Halide-Directed Synthesis of Square Prismatic Ag Nanocrystals by the Polyol Method

Abstract

Achieving shape control of high-quality metal nanocrystals is a critical challenge in the fabrication of bottom-up plasmonic materials. Here, we synthesize a uniquely anisotropic Ag nanocrystal shape using a modified polyol method. Single-crystalline Ag square prism nanocrystals, which possess two square facets and four rectangular facets, with uniform size distributions and a high yield (≤96%) are generated by the controlled addition of Br– anions during the nucleation and growth process. Br– acts as a reshaping agent for the generation of single-crystalline seed nanoparticles that direct subsequent anisotropic growth in the ⟨100⟩ direction. Nanocrystal growth and shape development are monitored through optical absorption spectroscopy, which reveals the localized surface plasmon resonances of the square prisms. Electrodynamic simulations indicate strong near-field enhancement associated with the high aspect ratio shape and the potential application of these nanocrystals as optical nanoantenna in plasmonic platforms, such as surface-enhanced Raman spectroscopy sensors and optoelectronic junctions.