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Science 12 May 2000:
Vol. 288. no. 5468, pp. 1029 - 1033
DOI: 10.1126/science.288.5468.1029
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Reports

Structure of the Hydrated alpha -Al2O3 (0001) Surface

Peter J. Eng, 1* Thomas P. Trainor, 2 Gordon E. Brown Jr., 23 Glenn A. Waychunas, 4 Matthew Newville, 1 Stephen R. Sutton, 1 Mark L. Rivers 15

The physical and chemical properties of the hydrated alpha -Al2O3 (0001) surface are important for understanding the reactivity of natural and synthetic aluminum-containing oxides. The structure of this surface was determined in the presence of water vapor at 300 kelvin by crystal truncation rod diffraction at a third-generation synchrotron x-ray source. The fully hydrated surface is oxygen terminated, with a 53% contracted double Al layer directly below. The structure is an intermediate between alpha -Al2O3 and gamma -Al(OH)3, a fully hydroxylated form of alumina. A semiordered oxygen layer about 2.3 angstroms above the terminal oxygen layer is interpreted as adsorbed water. The clean alpha -Al2O3 (0001) surface, in contrast, is Al terminated and significantly relaxed relative to the bulk structure. These differences explain the different reactivities of the clean and hydroxylated surfaces.

1 Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA.
2 Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA.
3 Stanford Synchrotron Radiation Laboratory, Stanford, CA 94309, USA.
4 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
5 Department of Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA.
*   To whom correspondence should be addressed. E-mail: eng{at}cars.uchicago.edu

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