Surface Science 120 (1982) 427-434 North-Holland Publishing Company 427 ION-ELECTRON EMISSION: THE EFFECT OF OXIDATION J. FERRbN *, E.V. ALONSO, R.A. BARAGIOLA and A. OLIVA-FLORIO + Centro Aidmico Bariloche ** and Instiiuto Balseiro ***, 8400 Bariloche, Argentina Received 8 February 1982; accepted for publication 13 May 1982 We have studied electron emission from Al and MO surfaces by 4-60 keV Ar+ ions under ultrahigh-vacuum conditions and as a function of oxygen exposure. We found that the dependence of the electron yield y on oxygen exposure, for a given metal. is similar to that of +, the work function of the surface. Comparison of the results for Al and MO shows, however, that the magnitude of the change in y cannot be attributed solely to a change in $I. We propose that the effect of oxygen exposure on electron emission induced by ions, and by extension by photons and electrons, is related to a change in the escape probability of the electrons over the modified surface barrier. and to the emission of electrons from the oxide layer in the presence of the surface dipole field. 1. Introduction It has been known for many decades that electron emission from surfaces, be it induced by photons [l], electrons [2] or ions [3-61, is strongly influenced by gas adsorption. Historically, this sensitivity was considered a nuisance in experimental work, and prompted the adoption of ultrahigh-vacuum tech- niques when they became available. Some early attempts were made to explain the effect of adsorption, but the topic was neglected for a long time until spectroscopic tools, based on measurements of energy distribution of electrons ejected from solids by different probes, became developed and applied to the study of gas adsorption. These spectroscopic tools, however, are concerned in most cases with the details of the shape of the energy distribution curves, but not with the absolute magnitude of the yields. In the specific case of ion bombardment, which is the technique used in the present study, there exist few investigations devoted to systematic observations on the quantitative effect of adsorption on the electron yield, y. Hagstrum [7] found that the potential emission of electrons from W, induced by slow He+ and Nef ions, decreases upon exposure to H,, N, or CO. He explained this in t Deceased. * Present address: INTEC, Gtiemes 3450, 3000 Santa Fe, Argentina. ** Comision National de Energia Atomica. *** Comisibn National de Energia Atomica and Universidad National de Cuyo. 0039-6028/82/0000-0000/$02.75 0 1982 North-Holland