Areal Coverages Research Articles

Dependence of Plasmonic Properties of Silver Island Films on Nanoparticle Size and Substrate Coverage

Localized surface plasmon resonance displayed by metal nanoparticles has been studied in silver island films prepared by the simple technique of vacuum evaporation, which is one of the options that is easily adaptable for large area and low cost applications. Silver island films with varying island sizes and areal coverages are prepared by depositing silver films with varying thicknesses followed by annealing. The optical properties of the samples have been explained in terms of dependence of scattering and absorption on the metal island size, interparticle interaction and matrix effects, and the wavelength range over which the plasmonic effects are present.

Flexible Electronics: Stretchable Semiconductor Technologies with High Areal Coverages and Strain‐Limiting Behavior: Demonstration in High‐Efficiency Dual‐Junction GaInP/GaAs Photovoltaics (Small 12/2012)

The cover image illustrates a high-performance, stretchable, photovoltaic module that combines microscale, dual-junction GaInP/GaAs solar cells (i.e., 2 J microcells) in an interconnected square array, mounted on a structured substrate of the elastomer poly(dimethylsiloxane) (PDMS). The raised features of relief on the PDMS provide mounting locations for the microcells; notches on the four sides of each feature accommodate thin ribbon interconnects that buckle downward into the separating trenches. This layout allows for reversible, elastic responses to large-scale deformations and, at the same time, naturally limits their magnitudes to avoid damage to the interconnects and microcells, even when the latter are present at high areal coverages. For further information, please read the Communication “Stretchable Semiconductor Technologies with High Areal Coverages and Strain-Limiting Behavior: Demonstration in High-Efficiency Dual-Junction GaInP/GaAs Photovoltaics” by J. A. Rogers and co-workers beginning on page 1851.

Stretchable Semiconductor Technologies with High Areal Coverages and Strain‐Limiting Behavior: Demonstration in High‐Efficiency Dual‐Junction GaInP/GaAs Photovoltaics

Notched islands on a thin elastomeric substrate serve as a platform for dual-junction GaInP/GaAs solar cells with microscale dimensions and ultrathin forms for stretchable photovoltaic modules. These designs allow for a high degree of stretchability and areal coverage, and they provide a natural form of strain-limiting behavior, helping to avoid destructive effects of extreme deformations.

In situ high-temperature scanning tunneling microscopy study of bilayer graphene growth on 6H-SiC(0001)

Using in situ high-temperature (1395K), ultra-high vacuum, scanning tunneling microscopy (STM), we investigated the growth of bilayer graphene on 6H-SiC(0001). From the STM images, we measured areal coverages of SiC and graphene as a function of annealing time and found that graphene grows at the expense of SiC. Graphene domains were observed to grow, at comparable rates, at (I) graphene-free SiC step edges, (II) graphene–SiC interfaces, and (III) the existing graphene domain edges. Based upon our results, we suggest that the rate-limiting step controlling bilayer graphene growth is the desorption of Si from the substrate.

Imbricate Scales as a Design Construct for Microsystem Technologies

Spatially overlapping plates in tiled configurations represent designs that are observed widely in nature (e.g., fish and snake scales) and man-made systems (e.g., shingled roofs) alike. This imbricate architecture offers fault-tolerant, multifunctional capabilities, in layouts that can provide mechanical flexibility even with full, 100% areal coverages of rigid plates. Here, the realization of such designs in microsystems technologies is presented, using a manufacturing approach that exploits strategies for deterministic materials assembly based on advanced forms of transfer printing. The architectures include heterogeneous combinations of silicon, photonic, and plasmonic scales, in imbricate layouts, anchored at their centers or edges to underlying substrates, ranging from elastomer sheets to silicon wafers. Analytical and computational mechanics modeling reveal distributions of stress and strain induced by deformation, and provide some useful design rules and scaling laws.

