bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical and Microstructural Investigation of the Aggregate and Cement Interface
Authors: Li Zongjin , Shah Surendra P. , Aquino Matthew J.
Published: April 2011

The understanding of the interface between aggregate and cement is crucial in determining the properties of concrete. Recently, a pushout experimental technique and a theoretical model have been developed to determine the stiffness, strength and surface energy of the interface layer. The validity of these material parameters was verified in the present study by examining the effect of diameter and embedment length of aggregate. In addition, the effect of the pretreatment of aggregate surface and various admixtures was investigated. All pushout tests were performed in a closed-loop manner to obtain the load vs. displacement relationship.

The interfacial zone was further investigated by using backscattered electron imaging and energy dispersive analysis of x-rays (EDAX) to characterize the microstructure of the interface. The relationship between mechanical properties and microstructure of interfacialzone was studied. It was shown that the microstructure of the interface plays a substantial role in the mechanical behavior of the aggregate/cement bond.
Modelling the D.C. Electrical Conductivity of Mortar
Authors: Garboczi E.J. , Schwartz L.M. , Bentz D.P.
Published: April 2011

The interfacial zone separating cement paste and aggregate in mortar and concrete is believed to influence many of the properties of these composites. This paper presents a theoretical framework for quantitatively understanding the influence of the interfacial zone on the overall electrical conductivity of mortar, based on realistic random aggregate geometries. These same ideas may also be used to approximately predict the fluid permeability of mortar.
Moisture Permeability of Mature Concrete and Cement Paste
Authors: Hedenblad Göran
Published: April 2011

Moisture permeabilities (δv,) of mature concrete and cement paste with water-cement ratio (wo/C) 0.4, 0.5 and 0.6 have been determined as functions of the relative humidity (RH). These δv, can be used to calculate δv, of the aggregates including the interfacial transition zone (ITZ). δv, of granite has been preliminarily determined as a function of RH.
Fiber-Matrix Interfacial Area Reduction in Fiber Reinforced Cements and Concretes at Moderate to High Fiber Volume Fractions
Authors: Karam Gebran N.
Published: April 2011

The area and properties of the fiber-matrix interface in fiber reinforced cements and concretes determines the amount of stress transferred forth and back between the cement paste and the reinforcement and hence controls the mechanical properties of the composite. Fiber-fiber interaction and overlap of fibers with fibers, voids and aggregates can dramatically decrease the efficiency of the reinforcement by reducing this interfacial area. A simple model to account for this reduction is proposed and ways to integrate it in the models describing the mechanical properties of short fiber reinforced concretes are presented. The parameters of the model are evaluated from previously published data sets and its predictions are found to compare well with experimental observations; for example, it is able to predict the non-linear variation of bending and tensile strength with increasing fiber volume fraction as well as the existence of an optimal fiber content.
New Anion Exchangeable Layered Mixed Basic Salt, Ni1-xZn2x(OH)2(OCOCH3)2x·nH2O
Authors: Yamanaka Shoji , Ando Kazunari , Ohashi Masao
Published: April 2011

A new anion exchangeable layered compound with a composition of Ni1-xZn2x(OH)2(OCOCH3)2x·nH2O (0.15 < x < 0.25) was prepared by hydrothermal hydrolysis of Ni-Zn mixed acetate solutions. The structure is related to zinc basic salts such as Zn5(OH)8Cl2·nH2O and Zn5(OH)8Cl2·nH2O; nickel ions form brucite-type hydroxide layers with vacanciesNi1-x(OH)2, and zinc ions occupy the tetrahedral sites above and below the vacant sites outside the hydroxide layers. Acetate ions are weakly bound to the Zn2+ ions, completing the tetrahedra, and easily exchanged with most of inorganic as well as organic anions. The reactions are reversible. Exchange with [Si8O20]8- ions resulted in the formation of two-dimensional silicate layers analogous to those of 2:1 type clay minerals.
Porous Spheroidal Hydrotalcite Aggregates
Authors: D. Cox Sherman , J. WISE Kenneth
Published: April 2011

Controlled precipitation conditions allow the formation of highly porous, spheroidal aggregates of hydrotalcite. The aggregate structure resembles a house-of-cards, being composed of interconnected thin plates. The aggregate size can vary over a range of about 1 to 60 μm by altering precipitation conditions such as mixing shear, temperature, addition rates and addition order. These materials are low in bulk density and highly absorptive. The aggregate structure is maintained during calcination. The micro and meso-pore size distribution is very similar to conventionally prepared hydrotalcite, but the macroporosity is dominated by the voids between spheroids. The characteristics of these aggregates point to potential applications in areas such as catalysis and separation.
Preparation and Properties of Clays Pillared with Al2O3-NiO Mixed Oxide
Authors: Yamanaka Shoji , Yamamoto Hironori
Published: April 2011

Montmorillonite was pillared with Al2O3-NiO mixed oxide by ion-exchange combined with titration process; the interlayer Na ions of montmorillonite were first exchanged with aluminum hydroxide polycations, and then nickel hydroxide was precipitated between the layers by a titration method. The aluminum hydroxide pillars reacted with the nickel hydroxide at room temperature, and the microporous structure was much stabilized against heating. The specific surface area as high as 300 m2/g was maintained up to 700°C.
Rectorite Pillared with Ce-Modified Aluminum Oxide
Authors: Wu Jianxin , Rakiewicz Edward F. , Gatte Robert R.
Published: April 2011

