Understanding Symmetry Breaking at the Single-Particle Level via the Growth of Tetrahedron-Shaped Nanocrystals from Higher-Symmetry Precursors

Abstract

The vast majority of single crystalline metal nanoparticles adopt shapes in the O h point group as a consequence of the symmetry of the underlying face-centered cubic (FCC) crystal lattice. Tetrahedra are a notable exception to this rule, and although they have been observed in several syntheses, their growth mechanism, and the symmetry-reduction process that necessarily characterizes it, is poorly understood. Here, a symmetry breaking mechanism is revealed by in situ liquid flow cell transmission electron microscopy (TEM) observation of seeded growth in which tetrahedra nanoparticles are formed from higher symmetry seeds. Real-time observation of the growth demonstrates a kinetically driven pathway during which rhombic dodecahedra nanoparticles transition to tetrahedra through tristetrahedra intermediates, with an accompanying surface facet evolution from {110} to {111} via {hhl} (where h > l), respectively. On the basis of these data, we propose a mechanism that relies on a rapid loss of inversion symmetry in the initial stages of the reaction, followed by differential reactivity of tips vs faces under conditions of relatively high supersaturation and moderate ligand concentration. The application of these insights to ex situ synthesis conditions allowed for an improved yield of tetrahedra nanoparticles. This work sheds an important mechanistic light on the crystallographic underpinnings of nanoparticle shape and symmetry transformations and highlights the importance of single-particle characterization tools for monitoring nanoscale phenomena.

Colloidal Synthesis of Metal Nanocrystals: From Asymmetrical Growth to Symmetry Breaking

“…(B) In situ TEM images and the corresponding geometrical models showing the transition from a rhombic dodecahedron to a tetrahedron (scale bars: 25 nm). Adapted with permission from ref . Copyright 2021 American Chemical Society.…”

“…In a recent paper, a versatile method was reported for effectively screening more than one reaction parameters to capture and scrutinize specific symmetry breaking behaviors (Figure 45). 423 By flushing the metal precursor (HAuCl 4 ) solution into a liquid cell to create continuous and opposing concentration gradients of HAuCl 4 and ligands (cetylpyridinium chloride and CTAB), a variety of reaction conditions for the growth from Au rhombic dodecahedral seeds were probed in one experiment. It was found that at relatively high and low concentrations for the ligands and precursor, respectively, conformal growth of the seeds gave rise to pseudospherical nanocrystals (i.e., the thermodynamic product), whereas the opposite conditions resulted in a dendritic morphology (i.e., the kinetic product).…”

Atom-dispersed Au combined with nano-Au on halloysite nanotubes with closo-dodecaborate promotes synergistic effects for enhanced photocatalysis

“…2b), consistent with those reported in the literature. 25 The reason for obtaining tiny Au NPs is that [B 12 H 12 ] 2− is immobilized on the surface of HNTs, and correspondingly formed Au NPs cannot agglomerate in large quantities compared with Na 2 B 12 H 12 @Au (Fig. S2 †).…”

Assembling Biocompatible Polymers on Gold Nanoparticles: Toward a Rational Design of Particle Shape by Molecular Dynamics

“…Salassi et al highlight how different shapes and sizes of AuNPs lead to their different kinds of wrapping with organic ligands. Not surprisingly, other recent works have shown evident effects of the NP surface topology on specific polymer adsorption. − …”

“…Not surprisingly, other recent works have shown evident effects of the NP surface topology on specific polymer adsorption. 26 − 28 …”