Origin of the thermal stability of oxygen molecules on the ytterbium nanofilm surface

The effect of temperature on the properties of O$_2$–Yb–Si(111) film structures has been studied using X-ray photoelectron spectroscopy. It is established that the adsorption of oxygen molecules on the ytterbium nanofilm surface is non-dissociative and leads to the formation of a stable adsorption complex, which is not destroyed when heated at 900–1050 K. The high thermal stability of this complex is due to the fact that the adsorbed molecules have a dipole moment and are oriented to the surface by the negatively charged end and into the vacuum by the positively charged one. It is shown that the molecule polarization depends on the thickness of ytterbium nanofilms (size effect). A model is proposed that allows us to qualitatively explain the results obtained.