Field ion appearance energy spectroscopy of CO + originated from Rh(111) and Au(111) surface step sites

Abstract

Field ionization of CO at step sites of Rh(111) and Au(111) was studied with field ion microscopy and mass-to-charge resolved field ion energy spectroscopy. Using a newly developed retarding potential technique, absolute values for CO + field ion appearance energies were derived from measurements of the high energy onset of ion retardation curves and from in situ measurements of the work function of the retarding electrode. From analyses of the CO + field ion appearance energies, field ionization of CO on Rh and Au surfaces was found to proceed by field desorption. Applying a thermionic cycle, field-dependent values of the binding energy for CO on Rh(111) and Au(111) were derived. For comparison, CO field ionization was also studied at a passivated Rh surface. The mechanism of field ion imaging of metal surfaces with CO + ions and the field-dependent chemisorption of CO on different metal surfaces is discussed on the basis of experimental results and theoretical calculations.