Ion-electron emission: The effect of oxidation

Abstract

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 γ on oxygen exposure, for a given metal, is similar to that of φ, the work function of the surface. Comparison of the results for Al and Mo shows, however, that the magnitude of the change in γ cannot be attributed solely to a change in φ. 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.