Surface Plasmon Resonance Properties of Silver Nanocrystals Differing in Size and Coating Agent Ordered in 3D Supracrystals

Silver nanocrystals differing in coating agent and size self-assembled into thin supracrystalline films. The surface plasmon resonance (SPR) properties of these assemblies are presented herein. Nanocrystal size, interparticle distance, and coating agent play key roles in the plasmonic coupling of Ag nanocrystals within supracrystals. Here, we demonstrate experimentally that the predictions for 2D self-assemblies remains valid for thin 3D superlattices. The absorption spectra in the visible range were found to be markedly dependent on the incidence of the light source and confirmed the appearance of a splitting of the dipolar surface band into two components at increasing incidence angle. The major parameter inducing the splitting of the SPR band was found to be the relative ratio between the average distance of the nanocrystals and their diameters. The nature of the coating agent was also found to be of particular importance: Theoretical predictions and experimental data were in agreement for alkylamine-coated nanocrystals but differed for thiol-coated nanocrystals.