Plasmonic nanocrevice metasurfaces via block copolymer directed self-assembly for controlled anisotropic near-field...

The crevice-like nanogap stands out as one of the most potent geometries for generating intense electromagnetic field localization; however, scaling such ultrasmall nanogaps into high-density metasurfaces remains a significant challenge. We report the fabrication of dense nanocrevice metasurfaces via the directed self-assembly (DSA) of a high-χ block copolymer (BCP). Using a poly(1,1-dimethylsilacyclobutane)-block-polystyrene (PDMSB-b-PS) block copolymer with a 9 nm half-pitch, we produce periodic, anisotropic Au nanocrevice metasurfaces with sub-10 nm gap features. Comprehensive optical characterization and finite-difference time-domain (FDTD) simulations reveal a robust, tunable optical plasmonic resonance localized within the nanocrevices. Utilizing surface-enhanced Raman spectroscopy (SERS) as a sensitive probe of the near-field, we validate that these structures deliver significant field enhancement. Optimal performance is achieved at a specific Au thickness using 638 nm excitation, a condition that aligns with both the simulated resonance and experimental reflectance, thereby maximizing plasmonic enhancement. Furthermore, we demonstrate a tunable polarization response, showing that the SERS anisotropy ratio can be tuned simply by varying the deposited metal thickness. This work establishes DSA as a scalable route to designer plasmonic metasurfaces, providing a versatile platform for advanced plasmonics and polarization-resolved spectroscopy.