bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Positron Annihilation Lifetime Study of Poly(Bisphenol-a Carbonate)
Authors: Jones P. L. , Hill A. J. , Pearsall G. W. , Lind J. H. 
Published: March 2011

ABSTRACTPositron annihilation lifetime spectroscopy has proven to be sensitive to glass transitions and other free volume dependent phase transitions in amorphous and semicrystalline polymers. The thermal dependence of the lifetime spectra of positrons in compression-molded poly(bisphenol-A carbonate) has been measured from 253K to 323K, then modelled using a three component fit. The longest-lived component lifetime τ3 was found to vary linearly with increasing temperature independent of thermal history. The corresponding component intensity I3 was found to vary in a non-linear fashion with increasing temperature, exhibiting a significant dependence on thermal history. The observed thermal response of τ3 and I3 is discussed in terms of both molecular relaxation and the ductile-to-brittle transition behavior of poly(bisphenol-A carbonate).
Correlation of Electrical Properties with Structure Imaging of Semiconductor Interfaces
Authors: Batstone J.L. , Gibson J.M. , Tung R.T. , Levi A.F.J. , Outten C.A. 
Published: March 2011

ABSTRACTHigh resolution electron microscopy (HREM) is recognised as a powerful technique for thedetermination of atomic structures at crystal defects and interfaces. The application ofHREM to the study of insulator/semiconductor and metal/semiconductor interfaces is of particular technological interest. Correlation of electrical properties withinterface structure has been performed, taking advantage of the resolution available in the JEOL 4000EX. Images are usually obtained in a <110> projection, however in the JEOL 4000EX (point-to point resolution <1.7A). we have imaged semiconductor interfaces in the <100=direction using the (220) planes of 1.92Å spacing revealing all atomic columns in silicon, permitting “structure images” of interfaces to be obtained. Two types of interface have been studied at <1.9Å resolution. The roughness of the important crystalline Si/amorphousSiO2interface observed in implanted buried oxide layers and after wet and dry oxidation of silicon is relevant for the correlation of carrier mobilities with interface structure. Analysis of both the NiSi2/Si(100) and AI/AIGaAs(100) crystal/crystal interfaces where a periodic structure is observed in the plane of the interface allows the use of rigid shift measurements and multislice image calculations to determine an atomistic model. The influence of the NiSi2/Si interface structure on the Schottky barrier height is discussed.
Structural Studies of Nucleation and the Initial Stages of Growth of Epitaxial Gaas on Si(100) Substrates
Authors: Hull R. , Fischer-Colbrie A. , Rosner S.J. , Koch S.M. , Harris J.S. 
Published: March 2011

ABSTRACTNucleation and growth of GaAs fIlms deposited by Molecular Beam Epitaxy upon Si(l00) substrates are studied by transmission electron microscopy. The initial nucleation of GaAs consists of approximately hemispherical islands associated with steps upon the substratesurface and coherently strained to the substrate lattice. As the island size increases, crystalline defects relax the strain between epilayer and substrate. Island coalescence is a secondary defect generation mechanism. Subsequent growth of the epitaxial GaAs layer reveals a progressive deterioration of the GaAs/Si interface planarity and the growth and eventual dissolution of amorphous or misoriented crystalline regions at the GaAs/Si interface.
Tem Study of the Accidental Modulation of Mbe Grown AlxGal-x As
Authors: Britton E.G. , Stobbs W.M. 
Published: March 2011

ABSTRACTComposition modulations with a wavelength of -1-3 nm have been observed by transmission electron microscopy in nominally uniform AlxGa1-x As grown by molecular beam epitaxy. We describe the characterisation of this phenomenon and discuss its possible origins, in the light of the reported existence of a long range ordered structure.
Hrem of Grain Boundaries in Oxides
Authors: Merkle Karl L. 
Published: March 2011

