Reversible, mechanically-activated switching in pyridine single molecule junctions

We measured the conductance of single pyridine-terminated molecules by mechanically forming and breaking Au point contacts with a modified STM in a solution of molecules. Conductance traces recorded while stretching the junction reveal two distinct steps at different conductance, both due to the formation of a single molecule junction between gold electrodes. To better understand the origin of this bi-stable conductance signature, we devise a new method to experimentally determine the distance between the gold electrodes for any given molecular conductance. We find a clear correlation between the level of conductance and the distance between gold electrodes, with the lower conductance corresponding to a molecule fully stretched between the contacts and the higher conductance to a molecule bound at an angle. The dependence of conductance on metal-molecule contact geometry allows us to reversibly switch between conductance states by elongating and compressing the junction.