bluuebunny/crossref_metadata_2025 huggingface dataset:
The anticonvulsant remacemide and its metabolite AR‐R12495AA attenuate spinal synaptic transmission and carrageenan‐induced inflammation in the young rat
Authors: Asghar A.U.R. , Hasan S. S. , King A. E.
Published: July 2002

The effects of the anticonvulsants remacemide [(±)‐2‐amino‐N‐(1‐methyl‐1,2‐diphenylethyl)‐acetamide hydrochloride] and its des ‐glycinated metabolite AR‐R12495AA [(±)‐1‐methyl‐1,2‐diphenylethylamine‐ monohydrochloride] on primary afferent‐induced synaptic transmission and frequency‐dependent summation of synaptic potentials were assessed in the young rat spinal cord in vitro. Behavioural studies in the rat determined the effects of these anticonvulsant compounds in the carrageenan model of inflammation. Recordings of the extracellular dorsal root‐evoked ventral root potential (DR‐VRP) revealed a significant reduction of the duration and t1/2 decay of the long latency, slow DR‐VRP by remacemide (50 and 100 μM) and AR‐R12495AA (25, 50 and 100 mM). The short‐latency, fast monosynaptic DR‐VRP peak was reduced by only the highest concentration of AR‐R12495AA (100 μM). In intracellular dorsal root‐evoked excitatory postsynaptic potentials (DR‐EPSPs) of single ventral horn neurons, AR‐R12495AA (100 μM) attenuated the time course of the long‐latency (slow) EPSP. Frequency‐dependent (0.5–2.0 Hz) summation of dorsal root‐evoked synaptic events (recorded extracellularly as the cumulative ventral root depolarization (CVRD), and intracellularly as wind‐up) was attenuated by remacemide (100 μM) and AR‐R12495AA (50 and 100 μM). Pre‐treatment with intra‐peritoneal injection of 75 mg/kg of remacemide or AR‐R12495AA caused a significant reduction of carrageenan‐induced mechanical hyperalgesia and oedema. These electrophysiological and behavioural data provide evidence that remacemide and AR‐R12495AA may also possess analgesic and anti‐inflammatory activity. Copyright 2000 European Federation of Chapters of the International Association for the Study of Pain
Synthesis of Oligo(diazaphenyls). Tailor-Made Fluorescent Heteroaromatics and Pathways to Nanostructures
Authors: Gompper Rudolf , Mair Hans-Jürgen , Polborn Kurt
Published: July 2002

Oligoaza derivatives of biphenyl, terphenyl, quaterphenyl, quinquephenyl, sexiphenyl, septiphenyl, octiphenyl, noviphenyl, deciphenyl and dodeciphenyl and
poly(pyrimidinylenephenylene) can be synthesized from readily accessible vinamidinium salts and amidines or N,N,N'-tris(trimethylsilyl)amidines. The fluorescence
of these systems can be tuned over a wide spectral range by varying number and positions of N atoms. Oligo(diazaphenyls) are thermally and photochemically stable,
are easier to reduce than oligophenyls, can be dissolved at any rate in strong acids and show strong blue fluorescence in solution as well as in the solid state.
Trichothecenes Production by the Hypocrealean Epibiont of Baccharis coridifolia
Authors: Rosso L. , Maier M. S. , Bertoni M. D.
Published: July 2002

Abstract: The Hypocrealean epibiont of Baccharis coridifolia has been shown to synthesize de novo a series of macrocyclic trichothecene antibiotics, such as roridin A, roridin E, verrucarin A and verrucarin J. The structures of the compounds were determined by spectroscopic methods (1H‐ and 13C‐NMR and FABMS).
Flowering and Pollination of Philodendron melinonii (Araceae) in French Guiana
Authors: Gibernau M. , Barabé D. , Labat D.
Published: July 2002

Abstract: The pollination ecology of Philodendron melinonii was studied at two locations in French Guiana. Inflorescences of P. melinonii were regularly visited by Cyclocephala colasi, a scarab beetle also found in inflorescences of P. solimoesense in the same area. The flowering cycle lasted two days and the inflorescence exhibited features typical for beetle pollination (e.g., floral chamber, food rewards, flower heating). The flowering process is well synchronized with the night activity of Cyclocephala visitors. The spadix temperature was measured during the entire flowering cycle in the field in French Guiana and in greenhouse conditions at the Montreal Botanical Garden. Both measurements gave a similar temperature pattern with a two hour delay at the Botanical Garden. The spadix warmed up twice during the flowering period and its temperature was not significantly different from that of ambient air between the two peaks. These two temperature peaks are also well synchronized with the arrival and departure of the beetles on two consecutive nights.
A Study on Polymorphism in Aster tripolium L. (Sea Aster)
Authors: Huiskes A. H. L. , Koutstaal B. P. , Wielemaker‐Van den Dool A. , Markusse M. M.
Published: July 2002

Abstract: Genotypic and environmental variation in Aster tripolium L. was studied in common garden experiments and in transplantation experiments in different saltmarsh sites along the estuarine gradient of the Westerschelde and along the elevation gradient of individual saltmarshes. Analysis of the variation in a number of morphologic characters of the inflorescences indicated that this variation is both environmentally as well as genetically controlled. Morphologic differences between an Aster tripolium population of a brackish marsh and a number of populations of a saline marsh were unchanged whether the plants were growing in their original habitat or in a transplant habitat. The population from the brackish marsh had smaller inflorescences with ray florets and a predominantly biennial life cycle, in contrast with the populations of the saline marsh, which had larger inflorescences usually without or with a few ray florets and showed a tendency to a perennial life cycle. We concluded that the variation between the populations of the saline and the brackish marsh is mainly genetically controlled, while the variation within the saline marsh is mainly environmentally controlled.
Phosphate Induces Rapid H2O2 Generation in Soybean Suspension Cells
Authors: Shigaki T. , Bhattacharyya M. K.
Published: July 2002

