bluuebunny/crossref_metadata_2025 huggingface dataset:
Diet-induced loss of adipose hexokinase 2 correlates with hyperglycemia
Authors: Shimobayashi Mitsugu , Thomas Amandine , Shetty Sunil , Frei Irina C , Wölnerhanssen Bettina K , Weissenberger Diana , Vandekeere Anke , Planque Mélanie , Dietz Nikolaus , Ritz Danilo , Meyer-Gerspach Anne Christin , Maier Timm , Hay Nissim , Peterli Ralph , Fendt Sarah-Maria , Rohner Nicolas , Hall Michael N
Published: March 2023

Chronically high blood glucose (hyperglycemia) leads to diabetes and fatty liver disease. Obesity is a major risk factor for hyperglycemia, but the underlying mechanism is unknown. Here, we show that a high-fat diet (HFD) in mice causes early loss of expression of the glycolytic enzyme Hexokinase 2 (HK2) specifically in adipose tissue. Adipose-specific knockout of Hk2 reduced glucose disposal and lipogenesis and enhanced fatty acid release in adipose tissue. In a non-cell-autonomous manner, Hk2 knockout also promoted glucose production in liver. Furthermore, we observed reduced hexokinase activity in adipose tissue of obese and diabetic patients, and identified a loss-of-function mutation in the hk2 gene of naturally hyperglycemic Mexican cavefish. Mechanistically, HFD in mice led to loss of HK2 by inhibiting translation of Hk2 mRNA. Our findings identify adipose HK2 as a critical mediator of local and systemic glucose homeostasis, and suggest that obesity-induced loss of adipose HK2 is an evolutionarily conserved mechanism for the development of selective insulin resistance and thereby hyperglycemia.
Experimental investigation of High-Performance Concrete subjected to high temperatures
Authors:   Department of Electrical Engineering and Electronics, Universidad San Francisco de, Quito, Ecuador Ecuador, Bravo Hidalgo D. , Kessel O. ,   Department of Civil Engineering, University Mohamed El Bachir El Ibrahimi of Bordj Bou Arreridj, El-Anasser, Algeria, Bennia A. ,   Department of Electromechanics, University Mohamed El Bachir El Ibrahimi of Bordj Bou Arreridj, El-Anasser, Algeria, Abderraouf Belkadi A. ,   Department of Civil Engineering, University Mohamed El Bachir El Ibrahimi of Bordj Bou Arreridj, El-Anasser, 34030, Algeria, Kamel Khouadjia M. ,   5Laboratory of Materials and Durability of Constructions, University Mentouri of Constantine, Algeria
Published: March 2023

In this paper, we present an experimental study and statistical modeling of High-Performance Concrete subjected to high temperatures. The main objective of this study is to examine the effect of concrete age subjected to high temperature cycles (ranging from 20 °C to 1000 °C) on the physical and the mechanical properties of (HPC). The compressive strength, flexural strength, dynamic modulus and the physical characteristics were evaluated based on the mass loss and ultrasonic pulse velocity. The experiments have been performed at different age 90 and 210days. The analysis of the results shows that increasing temperature decreases the mechanical properties of the concrete especially after 90 days. The factorial design and analysis of variance (ANOVA) were used to establish the influence of experimental parameters on the HPC. Based on several criteria, mathematical models can be used to predict HPC properties under high temperature.
Molecular characterization of an additional shrimp hyperglycemic hormone: cDNA cloning, gene organization, expression and biological assay of recombinant proteins1
Authors: Gu Pei-Li , Yu Kei Li , Chan Siu-Ming
Published: July 2002

The crustacean eyestalk CHH/MIH/GIH neurohormone gene family represents a unique group of neuropeptides identified mainly in crustaceans. In this study, we report the cloning and characterization of the cDNA and the gene encoding the hyperglycemic hormone (MeCHH‐B) of the shrimp Metapenaeus ensis. The amino acid sequence of MeCHH‐B shows 85% identity to that of MeCHH‐A (formerly MeCHH‐like neuropeptide). Two separate but identical MeCHH‐B genes were identified in the genome of shrimp by library screening and they are located on different CHH gene clusters. The organization of the MeCHH‐B gene is identical to other members of the CHH/MIH/GIH neurohormone family. MeCHH‐B is expressed at a constant level in the eyestalks of juveniles and mature females. Unlike the MeCHH‐A gene, a low level of MeCHH‐B transcripts can also be detected in the central nervous system. Interestingly, the expression pattern of MeCHH‐B in the eyestalk of vitellogenic females is reversed to that of the MeCHH‐A gene. At the middle stage of gonad maturation, a minimum level of MeCHH‐B transcript was recorded and a maximum level of MeCHH‐A transcript was detected. Recombinant proteins for MeCHH‐A and MeCHH‐B were produced by a bacterial expression system. The hemolymph glucose level of bilaterally eyestalk‐ablated shrimp increased two‐fold 1 h after the rCHH injection and then returned to normal after 2 h. The hyperglycemic effect of these fusion proteins is comparable to that of de‐stalked shrimp injected with crude extract from a single sinus gland.
Mutation of MyoD‐Ser237 abolishes its up‐regulation by c‐Mos
Authors: Pelpel Karine , Leibovitch Marie-Pierre , Fernandez Anne , Leibovitch Serge A.
Published: July 2002

