The interaction of oxygen with gadolinium: UPS and XPS studies

Abstract

The interaction of oxygen with evaporated Gd films at 300 K has been studied for the first time using AlK α XPS and Hel and Hell UPS. The characteristic changes in the Gd(6s5d) and O(2p) valence bands, Gd(4f), Gd(5p) and Gd(4d) core levels, and O(2s) and O(1s) core levels were studied. Evidence is presented for the initial formation of an intermediate oxidation state at low exposure (characterized by a new Gd valence band with a maximum in the DOS at ∼ 2.5 ev below EF and an ∼ 0.6 eV shift in Gd(4f)) prior to formation of Gd2O3 where the Gd(6s5d) valence band disappears completely, as expected for Gd3+. In the higher exposure range there is little further increase in the oxide thickness, which is estimated as ≥ 20 A ̊, but there is a slow replacement of O by OH, as characterized by a second O(1s) feature at 532.3 eV and OH 1π and 3σ orbitals in UPS at ∼ 6.7 and 11.5 eV. The interpretations are supported by parallel studies on bulk Gd2O3 and by Ar+ sputtering experiments. Comparisons are made to other rare earth oxidation studies. © 1985.