bluuebunny/crossref_metadata_2025 huggingface dataset:
Intergenerational Transfer of Ethnic Medicine Knowledge by Tribal Communities of Malappuram District in Kerala, India
Authors: Shamna N. , Krishnankutty M. Jayasree , Sindhu P. V.
Published: June 2022

The present study aimed to study the intergenerational transfer of the ethnic medicines related knowledge among the tribes people of Kerala. The study was conducted among three tribal communities in the Malappuram district of Kerala, a district that has a high number of tribal communities. Paniyans, Aranadans, and  Kattunaikkans are the predominant tribal communities in Malappuram. These communities are living on the fringes of Nilambur forests and depend on the forest for their livelihood.  The study showed that 36.7% of elderly tribespeople have ethnic medicine knowledge compared to middle-aged (27.54%) and young people (26. 15%). Further, the young tribespeople shared about 97 citations (single or combinations of medicinal plants to treat a particular ailment/ for a single health condition), making an average of 5.7 citations per young person. Middle-aged tribespeople shared a total of 87 citations, which created an average of 4.58 citations per middle-aged person. And among the elderly category, they shared about 144 citations, which made the largest average citation of 8.47 among all the three age categories. The respondents with ethnic medicine knowledge were further asked whether they were ready to pass this knowledge to the next generation or not. The majority (51%) of respondents responded that they would pass the knowledge to the next generation only if they showed interest in it. 41.5% of the respondents expressed that they are ready to pass their knowledge to the next generation, and 8 percent of the respondents would never pass their knowledge to the next generation. A chi-square test was done to know the significance of the relationship between age and readiness.

The test revealed that there is a significant relationship between the variable's age and their readiness to share their ethnic medicine knowledge. That is, the elderly tribal people are less ready to share their ethnic medicine knowledge with others. The study also documented the ethnic medicine knowledge of the tribal respondents in three age groups. It was found that the old age tribes people know the usage of 75 plant species to cure various diseases and also for different health conditions, whereas the middle-aged group of tribespeople expressed about 44 plants and young people shared only 30 plants. The study indicated that the ethnic medicine knowledge of tribespeople is decreasing from the old generation to the young generation. Serious efforts should be taken to conserve this valuable knowledge.
A Conceptual Framework to Measure the Relationship between Social Media and the Decision-Making Process of Plastic Surgery Consumers in Jordan
Authors: Kassab Abeer , Masoud Emad
Published: June 2022

Aims: This article describes a unifying conceptual framework to measure the impact of social media on the decision-making process of plastic surgery consumers.

Methodology: A conceptual framework for the plastic surgery consumers was developed based on the work of (Blakey, 2011; Schwarz et al., 2013; and Roberts & Lilien, 1993), and a conceptual model was previously developed by Akar et al. (2015).

Results: The conceptual framework consists of three components that can be considered in relationship to each other: Social Media, Social Influence Process, and Decision-Making. Although the availability of measures for each of these components varies, the framework can be used to examine the relationship between Social Media and the Decision-Making Process of Plastic Surgery Consumers in Jordan.

Conclusion: A conceptual framework that illustrates the relationships between social media and the decision-making process is an essential step toward providing a scientific base for studying plastic surgery consumers in Jordan.
N, P and K Uptake by Crop and Weed as Influenced by Nutrient Levels and Weed Management in Mustard
Authors: Tyagi Shashank , Kumar Arun , Paul S.C. , Acharya S.S.
Published: June 2022

A field experiment was conducted in Rabi season of 2018-19 and 2019-20 at Research farm of Bihar Agricultural College, Sabour to assess the impact of nutrient and weed management on N, P and K uptake by crop and weed in mustard. This experiment with 3 nutrient levels (N1-soil test-based recommended dose of fertilizer (RDF), N2-100 % RDF, N3-125 % RDF) in main plot; 8 weed management (W1-Weedy, W2-Hand weeding (HW), W3-pendimethalin, W4-pendimethalin followed by (fb) quizalofop, W5-pendimethalin fb clodinafop, W6-oxyflourfen, W7-oxyflourfen fb quizalofop, W8-oxyflourfen fb clodinafop) in sub plots, laid in split plot design. Results indicated that in 2018-19, N, P and K uptake by mustard was found maximum under 125% RDF. Hand weeding exhibited highest N, P and K uptake by crop over weedy. Among herbicides, maximum N, P and K uptake by crop was noted with pendimethalin 30 EC 1.0 kg a.i. ha-1 PE fb quizalofop 5 EC 60 g a.i. ha-1 PoE. In 2019-20, hand weeding at 25 and 50 DAS along with 125% RDF exhibited highest N, P and K uptake by crop. Among herbicides, application of pendimethalin 30 EC 1.0 kg a.i. ha-1 PE fb quizalofop 5 EC 60 g a.i. ha-1 PoE along with 125% RDF exhibited highest N, P and K uptake by the crop. In both the years 2018-19 and 2019-20, hand weeding at 25 and 50 DAS along with 125% RDF exhibited N uptake by weeds, zero value being lower than weedy. In 2018-19, application of pendimethalin 30 EC 1.0 kg a.i. ha-1 PE fb quizalofop 5 EC 60 g a.i. ha-1 PoE along with 125% RDF exhibited the lowest N and K uptake by weeds. Among nutrient levels, application of 125% RDF exhibited the lowest P uptake by weeds, however, among herbicides; application of pendimethalin 30 EC 1.0 kg a.i. ha-1 PE fb quizalofop 5 EC 60 g a.i. ha-1 PoE registered the lowest P uptake by weeds. In 2019-20, application of pendimethalin 30 EC 1.0 kg a.i. ha-1 PE fb quizalofop 5 EC 60 g a.i. ha-1 PoE along with 125% RDF exhibited the lowest N, P and K uptake by weeds. Thus it was concluded that pendimethalin 1.0 kg a.i. ha-1 PE fb quizalofop 60 g a.i. ha-1 PoE along with 125% RDF (100:50:50:25:6.25 kg NPKSZn ha-1) enhanced N, P and K uptake by crop though hand weeding at 25 and 50 DAS along with 125% RDF (100:50:50:25:6.25 kg NPKSZn ha-1) exhibited significant improvement in nutrient uptake by crop.
Research on Psychology Evaluation Method of Nuclear Power Plant Operators
Authors: Fang Xiang , Fang Jingxuan
Published: June 2022

