We demonstrate the nanofabrication of flexible plasmonic sensors comprising of gold nanocones achieved by nanoimprint lithography on polycarbonate (PC) sheets. Thermal imprinting was performed consistently over a large area (roughly the size of a 6 in. wafer) with a batch process; this can be extended to a continuous process using UV roll-toroll nanoimprinting. This provides a process to scale up the fabrication of continuous imprinted rolls of PC sheets at an optimal rate of 3−5 m/min. The geometry of the peaks and the valleys of the nanocones in the as-imprinted PC is defined by the nickel mold used during imprinting; however, the gaps between the nanocones are tailored by varying the thickness of the gold deposited onto the substrate. Two different thicknesses of gold were deposited to study the effect of geometry on plasmonic sensing. The resulting PC sheet with gold coating enables highly sensitive detection of analytes by Surface Enhanced Raman Spectroscopy (SERS) by virtue of plasmonic hotspots generated at the valleys, whose presence was confirmed by scattering scanning near-field optical microscopy. This is promising, particularly when the SERS substrate developed is highly reproducible, cost-effective, transparent, and flexible, finding application in nanoplasmonic sensing and on-field environmental monitoring, where rigid SERS substrates would not be appropriate.

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A subwavelength lithography method is demonstrated theoretically and experimentally through the interference of transverse electric (TE) modes in a metal-dielectric waveguide (MDW). Like surface plasmon polaritons (SPPs) on metal surfaces, the TE modes have evanescent waves leaking out of the MDW and are used to do subwavelength patterning but with larger pattern area than SPPs for their low propagation loss. The patterning resolution and depth could be optimized by modifying the thickness of the dielectric layer in the MDW. Two-dimensional subwavelength patterning using TE modes is also proposed with azimuthally polarized light exposure.