Memory Effects and Complex Patterns in a Catalytic Surface Reaction

Rate oscillations and spatio-temporal pattern formation in catalytic CO oxidation on a Pt(110) surface are driven by the 1 × 1 ⇄ 1 × 2 phase transition of the Pt surface. The mass transport of Pt atoms associated with this phase transition necessarily generates some roughening of the surface. By using low energy electron microscopy (LEEM) to image the laterally varying adsorbate concentrations it is shown that this reversible roughening is part of the pattern-forming process establishing a memory effect in the oscillatory medium. As a result complex and unusual patterns form under oscillatory conditions. Different types of pattern, each with a characteristic size, coexist such that a hierarchy of length scales is established.