Some metallic adsorbed atoms on fcc metal surfaces can exchange with substrate atoms well below the room temperature. For homogeneous systems, the atomic exchange is a mechanism for self-diffusion. For heterogeneous systems, it is a mechanism for point alloy formation of only the top surface layer but it will also induce self-diffusion. We present experimental evidence found from FIM, HREELS and LEIS studies. These experiments and their relations to available theories and molecular dynamic simulations of this phenomenon are also mentioned. In addition, we present evidence for the ascending motion of step edge atoms to the upper terrace for the Ir (111) surface, and the result of a measurement of the potential barrier height of the ascending motion and the dissociation energy of step edge atoms to the lower terrace.
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