A scanning tunneling microscopy study of surface segregation of Sb at a Cu(111) surface

Surface segregation of Sb from the bulk of a Cu–0.45 at.% Sb single-crystal, annealed in situ at 400°C, is studied in the (111) surface plane, employing an ultrahigh vacuum scanning tunneling microscope (STM). The STM images demonstrate that Sb atoms segregate substitutionally and do not exist as adatoms at the (111) surface. Furthermore, the STM images reveals that the six Cu atoms surrounding each Sb atom, in the (111) plane, are significantly perturbed in terms of either electronic density or their atomic positions. The Cu atoms appear to be vertically and laterally displaced from their expected positions, thereby leading to an unexpected broken surface symmetry in the STM images.