Desorption of positive and negative ions from SiO2/Si surfaces by electron excitation of core levels.

Abstract

Electron-stimulated desorption of positive and negative oxygen ions and positive, multiply charged silicon ions from thin ${\mathrm{SiO}}_{2}$/Si films has been studied as a function of impact electron energy. Thresholds observed for ${\mathrm{O}}^{+}$ are correlated with core-level binding energies of substrate atoms. Desorption of negative ions closely follows threshold behavior of positive ions; it is explained in terms of a charge-exchange process in which the outgoing positive ions (or neutrals) capture electrons in the surface region and desorb as negative ions. Desorption of multiply charged silicon ions is also related to creation of core holes, but requires some additional, multielectron excitations.