Nuclear power plant operators play a more and more important part to plant safe operation. The paper analyzes and discusses the qualitative and quantitative evaluation methods for the operators. The comparison-analysis of the scope and result of application has been done between the method of outline figure fitted and the method of fuzzy synthetic evaluation. The research can be referenced in the evaluation of operators.
Dissection of the maturation reactions of the [NiFe] hydrogenase 3 from Escherichia coli taking place after nickel incorporation
Authors: Magalon Axel , Böck August
Published: July 2002

The steps in the maturation of the precursor of the large subunit (pre‐HycE) of hydrogenase 3 from Escherichia coli taking place after incorporation of both iron and nickel were investigated. Pre‐HycE could be matured and processed in the absence of the small subunit but association with the cytoplasmic membrane required heterodimer formation between the two subunits. Pre‐HycE formed a complex with the chaperone‐like protein HypC in the absence of the small subunit and, in this complex, also incorporated nickel. For the C‐terminal processing, HypC had to leave the complex since only a HypC‐free, nickel‐containing form of pre‐HycE was a substrate for the maturation endopeptidase.
VIP and the potent analog, stearyl‐Nle17‐VIP, induce proliferation of keratinocytes
Authors: Granoth Ruth , Fridkin Mati , Gozes Illana
Published: July 2002

Vasoactive intestinal polypeptide (VIP) exhibits effects on cell proliferation. Here, VIP, as well as the related peptide, pituitary adenylate cyclase activating peptide (PACAP), promoted human keratinocyte division. Stearyl‐Nle17‐VIP (SNV) was identified as a superior mitogen for the keratinocytic cell line, HaCaT, both in potency (fM–nM concentrations) and efficacy. Reverse transcription‐polymerase chain reaction detected in keratinocytes only PACAP mRNA and the relevant type 1 (VPAC1R) and type 2 (VPAC2R) receptors, while VIP and the third receptor (PAC1) transcripts were absent. Upon serum deprivation of HaCaT, the VPAC1R mRNA was apparently increased, while the VPAC2R transcript remained constant. Incubation of HaCaT with VIP or SNV increased nitric oxide and cGMP formation. In contrast to VIP, SNV did not augment cAMP. Thus, the paracrine VIP, and autocrine PACAP, related pathways leading to keratinocyte proliferation may involve VPAC1R/VPAC2R and nitric oxide/cGMP production.
Novel approaches to retard ventricular remodeling in heart failure
Authors: Spinale Francis G.
Published: July 2002

While the etiologies of congestive heart failure (CHF) are diverse, a common event in the progression of this disease process is LV remodeling, increased wall stress, and subsequent pump dysfunction. Therapeutic approaches for CHF have been focused upon reducing LV afterload through vasodilator therapy, or by blocking/interrupting the effects of neurohormonal stimuli. However, another therapeutic approach would be to directly intervene in the LV remodeling process with CHF. An important determinant in the maintenance of myocyte shape, alignment and transduction of myocyte shortening into an overall ejection is the structural support provided by the fibrillar collagen matrix. As in most tissue remodeling processes, LV myocardial remodeling with CHF is accompanied by changes in the structure and composition of the collagen matrix. Matrix metalloproteinases (MMPs) are an endogenous family of zinc‐dependent enzymes which have been identified to be responsible for matrix remodeling and alterations in MMP expression and activity have been identified in clinical and animal models of CHF. Moreover, alterations in the tissue inhibitors of MMPs (TIMPs) have also been identified to occur in the end‐stage CHF myocardium. Thus, it is very likely that increased MMP activity and reduced inhibitory control of the TIMPs contribute to the LV remodeling process with CHF. A number of bioactive peptides and cytokines influence MMP and TIMP expression and activity. In addition, pharmacologically active MMP inhibitors have been synthesized and are currently under study. Accordingly, the control of MMP and TIMP expression and activity within the failing myocardium represents a new and potentially significant therapeutic target for CHF.
Characterization of the Chemoenzymatic Synthesis of N‐Acetyl‐d‐neuraminic Acid (Neu5Ac)
Authors: Blayer Simone , Woodley John M. , Lilly Malcolm D. , Dawson Michael J.
Published: July 2002

The characterization of the chemoenzymatic synthesis of N‐acetyl‐d‐neuraminic acid using a base‐catalyzed epimerization and Neu5Ac aldolase‐catalyzed condensation is presented. The characterization has been used to exemplify a structured approach to biotransformation process design. In addition, the option of integration of the epimerization with the biotransformation (at alkaline pH) was considered. Process operating windows have been generated as a result of this approach, defining possible operating regions for subsequent scale‐up.
Selective Precipitation of Antibody with Ligand‐Modified Phospholipids: Effect of Lipid Chain Length
Authors: Kilpatrick Peter K. , Lisi James F. , Carbonell Ruben G.
Published: July 2002

