Symposium Organizers
Carol Thompson Northern Illinois University
Hermann A. Duerr BESSY GmbH
Michael F. Toney Stanford Synchrotron Radiation Laboratory
Do Young Noh Gwangju Institute of Science and Technology
D1: Stress, Strain, and Deformations
Session Chairs
Monday PM, November 26, 2007
Liberty (Sheraton)
9:30 AM - D1.1
Stress Distributions and Thermomechanical Response of Thin Metal Films with Mixed Texture.
Aaron Vodnick 1 , Shefford Baker 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractThin metal films are often subjected to extreme stresses due to differential thermal expansion with the substrates on which they are deposited. Such stresses can lead to failure in nano- and micro-fabricated devices, thus there is much interest in understanding the stress states in such films. Many mechanical characterization methods treat a thin metal film as a continuum, analyzing the “macroscopic” behavior by assuming a biaxial stress state. However, metal films tend to be highly oriented, with microstructures consisting of only a few preferred crystallographic orientations. X-ray diffraction provides a unique tool, allowing us to probe the mechanical response of each texture component individually; a key to understanding, and possibly tailoring, global behaviors. High intensity synchrotron x-rays provide a unique tool for investigating these thermomechanical behaviors at elevated temperatures in real-time, where rapid data collection is paramount. Time-sensitive experiments at the Cornell High Energy Synchrotron Source were used to study both texture formation and stress evolution during thermal cycling of thin Ag and Cu films with varied interface properties. Results show stress distributions govern the active deformation processes as a result of large out-of-plane stresses arising from texture interactions.
9:45 AM - D1.2
In-situ Observation of Material States under Severe Thermo-mechanical Processing using Novel Time-Resolved Neutron-Diffraction Method.
Wan Chuck Woo 1 2 , Zhili Feng 1 , Xun-Li Wang 3 , Donald Brown 4 , Bjorn Clausen 4 , Camden Hubbard 1 , Stan David 1
1 Materials Science and Technology, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials science and Engineering, The University of Tennessee, Knoxville, Tennessee, United States, 3 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Materials Science and Technology , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIn-situ material-states observation under real-world material processing environments has been one of the challenging issues in materials science and engineering. Due to the deep-penetration capability of neutrons, the neutron-diffraction technique has been widely used for understanding material structures and properties. However, the transient behaviors have been difficult to measure directly due to the limited neutron flux. The present authors have developed a novel experimental measurement technique and data analysis method, based on so-called quasi-steady state phenomenon that enabled access to transient behaviors in real-time.Magnesium alloys have recently received tremendous attention in the automotive industry as a lightweight structural material for energy efficient vehicles. Since the Mg alloys has the hexagonal-close packed (hcp) lattice structure, it has a distinctive deformation characteristics compared to the commonly used face-centered cubic (fcc) structural materials such as steels and Al alloys. Understanding and quantifying the deformation behavior and microstructure changes of Mg alloys under manufacturing processes including the complex forming and other thermo-mechanical processes are essential to the accelerated use of Mg alloys in automotive industry.In this study, we will present the in-situ, time-resolved neutron diffraction experimental results, which were performed “during” real severe-plastic-deformation processing to investigate the transient lattice-parameter changes in a Mg alloy (AZ31-B) plate. Specifically, a specially designed portable thermo-mechanical processing system, which was modified using the friction-stir welding machine, was built and installed inside a neutron beam room for the real-time experiments. The evolution of the lattice-strain components and the variations of the peak intensities/shapes in Mg alloys during processing will be presented to illustrate the rapidly changing complex material states. The transient material states potentially include transient temperature/stress fields and the evolution of texture/microstructure.Acknowledgements: This research is sponsored by the Laboratory Directed Research and Development program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725. It is also in part supported by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the Automotive Lightweighting Materials Program and the NSF International Materials Institutes Program under contract DMR-0231320.
10:00 AM - D1.3
In-situ Measurement of Strain Evolution in Deposited and Thermally Grown Polycrystalline Films.
Boyd Veal 1 , Arvydas Paulikas 1 , Jeffrey Elam 2 , Michael Pellin 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Energy Systems Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe have developed a technique, using x-ray synchrotron radiation, to measure biaxial in-plane strains in polycrystalline films. An adaptation of the well known sin2ψ method, this technique acquires, in a single exposure, the elliptically distorted Debye-Scherrer diffraction pattern from a stressed film. Analysis of the elliptical distortion yields the biaxial strain. Measurements of strain are obtained with high accuracy and precision (~ 10-5), and with time resolution of 5 min between points. Strains were measured, in-situ, in films of ZrO2 (300 °C substrate deposition temperature) and In2O3 (275 °C deposition) as samples were heated in air to 1100 °C. The samples, deposited on Si substrates, were prepared using the ALD (atomic layer deposition) technique. Both films showed large compressive stresses following deposition. With heating, the compressive stress initially increased, a consequence of the coefficient of thermal expansion (CTE) difference between film and substrate. At higher temperatures (T > 600 °C for ZrO2 and T > 300 °C for In2O3), the compressive stresses were relieved by plastic flow in the film. With cooling from 1100 °C, and with subsequent thermal cycling to 1100 °C, film stresses were tensile, reflecting the high temperature strain relieved condition and the CTE difference on cooldown. The ZrO2 film, as deposited, contained a mixture of monoclinic and tetragonal phases. As the sample was heated, the tetragonal phase converted to the monoclinic phase, the stable low temperature form. Strains were also measured in Al2O3 thermally grown, at 1100 °C in air, on β-NiAl substrates. The transformation of early-formed θ-Al2O3 to α-Al2O3 results in the generation of a large tensile stress (~ 1 GPa) resulting from a volume contraction associated with the transformation. The transformation was monitored with intensity measurements of diffraction lines from the θ and α phases. Creep in α-Al2O3 was measured, at temperatures between 950 – 1100 °C, by exploiting the CTE difference between metal substrate and the oxide, to impose a stress on the oxide. Stress relaxation was then monitored isothermally to determine creep rates vs temperature at a fixed level of stress. At low stress levels, the plastic flow is consistent with a diffusional creep (Coble) mechanism.
10:15 AM - D1.4
Grain-Scale Strain and Orientation Measurements during Electromigration in an Al Conductor Line by Synchrotron X-Ray Microbeam Diffraction.
Hongqing Zhang 1 , George Cargill 1 , Linda Ge 2 , Antoinette Maniatty 2 , Wenjun Liu 3
1 MSE, Lehigh Univ, Bethlehem, Pennsylvania, United States, 2 Mechanical, Aerospace, and Nuclear Engineering, 2.Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractAn Al conductor line, 2.6 µm wide, 0.75 µm thick and 30 µm long, with SiO2 passivation was stressed with current density 1.54MA/cm2 at 190C, and the strain developed during electromigration was measured in-situ by white beam synchrotron x-ray microdiffraction on Advanced Photon Source Beam Line 34-ID. The x-ray beam was 0.4 µm in diameter. Grain-scale deviatoric strain measurements were made repeatedly for 40 hours. A strong strain gradient developed along the conductor line during electromigration, although no voids or extrusions were visible. Grain-scale strain measurements showed large variations, even within individual grains. Orientation maps showed near-bamboo grain structure. Complementary grain structure information from FIB, EBSD, and TEM images of the same conductor line will also be reported. Results from an approximate analytic model, using the Eshelby inclusion theory, and finite element simulations will be compared with the x-ray microbeam diffraction results.
10:30 AM - D1.5
Application of Synchrotron XRD Stress Measurements on Copper/low-k and Copper/ultra-low-k Interconnect Structures in Semiconductor Industry.
Hartmut Prinz 1 , Inka Zienert 1 , Jochen Rinderknecht 1 , Holm Geisler 1 , Ehrenfried Zschech 1 , Seung-Hyun Rhee 2 , Paul Besser 3 , Norbert Schell 4 , Baehtz Carsten 5
1 , AMD Saxony LCC & Co. KG, Dresden Germany, 2 AMD Logic Technology Development, AMD-IBM alliance, East Fishkill, New York, United States, 3 , AMD, Sunnyvale, California, United States, 4 GKSS Geesthacht, Hasylab, Hamburg Germany, 5 Rossendorf-Beamline (BM20), ESRF, Grenoble France
Show AbstractMotivation: The stress state is a very important property of the interconnect layer in modern semiconductor devices as it has a direct influence on the stressmigration and electromigration reliability. Stress gradients within structures may build up due to thermal mismatch and special geometries and can lead to device failure by stress migration. On the other hand stress gradients build up during electromigration acting as a counterforce to the electrical current and preventing device failures by electromigration voiding. Modern low-k and ultra low-k materials show thermal expansion coefficients in the same range as copper (16x10-6K-1), so the thermal mismatch within the layer is much lower when compared to silicon dioxide (0.5x10-6K-1) dielectric layers, however the thermal mismatch to the Si substrate (4.7x10-6K-1) is higher and goes in the opposite direction. The much softer low-k and ULK materials also show elastic deformation at a lower stress level and possibly prevent the formation of a higher back stress as a counterforce during electromigration. Experimental: The authors performed several synchrotron XRD stress measurements at the Rossendorf Beamline (ROBL) at the ESRF (Grenoble, France). Arrays of copper line structures with different dielectric materials, protecting capping layer and line widths were measured at temperatures between 25-400°C in a 4-circle goniometer. The higher copper (311) reflection was chosen for better resolution and an area detector was used to reduce measurement times. The data was taken at a single reflection in side inclination mode with a wide variation in Chi (20 ±10°, -20 ±10°, 40 ±10°, -40 ±10°) and Psi (0, 45, 90). This data was then used to fit the fundamental stress equation. Results: For different manufacturing technologies the signal quality, data collection conditions and the resulting stress states are shown and discussed. Comparisons with laboratory setup results show that synchrotron radiation XRD is the only method to measure the temperature dependent average internal copper stress in an intermediate spatial resolution. The high beam brilliance enables spot sizes of less than 200µm, but even here the small amounts of diffracting material start to become a problem. Samples manufactured with the newest technology showed nearly no intensity in the (311) reflection. A large effort of optimization is needed here to keep the method usable for future challenges.The results show that the overall stress state of the copper interconnects decreases with the implementation of the softer low-k and ULK materials, as well as the temperature dependence of the stress state. This is a positive point for the new technologies as it should reduce the risk of stress migration. However for electromigration the relatively low level of stress might become a disadvantage if it is caused by elastic deformation of the low-k or ULK material and not by a lower thermal mismatch.
10:45 AM - D1: Stress
BREAK
11:15 AM - **D1.6
Size Effects in Plasticity using In-situ Mechanical Testing.
Helena Van Swygenhoven 1 , Stefan Brandstetter 1 , Robert Maass 1 , Steven Van Petegem 1 , Bernd Schmitt 1 , Daniel Grolimund 1 , Peter Derlet 1
1 , Paul Scherrer Institute, Villigen Switzerland
Show AbstractApplications of metals in micro-nanotechnology deal with size effects coming from either a microstructural lengthscale in the nanometer range or an object size lengthscale in the micron or sub-micron range. In both types of confinements an increase in strength is observed, often reaching values that seem to be far beyond classical predictions. Exploring and understanding the strengthening mechanisms require real-time resolved in-situ mechanical testing, revealing the dynamics of the deformation mechanism, disclosing the experimental boundary conditions of newly developed testing techniques and providing the appropriate input for computational predictive modelling. Two in-situ testing facilities have been developed at the Swiss Light Source (SLS) to study size effects in plasticity. By performing in-situ powder diffraction (MS/SLS) on nanocrystalline metals during tensile or compression testing, it has been possible to demonstrate that at small grain sizes deformation mechanism do not leave dislocation debris [Science 304(2004) 273, APL., 87,(2005)231910]. In-situ experiments underline the role played by the pre-existing internal strains in undeformed nanocrystalline structures [APL 89 (2006) 73102] and demonstrate the presence of large microplastic strains before the onset of macroplasticity [Adv. Mat. 18(2006) 1545]. To address small scale plasticity in object size confined structures, real time in-situ white-beam Laue microdiffraction experiments at MicroXAS (SLS) are carried out during compression of single crystal micron-sized pillars. The experiments demonstrate the importance of pre-existing strain gradients as a result of FIB synthesis [APL, 89(2006)151905]. The evolution of the Laue patterns of the Au pillars demonstrate the occurrence of crystal rotation and strengthening can be explained by plasticity starting on a slip system that is geometrically not predicted but selected because of the character of the pre-existing strain gradient.
11:45 AM - D1.7
Temperature Dependent Residual Stresses and Plasticity in Nanofilamentary Cu/Nb Wires: in-situ Tensile Tests under Neutron Beam.
Vanessa Vidal 1 , Ludovic Thilly 2 , Steven Van Petegem 3 , Uwe Stuhr 3 , Florence Lecouturier 4 , Pierre-Olivier Renault 2 , Helena Van Swygenhoven 3
1 , MES, Toulouse France, 2 , University of Poitier, Futuroscope France, 3 , Paul Scherrer Institute, Villigen Switzerland, 4 , LNCMP, Toulouse France
Show Abstract12:00 PM - D1.8
In-Situ Neutron Diffraction Study of the Behavior of AL6XN Stainless Steel Under Biaxial Loading.
