2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/16837We report scanning tunneling microscopy observations, which imply that all atoms in a close-packed copper surface move frequently, even at room temperature. Using a low density of embedded indium `tracer' atoms, we visualize the diffusive motion of surface atoms. Surprisingly, the indium atoms seem to make concerted, long jumps. Responsible for this motion is an ultra-low density of surface vacancies, diffusing rapidly within the surface. This interpretation is supported by a detailed analysis of the displacement distribution of the indium atoms, which reveals a shape characteristic for the vacancy mediated diffusion mechanism that we propose.4 pages; for associated movie, see http://www-lion.leidenuniv.nl/sections/cm/groups/interface/projects/thermoMaterials ScienceStatistical Mechanicstext