Gating the Rectifying Direction of Tunneling Current through Single-Molecule Junctions

In electronic functional chips, one of the most crucial components is the field-effect transistor (FET). To meet the urgent demands for further miniaturization of electronic devices, solid-state single-molecule transistors by molecular orbital gating have been extensively reported. However, under negative bias and positive bias, achieving a distinct gating effect is extremely challenging because molecular orbital gating is independent of the bias polarity. Here, we demonstrated that rectifiers can be realized in single-molecule junctions with a symmetric molecular structure and an electrode material by simply breaking the symmetry of the electrode's chemical potential via ionic adsorption. We further demonstrated that the tunneling current can be gated with opposite change tendencies under negative and positive bias by applying an ionic gating voltage, which eventually results in a reversal of the rectifying direction. Our experiments elucidate that, unlike the classical mechanism for solid molecular FET, the modulation of the electrode's chemical potential, rather than the regulation of molecular orbitals, might dominate the electron transport in the ionic liquid environment upon a gating voltage. Our study gains deeper insights into the mechanism of ionic liquid gating and opens a window for designing high-performance electrochemical-based functional devices.