It was recalled that recent papers had presented perhaps the first experimental evidence, based upon scanning tunnelling microscopic images, that impure In atoms which were embedded into the first close-packed layer of a (001) Cu surface were not localized but instead made long concerted excursions. Such excursions occurred due to a continuous reshuffling of the surface, following the exchange of positions of impure and host atoms with naturally occurring surface vacancies. An original lattice-gas model, with asymmetrical exchange probabilities, was formulated. Its numerical solutions were in good agreement with experimental data.

Atomic Slide Puzzle - Self-Diffusion of an Impure Atom. O.Bénichou, G.Oshanin: Physical Review E, 2001, 64[2], 020103 (4pp)