Abstract: Involvement of reactive oxygen species has been implicated in plant defence against pathogens. We report here a novel pathway of H2O2 generation induced by the addition of phosphate in soybean (Glycine max L.) cell suspension cultures. This H2O2 generation was initiated shortly after the addition of phosphate, and lasted only approximately one hour, as opposed to several hours observed during an attack by an avirulent strain of the bacterial pathogen Pseudomonas syringae pv. glycinea (Psg). In addition, when cell cultures were treated with both phosphate and the avirulent pathogen, two distinct oxidative burst events were observed. In contrast to DPI‐sensitive Psg‐induced H2O2 generation, phosphate‐induced H2O2 generation was insensitive to this NADPH oxidase inhibitor. This suggests that an NADPH oxidase‐independent pathway may be involved in the phosphate‐induced H2O2 accumulation, which could be involved in sensing of phosphate availability in the environment.
Mycorrhiza of Brazil Pine (Araucaria angustifolia [Bert. O. Ktze.])
Authors: Breuninger Magdalena , Einig W. , Magel E. , Cardoso E. , Hampp R.
Published: July 2002

Abstract: Tropical and subtropical forests once covered large areas of Central and South America. An important member of forests of the southern hemisphere is the genus Araucaria. Because of clear cutting only small remnants of Araucaria angustifolia forests still exist in Southern Brazil. Attempts at reforestation have had only limited success because of lack of knowledge about the environmental requirements of this species. This is especially true with respect to the root/fungus symbiosis (mycorrhiza) which is necessary for enhanced water and nutrient uptake and present in more than 90 % of land plants. Analysis of the root systems of Araucaria trees from forest and grassland (campo) sites revealed mycorrhizal structures (appressoria, penetration and coiled hyphae, vesicles, arbuscules, spores) which are characteristic for the arbuscular mycorrhiza (AM) type. The spores of AM fungi at both sites ‐ forest and campo ‐ were identified. The biodiversity at the forest site was much higher, with 13 species, whereas only 6 different species could be identified at the campo site. Glomus and Acaulospora were the only genera present at the campo. The forest, however, also contained spores of Entrophospora and Scutellospora. In addition to the greater biodiversity, the spore number in soil as well as the percent mycorrhizal colonization in roots were significantly higher at the forest site than at the campo site. Because of the low frequency of hyphal coils and the dominating intercellular growth of hyphae, these mycorrhizas can be classified as an Arum‐type, which is the first report of this kind in gymnosperms.
Phylogenetic Relationships between Asplenium bourgaei (Boiss.) Milde and A. jahandiezii (Litard.) Rouy Inferred from Morphological Characters and rbcL Sequences
Authors: Schulze G. , Treutlein J. , Wink M.
Published: July 2002

Abstract: Micromorphological analysis reveals that A. jahandiezii, which occurs as a local endemic taxon in the Grand Canyon du Verdon in southern France, shows substantial differences to A. bourgaei, from the eastern Mediterranean region, in the surface structure of perispores, sporangial indehiscence and the size of stomatal subsidiary cells. Nucleotide sequences and genetic distances (0.9 % nucleotide substitutions) of the rbcL gene support the view that both taxa are related but distinct sibling species. Both species form a monophyletic group together with Asplenium fontanum and A. majoricum.
Excess stress and the stability of strained heterostructures
Authors: Tsao J. Y. , Dodson B. W.
Published: July 2002

We derive stability criteria for arbitrary strained heterostructures. The criteria are based on evaluating the excess stress as a continuous function of position within a structure for the two well-known Matthews–Blakeslee [J. W. Matthews and A. E. Blakeslee, J. Cryst. Growth 27, 118 (1974)] dislocation mechanisms for strain relief by plastic flow. If the excess stress for either mechanism exceeds zero anywhere within the structure, then the structure is unstable or metastable to strain relief by that mechanism.
High-efficiency, continuous-wave, epitaxial surface-emitting laser with pseudomorphic InGaAs quantum wells
Authors: Gourley P. L. , Lyo S. K. , Dawson L. R.
Published: July 2002

We report the first continuous-wave (cw) photopumped operation of surface-emitting lasers comprising pseudomorphic InGaAs quantum wells. The lasers were grown by molecular beam epitaxy and incorporate epitaxial quarter-wave AlAs/GaAs mirrors surrounding an active region. In the active region, 50 Å InGaAs quantum wells are distributed with half-wave periodicity to center on cavity standing wave maxima. Lasing is observed from 78 to 250 K in the spectral range 920–950 nm, where the GaAs substrate is transparent. Thresholds were as low as 1.5×104 W/cm2, and overall (differential) output power efficiency was as high as 35% (85%) with up to 60 mW in a low divergence beam. Both periodic gain and biaxial compressive layer strain contribute to the reduced lasing threshold. The laser gain length is only 550 Å (11 quantum wells). The possibility of surface-emitting lasing in single quantum wells is discussed.
Characteristics of rare-earth element erbium implanted in silicon
Authors: Tang Y. S. , Heasman K. C. , Gillin W. P. , Sealy B. J.
Published: July 2002

Rare-earth element erbium implanted into silicon was studied by photoluminescence and Rutherford backscattering analysis. Two sets of luminescent bands related to the weakly crystal field split spin-orbit levels 4I13/2→4I15/2 of Er 3+ (4f 11) at different lattice sites having different symmetries were observed.
Indium adatom migration during molecular beam epitaxial growth of strained InGaAs/GaAs single quantum wells
Authors: Arent D. J. , Nilsson S. , Galeuchet Y. D. , Meier H. P. , Walter W.
Published: July 2002

