New advancements in the theory of the Auger parameter: Applications to the characterization of small metallic particles

A simple electrostatic model permits the calculation of the Auger parameter shifts of core-ionized atoms in compounds with respect to the free atom in the gas phase. It is shown that the Auger parameter shift is a function of the number, distance, electronic polarizability and local geometry of the nearest-neighbour ligands around the core-ionized atom. We have investigated the relationship between the Pd Auger parameter shifts and the nuclearity of Pd clusters entrapped in Y zeolites. It is shown that our model is useful to estimate this dependence. It is demonstrated that the Auger parameter shift depends not only on the nuclearity and geometry of the cluster but also on the nature of the heteroatoms in its close vicinity. This result could be explained by the influence of these heteroatoms on the electronic polarizability of the surface Pd atoms of the cluster. The model has been applied also to the characterization of small copper clusters entrapped in A zeolite and supported on (0001) α-alumina surfaces. In any case, we demonstrate that the screening properties of both metal bulk and clusters of very low nuclearity are very similar.