Field ion microscopy study of CO oxidation on palladium field emitter : field effects and imaging mechanism

Field ion microscopy (FIM) was applied in an attempt to monitor the kinetic oscillations in the CO oxidation rate. However, major difficulties arise due to field effects that enhance the CO dissociation leading to rapid poisoning of the surface with the formed carbon. On the other hand, it was found that the ionization of molecular oxygen that acts as the imaging gas under reaction conditions, occurs preferentially on oxygen adsorption sites in agreement with the mechanism of resonant field ionization. The imaging mechanism based on local work function influences on field ionization efficiency was discussed in view of the data obtained and was shown to be incorrect.