X-ray Standing Waves and Surface EXAFS Studies of Electrochemical Interfaces

Because of their penetrative power, X-rays are ideally suited for in-situ studies of interfaces in general and solid/liquid interfaces in particular. The recent advent of powerful X-ray synchrotron sources has made experiments of this type feasible. Synchrotron sources offer a broad spectral range of polarized, highly collimated X-rays with intensities that are 10{sup 3}-10{sup 6} higher than those of conventional sources. Moreover, third-generation synchrotron sources, with their projected increase in brightness on the order of 10{sup 4}, will allow for new types of experiments, including the study of dynamic processes in real time. There are a number of X-ray-based surface-sensitive techniques that can be employed in the study of solid/liquid interfaces, including surface EXAFS, X-ray standing waves (XSW), grazing incidence X-ray diffraction (GIXD), and others. In this Account the authors focus on the use of XSW and surface EXAFS. The authors begin with a brief theoretical description followed by experimental aspects of these techniques. The authors then discuss specific examples with emphasis on the underpotential deposition of copper on platinum in the presence and absence of coadsorbates, the potential dependent distribution of interfacial species, and potential dependent structural changes of a redox-active self-assembling monolayer. 33 refs., 7 figs.