Effect of the Chemical Potentials of Electrodes on Charge Transport across Molecular Junctions
Journal
Journal of Physical Chemistry C
Date Issued
2019-01-01
Author(s)
Peng, Hao Howard
Lin, Geng Min
Lin, Chih Hsun
CHUN-HSIEN CHEN
Wang, Tsai Hui
Ho, Ching Hwa
Hsu, Hsiu Fu
Abstract
© Copyright 2019 American Chemical Society. Charge transport across molecular junctions can be described by G = Gcontactexp(-βL), envisioned as sequential propagation through electrode-molecule contacts (Gcontact) and the molecular backbone (exp(-βL)). How Gcontact and exp(-βL) are modulated by the chemical potentials of the electrodes (EF), although essential, remains relatively unexplored because EF is typically driven by the applied Vbias and hence limited to a small range in that a large Vbias introduces complicated transport pathways. Herein, the interrelated EF and Vbias are electrochemically disentangled by fixing Vbias at a small value while potentiostatically positioning the electrode EF in a 1.5 V range. The results show that EF affects Gcontact more pronouncedly than the molecular backbone. For the covalently anchored acetylene-electrode (CC-Au) junctions, the energy level of the frontier molecular orbital (EFMO) is found to shift nonlinearly as EF changes; |EFMO-EF| is independent of EF in the range of-0.25 to 0.00 V (vs EAg/AgCl) and is narrowed by -32% at 0.00-0.75 V. These findings are elucidated by the refined Simmons model, Newns-Anderson model, and single-level Breit-Wigner formula and quantitatively shed light on the influence of electrodes on the molecular orbitals (viz., the self-energy, ς).
Type
journal article