EVIDENCE OF POST FIELD IONIZATION AND OBSERVATION OF NOVEL FEATURES IN THE ENERGY DISTRIBUTION OF FIELD EVAPORATED IONS

Abstract
When field evaporation is carried out under the condition where more than one charge States coexist, the energy distribution of higher charge state ions exhibits a low energy tail similar to that of gas ions in field ionization. Ions in the tail can only be produced by post field ionization. A double peak structure has been found in the energy distribution of Mo²⁺ where the low energy peak dominates at high field and the high energy peak dominates at low field, the origin of which is not yet understood. High temperature field evaporation produces Mo²⁺ ; this has interesting implications to Coulomb explosion and theory of field evaporation. The stability of this ion is probably the result of an effective screening of the two positive charges by the electronic charges in the ion.