bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Conductivity in Mesoporous and Microporous Pillared Layered Phosphate Structures
Authors: Ramos-Barrado J.R. , Criado C. , Maireles-Torres P. , Olivera-Pastor P. , RodrÍguez-Castellón E. , JimenÉz-López A.
Published: April 2011

The electrical relaxation and charge motion in porous solids (Lithium exchanged alumina pillared layered cc-tin phosphates (Li-PLP)) have been studied on the basis of the coupling model. The static dielectric constant and the dielectric susceptibility show a dependence on the basal distance which is correlated with the ion mean square displacement.
Towards the Rational Design and Synthesis of Zeolites
Authors: Burkett Sandra L. , Davis Mark E.
Published: April 2011

The mechanisms by which the geometries of organic structure-directing agents are translated into the product pore architectures in the syntheses of pure-silica and high-silica zeolites and of aluminum-rich zeolites are discussed. Two different mechanisms of structure direction and self-assembly via the formation of extended inorganic-organic composite structures or of purelyinorganic structures are proposed for the two different classes of materials. The primary impetus for developing a mechanistic understanding of zeolite synthesis is the ultimate goal of the rational design and synthesis of novel zeolite pore architectures. By considering issues such as hydrophobic hydration behavior of the structure-directing agent and the optimization of inorganic–organic van der Waals interactions, the successful design of structure-directing agents for the synthesis of new zeolite structures may be possible, particularly for high-silica systems.
Study of Production and Quality of Large (1–2 MM) Polystyrene Hollow Microspheres.
Authors: Merkuliev Yu. A. , Akunets A. A. , Bushuev V. S. , Dorogotovtsev V. M. , Gromov A. I. , Isakov A. I. , Nikitenko A. I. , Startsev S. A. , Tolokonnikov S. M. , Cook R. C.
Published: April 2011

We present a summary of the techniques used to produce hollow plastic microshells from solid polymer granules using drop tower techniques. Unlike solution drop tower techniques, the use of these granules allows one to produce good quality shells with diameters of 1 to 1.5 mm. The reasons for hollow plastic shell diameter limitations are discussed, and based on these studies we present a new drop tower furnace concept we call a ballistic furnace that has been designed to produce large (2 to 3 mm) polystyrene shells. The characteristics of the individual components such as the pellet injector and the fast cooling system are given.
Sol-Gel Derived Ceramic Bubbles
Authors: Moh Kyung H.
Published: April 2011

Sol-gel derived ceramic bubbles include shaped and fired, porous or impermeable nonvitreous ceramic microcapsules of metal oxide and non-oxide, are made by non-melt process involving the equilibrium boiling point method with controlled thermal gelation. Discrete, free-flowing, ceramic microbubbles consist of a non-oxide component and/or an oxide component having diameters in the range of I to 300 micrometers and each having a wall thickness of less than 10 percent of the diameter of the bubble. In this process, a sol precursor and a bloating agent, when added to a bubble promoting medium under proper conditions, provide green gelled microbubbles which after firing are strong, well formed, ceramic microbubbles. The microbubbles are non-vitreous, sol-gel derived, fine microstructured, uniform, hollow, smooth, and are essentially all oxide or non-oxide or combinations of both. The microbubbles can be used as fillers for metal, glass, ceramic, and polymer or filled with a selected solid, liquid or gas for purpose of storing, transporting, or facilitating the use of the same.
Permeability and Porosity of Bonded Hollow Sphere Foams for High Intensity Radiant Burners
Authors: McEntyre J. E. , Cochran J. K. , Lee K. J.
Published: April 2011

Bonded hollow sphere foams for this study were made from point-contact, slurry-bonded monosized spheres, 2.5 mm in diameter. The permeabilities of these foams are compatible with the diffuser base in radiant burners. For this study, the effect of quantity of bonding phase on interstitial porosity, permeability, and uniformity of gas flow through the foams was investigated. The relationship between permeability and porosity was modeled with the Kozeny-Carman equation. Attempts were made to correlate diffuser base permeability to operating characteristics of these burners.
Precision Shell Characterization Using Radial Averaging of X-ray Images — Part II
Authors: Stephens Richard. B.
Published: April 2011

Radial averaging of a circular X-ray image substantially improves the resolution and sensitivity with which surfaces and interfaces can be detected in our standard three-layer ICF capsule. We consider here the limits of this technique and the effects of likely changes in capsule composition and geometry.
Design Guidelines and Water Extraction Synthesis Capabilities for Hollow Ceramic Microspheres for Low Dielectric Constant Inorganic Substrates
Authors: Liu Jay G. , Wilcox David L.
Published: April 2011

This paper reports the use of hollow ceramic microspheres for a controlled porosity composite application and an emulsion/extraction method to make them. Design guidelines for this application are presented in which the physical properties and geometry of the microspheres are correlated to both dielectric constant and mechanical strength of the composites. The analytical modeling indicates that small size, thin walled ceramic microspheres with thermal expansion coefficients greater than that of common ceramic substrate matrices are needed to lower the dielectric constant significantly while retaining good mechanical strength. An emulsion/water extraction method was developed to prepare such hollow ceramic microspheres. This method shows promise for making very small (< 10 μm) hollow microspheres of various ceramic compositions. The capability and limitation of this synthesis route are shown.
Fabrication of Glass Micro- and Nanospheres from Liquid Precursors Using Droplet Generation and Sol-Gel Processing
Authors: Kim Kyekyoon
Published: April 2011

