Magic Pairs and Structural Transitions in Binary Metallic Clusters

Abstract

Structures and binding energies for bimetallic clusters consisting of a large variety of atomic species are obtained for all atomic sizes N≤40 and all concentrations, using an interatomic potential derived within a quasi-classical description. It is found that increasing the difference between the two types of atoms leads to a gradual disappearance of the well-known homo-atomic geometric magic numbers and the appearance of magic pairs corresponding to the number of atoms of each atomic species in binary nanostructures with higher stability. This change is accompanied by structural transitions and ground-state↔isomer inversions, induced by changes in composition or concentration. There is a clear tendency towards phase separation, the core-shell radial segregation being predominant (energetically favored) in this model.

Morphological instability of core-shell metallic nanoparticles

“…Besides being poorly miscible in bulk phases 42 , these systems have the element of larger atomic radius (Ag or Au) presenting smaller cohesive and surface energies than the other element. These features are all in favour of Ag or Au surface segregation in these nanoparticles, a behaviour that has been confirmed, both experimentally and computationally, by several studies 2,[5][6][7][9][10][11][13][14][15][16][17][19][20][21][22][23][24][25][29][30][31][32]35 . However, the fact that the cluster surface is expected to contain mostly Ag or Au does not determine completely chemical ordering.…”