Evidence of Optical Circular Dichroism in GaAs-Based Nanowires Partially Covered with Gold
Semiconductor nanostructures hybridized with metals have been known to
offer new opportunities in nonlinear optics, plasmonics, lasing, biosensors;
among them GaAs-based nanowires (NWs) hybridized with gold can offer new
functionalities, as chiral sensing and light manipulation, as well as circular
polarization sources. This study investigates GaAs–AlGaAs–GaAs NWs fabricated
by self-catalyzed growth on Si substrates, and partially covered with gold,
thus inducing the symmetry breaking and a potential chiral response. Three
different samples are investigated, each of them with a different morphology,
as the length and the overall diameter ranging from 4.6 to 5.19 ?m and from
138 up to 165 nm, respectively. The samples are first characterized by measuring
the absorption spectra by using a scattering-free photoacoustic (PA)
technique. Then, the circular dichroism (CD) is investigated by measuring PA
absorption for circularly polarized light under different incident angles at 532
and 980 nm. An efficient CD is found for proper configurations, and results are
in good agreement with extrinsic chiral theory predictions and numerical simulations.
It is therefore proven that these samples exhibit chiral behavior, and
can be further optimized. Moreover, PA technique can be used as an extremely
sensitive and efficient technique to characterize their “extrinsic” chirality.