ABSTRACTRecent progress in the understanding of the atomic structure of grain boundaries in ionic solids is briefly reviewed with emphasis on the application of the HREM technique to observations of tilt grain boundaries in NiO. The new generation of high-resolution electron microscopes which are capable of a point-to-point resolution of better than 2 Å have allowed atomic-scale observations that can be directly compared to theoretical grain boundary models. Agreements and differences between theory and experiment are discussed.The importance and significance of faceting and asymmetrical boundaries is pointedout.
Atomic Resolution Imaging of Surfaces By Electron Microscopy
Authors: Smith David J. 
Published: March 2011

ABSTRACTThe electron microscope can be operated in several different modes to provide atomic-level detail about surfaces. The REM technique with glancing-angle incidence permits the topography of bulk surfaces to be characterized with a resolution of better than 10A, and atomic-step-height features are visible. The standard TEM bright- and dark-field modes can also be used with appropriate samples to provide monolayer sensitivity. The profile imaging technique is ideal for following real-time dynamic processes. Typical vacuum levels ( ∼10−7 torr), and the lack of facilities for surface cleaning, currently impose a restriction on the materials which can be usefully studied in most available microscopes. Clean and well-defined environments for the sample, without any compromise of the microscope performance, will become increasingly common in the near future.
Surface Morphology of Single-Crystal Ceramics
Authors: Susnitzky D.W. , Carter C.B. 
Published: March 2011

ABSTRACTSurfaces of crystalline materials generally facet and form steps and ledges on low-index planes to reduce their total energy. A conventional wedge-shaped transmission electron microscope (TEM) thin foil, prepared slightly misoriented with respect to a low-index plane, provides a suitable geometry for the study of surface ledges, steps and facets. This TEM study characterizes the surface features of annealed thin foils prepared from various oxides with a range of nominally low-index orientations. Observations from single-crystal α-A12O3 and MgAl2O4 (spinel) will be included.The steps and facets typically form along energetically favorable, low-index planes and bound terraces of low-index orientation. The structure of these features are discussed. In addition, surface step movement has been observed and monitored through a series of reannealing experiments on the same foil.
X-Ray Diffuse Scattering from Cobalt Precipitates in Copper
Authors: Larson B. C. , Iida S. , Tischler J. Z. , Lewis J. D. , Ice G. E. , Habenschuss A. 
Published: March 2011

ABSTRACTLarge-angle diffuse scattering has been investigated for the purpose of studying coherent precipitates in a crystal lattice. Detailed calculations have been made of the scattering near Bragg reflections from cobalt precipitates in a copper host lattice. These calculations have been compared to x-ray diffuse scattering measurements made on aged (570°C for 17 hr.) Cu-0.95%Co crystals with x-rays of three different wavelengths at the NSLS. The results indicate that the size distribution, the concentration, and the internal strain of the precipitates can be determined from such diffuse scattering measurements.
High Temperature Studies of Stoichionetric Cerium Dioxide
Authors: Faber J. , Hitterman R. L. 
Published: March 2011

ABSTRACTHigh-resolution, neutron time-of-flight Bragg scattering measurements have been carried out on polycrystalline CeO2 as a function of temperature (20<T<1200C). Systematic deviations between theory and experiment for the integrated intensities of the Bragg reflections were observed; these deviations increased with increasing temperature. The deviations result from cubic anharmonic interactions that appear only on the oxygen sublattice. The results are discussed in terms of higher order cumulant tensor representations. We observe that these anharmonic interactions exhibit the same symmetry as those associated with defects incorporated into the fluorite lattice when CeO2 is made nonstoichiometric.
Chemical Reactions at the in Vacuo Au/Inp Interface
Authors: Williams R. Stanley , Tsai C. Thomas , Cirlin Eun-Hee 
Published: March 2011

ABSTRACTThe reaction between a Au film and an Inp substrate occurs much more readily in vacuo than under an external pressure of an inert ga. At atmospheric pressure, the compounds Au2P3 and the γ intermetallic compound (at times designated Au7In3, Au9In4, or Au2In) are formed at 450 °C and remain fairly stable even when annealed at 500°C for hours. Under ultra-high vacuum conditions, phosphorous readily escapes from the film when a sample is annealed at 300°C for 15 minutes, and the major reaction products are the ψ phase (Au3In2) and another intermetallic compound that is probably AuIn. The presence of an inert gas creates a kinetic barrier for the escape of phosphorous from the surface, and thus Au/InP behaves more like a closed thermodynamic system under pressure than in a vacuum.
Studies of Surface Composition and Phase Transition of Mo-5%Re(1O0)
Authors: Wang G. -C. , Zehner D. M. , Eaton H. C. 
Published: March 2011

