Assembly of anisotropic one dimensional Ag nanostructures through orientated attachment: on-axis or off-axis growth?

Recently it has been found that one dimensional (1D) Ag nanostructures can be synthesized through oriented attachment (OA) growth. In OA growth of 1D structures, nanoparticles (NPs) attach to the growing nanorods (NRs) via either on-axis or off-axis attachment. However, the thermodynamic basis for understanding the preference of each growth mode has remained unexplored until now. In this paper, molecular static calculations are performed to investigate the van der Waals interactions (vdW) in both on-axis and off-axis attachments of 1D Ag nano-structures. The correlation of parameters including the size, aspect ratio (AR), crystalline orientation of NR, the inter-particle separation and the off-axis approaching angle, with both OA attachments is investigated in detail. The results show that off-axis attachment is thermodynamically favorable compared to on-axis attachment in a typical OA growth, and straight on-axis OA growth are typically realized by tuning the other aspects of an OA growth system. Interestingly, it is found that the off-axis growth is both precursor-size dependent and crystalline-orientation dependent.