bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Metformin Combined with Dietary Intervention on Childhood Obesity and Insulin Resistance
Authors: Khater Marwa Ghareeb , El-Sawy Doaa Mohammed , El-Shafiey Rasha Mohammed Gamal , Attia Gihan Farouk , Hamam Mohammed Amr
Published: January 2023

Background: Obesity is a multifactorial disease with multiple comorbidities such as insulin resistance (IR), cardiovascular disease, diabetes mellitus, and hypertension. Puberty is physiologically responsible for IR. During this stage of life, insulin sensitivity decreases by 25–50% and then improves. A change in lifestyle that promotes healthy nutritional habits and physical activity, as well as complementary treatments such as metformin therapy, is recommended as the first line of treatment.

Aim of the Work: To assess the effect of metformin combined with dietary intervention on BMI and IR in obese children and adolescents in the prepubertal and pubertal stages.

Methods: This study included 90 children and adolescents divided into two groups: 60 obese children and adolescents with BMIs > the 95th percentile for their sex and age (30 prepubertal and 30 pubertal) and 30 healthy children and adolescents with BMIs between the 5th and 85th percentile for their sex and age (15 prepubertal and 15 pubertal). They underwent a thorough clinical evaluation, which included anthropometric measurements and investigations such as serum adiponectin, leptin, adiponectin-leptin ratio (ALR), plasminogen activator inhibitor-1 (PAI-1), a lipid profile, and HOMA-IR. Obese children and adolescents received metformin with dietary intervention for six months.

Results: After the therapeutic intervention, the anthropometric measurements (weights, weight Z-scores, BMIs, BMI Z-scores, waist and hip circumferences, and waist-hip ratios) and the lipid profile (total serum cholesterol, LDL-C, HDL-C, and serum triglycerides) improved significantly in both obese groups (prepubertal and pubertal). Prepubertal obese children significantly improved more than pubertal obese children and adolescents in inflammatory adipokines (leptin, adiponectin, PAF-1, and ALR) and insulin sensitivity markers after the therapy.

Conclusion: Puberty is a critical physiologic stage affecting the response to metformin, which should be studied further in pubertal obese children and adolescents, particularly the dose-effect relationship.
Ultrastructural study of intestinal lactase gene expression
Authors: Freund Jean‐Noël , Jost Bernard , Duluc Isabelle , Morel Gérard
Published: July 2002

Summary— The distribution of the mRNA encoding rat intestinal lactase‐phlorizin hydrolase (LPH) was analyzed by ultrastructural in situ hybridization, and compared to the distribution of the cognate protein. Different pictures were obtained depending on the epithelial cell position along the crypt‐villus axis: i) cells localized at the crypt base were devoid of LPH mRNA and protein; ii) cells of the crypt‐villus junction and of the villus base showed a high level of mRNA but a low amount of enzyme; and iii) enterocytes of the middle and upper part of the villi exhibited an intense protein immunolabeling, but a low content of LPH mRNA. The analysis of the intracellular distribution of the LPH mRNA revealed a gradient of concentration along the cellular axis, as the transcripts were the most abundant in the apical and subapical domains of the enterocytes. In addition, LPH mRNA labeling was often paired or arranged in a circular shape, suggesting that the transcripts may be located in closed vicinity to rounded structures within the cytoplasm. The results indicate that distinct patterns of mRNA and protein occur along the villus height during the continuous process of cell differentiation of the intestinal epithelium. In addition, the emergence of the functional polarity of the enterocytes comes together with the establishment of an intracellular gradient of concentration of the mRNA encoding a brush border enzyme. A link between the intracellular distribution of LPH mRNA molecules and the membranous flow is proposed.
SK2 encodes the apamin‐sensitive Ca2+‐activated K+ channels in the human leukemic T cell line, Jurkat
Authors: Jäger Heike , Adelman John P. , Grissmer Stephan
Published: July 2002

T cells express two different types of voltage‐independent Ca2+‐activated K+ channels with small (SK) and intermediate (IK) conductance that serve important roles in the activation of T lymphocytes. In contrast to the IK channels from T lymphocytes which are upregulated upon mitogen stimulation, SK channels of Jurkat T cells, a human leukemic T cell line, are constitutively expressed even in the absence of mitogenic stimulation. We have used patch‐clamp recordings from transfected or injected mammalian cells to show that the cloned SK2 channel demonstrates the biophysical and pharmacological properties of the majority of K(Ca) channels in Jurkat T cells. The cloned and native channels are voltage‐independent, Ca2+‐activated, apamin‐sensitive, show an equivalent voltage‐dependent Ba2+ block and possess a similar ion selectivity. In addition, we used the polymerase chain reaction to demonstrate the presence of SK2 mRNA in Jurkat T cells, whereas SK3 transcripts encoding the other cloned apamin‐sensitive SK channel were not detected. These data suggest that the voltage‐independent apamin‐sensitive K(Ca) channel in Jurkat T cells represents the recently cloned SK2 channel.
Degradation of Water‐Insoluble Dyes by Microperoxidase‐11, an Effective and Stable Peroxidative Catalyst in Hydrophilic Organic Media
Authors: Wariishi Hiroyuki , Kabuto Mari , Mikuni Junko , Oyadomari Masafumi , Tanaka Hiroo
Published: July 2002

