A fresh look at the electric-field dependence of surface-atom binding energy

This paper aims to clarify the theoretical concepts associated with the field dependence of surface-atom binding energy. The various coefficients involved are defined, and orbital-polarization and charge-transfer effects are distinguished. It is demonstrated that the latter, as well as the former, may have an F² form. A new empirical method of estimating the polarization-energy coefficient for a field-evaporating surface atom is described: this is based on the joint measurements of activation energy and onset appearance energy made by Ernst. His data for rhodium are reanalysed to give the value 1.05 ± 0.3 meV V^?2 nm². This value is then used to show that polarization-type effects will influence the interpretation of field-sensitivity data. Further experiments are called for.