Volatile Conductance\nSwitching in Molecular Device\nBased on Viologen Building Block

We reported unprecedented volatile conductance switching\nin molecular\ndevice based on viologen (VIO<sup>2+</sup>) molecules, typically HS-C<sub>6‑</sub>VIO<sup>2+</sup>-C<sub>6</sub>–SH. In symmetrical\nAg/S–C<sub>6</sub>-VIO<sup>2+</sup>-C<sub>6</sub>–S/Ag\njunction, we observed bipolar, volatile conductance switching with\nthe on/off ratio reaching up to 10<sup>6</sup>, and the on-state conductance\nwas approximately 35.7 μS at the threshold voltage of ±0.6\nV. In asymmetrical junctions, Au/S–C<sub>6</sub>-VIO<sup>2+</sup>-C<sub>6</sub>–S/Ag or Ag/S–C<sub>6</sub>-VIO<sup>2+</sup>-C<sub>6</sub>–S/Au, we observed unipolar, volatile switching\nwith the on/off ratio of 10<sup>6</sup> at the absolute threshold\nvoltage of 0.6 V. The conductance switching direction and the stability\nand reproducibility depend on the Ag–S interfacial bonding,\nthe ionic conductor, VIO<sup>2+</sup>, and the material of electrode.\nWe assigned the volatile, bipolar, or unipolar switching behavior\nto the formation of the weak silver filament. Our result proves that\ninterfacial bonding in combination with the ionic conductor medium\nshould be considered in the design and analysis of molecular electronics.