bluuebunny/crossref_metadata_2025 huggingface dataset:
Hrem of Grain Boundaries in Oxides
Authors: Merkle Karl L.
Published: March 2011

Recent 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

The 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

Surfaces 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

Large-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

High-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

The 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

Surface 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

Knowledge 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

The 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

Fly 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

Cement 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

Hardened 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

A 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.
Sources of Self-Hardening Properties in Fly Ashes
Authors: Joshi R. C. , Lam D. T.
Published: March 2011

Laboratory investigations of the self-hardening properties of selected subbituminous fly ashes have been conducted. Chemical analyses of the fly ashes are given in Table I. The self-hardening value of the fly ashes was determined by conducting unconfined compressive strength tests on compacted samples of the moistened ashes. Various physical and chemical tests were performed to identify the reaction products, if any, of the hardened compacted fly ash paste, and to delineate the source of self-hardening properties. Results from x-ray diffraction analyses, scanning electron microscopic examination and differential thermal analyses indicated that the hydration products include calcium silicate and aluminate hydrates, and ettringite. Chemical and physical tests conducted to evaluate pertinent fly ash properties included chemical analysis, water soluble fraction, dilute hydrochloric and hydrofluoric acid soluble fractions, heat of solution on dissolving in dilute hydrochloric acid, specific surface area, and electrical conductivity tests.
Restricted Hydration of Mass-Cured Concrete Containing Fly Ash
Authors: Mills R. H. , Buenfeld N.
Published: March 2011

Cement 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

The 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

Temperatures 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

An 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

An 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

Twenty 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.
The Fluids Experiment Apparatus (fea) and Rockwell's Industrial Space Processing Research Program
Authors: Martin Michael J.
Published: March 2011

Rockwell International has long endeavored to stimulate industrial utilization of space for materials processing. A successful introductory briefing program to acquaint nonaerospace industry with the space environment, microgravity process phenomena, experiment hardware, and the programs available to conduct research in space has encouraged several companies to initiate space processing research projects.

To help satisfy industry's microgravity experiment hardware requirements, Rockwell has developed a multipurpose materials processing laboratory for use on the Space Shuttle. The Fluids Experiment Apparatus (FEA) has been flown to perform floating zone crystal growth and purification research and is currently being used to support further crystal growth research with advanced materials for Rockwell. Other companies are preparing experiments that are expected to be conducted in the FEA on future Space Shuttle missions.

Rockwell is developing, with NASA, a program that will allow industry to plan and fly microgravity materials processing experiments within a few months–much faster than the current one to two year lead time. This low-cost program, patterned after the NASA Joint Endeavor Program, provides Space Shuttle flight services and use ot the FEA to conduct scientific investigations. Rockwell plans to offer experiment integration and support services to industry as needed.
Containerless Study of Metal Evaporation by Laser Induced Fluorescence
Authors: Sghiffman Robert A. , Nordine Paul C.
Published: March 2011

Laser induced fluorescence (LIF) detection of atomic vapors was used to study evaporation from electromagnetically levitated and CW CO2 laser heated molydenum spheres and resistively heated tungsten filaments. Electromagnetic (EM) levitation in combination with laser heating of tungsten, zirconium, and aluminum specimens was also investigated. LIF intensity vs temperature data were obtained for molybdenum ( 7S3 ) atoms and six electronic states of atomic tungsten, at temperatures up to the melting point of each metal. The detected fraction of the emitted radiation was reduced by self-absorption effects at the higher experimental temperatures.Vaporization enthalpies derived from data for which less than half the LIF intensity was self-absorbed were ΔHo0 = -636 ± 24 kJ/g-mol for Mo and 831 ± 32 kJ/g-mol for W. Space-based applications of EM levitation in combination with radiative heating are discussed.
Effects of an Applied Magnetic Field on Directional Solidification of Off-Eutectic Bi-Mn Alloys
Authors: Decarlo J. L. , Pirich R. G.
Published: March 2011

Off-eutectic compositions of Bi-Mn were directionally solidified in applied transverse magnetic fields up to 3 kG to determine the effects odn thermal and solutal convection. For Bi-rich compositions, the magnetic field appeared to increase mixing as determined from thermal, morphological, chemical and magnetic analyses. For Mn-rich compositions morphological and chemical analyses suggest some reduction in mixing due to application of the magnetic field. Conductivity gradients in the melt are suggested as a possible mechanism for the observed results.
Pressure Dependence of the Electrical Properties of Gabi Solidified in Low Gravity
Authors: Wu M. K. , Ashburn J. R. , Torng C. J. , Curreri P. A. , Chu C. W.
Published: March 2011

