APPEARANCE ENERGY SPECTROSCOPY OF FIELD IONS

Field ion appearance energies, derived from measurements of the high e nergy onset of ion retardation curves and from measurements of the eff ective work function of the retarder electrode, provide information on the energetics of ionization, desorption, and surface reaction proces ses occurring in high electric fields. The physical significance of ap pearance energies is discussed using arguments based on a thermionic c ycle and on total energy considerations. The present state of the art of retarding potential measurements is described and illustrated by th ree examples: (a) the field ionization of noble gases, (b) field desor ption of H-3+ (c) field evaporation of rhodium. For the latter, recent measurements on (111) and (100) facets characterized by probe-hole FI M are presented, and their implications for the determination of the c ohesive energy of metals will be discussed.