Molecular junctions are the smallest form of nanoelectronic circuits, consisting of one molecule bound between two metallic tips that function as electrodes. The properties of these junctions have been of great interest to the scientific community for decades; however, there is still much unknown about the transport of electrons through the junction, and how it is affected by various electronic and geometric properties of the bridging molecule and the electrodes. Our research uses density functional theory (DFT) to computationally examine the effects of chemistry at the molecule-electrode interface on the transport properties of the junction. Since the structures of molecular junctions cannot be directly ascertained in a laboratory and their measured conductance show large fluctuations, our goal is to develop fundamental structure-property relationships that can guide the design of effective molecular junctions. We are particularly interested in understanding how variations in the structure of the electrode affect junction conductance. The electrode tips are modeled using the (111) face of a gold crystal, and the conducting molecules of interest consist of a benzene ring with either thiol or amine terminal groups (i.e., benzenedithiol (BDT) or benzenediamine (BDA)), as well as various other aromatic molecules. Transport calculations have been performed on static model BDT-gold and BDA-gold junctions using non-equilibrium Green’s functions in combination with DFT (NEGF-DFT). <i>Ab initio </i>molecular dynamics calculations have been performed in conjunction with NEGF-DFT to calculate conductance histograms. Results show that models that include motion of electrode atoms are important to accurately capture the dynamical uncertainty of conductance in molecular junctions.

Effect of electrode surface structure on electron transport in molecular junctions

254th National Meeting (2017)

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