SURFACE-DIFFUSION OF PT ADATOMS ON NI SURFACES

The diffusion of individual Pt adatoms on the (100), (110), (311), and (111) surfaces of Ni has been investigated by field ion microscopy. On the (100) and (110) surfaces Pt adatoms replace Ni substrate atoms at temperatures below the onset of hopping displacements. The minimum temperature required for replacement is 250 and 105 K for the (100) and (110) surfaces, respectively. On the (311) and (111) surfaces, Pt adatoms migrate by conventional site-to-site hopping. The activation barriers for displacements on the (100), (110), and (311) planes are estimated from the migration temperatures and compared to activation barriers measured previously for self-diffusion on Pt and Ni.