Evolution of local conductance pathways in a single-molecule junction studied using the three-dimensional dynamic probe method

Abstract

Understanding of the dynamics of the bonding states of molecules with electrodes while the molecular conformation is changed is particularly important for elucidating the details of electrochemical devices as well as molecular devices in which the reaction dynamics of the electrodes and molecules plays an important role, such as in fuel cells, catalysis and bioelectrochemical devices. However, it has been difficult to make measurements when the distance between counter electrodes is short, namely, the molecule is raised from a lying form, almost parallel and close to the electrodes, toward a standing form and vice versa. We previously have developed a method called the three-dimensional (3D) dynamic probe method, which enables conductance measurement while the conformation of a single-molecule junction is precisely controlled by scanning tunneling microscopy (STM) techniques. Here, by combining this method with density functional theory (DFT) calculations, it has become possible to simultaneously consider the effects of the dynamics of molecular structures and the bonding states at the electrodes on the local transmission pathways, local-bond contributions to conductance. Here, by performing an analysis on 1,4-benzenediamine (BDA) and 1,4-benzenedithiol (BDT) single molecule junctions, we have observed, for the first time, the effect of a change in the molecular conformations and bonding states on the local transmission pathways for a short Au electrode distance condition. † Electronic supplementary information (ESI) available. See

Adsorption, Stretching, and Breaking Processes in Single‐Molecule Conductance of para‐Benzenedimethanethiol in Gold Nanogaps: A DFT‐NEGF Theoretical Study**

“…But combined with the non‐equilibrium Green's function (NEGF) approach, DFT is still meaningful as a basis for the relationship between conductance and interfacial structures in molecular junctions [25] . In addition, DFT is important for understanding the correlation between the electrical and mechanical properties of molecular junctions in the dynamic evolution processes, [26] enabling determining the stretching force required to break the molecular junctions and the identity of the chemical bonds broken. For example, the dynamic evolution of thiyl molecules sandwiched between two metal electrodes under pulling forces is studied extensively both experimentally and theoretically [27,28] .…”

Binding structure, breaking forces and conductance of Au-Octanedithiol-Au molecular junction under stretching processes: a DFT-NEGF study

“…It is a meaningful method as a basis for the relationship between energy, stretching force or conductance and interfacial structures in molecular junctions by combining with the nonequilibrium Green's function (NEGF) approach [16]. Thus, DFT-NEGF is an important method for us to understand the relationship of the specific structure and the molecular conductance, as well as the variation of the stress force under stretching cases of a molecular junction [17]. In order to focus on the relation between the structure and properties of a molecular junction under stretching process, it is necessary to make a molecular wire binding to both electrodes in a form simple enough, leading one to pay more attention to the interfacial adsorption points.…”