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Underlying Substrate (underlying + substrate)
Selected AbstractsSpin- and Spray-Deposited Single-Walled Carbon-Nanotube Electrodes for Organic Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Sungsoo Kim Abstract Organic bulk-heterojunction solar cells using thin-film single-walled carbon-nanotube (SWCNT) anodes deposited on glass are reported. Two types of SWCNT films are investigated: spin-coated films from dichloroethane (DCE), and spray-coated films from deionized water using sodium dodecyl sulphate (SDS) or sodium dodecyl benzene sulphonate (SDBS) as the surfactant. All of the films are found to be mechanically robust, with no tendency to delaminate from the underlying substrate during handling. Acid treatment with HNO3 yields high conductivities >1000,S,cm,1 for all of the films, with values of up to 7694,±,800,S,cm,1 being obtained when using SDS as the surfactant. Sheet resistances of around 100,,,sq,1 are obtained at reasonable transmission, for example, 128,±,2,,,sq,1 at 90% for DCE, 57,±,3,,,sq,1 at 65% for H2O:SDS, and 68,±,5,,,sq,1 at 70% for H2O:SDBS. Solar cells are fabricated by successively coating the SWCNT films with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS), a blend of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxy-carbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM), and LiF/Al. The resultant devices have respective power conversions of 2.3, 2.2 and 1.2% for DCE, H2O:SDS and H2O:SDBS, with the first two being at a virtual parity with reference devices using ITO-coated glass as the anode (2.3%). [source] Nanoparticle Arrays on Surfaces Fabricated Using Anodic Alumina Films as Templates,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2003M.S. Sander Abstract High density nanoparticle arrays on surfaces have been created using a template-assisted approach. Templates were produced by evaporating aluminum onto substrates and subsequently anodizing the aluminum to produce nanoporous alumina films. The resulting templates have a narrow distribution of pore sizes tunable from ,,25 to ,,70 nm. To demonstrate the flexibility of this approach for producing nanoparticle arrays on various substrates, templates have been fabricated on silicon oxide, silicon, and gold surfaces. In all cases, a final chemical etching step yielded pores that extended completely through the template to the underlying substrate. Because the templates remain in intimate contact with the substrate throughout processing, they may be used with either vacuum-based or wet chemical deposition methods to direct the deposition of nanoparticles onto the underlying substrates. Here we have produced gold nanodot arrays using evaporation and gold nanorod arrays by electrodeposition. In each case, the diameter and height of the nanoparticles can be controlled using the confining dimensions of the templates, resulting in high density (,,1010,cm,2) arrays of nanoparticles over large areas (>,1 cm2). [source] Self-Healing Polymer CoatingsADVANCED MATERIALS, Issue 6 2009Soo Hyoun Cho Self-healing coatings that autonomically repair and prevent corrosion of the underlying substrate are created through dispersion of microencapsulated healing agents in a polymer film. Following a damage event, these healing agents are released into the damaged region, passivating the substrate. This approach to self-healing coatings is quite general, and is effective for both model and industrially important coating systems. [source] Capillarity-Driven Assembly of Carbon Nanotubes on Substrates into Dense Vertically Aligned Arrays,ADVANCED MATERIALS, Issue 19 2007S. Kaur Carbon nanotubes are assembled into dense, vertically aligned arrays on substrates by using capillary forces. Modulating the interactions between the nanotubes and the underlying substrate provides control over the assembly of the nanotube array; capillary forces can either cause bending (left) or translation (right) of the nanotube array. The use of this densification strategy enables a four-fold increase in current density through nanotube arrays. [source] Precise Control over Molecular Dimensions of Block-Copolymer Domains Using the Interfacial Energy of Chemically Nanopatterned Substrates,ADVANCED MATERIALS, Issue 15 2004W. Edwards Epitaxial assembly of block-copolymer films (see Figure) onto chemically nanopatterned substrates results in arrays of nanoscopic domains that are defect-free, oriented, and registered with the underlying substrate. The range of dimensions of features (or periodicity of structures) that can be patterned with perfection and registration strongly depends on the interfacial energy between the substrate and the polymer film. [source] The spatiotemporal dynamics of a primary successionJOURNAL OF ECOLOGY, Issue 2 2008N. A. Cutler Summary 1Conceptual models of ecosystem development commonly predict a phase of initial colonization characterized by the nucleation, growth and coalescence of discrete patches of pioneer plants. Spatiotemporal dynamics during subsequent development may follow one of three different models: the classical model, in which initially discrete patches of competitive dominant (secondary) colonists coalesce to form a homogeneous cover; the patch dynamics model, in which renewal mechanisms such as disturbance create a shifting mosaic of patches at different stages; and the geoecological model, in which the vegetation gradually differentiates along edaphic gradients related to the underlying physical template. 2These models of spatiotemporal dynamics were tested using vegetation and soil data from an 850-year chronosequence, comprised of seven lava flows on Mt Hekla, Iceland. The scale and intensity of spatial pattern were quantified on each flow using spatial analyses (mean-variance ratios, quadrat variance techniques and indices of autocorrelation). Changes in spatial pattern with increasing terrain age were compared with predicted trajectories, in order to identify which of the models of spatiotemporal dynamics was most consistent with the observations. 