Combining multivariate statistical analysis with geographic information systems mapping: a tool for delineating groundwater contamination

Multivariate Statistical Analysis (MSA) has successfully been coupled with geographic information system (GIS) mapping tools to delineate zones of aquifer contamination potential. While delineating contaminants is key to site remediation, it is often compromised by a poor understanding of hydrogeologic conditions, and by uncertainties in contaminant observations. MSA provides improved estimates of contamination potential by augmenting observed contaminant concentrations with auxiliary information from other water-quality parameters. GIS is useful for organizing and managing water-quality information by visually communicating large amounts of information. The proposed method first establishes appropriate areal extents, GIS coverages, and scales for displaying groundwater contamination concentrations of tritium and the volatile organic contaminants trichloroethylene (TCE) and tetrachloroethylene (PCE) at the Savannah River Site, South Carolina, USA. Principal components analysis is used to group variables that are most indicative of contamination potential. Tritium contamination potential is best represented as the combination of tritium with the cations Al, Mg, Na and total dissolved solids, while PCE contamination potential is predicted using PCE and Cl. Maps of contamination potentials for 1993–1995 geochemical data compare favorably with measured contaminant concentrations during 1999. Cluster analysis of water-quality data groups geochemical and contaminant concentrations into zones of homogeneous behavior.

A field and numerical study of the evolution of sea-ice thickness in the Ross Sea, Antarctica, 1998-99

AbstractDuring two cruises in 1998 and 1999, we examined drift and ridging characteristics of sea ice in the Ross Sea, Antarctica. Mean ice thickness in the western Ross Sea in autumn was 0.5 m, while higher level-ice thicknesses, greater areal coverages of ridges and higher sails were found in the central and eastern Ross Sea in summer. Near the continent, ice drifted westward near the coast and turned eastward further north. We use a regional sea-ice−mixed-layer−pycnocline model to initiate backward trajectories at the time and location of field observations and examine the dynamic and thermodynamic processes that determine ice thickness along these trajectories. Model results agree with previously published field data to indicate that thermodynamic and dynamic thickening and snow-ice formation each contribute significantly to the ice mass of the summer ice field in the central and eastern Ross Sea. For first-year ice in the western Ross Sea, model results and field data both indicate that thermodynamic thickening is the dominant process that determines ice thickness, with dynamic thickening also contributing 20% to the net ice-thickening rate. However, model results fail to reproduce the prevalence of snow- ice formation that was seen in field data.

Biogenic emission inventory development: field assessment of the GAP vegetation database in California

Given the key role played by biogenic volatile organic compounds (BVOC) in tropospheric chemistry and regional air quality, it is critical to generate accurate BVOC emission inventories. Indeed, formulating effective air quality attainment strategies for formation of ozone, fine particles, and other secondary air pollutants may depend in some regions upon the strength of biogenic emissions, requiring the geolocated characterization of plant species and their areal coverages. Vegetation databases developed through remote sensing methods require calibration and validation from ground-based measurements to be reliably used for BVOC modeling. A recent GIS-based description of vegetation coverage in the natural areas of the US is provided by the Gap Analysis Program (GAP) database. We conducted an assessment of this database in central California through quantitative ground-based vegetation surveys in 18 polygons, using a modified stratified randomized sampling design, to evaluate the use of GAP for developing BVOC emission inventories. The plant species listed by GAP accounted for between 0% and 88% of the relative cover in the polygons, with a mean of 43%. Of the 76 species listed by GAP for which data were collected, 33 were found to be correctly listed within their respective assemblages, 13 were found to be listed for the wrong assemblage, and 30 were below percentages of co-dominants of any assemblage. Summed over all 18 polygons, BVOC emission indices based on field data were 20% less than those based on GAP, but for individual polygons differences ranged from −100% to more than +100%.

