bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the ITZ Damage on Durability of Reinforced Concrete in Chloride Environment
Authors: François Raoul , Arliguie Ginette
Published: April 2011

This paper deals with the effect of the ITZ on the service life of reinforced concrete. In the case of reinforced concrete structures, the penetration of chlorides does not depend only on concrete transfer properties but also on the loading applied, on the state of strains and on the exposure to the aggressive environment.

In order to take into account these different parameters, we have performed experiments on reinforced concrete elements, over a long period. The samples used have to be of an adequate size (3 meters long) and stored in a salt fog in a loading state so as to be representative of the actual operating conditions of the reinforced concrete structures.

The bending of the beams leads to the development of cracks which are neither preceded nor accompanied by microcracks, but the cement paste-aggregate interfaces are damaged in the tensile areas.

The service loading of reinforced concrete has two consequences : firstly, a cracking with widths ranging between 0.05 mm and 0.5 mm according to the intensity of the mechanical strength applied. Secondly, a damage of the ITZ in the tensile areas causing an increase of chloride penetration directly proportional to the intensity of the stress applied to the beam.

The model of the development of corrosion, worked out in relation with time and based on our results, emphasizes the influence of the paste-aggregate interface damage on the duration of the service life.
The Corrosion of Steel Reinforcement in Carbonated Concrete Under Different Humidity Regimes
Authors: Constantinou Anastasia G. , Scrivener Karen L.
Published: April 2011

In this investigation, four concretes (two mix designs and two curing regimes), containing reinforcing bars at covers 11 mm and 20 mm were carbonated fully in 100% CO2 and 65% relative humidity (RH). They were then placed in two different humidity environments (65% RH and 90% RH). The progress of the corrosion of the samples was followed electrochemically (using the linear polarisation technique) and microscopically (using a scanning electron microscope).

Electrochemical monitoring of the corrosion rate showed that corrosion started very soon after placement in the humidity regimes and generally increased with time. The water/cement ratio, the concrete cover of the reinforcement and the curing of the concrete had a significant effect the length of time taken to carbonate the specimens. However, the effect of these variables on the corrosion rate was negligible. In addition, the corrosion rate showed no dependance on the humidity regimes.

Microstructural examination of the samples revealed the existence of corrosion products at the steel/concrete interface after 6 months in the humidity regimes. There was more corrosion product in the samples at 90% RH. The samples with the low w/c showed more extensive cracking in the interfacial region.
Bonding and Interfacial Microstructure in Cementitious Matrices Reinforced by Woven Fabri
Authors: Peled A. , Yankelevsky D. , Bentur A.
Published: April 2011

High performance cementitious composites can be produced by reinforcement with a high volume of aligned fibers. One practical method of production of such composites would be based on the use of woven fabrics, where the bonding may be different from that predicted from evaluation of continuos aligned fibers. The present paper presents the study of the pull-out behavior of a fabric from a cementitious matrix. The influence of various fabric parameters were evaluated by comparing the pull-out of straight yams (fibers), crimped yams untied from the fabric and the fabric itself The influence of initial tensioning of the yams, which is an essential step in the production process, was also evaluated. SEM observations were carried out to interpret the pull-out curves in terms of microstructural characteristics. The crimped nature of the yam was found to be an important factor in enhancing the bond of the fabric, as it generated anchoring effects. Tensioning of the yam was detrimental to bond as it straightened the yarn and caused Poisson effects which damaged the interface.
Improving the Flexural Strength of Fibre Reinforced Oil Well Cementsby Addition of a Polymer Latex
Authors: Pafitis Demosthenis G.
Published: April 2011

Fibre-reinforced cements are proving to be useful in various oilfield applications. Low cost and increased toughness render glass fibre reinforced cements of particular interest. In most cases, improvements in toughness are the result of extensive fibre pull-out and this can be clearly observed in electron micrographs of fracture surfaces. This observation implies that there is much scope for improving the interfacial shear strength between the hydrated cement and glass fibres.Experiments have shown that increases in flexural strength and in energy to fracture can be achieved by incorporating small amounts of a polymer latex. Improvements of a factor of four in energy to fracture have been measured when approximately 0.8% by volume of a styrenebutadiene copolymer latex is added to a glass fibre reinforced class G oilwell cement. Experimental results suggest that this effect is not due to improvements in the strength of the cement matrix but due to an enhancement of the interfacial shear strength between fibre and cement.
Non-Aqueous Synthesis of Multicomponent Mesoporous Materials
Authors: Kim Anthony Y. , Liu Jun , Virden Jud W. , Bunker Bruce C.
Published: April 2011

A non-aqueous synthesis route broadens the spectrum of useful precursors and the range of compositions which can be achieved in the synthesis of ordered, mesoporous multicomponent materials. A formamide solution of surfactant (cetyltrimethylammonium chloride/hydroxide) allows for distribution of a water-sensitive metal oxide precursor prior to reaction. Hydrolysis of the metal oxide precursor and phase separation to the pure oxide are controlled by adding limited amounts of water. Subsequent addition of a second metal oxide source as an aqueous solution initiates the reactions leading to a mixed oxide having ordered mesopores. Ordered mesoporous titanium silicates having final Ti/Si mole ratios in excess of 1/20 are synthesized.
Production of Porous Materials by Dealumination of Alumina-Rich Zeolites
Authors: Le Van Mao R. , Denes G. , Vo N.T.C. , Lavigne J.A. , Le S.T.
Published: April 2011

