Solid-state molecular tunnel junctions are often assumed to operate in the Landauer regime, which describes essentially activationless coherent tunnelling processes. On the other extreme, Marcus theory is very successful in describing thermally-activated charge transfer processes in wet electrochemical environments. In practice, solid-state molecular junctions may behave in between these two extremes. Indeed, thermally activated transport phenomena are frequently observed in solid-state junctions but poorly understood. We will present experimental evidence for the transition from the Marcus to the inverted Marcus region in a solid-state molecular tunnel junction by means of intra-molecular orbital gating which 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 have profound implications for the interpretation of widely used temperature-dependent charge transport measurements.

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

255th National Meeting (2018)

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