Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue ACS Applied Materials & Interfaces Année : 2021

Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols

Résumé

A number of factors contribute to orbital energy alignment with respect to the Fermi level in molecular tunnel junctions. Here, we report a combined experimental and theoretical effort to quantify the effect of metal image potentials on the highest occupied molecular orbital to Fermi level offset, ε(h), for molecular junctions based on self-assembled monolayers (SAMs) of oligophenylene ethynylene dithiols (OPX) on Au. Our experimental approach involves the use of both transport and photoelectron spectroscopy to extract the offsets, ε(h)(trans) and ε(h)(UPS), respectively. We take the difference in these quantities to be the image potential energy eV(image). In the theoretical approach, we use density functional theory (DFT) to calculate directly eV(image) between positive charge on an OPX molecule and the negative image charge in the Au. Both approaches yield eV(image) ∼ -0.1 eV per metal contact, meaning that the total image potential energy is ∼-0.2 eV for an assembled junction with two Au contacts. Thus, we find that the total image potential energy is 25-30% of the total offset ε(h), which means that image charge effects are significant in OPX junctions. Our methods should be generally applicable to understanding image charge effects as a function of molecular size, for example, in a variety of SAM-based junctions.
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Dates et versions

hal-03467606 , version 1 (06-12-2021)

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Zuoti Xie, Valentin Diez Cabanes, Quyen van Nguyen, Sandra Rodriguez-Gonzalez, Lucie Norel, et al.. Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols. ACS Applied Materials & Interfaces, 2021, 13 (47), pp.56404-56412. ⟨10.1021/acsami.1c16398⟩. ⟨hal-03467606⟩
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