A comparative study of chemical and textural properties for materials obtained by three different methods of dealumination of alumina-rich parent Ca-A zeolite showed that the method using ammonium hexafluorosilicate (AFS) resulted in the most interesting developments of mesoporous materials, with much higher void volumes and cation exchange properties than obtained by acid leaching or hydrothermal treatment. AFS treatment on both the Na and Ca forms of zeolite A resulted in materials with 12 nm sized mesopores, whereas smaller mesopores of about 4 nm were obtained when using the higher Si/Al ratio parent zeolite Na-X. Pore size distribution profiles obtained for these new materials are fairly narrow, indicating homogeneous mesopore sized solids.
Open-Framework Solids with Diamond-Like Structures Prepared from Clusters and Metal-Organic Building Blocks
Authors: Yaghi Omar M. , Richardson D. A. , Li G. , Davis C. E. , Groy T. L.
Published: April 2011

The tetrahedral cluster Ge4S104- and the rodlike ligand 4,4′-bipyridine are utilized in addition copolymerization reactions with the metal (II) ions of Mn, Fe, Co, Cu, and Zn in the preparation of 3-D open-framework solids, MxCol-xGe4S10-2(CH3)4N (x = 0.86, M = Mn; x = 1, M = Mn, Fe, Co, and Zn), 1, and Cu(4,4′-bpy)2. PF6, 2, having diamond-like structures. These structures are viewed in terms of the cubic diamond structure, where the carbon atoms have been replaced by either a cluster or a metal ion and the C-C bond by a sulfide or the 4,4′-bpy. These compounds have been fully characterized by single crystal x-ray crystallography and their composition was confirmed by elemental analysis; they contain 3-D channel systems where cations or anions reside to balance the charge on the framework.
Ambient - Pressure Silica Aerogel Films
Authors: Prakash Sai S. , Brinker C. Jeffrey , Hurd Alan J. , Rao Sudeep M.
Published: April 2011

Very highly porous (aerogel) silica films with refractive index in the range 1.006-1.05 (equivalent porosity 98.5-88%) were prepared by an ambient-pressure process1,2. It was shown earlier using in situ ellipsometric imaging1 that the high porosity of these films was mainly attributable to the dilation or “springback” of the film during the final stage of drying. This finding was irrefutably reconfirmed by visually observing a “springback” of >600% using environmental scanning electron microscopy (ESEM). Ellipsometry and ESEM also established the near 100% reversibility of aerogel film deformation during solvent intake and drying. Film thickness profile measurements (near the drying line) for the aerogel, xerogel and pure solvent cases are presented from imaging ellipsometry. The thickness of these films (crack-free) were controlled in the range 0.1-3.5 μm independent of refractive index.
Conversion of Class-F Fly Ash to Zeolites
Authors: Shih Wei-Heng , Chang Hsiao-Lan , Shen Zhijian
Published: April 2011

Fly ash was chemically converted into zeolites. The conversion process not only eliminates the disposal problem of coal wastes but more importantly turns the waste material into a useful one. It was shown that fly ash can be converted into two forms of zeolites: P and faujasite, by varying the treatment condition. In addition, zeolite P was found to form earlier with higher treatment temperatures and adding quartz increased the amount of zeolite P formed. Seeding of faujasite was also studied.
Self-Assembly of Silicate/Surfactant Mesophases
Authors: Walker Scott A. , Zasadzinski J.A.
Published: April 2011

The synthesis of silicate/surfactant mesophases is driven by cooperative assembly of organic surfactant and inorganic silicate species, and the resultant mesophase morphology can be controlled by synthesis conditions (i.e., CTAB concentration in precursor solution and SiO2- CTAB mole ratio). The self-assembly process of these mesophases is driven complexation of the polyanionic silicate species with several CTAB cations to form a multi-tailed surfactant. One of these mesophases is a novel rippled lamellar phase in which the ripple wavelength and lamellar spacing are similar to the hexagonal mesophase rod center-to-center spacing; each of these dimensions are consistent with the length of two CTAB molecules.
Compressive Mechanical Behavior of Hollow Ceramic Spheres
Authors: Chung Jae H. , Cochran Joe K. , Lee Kon J.
Published: April 2011

Mechanical behavior of hollow ceramic spheres was evaluated using finite element analysis. Failure mode and strength of spheres were determined from stress analysis. A parametric study of strength as a function of wall thickness to sphere diameter ratios indicated that strength is a function of relative density squared. Strength of aluminium oxide hollow spheres made by the coaxial nozzle powder process agreed well with the finite element parametric model.
Electromagnetic Properties of Syntactic Foam Composites
Authors: Kemper Paul J. , Moore Rick
Published: April 2011

A numerical model based upon renormalized effective medium theory will be described. The model successfully predicts the frequency dispersive permittivity of finite thickness dielectric/ conducting microsphere composites, electrically lossy syntactic foams, where the conducting particulates have volumetric fraction of 0 to 50%. The composites display unique frequency dispersions which are associated with the composite dimensionality and fractal-like sphere surface morphology. Theory and measurement show the composites have critical volume fractions which can be 20% above theoretical values for conducting spheres, i.e 27-–31% and the frequency dispersion of the composite permittivity can be varied by controlling the nanoscale surface morphology and composite thickness. Supporting permittivity measurements in the frequency range of 1–100 GHz will be presented.
Modeling of Microencapsulated Polymer Shell Solidification
Authors: Boone Travis , Cheung Lisa , Nelson Donald , Soane David , Wilemski Gerald , Cook Robert
Published: April 2011

