the year.

LocalizationWe analysed the presence ofL. curasoaealong its distribution range in North America (between 14°N and 33°N). Study cases were also conducted in three Mexican localities: the Tehuacán Valley (17°48′–18°58′N and 96°48′–97°43′W), Sonoran Desert (28°41′N and 110°15′W), and the coast of Jalisco (19°32′N and 105°07′W).

MethodsGeographic evidence for latitudinal migration ofL. curasoaewas analysed using 94‐year capture records housed in twenty‐two collections of North America. Records were analysed using a Geographical Information System (GIS), in which floral resources and capture records were integrated. Monthly captures in the Tehuacán Valley were conducted during three years and bats abundance and reproductive status were correlated with the phenology of bat resources. Bat captures were also conducted during two consecutive years in an extratropical desert during winter and spring, and during one spring in the coast of Jalisco.

ResultsThe latitudinal migration ofL. curasoaein North America only occurs at latitudes near 30°N, whereas bats may be residents at latitudes lower than 21°N. Captures were associated always to the availability of floral resources in both geographical and local scales.

Main conclusionsThe existence of resident populations in the tropics with two reproductive events support the hypothesis that migration only occurs in the northern distribution limit of this nectar‐feeding bat.
Effects of temperature and moisture on disease and fruit body development of Mycosphaerella pinodes on pea (Pisum sativum)
Authors: Roger C. , Tivoli B. , Huber L.
Published: July 2002

The effects of temperature (5–30°C) and the duration of moisture on the development of ascochyta blight (Mycosphaerella pinodes) on pea seedlings, grown under controlled conditions, were investigated. The optimum temperature for monocyclic processes was 20°C. At this temperature, pycnidiospores germinated after 2 h, appressoria formed after 6 h and the germ‐tube penetrated the leaf cuticle after 8 h. Disease symptoms were evident after 1 day of incubation and the first pycnidia formed after 3 days. Longer wetting periods were required for disease development and pycnidial formation at non‐optimal temperatures. Disease severity and the number of pycnidia formed on leaves increased with temperature from 5 to 20°C, then decreased between 20 and 30°C. Polynomial equations were fitted to predict the stages of infection, incubation, latency and disease development as functions of temperature and duration of moisture. These equations allow comparisons of pathogen spread with plant development and could be incorporated into disease development models used for crop management programmes.
Use of Oseltamivir During Influenza Outbreaks in Ontario Nursing Homes, 1999–2000
Authors: Bowles Susan K. , Lee Wayne , Simor Andrew E. , Vearncombe Mary , Loeb Mark , Tamblyn Susan , Fearon Margaret , Li Yan , McGeer Allison , The Oseltamivir Compassionate Use Program Group
Published: July 2002

OBJECTIVES:

To describe the experience of Ontario long‐term care facilities that used oseltamivir during influenza outbreaks in 1999/2000.

DESIGN:

Case series.

SETTING:

Ten Ontario long‐term care facilities for older people and their residents.

PARTICIPANTS:

Older residents of long‐term care facilities.

INTERVENTION:

Oseltamivir for treatment or prophylaxis during 11 influenza outbreaks in 1999/2000.

MEASUREMENTS:

Control of outbreaks; pneumonia, hospitalization, and death complicating acute influenza.

RESULTS:

All outbreaks were due to influenza A//H3N2/Sydney/05/97. One facility elected to use oseltamivir for treatment and amantadine for prophylaxis. The remaining nine facilities (10 outbreaks) recommended oseltamivir for treatment and prophylaxis (after amantadine failure in five and as primary prophylaxis in five). Use of oseltamivir was associated with termination of the outbreak in all eight evaluable outbreaks. Overall, 178/185 (96%) case‐residents met the case definition of influenza and had complete data for evaluation. Of these, 63 (35%) were treated with antibiotics, 37 (21%) were diagnosed with pneumonia, 19 (11%) were hospitalized, and 16 (9%) died. Compared with residents receiving no therapy or who became ill while taking amantadine, residents who received oseltamivir within 48 hours of the onset of symptoms were less likely to be prescribed antibiotics, to be hospitalized, or to die (P <.05 for each outcome). These differences persisted and remained statistically significant when corrected for influenza immunization status. A total of 730 residents received oseltamivir prophylaxis for a median of 9 days (range 5–12). Of these, side effects were identified in 30 (4.1%), the most common being diarrhea (12 residents, 1.6%), cough (5, 0.7%), confusion (4, 0.5%) and nausea (4, 0.5%).

