Atomistic simulations of highly conductive molecular transport junctions under realistic conditions

Abstract

We report state-of-the-art atomistic simulations combined with high-fidelity conductance calculations to probe structure-conductance relationships in Au-benzenedithiolate (BDT)-Au junctions under elongation. Our results demonstrate that large increases in conductance are associated with the formation of monatomic chains (MACs) of Au atoms directly connected to BDT. An analysis of the electronic structure of the simulated junctions reveals that enhancement in the s-like states in Au MACs causes the increases in conductance. Other structures also result in increased conductance but are too short-lived to be detected in experiment, while MACs remain stable for long simulation times. Examinations of thermally evolved junctions with and without MACs show negligible overlap between conductance histograms, indicating that the increase in conductance is related to this unique structural change and not thermal fluctuation. These results, which provide an excellent explanation for a recently observed anomalous experimental result [Bruot et al., Nat. Nanotechnol., 2012, 7, 35-40], should aid in the development of mechanically responsive molecular electronic devices.

Stretching of BDT-gold molecular junctions: thiol or thiolate termination?

“…It has also been shown to improve the energy level alignment when the junction is formed, leading to values of G in better agreement with experiments. 12,13,15,16 The method, however, shows some limitations. The correction applied by ASIC depends on the atomic orbital occupation, not the molecular orbital occupation.…”

“…These results have been found in several studies reported in the literature for Au-BDT-Au (thiolate) junctions. 9,12,13,15,16,35 The resonant states at E F yield high values of G of 1.35G 0 , 0.45G 0 and 0.22G 0 for tip-tip, surface-adatom and adatom-adatom, respectively. The observed peaks at E F correspond to the hybridized Ψ 1 state of the BDT molecule.…”

Mechanism of the enhanced conductance of a molecular junction under tensile stress

“…[14][15][16] The fact that the bonding geometry most commonly realized in the experiments on Au-PDT-Au junctions [6] is known [14][15][16] obviated the need for us to perform relaxations/stretching for a large ensemble of different starting junction geometries such as was necessary in the study in Ref. 13 of Au-BDTAu junctions for which the bonding geometry most commonly realized in experiments has yet to be determined.…”

“…port calculations based on DFT with approximate selfinteraction corrections have been used in the recent theoretical study [13] of the conductance enhancement of Au-BDT-Au junctions under tensile stress. However, density functional theory is a tool designed specifically for calculating ground state total energies.…”

“…[7][8][9][10][11][12] However, another recent study [3] has indicated that the conductance of Au-BDT-Au junctions is controlled mainly by the strength of the molecule-electrode coupling rather than by the energy of a molecular electronic level. Most recently it has been proposed [13] that gold atomic chains formed at the molecule-electrode interfaces when the junction is stretched may be responsible for the large increase observed [2] in the conductance. Thus the origin of the observed behavior [2] remains controversial.…”