Two novel methods particularly suitable for continuously fabricating uniform glass spheres are described, one suitable for spheres micrometers to millimeters in diameter and the other for spheres of diameters in the submicron range, down to tens of nanometers. Both methods start from liquid precursors and combine droplet generation which is effected by a nozzle with sol-gel processing. One difference is that in the latter method, which is termed the charged liquid cluster beam (CLCB) technique, one employs flow-limited field-injection electrostatic spraying to further reduce the size of the drops to the nanometer range in the droplet generation process. Using the two methods, uniform hollow silica aerogel spheres, micrometer to millimeter in diameter, of controlled porosity and silica spheres with diameters in the nanometer range were produced. By utilizing the appropriate liquid precursors, the present methods can fabricate spheres composed of a variety of materials, including glass. Due to its ability to fabricate nanodrops, the CLCB technique is suited to fabricating nanoparticles as well as thin films of controlled stoichiometry and chemical composition.
Lebedev Physical Institute Activity in the Science and Technology Associated with Hollow Microsphere Fabrication and Applications
Authors: Merkuliev Yuriy A.
Published: April 2011

Work at the P. N. Lebedev Physical Institute on hollow microsphere technology started more than twenty years ago, based on the commercial technology developed in our country, on the experience of our colleagues involved in chemistry research, and on our knowledge of physics and hydrodynamics. We have developed new methods of hollow shell fabrication using a complex of universal installations for making shells of polymers, glass, and metals; equipment for shell characterization; and employing mathematical modeling of shell formation processes. Using these facilities and methods, the physical processes involved in the various hollow microsphere fabrication regimes are studied both experimentally and theoretically.
Hollow Borosilicate Microspheres from Aqueous Solution
Authors: Hagarman James A.
Published: April 2011

Metastable aqueous borosilicate solutions may be processed to hollow microspheres by a combination of liquid feed atomization and thermal exposure. Techniques for feed preparation and the relationships between feed composition, stability and processibility are discussed. Optimization of feed atomization, hollow sphere formation and finishing operations are discussed relative to density, size, strength, and chemical durability properties of finished products. The connection between finished properties and product utility is presented for several applications including lightweight fillers for thermoset resins and vinyl plastisols, and physical sensitizers for emulsion explosives.
Linear and Circular Dichroism in Angle Resolved Fe 3p Photoemission
Authors: Tamura E. , Waddill G. D. , Tobin J. G. , Sterne P. A.
Published: April 2011

Using a recently developed spin-polarized, fully relativistic, multiple scattering approach based on the layer KKR Green function method, we have reproduced the Fe 3p angle-resolved soft x-ray photoemission spectra and analyzed the associated large magnetic dichroism effects for excitation with both linearly and circularly polarized light. Comparison between theory and experiment yields a spin-orbit splitting of 1.0 – 1.2 eV and an exchange splitting of 0.9 – 1.0 eV for Fe 3p. These values are 50 – 100 % larger than those hitherto obtained experimentally.
X-Ray Scattering Studies of Interfacial Microstructures in Inx, Ga1−x As/GaAs Superlattices
Authors: Ming Z. H. , Soo Y. L. , Huang S. , Kao Y. H. , Stair K. , Devane G. , Choi-Feng C.
Published: April 2011

Interfacial microstructures in 100-period InxGa1−xAs(15Å)/GaAs(100Å) superlattices grown on GaAs (100) substrates by molecular beam epitaxy were studied by using large angle x-ray scattering techniques. Unusual satellite peaks in the lateral direction parallel to the sample surface were observed in a sample with x = 0.535 grown at 480°C, indicating an in-plane structural ordering. This result is confirmed by high resolution transmission electron microscopy observations that thickness modulation in the InxGa1−xAs layers gives rise to long-range lateral periodic arrays of cluster-like microstructures with spacing on the order of a few hundred Ångstroms. This thickness modulation is found to occur only in [110] direction, thus the material can be viewed as a somewhat disordered array of grown-in parallel quantum wires.
Exafs Studies and Simulations of Local Anisotropy in CO78CR22 Films
Authors: Kemner K. M. , Harris V. G. , Elam W. T. , Lodder J. C.
Published: April 2011

Extended x-ray absorption fine structure measurements of a Co78Cr22 film were performed using normal and glancing incident radiation in order to investigate, respectively, the in-plane and out-of-plane local structure and chemistry. The Fourier transformed EXAFS data of the in-plane and out-of-plane structures around the Co and Cr atoms illustrates the presence of an anisotropy. Analysis of the local environments around Co for the two sample orientations indicates the presence of Co-enriched clusters, while similar studies of the Cr environments indicate preferential ordering parallel to the film plane. Quantitative analysis of the higher order Fourier transform peaks shows a greater amount of disorder perpendicular to the film plane beyond that expected for a textured hcp film. These results are consistent with earlier reports of a high density of stacking faults or twinning planes perpendicular to the growth axis, supporting the interpretation that a platelet-like texturing exists within the columnar microstructure.
Static Displacements of Atoms in Crystalline Metallic Solid Solutions
Authors: Sparks Cullie , Ice Gene , Jiang Xiaogang , Zschack Paul
Published: April 2011

