Ag Thickness-Controlled Plasmonic Nanogaps in UV Nanoimprinted Nanocone Cluster Arrays for Surface-Enhanced Raman Spectroscopy

Abstract Plasmonic nanogaps formed on metallic nanostructures play a critical role in surface-enhanced Raman spectroscopy (SERS), but the scalable fabrication of high-density and morphology-controllable hotspots on polymer substrates remains challenging. In this work, we report a UV-nanoimprinted nanocone-cluster substrate with Ag-thickness-controlled plasmonic nanogaps for SERS applications. A high-aspect-ratio anodic aluminum oxide mold was used to replicate polymer nanocone arrays, and a lateral peel-off process was employed to induce nanocone clustering. Subsequent Ag deposition by intermittent sputtering enabled the evolution of cluster-like metallic morphologies and inter-nanocone gaps. Among the investigated Ag thicknesses, the AR3 nanocone-cluster SERS substrate with a total Ag thickness of 143 nm exhibited the highest melamine SERS signal at 700 cm⁻¹, reaching approximately 81 counts s⁻¹ mW⁻¹. Compared with the commercial AR2-ref reference substrate, AR3-NSS exhibited a broader Ag-thickness tolerance window and a lower polymer-related Raman background under the tested conditions. Within the AR3-NSS thickness series, the strongest SERS response was observed at 143 nm Ag thickness, which was consistent with the formation of a cluster-like Ag morphology with nanoscale inter-cluster gaps. The optimized substrate further exhibited good spatial uniformity over a 5 × 5 mm² area with a relative standard deviation of 9.44% and batch-to-batch reproducibility with a relative standard deviation of 8.33%. Using malachite green as a demonstration analyte, the substrate achieved a limit of detection of approximately 1.73 × 10⁻ 7 M and an apparent wet-state enhancement factor of 4.21 × 10 7 . These results suggest that demolding-induced nanocone clustering combined with Ag-thickness control provides a practical route for fabricating polymer-based plasmonic SERS substrates.