Fluctuations and critical phenomena in catalytic CO oxidation on nanoscalePt facets - art. no. 165417

Local fluctuations and fluctuation-induced transitions in catalytic CO oxid ation are studied with field electron microscopy on the (112) facets of a [ 100]-oriented Pt field emitter tip. The reaction is investigated in the bis table range close to the cusp point (critical point) that terminates the bi stability range in p(CO), T-parameter space. The amplitude and the spatial coherence of the fluctuations increase on approaching the critical point. T he fluctuations are spatially well correlated on each flat (112) facet, but their correlation decays rapidly across stepped regions that terminate the flat facets. On smaller (112) facets, an onset of fluctuation-induced tran sitions is observed earlier (i.e., further away from the critical point) th an for larger (112) facets. The behavior of the reaction system near the cu sp point appears to be similar to that of an equilibrium system near the cr itical point. The observed fluctuations are mimicked in a simple reaction m odel for CO oxidation on surfaces that incorporates both rapid diffusion of adsorbed CO, and superlattice ordering of adsorbed immobile oxygen. The st eady states of the model exhibit a cusp bifurcation, from a regime of bista bility to one of monostability. The fluctuations increase near this cusp po int, as in experiment. This behavior is analyzed via kinetic Monte Carlo si mulations and analytic procedures, focusing on the consequences for fluctua tion-induced transitions.