bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Commonly Available Food sources on Extension of Vase Life of Gladiolus (Gladiolus grandiflorus L.) cv. Swarnima
Authors: Sowjanya A. , Babu K. Kaladhar , Prasanth P. , Kumar S. Praneeth
Published: June 2022

The aim of this study was to investigate the effect of commonly available food sources in extending the vase life of cut gladiolus. It was carried out at Floricultural Research Station, Sri Konda Laxman Telangana State Horticultural University, Rajendranagar during 2020-2021. The preservatives used were Sugar (10, 20g), Coconut water (25, 50%), Sprite (50, 100 ml), Honey (5, 10%) and control (Distilled water) in Completely randomized design with nine treatments. Highest water uptake (22.62, 14.62, 11.29 g), transpirational loss of water (20.82, 13.00, 10.28 g), Water balance (6.80, 6.41, 6.01 g), Fresh weight change (106.69, 98.73, 89.36 % ), lowest optical density (0.037, 0.042, 0.054 nm) on 2nd, 4th and 6th day of vase life respectively, minimum number of days to first floret opening (1.69 days), maximum diameter of basal floret (10.33 cm) and longevity of basal floret (2.63 days), highest number of florets opened on spike when basal floret is fresh (2.33), number of florets opened per spike at the end of the vase life (10.89) and highest vase life (9.33 days) was recorded in treatment sprite 100 ml. Based on these findings it can be inferred that Sprite 100 ml can be used as an effective food source alternative to chemical preservatives to enhance the vase life of cut gladiolus.
Street Hawking among Children: A form of Child Abuse Often Overlooked
Authors: Obuzor I. , Gabriel-Job N.
Published: June 2022

Background: Despite efforts by the government to ensure that child labour is eradicated, children are still exposed to the menace of this abuse and other forms of abuse. This paper examined street hawking among children in Obio/Akpor L.G.A of Rivers State, Nigeria.

Methodology: This descriptive cross-sectional study used a purposive sampling method. 109 participants aged 10 - 17 years who hawked around two busy junctions in Obio/Akpor L.G.A Rivers State, Nigeria, were recruited for the study. An interviewer-administered questionnaire was used for data collection. Analysis was done with SPSS version 25.

Results: Participants comprised 109 child street hawkers, 67 (61.5%) female, 42 (38.5%) males. 72 (66.1%) of the participants lived with their parents, and more than half of their parents were traders. Reasons for hawking included the need to augment the family income, having lost a parent, and being forced by a guardian to hawk. 104 (95.4%) of the children reported not liking to hawk. 33 (30.3%) of the child street hawkers were school dropouts; more females, 27 (40.3 %), were school dropouts compared to their male counterparts, 6 (14.3 %). This sex difference was statistically significant (X2= 8.27, p= 0.004). Problems encountered while hawking included: accidents,  loss of money and goods, exposure to harsh weather, low self-esteem, and sexual  advances.

Conclusion: Street hawking among children is common despite its adverse effects on children. Education of the masses on the dangers of this menace is needed, and measures to alleviate poverty among the populace need to be radically pursued.
A photoaffinity ligand of the acetylcholine‐binding site predominantly labels the region 179–207 of the α‐subunit on native acetylcholine receptor from Torpedo marmorata
Authors: Dennis Michael , Giraudat Jérôme , Kotzyba-Hibert Florence , Goeldner Maurice , Hirth Christian , Chang Jui-Yoa , Changeux Jean-Pierre
Published: July 2002

Regions of the Torpedo marmorata acetylcholine receptor (AChR) α‐subunit involved in the binding of acetylcholine were probed with two different covalent ligands. The sulfhydryl‐directed affinity reagent 4‐(N‐maleimido)phenyltrimethylammonium iodide labeled a single α‐subunit cyanogen bromide fragment on the reduced AChR which was identified as α 179–207. The novel photoaffinity ligand p‐(N,N‐dimethylamino)‐benzenediazonium fluoroborate, on the other hand, labeled three distinct α‐chain cyanogen bromide fragments on the unmodified AChR in a carbamylcholine‐protectable manner. The major radiolabeled species was purified and identified by sequence analysis as α 179–207. The acetylcholine‐binding site on the native AChR may thus involve several distinct portions of the α‐chain, with the region α 179–207 making a major contribution to the site.
Effects of nicotinamide on hepatocyte viability and secretion of albumin and α1‐acid glycoprotein by adult rat hepatocytes in primoculture. Comparison with dexamethasone and recombinant human interleukin‐6
Authors: Barraud Béatrice , Balavoine Sophie , Feldmann Gérard , Lardeux Bernard
Published: July 2002

Summary— The effects of nicotinamide on hepatocyte viability and secretion of albumin and α1‐acid glycoprotein were studied in the absence or presence of dexamethasone and/or recombinant human interleukin‐6 either after cell attachment (2 h) or after 24, 48, and 72 h of culture. The evolution of hepatocyte survival during the culture was appreciated by measurement of total DNA content. The secretion of albumin and α1‐acid glycoprotein was measured after a 4‐h period following cell attachment or after 24, 48 and 72 h of culture. The important decrease of DNA content, mRNA levels and secretion of albumin and α1‐acid glycoprotein in control cultures after 2–3 days was not prevented by the addition of nicotinamide. In contrast, dexamethasone alone or with recombinant human interleukin‐6 improved DNA content and albumin secretion with no additional effect of nicotinamide. The secretion of α1‐acid glycoprotein was largely induced by dexamethasone alone or dexamethasone and recombinant human interleukin‐6. The increase of α1‐acid glycoprotein secretion was not modified by the addition of nicotinamide and averaged respectively 27‐ and 60‐fold for dexamethasone alone and dexamethasone and recombinant human interleukin‐6 after 48 h. These observations suggested that nicotinamide, at least in the conditions tested here, is unable to prevent alterations of hepatocyte viability and gene expression of cultured hepatocytes.
Impact of Cell Growth Morphology on Retroviral Transduction: Effect of Contact Inhibition
Authors: Kwon Young Jik , Peng Ching‐An
Published: July 2002

