Polarization‐Sensitive Au‐TiO ₂ Nanopillars for Tailored Plasmonic Enhanced Light‐Driven Reaction Activity

Abstract Plasmonic‐based metasurfaces play a crucial role in resonance‐driven photocatalytic reactions by effectively enhancing reactivity via localized surface plasmon resonances. Catalytic activity can be modulated by tuning the strength of plasmonic resonances in two primary nonthermal mechanisms: near‐field enhancement and hot‐carrier injection, which govern the population of energetic carriers excited or injected into unoccupied molecular orbitals. A set of polarization‐sensitive metasurfaces consisting of elliptical Au‐TiO 2 nanopillars, specifically designed to plasmonically modulate the reactivity of a model reaction: the photocatalytic degradation of methylene blue, is developed. Surface‐enhanced Raman spectroscopy allows to indirectly assess the yield by monitoring the product peak and shows polarization‐dependent yield rate modulated by a factor of 2 depending on the polarization – either x‐/y‐polarization in 10 s period, as quantified by the integrated area of the 480 cm −1 Raman peak and correlated with enhanced absorption at 633 nm. The single metasurface configuration enables continuous tuning of photocatalytic reactivity via active control of plasmonic resonance strength, as evidenced by the positive correlation between measured absorption and indicative product yield. This dynamic approach provides a route to tailor‐enhance or suppress resonance‐driven reactions, which can be further leveraged to achieve in multibranch reactions, guiding product yields toward desired outcomes.