Variation In Growth Parameters Research Articles

Fundamentals of Ge1−xSnx and SiyGe1−x-ySnx RPCVD epitaxy

We have studied epitaxial growth of Ge1−xSnx and SiyGe1−x-ySnx materials in 200mm and 300mm industrial CVD reactors using industry standard precursors. The growth kinetics of undoped GeSn were firstly studied via varying growth parameters including growth temperatures, GeH4and SnCl4precursor flows, which indicated that the material growth is highly dependent on surface kinetic limitations involving the SnCl4reaction pathway. Secondly, the growth kinetics of doped layer growth by varying the growth temperatures and the PH3and B2H6dopants flows were investigated. It was shown that B2H6had the effect of increasing the growth rate and decreasing the Sn incorporation whereas PH3had no effect on the growth rate but increased the Sn incorporation. Thirdly, the SiGeSn growth kinetics using SiH4, GeH4, and SnCl4as precursors were discussed, which revealed that the careful control of the growth rate was required to produce compositionally homogenous SiGeSn alloy. Moreover, the material and optical characterizations have been conducted to examine the material quality. Finally, the GeSn quantum well structure was grown to exhibit the precise control of the growth parameters.

Boron-doped few-walled carbon nanotubes: novel synthesis and properties

Few-walled carbon nanotubes offer a unique marriage of graphitic quality and robustness to ink-processing; however, doping procedures that may alter the band structure of these few-walled nanotubes are still lacking. This report introduces a novel solution-injected chemical vapor deposition growth process to fabricate the first boron-doped few-walled carbon nanotubes (B-FWNTs) reported in literature, which may have extensive applications in battery devices. A comprehensive characterization of the as-grown B-FWNTs confirms successful boron substitution in the graphitic lattice, and reveals varying growth parameters impact the structural properties of B-FWNT yield. An investigation into the optimal growth purification parameters and ink-making procedures was also conducted. This study introduces the first process technique to successfully grow intrinsically p-doped FWNTs, and provides the first investigation into the impact factors of the growth parameters, purification steps, and ink-making processes on the structural properties of the B-FWNTs and the electrical properties of the resulting spray-coated thin-film electrodes.

Heartwood assessment of natural Santalum album populations for agroforestry development in Sri Lanka

Sandalwood (Santalum album) is developing as an important agroforestry crop in Sri Lanka. The value of S. album depends upon the oil content in the heartwood and its composition with reference to sesquiterpene alcohols cis-α-santalol and cis-β-santalol. According to the popular belief in Sri Lanka, certain S. album trees do not produce oil even after maturity. Therefore the present study was conducted to identify the presence and the variation of essential oil, its composition and the variation of growth parameters of nine distinctive S. album populations growing under different agroecological zones in Sri Lanka. According to the results, heartwood content, oil content and its constituents varied within and between the populations. It was interesting to observe that cis-α-santalol and cis-β-santalol were not detected in certain S. album trees though the oil contents of those trees were higher than the average. Heartwood content of the trees did not show a correlation with oil content, dbh and height. However, the oil content was significantly correlated with tree dbh and height. Majority of the trees (62 %) had heartwood essential oil in compliance to ISO standards; only a 31 % of the total sampled trees had the essential oil content above 2 % (w/w). Dry mountainous Badulla district had the highest percentage of trees complying the ISO standards. These findings are vital for identifying suitable sources for agroforestry propagation of S. album.

Effects of Growth Parameters on the Analysis of Aspergillus flavus Volatile Metabolites

