Distribution Function Analysis
Amorphous materials are often utilized not only as structural and functional materials but also for the synthesis of nanocrystalline and non-equilibrium materials. To control materials properties and processing, it is necessary to obtain information on amorphous structures. Amorphous structures are not completely disordered but exhibit short-range order. The short-range ordered states can be evaluated by a variety of experimental techniques. Radial distribution function analysis is one of the useful ways for understanding atomic correlations and the correlation distances in amorphous networks. In this function, amorphous structures are characterized by the
probability of finding another atom at a distance between r and r+dr from a specific atom. Radial
distribution functions can be obtained by x-ray, neutron, and electron diffraction techniques. Among the diffraction techniques, electron diffraction has the following merits: (1) strong interaction between the material and electrons has the advantage of detecting light atoms; (2) thanks to short wavelength of high-energy electrons, an intensity profile up to high scattering angles is easily obtained; (3) local structures on the nano-scale can be obtained by a combination of other techniques, such as high-resolution electron microscopy and nano-beam spectroscopy analysis.
We have examined a variety of amorphous materials using radial distribution function
analyses based on electron diffraction techniques. In the present talk, I’ll show some examples of
radial distribution functions analyses of covalent amorphous materials.
Manabu Ishimaru is a professor in the Department of Materials Science and Engineering, Kyushu Institute of Technology. His current research interests focus on the structural characterizations of functional amorphous and/or nano-sized materials. He is experienced in transmission electron microscopy techniques, such as high-resolution electron microscopy and nanobeam electron diffraction, and computer simulations based on molecular-dynamics and Monte Carlo methods. Ishimaru received his BS (1989) and MS (1991) degrees in metallurgy from Tokyo Institute of Technology and PhD degree (1994) in materials science and technology from Kyushu University. He worked in Kyushu University as a research associate (1994-2000) and in Osaka University as an associate professor (2000-2013). He was a visiting researcher in the Materials Science and Technology Division at Los Alamos National Laboratory, USA from 1998 to 1999. He moved to the current position in 2013.
APMC11 / MST33 / AAT39 Conference May 23-27, 2016, Phuket, Thailand
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M7_1
Dr. Nirawat Thammajak
SLRI-GeM Consortium, Research Facility Division. Synchrotron Light Research Institute,
111 University Avenue, T. Suranaree, A. Muang, Nakhon Ratchasima 30000, THAILAND. E-mail: [email protected]
X-ray Absorption Spectroscopy for Gemology
and Mineralogy Applications:
A Case Study of Fresh-Water Cultured Pearls
X-ray Absorption Spectroscopy (XAS) is a powerful technique for studying local structure
in materials using an energy-tuneable source of x-rays from a synchrotron. The absorption of x-rays by an atom can provide a meaningful spectrum which qualitatively and quantitatively related to its chemical compositions, forms, and bonding structure. XAS is therefore sensitive to the oxidation state, coordination geometry, and the distances, coordination number and species of the atoms immediately surrounding the selected element. Hence, the technique is capable to provide an effective analysis of trace elements and dilute compositions, which commonly affect the color of gemstones. A study of gamma irradiated Freshwater Cultured Pearls (FWCPs) by the XAS technique led to a fundamental knowledge of coloring mechanism caused by a trace color-forming composition combined with the calcareous base material of the pearl. Different irradiation doses resulted in a shift of XAS spectra, including a development of a peak-shape feature near the absorption edge. This gamma dose dependence observed in the XAS spectra can provide a substantial evidence for irradiated pearl's identification. Besides, the revealed coloring mechanism can potentially be applied for FWCPs quality improvement. In a feasibility study, an intense x-ray white beam generated by a synchrotron was employed to alter the color of FWCPs. It was observed that an original white pearl was enhanced to a metallic-golden pearls, contrary to the metallic grey pearls obtained from gamma irradiation. This metallic gold color is very unique, and surprisingly; the natural iridescence of the irradiated pearl has also been slightly improved. It should be noted that the intense x-ray beam from a synchrotron stimulates the color change, but does not activate the pearls through nuclear reactions, as in the case of cobalt-60 gamma irradiation. It also has an extra advantage of the synchrotron's specific beam direction that can beneficially be applied with a photolithography technique for imprinting an irradiated pattern on pearls. This invention has already established a new technique of golden pattern imprinting process on FWCPs by means of the irradiation of intense x-rays through a designed mask that partially obscured the beam. The partly through x-ray beam resulted in a high-definition golden pattern with highly detailed line, as fine as micrometer level. ©All rights reserved.
Dr. Nirawat Thammajak is a scientist at Synchrotron Light Research Institute and a project leader for "SLRI-GeM Consortium", Synchrotron Technology for Gemology and Mineralogy Applications. He has accumulated experiences in chemistry research and experiments with leading synchrotron and neutron facilities around the world during his doctoral degree from University of Oxford. In 2016, he received the Very Good Invention Award in Physical Sciences from National Research Council of Thailand.
APMC11 / MST33 / AAT39 Conference May 23-27, 2016, Phuket, Thailand
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M8_1Professor Makoto Shiojiri Kyoto Institute of Technology, Kyoto 606-8585, JAPAN. E-mail: [email protected]