3The early stages of ecosystem development were characterized by colonization of the pioneer species, especially Racomitrium mosses, in discrete patches (,Pioneer colonization stage', < 20 years), which then grew laterally and coalesced to form a continuous, homogeneous carpet (,Pioneer expansion stage', 20,100 years). Later in the sequence, higher plants established in discrete patches within this pioneer matrix (,Higher plant colonization stage', 100,600 years). Over time, heterogeneity re-emerged at a larger spatial scale as the vegetation differentiated according to topographic variations in the underlying substrate (,Differentiation stage', > 600 years). 4Synthesis. The spatiotemporal dynamics observed in the early stages of this succession were consistent with a model of pioneer nucleation in micro-scale safe sites, followed by growth, coalescence and eventual fragmentation of pioneer patches. The spatial patterns which emerged later in development support the geoecological model, with spatial differentiation of vegetation related to meso-scale substrate topography. The findings provide insight on how vegetation patterns emerge at different stages of ecosystem development in response to differing scales of heterogeneity in the underlying physical environment. [source] Maximizing Esthetic Results in Posterior Restorations Using Composite OpaquersJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2001WALTER R.L. DIAS DDS ABSTRACT After removal of caries or a faulty existing restoration in a posterior tooth, frequently the pulpal floor is a dark substrate. Composites are translucent by nature, and even the more opaque shades transmit nearly 60% of visible light, meaning that composites require a certain thickness to maintain their intended shade, especially if the underlying substrate is particularly dark. Depending on the intensity of the dark substrate, even relatively thick composite restorations may not be capable of disguising the discolored dentin underneath. The substrate absorbs a significant part of the light that would otherwise reflect toward the occlusal surface, and the restoration has a nonvital monochromatic grayish color. Opaquers and tints (color modifiers) may be extremely useful to overcome this situation. In this study, composite restorations were placed in extracted teeth to demonstrate that the final esthetic results rely upon the optical properties of the background as well as those of the composite material itself. Preparations with simulated dark pulpal floors were restored without the use of opaquers and tint modifiers. After tooth hydration, the final shade was recorded with photographs. The restoration was removed and a new restoration was placed, but this time with a technique involving opaquer and tints. This article compares and discusses the outcomes of these two procedures. CLINICAL SIGNIFICANCE This demonstration shows a simple technique that can help dentists obtain predictable esthetic results in their daily practice with posterior composite restorations. [source] Mathematical Model for Surface-Initiated Photopolymerization of Poly(ethylene glycol) DiacrylateMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006Seda K Abstract Summary: A general mathematical model has been developed to describe the surface initiated photopolymerization of PEG-DA forming crosslinked hydrogel membranes upon the surface of a substrate. Such membranes are formed by photopolymerizing a PEG-DA prepolymer solution by initiation with eosin-Y-functionalized surfaces and TEA using VP as accelerator. Experimental measurements of the thickness of hydrogel membranes compare well with the model. The model is developed by using the pseudo-kinetic approach and the method of moments, and is capable of predicting the crosslink density and thickness of the hydrogel membrane. Parametric sensitivity of the effects of PEG-DA, VP and coinitiator TEA concentration towards the crosslink density and the thickness of the hydrogel is also investigated. The results obtained for different PEG-DA and VP concentrations suggest that the concentration ratio of these two monomers is a key parameter in controlling the gel thickness and permeability. This model can also be applied to systems where drugs, proteins or cells are encapsulated through surface initiated photopolymerization to predict the growth and crosslink density profiles of the encapsulating membrane. In a previous study we have experimentally demonstrated that these membranes could be made to attach covalently to the surface of the underlying substrate. Comparison of experimental measurements and model simulation of PEG-DA hydrogel membrane thickness versus laser duration at high PEG-DA concentrations. [source] In situ deformation of thin films on substratesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2009Marc Legros Abstract Metallic thin-film plasticity has been widely studied by using the difference between the coefficients of thermal expansion of the film and the underlying substrate to induce stress. This approach is commonly known as the wafer curvature technique, based on the Stoney equation, which has shown that thinner films have higher yield stresses. The linear increase of the film strength as a function of the reciprocal film thickness, down to a couple hundred nanometers, has been rationalized in terms of threading and interfacial dislocations. Polycrystalline films also show this kind of dependence when the grain size is larger than or comparable to the film thickness. In situ TEM performed on plan-view or cross-section specimens faithfully reproduces the stress state and the small strain levels seen by the metallic film during wafer curvature experiments and simultaneously follows the change in its microstructure. Although plan-view experiments are restricted to thinner