Microperoxidase‐11 (MP‐11), a heme‐containing undecapeptide, derived from horse heart cytochrome c was utilized as a peroxidative catalyst. Catalytic characteristics of MP‐11 in hydrophilic organic media were studied using 2,6‐dimethoxyphenol as a reducing substrate in a series of organic solvents at various concentrations, indicating that MP‐11 was active in water‐miscible organic solvents but at least 5% water was compulsory for the catalytic action. Thus, MP‐11 was not active in hydrophobic solvents. The pH of the water portion in the media affected the reaction rate. The optimal pH was found to be 9, where a release of protons from either an oxidizing or reducing substrate to the media was facilitated. The decolorization of water‐insoluble synthetic dyes by MP‐11 in 90% methanol was attempted. MP‐11 showed effective decolorization activities against either azo or anthraquinone dyes. The degradation pathway for Solvent Orange 7 was investigated in detail, showing that MP‐11 catalyzed the oxidative cleavage of the azo linkage to generate 1,2‐naphthoquinone and 2,4‐dimethylphenol as key intermediates.
Substrate and Enzyme Characteristics that Limit Cellulose Hydrolysis
Authors: Mansfield Shawn D. , Mooney Caitriona , Saddler John N.
Published: July 2002

The ability and, consequently, the limitations of various microbial enzyme systems to completely hydrolyze the structural polysaccharides of plant cell walls has been the focus of an enormous amount of research over the years. As more and more of these extracellular enzymatic systems are being identified and characterized, clear similarities and differences are being elucidated. Although much has been learned concerning the structures, kinetics, catalytic action, and interactions of enzymes and their substrates, no single mechanism of total lignocellulosic saccharification has been established. The heterogeneous nature of the supramolecular structures of naturally occurring lignocellulosic matrices make it difficult to fully understand the interactions that occur between enzyme complexes and these substrates. However, it is apparent that the efficacy of enzymatic complexes to hydrolyze these substrates is inextricably linked to the innate structural characteristics of the substrate and/or the modifications that occur as saccharification proceeds. This present review is not intended to conclusively answer what factors control polysaccharide biodegradation, but to serve as an overview illustrating some of the potential enzymatic and structural limitations that invariably influence the complete hydrolysis of lignocellulosic polysaccharides.
Multiple forms of the catalytic centre, CuZ, in the enzyme nitrous oxide reductase from Paracoccus pantotrophus
Authors: RASMUSSEN Tim , BERKS Ben C. , BUTT Julea N. , THOMSON Andrew J.
Published: July 2002

Nitrous oxide reductase catalyses the reduction of nitrous oxide to dinitrogen at a unique tetranuclear copper site, called CuZ, which has a central inorganic sulphide ligand. Limited incubation with oxygen during the preparation of nitrous oxide reductase from Paracoccus pantotrophus results in changed redox properties of the catalytic centre by comparison with anaerobic preparations. While the anaerobically purified enzyme has a catalytic centre which performs a single electron step at a midpoint potential of Em =+60mV versus the standard hydrogen electrode (n = 1), the altered centre shows no redox change under similar experimental conditions. Spectroscopic properties of this ‘redox fixed’ centre are similar to spectra of the reduced ‘redox active’ form of CuZ, although the positions and intensities of a number of transitions are changed in the optical spectrum. These observations are interpreted in terms of two forms of the catalytic centre, called CuZ and CuZ∗. The structural relationship between these forms is unclear. EPR and magnetic circular dichroism spectra suggest that the basic Cu4S structure is common to both. Curiously, steady-state activity of the aerobic enzyme preparation is slightly increased despite the fact the catalytic centre does not undergo detectable redox changes.
Domain IV of mouse laminin β1 and β2 chains
Authors: Sasaki Takako , Mann Karlheinz , Miner Jeffrey H. , Miosge Nicolai , Timpl Rupert
Published: July 2002

Domain IV, consisting of about 230 residues, represents a particular protein module so far found only in laminin β1 and β2 chains. Both domains were obtained by recombinant production in mammalian cells. They showed a globular structure, as expected from electron microscopic examination of laminins. Fragment β1IV was obtained as a monomer and a disulfide‐bonded dimer, and both were modified to ≈ 50% by a single chondroitin sulfate chain attached to Ser721 of an SGD consensus sequence. Dimerization is caused by an odd number of cysteines, with three of them having a partial thiol character. Whether both modifications also occur in tissue forms of laminin remains to be established. Fragment β2IV was only obtained as a monomer, as it lacked one crucial cysteine and the SGD sequence. It required, however, the presence of two adjacent LE modules for proper folding. Polyclonal antibodies raised against both fragments showed no cross‐reaction with each other and allowed establishment of β chain‐specific radioimmunoassays and light and electron microscopic immunostaining of tissues. This demonstrated a 5–25‐fold lower content of β2 compared with β1 chains in various tissue extracts of adult mice. Tissues derived from β2‐deficient mice failed to react with the β2‐specific antibodies but showed a twofold higher content of β1 than heterozygotes. The antibodies to β2 showed broader tissue staining than reported previously, including in particular a distinct reaction with the extrasynaptic endomysium of skeletal muscle. Immunogold staining localized both β chains primarily to basement membranes of kidney, muscle and various other tissues.
Insulin‐like growth factor binding protein‐1 in NIDDM: relationship with the insulin resistance syndrome
Authors: Mohamed‐Ali  , Pinkney  , Panahloo  , Cwyfan‐Hughes  , Holly  , Yudkin
Published: July 2002

OBJECTIVE

In order to examine the role of insulin‐like growth factors in the pathogenesis of accelerated macrovascular disease in noninsulin‐dependent diabetes mellitus (NIDDM), we investigated the relationship between the insulin resistance syndrome and the IGF axis.