Aspergillus flavus produces dangerous secondary metabolites known as aflatoxins, which are toxic and carcinogenic, and their contamination of agricultural products results in health issues and economic hardships in the U.S. and around the world. Early identification of aflatoxigenic isolates of A. flavus is the key in the management of these fungi. An emerging detection method for specific fungi identification involves the analysis of microbial volatile organic compounds (MVOCs) released by the fungi. Complicating this approach is the understanding that many factors influence metabolic production, including growth parameters, such as growth media, temperature, spore counts and oxidation stress. In addition, analytical and data analysis methods can also influence the results. Several growth and analysis methods were evaluated and optimized in order to better understand the effect of the methods on fungi MVOC signatures. The results indicate that carboxen/polydimethylsiloxane (CAR/PDMS) has the best extraction efficiency for the MVOCs emitted by A. flavus. Both chemical defined agar (CDA) and chemical defined liquid (CDL) are suitable growth media for MVOC emission studies. The highest MVOC production was found at 30 °C. Log transformation was considered one of the best data pretreatment methods when analyzing MVOC data and resulted in the best principal component analysis (PCA) clustering in the experiments with different growth media. This study aims to elucidate fungal volatile organic compounds (VOCs) differences due to variations in growth parameters as a first step in the development of an analytical method for the monitoring of aflatoxigenic A. flavus contamination in crop storage facilities.

Effects of Nitrogen Application on Growth and Ethanol Yield of Sweet Sorghum [Sorghum bicolor(L.) Moench] Varieties

A study was carried out in two locations, Ilorin (8° 29′ N; 4° 35′ E; about 310 m asl) and Ejiba (8° 17′ N; 5° 39′ E; about 246 m asl), at the Southern Guinea Savannah agroecological zone of Nigeria to assess the effect of nitrogen fertilizer on the growth and ethanol yield of four sweet sorghum varieties (NTJ-2, 64 DTN, SW Makarfi 2006, and SW Dansadau 2007). Five N fertilizer levels (0, 40, 80, 120, and 160 kg ha−1) were used in a 4 × 5 factorial experiment, laid out in split-plots arrangement. The application of nitrogen fertilizer was shown to enhance the growth of sweet sorghum as observed in the plant height, LAI, CGR, and other growth indices. Nitrogen fertilizer application also enhanced the ethanol yield of the crop, as variations in growth parameters and ethanol yield were observed among the four varieties studied. The variety SW Dansadau 2007 was observed as the most promising in terms of growth and ethanol yield, and the application of 120 kg N ha−1resulted in the best ethanol yield at the study area.

Incorporation Behaviors of In and Ga in the Two-Heater MOVPE Growth of InGaN Films

Incorporation behaviors of In and Ga of InGaN films grown by the two-heater metal-organic vapor-phase epitaxial horizontal reactor is investigated by varying growth parameters, such as the substrate temperature, ceiling temperature and reactor pressure. Two In loss mechanisms are observed by the analysis of the concentration and temperature profiles in the deposition zone. The gas-phase parasitic-loss mechanism (activation energy ∼ 34.2 ± 0.1 kcal/mol) is significant in the ceiling temperature Tceil ≥ 800°C and at substrate temperature (Tsub) of 600°C. The decomposition-loss mechanism, which arises from In desorption on the growing surface, is significant in Tsub > 625°C region. The desorption activation energy obtained is 28.0 ± 0.1 kcal/mol, which is close to that of InN (25–26 kcal/mol). This suggests the In decomposition-loss mechanism in InGaN growth does not differ substantially from that in binary InN growth. On the other hand, the gas-phase parasitic-loss mechanism of Ga is negligible in the growth condition that we have explored. Exception is found for reactor pressure at Tceil = 950°C, where both factors advantageous and disadvantageous to Ga incorporation are unambiguously observed. We have proposed explanation for the above observation.

Diversity of cultured bacteria from the perennial ice block of Scarisoara Ice Cave, Romania