Retrovirus‐mediated gene transfer is one of the most commonly used methods to deliver, integrate, and express the gene of interest because the retrovirus can insert the desired gene into the chromosome of the target cells with high stability. However, to deliver the gene successfully, the retrovirus requires active division to integrate reversely transcribed DNA into the chromosome of target cells. In this study, we focused on the effect of cell‐cell contact inhibition on the efficiency of retroviral transduction with two anchorage‐dependent cell lines: NIH 3T3 and 293 cells. These two cell lines have very different cell morphologies and growth patterns on surfaces. Human embryonic kidney epithelial 293 cells tend to stick together after dividing, while NIH 3T3 cells migrate to occupy available surface and spread. Experimental data indicate that the abatement of the transduction rate of 293 cells was initiated in the early stage of the culture, whereas effect of contact inhibition of NIH 3T3 cells on the transduction rate became dominating at the end of the culture period. Experimental results were also quantitatively illustrated by plotting normalized multiplicity of infection (MOI) versus normalized cell density. According to the outcomes, cell inoculation density plays an important role in optimizing the retroviral transduction rate. The optimal time of retroviral transduction should be confined to the accelerating growth phase for 293 cells and at the exponential growth phase for NIH 3T3 cells. The implication drawn from this study is that contact inhibition effect on retroviral transduction should be taken into account for large‐scale gene transfer systems such as the microcarrier bioreactor.
Production of Retrovirus and Adenovirus Vectors for Gene Therapy: A Comparative Study Using Microcarrier and Stationary Cell Culture
Authors: Wu Suh‐Chin , Huang Gloria Yia‐Ling , Liu Jin‐Hwang
Published: July 2002

In gene therapy, retrovirus and adenovirus vectors are extensively used as gene‐delivery vehicles and further large‐scale processing of these viral vectors will be increasingly important. This study examined stationary and microcarrier cell culture systems with respect to the production of a retrovirus vector (encoding a monounit hammerhead ribozyme gene with an intron) and an adenovirus vector (encoding a reporter lacZ gene). Cytodex 1 and Cytodex 3 solid microcarriers were found to be able to provide good cell growth and high‐titer vector production in suspension cultures. Porous microcarriers such as Cytopore 2 gave slightly lower but still efficient growth but produced significantly lower titers of retrovirus and adenovirus vector from the producer cells. The specific retrovirus production was not proportionally related to the specific growth rate of the producer cells. High MOI infection was essential for high‐titer production of adenovirus vector in 293 cells. Hydrodynamic shear forces on microcarrier‐grown cells increased the production yield for retrovirus vector but decreased for adenovirus vector. The cellular productivity was much more efficient for adenovirus vector produced in 293 cells as compared to the retrovirus vector produced in PA317‐RCM1 cells. These findings can provide further insight into the feasibility of applying microcarrier cell culture technology to produce gene‐therapy virus vectors.
Retinoic acid receptor-related orphan receptor (ROR) α4 is the predominant isoform of the nuclear receptor RORα in the liver and is up-regulated by hypoxia in HepG2 human hepatoma cells
Authors: CHAUVET Caroline , BOIS-JOYEUX Brigitte , DANAN Jean-Louis
Published: July 2002

The retinoic acid receptor-related orphan receptor α (RORα) is critically involved in many physiological functions in several organs. We find that the main RORα isoform in the mouse liver is the RORα4 isoform, in terms of both mRNA and protein levels, while the RORα1 isoform is less abundant. Because hypoxia is a major feature of liver physiology and pathology, we examined the effect of this stress on Rora gene expression and RORα transcriptional activity. HepG2 human hepatoma cells were cultured for 24h under normoxia (20% O2) or hypoxia (10, 2, and 0.1% O2) and the abundance of the Rora transcripts measured by Northern blot and semi-quantitative RT-PCR. Hypoxic HepG2 cells contained more Rora mRNA than controls. This was also observed in rat hepatocytes in primary culture. Cobalt chloride and desferrioxamine also increased the amount of Rora mRNA in HepG2 cells. It is likely that these treatments increase the amount of the RORα4 protein in HepG2 cells as evidenced by Western blotting in the case of desferrioxamine. Transient transfection experiments indicated that hypoxia, cobalt chloride, and desferrioxamine all stimulate RORα transcriptional activity in HepG2 cells. Hence, we believe that RORα participates in the control of gene transcription in hepatic cells and modulates gene expression in response to hypoxic stress.
Effect of starvation time on the prey capture behaviour, functional response and population growth of Asplanchna sieboldi (Rotifera)
Authors: Nandini S. , Sarma S. S. S.
Published: July 2002

1. We examined the effect of different periods of prior starvation(from 30 min to 16 h) on the prey capture behaviour, and functional and numerical responses of the predatory rotifer Asplanchna sieboldi using the rotifer Brachionus calyciflorus as prey.

2. Feeding activity (i.e. encounter, attack, capture and ingestion) by Asplanchna increased significantly with increasing prey densities from 2 to 16 mL−−1 and with increasing prior starvation periods from 0.5 to 8 h.

3. Asplanchna sieboldi showed a type II functional response at all the prior starvation periods tested. The asymptotic prey density was highest after 8 h of starvation.

