Increased image brightness caused by field adsorption in field-ion microscopy. II. Effects of field distortions in atomic orbitals

Abstract

We further substantiate the idea that exchange effects result in the observed alterations in He ionization rates associated with rare-gas atoms which are field adsorbed above metallic-tip surface atoms in the field-ion microscope. Theoretically, these effects are realized through the antisymmetrization of the initial and final electronic states appearing in the time-dependent perturbation theory for the ionization process. A previous transfer-Hamiltonian calculation is improved through the inclusion of field-induced distortions of the atomic orbitals. The field dependence of the enhancement factors associated with adsorbed He and Ne has been redetermined and the ratio of these calculated enhancement factors now lies in good agreement with Rendulic's observations.