Molecular electronics started with the idea of wiring an individual molecule to two metal electrodes, called single-molecule junctions, as an analogy of single electronic components in commercial microelectronic devices to overcome the limit of famous Moore's prediction. In a single molecular junction, perhaps the most elusive factor that influences the electron transport properties lies in the molecule-electrode contact interfaces. Despite continuous experimental achievements and the conceptual simplicity of molecular electronic devices, challenges for their theoretical understanding of the correlation between electron transport and molecular binding structures are still unresolved. Therefore, probing and controlling the structure and dynamics of single-molecule junctions and consequently controlling the molecular transport of these junctions are critical to the development of this field. The project will integrate molecular simulations for the self-assembly and nanocontact dynamics at surface and interface, and experimental mechanics and electron transport measurements of single-molecule junctions. The project will provide a deep understanding of many transition phenomena observed in molecular force and conductance measurements. If successful, the research will have tremendous impact on molecular electronics community and many other areas, such as energy research and molecular force spectroscopy. The education and outreach objective of this proposal is to tightly integrate the research efforts and results with graduate, undergraduate, and K-12 education and to globally disseminate both research and the education outcomes.
Although the electrical conductance and mechanical properties of single-molecule junctions have achieved significant progress over the past decade, challenges of a detailed understanding of molecular binding structures and electron transport, and the structure-force-conductance correlations, are still unresolved. This research will develop a combined molecular simulation and scanning probe microscope break-junction technique to probe and control the structure and dynamics in molecular electronics devices: (1) Performing molecular simulations by using as close as possible the experimental parameters, dynamics of electrode and realistic atomic interactions to understand the binding structure and force measurement in scanning probe experiment; (2) Developing a dual-mode feedback system with AC-coupled high speed amplifier at radio frequency to capture the key transitions of molecular binding sites that induce conductance changes. The experimental data at nanosecond (ns) timescale will be directly compared with molecular simulation results; (3) Using the coordinated molecular simulation and scanning probe break-junction experiment to probe the structure and dynamics of selected benchmark systems under different mode trainings. Multi-variable force-conductance two-dimensional cross-correlation histogram analyses for the force and conductance traces will be performed in experiments and simulations, and the distinct stable configurations of molecular junctions will be identified. The coordinated computational and experimental research project will also provide an interdisciplinary research for students in materials, mechanics, chemistry, electronics, and computational materials science.
