3d photoemission study of the intermediate valence of Sm on Si(001)

Overlayers of Sm on Si(001) were studied by x-ray photoemission spectroscopy and low-energy electron diffraction. Divalent Sm was observed in the low-coverage region while an average valence of approx.2.75 was observed for monolayer coverage. It is concluded that except for very low coverages the variation of the Sm valence is controlled by direct Sm-Sm interaction. A comparison between the Sm-coverage dependence of 3d spectra and previously obtained 4f spectra gives further evidence to the view that photoemission from Sm core levels gives reliable information about the valence.