Recently we have shown that Mos could activate myogenic differentiation by promoting heterodimerisation of MyoD and E12 proteins. Here, we demonstrate that MyoD can be efficiently phosphorylated by in vitro kinase assay with purified Mos immunoprecipitated from transfected cells. Comparative two‐dimensional tryptic phosphopeptide mapping combined with site‐directed mutagenesis revealed that Mos phosphorylates MyoD on serine 237. Mutation of serine 237 to a non‐phosphorylable alanine (MyoD‐Ala237) abolished the positive regulation of MyoD by Mos following overexpression in proliferating 10T1/2 cells. Taken together, our data show that direct phosphorylation of MyoD‐Ser237 by Mos plays a positive role in increasing MyoD activity during myoblast proliferation.
Youth employment, mental health and substance misuse: a challenge to mental health services
Authors: Mitchell D. P. , Betts A. , Epling M.
Published: July 2002

Employment is the cornerstone of social inclusion, the means by which individuals play a full and active part in society and has a pivotal role in helping young people to negotiate the transitional period between the child and adulthood. Employment therefore should be seen as a right and given a higher priority by health and social care agencies. There are numerous difficulties preventing some young people from achieving full employment and these are compounded for young people with concurrent mental health and substance misuse problems (dual diagnosis). The coexistence of these two problems is on the increase and they are recognized as significant barriers to employment. Unemployment may lead to social alienation, criminal or other antisocial activity and a higher incidence of suicide. Consequently, there is a danger of young unemployed people slipping into a spiral of self‐defeating, antisocial and risky behaviour. There is little evidence of health and social care agencies working in partnership with voluntary sector organizations to tackle the growing problem of dual diagnosis and youth unemployment, although there are obvious linkages between employment, psychological health, social inclusion and substance misuse. It is therefore worth exploring the issues surrounding work, mental health and substance misuse in young people if we are to generate new ways of thinking about and responding to the needs of this target group. This presents a challenge to mental health services, particularly nurses who face the impact of these issues in their day to day practice but often lack the preparation and support to adequately address them.
PARATHYROID CYSTS
Authors: Gough IAN R.
Published: July 2002

Parathyroid cysts are relatively uncommon. They may be non‐functioning or associated with primary hyperparathyroidism. Three patients are presented, including one with a large mediastinal parathyroid cyst, and these cases illustrate the range of pathological and clinical features.
Within and Between Plant Variation in Seed Number, Seed Mass and Germinability of Primula elatior: Effect of Population Size
Authors: Jacquemyn H. , Brys R. , Hermy M.
Published: July 2002

Abstract: In this study, natural variation of seed mass and seed number between and within individual plants of P. elatior, a common forest herb on rich soils in Flanders, was investigated for both small (< 50 flowering individuals) and large (> 1000 flowering individuals) populations. The relationship between seed number and seed mass at both the between and within population level was also quantified. We also investigated how population size affected germinability of seeds through the effects of seed mass. Seed number varied by a factor of twenty, whereas seed mass spanned, on average, a 3.5 range. In both cases variation was highest among populations, indicating that population size has important effects on seed number and seed mass. Next, seed number‐seed mass tradeoffs were significantly influenced by population size, with small populations showing strong negative relationships whereas in large populations seed mass was only marginally influenced by seed number. As to germination, larger seeds showed larger germination percentages only for the smallest population. In all other populations, seed mass had little effect on germination.
High-resolution electron microscopy of the c=30.5 Å and c=38.2 Å polytypoids in the Bi-Ca-Sr-Cu-O superconductor
Authors: Hetherington C. J. D. , Ramesh R. , O’Keefe M. A. , Kilaas R. , Thomas G. , Green S. M. , Luo H. L.
Published: July 2002

We report results of high-resolution structure imaging, image processing, and simulation of the c=30.5 Å (Tc =80 K) and c=38.2 Å (Tc =115 K) superconducting polytypoids in the Bi-Ca-Sr-Cu-O system. The increase in c parameter is due to the insertion of two layers of Cu-O perovskite+Ca atoms in each unit cell. From the processed image and simulations, it appears that the central Cu layer in the c=38.2 Å polytypoid may be oxygen deficient. In addition, the image simulation experiments suggest that the oxygen atoms in the Bi-O layers are located at the face center of the Bi lattice.
Fiber optical laser spot microscope: A new concept for photoelectrochemical characterization of semiconductor electrodes
Authors: Carlsson Per , Holmström Bertil , Uosaki Kohei , Kita Hideaki
Published: July 2002

A fiber optical laser spot microscope, which allows the simultaneous measurements of photocurrent and reflected light intensity or the measurement of laser spot photocurrent under the illumination of other light sources, has been developed to study semiconductor/electrolyte interfaces. The capability of this microscope was demonstrated on as-cleaved and Pt-treated p-InSe. The Pt treatment increased the photocurrent and improved the lateral resolution due to the increase of surface reaction rate. The higher photocurrent was observed at the spot where the reflectivity was higher. This behavior is considered to be due to an uneven distribution of platinum. The laser spot photocurrent image under the illumination of other light sources provided useful information to clarify whether the rate was controlled by surface or bulk properties of InSe.
Effects of microcracking on AlxGa1−xAs-GaAs quantum well lasers grown on Si
Authors: Deppe D. G. , Hall D. C. , Holonyak N. , Matyi R. J. , Shichijo H. , Epler J. E.
Published: July 2002

Data are presented demonstrating continuous (cw) 300 K operation of p-n AlxGa1−xAs-GaAs quantum well heterostructure lasers grown on Si and fabricated with naturally occurring microcracks running parallel to or perpendicular to the laser stripe. Operation for over 17 h is demonstrated for a diode with a parallel microcrack inside the active region. Diodes with microcracks perpendicular to the laser stripe exhibit relatively ‘‘square’’ light output versus current (L-I) characteristics and spectral behavior indicating internal reflections involving coupled multiple (internal) cavities. The lasers have operated (cw, 300 K) as long as 16 h.
Observations on intensity oscillations in reflection high-energy electron diffraction during gas source molecular beam epitaxy of InP
Authors: Morishita Yoshitaka , Maruno Sigemitsu , Gotoda Mitsunobu , Nomura Yoshinori , Ogata Hitoshi
Published: July 2002

