Size and shape effects on chemical ordering in Ni-Pt nanoalloys.

The atomic structure and chemical ordering of Ni-Pt nanoalloys of different sizes and shapes are studied by numerical simulations using Monte Carlo methods and a realistic interatomic potential. The bulk Ni-Pt ordering tendency remains in fcc nanoparticles but we show some chemical ordering frustrations linked to surface reconstructions depending on the cluster size and shape. A reversed temperature dependence of Pt surface segregation is also established.