Valence transition 2+ → 3+ induced in ytterbium nanofilms by CO and O2 molecules chemisorbed on their surface

• Published in: Physics of the solid state 2015-09, Vol.57 (9), p.1870-1877
• Main Authors: Buturovich, D. V., Kuz’min, M. V., Loginov, M. V., Mittsev, M. A.
• Format: Article
• Language: English
• Subjects: Physics; Physics and Astronomy; Solid State Physics; Surface Physics and Thin Films
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783415090061

Transformations of the surface and bulk of nanoscale ytterbium films during the surface interactions of these films with different ligand molecules have been studied. It has been shown that a combination of two factors, i.e., the existence of a lone electron pair in CO and O 2 molecules and the unoccupied 5 d level lying near the Fermi level in metallic divalent ytterbium, causes the formation of a stable chemisorption state of the molecule-nanofilm surface layer in which donor-acceptor bonds between gas molecules and surface metal ions are formed. As a result, ytterbium on the surface and in the bulk of the nanofilm is oxidized to a non-autonomous trivalent electronic state. The depth to which this transition propagates in the nanofilm has been determined; its anomalously large value (from 9 to 22 layers according to different estimates) has been explained. It has also been shown that the ligand molecule layer on the ytterbium surface is filled in two stages. The two-stage mechanism of this process is reflected by the nonmonotonic behavior of concentration dependences of the work function of CO-Yb and O 2 -Yb structures.