Measurement of diffuse x-ray scattering from binary crystalline solid solutions at more than one x-ray energy is a sensitive probe of the average interatomic distance between neighboring pairs of atoms. Deviations of these bond distances by as little as 0.001Å are easily detected in the diffuse scattering from binary alloys consisting of atoms nearby in the periodic table and/or where x-ray energies chosen near their absorption edges can change the scattering contrast. Individual bond distances (AA, AB and BB) are recovered out to several near neighbor shells by combining three scattering measurements at x-ray energies chosen for maximum and minimum contrast. Average bond distances recovered from four metal alloys Fe77.5Ni22.5, Fe46.5Ni53.5Cr47Fe53and Cr20Ni80 are discussed. We find that the interatomic distances measured for these alloys give interesting insights to atomic displacements in solid solutions. Nearest neighbor bond distances are not well represented by phenomenological models based on pure element atomic size and concentration dependence of the lattice constants. Radial and nonradial displacements are recovered from these measurements of diffuse scattering.
Acid-Site Characterization of Water-Oxidized Alumina Films by Near-Edge X-Ray Absorption and Soft X-Ray Photoemission
Authors: O'hagan P. J. , Merrill R. P. , Rhodin T. N. , Woronick S. C. , Shinn N. D. , Woolery G. L. , Chester A. W.
Published: April 2011

Hydroxylated alumina films have been synthesized by water oxidation of single crystal Al(110) surfaces. Thermal dehydroxylation results in anion vacancies which produce an Al(3s) defect state 3.5 eV below the conduction band edge. The defect-DOS exhibits a maximum for oxides heated to 648±25 K, which is just where the materials exhibit maximum Lewis acidity with respect to C2H4 Adsorbed C2H4 produces thermally reactive C2 species which interact covalently with the defect-DOS and nonbonding O(2p) states from the top of the valence band. C(1s) binding energies suggest significant charge transfer which is consistent with a carbenium ion. Ni deposits behave similarly but transfer charge directly to Al species and do not interact with O atoms at the defect site. The defect-DOS is regenerated when the C2 species decomposes or when Ni migrates thermally through the oxide layer.
Correlation of Xanes Features with the Scintillation Efficiencies of Ce Doped Alkaline Earth Lithium Silicate Glasses
Authors: Blanchard D L , Sunberg D S , Craig R A , Bliss M , Weber M J
Published: April 2011

Cerium activated glasses of composition 20Li2O·15MO·64.4SiO2·0.6Ce2O3 (where M is Mg, Ca, Sr, or Ba) exhibit scintillation efficiencies that vary by more than a factor of 2.5 with the alkaline earth. Previous work has suggested a correlation between the microstructure of these glasses and scintillation efficiency. Measurements of the Ce LIII x-ray absorption edge in the Mg, Ca and Sr glasses display a feature near the absorption edge that is suggestive of the presence of Ce4+. The area of this peak is, in fact, correlated with the scintillation efficiency of the glass. The amount of Ce4+ indicated by the intensity of this feature is, however, too high to be a permanent population. We suspect that the feature is a transient phenomenon related to creation of Ce4+ and trapped electrons due to photoionization by the x-ray beam.
Synchrotron White Beam Topography Studies of Screw Dislocations in 6H-Sic Single Crystals
Authors: Wang S. , Dudley M. , Carter C. H. , Tsvetkov V. F. , Fazi C.
Published: April 2011

Synchrotron white beam X-ray topography, along with optical microscopy and scanning electron microscopy, has been used to characterize structural defects which are potentially detrimental to device performance in PVT 6H-SiC single crystals. Line defects running along the [0001] axis, known as “micropipes”, were studied extensively. Detailed analysis of topographic image contrast associated with “micropipes”, based on the kinematical theory of X-ray diffraction, established that the so-called “micropipes” are screw dislocations with large Burgers vectors.
X-ray Microscopy of Polymeric Materials
Authors: Adel H. , Hsiao B. , Mitchell G. , Rightor E. , Smith A. P. , Cieslinski R.
Published: April 2011

We describe how the scanning transmission x-ray microscope at Brookhaven National Laboratory can be used to investigate the bulk characteristics of polymeric materials with chemical sensitivity at a spatial resolution of about 50 nm. We present examples ranging from unoriented multiphase polymers to highly oriented Kevlar fibers. In the case of oriented samples, a dichroism technique is used to determine the orientation of specific chemical bonds. Extension of the technique to investigate surfaces of thick samples is discussed.
Applications of the Xia Scanning Photoemission Spectromicroscope for Element Identification on Material Surfaces
Authors: Ko Cheng-Hao , Kirz Janos , Ade Harald , Hulbert Steve , Johnson Erik , Anderson Erik
Published: April 2011

The Second Generation Scanning Photoemission Microscope at the beamline X1A of the National Synchrotron Light Source (NSLS), X1A SPEM II, is designed for spatially resolved elemental and chemical analysis by X-ray Photoelectron Spectroscopy (XPS) on material surfaces. Based on Fresnel Zone Plate (ZP) microfocusing techniques with the use of a bright and coherent photon source, this microscope is capable of acquiring XPS spectra from a small area irradiated by the focused beam and taking element-specific (using photopeaks) or chemical-state-specific (by detecting the chemical core level shifts) images with a spatial resolution defined by the focused spot size.
Characterization of Defect Structures in Lely 6H-SiC Single Crystals Using Synchrotron White Beam X-Ray Topography
Authors: Huang W. , Wang S. , Dudley M. , Neudeck P. , Powell J. A. , Fazi C.
Published: April 2011