4. The instantaneous population growth rate of A. sieboldi ranged from 0.089 ± 0.044 (when starved for 8 h in every 24 h and at a prey density of 2 individuals mL−−1 for the other 16 h) to 1.015 ± 0.142 in the control (no starvation and at a prey density of 16 individuals mL−−1). The effect of starvation time on the numerical response was evident only at the higher prey density.
Characterization of ‘safe sites’ for pioneers in primary succession on recently deglaciated terrain
Authors: Jumpponen Ari , Väre Henry , Mattson Kim G. , Ohtonen Rauni , Trappe James M.
Published: July 2002

1 We characterized safe sites for individuals of five early colonizers (Abies lasiocarpa, Juncus drummondii, J. mertensianus, Saxifraga ferruginea, S. tolmiei) that had survived at least one growing season on the recently deglaciated forefront of the Lyman Glacier in the North Cascade Mountains, Washington, USA.

2 Sites with concave surfaces, coarse surface substrate and in the vicinity of large rocks were more likely to be colonized by pioneering plant species.

3 We speculate that the distribution of plants is determined by the presence of sites that facilitate seed trapping and protect seeds and seedlings from desiccation.

4 The data identify the abiotic factors that determine initial recruitment and spatial distribution of plants. Such controls precede biotic interactions in this primary successional sere.
New doping method for subhalf micron trench sidewalls by using an electron cyclotron resonance plasma
Authors: Mizuno B. , Nakayama I. , Aoi N. , Kubota M. , Komeda T.
Published: July 2002

A new doping method for the vertical sidewall of a trench by electron cyclotron resonance plasma is described. The plasma was produced under a pressure of 5×10−4 Torr. A doped layer was formed uniformly along the sidewall of a trench with subhalf micron width and an aspect ratio of 6.2. By using a de-ionized water cooling system, the wafer temperature was maintained below 120 °C and the boron dopant was introduced without damage to the photoresist.
Thin-film Bi-Sr-Ca-Cu-O high-temperature superconductors using pulsed laser evaporation from sintered disks
Authors: Guarnieri C. Richard , Roy R. A. , Saenger K. L. , Shivashankar S. A. , Yee D. S. , Cuomo J. J.
Published: July 2002

Films of the high-temperature superconductor in the Bi-Sr-Ca-Cu-O system were deposited by pulsed laser evaporation from a ceramic disk. Films deposited onto (100) MgO show x-ray diffraction patterns characteristic of c-axis textured Bi2(Sr,Ca,Bi)3Cu2Ox phase following annealing for 10 min at 850 °C in 20% O2-80% N2. These textured films have zero resistance at 78 K and show resistance drops near 110 K. The effects of the annealing environment on the electrical and structural properties are presented.
Hydrogen retention and release dynamics of amorphous carbon films exposed to a hydrogen plasma
Authors: Sugai H. , Yoshida S. , Toyoda H.
Published: July 2002

H2 and DH release was investigated in a pulsed deuterium discharge over a carbon thin-film deposited wall. A large quantity of hydrogen was desorbed by 300 eV D+2 irradiation from hydrogenated amorphous carbon (a-C:H) deposited by a hydrogen-admixed methane discharge. On the other hand, a strong pumping effect was observed in the case of films deposited by a helium-admixed discharge. The wall pumping effect was attributed to the presence of interstitial vacancies rather than dangling bonds in the films. A linear dependence of the hydrogen release rate on the ion bombarding current suggests that molecular formation is by direct hydrogen abstraction instead of recombination of two free hydrogen atoms. A dynamic model of hydrogen release and retention for a-C:H layers during hydrogen implantation is proposed. Corresponding calculations yield satisfactory agreement with observations when using appropriate rate constants for trapping and detrapping.
Use of superlattices to realize inverted GaAs/AlGaAs heterojunctions with low-temperature mobility of 2×106 cm2/V s
Authors: Sajoto T. , Santos M. , Heremans J. J. , Shayegan M. , Heiblum M. , Weckwerth M. V. , Meirav U.
Published: July 2002

Reproducible realization of high quality inverted interfaces (GaAs on AlGaAs) grown by molecular beam epitaxy is reported. Effective use of thin-layer GaAs/AlAs superlattices in place of an AlGaAs barrier was made to reduce the number of impurities and the roughness at these interfaces. The low-temperature (≂4 K) mobility for electrons at these interfaces is as high as 2×106 cm2/V s for an electron density of ≂5×1011 cm−2—a factor of four improvement over the highest mobility reported for inverted interfaces.
Molecular beam epitaxy growth of InSb films on GaAs
Authors: Davis John L. , Thompson Phillip E.
Published: July 2002

InSb films have been grown by molecular beam epitaxy on GaAs substrates. The procedure incorporated a low-temperature (300 °C) growth of a thin (300 Å) InSb interface layer prior to the InSb active layer growth at 380 °C. A beam equivalent pressure ratio of Sb4 to In of 4 led to samples with the highest 77 K Hall mobilities. Hall mobilities in excess of 35 000 cm2 /V s at 77 K and x-ray rocking curve widths less than 250 arcsec are routinely achieved in films 2–5 μm thick. The 77 K Hall electron mobilities are a factor of 4 greater than recently reported results. The x-ray rocking curve widths are also substantially less. Possible explanations for the improved film properties are discussed.
Magnetic hardening of Nd2(CoxFe1−x)14B systems
Authors: Fuerst C. D. , Herbst J. F.
Published: July 2002