We report the first observation of reflection high-energy electron diffraction intensity oscillations during the growth of InP using trimethylindium and phosphine in gas source molecular beam epitaxy (GSMBE). By optimizing the growth conditions, intensity oscillations more than 700 periods have been observed. The temperature and flux dependence of the oscillating behavior have been studied. Results indicate that the growth of InP by GSMBE is predominantly via a two-dimensional layer-by-layer mode.
Exponential gain in a Smith–Purcell amplifier
Authors: Schächter Levi , Ron Amiram
Published: July 2002

We study here the gain of an amplifier based on the Smith–Purcell effect. The grating is characterized by a reflection matrix and the gain, in the exponential region, is calculated as a function of the beam height and thickness.
Resonant photoluminescence excitation in GaAs grown directly on Si
Authors: Zemon S. , Jagannath C. , Shastry S. K. , Miniscalco W. J. , Lambert G.
Published: July 2002

We describe new results observed during resonant excitation in the excitonic region of GaAs grown directly on Si by organometallic vapor phase epitaxy. Two resolved features were found in the light-hole photoluminescence (PL) region, one identified with a free-exciton process and the other with donor-related transitions. Inhomogeneous line broadening was observed for the excitonic PL lines and related to stress fluctuations. Features which track the laser excitation line were observed and identified with a process in which a donor is excited from the n=1 ground state to an n=2 state.
Phase diagram and oxygen stoichiometry of Y-Ba-Cu-O thin films
Authors: Yang K. Y. , Homma H. , Lee R. , Bhadra R. , Grimsditch M. , Bader S. D. , Locquet J. P. , Bruynseraede Y. , Schuller Ivan K.
Published: July 2002

We have performed an exhaustive study of the phase diagram of Y-Ba-Cu-O thin films using chemical analysis, energy dispersive x-ray spectroscopy, Auger electron spectroscopy, and x-ray diffraction. We show that Raman scattering can provide information regarding impurity phases and oxygen stoichiometry in thin films
High-power GaAs/AlGaAs diode lasers grown on a Si substrate by metalorganic chemical vapor deposition
Authors: Connolly J. , Dinkel N. , Menna R. , Gilbert D. , Harvey M.
Published: July 2002

High-power GaAs/AlGaAs double-heterostructure lasers have been fabricated on Si substrates using a single-step metalorganic chemical vapor deposition process. An output power of 130 mW (per facet) and a slope efficiency of 38% have been obtained under pulsed operation. The peak emission wavelength of the laser was 8823 Å and the beam full width at half power for the parallel and perpendicular far-field radiation patterns were 6° and 41°, respectively.
XeF laser pumped by high-power sliding discharges
Authors: Gross R. W. F. , Schneider L. E. , Amimoto S. T.
Published: July 2002

We have developed a high-power XeF laser photolytically pumped by two surface discharges. The discharges slide along 760-mm-long by 12-mm-wide ferrite rods. They were energized by a single 6 μF capacitor at 50 kV in a fast discharge circuit. Each emitted up to 38 kW nm−1 cm−2 at 140 nm in 3-μs-long pulses. This powerful radiation source was used to photolyze mixtures of 450 Torr argon, 50 Torr nitrogen, and up to 12 Torr XeF2 in an active volume of about 1 ℓ. We extracted a maximum specific laser output energy density of 8 J/ℓ at 351 nm from the B–X transition of XeF.
Dynamics of photoexcited carriers in micron-size InP-InGaAsP etched microstructures probed by picosecond photoluminescence spectroscopy
Authors: Kash K. , Grabbe P. , Nahory R. E. , Scherer A. , Weaver A. , Caneau C.
Published: July 2002

We report the first use of picosecond photoluminescence spectroscopy to probe carrier relaxation in etched semiconductor microstructures. 2-μm-diam posts etched from double-heterostructure InP-InGaAsP epitaxial layers show anomalous time-dependent spectral broadening and blue shift of the quaternary layer band-edge luminescence. This new effect may be a result of modification of recombination processes upon microstructuring.
Dense plasma production for high rate sputtering by means of an electric mirror
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

The production of a new dense plasma for high rate sputtering with an electric mirror has been achieved. The plasma, with a density over 1012 cm−3 , is generated by an oscillating electron beam between two targets. Microwave excitation is detected from the dense plasma. Nonlinear interaction between the electron beam and the plasma plays an important role in increasing plasma density. The high film deposition rates over 3000 Å/min for Al have been realized.
New model for the Staebler–Wronski effect in an amorphous silicon hydrogen alloy
Authors: Tzeng Wen-Jer , Lee Si-Chen
Published: July 2002

The photoconductivity decay of an undoped amorphous silicon hydrogen alloy at different substrate temperatures is investigated. A model that attributes defect generation to recombinations through defects is used to describe the degradation kinetics. The typically observed 1/n power law decay with n close to integer can be easily explained using this model. The saturation behavior of photoconductivity suggests that the light-induced annealing process indeed exists near room temperature.
Evidence of arsenic-induced surface defects in high-dose As+-implanted rapidly annealed silicon
Authors: Kumar S. N. , Chaussemy G. , Canut B. , Laugier A.
Published: July 2002