films, cross-sectional samples where the film is reduced to a strip (or nanowire) on its substrate are a more versatile configuration. In situ thermal cycling experiments revealed that the dislocation/interface interaction could be either attractive or repulsive depending on the interfacial structure. Incoherent interfaces clearly act as dislocation sinks, resulting in a dislocation density drop during thermal cycles. In dislocation-depleted films (initially thin or annealed), grain boundaries can compensate for the absence of dislocations by either shearing the film similarly to threading dislocations or through fast diffusion processes. Conversely, dislocations are confined inside the film by image forces in the cases of epitaxial interfaces on hard substrates. To increase the amount of strain seen by a film, and to decouple the effects of stress and temperature, compliant substrates can also be used as support for the metallic film. The composite can be stretched at a given temperature using heating/cooling straining holders. Other in situ TEM methods that served to reveal scaling effects are also reviewed. Finally, an alternate method, based on a novel bending holder that can stretch metallic films on rigid substrates, is presented. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] Nitrogen Fixation in Bryophytes, Lichens, and Decaying Wood along a Soil-age Gradient in Hawaiian Montane Rain ForestBIOTROPICA, Issue 1 2003Virginia Matzek ABSTRACT We determined rates of acetylene reduction and estimated total nitrogen fixation associated with bryophytes, lichens, and decaying wood in Hawaiian montane rain forest sites with underlying substrate ranging in age from 300 to 4.1 million years. Potential N fixation ranged from ca 0.2 kg/ha annually in the 300-year-old site to ca 1 kg/ha annually in the 150,000-year-old site. Rates of acetylene reduction were surprisingly uniform along the soil-age gradient, except for high rates in symbiotic/associative fixers at the 150,000-year-old site and in heterotrophic fixers at the 2100-year-old site. Low fixation at the youngest site, where plant production is known to be N-limited, suggests that demand for N alone does not govern N fixation. Total N fixation was highest in sites with low N:P ratios in leaves and stem wood, perhaps because epiphytic bryophytes and lichens depend on canopy leachate for mineral nutrients and because heterotrophic fixation is partly controlled by nutrient supply in the decomposing substrate; however, differences in substrate cover, rather than in fixation rates, had the largest effect on the total N input from fixation at these sites. [source] Survival, Growth, and Ecosystem Dynamics of Displaced Bromeliads in a Montane Tropical Forest1BIOTROPICA, Issue 2 2002Jennifer Pett-Ridge ABSTRACT Epiphytes generally occupy arboreal perches, which are inherently unstable environments due to periodic windstorms, branch falls, and treefalls. During high wind events, arboreal bromeliads are often knocked from the canopy and deposited on the forest floor. In this study, we used a common epiphytic tank bromeliad, Guzmania berteroniana (R. & S.) Mez, to determine if fallen bromeliads can survive, grow, and reproduce on the forest floor and evaluate the potential impact of adult dispersal on plant and soil nutrient pools. Bromeliads were transplanted to and from tree stems and the forest floor and monitored intensively for six months; survival, growth, and impacts on ecosystem nutrient pools were followed on a subset of plants for 16 months. Six months after transplanting, bromeliad mortality was low (3%), and 19 percent of study individuals had flowered and produced new juvenile shoots. Mortality on the subset of plants followed for 16 months was 14,30 percent. Although survival rates were relatively high in all habitats, bromeliads transplanted to trees grew significantly more root length (x,± SE: 189 ± 43 cm) than those moved to the forest floor (53 ±15 cm) and experienced lower rates of leaf area loss. All transplanted bromeliads rapidly altered the substrate they occupied. Individuals transplanted to and among trees rapidly decreased base cation concentrations but significantly increased P concentrations of their underlying substrate. On the ground, bromeliads increased C, N, and P concentrations within nine months of placement. Our results suggest that in this montane tropical forest, bromeliads respond rapidly to displacement, locally modify their substrates, and can access the resources needed for survival regardless of habitat. [source] Nanoparticle Arrays on Surfaces Fabricated Using Anodic Alumina Films as Templates,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2003M.S. Sander Abstract High density nanoparticle arrays on surfaces have been created using a template-assisted approach. Templates were produced by evaporating aluminum onto substrates and subsequently anodizing the aluminum to produce nanoporous alumina films. The resulting templates have a narrow distribution of pore sizes tunable from ,,25 to ,,70 nm. To demonstrate the flexibility of this approach for producing nanoparticle arrays on various substrates, templates have been fabricated on silicon oxide, silicon, and gold surfaces. In all cases, a final chemical etching step yielded pores that extended completely through the template to the underlying substrate. Because the templates remain in intimate contact with the substrate throughout processing, they may be used with either vacuum-based or wet chemical deposition methods to direct the deposition of nanoparticles onto the underlying substrates. Here we have produced gold nanodot arrays using evaporation and gold nanorod arrays by electrodeposition. In each case, the diameter and height of the nanoparticles can be controlled using the confining dimensions of the templates, resulting in high density (,,1010,cm,2) arrays of nanoparticles over large areas (>,1 cm2). [source] | ||||||||||||||||