Indium composition variations in strained InGaAs/GaAs quantum wells grown on nonplanar substrates by molecular beam epitaxy have been analyzed by spatially and spectrally resolved low-temperature cathodoluminescence. For our growth conditions, the In adatom migration length on (100) facets has been determined to be ∼25 μm. A maximum relative increase of In incorporation of ≂6% on (100) ridges is observed and is found to be strain independent (In composition) for quantum wells nominally 35 and 70 Å thick with In composition of 0.10–0.22. Significantly asymmetric indium adatom migration is observed between adjacent (100) facets for ridges and grooves formed with (111)A and (311)A multifaceted sidewalls, indicating that multifaceting kinetically inhibits adatom migration. For structures designed for one-step growth of index-guided injection lasers with built-in nonabsorbing waveguides, we show that differences greater than 80 meV in the effective band gap of a 70 Å quantum well can be achieved between the gain region and the nonabsorbing waveguide without relaxing the strain.
Migration-enhanced epitaxy on a (111)B oriented GaAs substrate
Authors: Imamoto H. , Sato F. , Imanaka K. , Shimura M.
Published: July 2002

AlGaAs layers with a featureless specular surface morphology were grown successfully on an exactly (111)B oriented GaAs substrate by migration-enhanced epitaxy (MEE) even at growth temperatures below 500 °C. We have also observed reflection high-energy electron diffraction (RHEED) intensity oscillation of AlGaAs on a (111)B oriented substrate by MEE. The single quantum well (SQW) is prepared by MEE on a (111)B and a (100) substrate simultaneously, and the photoluminescence intensity from (111) SQW is shown to be about 50 times higher than that from (100) SQW.
Vapor deposition of high-purity GaAs epilayers using monoethylarsine
Authors: Speckman D. M. , Wendt J. P.
Published: July 2002

High-purity GaAs epitaxial layers have been successfully grown using the novel organoarsine reagent source, monoethylarsine (EtAsH2), with trimethylgallium (Me3Ga) as the gallium reagent. Films were found to be n type for all growth parameters examined (V/III=5–30, growth temperature=550–650 °C). Film quality improved as V/III ratio increased, whereas the optimum growth temperature ranged between 575 and 600 °C. The highest purity film produced using EtAsH2 and Me3Ga was grown using a V/III ratio of 30 and a growth temperature of 575 °C. This epilayer exhibited mobilities of 55 300 cm2/V s and 7200 cm2/V s at 77 and 300 K, respectively (as determined by van der Pauw–Hall measurements), and had a net carrier concentration of 6×1014 cm−3. These results closely rival those of the best arsine alternatives studied to date, and indicate that EtAsH2 is an extremely promising reagent to replace arsine for use in vapor deposition applications.
Direct demonstration of a misfit strain-generated electric field in a [111] growth axis zinc-blende heterostructure
Authors: Caridi E. A. , Chang T. Y. , Goossen K. W. , Eastman L. F.
Published: July 2002

We report the first direct demonstration of a strain-generated built-in electric field in a (111) oriented strained-layer heterostructure. We present a model which describes the accommodation of the misfit strain in a lattice-mismatched quantum well, and the resulting generation of a longitudinal electric field via the piezoelectric effect. On a (111)B GaAs substrate, we grew the quantum well in the intrinsic region of a p-i-n diode such that the strain-generated electric field in the quantum well opposes the weaker built-in electric field of the diode. Under reverse bias operation, photoconductivity measurements show a quadratic blue shift of the quantum well electroabsorption peaks, in contrast to the red shifts normally observed in the quantum-confined Stark effect. The measured blue shifts demonstrate an electric field strength of 1.7×105 V/cm, which agrees with theory to within the accuracy of the measured sample characteristics.
Ferrofluid-enhanced orientation of large anisometric colloids
Authors: Lu Min-Hua , Rosenblatt Charles
Published: July 2002

Aqueous suspensions of elongated, hollow tubules are shown to align in magnetic fields of order 10 G when mixed with a water-based ferrofluid. The tubule’s effective susceptibility anisotropy is obtained, and is found to be six orders of magnitude larger than in the absence of the ferrofluid. A geometry-based model is used to explain this effect.
24% efficient silicon solar cells
Authors: Wang A. , Zhao J. , Green M. A.
Published: July 2002

Significant improvements in silicon solar cell performance are reported using an improved high-efficiency silicon solar cell structure. This structure overcomes deficiencies in an earlier structure by locally diffusing boron into contact areas at the rear of the cells. Terrestrial energy conversion efficiencies up to 24% are reported for silicon cells for the first time. Air Mass 0 efficiencies lie in the 20–21% range, the first silicon cells to exceed 20% efficiency under space illumination.
Extremely low threshold current AlGaAs buried-heterostructure quantum well lasers grown by liquid phase epitaxy
Authors: Alferov Zh. I. , Andreyev V. M. , Mereutza A. Z. , Syrbu A. V. , Yakovlev V. P.
Published: July 2002

Data are presented on AlGaAs single quantum well buried-heterostructure lasers grown by two-step liquid phase epitaxy (LPE). The base laser structures were grown by low-temperature LPE in the temperature interval of 600–400 °C. Broad-area threshold current densities of 300 A/cm2 were measured for 1-mm-long lasers. The buried heterostructure was formed in the second LPE process including in situ selective mesa melt etching. Threshold currents of 1.3 mA in a continuous regime were obtained for uncoated lasers having 125-μm-long cavities.
Formation of carbon fibers in corona discharges
Authors: Brock J. R. , Lim P.
Published: July 2002

