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Measurement of c-axis angular orientation in calcite (CaCO 3 ) nanocrystals using X-ray absorption spectroscopy
P. U. P. A. Gilbert, Anthony Young and Susan N. Coppersmith
Proceedings of the National Academy of Sciences of the United States of America
Vol. 108, No. 28 (July 12, 2011), pp. 11350-11355
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/27978803
Page Count: 6
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We demonstrate that the ability to manipulate the polarization of synchrotron radiation can be exploited to enhance the capabilities of X-ray absorption near-edge structure (XANES) spectroscopy, to include linear dichroism effects. By acquiring spectra at the same photon energies but different polarizations, and using a photoelectron emission spectromicroscope (PEEM), one can quantitatively determine the angular orientation of micro- and nanocrystals with a spatial resolution down to 10 nm. XANES-PEEM instruments are already present at most synchrotrons, hence these methods are readily available. The methods are demonstrated here on geologic calcite (CaCO3) and used to investigate the prismatic layer of a mollusk shell, Pinctada fucata. These XANES-PEEM data reveal multiply oriented nanocrystals within calcite prisms, previously thought to be monocrystalline. The subdivision into multiply oriented nanocrystals, spread by more than 50°, may explain the excellent mechanical properties of the prismatic layer, known for decades but never explained.
Proceedings of the National Academy of Sciences of the United States of America © 2011 National Academy of Sciences