Surface self-diffusion on Pt(001) by an atomic exchange mechanism.

Field-ion microscopy has been used to map the surface sites visited by an individual Pt adatom migrating at 175 K on the Pt(001) plane and to determine its activation energy for surface diffusion. Atomic displacements are found to occur only in the (100) or (010) directions. A surprisingly low activation energy of 0.47 eV is measured. These results are consistent with a model in which the diffusion occurs by an adatom-substrate exchange mechanism. This mechanism is predicted theoretically for self-diffusion on Al(001).