Geographic Information System-Based Digital Catalog for Managing Subsurface Geotechnical and Geologic Data

Knowledge of surface and subsurface geology and geotechnical properties is fundamental to planning, developing, and modernizing transportation systems. Through dynamic coupling of readily available areal geographic information system coverages and subsurface borehole data stored in a relational database, a spatially referenced digital catalog of borehole data was created for two pilot areas in Rhode Island. The borehole database was populated with data derived from Rhode Island Department of Transportation geotechnical reports and supplemental data from the U.S. Geological Survey groundwater site inventory system and local storm water and sewer projects. Most of these data were previously maintained in paper format, making historical or interproject data comparisons virtually impossible. Unification of these data in a single relational database yields two primary benefits: ( a) historical data are readily accessible for review and therefore can be incorporated easily into the planning stages of new projects and ( b) sophisticated analysis of the region becomes possible with access to data from multiple projects with both spatial and temporal coverage. Geologic data include bedrock geology, surface outcrops, unconsolidated materials, soil type, topographic and orthophotographic base maps, and location of boreholes and wells. Subsurface data include land surface elevation, depth to water table, depth to bedrock, presence of fill, high and low blow-count zones, and organic sediment. The digital catalog is distributed on a CD-ROM that includes ArcView project files and an Access relational database. The borehole data are also accessible through the Internet, with retrieval access for all users and data entry privileges for registered users.

Mapping marine benthic biotopes using acoustic ground discrimination systems

This paper describes the use and appraises the performance of acoustic ground discrimination systems (AGDS) for marine benthic biotope mapping for those who are more familiar with satellite or airborne remote sensing. The operation of AGDS is described and the nature of the data produced compared with more conventional remotely sensed data. Analysis of the AGDS data involves the interpolation of track point data to create areal coverages that can then be interpreted using classification and image processing techniques. AGDS data have been shown to be variable both within and between surveys and systems which affects the performance of interpretation. Additionally, the marine environment imposes limitations on the way that ground sampling can be undertaken and the spatial extent of information that can be obtained. In summary, the main issues that contribute to variability and uncertainty of biotope maps based on AGDS-based methodology are: (1) errors in position fixing of both AGDS and the ground samples; (2) inconsistent performance of the AGDS system; (3) single frequency of AGDS and its effect on discrimination; (4) tracking intensity of AGDS survey; (5) heterogeneity of the seabed at the scale of resolution of the system; (6) lack of vista for designating training sites and the reliance on buffers around ground samples; (7) unsuitable biotope categories. Variability due to AGDS hardware is often beyond the control of surveyors, but quality control procedures can at least alert operators to poor quality data. Performance of AGDS surveys also depends on intensity of both tracking and ground sampling in relation to heterogeneity of the sea floor. This relationship can be investigated through exploratory spatial data analysis, particularly the variogram. The performance of biotope maps can be measured using error and similarity matrices. The accuracy of the biotope maps resulting from AGDS surveys is modest when compared with the performance of satellite or airborne remote sensing and the similarity between maps derived from different datasets can be low. It is misleading to base expectations of the performance of AGDS on satellite or airborne remote sensing systems. AGDS are low resolution systems with limited powers for discrimination between different ground types. However, they afford the opportunity to map benthic biotopes in environments where electromagnetic spectra-based systems cannot operate. Thus, AGDS is a useful tool for benthic ecologists to study the spatial distribution of biotopes on the sea floor although the limitations of AGDS for mapping may preclude their use for precise and accurate survey required for some monitoring applications.

On the role of grain boundary diffusion in fission gas release

It is generally believed that thermal fission gas release from LWR fuel occurs mainly via interconnected grain boundary bubbles. Grain boundary diffusion is not considered to be a significant mechanism. We investigated this supposition by two methods; first, by assessing the distance a gas atom can migrate in a grain boundary containing perfectly absorbing traps. For areal number densities and fractional coverages by the traps observed in fuel irradiated to burnups exceeding ∼20 MWd/kg, gas atoms will be trapped after a migration distance equal to the size of a grain or less. This supports the supposition for medium-to-high burnups. However, the above-mentioned model is inapplicable for trace-irradiated specimens. In our second analysis, we examined Xe release from trace-irradiated UO 2. The measurements indicated that the liberation involves more than only lattice diffusion at the specimen surface, and that the data are consistent with sequential lattice and grain boundary diffusion unimpeded by intergranular traps. The analysis also provided rough estimates of the grain boundary diffusion coefficient in UO 2.

