Structural Diversity in Dimension-Controlled Assemblies of Tetrahedral Gold Nanocrystals

Abstract

Polyhedron packings have fascinated humans for centuries and continue to inspire scientists of modern disciplines. Despite extensive computer simulations and a handful of experimental investigations, understanding of the phase behaviors of synthetic tetrahedra has remained fragmentary largely due to the lack of tetrahedral building blocks with tunable size and versatile surface chemistry. Here, we report the remarkable richness of and complexity in dimension-controlled assemblies of gold nanotetrahedra. By tailoring nanocrystal interactions from long-range repulsive to hard-particle-like or to systems with short-ranged directional attractions through control of surface ligands and assembly conditions, nearly a dozen of two-dimensional and three-dimensional superstructures including the cubic diamond and hexagonal diamond polymorphs are selectively assembled. We further demonstrate multiply twinned icosahedral supracrystals by drying aqueous gold nanotetrahedra on a hydrophobic substrate. This study expands the toolbox of the superstructure by design using tetrahedral building blocks and could spur future computational and experimental work on self-assembly and phase behavior of anisotropic colloidal particles with tunable interactions.

Controlled Self-Assembly of Gold Nanotetrahedra into Quasicrystals and Complex Periodic Supracrystals

“…The NC surface was well-passivated by the compact and densely packed saturated alkyl chains of MUA (Table S1 and Figure S3), which maximally preserves the tetrahedral shape of NCs. Deprotonated MUA ligands provide a balance between electrostatic repulsion and van der Waals attraction to impart hard particle-like interactions …”

“…■ RESULTS AND DISCUSSION Synthesis of Quasicrystalline Supracrystals. We synthesized single-crystalline gold nanotetrahedra bound by four {111} NC facets following previously reported seed-mediated growth methods with modifications 29,30 (Figures S1 and S2). The sharpness of nanotetrahedron vertices, which is quantified by the degree of truncation parameter t defined in Figure 1a, is evident from the representative HAADF-STEM image (Figure 1b).…”

“…Deprotonated MUA ligands provide a balance between electrostatic repulsion and van der Waals attraction to impart hard particle-like interactions. 29 Low-magnification SEM images reveal discrete supracrystals typically adopting a disk or dome shape with diameters of several micrometers (Figure 1c and Figure S4). The top of individual supracrystals features an undulating surface, and corresponding FFT pattern suggests a 12-fold rotational symmetry, which is incompatible with ordinary periodic crystals (Figure 1d).…”

Tunable orientation of two-dimensional assembled Au octahedron superlattices in polymer films as flexible SERS substrates

“…Ye's group reported that tetrahedral gold nanocrystals can be assembled into various ordered superstructures by controlling the surface chemistry of Au tetrahedra. 16 Besides 2D superlattices, 3D superlattices have long-range translational and orientational ordering. 17 3D superlattices comprising Au triangular nanoprisms and pentagonal Au bipyramids also exhibited orientation-dependent SERS activity.…”

Shape-Mediated Oriented Assembly of Concave Nanoparticles under Cylindrical Confinement

“…Assembling colloidal nanoparticles into long-range ordered superlattices has been spotlighted as a promising pathway to creating structured materials with varying degrees of complexity and potentially programmable functionalities. , The properties of self-assembled materials rely heavily on the particle alignment and orientation, which profoundly influence their properties and applications in the field of optics, magnetics, and mechanics. − Nonspherical, anisotropic nanoparticles are appealing building blocks for constructing superlattices with both positioning and orientational order, due to the directional energetic and entropic interactions induced by particle shape. − Among various anisotropic building blocks, nanoparticles with concave features are of particular interest because of their rich phase behavior made possible by their distinct geometric curvature. − Manna and co-workers synthesized colloidal CdSe-CdS octapods and obtained three-dimensional (3D) superlattices comprising interlocked particle chains under appropriate assembly conditions . Murray and co-workers realized linear liquid-crystalline superlattices based on the unidirectional assembly of Gd 2 O 3 tripodal nanoplates, and the structural diversity of the resulting superlattices could be further enriched upon coassembly of shape-complementary tripodal and rhombic nanoplates …”