2017/01/31 by Hyehwang Kim, Dvira Segal
Chemistry · Engineering · Physics and Astronomy · #Chemistry #Condensed matter physics #Conductance #Delocalized electron #Electrochemical Analysis and Applications #Electron #Materials science #Molecular Junctions and Nanostructures #Physics #Quantum and electron transport phenomena #Quantum mechanics #Quantum tunnelling #Superexchange #Thermal conduction #Variable-range hopping #cond-mat.mes-hall
paper · pdf · doi:10.1063/1.4981022
published as J. Chem. Phys. 146, 164702 (2017)
arxiv created 2017/01/31 · openalex publication_date 2017/04/24 · arxiv updated 2017/12/25 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The electrical conductance of molecular junctions may depend strongly on the temperature and weakly on molecular length, under two distinct mechanisms: phase-coherent resonant conduction, with charges proceeding via delocalized molecular orbitals, and incoherent thermally assisted multi-step hopping. While in the case of coherent conduction, the temperature dependence arises from the broadening of the Fermi distribution in the metal electrodes, in the latter case it corresponds to electron-vibration interaction effects on the junction. With the objective to distill the thermally activated hopping component, thus exposing intrinsic electron-vibration interaction phenomena on the junction, we suggest the design of molecular junctions with "spacers," extended anchoring groups that act to filter out phase-coherent resonant electrons. Specifically, we study the electrical conductance of fixed-gap and variable-gap junctions that include a tunneling block, with spacers at the boundaries. Using numerical simulations and analytical considerations, we demonstrate that in our design, resonant conduction is suppressed. As a result, the electrical conductance is dominated by two (rather than three) mechanisms: superexchange (deep tunneling) and multi-step thermally induced hopping. We further exemplify our analysis on DNA junctions with an A:T block serving as a tunneling barrier. Here, we show that the electrical conductance is insensitive to the number of G:C base-pairs at the boundaries. This indicates that the tunneling-to-hopping crossover revealed in such sequences truly corresponds to the properties of the A:T barrier.