Diffusion of individual Pt atoms on single-crystal surfaces of rhodium

The diffusion of individual Pt atoms on five low-index crystal planes of Rh has been investigated by field-ion microscopy. The activation energy of surface diffusion is found to depend strongly on the crystal plane and to increase in the order of (111)<(311)<(110)<(331)<(100). It ranges from below 0.22 eV on Rh(111) to 0.92 eV on Rh(100). The diffusion mechanism on all surfaces is site-to-site hopping, with the exception of Rh(110), where convincing evidence for exchange displacements is obtained. The reflection barrier against migration off the plane edge also exhibits a strong structure sensitivity, from a large reflection on Rh(311) to essentially none on Rh(100) and Rh(331). The results are compared with previous field-ion-microscope studies of self-diffusion on Rh and Pt.