Formation and properties of a binary adsorbed layer in a two-component adsorption system (Sm + Yb)-Si(111)

Low-energy electron diffraction, thermodesorption spectroscopy, and contact potential difference techniques were used in a first study on the coadsorption of Sm and Yb atoms on the Si(111) surface. At comparatively low coverages, in both one-component adsorption systems of the rare-earth metal-Si(111) type and the two-component system (Sm + Yb)-Si(111), the same sequence of diffraction patterns of the (n×1) type, where n=3, 5, and 7, was observed. This indicates that Sm and Yb atoms occupy the same adsorption centers in a mixed film. At higher coverages, at which the \((\sqrt 3 \times \sqrt 3 )R30^\circ \) reconstruction forms in the case of the Sm-Si(111) system and the surface undergoes the 2×1 reconstruction in the Yb-Si(111) system, the structure of the mixed film is governed by the ytterbium coverage θ(Yb). At low ytterbium coverages, θ(Yb)<0.15, superposition of the \((\sqrt 3 \times \sqrt 3 )R30^\circ \) and (2×1) diffraction patterns is observed. For θ (Yb)>0.15, however, the former pattern disappears, whereas the latter persists. A comparison of this evolution of a binary adsorbed layer with the properties of the Sm-Si(111) and Yb-Si(111) systems indicates its anomalous character.