Chiral Transformation of a Nanostructured Silver Film by Illumination with Circularly Polarized Light

Chiral plasmonic nanoparticles combine interesting geometrical and optical properties and hold great promise for applications in polarization optics, light sources, and enantioselective sensing. However, simple, low-cost, large-area, and reproducible routes to fabricate such chiral plasmonic nanostructures are still limited. Here, we demonstrate a scalable chiral optical imprinting of nanostructured Ag films in which an initially racemic ensemble of nanoparticle enantiomers is transformed into a chiral state under continuous-wave circularly polarized illumination. The imprinting is driven by plasmon-induced redox processes mediated by hot carriers and by surface diffusion of Ag⁺ ions and leads to a robust, unchanged circular dichroism upon flipping the sample, evidencing the formation of 3D chiral nanostructures. We identified two different irradiation regimes depending on the power density. At low-power densities, circularly polarized light creates asymmetrical distribution of electric field around nanoparticles that promotes the growth and stabilization of Ag nanoparticles with handedness matching the incident light polarization. The microscopic origin of the observed chiral growth was elucidated by numerical simulations of the near-field response and hot-carrier generation, which show that under circularly polarized illumination, size-asymmetric (achiral) Ag dimers act as plasmonic nanoantennas, giving rise to a strongly handed local hot-carrier generation profile. At high-power densities (>5 W·cm^-2), selective hot-carrier-driven photo-oxidation and thermally assisted coarsening of same-handed particles dominate, giving rise to inversion of the enantiomeric excess. The described transformations are observed only in the aged granular films, where a thin Ag₂O layer accelerates Ag atom/ion migration and facilitates nanoparticle reshaping. The resulting films exhibit a pronounced chiroptical response with a maximum g-factor of 1.2 × 10^-2 at 532 nm.