CONCLUSIONS:

Oseltamivir is safe and appears to be effective when used as treatment or prophylaxis to control outbreaks of influenza in older nursing home residents. J Am Geriatr Soc 50:608–616, 2002.
Direct writing of 10 nm features with the scanning tunneling microscope
Authors: Ehrichs E. E. , Yoon S. , de Lozanne A. L.
Published: July 2002

A scanning tunneling microscope (STM) has been used to write metallic lines and carbon lines with linewidths as small as 10 nm. Organometallic gases or surface organic contamination can be decomposed to deposit these lines in a single step. Computer control of the STM allows precise patterning of these lines on a silicon substrate.
Orientation-dependent phase modulation in InGaAs/GaAs multiquantum well waveguides
Authors: Das Utpal , Chen Yi , Bhattacharya Pallab K. , Berger Paul R.
Published: July 2002

The electro-optic effect and phase modulation in In0.2 Ga0.8 As/GaAs multiple quantum wells have been experimentally studied for the first time. The experiments were done with 1.06 and 1.15 μm photoexcitation which are, respectively, 25 and 115 meV below the electron–heavy hole excitonic resonance. Strong quadratic electro-optic effect was observed near the excitonic edge in addition to the linear effect. These are characterized by r63 =−1.85×10−19 m/V and (R33 −R13 )=2.9×10−19 m2 /V2 . In addition, we observe a dispersion in the value of r63 . The relative phase shifts are higher in the strained system at 1.06 μm than in lattice-matched GaAs/AlGaAs.
Metalorganic chemical vapor deposition and characterization of the In-As-Sb-Bi material system for infrared detection
Authors: Humphreys T. P. , Chiang P. K. , Bedair S. M. , Parikh N. R.
Published: July 2002

We report the first results pertaining to the growth by metalorganic chemical vapor deposition of InSb1−xBix (0.01<x<0.14) and InAs1−x−ySbyBix with 0.5<y<0.7 and 0.01<x<0.04 epitaxial films on both semi-insulating GaAs(100) and InSb(100) substrates. Electrical measurements for the undoped InSb0.99Bi0.01 epitaxial layers show a room-temperature mobility of 20 215 cm2/V s with a carrier concentration of ND−NA ∼1016 cm−3. A degradation in the surface morphology of the InSb1−xBix and InAsSbBi epitaxial films correspond to an increase in the InBi mole fraction was observed. We attribute this deterioration in surface morphology to the formation of polycrystalline phases of Bi and the growth of metallic bismuth-antimony crystallites.
Deformation potential and intervalley scattering: Hot-electron transistor analysis
Authors: Krishnamurthy Srinivasan , Sher A. , Chen A.-B.
Published: July 2002

The coupling constants for the intervalley scattering of electrons by acoustic and optical phonons are calculated based on empirical tight-binding band structures. The calculated intravalley and intervalley scattering rates based on these deformation potentials, polar optical phonon, impurity, and electron-electron interactions successfully explain the observed ratio of collector-to-emitter current as a function of injected electron energy in a GaAs hot-electron transistor.
Electroluminescence in diamond-like carbon films
Authors: Kim S. B. , Wager J. F.
Published: July 2002

White electroluminescence (EL) was observed for the first time from diamond-like carbon (DLC) films at room temperature. ac voltages in excess of 200 V were applied to a metal-insulator-semiconductor (i.e., DLC)-insulator-metal device structure to observe EL. At an applied voltage of 235 V, the brightness and efficiency were 0.5 fl and 0.002 lm/W, respectively.
Generation of interface states in nitrided oxide gate dielectrics by ionizing radiation and Fowler–Nordheim stressing
Authors: Dunn G. J.
Published: July 2002

Annealing of silicon dioxide gate dielectrics in ammonia is known to suppress interface state generation under ionizing radiation. However, under high field stress interface state generation in lightly nitrided oxides is found to be comparable to that in the unaltered oxide, while it is reduced in heavily nitrided oxides and eliminated altogether in reoxidized samples of either type.
Microstructure of Pb-modified Bi-Ca-Sr-Cu-O superconductor
Authors: Ramesh R. , Thomas G. , Green S. M. , Mei Yu , Jiang C. , Luo H. L.
Published: July 2002