M. Gharghouri 1 , T. Marin 2 , R. Rogge 1 , P. Dawson 2
1 Canadian Neutron Beam Centre, National Research Council Canada, Chalk River, Ontario, Canada, 2 Department of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States
Show AbstractIn-situ neutron diffraction measurements of lattice strain during uniaxial loading have provided a wealth of information that has been used to develop models of polycrystal plasticity in BCC, FCC, and HCP metals and alloys. The technique probes the mechanical response of different families of grains, defined by the crystallographic direction parallel to the scattering vector. In this work, lattice strains along the two principal stress directions were measured in-situ in AL6XN stainless steel subjected to biaxial loading conditions. A new fixture was developed for loading thin-walled tubular specimens through combinations of internal pressure and axial loading. The resulting biaxial stress state in the thin-walled gauge section of the specimens is dictated by the relative magnitudes of the axial load and pressure. Under these conditions, the orientations of the principal stress axes (σzz and σθθ in a cylindrical r, θ, z coordinate system) remain constant with respect to the initial crystallographic texture regardless of the level of biaxiality, a distinct advantage for diffraction experiments over the traditional tension/torsion tests for which this condition does not hold. Heavy water was used as the pressurizing fluid to reduce the attenuation in the peak measurements. For each test, the specimen was first pressurized to the level required to obtain a chosen value for σθθ. The axial load was then increased to reach the yield surface at different σθθ/σzz ratios (0, 0.4, 0.7, 1 according to Tresca), ranging from uniaxial to perfectly biaxial loading. Peaks were measured for the {200}, {220}, {222}, and {311} planes in the axial and hoop directions as a function of axial load. A sequence of axial loading/unloading cycles was applied for different levels of plastic deformation in order to investigate the elastoplastic transition, the evolution of load sharing among the various orientations during plastic deformation, and the behavior during unloading. Under uniaxial tension, the {200} reflection showed the highest axial strains, followed by the {311}, and {220}/{222} reflections. With increasing internal pressure (biaxiality), the axial lattice strains corresponding to a given axial stress tended to decrease, and the responses of the various reflections tended to merge. These observations suggest that, as the level of stress biaxiality increases, the resolved shear stresses on the slip systems become less dependent on grain orientation, causing the grain response in turn to become less orientation-dependent. The experimental program is being accompanied by a modeling effort in which aggregates of crystals are discretized with finite elements and subjected to the same loading histories as applied in the experiments. The exploration of the elastoplastic transition under a range of loading modes will stimulate a new wave of critique of existing approaches and possibly motivate the development of new modeling efforts for micromechanical formulations.
12:15 PM - D1.9
Study of Elastic Behavior of Metallic Thin Films by 2D Synchrotron XRD and in situ Tensile Testing.
Eric Le Bourhis 1 , Guillaume Geandier 1 , Pierre-Olivier Renault 1 , Philippe Goudeau 1 , Baptiste Girault 1
1 LMP UMR CNRS 6630, Univ. Poitiers, Futuroscope-Chasseneuil France
Show AbstractMechanical behavior characterization of polycrystalline thin films in relation with their microstructure is the preliminary step for the development of technological applications. However, in situ study of this relationship between mechanical properties and microstructure still remains too rarely explored. The considered approach in our work consists in preparing thin films with controlled microstructure, characterizing the mechanical response of these films thanks to the development of diffraction based techniques, and finally interpreting experimental results using mechanical modeling of elastic grain interaction for example [1,2]. This method is applied to model thin films such as tungsten (elastically isotropic) and gold (strongly anisotropic) [3] which are deposited on Kapton substrates by using well controlled ion beam sputtering techniques. The mechanical response is then characterized in the elastic and plastic domains through in situ tensile testing in diffractometers available at our laboratory and at synchrotron beam lines [1-3]. The use of synchrotron radiation (high flux, tunable wavelength) together with bi-dimensional CCD detectors, allows real-time captures of diffraction rings for all diffracting phases (Au, W, Cu/W and Au/W multilayers) during tensile testing. This combination allows accurate and reliable determination of intragranular strains (few seconds in the present case at 11.3.1 ALS beam line [1,4] against several hours in our laboratory). Sin2Ψ analysis is then applied to a large number of tests which then brings more detailed information on the mechanical behavior of thin films.[1] P.Goudeau, D.Faurie, B.Girault, P.-O. Renault, E. Le Bourhis, P. Villain, F. Badawi, O. Castelnau, R. Brenner, J.-L. Bechade, G. Geandier, N. Tamura (2006) “Strains, stresses and elastic properties in polycrystalline metallic thin films: in situ deformation combined with x-ray diffraction and simulation experiments”, Material Science Forum 524-525, pp. 735-740.[2] D. Faurie, P.-O. Renault, E. Le Bourhis, Ph. Goudeau, O. Castelnau, R. Brenner, G. Patriarche (2006) "Elastic behavior of polycrystalline thin films inferred from in situ micromechanical testing and modeling", Applied Physics Letters 89 (6), 061911. [3] D. Faurie, P.-O. Renault, E. Le Bourhis, Ph. Goudeau (2006) "Study of texture effect on elastic properties of Au thin films by X-ray diffraction and in situ tensile testing", Acta Materialia 54, pp. 4503-4513.[4] http://www-als.lbl.gov/, http://xraysweb.lbl.gov/BL1131/1131website/
12:30 PM - D1.10
Synchrotron X-ray Imaging of Nickel-Base Superalloy Microstructure and In Situ Crack Propagation.
Naji Husseini 1 , Divine Kumah 1 , Jian Yi 2 , Liu Liu 2 , Codrin Cionca 1 , Dohn Arms 3 , Wah-Keat Lee 4 , Eric Dufresne 3 , J. Jones 2 , Tresa Pollock 2 , Roy Clarke 1
1 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States, 2 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Sector 7, Advanced Photon Source, Argonne, Illinois, United States, 4 Sector 32, Advanced Photon Source, Argonne, Illinois, United States
Show AbstractNickel-base superalloys are used in harsh and demanding environments because of their exceptional mechanical strength, resistance to corrosion and oxidation, and high melting point. For these very reasons, they are commonly found in airplane and power plant turbines. The superalloys form single crystals via directional solidification along the <001> crystallographic direction and have a dendritic morphology expressed as four leaves in the <100> direction. While extensive work in superalloys has been done with SEM and TEM, high brilliance, tunable synchrotron x rays have some distinct advantages over these techniques. They can penetrate thick samples to map microstructure, resolve any compositional variations, and study the dislocation network resulting from mosaicity. Furthermore, the large field of view and rapid scan times allow crack propagation to be studied in situ and in real time. Using the undulator x-ray radiation in Sector 7ID of the Advanced Photon Source at Argonne National Laboratory, we imaged samples of Rene N5 superalloys with thicknesses up to 250 microns using transmission geometry. When the energy was tuned just below the nickel k-edge of 8.33 keV, the intensities on the resulting images contained information about variations in elemental concentrations at micron resolution. Image quality was enhanced by phase contrast. After calibrating with SEM, the intensity map showed high concentrations of tungsten and rhenium at the dendrite cores and a linear decrease in these two elements outward from the core. When the sample was rotated to the <222> Bragg diffraction condition, the intensity was reduced in areas with uniform lattice parameters and crystallographic orientations by approximately 75%. Therefore, any minor variation in lattice parameters or misorientation in the dendrite cores produced a brighter region in the image compared to the remainder of the sample. The misorientations ranged from 0 to 8 degrees and allowed the calculation of dislocation densities between 10^7 and 10^8 cm^-2. Crack propagation was studied by applying a static tensile load to the sample followed by cyclic tension and compression cycles to failure using an ultrasonic transducer. Although induced cracks grew more easily in the interdendritic region, they required many more loading cycles to continue through the dendrite itself, where they grew along the <111> crystallographic plane. When the sample was rotated to satisfy the <222> condition, strain fields became visible and were used to anticipate the crack’s path. Understanding microstructure and crack propagation will ultimately improve the reliability of superalloys in their crucial applications.
12:45 PM - D1.11
Geometrically Necessary Dislocations Near a Grain Boundary in a Ni Bicrystal from X-ray Microdiffraction and Strain Gradient Crystal Plasticity.
R. Barabash 1 , J. Pang 1 , G. Ice 1 , T. Ohashi 2
1 Materials Science and Technology Div., Oak Ridge National Laboratory, Oak Ridge TN, Tennessee, United States, 2 , Kitami Institute of Technology, Kitami Japan
Show AbstractWe report the inhomogeneities of plastic deformation close to the grain baoundary in the natural Ni bicrystal during uniaxial pulling. Focused, polychromatic synchrotron X-ray microbeam together with orientation imaging microscopy, scanning electron microscopy, and finite element simulations were used to characterize the physics of geometrically necessary dislocations formation and collective behaviour during plastic deformation. Crystallographic orientation of the grain essentially determined it’s plastic response during deformation. Finite element simulations were used to understand the influence of grain orientation and initial structural inhomogeneities on the geometrically necessary dislocations arrangement and distribution. Strain in both grains increases in the vicinity of the coherent boundary.
D2: Transitions I
Session Chairs
Monday PM, November 26, 2007
Liberty (Sheraton)
2:45 PM - D2.2
Real Time X-ray Diffraction Studies of Phase Transformations During Rapidly Propagating Reactions in Nanolaminate Foils.
Jonathan Trenkle 1 , Lucas Koerner 2 , Mark Tate 2 , Sol Gruner 2 3 , Timothy Weihs 1 , Todd Hufnagel 1
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Physics, Cornell University, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States
Show AbstractReactive multilayer foils are composed of alternating nanoscale layers of materials that have large negative heats of mixing. When a small potential is applied, atomic mixing occurs, releasing heat. The heat then travels primarily along the foil, facilitating further atomic mixing. In this way, a self-propagating reaction is sustained, which can travel ∼1 m s−1 and reach temperatures in excess of 1300 K in microseconds, depending on the foil design. Through vapor deposition and design of the layering and chemistry, we can precisely control the reaction characteristics, making these materials ideal for investigating compound formation under unique thermodynamic and kinetic conditions (due to the steep concentration and thermal gradient), especially at heating rates not easily achievable (>107 K s−1 ). In situ characterization, however, is a considerable challenge. Characterizing the processes in the reaction zone requires both temporal resolution better than ∼100 μs (the time required for the reaction front to pass a fixed location) and spatial resolution of < 100 μm (the approximate width of the reaction zone). We have successfully used synchrotron x-ray radiation and a pixel array detector at the Cornell High Energy Synchrotron Source to study phase evolution in situ during self-propagating reactions in Al/Ni reactive multilayers (with overall composition near Al3Ni2). The time resolution (≈50 μs) and spatial resolution(≈60 μm) of the measurements was sufficient to allow us to observe the phase transformation sequence in detail, identifying key transformations in the development of the final structure. For example, within the first 200 μs of the reaction, all of the Al and Ni is consumed to form an amorphous phase and cubic AlNi. We do not observe complete melting of the Al or Ni. In the case of Al, this suggests significant superheating despite the presence of many heterogenous nucleation sites. Near peak reaction temperatures, 300 μs later, the system approaches equilibrium (AlNi and liquid Al-Ni). Finally, equilibrium hexagonal Al3Ni2 forms by a peritectic reaction during cooling some 38 ms later.Our results differ significantly from what has been observed in these foils at slower heating rates (∼10 K min-1) and when quenching the propagating reaction front. In those experiments, the formation of intermediate, metastable crystalline phases (Al9Ni2 and Al3Ni) prior to final phase formation are observed. The presented in situ experiments, thus, provide a more accurate picture of the phase progression in unabated, self-propagating reactions. In this presentation, we will describe the details of the experiments, the kinetics of the phase evolution in self-propagating reactions in Al/Ni reactive multilayer foils, and conclude with a discussion of the potential for future study using these materials.
3:00 PM - D2.3
Time-resolved X-ray Diffraction of Phase Transformations in the Sm-Co(Fe) System.
Jeffrey Shield 1 2 , Julia Kostogorova-Beller 1 2 , Matthew Kramer 3 4
1 Mechanical Engineering, University of Nebraska, Linoln, Nebraska, United States, 2 Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska, United States, 3 Ames Laboratory, Iowa State University, Ames, Iowa, United States, 4 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractTime-resolved x-ray diffraction experiments using synchrotron radiation at the Advanced Photon Source have been utilized to investigate the phase stabilities in Sm-Co(Fe) permanent magnets. Full pattern x-ray diffraction patterns with the wave momentum number (Q = 4πsinΘ/λ) ranging from 5 to 75 nm-1 were obtained every 10 seconds at a heating rate of 10 K/min. The patterns were sequentially Rietveld refined to obtain lattice parameter data as a function of temperature. The as-quenched rapidly solidified alloys were in the disordered TbCu7-type structure, which transformed to the ordered Th2Zn17-type structure upon heating. The ordering process involves the superstructural arrangement of transition metal dumbbells. A second ordered structure with the Th2Ni17 structure type was also evident. Deviations from linearity in the lattice parameter-temperature relationships suggest that the transformation proceeds by the nucleation and growth of ordered domains. Analysis of the diffraction data also allowed for the determination of the kinetic parameters, and it was determined that the transformations could be described using JMAK theory. Using time-resolved x-ray diffraction to determine the kinetics has distinct advantages over thermal methods. For example, transformations such as this have a low enthalpy, making the heat evolved difficult to measure. X-ray diffraction, however, can clearly elucidate phase evolution, and lattice parameter changes are large enough to determine onset temperatures. Furthermore, structural details of the transformation can be determined, such as the growth rate by monitoring peak widths or the evolution of metastable phases.The in situ x-ray diffraction experiments also revealed some anomalous phase relationships. The Sm2(Co,Fe)17 compound transformed to the Th2Zn17-type structure, indicating complete miscibility of Co and Fe, which coexisted with the Th2Ni17-type phase. However, at higher temperatures two Th2Zn17-type structures were observed, indicating Co and Fe immiscibility and formation of distinct Sm2Co17 and Sm2Fe17 phases. At higher Fe content, miscibility returned for the Th2Zn17-type structure, but immiscible Th2Ni17-type structures were evident.
3:15 PM - D2.4
Determination of the Short-Range Order in Supercooled Liquids Beam-Line Electrostatic Levitation (BESL).
