Characterization of Chiral Near Field Within Nanogaps Using Surface-Enhanced Raman Scattering

Chiral nanogap antennas, which exhibit specific chiroptical responses, hold exceptional potential in various chiral applications, including polarization converters, asymmetric catalysis, label-free chiral recognition, and chiral sensing. However, characterizing the chiral optical fields within nanogaps presents considerable challenges owing to their complex light field responses and spatial dimensions. In this study, the strong modulation of helicity-resolved surface-enhanced Raman spectroscopy (SERS) signals in graphene by chiral plasmonic antennas, offering a promising approach to characterize chiral near fields within nanogaps is demonstrated. The SERS of achiral monolayer graphene is performed within plasmonic nanogap antennas, including single gold nanorods (GNRs) and GNR dimers on gold microflakes. The Raman scattering intensity of graphene within these nanogap antennas is enhanced approximately sixfold. Furthermore, the degree of cross-circularly polarized Raman intensity reaches up to approximate to 45%, indicating a robust chiral optical field. Moreover, under opposite circularly polarized light excitation, the SERS of graphene reveals varying emission intensities attributed to the modulation arising from the chiral antennas in both the excitation and emission processes of Raman scattering. Furthermore, the degree of chirality depends on the antenna configuration and the excitation laser wavelength. The chiral near-field within plasmonic nanogaps using helicity-resolved surface-enhanced Raman scattering is investigated. The degree of chirality in the Raman scattering from achiral monolayer graphene depends on antenna configuration and the excitation laser wavelength. The chiral modulation of Raman scattering is due to the chiral near-field of antennas during both the excitation and emission processes.image