Reversible, Tunable, Electric-Field Driven Assembly of Silver Nanocrystal Superlattices.

Nanocrystal superlattices are typically fabricated by either solvent evaporation or destabilization methods that require long time periods to generate highly ordered structures. In this paper, we report for the first time the use of electric fields to reversibly drive nanocrystal assembly into superlattices without changing solvent volume or composition, and show that this method only takes 20 min to produce polyhedral colloidal crystals, which would otherwise need days or weeks. This method offers a way to control the lattice constants and degree of preferential orientation for superlattices and can suppress the uniaxial superlattice contraction associated with solvent evaporation. In situ small-angle X-ray scattering experiments indicated that nanocrystal superlattices were formed while solvated, not during drying.