K. Kelton 1 , T. Kim 1 , K. Sahu 1 , A. Gangopadhyay 1 , A. Goldman 2 , J. Rogers 3 , R. Hyers 4
1 Physics, Washinton University St. Louis, St. Louis, Missouri, United States, 2 Ames Laboratory USDOE and Department of Physics and Astronomy, Iowa State Univeristy, Ames, Iowa, United States, 3 , NASA Marshall Space Flight Center, Huntsville, Alabama, United States, 4 , University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractX-ray diffraction measurements of supercooled liquids using electrostatic levitation (Beamline Electrostatic Levitation, BESL) have led to new insight into the structures of liquids and the phase transitions that occur there. Some studies of transition metal and silicon liquids are discussed for illustration. Icosahedral short-range order (ISRO) is found to be prominent in the structures of transition metal elemental liquids. In a TiZrNi alloy this developing ISRO favors the transformation of the liquid to a metastable icosahedral quasicrystal phase, instead of the stable tetrahedrally-coordinated crystal C14 Laves phase. This demonstrates a clear connection between the nucleation barrier and the local structure of the liquid, one of a growing number of cases where the nucleation of the ordered phase is coupled with other processes and phase transitions. In a different system, liquid silicon, theoretical studies using model and ab-inito potentials have predicted the existence of a liquid/liquid phase transition corresponding to a continuous change of the A5 (white tin) local structure to an A4 diamond cubic structure, which is characteristic of crystal Si. In contrast BESL studies showed no evidence of a first order liquid-liquid phase transition over the measured temperature range (1100oC to 1600oC). The coordination number remained constant, in conflict with earlier measurements. An analysis of the atomic structures determined from the measured S(q) using a Reverse Monte Carlo simulation in terms of the Honeycutt-Anderson and bond orientational order parameter techniques indicate that that the supercooled liquid silicon maintains the A5 structure (with some A4), with the coherence length of the A5 order increasing with supercooling. These results are presented and further studies are discussed. - Supported by NASA under contract NNM04AA016 and the NSF under grants DMR 03-0710 and DMR-06-06065.
3:30 PM - D2.5
Pressure Enhancement of Negative Thermal Expansion Behavior and Induced Framework Softening in Zinc Cyanide.
Karena Chapman 1 , Peter Chupas 1
1 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe flexibility of open framework network solids is associated with structural distortions in response to applied pressures. While such pressure-induced structural transitions are well understood for traditional oxide-based materials including dense mineral oxides and open framework zeolites, the pressure response of more extended coordination (or metal-organic) frameworks has yet to be explored. In such systems, the more open structure and complex connectivities are likely to enhance framework flexibility and yield more extreme and exotic pressure-dependent behavior. Moreover, novel pressure-induced behavior would be anticipated at more moderate pressures than for oxides; pressures such as are routinely encountered in practical applications. Consequently, understanding the impact pressure on the structure and functional properties of coordination framework systems is not only of fundamental interest, but is relevant to their practical application. Here we explore pressure-dependent behavior of the zinc cyanide framework using in situ neutron powder diffraction and uncover an unusual pressure-induced framework softening and enhancement of negative thermal expansion behavior; phenomena linked to increased framework flexibility at high pressure.
3:45 PM - D2: Transitions
BREAK
4:15 PM - **D2.6
Domain Structure and Switching Dynamics in Ultra Thin Films and Nano-islands of Ferroelectrics.
Sunggi Baik 1
1 Materials Science and Engineering, POSTECH, Pohang Korea (the Republic of)
Show Abstract Integration of ferroelectrics to current high-density electronics including memory and storage devices has raised the long-standing fundamental issue on ferroelectric phase transition – the size effect. Many theoretical and experimental studies have been focused to identify the critical sizes or size ranges below which ferroelectric behaviors are modified and often degraded. Various extrinsic factors affecting the critical sizes have been identified and separated from intrinsic effects. Our recent study on structures and properties of PZT ultra thin films and nano-islands will be described in detail. Evolution of unique domain structures were characterized as a function of film compositions, substrate selection, film thickness, and 2D planar size employed in nanostructure fabrication. Domain structure and crystalline quality of the films and nano-islands are studied and quantified by two-dimensional reciprocal space mapping technique using synchrotron XRD and imaging. Domain switching dynamics are studied also by synchrotron XRD and PFM. Attempts have been also made theoretically to establish the correlation with various electrical and thermomechanical factors involved in nanostructure processing. Implication of the results for device applications will be discussed.
4:45 PM - **D2.7
Chemical Control of Ferroelectric Switching in PbTiO3 Films.
Dillon Fong 1 , R. Wang 2 , F. Jiang 1 , P. Fuoss 1 , S. Streiffer 2 , J. Eastman 1 , G. Stephenson 1 , K. Latifi 3 , Carol Thompson 3
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Physics, Northern Illinois University, DeKalb, Illinois, United States
Show AbstractUsing real-time grazing-incidence synchrotron x-ray scattering, we observe that the direction of polarization in a ferroelectric thin film can be reversibly switched by changing its surface chemical environment between oxidizing and reducing conditions.The reorientable spontaneous electric polarization of ferroelectric materials gives them unusual dielectric properties and utility for information storage. Although polarization orientation is typically switched by applying a voltage across electrodes, we find that the polarization can also be reversibly switched by changing the chemical environment in contact with one surface of a ferroelectric film. Oxidizing or reducing conditions induce outward or inward polarization, respectively, in PbTiO3 films grown on conducting SrRuO3 on (001) SrTiO3 substrates. Such chemical switching has broad implications for new types of chemical actuators, catalysts and sensors for surface reactions, and for manipulation of ferroelectric domain patterns. Work supported by the U. S. Department of Energy under Contract No. DE-AC02-06CH11357.
5:15 PM - D2.8
In Situ X-Ray Studies of Domain Structure in Epitaxially Strained La1-xSrxMnO3 Thin Films.
Paul Fuoss 1 , Jeffrey Eastman 1 , Dillon Fong 1 , Peter Baldo 1 , Paul Salvador 2 , Joanna Meador 2 , Balasubramanian Kavaipatti 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science and Engineering Department, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractManganites such as Sr-doped LaMnO
3 (LSMO) are complex oxides that are of great interest for both their magnetic properties, and their electronic conduction and catalytic behavior when used in cathode heterostructures for solid oxide fuel cells. In this presentation, the structure of epitaxial coherently-strained LSMO thin films determined using in situ x-ray scattering in various temperature and oxygen partial pressure environments will be described. For 30% Sr (i.e., La
0.7Sr
0.3MnO
3) single crystal epitaxial films with thicknesses of 5-to-75 nm grown by pulsed-laser deposition on SrTiO
3 (001) substrates, we observe strong scattered intensities at half-order positions (e.g., 3/2, 1/2, 1/2), indicating a periodicity that is double that of the normal unit cell in all three dimensions. Observed reflection locations are consistent with what would be predicted if octahedral oxygen cages are tilted about the same axis, but in opposite directions in adjacent unit cells. Satellites indicating a domain structure are also observed adjacent to all half-order and normal Bragg peaks. We find that these satellites exhibit a more complex behavior than has been reported for satellites attributed recently to microtwinning in La
0.9Sr
0.1MnO
3 thin films (1,2). In particular we observe that the symmetry of satellite distributions varies for different ½-order peaks, indicating a three-dimensionally-complex domain structure. By growing LSMO films of various compositions on substrates including SrTiO
3, NdGaO
3, and DyScO
3 that possess different lattice parameters, we are systematically exploring the effects of misfit strain on the structure of these films. We will also discuss the effects of sample environment (e.g., temperature and oxygen partial pressure) and film thickness on observed behavior. For example, we have observed that Sr surface segregation occurs in these films at 700° when the oxygen partial pressure is reduced from 100 to 0.01 Torr. This work is supported by the U. S. Department of Energy under Contract No. DE-AC02-06CH11357.
1. S.H. Seo, H.C. Kang, H.W. Jang, D.Y. Noh, Phys. Rev. B 71, 0124212 (2005).
2. U. Gebhardt et al., Phys. Rev. Lett. 98, 096101 (2007).
5:30 PM - D2.9
In-situ X-ray Studies of Current Conditioning in High Temperature Solid Oxide Fuel Cells.
Kee-Chul Chang 1 , Bilge Yildiz 3 , Deborah Myers 2 , John Carter 2 , Hoydoo You 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Chemical Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSynchrotron x-ray techniques are uniquely suited for probing interfaces under extreme conditions of high temperature and/or high pressure (compared to vacuum) because hard x-rays can penetrate such environments while also being sufficiently sensitive to the interfaces. In this regard, x-rays are ideal for the in-situ study of the solid oxide fuel cells (SOFCs) which operate at temperatures between 700 to 1000°C in atmospheric pressure. One of the many remaining questions around the reaction mechanisms at SOFC electrodes is the origin of "current conditioning" — the transient enhancement of reactivity at the electrode with initial DC polarization. We studied model dense thin-film SOFC electrodes composed of either La0.8Sr0.2MnO3 (LSM) or La0.8Ca0.2MnO3 (LCM) deposited on single crystal yttria-stabilized zirconia electrolytes which were operated as half cells with applied potential. We used x-ray reflectivity and x-ray absorption spectroscopy to monitor the morphological and chemical state changes in the manganite film, respectively. The x-ray fluorescence yields from our experiments shows that the La and Sr concentration changes with the application of potential and correlates with current conditioning. This opens the possibility that the La occupied A-sites of the perovskite structure may play a greater role in the current conditioning of SOFCs, contrary to prevailing theory.
5:45 PM - D2.10
In-situ High-Pressure XPS and XAS Investigation of the Effect of Pt Cluster Size on the Oxidation of NO on Supported and Model Pt Catalysts.
Robert Rioux 1 , Shadab Mulla 2 , Andrew Smeltz 2 , Ajay Joshi 2 , Bongjin Mun 3 , Jeffrey Miller 4 , A. Kropf 5 , William Epling 6 , Dmitry Zemlyanov 7 , W. Delgass 2 , Fabio Ribeiro 2
1 Chemistry and Chemical Biology Department, Harvard University, Cambridge, Massachusetts, United States, 2 Chemical Engineering, Purdue University, West Lafayette, Indiana, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 British Petroleum Research Center, British Petroleum , Naperville, Illinois, United States, 5 Chemical Engineering, Argonne National Laboratory, Naperville, Illinois, United States, 6 Chemical Engineering Department, University of Waterloo, Waterloo, Ontario, Canada, 7 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractThe three-way catalyst operates effectively within a very narrow stoichiometric regime leading to exhaust gas with properly balanced levels of CO, H2 and hydrocarbon for nitrogen oxides (NOx) reduction. The operation of gasoline engines at lean conditions leads to increased fuel efficiency and reduced CO2 emissions, but is unable to reduce NOx in the oxygen-rich environment. One proposed solution for NOx abatement in lean-burn engines is NOx storage/reduction (NSR). NSR catalysts composed of platinum and barium most effectively store NOx as NO2, but the NOx content from a typical engine is composed of 95% NO and 5% NO2. Therefore it is important to understand the kinetics and mechanism of NO oxidation to NO2 on Pt under reaction conditions.The rate of NO oxidation is sensitive to particle size; larger particles (> 5 nm) are more active on a surface atom basis than smaller particles (1-3 nm). Detailed analysis of the particle size distribution by transmission electron microscopy (TEM) and rate measurements on monodisperse-supported Pt catalysts and a Pt(111) single crystal suggests that large particles are responsible for most of the observed activity. The synchrotron measurements described below support the view that the smaller particles are deactivated by over-oxidation while the larger particles remain active with only the surface being partially oxidized.We utilized the APS synchrotron source to perform x-ray absorption (XAS) on nanometer sized Pt clusters and the ALS source for x-ray photoelectron spectroscopy (XPS) measurements on single-crystal Pt surfaces. The measurements were made under NO oxidation reaction conditions. XAS experiments demonstrate small particles (1-3 nm) are fully oxidized (no detectable metallic Pt) upon exposure to NO/O2/NO2, while large particles (8-9 nm) are primarily metallic under steady-state conditions. The oxidation was time dependent with Pt0 oxidizing completely to Pt2+ and Pt4+ in 2 nm particles, while Pt0 oxidized partially to Pt2+ in the larger particles. The fraction of Pt remaining metallic under steady-state conditions was found to increase linearly with the particle size. The coverage of oxygen on a Pt(111) single crystal during exposure to a high-pressure NO2 environment was measured by XPS. A coverage of 0.7±0.1 ML was measured and the Pt binding energy did not increase in the presence of 0.2 Torr NO2 at 523 K suggesting that Pt remained metallic on large single crystals. Although XAS does not have the precision to quantify the amount of surface oxygen on the active Pt clusters, carbon monoxide titration of adsorbed oxygen after reaction demonstrated that the amount of surface oxygen increased to the equivalent of about one monolayer.
D3: Poster Session I: Materials in Transition
Session Chairs
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - D3.1
3D X-Ray Microscopy Investigation of Dislocation Microstructures in Deformed Materials.
B. Larson 1 , Jon Tischler 1 , Anter El-Azab 2 , Wenjun Liu 3
1 MST, Oak Ridge National Lab., Oak Ridge, Tennessee, United States, 2 School of Computational Science, Florida State Univ., Tallahassee, Florida, United States, 3 XOR/UNI, Advanced Photon Source, Argonne, Illinois, United States
Show AbstractDeformation is one of the oldest materials processing techniques for modifying the properties of structural materials, e.g. hammering, rolling, bending. Despite its importance, both fundamentally and technologically, deformation remains one of the most difficult materials processes to understand from a first principles standpoint. This is because of the complex and collective nature of dislocation interactions, which leads to dislocation aggregation on mesoscopic length scales. We have used submicron-resolution 3D x-ray microscopy on the XOR/UNI Sector 34 beamline at the Advanced Photon Source to study dislocation microstructures in thin (35 micron) Si plates that were plastically deformed by annealing to 700 C while cylindrically bent to a 5 mm radius. Methods for performing non-destructive, quantitative, 3D measurements of local dislocation densities through submicron-resolution 3D x-ray microscopy measurements of elastic and plastic strain distributions will be discussed in terms of dislocation density tensors. Local deformation induced rotations and dislocation density distributions will be presented for the plastically deformed Si plates and application to nanoindentation induced deformation will be considered.*Research supported by the DOE, Office of Science, Division of Materials Sciences and Engineering under contract with UT-Battelle at ORNL. The APS is supported by the DOE Office of Science.
9:00 PM - D3.10
The High-pressure Behavior of Trinitro-triaminobenzene (TATB).
