Equilibrium shapes of supported silver clusters.

The morphology of silver nanoparticles supported on MgO smoke crystallites was studied by combining Transmission Electron Microscopy (TEM) and atomistic simulations of clusters of realistic size. Advantage was taken of the occurrence of well-defined complex MgO surfaces, including stepped surfaces and contact lines between stacked crystallites, to analyze Ag clusters of various orientations. Silver clusters were seen to adopt systematically the shape of a truncated octahedron irrespective of the support morphology. The (100)Ag//(100)MgO epitaxy was evidenced and (100), (111) and (110) facets were identified. The agreement between observed shapes and simulated profiles demonstrated that the formers were close to equilibrium which allowed the use of Wulff-Kaishew construction to determine the anisotropy ratios γ100/γ111 (1.03 ± 0.03) and γ110/γ111 (1.08 ± 0.03) and the Ag(100)/MgO(100) adhesion energy (0.58 ± 0.10 J m(-2)) for clusters large enough to escape stress effects.