FIELD-ION APPEARANCE SPECTROSCOPY - INVESTIGATIONS ON ION GENERATING PROCESSES AT FIELD EMITTER SURFACES

Integral energy distributions of field emitted singly and doubly charged metal ions (Cu+, Be+, Be++, Ni+, Ni++) are measured. Appearance Potentials APn (n = 1, 2) are derived from the onset of the energy distribution. With low emitter temperatures (≲300 K) experimental APn values coincide with values calculated from the image hump model of field evaporation, both for singly and doubly charged species. With high emitter temperatures (≳900 K) AP1 values of singly charged ions reflect the first ionization potential I1 of gaseous metal atoms. A few ions display AP1 values down to 5 eV below I1. This is explained by field ionization of electron excited atoms. © 1979.