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Chiral plasmonic nanostructures attract attention because those could be applied to enantioselective chemical sensors, optical isolators, light sources for circularly polarized light (CPL), metasurfaces, and metamaterials. In many cases, chiral plasmonic nanostructures are fabricated by a top-down method such as electron beam lithography (EBL). Since EBL is time-consuming and expensive, we have developed photoelectrochemical methods in which a site-selective reaction is driven by optical near field generated around anisotropic metal nanoparticles under right- or left-CPL. As anisotropic metal precursors for preparation of chiral nanoparticles, we have used gold or silver nanocuboids, nanorods, nanocubes, and triangular or hexagonal nanoplates so far. 1-5 In the present work we demonstrate that laterally isotopic, circular nanodisks can also be used as precursors for the preparation of chiral nanostructures. We prepared ensembles of circular gold nanodisks on a glass plate by a nanosphere lithography method. A glass plate was coated with a gold thin film, and an array of polystyrene spheres (500 nm diameter) was prepared on the gold film. The polystyrene spheres were etched by oxygen plasma, and the exposed gold film was etched by argon ion milling. As a result, an ensemble of gold nanodisks (~200 nm diameter) was obtained. Each nanodisk was capped with a polystyrene cone, and the cap was removed by sonication in toluene if necessary. We used both capped and uncapped nanodisk ensembles. The ensemble was irradiated with visible right- or left-CPL in the presence of silver ions and sodium citrate. The obtained Au-Ag nanostructures exhibited circular dichroism (CPL), indicating that the nanostructures have chirality. Initial deposition at arbitrary site may break the geometric symmetry, resulting in the growth into chiral structures. Saito, K.; Tatsuma, T. Nano Lett. 2018 , 18 , 3209–3212. Morisawa, K.; Ishida, T.; Tatsuma, T. ACS Nano 2020 , 14 , 3603–3609. Shimomura, K.; Nakane, Y.; Ishida, T.; Tatsuma, T. Appl. Phys. Lett. 2023 , 122 , 151109. Homma, T.; Sawada, N.; Ishida, T.; Tatsuma, T. ChemNanoMat 2023 , 9 , e202300096. Ishida, T.; Isawa, A.; Kuroki, S.; Kameoka, Y.; Tatsuma, T. Appl. Phys. Lett. 2023 , 123 , 061111.
Tatsuma et al. (Fri,) studied this question.