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

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 SF₆ 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.