We report the results of a systematic effort to optimize the hard magnetic properties of melt-spun ribbons containing the pseudoternary compound Nd2(CoxFe1−x)14B as the principal constituent. Cobalt concentrations x=0, 0.25, 0.50, 0.75, and 1 were examined. For each x the ingot composition was varied so as to maximize the energy product of rapidly solidified ribbons. We find that the optimum composition, especially the boron content, is sensitively dependent on x, a result of technological significance.
Fast diffusers Cu and Ni as the origin of electrical activity in a silicon grain boundary
Authors: Maurice J.-L. , Colliex C.
Published: July 2002

Grain boundary (GB) electrical activity is increased by heat treatment in silicon; the origin of the phenomenon is a subject of controversy and is often attributed to oxide precipitation. This letter presents microanalytical results (conventional and scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and electron energy loss spectroscopy), obtained on a Σ=25 bicrystal before and after annealing in sealed ampoules at 900 °C. The enhancement of the electrical activity, confirmed by electron beam induced current and deep level transient spectroscopy, is shown to appear at the boundary simultaneously with precipitates containing copper and nickel. The major role of the fast diffusing 3d metals on the GB electrical properties is demonstrated.
Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1−xAs
Authors: Zarem H. A. , Lebens J. A. , Nordstrom K. B. , Sercel P. C. , Sanders S. , Eng L. E. , Yariv A. , Vahala K. J.
Published: July 2002

The ambipolar diffusion length and carrier lifetime are measured in AlxGa1−xAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented.
Impurity induced disordered quantum well heterostructure stripe geometry lasers by MeV oxygen implantation
Authors: Bryan R. P. , Coleman J. J. , Miller L. M. , Givens M. E. , Averback R. S. , Klatt J. L.
Published: July 2002

Data are presented on stripe geometry AlGaAs-GaAs graded barrier quantum well heterostructure lasers formed by MeV oxygen implantation and annealing. Low-dose implants are found to suppress lateral carrier diffusion but do not result in compositional disordering. High-dose implants form both a semi-insulating and a compositionally disordered region leading to index-guided buried-heterostructure laser operation. However, the concentration of oxygen which spreads laterally under the implantation mask during high-dose implants is sufficient to partially compensate the stripe region for narrow stripe widths and thereby significantly increases the threshold current.
Interband tunneling in polytype GaSb/AlSb/InAs heterostructures
Authors: Luo L. F. , Beresford R. , Wang W. I.
Published: July 2002

Polytype heterostructures of GaSb/AlSb/InAs show interband tunneling due to the 0.1 eV overlap of the InAs conduction band and the GaSb valence band. This broken-gap configuration results in a novel mechanism for negative differential resistance that has potential applications in high-speed devices. We have demonstrated for the first time interband tunneling in single-barrier and double-barrier polytype heterostructures. Single-barrier structures show negative differential resistance due to the change in interband tunneling with applied bias. A peak-to-valley ratio of 2.7:1 at 77 K was observed in this case. Double-barrier structures using an InAs quantum well exhibit resonant interband tunneling with a peak-to-valley current ratio of more than 60:1 at 77 K. This structure is promising for applications to three-terminal devices because of the very wide quantum well that can be achieved.
Calculation of two-dimensional quantum-confined structures using the finite element method
Authors: Kojima Keisuke , Mitsunaga Kazumasa , Kyuma Kazuo
Published: July 2002

The finite element method was used for calculating the wave functions and energy levels of electrons in arbitrarily shaped two-dimensional quantum-confined structures. The calculated results indicate the possibility of quasi-quantum wires by simply growing single quantum wells on corrugated substrates.
Density of electronic states in a biased resonant tunneling structure
Authors: Pandey L. N. , Sahu D. , George Thomas F.
Published: July 2002

We calculate the change in the density of states due to a biased resonant tunneling structure. The maximum of the density of states near resonance gets shifted towards the low-energy side compared to the unbiased case, as does the transmission coefficient, although the two need not be identical. For the case of asymmetric barrier heights, the left-right symmetry of the density of states is broken when the field is nonvanishing.
Dislocation generation of GaAs on Si in the cooling stage
Authors: Tachikawa Masami , Mori Hidefumi
Published: July 2002

I n situ measurements are carried out for the etch pit density (EPD) of GaAs on Si at growth temperature using a newly developed HCl-GaCL vapor phase etching method. The EPD obtained is 4×104 cm−2 at growth temperature. However, after the temperature cools down to room temperature, the EPD is 8×106 cm−2 using molten KOH etching. GaP on Si is also carried out, and almost the same result is obtained; that around 107 cm−2 dislocations are generated in the cooling stage. This is the first evidence that thermal stress in the cooling stage determines the quality of GaAs and GaP heteroepitaxial layers on Si.
Band-gap narrowing in ordered and disordered semiconductor alloys
Authors: Wei S.-H. , Zunger Alex
Published: July 2002

Either spontaneous or artificial ordering of semiconductor alloys into CuAu-like, chalcopyrite, or CuPt-like structures is predicted to be accompanied by a reduction in the direct band gaps relative to the average over the binaries. In this letter calculated results are presented for seven III-V and II-VI alloys. We identify the mechanism for this band-gap narrowing as band folding followed by repulsion between the folded states. The latter is coupled by the non-zinc-blende component of the superlattice potential. The same physical mechanism (but to a different extent) is responsible for gap bowing in disordered alloys.
Si(100)-(2×1)boron reconstruction: Self-limiting monolayer doping
Authors: Headrick R. L. , Weir B. E. , Levi A. F. J. , Eaglesham D. J. , Feldman L. C.
Published: July 2002