Cave ice ecosystems represent a poorly investigated glacial environment. Diversity of cave ice bacteria and their distribution in perennial ice deposits of this underground glacial habitat could constitute a proxy for microbial response to climatic and environmental changes. Scarisoara Ice Cave (Romania) hosts one of the oldest and largest cave ice blocks worldwide. Here we report on cultured microbial diversity of recent, 400, and 900 years-old perennial ice from this cave, representing the first characterization of a chronological distribution of cave-ice bacteria. Total cell density measured by SYBR Green I epifluorescence microscopy varied in the 2.4 x 104 – 2.9 x 105 cells mL-1 range. The abundance of cultured bacteria (5 x 102 – 8 x 104 CFU mL-1) representing 0.3-52% of the total cell number decreased exponentially with the ice age, and was higher in organic rich ice sediments. Cultivation at 4˚C and 15˚C using BIOLOG EcoPlates revealed a higher functional diversity of cold-active bacteria, dependent on the age, sediment content and physicochemical properties of the ice. The composition dissimilarity of ice microbiota across the ice block was confirmed by growth parameter variations when cultivated in different liquid media at low and high temperatures. PCR-DGGE and sequencing of bacterial 16S rRNA gene fragments from the cultured ice samples led to the identification of 77 bacterial amplicons belonging to Gammaproteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria, showing variation in distribution across the ice layers. Several identified OTUs were homologous to those identified in other glacial and karst environments and showed partial conservation across the ice block. Moreover, our survey provided a glimpse on the cave-ice hosted bacteria as putative biomarkers for past climate and environmental changes.

Understanding Field-Dependent Leakage Current Mechanisms in Amorphous Hydrogenated Boron Carbide As a Function of Electronic, Dielectric, and Disorder Parameters

Thin-film carborane-based amorphous hydrogenated boron carbide (a-B x C:H y ), grown by plasma-enhanced chemical vapor deposition (PECVD), has emerged as a promising semi-insulating, low-dielectric-constant (low-κ) (κ < 3.5) material for intra/interlayer dielectric (ILD) and/or copper diffusion barrier/etch stop applications. Of the many integration challenges faced by candidate materials for low-κ ILDs or more specialized layers, one of the most important is the need for extremely low leakage currents up to high electric fields. In the case of a-B x C:H y , the leakage current at a given field can span nearly ten orders of magnitude, depending on the fabrication conditions and resulting physical properties of a given film. In order to go beyond a brute force process–property approach toward optimizing the electrical properties in thin-film a-B x C:H y , we explore their origin and relationship to electronic, dielectric, and disorder properties. This contribution will describe the charge transport mechanisms in a-B x C:H y films in different electric field regimes, which include Ohmic, space-charge-limited-current, and Poole–Frenkel behavior. These mechanisms, and the underlying electrical properties that define these mechanisms (e.g., resistivity, mobility, trapping), are related to individual and combined electronic (band gap), dielectric (electronic and atomic/distortion polarization), and disorder (Urbach energy, Tauc parameter, dispersion energy) parameters. We further discuss how balancing the contributions of these different parameters via hydrogen and carbon content, through varying growth parameters, allows us to control the underlying charge transport mechanisms at both low and high fields, to ultimately obtain leakage currents on the order of 10–8 A/cm2or lower at 2 MV/cm. Figure 1. (a) Leakage current density (J) as a function of electric field (E) for a selection of a-B x C:H y films. (b) and (c) Correlations between charge transport and disorder parameters: zero-field mobility extracted from steady-state space-charge-limited current measurements (μ 0(SS-SCLC)) as a function of E g E u B –1/2 disorder parameter, and resistivity (ρ) extracted in Ohmic regime as a function of dispersion energy (E d). Figure 1

Erbium doped GaN synthesized by hydride vapor-phase epitaxy

New and improved gain materials for solid-state high power and high energy lasers are highly sought. GaN satisfies many of the criteria of an excellent lasing gain medium including its higher thermal conductivity and lower thermal expansion coefficient than traditional gain materials such as yttrium aluminum garnet (YAG) crystals doped with neodymium emitting 1.06 μm wavelength. Single crystals of erbium doped GaN (Er:GaN) thick layers have been successfully synthesized by hydride vapor-phase epitaxy. By utilizing a thin GaN epilayer grown on c-plane sapphire using metal organic chemical vapor deposition as a template and varying growth parameters including the NH3 flow rate, thick layers of Er:GaN which exhibit the desired Er3+ related emission at 1.54 μm window at room temperature have been realized for the first time. The work opens up the feasibility to utilize Er:GaN bulk crystals as a gain medium for next generation solid-state high power and high energy lasers operating in the eye-safer 1.5 μm window.