A finite element transport model has been developed and implemented to complement experimental efforts to improve the quality of ICF target shells produced via controlled-mass microencapsulation. The model provides an efficient means to explore the effect of processing variables on the dynamics of shell dimensions, concentricity, and phase behavior. Comparisons with experiments showed that the model successfully predicts the evolution of wall thinning and core/wall density differences. The model was used to efficiently explore and identify initial wall compositions and processing temperatures which resulted in concentricity improvements from 65 to 99%. The evolution of trace amounts of water entering into the shell wall was also tracked in the simulations. Comparisons with phase envelope estimations from modified UNIFAP calculations suggest that the water content trajectory approaches the two-phase region where vacuole formation via microphase separation may occur.
Development of Low Density, Low Atomic Number Foam Shell with Gas Barrier for Laser Fusion Target
Authors: Takagi Masaru , Norimatsu T. , Izawa Y. , Nakai S.
Published: April 2011

Low density foam shells with high optical transmittance for fuel targets for the coming upgrade laser systems were developed by increasing the polymerization initiator for trimethylolpropane trimethacrylate in an oil phase of a water/oil/water emulsion. Foam with similar performance was fabricated using reduction-oxidation polymerization of ethyleneglycol dimethacrylate. These results showed that a cryogenic fuel layer sustained by these foam layers can be charecterized using optical interference technique.
Review of Low Dielectric Constant Thick Film Electronic Ceramics Using Hollow Microspheres
Authors: Kellerman David W.
Published: April 2011

High speed interconnects for semiconductor devices require low dielectric constant materials to minimize propagation delays and capacitive line loading. Ceramics and thick film materials have been utilized to package these semiconductor devices, however their dielectric constants are prohibitively high. Hollow microspheres have been added to thick film glass and ceramic composite materials to lower the dielectric constant of those materials. This paper will review papers presented on the work done at Digital Equipment Corporation and EMCA-Remex to develop high speed integrated circuit packages with low dielectric constants.

Presented will be the development and characterization of the low dielectric constant thick film material, processes used to fabricate devices with the low dielectric constant material, and development of the application of the material to an advanced ceramic integrated circuit package.
Uniform Solid and Hollow Metal Spheres: Formation in a Pulsed Micro-Arc and Applications
Authors: Dreizin Edward L.
Published: April 2011

A novel process for producing monodisperse metal spheres with diameters from 50 to 1000 μm has been developed. The process involves melting a consumable wire-electrode in a pulsed micro-arc, so that a single metal droplet is formed and separated in each pulse. Subsequent droplet cooling determines the final properties of the metal spheres. Control of the droplet initial temperature from the melting to the boiling point, together with variation of the cooling medium, allows production of metal spheres with unique properties, e.g., solid, internally oxidized, or hollow granules. Uniform diameter spherical particles of Al, Cu, Mo, Ni, Ta, W, Ti, Zr, and some alloys such as stainless steel, nichrome, monel, have been produced. Applications of the process include production of uniform spherical metal particles for metal combustion studies, development of a novel droplet welding technique, and production of particles for experimental simulation of micrometeoroid-surface interactions. Other possible uses may be in energy-absorbing structures, composite materials, metal micro-dosing, and micromechanical device production.
Distributions of Latex Particles Deposited from Water Suspensions
Authors: Bediwi A. B. El , Kulnis W. J. , Luo Y. , Woodland D. , Unertl W. N.
Published: April 2011

We used the atomic force microscope to determine the distributions of 150–200 nm diameter styrene-butadiene (SB) latex spheres with TR. = 45 °C deposited at sub monolayer coverages from water suspensions onto mica, glass, calcite and cellophane surfaces. Two deposition methods are used: drying of μl drops and dipping. For drop drying, the distributions are extremely inhomogeneous. A high density ring forms at the boundary of the area wet by the drop. At low suspension densities on cellophane, the ring is a close-packed monolayer several micrometers wide. Thicker rings form on calcite and glass. Inside the rings, the particle density is very low and non uniform; e.g., monolayer thick islands form on mica, short chains are predominant on calcite, small clusters form on glass, and isolated spheres occur on cellophane. Particle densities are substantially reduced near some substrate defects but are enhanced near others. For the dipping method, homogeneous distributions are obtained on glass and cellophane. The density of adsorbed particles increases linearly with immersion time and the distribution of monomers, dimers, and trimers is not characteristic of random adsorption.
Spherical Particles of Pure and Manganese Doped Zinc Oxide and Zinc Hydroxicarbonate
Authors: Zampronio Cleidiane G , Davolos Marian R. , Stucchi Elizabeth B. , Jafelicci Miguel
Published: April 2011

Pure and manganese doped zinc hydroxicarbonate are precursors for materials based on zinc oxide with electrical and luminescent properties. This paper reports on investigation of the effect of chloride and sulfate anions in the morphology of pure and doped precursors obtained by aging diluted zinc salt solutions in presence of urea, and their thermally decomposed products Characterization was carried out by XRI), IR and SEM techniques. Hydrozincite Zn5(OH)6(CO3)2 and zincite ZnO with spherical shaped particles of 5–10 ptm were obtained independent of anion used Moreover, in a chloride medium the spheres are organized in an arrangement of acicularly crystallized units as spherulitic aggregates, and in sulfate medium porous spherical particles were observed In addition, there is a good topotaxic relationship between the precursor and oxide
Sonochemically Produced Hemoglobin Microbubbles
Authors: Wong Mike , Suslick Kenneth S.
Published: April 2011