Lewis Stevens 1 , Daniel Hooks 1 , Dana Dattelbaum 1
1 Dynamic and Energetic Materials, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractBalancing detonation power with relative insensitivity is a primary concern in the development of next generation high explosives. This approach has yielded many novel insensitive high explosives (IHEs), of which TATB is particularly attractive. The insensitivity of TATB is coupled with a high density (ρ ~ 1.93 g/ml) and a relatively high detonation pressure (~ 26 GPa) and detonation velocity (~7.66 km/s). Given these characteristics, TATB is widely used in plastic-bonded explosives (PBXs). Although TATB was first synthesized in 1888, which predates that of some other common explosives, TATB is comparatively less characterized than its more powerful yet more sensitive counterparts. Using X-ray powder diffraction in conjunction with a diamond-anvil cell (DAC), the unit-cell volume of TATB has been measured to 13 GPa. The resultant isotherm compares well with a previous experimental work and is intermediate to two theoretically predicted isotherms. Analysis of the isotherm using a series of isothermal equations of state provided a determination of the isothermal bulk modulus (Ko) and its pressure derivative (Ko′) for TATB. For comparison to shock experiments on pressed TATB powder and its plastic-bonded formulation PBX 9502 (95% TATB, 5% Kel-F 800), our P-V isotherm was transformed to the pseudo-velocity Us-up plane. While our results agree well with previous experimental reports, we observe a subtle cusp in the P-V isotherm at approximately 8 GPa. This cusp becomes more distinct when observed in the Us-up plane. The possible origins of this cusp are discussed in relation to similar observations for anthracene and pyrolytic graphite.
9:00 PM - D3.11
Crystal Structure of Ti-Beta-21S up to 71 GPa.
Nenad Velisavljevic 1 , Gary Chesnut 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractCrystal structure of Ti-Beta-21S (TIMETAL 21S®), a high-strength, high-temperature, beta-stabilized alloy of Ti, Mo, Nb, and Al was studied to 71 GPa at room temperature-pressure (RTP), using a diamond anvil cell and angle dispersive x-ray diffraction. Initially, this alloy is a mixture of bcc (beta) and hcp (alpha) phases. Over the pressure range of this study the beta phase remains stable. For the alpha phase a decrease in the c/a ratio from 1.60 at room temperature and pressure to 1.57 at 37 GPa is observed, followed by a sudden increase to 1.61 above 40 GPa. We then observe a steady value for the c/a ratio above 40 GPa and up to 67 GPa. Furthermore, comparison of the diffracted peak intensities for the two phases shows that the intensity of the alpha phase peaks starts to decrease above 58 GPa, while the beta phase peak intensity is increasing. Above 67 GPa only the beta phase diffraction peaks are observed, indicating a structural phase transition, hcp to bcc has occurred, and the sample is comprised of only a single, beta, phase.
9:00 PM - D3.2
The Bauschinger Effect in Nanofilamentary Cu/Nb Wires Evidenced by In-situ Tensile Tests under Synchrotron Radiation.
Ludovic Thilly 1 , Steven Van Petegem 2 , Pierre-Olivier Renault 1 , Vanessa Vidal 3 , Florence Lecouturier 4 , Stefan Brandstetter 2 , Bernd Schmitt 2 , Helena Van Swygenhoven 2
1 Lab. Metallurgie Physique, University of Poitiers, Futuroscope France, 2 , Paul Scherrer Institute, Villigen Switzerland, 3 , CEMES, Toulouse France, 4 , LNCMP, Toulouse France
Show AbstractNanocomposite wires are processed by severe plastic deformation (Accumulative Drawing and Bundling) to obtain a multiscale Cu matrix embedding Nb nanotubes. They exhibit high strength that results from size effects in the Cu nanochannels and in the Nb nanotubes (Scripta Mat 57 (2007) 245).The macroscopic stress-strain curve during tensile loading-unloading cycling exhibits an increasing hysteresis, evidencing the presence of internal stresses (Bauschinger effect). By performing such load-unload experiments in-situ under synchrotron radiation at the Swiss Light Source, it is possible to follow continuously the difraction peak positions and peak widths of the large and the fine Cu channels as well as the Nb nanotubes, revealing the details of the load sharing and deformation mechanisms responsible for the Bauschinger effect.During tensile loading, the large Cu channels provide most of the plastic strain and dislocation storage can be evidenced. The fine Cu channels and Nb nanotubes however mainly store elastic energy. Upon tensile unloading, this energy is partly released via reverse yielding in compression of the large Cu channels: in other words, the large Cu channels are subjected to a built-in true Bauschinger test (inversion of load direction). The observed large plastic strain gradient, added to the sink character of the Cu-Nb interfaces, induce the continuous build-up of internal stresses during co-deformation.These results evidence unambiguously the reverse yielding of the soft phase in composite material with strong yield stress mismatch and bring further understanding to the complex residual stress state of nanocomposite materials obtained by severe plastic deformation processes where repeated loading-unloading cycles are applied (APL 90 (2007) 241907).
9:00 PM - D3.3
The Use of Synchrotron Radiation for the Determination of Plastic Properties of Silicon Below the usual Brittle to Ductile Transition Temperature.
Jacques Rabier 1 , Pierre-Olivier Renault 1 , Dominique Eyidi 1 , Jean-Luc Demenet 1 , Jiuhua Chen 2 , Hélène Couvy 2 , Liping Wang 2
1 Laboratoire de Métallurgie Physique, UMR 6630 CNRS-Université de Poitiers, Chasseneuil Futuroscope Cedex France, 2 Mineral Physics Institute, Stony Brooks University, Stony Brooks, New York, United States
Show Abstract9:00 PM - D3.4
Development of Texture and Intergranular Stress in a Nickel-based Alloy: Simulations and In-Situ Neutron-Diffraction Measurements.
E-Wen Huang 1 , Nan Jia 2 , Yandong Wang 1 2 , Bjorn Clausen 3 , Peter Liaw 1 , Hahn Choo 1 , Lee Pike 4 , Dwaine Klarstrom 4
1 Materials Science & Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyan China, 3 Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Department of Technology Engineering, Haynes International Inc., Kokomo, Indiana, United States
Show AbstractIn-situ neutron-diffraction measurements were conducted to monitor the lattice-strain evolutions of a single-phase, face-centered-cubic (FCC), nickel-based alloy during a strain-induced monotonic-tension experiment at room temperature. The nickel-based alloy is a newly developed corrosion-resistant type superalloy (Ni-21Cr-17Mo in weight percentage). The evolution of the lattice strains under the applied stress was simulated by visco-plastic self-consistent (VPSC) and Taylor’s models, which was further compared with the experimental measurements. Moreover, based on the materials parameters obtained from the above simulations, the texture evolutions were simulated with a plastic strain from 0% to 30% engineering strains. The agreement between the experimental and the simulated results demonstrate that the main deformation mechanisms may be captured by the existing models while the discrepancy between the experimental and the simulated results shows that the detailed microstructural information should be included for developing the new simulation methods.AcknowledgementsThis research is supported by the National Science Foundation (NSF), International Materials Institutes (IMI) Program (DMR-0231320) and the National Natural Science Foundation of China (Grant Number: 50671022), PRC. The Lujan Neutron Scattering Center at LANSCE is funded by the Department of Energy’s Office of Basic Energy Science. The Los Alamos National Laboratory is operated by the Los Alamos National Security LLC under the DOE Contract DE-AC52-06NA25396.
9:00 PM - D3.5
In-Situ Neutron Diffraction Study of Gas Tungsten Arc Welding of a 1018 Plain Carbon Steel.
M. Gharghouri 1 , D. Dye 2 , M. Watson 1 , I. Moner 1 , K. Conlon 3
1 Canadian Neutron Beam Centre, National Research Council Canada, Chalk River, Ontario, Canada, 2 Department of Materials, Imperial College London, London United Kingdom, 3 Fuel Development Branch, Atomic Energy of Canada Ltd., Chalk River, Ontario, Canada
Show AbstractWelding is the dominant method of joining in manufacturing. Gas Tungsten Arc Welding (GTAW) uses a tungsten electrode in combination with an inert-gas shroud to protect the material from oxidation. GTAW produces high-quality welds and is applicable to most metals. The rapid heating and cooling cycles that occur in fusion welding result in stress and temperature distributions, and metallurgical changes, that must be understood in order to validate and improve models of welding. Neutron diffraction has been used extensively to characterize the residual stress field and volume fractions of the phases present in and around welds. These measurements are useful for predicting failure, or to determine the effectiveness of an annealing treatment, but do not provide information on the distributions of phases, temperatures, and stresses that occur during welding. In-situ neutron diffraction studies of dynamic processes such as welding require that a quasi-steady state be established to allow data collection under constant conditions for a finite time. An instrument for in-situ studies of GTAW was designed at the Canadian Neutron Beam Centre. A tubular specimen is rotated and translated past a stationary welding torch such that the beam samples material at a fixed position relative to the torch. The tubular geometry allows long spiral welds without the need for excessive linear travel, thereby affording sufficient time for data collection. Stress, temperature, and phase maps can are obtained by moving the sampling volume relative to the torch. The conditions established show exceptional reproducibility, allowing diffraction peak data to be collected in the hoop, radial, and axial directions for identical conditions in separate experiments. In this work, the stress, phase, and temperature fields around a weld in a 1018 plain carbon steel were measured. This material was chosen because it is well-understood and available in seam-welded tubular form (data collection was suspended while the GTAW weld crossed the seam weld). The wall thickness of the tubes was such that no filler was required. Maps of lattice spacing as a function of location around the torch are a convolution of the effects of temperature and thermal stress. Close to the torch, strong gradients are observed, which drop off with distance, and essentially disappear 30 mm from the torch. Peak intensity varies proportionately with the volume of material correctly oriented for Bragg diffraction, and is thus a measure of the volume fraction of the corresponding phase in the sampling volume. Data collected for several ferrite and austenite reflections, show that high-temperature δ-ferrite is the dominant solid phase close to the torch. The δ-ferrite gives way to γ-austenite with increasing distance from the torch, reaching a minimum at about 15 mm ahead of or behind the torch. Beyond this distance, the austenite in turn gives way to low-temperature α-ferrite, and cementite.
9:00 PM - D3.6
Effect of Phase Transformation on the Tensile Behavior in Transformation-Induced Plasticity (TRIP) Steels Studied by Neutron and Synchrotron X-ray Diffraction
Sheng Cheng 1 2 , Xun-Li Wang 2 , Hahn Choo 1 3 , Yandong Wang 1 , Zhili Feng 3 , Bjorn Clausen 4 , Jon Almer 5 , Peter Liaw 1
1 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 5 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show Abstract9:00 PM - D3.9
Resonant X-ray Studies of the Atomic Structure of Pd-Ni-P Bulk Metallic Glasses at the Palladium and Nickel K Absorption Edges.
Stephan Hruszkewycz 1 , Todd Hufnagel 1 , Sean Brennan 2
1 , Johns Hopkins Univeristy, Baltimore, Maryland, United States, 2 , Stanford Synchrotron Radiation Laboratory, Menlo Park, California, United States
Show AbstractComplete determination of the structure of amorphous materials is challenging because any one experimental technique provides only limited information. Our work focuses on using several different techniques to generate complementary data sets, which can be used as constraints on computer-generated models of the structure. For example, we are using resonant x-ray scattering, fluctuation electron microscopy, and neutron scattering data as simultaneous constraints on Reverse Monte Carlo models of the structure of Pd-Ni-P bulk metallic glasses.In this talk, we compare results from resonant x-ray experiments done at the palladium and nickel of Pd-Ni-P samples processed in different ways. Because the differences in structure are small, high quality data are essential. To collect near-edge elastic scattering data, a focusing graphite analyzer crystal was used together with a one dimensional position sensitive detector. This provides an energy resolution of 0.5% at the Pd K edge and 0.2% at the Ni K edge, sufficient to discriminate the elastic scattering from the various inelastic contributions. We obtained a full set of Pd- and Ni-edge differential structure factors for annealed, as cast, and homogeneously deformed specimens. We observe the largest difference in structure when comparing samples prepared with different cooling rates; more slowly-cooled samples display greater structural order in the first- and second-nearest neighbor atomic shells. Although structural relaxation increases the structural order in all cases, differences in structure between specimens cast at different cooling rates persist.We have also used the Pd- and Ni-edge differential structure factors as input to Reverse Monte Carlo simulations of the structure of these alloys. The species-specific nature of the resonant scattering data provide more stringent constraints on the resulting atomic models than traditional, non-species-specific (single energy) scattering data. The results of these investigations, together with fluctuation electron microscopy simulations of the atomic models, will also be discussed
Symposium Organizers
Carol Thompson Northern Illinois University
Hermann A. Duerr BESSY GmbH
Michael F. Toney Stanford Synchrotron Radiation Laboratory
Do Young Noh Gwangju Institute of Science and Technology
D4: Transitions II
Session Chairs
Tuesday AM, November 27, 2007
Liberty (Sheraton)
9:30 AM - **D4.1
Magnetism at Interfaces in Spintronics Thin Film Systems.