One-step growth of SmFeAs(O,F) films by molecular beam epitaxy using FeF2 as a fluorine source

We report on one-step growth of superconducting SmFeAs(O,F) films without post-growth fluorine diffusion. One-step growth is a prerequisite for multilayer deposition, which is required for fabricating sandwich-type Josephson junctions; however, it has not been achieved because of a lack of a suitable fluorine source. We found that FeF2, a ‘soft’ fluoride, decomposes at relatively low temperatures (∼650 °C) and supplies fluorine as well as Fe to films. The use of FeF2 has enabled us to perform reproducible growth of SmFeAs(O,F) films with a systematic change of the film’s properties by varying growth parameters. Now, single-phase single-crystalline SmFeAs(O,F) films with are routinely prepared. Furthermore, the c-axis lattice parameter of the films are varied in a systematic manner with the FeF2 deposition rate, indicating that the F doping level seems to be controllable. The comparison of one-step growth and our previous two-step growth demonstrates that a more homogeneous F concentration is achieved by one-step growth, whereas higher F concentration is achieved by two-step growth.

A compendium of cell and natural unit biovolumes for &gt;1200 freshwater phytoplankton species

Cell size determination is a critical part of sampling phytoplankton communities, as size is both a fundamental trait determining species' ecological niches and a quantity necessary for generating unbiased estimates of community composition. The sizes of algal cells span orders of magnitude, driving variation in growth parameters, sinking rates, herbivore defense, and biogeochemical roles. Size variation occurs at both intra‐ and interspecific levels. Many central questions in community and ecosystem ecology require estimating and comparing the relative abundances of species. Cell counts provide insufficient estimates, due to interspecific variation in cell size, as they over‐estimate the importance of abundant, small species. While cell size (or biovolume) estimation has become standard practice in limnology, many older data sets lack this information, limiting their interpretation and utility. To address these challenges, and advance the study of freshwater phytoplankton communities, we have compiled a database of &gt;260 000 algal biovolume estimates, spanning ∼400 genera and ∼1200 species. This represents the most extensive, standardized, and taxonomically diverse data set of its kind, drawing on both publicly and privately held sources. Estimates of the sizes of colonies or filaments are included, where applicable. With these data researchers will be able to account for intra‐ and interspecific variation in cell size, enabling new and improved analyses of classic data sets.

Estimating Ages of Turtles from Growth Data

Abstract Age estimation is important for management of turtle populations, but techniques such as growth ring counts or skeletochronology may be unreliable or impossible to perform. An alternative is to estimate age from growth models using Bayesian inference. However, individual variation in growth parameters needs to be incorporated into these models for them to generate realistic prediction intervals. For long-lived ectotherms such as chelonians, it is also important that models allow for changes in growth at sexual maturity, and that the growth models are combined with prior distributions reflecting realistic age structures. We describe how a hierarchical biphasic growth model fitted to a long-term data set of carapace length measurements for North American snapping turtles was combined with prior age distributions generated from survival estimates for the same population. The model was used to generate individual posterior age distributions for turtles captured on 2 or more occasions, and also for hy...

Phenotypic variation of 38 European Ambrosia artemisiifolia populations measured in a common garden experiment

The knowledge of phenotypic variation in the European range of the highly allergenic Ambrosia artemisiifolia L. (common ragweed) is not entirely complete, even though it is an invasive species of utmost concern. We hypothesized the prevalence of phenotypic differentiations between common ragweed populations in the introduced range, and we assumed that those differentiations were related to environmental conditions at the points of origin. Using a common garden experiment, we investigated biomass allocation, growth rates, and flowering phenology of 38 European common ragweed populations originating from a major geographical gradient. We observed considerable phenotypic variation in growth parameters and flowering phenology, e.g. mean aboveground biomass varied from 23.3 to 47.3 g between the populations. We were able to relate most measured traits with environmental parameters prevailing at the points of origin. For example, early growth of ruderal populations was highly correlated with temperature and precipitation at the point of origin. Late growth and flowering phenology were highly correlated with latitude, i.e. individuals from northern populations grew smaller and flowered and dispersed their pollen and seeds up to 5 weeks earlier than individuals from southern populations. We also found a longitudinal gradient in flowering phenology which has not yet been described. The existence of such a high variability in the introduced range may facilitate further range expansion. We suggest that the correlation with environmental variables rests upon genetic variation possibly due to adaptations to the respective environment. To clarify if such adaptation results from multiple events of introduction or as evolutionary response after introduction, genetic investigations are needed.