Immiscible GaBi alloys were solidified during free fall in the Marshall Space Flight Cente4 drop tower which provides about 4.5 seconds of low gravity (about 10−4 g, g = 980 cm/s2 ). We have measured the electrical resistivity and magnetic susceptibility as a function of pressure (up to 18 kbar) and temperature (300K to 4.2K) of drop tower (DT) sample and ground control (GC) sample prepared under identical conditions except for gravity. At ambient pressure the electrical resistance of the DT sample exhibits a broad maximum at 100K, while that of GC sample decreases rapidly as temperature decreases. Both DT and GC samples becomesuperconducting at 7.7K (Tc2). However, a minor second superconducting phase with a transition temperature at 8.3K (Tc1) is observed only in the DT samples.
Detection of SUB-PPM Impurity Levels by Selectively Excited Photoluminescence in Fluoride Glass Optical Fibers
Authors: Miniscalco W. J. , Thompson B. A.
Published: March 2011

A technique is presented which addresses the problem of analyzing impurities in heavy metal fluoride glass optical fibers at the extremely low levels required for long distance applications. The procedure uses selectively excited fiber impurity luminescence (SEFIL), and is extremely sensitive due to the zero-background nature of luminescence and the long interaction lengths afforded by optical fiber. The technique has been rendered quantitative through the use of standards and the normalization of the impurity emission by the Raman scattering intensity. A SEFIL analysis of two fibers with differing origins and designs is reported. The ultimate detection limits are estimated to be <1 ppb-wt for Fe3+ and ≤ 0.001 ppb-wt for Nd3+ and Pr3+.
Glasses and Optical IR Fibers of As2Se3−xTex
Authors: Croitoru N. , Shamir N. , Mendlovic D. , Dror J. , Lereah Y.
Published: March 2011

Chalcogenide glasses of As2Se3−xTex (O<x<3) were made with special care, using very pure raw materials in order to avoid traces of oxygen. From these materials optical fibers were pulled, and the attenuation of CO2 laser light (wavelength λ = 10.6 μm) transmitted through these fibers was measured as a function of the Te content (x). The fiber's surface and cross-section were examined, using both the scanning electron and optical microscopes, and they directly revealed the increase in the concentration of the defects while x was increasing. The influence of the physical and mechanical properties on the concentration of defects was studied by measuring the optical absorption (α) and the microhardness (VH) of the raw materials. Slabs of As2Se3−xTex were made, and in these samples the α, VH, and glass transition temperature (Tg) as a function of x were measured. In the infrared region of the spectra at λ = 10.6 μm, the α in both the slabs and pulled fibers increased, and the VH and Tg decreased with the increase of x. This can be explained by the increase of the concentration of the defects (small crystallites) which appeared during the fiber pulling.
Drawing or Photon Induced Defects in Silica Based Waveguides
Authors: Kawazoe H.
Published: March 2011

A model reaction is proposed which can totally explain formation of the defects detected in SiO2: GeO2 glasses such as E', NBOHC, T-T, bonding, peroxy linkages, and T=O or T(II) species, where T is Si or Ge. The initial reaction is radical decomposition of T-O bonds at high temperatures and the defects are products of the secondary reaction between the initial radical species. The net reaction is expressed as 2TO2⇄2TO+O2, which predicts the dependence of concentration of the radical species on PO2 during processing.
High Field Magnetization Step in Zn1−xMnxTe
Authors: Barilero G. , Rigaiux C. , Hau Nguyen Hy , Plcoche J. C. , Giriat W.
Published: March 2011

High field magnetization experiments are reported for dilute Zn1−xMnxTe alloys (x≃0.03) at T=1.3K. The first magnetization step is analyzed including effects of internal field due to the interactions of Mn-Mn pairs with the remaining spins. An accurate estimate of the nearest neighbor (NN) exchange constant is obtained which agrees quite well recent neutron scattering experiments.
The Relevance of Long-Range Interactions in Diluted Magnetic Semiconductors
Authors: De Jonge W. J. M. , A Twardowski , C.J.M. Denissen
Published: March 2011

