ADSORBATE SUBSTRATE BONDING AND DYNAMICS AS DETERMINED BY SEXAFS

A review is given of surface extended X-ray absorption fine structure (SEXAFS) data taken at the N and O K-edges of atomic and molecular ads orbates on Cu and Ni surfaces. The theory of the dynamic analysis of S EXAFS data is briefly presented. We conclude that a dynamic analysis i s also necessary in many cases for a reliable structural determination . This result is particularly important in the case of reconstructed s urfaces where the structural and dynamic contributions in the SEXAFS a mplitude and phase can be of comparable strength. An analysis of the d ynamic part of the disorder allows one to distinguish between reconstr ucted and unreconstructed systems. Furthermore, the use of model pair potentials allows for a discussion of surface reconstruction in terms of simple physical parameters. Finally a short discussion is given of the photon flux and stability required for a state of the art SEXAFS e xperiment, in view of the availability of the improved third generatio n soft X-ray sources.