The microstructure of samples with and without Pb addition has been characterized by transmission electron microscopy. An amorphous Pb-rich grain boundary phase has been found in Pb-doped samples. It is suggested that a Pb-rich liquid phase assists sintering and homogenization of the composition of the superconducting phase to attain the higher zero Tc. In both samples, Ca replacement by Bi has been found. The implications of such a replacement are briefly discussed.
Low-temperature silicon selective deposition and epitaxy on silicon using the thermal decomposition of silane under ultraclean environment
Authors: Murota Junichi , Nakamura Naoto , Kato Manabu , Mikoshiba Nobuo , Ohmi Tadahiro
Published: July 2002

An ultraclean hot-wall low-pressure chemical vapor deposition (CVD) system was developed and Si films were deposited on single-crystal Si and SiO2 using ultraclean SiH4 and H2 gases in the temperature range 600–850 °C under an ultraclean environment. As a result of ultraclean processing, an incubation period of Si deposition only on SiO2 was found, and low-temperature Si selective deposition and epitaxy on Si were achieved without addition of HCl under deposition conditions where only nonselective polycrystalline Si growth could be obtained in conventional CVD systems.
Study of the D
X center fine structure in ion-implanted Al0.27Ga0.73As processed by rapid thermal annealing
Authors: Campbell A. C. , Dodabalapur A. , Crook G. E. , Streetman B. G.
Published: July 2002

Ion implantation is used to modify the local environment of the DX center in Si-doped Al0.27Ga0.73As grown by molecular beam epitaxy (MBE), and the variations in DX center properties with subsequent rapid thermal annealing processes are examined using deep level transient spectroscopy. In the as-grown sample, two DX center peaks are found with the same activation energy of 0.46±0.01 eV, but with widely different cross sections. The main DX center peak ME3, which appears at higher temperatures due to its smaller cross section, remains stable throughout the experiments. The second DX center peak ME2 has a much larger cross section, and appears at a lower temperature. The capture properties of this subsidiary DX center peak are markedly altered in the ion-implanted samples. Samples which were subject solely to the rapid thermal annealing processes have stable DX center trap signatures, indicating that arsenic loss during annealing does not significantly influence the DX center characteristics. It is proposed that regions of incomplete ordering and defect complexing in the AlGaAs film give rise to the various subsidiary DX center peaks observed.
Low-temperature measurement of the fundamental frequency response of a semiconductor laser by active-layer photomixing
Authors: Newkirk Michael A. , Vahala Kerry J.
Published: July 2002

We use the active-layer photomixing technique to directly modulate the output of a GaAs semiconductor laser operating at temperatures as low as 4.2 K. The technique produces modulation with nearly perfect immunity to device parasitic effects, revealing the laser diode’s intrinsic modulation response. At 4.2 K the parasitic corner frequency is estimated to be 410 MHz, yet the response appears ideal out to 15 GHz. We measure the dynamical parameters governing the response function, the relaxation resonance frequency, and the damping rate, and discuss their low-temperature behavior.
Two-dimensional hole gas in Si/Si0.85Ge0.15/Si modulation-doped double heterostructures
Authors: Wang P. J. , Fang F. F. , Meyerson B. S. , Nocera J. , Parker B.
Published: July 2002

Si/Si0.85Ge0.15/Si p-type modulation-doped double heterostructures have been grown by the ultrahigh vacuum/chemical vapor deposition technique, and mobility enhancement has been observed at low temperatures. For heterostructures with Si layers doped with boron to ∼1×1019 cm−3, hole mobilities of ∼900 cm2/V s at 14 K have been obtained. No carrier freeze-out behavior has been observed at low temperatures. The existence of two-dimensional hole gas was determined by the tilted-field Shubnikov–de Haas measurement. Both Si/SiGe and SiGe/Si heterointerfaces were found to be equivalent and of excellent interfacial quality. The valence-band maximum of Si0.85Ge0.15 alloy has been estimated to be ≂0.95 meV higher than that of Si. A hole effective mass of 0.44±0.03m0, which is consistent with the interpolation of the bulk band structures for the Si0.85Ge0.15 alloy, has been obtained for the heterostructure.
Low-resistance nonspiking ohmic contact for AlGaAs/GaAs high electron mobility transistors using the Ge/Pd scheme
Authors: Wang L. C. , Lau S. S. , Hsieh E. K. , Velebir J. R.
Published: July 2002

