ABSTRACT
When the practical working analyst sets out to solve a particular problem, he/she should rst consider what information about the surface composition is needed in order to solve the problem, because the spectra that should be acquired, as well as the subsequent nature of the analysis, depend on the speci c aim of the analysis. Is mere identi cation of the presence or not of a given element in the near-surface region (ca. 5 nm) suf cient? Is it necessary to know the precise number of atoms in this region? Is it important to know the chemical state of the atoms? Is the depth distribution over the outermost 5-10 nm important? Perhaps it is of crucial importance to know whether atoms that were deposited intentionally on the surface have stayed there or have moved inside over distances of a few atomic layers, whether they have agglomerated and formed islands or spheres on the surface, or if they have covered the surface completely as, e.g., a protective layer. It is amazing that XPS (and to a lesser extent AES) can provide answers to these vastly varied questions [1].
