The valence of Sm overlayers deposited on a polycrystalline Nb substrate has been studied in-situ by photoemission spectroscopy using synchrotron radiation. The Sm valences are determined by resonantly enhanced emissions from trivalent (4f^5) and divalent (4f^6) states at photon energies of 141 eV and 135 eV respectively. For coverages of less than one monolayer trivalent 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 peaks are almost completely suppressed upon exposure of 0.1 langmuir of oxygen, which suggests that the mixed valence in Sm is heterogeneous.
Chinese Journal of Physics=中國物理學刊 38(2-I)，pp.146-149