A (2×1) surface reconstruction distinct from the clean Si(100)-(2×1) surface is formed by depositing boron onto silicon in ultrahigh vacuum. Overgrowth of epitaxial silicon at low temperature preserves a (2×1) superstructure of substitutional boron. Hall-effect measurements at 4.2 K show complete electrical activity for boron coverages of 1/2 monolayer, but additional boron above 1/2 monolayer is not electrically active.
Implantation profile of low-energy positrons in solids
Authors: Asoka-Kumar P. , Lynn K. G.
Published: July 2002

A simple form for an implantation profile of monoenergetic, low-energy (1–10 keV) positrons in solids is presented. Materials studied include aluminum, copper, molybdenum, palladium, and gold with atomic number ranging from 13 to 79. A simple set of parameters can describe the currently used Makhov profile in slow positron studies of solids. We provide curves and tables for the parameters that can be used to describe the implantation profiles of positrons in any material with atomic number in between 13 and 79.
ZnSe field-effect transistors
Authors: Dreifus D. L. , Sneed B. P. , Ren J. , Cook J. W. , Schetzina J. F. , Kolbas R. M.
Published: July 2002

We report the first demonstration of ZnSe metal-semiconductor field-effect transistors. These new devices were fabricated from n-type Cl-doped epitaxial ZnSe layers grown by molecular beam epitaxy on (100) oriented semi-insulating Cr-doped GaAs substrates. Epitaxial layers with room-temperature carrier concentrations of 1.6×1017 cm−3 and electron mobilities ranging from 400 to 500 cm2/V s were used for device fabrication. Au was used as a Schottky gate contact. Either In or a multilevel metallization scheme using Cr and In was employed for the source and drain ohmic contacts. Depletion-mode transistor operation was observed for structures with 5 and 100 μm gate lengths and varying gate widths. The 5 μm gate length by 200 μm gate width device structures exhibited transconductances of 0.5 mS/mm.
Barrier height variation in Al/GaAs Schottky diodes with a thin silicon interfacial layer
Authors: Costa J. C. , Williamson F. , Miller T. J. , Beyzavi K. , Nathan M. I. , Mui D. S. L. , Strite S. , Morkoç H.
Published: July 2002

Al/n-GaAs and Al/Si/n-GaAs structures with thin silicon interfacial layers were grown in situ by molecular beam epitaxy and their electrical characteristics were measured. Effective barrier heights between 0.30 and 1.04 eV were determined through I-V and C-V measurements in the Al/Si/n-GaAs structures under varying conditions of deposition of the silicon layer, in contrast to a barrier height of 0.78 eV without the silicon layer. The conduction-band offset between Si and GaAs is estimated to be of the order of 0.3±0.05 eV. The results indicate that the Fermi level at the interface of GaAs on Si in the Al/Si/n-GaAs structure is unpinned from its midgap value.
Optimization of barrier thickness for efficient carrier capture in graded-index and separate-confinement multiple quantum well lasers
Authors: Blom P. W. M. , Haverkort J. E. M. , Wolter J. H.
Published: July 2002

We present results from numerical calculations on the carrier capture efficiency in separate- confinement and graded-index separate-confinement multiple quantum well (MQW) lasers. We find that the capture time oscillates as a function of the well width as well as the barrier width between the wells, due to a changing overlap of the barrier wave functions with the bound states in the wells. We show that one order of magnitude improvement in the carrier capture efficiency can be accomplished by properly choosing the dimensions of the layers in the active region of the MQW laser.
Very high carbon incorporation in metalorganic vapor phase epitaxy of heavily doped p-type GaAs
Authors: Hanna M. C. , Lu Z. H. , Majerfeld A.
Published: July 2002

Very high C incorporation (≳1020 cm−3) in GaAs was achieved by atmospheric pressure metalorganic vapor phase epitaxy (AP-MOVPE) using CCl4 as a dopant gas. Hole densities up to p=1.2×1020 cm−3 (at least three times higher than previously reported by MOVPE) were obtained at a growth temperature of 600 °C and a V/III ratio of 2.8. The highest atomic C concentration was 1.5×1020 cm−3. The hole mobilities were ∼50% larger than previously reported. CCl4 was found to suppress the formation of gallium droplets and whisker growth which normally occur under low-temperature, low V/III ratio growth conditions, allowing the growth of thin (<1 μm) heavily doped layers with mirror-like surface morphologies. Layers with p∼1×1020 cm−3 showed a lattice contraction with Δa/a=−9.3×10−4. Photoluminescence studies indicate a significant band-gap shrinkage at high doping levels.
Robust infrared gratings in photorefractive quantum wells generated by an above-band-gap laser
Authors: Nolte D. D. , Wang Q. , Melloch M. R.
Published: July 2002

Probe beam intensities more than an order of magnitude larger than pump beam intensities do not erase photorefractive gratings during nondegenerate four-wave mixing in photorefractive GaAs/AlGaAs quantum wells. The pump and probe laser wavelengths are absorbed in spatially separated regions of the multilayer structure. The photoconductivity of a probe beam around 840 nm is confined to the GaAs quantum wells and cannot easily erase the trapped space-charge gratings in the AlGaAs barriers written by an above-band-gap HeNe laser at 633 nm. This allows a weak visible control beam to modulate a strong infrared signal beam.
X-ray analysis of GaAs layers on GaAs(001) and GaAs(111)B surfaces grown at low temperatures by molecular beam epitaxy
Authors: Capano M. A. , Yen M. Y. , Eyink K. G. , Haas T. W.
Published: July 2002