We examine carbon fibers grown at the ends of corona wires during negative point-to-plane corona discharges in hydrocarbon atmospheres. Under certain growth conditions, these fibers are hollow tubes with smooth walls; under other growth conditions, the fibers are also hollow tubes, but have rough surfaces. Scanning electron micrographs of these fibers are discussed and possible applications for these fibers are noted.
Controlled sublimation growth of single crystalline 4H-SiC and 6H-SiC and identification of polytypes by x-ray diffraction
Authors: Kanaya Masatoshi , Takahashi Jun , Fujiwara Yuichiro , Moritani Akihiro
Published: July 2002

Polytype-controlled crystal growth of SiC was carried out by using a sublimation method. Production yields as high as 80% and 85% for 4H and 6H single crystals were obtained, respectively. We observed in x-ray diffraction pattern of SiC that space-group-forbidden peaks appear periodically among (000l) peaks. Their intensity is strong enough to be distinguished. These peaks represent the periodicity along the c axis of each polytypic modification of SiC. X-ray diffractometry using these peaks is quite useful and easy for a clear identification of the SiC polytypes.
(311)A substrates suppression of Be transport during GaAs molecular beam epitaxy
Authors: Mochizuki Kazuhiro , Goto Shigeo , Kusano Chuushiro
Published: July 2002

The influence of substrate orientation on Be transport during GaAs molecular beam epitaxy is studied by secondary-ion mass spectrometry. Substrates are misoriented from (100) toward (111)A, and the epitaxial growth is performed at 630 °C for Be doping at (5–7)×1019 cm−3. Surface segregation and anomalous diffusion similarly depend on substrate orientation. With (311)A orientation, the Be transport is dramatically reduced from its value with conventional (100) orientation. These results are qualitatively explained by considering the effect of atomic steps on the growing surface.
Confocal resonators for measuring the surface resistance of high-temperature superconducting films
Authors: Martens J. S. , Hietala V. M. , Ginley D. S. , Zipperian T. E. , Hohenwarter G. K. G.
Published: July 2002

A quasioptical technique of measuring superconductor surface resistance using a confocal resonator has been developed. The method has advantages of nondestructive analysis, high sensitivity, easy extension to higher frequencies, convenient experimental setup, and flexibility in sample size. Tl-Ca-Ba-Cu-O high-temperature superconducting films have been measured with this technique and the measured surface resistances were less than 0.01 Ω at 36.135 GHz and 77 K. The measurements have been performed from 29 to 39 GHz, and all films showed roughly a quadratic dependence of surface resistance with frequency.
Resonance effects in Raman scattering from polycrystalline diamond films
Authors: Wagner J. , Wild C. , Koidl P.
Published: July 2002

We report on a Raman spectroscopic study of polycrystalline diamond films using a wide range of incident photon energies (1.16–4.82 eV). The scattering intensity of amorphous sp2-bonded carbon is found to vary considerably as a function of the incident photon energy as compared to the strength of the 1332 cm−1 Raman line from sp3-bonded diamond. There is also a frequency downshift of the apparent peak position for scattering from the sp2-bonded carbon with decreasing photon energy. Excitation in the infrared range is shown to give a high sensitivity to scattering from amorphous sp2-bonded carbon whereas ultraviolet excitation enhances the 1332 cm−1 signal from crystalline diamond considerably even in nanocrystalline films.
High-field transport transient of minority carriers in p-GaAs
Authors: Alencar A. M. , Nobre F. A. S. , Sampaio A. J. C. , Freire V. N. , Alzamir J. , da Costa P.
Published: July 2002

The time evolution of the minority electron velocity and temperature in p-GaAs towards the steady state is calculated for high-electric fields and doping concentrations of 1.5×1017 and 1.5×1018 cm−3. It is shown that the velocity overshoot is less pronounced for high doping concentration. The electron-hole interaction reduces the overshoot effect, which indicates its role in the high-field transport transient of minority carriers in p-GaAs.
Blue-green injection laser diodes in (Zn,Cd)Se/ZnSe quantum wells
Authors: Jeon H. , Ding J. , Patterson W. , Nurmikko A. V. , Xie W. , Grillo D. C. , Kobayashi M. , Gunshor R. L.
Published: July 2002

Laser diode action in the blue-green has been observed from (Zn,Cd)Se quantum wells within ZnSe/Zn(S,Se) p-n heterojunctions up to 250 K. Operation is reported for two different configurations for which the GaAs substrate serves either as the n- or p-type injecting contact. In pulsed operation, output powers exceeding 0.6 W have been measured in devices prepared on both n-type and p-type GaAs epitaxial buffer layers and substrates.
Theory of dopant diffusion assuming nondilute concentrations of dopant-defect pairs
Authors: Law M. E. , Park H. , Novell P.
Published: July 2002

Current dopant diffusion theory is based on dopant-point-defect interaction, and assumes that the number of dopant-defect pairs is much smaller than the unpaired dopant concentration. In cases where a large number of excess defects are created from implantation damage, this may no longer be a valid assumption. A new derivation of the dopant and defect equations is presented which is valid for any concentration of dopant-defect pairs.
Island formation in ultra-thin InAs/InP quantum wells grown by chemical beam epitaxy
Authors: Carlin J. F. , Houdré R. , Rudra A. , Ilegems M.
Published: July 2002

We have studied the effect of growth interruptions on 2-monolayers-thick InAs/InP strained quantum wells (QW) grown by chemical beam epitaxy. The main feature is the formation of up to 8-monolayers-thick InAs islands during As2 annealing of the QW. Their formation is characterized by a two to three dimensional transition of the reflection high-energy electron diffraction pattern and multiple-lines photoluminescence spectra. An increase of a short range roughness at the InP-InAs interface due to As2 annealing of InP is also observed.
Reactivity of C60 in pure oxygen
Authors: Chen H. S. , Kortan A. R. , Haddon R. C. , Kaplan M. L. , Chen C. H. , Mujsce A. M. , Chou H. , Fleming D. A.
Published: July 2002