DESIGN

Cross‐sectional analysis of the relationship between insulin resistance syndrome variables and concentrations of IGF‐1, IGF‐2, IGFBP‐1 and IGFBP‐3 in 80 subjects with NIDDM.

RESULTS

After correcting for age, sex and body mass index, concentrations of IGFBP‐1, correlated with those of HDL‐cholesterol (r = 0.40; P < 0.001), triglycerides (r = − 0.24; P = 0.04), insulin (r = − 0.39; P < 0.001), intact proinsulin (r = − 0.32; P = 0.006), des 31,32 proinsulin (r = − 0.40; P = 0.001), and with insulin sensitivity (r = 0.38; P = 0.001) and PAI‐1 activity (r = − 0.24; P = 0.05); IGF‐1 levels only correlated with those of HDL‐cholesterol (r = − 0.33; P = 0.005), and this was not explained by IGFBP‐1 or insulin sensitivity. With additional correction for insulin, concentrations of IGFBP‐1 still correlated with HDL‐cholesterol (r = 0.40; P < 0.001), but not those of triglycerides or PAI‐1 activity. There were no significant relationships between levels of IGF‐2 and any of the variables investigated, and IGFBP‐3 levels only correlated with those of total cholesterol (r = 0.24, P = 0.04).

CONCLUSIONS

In NIDDM, concentrations of IGFBP‐1 are related to those of insulin, insulin sensitivity, serum lipoproteins and PAI‐1 activity. The relationship between concentrations of IGFBP‐1 and HDL‐cholesterol is not explained by insulin. Concentrations of IGF‐1 are linked to HDL‐cholesterol, and this is not explained by levels of IGFBP‐1. IGFBP‐1 concentrations were related to PAI‐1 activity, and this may be explained by insulin, which regulates the production of IGFBP‐1 and PAI‐1.
An unusual swelling following endodontic and prosthodontic treatment of a mandibular molar due to a foreign body reaction
Authors: Ree M. H.
Published: July 2002

Aim

The purpose of this case report is to stress the importance of taking a proper history and the appropriate evaluation of diagnostic tests in order to prevent incorrect diagnosis and treatment. Moreover, the management of postoperative problems in a healthcare system in which specialists take on specific parts of the treatment is discussed.

This article describes the diagnosis and treatment of an unsuspected flare‐up 1 week after root canal treatment. The swelling and pain appeared to be associated with an accidentally embedded piece of impression material. General practitioners and specialists should be aware of alternate treatment plans and treatment procedures and take these into consideration whenever there is a postoperative problem to be solved.

Key learning points

Impression materials can cause a foreign body reaction when embedded in the soft tissues.

History taking and evaluation of diagnostic tests are of paramount importance in order to prevent incorrect diagnosis and treatment.

Both general practitioners and specialists have the responsibility to evaluate patients with a broad vision.
Developmental control of Xa21‐mediated disease resistance in rice
Authors: Century Karen S. , Lagman Regina A. , Adkisson Michael , Morlan John , Tobias Renee , Schwartz Keri , Smith Aubrey , Love Jaime , Ronald Pamela C. , Whalen Maureen C.
Published: July 2002

The rice resistance gene Xa21 confers resistance against the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo). The molecular genetic mechanism controlling the integration of the Xa21‐mediated disease resistance response with the developmental program in rice is under study in this model system. Reproducible means of infecting plants at certain developmental stages were designed based on the timing of full expansion of the leaf. Xa21‐resistance progressively increases from the susceptible juvenile leaf 2 stage through later stages, with 100% resistance at the adult leaf 9/10 stage. We found that Xa21 expression is independent of plant developmental stage, infection with Xoo, or wounding. Expression of the Xa21 gene transcript is not correlated with expression of Xa21 disease resistance indicating that the developmental regulation of Xa21‐resistance is either controlled post‐transcriptionally or by other factors.
Use of Atraumatic Spinal Needles Among Neurologists in the United States
Authors: Birnbach David J. , Kuroda Maxine M. , Sternman David , Thys Daniel M.
Published: July 2002

Objective.—To evaluate atraumatic spinal needle use among US neurologists.

Background.—Postdural puncture headache following lumbar puncture may be dramatically reduced through the use of atraumatic pencil‐point spinal needles. It was hypothesized that atraumatic spinal needles are rarely used by members of specialties outside of anesthesiology. To determine the extent to which atraumatic spinal needles are currently being used for lumbar puncture in the United States, American neurologists (one group of physicians who regularly perform lumbar punctures) were surveyed.

Methods.—A questionnaire was mailed to all 7798 members of the American Academy of Neurology listed in the membership directory. The questionnaire included items pertaining to age, practice setting, knowledge of pencil‐point (atraumatic) spinal needles, and lumbar puncture practices.

Results.—Only a fraction (2%) of the neurologists surveyed routinely use atraumatic spinal needles. Almost half of the responding neurologists reported having no knowledge of pencil‐point spinal needles. Among those who did have knowledge of these new spinal needles, the most common reasons given for not using them were nonavailability and expense.

