Shape-controlled self-assembly of colloidal nanoparticles

In this paper, we have successfully directed self-assembly of colloidal nanoparticles (NPs) of Au and CdTe into perfect hexagonal microflakes or ultralong microwires, via stepwise reducing the electrostatic repulsion potential of neighboring NPs in their dispersions with the help of l-cysteine. The hexagonal microflakes were formed via slow self-assembly of short NP chains, while the ultralong microwires were formed via the fast self-assembly of long NP chains. The microwires were kinetically stable and gradually transformed to flakes during incubation in water. This underlines a pronounced correlation of the shape of the resulting supracrystals with the length of the starting NP chains and their self-assembly kinetics. This correlation should provide a fundamental basis not only for better interpretation and even prediction of shape-controlled crystallization but also for organization of nanoscale building blocks to mesoscopic and macroscopic artificial solids.