Anisotropic Circular Dichroism in Aligned Chiral Tellurium Nanorods

The anisotropic chiroptical activity of chiral tellurium nanorods (Te NRs) is studied experimentally via circular dichroism (CD) measurements of macroscopically aligned samples. Te NRs with chiral, twisted prismatic shapes, and aspect ratio of ~4 are synthesized using the chiral ligand D-penicillamine and the surfactant sodium dodecyl sulfate. The anisotropy of their optical activity is studied at two different configurations with the long axis of the NRs oriented parallel and perpendicular to the CD probe beam. The parallel alignment is achieved in aqueous suspension using an alternating electric field that acts on their polarizability anisotropy, estimated to be 3.8 × 10⁻³⁰ F m². The perpendicular orientation is measured in a film of the NRs, prepared at a liquid water–organic interface such that the NRs are deposited on a substrate with their long-axis in-plane. Finite-element electromagnetic simulations reproduce well the experimental CD spectra, demonstrating that the optical activity is dominated by the chiral shape-related Mie-type resonances. Both the experimental results and simulations show that the CD spectrum is practically inverted between the two light incidence orientations, a phenomenon that appears general to twisted anisotropic nano-objects.