Nothing moves a surface: vacancy mediated surface diffusion
  We 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. 
R. van Gastel (1), E. Somfai (2), S. B. van Albada (1), W. van   Saarloos (2), J. W. M. Frenken (1) ((1) Kamerlingh Onnes La...