Valence changes of Sm atoms adsorbed on Mo (2Â 1Â 1) surface

Adsorption of Sm thin layers on the Mo (2 1 1) face was investigated by using Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS) and changes of the work function measurements (Δϕ). The layer growth mode and the valence change of Sm atoms were determined. The Sm layer growth mode is layer-by-layer, at least to 3 ML, followed by the crystallite growth. It was found out that for θ < 0.3 ML Sm atoms are adsorbed only in divalent state. At coverage about 0.5 ML the number of both trivalent and divalent atoms is comparable. At θ = 1 ML, 11% of Sm atoms are divalent, and 89% trivalent. The second layer is composed of only divalent atoms. The first two layers have different surface densities, namely 6.15 × 1014 atoms/cm2 for the first layer, and 5.56 × 1014 atoms/cm2 for the second. Divalent Sm atoms creating the second layer form islands with the p(3 × 1) structure observed by LEED and STM.