Ge Mediated Surface Preparation for Twin Free 3C-SiC Nucleation and Growth on Low Off-Axis 4H-SiC Substrate

In this work, we report on the effect of adding GeH4 during 3C-SiC heteroepitaxial growth on low off-axis 4H-SiC substrate using chemical vapor deposition technique. When added together with SiH4 and C3H8, GeH4 does not significantly modify the 3C layer quality which contains a high density of twin boundaries. But when it is introduced before the growth, i.e. during a surface pretreatment step at 1500°C, a remarkable change in the layer morphology is seen. Furthermore for optimal GeH4 flux, twin boundaries are completely eliminated. Investigation of the results obtained when varying growth parameters (temperature, C/Si ratio, gas composition during the surface preparation) allowed proposing a mechanism leading to twin boundary elimination. It involves a transient homoepitaxial growth step followed by 3C nucleation when large terraces are formed by step faceting. Preliminary electrical characterizations of the twin free 3C-SiC layers, using conductive atomic force microscopy (c-AFM), are given.

Atomic layer deposition of Zn1−x Mg x O:Al transparent conducting films

Aluminum-doped zinc magnesium oxide (Zn1−xMgxO:Al) films with the Mg content from x = 0 to 0.48 were obtained using atomic layer deposition (ALD). Together with the thorough studies of the properties of the deposited films, the ALD growth parameters conditioning possible applications of Zn1−xMgxO:Al films as transparent electrodes are investigated. Very low film resistivities (≤~10−3 Ω cm) and the metallic-type conductivity behavior at room temperature for Zn1−xMgxO:Al films are observed for Mg content x < 0.19. The Mg content of x = 0.19 results in the optical absorption edge of Zn1−xMgxO:Al films at 3.81 eV (325 nm). Other film parameters like work function or sheet resistance can be easily modified by variation of growth parameters.

Effect of variations in growth parameters on cellulase activity of Trichoderma viride NSPR006 cultured on different wood-dusts

Aims: The biotechnology research into agro wastes has been driven by the need to screen organisms for hyperproduction of novel extracellular enzymes in which cellulase plays a significant role. Therefore, the aim of the study was to pre-screen selected fungal strains and optimize cultural conditions for cellulase production by Trichoderma viride NSPR006 cultured on pretreated sawdust as lignocellulosic substrate. Methodology and results: The selected fungal isolates namely Trichoderma viride NSPR006, Botrydiplodia NSPR007 and Acremonium butyri NSPR06B obtained from the culture collection of the Nigerian Stored Products Research Institute Ilorin, Kwara State, Nigeria were screened for the production of cellulase in mineral salt medium in which carboxymethylcellulose (CMC) had been incorporated as the sole carbon source. All the tested fungal isolates produced cellulase with differences in the amount of enzyme production. Of all the selected fungal isolates screened, Trichoderma viride NSPR006 was found to yield highest cellulase activity compared to the other isolates. Among tested carbon sources, Pachyslasma tessmani wood dust at 3% level proved to the best for cellulase production. Of the entire tested organic nitrogen sources, locust beans were observed to yield maximum cellulase activity (0.194 µmol/min/mL). The optimum temperature, incubation time and pH for maximum cellulase production were 28 °C, 72 h and 6.5, respectively. Conclusion, significance and impact of study: Outcome of this study shows the effectiveness of pre-treatment of wood dust as low cost system for hyper-production of cellulase for industrial application. Also, the work revealed the use of pretreated wood dust as substitute to commercial substrate known to be expensive in cellulase production.

Nature of V-Shaped Defects in GaN

GaN films with thicknesses up to 3 mm were grown in two custom-made halide vapor phase epitaxy (HVPE) reactors. V-shaped defects (pits) with densities from 1 to 100 cm-2 were found on the surfaces of the films. Origins of pit formation and the process of pit overgrowth were studied by analysing the kinematics of pit evolution. Two mechanisms of pit overgrowth were observed. Pits can be overgrown intentionally by varying growth parameters to increase the growth rate of pit facets. Pits can overgrow spontaneously if a fast-growing facet nucleates at their bottom under constant growth conditions.

