AFM-IR, s-SNOM
For the first time, the combination of the complimentary nanoscale imaging techniques, AFM-IR and s-SNOM have been used to investigate the role of chirality in the origins of circular dichroism in 2D nanoscale materials. Chiral molecules are a certain type of molecule that have a non super imposable mirror image. These mirror images of chiral molecules are often called left handed and right handed, and due to the vector nature of light, it can also exist with two forms of handedness, left and right circularly polarized. Fully two-dimensional (2D) metamaterials, also known as metasurfaces, comprised of planar-chiral plasmonic metamolecules that are just nanometres thick, have been shown to exhibit chiral dichroism in transmission (CDT). Theoretical calculations indicate that this surprising effect relies on finite non-radiative (Ohmic) losses of the metasurface. Until now this surprising theoretical prediction has never been experimentally verified because of the challenge of measuring non-radiative loss on the nanoscale. s-SNOM is used to map the optical energy distribution when the structures are exposed to RCP and LCP IR radiation while AFM-IR was then used to detect the drastically different Ohmic heating observed under RCP and LCP radiation. For the first time it has been conclusively established the circular dichroism observed in 2D metasurfaces is attributed to handedness dependent Ohmic heating.