Oriented Attachment: A Unique Mechanism for the Colloidal Synthesis of Metal Nanostructures

Abstract

Rational synthesis of nanostructures with desired properties critically depends on our understanding of the growth mechanism. In addition to the traditional mechanism involving atomic addition, oriented attachment (OA) has received increasing attention in recent years. Employing nanocrystallites as building blocks, OA offers an important route to anisotropic growth, inclusion of defects, and formation of nanostructures with branched morphology. With a focus on metals, here we offer a brief account of recent progress in understanding OA and how it can be adapted for the colloidal synthesis of nanostructures with diverse compositions and morphologies. We start with a discussion on the current understanding of OA based on computational simulations and experimental studies, followed by typical examples of metal nanostructures produced through OA. Finally, we showcase the catalytic and plasmonic applications enabled by those nanostructures, together with perspectives on the challenges and opportunities.

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

“…From a thermodynamic point of view, oriented attachment is driven by the energy reduction when the faces of a pair of nanocrystallites attach and merge. ,, The alignment and thereby elimination of facets high in energy will force the system to achieve the minimum total surface free energy and therefore a thermodynamically stable state . In practice, the preferred facet for attachment can vary depending on the capping agent, solvent, and constituent metals, among others. − In most cases, facets that are not adequately covered by the capping agent will be favored for oriented attachment .…”

“…Even with a small misorientation between the building blocks, the final product can still be single crystal due to the reorientation of the particles upon contact and diffusion of the constituent atoms . On the contrary, a twin plane will be generated at the coalesced interface and incorporated into the final structure if the nanocrystallites merge through the same crystallographic planes that are arranged in a mirror image of each other (Figure C). , When two entirely different crystal planes are attached together, the resulting disruption in the original atomic stacking can cause the formation of stacking faults in the final structure . In the case where the attached facets are not perfectly flat, dislocations will be created in the nanostructure due to the resulting misalignment and distortion of the interface.…”

“…Although these structural defects could be removed through lattice relaxation to lower the total surface energy, they are usually preserved in the final structures, providing evidence for the attachment growth mechanism. In comparison with the conventional growth pathway involving atomic addition, oriented attachment offers a more powerful route to nanostructures abundant in defects . In return, the unique assortment of defects can augment the properties of these nanostructures toward various catalytic reactions.…”

“…Overall, asymmetrical growth and the accompanying symmetry breaking event are often seen in attachment growth, while atomic addition can result in both symmetrical and asymmetrical growth. 79 Some mechanistic details of these two methods are discussed in the following two subsections.…”

Oriented Attachment Crystal Growth Dynamics of Anisotropic One-dimensional Metal/Metal Oxide Nanostructures: Mechanism, Evidence, and Challenges

“…The main simulation methods are molecular dynamics (MD), density functional theory (DFT), ab initio, and Monte Carlo (MC) calculations. These methods provide insight into the thermodynamics, kinetics, and driving forces of crystal growth mechanisms [85,86]. Although computational simulations involved with faster timescales than experiments, they provide a valid approach to understand crystal growth dynamics with a good agreement with experimental results.…”