We report on the simultaneous, molecular beam epitaxy growth of GaAs on GaAs(001) and GaAs(111)B substrates at low temperatures. The crystallinity of the low-temperature GaAs layers was assessed using a double-crystal x-ray diffractometer and a wide-angle diffractometer with a rotating specimen stage. Layers were grown at 200 and 250 °C to a thickness of 3 μm on both (001) and (111) orientated substrates and an additional 3 μm layer was grown on GaAs(111)B at 300 °C. Double-crystal diffractometry confirmed the presence of a single crystalline layer, with a growth-temperature-dependent excess As concentration, on the (001) substrates. On the (111) substrates, only a polycrystalline layer was observed. A possible explanation for these observations based on growth surface roughening is presented.
Density of states distribution in diamond thin films
Authors: Mort J. , Machonkin M. A. , Okumura K.
Published: July 2002

Space-charge-limited hole currents in nominally undoped diamond thin films have been studied using thin, highly boron-doped (p+) diamond layers as injecting contacts. The results obtained from these p+-p-Si structures have been analyzed to determine, for the first time, the bulk distribution of localized states N(E) in polycrystalline diamond thin films. The values of N(E), covering an energy range of about 0.8–0.6 eV above the valence band, indicate that the density of states at 0.8 eV is about 1015 cm−3 eV−1 but rises rapidly, within the 0.2 eV, to about 1018 cm−3 eV−1.
Use of a valved, solid phosphorus source for the growth of Ga0.5In0.5P and Al0.5In0.5P by molecular beam epitaxy
Authors: Wicks G. W. , Koch M. W. , Varriano J. A. , Johnson F. G. , Wie C. R. , Kim H. M. , Colombo P.
Published: July 2002

We report on a new method for the generation of phosphorus beams in molecular beam epitaxy: the use of a valved, solid cracker source. The valved solid source avoids previous difficulties associated with the use of solid phosphorus, and provides an attractive alternative to the use of phosphine. The use of red phosphorus does not interfere with the subsequent growth of high quality arsenides in the same growth chamber. The performance of this valved phosphorus source is illustrated by the growth of two ternary phosphides, Ga0.5In0.5P and Al0.5In0.5P. The quality of the phosphides reported here is comparable to the best results reported by other growth techniques. The effects of composition, growth temperature, and P2 flux on the films’ characteristics are reported. Indium desorption during growth is found to be substantially greater in AlInP than in GaInP.
Log-periodic antennas for pulsed terahertz radiation
Authors: Dykaar D. R. , Greene B. I. , Federici J. F. , Levi A. F. J. , Pfeiffer L. N. , Kopf R. F.
Published: July 2002

A new type of log-periodic antenna, the wire log-spiral, has been designed and implemented on GaAs substrates with low-temperature grown GaAs photoconductors. The new antenna is compared to two traditional antenna designs (log-periodic and dipole) used for the detection of pulsed THz radiation.
Correlation of texture with electromigration behavior in Al metallization
Authors: Knorr D. B. , Tracy D. P. , Rodbell K. P.
Published: July 2002

Aluminum films deposited at three different conditions, such that texture is the only microstructural variable, were tested for electromigration behavior. Texture analysis shows that random and (111) fiber texture components are present in the films deposited by both partially ionized beam (PIB), physical vapor deposition and sputtering. Two parameters are required to properly quantify the texture: (111) volume fraction and the distribution (half-width) of the (111) fiber component. As the (111) texture becomes stronger, the median time to failure increases, while the failure standard deviation decreases. Previous texture correlations are based on incomplete information, so they cannot predict electromigration behavior in all cases.
Involvement of the topmost Ge layer in the Ge surface segregation during Si/Ge heterostructure formation
Authors: Fujita K. , Fukatsu S. , Yaguchi H. , Shiraki Y. , Ito R.
Published: July 2002

Surface segregation of Ge atoms during Si/Ge heterostructure formation by molecular beam epitaxy has been investigated by x-ray photoemission spectroscopy varying the Ge layer thickness. It has been found that only the Ge atoms of the topmost layer are involved in the surface segregation, leaving the rest of the Ge atoms intact. This result supports the basic idea of the two-state-exchange model.
Local mirror temperatures of red-emitting (Al)GaInP quantum-well laser diodes by Raman scattering and reflectance modulation measurements
Authors: Epperlein P. W. , Bona G. L. , Roentgen P.
Published: July 2002

Temperature rises were measured on cleaved, uncoated mirror facets of junction-side-up mounted (Al)GaInP laser diodes as a function of the injection current by Raman spectroscopy via the Stokes/anti-Stokes phonon line intensity ratio and the phonon line shift as well as by reflectance modulation as a novel application for laser mirror characterization. Below the threshold current the temperature rise is due to Joule heating of the drive current across the ohmic resistor and is ΔT≂35 K at threshold. Above threshold a significant power-dependent heating caused by absorption of laser radiation is superimposed. In this regime the temperature increase is considerably high, i.e., ΔT≥100 K at 4 mW for 5-μm-wide ridge lasers. The different measurement techniques have produced consistent data.
Resonant tunneling in coupled quantum dots
Authors: Tewordt M. , Asahi H. , Law V. J. , Syme R. T. , Kelly M. J. , Ritchie D. A. , Churchill A. , Frost J. E. F. , Hughes R. H. , Jones G. A. C.
Published: July 2002

Resonant tunneling in GaAs-AlGaAs triple barrier diodes is studied as a function of the diode diameter between d=8 μm and d=100 nm. We observe, only in the very small diodes, a novel spikelike fine structure in the current-voltage characteristics within the conventional resonant tunneling peaks. These spikes are assigned to resonant tunneling between coupled quantum dots. Furthermore, a much stronger quenching of the conventional resonance peaks at lower bias is observed with decreasing diode diameters as compared to the higher bias peaks. This effect is clearly reproducible and may be an indication that the low bias peaks employ different tunneling mechanisms than the high bias peaks.
Luminescence and Raman measurements of InyGa1−yP (0.3<y<0.5) grown by gas-source molecular beam epitaxy
Authors: Zachau M. , Masselink W. T.
Published: July 2002

