Electron transport in single molecules measured by a distance-modulation assisted break junction method

We describe a method to determine whether a measured current in a break junction is due to electron tunneling via space or conduction through a molecule bridged between two electrodes. By modulating the electrode separation, we monitor both the DC and the AC components of the current. The AC component indicates if a molecule is connected to the electrodes while the DC component is the transport current through the molecule. This method allows us to remove the tunneling background from conductance histograms and unambiguously measure the I-V characteristic of single molecules. Furthermore, it provides valuable information about the electromechanical properties of single molecules.