The selective precipitation from aqueous solutions of goat polyclonal anti‐biotin antibody (pABA) by complexation with ligand‐modified phospholipids (LMPs) is described. In this study, the effect of varying the acyl chain length of the LMP from six to 18 carbon atoms on the rate and yield of precipitation is detailed. As the acyl chain length increases, the hydrophobic driving force for interaction of ligand‐bound antibody molecules also increases, resulting in a larger yield of precipitated antibody. The rate of selective precipitation, however, is observed to pass through a sharp maximum at an acyl chain length of 10–12 carbon atoms. In the range of target antibody and LMP concentrations studied (1–10 μM), the maximum rates of precipitation are observed for those LMPs in sufficiently low concentrations in aqueous solution to be below their critical micelle concentration (CMC) . The longer chain length LMPs (12–18 carbon atoms at concentrations of 5–10 μM) gave considerably slower rates of precipitation and were all observed to be micellar solutions. The yield of target antibody as a percentage of antibody precipitated was not observed to pass through a maximum, rather all LMPs with acyl chain lengths longer than 12 carbon atoms were observed to give the maximum yield. Thus the optimal structure of an LMP for precipitation of a target antibody corresponds to the maximum chain length (10 carbon atoms) at a concentration level (5–10 μM) which still falls below its CMC. The kinetics of precipitation, as monitored by measuring turbidity, are well modelled by a theory which combines the Mie theory of light scattering with the Smoluchowski theory for the kinetics of precipitation. The maximum rate constants corresponding to Smoluchowski kinetics for precipitating pABA were approximately 25 000–30 000 M−1 s−1, while the maximum yields were 65–70%. The molecular picture which emerges is one in which the optimal rate is obtained by maximizing hydrophobic driving force for interaction of LMP acyl chains while still maintaining a submicellar state of aggregation.
Characterization of Lactobacillus Carbohydrate Fermentation Activity Using Immobilized Cell Technique
Authors: Cortón Eduardo , Piuri Mariana , Battaglini Fernando , Ruzal Sandra M.
Published: July 2002

A microbial bioreactor based on calcium alginate immobilized Lactobacillus cells coupled to a pH electrode was developed for quantitative determination of carbohydrate fermentation activity. A high biomass (1010 cfu mL−1) and particular pregrowth conditions were needed. Reduction of catabolite repression by monosaccharides was achieved by pregrowth in lactose. The evolution of acid production in a continuous flow‐stopped flow bioreactor was monitored for different sugar solutions in contact with the immobilized bacteria. The resulting slopes (ΔmV/Δt) were used to quantify the fermentation capability for a defined sugar related to that of glucose, which was taken as 100%. The procedure is simple, being based on pH variation that can give quantitative results compared to other reported techniques for carbohydrate fermentation pattern from which only qualitative results are obtained. In addition, it offers reduction in time and costs and is a suitable tool for the rapid analysis of isolated strains and in studies of modifications of sugar metabolism in mutants.
Mediterranean v. continental small mammal communities and the environmental degradation of the Dinaric Alps
Authors: Kryštufek Boris , Griffiths Huw I.
Published: July 2002

In order to test for the existence of distinct, regionally‐based small mammal faunas, distributional patterns were examined in thirty one species of small mammals (insectivores and rodents) inhabiting the Dinaric Alps (western Balkans). The small mammal fauna was found to consist of three groups: a group of ‘generalist’ species that occurred throughout the study area, plus distinct coastal and continental small mammal assemblages. The continental small mammal assemblage is considerably more species‐rich, whilst that of the coastal zone is largely restricted to generalists and species with geophilic or fossorial life‐styles (many of which are also commensal with humans). The two assemblages appear to be associated with different vegetation types, and the transition between them lies on the coastal slopes of the Dinaric Alps at c. 700–900 m of altitude. We discuss possible determinants of assemblage composition and species richness, and particularly the possible role of prehistoric environmental degradation in the context of the reduced species‐richness of the coastal zone.
Opsonization of Toxoplasma gondii tachyzoites with nonspecific immunoglobulins promotes their phagocytosis by macrophages and inhibits their proliferation in nonphagocytic cells in tissue culture
Authors: Vercammen Martine , Scorza Tatiana , El Bouhdidi Ayachi , Van Beeck Kris , Carlier Yves , Dubremetz Jean Francois , Verschueren Hendrik
Published: July 2002

We have recently shown that Toxoplasma gondii tachyzoites grown in in vitro culture can bind unspecific immunoglobulin (Ig) through their Fc moiety. We show now that Fc receptors are also present on T. gondii within the host animal, and that intraperitoneal parasites in immunocompetent mice are saturated with unspecific Ig. We have also investigated the effect of the parasite's Fc receptor on the interaction of tachyzoites with mammalian cells, using the Vero cell line as a model for nonphagocytic host cells and murine peritoneal macrophages in primary culture as a model for phagocytic cells. Coating of tachyzoites with parasite‐unrelated Ig did not enhance their invasive capacity in either target cell type, but slightly decreased the parasite proliferation. Moreover, phagocytosis by macrophages was increased by approximately 50% when parasites were coated with unspecific Ig. These results indicate that the Fc receptor on T. gondii affects the balance between invasion and phagocytosis in a way that is detrimental to the parasites.
Spatial integration of signal information in Gabor stimuli
Authors: Syväjärvi Antti , Näänen Risto , Rovamo Jyrki
Published: July 2002

