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Transition from direct to inverted charge transport Marcus regions in molecular junctions via molecular orbital gating


Solid-state molecular tunnel junctions are often assumed to operate in the Landauer regime, which describes essentially activationless coherent tunnelling processes. In solution, on the other hand, charge transfer is described by Marcus theory, which accounts for thermally activated processes. In practice, however, thermally activated transport phenomena are frequently observed also in solid-state molecular junctions but remain poorly understood. Here, we show experimentally the transition from the Marcus to the inverted Marcus region in a solid-state molecular tunnel junction by means of intra-molecular orbital gating that can be tuned via the chemical structure of the molecule and applied bias. In the inverted Marcus region, charge transport is incoherent, yet virtually independent of temperature. Our experimental results fit well to a theoretical model that combines Landauer and Marcus theories and may have implications for the interpretation of temperature-dependent charge transport measurements in molecular junctions.

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Fig. 1: Illustrations of the junctions and description of the combined Marcus–Landauer model.
Fig. 2: Temperature-dependent measurements of the SAM-based junctions.
Fig. 3: Temperature-dependent measurements of the single-molecule junctions.
Fig. 4: Fits to the combined Marcus–Landauer theory.


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L.Y., L.J.W., L.J., H.V.A. and C.A.N. acknowledge the Ministry of Education (MOE) for supporting this research under award no. MOE2015-T2-1-050, and the National Research Foundation, Prime Minister’s Office, Singapore, under its Medium-sized Centre Program. A.R.G., M.A.A. and E.B. acknowledge support from the National Science Foundation (grants NSF-ECCS #1402990 and #1518863). Yu Xiaojiang is kindly acknowledged for assisting at the SINS beam line at SSLS under NUS core support C-380-003-003-001.

Author information




L.J.W. synthesized and characterized the ferrocene-based molecules. L.Y. conducted the temperature-dependent measurements and characterized the ferrocene-based SAMs. L.J. performed the charge transport measurements at room temperature. H.V.A. performed the DFT calculations. A.R.G. conducted the single-molecule transport measurements and fitted the data to a double quantum dot model. M.A.A. assisted with the single-molecule measurements. E.B. supervised the single-molecule experiments and fitted the SAMs data. C.A.N. conceived and supervised the project. All the authors contributed to the writing of the article and interpretation of the results.

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Correspondence to Enrique Barco or Christian A. Nijhuis.

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The authors declare no competing interests.

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Supplementary Information

Supplementary Figures 1–43, Supplementary Tables 1–4, Supplementary Methods, Supplementary discussions.

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Yuan, L., Wang, L., Garrigues, A.R. et al. Transition from direct to inverted charge transport Marcus regions in molecular junctions via molecular orbital gating. Nature Nanotech 13, 322–329 (2018).

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