Long‐range surface plasmon enhanced Raman spectroscopy at highly damping platinum electrodes

Knowledge of electrode/electrolyte interfacial structures is the first step toward a better understanding of electrochemical reactions. Among several surface‐specific vibrational spectroscopy, plasmonic enhancement of Raman scattering signals is recognized as a powerful method for in situ observation of electrochemical metal/dielectric interfaces. However, the applicability of this technique is governed by the resonance behavior of surface plasmons at the interface. Although platinum group metals are one of the most interesting materials for electrocatalysis, surface plasmon polaritons are largely damped at these surfaces by their localized d‐electrons. Thus, the plasmon enhanced Raman spectroscopy is normally useless for studying such catalytic surfaces. In this work, the attenuation of surface plasmons at highly damping Pt surface is reduced using a symmetric slab mode, which is a strongly coupled surface plasmons excited at both interfaces of a thin metal film. The prolonged propagation of surface plasmons in this double‐interface configuration leads to a substantial enhancement of local fields even at lossy Pt surface. The theoretical calculation indicates that the enhancement factor of Raman scattering intensity can reach the order of 10 4 at Pt/solution interfaces in this coupled plasmon mode. We experimentally demonstrate that Raman scattering signals are indeed significantly enhanced at Pt surface under electrochemical conditions. This strategy provides us a novel surface‐specific spectroscopic method for the molecular‐scale investigation of electrocatalytic reactions.