Rectorite clay was pillared with an Al/Ce-cluster pillaring agent made from aluminum chlorhydrol and cerium nitrate. The resulting product had an interlayer distance of 15.7 Å, which was significantly larger than the interlayer distance obtained using conventional aluminum chlorhydrol as the pillaring agent (8.4 Å). Argon adsorption analysis indicates that the pores of the AL/Ce-cluster pillared rectorite are non-uniform, with pore diameters ranging from 5 to 16Å. 29Si MAS NMR studies showed that calcining the natural rectorite changes the silicon environment, while the pillared rectorite clays are much more resistant to such changes upon calcination. It is suggested that pillaring reactions enhance the thermal stability of the rectorite by stabilizing the local silicon environment in the clay.
The Synthesis of an Interstratified Layered Oxide from Exfoliated Precursors
Authors: Smith Richard L. , Rohrer Gregory S.
Published: April 2011

Aqueous suspensions of exfoliated Li0.25MoO3 and Na-montmorillonite have been combined and dried to form interstratified solids. X-ray diffraction patterns of ethylene glycol treated films show that the d-spacing of restacked materials varies with composition between the limits established by the two end members. Based on these data, we conclude that the new materials are composed of individual layers from each of the precursor compounds, arranged in a random fashion. It is likely that other layered solids can be exfoliated and restacked to form new interstratified materials.
Processing and Characterization of High Porosity Aerogel Films
Authors: Hrubesh Lawrence W. , Poco John F.
Published: April 2011

Aerogels are highly porous solids having unique morphology among materials because both the pores and particles making up the material have sizes less than wavelengths of visible light. Such a unique morphology modifies the normal molecular transport mechanisms within the material, resulting in exceptional thermal, acoustical, mechanical, and electrical properties. For example, aerogels have the lowest measured thermal conductivity and dielectric constant for any solid material. Special methods are required to make aerogel films with high porosity. In this paper, we discuss the special conditions needed to fabricate aerogel films having porosities greater than 75% and we describe methods of processing inorganic aerogel films having controllable thicknesses in the range 0.5 to 200 micrometers. We report methods and results of characterizing the films including thickness, refractive index, density (porosity), and dielectric constant. We also discuss results of metallization and patterning on the aerogel films for applications involving microminiature electronics and thermal detectors.
Synthesis and Structure of Ultrafine Zeolite KL (LTL) Crystallites and their Use for Thin Film Zeolite Processing
Authors: Tsapatsis Michael , Okubo Tatsuya , Lovallo Mark , Davis Mark E.
Published: April 2011

Synthesis conditions were identified leading to agglomerates of nearly cylindrical zeolite nanocrystals with dimensions less than 50 nm in the channel direction and approximately 10 nm in diameter (in the direction perpendicular to the zeolite channels). The nanocrystals form agglomerates with approximate particle sizes ranging from 20 to 400 nm as determined by DLS. Washing with repeated centrifugation and sonication results in stable (over long periods of time) colloidal suspensions of the zeolite particles in water (pH ∼ 7) with zeolite concentrations of lOg/l. The average zeolite particle size of the suspension can be as low as 20 nm as determined by DLS. Films free of microcracks were prepared from these suspensions by evaporation of water.
A New Templating Route to Ordered Mesoporous Materials
Authors: Tanev Peter T. , Pinnavaia Thomas J.
Published: April 2011

A new templating route to ordered mesoporous materials is demonstrated based on hydrogen bonding interactions and self-assembly between neutral primary amine surfactants (S°) and neutral inorganic precursors (1°). The S° I° templating pathway affords ordered mesoporous materials with thicker framework walls, smaller X-ray scattering domain sizes, and substantial textural mesoporosities in comparison to MCM-41 materials templated with quaternary ammonium cations. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods.
Spectroscopic Investigations of Mesoporous M41S Silica Phases
Authors: FrÖBa Michael , Behrens P. , Wong Joe , Engelhardt G. , Haggen-Müller CH. , Van De Goor G. , Rowen M. , Tanaka T. , Schwieger W.
Published: April 2011

Mesoporous silica phases of the M41S type were investigated by SiK XANES spectroscopy and the results compared with the information provided by 29Si MAS NMR spectroscopy. The results show that the pore walls are more ordered than in “truly” amorphous silica phases (as, e.g., glass) and indicate a relationship of their structure to layered silicates.
Production of Hollow Microspheres for Inertial Confinement Fusion Experiments
Authors: Cook Robert
Published: April 2011

The targets used in inertial confinement fusion (ICF) experiments at the Lawrence Livermore National Laboratory are plastic capsules roughly 0.5 mm in diameter. This paper reviews the fabrication of these capsules, focusing on the production of the thinwalled polystyrene microshell mandrel around which the capsule is built. The relationship between the capsule characteristics, especially surface finish, and capsule performance is discussed, as are the methods of surface characterization and modification necessary for experiments designed to study the effects of surface roughness on implosion dynamics. Targets for the next generation of ICF facilities using more powerful laser drivers will have to be larger while meeting the same or even more stringent symmetry and surface finish requirements. Some of the technologies for meeting these needs are discussed briefly.
Automated Line Development for Control and Selection of Shells for Laser Fusion Target
Authors: Veselov A. V. , Beinik A. Ja. , Zaharov A. V. , Inozemtsev A. P. , Komleva G. V. , Punin W. T.
Published: April 2011

Methods for control of the shell diameter, wall thickness and wall nonuniformity and also methods for selection of shells in fluid have been developed and investigated. The methods allow us to separate shells according to the diameter with 0.25 μ;m accuracy, to the wall nonuniformity with 5–7% accuracy, to make measurements of the diameter with 0.35 μ;m accuracy and wall thickness with 3–10%.

