Size Tunable Synthesis of Covalently Linked Nanoparticle Superlattices via Temperature Control

Abstract

Nanoparticle superlattices (NPSLs) are of great current interest for their unique emergent physical and chemical properties. The size of NPSLs as well as composition, symmetry, and lattice parameters play an important role in determining their properties as the nanoparticles' properties are significantly varied with size. However, the precise size control of NPSLs is still a challenge. Here, we report a size-tunable synthesis of covalently linked NPSLs by temperature control, for which the aldol reaction is used as a model covalent bonding forming reaction. The NPSLs formed by covalent bonding interaction in conjunction with slow solvent evaporation show mostly a hexagonal platelet shape with face-centered cubic symmetry. The average size of NPSLs increases more than 10 times, from 1.1 to 12.2 mu m, as the reaction temperature decreases from 90 to 4 degrees C, showing dispersity of 16-21%. This is essentially the same as the temperature-induced size control of nanoparticles, suggesting that the NPSL formation mechanism by the covalent bonding interaction in conjunction with slow evaporation resembles the nanoparticle formation mechanism. The temperature-induced size control of NPSLs demonstrated in this study is very simple and provides a submicrometer scale size control of NPSLs. This new method enables us to finely tune the optical properties of three-dimensional NPSLs, which is a solid step forward for realizing optical and other potential applications of NPSLs.