We studied spatial integration of Gaussian weighted cosine gratings (Gabor gratings) in contrast detection by using a two‐alternative forced‐choice method. The Gabor gratings, which were either complete or sharply truncated to a square shape, were presented either in the presence or absence of static noise. Contrast thresholds were determined for different truncation areas and different widths of the two‐dimensional Gaussian weighting function. Contrast detection performance was found to depend only on the effective spatial spread of the stimuli. The spatial spread is a physical description of signal area, which takes into account the spatial inhomogeneity of the signal. The highest detection efficiencies were obtained when the spatial spread was small independently of whether the stimuli were sharply truncated or complete smooth Gabor gratings. The results show that the contrast detection mechanism takes into account the shape of the signal window and does not collect information outside the area of the signal.
The influence of heterophoria measurements on subsequent associated phoria measurement in a refractive routine
Authors: Brautaset R.L. , Jennings J.A.M.
Published: July 2002

The influence of measuring heterophoria on a subsequent associated phoria measurement was investigated in 50 subjects. After refraction, heterophoria was measured by either von Graefe’s technique or Maddox rod and wing. The effect of these procedures was assessed by associated phoria measurements taken before and after the dissociated measures. It is shown that subjects with a history of unstable binocular vision are likely to have an associate phoria induced or changed by the previous dissociated phoria measurement, particularly if von Graefe’s technique is employed. It is recommended that, especially for near, associated phoria should be assessed before the dissociated phoria in subjects who are regarded as having a history of unstable binocular vision.
C‐Banding Patterns and Quantitative Karyotype Characteristics of Bulgarian Species of Crepis (Asteraceae)
Authors: Dimitrova D. , Greilhuber J.
Published: July 2002

Abstract: Giemsa C‐banded idiograms were established from eight Crepis species of Bulgarian origin (Crepis viscidula, C. paludosa, C. conyzaefolia, C. bithynica var. bithynica and var. fodorii, C. pulchra, C. sancta, C. setosa, and C. zacintha) that had been previously studied for genome size and karyotype shape using classical methods. All taxa are diploids with descending chromosome numbers, x = 6, 5, 4, and 3. Satellites were always heterochromatic. Small but distinct centromeric bands were of general occurrence (except perhaps in C. paludosa) and terminal bands were present at least in some chromosomes of the karyotypes. Higher amounts of heterochromatin in the form of terminal and intercalary bands were found in C. bithynica and C. zacintha, but banding patterns were not so specifically similar as to indicate common origin. There are a number of particular karyotypic characters which may turn out to be phylogenetically significant when corresponding information on many related taxa becomes available. Correlations of karyotypic parameters were calculated. In heterochromatin only percent heterochromatin, but not absolute heterochromatin amount, and genome size were significantly correlated. This is the result of a strong euchromatin variation but independent heterochromatin variation.
Technique for selective etching of Si with respect to Ge
Authors: Bright A. A. , Iyer S. S. , Robey S. W. , Delage S. L.
Published: July 2002

A technique to selectively etch silicon with respect to germanium is described. The method relies on an observed small difference in the effects of polymeric etch-inhibiting layers on the two materials. In a CF4/H2 plasma, the observed polymer point for Ge is 1–3% lower than for Si. This produces a narrow process window in which Si is etched while etching of Ge is suppressed. This technique has applications to etching of pure Si layers over Ge as well as Si-Ge alloys for device applications.
Planar doping with gallium of molecular beam epitaxial ZnSe
Authors: de Miguel J. L. , Shibli S. M. , Tamargo M. C. , Skromme B. J.
Published: July 2002

A new approach to doping in ZnSe, which involves Ga deposition in spatially separated atomic planes (planar doping), is reported. The dependence of doping efficiency on the particular surface termination (Zn or Se stabilized) maintained during the deposition of the Ga dopant is investigated by Hall measurements and low-temperature photoluminescence spectroscopy, and the results are compared to those obtained for uniform doping. Under our growth conditions and for the same average amount of Ga atoms arriving at the ZnSe surface, the doping efficiency is dramatically enhanced in the case of Ga planar doping on Zn terminated surfaces. This enhancement correlates with the reduction of the broad deep luminescence bands that dominate under the other doping conditions, indicating an effective reduction of the self-compensating mechanisms. Under optimized conditions, n-type ZnSe with carrier concentration in the 1018 cm−3 range is achieved.
Application of spectroscopic ellipsometry to complex samples
Authors: Freeouf J. L.
Published: July 2002

Several heterostructure samples of varying complexity were studied by spectroscopic ellipsometry. The analysis of this data, requiring computer modeling for optimum correlation between model and experiment, demonstrates the ability of this technique to apply multiparameter analysis to complex samples. Our results provide an absolute measure of up to seven material parameters, with 90% confidence limits in the range 0.1–2% for at least the four most sensitive parameters. Such accuracies are improved by a factor of 5–10 over previous reports for such complex samples. Furthermore, the method is demonstrated to provide sensitive detection of interfaces, even when buried under ≥0.5 μm of GaAs.
Epitaxy of CoSi2 on Si (111) at low temperature (≤400 °C)
Authors: Haderbache L. , Wetzel P. , Pirri C. , Peruchetti J. C. , Bolmont D. , Gewinner G.
Published: July 2002