These methods allowed us to develop the automated process cycle of control and selection of shells for laser fusion targets. A model automated line has been developed and joint operation of units has been investigated. The calculated automated line throughput during the shell analysis is 50–300 shells per hour, the control and selection accuracy for the diameter, thickness, and wall nonuniformity is 1%, 3–10% and 1–3%, respectively.

Thus the foundations have been laid for an automated, high-quality target production technology for power stations based on laser fusion.
Fabrication Method for Hollow Microspheres Made of High-Strength Glasses
Authors: Dorogotovtsev Valery M.
Published: April 2011

Lasting storage of hydrogen, its isotopes and other gases under high (1–2 thousand atm) pressure inside hollow microspheres as well as production of low-density syntaxis poroplasts to withstand high external loads - all these need hollow microspheres of high mechanical strength. By modern commercial technology the microspheres are mainly obtained from water- soluble alkali-silicate or alkali-boro-silicate glasses. These microspheres are not strong, their strength being 1000–1500 MPa.. Besides the low resistivity to hydrolysis and chemicals also restrict their applications. To gain strength 1.5–2 times higher the additional modification of microspheres is done either by leaching, or by annealing, or by ion exchange. Microspheres of stronger glasses being usually multi-component require a technology fitted to produce highly uniform glass [1,2].

A new fabrication method is presented to produce hollow microspheres of various glasses. They include simple alkali and alkali-boro-silicate glasses as well as multi-component glasses of commercially available compositions, alkali-free, refractory, and high-strength glasses.
Synthesis and Characterization of PZT Coatings on Glass Microspheres
Authors: Jardine A. Peter
Published: April 2011

Synthesis of Pb(Ti,Zr)O3 (PZT) coatings onto glass microspheres was demonstrated using solgel techniques. Characterization of the coatings was performed using XRD and SEM to demonstrate that piezoelectric PZT coating are possible. This study represents an initial feasibility study into the manufacture of so-called “smart” material fabrication utilizing different geometries.
Compressive Deformation of Hollow Microsphere Reinforced Metal Matrix Composites
Authors: Kiser M. T. , He M. , Wuj B. , Zok F. W.
Published: April 2011

The compressive deformation characteristics of hollow alumina microsphere reinforced aluminum matrix composites have been studied through both experiments and finite element analysis of unit cell models. Tests have been performed on composites containing around 50 volume percent of microspheres. The effects of the matrix flow stress and microsphere morphology (characterized by the ratio of wall thickness to radius) have been examined. The measured strength enhancement due to the hollow microspheres was found to be considerably less than that predicted by the FEM calculations; a result of microsphere cracking. Experiments have been conducted to document the progression of such damage following casting and mechanical deformation. The potential of this class of composite for impact energy absorption applications is also explored.
A Method for Rotation of Spherical Shells by Any Law with a Small Center Beating.
Authors: Veselov A. V. , Golubinskij A. G. , Zaharov A. V. , Malkov A. V.
Published: April 2011

To provide control of the whole surface the shell should be rotated. But the shell center beating within 1 μm gives thickness variations from 90 to 1200 Å. For high accuracy of measurements it is necessary to decrease the shell center beating upon rotation down to 0.1–0.2 μm. This problem can be solved using the proposed method for rotation of shells.

Several units for rotation of shells have been developed and investigated. Those laws of rotation have been selected which allow to inspect the whole surface of the sell.

Obvious advantages of the proposed method are the following: ease of installation and removal of the shell in the unit, automated installation of the shell in the desired position, high speed of rotation, small beating of the shell center during its rotation, wide access to the shell surface to be controlled, any required law of the shell rotation.
Fiber-Optic Microsensors Using Porous, Dye-Doped Silica Gel Microspheres
Authors: Pope Edward J. A.
Published: April 2011

Dye-doped porous silica microspheres can be prepared from liquid solution at temperatures near ambient. Microsphere diameter can be controlled between approximately 5.0 microns to in excess of a millimeter. The resulting microspheres can be attached to the distal end of an optical fiber in which the proximal end is attached to a spectrophotometer. Depending upon the organic species doped into the microsphere, a wide variety of sensing functions are possible. In this paper, the use of microsensors for measuring pH, temperature, and solvent content of aqueous solutions is demonstrated. Potential utility of this type of sensor to heavy metals detection and biomedical diagnostics is also discussed.
Controlled Multi-Stage Self-Assembly of Vesicles
Authors: Walker Scotr A. , Chiruvolu S. , Zasadzinski J. A. , Schmitt F.-J. , Israelachvlli J. N.
Published: April 2011