Conclusions.—Atraumatic spinal needles for lumbar puncture have been shown to dramatically decrease the risk of postdural puncture headache. Although the use of these needles is standard practice among anesthesiologists, they have not been adopted by other medical specialties. This may lead to unnecessary morbidity among patients undergoing lumbar puncture.
Epitaxial growth of yttria-stabilized zirconia films on silicon by ultrahigh vacuum ion beam sputter deposition
Authors: Legagneux P. , Garry G. , Dieumegard D. , Schwebel C. , Pellet C. , Gautherin G. , Siejka J.
Published: July 2002

Yttria-stabilized zirconia (YSZ) films have been grown on Si (100) substrates by ion sputter deposition using ultrahigh vacuum system with in situ diagnostic equipment. Epitaxial conditions of YSZ (100) films were achieved between 700 and 800 °C by using an oxygen partial pressure around 3×10−4 Pa during the deposition. The film stoichiometry was measured by Rutherford backscattering spectrometry and nuclear reaction analysis. Crystalline quality of the YSZ layers was determined by x-ray diffraction, channeling of 4He+ ion beam, and in situ reflection high-energy electron diffraction pattern.
Distinct observation of interwell coupling effect on optical transitions in double quantum wells in an electric field
Authors: Tokuda Yasunori , Kanamoto Kyozo , Tsukada Noriaki , Nakayama Takashi
Published: July 2002

We present results of an experimental study of interwell coupling effects using asymmetric double quantum well structures under electric fields. Data were obtained by means of photocurrent spectroscopy. It was concluded that remarkable variations in both energy and intensity of excitonic transitions, which were observed for the strongly coupled quantum wells, originate from the intersection of two quantized levels in the conduction band.
Laser-induced metal deposition on semiconductors from liquid electrolytes
Authors: Nánai L. , Hevesi I. , Bunkin F. V. , Luk’yanchuk B. S. , Brook M. R. , Shafeev G. A. , Jelski Daniel A. , Wu Z. C. , George Thomas F.
Published: July 2002

Maskless deposition of gold and copper from electrolyte solutions onto n-doped semiconductors (GaAs, Si) is investigated. The metal deposits are found to have lateral dimensions of about 1 μm and are in barrier contact with the semiconductor. The proposed deposition mechanism is governed by the electric fields resulting from the Dember effect, the p-n junction, and the thermal emf.
Patterned quantum well semiconductor laser arrays
Authors: Kapon E. , Harbison J. P. , Yun C. P. , Florez L. T.
Published: July 2002

Low-threshold arrays of GaAs/AlGaAs patterned quantum well semiconductor lasers were grown by molecular beam epitaxy on periodically corrugated substrates. Uncoated arrays of ∼14 lasers operated with threshold curents of 3.6 mA per laser and emitted up to 375 mW from a single facet under pulsed conditions. The array lasers were not phase locked because of the tight optical confinement in each array channel. A red shift of 300 Å (55 meV) was observed in the emission wavelength of the patterned array compared to that of nonpatterned lasers made on the same substrate. The red shift results from migration effects in the growth on the nonplanar surface, which leads to thicker quantum well active regions at the array channels. This effect illustrates the usefulness of the growth of quantum well heterostructures on nonplanar substrates for lateral band-gap engineering.
Practical quantitative theory of photoacoustic pulse generation
Authors: McDonald F. Alan
Published: July 2002

The problem of photoacoustic pulse generation is treated using generalized thermoelastic equations, specifically incorporating the hyperbolic heat conduction equation to avoid an infinite thermal propagation velocity. The assumption of equality of longitudinal and thermal velocities leads to a simplification of the solution in certain limiting cases, enabling insights into the character of the solution, without appreciably affecting the numerical results. The effect(s) of approximations made by previous authors may also be assessed. Numerical Hankel–Laplace transform inversion is shown to be practical for the general case, allowing such calculations to be duplicated by others.
Realization of a three-terminal resonant tunneling device: The bipolar quantum resonant tunneling transistor
Authors: Reed M. A. , Frensley W. R. , Matyi R. J. , Randall J. N. , Seabaugh A. C.
Published: July 2002

A new three-terminal resonant tunneling structure in which current transport is controlled by directly modulating the potential of the quantum well is proposed and demonstrated. Typical current gains of 50 at room temperature are observed.
Determination of energy-band dispersion curves in strained-layer structures
Authors: Jones E. D. , Lyo S. K. , Fritz I. J. , Klem J. F. , Schirber J. E. , Tigges C. P. , Drummond T. J.
Published: July 2002

Simultaneous measurement of both the conduction- and valence-band dispersion curves in single strained-layer structures is presented. These measurements rely on the application of recent observations regarding breaking of the usual selection rules for interband magnetoluminescence transitions in modulation-doped structures. Low-temperature magneto-luminescence data for three representative InGaAs/GaAs n-type single-strained quantum well structures are presented. For energies approaching 50 meV above the band gap, we find that the conduction band is parabolic with an effective mass of 0.071m0. Over the same energy range, the valence bands are highly nonparabolic.
Large magnetic hysteresis in a melt-textured Y-Ba-Cu-O superconductor
Authors: Jin S. , Sherwood R. C. , Gyorgy E. M. , Tiefel T. H. , van Dover R. B. , Nakahara S. , Schneemeyer L. F. , Fastnacht R. A. , Davis M. E.
Published: July 2002

Melt-textured YBa2Cu3O7−δ superconductor with a long and well-aligned grain structure is shown to exhibit magnetic hysteresis at 77 K which is the largest ever reported for bulk polycrystalline Y-Ba-Cu-O. The large ΔM resulted in a magnet-like behavior as well as a strong suspension phenomenon. It is shown, contrary to the previous reports, that the suspension behavior observed in Y-Ba-Cu-O is a generic consequence of large grain size, and not due to the presence of Ag oxide or Ag particles. There appears to be no substantial enhancement in flux pinning and Jc by these particles. Comparisons of magnetization behavior in various YBa2Cu3O7−δ samples (polycrystals, silver-oxide doped, melt-textured, and single crystals) indicated that for applied fields substantially larger than Hc1 the current flow that gives rise to the observed magnetization is intragranular. The pinning force and hence the critical current is roughly the same [Jc (magn)∼104 A/cm2] within a factor of ∼2 regardless of grain size, grain boundary configuration, presence of second phase particles, or increased dislocation and twin densities.
Selective area crystallization of amorphous silicon films by low-temperature rapid thermal annealing
Authors: Liu Gang , Fonash S. J.
Published: July 2002

