bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pulsed Plasma Polymerizations: Film Chemistry Control and Applications
Authors: WU Yuliang , Han Licheng M. , Thomes Brett E. , Qiu Haibo , Savage Charles R. , Lee Wei W. , Timmons Richard B. 
Published: April 2011

AbstractFilm chemistry control issues, as well as key properties of polymers synthesized under pulsed plasma conditions, are discussed. Distinctions between pulsed and continuous wave plasmas are examined, particularly as they relate to differences in the energy efficiency of film formation rates and to the range of available power inputs. Film stabilities, with special reference to polymers formed under very low power input conditions, are considered. Finally, selected applications involving use of the inherently high film chemistry controllability made available by the variable duty cycle pulsed plasma technique are described.
Highly Reflective and Surface Conductive Silver-Polyimide Films Fabricated Via Reduction of Silver(I) in a Thermally Curing Poly(Amic Acid) Matrix
Authors: Southward R. E. , Thompson D S. , Thompson D. W. , Scott J. L. , Broadwater S. T. 
Published: April 2011

AbstractHighly reflective and surface conductive silvered polyimide films have been prepared by the incorporation of the (1,1,1-trifluoro-2,4-pentanedionato)silver(I) complex into a dimethylacetamide solution of the poly(amic acid) formed from 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 4,4'-oxydianiline (ODA). Thermal curing of the silver(I)- containing poly(amic acid) films leads to cycloimidization with concomitant silver(I) reduction yielding a reflective and conductive silvered film surface.
The Effects of Ground and Space Processing on the Properties of Organic, Polymeric, and Colloidal Materials
Authors: Frazier Donald O. , Paley Mark S. , Penn Benjamin G. , Abdeldayem Hossin A. , Smith David D. , Witherow William K. , Carswell William E. , Zugrav Maria I. 
Published: April 2011

AbstractIn recent years, a great deal of interest has been directed toward the use of organic materials in the development of high-efficiency optoelectronic and photonic devices. There is a myriad of possibilities among organic materials, which allows flexibility in the design of unique structures with a variety of functional groups. The use of nonlinear optical (NLO) organic materials as thin-film waveguides allows full exploitation of their desirable qualities by permitting long interaction lengths and large susceptibilities allowing modest power input. There are several methods in use to prepare thin films such as Langmuir-Blodgett (LB) and self-assembly techniques,2-4 vapor deposition.5-7 growth from sheared solution or melt,8,9 and melt growth between glass plates.10 Organic-based materials have many features that make them desirable for use in optical devices, such as high second- and third-order nonlinearity, flexibility of molecular design, and damage resistance to optical radiation. However, processing difficulties for crystals and thin films has hindered their use in devices.We discuss the potential role of microgravity processing of a few organic and polymeric materials. It is of interest to note how materials with second- and third-order NLO behavior may be improved in a diffusion-limited environment and ways in which convection may be detrimental to these materials. We focus our discussion on third-order materials for all-optical switching, and second-order materials for frequency conversion and electro-optics. The goal of minimizing optical loss obviously depends on processing methods. For solution-based processes, such as solution crystal growth and solution photopolymerization, it is well known that thermal- and solutal-density gradients can initiate buoyancy-driven convection. Resultant fluid flows can affect transport of material to and from growth interfaces and become manifest in the morphology and homogeneity of the growing film or crystal. Likewise, buoyancy-driven convection can hinder production of defect-free, high-quality crystals or films during crystal and film growth by vapor deposition.
Magnetic Levitation of Liquid Droplets
Authors: Beaugnon E. , Tournwer R. 
Published: April 2011

AbstractThe magnetic levitation of diamagnetic materials in a high field superconducting magnet is presented. The magnetic force is determined from numerical calculations of the magnetic field components and the stability of levitation is studied using energy calculations. Amongst the numerous materials that can be levitated, experiments are shown for ethanol droplets.
Microgravity Solidification of Immiscible Alloys
Authors: Andrews J. B. , Hayes L. J. , Arikawa Y. , Coriell S. R. 
Published: April 2011

