Field ion microscope studies of exchange-mediated, atom-displacement processes on metal surfaces

The contributions of field ion microscopy to the discovery and understanding of exchange-mediated, atom-displacement processes on metal surfaces are reviewed. Experimental evidence leading to the confirmation of the exchange mechanism on the (110) and (100) surfaces of fcc metals is presented along with a discussion of the fundamental and technological implications of atomic exchange processes. Chemical trends in the preferred diffusion mode for various adatoms on fcc (100) surfaces are extracted from field ion microscope investigations. The results indicate that the propensity for exchange versus hopping motion is not correlated with macroscopic surface or bulk properties of the metals, but may be correlated with the amount of surface-atom relaxation induced by the presence of the adatom. Also discussed are the role of exchange processes in the diffusion of small clusters and the effect of an externally applied electric field on the exchange-displacement rate and transport mechanism.