Wide-Field Opto-Iontronic iSCAT Mapping of Interfacial Charging and Electrical Connectivity

Abstract

Spatial variations in electrical connectivity and interfacial ion accumulation can strongly influence electrochemical performance, yet these properties are difficult to visualize directly with conventional ensemble measurements. Here, we introduce potential-modulated opto-iontronic microscopy, an interferometric scattering microscopy (iSCAT) approach for wide-field imaging of electric-double-layer (EDL) dynamics at nanostructured electrodes. Sinusoidal potentials were applied to focused-ion-beam-fabricated indium tin oxide (ITO) nanoholes, and the optical response was extracted at the modulation frequency by Fourier demodulation. The optical modulation amplitude increased approximately linearly with modulation voltage above a low-voltage roll-off and decreased with increasing frequency, consistent with kinetically limited interfacial charging. We then mapped the potential-synchronized optical amplitude across patterned ITO electrodes. Electrically isolated blocks exhibited strongly suppressed modulation signals, whereas electrically connected and partially milled nanogrid structures showed pronounced responses. These results demonstrate label-free optical mapping of local charging dynamics and electrical connectivity at heterogeneous electrochemical interfaces using a commercially available iSCAT platform.