AbstractThis paper covers findings obtained from the microgravity directional solidification of immiscible aluminum-indium alloys during the Life and Microgravity Spacelab Mission in 1996. Three alloys, one of monotectic composition and two alloys containing an excess of indium above the monotectic (i.e., hypermonotectic compositions) were solidified using the Advanced Gradient Heating Facility (AGHF). Samples were processed in specialized ampoule assemblies containing pistons and a high temperature spring in a partially successful attempt to prevent void formation due to thermal contraction of the melt and solidification shrinkage. A comparison of compositional variations between microgravity processed and ground processed samples revealed compositional variations along the length of ground processed samples which were representative of results anticipated due to convective mixing in the melt. Flight samples showed an initial compositional variation indicative of minimal mixing in the melt. However, a discontinuity in the microstructure was observed which coincided with the presence of a void in the flight sample.
Creep of Fully Lamellar Near γ-TiAl Intermetallics
Authors: Beddoes J. , Zhao L. , Chen W. R. , Du X. 
Published: April 2011

ABSTRACTThe influence of the fully lamellar morphology and third phase β on the creep properties of near γ-TiAl intermetallics is presented. Specifically, the effect of improved microstructural control obtainableby a stepped cool, involving furnace cooling and air cooling from the a single phase, on creep resistanceis demonstrated for three near γ-TiAl intermetallics: binary Ti-48AI, ternary Ti-48A1–2W and Ti-47A1–2Nb-IMn-0.5W-0.5Mo-0.2Si. The results indicate that appropriate stepped cooling can be used to reducethe lamellar interface spacing without the formation of Widmanstatten, feathery γ or γM structures, leadingto longer creep life and reduced creep strain rates. A second benefit of stepped cooling is preventionof βformation during cooling from the α phase, allowing controlled β precipitation during aging at 950 C. Creep tests on variously aged Ti-48A1–2W indicate that β precipitation along lamellar grain boundariesimproves creep resistance. Development of a uniform fully lamellar structure in Ti-47A1–2Nb-1Mn-0.5W-0.5Mo-0.2Si significantly improves creep resistance. Applying the stepped cool to this alloy allowsthe precipitation of β and silicides to be controlled during lower temperature aging.
Yield Stress Anomaly for 1/2〈112] {1111} Slip in y-Titanium Aluminide
Authors: Jiao S. , Bird N. , B. P. , Taylor G. 
Published: April 2011

ABSTRACTTransmission electron microscopy (TEM) studies of dislocation structures in single crystals of TiAl containing 54.5 or 54.7 at% Al deformed at different temperatures revealed the occurrence of slip on ½〈112]{ {111} at room temperature and near the peak of the yield stress anomaly (YSA). Measurements of the corresponding yield stresses revealed the existence of a YSA for this type of slip. Weak-beam TEM showed the presence of locks at room temperature for 30° dislocations and at high temperatures for edge dislocations. Both types of locks involve dissociation on two intersecting { 1111} type planes, driven by reduction in elastic strain energy. The edge dislocation dissociation at high temperatures involves both climb and glide.
Precipitation and Creep Strengthening Mechanisms in K5 Series γ-TiAl Alloys
Authors: Gouma P. I. , Subramanian K. , Kim Y-W. , Mills M. J. 
Published: April 2011

ABSTRACTA new generation of wrought γ-TiAl alloys having a good balance of properties at both low and high temperatures has recently been developed. Addition of light elements (C, Si) to the base alloy of this system (K5 material) has been shown to increase the creep strength of the material significantly. The microstructure of the materials with superior creep performance was found to consist of wellaligned rows of fine precipitates, delineating partially dissolved α2 laths. These precipitates were found to interact strongly with dislocation structures. This paper studies the mechanisms for α2 dissolution and fine particle precipitation in annealed samples of the K5 series alloys. Microstructural design issues that would allow for optimization of the particular strengthening mechanism will also be discussed.
Comparative Study of the Microstructure and Tensile Properties of Ni-Al Alloys with Fe and Cr Additions
Authors: Pekarskaya E. , Humphreys C. J. , Jones C. N. 
Published: April 2011

ABSTRACTThe tensile behaviour of Ni-32at.% Al-5at.% Fe and Ni-32at.% Al-12 at.% Cr two-phase intermetallic compounds has been studied in the 20–750°C temperature range. TEM studies of the defect structures have been performed. Both alloys exhibit a brittle behaviour at room temperature, while at high temperature the Ni-Al-Cr alloy appears to be much more ductile that the Ni-Al-Fe alloy. Various reasons for the limited ductility and the brittle-to-ductile transition in these alloys are discussed.
Analysis of Weak-Beam Contrast from SESF/SISF Fault Pairs Associated with ½ <112] Superdislocations in TiAl
Authors: Kumar Mukul , Sriram S. , Schwartz Adam J. , Vasudevan Vijay K. 
Published: April 2011