Examination of Auger transition structures of As and x-ray photoelectron spectra of Si indicates a strong influence of the As ion implantation stage on the surface characteristics of (100) silicon. Rapid thermal annealing resulted in the electrical activation of a major portion of arsenic in the implanted zone, but a shallow region confined within a depth of ≊200 Å from the surface contained As complexed with Si and O atoms. Surface characterization results agree with the observed degradation in transport properties of solar cells constructed on the As+ implanted and rapidly annealed (100) p-silicon substrates.
Enhanced Sb diffusion in Si under thermal Si3N4 films during annealing in Ar
Authors: Ahn S. T. , Kennel H. W. , Plummer J. D. , Tiller W. A.
Published: July 2002

The effect of the presence of a thermally grown Si3N4 film on Sb diffusion in Si during annealing in Ar at 1100 °C has been investigated. Enhanced Sb diffusion under thermal nitride was observed and the enhancement effect disappeared when the nitride was removed before Ar annealing. These results strongly suggest that the enhanced Sb diffusion observed during thermal nitridation of Si is not directly related to the growth of thermal nitride. These effects are instead attributed to stresses in the thermal nitride film. Possible mechanisms of dopant diffusion affected by stresses in thin films are discussed.
Determination of oxygen content in high T
c superconductors by a charged particle activation method
Authors: Tao Z. , Alburger D. E. , Jones K. W. , Yao Y. D. , Kao Y. H.
Published: July 2002

A new method for determining the oxygen content in high Tc superconductors has been demonstrated using a charged particle activation technique. This method allows a measurement of the concentration of 16O atoms in the superconducting material by detection of the 17F produced with the 16O(d,n)17F nuclear reaction. By way of example, this technique is applied to the determination of oxygen content in a series of high Tc Y-Ba-Cu-O samples in which the stoichiometry is varied by reducing the copper concentration. The stabilized oxygen content shows a nonlinear dependence on the copper deficiency in these specimens.
Emission spectra from ArF laser ablation of high T
c superconductor Bi2CaSr2Cu2O9
Authors: Deshmukh Subhash , Rothe Erhard W. , Reck Gene P. , Kushida T. , Xu Zai Gui
Published: July 2002

A 193 nm excimer laser is used to ablate a Bi2CaSr2Cu2O9 superconductor and samples of Bi2O3, CaO, CuO, and Sr(OH)2⋅8H2O. Emission spectra generated during ablation are presented. These emissions are from simple atomic and diatomic species. Our observations show that the emission can be used to characterize the bulk material.
Self-biasing effects on plasma etching characteristics of Si and SiO2
Authors: Cooke M. J. , Pelletier J.
Published: July 2002

The effects of ion energy on the etching characteristics of Si and SiO2 are studied in a SF6 multipolar microwave plasma in the 0–400 eV range. For constant plasma conditions, the ion energy is varied by using independent rf wafer biasing. The variations observed in the anisotropy and etch rates of Si and SiO2 are discussed in the light of previous experimental results and in terms of the current models for plasma etching.
Superconducting contacts on YBa2Cu3O7−x in magnetic fields
Authors: Wieck A. D.
Published: July 2002

The contact resistance Rc of pressed and diffused gold contacts on polycrystalline YBa2Cu3O7−x is known to vanish below the critical temperature Tc≊90 K. The lack of a voltage drop over the contacts at finite currents strongly suggests pair tunneling between the high Tc superconductor and the adjacent gold layer, becoming superconducting via the proximity effect. Comparison of the current-voltage characteristics with those calculated including a Josephson current reveals a point contact structure rather than a homogeneous contact area. The contacts are studied at high currents up to I=19 A at different temperatures and magnetic fields. Staying superconducting at externally applied magnetic fields B up to B=30 mT, Rc rises monotonically with increasing magnetic field to Rc=180 μΩ at B=100 mT. This very low contact resistance persists essentially up to B=10 T, opening the possibility to design high magnetic field devices with negligible contact power dissipation.
Submicron-gate In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterojunction metal-semiconductor field-effect transistors grown by molecular beam epitaxy
Authors: Kuang J. B. , Tasker P. J. , Chen Y. K. , Wang G. W. , Eastman L. F. , Aina O. A. , Hier H. , Fathimulla A.
Published: July 2002

We report the dc and microwave performance of i-InAlAs/n+-InGaAs/i-InAlAs heterojunction metal-semiconductor field-effect transistors (MESFETs) with gate lengths from 0.25 to 0.35 μm. At 10 GHz, an extrinsic transconductance (gm) of 507 mS/mm, a current gain cutoff frequency (ft) of 49.5 GHz, and a power gain cutoff frequency (fmax) of 70.5 GHz were observed for a 0.25 μm gate device. For a 0.3 μm gate device, a gm of 545 mS/mm, an ft of 42 GHz, and an fmax of 114 GHz were measured. Output conductance as low as 7.7 mS/mm was measured. The voltage gain for measured devices is well above 20 for a wide range of bias conditions.
Measurements of fractal dimension for Co-Si interfacial layers
Authors: Cho N. I. , Bené R. W.
Published: July 2002

We report on measurements of fractal dimension for ultrathin cobalt films deposited onto silicon substrates. A new method has been used for the fractal dimension measurements, which involves an image processing of transmission electron microscopy (TEM) bright field image of the ultrathin film structure. The TEM image is digitized by 512×512 pixels with intensity levels from 0 to 255, and topographic contour lines which connect the same intensity levels are obtained from the digitized image. The fractal dimension (D) of the ultrathin film structure is calculated from the contour lines by using a relation (L=AD/2) between the areas (A) and perimeters (L) for each of the closed lines as suggested by Mandelbrot [Fractal Geometry of Nature (Freeman, New York, 1982), Chap. 12]. Results of the measurements indicate that the Co-Si interfacial dimension is increased from 2.0 to near 2.5 as the reaction is progressed. The results are compared with the fluctuating fractal dimension calculated from the noise exponent data.
Thermal annealing and zinc doping effects on the lattice constant of organometallic vapor phase grown GaAs epilayers on heavily In-doped substrates
Authors: Imai Tetsuji , Fuke Shunro , Mori Katsumi , Kuwahara Kazuhiro
Published: July 2002

