Controlled Fabrication of Nanogaps for Molecular Electronics

We have developed a controlled and highly reproducible method of making nanometer-spaced electrodes using electromigration in ambient lab conditions. This advance has several advantages over the typical method at liquid-helium temperatures. One advantage is that it will make feasible electrical measurements of molecules that do not survive a sub-freezing environment. A second advantage is that it yields nanogaps of desired tunneling resistance, as opposed to the random formation at liquid-helium temperatures. We discuss how the nanogap evolves through three regimes -- a bulk-neck regime where electromigration is triggered at constant temperature, then a few-atom regime characterized by quantized plateaus in the conductance, and finally to a tunneling regime across the nanogap once the conductance falls below the conductance quantum ($G_o=2e^2/h$). We end with a discussion on the electronic properties of molecules measured using the new electrodes.