Engineering Chiral Plasmonic Nanocrystals via Controllable Photoetching of Silver Nanorods with Circularly Polarized Light

Chiral plasmonic nanostructures have shown great potential for photonics and sensing applications. Chiral molecules and micelles have been demonstrated to be effective sources of chirality, enabling the colloidal production of large-scale, homogeneous chiral plasmonic nanocrystals. Recent investigations have explored the use of circularly polarized light (CPL) as a chirality source to fabricate chiral Au/PbO₂ heterostructures or as an additional ingredient in chiral molecule-directed synthesis to enhance the optical dissymmetry of the nanocrystals further. However, the mechanism by which these chiral structures develop with CPL has remained largely unexplored. Our latest study has revealed that the wavelength of CPL is a critical factor in determining the shape of chiral Au/PbO₂ heterostructures and their resulting chiroptical properties. Here, we further demonstrate that the asymmetry of the initial plasmonic nanocrystals plays a crucial role in generating more chiral nanostructures. Specifically, we utilized silver nanorods with varying aspect ratios as the starting materials. Ag was oxidized at selective sites upon circularly polarized excitation to create chiral structures. Our results indicate that the optical activity of resulting chiral nanostructures increases with the aspect ratio of the starting nanocrystals. Besides, tuning the excitation wavelength with Ag nanorods of a larger aspect ratio can yield higher contrast of chiral morphologies due to the larger number of higher-order modes accessible in these nanocrystals. Our study underscores the importance of carefully selecting the starting material and excitation wavelength to maximize chiral plasmonic nanocrystals' shape and optical dissymmetry when using CPL as the chirality source. Besides, the non-toxic chiral Ag nanocrystals are more suitable for bio-compatible systems than chiral Au/PbO₂ nanostructures.