Using high-intensity ultrasound, we have developed a method for the synthesis of airfilled hemoglobin (Hb) microbubbles (≈2.5 μm in diameter). Transmission electron, scanning electron, and optical microscopy show spherical particles with a shell thickness of approximately 35 nm, or roughly six protein molecules thick. The mechanism of microbubbles formation has been determined to involve both the dispersion of gas into micron-sized bubbles and the chemical cross-linking of cysteine residues between protein molecules. The primary oxidizing agent is superoxide (HO2), which is sonochemically produced from oxygen and water during acoustic cavitation. The Hb microbubbles possess many of the desired characteristics of a blood substitute. The microbubbles are smaller than red blood cells and will not block capillaries. The microbubbles are air-filled and provide a large O2carrying capacity. The hemoglobins of the microbubbles retain their ability to bind oxygen reversibly. In addition, the oxygen affinities are similar to those of native Hb. Even more surprisingly, microbubbles show extensive cooperativity, as indicated by Hill coefficients as high as 18, which means that in the microbubble shell, there is communication between several of the crosslinked Hb tetramers upon binding oxygen. The Hb microbubbles show minimal degradation (>25%) after storage for six months at 4 °C.
Defects in Quasi-One Dimensional Oxide Conductors: K0.3MoO3
Authors: Smith Kevin E. , Breuer Klaus , Goldberg David , Greenblatt Martha , McCarroll William , Hulbert Steve L.
Published: April 2011

The electronic structure of the prototypical quasi-one dimensional (1D) conductor K03MoO3 has been studied using high resolution photoemission spectroscopy. In particular, the electronic structure of defects was investigated in order to understand the mechanism for charge density wave pinning and destruction of the Peierls transition. Defects were found to radically alter the electronic structure close to the Fermi level (EF), thus strongly modifying the structure of the Fermi surface. While a low emission intensity at EF has been interpreted as evidence for a Luttinger liquid ground state in a ID metal, we show that non-stoichiometric surfaces lead to similar effects. The nature of the ground state is discussed in the context of these results.
Luminescence Spectroscopy on Individual Nanostructures and Impurity Atoms Using Stm and Sem
Authors: Samuelson Lars , Gustafsson Anders , Hessman Dan , Lindahl Joakim , Montelius Lars , Petersson Anders , Pistol Mats-Erik
Published: April 2011

In the exploration of the nano-world of semiconductors there is a strong focus on low-dimensional structures and ultra-small devices. Two fundamental problems, which challenge progress in this field are: (i) large ensembles of nano-objects, like Quantum Dots (QDs), do not have identical geometrical shapes and electronic properties, and, (ii) the properties of a low-dimensional structure can be dominated by a few impurity atoms, whereas the properties of a macroscopic structure is determined by the quasi-continuous background of dopant impurities. To allow QDs and discrete impurities to be studied, novel experimental techniques are required. In this paper we describe how local luminescence has been excited from single QDs using electrons injected from a Scanning Electron Microscope (SEM), from the tip of a Scanning Tunneling Microscope (STM) or using highly focused photons for excitation. We present images of QDs as well as characteristic spectra of individual QDs. We finally show how the local character of the excitation enables us to excite and image individual impurities in low-dimensional structures, including the measurement of characteristic emission spectra from a single impurity atom in GaAs.
Ge δ-Layers on Si(111) and Si(001) Grown by MBE and SPE
Authors: Falta J. , Gog T. , Materlik G. , Müjller B. H. , Hoegen M. Horn-Von
Published: April 2011

Ge δ-layers on Si(111) and Si(001), grown by molecular beam epitaxy (MBE) and solid phase epitaxy (SPE) were characterized in-situ by high-resolution low-energy electrondiffraction and post-growth by x-ray standing waves. LEED intensity oscillations are used to determine the growth mode of Ge on Si which is found to proceed in a double bilayer fashion for Ge on Si(111). X-ray standing waves are employed to investigate crystal quality of the Ge layer. SPE on Si(111) requires high annealing temperatures (600°C) for sufficient recrystallization of defects in the Ge δ-layer. On Si(001), Ge δ-layers of surprisingly high crystalline quality are grown by solid phase epitaxy at room temperature.
Strain Measurements and Laue Diffraction with Microbeams
Authors: Wang P.-C. , Cargill G. S. , Noyan I. C.
Published: April 2011

We describe a system being developed to use x-rays for spatially resolved measurements of strain, microstructure and composition in thin films. These capabilities are particularly important for improved understanding of electromigration, stress relaxation, and associated reliability issues in microelectronics. The system uses white radiation collimated and focused with a tapered glass capillary, an area CCD detector for measuring Laue patterns, and an energy sensitive Si detector for measuring lattice spacings. Examples are shown of strain measurements
for a 4 μm thick Al film on a Si substrate with 300 μm and 30 μm x-ray beams; of Laue diffraction from a single grain for a 40 μm thick Al foil with a 0.3 μm x-ray beam; and of x-ray fluorescence mapping for a patterned Cu film with a 30 μm x-ray beam.
In-Situ X-Ray Diffraction and Resistivity Analysis of CoSi2 Phase Formation with and without a Ti Interlayer at Rapid Thermal Annealing Rates
Authors: Cabral C. , Clevenger L. A. , Stephenson G. B. , Brauer S. , Morales G. , Ludwig K. F.
Published: April 2011