ABSTRACTThe diffraction contrast from dissociated ½<112] superdislocations in γ-TiAl intermetallic alloy cannot always be analyzed using conventional rules of diffraction contrast. In particular, the configuration involving three similar Shockley partials on adjacent planes has often been ruled out due to the absence of fringes indicating the presence of stacking faults. In order to determine the dissociated configuration, weak-beam transmission electron microscope observations of edge-oriented ½<112] superdislocations have been correlated with computer simulated images. Dissociation of these superdislocations into three similar ⅙<112] partial dislocations bounding a superlattice extrinsic and intrinsic stacking fault pair has been consequently determined from these analyses. It has been found that diffraction contrast alone cannot distinguish between the various configurations that lead to the formation of the fault pair, but the formation of an antiphase boundary or complex stacking fault linked dissociation or locking by stair rod dislocations can be ruled out.
Elastic Constants and Coefficients of Thermal Expansion of Laves Phase Cr2X (X=Hf, Nb, Ta, Zr) Alloys
Authors: Hong Suklyun , Fu C. L. 
Published: April 2011

ABSTRACTTo examine the effect of thermal expansion mismatch on cracking in two-phase Cr-Cr2X (X=Hf, Nb, Ta, Zr) alloys, we calculate the elastic constants and associated elastic anharmonicity by the local-density-functional approach from which the coefficients of thermal expansion (CTEs) of Cr and Cr2X are determined. The calculation shows that the CTE of Cr at high temperatures is notably larger than those of Cr2X. If the difference in CTE between Cr and Cr 2X is a primary source of crack initiation, our results fail to explain the experimental observation that, among Cr-Cr2X alloy systems, the ingot cracking occurs mainly in Cr-Cr2Nb. We suggest that for the cracking to occur, thermal mismatch stresses are retained by a hard and supersaturated Cr matrix (e.g., due to the relatively high solubility of Nb in Cr in the case of Cr-Cr2Nb). On the other hand, a soft Cr matrix can accommodate the thermal misfit dislocations plastically even when the CTE difference between Cr and Cr2X is large (e.g., in the case of Cr-Cr2Zr).
Microstructural Stability Of a NiAI-Mo Eutectic Alloy
Authors: Kush M. T. , Holmes J. W. , Gibala R. 
Published: April 2011

ABSTRACTThe microstructural stability of a directionally-solidified NiA1–9 at.% Mo quasi-binary alloy was investigated under conditions of thermal cycling between the temperatures 973 K and 1473 K utilizing time-temperature heating and cooling profiles which approximate potential engine applications. Two different microstructures were examined: a cellular microstructure in which the faceted secondphase Mo rods in the NiAl matrix formed misaligned cell boundaries which separated aligned cells approximately 0.4 mm in width and 5–25 mm in length, and a nearly fault-free fully columnar microstructure well aligned along the [001] direction. Both microstructures resisted coarsening under thermal cycling, but plastic deformation induced by thermal stresses introduced significant specimen shape changes. Surprisingly, the cellular microstructure, for which the cell boundary region apparently acts as a deformation buffer, exhibited better resistance to thermal fatigue than the more fault-free and better aligned columnar microstructure.
Structural Studies Of Al55 Si7Cu25.5 Fe12.5 1/1-Cubic Approximant By Means Of X-Ray Rietveld, Method And Haadf-Stem
Authors: Yamada H. , Takeuchi T. , Mizutani U. , Tanaka N. 
Published: April 2011

AbstractBy combining the powdered x-ray Rietveld analysis and the High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM), we have made the detailed structural analysis for the Mackay-type Al55Si7Cu25.5Fe12.5, 1/1-cubic approximant. Electron diffraction measurements revealed its space group to be Pni3. Both position and occupancy in every atomic site are refined by means of the Rietveld analysis. The factors Rwp and Riwhich are taken as measures for the precision of the Rietveld analysis, are reduced to 2.57 and 3.89 %, respectively. The refined structure of this approximant is a simple cubic with the lattice constant of 12.31916(2) Å. Two different icosahedral clusters consisting of triply stacked atomic shells exist at the vertex and body centered positions in the CsCl-type unit cell. In addition, we propose that there exists most likely a “structural disorder” in the first shell of the cluster in one of the sublattices. The HAADF images taken along [100] and [111] directions agree with the projection images calculated from the Rietveld-refined structure, lending a strong support to the validity of the present atomic structure model deduced from the Rietveld analysis.
Interfaces In Quasicrystalline Systems
Authors: Divakar R , Sundararaman D , Ranganathan S 
Published: April 2011

