University of Limerick
Thompson_2023_Resolving.pdf (2 MB)

Resolving charge transfer mechanisms in molecular tunnel junctions using dynamic charge transfer and static current–voltage measurements†

Download (2 MB)
journal contribution
posted on 2024-02-01, 16:23 authored by Liang CaoLiang Cao, Ziyu ZhangZiyu Zhang, DAMIEN THOMPSONDAMIEN THOMPSON, Dong‐Chen Qi, Christian A. Nijhuis

Understanding charge transfer (CT) dynamics is important for controlling the tunneling mechanism in molecular junctions. Synchrotron-based core-hole clock (CHC) spectroscopy can quantify the femtosecond-scale CT time tCT across the metal–molecule interface, which affects the current density (J) produced with applied bias (V) in the junctions. However, directly determining the tunneling behavior from a comparison of the CHC tCT and the J(V) measurement of a junction requires prior knowledge of the molecular orbitals involved. To solve this problem, we examined CT dynamics across self-assembled monolayers (SAMs) based on oligophenylene ethynylene (OPE) wires with ferrocene (Fc) terminal groups with Au, Ag and Pt bottom electrodes. Density functional theory (DFT) helped identify the donor and acceptor levels, which are typically the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The measured J(V) response of the SAM junctions with gallium-indium (EGaIn) alloy as the top electrode demonstrates that the tunneling decay coefficient b provides an intensive parameter to assess CT efficiency. We find that more delocalized molecular wavefunctions (in this case, LUMO+2, with contributions from Fc and OPE) facilitate faster and more efficient CT than more localized acceptor levels (here, the more iron-centered LUMO+1). These orbital-specific effects explain why we measure comparable b values for CT via LUMO+1 and J via HOMO and LUMO at +1 V bias. Our study highlights the utility of tCT measured by CHC in experimentally confirming the orbitals participating in charge transport measurements and shows that higher-lying delocalized orbitals can in some instances dominate over frontier orbitals despite larger energy offset (or increase in tunneling barrier height)


SSPC_Phase 2

Science Foundation Ireland

Find out more...



Journal of Materials Chemistry C 12, pp.1701-1709


The Royal Society of Chemistry

Other Funding information

National Research Foundation (NRF) for supporting this research under its Medium Sized Centre Programme and the Competitive Research Programme (CRP; NRF-CRP17-2017-08). Australian Research Council (grant no. DP230101904). National Natural Science Foundation of China (Grant No.12074385)

Also affiliated with

  • Bernal Institute

Sustainable development goals

  • (9) Industry, Innovation and Infrastructure
  • (15) Life On Land

Department or School

  • Physics

Usage metrics

    University of Limerick


    Ref. manager