Homogeneous intermediate valence of Sm on Al(111)

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Abstract
Ordered and disordered monolayers and submonolayers of Sm were formed on Al(111). The ordered monolayer has the structure Al(2×2)Sm. Valence-band and Sm 3d core-level photoemission spectra were taken using Al Kα radiation. The data show that the 3d core spectrum is a true replicate spectrum and allows a measurement of the valence. Sm in ordered overlayers always exhibited a valence of 3, whereas in disordered overlayers the Sm atom presented a valence of 2.4 at very low coverage, rising to a value of 2.8 at multilayer coverage. It is argued that the measured valence for the disordered submonolayer is site independent and homogeneous. The interaction with the aluminum substrate is sufficient to promote intermediate valence in the isolated adsorbed Sm atom, leading to a valence of 2.4.