Auger-Electron-Probe Time-Resolved Surface XAFS Technique and Its Application to Study of Surface Dynamics

我们发展了一种快速表面X射线吸收精细结构（XAFS）技术，利用能量色散的同步辐射X射线照射固体基底，同时以空间分辨的方式收集吸收X射线的表面物种发射的俄歇电子。在本项目中，我们的目标是进一步开发这项技术及其在固体基质上化学反应机理研究中的应用。目前的改进，使我们能够跟踪的变化，同时在表面和气相物种每约1秒。如果这种技术应用于可重复的过程中，我们可以检测亚单层表面物种的时间分辨率为10毫秒，通过使用时间门的检测器。此外，我们扩展了这种技术的波动器为基础的时间分辨X射线光电子能谱，这使我们能够观察动态过程的亚单层表面物种的时间分辨率为2毫秒。实时监测表面反应动力学的基础上，这些技术提供了以下三个主要的研究成果，从来没有实现以前的方法。(1)在Rh上NO还原反应条件下，发现了一条以NO二聚体为反应中间体的新反应途径;（2）在Pd上CO氧化反应条件下，表面氧的相变与反应活性之间的关系;（3）在Pd上CO氧化反应条件下，表面氧的相变与反应活性之间的关系; NO脉冲分子束诱导寿命小于毫秒级的密度吸附态--表面快速观测技术的发展现状物种及其应用表面动态过程开辟了一条途径，研究新的动态过程，还没有发现与以前的静态表面技术。

We have developed a fast surface x-ray absorption fine structure(XAFS)technique where solid substrates are irradiated by energy-dispersed synchrotron-radiation x rays and auger electrons emitted from x-ray absorbing surface species are collected at once with a spatially resolved way. In this project we aimed further development of this technique and its application to mechanistic studies on chemical reactions on solid substrates. The present improvement enabled us to trace changes in both surface and gas-phase species simultaneously every approximately 1 s. If this technique is applied to repeatable processes, we can detect submonolayer surface species with a time resolution of 10 ms by using a time gate for the detector. Furthermore we extended this technique to the undulator-based time-resolved x-ray photoelectron spectroscopy, which enabled us to observe dynamic processes of submonolayer surface species with a time resolution of 2 ms.Real-time monitoring of surface reaction kinetics based on these techniques provided following three major achievements in research that have never been achieved by previous methods.(1) Finding of a novel reaction pathway involving a NO dimer as a reaction intermediate under the reaction condition of NO reduction on Rh(2) Elucidation of cirrelation between phase transition of surface oxygen and reactivity under the reaction condition of CO oxidation on Pd(3) Detection of a transient high-density adsorption state with a life time of less than millisecond order induced by NO pulsed molecular beamThe present development of the fast observation technique for surface species and its application to surface dynamic processes open a way to study novel dynamic processes that have not been detected with previous static surface techniques.