Angstrom-distance rulers using single molecule conductance measurements

Electron transport through single metal-molecule-metal junctions are exquisitely sensitive to the atomic scale geometry of the junction. Here, we use conductance signatures of single molecules on metal electrodes measured using the Scanning Tunneling Microscope-based Break Junction (STM-BJ) technique to map the Angstrom-scale arrangement of the atoms in the junctions. Using our “pull-push” technique, where we repeatedly pull apart, hold and then push the electrodes together in the presence of diamine molecules, we determine the conductance and geometry signatures of a series of these molecules. We find that the molecular conductance can be used to determine the distance between electrodes with Angstrom-scale precision. We discover that the odd or even number of carbon atoms in an alkanediamine molecule affects the mean elongation that the single molecule junction can sustain. Furthemore, by analyzing the statistical probability of forming the junctions with molecules of different lengths, we can we infer the average shape of our electrodes.