Interaction ofHe+andNe+ions with Ni(100)-K and Cu(100)-K surfaces having variable potassium coverage

This paper presents an electron-spectroscopic study employing slow ${\mathrm{He}}^{+}$ and ${\mathrm{Ne}}^{+}$ ions incident on Ni(100) and Cu(100) surfaces with varying amounts of adsorbed potassium. Investigation of the changes in electron-energy spectra as the work function of the surface is varied probes the pattern of resonance tunneling, excitation conversion, and Auger electron-ejection processes. When the surface is clean the work function φ is high and the mode of electron ejection is the two-electron process of Auger neutralization of the incident ions yielding a folded two-electron spectrum. As the macroscopic φ is reduced by K adsorption the surface develops more and more regions near K atoms where the local φ is small, permitting resonance neutralization of the incident ion to form a metastable atom which on Auger deexcitation ejects electrons in a one-electron spectrum.