Post-Ionization of Field-Evaporated Ions

Abstract

It is shown that the final observed charge state of a field-evaporated ion can be explained by the occurrence of post-ionization whereby an ion being accelerated away from a metal surface in a strong electric field loses one or more electrons by tunneling into the substrate. Calculations using an approximate analytic formula derived from a simple model potential predict the probability of post-ionization for many different elements.