ABSTRACTSurface composition of a clean Mo-5%Re(100) alloy was determined quantitatively by Auger Electron Spectroscopy and X-Ray Photoelectron Spectroscopy. A slight enrichment of Re on the alloy surface was found at and below room temperatures and the result is consistent with the prediction by a graphical approach for segregation. The change of surface composition due to gas contamination and sputtering were also studied. In contrast to the pure Mo(100) surface where a structural phase transition occurs below room temperature, low energy electron diffraction showed no structural change down to 160 K. However, for H, CO, N chemisorptions and C segregation on the alloy surface, LEED patterns similar to the ones observed from a pure Mo(100) surface were observed.
An Experimental Measurement of the Permeability of Deformable Porous Media
Authors: Ambari A. , Gauthier-Manuel B. , Guyon E. 
Published: March 2011

ABSTRACTKnowledge of the evolution of the permeability of cement throughout the course of hydration provides a suitable means to evaluate the evolution of the pore structure. The main difficulty is to measure permeability without disturbing the tenuous structure of the material at the beginning of the hydration. We have developed a differential permeability technique in which the applied flow is sufficiently weak that the structure of the medium is not disturbed. As an example of application of this technique we present measurement of the evolution of the critical permeability during a sol-gel transition.
Effects of Aggregate Fineness and Added Calcium Hydroxide on Portland Cement Mortar Crack Propagation
Authors: Detriche C. H. , Ollivier J. P. , Ramoda S. A. 
Published: March 2011

ABSTRACTThe resistance of a coherent granular material, such as mortar or concrete, to crack propagation cannot be appreciated without taking into account the heterogeneity of the material. Heterogeneity results from the presence of aggregates and from the local modifications of the composition and of the behavior introduced by these aggregates in the volumes of intergranular paste situated close to their interface, the “aureoles de transition.” It is possible to modify the characteristics of these zones to develop the global response of the material.
The Diffusion of Chloride Ions in Fly Ash/Cement Pastes and Mortars
Authors: Malek R. I. A. , Roy D. M. , Licastro P. H. 
Published: March 2011

ABSTRACTFly ashes having three distinctly different levels of calcium, designated low-calcium (Class F), intermediate-calcium (Class F/C), and high-calcium (Class C), comprised the basic material for the present study. Pastes and mortars were made using cement and one of three types of fly ashes at various levels of replacement and water-solid ratios. Chloride ion diffusion was measured by applying an electrical potential across cured cylindrical samples and measuring the amount of current passed in a certain period of time (proportional to amount of CE” passed in this time). Other supportive measurements were made, e.g. porosity, pore size distribution, water permeability and surface area. The Cl− ion diffusivity was correlated with the chemical composition of fly ash, mix proportion, and water permeability of the hardened paste or mortar.
Restricted Hydration of Mass-Cured Concrete Containing Fly Ash
Authors: Mills R. H. , Buenfeld N. 
Published: March 2011

ABSTRACTCement paste and concrete specimens containing three different mixtures of portland cement (PC) and high-lime fly ash (FA) were subjected to various curing conditions, and the strengths, non-evaporable water, and porosities compared with control mixes containing portland cement only. Strength and porosity data indicated that the cementing action of the mixtures was in all cases inferior to portland cement. For each mixture the strength loss resulting from imperfect curing, i.e. sealed or exposed to 50% relative humidity, was greater than for portland cement. In the case of concrete drying from one surface, strength differences were found, but these were not as clearly defined as those obtained in the paste specimens.
Study of the microstructure and Frost Behavior of HCP by Measuring the Dynamic Modulus of Elasticity
Authors: Setzer M. J. 
Published: March 2011