Data are presented yielding evidence on the long-range character of magnetic interactions in Diluted Magnetic Semiconductors. The radial dependence of these interactions is deduced from the concentration dependence of the freezing temperature. It is shown that calculations of the thermodynamic properties, which include this long-range interaction, are in fair agreement with the experimental data.
Band Structure and Electronic Excitations in Cdl-xMnxTe
Authors: Wei Su-Huai , Zunger Alex
Published: March 2011

We have performed spin-polarized, self-consistent local spin density total energy and band structure calculations for the prototype semimagnetic semiconductor alloy Cd1-xMnxTe. Based on the calculated band structures and taking into account the many body effects of localized states, we propose a schematic energy level diagram to interpret the d→d*, p→d, and photoemission transitions in Cd1-xMnxTe.
The Connection Between Structural Disorder and Semimagnetic Properties in Implanted CdTe
Authors: Jiménez-González H. J. , Lusnikov A. , Dresselhaus G. , Braunstein G. H. , Withrow S. P.
Published: March 2011

The structural disorder and annealing characteristics of dilute magnetic semiconductors synthesized by implantation of Mn ions into CdTe are studied. After implantation but prior to annealing, the implanted Mn ions reside at random sites in a highly disordered CdTe lattice. To separate magnetic and nonmagnetic effects we have implanted CdTe with nonmagnetic Zn ions under the same conditions as the Mn ions (energy 60 keV, fluence 1016 cm−2). Various annealing conditions are applied to monitor the decrease in intensity of the disorder-induced photoluminescence peaks and the increase of the peak intensity of the CdTe-like exciton line is reduced.
Dilute Magnetic Semiconductor Superlattices Containing Hg1-xMnxTe
Authors: Harris K. A. , Hwang S. , Burns R. P. , Cook J. W. , Schetzina J. F.
Published: March 2011

Superlattices containing alternating layers of Hg1-xMnx Te and HgTe have been successfully grown by molecular beam epitaxy. These structures are the first superlattices containing layers of a mercury-based dilute magnetic semiconductor to be grown by any thin film technique. The optical and electrical properties of these novel magnetic multilayers are presented and discussed.
Hg1−x−yMnxCdyTe Alloys for 1.3−1.8 μm Photodiode Applications
Authors: Shin S. H. , Pasko J. G. , Lo D. S. , Tennant W. E. , Anderson J. R. , Gorsk M. , Fotouhi M. , Lu C. R.
Published: March 2011

HgMnCdTe/CdTe photodiodes with responsivity cutoffs of up to 1.54 pm have been fabricated by liquid phase epitaxy (LPE). The mesa device structure consists of a boron-implanted mosaic fabricated on a p-type Hg1−x−yMnxCdyTe layer grown on a CdTe substrate. A reverse breakdown voltage (VB) of 50 V and a leakage current density of 1.5 × 10−4 A/cm2 at V = −10 V was measured at room temperature (295K). A 0.75 pF capacitance was also measured under a 5 V reverse bias at room temperature. This device performance based on the quaternary HgMnCdTe shows both theoretical and practical promise of superior performance for wavelengths in the range 1.3 to 1.8 μm for fiber optic applications.
Investigations of Cd0.9Mn0.1Te Doped with Au, Cu, As and P Acceptors Using Optical Absorption and Photoluminescence
Authors: Misiewicz J. , Wrobel J. M. , Becla P. , Heiman D.
Published: March 2011

Using absorption and photoluminescence investigations the energies of shallow acceptors are determined as follows: 0.11 eV for P; 0.12 eV for As; 0.17 eV for Cu and 0.18 eV for Au. Deep level energies are found as 0.28 eV for P; 0.29 eV for As; 0.41 eV and 0.92 eV for Cu; and 0.33 eV, 0.69 eV and 1.25 eV for Au dopants. Acceptor concentrations in the 1017cm−3 range are achieved for As and P dopants, but for Au and Cu high compensation is found.
Properties of a Constricted-Tube Air-Flow Levitator
Authors: Rush J. E. , Stephens W. K. , Ethridge E. C.
Published: March 2011

A constricted-tube gas flow levitator first developed by Berge, Oran, and Theiss shows promise both as a spacepositioning device and as a levitator for ground-based work. We present results of laboratory studies which were designed to predict the behavior of the device in a low-g environment.
Bubble Motion in a Rotating Liquid Body
Authors: Annamalai P. , Subramanian R. S. , Cole R.
Published: March 2011

