Modeling Single Molecule Junction Mechanics as a Probe of Interface Bonding

Abstract

Using the atomic force microscope based break junction approach, applicable to metal point contacts and single molecule junctions, measurements can be repeated thousands of times resulting in rich data sets characterizing the properties of an ensemble of nanoscale junction structures. This paper focuses on the relationship between the measured force extension characteristics including bond rupture and the properties of the interface bonds in the junction. A set of exemplary model junction structures have been analyzed using density functional theory based calculations to simulate the adiabatic potential surface that governs the junction elongation. The junction structures include representative molecules that bond to the electrodes through amine, methylsulfide and pyridine links. The force extension characteristics are shown to be most effectively analyzed in a scaled form with maximum sustainable force and the distance between the force zero and force maximum as scale factors. Widely used, two parameter models for chemical bond potential energy versus bond length are found to be nearly identical in scaled form. Furthermore, they fit well to the present calculations of N-Au and S-Au donor-acceptor bonds, provided no other degrees of freedom are allowed to relax. Examination of the reduced problem of a single interface, but including relaxation of atoms proximal to the interface bond, shows that a single-bond potential form renormalized by an effective harmonic potential in series fits well to the calculated results. This allows relatively accurate extraction of the interface bond energy. Analysis of full junction models show cooperative effects that go beyond the series inclusion of the second bond in the junction, the spectator bond that does not rupture.

arXiv comment15 pages, 11 figures. Revised version to clarify several points, particularly junction stability arguments, inclusion of 2 new figures and some additional references

References in corpus (14)

• Van der Waals density functionals applied to solids
• Advances in atomic force microscopy
• Dependence of Single Molecule Junction Conductance on Molecular Conformation
• Single-Molecule Circuits with Well-Defined Molecular Conductance
• Mechanical properties and formation mechanisms of a wire of single gold atoms
• Formation and Evolution of Single Molecule Junctions
• Structure and conductance histogram of atomic-sized Au contacts
• Theoretical analysis of the conductance histograms and structural properties of Ag, Pt and Ni nanocontacts
• Nature of well-defined conductance of amine anchored molecular junctions
• Forces and conductances in a single-molecule bipyridine junction
• Mechanical annealing of metallic electrodes at the atomic scale
• Structural Origins of Conductance Fluctuations in Gold-Thiolate Molecular Transport Junctions
• The Influence of Molecular Adsorption on Elongating Gold Nanowires
• Resistive and rectifying effects of pulling gold atoms at thiol-gold nano-contacts

Cited by in corpus (4)

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