Prospects of Research in Pathology, Abstract 25, State-of-the-art-lecture

Given the key role played by biogenic volatile organic compounds (BVOC) in tropospheric chemistry and regional air quality, it is critical to generate accurate BVOC emission inventories. Indeed, formulating effective air quality attainment strategies for formation of ozone, fine particles, and other secondary air pollutants may depend in some regions upon the strength of biogenic emissions, requiring the geolocated characterization of plant species and their areal coverages. Vegetation databases developed through remote sensing methods require calibration and validation from ground-based measurements to be reliably used for BVOC modeling. A recent GIS-based description of vegetation coverage in the natural areas of the US is provided by the Gap Analysis Program (GAP) database. We conducted an assessment of this database in central California through quantitative ground-based vegetation surveys in 18 polygons, using a modified stratified randomized sampling design, to evaluate the use of GAP for developing BVOC emission inventories. The plant species listed by GAP accounted for between 0% and 88% of the relative cover in the polygons, with a mean of 43%. Of the 76 species listed by GAP for which data were collected, 33 were found to be correctly listed within their respective assemblages, 13 were found to be listed for the wrong assemblage, and 30 were below percentages of co-dominants of any assemblage. Summed over all 18 polygons, BVOC emission indices based on field data were 20% less than those based on GAP, but for individual polygons differences ranged from −100% to more than +100%.

Clustering on surfaces at finite areal coverages

Clustering is a phase separation process often observed in growth on surfaces and of technological relevance in heteroepitaxy. Cluster size distributions for three-dimensional cluster ripening on surfaces has been studied to test predictions for the dependence of ripening on finite areal cluster fractions. We show that the distribution broaden relative to the mean field model and also exceed the increase in width predicted in simulations for three-dimensional systems caused by the interaction between neighboring clusters. The observed data are in significant disagreement with the model and the simulations in respect of the skewness of the cluster size distributions which can be associated with unexpectedly intensive coalescence effects even at areal coverages as low as 10%.

Response of ducks to glyphosate-induced habitat alterations in wetlands

The effects of glyphosate herbicide-induced changes in wetland emergent vegetation (largely cattails,Typha spp.) on densities of ducks (Anatinae) were assessed in northeastern North Dakota. In 1990 and 1991, 17 cattail-dominated wetlands were randomly assigned to 0% (reference wetlands), 50%, 70%, or 90% areal spray coverages with glyphosate herbicide. Densities of green-winged teal (Anas crecca), bluewinged teal (Anas discors), gadwalls (Anas strepera), and ruddy ducks (Oxyura jamaicensis) were similar among treatments during both post-treatment years (P≥0.1). One year post-treatment, mallard (Anas platyrhynchos) and northern pintail (Anas acuta) abundances did not differ among treatments (P≥0.1), whereas two years post-treatment their abundances were greater in the sprayed wetlands than in the reference wetlands (P≤0.1). Densities of northern shovelers (Anas clypeata) and redheads (Aythya americana) differed among treatments in both post-treatment years, with the 50% sprayed wetlands harboring more ducks than did the other three treatments. Percent coverage and hectares of open water were positively correlated with numbers of diving ducks (Aythyini and Oxyurini) (P≤0.1). Dabbling duck (Anatini and Cairinini) numbers correlated positively with hectares of open water and dead vegetation, whereas their numbers were negatively correlated with percent coverage of live vegetation (P≤0.1). Results of this study suggest that numbers of ducks were positively influenced by creating a mosaic of open water, live vegetation, and dead vegetation with glyphosate herbicide.

