Unveiling Growth Pathways of Multiply Twinned Gold Nanoparticles by In Situ Liquid Cell Transmission Electron Microscopy

Abstract

A mechanistic understanding of the growth of multiply twinned nanoparticles (MTPs), such as decahedra (Dh) and icosahedra (Ih), is crucial for precisely controlled syntheses and applications. Despite previous successes, no consensus has been reached regarding the multiple competing growth pathways for MTPs proposed thus far, in part due to the lack of information about their nucleation and growth dynamics. Here, we used decahedral and icosahedral gold nanoparticles as a model system in conjunction with in situ liquid cell transmission electron microscopy (LCTEM) to investigate the nucleation and growth dynamics of MTPs in aqueous solution; two growth pathways were successfully identified: (A) nucleation-based layer-by-layer growth from a rounded multiply twinned seed and (B) the successive twinning and growth of tetrahedra. The LCTEM results enabled us to directly and conclusively identify the growth behaviors of intermediate products. The internal strain relaxation mechanisms and growth kinetics differ for the two pathways: in pathway A, a MTP grew by the opening and closing of re-entrant grooves at the twin boundaries, which was not found in pathway B. We also analyzed different MTP growth pathways from an energetic perspective and discussed how the preferred pathway (A or B) is related to factors, such as the initial seed yield and the sizeand morphology-dependent formation of MTPs. Our results contextualize the current understanding of MTP formation mechanisms and provide insightful guidance for the precisely controlled synthesis of MTPs for practical applications.

Twin Pathways: Discerning the Origins of Multiply Twinned Colloidal Nanoparticles

“…[31] Thes tudies described above pioneered the concept of twin boundary growth in MTP synthesis.H owever,t hey do not provide direct, time-series observations of NP evolution. This direct evidence was only recently provided through the in situ TEM studies of Ma et al [22] Through an electroninduced reaction in al iquid cell, the authors recorded the continuous growth from single tetrahedral Au NPs to Dh and Ih shapes (Figure 4C,D). This process involves the formation of new twin boundaries through both surface growth and grain extension.…”

“…However, they do not provide direct, time‐series observations of NP evolution. This direct evidence was only recently provided through the in situ TEM studies of Ma et al [22] . Through an electron‐induced reaction in a liquid cell, the authors recorded the continuous growth from single tetrahedral Au NPs to Dh and Ih shapes (Figure 4 C,D).…”

“…[20b] Using al iquid cell for in situ TEM, Ma et al observed the nucleation and LbL overgrowth of Au NPs initiated by electron irradiation in an aqueous solution. [22] In the examples shown in Figure 2C,D,w ell-defined Dh and Ih NPs directly grew from small seeds with the same twin configuration. Indeed, the deposition of materials during an ideal overgrowth process only enlarges each grain and does not introduce new boundaries or defects.…”

“…Using a liquid cell for in situ TEM, Ma et al. observed the nucleation and LbL overgrowth of Au NPs initiated by electron irradiation in an aqueous solution [22] . In the examples shown in Figure 2 C,D, well‐defined Dh and Ih NPs directly grew from small seeds with the same twin configuration.…”

“…C,D) Time-series in situ liquid cell TEM images (a) and corresponding structural illustrations(b) of nucleation-based LbL growth of Dh (C) and Ih (D) Au NPs. Blue and green arrows indicate twin boundaries and re-entrantg rooves, respectively.Reprinted from Ref [22]. with permission, copyright 2020 AmericanC hemical Society.…”