Development of Energy-Dispersed Surface XAFS Method

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The purpose of this research project is to develop a novel surface XAFS technique using energy-dispersed soft x rays and to apply it to studies of surface reactions as a tool for real-time monitoring of the reactions. In the first year of this project, we constructed the experimental setup for the dispersed-surface-XAFS at beamline 7A in KEK-PF that belongs to Research Center for Spectrochemistry of the University of Tokyo. With this technique, the typical data acquisition time is reduced by a factor of ten compared to the conventional method, which enables us to conduct in-situ tracing of surface dynamic processes. In the second year, this measurement system has been further improved by replacing a plane mirror with a cylindrical mirror to obtain better photon focusing on the sample and by modification of the electron lens system of the spatially-resolved electron energy analyzer to get better electron focusing on the detector, which resulted in significant increases both hi signal intensity and energy resolution. Furthermore, this technique was applied to a surface reaction. The reaction studied here was CO oxidation reaction on Pt(111). Although this reaction is one of the most studied catalytic reactions, only recent STM study has provided information about the atomic-level aspect of the surface species under the reaction. The STM study seems to reveal the reaction mechanism but does not guarantee that all the surface species are clearly imaged and that the observed local area is representative of the whole surface. We have investigated this reaction with the dispersive-surface-XAFS technique in the same condition as used in the STM study and found two reaction processes with different reaction orders, one of which was not observable by STM due to fast diffusion of the reaction species. To summarize, we have successfully developed the dispersed-surface-XAFS technique as a new powerful tool for studies of surface dynamic processes.