Impact of Solvent Electrostatic Environment on Molecular Junctions Probed via Electrochemical Impedance Spectroscopy

The electrostatic environment around nanoscale molecular junctions modulates charge transport; solvents alter this environment. Methods to directly probe solvent effects require correlating measurements of the local electrostatic environment with charge transport across the metal-molecule-metal junction. Here, we measure the conductance and current-voltage characteristics of molecular wires using a scanning tunneling microscope-break junction (STM-BJ) setup in two commonly used solvents. Our results show that the solvent environment induces shifts in molecular conductance, which we quantify, but more importantly we find that the solvent also impacts the magnitude of current rectification in molecular junctions. By incorporating electrochemical impedance spectroscopy into the STM-BJ setup, we measure the capacitance of the dipole layer formed at the metal-solvent interface and show that rectification can be correlated with solvent capacitance. These results provide a method of quantifying the impact of the solvent environment and a path toward improved environmental control of molecular devices.