The association of lipid or surfactant molecules into spherical vesicles in solution constitutes a primary self-assembly process, although typical vesicles are not the equilibrium form of aggregation for most lipids. Such meta-stable vesicles can undergo a secondary self-assembly into higher order structures in a controlled and reversible manner by means of site-specific ligandreceptor coupling. Cryo-electron microscopy shows these structures to be composed of tethered vesicles in their original, unstressed state. In contrast, vesicles aggregated by non-specific forces are deformed. In this work, we show that equilibrium vesicles can also undergo a secondary selfassembly via ligand-receptor interactions, as evidenced by freeze-fracture electron microscopy. Such site-specific vesicle aggregation provides a practical mechanism for the production of stable, yet controllable, microstructured materials.
Magnetic X-Ray Circular Dichroism in Spin-Polarized Photoelectron Diffraction
Authors: Waddill G. D. , Tobin J. G. , Guo X. , Tong S. Y.
Published: April 2011

The first structural determination with spin-polarized, energy-dependent photoelectron diffraction using circularly-polarized x-rays is reported for Fe films on Cu(001). Circularly-polarized x-rays produce spin-polarized photoelectrons from the Fe 2p doublet, and intensity asymmetries in the 2p3/2 level are observed. Fully spin-specific multiple scattering calculations reproduce the experimentally-determined energy and angular dependences. A new analytical procedure which focuses upon intensity variations due to spin-dependent diffraction is introduced. A sensitivity to local geometric and magnetic structure is demonstrated.
Resonant Soft X-Ray Fluorescence Studies of Novel Materials
Authors: Carlisle J. A. , Shirley E. L. , Terminello L. J. , Hudson E. A. , Jia J. J. , Callcott T A. , Himpsel F. J. , Ederer D. L. , Perera R. C. C.
Published: April 2011

We are using resonant soft x-ray fluorescence at the Advanced Light Source to probe the electronic and geometric structure of novel materials. In the resonant process, a core electron is excited by a photon whose energy is near the core binding energy. In this energy regime the absorption and emission processes are coupled, and this coupling manifests itself in several ways. In boron nitride (BN), the resonant emission spectra reflect the influence of a “spectator” electron in an unoccupied excitonic state. The resonant emission can be used to distinguish between the various bulk phases of BN, and can also be used to probe the electronic structure of a monolayer of BN buried in a bulk environment, where it is inaccessible to electron spectroscopies. For highly-oriented pyrolytic graphite (HOPG) a coherent absorption-emission process takes place in the resonant regime, whereby crystalline momentum is conserved between the core excited electron and the valence hole which remains after emission
Magnetic Compton Scattering Studies of the Invar Effect in Fe3Pt
Authors: Yahnke C. J. , Srajer G. , Haeffner D. R. , Mills D. M. , Assoufid L.
Published: April 2011

We have measured the magnetic Compton profile (MCP) of ordered and disordered Fe 3Pt samples both above and below their Curie temperature. From these measurements, we have determined the average moment per atom at room temperature to be 2.81μB ± 0.04μB for disordered Fe3Pt and 1.78μB ± 0.05μB for ordered Fe3Pt. At temperatures above Tc, we measured a substantial reduction in the moment (0.6μB ± 0.10μB for disordered Fe3Pt and 0.64μB ± 0.13μB ± for ordered Fe3Pt) and a change in the shape of the MCP. This suggests that the mechanism behind the Invar effect in Fe3Pt can be described by a high-spin to low-spin magnetic phase transition. The experimental MCPs for both ordered and disordered Fe3 Pt are analyzed within the framework of the Weiss 2γ model.
High Resolution Synchrotron X-Ray Diffraction Tomography of Polycrystalline Samples
Authors: Stock S. R. , Guvenilir A. , Piotrowski D. P. , Rek Z. U.
Published: April 2011

The macroscopic response of polycrystalline materials to loading depends on both the spatial distribution of strain and the variation of microtexture on the scale of 100 μm. Nondestructive measurements are needed if the three-dimensional evolution of strain is to be studied. This paper describes approaches for high resolution synchrotron polychromatic x-ray diffraction tomography of polycrystalline materials. Preliminary experiments are reported on partially cracked compact tension samples of Al-Li 2090 and on model samples of randomly-packed, millimeter-sized pieces of Si wafers. Polychromatic beams collimated to 100 μm diameter have been used, and the distribution of diffracted intensity has been collected on high resolution x-ray film as well as on image storage plates. The depths of diffracting volume elements are determined from the changes in the spatial distribution of diffracted intensity with varying sample to detector separation.
Dislocation Mobility in HCL-Doped Ice
Authors: Hu Xiaohong , Jia Kunlun , Liu Fuping , Baker Ian , Black David
Published: April 2011

Dislocation velocities have been measured in both lightly and heavily HCl-doped ice single crystals using synchrotron-based, monochromatic X-ray topography. In the temperature range −10°C to −30°C, a concentration of ˜1 × 10−6M was found not to affect the mobility of either 60° or screw basal dislocations, confirming the earlier observations of C. Shearwood and R. W. Whitworth [Philosophical Magazine A65, 1992, 85]. However, heavier doping (˜1.9 × 10−4M) increased the basal dislocation velocity, compared to pure ice, by a factor of 2.6 at −16.4°C.
Densification of Sio Gel Films by Synchrotron Radiation and its Dependence on Photon Energy
Authors: Imai Hiroaki , Awazu Koichi , Yasumori Masaru , Hirashima Hiroshi , Onuki Hideo
Published: April 2011

