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Mechanically controlled binary conductance switching of a single-molecule junction
Quek, Su Ying,Kamenetska, Maria,Steigerwald, Michael L.,Choi, Hyoung Joon,Louie, Steven G.,Hybertsen, Mark S.,Neaton, J. B.,Venkataraman, Latha Springer Science and Business Media LLC 2009 Nature nanotechnology Vol.4 No.4
<P>Molecular-scale components are expected to be central to the realization of nanoscale electronic devices. Although 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. To date, 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 nitrogen-gold 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.</P>
Conductance and Geometry of Pyridine-Linked Single-Molecule Junctions
Kamenetska, M.,Quek, Su Ying,Whalley, A. C.,Steigerwald, M. L.,Choi, H. J.,Louie, Steven G.,Nuckolls, C.,Hybertsen, M. S.,Neaton, J. B.,Venkataraman, L. American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.19
<P>We have measured the conductance and characterized molecule−electrode binding geometries of four pyridine-terminated molecules by elongating and then compressing gold point contacts in a solution of molecules. We have found that all pyridine-terminated molecules exhibit bistable conductance signatures, signifying that the nature of the pyridine−gold bond allows two distinct conductance states that are accessed as the gold−molecule−gold junction is elongated. We have identified the low-conductance state as corresponding to a molecule fully stretched out between the gold electrodes, where the distance between contacts correlates with the length of the molecule; the high-conductance state is due to a molecule bound at an angle. For all molecules, we have found that the distribution of junction elongations in the low-conductance state is the same, while in the high-conductance state, the most likely elongation length increases linearly with molecule length. The results of first-principles conductance calculations for the four molecules in the low-conductance geometry agree well with the experimental results and show that the dominant conducting channel in the conjugated pyridine-linked molecules is through the π* orbital.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-19/ja1015348/production/images/medium/ja-2010-015348_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja1015348'>ACS Electronic Supporting Info</A></P>