Undoped and Zn-doped (∼3×1020/cm3) GaAs epilayers are grown on In-doped (order of 1020/cm3) GaAs substrates by the organometallic vapor phase epitaxy method. By thermal annealing of the undoped epilayer, changes in the perpendicular lattice constant a⊥, together with the apparent changes in surface morphology such as the appearance of a cross-hatched structure or a narrowing of the cross-hatched line spacing, are observed. It is also found that Zn doping is very effective to obtain thick, coherently grown epilayers on In-doped GaAs substrates. No appreciable changes in a⊥ and no generation of misfit dislocations are found because of the hardening of the crystalline lattice, similar to the case of In doping to GaAs bulk crystals.
Spatial charge distribution in the plasma-enhanced chemical vapor deposited nitrogen-rich silicon nitride
Authors: Kanicki J. , Hug S.
Published: July 2002

Gate quality N-rich silicon nitride films, with low bulk dangling bond densities, have been prepared by plasma-enhanced chemical vapor deposition at a substrate temperature of 400 °C. Films of different thicknesses, ranging from 200 to 10 500 Å, were obtained by varying the deposition time. The dielectric constant was found to be around 6.6 for this material, independent of the film thickness. The flatband voltage shift was also found to be proportional to the silicon nitride thickness, which suggests that a centroid of the trapped charge is located close to (within a region narrower than 200 Å) the silicon/nitride interface. For films thicker than 200 Å, the effective charge and effective trapped carrier density were found to be Qeff≂2×10−7 C cm−2 and Neff≂1×1012 cm−2.
Microwave surface resistance of bulk Tl-Ba-Ca-Cu-O superconductors
Authors: Newman H. S. , Singh A. K. , Sadananda K. , Imam M. A.
Published: July 2002

The first measurements of the microwave surface resistance at 18 GHz of bulk Tl-Ba-Ca-Cu-O superconductors produced by the hot isostatic pressing (HIP) process are reported. The superconducting samples, prepared by solid-state reaction with subsequent sintering and consolidation to obtain ideal density, were measured by replacing the end wall of a TE011 circular mode gold-plated copper cavity with the sample and determining the cavity Q for the temperature range 4–300 K. Results indicated that HIP samples which underwent subsequent annealing exhibit, below the critical temperature, a surface resistance approaching an order of magnitude less than copper.
High-power 1.3 μm superluminescent diode
Authors: Kwong Norman S. K. , Bar-Chaim Nadav , Chen Tirong
Published: July 2002

Superluminescent diodes with high output power (10 mW at 175 mA), wide spectral width (28 nm), low spectral modulation depth (<15%), wide frequency modulation bandwidth (570 MHz), and high single-mode fiber coupling efficiency (40%) are reported. The structure is based on a buried crescent laser structure with an antireflection coating and a ‘‘short-circuit’’ absorber to suppress lasing.
Monte Carlo analysis of high-field hole diffusion coefficients in nondegenerate GaAs
Authors: Joshi R. , Grondin R. O.
Published: July 2002

We examine the field dependence of the carrier diffusion coefficients in GaAs using an ensemble Monte Carlo technique. An analysis for the field dependence of the hole diffusivity is presented for the first time. Unlike for the electrons, no significant interband transfer effects are observed. The hole diffusivity is seen to decrease monotonically with increasing field.
Pt/Ti/p-In0.53Ga0.47As low-resistance nonalloyed ohmic contact formed by rapid thermal processing
Authors: Katz A. , Dautremont-Smith W. C. , Chu S. N. G. , Thomas P. M. , Koszi L. A. , Lee J. W. , Riggs V. G. , Brown R. L. , Napholtz S. G. , Zilko J. L. , Lahav A.
Published: July 2002

Very low resistance nonalloyed ohmic contacts of Pt/Ti to 1.5×1019 cm−3 Zn-doped In0.53Ga0.47As have been formed by rapid thermal processing. These contacts were ohmic as deposited with a specific contact resistance value of 3.0×10−4 Ω cm2. Cross-sectional transmission electron microscopy showed a very limited interfacial reacted layer (20 nm thick) between the Ti and the InGaAs as a result of heating at 450 °C for 30 s. The interfacial layer contained mostly InAs and a small portion of other five binary phases. Heating at 500 °C or higher temperatures resulted in an extensive interaction and degradation of the contact. The contact formed at 450 °C, 30 s exhibited tensile stress of 5.6×109 dyne cm−2 at the Ti/Pt bilayer, but the metal adhesion remained strong. Rapid thermal processing at 450 °C for 30 s decreased the specific contact resistance to a minimum with an extremely low value of 3.4×10−8 Ω cm2 (0.08 Ω mm), which is very close to the theoretical prediction.
Observations of barrier recombination in GaAs-AlGaAs quantum well structures
Authors: Blood P. , Tsui E. S-M. , Fletcher E. D.
Published: July 2002

Using laser structures with a window in the contact stripe, we have observed recombination from the wells and barrier regions of GaAs-AlGaAs quantum well lasers. The magnitude of the ratio of emission intensities from the barrier and the well, and the dependence of this ratio upon injection current, are in good agreement with a calculation in which the carrier populations in well and barrier are in thermal equilibrium at the lattice temperature (300 K).
Phase coherence length of electron waves in narrow AlGaAs/GaAs quantum wires fabricated by focused ion beam implantation
Authors: Hiramoto Toshiro , Hirakawa Kazuhiko , Iye Yasuhiro , Ikoma Toshiaki
Published: July 2002

