Silicide formation and valence switching at the Eu-Si interface monitored by electron energy loss spectroscopy in the reflection mode

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Abstract
Electron energy loss spectroscopy in the reflection mode is used to probe changes in the electronic environment and valence changes at Eu-Si interfaces. Reaction of divalent Eu and Si leads to depletion of dipolar electronic excitations at around 4 eV and formation of a divalent silicide with a bulk plasmon energy h omega p=12 eV. At primary energies less than 200 eV 4fn-4fn spin flip excitations are accentuated: modifications in the excitation spectrum on valence change for divalent Eu(n=7) to trivalent Eu(n=6) on oxidation are demonstrated, and the effect is used in monitoring valence switching during successive oxidation/heating cycles on the silicide.