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Abstract

Field ionization (FI) experiments characterized by field ion imaging and by field ion appearance spectroscopy have been performed of Ne on Rh(012) at emitter temperatures of 79 K, and slightly above at 107 K, as well as of Ne with admixed Ar on Rh(111) at 79 K, and also of CO on Rh(111) in the temperature range of 79–300 K. The results obtained for rare gas FI give evidence of weakly bound image gas atoms on the interior sites of crystal facets playing an active role in imaging gas accommodation. These atoms are as necessary for localized FI as arc the earlier suggested actively involved field-adsorbed atoms on the imaged surface step sites of the emitter. FI of CO was found to proceed by field desorption. From analyses of the appearance energies of CO⁺, arguments have been derived that the earlier model of localized FI, at which at the instant of FI a touching of imaging gas at the sites of strong field adsorption was assumed, is of minor importance and should be replaced in favour of a collision-induced exchange process prior to FI being sufficient and necessary for highest contrast field ion images.