From Low Symmetry to High Dissymmetry: Chiral Plasmonic Films of Binary and Nanobipyramid Assemblies

Thin films exhibiting plasmonic circular dichroism (PCD) represent a promising class of materials for technologies based on light processing. However, their potential is limited by the relatively low selectivity of interactions with circularly polarized photons of a given handedness and restricted tunability of the chiroptical properties. This article aims to resolve these problems with two innovations. First, it assembles gold nanobipyramids (NBPs), a promising building block for plasmonics, and arrange them in helical assemblies using a liquid-crystalline (LC) template. By optimizing the organic coating of NBPs, their size, and loading in the thin film, it achieves PCD films with state-of-the-art dissymmetry, g-factor on the order of 10$^{−2}$. This study unequivocally evidence the properties by Mueller Matrix polarimetry and identify plasmonic coupling between particles as the driving force for the origin of the PCD properties using T-matrix theoretical modeling. Second, spectral and dynamic PCD engineering is achieved by varying particle sizes, co-assembling NBPs with nanospheres, and reversible melting and crystallization of the thin film. ... mehrOverall, this work unlocks the potential of NBPs and binary assemblies based on NBPs for chiral plasmonics, providing a strategy for thin film materials displaying spectral and temporal PCD response with high dissymmetry factors.