The Importance of Electrical Impedance Spectroscopy and Equivalent Circuit Analysis on Nanoscale Molecular Electronic Devices

To understand the electrical and charge transport phenomena in either single or large-scale molecular junctions, direct current (DC) measurements are mainly utilized. The current-voltage data obtained from DC measurements on molecular junctions (MJs) are employed to infer charge transport parameters, including barrier height, contact resistance, attenuation factor (beta), and underlying transport mechanisms. However, DC measurements can not separate the individual electrical components, as it produces a total current that flows in the molecular junctions. Contact resistance obtained from the DC measurements by extrapolating plot of resistance versus chain length can not make exact value. In addition, defected SAMs-based MJs or junctions having a protective layer, DC measurements alone can predict neither proper electrical values nor the correct transport mechanisms and it lacks frequency response. Electrical impedance spectroscopy (EIS) along with the circuit model enables the identification of individual electrical components of the molecular junctions and faultless contact resistance values that facilitate the model of actual transport mechanisms. In this Review, the working principle of electrical impedance spectroscopy and circuit modeling to digitize the experimental results on various molecular junctions, is discussed. Overall, the EIS technique can serve as an excellent analytical tool for the proper electrical characterization that is highly desirable for molecular electronics.