title: Mapping the Transmission Functions of Single-Molecule Junctions.
abstract: Charge transport phenomena in single-molecule junctions are often dominated by tunneling, with a transmission function dictating the probability that electrons or holes tunnel through the junction. Here, we present a new and simple technique for measuring the transmission functions of molecular junctions in the coherent tunneling limit, over an energy range of 1.5 eV around the Fermi energy. We create molecular junctions in an ionic environment with electrodes having different exposed areas, which results in the formation of electric double layers of dissimilar density on the two electrodes. This allows us to electrostatically shift the molecular resonance relative to the junction Fermi levels in a manner that depends on the sign of the applied bias, enabling us to map out the junction's transmission function and determine the dominant orbital for charge transport in the molecular junction. We demonstrate this technique using two groups of molecules: one group having molecular resonance energies relatively far from EF and one group having molecular resonance energies within the accessible bias window. Our results compare well with previous electrochemical gating data and with transmission functions computed from first principles. Furthermore, with the second group of molecules, we are able to examine the behavior of a molecular junction as a resonance shifts into the bias window. This work provides a new, experimentally simple route for exploring the fundamentals of charge transport at the nanoscale.
authors.forename: Brian
authors.initials: B
authors.lastname: Capozzi
authors.forename: Jonathan Z
authors.initials: JZ
authors.lastname: Low
authors.affiliation: School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology , Wuhan 430070, China.
authors.forename: Jianlong
authors.initials: J
authors.lastname: Xia
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Physics, University of California , Berkeley, California 94720, United States.
authors.forename: Zhen-Fei
authors.initials: ZF
authors.lastname: Liu
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Physics, University of California , Berkeley, California 94720, United States.|Kavli Energy Nano Sciences Institute at Berkeley , Berkeley, California 94720, United States.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Neaton
authors.forename: Luis M
authors.initials: LM
authors.lastname: Campos
authors.forename: Latha
authors.initials: L
authors.lastname: Venkataraman
keywords: electrochemical gating; electronic transport; resonant transport; single-molecule junctions; transmission function