Wide-Field Electrochemical Impedance Microscopy Beyond MHz

Electrochemical impedance spectroscopy (EIS) represents a fundamental electrochemical methodology for investigating electrochemical phenomena through wide-frequency impedance measurements under modulated potential conditions. Traditional EIS approaches suffer from a fundamental limitation: the absence of spatial discrimination capabilities, which prevents comprehensive characterization of impedance heterogeneity across interfacial regions. Although optical-electrochemical impedance microscopy (oEIM) has recently addressed this gap by enabling spatially resolved impedance visualization without microelectrode scanning requirements, operational frequencies have been restricted to sub-kHz ranges due to conventional camera frame rate limitations. This study overcomes these constraints by incorporating time-gated phase-locked imaging technology into oEIM systems, achieving unprecedented wide-field impedance characterization at modulation frequencies exceeding 1 MHz. Demonstrating this capability using commercial light-emitting diode devices, we successfully generated spatial maps of submicrosecond response time constant and achieved decoupling visualization of resistance and capacitance density maps, enabling enhanced detection and categorization of subsurface structural anomalies. This technological breakthrough extends oEIM operational bandwidth by over 3 orders of magnitude (from sub-kHz to beyond MHz frequencies), establishing new methodological paradigms for characterizing submicrosecond electrochemical phenomena at heterogeneous interfaces.