Dynamics of surface reactions studied by field emission microscopy and atom-probe mass spectrometry

Recent progress in imaging surface chemical reactions and adsorbate-induced reconstruction by means of field ion microscopy is reviewed. Achievements and prospects of a local chemical analysis during imaging are also presented and discussed. Major shape transformation is reported to occur during the field-free interaction of oxygen with Rh crystal tips. Rather than hemispherical when clean they appear polyhedral after reaction at temperatures between 500 and 550 K. Kinetic non-linearities are found in both the NO and NO2 reaction with hydrogen on the surface of a pyramidal Pt crystal tip. Oscillatory reaction behavior is observed for both reactions. In the NO2-H2 case explosive ignition in [0 1 2] planes is followed by one-dimensional chemical wave propagation along the <1 0 0> zone lines. Atom-probe time-of-flight mass spectrometry demonstrates that water (field ionized as H2O+ and H3O+) is the product of the catalytic reaction. During the NO/H2 reaction, dynamic formation and motion of small islands are observed. These islands appear on the (0 0 1) pole and are interpreted as being due to adsorbed hydroxyl species. Island sizes are confined to the equivalent of 10-30 Pt atoms.