REACTION-DIFFUSION FRONT PROPAGATION ACROSS STEPPED SURFACES DURING CATALYTIC-OXIDATION OF CO ON PT(100)

High-resolution microscopy studies of the removal of CO-adlayers on Pt (100) by exposure to oxygen reveal that reaction-diffusion front propa gation is impeded both by mesoscopic step bunches and by monoatomic st eps. The resulting ''stop-and-go'' nature to front propagation can be characterized in terms of a time delay for crossing each step bunch or step, at least when the separation of these defects is comparable to or exceeds the width of the front. Here, eve quantify this time delay in terms of the reduced diffusion coefficient for CO in step bunch reg ions and the width of these regions, or in terms of the reduced hop ra te for CO across monoatomic steps. We also briefly examine front propa gation across arrays of more closely spaced steps. Results facilitate assessment of terrace diffusivities from average or macroscopic front propagation velocities across multiply stepped surfaces. (C) 1998 Else vier Science B.V. All rights reserved.