In the reduction of NO with ${\mathrm{H}}_2$ on a Rh(110) surface rectangularly shaped target patterns and spirals with sharp corners have been observed. These patterns can be reproduced with a simple model assuming that the (anisotropic) diffusion is state dependent. Such a dependence is realized in the system Rh(110)/NO + ${\mathrm{H}}_2$ by the presence of different adsorbate-induced reconstructions with varying substrate geometries.

• Received 2 September 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.3483