ABSTRACTHardened cement paste can be regarded as a highly dispersed system of solid particles, air voids and water filled pores ranging in size from a submicroscopic to a macroscopic scale. Using a statistical model, the elastic moduli of solid particles, air voids and pore water can be combined appropriately to find a correlation between the modulus of hardened cement paste and the moduli, as well as respective volume fractions, of its constituents. Ice formation and the addition of aggregates in a mortar can easily be taken into account. On this basis the measurement of the dynamic elastic modulus of hardened cement paste and mortar at different temperatures and its evaluation provides much interesting data. The interaction of particles and pores is better understood. The ice formation can be studied. Since the freezing temperature of pore water is lowered in small gel pores, the pore size distribution can be calculated. Frost damage is observed directly. Therefore, this method is a valuable tool to improve the Munich model of hardened cement paste.
A Model for Particle Size and Phase Distributions in Ground Cement Clinker
Authors: Brown P. W. , Galuk K. G. 
Published: March 2011

ABSTRACTA model has been developed to describe a granule of unground clinker, to simulate the grinding process by the removal of particles according to a user-defined particle size distribution, and to characterize the exposed surface areas and volumes of each clinker phase present. The composition of the clinker granule and the distribution of phases within the granule are also user defined.
Restricted Hydration of Mass-Cured Concrete Containing Fly Ash
Authors: Mills R. H. , Buenfeld N. 
Published: March 2011

ABSTRACTCement paste and concrete specimens containing three different mixtures of portland cement (PC) and high-lime fly ash (FA) were subjected to various curing conditions, and the strengths, non-evaporable water, and porosities were compared with control mixes containing portland cement only. Strength and porosity data indicated that the cementing action of the mixtures was, in all cases, inferior to portland cement. For each mixture the strength loss resulting from imperfect curing, i.e. sealed or exposed to 50% relative humidity, was greater than for portland cement. In the case of concrete drying from one surface, strength differences were found, but these were not as clearly defined as those obtained in the paste specimens.
Effect of Fly Ash Incorporation on Rheology of Cement Pastes
Authors: Rattanussorn M. , Roy D. M. , Malek R. I. A. 
Published: March 2011

ABSTRACTThe predominant spherical shape of fly ash particles combined with mainly glassy composition and texture of its surfaces have a special effect on rheology of cement pastes containing fly ash. The early ages rheological behavior of cement pastes (ASTM Type I) incorporating 30% low-calcium fly ash was monitored by measuring viscosity of the fresh pastes prior to initial hardening and stiffening (up to −2 hours) as a function of time. The viscosities were determined using a co-axial rotoviscometer (HAAKE). The effects of fly ash content, water to cement ratio, and presence and concentration of superplasticizer, were evaluated. In addition, the dispersivity of fly ash spheres was evaluated by determining the zeta-potential of fly ash suspensions in water using a microelectrophoresis technique and the results were correlated to the chemical composition of fly ash as well as the viscosities of fresh pastes.
Modeling of Temperatures in Cementitious Monoliths
Authors: Kaushal S. , Roy D. M. , Licastro P. H. 
Published: March 2011

ABSTRACTTemperatures in large cementitious monoliths (works) can rise very high due to unfavorable thermal properties such as low conductivity and high diffusivity of the monolith and the surrounding media. Heat moderation becomes necessary in such situations to avoid excessive thermal stresses. Moderation due to the addition of inert additives such as sand in mortars is compared to that obtained by the addition of reactive but low heat evolution substituents such as Class C and Class F fly ashes. Substitution of cement by slag has also been considered. The hydration temperatures for the extreme conditions (adiabatic) have been experimentally measured and compared to those predicted under real conditions. Such a simulation has been made by measuring the thermal properties and analyzing the temperature distribution due to exothermic reactions as predicted by a finite differences computer model. In general, lower temperatures can be maintained by increasing the thermal conductivity and heat capacity of the hydrating material. This material can be tailored for both heat evolution and setting times by incorporating inert additives such a sand (quartz) and/or reactive additives such as slag and fly ash.
Variability and Trends in Iowa Fly Ashes
Authors: Schlorholtz Scott , Bergeson Ken , Demirel Turgut 
Published: March 2011

