Interface-Mediated Enhancement of Chiroptical Activity in Semiconducting-Metal Hybrid Nanohelices

Strong chiroptical activity has been an active area of research due to potential applications in polarization control and enhanced molecular sensing. However, the creation and investigation of hybrid chiral nanostructures, consisting of multiple active materials, are relatively unexplored areas. In this work, we fabricated nanohelices with a semiconducting material, titanium dioxide, which were "decorated" with a plasmonic material, gold (Au), via physical vapor deposition. Due to the hybrid nature of the samples, we observed broadband chiroptical activity spanning from the ultraviolet through visible wavelengths, which is not observed with either material alone. Remarkably, the magnitude of the visible-wavelength chiroptical activity was found to be highly enhanced and highly sensitive to the amount of Au. This dramatic signal enhancement and high sensitivity cannot be explained by a simple algebraic addition of the optical activities of the two underlying materials and is thus expected to be a result of the plasmonic–semiconducting interface.