Energy anisotropy of bimetal core–shell nanorods and its effects on morphology

A thermodynamic analysis in the equilibrium state is presented to investigate the morphology evolution of silver and palladium epilayers deposited on gold nanorods (GNRs). With regard to Ag epilayers on GNRs, the misfit strain has a notably small value of 0.002 44 and the stored strain energy is three orders of magnitude lower than the energy contribution from the surface and interface. Consequently, Ag epilayers are preferred on the {111} facets on the two ends of the GNRs due to surface and interface energy minimization, and the growth of dumbbell-shaped structures is thus promoted. The reverse is the case for Pd epilayers on GNRs. The larger misfit strain of 0.048 83 increases the strain energy to the same magnitude as surface and interfacial energies. Long-time growth of Pd epilayers is favored along the {100} surfaces of the GNRs for strain energy minimization, and rectangular core–shell nanorods emerge. The theoretical analysis is consistent with relevant experimental results. (Some figures in this article are in colour only in the electronic version)