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The characterization of ordering and kinetics at nanostructured surfaces and interfaces has become increasingly critical to understand and optimize the synthesis of ordered nanomaterials on nanometer length scales. This requires innovative in situ and time-resolved surface probes that can also be applied to various experimental environments. Grazing-incidence x-ray scattering is an ideal tool for the studies. At the Advanced Photon Source, using high-resolution small-angle x-ray scattering in grazing-incidence geometry (GISAXS), we successfully captured the growth kinetics of two-dimensional nanocrystal superlattices at the liquid/air interface and identified their ordering, phases and phase transitions in a quantitative manner. As one of the greatest challenges associated with the grazing-incidence technique, a precise reconstruction of the real-space nanostructures from their scattering data requires a comprehensive model in the presence of electric-field intensity enhancement at the grazing-incidence angles. To this end, a rigorous grazing-incidence scattering theory has been developed to analyze the buried nanostructures involving multiple interfaces, which thus far has been difficult, if not impossible. Finally, I will discuss a promising direction for creating an innovative class of materials and structures capable of new functionalities with improved self-assembly efficiencies. This involves supramolecular self-assembly at multiple-level of energy landscapes and length scales, whose structure, kinetics and dynamics can be elucidated by the grazing-incidence x-ray scattering measurements with either incoherent or coherent x-rays.
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This talk will cover two topics on addressing key issues at the frontier of explorations of surface/interface phenomena in advanced materials by using synchrotron x-ray diffraction/scattering techniques. One is to perform atomic structural imaging of complex epitaxial systems that exhibit novel physical properties by combining high precision synchrotron surface x-ray diffraction technique and phase retrieval direct methods. Another is to investigate surface morphology evolution involving energetic processes by synchrotron x-ray surface scattering technique in-situ and in real-time.
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The macroscopic mechanical properties of composites and two-phase alloys are controlled by the interaction of components and phases on a microscopic length scale. In this seminar in situ studies are presented which were carried out at synchrotron and neutron radiation sources which gave quantitative insight into this interaction. Emphasis is placed on the internal load transfer in particle or fiber reinforced metal matrix composites. Both methodology and materials science are discussed.
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Purpose: The purpose of this study is to characterize certain aspects of the microscopic structures of cortical and trabecular bone using the Fourier x-ray scattering imaging method. Materials and Methods: The hind limb of a rat and the toe of a pig were imaged ex-vivo under NIH Animal Care and Use Committee approved protocols. A Fourier x-ray scattering imaging device uses a grid mask to modulate the cone-beam and Fourier spectral filters to isolate the harmonic images. It acquires attenuation, scattering and phase-contrast (PC) images in a single exposure. In rat tibia cortical bone, scattering image intensities from orthogonal grid orientations were compared using Wilcoxon signed rank tests. In the pig’s toe, the heterogeneity of scattering and PC signals were compared between trabecular and compact bone regions of uniform attenuation using F-tests. Results: In cortical bone, the scattering image intensity is significantly higher (P<10-15) when the grid is parallel to the periosteal surface. Trabecular bone appears highly heterogeneous in the scattering and PC images when compared to cortical bone (P<10-27). Conclusion: The ordered alignment of the mineralized collagen fibrils in compact bone is reflected in its anisotropic scattering image intensity. In trabecular bone, the porosity of the mineralized matrix can explain the granular pattern in the scattering and PC images.
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The main advantage of combining Brillouin spectroscopy (BS) with high-resolution x-ray diffraction (XRD) techniques is the ability to perform simultaneous measurements of velocities and elastic moduli (by Brillouin spectroscopy) and the volume/density (by XRD), independent of any pressure standard. With this unique system, located in the 13BM-D station (GSECARS, APS), it is now possible to study materials with BS and XRD in-situ at high pressure-temperature conditions that provide information essential for interpreting seismic observations and constraining models of the composition and evolution of the Earth. Although the system is designed to be very user-friendly, successful BS measurements at high pressure using diamond anvils requires special preparation and a thorough understanding of the peculiarities of the on-line high pressure BS technique. To help our users make the best use of this exceptional technique, we are organizing this COMPRES/GSECARS-supported workshop focusing on the major topics relevant to high pressure research using Brillouin spectroscopy combined with high-resolution x-ray diffraction techniques.
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