Superficial segregation in nanoparticles from facets to infinite surfaces

F. Lequien (1) , J. Creuze (1) , F. Berthier (2) , B. Legrand (3)

1 ICMMO - Institut de Chimie Moléculaire et des Matériaux d'Orsay
2 LEMHE - Laboratoire d'étude des matériaux hors équilibre
3 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

We compare the superficial segregations of the Cu-Ag system for a nanoparticle and for surfaces that are structurally equivalent to each of its facet. Based on a lattice-gas model and within a mean-field formalism, we derive segregation isotherms at various temperatures in the canonical ensemble, i.e., for a given overall solute concentration, and in the semi-grand canonical ensemble, i.e., for a given bulk solute concentration. If both processes are very similar for high temperatures, they differ substancially at lower temperatures. Due to the finite-size effect and the indirect coupling between facets and edges, the relative position of the phase transitions of the facets and the corresponding surfaces are inversed when displayed as function of the solute bulk concentration. Moreover, we show that working in the semi-grand canonical ensemble is a much more efficient way to study this phenomenon, although nanoparticles are canonical- objects in essence.

Keywords: Nanoparticle / segregation / phase transition / Cu-Ag

Domains: Nuclear Experiment [nucl-ex]; Nuclear Theory [nucl-th]

F. Lequien, J. Creuze, F. Berthier, B. Legrand. Superficial segregation in nanoparticles from facets to infinite surfaces. Journal of Chemical Physics, 2006, 125 (9), pp.094707. ⟨10.1063/1.2245804⟩. ⟨cea-02356034⟩