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The interaction of COO2 gas mixtures with Au tips: in situ imaging and local chemical probing

The interaction of CO/O2 gas mixtures with gold has been studied by means of video‐field ion microscopy (FIM) under truly in situ conditions on the surfaces of small Au tips. To elucidate the local surface composition while imaging, atom‐probe studies have been performed using field pulses in a pulsed field desorption mass spectrometry (PFDMS) set‐up. The interaction of pure CO with Au field‐emitter tips at 300 K causes Au carbonyl to be formed on the surface, and these appear as singly and doubly charged cations AuCOn+ and Au(CO)n+2 in PFDMS spectra. The formation of these species is promoted by applying a steady electric field of several volts per nanometre. Video‐FIM reveals bright spots associated with the adsorption of oxygen during the extended interaction of oxygen gas with the Au surface. Dosing the Au tip with mixtures of O2 and CO causes chemical waves to move across the surface. Local chemical probing by pulses reveals that the occurrence of the wave is associated with the transition from a weakly oxygen‐covered to a CO‐covered surface (dominated by Au carbonyls). We conclude that the moving wave consists of Au sub‐carbonyls. The results demonstrate the usefulness of combined video‐FIM and atom‐probe studies to elucidate reaction mechanisms under model conditions of low gas pressures (⩽10−2 Pa) on a well‐defined gold crystallite. Copyright © 2007 John Wiley & Sons, Ltd.