Dynamics of adsorbate islands with nanoscale resolution

Surface catalytic processes produce, under certain conditions, small cluste rs of adsorbed atoms or groups, called islands which, after they have been formed, move as individual entities. Here we consider the catalytic reducti on of NO with hydrogen;en platinum. (i) Using video field ion microscopy, w e observe the dynamic motion of small hydroxyl islands on the Pt(001) plane ; despite changes in their morphology, the islands dimensions are confined to values corresponding to 10 to 30 Pt atoms suggesting cooperative effects to be in operation. (ii) We construct an automaton (or lattice Monte-Carlo ) model on the basis of a set of elementary processes governing the microsc opic dynamics. The agreement between the simulation results and the experim ental observations suggests a possible mechanism for the formation and dyna mics of hydroxyl islands.