The phase coherence length Lφ of electron waves in the one-dimensional weak localization regime was studied in selectively doped AlGaAs/GaAs quantum wires fabricated by focused ion beam implantation. Estimated Lφ by fitting the modified weak localization theory to the data is ∼1.2 μm at 0.3 K, nine times longer than in the n-GaAs wires. This difference is well explained by the mobility dependence of Lφ, and shows the advantage of selectively doped structures to obtain long Lφ. Lφ increased with decreasing temperature and saturated below ∼3 K, indicating the existence of temperature-independent phase breaking mechanisms.
Electron and x-ray diffraction study of ZnTe-ZnS strained-layer superlattices grown by molecular beam epitaxy
Authors: Karasawa Takeshi , Ohkawa Kazuhiro , Mitsuyu Tsuneo
Published: July 2002

Reflection high-energy electron diffraction observation during the growth of ZnTe-ZnS strained-layer superlattices shows that sharp streaks of the substrate were replaced by a spotty pattern which eventually elongated into streaks. X-ray diffraction data of the superlattice with small period show satellite peaks around an intense central peak. These studies indicate a good superlattice structure for the samples with small (<50 Å) periods.
Analysis of all-optical integrated beam scanning devices
Authors: Assanto G. , Stegeman G. I. , Vitrant G.
Published: July 2002

We study the operation of an all-optical, integrated, beam scanning device based on nonlinear grating coupling between radiative and guided-wave beams. Diffusive nonlinearities are considered and the salient features are compared with previous experimental results obtained in ZnS waveguides.
Na+ ion implanted ZnSe epitaxial layers grown by atmospheric pressure metalorganic vapor phase epitaxy
Authors: Yodo Tokuo , Yamashita Ken
Published: July 2002

We have introduced Na impurities by ion implantation into undoped ZnSe heteroepitaxial layers grown at 250 °C by atmospheric pressure metalorganic vapor phase epitaxy. The implanted Na impurity forms not only an acceptor level but also a deep level. The formation of implanted Na acceptor levels begins to increase at relatively low annealing temperatures (less than 450 °C). Annealing between 451 and 557 °C is the optimum condition to form acceptor levels effectively while generating a low density of deep levels. Annealing of temperatures significantly higher than 550 °C does not form Na acceptors, but generates deep levels.
Oriented thin films of YBaCu(F)O with high T
c and J
c prepared by electron beam multilayer evaporation
Authors: Wang X. K. , Sheng K. C. , Lee S. J. , Shen Y. H. , Song S. N. , Li D. X. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

Thin films of YBaCu(F)O were deposited on SrTiO3(100) substrates by multilayer deposition from three electron guns containing Y, BaF2, and Cu under a pressure of 5×10−5 Torr of O2. The films were later annealed in a separate chamber under a flowing O2-H2O atmosphere. X-ray diffraction studies reveal that the resulting structure is highly oriented with the a axis perpendicular to the substrate. Scanning electron micrographs show a morphology consisting of an array of orthogonal, interconnecting bars with well-developed junctions. High-resolution electron microscopy and electron diffraction patterns show that these junctions are atomically abrupt and that the associated c axes are mutually perpendicular. These epitaxial films show a sharp resistive transition with Tc(R=0) as high as 90 K. The zero field critical current density, determined from magnetization measurements, is 2.9×106 A/cm2 at 4.2 K and 5.0×104 A/cm2 at 77 K.
Resonant tunneling in crossed electric and magnetic fields
Authors: England P. , Hayes J. R. , Helm M. , Harbison J. P. , Florez L. T. , Allen S. J.
Published: July 2002

A wide (80 nm) double-barrier resonant tunneling structure shows 25 features in the current-voltage characteristic associated with resonances in the quantum well. When a transverse magnetic field is applied to the structure, the features weaken and shift to higher energies. We give a quantum mechanical description of this phenomenon which is able to account quantitatively for the magnitude of the shifts.
Detection of pulse to pulse timing jitter in periodically gain-switched semiconductor lasers
Authors: Böttcher E. H. , Bimberg D.
Published: July 2002

Methods to assess pulse to pulse timing jitter in periodicallly gain-switched semiconductor lasers are investigated. The power spectrum of the optical pulse train for mutually incoherent fluctuations of the turn-on delay time and the pulse amplitude is calculated. The result shows that a measurement of the power spectrum alone is not sufficient for the characterization of the inherent timing jitter. Additional knowledge of the optical waveform and the transfer characteristics of the detection system is necessary.
Optical third-harmonic generation from poly-(2,5-dimethoxy p-phenylene vinylene) thin film
Authors: Kaino Toshikuni , Kobayashi Hideki , Kubodera Ken-ichi , Kurihara Takashi , Saito Shogo , Tsutsui Tetsuo , Tokito Shizuo
Published: July 2002

Third-harmonic generation has been measured in poly(2,5-dimethoxy p-phenylene vinylene) thin film. The third-order optical susceptibility, χ(3), was evaluated to be 5.4×10−11 esu at 1.85 μm wavelength. This χ(3) value is about one order higher than that for poly(p-phenylene vinylene) and almost the same value as for poly(n-BCMU diacetylene) which possesses the highest χ(3) value among processible (solvent castable) polymeric materials.
Single-beam overwriting with melt-erasing process in an InSbTe phase-change optical disk
Authors: Maeda Yoshihito , Andoh Hisashi , Ikuta Iaso , Nagai Masaichi , Katoh Yoshimi , Minemura Hiroyuki , Tsuboi Nobuyoshi , Satoh Yoshio , Gotoh Norio , Ishigaki Masaji
Published: July 2002

