Self-assembly of high-index faceted gold nanocrystals to fabricate tunable coupled plasmonic superlattices.

Abstract

Herein, we present an effective bottom-up strategy to fabricate unprecedented macroscopic two-dimensional (2D) plasmonic gold superlattices composed of high-index faceted gold nanocrystal building blocks (NBBs) at the air-liquid interface. In this approach, a synergistic electrostatic and layered self-assembly technique was executed using unique icosidodecahedral gold nanocrystals. It showed that centimeter-squared areas of close-packed monolayer films were formed, and the interparticle spacing of neighbouring Au NBBs could be facilely manipulated from hundreds to several nanometers. Optical characterization demonstrated that particular plasmonic coupling could occur and enhance in a wide spectral range (visible and near-IR) as the self-assembled Au superlattices were tuned for an appropriate gap distance and specific NBB size; however, the orientation of individual NBBs remained somewhat unorganized. Thus, the well pronounced shift of localized surface plasmon resonances (LSPR) and the in-depth resonance splitting behaviors were presented in our investigations. Furthermore, corresponding electromagnetic simulations showed good agreement with the experimental results; this indicated that a new class of tunable coupled plasmonic Au superlattices was realized. This study complements the insights into the plasmonic coupling of layered Au superlattices and enables the colloidal self-assembly to extend to unconventional NBBs; thus, it may facilitate the design of novel plasmonic metamaterials or other superstructures for desired functionalities and applications in the future.