Independent switchable atomic silver quantum transistor via potential-driven surface reconstruction

Atomic-scale quantum conductance switches based on metallic quantum point contacts allow controlled binary switching of the electrical current between a conducting "on state" and a non-conducting "off state" via an independent gate electrode. Although silver-based quantum switches operate via electrochemical conductance modulation, the underlying atomic-scale mechanisms remain unclear. In this study, we employed density functional theory combined with the computational hydrogen electrode (CHE) framework to investigate nitrate anion adsorption on Ag(100), Ag(111), and Ag(511) surfaces under varying electrochemical potentials. The stable configurations of nitrate adsorption on the electrode surfaces as a function of electrode potential are determined using the grand canonical approach within the CHE framework, revealing the surface reconstruction of Ag(511) analogous to the formation of nascent Ag-NO3 complexes. The thermodynamic analysis indicates that the critical phase transition occurs in agreement with the experimental switching threshold. Electronic structure calculations reveal metallic to semiconducting transitions in the reconstructed Ag-NO3 complex layers, elucidating the mechanism of conductance modulation. The "off state" corresponds to insulating Ag-NO3 surface complexes, while the "on state" arises from metallic Ag-Ag bridging at lower nitrate coverage under lower control voltage. This study establishes a general framework for anion-mediated quantum switching in transition metals and provides a design for nanoscale electrochemical devices.