In pure oxygen at moderate temperatures of 200 °C, an fcc C60 transforms into amorphous carbon-oxygen compounds and the icosahedral C60 molecular structure is destroyed. The maximum oxygen uptake of pure C60, O/C60, is 12. Isothermal TGA transformation curves are sigmoid-shaped with the kinetic exponent n∼5/2 which conforms with a two-dimensional nucleation and growth mode. The heat of formation for the carbon-oxygen compounds is 90 kcal/mol O, and the formation energy for the reaction: 60C (graphite)→C60 molecule is estimated to be ∼600 kcal/mol.
Vertically stacked multiple-quantum-wire semiconductor diode lasers
Authors: Simhony S. , Kapon E. , Colas E. , Hwang D. M. , Stoffel N. G. , Worland P.
Published: July 2002

We report the structure and lasing characteristics of GaAs/AlGaAs vertically stacked multiple-quantum-wire (QWR) semiconductor lasers grown by organometallic chemical vapor deposition on V-grooved substrates. The active region in these lasers consists of three crescent-shaped wires, placed at the center of a single-mode optical waveguide. The higher optical confinement factor, compared to single-QWR structures, leads to reduced threshold currents, as low as 0.6 mA for high-reflection coated devices at room temperature. The lower threshold carrier density results in oscillation at a lower QWR subband as compared to single-QWR laser structures.
Electrooptic modulation in polar growth axis InGaAs/GaAs multiple quantum wells
Authors: Campbell I. H. , Watkins D. E. , Smith D. L. , Subbanna S. , Kroemer H.
Published: July 2002

We present electrooptic modulation results on [100], [211]A and [211]B oriented InGaAs/GaAs multiple quantum wells. Internal electric fields are generated by a combination of strain, due to lattice mismatch, and the piezoelectric properties of III-V semiconductors in the [211] structures. These fields have opposite orientation in the [211]A and [211]B samples. They do not occur in the [100] samples. The total electric field is a superposition of the strain-generated field, the built-in field from the p-n junction and any externally applied field. We show that whereas in the conventional [100] structures the exciton energy is a quadratic function of applied field, the strain-generated fields cause a linear shift in the exciton resonance with applied field in the [211] structures. In addition, the direction of the excitonic shift is opposite in the [211]A and [211]B samples, because the sign of the strain-generated fields are opposite for these samples.
Surface and interface structures of S-passivated GaAs(111) studied by soft x-ray standing waves
Authors: Sugiyama Munehiro , Maeyama Satoshi , Oshima Masaharu , Oigawa Haruhiro , Nannichi Yasuo , Hashizume Hiroo
Published: July 2002

Surface and interface structures of S-passivated GaAs(111)A and (111)B with and without CaF2 overlayers have been investigated using the soft x-ray standing-wave technique. On the GaAs(111)A surface S atoms are located on top of the first layer Ga atoms, while on the GaAs(111)B surface S atoms replace the first layer As atoms. This is in agreement with the photoemission results. It is found that CaF2 deposition and post-annealing does not change the position of S atoms. A well-ordered S structure for S/GaAs(111)B is maintained, indicating a high stability of S—Ga bonds. This is in contrast to the low coherent fraction for the S interlayer atoms observed from the CaF2/S/GaAs(111)A system.
Formation of lateral quantum wells in vertical short-period superlattices by strain-induced lateral-layer ordering process
Authors: Cheng K. Y. , Hsieh K. C. , Baillargeon J. N.
Published: July 2002

The lateral quantum wells formed in vertical (GaAs)n/(InAs)n and (GaP)n/(InP)n short-period superlattices (SPS) grown on nominally (100) InP and GaAs substrates, respectively, have been examined. The strain induced from the deviation of superlattice periodicity from na0 is the major driving force of the lateral modulation of the composition along the [110] direction, where the integer n is the number of monolayers of each binary compound within a period of SPS structure and a0 is the lattice constant of the substrate material. When the deviation of the superlattice periodicity from na0 is larger than ∼4%, both (GaAs)n/(InAs)n and (GaP)n/(InP)n ordered vertical SPS layers were found to have a lateral periodic modulation of composition with periodicities as small as ∼200 Å. This effect is enhanced when n was increased from 1 to 2.
Domain inversion in LiNbO3 using direct electron-beam writing
Authors: Nutt Alan C. G. , Gopalan Venkatraman , Gupta Mool C.
Published: July 2002

A 3-μm periodic domain-inverted pattern on the C− face of LiNbO3 has been written using direct electron-beam writing for first-order gratings used in second harmonic generation. The domain formation mechanism has been investigated, especially the shape of the domain and need for a conductor on the C+ face during the electron-beam writing process.
Strained InGaAs/GaAs single quantum well lasers with saturable absorbers fabricated by quantum well intermixing
Authors: Yamada N. , Harris J. S.
Published: July 2002

We report successful intermixing of strained InGaAs/GaAs quantum wells utilizing SiO2 with rapid thermal annealing and application of this technique to create a strained InGaAs single quantum well (SQW) laser with a monolithic saturable absorber section. The InGaAs SQW in the gain section was blue-shifted relative to that in the absorber section to obtain strong absorption and its saturation. The output power of the device jumps abruptly to a level higher than 10 mW when the dc injection current reaches the threshold of 58 mA. Gain-switched pulses have pulsewidth of 34.4 ps and high peak power of 330 mW.
Noncritical quasiphase-matched second harmonic generation in LiB3O5 crystal at room temperature
Authors: Mao Hongwei , Fu Fongchen , Wu Baichang , Chen Chuangtian
Published: July 2002