Seagrass loss associated with boat moorings at Rottnest Island, Western Australia

Loss of seagrasses caused by mooring damage at Rottnest Island, Western Australia, was studied using aerial photographs taken between 1941 and 1992. The temporal decline of seagrass beds damaged by moorings was studied by comparing areal coverages of seagrasses and sand patches, and increases in the length of the exposed seagrass edge within seagrass beds. The study concentrated on Rocky Bay and Thomson Bay where the bulk of permanent moorings are located. Rocky Bay is more exposed to the prevailing westerly swell direction and Thomson Bay is a protected east facing bay. The loss of seagrasses associated with moorings in Rocky Bay has been dramatic, with 18% of seagrass area lost between 1941 and 1992, and 13% between 1981 and 1992. The exposed edge of the beds increased by 230% between 1981 and 1992. Sand patches associated with moorings have coalesced in the shallow central west part of the bay. The change from single weighted swing moorings to three chained cyclone moorings has resulted in greater loss of seagrasses. Single cyclone moorings produce three circular holes in the seagrass bed. The areal loss recorded from Thomson Bay was less than 5%, yet the exposed edge of the seagrass beds doubled between 1941 and 1992. Fragmentation of the bed was visible near heavy use areas. Some regrowth was recorded to the north of the main ferry jetty where the sedimentary environment is depositional. The effects of moorings on seagrasses at Rottnest Island varied from devastating in Rocky Bay to small in Thomson Bay. The differences seem to be related to exposure to prevailing swell and whether the environments are erosional or depositional. Thus a single management protocol, such as cyclone moorings versus swing moorings, is inappropriate. Physical environments need to be assessed before determining the number and types of moorings allowable in bays at Rottnest Island.

Charon: More than Water Ice?

A significant non-H 2O ice component may be present on the surface of Pluto's satellite Charon and yet remain undetected by existing observations. This suggestion arises from a comparison of calculated reflectance spectra with Charon's 1.5- to 2.5-μm reflectance spectrum. The calculated spectra rely upon descriptions of the interaction of light scattered from particulate surfaces and the optical constants of H 2O, CH 4, and CO 2 ices. Calculated spectra of mixtures composed of H 2O and CO 2 ice remain consistent with the observed spectrum of Charon for high abundances of CO 2 (≈50% relative mass fraction) in intimate mixtures, and for areal coverages of about 40% CO 2 in spatial mixtures. Calculations for mixtures of H 2O and CH 4 ice indicate that ≥5% relative mass fraction of CH 4 in intimate mixtures and ≥5-10% areal coverage of CH 4 in spatial mixtures result in spectra that cannot reproduce the observed Charon spectrum. Calculated spectra of three-component intimate mixtures of H 2O, CH 4, and CO 2 ices with similar grain sizes can fit the observed spectrum of Charon only for low abundances of CH 4 (≤ 5%). If the CH 4 ice grain size is much greater than the other components, then the spectrum of Charon can be modeled by calculated spectra containing up to ≈30% CH 4 in the intimate mixtures. Calculated spectra for spatial mixtures of H 2O, CH 4, and CO 2 ices indicate that ≤5-10% areal coverage of CH 4 can be incorporated and remain consistent with the observational data. The suggestion of significant amounts of non-H 2O components on Charon can be tested as Earth-based telescopic instrumentation improves. This suggestion should be considered during instrumental design for spacecraft destined for the Pluto-Charon system.