AbstractStructural relations between quasicrystalline and related crystalline rational approximant phases have been of interest for some time now. Such relations are now being used to understand interface structures. Interfaces between structural motif - wise related, but dissimilarly periodic phases are expected to show a degree of lattice match in certain directions. Our earlier studies in the Al-Cu-Fe system using the HREM technique has shown this to be true. The structural difference leads to well defined structural ledges in the interface between the icosahedral Al-Cu-Fe phase and the monoclinic Al13Fe4 type phase. In the present paper we report our results on the HREM study of interfaces in Al-Cu-Fe and Al-Pd-Mn systems. The emphasis will be on heterophase interfaces between quasiperiodic and periodic phases, where the two are structurally related. An attempt will be made to correlate the results with calculated lattice projections of the two structures on the grain boundary plane.
Surface Characteristics Of Quasicrystalline Materials: An Overview Of Work Conducted At Ames Laboratory
Authors: Jenks C. J. 
Published: April 2011

AbstractOver the last few years, work in our laboratories in Ames has focussed on elucidating the surface characteristics of Al-based quasicrystalline materials, namely icosahedral (i-) Al-Cu-Fe and i-Al-Pd-Mn. Our work involves the study of the clean surfaces of these materials under ultrahigh vacuum conditions. We find that surfaces cleaned by Ar+ sputtering are depleted in Al relative to the bulk composition. Single grains, after sputtering, undergo a two-stage regrowth process as they are annealed. After heating to about 600 K, a crystalline overlayer is formed. This is rather abruptly replaced at about 750 K by a surface that appears quasicrystalline within the resolution of the experimental techniques used. Calculations based on low-energy electron diffraction (LEED) measurements of this higher temperature state indicate that the Al-rich layers in the bulk model of these materials are the favored surface terminations. Results of low-energy ion scattering (LEIS) corroborate this finding. Consistent with this, we find that the oxidation behavior and general reactivity of these materials are analogous to pure Al.
Metal-Insulator Transitionlike Behavior In Several Icosahedral Phases
Authors: Poon S. J. , Zavaliche F. , Beeli C. 
Published: April 2011

AbstractThe highly non-metallic electron transport properties in icosahedral Al70.5Pd21(Re,Mn)8.5 phases and their dependence on alloy composition and sample preparation are reviewed and fuirther studied. The study has led to the highest resistivity ratios ρ(4.2K)/ρ(295K)˜280 reported so far on i-AIPdRe alloys. Similar investigation has also resulted in enhanced resistivity ratios in i-AlCuOs. Evidences for the metal-insulator transition in these i-alloys are documented and discussed in light of the new results. Electron diffraction studies (article by Beeli, Poon, Guo, and Haussler in this Conference Proceedings) have provided evidence for electron localization induced by phason disorder. These findings may provide the basis for understanding the nature of electronic states and effects of disorder on electron localization in quasiperiodic systems.
Dielectric Relaxation in Filled Nematic Liquid Crystals
Authors: Sinha G.P. , Kreuzer M. , Aliev F.M. 
Published: April 2011

ABSTRACTNematic liquid crystals filled with Aerosil particles are new heterogeneous materials important for different optoelectronic applications. These materials are suspensions of small silica particles, about 10-17 nm in diameter, dispersed in nematic liquid crystals. The particles are known to form a network structure dividing liquid crystal into domains with linear size approximately 250 nm. We used both hydrophilic and hydrophobic particles, filling them with the nematic liquid crystal-5CB.Broad band dielectric spectroscopy (1 mHz - 1.5 GHz) was applied for the investigation of these materials. Two bulk-like modes due to the rotation of molecules around the short axis and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and the dispersion of dielectric permittivity due to conductivity were also observed. The modification of the surface of the particles has stronger influence on the slow process and is less important for the molecular modes. The contribution of the slow process for the hydrophilic sample to the total polarization is greater than for the hydrophobic sample. In addition, the corresponding characteristic frequencies are lower for the case of hydrophilic samples. These facts suggest that the low frequency relaxation is an Aerosil particle-liquid crystal interface related phenomena and the origin of this process maybe explained on the basis of surface induced polarization.
Interface Governed Magnetostriction in Ultra Thin CoFe and Fe Films
Authors: Mattheis R. , Langer J. , Senz S. , Berg H. A. M van den 
Published: April 2011