Defect structures in Lely SiC single crystals have been studied using synchrotron white beam X-ray topography. Basal plane dislocations and stacking faults probably generated during post-growth cooling are clearly revealed. For both perfect dislocations and partial dislocations bounding the stacking faults, Burgers vectors and line directions are determined from contrast extinction analysis as well as projected direction analysis on different topographic images. The fault planes and fault vectors of the stacking faults were determined using contrast extinction analysis. Possible dislocation generation mechanisms are briefly discussed.
Extended X-Ray Absorption Fine Structure Studies of MnZn-Ferrite Films
Authors: Dorsey Paul C. , Harris Vincent G. , Chrisey Douglas B. , Lubitz Peter , Horwitz James S. , Koon Norman C.
Published: April 2011

The magnetic properties of MnZn-ferrite are greatly affected by the distribution and valence state of the magnetic and nonmagnetic metallic ions on the tetrahedral (A) and octahedral (B) sites in the spinel ferrite unit cell. A primary factor which can affect the distribution and valence state of the metallic ions is the stoichiometry of the ferrite. In this paper we report on the results of the site occupancy of the transition metal ions in a series of MnZn-ferrite films using extended x-ray absorption fine structure (EXAFS). The EXAFS data are correlated with the film composition and those magnetic properties which are sensitive to the ionic distribution (e.g., magnetic anisotropy field and magnetization) in order to confirm the use of EXAFS as a technique for the investigation of metallic ion distribution in spinel ferrites.
Magnetic and Structural Properties of Fe/Pd Multilayers Studied by Magnetic X-Ray Dichroism and X-Ray Absorption Spectroscopy
Authors: Mini S. M. , Fullerton Eric E. , Fontaine A. , Sowers C. H. , Bommannavar A. S. , Traverse A. , Baudelet F. , Pizzini S.
Published: April 2011

The results of magnetic circular x-ray dichroism (MCXD) measurements and extended x-ray absorption fine structure measurements (EXAFS) of the Fe K-edges of textured Fe(110)/Pd(111) multilayers are reported. The EXAFS results indicates that the iron in the system goes from bcc to a more densely packed system as the thickness of the iron layer is decreased. The magnetic properties were measured by SQUID magnetometry from 5 - 350 K. For all the samples, the saturation magnetization was significantly enhanced over the bulk values indicating the interface Pd atoms are polarized by the Fe layer. The enhancement corresponds to a moment of ≈2.5μB per interface Pd atom.
Materials Science Applications of the New National Institute of Standards and Technology Powder Diffractometer
Authors: Stalick J. K. , Prince E. , Santoro A. , Schroder I. G. , Rush J. J.
Published: April 2011

The new high-resolution neutron powder diffractometer BT-1 at the NIST reactor has proven to be a powerful and versatile instrument in its first year of operation. With 32 detectors arranged at 5° intervals and a 12° 2θ scan range, powder diffraction patterns can be collected to 167° 2θ. There is a choice of three monochromator take-off angles (75°, 90°, and 120°) so that the peak-width minimum can be matched to the rf-spacing range that is most important for each sample; all choices have a wavelength close to 1.54 Å. Data can be collected on sample sizes ranging from 200 mg to 30 g. Temperatures of 0.3 K to 1400 K are routinely available, and a magnetic field of 7T can be applied with a superconducting magnet. Typical data collection times range from 1-12 hours depending upon sample size and desired resolution. Examples are given of a variety of materials applications.
The Multiple Disk Chopper Neutron Time-of-Flight Spectrometer at Nist
Authors: Altorfer Felix B. , Cook Jeremy C. , Copley John R. D.
Published: April 2011

A highly versatile multiple disk chopper neutron time-of-flight spectrometer is being installed at the Cold Neutron Research Facility of the National Institute of Standards and Technology. This new instrument will fill an important gap in the portfolio of neutron inelastic scattering spectrometers in North America. It will be used for a wide variety of experiments such as studies of magnetic and vibrational excitations, tunneling spectroscopy, and quasielastic neutron scattering investigations of local and translational diffusion. The instrument uses disk choppers to monochromate and pulse the incident beam, and the energy changes of scattered neutrons are determined from their times-of-flight to a large array of detectors. The disks and the guide have been designed to make the instrument readily adaptable to the specific performance requirements of experimenters. We present important aspects of the design, as well as estimated values of the flux at the sample and the energy resolution for elastic scattering. The instrument should be operational in 1996.
Non-Standard Fickian Self-Diffusion of Isotopically Pure Boron Observed by Neutron Reflectometry and Depth Profiling
Authors: Baker Shenda M. , Wu K. , Smith G. S. , Hubbard K. M. , Nastasi M. , Downing R. G. , Lamaze G. P.
Published: April 2011

Neutron reflectometry (NR) studies1 of thin films of amorphous 11B/l0B on silicon indicate that a non-standard form of Fickian diffusion occurs across the boron interface upon annealing. In order to verify this observation, the samples were examined by neutron depth profiling (NDP). Comparison of the results from models of a step function, standard Fickian diffusion and Fickian diffusion with a fixed composition at the interface were made and compared to the previous NR results. The diffusion constant resulting from the non-standard Fickian model for the NDP data differs slightly from that obtained from the commonly used Fickian diffusion model and is not inconsistent with the NR results. This finding suggests that more information regarding diffusion at interfaces can be gained from these higher resolution neutron scattering techniques.
Growth and Dissolution of Protective Oxide Films on Titanium: an in-Situ Neutron Reflectivity Study
Authors: Wlesler D.G. , Majkrzak C.F.
Published: April 2011