We report the first demonstration of selective area crystallization of amorphous silicon films using low-temperature rapid thermal annealing. Crystallization temperatures as low as 500 °C were achieved with the help of a thermally evaporated ultrathin metal layer. The selective area crystallization was accomplished by using this ultrathin metal layer to define the region to be crystallized. The edge between two regions, that which has been crystallized and that which has not, is found to be very sharp.
Dependence of threshold current density on quantum well composition for strained-layer InGaAs-GaAs lasers by metalorganic chemical vapor deposition
Authors: Beernink K. J. , York P. K. , Coleman J. J.
Published: July 2002

A series of separate confinement InxGa1−xAs-GaAs (0.08<x<0.42) strained-layer quantum well lasers with 70 Å well thickness has been grown by metalorganic chemical vapor deposition. Data are presented on emission wavelengths and threshold current densities (Jth) as a function of composition. A minimum in Jth of 140 A/cm2 was observed for devices with In0.24Ga0.76As wells. The dependence of Jth on well composition is explained by a balance between strain effects and carrier confinement in the quantum well.
New model for damage accumulation in Si during self-ion irradiation
Authors: Holland O. W. , Pennycook S. J. , Albert Gerald L.
Published: July 2002

The dependence of the damage produced by self-ion implantation in Si on dose is determined and is shown to exhibit two distinct behaviors: an initial sublinear increase of damage with dose, followed by a period of greatly accelerated growth. Ion backscattering analysis using both single- and double-alignment channeling measurements is used to determine the distribution of damage in the samples. The nature of the damage is determined from its thermal annealing behavior and differences in the spectra recorded in the two channeling configurations. Damage is found to consist predominantly of two components: simple defects, such as divacancies, and regions of amorphous Si. The behavior of these components is shown to be divergent at the fluence which separates the two different growth regimes. A model is proposed which considers the amorphization process in Si as a critical-point phenomenon, one in which the onset of amorphization leads to a cooperative behavior among the various types of damage resulting in a greatly accelerated transition.
Characterization of ground-state neutral and ion transport during laser ablation of Y1Ba2Cu3O7−x using transient optical absorption spectroscopy
Authors: Geohegan D. B. , Mashburn D. N.
Published: July 2002

Transient optical absorption spectroscopy has been utilized for the first time to study the transport of ground-state Y, Ba, Cu, and Ba+ following excimer laser ablation of Y1Ba2Cu3O7−x pellets. Spectral broadening of the atomic lines monitored in both absorption and emission is reported, indicating the existence of gas phase collisions in the plume of ejected material. Time-of-flight velocity distributions of the nonemitting neutrals and ions determined by the absorption technique are broadened and shifted to lower velocities than the velocity distributions inferred from excited-state fluorescence in the plume. Absorption by ground-state Y+, YO, BaO, and CuO also has been observed with this technique. The absorption technique, and its application as an in situ monitor of neutral and ion transport during deposition of superconducting thin films, is described.
Influence of entropy properties on measured trap energy distributions at insulator-semiconductor interfaces
Authors: Engström Olof
Published: July 2002

By using a thermodynamical approach to the ensemble of interface traps of insulator-semiconductor interfaces, it is demonstrated that the entropy properties of the traps may have a considerable influence on measured energy distributions. Because experimentally obtained distributions are given on a free-energy scale, thermodynamics must be utilized when comparing with theoretical distributions of eigenenergy scales. Both the U-shaped energy distributions profiles, normally found for silicon–silicon dioxide structures, and the peaks, obtained in these distributions for samples being exposed to radiation or bias stress, would occur for reasonable entropy distributions even if the interface state distribution on an eigenenergy scale were constant.
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u grown YBa2Cu3O7−d thin films from single-target magnetron sputtering
Authors: Eom C. B. , Sun J. Z. , Yamamoto K. , Marshall A. F. , Luther K. E. , Geballe T. H. , Laderman S. S.
Published: July 2002

Using single-target off-axis sputter deposition, high quality superconducting films of YBa2Cu3O7−δ were made in situ. These films have properties which are distinctly different from those of bulk ceramics and of post-deposition annealed films. Their superconducting resistive transitions remain sharp regardless of the value of Tc between 75 and 86 K. Normal-state conductivities are as high or higher than the best single crystals. Critical current densities as high as 6×107 A/cm2 at 4.2 K. Tc (R=0) falls off with film thickness down to 10 K for 35–40 Å films. All of the above properties are relatively insensitive to compositional variation. The results can be explained if the in situ growth results in well-formed CuO2 planes with defects occurring elsewhere.
Oxygen content control for as-deposited YBa2Cu3Ox thin films by oxygen pressure during rapid cooling following laser deposition
Authors: Ohkubo M. , Kachi T. , Hioki T. , Kawamoto J.
Published: July 2002

