title: Non-exponential Length Dependence of Conductance in Iodide-Terminated Oligothiophene Single-Molecule Tunneling Junctions.
abstract: An exponential decrease of molecular conductance with length has been observed in most molecular systems reported to date, and has been taken as a signature of non-resonant tunneling as the conduction mechanism. Surprisingly, the conductance of iodide-terminated oligothiophene molecules presented herein does not follow the simple exponential length dependence. The lack of temperature dependence in the conductance indicates that tunneling still dominates the conduction mechanism in the molecules. Transition voltage spectroscopy shows that the tunneling barrier of the oligothiophene decreases with length, but the decrease is insufficient to explain the non-exponential length dependence. X-ray photoelectron spectroscopy, stretching length measurement, and theoretical calculations show that the non-exponential length dependence is due to a transition in the binding geometry of the molecule to the electrodes in the molecular junctions as the length increases.
authors.affiliation: Center for Biosensors and Bioelectronics, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.|School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Limin
authors.initials: L
authors.lastname: Xiang
authors.affiliation: Center for Biosensors and Bioelectronics, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hines
authors.affiliation: Center for Biosensors and Bioelectronics, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.|School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Julio L
authors.initials: JL
authors.lastname: Palma
authors.affiliation: Laboratory of Advanced Materials, Fudan University , Shanghai 200438, P.R. China.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Lu
authors.affiliation: School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Vladimiro
authors.initials: V
authors.lastname: Mujica
authors.affiliation: Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Ratner
authors.affiliation: Laboratory of Advanced Materials, Fudan University , Shanghai 200438, P.R. China.
authors.forename: Gang
authors.initials: G
authors.lastname: Zhou
authors.affiliation: Center for Biosensors and Bioelectronics, Biodesign Institute, Arizona State University , Tempe, Arizona 85287, United States.|School of Electrical, Computer and Energy Engineering, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Nongjian
authors.initials: N
authors.lastname: Tao