The chemical state vector: a new concept for the characterization of oxide interfaces

Abstract

AbstractFor certain metal oxides deposited as a thin film on the surface of another oxide, changes may occur in the binding energy (BE) of the photoelectron peaks as well as in the kinetic energy (KE) of the Auger peaks of the deposited cation and consequently in its Auger parameter. These changes are illustrated here for the systems formed by SiO2 deposited onto TiO2 and Al2O3. Shifts by −1.3 and −1.0 eV in the Si 2p BE and by 2.3 and 0.7 eV in the KE of the Si KLL Auger peak are found for these two systems when comparing the values obtained for small amounts of SiO2 directly interacting with the support with those of a thick film of this material.The different values of these electronic parameters obtained for increasing amounts of SiO2 can be represented in a Wagner plot. The tendency and magnitude of the changes are similar to those found for Si in phyllosilicate or zeolite compounds with different Si/Al ratios.To systematize these changes in the electronic parameters of the deposited phase the new concept of ‘chemical state vector’ is proposed. It is defined as the vector that connects the two extreme points of a Wagner plot dot graph where the BE of photoelectron peaks is represented versus the KE of the Auger peaks for a cation M of a given MO/M′O interface. The possibilities and limitations of this concept are discussed with regard to the SiO2/TiO2 and SiO2/Al2O3 interface systems reported in this paper and the data for other MO/M′O systems taken from previous works. Copyright © 2001 John Wiley & Sons, Ltd.