January 2006 Archives

Professor E. Ma (Johns Hopkins University, USA) and his colleagues recently succeeded in explaining the atomic packing of metallic glasses, which are of great importance due to their distinctive mechanical and magnetic properties. The structure is known as 'amorphous' (non-crystalline) and shows no sharp Bragg peaks in the X-ray diffraction pattern. The research group adopted quite a unique strategy; first, they aimed at obtaining 3D pictures in the short-to-medium range, unlike conventional atomic-level analysis, which looks only at short-range order, and secondly, they did not resort to a predetermined structural model but used reverse Monte Carlo simulations based on experimental X-ray diffraction and absorption data. One of their key findings was that metallic glass atoms do not arrange themselves in a completely random way. Instead, groups of 7-15 atoms tend to arrange themselves around a central atom, forming 3D shapes called Kasper polyhedra, which join together in unique ways as small nanometer-scale clusters. For more information, see the paper, "Atomic packing and short-to-medium-range order in metallic glasses", H. W. Sheng et al., Nature, 439, 419-425 (2006).

Generally, relaxor ferroelectrics exhibit a strong polarization dependence on the applied electric field, which so far has been explained by the behavior of the polar nano-regions (PNRs). Recently, scientists at the U.S. Department of Energy's Brookhaven National Laboratory investigated the short-range polar order of Pb(Zn_1/3Nb_2/3)O₃ (PZN) under an electric field. X-ray diffuse scattering is very sensitive to local inhomogeneities and the results indicated an unexpected redistribution of PNRs in real space, i.e., the PNR fields preferred to line up perpendicular to the external field instead of aligning with it. The experiments were done at the beamline X22B at the National Synchrotron Light Source (NSLS, at Brookhaven National Laboratory). For more information, see the paper, "Electric-field-induced redistribution of polar nano-regions in a relaxor ferroelectric", G. Xu et al., Nature Materials, in the January 15, 2006, online edition.

The distribution of ions in solution at an interface is key to the fundamental understanding of electrochemistry as well as to the design of materials and devices such as biomembranes. So far, classical descriptions of ion distributions, such as the Guoy-Chapman theory (see, G. Gouy, C. R. Acad. Sci. 149, 654 (1910) and D. L. Chapman, Phil. Mag. Ser. 6 25, 475 (1913)), which ignores the details of molecular structure, have been widely used. Professor M. Schlossman (University of Illinois at Chicago) and his colleagues recently performed very precise X-ray reflectivity measurements to obtain experimentally ion distributions at the interface between solutions (0.01 ~0.08M) of tetrabuytlammonium (TBA) tetraphenylborate (TPB) in nitrobenzene and aqueous TBA bromide. They found significant deviations from the Guoy-Chapman theory in describing their data. However, on the other hand, molecular dynamics calculations produced potentials that could be used to predict distributions with the Poisson-Boltzmann equation without adjustable parameters. The experiments were done at the Chemistry and Materials section of the Consortium for Advanced Radiation Sources (ChemMatCARS) beamline 15-ID at the Advanced Photon Source (APS, at Argonne National Laboratory). For more information, see the paper, "Ion Distributions near a Liquid-Liquid Interface", L. Guangming et al., Science, 311, 216-218 (2006).

The Science and Technology Foundation of Japan announced the names of the two laureates for the 2006 (22^nd) Japan Prize. They are U.K. scientist, Sir John Houghton CBE FRS, for "Pioneering research on atmospheric structure and composition based on his satellite observation technology and for promotion of international assessments of climate change" in the prize category of "Global Change" and Dr. Akira Endo of Japan for "The Discovery of the Statins" in the prize category of "The development of Novel Therapeutic Concepts and Technologies". The two scientists will receive certificates of merit, and commemorative medals. There is also a cash award of fifty million Japanese yen for each prize category. The presentation ceremony is scheduled to be held in Tokyo at the National Theatre on Thursday 20 April 2006, in the presence of the emperor and empress. The prize categories for the 2007 (23^rd) Japan Prize will be "Innovative Devices Inspired by Basic Research" and the "Science and Technology of Harmonious Co-Existence". For further details of the Japan Prize, contact The Science and Technology Foundation of Japan, Phone: +81-3-5545-0551, Fax +81-3-5545-0554, info@japanprize.jp, http://www.japanprize.jp/English.htm

Imaging with coherent X-rays at high spatial resolution is a promising technique for obtaining information on the internal structures of non-crystalline specimens. Researchers at Cornell High Energy Synchrotron Source (CHESS, Cornell University, USA) recently succeeded in extending the Fresnel theory to retrieve phase information needed for a full image reconstruction. The algorithm gives 3D full field imaging with X-rays. This new scheme has been developed for coherent X-rays, but the distorted-object concept can be applied to other diffraction and imaging fields such as using visible light, electrons, and neutrons. The method is particularly important with respect to the utilization of future X-ray sources that have fully coherent photon beams. Part of their work was published in Phys. Rev. B 72, 033103 (2005). For more information, visit http://news.chess.cornell.edu/index.html