Orbital alignment as a key determinant of nanotransport in molecular tunnel junctions despite fermi level pinning: exponential correlation with molecule-electrode coupling
At first glance, interrogating the impact of molecular orbital alignment on charge transport in molecular tunnel junctions may appear out of place, given the well-documented strong Fermi level pinning effect. To demonstrate that the contrary is true, we investigated molecular junctions based on self...
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| Main Authors: | , |
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| Format: | Article (Journal) Editorial |
| Language: | English |
| Published: |
September 15, 2025
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| In: |
The journal of physical chemistry letters
Year: 2025, Volume: 16, Issue: 3, Pages: 9963-9971 |
| ISSN: | 1948-7185 |
| DOI: | 10.1021/acs.jpclett.5c02168 |
| Online Access: | Verlag, kostenfrei, Volltext: https://doi.org/10.1021/acs.jpclett.5c02168
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| Author Notes: | Ioan Bâldea and Zuoti Xie |
| Summary: | At first glance, interrogating the impact of molecular orbital alignment on charge transport in molecular tunnel junctions may appear out of place, given the well-documented strong Fermi level pinning effect. To demonstrate that the contrary is true, we investigated molecular junctions based on self-assembled monolayers (SAMs) of alkyl monothiols (CnT) and dithiols (CnDT) with Ag, Au, and Pt electrodes using the conducting probe atomic force microscopy (CP-AFM) platform. Analysis of these data reveals that the HOMO-metal electronic coupling Γ and the low bias conductance G are exponentially correlated with the HOMO energy offset relative to the Fermi level ε0 = EMO - EF (Γ ∝ exp(−α̅|ε0|), G ∝ exp(−α|ε0|), α ≈ 2α̅). This impact is remarkably strong: for CnT junctions, a reduction by only 25% in |ε0| translates into an increase of Γ by 1 order of magnitude and of G by 2 orders of magnitude. More broadly, this exponential correlation of Γ and G with ε0 offers deeper insight into nanotransport and extends understanding of the previously reported exponential dependence of Γ and G on the SAM-induced work function shift ΔΦ, which reflects the linear correlation between ε0 and ΔΦ. From a fundamental perspective, it is crucial to highlight that our data validate a formula for Γ (a property which depends on both electrodes of a junction), which features (i) ε0 rather than ΔΦ (i.e., a property of a full junction versus a property of a “half a junction”) and (ii) ε0 rather than its square root in the exponent, thereby invalidating the widely employed tunneling barrier picture. |
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| Item Description: | Gesehen am 19.01.2026 |
| Physical Description: | Online Resource |
| ISSN: | 1948-7185 |
| DOI: | 10.1021/acs.jpclett.5c02168 |