We have measured the luminescence, luminescence excitation, and Raman spectra of undoped InyGa1−yP (0.3<y<0.5) films grown by gas-source molecular beam epitaxy on GaAs substrates. We observe strong excitonic luminescence over the entire composition range investigated. The band gap derived from the luminescence excitation spectra corresponds to that of a fully relaxed InGaP film with no residual strain, which is confirmed by the Raman measurements. The dependencies of the Raman modes on alloy composition and ordering effects are discussed.
Effect of oxygen on boron doping in chemical vapor deposition of diamond as deduced from cathodoluminescence studies
Authors: Ruan J. , Kobashi K. , Choyke W. J.
Published: July 2002

Diamond films were grown using microwave-plasma enhanced chemical vapor deposition. Boron doping in these films were achieved by using 0–1 ppm diborane (B2H6) in the reaction gas mixture during the deposition process. Some samples were deposited using 0.1% oxygen in the reaction gas mixture. We have employed cathodoluminescence to analyze the deposited diamond films and found that the boron concentration in diamond films is significantly reduced when oxygen was used in the deposition. For example, our result indicates that the boron concentration in films doped with 1.0 ppm B2H6 with the addition of 0.1% oxygen is close to that of films doped with 0.01 ppm B2H6 without using oxygen. Therefore, the probability of boron incorporation in diamond films is reduced by a factor of roughly 100 when 0.1% oxygen is used compared with the case where no oxygen is used.
Practical adaptation in bulk superconducting magnetic bearing applications
Authors: McMichael C. K. , Ma K. B. , Lamb M. A. , Lin M. W. , Chow L. , Meng R. L. , Hor P. H. , Chu W. K.
Published: July 2002

Lifting capacities greater than 41 N/cm2 (60 psi) at 77 K have been achieved using a combination of permanent magnets and high quality melt-textured YBa2Cu3O7−δ (YBCO). The key concept of this hybrid superconducting magnetic bearing (HSMB) is the use of strong magnetic repulsion and attraction from permanent magnets to support high loads in conjunction with flux pinning in a type II superconductor to counteract instabilities in a system consisting of magnets only. To illustrate this concept, radial and axial forces between magnet/superconductor, magnet/magnet, and magnet/superconductor/magnet, were measured and compared for the thrust and journal bearing configurations on a bearing prototype.
Silver on diamond Schottky diodes formed on boron doped hot-filament chemical vapor deposited polycrystalline diamond films
Authors: Zhao G. , Stacy T. , Charlson E. J. , Charlson E. M. , Chao C. H. , Hajsaid M. , Meese J. , Popovici G. , Prelas M.
Published: July 2002

Schottky diodes were fabricated using sputter deposited silver contacts to boron doped polycrystalline diamond thin films grown by a hot-filament chemical vapor deposition process with trimethyl borate as an in situ dopant source. High forward current density and a high forward-to-reverse current ratio were exhibited by these diodes. Current density-voltage and capacitance-voltage-frequency characteristics of these diodes are very similar to those of Schottky diodes fabricated using a single-crystal diamond substrate.
Graded band gap ohmic contact to p-ZnSe
Authors: Fan Y. , Han J. , He L. , Saraie J. , Gunshor R. L. , Hagerott M. , Jeon H. , Nurmikko A. V. , Hua G. C. , Otsuka N.
Published: July 2002

We describe a low-resistance quasi-ohmic contact to p-ZnSe which involves the injection of holes from heavily doped ZnTe into ZnSe via a Zn(Se,Te) pseudograded band gap region. The specific contact resistance is measured to be in the range of 2–8×10−3 Ω cm2. The graded heterostructure scheme is incorporated as an efficient injector of holes for laser diode and light emitting diode devices, demonstrating the usefulness of this new contact scheme at actual device current densities.
Lattice disorder, facet heating and catastrophic optical mirror damage of AlGaAs quantum well lasers
Authors: Epperlein P. W. , Buchmann P. , Jakubowicz A.
Published: July 2002

Raman microprobe spectra from dry-etched, coated (110) AlGaAs single quantum well laser mirrors show, apart from the allowed phonon modes, a series of symmetry forbidden modes whose strength is dependent on the mirror treatment prior to coating. A particularly strong mode at 193 cm−1 can be attributed to disorder activated longitudinal acoustic phonon scattering in addition to—and this is new—the Eg-mode of elemental arsenic. The existence of lattice disorder and arsenic clusters is confirmed by Rayleigh scattering and energy dispersive x-ray spectroscopy. The optical power level at catastrophic optical mirror damage and the local mirror temperatures of the biased laser are found to have a strong dependence on mirror disorder.
Silicon solar cell of 16.8 μm thickness and 14.7% efficiency
Authors: Werner Jürgen H. , Kolodinski Sabine , Rau Uwe , Arch John K. , Bauser Elisabeth
Published: July 2002

Liquid phase epitaxy provides a new impetus for thin film photovoltaics based on silicon; we apply this method for about 20-μm-thick solar cells with high efficiencies. The analysis of internal quantum efficiency measurements reveals that the open circuit voltages around 660 mV arise from an excellent electronic quality of our thin silicon films. Their effective minority carrier diffusion lengths range up to 317 μm, a value that exceeds the thickness of the layers by an order of magnitude. The conversion efficiencies exceed 14% with a record value of 14.7% for a 16.8-μm-thick epitaxial layer without special antireflecting coatings. The high open circuit voltages promise a possible boost of the efficiency toward 20% by applying light trapping schemes to optimize the short circuit current.
Determination of silicon point defect properties from oxidation enhanced diffusion of buried layers
Authors: Agarwal Anuradha M. , Dunham Scott T.
Published: July 2002

