XSD Seminars 2008

Dr. Ayman Said, XOR-IXN, will give an introductory presentation on analyzers for the HERIX instrument in Sector 30. The floor will then be open for discussion of issues surrounding crystal analyzer in inelastic x-ray scattering experimentation. Pizza and Cold Drinks will be provided.
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Ted Farrington will give an overview of the global PepsiCo organization of which Frito-Lay North America (FLNA) is a division. Within FLNA R&D he is building a Process Technology Research Center to develop new technology for the processing of healthy snack foods from fruits, vegetables, legumes, etc. Collaborative research is underway at government labs, universities and other companies around the world on alternatives to frying and other high temperature processes. He will also describe previous work he has done at DOE labs in the imaging area. Jung Han will introduce the goal, mission and activities of PepsiCo Fruit and Vegetable Research Center which was established in 2006 for the purpose of advancing PepsiCos health and wellness initiatives by providing knowledge on fruits and vegetables that would permit year round manufacturing of value-added, convenient and healthful food products.
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In recent years, marriage between lasers and accelerators becomes one of the most fruitful R&D areas in accelerator research aiming at the next generation light sources.A review of application of ultrafast laser to accelerators is given, including measurement of FELs, theoretical schemes of generating ultrafast of x-ray, gamma ray, and positron sources, THz generation, spatiotemporal laser pulse shaping for photoinjector drive lasers, and simulation of laser wake field accelerators.
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The natural world does not consist solely of uniform thin films; instead, nanoscale variations in chemistry and structure are the norm. As a result, the power of traditional synchrotron analysis methods including spectroscopy and diffraction can be dramatically extended by combining them with x-ray imaging techniques to gain new insights into the complexities of nature. At the same time, exciting new capabilities are emerging in electron microscopy. Exploiting these new possibilities demands that he right approach be used for the right problem, that the sample be made maximally tolerant of detailed investigation (such as through the use of cryo methods), and that the full complexity of data can be understood and exploited. Examples in x-ray spectromicroscopy, phase contrast imaging, and coherent lensless imaging will be shown to illustrate these larger goals.
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The talk will describe a range of x-ray detector developments that are ongoing at BNL, including 1D and 2D devices for diffraction and scattering, and spectroscopic applications.
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Semidilute solutions are characterized by the overlapping of linear polymer chains with each other. Dynamics of semidilute solutions has been well described by the Brownian motion of monomer units (“blob”) between two neighboring entanglement points and the reptation of the entire chain in a “tube” made of other surrounding chains. In the past, many dynamic laser light-scattering (LLS) measurements showed that besides the fast relaxation related to the “blobs”, there exists an additional slow relaxation mode. In the earlier time, such a slow mode was wrongly identified as the reptation. LLS cannot distinguish one chain from another in a semidilute solution so that it cannot observe the chain reptation. Later, this slow mode was attributed to possible problems in the sample preparation, such as dust particles or a concentration gradient. Whether this slow mode is real has remained a challenging problem since 80’s. To avoid these potential problems, we used different un-conventional ways, instead of a simple increase of polymer concentration, to induce an in situ dilute-semidilute transition. These methods include the temperature-induced coil-to-globule transition of long polystyrene chains, in situ high-vacuum anionic polymerization of styrene in cyclohexane, and in situ RAFT living bulk polymerization of methyl methacrylate. Our results confirm that this slow mode is real with no ambiguity and showed that it appears whenever the solvent quality becomes less good. Our study leads to a fundamental question whether semidilute solutions are “homogeneous” as stated in textbooks and previous theories. By considering that the segments or monomer units near the entanglement points are different from those in the middle between two neighboring entanglement points; namely, semidilute solutions are “inhomogeneous”, we can satisfactorily explain the existence of the two modes.
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By tuning the incident x-ray energy close to the Ta-LIII edge, we studied resonant (elastic) x-ray diffraction (RXD) from the charge density waves (CDWs) of 1T-TaS2. Our goal was to separate the scattering from the periodic modulation of the conduction electron density from that of the lattice distortion wave. In addition to resonant diffraction studies, various x-ray techniques, including XANES, polarization analysis, and a temperature study, were utilized. We find that two physical effects prevent separating the CDW charge modulation scattering using energy or polarization. (i) The core-hole lifetime of the Ta-LIII resonance is much larger than the CDW band gap in 1T-TaS2 and smears out the CDW anomaly in the electronic density of states. (ii) Resonant scattering from Ta 5d band states not associated with the CDW dominate over resonant scattering from the CDW, smearing out the polarization signature. Our results highlight the principles of RXD when the technique is used to study novel states found in the conduction bands of transition metal compounds and point out which types of systems are most promising.