It has been demonstrated, using synchrotron radiation, that at rapid thermal annealing rates (3°C/s) the formation of CoSi2 shifts to higher temperatures when a thin Ti interlayer is placed between Co and polycrystalline Si. It has also been shown that the Ti interlayer reduces the temperature range between the start of CoSi formation and CoSi2 formation (i.e. the range over which CoSi is present). 13 nm of Co deposited by physical vapor deposition on polycrystalline Si with and without either a 2 nm or 3.4 nm interlayer of Ti was analyzed in-situ by monitoring x-ray diffraction (XRD) peak intensity as a function of temperature using monochromatic radiation from a synchrotron beam line and by monitoring resistivity as a function of temperature in a rapid thermal annealing (RTA) system. The XRD analysis indicates that the phase formation proceeds from CoSi to CoSi2 in a temperature range that decreases from about 200°C to 140°C to 115°C with pure Co, Co/2 nm Ti and Co/3.4 nm Ti films respectively. The onset of the CoSi formation increases by about 135°C and 160° for Co/ 2 nm Ti and Co/3.4 nm Ti compared to pure Co. The CoSi temperature range decreases from about 75°C in pure Co to less than 50°C in Co/Ti. In-situ RTA resistance along with in-situ XRD analysis indicates that the onset formation temperatures for CoSi are about 440°C, 575°C and 600°C and the temperatures for the completion of CoSi2 formation are about 640°C, 715°C and 715°C for Co, Co / 2 nm Ti and Co / 3.4 nm Ti films respectively. The results are consistent with the Ti interlayer acting as a diffusion barrier during the initial stages of the Co-Si reaction.
Studies of Calcium-Nickel-Potassium Oxide Films by Synchrotron X-Ray Fluorescence Microscopy
Authors: Perry D. L. , Thompson A. C. , Russo R. E. , Mao X. L.
Published: April 2011

The use of synchrotron x-ray fluorescence microscopy to study the composition and homogeneity of laser deposited films of calcium-nickel-potassium oxides is described. Experimental conditions for preparing the films are given, and the results are discussed with respect to the x-ray fluorescence data concerning the distribution of the three metals in the films.
Electron Transport and Photoemission Studies of Amorphous CaAl Thin Films
Authors: Morton Simon A. , Greig D. , Walker C. G. H. , Mayeya F. , Howson M. A. , Mat-Hew J. A. D. , Norman D.
Published: April 2011

Amorphous alloys of the binary system CaAl are known to have highly unusual electron transport properties with resistivities up to 450μΣcm and a Hall coefficient that deviates from free electron values at Ca concentrations higher than 45 atomic percent. For amorphous CaMg alloys, on the other hand, the resistivity is very much less and this great difference between the two sets of alloys is not fully understood.

We report on the correlation of photoemission and transport measurements made on two sets of amorphous CaAl and CaMg alloys prepared by magnetron sputtering in such a way that we could carry out both sets of measurements within the same UHV system. A special feature of the measurements was that the electrical resistivity was also measured in-situ using a specially designed 4-point probe to check for amorphicity and to compare with transport experiments carried out elsewhere.

Photoemission studies were carried out in the energy range 15–50 eV with tuneable synchrotron radiation enabling us to examine the Ca 3p-3d photoemission resonance in detail. The main result from the present series of experiments was that whereas in the CaAl alloys the Fermi edge developed a shoulder at high concentrations of Al, this feature was completely absent in CaMg. At the same time the intensity of the Ca 3p-3d photoemission resonance revealed the presence of d-states in both sets of alloys, indicating that the presence of these dstates cannot, by itself, explain the high resistivity of CaAl.
Magnetic Structure of Multilayers from Soft-X-Ray Magnetic Circular Dichroism
Authors: Chen C. T. , Idzerda Y. U. , Kao C.-C. , Tjeng L. H. , Lin H.-J. , Meigs G.
Published: April 2011

Soft-x-ray magnetic circular dichroism (MCD) is the difference between the absorptivity or reflectivity of left and right circularly polarized soft-x-rays at the magnetically interesting L2,3- edges of 3d transition metals or the M4,5-edges of the 4f rare earth elements. Thanks to its large absorption cross-section and strong MCD effect, this technique has become a powerful new means for probing, in an element- and site-specific manner, the magnetic properties of ultra-thin films and multilayers. Soft-x-ray MCD experiments, recently conducted at the Dragon beamline, are utilized to demonstrate the recent progress in this technique and its applications in the research of magnetic thin films.
What Can we Learn from off-Specular Neutron Reflection?
Authors: Pynn Roger
Published: April 2011

This paper provides a brief introduction to the subject of off-specular neutron scattering by rough interfaces. Such scattering can be calculated using the distorted-wave Born approximation (DWBA) in which the neutron wavefunctions for a system with smooth interfaces are used as the basis for perturbation theory. Although it has been applied successfully to model the scattering from rough surfaces, the DWBA has several quantitative and qualitative limitations, some of which are described in this paper. When it is applied to multilayer systems, the DWBA correctly predicts a number of qualitative features of the diffuse scattering, including fringes of scattering that result from correlations between the roughnesses of neighbouring interfaces. A remarkable feature of diffuse neutron reflection is the range of length scales within a surface or interface that is probed. This is illustrated here by data obtained with a self-assembled multilayer of organic molecules where distances between 500 Å and 3 μm parallel to the layers are probed.
Reflection of Neutrons from an Optical Grating
Authors: Munter Alan E. , Adenwalla S. , Felcher G.P. , Zhou X.L.
Published: April 2011

