Sat, April 06, 2002

Dr. Alexander S. Mikhailov

On Apr 5(Fri), we invited Dr. Alexander S. Mikhailov from Fritz Haber Institute of the Max Planck Society, Germany. We also joined his lecture entitled, "Nonequilibrium Stationary And Traveling Nanostructures In Surface Chemical Reactions".

"Nonequilibrium Stationary And Traveling Nanostructures In Surface Chemical Reactions"

Alexander S. Mikhailov
Department of Physical Chemistry,
Fritz Haber Institute of the Max Planck Society,
Berlin (Dahlem), Germany

Surface chemical reactions play a central role in the processes of heterogeneous catalysis, which are broadly used in chemical industry and environmental technology. In a typical catalytic process, the molecules of reactants are adsorbed from the gas phase onto a metal surface, diffuse on it, and react to form a product that goes back to the gas phase. Thus, the reaction proceeds within an atomically thin adsorbate layer on the surface of a metallic catalyst. The concentration patterns developing on the surface are observed using electron microscopy. Scanning tunneling microscopy allows furthermore to view such reactions with an atomic resolution, tracing diffusive motions of single atoms and monitoring individual reaction events. Lateral interactions between adsorbed molecules are typically present. Attractive interactions can lead to a condensation phase transition inside an adsorbate, converting it into a two-dimensional reactive fluid. On the other hand, adsorption of molecules may also induce a structural phase transition in a metal catalyst, accompanied by a rearrangement of atoms in its top layer. Hence, surface chemical reactions are often coupled to phase transitions. Our theoretical analysis shows that this can lead to the formation of a large variety of nonequilibrium nanostructures in such systems. Localized stationary structures, representing nonequilibrium chemical nanoreactors, are possible. Periodic stationary patterns with the wavelength controlled by the chemical reaction can spontaneously develop. Traveling nanostructures, representing atomic reactive clusters, may also be observed.

posted at April 6, 2002 12:11 PM

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Polymer Molecular Engineering Laboratory
Department of Polymer Science and Engineering,
Kyoto Institute of Technology,
Matsugasaki, Sakyo-ku, Kyoto 606-8585, JAPAN