Single bubble behavior inside a rotating liquid-filled sphere is studied both experimentally and theoretically. In the limit of small values of the Taylor number, a quasi-static theoretical description of the motion of the bubble is developed. The analytical result thus obtained is compared with experiment and predicts the bubble trajectory as well as its asymptotic location which, in the presence of gravity, is not exactly on the axis of rotation.
Isoelectric Focusing in Space
Authors: Bier M. , Egen N. B. , Mosher R. A. , Twitty G. E.
Published: March 2011

The potential of space electrophoresis is conditioned by the fact that all electrophoretic techniques require the suppression of gravity-caused convection. Isoelectric focusing (IEF) is a powerful variant of electrophoresis, in which amphoteric substances are separated in a pH gradient according to their isoelectric points. A new apparatus for large scale IEF, utilizing a recycling principle, has been developed. In the ground-based prototype, laminar flow is provided by a series of parallel filter elements. The operation of the apparatus is monitored by an automated array of pH and ultraviolet absorption sensors under control of a desk-top computer. The apparatus has proven to be useful for the purification of a variety of enzymes, snake venom proteins, peptide hormones, and other biologicals, including interferon produced by genetic engineering techniques. In planning for a possible space apparatus, a crucial question regarding electroosmosis needs to be addressed. To solve this problem, simple focusing test modules are planned for inclusion in an early Shuttle flight.
Surface Tension Driven Flow in Glass Melts and Model Fluids
Authors: McNeil Thomas J. , Cole Robert , Shankar Subramanian R.
Published: March 2011

Experiments on surface tension driven flow in nominally cylindrical columns of a glass melt and silicone oils are described and results are presented. Predictions from an appropriate theoretical model are included. Conclusive proof has been obtained for the dominance of surface tension driven flow in these systems under the conditions of the present investigation.
Semiconductor Crystal Growth and Segregation Problems on Earth And in Space
Authors: Gatos Harry C.
Published: March 2011

Crystals grown from the melt exhibit compositional and structural defects which limit the exploitation of their full potential in solid state electronics. The origin of these defects is related primarily to gravity-induced convective currents in the melt. In semiconductor compounds additional problems are introduced from variations in stoichiometry. Progress has been made recently in relating qualitatively, and in some instances quantitatively, the growth parameters to the materials properties of the crystals, and in turn to their electronic properties. Overcoming the presence of gravitational forces in space eliminates or minimizes convective interference and, thus, the quantitative assessment of the key growth parameters controlling the chemical and structural perfection of single crystals becomes possible. Results (obtained on earth) will be presented on the growth-property relationships of elemental and compound semiconductors. The advantages, as well as the limitations, that zero gravity conditions present for crystal growth will be discussed.
Electrical Characterization of Hg1−xCdxTe Alloys
Authors: Lehoczky S. L. , Summers C. J. , Szofran F. R. , Martin B. G.
Published: March 2011

Theoretical models are described for calculations of charge-carrier concentrations, Fermi energy, and conduction-electron mobility as functions of x, temperature, and ionized- and neutral-defect concentrations in Hg1−xCdxTe alloys. Measurements are reported of electron concentration and electron mobility from 5–300 K for alloys with 0.17 < ˗ < 0.30. The electrical data are in reasonable agreement with theory and were analyzed to obtain estimates of donor and acceptor state concentrations. The electron inobilities are calculated in terms of a microscopic theory of electrical conduction derived from the solution of the Boltzmann equation for the perturbed steady-state electron distribution function and show that longitudinal opticalphonon and charged and neutral defect scattering are the dominant mobility-limiting mechanisms.
Gravity-Driven Convection Studies in Compound Semiconductor Crystal Growth by Physical Vapor Transport
Authors: Zoutendyk John A. , Akutagawa Wesley M.
Published: March 2011

Gravity-driven convection can alter the diffusive-advective mass transport behavior in the growth of crystals by physical vapor transport. Specially designed and constructed transparent furnaces are being used in our laboratory to study the effects of gravity in crystal growth of the compound semiconductors PbTe and CdTe.
Influence of Diffusion and Convective Transport on Dendritic Growth in Dilute Alloys
Authors: Glicksman M. E. , Bahadur Singh Narsingh , Chopra M.
Published: March 2011

Extensive experimentation has been carried out in which the kinetics and morphology of dendritic growth were measured as a function of thermal supercooling, solute concentration, and spatial orientation of the dendritic growth axis. The crystal growth system studied is succinonitrile [NC(CH2)2CN] with additions of argon (up to 0.1 mole %). This system is especially useful as a model for alloy studies because kinetic data are available for high purity (7–9's) succinonitrile. The addition of argon provides a simple, controllable dilute solute that now permits the first comparably detailed dendritic growth studies on binary alloys.

