VALENCE VARIATIONS IN THE MONOLAYER REGIME OF SM ON THE NB(110) SURFACE

Sm overlayers in the monolayer regime, deposited on a Nb(110) single-c rystal surface at room temperature, have been studied by means of high -resolution photoelectron spectroscopy of the Nb 3d(5/2) core level an d the Sm valence band, in the submonolayer regime, the Sm valence vari es from mainly divalent for very low coverages to essentially trivalen t close to a complete monolayer. Above 1 ML, a new divalent component appears in the Sm 4f spectra, corresonding to divalent Sm in the secon d layer. The mixed valence in this overlayer system is concluded to be heterogeneous (all Sm atoms have integer but site-dependent valence). Sm forms ordered overlayers on Nb(110) and the Sm growth is consisten t with a layer-by-layer growth mode (Frank-van der Merwe growth). (C) 1998 Elsevier Science B.V. All rights reserved.