Claus Schneider 1 , Martina Mueller 1 , Frank Matthes 1 , Ingo Krug 1 , F. Hillebrecht 1
1 Institute of Solid State Research IFF-9, Research Center Jülich, Juelich Germany
Show AbstractDevice structures employed in spintronics are often composed of complex magnetic layer stacks. The magnetic and magnetotransport properties of these systems are often determined by the interfaces between the layers rather than the characteristics of the individual layer. Magnetic coupling phenomena and spin-dependent transport processes are sensitively affected by the magnetic nanostructure and atomic arrangement at the interfaces. In order to shed light on the interface magnetism we have studied two model systems for spintronic applications: MgO/Fe(001) and NiO/Fe3O4(011).The Fe/MgO system is well known for its high tunneling magnetoresistance effects [1,2], presumably caused by coherent tunneling through matched electronic states. Using spin-polarized photoemission spectroscopy, we have studied the spin-split electronic states in epitaxial Fe(001) and Co(001) layers upon deposition of ultrathin MgO films of variable stoichiometry [3]. Whereas for stoichiometric MgO overlayers the Fe spin polarization remains unchanged, overoxidation of the Mg leads to a clear reduction of the Fe spin polarization. This is caused by the formation of interfacial FeO resulting in clear spectral fingerprints in the oxygen-related electronic states. An oxygen deficiency in the MgO layer, however, causes a significant increase of the Fe spin polarization, which may be explained through the electronic interaction with O vacancies. Similar results are obtained for Co/MgO interfaces.The interface between antiferromagnets (AF) and ferromagnets (FM) gives rise to the phenomenon of exchange bias, which is often used to define a magnetic reference in magnetic layer structures. We have chosen the combination NiO (AF) and Fe3O4 (FM) which represents an interesting model system. Oxidic interfaces promise higher structural and magnetic quality than metallic ones. Moreover, NiO/Fe3O4 can be grown epitaxially with an almost perfect lattic match. In our studies we addressed the magnetic coupling of ultrathin NiO overlayers on Fe3O4 single crystal surfaces by means of soft x-ray photoemission microscopy. By exploiting circular (XMCD) and linear (XMLD) magnetodichroic contrast mechanisms, we find clear evidence for a spin-flip coupling between AF and FM along the (011) direction, which may be mediated through the superexchange interaction across the interface. In addition, we observe a proximity effect on the NiO-side of the interface, leading to a sizable ferromagnetic response of the interfacial NiO layer. Further studies addressed the coupling behavior along the (111) and (001) axes, which exhibit distinctly different properties.References: [1] S. Yuasa et al., Nat. Mat. 3, 868 (2004); [2] S. S. P. Parkin, et al., Nat. Mat. 3, 862 (2004); M. Müller et al., J. Appl. Phys. 101, 09G519 (2007).
10:00 AM - D4.2
Magnetic Structures and Magneto-volume Effects in Mn3Cu1-xGexN.
Satoshi Iikubo 1 , Katsuaki Kodama 1 , Koshi Takenaka 2 3 4 , Hidanori Takagi 2 3 , Shinichi Shamoto 1
1 Quantum BeamScience Directorate, Japan Atomic Energy Agency, Naka, Ibaraki, Japan, 2 The Institute of Physical and Chemical Research, RIKEN, Wako, Saitama, Japan, 3 , Japan Science and Technology Agency, Kawaguchi, Saitama, Japan, 4 engineering, Nagoya university, Nagoya, Aichi, Japan
Show AbstractThe giant negative thermal expansion (NTE) up to α ~ 2 ×10-5 /K in the temperature range of 270 < T < 350 K (α is coefficient of linear thermal expansion) was reported by Takenaka and Takagi[1] in Mn3Cu0.5Ge0.5N. The amplitude of this system is one of the largest ones in all NTE materials, which have already been used in a wide area of technical application. The NTE caused by Magneto-Volume Effect (MVE) appears above x>0.15 and is broadened against T by further Ge-doping. The mechanism of MVE is a basic problem closely connected to the emergence of the magnetism in the itinerant electron system. Therefore it is expected to understand the microscopic mechanism of the MVE in this system for both basic and application studies. Neutron powder diffraction measurements have been carried out to study magnetic properties of Mn3Cu1-xGexN.For x=0, where the MVE is negligibly small, the observed peaks can be explained by tetragonal crystal structure and complex-type ferromagnetic structure. Above x=0.15, the present study revealed that magnetic structure change to Γ5g anti-ferromagnetic structure in cubic crystal structure. Magnetic reflections exhibit sharp increases at x~0.15 with decreaseing T and they gradually increase at x=0.5 with decreasing T in the temperature range from 360 to 320 K. The MVE of this system and the ordered Γ5g anti-ferromagnetic moment shows similar T-dependences. In the conventional theoritical works, the MVE follows the just amplitude of magnetic moment. This result strongly suggests that magnetic structure is a key ingredient for large magneto-volume effect in this itinerant electron system. This non-collinear Γ5g anti-ferromagnetic magnetic sturucture is formed due to the anti-ferromagnetic interaction between nearest neighbor Mn moments in the corner-shared octahedra of the anti-perovskite structure, so-called geometrical flustration lattice. The large magneto-volume effect is possibly ascribed to the geometrical frustration. This experimental result proposes the necessity of new theoretical framework on MVE which takes account of the ordered magnetic structure.[1] K. Takenaka and H. Takagi, Appl. Phys. Lett. 87, 26190 (2005).
10:15 AM - D4.3
Study of Phonons in Plutonium near the δ-to-α' Phase Transition by X-ray Thermal Diffuse Scattering.
Ruqing Xu 1 , Joe Wong 2 , Paul Zschack 3 , Hawoong Hong 1 , Tai Chiang 1
1 , University of Illinois, Urbana, Illinois, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe 5f electrons in Pu can be either bonding or localized, depending sensitively on the temperature, pressure, and impurity doping. As a result, pure Pu and doped Pu display a rich phase diagram with a large number of phases under modest temperature and pressure variations. In a recent study of the phonon dispersion relations of Ga-stablized δ-Pu at room temperature and ambient pressure, a pronounced deepening of the TA[111] phonon branch near the L point was reported. This phonon softening was suggested to be related to a lattice shearing mechanism that could lead to the structural phase transition from the fcc δ phase to the monoclinic α' phase at about 170 K. Here we report a measurement of x-ray thermal diffuse scattering from a δ-Pu crystal (with 0.6 wt% Ga) at temperatures from 307 K to 200 K. The results show little change of the phone frequency near the L point. The implications regarding the relationship between the soft mode and the phase transition will be discussed.
10:30 AM - D4: Trans2
BREAK
11:00 AM - **D4.4
Re-entrant Vitrification: Becoming a Glass on Cooling and on Heating.
Xinhui Lu 1 , Simon Mochrie 1 2 , Suresh Narayanan 3 , Alec Sandy 3 , Michael Sprung 3
1 Department of Physics, Yale University, New Haven, Connecticut, United States, 2 Department of Applied Physics, Yale University, New Haven, Connecticut, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractUnderstanding the glass transition remains a grand challenge for condensed matter science with applications in such diverse areas as protein folding, food science, and the flow of granular materials. Especially remarkable then are recent predictions that, in systems with short-ranged attractions, a dense liquid may become a glass on cooling and on heating. At high temperatures, the attractions play no role and, at high densities, a repulsion-dominated glass is realized, familiar from systems with hard-sphere-type interactions. However, as the temperature is decreased, surprisingly attractions cause the glass to melt. On further cooling, the resultant liquid re-vitrifies into an attraction-dominated glass. The intermediate liquid is itself highly unusual in that its density fluctuations are predicted to relax logarithmically in time. By exploiting fluid-mediated attractions between silica particles in a near-critical water-lutidine binary mixture to control the attraction strength, and multispeckle x-ray photon correlation spectroscopy (multispeckle XPCS) to characterize the collective dynamics, we show that re-entrant glassy behavior and logarithmic relaxations are realized in this model system, simply by changing temperature. We are thus able to present in detail how the non-ergodicity of the repulsive glass decreases upon attraction-driven melting, and how relaxations in the intermediate fluid arrest as the attactive glass phase is approached. (This work is supported by NSF DMR-0453856.)
11:30 AM - D4.5
Control of Chain Entanglement Distribution of Polymer Melt by Cyclic Deformation.
Masaki Kakiage 1 2 , Syozo Murakami 3 , Takeshi Yamanobe 1 , Hiroki Uehara 1
1 Department of Chemistry and Chemical Biology, Gunma University, Kiryu, Gunma, Japan, 2 , Research Fellow of the Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo, Japan, 3 , Heian Jogakuin University, Takatsuki, Osaka, Japan
Show AbstractPure semicrystalline polymer materials, including the simplest polymer of polyethylene (PE), alone formed the nanometer-sized phase separation composed by crystalline and amorphous components. We thought that novel nanoarranged materials could be created by this self-assembly ability. Our previous report revealed that the nanoperiodic structure consisting of lozenge crystalline blocks and amorphous meshes was observed across whole region of the ultra-high molecular weight PE (UHMW-PE) sample drawn under specific conditions. Here, block copolymer, which is a typical self-assembly material, exhibits several types of microphase separations due to “linking points” between both segments. This logic predicts that “molecular entanglements” for UHMW-PE act as the “linking points” for block copolymer, regarding the formation of corresponding nanoperiodic structures.Considering that the segment with entanglements is included within an amorphous phase, the entanglements can be successfully arranged at the branch points for a linear low-density PE (LLDPE), that the amorphous phase is enhanced in comparison with the usual PE with no branch. Furthermore, for a metallocene-catalyzed one, it can be said that these branch points exist homogeneously. It is expected that homogeneous entanglement distribution is enabled by activated molecular motion, induced by orientation/relaxation in a molten state. Here, we previously clarified that entanglement phase separation occurred during melt-drawing of UHMW-PE. Therefore, in this study, phase development during such cyclic deformation in the molten state for the metallocene-catalyzed UHMW-LLDPE was analyzed by in-situ small-angle X-ray scattering (SAXS) measurement using a synchrotron radiation.Stress profile recorded during cyclic deformation in the molten state (150 oC) exhibited the decrease of the average stress at the initial stage and finally achieved at a constant level. This indicates that the entanglement distribution is saturated by cyclic deformation at this later stage. The concentrated scattering on the meridian attributed to lamellar crystals was recognized in the SAXS pattern of the sample after cyclic deformation, followed by slow cooling to room temperature. This result indicates that the arranged lamellar structure with its normal parallel to the deformation direction is formed for the sample after cyclic deformation. However, no streak was observed on the equator, meaning that extended-chain crystals were not formed. These results demonstrate that the homogeneous entanglement distribution is possibly achieved by cyclic deformation in the molten state and resultant lamellar structure reflects such prior entanglement distribution. This knowledge suggests that the control of nanoperiodic structure for polymeric materials is enabled by the processing with space-time conversion deformation, focusing on the molecular entanglement network. This work was partly supported by NEDO of Japan (ID: 04A37008).
11:45 AM - D4.6
The Dynamics of a Copolymer in a Homopolymer Matrix using Neutron Reflectivity.
Mark Dadmun 1 2 , Sudesh Kamath 1
1 Chemistry Dept., University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe effect of copolymer composition on their dynamics in a homopolymer matrix has been studied using neutron reflectivity (NR). The mutual and tracer diffusion coefficients, the effective friction coefficients, and the relaxation times for these copolymers were determined. The results demonstrate that copolymer composition has a significant impact on their dynamics. Analysis of the friction factor using the Lodge-Mcleish model indicates that the local composition around a copolymer is richer in styrene than the model predictions. We attribute this to the fact that the model uses only chain-connectivity to calculate the self-concentration and ignores contributions due to thermodynamic interactions between the two blend components. Our data indicate that the local environment around a copolymer is richer in styrene, which is in agreement with our simulation results and indicates that the styrene monomers in the copolymer aggregate together to minimize contact with the PMMA matrix.
12:00 PM - D4.7
Dynamics of Polymer-Polymer Dewetting in Thin Bilayer Films.
Dennis Liang 1 , Jyotsana Lal 1 , Larry Lurio 3 2 , Mrinmay Mukhopadhyay 4 2
1 Intense Pulsed Neutron Source, Argonne National Lab, Argonne, Illinois, United States, 3 Physics, Northern Illinois University, DeKalb, Illinois, United States, 2 Advance Photon Source, Argonne National Lab, Argonne, Illinois, United States, 4 Physics, University of California, San Diego, San Diego, California, United States
Show AbstractWe present an x-ray photon correlation spectroscopy (XPCS) study of polymer-polymer dewetting in thin bilayer films. XPCS at grazing incidence has been empolyed successfully to probe capillary wave dynamics in polymer thin films. We further utilized this technique to monitor the early stages of liquid-liquid dewetting by measuring dynamics at the top and buried interfaces of bilayer polymer thin films. Preliminary results, both from the XPCS data and from surface images obtained through atomic force microscopy, strongly indicate that the dewetting process depends not only on the thin film thicknesse but also the viscosity of the bottom polymer layer. The dewetting process crosses over from hole-nucleation to spinodal dewetting as viscosity of the bottom layer is increased. Furthermore, the dynamical information of polymer dewetting, obtained from two-time autocorrelation analysis of XPCS study, shows non-diffusive behavior. These results will be discussed in further detail.
12:15 PM - D4.8
SAXS and GISAXS of Side Chain Liquid Crystalline Block Copolymers: In-situ Studies of the Self-assembly Behavior and Effects of LC Anchoring and LC Content.
Eric Verploegen 1 , Tejia Zhang 2 , Paula Hammond 3
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe bulk and thin film self-assembled morphologies of siloxane based side chain liquid crystalline block copolymers (SCLCBCP) are investigated using small angle X-ray scattering (SAXS) and grazing incidence small angle X-ray scattering (GISAXS), respectively. The synthetic methods used allow for systematic variations of the liquid crystal (LC) content in the block copolymer. The effects of the variation in LC content upon the self-assembly behavior is detailed. The anchoring of the smectic LC mesophase to the inter-material dividing surface (IMDS) was found to have significant effects on the orientation of the morphology in response to mechanical deformation. In-situ SAXS experiments were performed allowing for direct observation of the evolution of the morphology during oscillatory shear. Additionally, GISAXS enabled the study of the effects of thermal annealing upon the self-assembly of SCLCBCP thin films with respect to the substrate. It was found that the orientation of the as-cast morphology is determined by the response of the LC mesophase to the shear flow from the spin casting process. After thermal annealing the morphology reorients in order to minimize the surface energy and achieve the equilibrium conformation of the system.
D5: Growth and Crystallization
Session Chairs
Tuesday PM, November 27, 2007
Liberty (Sheraton)
2:30 PM - **D5.1
Transitions in Selected Selfassembled Nanostructured Soft Materials.