The interaction of synchrotron radiation (SR) emitted from a polarizing undulator with SiO2 gel films was investigated by ellipsometry and infrared spectroscopy. The photon energy in SR was varied in the range of 6.4−17.8 eV using an Onuki-type undulator in order to study the energy dependence of the interaction. We found that an increase of refractive index, a decrease of thickness of the films and a loss of OH groups were induced by photons with energies above ˜9 eV although any changes were not observed with photons below ˜7 eV. These results suggest that SiO2 gel films are densified through electronic processes stimulated by the energetic photons.
Magnetic X-Ray Circular Dichroism in Nickel-Gold Multilayers
Authors: Jankowski A. F. , Waddill G. D. , Tobin J. G.
Published: April 2011

Magnetic circular dichroism in x-ray absorption is used to investigate the in-plane, remnant magnetization of well-characterized Ni0.48/Au0.52 multilayers. Large superlattice strains are found in this multilayer system for samples with a 2nm layer pair spacing. A larger dichroism is found in the Ni 2p absorption edge for a 1.8nm than for a 4.4nm layer pair sample. The larger dichroism is consistent with a larger magnitude of in-plane strain for the Ni layers and a larger total magnetic anisotropy energy as previously shown from magnetization curves.
The Paramagnetic Correlation Length of Mn Thin Films
Authors: MclLroy D. N. , Dowben P. A.
Published: April 2011

We have utilized Ginzberg-Landau mean field theory to analyze the branching ratio and soft X-ray magnetic circular dichroism measurements of the L3 and L2 adsorption edges of thin Mn overlayers on ferromagnetic fcc Co(001) at room temperature. We have determined a short range magnetic correlation of 4.25Å and that the long range magnetic magnetic order has a decay length of 1.29Å. These results indicate that the first monolayer of Mn ferromagnetically couple with the Co substrate. The paramagnetic Mn layer exhibits short range magnetic order, but lacks long range magnetic order. Due to the exponential decrease of both the branching ratio and dichroism signals, we have concluded that the magnetization of the Mn overlayer is substrate induced.
The Mit Specular and Diffuse Neutron Reflectometer for the Investigation of Surfaces & Interfaces
Authors: Ku Chwen-Yuan , Zhou Xiao-Lin
Published: April 2011

A specular and diffuse neutron reflectometer was designed at the Massachusetts Institute of Technology nuclear reactor, MITR-II, and the description of the facility is presented in this paper. This reflectometer uses a horizontal sample geometry so that both solid and liquid samples can be measured. To minimize sample or beam motion and reduce measurement time, two neutron beams are extracted from the same beam port and are incident simultaneously on the same sample surface at grazing incident angles of 0.2 and 1.5 degrees, respectively. The reflected neutrons are detected by a linear position sensitive detector and energy-analyzed by the time-of-flight method. The reflection flight path is enclosed in an evacuated chamber to reduce background counts. The reflectometer performance is estimated as 0.004-0.33 Å-1 dynamic range, 5% Q resolution, 1-10-7 measurable specular reflectivity range, and a 4 orders of magnitude range in diffuse reflectivity counts. Diffuse reflectivity can be measured as a two-dimensional function of both the wavelength and the in-plane diffuse reflection angle. The instrument can be used to investigate a wide range of surface systems of condensed and soft-condensed matters.
Real Time Neutron Diffraction Experiments Using Bragg Edges
Authors: J Trela Walter , Meggers Kay , G Priesmeyer Hans
Published: April 2011

Time resolved phase transition and strain experiments have been performed on the millisecond time scale using a Bragg-edge transmission technique that has been developed at the Los Alamos National Laboratory. The precision with which lattice parameters can be determined from edge positions is sufficient to perform high-resolution strain measurements in uniaxial stress.
Deconvolution of Neutron Scattering Data from a Pulsed Spallation Source
Authors: Richardson J. W. , Birtcher R. C. , Chan S.-K.
Published: April 2011

Diffraction peak shapes generated from high purity, low strain uranium silicide powder have been used to deconvolute diffraction peaks from radiation damaged material. The deconvolution was based on the assumption that defect scattering near a strained Bragg peak could be represented as the summation of a series of discrete peaks with the same convoluted peak shape measured for unirradiated material in the same range of d-spacing. Discrete peaks were taken to have the same density as the measured time of flight data so that a deconvoluted scattering intensity was generated at each experimental point. This deconvolution technique accounts in a natural manner for peak asymmetries arising from the time structure of the neutron pulse shape and instrument broadening without arbitrary analytical functions and fitting parameters.
The Phase of Scattering Profiles & X-Ray/Neutron Reflectivity
Authors: Pershan P.S.
Published: April 2011

The phase problem that troubles x-ray diffraction is also a problem for x-ray and neutron reflectivity; however, there are a range of small angles just beyond the critical angle for which the reflectivity contains information on the phase of the surface scattering amplitude. In principle this phase information can be used to determine the asymmetry of the normal gradient of the scattering amplitude density. We discuss here practical conditions under which this symmetry can, or cannot, be extracted from reflectivity data.
Analyzing Specular Reflectivities with Parametric B-Splines
Authors: Berk N. F. , Majkrzak C. F.
Published: April 2011

A method of using parametric B-spline curves to interpret neutron and x-ray specular reflectivity spectra is described. The introduction of parametric curves for scattering length density profiles greatly expands the function space accessible to low-dimensional representations but also requires means to restrict the space to physically acceptable functions. A practical fitting procedure is outlined, and two examples are shown.
The Determination of the Structure and Coverage of Nonionic Surfactant Monolayers at the Air-Water Interface Using Neutron Reflection Technique
Authors: Lu Jian R. , Thomas Robert K.
Published: April 2011