The epitaxial growth of thin CoSi2 films on a Si(111) surface has been studied using surface techniques such as low-energy electron diffraction and photoemission spectroscopy. Various preparation methods at low temperature (≤400 °C) are investigated. Both layer by layer growth and coevaporation invariably exhibit a bulk and surface excess of Si. In contrast a different preparation method where the Co atoms were evaporated onto the Si(111) substrate maintained at ∼360 °C produces CoSi2 films exposing a Co-rich CoSi2 surface without any Si excess in bulk. It is concluded from these experiments that at ∼360 °C diffusion of Si from substrate through the CoSi2 layer is much easier than usually expected and quite sufficient to sustain further CoSi2 growth without any extra Si supply.
Spectroscopic analysis of electronically excited species in XeCl excimer laser-induced plasmas from the ablated high-temperature superconductor YBa2Cu3O7
Authors: Auciello O. , Athavale S. , Hankins O. E. , Sito M. , Schreiner A. F. , Biunno N.
Published: July 2002

Optical spectroscopic analyses have been performed to study luminescence from plasmas produced by ablation of YBa2Cu3O7 single-phase high Tc bulk superconductors exposed to XeCl excimer laser (308 nm) pulses. Only excited atomic neutral and single ionized species (Cu/Cu+, Ba/Ba+, Y/Y+) were observed within the experimental resolution of an optical multichannel analyzer detection system, when irradiating the targets in vacuum (∼10−5–10−4 Torr). Conspicuously absent in the spectra (300–800 nm range) are molecular emission bands that would appear if large excited molecules or fragments were present. Implications of the present results are discussed which relate to an early hypothesis about the laser ablation mechanism and their influence on high Tc film characteristics.
Rectangular and L-shaped GaAs/AlGaAs lasers with very high quality etched facets
Authors: Behfar-Rad A. , Wong S. S. , Ballantyne J. M. , Soltz B. A. , Harding C. M.
Published: July 2002

GaAs/AlGaAs semiconductor lasers with very high quality etched facets have been fabricated. Laser facets are formed by the chemically assisted ion beam etching technique with SiO2 as the etch mask. The threshold current densities of lasers produced with this technique are almost identical to comparable lasers with one etched and one cleaved facet. L-shaped lasers, which make use of total internal reflection, have also been fabricated. The threshold current density of L-shaped lasers is similar to that of rectangular lasers with comparable cavity length.
Compact E parallel B type end-loss ion mass-resolving energy analyzer
Authors: Nakashima Yousuke , Yokoyama Minoru , Imai Yoshio , Yatsu Kiyoshi , Miyoshi Syoichi
Published: July 2002

A compact E parallel B (E∥B) type end-loss ion mass-resolving energy analyzer was fabricated and tested. In the analyzer, a small-angle deflection magnet and a preaccelerator/decelerator of end-loss ions are adopted in order to reduce the size and to expand an energy range with a sufficient energy resolution. Orbit calculations in the E∥B fields including the influence of fringe fields were made by a Monte Carlo code in which the effects of finite radius and angle of the incident ions are taken into consideration. Preliminary measurements on the GAMMA 10 tandem mirror were successfully performed and it was confirmed that the analyzer has capabilities for the spectrometer of end-loss ions.
Silicon segregation in delta-doped GaAs characterized by Auger electron spectroscopy
Authors: Webb Chris
Published: July 2002

We have used Auger electron spectroscopy as a direct measure of silicon segregation in molecular beam epitaxy grown delta-doped GaAs. We find that this technique allows very precise detection of Si segregation. Spectra have been obtained, as a function of temperature, from samples in which Si has been deposited in the normal delta doping manner and then typically 10 Å of GaAs deposited on top. Si segregation is manifested at higher temperatures by the absence of the expected attenuation of the Auger signal. Our results show that Si segregation in GaAs is measurable at temperatures above 520 °C.
High quality In0.53Ga0.47As Schottky diode formed by graded superlattice of In0.53Ga0.47As/In0.52Al0.48As
Authors: Lee D. H. , Li Sheng S. , Sauer N. J. , Chang T. Y.
Published: July 2002

A high quality In0.53Ga0.47As Schottky barrier diode fabricated by using a thin graded superlattice (SL) of In0.53Ga0.47As/In0.52Al0.48As grown by molecular beam epitaxy is reported for the first time in this letter. The effective Schottky barrier heights of ∼0.71 and ∼0.60 eV were obtained for the Au- and Cr-Schottky contacts, respectively. Excellent current-voltage and capacitance-voltage characteristics were obtained for these diodes. The graded InGaAs/InAlAs SL structure allows one to circumvent the problem of carrier pileup associated with abrupt heterostructures, and hence is advantageous for forming Schottky contacts on InGaAs for high-speed optoelectronic device applications.
Detection of water-related charge in electronic dielectrics
Authors: Lifshitz N. , Smolinsky G.
Published: July 2002

We observed an unusual behavior of low-temperature silicon dioxide based materials in the metal-oxide-semiconductor system. We used the triangular voltage sweep (TVS) technique to detect the motion of mobile charge in the dielectrics. The observed TVS spectra were different from those usually attributed to common contaminants in silicon dioxides, such as sodium. We came to the conclusion that these unusual TVS traces are due to the motion of protons formed through the electrical decomposition of water absorbed in these materials. The unique features of the water-related TVS traces may provide a method for detection of water-related instability in electronic dielectrics.
Metal clusters in ion plating
Authors: Fancey K. S. , Matthews A.
Published: July 2002

Conventional ion plating theory assumes that the metal vapor arrives at the substrate in monatomic form. Our results suggest this is not the case, and that a large proportion of the metal arrives as clusters. This is based on measurements of the cathode fall distance before and during titanium deposition in a thermionically supported argon glow discharge. The results have been used to evaluate the charge-to-mass ratio of the metal species in accordance with the Child–Langmuir equation. This predicts that some titanium is present as atomic clusters which contain at least tens of atoms per unit charge. Also we show that at least 90% of the ion current arriving at the substrate is carried by the metallic species.
Comparative photoluminescence study of hydrogenation of GaAs, AlxGa1−xAs, and AlAs
Authors: Pavesi L. , Martin D. , Reinhart F. K.
Published: July 2002

