Ion‐Induced Hydrophilic Switching Enables Nanostructure Morphology Control for Superior Nanoplasmonic Sensing

Abstract Controlling the morphology of dewetted ultrathin gold films is critical for achieving reproducible and high‐performance plasmonic sensors, yet scalable approaches remain limited. Localized surface plasmon resonance (LSPR) sensors rely on uniform metallic nanoislands whose morphology dictates optical sensitivity and signal reproducibility. Conventional solid‐state dewetting often produces non‐uniform nanostructures due to uncontrolled interfacial energy and adatom mobility, restricting wafer‐scale reproducibility. Here, a brief SF ₆ plasma pre‐treatment is introduced that induces ion‐mediated hydrophilic switching of glass surfaces, enhancing Au adatom mobility and promoting uniform nanoisland formation during thermal dewetting. The resulting structures exhibit reduced size dispersion and narrower interparticle gaps, yielding a 17.8% increase in refractive‐index sensitivity (from 80.79 ± 19.36 to 95.21 ± 6.56 nm RIU ⁻¹ ) with improved linearity and spectral reproducibility. Complementing these experiments, a modified Cahn–Hilliard phase‐field model embedding an explicit Au–substrate adhesion term (α) quantitatively reproduces the observed morphology and provides a predictive framework for tuning film evolution. This integrated experimental–theoretical‐simulation approach demonstrates that substrate‐wettability engineering via plasma activation offers a scalable, lithography‐free strategy for wafer‐level fabrication of uniform nanoplasmonic sensors, establishing a foundation for theory‐informed design of next‐generation plasmonic and photonic devices.