Structural Information from Stimulated Desorption: A Critical Assessment

Abstract

Stimulated desorption, that is desorption induced by electronic transitions in surface complexes /1/ can be used to obtain structural information in several ways. The two most important ones are known unter the acronyms PSD-EXAFS and ESDIAD. PSD (photon stimulated desorption)-EXAFS is the use of an ionic desorption signal caused by photon absorption (tunable radiation, i.e. from a synchrotron source) above a core excitation threshold of a surface atom, as a probe to follow the fine structure of its x-ray absorption cross section close to and far from threshold (NEXAFS/XANES and EXAFS, respectively) /2/. These data can then be evaluated in terms of interatomic distances. In ESDIAD (electron stimulated desorption ion energy distributions) /3/, the often very sharp angular distribution of ions desorbing after stimulation by electron impact are used to obtain information about the orientation of the broken bond in the adsorbate. Both methods can in principle yield some unique features of surface geometry; both do not need long range order, but only a constant short range correlation. However, they also contain a number of pitfalls and difficulties which have to be addressed in each case to be avoided as far as possible, and which in part stem from the same characteristics of stimulated desorption which contribute to its advantages.