Jon Fossum 1
1 Department of Physics, Norwegian University of Science and Technology - NTNU, Trondheim Norway
Show AbstractIn the general context of selfassembly of nanoparticles, and transitions in such structures, we study interconnected universal complex physical phenomena such as:(i) Spontaneous gravitationally induced phase separation and nematic self-assembly in systems of anisotropic nanoparticles in aqueous suspension, including studies of isotropic to nematic transitions [1,2].(ii) Transitions from biaxial to uniaxial nematics by application of external magnetic field to selfassembled systems of the same anisotropic (diamagnetic) nanoparticle systems [3].(iii) Guided self-assembly into chainlike structures of the same anisotropic nanoparticles in oil suspension when subjected to external electrical fields (electrorheological structures of polarized nanoparticles), and the stability of, and transitions of, such structures, when subjected to external mechanical stress [4,5].The model particles we have been studying are clay platelet nanoparticles, and the experimental techniques include synchrotron X-ray scattering, neutron scattering, rheometry. microscopy and magnetic resonance. We have demonstrated that clays may be used as good model systems for studies of universal physical phenomena and transitions in selfassembled nanostructured soft and complex matter. Self-assembly and related transitions in clay systems in particular, may have practical relevance for nano-patterning, properties of nanocomposites, and macroscopically anisotropic gels, among many other applications [6]Acknowledgments: Collaborators, postdocs and students at NTNU, UiO, IFE, BNL, LNLS, UFPE, UnB, GIST/PLS, Univ.Paris 7 and other places. This research has been supported by the Research Council of Norway (RCN), through the NANOMAT, SUP and FRINAT Programs.References [1] J.O. Fossum, E. Gudding, D.d.M. Fonseca, Y. Meheust, E. DiMasi, T. Gog, C. Venkataraman, Observations of orientational ordering in aqueous suspensions of a nano-layered silicate, ENERGY The International Journal, 30, 873 (2005)[2] D.d.M. Fonseca, Y. Méheust, J.O. Fossum, K.D. Knudsen, K.J. Måløy, K.P.S. Parmar, Phase behavior of platelet-shaped nanosilicate colloids in saline solutions: A small-angle X-ray scattering study, J. Appl. Cryst. 40, 292 (2007)[3] E.N. de Azevedo, M. Engelsberg, J.O. Fossum, R. E. de Souza, Anisotropic water diffusion in nematic self-assemblies of clay nano-platelets suspended in water, Langmuir 23, 5100 (2007)[4] J.O. Fossum, Y. Meheust, K.P.S. Parmar, K.D. Knudsen, K.J. Måløy, D.d.M. Fonseca, Intercalation-enhanced electric polarization and chain formation of nano-layered particles, Europhys. Lett., 74, 438 (2006), and in the Scientific Highlights 2006 of the European Synchrotron Radiation Facility - ESRF (2007)[5] K.P.S. Parmar, B. Schelderupsen, Y. Meheust, J.O. Fossum, Electrorheological suspensions of laponite in oil: rheometry studies under steady shear, submitted to Langmuir (2007) [6] F. Bergaya, B.K.G. Theng, G. Lagaly, editors. Handbook of Clay Science, Elsevier (2006)
3:00 PM - D5.2
In-situ GISAXS on Nanocomposite Films of CdS Nanoparticles and Polymers.
Tiziana Di Luccio 1 , Dina Carbone 2
1 FIM-MATNANO, ENEA, Portici Italy, 2 , European Synchrotron Radiation Facility ESRF, Grenoble France
Show AbstractWe study CdS nanoparticle/polymer nanocomposites for organic electronics and sensor applications. Organic based devices can benefit from the tunable color luminescence of the inorganic nanoparticles and their performance and lifetime can be ultimately improved by a homogeneous dispersion of the particles in the organic material.The growth of CdS nanoparticles in polymer films was investigated by means of in-situ x-ray scattering experiments performed at the ESRF (beamline ID01) and HASYLAB (beamline W1) synchrotron radiation facilities. The nanoparticles were synthesized by thermal decomposition of a Cd thiolate precursor dispersed in a polymer. A cyclic olefin copolymer was used as a matrix for its low autoflorescence and low water absorption. Two kinds of samples were prepared from a precursor/polymer solution: (a) a bulk polymer foil obtained by spin casting the solution is first annealed, then redissolved and spin coated; (b) the solution is spin coated and successively annealed.X-ray reflectivity on the films of kind (a) shows thickness fringes corresponding to a thickness of about 260Å. Such a value is comparable with the thickness of the polymer film without nanoparticles. Correspondingly, grazing incidence diffraction (GID) reveals the Bragg reflections of the CdS nanoparticles.The in-situ experiments were performed on the samples of kind (b). They consisted of wide angle diffraction and grazing incidence small angle scattering (GISAXS) measurements recorded during the thermal treatment of the precursor/polymer films from room temperature up to 250°C. At room temperature the diffraction curves show that the initial precursor structure is characterized by regular spaced peaks due to the lamellae phase of the Cd thiolate molecules. All the precursor peaks disappear as the annealing temperature reaches 100°C. The GISAXS data show a peak at room temperature at a momentum transfer value q ~ 0.2Å-1. This peak becomes less intense and shifts to lower q-values as the temperature is increased. Such effect is related to the precursor decomposition and the growth of the nanoparticles. Under UV excitation the films show photoluminescence in the range 400 – 600 nm, depending on the annealing temperature. The nanoparticle growth mechanism and their structural properties are discussed on the basis of the x-ray and optical data.
3:15 PM - D5.3
Grazing-Incidence Small-Angle X-Ray Scattering Studies of Nanoparticle Self-Assembly.
Darren Dunphy 1 , Carlee Ashley 1 , Hongyou Fan 2 , David Peabody 1 , Michael Sprung 3 , Jin Wang 3 , C. Brinker 2 1
1 , University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Labs, Albuquerque, New Mexico, United States, 3 , Advanced Photon Source/Argonne National Labs, Argonne, Illinois, United States
Show AbstractThe organization of nanoscale building blocks of both synthetic and biological origin into thin films with well-defined long-range order through self-assembly has been touted as a powerful route to materials with new or improved electrical, optical, and magnetic properties. Optimization of film structure, as well as design of assembly pathways to new (i.e. non-close packed) lattice types, requires a thorough understanding of the physics, chemistry, and material science of the self-assembly process. To this end, we report here on our use of Grazing Incidence Small Angle Scattering (GISAXS) coupled with 2D CCD detection, performed at the Advanced Photon Source, to follow the real-time development of structure in model systems of nanoparticle self-assembly (2D monolayer films of 28 nm viral particles with perfect monodispersity, and 3D 3 nm gold nanocrystal/silica composite films) with high sensitivity and rapid frame rate (< 10 seconds). In the viral particle system, highly ordered hexagonally close-packed monolayers were observed during film deposition by a convective assembly technique. Comparison of data obtained with two different types of viral particle, as well as under different coating conditions, shows the promise of GISAXS studies in understanding how particle-particle and particle-substrate interactions control film order and structure. For the second system, hydrophilic gold nanoparticles co-assembled with a silica matrix, we obtain distorted face-centered cubic particle packing; observation of a transient ordered phase during particle assembly without silica demonstrates that long-range particle-particle interactions are largely responsible for film structuring. In addition to summarizing our results on these two particle assembly processes, we will describe our continuing efforts to extend GISAXS studies to particle assembly inside external fields (both magnetic and electric).
3:45 PM - D5.5
Nano-engineering by MeV Ion Beams.
Yogendra Mishra 1
1 Materials Science , Inter University Accelerator Centre, New Delhi, Delhi, India
Show AbstractThin silica films embedded with Au nanoparticles were prepared by atom beam co-sputtering and RF-magnetron sputtering. The growth kinetics of Au nanoparticles in atom beam co-sputtered film, under 90 MeV Ni ion irradiation, was studied by in-situ X ray diffraction experiment in the materials science beam line at IUAC, New Delhi. The growth of nanoparticles from 4 nm (for pristine) to 9 nm at a fluence of 1x 1014 ions/cm2 was observed [1] with rapid growth upto the size track diameter, however slowed beyond it. 120 MeV Au ion irradiation of RF magnetron sputtered films resulted the elongation of Au nanoparticles along ion beam direction. The aspect ratio of elongated nanoparticles (Au nanorods) is found to be ~ 3.5, which mainly depends on the electronic energy deposited within the system. Hence the present work reports that the ion irradiation is an effective tool for tailoring the size, shape and size distribution of nanoparticles. The results are discussed in the framework of thermal spike model.[1] Y. K. Mishra et al. Appl. Phys. Lett. 90 (2007) 73110.
4:00 PM - D5: Growth
BREAK
4:30 PM - **D5.6
Mineralization at Organic Templates - Mechanisms Illuminated by In-situ X-ray Scattering.
Elaine DiMasi 1
1 National Synchrotron Light Source Dept., Brookhaven National Laboratory, Upton, New York, United States
Show AbstractBiomineralization is the process by which living organisms create hierarchically structured mineral-organic composite materials. Biominerals inspire research to understand and create new composite materials for technology and medicine. For this reason, mineralization of organic templates has been pursued ardently for 20+ years, with particular attention to the possibility that structural relationships may exist between mineral crystal faces and organized organic assemblies. Studies have ranged from examination of the organic components of mollusk shells to the development of surfactants which self-assemble into monolayers with tunable properties. X-ray diffraction measurements have always played a role in determining bulk mineral polytype and orientation. However, more recently, in-situ scattering studies have given us the ability to probe monolayer interfaces, detect amorphous phases, and make time resolved measurements. It has also become possible to determine the subtle structural changes that take place in the organization of organic phases in the presence of cations and during mineral growth. In this talk, calcium carbonate mineralization at organic templates generally, and at self-assembled monolayers specifically, will be reviewed. We will present examples of different types of templating mechanisms which have been probed. In more detail we will present recent results on bis-urea based surfactants designed to assemble into monolayers with increasing degrees of structural adaptability. In-situ x-ray scattering from these monolayers shows that they are unique in their ability to form both 1D and 2D order, based on choice of headgroup, and sensitive to the presence of Calcium cations in the subphase. We will argue that structural adaptability of an organic template is a key tool to be exploited in the design of synthetic organic scaffolds for mineralization, and discuss possible relationships to tissue engineering applications.
5:00 PM - **D5.7
Structure of the Iron-oxide Aqueous Solution Interface via Surface X-ray Scattering and Density Functional Theory.
Tom Trainor 1 , Kunaljeet Tanwar 1 , Sarah Petitto 1 , Sanjit Ghose 2 , Cynthia Lo 3 1 , Peter Eng 2 , Anne Chaka 3
1 Chemistry, University of Alaska Fairbanks, Fairbanks, Alaska, United States, 2 CARS, University of Chicago, Chicago, Illinois, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractChemical processes occurring at the mineral-water interface play a particularly important role in dictating the geochemistry of natural waters. Despite the importance of these systems a detailed understanding of the molecular scale factors that control interface reactivity is lacking, due in large part to the difficulty in studying heterogeneous systems under realistic environmental conditions. Synchrotron based surface x-ray scattering provides a unique approach for developing an accurate model of mineral-water interface structure, and understanding structural modifications that result from changes in (bio)geochemical conditions. Such models are critical to furthering the development of a structure based understanding of environmental interface systems and improving both conceptual and quantitative models of environmental chemical pathways. We will present an overview of our recent work focused on determining the structure of low index faces of common iron-(hydr)oxide phases (hematite, goethite and magnetite) utilizing synchrotron based surface x-ray diffraction. Iron-oxides are of particular interest due to their widespread occurrence, typically high specific surface area, and high surface reactivity, making them important scavengers of aqueous trace metals, and substrates that support the heterogeneous transformation of aqueous contaminants. Specifically, we will focus on the changes in surface structure associated with variations in common geochemical variables, including: (i) the influence of water on the resulting surface structures, (ii) the surface modification of hematite due to reaction with aqueous Fe(II), and (iii) the resulting changes in surface reactivity with respect to aqueous Pb(II) adsorption. The experimental models will be compared with the results of periodic density functional theory and ab initio thermodynamic calculations to provide a detailed interpretation of the energetics of the systems under investigation.
5:30 PM - D5.8
In situ Investigation of Solid/liquid Interfaces with Multilayer-generated X-ray Standing Waves.
D. Novikov 1 , J. Daillant 2 , L. Girard 2 , P. Guenoun 2 , R. v. Klitzing 3 , H. Schollmeyer 4
1 Hamburger Synchrotronstrahlungslabor HASYLAB, Deutsches Elektronen-Synchrotron DESY, Hamburg Germany, 2 Service de Chimie Moléculaire/LIONS, CEA Saclay bât. 125, Gif-sur-Yvette France, 3 Stranski-Laboratorium für Physikalische und Technische Chemie, Technische Universität Berlin, Berlin Germany, 4 Insitute for X-Ray Physics, Georg-August-University Goettingen, Goettingen Germany
Show AbstractWe present a first in situ investigation of ion absorption processes on free and polymer-coated solid/liquid interfaces with a novel multilayer-based x-ray standing waves method.X-ray standing waves (XSW) is a well established method used for probing of atomic structure in bulk crystals and at interfaces[1,2]. Recently, a new approach using standing wave formed by Bragg reflection on periodic multilayers (ML) has been successfully used for studies of atomic and magnetic structures at internal interfaces [ 3,4]. In our work, we have used the x-ray standing wave formed above the surface of a multilayer to investigate ion concentration profiles in aqueous solutions on solid-liquid and solid/polymer/liquid interfaces. In particular, the chosen standing wave period of 30 nm allowed us to probe the diffuse Gouy-Chapman layer and compare the effects of Cl- and I- anions and mono-, di- and trivalent cations over a silicon surface. Besides, we studied the effects of bromide ion ab- and desorption in PPS/PAH system [5]. The measurement were carried out at BW1 undulater beamline at HASYLAB, Germany. The novel approach to in situ XSW investigation allows to tailor the period and phase of the x-ray standing waves according to the properties of the transition layers above the ML surface, both normal to the surface and in a lateral direction. It is also possible to choose freely the material of the top-most layer of the solid substrate. In contrast to the traditional techniques, the probed distance can be varied in a range from several nanometers to several tens of nanometers, and the wavelength of the radiation can be matched to the absorption edges of the materials under investigation. The direct control of the generated wavefields through incident beam parameters allows for fast time-resolved studies and pump-probe mode experiments. In the presentation, we shall also discuss the wide possibilities that the method of multilayer-generated XSW opens for research under ambient conditions, i.a. in wet and gas reaction cells. [1] J. Zegenhagen, Surf. Sci. Rep. 18, 202 (1993)[2] M. Bedzyk, D. Bilderback, G. Bommarito, M. Caffrey, and J. Schildkraut,Science. 241, 1788 (1988)[3] See-Hun Yang et al J. Phys.: Condens. Matter 14, L407 (2002)[4] S. Bera, K. Bhattacharjee,G. Kuri, B. N. Dev PRL 98, 196103 (2007)[5] H.Schollmeyer, P.Guenoun, J.Daillant, D.V.Novikov, R.Klitzing J. Phys. Chem. B 111, 4036 (2007)
5:45 PM - D5.9
Utilizing X-Ray Scattering to Monitor the Competitive Adsorption of Lung Surfactant and Serum Proteins at the Air-Liquid Interface.