ABSTRACTAn investigation has been made of the variability of physical and chemical properties of high-calcium (Class C) fly ashes from four Iowa power plants. The investigation summarizes results obtained from three years (1983 through 1985) of monitoring of the various power plants. All four of the power plants burn low-sulfur, sub-bituminous coal from Wyoming. Fly ash samples were obtained from the power plants in accordance to the procedures described in ASTM C 311. Laboratory testing methods were similar to those specified by ASTM C 311. During the three year period, 102 samples were subjected to chemical and physical analysis while an additional 349 samples were subjected to physical analysis only. In general, the four power plants produce fly ashes of similar mineralogy and chemical composition. The observed time variation of the chemical composition of fly ash from a single power plant was quite small. The sulfur content consistently showed the largest coefficient of variation of the 10 elements studied. Physical characteristics of the fly ashes (as measured by ASTM tests) were also fairly uniform over long periods of time, when considered on an individual power plant basis. Fineness, when measured by wet washing using a 325 mesh sieve, consistently exhibited the largest coefficient of variation of any of the physical properties studied.
Floating-Zone Processing of Indium in Earth-Orbit
Authors: Murphy Shawn P. , Hendrick J. J. , Martin M. J. , Grant R. W. , Lind M. D. 
Published: March 2011

AbstractAn experiment in floating-zone processing of indium was performed on Space Transportation System (STS) Flight 41-D on September 4, 1984. An indium crystal 1 cm in diameter and 7 cm long was grown. The polycrystal-line indium used as the feedstock had been doped with approximately 100 ppm thallium to investigate the distribution coefficient of thallium in indium; the result was K =CS/CL< 0.03. Indium was chosen for study because its low melting point and the low vapor pressure of the melt at that temperature would simplify the apparatus and reduce the electrical energy and cooling requirements. Another advantage is that the properties of liquid indium probably preclude time-dependent thermocapillary flows. The experiment also served as the first flight test of the Fluids Experiment Apparatus (FEA), a new multiple-purpose apparatus we have developed for low-cost, entry-level materials processing, physics and chemistry experiments in Earth-orbit. The experiment confirmed the flight-worthiness of the FEA and the suitability of indium for exploratory floating-zone experiments in Earth-orbit.
The First Products Made in Space: Monodisperse Latex Particles
Authors: Vanderhoff J. W. , El-Aasser M. S. , Kornfeld D. M. , Micale F. J. , Sudol E. D. , Tseng C.-M. , Sheu H.-R. 
Published: March 2011

AbstractTwenty monodisperse polystyrene latexes were made by seeded emulsion polymerization in the MLR-SEP flight hardware on theSTS-3 and STS-4 flights of the Columbia and the STS-6, STS-7, and STS-11 flights of the Challenger. Two polymerizations were small-particle-size controls; the other eighteen were of large particle size. Of these, six failed: four on STS-4 owing to malfunction of the flight hardware; one on STS-6 owing to a broken wire; one on STS-11 owing to a broken stirrer shearpin. Nine monodisperse latexes of 4–30 μm size had narrower particle size distributions than the ground-based controls. The 10 μm STS-6 latex and the 30 μm STS-11 latexes were accepted by the National Bureau of Standards as Standard Reference Materials, the first products made in space for sale on earth. The polymerization rates in space were the same as on earth within experimental error. The flight polymerizations produced only negligible amounts of coagulum; the ground-based control polymerizations produced increasing amounts with increasing particle size, so that these controls were discontinued after the STS-7 experiments. These results confirmed the original rationale of the experiments that polymerization in space would give more uniform large-particlesize monodisperse latexes with less coagulum by: 1. the better uniformity of all 5 μm or larger flight latexes; 2. the more perfect sphericity of the 10 and 30 μm particles; 3. the smaller number of offsize larger particles; 3. the negligible amounts of coagulum; 4. the broadening of the particle size distribution and the formation of more larger offsize particles during the completion on earth of the polymerization of the partially converted STS-4 flight latexes.