Nonspiking (nonalloyed) Ge/Pd ohmic contact formed via solid phase reaction on an AlGaAs/GaAs high electron mobility transistor (HEMT) was investigated. The surface morphology of the Ge/Pd contact is smooth and planar with a typical contact resistivity of about 3×10−7 Ω cm2. The current-voltage characteristics of the HEMTs with the Ge/Pd contacts are similar to those with the conventional AuGe/Ni spiking (alloyed) contacts. Since only a thin substrate surface layer of 100–200 Å was reacted with the Ge/Pd contact, we can conclude that ohmic contacts can be made to the two-dimensional electron gas without deep penetration of the metallization. This observation is in agreement with the concept that transport due to tunneling is significant across heterojunctions. The Ge/Pd contact may be potentially useful in HEMT integrated circuit technology.
Image current guiding of a relativistic electron beam in a foil focusing system
Authors: Humphries S. , Ekdahl Carl , Woodall D. M.
Published: July 2002

Intense relativistic electron beams can be focused by arrays of transverse conducting foils or meshes. The meshes cancel beam-generated radial electric fields, allowing a self-pinched equilibrium. The experiments reported confirm that foil focusing systems can also steer high-current beams. We applied a dipole perturbation field to deflect a 3.8 kA, 280 keV beam in a foil array. We found that image current forces centered the beam in the transport pipe. The measured deflection was more than an order of magnitude smaller than the predicted value for single electron orbits. The results show that foil focusing may have application to recirculating accelerators for high-current electron beams.
Magnetotransport studies of charge accumulation in an AlInAs/GaInAs tunneling structure
Authors: Ben Amor S. , Martin K. P. , Rascol J. J. L. , Higgins R. J. , Potter R. C. , Lakhani A. A. , Hier H.
Published: July 2002

We report a study of the current-voltage characteristics of a double barrier, lattice matched, quantum well tunneling structure in a quantizing magnetic field (B∥J). Experiments were conducted at fields up to 23 T at 1.5 K. The heterostructure investigated had 400 Å spacer layers in the emitter and collector, a barrier width of 72 Å, and a 43-Å-wide quantum well. This structure showed one negative differential resistance region with a peak-to-valley ratio of 23 at 4.2 K. We observed magnetoquantum oscillations, periodic in 1/B, associated with tunneling from a quantized state in the emitter. The overall magnetoconductance dramatically changed with applied bias. We associated these variations with a field-induced increase of the impedance of the undoped spacer layers. The frequency of these oscillations increased linearly with applied bias. A discontinuity in this dependence is observed around the peak bias voltage which is the direct result of the dynamical storage and release of charge in the well.
Amorphous silicon solar cells with ethylene-based p+ layers
Authors: Wiedeman S. , Smoot M. , Fieselmann B.
Published: July 2002

The use of ethylene (C2H4) rather than methane (CH4) as the source of carbon in the hydrogenated amorphous silicon carbide (a-SiC:H) p+ layer of hydrogenated amorphous silicon (a-Si:H) based solar cells deposited in a glow discharge has been explored. Device results are presented to demonstrate the utility of ethylene-based a-SiC:H for use in the p+ layer. Device results and material measurements reveal that the use of ethylene under the proper conditions can yield p+ a-SiC:H which has optical and transport properties which are at least as suitable as methane-based material.
Interaction of Be and O in GaAs
Authors: Von Neida A. E. , Pearton S. J. , Hobson W. S. , Abernathy C. R.
Published: July 2002

Oxygen implanted at a concentration above that of the acceptors in p-type GaAs is shown to create thermally stable, high-resistivity material only in the case of Be doping in the GaAs. The effect is not seen for Mg, Zn, or Cd doping. Similarly, there is no apparent interaction of O with n-type dopants (S or Si) in our measurements. The Be-O complex in p-type GaAs is a deep donor, creating material whose sheet resistivity shows an apparent thermal activation energy of 0.59 eV for a structure involving a thin layer (5000 Å) of oxygen compensated, Be-doped GaAs on a semi-insulating substrate.
Oxidation of silicon with a 5 eV O− beam
Authors: Hecht M. H. , Orient O. J. , Chutjian A. , Vasquez R. P.
Published: July 2002

A silicon wafer has been oxidized at room temperature in vacuum using a pure, ground-state beam of O− ions. The beam was of sufficiently low energy that no displacement damage or implantation was energetically possible. The resulting SiO2 films were analyzed with x-ray photoelectron spectroscopy. A logarithmic dependence of oxide thickness on dose was observed, with an extrapolated oxidation efficiency of unity for the clean silicon surface. A distinct initial oxidation phase was observed, with an anomalously high level of silicon suboxides. In addition, the valence-band offset between the silicon and the oxide was unusually small, suggesting a large interfacial dipole.
Interface-trap transformation at radiation-damaged (111)Si/SiO2 interface
Authors: Wang Yu , Ma T. P. , Barker R. C.
Published: July 2002

