Utilizing individual atoms or molecules as functional units in electronic circuits meets the increasing technical demands for the miniaturization of traditional semiconductor devices. To be of technological interest, these functional devices should be high-yield, consume low amounts of energy, and operate at room temperature. In this study, we developed nanodevices called quantized conductance atomic switches (QCAS) that satisfy these requirements. The QCAS operates by applying a feedback-controlled voltage to a nanoconstriction within a stretched nanowire. We demonstrated that individual metal atoms could be removed from the nanoconstriction and that the removed metal atoms could be refilled into the nanoconstriction, thus yielding a reversible quantized conductance switch. We determined the key parameters for the QCAS between the “on” and “off” states at room temperature under a small operating voltage. By controlling the applied bias voltage, the atoms can be further completely removed from the constriction to break the nanowire, generating single-atom nanogaps. These atomic nanogaps are quite stable under a sweeping voltage and can be readjusted with subangstrom accuracy, thus fulfilling the requirement of both reliability and flexibility for the high-yield fabrication of molecular devices.Keywords: electromigration; molecular devices; molecular electronics; nanogaps; quantized conductance switches; single-atom memory

In this work, the formation of single oligothiophene molecular junctions was studied using density functional theory. The elastic scattering Green’s function method was applied to investigate the electron-transport properties of the molecular junctions and their conductance switching properties caused by an electrochemical gate. Given four configurations, the optimized structures and breakdown forces of the molecular junctions were obtained. The breakdown of the oligothiophene molecular junctions is likely to occur at the Au–S bond as the electrodes are pulled. The simulated results show that the experimental findings that the four-repeating-unit oligothiophene is more conductive than the three-repeating-unit oligothiophene are due to their different configurations. The oligothiophenes’ electronic structures are sensitive to the gate field, and their conductance switching properties are explained when a gate field is applied.