Photoemission study of praseodymia in its highest oxidation state: the necessity of in situ plasma treatment.

A cold radio frequency oxygen plasma treatment is demonstrated as a successful route to prepare clean, well-ordered, and stoichiometric PrO(2) layers on silicon. High structural quality of these layers is shown by x-ray diffraction. So far unobserved spectral characteristics in Pr 3d x-ray photoelectron (XP) spectra of PrO(2) are presented as a fingerprint for praseodymia in its highest oxidized state. They provide insight in the electronic ground state and the special role of praseodymia among the rare earth oxides. They also reveal that former XP studies suffered from a significant reduction at the surface.