Noncritical quasiphase-matched (NQPM) second harmonic generation (SHG) in LBO crystal at room temperature is reported. It is observed that the SHG conversion efficiency increases approximately as the square of the number of LBO sheets. The dependence of SHG conversion efficiency on incident angle and the intensity of the fundamental wave at 1064 nm were also measured. Using a 4 mm thick NQPM LBO frequency doubler, a maximum conversion efficiency of 12% is obtained at a pump intensity of 0.254 GW/cm2.
Photoreflectance study of AlAs/GaAs gradient period superlattice
Authors: Xu Hongwei , Zhou Xiaochuan , Xu Guichang , Du Quangang , Wang Enge , Wang Dingsheng , Zhang Lingjun , Chen Chenjia
Published: July 2002

An attempt has been made to explore the possibility of constructing, according to certain design requirements, a graded band-gap barrier by gradient period (AlAs)n/(GaAs)m superlattice with n and m varying in the range from 1 to 9 monolayers. Photoreflectance spectra show a series of oscillations which are attributed to Franz–Keldysh oscillation induced by quasielectric field in the gradient period superlattice regions. It indicates that a graded band gap is formed in this structure. The slope of the band gap in the graded region determined experimentally from the energy of the extrema of this oscillation is in good agreement with theoretical prediction.
Combined distributed feedback and Fabry–Perot structures with a phase-matching layer for optical bistable devices
Authors: He J. , Cada M.
Published: July 2002

A combined distributed feedback and Fabry–Perot (DFB/FP) structure with a phase-matching layer is proposed for optical bistable devices. Using a simple and versatile nonlinear transfer-matrix method, we demonstrate that the DFB/FP structure can have a much lower bistability threshold than a single DFB structure with a comparable total thickness. The combined structure can also have lower threshold and less sensitivity to absorption than a traditional nonlinear Fabry–Perot etalon.
Incorporation of high concentrations of erbium in crystal silicon
Authors: Polman A. , Custer J. S. , Snoeks E. , van den Hoven G. N.
Published: July 2002

High concentrations (≊1020/cm3) of Er have been incorporated in crystal Si by solid phase epitaxy of Er-implanted amorphous Si. This concentration is some 2 orders of magnitude higher than has previously been achieved. During thermal recrystallization of the amorphous layer, segregation and trapping of Er occurs at the moving crystal/amorphous interface. As long as the concentration of Er trapped in the crystal remains below a critical level, perfect epitaxial regrowth occurs. This concentration limit is temperature dependent, decreasing from 1.2±0.2×1020/cm3 at 600 °C to 6±2×1019/cm3 at 900 °C.
Biexciton lasing in CuCl quantum dots
Authors: Masumoto Yasuaki , Kawamura Tomohiro , Era Koh
Published: July 2002

Lasing of CuCl microcrystals embedded in a NaCl single crystal was observed for the first time. The lasing takes place at 77 K in a sample sandwiched between dielectric mirrors under pulsed ultraviolet laser excitation. The lasing transition is that from biexciton to exciton. The lasing is observed up to 108 K. The optical gain of the sample is almost the same as that of a CuCl bulk crystal in spite of the low concentration of CuCl in the NaCl matrix.
Blue-green injection lasers containing pseudomorphic Zn1−xMgxSySe1−y cladding layers and operating up to 394 K
Authors: Gaines J. M. , Drenten R. R. , Haberern K. W. , Marshall T. , Mensz P. , Petruzzello J.
Published: July 2002

We describe the performance of blue-green injection lasers containing Zn1−xMgxSySe1−y cladding layers. The devices have yielded the lowest reported threshold current densities (500 A/cm2) and the highest reported pulsed output powers (500 mW) at room temperature. Lasing has been observed at temperatures as high as 394 K. The room temperature and 85 K lasing wavelengths are 516 and 496 nm, respectively. The use of Zn1−xMgxSySe1−y, instead of ZnSzSe1−z, cladding layers provides a clear improvement in optical confinement, demonstrated by the widening of the far-field pattern in the direction perpendicular to the layers. The lasers are separate-confinement heterostructures with a ZnS0.06Se0.94 waveguiding region and a single Cd0.2Zn0.8Se strained quantum well. The entire structure is pseudomorphic with the GaAs substrate.
Epitaxial τMnAl/NiAl magnetic multilayers on AlAs/GaAs
Authors: Tanaka M. , Harbison J. P. , Sands T. , Cheeks T. L. , De Boeck J. , Hwang D. M. , Florez L. T. , Keramidas V. G.
Published: July 2002

We have successfully grown a novel type of epitaxial metallic multilayers consisting of ultrathin ferromagnetic tetragonal τMnAl and nonmagnetic (CsCl-type) NiAl on (001) GaAs substrates using molecular beam epitaxy. Reflection high energy electron diffraction and cross-sectional transmission electron microscopy (TEM) show that monocrystalline MnAl/NiAl multilayers are formed with the expected epitaxial orientations and that the c axis of the tetragonal structure of the ultrathin MnAl film is aligned perpendicular to the substrate. Composition modulation is clearly evidenced by TEM even when the thickness of each MnAl and NiAl layer is as thin as 3 monolayers. Perpendicular magnetization of the MnAl/NiAl multilayers is shown by both magnetization and magnetotransport measurements at room temperature, exhibiting remarkably square hysteresis loops, high values (Mr≳300 emu/cm3) of remanent magnetization, and relatively low values of coercive field (0.2<Hc<1 kOe).
Radiation trapping forces on microspheres with optical tweezers
Authors: Wright W. H. , Sonek G. J. , Berns M. W.
Published: July 2002

