Science Highlights 2003

Science highlights of research occuring at the APS.

Inelastic X-ray Scattering Reveals Microscopic Transport Properties of Molten Aluminum Oxide (Oct. 2)
Levitated liquid-aluminum-oxide sample in a super-cooled state at ~1800 C. The sample is levitated by an oxygen gas stream and heated by a 270-W CO2 laser. The article reports on inelastic x-ray measurements performed on this sample. The transport properties of high-temperature oxide melts are of considerable interest for a variety of applications, including modeling the Earth's mantle, optimizing aluminum production, confining nuclear waste, and investigating the use of aluminum in aerospace propulsion. The experimental techniques described here, using high resolution inelastic x-ray scattering at X-ray Operations and Research beamline 3-ID-C at the APS, supply fundamental insights into the behavior of liquid oxides that help provide a basis for these and other advanced applications.
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Synthesis and Analysis of TiO²-Oligonucleotide Hybrid Nanoparticles (Sept. 26)
Scan of a 21 x 21-m area with a single nucleus containing 3.6 x 106 nanoparticles. New developments in nanotechnology offer the creation of chemical-biological hybrid nanocomposites, which can be introduced into cells to initiate intracellular processes or biochemical reactions. Researchers synthesized TiO²-oligonucleotide nanocomposites made of DNA oligonucleotides attached to 45-Å TiO² nanoparticles and tested them by using the 2-ID-E beamline at the X-ray Operations and Research sector 2 of the APS.
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Demonstration of the Influence of Local Icosahedral Order on the Nucleation Barrier of Metallic Liquids (Sept. 26)
Electrostatically levitated 2.5-mm-diameter droplet of molten Ti39.5Zr39.5Ni21, held near the liquidus temperature (1083K). It has been known for over 50 years that, under carefully controlled conditions, metallic liquids can be cooled far below their equilibrium melting temperatures (undercooled) before crystallization takes place. To explain this surprising result, F. C. Frank theorized that as metallic liquids cool, (1) local structures develop in the liquid phase containing icosahedral short-range order, which is incompatible with the long-range periodicity of the crystalline phase, and that (2) this incompatibility creates a barrier to the formation of the crystalline phase. The first direct experimental confirmation of Frank's hypothesis took place at MU-CAT's 6-ID-D beamline at the APS.
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X-ray Scattering Reveals Unusual Growth of Lead on Silicon (Sept. 24)
$X-ray diffraction images taken with a CCD camera during growth of Pb films on Si(111). The interference fringes yield information about island height and layer thickness.$ Most thin films grow on substrates in only three ways: layer by layer, formation of atomic islands, or layers followed by islands. The particular growth mode that a given material will follow crucially depends on the relative magnitudes of the surface energy of the film versus the interfacial energy of the film on the substrate. A team of researchers using real-time x-ray scattering measurements at sector 33 of the UNI-CAT station at the APS found that lead films grown on silicon adopt a completely novel pattern of growth. As shown by this work, taking into the consideration the global energy picture and not just the local energy landscape is essential in understanding the complete story of thin-film growth.
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A New Concept for Variable-Period Undulators (Aug. 5)
The May 2003 issue of the Journal of Synchrotron Radiation has as its cover story an article by Gopal Shenoy (XFD), John Lewellen (ASD), Deming Shu (XFD), and Nikolai Vinokurov (XFD/Budker Institute of Nuclear Physics) on a new concept for variable-period undulators.
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Shining Light on a New Gene Therapy (Jul. 30)
Brilliant x-ray beams from the Advanced Photon Source are playing a crucial role in the development of a novel, light-activated hybrid "nanodevice" that one day may be used to target the defective genes that play a role in cancer, neurological diseases, and other conditions.
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COBRA: Determining Atomic Positions in Thin-Film Structures and Interfaces (Jan. 27)
COBRA electron density map of a Gd2O3 film on a gallium arsenide substrate. The peaks correspond to folded Gd atomic positions parallel to the plane of the substrate. Coherent Bragg rod analyses (COBRA) experiments using synchrotron x-rays at Argonne's Advanced Photon Source (MHATT-CAT and PNC-CAT beamlines) reveal for the first time the sub-angstrom atomic interaction of epitaxial films with substrates. Information on how atoms in the adjoining layers of the film and substrate rearrange to mimic each other may lead to improvements in semiconductor manufacturing and the development of novel heterostructure materials, such as multilayer ferroelectrics, magnetic nanostructures and thin film superconductors.
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