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The degree of coherence of third generation sources over the acceptance of mirrors used to manipulate X-ray beam properties is medium to large, depending on the applications. With the improvement of metrology and manufacturing techniques used by the optics industry, coherence preservation by these devices becomes possible. The traditional way of specifying mirrors deserves a second look. A simplified formalism is presented, permitting the prediction of the effects of figure errors on wavefront and intensity distributions. Applications are presented for projection imaging, KB nanofocusing and elliptical toroid. Several X-ray in situ methods measuring the wavefront distortions and resulting effects on the beam are discussed, including one involving an APS beamline and an optics manufactured by the optics group. Several reflective systems produced by the WinlightX Corporation are described.
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Microrheology is a method of characterizing fluids by studying the motion of an embedded particle. Advances in the synthesis of new high viscosity fluids have increased the need to extend the applicability of this technique beyond currently accessable viscosities and moduli. X-rays are used to do single particle tracking of the rotational orientation of a tracer particle in fatty acids by tracking the Bragg intensity of alumina crystals in diffraction geometry. This technique allows the tracking of particles to sub-milliradian precision allowing for the determination of shear moduli in high viscosity fluids. We have observed multiple time scales of relaxation which is evidence of subdiffusive behavior.
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In addition to using high-energy x-rays to study bulk materials, the structure of surfaces and buried interfaces can also be explored. The penetrating power of high-energy x-rays permit not only bulk materials to be studied but also enables buried interfaces to be examined. Some examples will be shown that demonstrate other advantages, such as decreased scattering angles and flatter Ewald spheres, which facilitate real-time measurements.
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Solid solutions of (1-x)Pb(Mg_1/3Nb_2/3)-xPbTiO₃ (PMN-xPT) and (1-x)Pb(Zn_1/3Nb_2/3O₃)- xPbTiO₃ (PZN-xPT) have attracted much interests as high performance piezoelectric actuator and transducer materials. Recent x-ray and neutron diffraction studies have shown various intermediate monoclinic (M) phases that structurally ‘bridge’ the rhombohedral (R) and tetragonal (T) ones across the morphtropic phase boundary (MPB). Systematic investigations of (001) and (110) electric (E) field-temperature phase diagrams of PMN-xPT crystals have demonstrated that the phase stability of PMN-xPT crystals is quite fragile: depending not only on modest changes in E (≤0.5kV/cm), but also on the direction along which E is applied. Following the two phase diagrams, the monoclinic M_C or orthorhombic (O) phase is always observed to be associated with the T phase, whereas the monoclinic M_A or M_B phase is always observed to be associated with the R phase. These observations demonstrate the existence of an important crystallographic relationship/transformation. An alternative interpretation for the observed phase fragility is the “ferroelectric adaptive phase” model, which theorized that the monoclinic phases are miniaturized T or R nanotwins (~10nm) determined by elastic lattice accommodation under the misfit strain and electric field. Our investigations provide significant insights of how to design materials with better performance through the domain engineering and may stimulate further research interest in the x-ray diffraction of nanotwins in ferroelectrics.
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The absorption of light by materials proceeds through the formation of excitons, which are states in which an excited electron is bound to the valence hole it vacated. Understanding the structure and dynamics of excitons is important, for example, for developing technologies for light emitting diodes or solar energy conversion. However, there has never been an experimental means to study the time-dependent structure of excitons directly. In this talk causality-inverted inelastic x-ray scattering (IXS) is used to reconstruct the exciton in the prototype insulator LiF, with resolutions Dt = 20.67 as (2.067 x 10^-17 s) in time and Dx = 0.533 Å (5.33 x 10^-11 m) in space. The exciton has a modulated internal structure and is coherently delocalized over two unit cells of the LiF crystal (8 Å). This structure changes only modestly during the course of its life, establishing it unambiguously as a Frenkel exciton and thus amenable to a simplified theoretical description. This study resolves an old controversy about excitons in the alkali halides and demonstrates the utility of IXS for imaging electron dynamics in condensed matter.
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From the beginning of its discovery the Mössbauer effect has continued to be one of the most powerful tools with broad applications in diverse areas of science and technology. With the advent of synchrotron radiation sources such as the Advanced Photon Source (APS), the European Synchrotron Radiation Facility (ESRF) and the Super Photon Ring-8 (SPring-8), the tool has enlarged its scope and delivered new capabilities. The popular techniques most generally used in the field of materials physics, chemical physics, geoscience, and biology are hyperfine spectroscopy via elastic nuclear forward scattering (NFS), vibrational spectroscopy via nuclear inelastic scattering (NRIXS), and, to a lesser extent, diffusional dynamics from quasielastic nuclear forward scattering (QNFS). As we look ahead, new storage rings with enhanced brilliance such as PETRA-III under construction at DESY, Hamburg, and PEP-III in its early design stage at SLAC, Stanford, will provide new and unique science opportunities. In the next two decades, x-ray free-electron lasers (XFELs), based both on self-amplified spontaneous emission (SASE-XFELs) and a seed (SXFELs), with unique time structure, coherence and a 5-6 orders higher average brilliance will truly revolutionize nuclear resonance applications in a major way. This overview is intended to briefly address the unique radiation characteristics of new sources on the horizon and to provide a glimpse of scientific prospects and dreams in the nuclear resonance field from the new radiation sources. We anticipate an expanded nuclear resonance research activity with applications such as spin and phonon mapping of a single nanostructure and their assemblies, interfaces, and surfaces; spin dynamics; nonequilibrium dynamics; photochemical reactions; excited-state spectroscopy; and nonlinear phenomena.
