title: Length dependence of charge transport in nanoscopic molecular junctions incorporating a series of rigid thiol-terminated norbornylogs.
abstract: Four tetrathiol-terminated norbornane homologues were synthesized and self-assembled monolayers (SAMs) of these molecules were formed on Au via adsorption from CH2Cl2. SAMs were characterized structurally via spectroscopic ellipsometry (SE), reflection-absorption infrared spectroscopy (RAIRS), Rutherford backscattering spectrometry (RBS), and X-ray photoelectron spectroscopy (XPS). Results of these analyses show that the rigid norbornylogs form monolayers that have a surface coverage slightly lower than that of alkanethiols, and that they exhibit a nonmonotonic dependence of film thickness on molecular length. Nanoscale molecular junctions incorporating these SAMs were formed and characterized electrically using conducting probe atomic force microscopy (CP-AFM). The resistances of these junctions scale exponentially with the contour length of the molecules, with beta = 0.9 A(-1), consistent with a nonresonant tunneling mechanism. Further, the resistance of norbornyl SAMs correlates well with the resistance of alkanedithiol SAMs of similar length, suggesting that the norbornyl molecules form sulfur-metal bonds on both ends of the junction.
authors.affiliation: Department of Chemistry, University of Minnesota, 209 Pleasant Street SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Beebe
authors.forename: Vincent B
authors.initials: VB
authors.lastname: Engelkes
authors.forename: Jingquan
authors.initials: J
authors.lastname: Liu
authors.forename: J Justin
authors.initials: JJ
authors.lastname: Gooding
authors.forename: Paul K
authors.initials: PK
authors.lastname: Eggers
authors.forename: Yongseok
authors.initials: Y
authors.lastname: Jun
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Zhu
authors.forename: Michael N
authors.initials: MN
authors.lastname: Paddon-Row
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Frisbie