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International audience; Monte Carlo simulations within a Tight-Binding Ising Model (TBIM) have been performed on bulk, surfaces, and nanoclusters of Ni c 1 Pt c alloys in order to describe and understand the competition between surface segregation and chemical ordering phenomena in nanoalloys. The effective pair interactions obtained from the DFT calculations have been applied in Monte Carlo simulations to determine the bulk and alloy surfaces configurations. The order-disorder transition temperatures in the bulk compare well with experimental data and the bulk phase diagram from the model have been compared to that determined experimentally to validate the fit. The (111), (100) and (110) crystallographic orientations surfaces Ni Pt c c 1 are treated. The three driving forces for the segregation of surfaces have be studied in both diluted limits, together with the phenomenon of segregation at high temperature (in the disordered state) over the entire concentration range. Finally, we analyze the competition between superficial segregation and low temperature chemical order and conclude with a similar approach on truncated octahedra of 1289 and 405 atoms.

International audience; We have investigated the growth of Ni on Pt stepped surfaces with (1 1 1) terraces by means of potentials derived from the second moment approximation in a tight-binding model. The activation energies associated to these processes are determined. The Schwoebel barriers of Ni atoms descending steps of Pt stepped surfaces are calculated for different kinds of straight steps (A and B steps) differing by the orientation of the ledge. In addition, we study the diffusion of Ni adatoms at fcc or hcp sites in the presence of small adislands on the terraces, in the vicinity of the A and B steps. We show that a good estimate of the potential wells and diffusion barriers could be given by introducing a lateral effective pair interaction model, the interactions extending up to the next nearest neighbors. Finally, we have carried out Kinetic Monte-Carlo simulations to investigate the Ni wire formation at Pt step edges and the influence of the exchange processes in the alloy formation.