As-deposited epitaxial YBa2Cu3Ox thin films have been prepared by ArF excimer laser deposition followed by a rapid cooling with controlled oxygen pressure. The best film after the rapid cooling has a Tc with a zero resistance of 88 K and a Jc (77 K) of 5.5×105 A/cm2. It has been observed that the c-lattice parameter decreases, that is, the oxygen content x increases from ∼6 to 7, with increasing oxygen pressure during the rapid cooling. The relation between x and oxygen pressure is almost consistent with that for a powder sample being in a thermal equilibrium. We conclude that the oxygen content in the as-deposited films is determined by the thermal equilibrium oxygen content during the cooling process.
Optical phonon-assisted tunneling in double quantum well structures
Authors: Oberli D. Y. , Shah Jagdeep , Damen T. C. , Kuo J. M. , Henry J. E. , Lary Jenifer , Goodnick Stephen M.
Published: July 2002

Using subpicosecond time-resolved luminescence spectroscopy, we show that the tunneling rate for electrons in an asymmetric double quantum well structure changes dramatically as the energy separation between the two lowest conduction subbands of the coupled well system is tuned through the optical phonon energy. We model these experiments using an ensemble Monte Carlo simulation and obtain a good quantitative agreement between the two. These results demonstrate the importance of phonon-assisted tunneling processes and raise a number of interesting questions concerning the nature of phonons and carrier-phonon interactions in these structures.
Gain characteristics of strained quantum well lasers
Authors: Welch D. F. , Streifer W. , Schaus C. F. , Sun S. , Gourley P. L.
Published: July 2002

InGaAs/AlGaAs laser diode arrays fabricated with differing amounts of In in the quantum well active layer are characterized by threshold currents of 115 A/cm2, transparency currents of 50 A/cm2, optical losses of 3 cm−1, and wavelengths to 960 nm for In compositions of 20%. Gain coefficient measurements indicate an increase from 0.0535 to 0.0691 cm μm/A for quantum well lasers with 0% InAs and 10–20% InAs, respectively. The maximum output power achieved for a device with a 100 μm aperture is 3 W cw.
Do thermal spikes contribute to the ion-induced mixing of Ni into Zr, Ti, and Pd?
Authors: Bo/rgesen P. , Lilienfeld D. A. , Johnson H. H.
Published: July 2002

Low-temperature ion beam mixing rates for Ni-Ti, Zr-Ni, and Pd-Ni bilayers significantly exceeded binary collision estimates, and appeared quite sensitive to thermodynamic driving forces. In the absence of a temperature dependence such a behavior is commonly ascribed to interdiffusion within thermal spikes. However, the Ni-Ti mixing rate was seen to vary linearly with nuclear damage energy for irradiation with 600 keV Xe, Kr, or Ar, 300 keV Ne or N, or 200 keV N ions, or 1 MeV Au ions (literature value). This excludes overlapping thermal spikes. An expression was derived for mixing due to nonoverlapping thermal spikes, but this could also not explain our results.
Nematic liquid crystal modulator with response time less than 100 μs at room temperature
Authors: Wu Shin-Tson
Published: July 2002

A high-speed nematic liquid crystal modulator with response time less than 100 μs at room temperature was demonstrated. The effects that contribute to the observed high speed are the transient nematic effect, a new liquid crystal mixture, and a holding voltage technique.
Optical properties of diamond at pressures of the center of Earth
Authors: Vohra Yogesh K. , Xia Hui , Luo Huan , Ruoff Arthur L.
Published: July 2002

The optical properties of type Ia natural diamond were investigated to 364±9 GPa in a diamond anvil cell. The pressures were measured by x-ray diffraction on tungsten sample using a synchrotron x-ray source. The secondary absorption edge of diamond decreased from its ambient value of 3.7 to 2.5 eV at 364 GPa. The visible diamond luminescence at pressures above 300 GPa is different from the characteristic red luminescence of type Ib synthetic diamond. These are the first optical and structural observations at calibrated static pressures exceeding the pressure at the center of Earth.
Efficient type I blue second-harmonic generation in periodically segmented KTiOPO4 waveguides
Authors: van der Poel C. J. , Bierlein J. D. , Brown J. B. , Colak S.
Published: July 2002

We report type I phase-matched blue second-harmonic generation from periodically segmented channel ion-exchanged waveguides in KTiOPO4 with output wavelengths from 0.38 to 0.48 μm and efficiencies exceeding 50%/W cm2. Evidence is presented suggesting that these efficiencies result from ferroelectric domain reversals induced by waveguide fabrication. Waveguide structure, wavelength, and output power characteristics are presented.
Exciton saturation in electrically biased quantum wells
Authors: Fox A. M. , Miller D. A. B. , Livescu G. , Cunningham J. E. , Henry J. E. , Jan W. Y.
Published: July 2002

We have measured the heavy hole excitation saturation intensity in GaAs/AlGaAs quantum wells as a function of applied electric field and AlGaAs barrier design. We find that the saturation intensity increased with increasing applied field, and decreasing barrier thickness or height, because of increased carrier sweep-out rates. Time-resolved sweep-out time and temperature-dependent saturation intensity measurement point out the roles of both thermionic emission and tunneling in the field and barrier-dependent carrier escape time. By reducing the barrier Al composition from 30 to 20%, we achieved an increase in the saturation intensity by a factor of ∼6.
Amplitude dependence of magnetic stiffness in bulk high-temperature superconductors
Authors: Basinger S. A. , Hull J. R. , Mulcahy T. M.
Published: July 2002

