Mechanically Tuned Thermopower of Single‐Molecule Junctions

In this paper, the tuning of the thermopower with single-molecule junctions of fullerene (C-60), 4,4 '-bipyridine (BPY), and p-phenylenediamine (PPD) using scanning tunneling microscopy (STM)-based break junction technique is demonstrated. Single-molecule junctions are prepared in a nanogap between a Au-STM tip and a Au(111) electrode. Upon applying a temperature difference across the junction, a thermoelectric voltage is generated across it. By mechanically controlling the tip-electrode separation distance, the thermoelectric voltage of the junction is tuned. The absolute value of the thermopower decreases with decreasing tip-electrode separation distance for BPY and PPD, while it increases for C-60. Atomistic simulations of the junction illustrate how this arises from shifts in the conduction orbital energies induced by the mechanical compression of the junctions.