Photoemission study of Sm overlayers deposited on Nb

The valence of Sm overlayers deposited on a polycrystalline Nb substrate ha s been studied in-situ by photoemission spectroscopy using synchrotron radi ation. The Srm valences are determined by resonantly enhanced emissions fro m trivalent (4f(5)) and divalent (4f(6)) states at photon energies of 141 e V and 135 eV respectively. For coverages of less than one monolayer trivale nt Sm dominates. Divalent peaks start to grow at the coverage of about one monolayer. In the mean time the relative intensity of the contribution from the divalent state increases with film thickness, indicating an influence of Sm valence by the Nb substrate near the interface region. The divalent p eaks are almost completely suppressed upon exposure of 0.1 langmuir of oxyg en, which suggests that the mixed valence in Sm is heterogeneous.