Solid waste management of temple floral offerings by vermicomposting using Eisenia fetida

Recycling of temple waste (TW) mainly comprising of floral offerings was done through vermitechnology using Eisenia fetida and its impact on seed germination and plant growth parameters was studied by comparing with kitchen waste (KW) and farmyard waste (FYW) vermicompost (VC). The worm biomass was found to be maximum in TW VC compared to KW and FYW VCs at both 40 and 120days old VCs. Physico-chemical analysis of worm-worked substrates showed better results in TW VC especially in terms of electrical conductivity, C/N, C/P and TK. 10% TW VC–water extract (VCE) showed stimulatory effect on germination percentage of chickpea seeds while KW and FYW VCE proved effective at higher concentration. Variation in growth parameters was also observed with change in the VC–soil ratio and TW VC showed enhanced shoot length, root length, number of secondary roots and total biomass at 12.5% VC compared to KW and FYW VC.

Synthesis of copper submicro/nanoplates with high stability and their recyclable superior catalytic activity towards 4-nitrophenol reduction

Due to the difficulty in morphology control of planar copper structures, far fewer studies have explored the shape effect on catalytic activity of copper materials. Here, PVP-stabilized copper plates are prepared via the reduction of the Cu(II)–tartrate complex by NaH2PO2 in the presence of PVP under an ambient atmosphere. Based on the systematic studies of varying growth parameters and theoretical simulations, we have discovered the critical factors for synthesizing planar copper crystals. The size of the copper plates can be tuned by adjusting the relative amounts of tartrate, or by changing the types of complex regents with different complexing abilities. The oxidative stability of the resultant copper plates is examined, and their catalytic properties are evaluated. In all cases, the as-prepared submicro/nanoplates show excellent catalytic activity compared with other copper catalysts. Notably, the resultant PVP-stabilized Cu catalyst with submicron size exhibits high stability not only in ambient air, but also toward reduction of p-nitrophenol. It is found that Cu plates are stable and do not lose their structural integrity during reduction catalysis. High stability under the reaction conditions enables the recyclability of the as-fabricated copper plates. We expect catalysts based on copper with plate shapes to meet the increasing demands of industrial applications at reduced costs.

Application of hierarchical biphasic growth models to long-term data for snapping turtles

Somatic growth rates are critical to the population dynamics of long-lived ectotherms. While the von Bertalanffy (VB) growth curve has been used extensively to model growth of such animals, the conventional form of the model fails to account for individual variation or for changes in resource allocation after sexual maturation. Bayesian modelling has recently been used in fisheries research to fit a modification of the VB model that is both hierarchical (allowing individual variation in growth parameters) and biphasic (allowing an age-specific change in growth rate). We extend this approach by developing a range of hierarchical biphasic models allowing a size- rather than age-dependent change of one or more growth parameters in one or both sexes. We applied the approach to a long-term data set of growth measurements for snapping turtles (Chelydra serpentina), as data on nesting status show females begin nesting predictably at about 24cm carapace length. The data consisted of 1996 carapace-length measurements taken from 1972 to 2005 in Algonquin Park, Canada, from 317 individual turtles. These included 24 turtles of known age, most of which were juveniles of unknown sex, and 293 turtles of unknown age, most of which were adults of known sex. The modelling revealed substantial individual variation in both the asymptotic size (a) and growth rate (k) parameter, and clear evidence of biphasic growth. The model that best explained the data (based on DIC) was that males and females grow similarly until they reach 24cm, after which females shift trajectory towards a reduced asymptotic size target. The number of years taken to reach 24cm was estimated to range from 11 to 44 years in 95% of individuals, with asymptotic size ranging from 38.2 to 40.9 in males and 31.0 to 33.6 in females. Our approach is applicable to a range of long-lived ectotherms likely to have size-dependent biphasic growth, and provides essential information for modelling the long-term dynamics of populations under threat.