Surface reactions on rare earth metals monitored by work function measurements

Abstract

Surface reactions on clean, oxidized, and partially hydrided rare earth metal films with O 2, H 2, H 2O, CO, and CO 2 were monitored by dynamic work function measurements under ultrahigh vacuum conditions. The work function data are discussed in the light of electron spectroscopic evidence, where available. The main results of this study are: Initial oxidation of Yb seems to follow a different oxidation mechanism as compared to other rare earth metals. Reaction of H 2O with clean, oxidized, and hydrided rare earth metal surfaces yields surface hydroxyl species. H 2 uptake on divalent Yb metal is much slower than on trivalent Er metal, but occurs at a comparable rate on the oxidized systems. On oxidized surfaces, surface OH formation is substantiated for room-temperature reaction with H 2. The Δφ data indicate high reactivity of CO and CO 2 toward clean rare earth metal surfaces and are consistent with dissociative adsorption of both molecules.