Abstract
Photoemission measurements using synchrotron radiation and x-ray photons [x-ray photoemission spectroscopy (XPS)] have been performed on PbTe(111) and ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Eu}}_{\mathit{x}}$Te(111) samples with different relative Eu content x. XPS studies of the stoichiometry of the samples showed a strong influence of the surface cleaning procedure involving ion bombardment and annealing on the Eu content. The partial valence-band spectra of Eu in ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Eu}}_{\mathit{x}}$Te have been studied by exploiting the resonant enhancement of the photoemission cross section of the Eu 4f-derived states at the 4d-4f excitation threshold. The major Eu 4f contributions are found at 1.6 eV below the valence-band maximum, which is on resonance at 140.1 eV, and at 7.3 and 10.5 eV binding energy with a complex resonance structure with maxima at 137.1, 143, and 150 eV. From a detailed analysis of the structure of the resonances as obtained by constant-initial-state spectroscopy and comparison with data for other Eu compounds we conclude that Eu is present in the trivalent as well as the divalent state in ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Eu}}_{\mathit{x}}$Te. The relative amount of Eu ions in the divalent or trivalent state is found to depend on the Eu content x. Angle-resolved spectra in off-normal directions give a strong indication for ascribing the valence change to a surface effect. \textcopyright{} 1996 The American Physical Society.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call