Applications of Auger Photoelectron Coincidence Spectroscopy (APECS) to understanding inner-shell transitions

Auger electron spectroscopy (AES) is widely used as a means of quantitative surface analysis. The Auger decay process is complex, involving at least three electrons. Often there are a number of competing decay channels open which result in complex spectral features. Transition rates into these channels can depend on quantities like the valence band width that can be determined by the chemical environment and the crystalline structure. APECS is a means of simplifying Auger spectra. In an APECS spectrum, Auger electrons are only counted when a photoelectron is collected in coincidence. This has a number of consequences. The origin of the Auger ionisation is known, only those features due to the particular ionisation are present and the mean free path (MFP) of the collected electron is smaller than if collected in the standard, singles mode. This means that the origins of particular spectral features can be identified and comparison between theory and experiment can be made more readily. Several examples of how APECS has been used to study the LVV spectra of a number of 3d transition metals are presented. An analysis of the deformation in line shape that occurs when data is collected in coincidence is also presented.