L₂L₃V Coster Kronig decay in Fe, Ni and NiO: The near edge region

In this work we deal with the relaxation of the 2p core hole in transition metals via LVV Auger decay, a specific aspect in itself, though contributing a piece of information for a more general understanding of charge redistribution in the final states of both primary photoemission and following de-excitation process. In the past, the analysis of the process was performed mainly by high energy photoemission spectroscopy (PS) experiments, either standard PS [1,2] or coincidence spectroscopy [3,4]. We have carried out a study of the Coster Kronig (CK) decay in Fe, Ni and NiO by PS using synchrotron radiation. In particular, we have measured the branching ratio β between the direct L₂VV and L₂L₃V→L′₃VVV CK transitions. β has been determined as a function of the photon energy in the proximity of the L₂ edges. For all samples β becomes independent upon the photon energy already at few eV above threshold. Nonetheless, the asymptotic value is found to be larger in the metals than in the insulator, this reflecting the different localization of the electronic states involved in the cascade process. Capability and limitations of the method used for the quantitative evaluation of β are also discussed.