Surface Science 189/190 (1987) 459-465 North-Holland, Amsterdam 459 EELFS STUDY OF OXYGEN CHEMISORPTION ON COBALT A. ATREI, U. BARDI, G. ROVIDA, M. TORRINI, E. ZANAZZI Dipartimento di Chimica, via G. Capponi 9, Firenze, Italy and M. MAGLIETTA Dipartimento di Energetica, via di S. Marta 3, Firenze, Italy Received 30 March 1987; accepted for publication 15 May 1987 The chemisorption of oxygen on the (1120) surface of a cobalt single crystal at monolayer level and the oxide formed on a polycrystalline sample was studied by EELFS. From the radial distribution functions the distances of the neighbors of the oxygen atom are derived and the reliability of the technique for the oxygen adsorption is discussed. 1. Introduction The aim of this work was to apply the electron energy loss fine structure (EELFS) technique to derive structural information on oxygen adsorbed on cobalt, both at the monolayer level and at the onset of the oxide formation, as part of a research on the mechanism of carbon monoxide dissociation. The study was mainly conducted on the Co(112) face, since this surface, which has a non-compact structure, was reported to be more active for the CO dissocia- tion [1]. Moreover, this investigation was also performed to check the applica- tion of EELFS to the determination of the oxygen-metal interatomic distance. In fact, although reliable results were obtained in the case of carbon [2], the applicability of EELS to the adsorption of oxygen is expected to be more critical, because of the lower ionization probability of the ls level of oxygen. Previous EELFS investigations of oxygen adsorption on metals reported in the literature are: O on Fe(ll0) [3], in which, however, only the radial distribution around the metal atom was investigated; O on polycrystalline A1 [4], in which case an oxide-like layer was investigated, after 100 L exposure; O on Ni(100) [5] in which case the results refer to exposures of 25 L, while the formation of oxide has been reported at 15 L [6]. Therefore, reasonable doubt could arise on the capability of the technique to give reliable interatomic 0039-6028/87/$03.50 9 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)