Voltage-induced modulation of interfacial ionic liquids measured using surface plasmon resonant grating nanostructures.

This article focuses on using surface plasmon resonance (SPR) in gold (Au) gratings to measure electro-optic modulation—specifically, refractive index changes due to the Pockels effect—in ionic liquids (ILs) at electrode interfaces under applied voltage. By monitoring shifts in the plasmon resonant angle and reflectivity at 785 nm illumination, the study quantifies local refractive index changes within the electrical double layer (EDL) formed at the IL–electrode interface. Finite difference time domain (FDTD) simulations correlate the observed optical shifts to the EDL's thickness and refractive index perturbation, estimating an interfacial layer thickness of approximately 8 nm with a local index change of about 0.1 refractive index units. This approach offers a sensitive, nanoscale probe of voltage-induced ionic ordering and dynamics at electrochemical interfaces, with potential applications in studying interfacial phenomena in electrochemistry and related fields.