High-frequency phenomena and electrochemical impedance spectroscopy at nanoelectrodes

Electrochemical impedance spectroscopy (EIS) is a powerful probe of the processes taking place at an electrode. Depending on frequency, it is sensitive to the solid-liquid interface as well as to processes taking place in the solution further from the electrode. In principle, shrinking electrode dimensions allows probing these processes on the nanometer scale. In practice, however, this represents a formidable challenge. Signals resulting from the stray capacitance of the interconnects can dramatically exceed those from the electrode itself. Furthermore, miniaturized electrodes exhibit faster dynamics, and thus necessitate working at higher frequencies in order to achieve comparable performance. Here we discuss recent advances in nanoscale impedance measurements. We begin with a theoretical discussion of the main concepts and inherent tradeoffs, followed by a review of recent experimental efforts. As this field remains in its infancy, we place particular emphasis on the conceptual and technical aspects of the approaches being developed.