ADSORBATE-INDUCED STEP-DOUBLING RECONSTRUCTION OF A VICINAL METAL-SURFACE - OXYGEN ON RH (332)

Morphological transitions induced by oxygen on a stepped rhodium surface, Rh{332}, have been studied using LEED. The stable clean surface is made up of a series of six-atom-wide terraces separated by monatomic steps. At low coverages (theta almost-equal-to 0.1 ML) oxygen induces a restructuring of the surface surface at temperatures in the range 430-510 K, with a doubling of step height and terrace width compared to the clean surface. With additional exposure to oxygen (theta almost-equal-to 0.6 ML) the surface returns to the step structure of the clean sample. Both processes are reversible. A metastable double-step structure of the clean surface was produced by the catalytic removal of oxygen from the reconstructed surface with hydrogen at 360 K. The kinetics of these phase transitions has been investigated using LEED. Kinetic modelling provides a determination of kinetic parameters for the escape of rhodium atoms from single and double step edges. A reconstruction mechanism is presented, and the driving forces are discussed.