Self-Organization of Ultrathin Vanadium Oxide Layers on a Rh(111) Surface during a Catalytic Reaction. Part I: A PEEM Study

摘要

Self-organization of ultrathin vanadium oxide layers (θ_V < 0.5 MLE) on a Rh(111) surface during the H2 + O2 reaction has been investigated in the 10~(-6)-10~(-4) mbar range using photoemission electron microscopy (PEEM) as a spatially resolving method. We observe that the homogeneous state is transformed via reaction fronts into macroscopic quasi-stationary patterns. In these patterns a condensation of V and O into stripes or islands takes place (θ_V < 0.5 MLE). The coarsening of the patterns with time follows a power-law dependence. The patterns are a nonequilibrium structure explained here tentativelyas a result of reactive phase separation. Formation of the oxide distribution patterns is associated with a considerable memory effect. This memory effect can be exploited for microstructuring of the surface by applying a schedule for parameter variation. Decoration of such microstructures with nickel leads to channel-like structures through which pulses propagate during the H2 + O2 reaction.