Specular and off-specular neutron intensities were measured at grazing incidence from an optical grating. The periodicity of the grating was determined from the locations of the intensity peaks in the off-specular data. An analysis of the widths of the off-specular intensity peaks showed that the effect of the coherence length of the neutron beam on the determination of a surface length scale of approximately 30 μm was negligible when compared to that of the instrument resolution.
Bulk and Surface Structure of a Ternary Microemulsion
Authors: Lee D. D. , Chen S. H. , Satija S. K. , Majkrzak C. F.
Published: April 2011

Microemulsions are isotropic mixtures of water, oil, and surfactant which self-assemble to form interfacial monolayers with a characteristic length scale on the order of hundreds of Angstroms. Small angle neutron scattering was used to determine the bulk structure of a wateroctane-C10E4 bicontinuous microemulsion. The mean curvature of the surfactant film was verified to be near zero by independently measuring the scattering contributions from the water-surfactant and oil-surfactant interfaces through hydrogen-deuterium contrast variation. The exponentially damped, oscillatory scattering length density profile of the microemulsion near a hydrophobic silicon surface was also observed with neutron reflectivity. The surface reflectivity results as well as the bulk small angle scattering measurements are explained using a simple Ginzburg-Landau theory.
Instrumentation for Neutron Scattering at the National Institute of Standards and Technology
Authors: Kamitakahara W.A. , Rush Jj. , Rowe J.M. , Prask Hj.
Published: April 2011

The National Institute of Standards and Technology (NIST) offers a wide range of neutron beam instruments to the U.S. community. Many of these are of recent construction, and are located in the Cold Neutron Research Facility, a large guide hall with fifteen experimental stations on seven neutron guides. A new liquid hydrogen cold source is being installed. Thermal neutron instruments in the reactor confinement are to be upgraded over the next few years.
Radius of Gyration Scaling in the Semidilute Regime
Authors: Barker J.G. , Mayes A.M. , Briber R.M. , Orts W.J.
Published: April 2011

Small-angle neutron scattering is used to investigate swelling effects of polystyrene in carbon tetrachloride and cis-decalin in the semidilute regime. The observed scaling exponent m where Rg2 ~ ф-m was m=0.15±0.01 both in carbon tetrachloride and in cis-decalin at T=180 C, which is much weaker than the theoretical prediction m=0.25. A review of the literature has found the scaling exponent to vary from 0.1 to 0.25. Possible causes for this variation in the observed scaling exponent are discussed.
Intercalation of Organic Compounds in Lipid Bilayers
Authors: Hamacher K.A. , Kaiser H. , Kulasekere R. , Worcester D.L.
Published: April 2011

Using neutron diffraction we studied the incorporation of small hydrophobic compounds into bilayers consisting of phosphatidylcholine (PC) and cholesterol. They were found to be localized in a narrow band at the center of the hydrocarbon region, between the two halves of the bilayer. The structures formed by introduction of the compounds are therefore intercalated structures with the long axis of the intercalated molecules lying in the plane of the bilayer. We worked with several bilayers which differed by the length of the hydrocarbon chain of the PC. The quality of the localization depended on the presence of cholesterol, the water content and the PC chain length.
Novel Kinetic Effects in Vkcoelasttc Surfactant Solutions Under Shear
Authors: Butler P.D. , Magid L.J. , Kreke P.J. , Hayter J.B. , Hamilton W.A. , Hammouda B.
Published: April 2011

Using small-angle neutron scattering (SANS), we have investigated the transient alignment and relaxation under Couette shear of viscoelastic aqueous micellar solutions of cetyltrimethylarmmonium 3,5-dichlorobenzoate (CTA3,5C1) and CTA3,5C1/CTAB mixtures at concentrations well above ф* (but below 1.0 wt. %). Time constants of the order of ten's of minutes are reported for alignment and relaxation, orders of magnitude slower than any previously observed in similar micellar systems. The collective properties of the network of entangled, threadlike micelles, rather than the individual micellar segments, dominate the alignment and relaxation behavior. At low micellar surface charge density (σ) (e.g., in pure CTA3,5C1), the first observation of alignment proceeding in two stages has been made. Increasing a decreases by an order of magnitude the shear rate required to reach full alignment and provides a comparable decrease in the rate constant for relaxation after cessation of shear.
A Study of Tio2 Aerogels Pore and Ramified Structure by Small-Angle Neutron Scattering
Authors: Zhu Zhu , Lin Min , Dagan Geula , Tomkiewicz Micha
Published: April 2011

The microstructral characteristics of titanium dioxide aerogels were studied by Small Angle Neutron Scattering (SANS). A variety of models were used to extract the morphological parameters from the SANS data. The evaluation of scattering data was found to be consistent with nitrogen gas adsorption and TEM measurements of a model of aerogel consisting of a light density matrix in which meso- and macro-pores are embedded.
Small-Angle Scattering Methods for Studying the Sintering of Nanophase Ceramic Compacts
Authors: Krueger Susan , Allen Andrew J. , Skandan Ganesh , Long Gabrielle G. , Hahn Horst , Kerch Helen M.
Published: April 2011

