The diffusion of individual Pt atoms on 5 low-index crystal planes of Rh was investigated by using field-ion microscopic techniques. It was found that the activation energy for surface diffusion depended strongly upon the crystal plane, and increased in the order: (111) < (311) < (110) < (331) < (100) (table 21). The data for (311) could be described by:

D (cm2/s) = 0.00016 exp[-0.44(eV)/kT]

The diffusion mechanism which operated on the surfaces was site-to-site hopping; apart from (110), where evidence for the occurrence of exchange displacements was obtained. The reflection barrier to migration off the plane edge also exhibited a strong structure-sensitivity; from a large reflection on (311) to essentially none on (100) and (331).

G.L.Kellogg: Physical Review B, 1993, 48[15], 11305-12

Table 21

Activation Energies for Pt Diffusing on Rh Surfaces