This letter presents the results of our recent study on the post-irradiation behavior of the interface trap distribution in metal-SiO2-Si capacitors made on Si substrates of (111) orientation. It will be shown that the interface trap distribution in these (111) samples measured immediately after x-ray irradiation is qualitatively similar to what was observed in the (100) counterpart: a prominent peak appears in the upper half of the Si band gap (Ev+0.75 eV). Subsequent time-dependent evolution behavior of this peak, however, is distinctly different for samples with the two different orientations. While in (100) samples a second peak in the lower half of the band gap would develop over time, resulting in a double-peak interface trap distribution [see, for example, E. F. da Silva, Y. Nishioka, and T.-P. Ma, Appl. Phys. Lett. 51, 270 (1987)], the most salient feature observed in (111) samples is the gradual shift of the peak position with time toward the lower half of the Si band gap, and eventually a single peak will reside below midgap. The movement of this peak has been found to be thermally accelerated, with an apparent activation energy of about 0.4±0.1 eV. It has also been found that the gate-induced compressive strain at the Si/SiO2 interface plays an important role in the peak movement. In addition, the presence of a gate bias and its polarity also significantly affect the post-irradiation behavior of the interface trap distribution. The results may be explained in terms of the atomic relaxation of the bonding defect at the (111)Si/SiO2 interface.
Measurements of the magnetic penetration depth in YBa2Cu3O7−δ thin films by the microstrip resonator technique
Authors: Anlage Steven M. , Sze Hsuan , Snortland Howard J. , Tahara Shuichi , Langley Brian , Eom Chang-Beom , Beasley M. R. , Taber Robert
Published: July 2002

We have utilized the superconducting microstrip resonator technique to measure the magnetic penetration depth in high Tc oxide thin films in the 1–25 GHz regime. This technique is particularly well suited for thin films, where the absolute value of the penetration depth can be accurately determined. Results for high Tc superconducting thin films show that the value of the penetration depth is sensitive to the preparation conditions of the film, and the temperature dependence is that expected of conventional superconductors.
InGaAs/GaAs strained quantum wells with a 1.3 μm band edge at room temperature
Authors: Melman P. , Elman B. , Jagannath C. , Koteles Emil S. , Silletti A. , Dugger D.
Published: July 2002

The fabrication of long-wavelength optoelectronic devices on GaAs substrates is an attractive method for monolithic integration of optical and electronic devices on a single chip for applications in telecommunications. In this letter we describe our studies of one such scheme using a novel structure for spatially separating a portion of the biaxial compressive stress due to lattice mismatch of the layers from the well layer, and demonstrate its feasibility. High quality pseudomorphic strained InGaAs quantum wells were grown on GaAs substrates by molecular beam epitaxy with a band edge between 1.3 and 1.4 μm at room temperature. Low-temperature photoluminescence spectroscopy as well as polarization-dependent absorption measurements in a waveguide geometry was used to characterize the structures.
Performance of dc SQUIDs with resistively shunted inductance
Authors: Foglietti V. , Gallagher W. J. , Ketchen M. B. , Kleinsasser A. W. , Koch R. H. , Sandstrom R. L.
Published: July 2002

We have fabricated and characterized the noise performance of well-coupled Nb-Pb alloy edge junction dc superconducting quantum interference devices (SQUIDs) with a resistively shunted inductance. The extra damping resistor removes the resonances in the current-voltage characteristics resulting in a very low value of the extrinsic energy sensitivity in flux-locked-loop operation. Numerical simulations, with the junction capacitance included, indicate that the damping resistance does not degrade noise performance until it is significantly less than the junction-shunting resistance. We also tested different SQUID designs and demonstrated that a large SQUID inductance, proposed earlier to be desirable when resistively shunted, can seriously affect the low-frequency flux noise.
Surface stress effects on the critical film thickness for epitaxy
Authors: Cammarata R. C. , Sieradzki K.
Published: July 2002

An analysis of the critical thickness dependence on misfit for epitaxy is presented including effects due to surface stresses. It is shown that these surface stress effects, which have not been included in previous theories of epitaxy, can have a major influence on the critical thickness, especially for relatively large misfits. A simple model incorporating effects due to compressive surface stresses is given which, compared to previous theories, predicts significantly larger (smaller) critical thicknesses when the stress-free lattice parameter of the film is greater (less) than the lattice parameter of the substrate.
Direct observation of GaAs atomic layer epitaxy by reflection high-energy electron diffraction
Authors: Chiu T. H.
Published: July 2002

