title: Conductance and geometry of pyridine-linked single-molecule junctions.
abstract: 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 pi* orbital.
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
authors.forename: M
authors.initials: M
authors.lastname: Kamenetska
authors.forename: Su Ying
authors.initials: SY
authors.lastname: Quek
authors.forename: A C
authors.initials: AC
authors.lastname: Whalley
authors.forename: M L
authors.initials: ML
authors.lastname: Steigerwald
authors.forename: H J
authors.initials: HJ
authors.lastname: Choi
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
authors.forename: C
authors.initials: C
authors.lastname: Nuckolls
authors.forename: M S
authors.initials: MS
authors.lastname: Hybertsen
authors.forename: J B
authors.initials: JB
authors.lastname: Neaton
authors.forename: L
authors.initials: L
authors.lastname: Venkataraman