We have studied oxygen interaction with Au crystals (field emitter tips) using time-resolved (atom-probe) field desorption mass spectrometry. The results demonstrate no adsorption to take place on clean Au facets under chosen conditions of pressures (p < 10(-4) m/bar) and temperatures (T = 300-350 K). Steady electric fields of 6 V/nm do not allow dissociating the oxygen molecule. The measured O2+ intensities rather reflect ionization of O2 molecules at critical distances above the Au tip surface. Certain amounts of Au-O2 complex ions can be found at the onset of Au field evaporation. Calculations by density functional theory (DFT) show weak oxygen end-on interaction with Au10 clusters (Delta E = 0.023 eV) and comparatively stronger interaction with Au1/Au(100) model surfaces (Delta E = 0.25 eV). No binding is found on {210} facets. Including (positive) electric fields in the DFT calculations leads to an increase of the activation energy for oxygen dissociation thus providing an explanation for the absence of atomic oxygen ions from the field desorption mass spectra.

We have studied the catalytic reduction of nitric oxide (NO) with hydrogen (H 2 ) on platinum using both field ion microscopy (FIM) and pulsed field desorption mass spectrometry (PFDMS). Under certain conditions of temperature and gas pressure this reaction exhibits non-linear behaviour, i.e. hysteresis effects and rate oscillations occur. Ensembles of kink sites of the <100> zones are found to act as pacemakers, which is in line with earlier studies demonstrating f012g planes to ignite in a quasi-concerted manner.1,2 Experiments with tips of varying radius of curvature always lead to the same sequence of image patterns. Large variations in the H 2 partial pressure has little influence on the frequency of the rate oscillations.Using PFDMS under the reaction conditions we show that NO + rather than H 2 O + /H 3 O + (the neutrals are formed during the reaction process) is the imaging species in FIM. Interestingly, PtO n+ x .x ≤ 3/ are seen in the mass spectra, indicating that the reaction is controlled by a vacant site mechanism with the inclusion of partial oxidation of the Pt surface.

We show that gold mono- and di-carbonyls are formed on gold field emitter tips during interaction with carbon monoxide gas at room temperature and in the presence of high electrostatic fields. The experiments are done in a time-of-flight atom probe to obtain mass spectra. The yield of monocarbonyl cations is about twice that of di-carbonyl ions. Density functional theory calculations are reported that explain the field stabilization of adsorbed carbonyls and the desorption yield of their cations.

We present dynamic studies of surface reactions using video-Field Ion Microscopy (FIM) along with Pulsed Field Desorption Mass Spectrometry (PFDMS). Catalytic water formation is followed using rhodium and platinum 3D field emitter crystals for the oxidation of hydrogen with either oxygen (Rh) or NO (Pt). Strongly non-linear dynamics are observed with nanoscale spacial resolution. For both reactions quasi-oscillatory behaviour exists under certain conditions of temperatures and partial pressures. An influence of the probing electric field is observed and possibly essential in establishing oscillatory behaviour. Local chemical probing of selected surface areas with up to 400 atomic surface sites proves catalytic water formation to take place. Since water ions (H 2 O + / H 3 O + ) cause image formation of the O 2 -H 2 reaction on Rh, respective videos provide space-time resolved information on the catalytically active sites. Atom-probe data also reveal that the surface of the Rh sample reversibly switches from a metallic to an oxidized state during oscillations. As to the NO-H 2 reaction on Pt, fast ignition phenomena are observed to precede wave fronts. After catalytic water formation, NO molecules diffuse into emptied areas and cause high image brightness. Depending on the size of the Pt crystal, the reaction may ignite in planes or kinked ledges along the <100> zone lines. Thus FIM provides clear experimental evidence that kinks are more reactive than steps in the catalytic NO + H 2 reaction. Pt surface oxidation occurs and has probably been underestimated in previous FIM studies.

The interaction of CO/O 2 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 AuCO n+ and Au(CO)