One dramatic influence of the solute, at fixed thermal supercooling, is to increase the growth velocity (to a maximum) and correspondingly decrease intrinsic crystal dimensions (tip radius). Morphological measurements will be described in detail relating tip size, perturbation wavelength, supercooling, and solute concentration. The analysis of these effects based on morphological stability theory will also be discussed. Finally, experiments permitting the separation of convective and diffusive heat transport during crystal growth of succinonitrile will be described briefly. These studies clearly underscore the importance of gravitationally-induced buoyancy effects on crystal growth kinetics and morphology.
Solidification of Undercooled Monotectic Alloys
Authors: Perepezko J. H. , Galaup C. , Cooper K. P.
Published: March 2011

During the processing of monotectic alloys large compositional segregation of the liquid can precede final solidification. Under normal treatment a coarse scale phase distribution is obtained as a result of convection and sedimentation effects which may be minimized by microgravity processing. In undercooled droplets (5–20μ) of Bi-Ga alloys with compositions near the monotectic point, a finescale segregation has been observed and is similar to that formed during a microgravity treatment of bulk samples. Near the critical point of the miscibility gap, Bi-rich alloys exhibit an undercooling prior to phase separation, while in Ga-rich alloys the onset of phase separation is at the miscibility gap boundary. Similarly, in Cu-Pb alloys an undercooling below the miscibility gap prior to phase separation is observed for Cu-rich alloys, but not for Pb-rich alloys near the critical point. These observations are consistent with the operation of a critical point wetting behavior which can modify the liquid segregation pattern during microgravity treatment.
Suppression of Marangoni Convection With Oxide Films
Authors: Verhoeven J. D. , Noack M. A. , Bevolo A. J.
Published: March 2011

This research is an effort to determine whether surface tension driven convection in molten tin can be eliminated by the formation of one to several monolayers of oxide on the molten tin surface. Initial work is presented describing Auger and electron loss spectroscopies used to detect SnD and SnO2 on molten tin surfaces in a UHV system; Progress on efforts to produce and monitor controlled oxide layers of 8 to 20 Å upon floating zones in a disk geometry is presented.
Influence of Gravity Driven Convection on the Directional Solidification of Bi/MnBi Eutectic Composites
Authors: Pirich Ron G. , Larson D.J.
Published: March 2011

The role of gravity on Bridgman-Stockharger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA sounding rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Ri/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnRi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed,normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50%, for the lowgravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97% of the theoretical maximum.

Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnBi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.
Solidification of Hypermonotectic Al-In Alloys Under Microgravity Conditions
Authors: Potard Claude
Published: March 2011

Four samples of the Al-In system having monotectic and hypermonotectic compositions were solidified under microgravity during the NASA-SPAR IX flight of January 20th,1981. The experimental thermal and physico-chemical conditions actually achieved have been analysed. Radiographic and metallographic observations of the samples show a non-regular dispersed primary phase inside the monotectic matrix. These observations are commented on the basis of capillarity and solidification aspects.
The Influence of Gravity on the Solidification of Monotectic and Near Monotectic Cu-Pb Alloys
Authors: Bergman A. , Carlberg T. , Fredriksson H. , Stjerndahl J.
Published: March 2011

Unidirectional solidification experiments with monotectic and near monotectic Cu-Pb alloys have been performed with the growth direction both parallel and antiparallel to the gravity vector. It was found that a more regular composite structure was possible to achieve in the samples solidified parallel to the gravity vector. It was also found that the amount of lead rich phase, regularily incorporated in the structure, was less than one would expect theoretically. It is proposed that monotectic alloys can solidify to two different kinds of composite structures. One, which can be described by the theory of coupled growth of a rod eutecticum, and the other similar to the growth of primary rods.
Thermophysical Properties of Germanium for Thermal Analysis of Growth from the Melt
Authors: Crouch Roger K. , Fripp A. L. , Debnam W. J. , Taylor R. E. , Groot H.
Published: March 2011