Single-beam overwriting with melt-erasing process was made in a 5.25-in.-diam phase-change optical disk using an In22Sb37Te41 recording film. In the overwriting between 2 and 3 MHz signals at the linear velocity of 3–11 m/s, a carrier to noise ratio (C/N) more than 46 dB and an erasability less than −35 dB could be obtained. This high erasability was found to be due to the melt-erasing process. This disk presents highly erasable overwriting and long data retention time supported by an activation energy of 2.3 eV and a temperature of 230 °C for crystallization of the amorphized part.
Lorentz microscopy on dynamically written domains in GdTbFe
Authors: Greidanus F. J. A. M. , Jacobs B. A. J. , den Broeder F. J. A. , Spruit J. H. M. , Rosenkranz M.
Published: July 2002

In this letter a new method for the observation of thermomagnetically written domains using Lorentz electron microscopy is discussed. Domains are written in a GdTbFe layer deposited on a specially prepared silicon wafer disk, provided with Si3N4 windows. This allows direct observation by Lorentz microscopy of the magnetization patterns dynamically written under recording conditions. It is shown that by locally heating the GdTbFe layer with a continuous laser beam, combined with high-frequency switching of the magnetic field, very high storage densities can be achieved. Domains with a length of 0.25 μm in the direction of disk rotation could be written.
High quality electron system with variable electron layer thickness in a parabolic quantum well
Authors: Sajoto T. , Jo J. , Santos M. , Shayegan M.
Published: July 2002

We report the realization of a high quality electron system with variable areal density (ns ) in a selectively doped, parabolic Ax Ga1−x As well. For each ns, quantum oscillations in the magnetoresistance are analyzed to obtain the electron densities of the electric subbands. These densities are in good agreement with the predictions of self-consistent calculations of the subband structure. The data reveal that with increasing ns , the width of the electron system increases so that the effective three-dimensional density and the Fermi energy remain essentially constant. The dependence of the low-temperature electron mobility on ns is also reported.
Orientation-dependent metalorganic vapor phase epitaxy regrowth on GaInAsP/InP laser structures
Authors: Fidorra F. , Harde P. , Venghaus H. , Grützmacher D.
Published: July 2002

GaInAsP/InP lasers made by low-pressure metalorganic vapor phase epitaxy regrowth on patterned surfaces exhibit yield and performance dependent on laser stripe orientation. Structures with stripes parallel to the 〈011〉 and 〈01̄1〉 directions are investigated by secondary ion mass spectroscopy (SIMS). Three-dimensional SIMS profiles taken with high horizontal resolution using the checkerboard matrix gate technique yield unexpected results for structures with stripes parallel to the 〈01̄1〉 direction: phosphorus is found in the nominal GaInAs layer, its distribution is strongly inhomogeneous. Zn diffused into the GaInAs layer exhibits also pronounced spatial variations. Unwanted P outdiffusion and anomalous Zn diffusion are attributed to reduced crystalline perfection of the InP above 〈01̄1〉 oriented laser stripes.
Formation of low reverse current ion-implanted n+p junctions by low-temperature annealing
Authors: Ishihara Y. , Okita A. , Yoshikawa K. , Shibata T. , Ohmi T. , Nitta T. , Sugiura J. , Ohwada N.
Published: July 2002

By employing stress compensation technology in conjunction with an ultrahigh vacuum ion implanter, we have obtained two orders of magnitude smaller reverse-bias current levels in n+p junctions annealed at 550 °C as compared to the previous data. When samples are made with an optimum stress compensation condition, the magnitude of reverse-bias currents in n+p junctions as well as the carrier deactivation during post-implantation anneal becomes smallest. In order to further reduce the reverse-bias current level, it is shown that the elimination of contamination involvement during the implantation process is most essential.
Simple measuring method for electro-optic coefficients in poled polymer waveguides
Authors: Horsthuis Winfried H. G. , Krijnen Gijs J. M.
Published: July 2002

A simple measuring technique for the linear electro-optic coefficients in electro-optic waveguides is described. The method is based on the direct evaluation of synchronous angle measurements obtained by prism coupling. No waveguide or electrode patterning is required. A model has been developed in order to simulate the relation between change in synchronous angle and applied electric field across the electro-optic waveguide. The measured values of the electro-optic coefficients in poled polymer waveguides are reported.
Photon emission from avalanche breakdown in the collector junction of GaAs/AlGaAs heterojunction bipolar transistors
Authors: Chen J. , Gao G. B. , Huang D. , Chyi J. I. , Ünlü M. S. , Morkoç H.
Published: July 2002

The base-collector junction of GaAs/AlGaAs single heterojunction bipolar transistors has been observed to emit light at avalanche breakdown. The spectral distribution curve exhibits broad peaks at 2.03 and 1.43 eV, with the intensities dependent upon the reverse current. These observations suggest that electrons, excited to the upper conduction band by the field, lose their energy by impact ionizing electron-hole pairs and producing the 2.03 eV light, which corresponds to the threshold energy for electron impact ionization. The band-edge emission is the result of direct-gap free-carrier recombination and self-absorption of the high-energy transition.
Deep ultraviolet laser etching of vias in polyimide films
Authors: Treyz G. V. , Scarmozzino R. , Osgood R. M.
Published: July 2002

A deep ultraviolet cw laser has been used to form vias in a polyimide film. The etched features have smooth sidewalls and high aspect ratios. The observations are consistent with an etching mechanism based on thermal decomposition.
Recombination processes in quantum well lasers with superlattice barriers
Authors: Blood P. , Fletcher E. D. , Foxon C. T. , Griffiths K.
Published: July 2002

