SHG reveals extrinsic chiral symmetry on gold nanostructures

Schematic model and SEM images of the nanowires sample (left panels);
SHG signal generated in reflection configuration, the nanowires are oriented as indicated on the top illustrations (right panels).


Optical second harmonic generation (SHG) is a very sensitive technique to characterize the symmetry and morphology of nanopatterned surfaces. In particular the chirality of a metasurface can be effectively investigated by SHG with high visibility. Among chiral symmetry, the extrinsic or pseudo-chirality is investigated for different potential applications.
Extrinsic chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Here we show how SHG measurements can lead to the clear identification of the symmetries that are present in a self-assembled metasurface formed by tilted gold nanowires on a silicon substrate.