Patrick Stenger 1 , Guohui Wu 1 , Eva Chi 2 , Shelli Frey 2 , Jaroslaw Majewshi 3 , Ka Yee Lee 2 , Joseph Zasadzinski 1
1 Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California, United States, 2 Department of Chemistry, University of Chicago, Chicago, Illinois, United States, 3 Manuel Lujan Jr. Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractUtilizing in situ grazing incidence x-ray diffraction (GIXD) and x-ray reflectivity (XR), we have examined the surface ordering of lung surfactant (LS) at the air-liquid interface, the competitive adsorption of albumin and the enhancement of LS adsorption by polyethylene glycol (PEG). Lung surfactant (LS) is a unique mixture of lipids and proteins that lines the alveoli and lowers the surface tension in the lungs, thereby insuring a negligible work of breathing. The adsorption of LS to the alveolar air-liquid interface is strongly inhibited by the competitive adsorption of surface active serum proteins such as albumin, and is likely the explanation of LS inactivation in Acute Respiratory Distress Syndrome (ARDS). In vitro, the adsorption of LS to the interface is restored by the addition of hydrophilic non-adsorbing polymers such as polyethylene glycol (PEG) suggesting a promising therapy for ARDS. XR measurements confirm that albumin imposes a steric barrier to LS adsorption, inhibiting the LS characteristic GIXD peaks. In the LS free system, scattering experiments show no evidence of PEG surface ordering while LS on a PEG subphase shows only a subtle lateral condensation of the LS. However, the addition of PEG to albumin inhibited LS restores the LS characteristic peaks though initially the interface is heterogeneous containing both albumin and LS regions. Progressive cycling shows the LS fully replacing the albumin on the interface, restoring the GIXD and XR signature of pure LS. The scattering results are consistent with recent work which proposed that albumin creates a physical barrier which eliminates surfactant adsorption and that PEG in not surface active and does not significantly change LS surface ordering. These results are also consistent with fluorescence images which progressively show penetration of LS into an albumin covered interface, coexistence of ~1000 μm albumin and LS regions and squeeze-out of the albumin until complete expulsion from the interface. The scattering data are consistent with a recently proposed mechanism for enhanced LS adsorption whereby a PEG induced depletion attraction between the LS aggregates and the interface is responsible for the restoration of LS adsorption to the interface even in the presence of albumin.
D6: Poster Session II: Materials in Transition
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - D6.1
In-situ X-ray Absorption Spectroscopy Studies of Vanadium Dioxide Thin Films across the Metal-insulator Phase Transition Boundary.
Dmitry Ruzmetov 1 , Sanjaya Senanayake 2 , Venkatesh Narayanamurti 1 , Shriram Ramanathan 1
1 SEAS, Harvard University, Cambridge, Massachusetts, United States, 2 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractVanadium oxide is a fascinating material that undergoes phase transition from insulator to metallic state followed by impressive changes in the electrical conductivity and optical reflectance. Understanding the origins of phase transitions and associated phenomena such as hysteresis are of great scientific and technological importance. In this paper, we report our recent results on electronic structure studies and electrical properties of crystalline VO2 films synthesized by RF-sputtering. In-situ temperature-dependent X-ray absorption (XAS) and photoemission (XPS) spectroscopy of the V 2p edges and O 1s edge was performed on VO2 thin films synthesized by RF sputtering at various conditions. Distinct changes of the electronic structure depending on the film quality, whether the sample is above or below the metal insulator transition (MIT) temperature, and thermal history of the sample are observed. The spacing between 3dπ and 3dσ band peaks probed by O- edge XAS decreases by 0.8eV with concurrent peak broadening for the sample sputtered at lower substrate temperature and consequently having more polycrystalline and disordered character. There is a similar tendency in the V 2p3/2 and 2p1/2 edges, i.e. the convergence of the doublets for the disordered sample. The temperature dependence of the XAS V and O edges including repeated crossing of the MIT has been studied. The reversible switches of the 3dπ and 3dσ band peak widths in the O-edge on different sides of the MIT are measured while the peak separation remains the same. The abruptness of the band structure transformation at MIT suggests that the band width changes are determined by the VO2 MIT phase rather than gradual evolution with temperature. The fine structure results are correlated to detailed electrical properties measured on microscale devices fabricated from identical samples. The sharpness of the metal-insulator transition, width and hysteresis are related to the synthesis conditions closely and tunable. Importance of the electronic structure studies will be emphasized with relevance to potential implications in advanced electronic devices incorporating functional oxide materials. The XAS experiments were performed at beamline U12a, NSLS, Brookhaven National Laboratory.
9:00 PM - D6.10
In situ and Real-time Study of Ga Adsorption/desorption Under Ultra-high Vacuum.
Nathalie Bouet 1 , Yiyi Wang 1 , Ahmet Ozcan 2 , Christopher Sanborn 1 , Eitan Anzenberg 1 , Karl Ludwig 1
1 Physics Department, Boston University, Boston, Massachusetts, United States, 2 Semiconductor Research and Development Center, IBM, Hopewell Junction, New York, United States
Show AbstractSupported nanoparticles are one of the most promising fields for the development of new devices in fields such catalysis, optics, magnetic data storage, optoelectronics... For all these applications, the control of the properties is strongly related to the size, distribution, morphology and crystalline structure of the nanoparticles on the surface of the substrate. For self-assembled nanoparticles, this control can be done thanks to a good understanding of the processes involved during the growth. In the case of GaN, plasma-assisted MBE (PA-MBE) allows one to grow high quality films as well as nanostructures [1,2]. Because PA-MBE is an atomic deposition process, the main step is the Ga deposition on the substrate's surface. However only a few in-situ studies are reported on the process of adsorption of Ga and subsequent growth on surfaces [3]. Our group has recently reported an adsorption/desorption study of Ga on c-sapphire under high flux of Ga [4]. In the work presented here, we performed in situ real-time grazing incidence small-angle scattering experiments (GISAXS) to study the adsorption/desorption of Ga on a-plane and c-plane oriented sapphire surfaces. The effect of substrate temperature has been investigated as well. For a given substrate, the temperature is the major key to control the sticking coefficent of the atoms arriving on the surface, the atomic and aggregates diffusion, the density of nanoparticles as well as of the atomic desorption. Overall, the results showed that the adsorption/desorption behavior is strongly influenced by both the nature of the substrate and the temperature. The exposure of the substrate to a low pressure vapor of Ga from an effusion cell was conducive to the formation of droplets for the two kinds of substrates. Nevertheless, adsorption behaviors are found to be very different for the two sapphire orientations. It appears that under similar deposition conditions the adsorption rate, growth processes or/and stages achieved are shifted in temperature.This work is partially supported by DOE DE-FG02-03ER46037[1] H. Sekiguchi, T. Nakazato, A. Kikuchi, K. Kishino, Journal of Crystal Growth 300 (1), pg. 259 (2007)[2] C. Adelmann, B. Daudin, R.A. Olivier, G. A. D. Briggs, R. E. Rudd, Physical Review B 70, pg. 125427 (2004)[3] G. Koblmuller, R. Averbeck, H. Riechert, and P. Pongratz, Physical Review B 69, pg. 035325 (2004)[4] A.S. Özcan, Y. Wang, G. Ozaydin, K.F. Ludwig, A. Bhattacharyya, T.D. Moustakas, P.D. Siddons, Journal of Applied Physics 100, pg. 084307 (2006)
9:00 PM - D6.3
Synchrotron X-ray Studies of Phase Structure of Blends of Isotactic with Atactic Polystyrene.
Huipeng Chen 1 , Hui Xu 1 , Peggy Cebe 1
1 Physics and Astronomy, Tufts University, Medford, Massachusetts, United States
Show AbstractBlends of isotactic polystyrene (iPS) with non-crystallizable atactic polystyrene (aPS) were studied by synchrotron small angle X-ray scattering and differential scanning calorimetry. The iPS/aPS blends, prepared by solution casting, were found to be miscible in the melt over the entire composition range. Both quenched amorphous and semicrystalline blends exhibit a single, composition dependent glass transition temperature, depressed from that of either homopolymer component. Addition of aPS causes a decrease in crystallinity and in the rigid amorphous fraction, and suppression of the reorganization or recrystallization of iPS during thermal scanning. X-ray scattering shows that the long period in the iPS/aPS blends is greater than in the iPS homopolymer, and long period increases slightly as aPS content increases. Comparison of the volume fraction of phase 1 with the volume fraction crystallinity from DSC suggests that more and more amorphous phase is rejected outside the lamellar stacks as aPS content increases. The effect of aPS addition is to reduce the confinement of the amorphous phase chains. The cooperativity length, which is calculated from thermal analysis of the Tg region, increases with aPS addition. The interlamellar and extra-lamellar amorphous chains both contribute to the glass transition relaxation process. (Research is supported by the National Science Foundation, Division of Materials Research, Polymers Program, through DMR-0602473.)
9:00 PM - D6.4
Structural Changes during Drawing of Ethylene-alt-Tetrafluoroethylene Copolymer Film as Analyzed by In-situ X-ray Diffraction Measurements.
Yasunori Ono 1 , Masaki Kakiage 1 , Takeshi Yamanobe 1 , Tadashi Komoto 1 , Yoshiaki Higuchi 2 , Hiroki Kamiya 2 , Kiyotaka Arai 3 , Syozo Murakami 4 , Hiroki Uehara 1
1 Department of Chemistry, Gunma University, Kiryu, Gunma, Japan, 2 R & D Division, Asahi Glass Company, Ichihara, Chiba, Japan, 3 Central Laboratory, Asahi Glass Company, Yokohama, Kanagawa, Japan, 4 , Heian jogakuin University, Takatuki, Osaka, Japan
Show Abstract9:00 PM - D6.5
Effect of Homopolymers on the Phase Behavior of Block Copolymer/ Inorganic Nanoparticle Complexes in a Selective Solvent.
Vilas Pol 1 , Chieh-Tsung Lo 2 , Byeongdu Lee 2 , Randall Winans 2 , Pappannan Thiyagarajan 1
1 Intense Pulsed Neutron Sourc, Argonne National Laboratory, Argonne, Illinois, United States, 2 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSolvent selectivity is an important parameter that determines the phase behavior of block copolymer solutions and hence its role has to be considered in solution-based synthetic routes for tailoring morphologies of nanocomposites. To control the dispersion and loading of nanoparticles in block copolymer nanocomposites, surface modified inorganic particles with compatible polymer as well as homopolymers are used. It is of great interest to learn about effect of homopolymers on the phase behavior of block copolymer/nanoparticle complexes in selective solvents as a function of composition and temperature. SANS studies have been carried out on the phase behavior of complexes of poly(styrene-b-2-vinylpyridine) (PS-PVP) and PS homopolymer with various MW in the range of 2-15k and those of PS-PVP and thiol-terminated PS stabilized Au nanoparticles as well as ternary complexes comprising PS-PVP, Au nanoparticles and PS homopolymer in toluene-d, a selective solvent for PS. Comparison of the phase behavior of the neat and Au-containing PS-PVP solutions as a function of temperature and concentration shows dramatic shifts in the order-disorder and order-order transition temperatures. These effects can be understood by a model wherein the added nanoparticles that sequester in the preferred PS domains increase the interfacial curvature, leading to the changes in the nanostructure of the complex. In the case of PS-PVP/20% PS homopolymer complexes we observe a monotonic increase in the domain size with PS molecular weight up to 10k, above which the domain size does not change. However, the complexes with homopolymers tend to be in disordered phase at all polymer concentrations and temperatures. Although the increase in domain size with different MW is expected due to their partitioning in the PS domain, the reduction in the degree of segregation is unexpected. The ternary complex of PS-PVP/20% Au/PS (2K), with various concentrations also shows disordered phases at lower complex concentration, but lamellar phases are seen at higher concentration. Interestingly, the domain size monotonically increases with increasing PS concentration and the ODT significantly increases with the addition of PS. Based on these results a comprehensive picture on the effects of the homopolymers on the phase behavior of PS-PVP/Au complexes will be presented. Acknowledgment: Work benefited from the support by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract DE-AC02-06CH11357.
9:00 PM - D6.6
Analytical Study on Initial Growth Stage of Metal Atomic Layer Deposition By Synchrotron Radiation X-Ray Reflectivity Analysis.
Han-Bo-Ram Lee 1 , Woo-Hee Kim 1 , Yong Jun Park 1 , Sunggi Baik 1 , Hyungjun Kim 1
1 Material Science and Engineering, POSTECH(Pohang University of Science and Technology), Pohang Korea (the Republic of)
Show AbstractMetal atomic layer deposition (ALD) has been attracted increasing interest in possible applications of both conventional and emerging device in nanoscale regime due to its excellent conformality and thickness controllability. Since the growth by ALD is strongly dependent on initial surface state and reaction, the understanding of initial growth stage of metal ALD is essential for various applications. In this study, the initial growth of two metal ALD systems, Ru and Co, was investigated by synchrotron radiation X-ray reflectivity (SR-XRR) analysis. Ru and Co were deposited by thermal and plasma-enhanced ALD, the initial growths of each other were comparatively studied. Together with SR-XRR results, ALD metal films early deposited were analyzed by atomic force microscope. The results showed that the nucleation of ALD metal affected film growing which was strongly related initial surface reaction.
9:00 PM - D6.7
Ga Droplet Mediated Surface Ordering of GaP(111)B - Structure and Dynamics.
