Coordination-dependent valence state of Sm adsorbed on Cu(1 0 0) and (1 1 0) studied by STM and XPS

Geometric and electronic structures of Sm adlayers on Cu(1 0 0) and (1 1 0) were studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The present results, in addition to the previous results for Sm/Cu(1 1 1) [Y. Nakayama, H. Kondoh, T. Ohta, Surf. Sci. 552 (2004) 53], indicate that the valence state of Sm adsorbed on Cu surfaces is determined by Sm–Sm and Sm–Cu coordination numbers. We propose that the valence state of the adsorbed Sm atoms can be explained by a simple thermodynamic equation including the coordination numbers.