Nonmonotonic dependence of the work function of ytterbium nanofilms deposited on the Si(111)7 × 7 surface at room temperature on the film thickness

Abstract

The dependences of the work function of ytterbium nanofilms on their thickness are studied. The films are evaporated at room temperature on the Si(111)7 × 7 surface of silicon samples doped to different levels and having different types of conduction (n and p). It is shown that these dependences exhibit a pronounced nonmonotonic behavior, which does not depend on the type of silicon used. It is established that the amplitude of the nonmonotonic variations in the work function is governed by the surface microroughness of the deposited layers, so that larger amplitudes correspond to smoother films. The variations in the work function of the films due to the deposition of electrically negative Si atoms on their surface are investigated. It is revealed that the sign of the variation depends on the film thickness. This result strange at first glance is associated with the fact that the electron density distribution at the metal-film-vacuum interface depends nonmonotonically on the amount of deposited ytterbium. This nonmonotonic behavior is a manifestation of electron density standing waves (Friedel oscillations) generated in the films by the ytterbium-silicon interface.