The coverage and structure of the monododecyl ethers of oligoethylene glycols, C12Em where m = 2, 4, 6 and 8, adsorbed at the air-water interface have been studied by neutron reflection. At their c.m.c.s, the area per molecule is 33 ± 3 Å2 for C12E2, 44 ± 3 Å2 for C12E4 55 ± 3 Å2 for C12E6 and 62 ± 3 Å2 for C12E8. In terms of the width of a Gaussian distribution at 1/e of its height the thicknesses of the dodecyl chains are found to be constant at 16 ± 2 Å and those of the heads to vary from 11 to 19±2Å from m = 2 to 8. There is also found to be some overlap between the two chains at the interface.
An in Situ Small Angle Neutron Scattering Investigation of AgO.7Au0.3 Dealloying
Authors: Corcoran Sean G. , Wiesler David , Barker John , Sieradzki Karl
Published: April 2011

In situ small angle neutron scattering (SANS) was used to characterize the formation of the random 3-dimensional porous structure created during the free corrosion of a Ag0.7Au0.3 alloy in concentrated HNO3. The evolution of the porosity was followed in situ for a period of 21 hours. The average ligament width evolved from a size of approximately 6 nm following only 7 minutes of dealloying to approximately 22.5 nm after 21 hours of de-alloying. Using a model developed by N.F. Berk (Phys. Rev. Lett., 58 (1987) 2718) for the scattering properties of random porous media, we were able to characterize the average ligament width distribution as a function of time. Our results represent the first in situ nanoscale characterization of the formation of 3-dimensional porosity in a corrosion system.
Internal Strain Measurement Using Pulsed Neutron Diffraction at Lansce
Authors: Goldstone J. A. , Bourke M. A. M. , Shi N. , Lujan Manuel
Published: April 2011

The presence of residual stress in engineering components can effect their mechanical properties and structural integrity. Neutron diffraction in the only technique that can make nondestructive measurements in the interior of components. By recording the change in crystalline lattice spacings, elastic strains can be measured for individual lattice reflections. Using a pulsed neutron source, all lattice reflections are recorded in each measurement, which allows for easy examination of heterogeneous materials such as metal matrix composites. Measurements made at the Manuel Lujan Jr. Neutron Scattering Center (LANSCE) demonstrate the potential at pulsed sources for in-situ stress measurements at ambient and elevated temperatures.
Estimation of Residual Stress in Cold Rolled Iron-Disks Using Magnetic and Ultrasonic Methods and Neutron Diffraction Technique
Authors: Aksenov V.L. , Balagurov A.M. , Bokuchava G.D , Schreiber J. , Taran Frank Yu.V.
Published: April 2011

Variation of internal stress states in cold rolled sheet metal can essentially influence the result of forming processes. Therefore it is important to control the forming process by a practicable in line testing method. For this purpose magnetic and ultrasonic nondestructive methods are available. However, it is necessary to calibrate these techniques. This paper describes a first step of such a calibration procedure making use of the neutron diffraction method. On the basis of the diffraction results an assessment of the magnetic and ultrasonic methods for the estimation of residual stress in the cold rolled iron-disks was made. Reasonable measuring concepts for practical applications to forming processes with cold rolled sheet metal are discussed.
Elevated Temperature Neutron Measurements of Thermal Residual Stresses in a Sic Fibre Reinforced Al Alloy
Authors: Ceretti Monica , Kocsis M. , Lodini A.
Published: April 2011

The main objective of the present investigation is to determine the evolution of residual stresses by neutron powder diffraction in an Al/SiC composite (Al 7075 reinforced by 27 vol.% SiC whiskers), originating from thermal treatment and mechanical loading. The results show that residual stresses in the matrix and in the reinforcement decrease in magnitude with increasing temperature and they reach the stress free state at the 'equivalent temperature'. As the temperature further increases, these stresses increase numerically in a reverse sense for both phases. The data obtained are analysed in terms of a simple model based on Eshelby's equivalent inclusion method.
Neutron Powder Diffraction Studies of Portland Cement and Cement Compounds
Authors: Berliner R. , Ball C. , West Presbury B.
Published: April 2011

Neutron powder diffraction data from phase-pure cement compounds has been used to develop structural models suitable for profile refinement of cements. These models were then applied to the determination of cement compound phase abundance in clinkers. This paper reports on the results of clinker phase analysis by powder neutron diffraction and summarizes the results of the refinements of neutron diffraction data from phase-pure cement compounds. The profile refinements provide generally good agreement with cement compound phase abundance measurements of NIST reference clinker specimens by chemical, optical and X-ray methods.
Using Quasielastic Neutron Scattering Techniques To Quantify Freezable Water In Portland Cement Paste
Authors: Gress D.L. , El-Korchi T. , Livingston R.A. , Neumann D.A. , Rush J.J.
Published: April 2011