Magnetic stiffness has been measured in several vibratory systems composed of a permanent magnet elastically suspended above a stationary high-temperature superconductor at 77 K. For Y-Ba-Cu-O, Ag/Y-Ba-Cu-O, (Pb-Bi)-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O sintered disks, both the vertical and horizontal magnetic stiffnesses increase strongly as the magnet’s oscillation decays, down to amplitudes of 1 μm. Vertical stiffness is about twice as strong as horizontal stiffness, and both are much stronger than the gradient of the levitation force for large monotonic changes in magnet height over the superconductor. These results are not deducible from contemporary magnetization measurements, and elastic pinning of flux lines are believed to contribute significantly to the stiffness.
Infrared quenching and thermal recovery of thermally stimulated current spectra in GaAs
Authors: Fang Z-Q. , Look D. C.
Published: July 2002

Thermally stimulated current (TSC) spectra stimulated by infrared (hν≤1.12 eV) light at 90 K have been used to study the photoquenching and thermal recovery of several dominant TSC peaks in Ga-rich, semi-insulating GaAs. The filling-pulse-length dependence of the quenching for these traps, and the temperature dependence of their recovery are clearly identified with the ground-to-metastable state transition of EL2. The data are consistent with the traps having a direct association with EL2 or EL2* rather than an indirect association which could result from a change in the dominant-free carriers as EL2 transforms to EL2*. If so, they likely are various point defects or impurities complexed with the arsenic antisite.
Manipulation of nucleation sites in solid-state Si crystallization
Authors: Kumomi Hideya , Yonehara Takao , Noma Takashi
Published: July 2002

Single grains of Si crystal are manipulated, for the first time, in solid-state crystallization of amorphous Si films. The artificial nucleation sites are introduced by employing the self-ion implantation. The nucleation and growth, during the subsequent thermal annealing strongly depends on the ion dose and energy. Preferential growth of the single nucleus takes place exclusively at each site and continues to propagate over them. Consequently, the location of grains is controlled, and the size distribution is remarkably shrunken in contrast to the films crystallized by random nucleation.
Limiting conditions of Si selective epitaxial growth in Si2H6 gas-source molecular beam epitaxy
Authors: Aketagawa K. , Tatsumi T. , Sakai J.
Published: July 2002

The limiting conditions are presented of selective epitaxial growth (SEG) on a SiO2-patterned Si (001) substrate for Si gas-source molecular-beam epitaxy by use of 100% Si2H6. In the initial stage of growth, epitaxial Si was selectively grown on a Si surface in the wide temperature range of 500–850 °C. On the other hand, polycrystalline Si nucleation on a SiO2 surface was intimately related to the total volume of supply gas. At a substrate temperature of 700 °C and a Si2H6 flow rate of 60 sccm, a SEG layer could be deposited at a rate as high as 645 Å/min.
In situ deposition of epitaxial PbZrxTi(1−x)O3 thin films by pulsed laser deposition
Authors: Horwitz J. S. , Grabowski K. S. , Chrisey D. B. , Leuchtner R. E.
Published: July 2002

Epitaxial thin films of PbZrxTi(1−x)O3 (PZT) with 0≤x≤0.6 have been deposited in situ by pulsed laser deposition from stoichiometric targets onto 〈100〉 oriented single crystals of MgO and SrTiO3. Film composition was extremely sensitive to the substrate temperature and the oxygen deposition pressure. In a high (200–300 mTorr) oxygen ambient, phase-pure 〈100〉 oriented PZT films (x=0.54) were formed at a substrate temperature of 550 °C on SrTiO3. On MgO, competition between formation of the ferroelectric phase and a nonferroelectric (pyrochlore) phase was observed for compositions near the morphotropic phase boundary (x∼0.54). Polycrystalline PZT films which were 70%–90% PZT were also deposited on Pt coated Si and GaAs under similar conditions.
X-ray diffraction determination of interfacial roughness correlation in SixGe1−x/Si and GaAs/AlxGa1−xAs superlattices
Authors: Phang Y. H. , Savage D. E. , Kuech T. F. , Lagally M. G. , Park J. S. , Wang K. L.
Published: July 2002

Vertically correlated roughness in SixGe1−x/Si and GaAs/AlxGa1−xAs superlattice films has been investigated. In all films, a significant fraction of the total roughness is correlated with lateral correlation lengths from ∼1000 to ∼4500 Å.
Suppression of stress-induced leakage current in ultrathin N2O oxides
Authors: Ahn J. , Kim J. , Lo G. Q. , Kwong D. L.
Published: July 2002

In this letter, the stress-induced leakage current (SILC) is studied in N2O gate oxide. Compared to control thermal oxide grown in O2, N2O oxide shows suppressed SILC, and the suppression is more pronounced under substrate electron injection. Moreover, the dependence of SILC on stress current density is smaller for N2O oxide. The suppressed SILC in N2O oxide is attributed to the nitrogen incorporation during N2O oxidation, which reduces the electron trap generation rate and the density of weak oxide spots.
Spectral measurement of timing jitter in gain-switched semiconductor lasers
Authors: Leep David A. , Holm David A.
Published: July 2002

We calculate the power spectrum of a periodically gain-switched semiconductor laser having intrinsic timing jitter and pulse-energy fluctuations that are uncorrelated from pulse to pulse. The results, in accord with measurements and numerical simulations, show that rms values of uncorrelated jitter can be determined with subpicosecond sensitivity from measured photocurrent spectra.
Optical and structural investigation of SiGe/Si quantum wells
Authors: Vescan L. , Hartmann A. , Schmidt K. , Dieker Ch. , Lüth H. , Jäger W.
Published: July 2002