Low-temperature photoluminescence (PL) measurements of GaAs, AlxGa1−xAs, and AlAs samples grown by molecular beam epitaxy have been carried out to study the effects of hydrogen diffusion. Following exposure to a hydrogen plasma, the PL spectra of AlxGa1−xAs change. In particular, direct gap AlxGa1−xAs shows a strong increase in the total PL intensity whereas the PL spectra of indirect gap AlxGa1−xAs show an increase in the excitonic-related recombinations after hydrogenation; the binary compounds present less dramatic changes. We interpret our results in terms of hydrogen passivation of deep and shallow centers (DX), whose densities are higher for aluminum concentration near the direct to the indirect gap crossover.
Ge segregation at Si/Si1−xGex interfaces grown by molecular beam epitaxy
Authors: Zalm P. C. , van de Walle G. F. A. , Gravesteijn D. J. , van Gorkum A. A.
Published: July 2002

The interface quality of Si/Si1−xGex (0.08≤x≤0.33) interfaces grown by molecular beam epitaxy has been studied by means of secondary-ion mass spectrometry. Ge segregation occurs into the Si capping layers. The segregation is characterized by a 17 nm/dec slope; the total amount of segregated Ge corresponds to a few tenths of a monolayer. The phenomenon is independent of the Ge fraction and does not depend on temperature as long as crystal growth is perfect. A possible explanation is given in terms of a Ge adlayer that is formed during growth as a result of site exchange between subsurface Ge and surface Si atoms. This adlayer is incorporated slowly during further Si growth. The Ge segregation can be suppressed by having an adlayer of Ga on the surface of the growing structure.
Injection in a continuum miniband: Observation of negative transconductance in a superlattice-base transistor
Authors: Beltram Fabio , Capasso Federico , Hutchinson Albert L. , Malik Roger J.
Published: July 2002

We report the first observation of electron injection in a continuum miniband and of the associated negative transconductance in a semiconductor heterostructure. In a superlattice-base unipolar transistor, electrons are injected into a miniband lying in the classical continuum of energy. They are collected by a compositionally graded collector barrier. Negative transconductance is observed due to suppression of miniband conduction in the base.
Ion beam induced epitaxial crystallization of GexSi1−x/Si structures
Authors: Elliman R. G. , Ridgway M. C. , Williams J. S. , Bean J. C.
Published: July 2002

GexSi1−x alloy layers grown on (100) silicon substrates by molecular beam epitaxy and amorphized by ion irradiation at −196 °C are shown to recrystallize epitaxially during subsequent ion irradiation at 275 °C. This ion beam annealing process has been examined for two different sample configurations: the first consisting of a thin amorphous layer extending from the surface to about half the thickness of the alloy layer, and the second consisting of a thick amorphous layer extending beyond the alloy layer into the underlying silicon. In both cases, ion beam annealing results in epitaxial crystallization of the alloy layer. Results are reported for alloy composition in the range from Ge0.1Si0.9 to Ge0.8Si0.2.
Measuring the coherence length of mode-locked laser pulses in real time
Authors: Dominic Vince , Yao X. Steve , Pierce R. M. , Feinberg Jack
Published: July 2002

We demonstrate a new technique for displaying the electric field autocorrelation function of a laser pulse in real time, using two-beam coupling in a photorefractive crystal. This technique does not require phasematching, is simple to align, and can be used over the entire visible and near-infrared regions of the spectrum, even with weak laser beams.
Miniband conduction of minority electrons and negative transconductance by quantum reflection in a superlattice transistor
Authors: Vengurlekar A. S. , Capasso F. , Hutchinson A. L. , Tsang W. T.
Published: July 2002

Transport of electrons tunnel injected into a superlattice (SL) is studied. The SL is placed in the base of an n-p-n bipolar transistor. By varying the emitter-base forward bias (VEB), the energy of electrons injected into the base is varied. From the emitter and collector current measurements in the common-base configuration, it is found that the electron transmission to the collector is strongly dependent on the injection energy, the currents showing a sharp peak, and the associated negative transconductance. The measurements show excellent agreement with the calculated values of VEB at the onset of miniband conduction and at the suppression of injection into the SL due to enhanced quantum reflection by the SL minigap. The transfer characteristics also reveal a low-current gain regime of electron transport below the onset of miniband conduction, implying conduction mediated by subminiband gap states.
Impurity-band transport near the metal–insulator transition in ZnSe epilayers grown by molecular beam epitaxy
Authors: Marshall T. , Gaines J.
Published: July 2002

Electrical transport is studied in a number of ZnSe epilayers with donor concentrations in the range 1–3×1017 cm−3. Hall effect data are taken over the temperature range 10–300 K, and magnetoresistance data over the range 10–50 K. Transport is shown to be consistent with a two-carrier model, the second species being identified with transport in an impurity band distinct from the conduction band. At low temperature, the conductivity σ exhibits a log σ∝−(T0/T)1/4 behavior, and the samples show negative magnetoresistance. Moreover, both the parameter T0 and the magnetoresistance tend toward zero as the dopant concentration increases toward that of the metal–insulator transition.
Planar array of superheated superconductors: An improved superheated superconducting granule detector
Authors: Le Gros M. , Da Silva A. , Turrell B. G. , Kotlicki A. , Drukier A. K.
Published: July 2002

