Dopant Mediated Assembly of Nanorods into Atomically Coupled 2D Sheets in Solution

Self and directed assembly of nanorods into ordered superstructures is an area of intense research interest as in such architectures, the discrete size defined properties of each nanostructure can be collectively harnessed at a scale amenable to real application. The formation of vertically aligned nanorods into hexagonal superlattices is a recent development leading to structured arrays suited for high-density applications. Spontaneous supercrystal organization in nanorods requires low polydispersity in both diameter and length, which can complicate the assembly compared to that of spherical nanocrystals. These nanorods can be pre-assembled as 2D sheets during synthesis by incorporating certain amount of foreign ion or dopant in the nanorod structure. Further, dispersed solution containing 2D sheets can be deposited in any substrate by either spin coating or drop casting to form thin film of micrometre-sized superlattice. In this work, we focus on understanding how dopant incorporation on the nanorod modifies their surface chemistry to from vertically aligned nanorod superstructure (2D sheets) in solution. We demonstrate by using synchrotron small-angle x-ray scattering (SAXS) and dynamic light scattering, that optimum concentration of dopant is required to tune the nanorod-nanorod interaction (repulsive and attractive) in solution to nucleate the self-assembly process. These 2D sheets of nanorods were extensively studied by SAXS, XPS, HRSTEM, HRSEM and SAED.