Using Surface Phonons as a Guide for Optimizing SERS and Light-Driven Processes †

Ivano Alessandri

doi:10.53941/ps.2026.100016

Abstract

The characterization of surface plasmon–polaritons (SPPs) involved in surface-enhanced Raman scattering (SERS) and plasmon-driven photochemical processes is commonly performed through auxiliary techniques such as optical-, electron energy loss- or scanning probe-spectroscopy that neither reproduce the actual excitation conditions of a microRaman setup nor provide a direct, in situ probe of light confinement in real experiments. Here, we demonstrate an alternative approach based on the intrinsic Raman response of TiO₂ hollow-shell cavities coated with ultrathin gold layers (T-horex@Au). The Raman spectra of these hybrid core/shell structures exhibit an additional mode that cannot be assigned to bulk TiO₂ phonons. Confocal microRaman analysis reveals a clear dependence of this mode’s intensity on the laser penetration depth, enabling its attribution to surface phonon modes activated at the Au/TiO₂ interface. This plasmon-mediated activation takes advantage of interfacial symmetry lowering and efficient electromagnetic field confinement. The simultaneous observation of this mode together with conventional Raman signals provides a direct, non-perturbative diagnostic of SPP excitation quality under realistic experimental conditions. Exploiting this feature, we show that the Raman enhancement induced by identical gold layers is strongly substrate-dependent and that the intensity of the TiO₂ surface mode can be used as an internal standard to optimize and tune SERS performance. This strategy offers a practical route for large-scale fabrication and rapid optimization of metal/TiO₂-based SERS substrates, opening intriguing perspectives for real-time control and monitoring of plasmon-driven photocatalytic and photochemical reactions at solid interfaces.

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