Volatile Conductance Switching in Molecular Device Based on Viologen Building Block

We reported unprecedented volatile conductance switching in molecular device based on viologen (VIO2+) molecules, typically HS-C6-VIO2+-C6–SH. In symmetrical Ag/S–C6-VIO2+-C6–S/Ag junction, we observed bipolar, volatile conductance switching with the on/off ratio reaching up to 106, and the on-state conductance was approximately 35.7 μS at the threshold voltage of ±0.6 V. In asymmetrical junctions, Au/S–C6-VIO2+-C6–S/Ag or Ag/S–C6-VIO2+-C6–S/Au, we observed unipolar, volatile switching with the on/off ratio of 106 at the absolute threshold voltage of 0.6 V. The conductance switching direction and the stability and reproducibility depend on the Ag–S interfacial bonding, the ionic conductor, VIO2+, and the material of electrode. We assigned the volatile, bipolar, or unipolar switching behavior to the formation of the weak silver filament. Our result proves that interfacial bonding in combination with the ionic conductor medium should be considered in the design and analysis of molecular electronics.