Studies of microstructure evolution as a function of sintering parameters are necessary to better control the microstructure of nanophase ceramic compacts during processing. Small-angle scattering provides a comprehensive probe of the statistically-representative microstructures present in nanophase ceramics. A complete characterization includes complementary density, electron microscopy, nitrogen desorption and x-ray diffraction measurements. Small-angleneutron and ultra-small-angle x-ray scattering have been used to determine the effects of different sintering temperatures, pressures and additives during sintering of nanophase zirconia compacts. The samples were of sufficient size and uniformity to permit absolute calibration of the scattering data, making it possible to confirm that scattering from the pore/grain interface dominates the total scattering cross-section. A quantitative microstructural model was developed for this system, resulting in the determination of specific pore surface area, total pore volume fraction, pore number size distribution and grain size as a function of sintering parameters.
Copper Oxide Superconductors Through 1994
Authors: Cava R. J.
Published: April 2011

This paper briefly describes the chemistry and structures of known copper oxide superconductors as of November 1994. A tabulation of the unique, reliably superconducting cuprates is presented, with year of discovery, as is a simple classification scheme. Recent trends in new materials research are described.
Determination of The Local Atomic Structure of LA2-x(SR,BA)xCUO4 Materials From Neutron Powder Diffraction Data
Authors: Billinge S. J. L. , Kwei G. H.
Published: April 2011

We describe the use of neutron powder diffraction for studying the local structure of high-temperature superconductors. This is accomplished by carrying out a pair distribution function (PDF) analysis. This approach does not presume a periodic structure and allows short range deviations from perfect crystalline order to be observed. Data from a sample of La2CuO4 collected on two different diffractometers are compared to determine the degree of reproducibility of the results. It is found that the data reproduce very well; however, a model-PDF, fit to the data assuming the average crystal structure in the low-temperature-orthorhombic (LTO) phase, differs from the data in a number of significant ways. This is related to earlier observations that the local structure of the La1.875Ba0.125CuO4 compound differs from the average crystal structure.
Magnetic Structures in RNi2B2C (R = Ho, Er) Superconductors
Authors: Stassis C. , Goldman A. I. , Dervenagas P. , Zarestky J. , Canfield P. C. , Cho B. K. , Johnston D. C. , Sternlieb B.
Published: April 2011

Single crystal neutron diffraction techniques have been employed to study the evolution of magnetic structures in RNi2B2C compounds in an attempt to understand the relationship between magnetic ordering and superconductivity in several members of this series. For HoNi2B2C, below the superconducting transition (Tc = 8 K), an incommensurate magnetic structure characterized by two wave vectors (0.585 a* and 0.915 c*) is found in a narrow temperature range between 4.7 K and 6 K. This is the same temperature range where bulk measurements find a deep minimum in the upper critical field, Hc2. Below 4.7 K, HoNi2B2C is a simple collinear antiferromagnet. ErNi2B2C (Tc = 11 K) orders in an incommensurate modulated antiferromagnetic state characterized by an ordering wave vector 0.553 ā * below 7 K, which coexists with superconductivity.
Neutron Diffraction Studies on Recrystallization of Solution Derived Lead Zirconate Titanates
Authors: Morosin B. , Lawson A. C. , Kwei G.H. , Voigt J. A. , Tuttle B. A.
Published: April 2011

We performed neutron powder diffraction on solution-derived lead zirconate titanates (PZT). Three compositions, PZT 45/55, PZT 20/80 and PbTiO3, were investigated. The materials were annealed so that the perovskite phase had just begun to grow from the precursor phase. In our materials this precursor phase is the pyrochlore rather than fluorite phase. The results show that in the pyrochlore phase, the (Ti,Zr) and the Pb are ordered in their crystallographic sites while the O are essentially disordered in both of the two usual pyrochlore anion sites.
Neutron Scattering Studies of Network Glasses
Authors: Wright Adrian C. , Vessal Behnam , Bachra Bilber , Hulme Robert A. , Sinclairc Roger N. , Clare Alexis G. , Grimley David I.
Published: April 2011

A review is presented of recent neutron diffraction studies of silicate and borate glasses, using a combination of steady-state reactor and pulsed neutron sources. The samples studied include both single component glasses and binary systems, consisting of a network modifier plus a network former, and the data have been extended to high magnitudes of the scattering vector, Q, to achieve high real-space resolution. Peak fitting techniques are employed to extract the detailed geometry of the basic structural units and to investigate the distortions caused by the introduction of network modifiers. The data are compared to various structural models and conclusions are drawn not only with regard to the validity of the structural models themselves but also concerning the environment of the network modifying cations.
The Structure of Lead-Indium Phosphate Glass
Authors: Suzuya K. , Price D. L. , Loong C.-K. , Sales B. C. , Boatner L. A.
Published: April 2011