In this letter we report photoluminescence and structural results obtained on asymmetrically strained Si0.7Ge0.3/Si single and multiple quantum wells epitaxially grown by low pressure chemical vapor deposition. Well-resolved peaks were obtained which can be attributed to quantum well excitons and their transversal optical phonon replica. A good correlation between peak properties and structure results was found. From the photoluminescence peak energies a valence band offset of 0.27 eV and an effective hole mass of 0.25 were estimated.
Photoluminescence from electron-hole plasmas confined in Si/Si1−xGex/Si quantum wells
Authors: Xiao X. , Liu C. W. , Sturm J. C. , Lenchyshyn L. C. , Thewalt M. L. W.
Published: July 2002

We report the first observation of photoluminescence from electron-hole plasmas in Si/Si0.8Ge0.2/Si quantum wells. While at liquid helium temperature, luminescence due to shallow bound excitons is observed. At 77 K electron-hole plasma (EHP) luminescence dominates the spectra over a wide range of pump powers. Convolution of the occupied electron and hole densities of states gives an excellent fit to the photoluminescence line shape. A band-gap reduction of up to 15 meV at high carrier densities is observed for wide quantum wells, but no such shift is detected for narrow quantum wells.
Time resolved measurements of cross-well transport in a multiple quantum well p-i-n modulator at high photogenerated carrier densities
Authors: Miller A , Park C. B. , LiKamWa P.
Published: July 2002

Carrier sweep-out rates from GaAs/AlGaAs multiple quantum wells have been measured as a function of excitation level on picosecond time scales at different values of applied electric field. A minimum rate of ∼20 ps was observed under resonant tunneling conditions at low generated carrier densities. At higher excitation levels, the effects of space charge build-up were found to significantly alter the transient nonlinear optical response due to changes in the time constant associated with vertical carrier transport.
Magnetic force microscope using a direct resonance frequency sensor operating in air
Authors: Kikukawa A. , Hosaka S. , Honda Y. , Tanaka S.
Published: July 2002

A magnetic force microscope (MFM) using a direct resonance frequency sensor which can be operated in the air has been developed. This instrument is simple and easy to handle because a vacuum system is not needed. The cantilever is used as a resonator in the oscillator, and its oscillating frequency is detected by a frequency modulation (FM) demodulator. A phase locked loop (PLL) FM demodulator is used which is less affected by noise. The cantilever is fabricated by Si microprocessing and its tip formed by precise focused ion beam (FIB) milling. MFM images demonstrate that this instrument has a performance almost the same as that which can be achieved in vacuum. It also has a scanning speed which is approximately 10 times as fast as that of an instrument using conventional slope detection techniques, and its signal-to-noise ratio is comparable to that of conventional systems.
Observation of scattering of particles produced by laser ablation on a substrate by laser induced fluorescence
Authors: Okada Tatsuo , Nakayama Yasushi , Kumuduni Wanniarachchi K. A. , Maeda Mitsuo
Published: July 2002

The scattering of Ba atoms produced from an ArF laser ablated YBa2Cu3O7−δ target on a Si substrate was directly observed by laser induced fluorescence spectroscopy. A gated diode array determined the spatial and the time of flight (TOF) distributions of the scattered Ba atoms on the substrate. It is shown that a sticking coefficient of Ba atoms was less than unity and Ba atoms were scattered roughly isotropically. The velocity of the scattered atoms is estimated from the TOF distribution.
Heavy p-doping of ZnTe by molecular beam epitaxy using a nitrogen plasma source
Authors: Han J. , Stavrinides T. S. , Kobayashi M. , Gunshor R. L. , Hagerott M. M. , Nurmikko A. V.
Published: July 2002

The successful p-doping of ZnSe and Zn(S,Se) using a nitrogen plasma source during growth by molecular beam epitaxy has been an important factor leading to the recent realization of blue-green diode lasers and light-emitting diodes. This letter reports the results of the nitrogen doping of ZnTe using similar techniques. Doping levels approaching the 1019 cm−3 range are reported along with electrical, optical, and microstructural characterization. Highly doped ZnTe provides an opportunity for forming an ohmic contact to p-ZnSe.
Measurement of damage profile in semiconductors: A sensitive optical technique
Authors: Shwe C. , Gal M.
Published: July 2002

We have used differential reflectance spectroscopy in combination with chemical-etch removal of surface layers to measure the depth profile of damage in GaAs. Damage was created by one of several ion-assisted processes, including sputter etching, reactive-ion etching, hydrogenation, and ion implantation. The sensitivity of this optical technique is shown to be comparable or greater than that obtained by other previous methods. From our measurements we estimate the lowest detectable damage level to be equivalent to damage created by 50 keV He+ ions at an ion dose of 1×108 ions/cm2. The depth resolution of this method is approximately 60 Å. Two examples of measured damage profiles are shown in this communication.
Formation of epitaxial CoSi2 on Si(100): Role of the annealing ambient
Authors: Vantomme André , Nicolet Marc-A. , Bai Gang , Fraser David B.
Published: July 2002

With a thin Ti layer interposed between a Si(100) substrate and a Co overlayer, the inversion of the Co and Ti films and the formation of a partly relaxed epitaxial CoSi2 layer on Si(100) can be obtained by steady-state annealing in inert as well as reactive ambients. A reactive ambient chemically binds the Ti near the surface as an oxide or nitride layer, which preserves the bilayer structure during a high temperature treatment. In a nonreactive ambient, the Ti and CoSi2 layers react further, resulting in a uniform layer of Co0.25Ti0.75Si2 and CoSi2. An eptiaxial orientation of CoSi2 is retained even in that case.