Electrostatic gating of single-molecule junctions based on the STM-BJ technique

Abstract

The gating of charge transport through single-molecule junctions is considered a critical step towards molecular circuits but remains challenging. In this work, we report an electrostatic gating method to tune the conductance of single-molecule junctions using the scanning tunneling microscope break junction (STM-BJ) technique incorporated with a back-gated chip as a substrate. We demonstrated that the conductance varied at different applied gating voltages (V_gs). The HOMO-dominated molecules show a decrease in conductance with an increase in V_g, and the LUMO-dominated molecules show the opposite trend. The measured conductance trends with V_g are consistent with the transition voltage spectroscopy measurements. Moreover, the transmission functions simulated from density functional theory (DFT) calculations and the finite element analysis all suggest that V_g changed the energy alignment of the molecular junction. This work provides a simple method for modulating the molecular orbitals’ alignment relative to the Fermi energy (E_f) of metal electrodes to explore the charge transport properties at the single-molecule scale.