Lead-indium phosphate glasses exhibit a number of useful properties such as a high index-of-refraction, low preparation temperature and melt viscosity, and good chemical durability. The structure of such a glass (composition in wt. %: 65 PbO, 29 P2O5, 6 In2O3) has been investigated by total neutron scattering using the GLAD diffractometer at Argonne's spallation neutron source IPNS. Peaks corresponding to the P-O, Pb-O/In-O, and 0-0 pairs were observed in the radial distribution function. The short-range structure in the glass, in terms of average coordination numbers and bond distances, is compared with those of a pure P2O5 glass and with the crystal structure of lead pyrophosphate, Pb2P2O7. Unlike silicate glasses in which the SiO4 tetrahedra form a 3-dimensional network, the PO4 tetrahedra in phosphate glasses form a chain-like structure. The structural modification by the lead cations in phosphate glasses appears to occur mainly in the medium range affecting the lengths and connectivity of the chain-like structure.
Crystal Field and Exchange Interactions in DyT4Al8 (T = Fe and Mn)
Authors: Loewenhaupt M. , Loong C.-K. , Tils P. , Hahn W.
Published: April 2011

We investigated the magnetic excitations in polycrystalline samples of hard magnet related compounds DyFe4Al8 and DyMn4Al8 by neutron spectroscopy. For both compounds the magnetic spectra at energies below 40 meV are dominated by the response of the Dy3+ ions. In DyMn4Al8 we observed pure crystal-field transitions within the Dy3+ J=15/2 ground multiplet which is split into 8 doublets under the low point-group symmetry of 4/mmm. In DyFe4Al8 the Dy crystal-field-split states are perturbed by the molecular fields of the ordered Fe sublattice.
One-Dimensional Sans Employing Bent-Single Crystal Optics: Theory and Demonstration
Authors: Heuser B. J. , Popovici M. , Berliner R.
Published: April 2011

A recent small-angle neutron scattering (SANS) instrumentation development at the University of Missouri Research Reactor Center (MURR) using bent, double Si crystal diffraction is presented. Neutron rocking curves of flat single crystals are only a few seconds of arc with correspondingly low integrated intensities. The rocking curve can be significantly broadened if the crystals are bent. However, the phase-space acceptance and emergence windows of two bent crystals in parallel can be matched only if the reflecting planes have different d-spacing. We have used a combination of the Si (111) and (220) reflections in the work presented here. The peak intensity of the rocking curve with this configuration was approximately 2.5 x 105 neutrons per second over a 5 cm2 area of sample at 1.5 Å. The rocking curve wings fell sharply (approximately as Q"11), permitting accurate scattered intensity measurements down to a minimum Q value of 0.005 1/Å at a Q resolution of 0.003 1/Å. The technique also offers the possibility of variable resolution without too much difficulty; changes up to a factor of 2 can be made by adjusting the sample-to-analyzer crystal distance, while changes of a factor of 10 can be made by using different Si reflections. Since the incident neutron wavelength can be tuned to the peak of the leakage spectrum, this technique is ideal for low-flux reactors, which otherwise cannot be used for SANS research. The usefulness of one-dimensional SANS is demonstrated by measurements of Portland cement.
The Electronic Contribution to The Elastic Constants of Strained III-V Materials Under High Magnetic Fields
Authors: Ghatak Kamakhya P , Nag B. , Mazumder G.
Published: April 2011

In this paper an attempt is made to study the electronic contribution to the elastic constants of strained III-V materials under high magnetic fields on the basis of k.p theory. It is found taking strained Hgi - x CdxTe and Ini - xGaxAsyPi-y lattice matched InP as examples that they increase with increasing doping and oscillate with inverse magnetic field respectively. The strain enhances the numerical values of the elastic constants. The theoretical formulation is in quantitative agreement with the suggested experimental method of determining the above contributions for degenerate materials having arbitrary dispersion laws. In addition, the well-known results for strain free wide gap materials in the absence of magnetic field have been obtained from our generalized analysis under certain limiting conditions.
Spectroscopic Ellipsometry and Band Structure of Si1–yCy Alloys Grown Pseudomorphically on Si (001)
Authors: Zollner Stefan , Herzinger Craig M. , Woollam John A. , Lyer Subramanian S. , Powell Adrian P. , Eberl Karl
Published: April 2011

We have measured the dielectric functions of three Si1−yCy, alloys layers (y ≤1.4%) grown pseudomorphically on Si (001) substrates using molecular beam epitaxy at low temperatures. From the numerical derivatives of the measured spectra, we determine the critical point energies E′0 and E1 as a function of y (y ≤ 1.4%) using a comparison with analytical line shapes and analyze these energies in terms of the expected shifts and splittings due to negative hydrostatic pressure, shear stress, and alloying. Our data agree well with the calculated shifts for El, but the E′0 energies are lower than expected. We discuss our results in comparison with recent tight-binding molecular dynamics simulations by Demkov and Sankey (Phys. Rev. B 48, 2207, 1993) prediciting a total breakdown of the virtual-crystal approximation for such alloys.
Effects of Substrate Misorientation Direction on Strain Relaxation at InGaAs/GaAs(001) Interfaces
Authors: Goldman R.S. , Wieder H.H. , Kavanagh K.L.
Published: April 2011

We have investigated the effects of substrate misorientation direction on strain relaxation at InGaAs/GaAs(001) interfaces. Calculations of the shear stresses due to the misfit strain, resolved on the glide plane in the glide direction, suggest that the dislocation glide force and the activation energy for dislocation nucleation are essentially identical for the α and β slip systems. However, experimental results indicate that asymmetries in strain relaxation are sensitive to A-type misorientation and/or step-edge densities. Thus, a dislocation nucleation source or glide velocities sensitive to step densities or local roughness may explain these results.