The structure and morphology of titanium thin film electrodes have been investigated by neutron reflectometry. This technique yields a detailed depth profile of the scattering density, which is used to determine hydrogen and oxygen concentration profiles within the electrode. By depositing the electrode on a thick silicon crystal window, we are able to monitor the growth and dissolution of the protective oxide film covering the titanium as a function of time, electrode potential, and electrolyte composition. We find that, in 0.1 N sulfuric acid, the oxide dissolves at 0.7 A/h and is self-healing, meaning that as the oxide dissolves the metal underneath is oxidized to maintain a protective barrier. In contrast, when a -2 V cathodic bias is applied to a passive film, the oxide thins with no compensating oxide growth underneath, and the film undergoes electrochemical breakdown.
Collapse of Isolated Chains in a Network
Authors: Briber R. M. , Liu X. , Bauer B.J.
Published: April 2011

In this study we use small angle neutron scattering to investigate the conformation of linear deuterated polystyrene chains trapped in a crosslinked protonated polystyrene matrix. The second virial coefficient was obtained as a function of crosslink density for a wide range of crosslink density. It is shown that the second virial coefficient decreases with increasing crosslink density. By extrapolating the scattering to zero concentration of the linear chain at all values of q, the single chain scattering was obtained and radius of gyration was measured the function of network density. It was found that when the network density is low (NI < Nc where NI and Nc are the number of monomer units in the linear chain and the monomer units between crosslinks, respectively) the radius of gyration does not change. As the network density increases (NI > Nc ) radius of gyration decreases. In this region the inverse of the radius of gyration varies linearly with the inverse of Nc. When the crosslink density is very high (NI » Nc ), segregation of linear polymer chains occurs. These results are in agreement with prediction and computer simulation results of polymer chain conformation in a field of random obstacles where the crosslink junctions act as the effective obstacles.
The Early Days of Neutron Scattering
Authors: Shull Clifford G.
Published: April 2011

I am sure that Bertram Brockhouse would join me, if he were present with us, in saying how immensely grateful we are to the Royal Swedish Academy of Sciences for affording us the high honor of being named Nobel Laureates in recent days. Being selected as such is a dream for any scientist who hopes that his work will prove useful to others. It is especially gratifying to me to have met at this symposium with so many of you who have contributed greatly to bringing this field of neutron scattering to its present state of usefulness and prominence.
Sans Study of Phase Separation in Solid 3He-4He
Authors: Koster J.P. , Nagler S.E. , Adams E.D. , Wignall G.D.
Published: April 2011

Small angle neutron scattering has been used to study phase separation in a quantum alloy, solid 3Hex-4He1-x. The onset of phase separation is marked by a dramatic increase in the measured scattering. A simple interpretation of the results suggests that the late-stage phase separation kinetics are dominated by an increase in the concentration of 3He atoms in preexisting precipitate regions.
Neutron Scattering from a Ferrofluid
Authors: Lin Min Y. , Luo Weili , Lynn Jeffrey
Published: April 2011

Small angle neutron scattering experiments were performed on a eicosane-based ferrofluid. An average size of 88 Å can be extracted from the data, in agreement with results from electron microscopy. Below the frozen temperature of eicosane, however, the particles are seen to be in larger aggregates with a fractal dimension of 2.15, similar to those formed under reaction-limited cluster aggregation (RLCA) conditions. At high concentrations, particles form larger aggregates even in the liquid state. Applying a magnetic field introduces new structure and changes the density inside the aggregates.
New Developments in Multiple Small-Angle Neutron Scattering Studies of Advanced Ceramics
Authors: Allen Andrew J. , Berk Norman F. , Krueger Susan , Long Gabrielle G. , Kerch Helen M. , Ilavsky Jan
Published: April 2011

An enhanced multiple small-angle neutron scattering (MSANS) formulation has been developed to interpret the beam-broadening, arising from coarse, concentrated pore/grain microstructures in porous ceramics and similar materials. Prolific scattering from such systems precludes single-scattering studies (apart from Porod surface determinations). Previous MSANS techniques, which have been developed to extract the mean pore dimensions, either treat a range of scattering morphologies, while assuming that the scattering is in the diffraction limit, or they consider refraction effects, while assuming that the scattering features are spherical. Many systems of interest violate both these assumptions. In the enhanced formulation, the previous method, which allowed fully for refraction, is extended to non-spherical scattering morphologies. Applications of the MSANS formulation to sintering studies of Si3N4 and silica gels, and to the microstructural characterization of plasma-spray coatings are currently of interest.
Analyses of Creep Pores in Liquid-Phase-Sintered Alumina by Means of Joint Use of Conventional and High-Resolution Sans
Authors: Klatt M. , Bellmann D. , Kampmann R. , Wagner R. , Wolf C. , HÜbner H.
Published: April 2011

Failure of ceramic materials for high-temperature applications is initiated by the formation of creep pores. Thus, the determination of the sizes and number densities of pores induced during creep testing is one key to a understanding of their failure mechanisms and related life-time predictions. For this purpose small-angle neutron scattering (SANS) techniques are one of the most potential tools as demonstrated by an analysis of creep pores in liquid-phase-sintered, hot isostatically pressed alumina. The exploration of creep induced pores requires the analysis of SANS intensity over an extremely extended region of scattering vectors, the scanning of which needs joint use of both conventional SANS and double crystal diffractometry (DCD), an ultra small angle scattering technique.
The Determination of Macrostresses (Type-I Stresses) and Microstresses (Type-Ii Stresses) by Neutron Diffraction
Authors: Holden T.M.
Published: April 2011