Emelie Hilner 1 , Alexei Zakharov 2 , Lisa Klanner 1 , Edvin Lundgren 1 , Jesper Andersen 1 , Anders Mikkelsen 1
1 Synchrotron Radiation Research, University of Lund, Lund Sweden, 2 MAX-lab, University of Lund, Lund Sweden
Show Abstract9:00 PM - D6.8
Interface Structure and Initial Microstructure of TaN Films, Deposited by Atomic Layer Deposition, Characterized by XRR and GISAXS Methods Using Synchrotron Radiation.
Yong Jun Park 1 2 , Dong Ryeol Lee 1 , Moon-Kyun Song 3 , Suk-Hoon Kim 3 , Shi-Woo Rhee 3 , Sunggi Baik 2
1 Beamline division, Pohang Accelerator Laboratory, Pohang Korea (the Republic of), 2 MSE, POSTECH, Pohang Korea (the Republic of), 3 Chem. Eng., POSTECH, Pohang Korea (the Republic of)
Show Abstract9:00 PM - D6.9
Time-resolved X-ray Studies of the Growth Mechanisms Operant During Pulsed Laser Deposition of SrTiO3.
Gokhan Arikan 1 2 , John Ferguson 1 3 , Darren Dale 4 , Arthur Woll 4 , Joel Brock 1 2
1 Cornell Center for Materials Research, Cornell University, Ithaca, New York, United States, 2 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 , Cornell High Energy Synchrotron Source, Ithaca, New York, United States
Show Abstract
Symposium Organizers
Carol Thompson Northern Illinois University
Hermann A. Duerr BESSY GmbH
Michael F. Toney Stanford Synchrotron Radiation Laboratory
Do Young Noh Gwangju Institute of Science and Technology
D7: Surfaces and Particles
Session Chairs
Wednesday AM, November 28, 2007
Liberty (Sheraton)
10:00 AM - D7.1
Real-time X-ray Scattering Studies of Surface Morphology Evolution during the Sputter Deposition of WSi2 Amorphous Films.
Lan Zhou 1 , Hua Zhou 1 , Randy Headrick 1 , Albert Macrander 2 , Nathalie Bouet 3 , Karl Ludwig 3
1 physics department, university of vermont, Burlington, Vermont, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 3 Physics Department, Boston University, Boston, Massachusetts, United States
Show Abstract10:15 AM - D7.2
Synchrotron-based in situ Diffuse Scattering Study of Strontium Titanate Homoepitaxy Using Pulsed Paser Deposition.
Arthur Woll 1 , Gokhan Arikan 2 3 , John Ferguson 2 4 , Mark Tate 5 , Joel Brock 2 3
1 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States, 2 Cornell Center for Materials Research, Cornell University, Ithaca, New York, United States, 3 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 4 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 5 Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York, United States
Show AbstractWe have used synchrotron-based in-situ x-ray scattering at the Cornell High Energy Synchrotron Source to study SrTiO3 homoepitaxy using Pulsed Laser Deposition (PLD). A CCD detector operating in streak-camera mode was used to simultaneously capture specular and diffuse scattering parallel to the substrate surface with a temporal resolution of ~0.2 seconds. The average inter-island spacing is obtained directly from the diffuse scattering, and was measured in real time for growth parameters spanning three orders of magnitude in growth rate, two orders of magnitude in oxygen partial pressure, and from 615°C to 1000°C. In accord with standard nucleation theory, the island density is strongly dependent on substrate temperature and flux. However, interesting departures from steady-state growth due to the pulsed nature of PLD are also observed. For example, the inter-island spacing grows continuously from the earliest moments of deposition, suggesting a strong role played by coarsening of single-unit-cell islands. In addition, the inter-island spacing at half-monolayer coverage does not show a simple logarithmic dependence on laser repetition rate, but instead appears to approach asymptotic limits at the low (0.05 Hz) and high (50 Hz) extremes. Additional, general features of the data are presented and compared with standard nucleation theory to gain insight into differences between PLD and continuous, non-hyperthermal deposition techniques.
10:30 AM - D7.3
Real-Time X-Ray Diagnostics of the Growth of Organic Thin Film Crystals.
Aram Amassian 1 , Vladimir Pozdin 1 , Sugandha Bhargava 2 , Sukwon Hong 2 , Tushar Desai 2 , John Ferguson 1 , Alexis Papadimitratos 1 , Detlef Smilgies 3 , Arthur Woll 3 , Joel Brock 4 , George Malliaras 1 , James Engstrom 2
1 Materials Science and Engineering, Cornell , Ithaca, New York, United States, 2 School of Chemical and Biomedical Engineering, Cornell, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell, Ithaca, New York, United States, 4 School of Applied and Engineering Physics, Cornell, Ithaca, New York, United States
Show AbstractWe have performed anti-Bragg and grazing incidence wide area X-ray scattering measurements in situ and in real time during the growth of organic thin films of pentacene. Experiments were carried out on films deposited from both thermal and supersonic molecular beam sources. Real-time data offered new insights into the morphological evolution and crystallite growth on amorphous surfaces from small molecules possessing anisotropic van der Waals interactions. We reveal novel growth behavior (persistent 2D growth at high deposition rate) and the formation of new polymorphs of pentacene when operating in conditions favoring formation of van der Waals clusters in the molecular beam.
10:45 AM - D7.4
In situ X-ray Scattering Study of the Formation of Au Nano Crystals During Thermal Annealing.
Ki Hyeon Ryu 1 , Hyon Chol Kang 2 , Sung Pyo Lee 1 , Do Young Noh 1
1 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 2 Advanced Photonic Research Institute, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractThe formation of Au nano crystals during thermal annealing was investigated by in situ synchrotron x-ray scattering and atomic force microscopy. Au thin films with a thickness of ~16 nm were deposited on sapphire(0006) substrates by electron-beam evaporation, and then annealed in air at 400 C. Upon annealing, Au thin films transformed into Au nano-crystals. We observed a two-step transformation process by monitoring the high-Q Bragg reflection and low-Q reflectivity. In the initial stage, polygonal-shape holes, mostly triangular and hexagonal, were nucleated in the films. After about 70 minutes, the positional order of the holes was abruptly reduced due to the coalescence of them that results in the formation of Au nano-crystals. The correlation of the holes was studyed by measuring the satellite peaks in the transverse scans across the low Q specular reflectivity rod. Au crystals have a well-defined flat-top surface with the <111> surface normal direction and the facets in the in-plane direction. They became larger and thicker during the cluster migration process as the annealing proceeded further.
11:00 AM - D7: SurfPart
BREAK
11:30 AM - D7.5
Synthesis of Co3O4 Nanocubes; An in-situ Synchrotron Powder Diffraction Study.
Heidi Nielsen 1 , Ulrike Grossner 1 , Poul Norby 1 2
1 Centre of Materials Science and Nanotechnology (SMN), University of Oslo, Oslo Norway, 2 Department of Chemistry, University of Oslo, Oslo Norway
Show AbstractNanoparticles of cobalt spinel, Co3O4, are promising for a wide range of technological applications such as sensors, energy storage, spintronics and medical applications. Several synthesis roads are available for formation of Co3O4 nanoparticles. However, for applications in nanodevices, self-organization into nanostructures is necessary making formation of monodisperse, non agglomerated nanocrystals important. We have prepared well facetted nanoncrystals using different synthesis methods. In this study we have used in-situ synchrotron powder diffraction to follow and compare formation mechanisms. We have studied two synthesis methods: (i) Hydrothermal formation (200°C) of Co3O4 nanocubes in a basic solution containing tetraethylammonium hydroxide. (ii) A surfactant based synthesis (polyoxyethylene(20) sorbitan trioleate, TWEEN-85) performed at temperatures below 100°C. To compare and further understand the initial stages of Co3O4 formation, in-situ synchrotron X-ray powder diffraction experiments were performed at the Swiss-Norwegian Beamlines at ESRF. The reactions were performed in a capillary based micro reaction cell. Special emphasis is given to the role of intermediate phases in the reaction, including Co(OH)2 and other layered phases.
11:45 AM - D7.6
Small-angle X-ray and Neutron Scattering Studies of Solution-mediated Nucleation and Growth of Nano-crystalline Ceria using an In-situ Reaction Flow Cell.
Andrew Allen 1 , Vincent Hackley 1 , Jan Ilavsky 2 , Pete Jemian 2 , Joan Raitano 3 , Siu-Wai Chan 3
1 Materials Science and Engineering Lab., NIST, Gaithersburg, Maryland, United States, 2 Advanced Photon Source , Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Applied Physics and Applied Mathematics, Columbia University, NewYork, New York, United States
Show AbstractSolution-mediated reaction routes are increasingly exploited for the formation of non-agglomerated and mono-dispersed nano-scale particle systems. To gain insights into such processes, small-angle X-ray and neutron scattering (SAXS and SANS) can provide representative and quantitative microstructure characterization, for example, of a nucleating solid phase from solution. A remote-controlled, isothermal, circulating fluid flow cell offers several advantages in such studies: the fluid flow prevents settling out of coarse particulates from suspension, and control and online monitoring of flow rate, temperature, and suspension conditions such as pH, permit real-time studies of solution-mediated processes over several hours. By flowing liquid samples, X-ray induced damage to soft materials and the generation of air bubbles can be reduced or eliminated. When used in conjunction with the small X-ray beams available at a 3rd generation synchrotron source and the nanometer-to-micrometer scale range accessible in ultrasmall-angle X-ray scattering (USAXS) studies, one can measure, in situ and in real time, structural characteristics in the scale range from one nanometer to several micrometers in a system evolving in response to changing physical and chemical conditions. Nanocrystalline ceria (n-ceria) is important for a broad array of applications, including catalysts, solid oxide fuel cell electrolytes, gas sensors, optical coatings, and electronic materials. Frequently, these applications require well-crystallized material with a narrow particle size distribution. A promising soft-chemical route for producing monodisperse, nano-scale ceria particles is based on the homogeneous precipitation method. Using an isothermal capillary flow-cell, we present a real-time, in situ USAXS study of the homogeneous n-ceria precipitation and growth from a mixed cerium nitrate / hexamethylenetetramine (HMT) solution. Previously, the growth process was believed to occur in two steps: an initial nucleation event followed by slow and continuous growth at the particle surface without further nucleation. The USAXS results reveal a more complex picture, with very fine-scale cerium clusters that increase in volume fraction, but not in size, before and after the main ceria particle nucleation phase. SANS experiments using H2O/D2O isotope variation have shown that the fine features are complexed to HMT. The primary ceria particle population forms from these and continues to coarsen over time. USAXS measurements yield the nanoparticle size distributions, volume fractions and surface areas for each population versus reaction time, temperature, and component concentration [1]. Implications for harvesting particles of given size will be discussed.[1] A.J. Allen, V.A. Hackley, P.R. Jemian, J. Ilavsky, J. Raitano and S.-W. Chan; “In situ ultrasmall-angle X-ray scattering study of solution-mediated precipitation of nanocrystalline ceria,” J. Appl. Cryst., submitted (2007).
12:00 PM - D7.7
Probing the Mechanism and Kinetics for the Formation and Growth of Catalytic Nano-Particles with Time-Resolved Pair-Distribution-Function Analysis.
Peter Chupas 1 , Karena Chapman 1 , Clare Grey 2
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York, United States
Show AbstractHighly-dispersed supported metal nano-particles find widespread application in catalysis, including in hydrocarbon reforming, hydrogen production, and fuel cells. A key step in the development of catalytic materials with controlled reactivity, is the understanding of the fundamental mechanisms that drive the formation of catalytic nano-particles. Critical to this goal is the ability to discriminate between the separate processes including the initial reaction of precursors and the subsequent nano-particle sintering. Recently, the Pair-Distribution-Function (PDF) method has emerged as a powerful technique to probe the structure of nano-scale materials, with atomic-scale resolution across the entire length scale of the nano-particle, although to date this has been limited to studies of static materials prepared ex-situ. Here we use time-resolved PDF methods, with time resolution as fast as 30 milliseconds, to monitor the structural evolution and kinetics associated with the formation of catalyst nano-particles. We apply differential-PDF methods, which allow the atom-atom correlations involving on the supported metal to be separated from those of the support material (eg. TiO2, SiO2, or Al2O3), to probe the structure of the nano-particles directly.
12:15 PM - D7.8
In-situ SANS Study of the Thermal Stability of Nanoclusters in Oxide-Disperson-Strengthened Ferritic Alloys.
Xun-Li Wang 1 , Chain Liu 2 3 , Uwe Keiderling 4 , Michael Miller 2 , Chong Fu 2
1 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 4 Berlin Neutron Scattering Center , Hahn-Meitner-Institut, Berlin Germany
Show AbstractOxide-dispersion-strengthened (ODS) ferritic alloy (Fe-14Cr-3W+0.25Y2O3+0.4Ti, wt %) exhibits excellent mechanical properties at elevated temperatures. At temperatures between 650 and 900 °C, for example, the creep rate of the ODS alloy is six orders of magnitude lower as compared to the parent material containing no yttrium oxide. This level of improvement represents a major breakthrough in the use of ferritic alloys for high temperature structural applications. It has been suggested that the unusually low creep rate in ODS alloy is related to the formation of nanoclusters enriched with Y, Ti and O elements in the alloy. We have therefore conducted an in-situ small angle neutron scattering (SANS) experiment to identify the nanoclusters in the ODS ferritic alloy, and to study their thermal stability. The measurements were carried out using the V4 instrument at the Hahn-Meitner-Institute in Berlin, Germany, with a high temperature vacuum furnace capable of reaching 1600 °C. By fitting the SANS data with log-normal size distributions, two types of nano-scale particles were identified, with the diameters centering around 2 and 12 nm, respectively. In-situ SANS experiments further reveal that the 2-nm clusters are stable even at 1400 °C, whereas the 12-nm particles coarsen significantly starting at 1200 °C. Both types of nanoclusters were also revealed by TEM and atom probe tomography. These experimental results, along with first-principle calculations, provide important clues on the unusual thermal stability of these nanoclusters in the ferritic alloys at high temperatures. This research was sponsored by the U.S. Department of Energy, Division of Materials Sciences and Engineering, under Contract DE-AC05-00OR22725 with Oak Ridge National Laboratory managed by UT-Battelle.