An Atomic View of Surface Diffusion on Metals

Abstract

AbstractAtomic migration in crystals is obscured by the crystal itself, and it has therefore taken ingenious indirect methods to study the diffusion process. In contrast, diffusion at surfaces is amenable to fairly direct examination, on the atomic level, through the use of the field-ion microscope. By combining measurements of the mean-square displacement with determinations of the distance distribution function, considerable detail about atomic jumps in diffusion can be obtained. Here we will briefly review results obtained by field-ion microscopic examination of single metal atoms and metal clusters diffusing on metal crystals.What is noteworthy in the diffusion of single metal atoms is the variety of behavior which is dictated by the nature of the substrate, and the occasional complexity of the diffusion process. Examples of substrate-specific effects in atomic migration will be given for both fcc and bcc metals. Another surprising aspect of diffusion on metal surfaces is the role of clusters. These are stable at relatively high temperatures, and often diffuse at rates comparable to those of single atoms. The status of such cluster studies will be briefly examined, not only for their significance in surface transport, but also for their interest in understanding cohesion at metal surfaces.