Appearance energy spectroscopy of field ions

Field ion appearance energies, derived from measurements of the high energy onset of ion retardation curves and from measurements of the effective work function of the retarder electrode, provide information on the energetics of ionization, desorption, and surface reaction processes occurring in high electric fields. The physical significance of appearance energies is discussed using arguments based on a thermionic cycle and on total energy considerations. The present state of the art of retarding potential measurements is described and illustrated by three examples: (a) the field ionization of noble gases, (b) field desorption of H+3, (c) field evaporation of rhodium. For the latter, recent measurements on (111) and (100) facets characterized by probe-hole FIM are presented, and their implications for the determination of the cohesive energy of metals will be discussed