Quasi-elastic neutron scattering provides detailed information of the atomic and molecular interactions responsible for a material's properties and is a direct and nondestructive method of measuring the motion of hydrogen. This technique was utilized to evaluate the state of water in a cementitious material. The relative amount of freezable water that existed in a saturated type I portland cement paste with water/cement ratios of 0.3, 0.4, and 0.5 was determined over a temperature ranging from +3 C to - 40 C. The amount of frozen water relative to the total water content was related to the water filled pore size predicted to be freezable at each temperature. The proportion of immobilized water increased for all water cement ratios gradually with decreasing temperatures below 0 C until most of the water was immobile at -40 C. The relative proportion of immobile water at 3 C was found to be inversely related to the water/cement ratio, which suggested a smaller fraction of large pores for small water/cement ratios. The findings also suggested the immobilization water was independent of water/cement ratio for pores smaller than 15nm.
Anisotropic Magnetization of HoNi2B2C
Authors: Canfield P.C. , Cho B.K. , Johnston D.C. , Hundley M.F.
Published: April 2011

Anisotropic, temperature dependent magnetization measurements on single crystals of HoNi2B2C indicate that there is a cascade of magnetic transitions in zero and low applied magnetic fields. Comparison of the temperature dependence of the specific heat and d(χT)/dT data shows a remarkable agreement in the low field limit, supporting the use of d(χT)/dT as a method of determining the magnetic transition temperatures as a function of applied field. The magnetic transition temperatures determined by this analysis are remarkably sensitive to the applied field and highly anisotropic. Comparison to similar data for ErNi2B2C show that the sensitivity and anisotropy are common features. These data emphasize the importance of anisotropic measurements of field dependent properties on single crystal samples, since the application of a magnetic field to a polycrystalline sample will effectively broaden the transition temperatures.
Polarized Neutron Glancing-Angle Diffraction Study of Magnetic Structure at the Y/Gd(0001) Interface
Authors: Ankner J.F. , Gallagher P.D. , Schreyer A. , Zhang H. , Majkrzak C.F. , Satija S.K. , Zabel H. , Matheny A. , Flynn C.P.
Published: April 2011

By exciting diffraction in the Laue geometry by specularly reflected beams, penetrating x-rays and neutrons can be used to probe surface and interfacial atomic structure. We present the first such measurement utilizing polarized neutrons with both incident- and exit-angle resolution. We have observed the evolution of magnetic order by monitoring the in-plane (1010) Bragg peak from an epitaxially grown film consisting of 150 Å Y(0001) on 5000 Å Gd(0001). Magnetic scattering increases as the film is cooled from the Gd bulk Curie temperature (293K) to 100 K. The gross features of the data can be captured by a simple two-layer model, but sufficient disagreement remains that one may yet hope to extract non-trivial structure at the Y/Gd interface.
Field-Induced Decoupling of NiO-Magnetite Multilayers
Authors: Erwin R.W. , Borchers J.A. , Berry S.D. , Lind D.M. , Lochner E. , Shaw K.A.
Published: April 2011

NiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite ferrimagnetic correlations confined to a single layer due to stacking faults of the spinel structure at the interfaces[l, 2, 3, 4]. A systematic study of the field-dependence of the interlayer coupling in a series of NiO-magnetite multilayers has been made using neutron diffraction. Both NiO and magnetite single thin films were included in the measurements for comparison. In the magnetite film, intensity changes with magnetic field are consistent with domain reorientation of the net ferrimagnetic moments, while in the NiO film there are essentially no intensity changes. There is no significant field dependence of the magnetic correlation lengths in either film. For multilayers where the ratio of NiO to magnetite layer thickness is far from unity, the field dependence approximates that of the bulk films. However, for a Fe3O4(68Å)|NiO(34Å) multilayer the NiO antiferromagnetic intensity decreases with increasing field, and there is a broadening of the NiO peak on the order of 30 percent. Concomitantly, the magnetite spins rotate collinear with the field, as expected, due to the net 4.2 μB moment per unit-cell. The NiO moments appear to rotate into domains where the direction of propagation of the ferromagnetic sheets is closer to the field direction.
Neutron Scattering at the High Flux Isotope Reactor at Oak Ridge National Laboratory
Authors: Yethiraj Mohana , Fernandez-Baca Jaime A.
Published: April 2011

Since its beginnings in Oak Ridge and Argonne in the late 1940's, neutron scattering has been established as the premier tool to study matter in its various states. Since the thermal neutron wavelength is of the same order of magnitude as typical atomic spacings and because they have comparable energies to those of atomic excitations in solids, both structure and dynamics of matter can be studied via neutron scattering. The High Flux Isotope Reactor (HFIR) provides an intense source of neutrons with which to carry out these measurements. This paper summarizes the available neutron scattering facilities at the HFIR.
Crystal Structure, Short-Range Oxygen Defects, and Water Adsorption in La- and Nd-Modified ZrO2
Authors: Loong C.-K. , Richardson J. W. , Iton L. E. , Ozawa M.
Published: April 2011

Doping Rare-earth (RE) elements to ZrO2 helps stabilize the cubic and tetragonal phases and improves resistance to thermal shock and sintering at high temperatures. Since a RE ion has a lower valency (3+) than Zr ion (4+), oxygen vacancies are formed to preserve electroneutrality. We have studied the crystal structure of La0.1Zro.9O1.95 and Nd0.1Zr0.9O1.95 by neutron diffraction and examined the associated oxygen defects by a Fourier transform of the filtered residual diffuse scattering. The hydration process was investigated by inelastic neutron-scattering measurements of the hydrogen vibrational density of states of the surface hydroxyl groups and physisorbed water on these fine powders. We compare the O-H stretch vibrations from samples with only surface hydroxyl groups to multilayer coverage of water molecules. The decreasing energies and increasing widths of the O-H stretch bands with increasing H2O coverage indicate the influence of hydrogen bonding on the motion of water molecules. Similar elastic and inelastic experiments were also performed on a high surface-area pure ZrO2 powder.
Neutron and Raman Spectroscopes of 134 and 134a Hydrofluorocarbons Encaged in Na-X Zeolite
Authors: Udovic T. J. , Nicol J. M. , Cavanagh R. R. , Rush J. J. , Crawford M. K. , Grey C. P. , Corbin D. R.
Published: April 2011