The thermal diffusivity of Ge has been measured over a temperature range from 300° C to 1010° C which includes values for the melt. Specific heat has been measured from room temperature to 727° C. Thermal conductivity has been calculated over the same temperature range as the diffusivity measurements. These data are reported along with the best values from the literature for the other parameters which are required to calculate the temperature and convective fields for the growth of germanium by the Bridgman method. These parameters include the specific heat, the viscosity, the emissivity, and the density as a function of temperature.
Polymer Coating of Glass Microballoons Levitated in a Focused Acoustic Field
Authors: Young Ainslie T. , Lee Mark C. , Feng I-An , Elleman Daniel D. , Wang Taylor G.
Published: March 2011

Inertial confinement fusion (ICF) glass microballoons (GMBs) levitated in a focusing radiator acoustic device can be coated with liquid materials by deploying the liquid into the levitation field with a stepped-horn atomizer. The GMB can be forced to the center of the coating liquid with a strong acoustically generated centering force. Water solutions of organic polymers, uv-curable liquid organic monomers, and paraffin waxes have been used to prepare solid coatings on the surface of GMBs using this technique.
Crystal Nucleation in Pd-Si Alloys
Authors: Drehman A.J. , Turnbull D.
Published: March 2011

We report here a study of the crystal phase nucleation in undercooled droplets of Pd-Si alloys with composition near the Pd84.5Si15.5 eutectic composition. Molten droplets are released at the top of a drop tube and solidify (to either a crystalline or glassy state) during descent. This provides a containerless (and nearly gravity free) environment so that nucleation due to container walls or vibrations is eliminated. We found that crystallization, due to homogeneous nucleation, is bypassed in droplets of 1 mm diameter when cooled at 760 K/sec. From this an upper limit of the homogeneous nucleation rate is estimated. Results are compared with our previously published study of nucleation in 0.06mm to 0.33 mm diameter droplets, which indicated that nucleation results from heterogeneous surface nucleation and that the number of these nuclei is dependent on the atmosphere in the drop tube.
Variation in the Properties of Superlattices with Band Offsets
Authors: McGill T. C. , Miles R. H. , Wu G. Y. , Watson T. J.
Published: March 2011

The implications for recent reports of large valence band offsets the HgTe-CdTe heterojunction are examined. The variation of the band gap and effective mass for transport normal to the layers in the superlattice is examined in detail.
Identification and Sources of Impurities in InGaAs Grown by Liquid Phase Epitaxy
Authors: Knight D. G. , Miner C. J. , Majeed A.
Published: March 2011

High purity In.53 Ga.47 As and InP with carrier concentrations [ND–NA] < 5×1015 cm−3 has been grown by the LPE technique on both n-type and semi-insulating substrates to detect and identify trace donor and acceptor impurities. Acceptor impurities have been detected in low temperature photoluminescence spectra where LPE melt baking and growth programs indicate a melt origin for two of these species, one of which is zinc. Data from semiconductor profiles provides evidence for sulfur and tin donor impurities, which comes from the rinse melt used to etch back substrates doped with the respective contaminants. Silicon and sulfur contaminants have been detected by SIMS measurements; and may arise not only from the indium and III-V materials, but also the graphite boat used to grow the epilayers. Volatile sulfur-containing compounds have been detected during high temperature bake-out of high purity graphite boats.
Infrared Reflectance Characterization of a GaAs-AlAs Superlattice
Authors: Zavada J. M. , Hubler G. K. , Jenkinson H. A. , Laidig W. D.
Published: March 2011

The optical properties of a GaAs-AlAs superlattice have been examined using the non-destructive technique of infrared reflectance spectroscopy. Through this technique, the absorption edge, the effective superlattice refractive index, the thickness, and the optical grading of the superlattice-substrate were determined. Location of the absorption edge was made from the reflectance spectrum and showed general agreement with photoluminescence measurements. A more detailed analysis of the infrared spectra indicated the presence of a transition region between the substrate and the superlattice. Based on a non-linear least squares method for fitting the experimental data, a dispersion relation for the dielectric function was obtained. This dielectric function yielded a value for the superlattice refractive index that was lower than that of the corresponding, homogeneous, AlGaAs alloy film for wavelengths between 1.0 and 2.5 micrometers.