Molecular-scale components are expected to be central to nanoscale electronic devices. While molecular-scale switching has been reported in atomic quantum point contacts, single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. Thus far, switching in single-molecule junctions has been attributed to changes in the conformation or charge state of the molecule. Here, we demonstrate reversible binary switching in a single-molecule junction by mechanical control of the metal-molecule contact geometry. We show that 4,4'-bipyridine-gold single-molecule junctions can be reversibly switched between two conductance states through repeated junction elongation and compression. Using first-principles calculations, we attribute the different measured conductance states to distinct contact geometries at the flexible but stable N-Au bond: conductance is low when the N-Au bond is perpendicular to the conducting pi-system, and high otherwise. This switching mechanism, inherent to the pyridine-gold link, could form the basis of a new class of mechanically-activated single-molecule switches.
@article{arxiv.0901.1139,
title = {Mechanically-Controlled Binary Conductance Switching of a Single-Molecule Junction},
author = {Su Ying Quek and Maria Kamenetska and Michael L. Steigerwald and Hyoung Joon Choi and Steven G. Louie and Mark S. Hybertsen and J. B. Neaton and L. Venkataraman},
journal= {arXiv preprint arXiv:0901.1139},
year = {2009}
}