Inelastic neutron scattering methods were used in conjunction with Raman spectroscopy to probe the vibrational density of states of the hydrofluorocarbons (HFCs) 134 (HF2C-CF2H) and 134a (F3C-CFH2) adsorbed in the cages of dehydrated Na-X zeolite. A comparison of the vibrational spectra of the encaged HFC species with those of their gas-phase analogs indicates that the HFCs adsorb nondissociatively at room temperature and are most likely associated with Na cations in the supercages at the SIII sites. Guest-host interactions are manifested by adsorption-induced perturbations of the gas-phase torsional and C-H stretching vibrations and the presence of additional features presumably due to low-energy whole-molecule vibrations and adsorbate-coupled zeolite framework vibrations. Moreover, although the 134 trans conformer is favored by 5 kJ/mole in the gas phase at 300 K, the gauche conformer seems to be more prevalent in the zeolite at this temperature and below. This suggests that a sizeable fraction of the Na-X adsorption sites provides a stabilizing configuration for the otherwise higher-energy gauche conformation, perhaps due to hydrogen-bonding interactions with the zeolite framework.
Wafer Curvature and Flatness Measurements Using The Magicmirror (Makyoh) Method
Authors: SzabÓ J. , Riesz Ferenc , SzentpÁli B.
Published: April 2011

A new method is presented for the measurement of the radii of curvature R of semiconductor wafers using the magic-mirror (Makyoh) technique. A flat mirror is placed beneath the sample, thus a second, “contour” image of the sample is formed beside the Makyoh image. From the ratio of the two image sizes, R can be determined using a set of reference curved mirrors. Model calculations show good agreement with the results. Other examples of assessing of the flatness of semiconductor samples are presented as well.
Critical Thickness for Strained Quantum Wires
Authors: Gosling T. J. , Freund L. B.
Published: April 2011

The stability of strained quantum wires against the propagation of threading dislocations is considered, using a critical thickness criterion due to Matthews and Blakeslee that is extensively used for strained layers. Given first are results for the critical mismatch at which a buried wire of a given thickness becomes susceptible to degradation. It is found that a wire, once buried, is extremely stable, being able to support, without loss of coherency, around five times the lattice mismatch that can be supported by a buried strained layer of the same thickness. It is concluded that if a strained wire contains dislocations then those dislocations must have been introduced during its growth, when the top surface of the wire is exposed. To investigate this, the results of finite element calculations are presented that give the critical relationship between mismatch and thickness during the growth of a triangular quantum wire being deposited in a [110]-oriented V-groove in a patterned (001) substrate. The results may be approximately expressed through an expression of the same form as that derived by Matthews and Blakeslee for a strained layer, but with modified coefficients obtained via the finite element analysis. Contact is made with the limited experimental evidence available.
The Growth and Optimization of InPSb/InGaAs/InAsSb Strained-Layer Superlattice Emitters by Metal Organic Chemical Vapor Deposition
Authors: Biefeld R. M. , Kurtz S. R.
Published: April 2011

We have prepared InAsSb/InGaAs strained-layer superlattices (SLS's) and InPSb confinement layers using metal-organic chemical vapor deposition (MOCVD) for use as infrared emitters. X-ray diffraction was used to determine lattice matching as well as composition and structure of the SLS's. Photoluminescence linewidth and intensity were used as a measure of the quality of the structures. Typical FWHM were less than 10 meV. The presence of interface layers were indicated by broadened x-ray diffraction peaks for samples grown under non-optimized conditions. Two types of interfacial layers apparently due to a difference in composition at the interfaces were observed with transmission electron microscopy (TEM). The width of the x-ray peaks can be explained by a variation of the interfacial layer thicknesses. Optimized growth resulted in SLS's with narrow x-ray peaks and high radiative efficiency. Room temperature LEDs operating between 4-5 μm have been prepared.
Photoelastic Waveguides Using Strain-Compensated InAsP/InGaP Multi-Quantum-Wells
Authors: Liu Q. Z. , Mei X. B. , Yu L. S. , Tu C. W. , Lau S. S.
Published: April 2011

Photoelastic optical waveguides using strain-compensated InAsP/InGaP multiplequantum-well (MQW) have been fabricated. Lateral light confinement for waveguiding is achieved by introducing stress into semiconductor heterostructures with stable WNi surface stressor stripes. The waveguides have been characterized at both 1.52 μm and 1.32 μm wavelength in term of TE/TM intensity ratio. At 1.52 μm, the waveguides favor the propagation of TE mode, and the TE/TM intensity ratio can be as large as 15 dB. At 1.32 μm, the TE and TM intensity can be comparable. Anisotropy of waveguides fabricated along [110] or [110] directions has also been observed in term of TE/TM intensity ratio, which suggests the presence of anisotropic property of the strain-compensated MQW.