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Spring 2009 Seminar Series
Wednesday, April 22, at 3:30 p.m.
Room 264 MacQuigg Labs
Laurence D. Marks
Professor of Engineering
Materials Science and Engineering
Northwestern University, Evanston, IL
Oxide Surfaces
Abstract
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. Some initial works applying these methods to more strongly correlated electron systems such as NiO [13] will also be described.
Bio
Laurence D. Marks is a Professor of Engineering in the Department of Materials Science and Engineering at the Robert R. McCormick School of Engineering and Applied Science at Northwestern University. He received his Ph.D. in physics in 1980 from Cambridge University. He was the recipient of a Sloan Foundation Fellowship in 1987, the Burton Medal from the Electron Microscopy Society of America for achievements in electron microscopy by a young researcher in 1989, and was elected a Fellow of the American Physical Society in 2002. His research interests cover a wide range of topics, such as direct methods, nanoparticles, surface structures, quantum electron crystallography, surface charge density, self-lubricating cutting tools, environmental catalysis, tribology and the nanoscale structure of cement. He is the author or co-author of more than 250 papers.
[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).
[13] Marks, L.D., J. Ciston, and A. Subramanian, 2008. In Preparation.
Please join our speaker for light refreshments in 479 Watts Hall following the talk.