We have invented a new superheated superconducting granule detector which is a prime candidate for sensing dark matter and which could prove very useful for other applications. The sensor element is a planar array of spherical granules for which the spread in transition temperatures is nearly an order of magnitude smaller than that for a colloidal device. The detecting efficiency for low-energy deposition is thereby significantly increased. Preliminary results are described.
Injection-locking characteristics of gain-guided diode laser arrays with an ‘‘on-chip’’ master laser
Authors: Hohimer J. P. , Myers D. R. , Brennan T. M. , Hammons B. E.
Published: July 2002

We report measurements of the injection-locking characteristics of a high-power continuous-wave diode laser array with an on-chip independently controlled master laser. This integrated injection-locked array emits a near-diffraction-limited single-lobed output beam at cw power levels up to 220 mW/facet. By controlling the current to the master laser, the single-lobed output beam can be electronically steered over a far-field angle of >1.7°. We also report preliminary studies of the coupling interaction in these integrated devices.
Contact resistance of silver-doped Y-Ba-Cu-O in a magnetic field
Authors: Jin S. , Graebner J. E. , Tiefel T. H. , Kammlott G. W.
Published: July 2002

The apparent contact resistance at the Ag-particle/superconductor interface in sintered YBa2Cu3O7−δ is found to increase considerably in applied magnetic fields (e.g., by ∼300% at H=200 G, at 77 K). However, in a melt-textured sample where the Ag particles are dispersed within the high Jc grain, no noticeable field dependence of ρc is obtained for H up to 1 T. The field dependence of apparent ρc in fine-grained material is, therefore, attributed mostly to the local current concentration in the superconductor near the Ag particles. It causes Jc to be locally exceeded, with the voltage drop contributing to the apparent ρc value even though the average current density in the superconductor matrix is well below the Jc value. The importance of avoiding local current concentration by proper design and processing of silver contacts, and minimizing low Jc(H) region near the interface, is pointed out.
Deep levels in Te-doped AlSb grown by molecular beam epitaxy
Authors: Nakagawa Atsushi , Pekarik John J. , Kroemer Herbert , English John H.
Published: July 2002

Deep electron traps in Te-doped AlSb have been investigated by deep level transient spectroscopy (DLTS). The diodes used for DLTS measurement were InAs/AlSb n-N isotype heterojunctions (quasi-Schottky barriers) with excellent rectification characteristics, grown on n+-GaAs substrates by molecular beam epitaxy. In the temperature range investigated, from 90 to 300 K, a number of electron trap levels were observed, not all of them well defined. The best-defined level was found to have a thermal electron emission energy of 0.26 eV, much shallower than the values 0.46–0.48 eV found by Takeda et al. for AlxGa1−xSb alloys with x≤05. This suggests a compositional dependence of the thermal emission energy for the deep electron trap level in AlxGa1−xSb in the range 0.4<x≤1.0, in contrast to the constant value reported for AlxGa1−xAs. Temperature-dependent Hall effect measurements gave an ionization energy of 100 meV, suggesting that EDX decreases with increasing Al content, as in (Al,Ga)As. In a sample doped with Te at a level of 3.1×1017 cm−3, the trap concentration was 2.0×1017 cm−3, indicating that Te-doped AlSb has a much larger number of deep electron traps than n-AlAs.
Electron focusing with multiparallel GaAs-AlGaAs wires defined by damageless processing
Authors: Nihey F. , Nakamura K. , Kuzuhara M. , Samoto N. , Itoh T.
Published: July 2002

Magnetoresistance modulation, resulting from electron focusing, is investigated with multiparallel GaAs-AlGaAs wires, which are defined by electron beam lithography and damageless wet-chemical etching. Distinct focusing peaks in magnetoresistance are observed, although the samples have wires longer than a ballistic mean free path, which is derived from the focusing peak intensity. Specularity coefficient p for the etched region boundary is also obtained as p≊1 from the focusing peak ratio. The mechanism limiting ballistic transport in the electron focusing condition is discussed, based on the temperature and the electron density dependence of the peak intensity.
Picosecond acoustic pulse reflection from a metal-metal interface
Authors: Svinarich Kathryn A. , Meng W. J. , Eesley G. L.
Published: July 2002

Picosecond duration laser pulses are used to generate ultrashort acoustic pulses in a bilayer metal film. Time-resolved transient piezoreflectance measurements permit the observation of acoustic reflections from a metal-metal interface within the film, as well as reflections from the film-substrate interface. We show that our measurements are well described by an abrupt interface model of acoustic mismatch.
Raman examination of a plasma arcjet deposited diamond film
Authors: Phelps Andrew W. , Stalder K. R.
Published: July 2002

A chemical vapor deposited diamond film was grown on a silicon substrate by the plasma arcjet method. The deposited film was circular and appeared to be radially zoned under visual examination. A secondary electron microscope was used to examine the surface morphology and microfocus Raman spectroscopy was used to examine the radial compositional variation of the film. Raman spectroscopy shows that the composition of the diamond film changed markedly in the space of hundreds of microns. Changes in the Raman spectra can be correlated with variations in morphology of the diamond film.
Photoemission studies of the hydrogenated silicon-gold interface
Authors: Lu Z. H. , Sham T. K. , Norton P. R.
Published: July 2002