Neutron diffraction has been used as tool for measuring stress fields (type-I stresses) and intergranular or microstresses (type-II stresses) for a decade. The experimental methods for measuring the two types of stresses are outlined. Emphasis is placed on maximizing the precision and accuracy of the measurements. Some serious sources of error in measurements near surfaces and some subtle wavelength effects are considered.
Micro Stresses in Welded High-Strength Stainless Steels
Authors: LukÁš P. , Janovec J. , Macek K. , Mikula P. , Strunz P. , VrÁna M. , Zaffagnini M.
Published: April 2011

The dependence of residual stresses in martensitic-austenitic age-hardenable steels on a different technological treatment (welding by electron beam, postweld heat treatment) were investigated using a neutron diffraction. Experiments were performed in NPI Řež on a high-resolution diffractometer equipped with cylindrically bent perfect crystals. The resolution of the instrument (Δd/d ≈ 10-4; d-lattice spacing) enabled us to investigate plastic strains in weld joints.
Neutron Powder Diffraction Refinement of the Nuclear and Magnetic Structures of HoNi2B2C at R.T., 10, 5.1 AND 2.2 K
Authors: Huang Q. , Santoro A. , Grigereit T.E. , Lynn J.W. , Cava R.J. , Krajewski J.J. , Peck W.F.
Published: April 2011

The nuclear and magnetic structures of HoNi2B2C have been investigated by neutron powder diffraction at room temperature and at 10, 5.1 and 2.2K. The compound crystallizes with the symmetry of space group 14/mmm and has room temperature lattice parameters a=3.5170(1) and c=10.5217(3) Å. No phase transitions of the nuclear structure have been observed in the range of temperatures examined. Magnetic peaks begin to appear at about 8K. The magnetic structure is the superposition of two configurations, one in which ferromagnetic sheets of holmium spins parallel to the a-b plane are coupled antiferromagnetically along the c-axis, and another in which the ferromagnetic planes are rotated away from the antiparallel configuration to give an incommensurate helicoidal structure with a period approximately equal to twelve times the length of the c-axis. The helicoidal structure competes with superconductivity while the antiferromagnetism coexists with it.
Investigation of Magnetic Structure of MnTe/CdTe Multilayers by Neutron Diffraction
Authors: Nunez V. , Giebultowicz T. M. , Faschinger W. , Bauer G. , Sitter H. , Furdyna J. K.
Published: April 2011

Neutron-diffraction studies of MnTe/CdTe superlattices with very thin CdTe spacers are reported. Results indicate the formation of spin helices (consistent with the tensile nature of strain in the MnTe layers) and coherence between the helices in different MnTe layers. Possible mechanisms for the interlayer correlations are discussed.
Neutron Scattering Study of the Magnetism in a Nanocrystalline/Amorphous Material
Authors: Rosov N. , Lynn J. W. , Fish G. E.
Published: April 2011

Recently developed nanocrystalline magnetic systems are of considerable interest fundamentally as well as technologically. One such material is Fe73.5B9Si13.5Cu1Nb3, which can be produced by heat treating the amorphous precursor. This forms a noncrystalline phase with typical dimension of 350 A as determined by neutron diffraction. Small angle neutron scattering (SANS) has been employed to investigate the properties of the nanocrystallized material over the temperature range from 10 K to 725 K, a regime where no significant structural changes are expected to occur. In zero field and low temperature (10K) we obtained an isotropic scattering pattern. The application of a relatively modest field to sweep out the domains changed the scattering to a "butterfly wings" pattern typical of patterns dominated by magnetic elastic intensity. Up to 450 K this pattern changed only modestly, while for substantially higher temperatures the ratio of inelastic to elastic scattering increased rapidly as the magnetic phase transition of the intergranular component (≃ 575 K) was approached. Triple axis inelastic measurements showed that the majority of the magnetic inelastic scattering was from the nanocrystalline phase.
Structures and Magnetic Properties of a Family of One-Dimensional Oxides, Sr3M′M″06 (M′ = Co, Ni, Zn and M″ = Pt, Ir)
Authors: Nguyen TU N. , Zur Loye Hans-Conrad
Published: April 2011

A family of one-dimensional oxides was synthesized by solid state techniques and their structures determined by powder X-ray and powder neutron Rietveld refinement. The compounds are structurally related to A4PtO6 (A = Ca, Sr, Ba), which contains infinite chains of alternating face-sharing PtO6 octahedra and AO6, trigonal prisms. The compounds exhibit a variety of magnetic properties. The structures and magnetic properties of some of these one-dimensional oxides are discussed.
Neutron Scattering Study of Vibrational Modes in Glassy Gel-xSnxSe2
Authors: Cappelletti R. L. , Kamitakahara W.A. , Islam Didarul
Published: April 2011

