Atomically Visualizing Elemental Segregation-Induced Surface Alloying and Restructuring.

Using in situ transmission electron microscopy that spatially and temporally resolves the evolution of the atomic structure in the surface and subsurface regions, we find that the surface segregation of Au atoms in a Cu(Au) solid solution results in the nucleation and growth of a (2 × 1) missing-row reconstructed, half-unit-cell thick L12 Cu3Au(110) surface alloy. Our in situ electron microscopy observations and atomistic simulations demonstrate that the (2 × 1) reconstruction of the Cu3Au(110) surface alloy remains as a stable surface structure as a result of the favored Cu-Au diatom configuration.