Shape-controlled growth of two-dimensional kagome-lattice colloidal crystals through nanoparticle capping

TL;DR

This paper presents a nanoparticle capping method using DNA-modified nanospheres to control the shape and heterogeneity of colloidal crystals, enabling shape manipulation independent of lattice symmetry.

Contribution

It introduces a novel capping strategy with DNA-modified nanospheres to selectively influence colloidal crystal growth and shape, independent of thermodynamic phases.

Findings

Controlled crystal shape from tetrahedral to microplates.

Selective capping on kagome lattice facets.

Slower growth of specific crystal facets.

Abstract

Organic capping ligands can selectively bind to crystal facets to modulate growth kinetics and are important in chemical synthesis of inorganic nanocrystals. Using the capping ligands for shape-controlled growth of colloidal crystals is challenging due to the size mismatch of molecules and nanoparticle building blocks. In existing synthetic pathways, colloidal crystal shapes are determined by their thermodynamically favored phases yet controlling their shapes independent of lattice symmetry is vital to study many solid-state properties. Here, we develop a nanoparticle capping strategy to control colloidal crystal shapes and structural heterogeneity. Au bipyramids were used as building blocks and assembled into rhombohedral colloidal crystals driven by DNA hybridization. In (111) planes of the crystals, bipyramids assembled into kagome lattices, featuring structure cavities organized in a hexagonal lattice. The rhombohedral crystals have truncated tetrahedral crystal habits, and the degree of truncation defines the exposed facets and crystal shapes. Our surface capping strategy is to introduce DNA-modified nanospheres as effective capping agents, which selectively register on the surface vacancies of the kagome facets and resemble the role of organic ligands in classic nanocrystal growth. Such selective capping is driven by maximizing DNA hybridization and leads to slower growth of the (111) kagome facets, changing the crystal shape from three-dimensional truncated tetrahedra to two-dimensional layered microplates with structural heterogeneity and shape anisotropy. This study underpins the importance of capping agents in colloidal crystal growth and inspires effective ways to control the growth kinetics and heterostructures of colloidal crystals.