The neutron vibrational density of states has been determined from neutron time-of-flight scattering in g-Ge1-xSnxSe2 with x = 0, 0.3, 0.35, and 0.5 to search for "floppy" modes. Previously Raman and Mossbauer studies1 have been interpreted on the basis that the addition of Sn to the GeSe2 network reduces the average number of mechanical constraints per atom allowing one to tune through the rigidity percolation threshold near x = 0.35. A comparison of the VDOS measured in this work below 10 meV for all samples shows that they are nearly identical indicating no evidence of the existence of floppy modes in these samples. Ab initio molecular dynamics2 calculations of the VDOS show good agreement with the measured results for g-GeSe2.
Spin-Density-Wave Magnetism in Dilute Copper-Manganese Alloys
Authors: Lamelas F. J. , Werner S. A. , Shapiro S. M. , Mydosh J. A.
Published: April 2011

Elastic neutron-scattering measurements on two samples of Cu alloyed with 1.3% Mn and 0.55% Mn show that the spin-density-wave (SDW) features found in more concentrated alloys persist in the limit of very dilute alloys. These features consist of temperature-dependent incommensurate peaks in magnetic neutron scattering, with positions and strengths which are fully consistent with those in the concentrated alloys. The implications of these measurements are twofold. First, it is clear from our data that SDW magnetic ordering occurs across the entire range of CuMn alloys which have typically been interpreted as spin glasses. Second, the more fundamental significance of this work is the suggestion via extrapolation that a peak in the magnetic susceptibility χ(q) occurs in pure copper, at a value of q given by the Fermi-surface diameter 2kF.
Inelastic Neutron Scattering by Pristine And Doped Phases of Polyacetylene
Authors: Papanek P. , Fischer J. E. , Sauvajou J. L. , Dianoux A. J. , Mcneillis P. M. , Mathis C. , Francois B.
Published: April 2011

Inelastic incoherent neutron-scattering spectra of cis-, trans- and Na-doped polyacety-lene are presented. The experiments were performed with time-of-flight and filter-analyzer spectrometers on stretch-oriented samples such that the polarization of vibrational modes could also be determined.
Orientational Dynamcs in White Phosphorus (P4)
Authors: Kamitakahara W.A. , Gompf F. , Neumann D.A.
Published: April 2011

Above To = 196 K, white phosphorus, a solid composed of P4 molecules, exhibits a plastic crystal phase. Below this temperature, the structure is triclinic and orientationally ordered, with six molecules in a unit cell. Using inelastic neutron scattering on a polycrystalline sample, observations were made of the rapid reorientational motions above To, and the librational modes below To. In addition, neutron powder diffraction was used to investigate the crystal structures above and below To.
Neutron Scattering, Momentum Distributions and Final State Effects
Authors: Glyde Henry R.
Published: April 2011

Inelastic neutron scattering measurements of the atomic momentum distribution, the atomic kinetic energy and other single atom properties in quantum liquids and liquid neon are presented. The data were taken on the MARI instrument at ISIS and analyzed using a new method. The measurements have sufficient precision to show that n(k) in a normal Bose liquid differs significantly and unambiguously from the classical, Maxwell-Boltzmann distribution. The final state broadening function is also extracted from the data and found to be similar in liquid 3He and 4He.
Small Angle Neutron Scattering at Mcmaster University
Authors: Avelar J.M. , Mason P.C. , Gaulin B.D. , Copley J.R.D.
Published: April 2011

We describe the Small Angle Neutron Scattering spectrometer at McMaster University. We then discuss three examples of recent studies using this instrument: (1) the membrane-water interface in multilamellar vesicles; (2) magnetic ordering of Ni0.8Co0.2/Cu multilayers; and (3) precipitate sizes in titanium stabilized interstitial-free steels.
Small-Angle Neutron Scattering in a High-Temperature Furnace
Authors: Long G.G. , Kerch H.M. , Krueger S. , Allen A.J. , Burdette H.
Published: April 2011

Small-angle neutron scattering (SANS) is increasingly used to obtain statistically-representative data on particle or pore sizes, number and volume fractions, morphology and total surface areas in technological materials. Until recently, however, it had not been possible to perform in-situ microstructural investigations during thermal treatment. This paper reports on a new high-temperature (up to 1700°C) SANS furnace for materials research. Two interchangeable inner furnaces were built for a single outer atmosphere chamber so that either an oxidizing, a reducing, or a neutral environment can be used. Results derived during sintering of a controlled-porosity silica gel will be presented. The new furnace has made it possible for the first time to measure total porous surface areas and the evolution of pore sizes in situ during densification without interruption. Such measurements are expected to lead to improved process models offering quantitative predictability of product microstructures from the processing history of real materials.
Growth and properties of epitaxial PbSe on Si(111) and Si(100) without buffer layer
Authors: Müller P. , Tiwari A.N. , Zogg H.
Published: April 2011

Narrow gap IV-VI materials like PbS, PbSnSe and PbSnTe are used for infrared detector device fabrication [1,2]. Earlier an intermediate Ila-fluoride buffer layer, which consisted of a BaF2/CaF2-stack of about 2000 Å thickness, was used to get epitaxial high quality layers on silicon substrates. This buffer is now reduced to a much thinner layer of only about 20 Å thick CaF2, regardless the large lattice mismatch between layer and substrate [3,4,5]. The question therefore arises if high quality IV-VI layers can be grown on Si-substrates without any buffer layer as e.g. in CdTe/Si or GaAs/Si systems.