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Abstract: The 11-BM diffractometer produces high-throughput powder diffraction data without compromising resolution or sensitivity. Staring with "Why", this talk will provide examples of how structure determination from high resolution powder diffraction allows otherwise insolvable molecular structures to be determined and will show how this scientific knowledge drives technological innovation. This type of research drove the creation of the 11-BM instrument, which will provide world-class capabilities for such measurements to users on a mail-in basis. The talk will present some of the unique design features and will summarize recent commissioning results. To run an instrument that can accommodate at least 150 samples per week, likely serving multiple research groups every day, will require innovations in management of user-supplied metadata, as well as automated data reduction and data quality analysis procedures, only some of which have yet been developed.
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We discuss here the results of a synchrotron X-ray scattering study of the formation and ordering of gold nanoparticles at the toluene-water interface through a reduction reaction. The observed X-ray reflectivity and diffuse scattering data show the formation of a monolayer of "magic clusters" at the water-toluene interface. Each cluster consists of 13 nanoparticles with about 12 Å diameter, similar to Au-55 nanoparticles, with about an 11 Å organic layer and an in-plane cluster-cluster separation of 180 Å. The electron density profile of the monolayer of these clusters exhibits three layers of nanoparticles as a function of depth that evolves with time.
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Functional nanomaterials are often based on complex materials such as doped or multinary oxides. The synthesis of such materials is highly demanding because it requires the control of composition / stoichiometry on the level of a few thousand atoms per nanoparticle. We discuss approaches to solve this challenge and show detailed structural investigations with emphasis on EXAFS and data analysis using physical models.
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Progress in the Development of High-throughput Florescence Imaging Using Massively Parallel Detector Arrays and Real-time Spectral Deconvolution
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Resonant inelastic x-ray scattering (RIXS), and the related resonant x-ray emission spectroscopy (RXES) have proven themselves to be valuable means by which to study the electronic behavior of rare-earth containing materials, but what about non-resonant techniques? Applying bulk-sensitive, non-resonant inelastic x-ray scattering (NIXS) to rare earth materials, particularly cerium-containing ones, yields considerable information for resonances corresponding to N and O-shell initial states. A survey of the momentum-transfer dependence of these resonances will be presented with emphasis on the cerium valence and hybridization sensitivity of the 4d initial states.
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Projections indicate that fossil fuel use will be an important part of the energy portfolio for the US and the world. Advanced fossil-fuel technologies are being developed to improve the efficiency and reduce CO2 emissions. NETL is applying computational science at different scales to facilitate the development of these advanced technologies. At atomic-scales, computational chemistry is used for developing better CO2 and H2 membranes, CO2 sorbents, and catalysts. At device-scales, computational methods for modeling multiphase flow phenomena enable the description of gas-solids flows occurring in devices such as coal gasifiers. At the plant-scale, steady-state and dynamic models are used for the optimization and control of coal conversion plants. The APECS technology developed at NETL improves the fidelity of plant-scale models by including device-scale models. This presentation will describe the use of models at different scales and outlines a vision for combining models at different scales to accelerate fossil energy technology development.
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From the beginning of its discovery the Mössbauer effect has continued to be one of the most powerful tools with broad applications in diverse areas of science and technology. With the advent of synchrotron radiation sources, the tool has enlarged its scope and delivered new capabilities. The popular techniques most generally used in the field of materials physics, chemical physics, geoscience, and biology are hyperfine spectroscopy via elastic nuclear forward scattering (NFS), vibrational spectroscopy via nuclear inelastic scattering (NRIXS), and, to a lesser extent, diffusional dynamics from quasielastic nuclear forward scattering (QNFS). As we look ahead, new storage rings with enhanced brilliance such as PETRA-III under construction at DESY, Hamburg, and PEP-III in its early design stage at SLAC, Stanford, will provide new and unique science opportunities. In the next two decades, x-ray free-electron lasers (XFELs), based both on self-amplified spontaneous emission (SASE-XFELs) and a seed (SXFELs), with unique time structure, coherence and a 5-6 orders higher average brilliance will truly revolutionize nuclear resonance applications in a major way. This overview is intended to briefly address the unique radiation characteristics of new sources on the horizon and to provide a glimpse of scientific prospects and dreams in the nuclear resonance field from the new radiation sources. We anticipate an expanded nuclear resonance research activity with applications such as spin and phonon mapping of a single nanostructure and their assemblies, interfaces, and surfaces; spin dynamics; nonequilibrium dynamics; photochemical reactions; excited-state spectroscopy; and nonlinear phenomena.
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