The formation of the gold-silicon interface on c-Si(100) and hydrogen-passivated c-Si(100) has been studied by synchrotron radiation photoemission spectroscopy. The results show that the presence of Si-H on the surface (a) quenches the surface dangling bond states and (b) reduces the Au-Si interaction at the initial stages of interface formation. On clean c-Si(100), Au atoms interact with the surface silicon dangling bonds at submonolayer coverages. Rapid diffusion of Au into silicon is observed on both surfaces. A nonabrupt SixAu1−x -Si interface is formed for gold on either hydrogenated or pure c-Si(100).
Selective epitaxial growth by rapid thermal processing
Authors: Lee S. K. , Ku Y. H. , Hsieh T. Y. , Jung K. , Kwong D. L.
Published: July 2002

Rapid thermal processing chemical vapor deposition was employed for selective epitaxial growth of silicon. Defect-free epitaxial islands were grown into oxide windows with 〈110〉 sidewall orientation on (100) silicon substrates. The effects of growth temperature on the degree of faceting have been studied. The hydrogen prebake temperatures as low as 1000 °C have proven to be sufficient for high quality Si deposition without sidewall oxide undercutting.
Combined impurity gettering and defect passivation in polycrystalline silicon solar cells
Authors: Verhoef L. A. , Michiels P-P. , Sinke W. C. , Denisse C. M. M. , Hendriks M. , van Zolingen R. J. C.
Published: July 2002

Polycrystalline silicon wafers have been subjected to annealing (700 °C, 1 h) and to a hydrogen plasma (350 °C, 30 min) during the processing of solar cells. The annealing treatment enhances the bulk minority-carrier recombination lifetime by 19%, presumably by impurity gettering. The plasma treatment improves the lifetime by 26%; hydrogen passivation accounts for at least 2/3 of this improvement. Gettering and passivation are found to be complementary: application of both treatments results in a 43% increase in lifetime compared to standard.
Excitonic electroabsorption in extremely shallow quantum wells
Authors: Goossen K. W. , Cunningham J. E. , Jan W. Y.
Published: July 2002

We report the remarkable observation of strong room-temperature excitonic features in the absorption spectra of GaAs-AlxGa1−xAs quantum wells (QWs) for values of x as low as 0.02. This has important implications for high-power modulators, since saturation intensities have been shown to be higher in QW modulators with low barriers. In addition, very shallow QWs have enhanced electroabsorption at small biases because of ease of ionization. In our p-i(multi-QW)-n device with x=0.02, we obtain a transmission change from 29% to 47% for a voltage change from +1 to −3 V.
Nb/Al-AlOx/Nb superconductor detector using a single-crystal Nb layer
Authors: Kurakado Masahiko , Takahashi Toru , Matsumura Atsuki
Published: July 2002

Single-crystal Nb films coated with a thin polycrystalline Nb film were adopted as the bottom layer of Nb/Al-AlOx/Nb superconducting tunnel junctions. The junctions were applied to detection of x rays from 55Fe. The signal charge induced by each radiation was one order of magnitude larger than that from usual junctions and was two orders of magnitude larger than that from semiconductor Si detectors.
Picosecond carrier dynamics and tunneling-assisted recombination in photorefractive δ-doped superlattices
Authors: Ralph Stephen E. , Lacaita Andrea , Capasso Federico , Malik Roger J.
Published: July 2002

We report the first time-resolved photoluminescence of photorefractive δ-doped superlattices with picosecond resolution. The measurements were performed by the time-correlated photon counting technique. The subband luminescence shows that even at very high photogenerated carrier densities the screening of the internal electric fields remains incomplete. At short times (<500 ps) the dynamics of the structure is determined by recombination in flatband regions. On a longer time scale (1–100 ns) the structure returns to equilibrium via tunneling-assisted recombination. The corresponding lifetimes are consistent with estimates based on the calculated wave functions of the sawtooth structure.
Third-order, nonlinear optical interactions of some benzporphyrins
Authors: Rao D. V. G. L. N. , Aranda Francisco J. , Roach Joseph F. , Remy David E.
Published: July 2002

We measured third-order, nonlinear optical susceptibility χ(3) for a series of tetrabenzporphyrins in solution in tetrahydrofuran at 532 nm using degenerate four-wave mixing with picosecond pulses and obtained values of molecular second hyperpolarizability 〈γ〉. The corresponding macroscopic χ(3) values calculated for nine compounds with different substituent groups are four to five orders larger than CS2. For five of the compounds the χ(3) values are in the range 1.2–2.8×10−8 esu. Our experiments indicate that the nonlinearity is predominately electronic in origin with a response time faster than the 15 ps resolution of our system.
Excitonic photoluminescence spectra of AlxGa1−xAs grown by metalorganic vapor phase epitaxy
Authors: Olsthoorn S. M. , Driessen F. A. J. M. , Giling L. J.
Published: July 2002

Excitonic transitions were measured in AlxGa1−xAs, grown by metalorganic vapor phase epitaxy (MOVPE), at two different alloy compositions using high resolution photoluminescence spectroscopy. The first observation is reported of an excitonic spectrum which is separated into neutral donor, ionized donor, and neutral acceptor bound exciton transitions [(D0,X), (D+,X), and (A0,X)] at an aluminum fraction higher than 20%. A significant decrease in linewidth of the (D0,X) peak is found by decreasing the excitation density and by decreasing the laser spot size. This means that the linewidths of the various excitonic transitions are, apart from alloy broadening, strongly dependent on both the long range Coulombic potentials of the ionized impurities in our samples, and on clustering effects. Finally, linewidths of 1.75 and 2.5 meV were measured for the (D0,X) transitions for samples with Al fractions of 0.12 and 0.244, respectively. These are the smallest values ever reported in literature for samples grown by MOVPE.