The aim of this work is to grow IV-VI layers directly on Si-substrates without any buffer layers to study the growth kinetics and epitaxial quality. PbSe was chosen as a representant of IV-VI materials, and layers were grown on (111)- and (100)-oriented silicon substrates.
Schottky Diodes on Si1-x-yGexCy Alloys.
Authors: Mamnor M. , Guedj C. , Boucaud P. , Meyer F. , Bouchier D. , Bodnar S. , Regolini J.L.
Published: April 2011

We have recently investigated the properties of W/Si1-xGex films prepared by rapid thermal chemical vapor deposition (RTCVD). The barrier height on p-type, ΦBp, varies as the band gap with the germanium content for totally relaxed films, and increases with strain relaxation, while that on n-type remains rather constant. These results suggest that the Fermi level is pinned relative to the conduction band at the interface of the binary alloy and that the measurement of Schottky barriers is a suitable tool to follow band gap variations. In this work, the effects of carbon incorporation on Schottky barriers have been investigated. The study has been performed on Si1-x-yGexCy films (0≤y≤1.35% with x=10%). The strain retained in the films was determined by X-ray diffraction. Infrared absorption measurements have shown that the carbon is incorporated on substitutional sites. The electrical results indicate the same trends than those observed on the binary alloys, the barrier height on n-type remains rather constant while the barrier height on p-type varies. Adding C leads to an increase of ΦBp, but this increase is too large to be explained in terms of variation of the band gap. The influence of other parameters, such as the doping level and the hole effective mass is discussed.
Phase Separation In III-V Semiconductors
Authors: Hsieh K. C. , Cheng K. Y.
Published: April 2011

Data are presented to show the morphological instability as well as the occurrence of 1-dimensional phase separation through the spinodal decomposition process in the strained layer heteroepitaxy of short-period superlattices. Biaxial strain has been attributed to be the driving force. With a large net strain in the epitaxial film, > 3.5%, island growth of (InAs)1/(GaAs)1 on GaAs is observed. With a near zero net strain, however, 1-dimensional lateral compositional modulation is observed in the growth of (InAs)2/(GaAs)2 on InP and (InP)2/(GaP)2 on GaAs substrates. Both surface reaction and bulk diffusion take part in forming the ultimate modulation. A small but definitive hydrostatic strain in the metastable Al0.3Ga0.7As film grown at low temperature induces also a 1-dimensional compositional modulation upon annealing at 600°C, a direct evidence of the existence of a miscibility gap in strained AlxGa1-xAs.
Strained Layer Epitaxy on Rough Si Surfaces
Authors: Lowes T.D. , Zinke-Allmang M.
Published: April 2011

Lattice mismatch associated with heteroepitaxy imposes a significant limitation on the epitaxial compatibility between overlayer and substrate. In lattice mismatched systems the misfit may be accommodated to some extent by strain. However, in order to maintain misfit strain and avoid dislocation generation the epitaxial layer must not exceed a critical thickness. Some success has been reported in avoiding damaged epitaxial layers with thicknesses greater than the critical thickness by overgrowing on patterned or rough surfaces. For the case of Si, surface roughening by energetic Ar+ bombardment as a pre-growth roughening treatment is discussed and assessed. Evolution of surface features as a function of initial substrate treatment, ion accelerating potential, and the duration of bombardment are presented. Stability of the surface features generated by bombardment for typical overgrowth conditions was tested to assess feasibility of this technique for Si heteroepitaxy.
Photoluminescence Characterization of SiGe/Si Quantum-Well Wire Structures
Authors: Nilsson S. , Zeindl H. P. , Wolff A. , Pressel K.
Published: April 2011

Low-temperature photoluminescence measurements were performed in order to probe the optical quality of SiGe/Si quantum-well wire structures fabricated by electron-beam lithography and subsequent reactive ion etching, having the patterned polymethylmethacrylate resist as an etch mask. In addition, one set of quantum-well wire structures was post-treated by means of annealing in a hydrogen environment. Our results show that even for the smallest wires of about 100nm in width, the wires exhibit phonon-resolved photoluminescence spectra, similar to that from the molecular beam eptitaxially grown SiGe single quantum well which was used as starting material for the patterning process. After the patterning process a new sharp peak appears in the photoluminescence spectra at 0.97eV in photon energy. Our investigation suggests that this feature is introduced by damage during the patterning process and most probably identical to the G-line, which previously was identified as originating from the dicarbon centre (substitutional carbon-interstitial carbon) in Si. This centre is known to be a very common endproduct of irradiating Si near room temperature which is the case at our patterning process.
Photoreflectance Study of Strained InAIAs/InP Structures
Authors: Hwang Jenn-Shyong , Chou W. Y. , Tyan S. L. , Wang Y. C. , Tung J. H.
Published: April 2011

We have studied the photoreflectance spectra at 300 K from a series of strained In1−xAlxAs/InP (0.42<x<0.57) strained structures grown by molecular beam epitaxy. From the observed Franz-Keldysh Oscillation we evaluate the built-in de electric field and hence the surface potential under different strain. We found that the surface Fermi level is not pinned at midgap under different strainwhich results in contrast to AIGaAs and GaAs. In addition, from the observed dependence of the built-in electric field Fdc and surface potential barrier Vm on the top layer thickness, we conclude that the surface states are distributed over two separate regions within the energy band gap under different strain and the densities of the surface states are as low as (2,71α0.05)x 1011 cm−2 for the distribution near the conduction band and (4.29α0.05)x1011 cm-2 for the distribution near the valence band. The Fermi level is weakly pinned while the top layer thickness is within the characteristic region of each sample.