Initial adsorption kinetics of oxygen on a Cu0.82Li0.18 alloy surface studied by combined Auger electron spectroscopy, x-ray photoelectron spectroscopy, and time-of-flight spectrometry of direct recoils

Abstract

The initial adsorption kinetics of oxygen on the surface of a polycrystalline Cu0.82Li0.12 alloy were studied at room temperature by combined Auger electron spectroscopy (AES) and time-of-flight spectrometry of direct recoils. The latter is structure sensitive, and in the case of copperlike structures, probes mostly oxygen residing on the ‘‘rough’’ planes [i.e., planes consisting of ridges and troughs such as the (110) plane], whereas oxygen located on the ‘‘smooth’’ planes [e.g., the (100)] is ‘‘invisible’’ to that technique. On the other hand, AES probes all surface oxygen atoms regardless of their structural arrangement. The combined measurements thus enable distinction between adsorption processes occurring simultaneously on different structural arrays (i.e., different types of planes) present on the polycrystalline surface. The following conclusions were derived: (i) Oxygen is preferentially adsorbed on the rough planes. (ii) The initial adsorption on the rough planes takes place on sites neighboring to substitutional Li atoms, leading to initial sticking probabilities higher than in the case of pure polycrystalline copper. (iii) Oxygen induced surface segregation of Li occurs at room temperature. This ‘‘segregation’’ is actually an exchange between topmost Cu atoms and Li atoms in the second layer beneath the surface. (iv) Oxygen adsorbed on the rough planes migrates to the smooth planes (a ‘‘spillover’’ effect) leading to enhanced effective ‘‘sticking probabilities’’ on these planes.