Friday
20
Nov
2009
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Chemistry Colloquium
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Oxide Surfaces
Laurence Marks, Department of Materials Science and Engineering, Northwestern University
While it is probably fair to say that we understand relatively well the structure of metal surfaces as well as those of semiconductors, in many other cases particularly for oxides the situation is much less clear. Part of the problem is experimental, since unless the oxygen chemical potential is well controlled it is unlikely that one will obtain reproducible results. A second part of the problem is theoretical since the most common contemporary approach, DFT, can be quite unreliable when calculating the energies for oxides particularly those containing transition metal atoms. As a consequence it is still hard to guess a plausible structure for an oxide surface with much confidence.
One invaluable method that avoids the need to guess a plausible method is direct methods. Developed originally for bulk materials, with some attention to how they are done we were able a few years ago to apply them first for two-dimensional transmission electron diffraction data [1, 2], relatively quickly for two-dimensional surface x-ray diffraction data [3-5] and then extend them to three-dimensional surface x-ray diffraction data [6] basing the approach on a feasible set methodology [7]. The method has proved useful in determining some unexpected oxide structures which one would not have guessed [8-10], as well as a number of perhaps not so unexpected defect structures at surfaces [11, 12].
This presentation give an overview of some recent results on the structure of oxide surfaces, particularly combining direct methods and transmission electron microscopy with DFT analyses taking care with the choice of functional, as well as using auxiliary tools such as XPS to check the surface chemistry.
[1] C. J. Gilmore, L. D. Marks, D. Grozea, et al., Surface Science 381, 77 (1997).
[2] L. D. Marks, R. Plass, and D. Dorset, Surface Review and Letters 4, 1 (1997).
[3] E. Landree, L. D. Marks, P. Zschack, et al., Surface Science 408, 300 (1998).
[4] L. D. Marks, E. Bengu, C. Collazo-Davila, et al., Surface Review and Letters 5, 1087 (1998).
[5] L. D. Marks, D. Grozea, R. Feidenhans'L, et al., Surface Review and Letters 5, 459 (1998).
[6] L. D. Marks, Physical Review B 60, 2771 (1999).
[7] L. D. Marks, W. Sinkler, and E. Landree, Acta Crystallographica Section A 55, 601 (1999).
[8] D. Grozea, E. Bengu, C. Collazo-Davila, et al., Surface Review and Letters 6, 1061 (1999).
[9] C. Kumpf, L. D. Marks, D. Ellis, et al., Physical Review Letters 86, 3586 (2001).
[10] N. Erdman, K. R. Poeppelmeier, M. Asta, et al., Nature 419, 55 (2002).
[11] C. H. Lanier, J. M. Rondinelli, B. Deng, et al., Physical Review Letters 98 (2007).
[12] O. Warchkow, Y. M. Wang, A. Subramanian, et al., Physical Review Letters 100, 86102 (2008).
Organized By: BCPS
Contact: Ishaque Khan
e-mail: khan@iit.edu
Phone: 312.567.3431
Location: LS 111 |
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