title: Single-molecule circuits with well-defined molecular conductance.
abstract: We measure the conductance of amine-terminated molecules by breaking Au point contacts in a molecular solution at room temperature. We find that the variability of the observed conductance for the diamine molecule-Au junctions is much less than the variability for diisonitrile- and dithiol-Au junctions. This narrow distribution enables unambiguous conductance measurements of single molecules. For an alkane diamine series with 2-8 carbon atoms in the hydrocarbon chain, our results show a systematic trend in the conductance from which we extract a tunneling decay constant of 0.91 +/- 0.03 per methylene group. We hypothesize that the diamine link binds preferentially to undercoordinated Au atoms in the junction. This is supported by density functional theory-based calculations that show the amine binding to a gold adatom with sufficient angular flexibility for easy junction formation but well-defined electronic coupling of the N lone pair to the Au. Therefore, the amine linkage leads to well-defined conductance measurements of a single molecule junction in a statistical study.
authors.affiliation: Department of Physics, and Center for Electron Transport in Molecular Nanostructures, Columbia University, New York, New York 10027, USA. latha@phys.columbia.edu
authors.forename: Latha
authors.initials: L
authors.lastname: Venkataraman
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Klare
authors.forename: Iris W
authors.initials: IW
authors.lastname: Tam
authors.forename: Colin
authors.initials: C
authors.lastname: Nuckolls
authors.forename: Mark S
authors.initials: MS
authors.lastname: Hybertsen
authors.forename: Michael L
authors.initials: ML
authors.lastname: Steigerwald