In order to characterize fundamental silicon point defect properties, the enhanced diffusion of phosphorous buried layers as a function of depth into the silicon substrate was measured during interstitial injection via thermal oxidation of the wafer surface. The measurements were used to calculate the effective interstitial diffusivity in epitaxial silicon at 1100 °C. The experimental results were also interpreted using a physical model which includes bulk recombination of interstitials with vacancies and a fast interstitial diffusivity calculated from metal gettering. The model effectively accounted for the experimental data, and through comparison of the data with model simulations, the ratio of the concentrations of vacancies and interstitials in equilibrium was obtained.
Iron detection in the part per quadrillion range in silicon using surface photovoltage and photodissociation of iron-boron pairs
Authors: Lagowski J. , Edelman P. , Kontkiewicz A. M. , Milic O. , Henley W. , Dexter M. , Jastrzebski L. , Hoff A. M.
Published: July 2002

The photodissociation of iron-boron pairs in p-type silicon produces lifetime killing interstitial iron and may be combined with noncontact surface photovoltage (SPV) measurement of the minority carrier diffusion length to achieve fast detection of iron. We found that, for iron concentrations ranging from 8×108 to 1×1013 atoms/cm3, the pair dissociation using a white light (10 W/cm2) was completed within 15 s. Surface recombination was a major rate limiting factor. Passivation of the surface enhanced the rate by as much as a factor of 20. The photodissociation rate increased with increasing temperature, however, the increase was smaller than that of the thermal dissociation rate. These characteristics are consistent with a previously proposed recombination enhanced dissociation mechanism. For practical iron detection, it is important that the detection limit of the approach is close to one part per quadrillion.
Observation of intrinsic tristability in a resonant tunneling structure
Authors: Martin A. D. , Lerch M. L. F. , Simmonds P. E. , Eaves L.
Published: July 2002

A new technique has been developed to probe the region of apparent bistability due to a tunneling resonance in the characteristic of a semiconductor asymmetric double-barrier structure. The measuring circuit uses a voltage supply designed to have a load line with positive slope, equivalent to a voltage source and negative series resistance. The appearance of bistability and hysteresis in the characteristic is an artifact of the conventional measuring technique, which employs a load line with negative slope. The complete characteristic is found to be a continuous Z-shaped curve between 50 and 150 K, corresponding to tristability. Equivalent circuit models for the device and voltage supply predict a narrow range of circuit parameters for which a static operating point exists inside the tristable region.
Magnetic and magneto-optic properties of thick face-centered-cubic Co single-crystal films
Authors: Suzuki T. , Weller D. , Chang C.-A. , Savoy R. , Huang T. , Gurney B. A. , Speriosu V.
Published: July 2002

The present letter describes for the first time the magnetic and magneto-optical properties of thick fcc cobalt single-crystal films (≂1000-Å thickness). The magneto-crystalline anisotropy constants K1 and K2 are about −7.2×10 erg/cc and 2×10 erg/cc at 77 K, respectively. Both decrease in magnitude with increasing temperature in a range from 77 K to about 450 K. The easy axis is found to be 〈111〉. The polar Kerr angle for the fcc phase is much larger than that of the hcp phase by 0.1°–0.2° in a photon energy range from about 1 to 5 eV.
In situ laser-induced fluorescence studies of laser chemical vapor deposition of TiN thin films
Authors: Chen Xiangli , Mazumder Jyoti
Published: July 2002

TiN films are deposited on Si(100) from a reactant gas mixture of TiCl4, N2, and H2 by chemical vapor deposition with a CO2 laser. Pulsed dye laser-induced fluorescence spectroscopy is applied to obtain gas phase species concentration during deposition in order to study the reaction and film growth mechanisms. Ti atomic species are found close to the substrate surface with concentrations in the order of 1011 cm−3.
Writing erasable metallic patterns in insulating AlxGa1−xAs:DX
Authors: Thio Tineke , Linke R. A. , Devlin G. E. , Bennett J. W. , Chadi James D. , Mizuta M.
Published: July 2002

We have optically written persistent but erasable metallic features in insulating epilayers of AlxGa1−xAs doped with Si and Se, which form DX centers. The photocarriers, which remain in the AlxGa1−xAs layer, move freely in the conduction band but are confined to the exposed regions. We demonstrate this confinement by optical excitation in a striped pattern; the resulting modulation of the free carrier density is evinced by an anisotropy of the sample conductance parallel and perpendicular to the stripes. The anisotropy, like the photoconductivity itself, is persistent at low temperatures. Erasure is achieved by thermal annealing. We estimate that features can be written with better than 1000 Å resolution.
Photoluminescence studies of porous silicon carbide
Authors: Konstantinov A. O. , Henry A. , Harris C. I. , Janzén E.
Published: July 2002

A detailed investigation of the dependence of the photoluminescence from porous silicon carbide on preparation conditions and starting material is presented. Porous silicon carbide prepared from different polytypes shows almost identical emission spectra, demonstrating a clear impedance of the band-gap energy of a particular SiC polytype. Emission bands with peak energies of 2.43, 2.22, 2.07, and 1.93 eV were resolved with the use of selective excitation by tuning the excitation wavelength. The origin of luminescence is suggested to relate to defect states produced at the etched surface.