Morphology and phase stability of TiSi2 on Si

The formation mechanisms and properties of TiSi2 on Si are investigated. The particular emphasis is in relating the nucleation, morphology, and phase stability of the films. TiSi2 films were prepared by deposition of Ti on atomically clean silicon substrates in ultrahigh vacuum. The silicide formation was initiated either by in situ annealing or deposition onto heated substrates. The island formation of TiSi2 and surface and interface morphologies of TiSi2 were examined by scanning electron microscopy and transmission electron microscopy. The TiSi2 formation process was monitored with in situ Auger electron spectroscopy and low-energy electron diffraction to analyze the surface concentration and the surface structures, respectively. Raman spectroscopy was used for phase identification of the TiSi2. Titanium film thicknesses from 50 to 400 Å were examined. For all thicknesses studied, the C49 TiSi2 phase is observed to nucleate. Immediately after low-temperature deposition, the interface morphology was smooth, but after reaction and nucleation of the C49 TiSi2 phase a rough interface was observed. After higher-temperature annealing the transition to the C54 TiSi2 phase was observed. For TiSi2 on Si(111), the interface becomes smooth and flat. The temperature of the C49-to-C54 transition was observed to vary as a function of film thickness and substrate orientation. The films exhibited island formation after high-temperature annealing. For similar Ti thicknesses and annealing temperature, different areal coverages and island morphologies of TiSi2 on Si(100) and Si(111) were observed. The island morphologies are modeled and analyzed based on a liquid-liquid model, and the surface and interface energies for different TiSi2 island structures are deduced from contact angle measurements. The C49 nucleation, interface morphologies, surface morphologies, and the C49-to-C54 structural phase transition are discussed in terms of surface and bulk free-energy considerations.

Classification of a Wetland area along the upper Mississippi River with aerial videography

We evaluated the use of aerial videography for classifying wetland habitats along the upper Mississippi River and found the prompt availability of habitat feature maps to be the major advantage of the video imagery technique. We successfully produced feature maps from digitized video images that generally agreed with the known distribution and areal coverages of the major habitat types independently identified and quantified with photointerpretation techniques. However, video images were not sufficiently detailed to allow us to consistently discriminate among the classes of aquatic macrophytes present or to quantify their areal coverage. Our inability to consistently distinguish among emergent, floating, and submergent macrophytes from the feature maps may have been related to the structural complexity of the site, to our limited vegetation sampling, and to limitations in video imagery. We expect that careful site selection (i.e., the desired level of resolution is available from video imagery) and additional vegetation samples (e.g., along a transect) will allow improved assignment of spectral values to specific plant types and enhance plant classification from feature maps produced from video imagery.

Microstructure of epitaxial YBa2Cu3O7−x thin films grown on LaAlO3 (001)

We report a microstructural investigation of the epitaxial growth of YBa2Cu3O7−x (YBCO) thin films on LaAlO3 (001) substrates using transmission electron microscopy (TEM). Epitaxial films grow with two distinct modes: c epitaxy (YBCO) single crystal with the c axis normal to the surface) and a epitaxy (YBCO) single crystal with the c axis in the interfacial plane), where c epitaxy is the dominant mode grown in all samples 35–200 nm thick. In 35 nm YBCO films annealed at 850 °C, 97±1% of the surface area is covered by c epitaxy with embedded anisotropic a-epitaxial grains. Quantitative analysis reveals the effect of film thickness and annealing temperature on the density, grain sizes, areal coverages, and anisotropic growth of a epitaxy.

Geologic applications of space shuttle photography

Space Shuttle astronauts have used handheld cameras to take about 30,000 photographs of the earth as seen from orbit. These pictures provide valuable, true-color depictions of many geologically significant areas. While the photographs have areal coverages and resolutions similar to the more familiar Landsat MSS and TM images, they differ from the latter in having a wide variety of solar illumination angles and look angles. Astronaut photographs can be used as very small scale aerial photographs for geologic mapping and planning logistical support for field work. Astronaut photography offers unique opportunities, because of the intelligence and training of the on-orbit observer, for documenting dynamic geologic activity such as volcanic eruptions, dust storms, etc. Astronauts have photographed more than 3 dozen volcanic eruption plumes, some of which were not reported otherwise. The stereographic capability of astronaut photography also permits three-dimensional interpretation of geologic landforms which is commonly useful in analysis of structural geology. Astronauts have also photographed about 20 known impact craters as part of project to discover presently unknown examples in Africa, South America, and Australia.