Nano Lithographically Templated Assembly of 1D Nanostructures

One dimensional semiconductor (1D) nanomaterials are promising building blocks for future nanodevices and nanosystems. Yet, controlled and uniform assembly of these 1D nanostructure with precise location and orientation is still a major challenge towards their integration into functional nano scale devices. To address this challenge, Mokari et al reported synthesis of semiconductor nanorods with metallic tips, which can serve as natural anchors. However, the concept of controlled assembly of metal-tipped nanorods has been unexplored since then.

Recently, we demonstrated controlled assembly of Au tipped CdS nanorods (nanodumbbells) onto nanopatterned anchoring functionalities. The functionalities are made of nanoimprinted Au nanodots with immobilized thiol molecules. Here, we report detailed mechanism of Au-CdS-Au nanodumbbell assembly, by demonstrating two types of nanodumbbell anchoring. In the first type, one nanodumbbell anchors to one functionalized dot. In this case, many neighboring nanodumbbells are connected to each other with their free edges, either by side-by-side parallel connection due to antiparallel coupling between permanent dipole moments along the rod axis or van der Waals forces, or by end-to-end connection due to solvent evaporation. In the second type, a nanodumbbell is anchored to a pair of nanodots whose spacing matches the nanodumbbell length. Also, we used AFM to find that the anchored nanodumbbells, while chemically attached to the nanodots, lay on the surface, and are not suspended. Finally, we have studied the effect of assembly time and different solvents with various polarity on the assembly process. Our study provides an important insight onto the fundamental mechanism of the controlled assembly at the nanometer scale, and opens a pathway to the bottom-up realization of nanosystems with a structural and functional complexity unachievable nowadays.