Axial trapping forces exerted on microspheres are predicted using a Gaussian beam electromagnetic field model and a ray-optics model, and compared with experimental measurements. Ray-optics predicts a maximum trapping efficiency Q= −0.14 for optically trapped polystyrene microspheres in water, compared to a measured value of −0.12 ± 0.014 for 10 μm diam microspheres. When the microspheres are composed of amorphous silica, the predicted ray-optics Q decreases to −0.11, compared to a Q = −0.034 predicted by the electromagnetic field model, and a measured value of −0.012 ± 0.001 for 1 μm diam microspheres. These results indicate that the two models have applicability in two different size regimes, and thus, are complementary.
Direct formation of quantum-sized dots from uniform coherent islands of InGaAs on GaAs surfaces
Authors: Leonard D. , Krishnamurthy M. , Reaves C. M. , Denbaars S. P. , Petroff P. M.
Published: July 2002

The 2D–3D growth mode transition during the initial stages of growth of highly strained InGaAs on GaAs is used to obtain quantum-sized dot structures. Transmission electron micrographs reveal that when the growth of In0.5Ga0.5As is interrupted exactly at the onset of this 2D–3D transition, dislocation-free islands (dots) of the InGaAs result. Size distributions indicate that these dots are ∼300 Å in diameter and remarkably uniform to within 10% of this average size. The areal dot densities can be varied between 109 and 1011 cm−2. The uniformity of the dot sizes is explained by a mechanism based on reduction in adatom attachment probabilities due to strain. We unambiguously demonstrate photoluminescence at ∼1.2 eV from these islands by comparing samples with and without dots. The luminescent intensities of the dots are greater than or equal to those of the underlying reference quantum wells.
Ultrasensitive-hot-electron microbolometer
Authors: Nahum M. , Martinis John M.
Published: July 2002

We present measurements on a novel power detector which can be used as an ultrasensitive detector of millimeter and submillimeter radiation. The absorbing element consists of a thin film resistor strip which is connected to superconducting electrodes. This device exploits the Andreev reflection of electrons and the weak electron-phonon coupling at low temperatures to produce a large temperature rise for a small input power (≊10 mK/fW). The temperature rise of the electrons is detected by a tunnel junction where part of the metal strip forms the normal electrode. We have measured a voltage responsivity of approximately 109 V/W and an amplifier-limited electrical noise equivalent power ≊3×10−18 W Hz−1/2 at an operating temperature of 100 mK. If infrared radiation were efficiently coupled to the absorbing element with an antenna or a waveguide, then the sensitivity of this detector would be at least a factor of 10 better than the best available direct detector operating at the same temperature.
Monte Carlo analysis of noise spectra in Schottky-barrier diodes
Authors: González Tomás , Pardo Daniel , Varani Luca , Reggiani Lino
Published: July 2002

We present a microscopic analysis of current fluctuations in a GaAs Schottky-barrier diode under forward-bias conditions. The calculations are performed by employing a one-dimensional Poisson solver coupled self-consistently with an ensemble Monte Carlo simulator. Results support and complement previous findings of M. Trippe, G. Bosman, and A. van der Ziel [IEEE Trans. Microwave Theory Tech. MTT-34, 1183 (1986)] based on phenomenological models. In particular, the coupling between fluctuations in carrier velocity and self-consistent field is found to be essential in determining the noise spectra as a function of applied voltages.
Formation and microwave absorption of barium and strontium ferrite prepared by sol-gel technique
Authors: Sürig C. , Hempel K. A. , Bonnenberg D.
Published: July 2002

Ba and Sr ferrites are prepared by sol-gel technique with different Fe/Ba(Sr) ratios in the starting materials. Magnetization, coercive, and anisotropy field strength are determined depending on the heat treatment of the gel and the iron/barium(strontium) ratio in the starting material. A two-step heat treatment is used to prepare single-domain powders with high magnetization. These powders prepared by sol-gel technique show single-domain behavior with specific magnetization σS=649 A cm2/g and coercive field strength HcM=402 kA/m in the case of Ba ferrite and σS=695 A cm2/g and HcM=416 kA/m for Sr the ferrite. Al-substituted ferrites with high anisotropy field strengths are prepared additionally. Ferromagnetic resonance absorption is used to determine the anisotropy field strength and to investigate the formation process of the hexaferrite phase during the heat treatment. The beginning of hexaferrite formation occurs at annealing temperatures below 700 °C.
Determining the electric field in [111] strained-layer quantum wells
Authors: Tober Richard L. , Bahder Thomas B.
Published: July 2002

The electric field in a [111] growth-axis strained-layer quantum well embedded in a p-i-n diode is determined by measuring the polarization vector in the quantum well. The polarization is determined from the critical reverse bias necessary to produce zero electric field in the quantum well. The critical reverse bias is obtained from electroreflectance spectra, which have quantum well optical features that exhibit a 180° phase change at flat band. A depletion model of the p-i-n diode with an embedded quantum well is used to relate the electric field in the quantum well to the applied bias and the polarization vector in the well.
Strong luminescence intensities in Al0.22Ga0.78As grown on misoriented (111)B GaAs
Authors: Chin Albert , Cheng T. M. , Peng S. P. , Osman Ziad , Das Utpal , Chang C. Y.
Published: July 2002