ABSTRACTTwo different types of polycrystalline films, films with low (Fe) and films with high (Co50Fe50) saturation magnetostriction λs, were sandwiched between Cu to study the thickness dependence of λs in Cu/X/Cu systems. We utilised a new method (ROTMOKE) for a high accurate Hk determination. The values for X, were determined by analysing the change of Hk during application of compressive and tensile stress by cylindrical bending of the substrate joint with the film. For both systems, a remarkable contribution of the interface to the λs, was found. The sign of the interface contribution is opposed to the sign of bulk λs, leading to a zero transition of λs., For Fe this transition occurs at a thickness of 5 nm whereas for the CoFe film with a strong λs, value of the bulk of around 80 · 10−6 a transition was extrapolated at a thickness around 1 nm.
An In-Situ Study of the Segregation and the Strain Relaxation During Growth of Gold and Nickel Ultrathin Films
Authors: Labat S. , Gergaud P. , Thomas O. , Gilles B. , Marty A. 
Published: April 2011

ABSTRACTWe report on in-situ real time measurement of both stress and strain during growth of ultrathin layers, with submonolayer sensitivity. The in-plane parameter is measured by Reflection High Energy Electron Diffraction (RHEED) and the stress is determined via the measurement of the curvature. The system studied is Au/Ni (i.e. Au on Ni and Ni on Au). We have evidenced a large asymmetry in the two different growths: Au (on Ni) shows a progressive elastic strain relaxation whereas Ni (on Au) exhibits a strong interplay between the stress and the interfacial mixing.
Effect of ultra-thin Cu underlayer on the magnetic properties of Ni80Fe50 / Fe50Mn50 films
Authors: Liu C. , Shen L. , Jiang H. , Yang D. , Wu G. , Alexander C. , Mankey G. J. 
Published: April 2011

ABSTRACTThe Ni80Fe20/Fe50Mn50,thin film system exhibits exchange bias behavior. Here a systematic study of the effect of atomic-scale thin film roughness on coercivity and exchange bias is presented. Cu (t) / Ta (100 Å) / Ni80Fe20 (100 Å) / Fe50Mno50 (200 Å) / Ta (200 Å) with variable thickness, t, of the Cu underlayer were DC sputtered on Si (100) substrates. The Cu underlayer defines the initial roughness that is transferred to the film material since the film grows conformal to the initial morphology. Atomic Force Microscopy and X-ray diffraction were used to study the morphology and texture of the films. Morphological characterization is then correlated with magnetometer measurements. Atomic Force Microscopy shows that the root mean square value of the film roughness exhibits a maximum of 2.5 Å at t = 2.4 Å. X-ray diffraction spectra show the films are polycrystalline with fcc (111) texture and the Fe50Mn50 (111) peak intensity decreases monotonically with increasing Cu thickness, t. Without a Cu underlayer, the values of the coercivity and loop shift are, Hc = 12 Oe and Hp = 56 Oe, respectively. Both the coercivity and loop shift change with Cu underlayer thickness. The coercivity reaches a maximum value of Hc= 36 Oe at t = 4 Å. The loop shift exhibits an initial increase with t, reaches a maximum value of HP = 107 Oe at t = 2.4 Å, followed by a decrease with greater Cu thickness. These results show that a tiny increase in the film roughness has a huge effect on the exchange bias magnitude.
Capturing Properties of Two-Fold Coordinated Nitrogen Atom in Silicon Oxynitride
Authors: Novikov YU.N. , Morokov YU.N. , Gritsenko V.A. , Xu J.B. 
Published: April 2011

ABSTRACTElectronic structure of two-fold coordinated nitrogen atom ≡Si2N• in Si3N4 and SiOxNy is studied in different charged states by the semiempirical quantum-chemical method MINDO/3 taking into account an atomic relaxation. It is shown theoretically that the neutral paramagnetic defect ≡Si2N• captures an electron, therefore it is an electron trap in Si3N4 and SiOxNy. The calculations show that the capturing of hole by the ≡Si2N• defect can be energetically favorable only for large oxygen concentration in oxynitride. It is predicted that the electron localization by the ≡Si2N• defect will result in the ESR signal disappearance.