Controlled semiconductor nanorod assembly from solution: influence of concentration, charge and solvent natureElectronic Supplementary Information (ESI) available: nanorod concentration data for CdSe nanorods, SEM and TEM data for CdSe and CdS nanorods. See DOI: 10.1039/c1jm14382d

Spontaneous supercrystal organisation of semiconductor nanorods (CdS and CdSe) of different aspect ratios into ordered superstructures was obtained by controlled evaporation of a nanorod solution. The rods either align into two dimensional close packed perpendicular arrays or into one dimensional rail tracks depending on the total interaction energy between the rods in solution. A detailed study has identified critical factors that affect this interaction energy such as nanorod concentration, surface charge, dipole moment and solvent nature (polarity and volatility), thereby allowing a general approach to control the nature of nanorod assembly (1D or 2D). Molecular dynamics (MD) of small charged nanorods showed that opposite dipolar alignment (antiferromagnetic) was the preferred rod orientation during self-assembly. Here we report a comprehensive study of the critical factors that affect the spontaneous organisation of semiconductor nanorods (CdS and CdSe) into ordered superstructures from solution.