Strong enhancement in the luminescence intensity is observed in Al0.22Ga0.78As epitaxial layers grown on misoriented (111)B GaAs at 630 °C. For 3° misorientation, the luminescence intensity is almost 10 times that of (100) layers and the luminescence efficiency is an order of magnitude stronger than that of (100). (100) Al0.4Ga0.6As/GaAs quantum well laser diode structures grown under identical conditions with a low threshold current density of 150 A/cm2 are indications of excellent AlGaAs material quality. Electron mobility for 3° misoriented (111) Al0.25Ga0.75As is about 10% higher than that for side-by-side grown (100). The strong luminescence associated with a large red shift of 90 meV, the 10% mobility enhancement, and wirelike structure shown in transmission electron microscopy are indicative of the natural formation of quantized structures.
Epitaxial growth of BaMgF4 films on Si(100) and (111) substrates: An approach to ferroelectric/semiconductor heterostructures
Authors: Aizawa Kouji , Ishiwara Hiroshi , Kumagai Masao
Published: July 2002

Growth of BaMgF4 films on both Si(100) and (111) substrates has been attempted using molecular beam epitaxy. (011)- and (120)-oriented epitaxial films are successfully grown at temperatures ∼500 °C on Si(100) and (111) substrates, respectively. It has been found that the best channeling minimum yield in Rutherford backscattering spectrometry is about 0.55 for a BaMgF4(120) film on Si(111), and that the films are composed of crystallites whose orientations reflect the substrate symmetry.
Auger lifetime enhancement in InAs–Ga1−xInxSb superlattices
Authors: Youngdale E. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Grein C. H. , Young P. M. , Ehrenreich H. , Miles R. H. , Chow D. H.
Published: July 2002

We have experimentally and theoretically investigated the Auger recombination lifetime in InAs–Ga1−xInxSb superlattices. Data were obtained by analyzing the steady-state photoconductive response to frequency-doubled CO2 radiation, at intensities varying by over four orders of magnitude. Theoretical Auger rates were derived, based on a k⋅p calculation of the superlattice band structure in a model which employs no adjustable parameters. At 77 K, both experiment and theory yield Auger lifetimes which are approximately two orders of magnitude longer than those in Hg1−xCdxTe with the same energy gap. This finding has highly favorable implications for the application of InAs–Ga1−xInxSb superlattices to infrared detector and nonlinear optical devices.
Very large magnetoresistance in perovskite-like La-Ca-Mn-O thin films
Authors: McCormack M. , Jin S. , Tiefel T. H. , Fleming R. M. , Phillips Julia M. , Ramesh R.
Published: July 2002

Colossal magnetoresistance with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La-Ca-Mn-O thin films. This magnetoresistance value is about three orders of magnitude higher than is typically seen in the giant-magnetoresistance-type metallic, superlattice films. The temperature of peak magnetoresistance is located in the region of metallic resistivity behavior. As the magnetoresistance peak occurs not at the temperature of magnetic transition but at a temperature where the magnetization is still substantial, the spin-disorder scattering is not likely to be the main mechanism in these highly magnetoresistive films. The peak can be shifted to near room temperature by adjusting processing parameters. Near-room-temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be very detrimental to achieving large magnetoresistance in the lanthanum manganite compounds. The fact that the electrical resistivity of a material can be manipulated by magnetic field to change by orders of magnitude could be useful for various device applications.
Reflection of surface acoustic waves on domain walls in a LiNbO3 crystal
Authors: Roshchupkin D. V. , Brunel M. , Tucoulou R. , Bigler E. , Sorokin N. G.
Published: July 2002

This letter reports on a scanning electron microscopy study of reflection of surface acoustic waves on the domain walls in a LiNbO3 crystal. The regular domain structure with ∼5-mm period was formed in a LiNbO3 crystal by the method of aftergrowth thermoelectrical treatment. It is shown that the regular domain structure reflects surface acoustic waves on the domain walls in a ferroelectric LiNbO3 crystal.
Formation of GaAs ridge quantum wire structures by molecular beam epitaxy on patterned substrates
Authors: Koshiba S. , Noge H. , Akiyama H. , Inoshita T. , Nakamura Y. , Shimizu A. , Nagamune Y. , Tsuchiya M. , Kano H. , Sakaki H. , Wada K.
Published: July 2002

A ridge quantum wire structure has been successfully fabricated on a patterned (001) GaAs substrate by first growing a (111)B facet structure with a very sharp ridge and then depositing a thin GaAs quantum well on its top. Electron microscope study has shown that a GaAs wire with the effective lateral width of 17–18 nm is formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that one of the luminescence lines comes from the wire region at the ridge and its blue shift (∼60 meV) agrees with the quantum confined energy calculated for the observed wire structure.
Preparation of Pb(Zr,Ti)O3 thin films on electrodes including IrO2
Authors: Nakamura Takashi , Nakao Yuichi , Kamisawa Akira , Takasu Hidemi
Published: July 2002

The development of ferroelectric memory devices requires an improvement of the fatigue properties of ferroelectric thin films. Pb(Zr,Ti)O3(PZT) thin films obtained by the sol-gel method on Pt/Ti electrodes have reduced residual polarization by continuous polarization reverses about of 108 cycles. The electric characteristics such as fatigue properties have mostly depended on electrode materials. We propose Ir, IrO2, and these layer films as electrode materials and evaluate electric characteristics of PZT thin film capacitors. PZT thin films using Ir/IrO2 and Pt/IrO2 electrodes show no fatigue up to 1012 cycles of ±5 V switching pulses. Moreover, good properties of PZT capacitors, not only on SiO2 but also on polycrystalline silicon, were obtained by using IrO2.
Reflection Z-scan technique for measurements of optical properties of surfaces
Authors: Petrov D. V. , Gomes A. S. L. , de Araújo Cid B.
Published: July 2002

Spatial modification of a Gaussian beam by reflection on a surface of a high-absorbing material is investigated experimentally. A theoretical description in a geometrical-optics approach is given. The usefulness and sensitivity of the method for applications in measuring laser induced surface deformation and Kerr-like nonlinear coefficients is discussed.