Spontaneous emission spectra from GaAs quantum well lasers grown by molecular beam epitaxy show that the radiative recombination rate in (AlAs)(GaAs) superlattice barriers is greater than in alloy barriers of the same average composition (x=0.25) due to reduction in effective gap by superlattice effects. Measurements of emission spectra as functions of temperature show that these radiative processes account for a significant part of the temperature variation of the threshold current and we estimate that the nonradiative lifetime in the superlattice barriers is an order of magnitude longer than in alloy barriers grown under similar conditions.
Surface segregation of Ba in polycrystalline YBa2Cu3O7 oxides: The effect of silver
Authors: Schrott A. G. , Singco G. , Tu K. N.
Published: July 2002

We have investigated the effect of annealing polycrystalline YBa2Cu3O7−δ samples in a He ambient and in vacuum, on the composition of their internal surfaces. X-ray photoelectron spectroscopy (XPS) data indicate a decrease in the amount of BaCO3 but a higher proportion of Ba at the near-surface region upon low-temperature annealing in He or vacuum. The latter effect seems to derive from the presence of a surface barrier for oxygen outdiffusion, and can be prevented by diffusing Ag into the polycrystalline sample. Changes in the cutoff energies of the ultraviolet photoelectron spectra indicate that a submonolayer coverage of Ag is sufficient to produce a change in the work function of 0.3 eV, corresponding to the lowering of the surface barrier.
InGaP orange light-emitting diodes on Si substrates
Authors: Kondo Susumu , Nagai Haruo , Itoh Yoshio , Yamaguchi Masafumi
Published: July 2002

InGaP light-emitting diodes (LEDs) that operate in the 600 nm region were fabricated on Si substrates using GaAsP/GaAs buffer layers. InGaP layers were grown by metalorganic-chloride vapor phase epitaxy, and GaAs and GaAsP buffer layers were grown by metalorganic vapor phase epitaxy at atmospheric pressure. An orange color emission was observed under room light at 20 mA dc injection. No degradation was observed in LED characteristics after 2000 h operation at an injection current of 500 A/cm2 despite the high dislocation density of 108 cm−2.
Hydrogen surface coverage: Raising the silicon epitaxial growth temperature
Authors: Wolff S. H. , Wagner S. , Bean J. C. , Hull R. , Gibson J. M.
Published: July 2002

The chemisorption of molecular hydrogen onto the Si (100) surface is shown to disrupt the epitaxial growth of silicon and silicon/germanium alloys grown by molecular beam epitaxy. It is only after the substrate temperature is raised above the hydrogen desorption temperature, or the deposition rate is lowered, that high quality single-crystal films can be grown. The results also suggest the surface segregation of hydrogen during growth.
Interfacial work functions and extrinsic silicon infrared photocathodes
Authors: Coon D. D. , Devaty R. P. , Perera A. G. U. , Sherriff R. E.
Published: July 2002

It is shown that n+ and/or p+ contacts on p-i-n diodes can function as solid-state photoemitters at temperatures ≲20 K. Infrared radiation can excite electrons or holes over small n-i or p-i interfacial barriers and into the intrinsic region when the diode is forward biased. Photoelectric thresholds in the far infrared corresponding to 37 and 61 μm cutoffs have been observed for silicon devices using a Fourier transform spectrometer. Suggestions are made to tailor the cutoff wavelengths using different concentrations of various impurities near the metal-insulator transition. Epitaxially grown multilayered (superlattice) detectors are proposed.
Magnetization and flux creep in textured Bi(Pb)-Sr-Ca-Cu-O oxide superconductors
Authors: Kumakura H. , Togano K. , Yanagisawa E. , Maeda H.
Published: July 2002

Flux creep for textured Bi(Pb)-Sr-Ca-Cu-O tapes was investigated by means of dc magnetization measurement. Much improvement in flux pinning is attained by the grain orientation for a Bi-based oxide. However, flux-pinning energy U0 in a magnetic field of 10–85 kOe is as small as 10–20 meV at 4.2 K. This value is still very small for practical use.
Hall coefficient of c-axis oriented Bi-Sr-Ca-Cu-O 107 K films
Authors: Mukaida Masashi , Kuroda Ken’ichi , Miyazawa Shintaro
Published: July 2002

Electronic properties such as temperature dependence of resistance (R) and Hall coefficients (RH ) were measured for synthesized Bi-Sr-Ca-Cu-O thin films with a zero resistance temperature (TC ) of 107 K, 70 K, and bulk ceramics with a TC of 107 K. The extrapolation of the normal resistance to zero degrees was always negative for a high TC phase, but usually positive for a low TC phase. It was clearly recognized that temperature dependence of the Hall coefficient of a high TC phase film and bulk ceramics is stronger than that of a low TC phase film. In addition, the temperature dependence of the inverse Hall coefficient (1/RH ) of high TC phase films and bulk ceramics was proportional to temperature.
Study of Si/SiO2 interface by transverse acoustoelectric voltage measurements
Authors: Abbate A. , Palma F.
Published: July 2002

Improved acoustoelectric measurements allow a precise determination of surface trap level distribution in the silicon band gap at the Si/SiO2 interface. Two kinds of experiments are presented: the effect of a uniaxial compression and the effect of HCl annealing are monitored by transverse acoustoelectric voltage versus voltage measurements. Results indicate the presence of three energy trap levels, located at −0.2, −0.1, and +0.03 eV from the band midgap. A precise correspondence was found between the experimental results and a theory of the Si/SiO2 interface electronic state presented in the literature. This correspondence allows one to relate the first trap level to the presence of Na+ charges in the oxide while the last two levels can be related to Si dangling bonds.