Atomic layer epitaxy (ALE) of GaAs using trimethylgallium and triethylgallium by chemical beam epitaxy is reported. Reflection high-energy electron diffraction is employed to monitor the formation of each individual monolayer directly. A new (4×8) surface reconstruction, characteristic of an ordered chemisorbed molecular Ga monolayer, is observed for the first time. Each Ga atom in this transitional layer has at least one alkyl radical cleaved away. The stability of this transitional stage varies depending on the alkyl group involved and the temperature. Dynamical evolution of this adsorbed layer is described. The chemical properties of this overlayer dictate the GaAs ALE growth conditions.
Electron microdiffraction of faulted regions in Co-Cr and Co-Ni-Cr thin films
Authors: Hono K. , Demczyk B. G. , Laughlin D. E.
Published: July 2002

The planar defects which are commonly observed in deposited Co-Cr and Co-Ni-Cr magnetic thin films have been characterized by electron microdiffraction and trace analysis. It was unambiguously shown that these planar defects are (0001) stacking faults, which are thought to be formed to reduce the growth stress of the film during deposition.
Thermal dependence of voiding in narrow aluminum microelectronic interconnects
Authors: Sullivan Timothy D.
Published: July 2002

A model for the thermal dependence of atomic flux in passivated Al/AlSi very large scale integrated interconnects is presented. The model is derived from stress-induced alterations in the equilibrium vacancy concentration in the metal, and has an exponential form which can be interpreted as a temperature-dependent activation energy. The flux model together with the thermal hysteresis of stress reported for thin films can be used to describe a wide range of voiding behavior.
Organometallic chemical vapor deposition of superconducting, high T
c Pb-doped Bi-Sr-Ca-Cu-O thin films
Authors: Zhang J. M. , Marcy H. O. , Tonge L. M. , Wessels B. W. , Marks T. J. , Kannewurf C. R.
Published: July 2002

Highly oriented films of the high Tc Bi-Pb-Sr-Ca-Cu-O (BPSCCO)superconductor have been prepared by two organometallic chemical vapor deposition (OMCVD) approaches. In the first approach, Pb is introduced by alternate deposition of BSCCO and PbOx films using the volatile metalorganic precursors Cu(acetylacetonate)2, Sr(dipivaloylmethanate)2, Ca(dipivaloylmethanate)2, triphenyl bismuth, and tetraphenyl lead. In the second approach, Pb is incorporated into an OMCVD-derived BSCCO film by vapor diffusion using PbO as the source. X-ray diffractometry and scanning electron microscopy reveal that Pb doping significantly improves the crystalline orientation and the film morphology. Films deposited by both methods on [100] single-crystal MgO consist predominantly of the Bi2(Sr,Ca)3Cu2Ox phase and have a high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four-probe resistivity measurements indicate the onset of film superconductivity at ∼110 K and zero resistance by 80 K.
Characterization of strained InGaAs single quantum well structures by ion beam methods
Authors: Yu Kin Man , Chan K. T.
Published: July 2002

We have investigated strained InGaAs single quantum well structures using MeV ion beam methods. The structural properties of these structures, including composition and well size, have been studied. It has been found that the composition obtained by Rutherford backscattering spectrometry and particle-induced x-ray emission techniques agrees very well with that obtained by the ion channeling method.
Femtosecond measurements of the nonresonant nonlinear index in AlGaAs
Authors: LaGasse M. J. , Anderson K. K. , Wang C. A. , Haus H. A. , Fujimoto J. G.
Published: July 2002

Time-division interferometry with 430 fs tunable laser pulses is used for direct femtosecond measurements of the wavelength dependence of the nonresonant nonlinear index of refraction, n2, in AlGaAs waveguides at room temperature. Below band-gap n2 values of ∼10−12 cm2/W are observed with resonant enhancement as the laser wavelength is tuned toward the band edge.
‘‘Mushroom’’ double-channel double-heterostructure lead chalcogenide lasers made by chemical etching
Authors: Schlereth K.-H. , Böttner H. , Tacke M.
Published: July 2002

Double-channel double-heterostructure (DCDH) lead chalcogenide lasers were made using a chemical etchant. The etching rate depends strongly on the europium content of the ternary compound PbxEu1−xSe. This technique allows the development of selective etching processes for advanced laser design. The DCDH lasers show low-threshold current densities of 60 A/cm2 at 20 K and suppression of lateral modes.