Transport through self-assembled monolayer molecular junctions: Role of in-plane dephasing

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Abstract

Self-assembled-monolayer (SAM) molecular junctions (MJs) constitute a promising building block candidate for future molecular electronic devices. Transport properties of SAM-MJs are usually calculated using either the phenomenological Simmons model, or a fully coherent transport theory, employing the SAMs periodicity. We suggest that dephasing plays an important role in determining the transport properties of SAM-MJs. We present an approach for calculating the transport properties of SAM-MJs that inherently takes into account in-plane dephasing in the electron motion as it traverses the SAM plane. The calculation is based on the nonequilibrium Greens function formalism, with a local dynamics approximation that describes incoherent motion along the SAM plane. Our approach describes well the two hallmarks of transport through SAM-MJs, namely, the exponential decay of current with molecular chain length and the reduction of the current per molecule as compared to single-molecule junctions. Specifically, we show that dephasing leads to an exponential decay of the current as a function of molecular length, even for resonant tunneling, where the fully coherent calculation shows little or no length-dependence of the current. The dephasing is also shown to lead to a substantial reduction of the current in a SAM-MJ as compared to the single molecule junction, in a realistic parameter regime, where the coherent calculation shows only a very small reduction of the current. Finally, we discuss the effect of dephasing on more subtle transport phenomena such as the conductance even-odd effect and negative differential resistance.

Original languageEnglish
Pages (from-to)21119-21127
Number of pages9
JournalJournal of Physical Chemistry C
Volume118
Issue number36
DOIs
StatePublished - 11 Sep 2014

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