Nonequilibrium Anisotropic Colloidal Single-Crystal Growth with DNA*

Abstract

Anisotropic colloidal crystals are materials with novel optical and electronic properties. However, experimental observations of colloidal single crystals have been limited to relatively isotropic habits. Here, we show DNA-mediated crystallization of two types of nanoparticles with different hydrodynamic radii that form highly anisotropic, hexagonal prism microcrystals with AB 2 crystallographic symmetry. The DNA directs the nanoparticles to assemble into a non-equilibrium crystal shape that is enclosed by the highest surface energy facets (AB 2 (1010) and AB 2 (0001)). Simulations and theoretical arguments show that this observation is a consequence of large energy barriers between different terminations of the AB 2 (1010) facet, which results in a significant deceleration of the (1010) facet growth rate. In addition to reporting a hexagonal colloidal crystal habit, this work introduces a potentially general plane multiplicity mechanism for growing non-equilibrium crystal shapes, an advance that will be useful for designing colloidal crystal habits with important applications in both optics and photocatalysis.