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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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.
The authors declare no competing interests.
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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). https://doi.org/10.1038/s41565-018-0068-4
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