| 日時: |
2004-03-04 11:00 - 12:00 |
| 場所: |
放射光研究棟２F会議室 |
| 会議名: |
放射光セミナー「Photoemission Electron Microscopy: PEEM and other tools to image catalytic surface reactions」 |
| 講演者: |
Dr. Harm Hinrich Rotermund (Fritz-Haber-Institut der Max-Planck-Gesellschaft) |
| 講演言語: |
英語 |
| アブストラクト: |
This talk focuses on imaging of dynamic processes on surfaces, using light to illuminate the area of interest. The main emphasis will be on pattern formation during CO-oxidation on Pt surfaces. The most recent imaging techniques, mainly Ellipso-Microscopy for Surface Imaging (EMSI), based on an ellipsometry effect, and Reflection Anisotropy Microscopy (RAM) using different reflectivity properties of non-isotropic surfaces, expand the range of observable pressure conditions formerly only accessible by the Photoemission Electron Microscope (PEEM) by many orders of magnitude, thus bridging the pressure gap in imaging surface reactions. The underlying contrast mechanism of EMSI and RAM in comparison to that of a PEEM will be discussed.
Simple surface reactions like the CO-oxidation on single crystal Pt surfaces show a rich variety of pattern formation under specific reaction parameters. For a certain range of those control parameters, which are the partial pressures of the reactants and the temperature of the sample, self organization in form of pattern formation like spiral waves, target patterns, solitary waves and standing waves including chaotic behavior can be observed. These patterns have been successfully modeled using numerical simulations for the underlying reaction diffusion equations.
The interaction of a multitude of micrometer scale concentration waves and fronts on the surface complicate our understanding the underlying mechanisms for such pattern. Several ways of experimentally controlling these patterns, e. g. by micro-designed composite surfaces, or by impressing a feed back controlled locally varying temperature field onto the surface, will be discussed. Experiments with modified catalytic activity using stationary, inactive boundaries have therefore been designed to isolate individual features (for example single pulses) and interaction mechanisms in order to study them quantitatively [1]. Recently we have been able to dynamically change the surface catalytic activity in real time and space by focusing an addressable laser beam to differentially heat a Pt(110) single crystal surface [2]. Video sequences will demonstrate the great richness of spatio-temporal pattern formation during heterogeneously catalyzed surface reactions [3].
[1] M. Pollmann, H. H. Rotermund, G. Ertl, X. Li, and I. G. Kevrekidis, Phys. Rev. Lett. 86, 6038 (2001).
[2] J. Wolff, A. G. Papathanasiou, I. G. Kevrekidis, H. H. Rotermund, G. Ertl, Science 294, 134-137 (2001).
[3] J. Wolff, A. G. Papathanasiou, H. H. Rotermund, G. Ertl, X. Li, I. G. Kevrekidis, J. Cat. 216, 246, (2003)
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