Since Aviram and Ratner published their influential paper in 1974 theorizing that an organic molecule bound between two metal electrodes could act as a rectifier, the field of molecular electronics has grown substantially. As a result, a variety of theoretical models have been, and are employed, to fit experimental data to these models with the goal of accurately describing the conductance of various molecular electronic junctions. However, a variety of factors, such as binding site, effective electron mass, extinction coefficients, and applied bias voltage, all play a role in the conductance. Reported values for some of these parameters vary widely in the literature, and are only accessible to experimentalist through fitting data to one or more of such models. Herein we aim to gain a better fundamental understanding of the relationship of these parameters, with the conductance of molecular electronic junctions. To that end, we employ a combination of density functional theory and tunneling-based models to investigate the impact of the molecular binding site, effective electron mass, and voltage on a series of gold-alkanedithiol-gold junctions. We found that for alkanedithiols, irrespective of carbon number, the face-centered cubic three-fold hollow (FCC) site is favored over the on-top site, and likely is the most abundant configuration in experimental measurements. Furthermore, we found that changing the effective electron mass has significant impact on the conductance and therefore the extinction coefficient, and that independent of model used the extinction coefficient is almost constant in the low bias regime.

Developing tunneling-based atomistic models of Au-S-(CH2)n-S-Au molecular junctions

ACS Spring Meeting 2021

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