NIRT: Synthesis, Electrical and Optical Properties of Metal-Molecule-Metal Junctions formed by Self-Assembly

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This project aims to synthesize metal-organic semiconducting molecule-metal structures with nanoscale metallic contacts pre-assembled or templated by DNAs, or directly connected to the molecule as chemisorbed gold nanoparticles/nanowires. The metallic contacts will form ohmic contacts to molecular devices for circuits from DC to microwave frequencies. Precisely fabricated, ultrasmall gaps are not needed since the overall hybrid structure will be much longer than the organic molecule of interest. At optical frequencies, the metallic contacts will form an electromagnetic cavity around the molecular device, enhancing optical fields to be utilized in single-molecule spectroscopic measurements. Self-assembly of these new nanoscale objects will be investigated both theoretically and experimentally. Electrical devices will be fabricated to study charge transport through single molecules. New electrical, optical and physical phenomenon may arise from these unique nanoscale structures. The open planar geometry formed in this work is expected to allow electrostatic modification of electronic states using a nearby strongly-coupled gate electrode, and will reduce fluorescence quenching by nearby metallic electrodes. Single-molecule based transistors and light-emitting diodes may be generated from the proposed structures. The methods developed will lay the groundwork for developing molecular electronic and optical devices and integrating them into complex circuits. Intellectual Merit. Fundamental advances across disciplines are essential to the advancement of nanoscale devices and to understanding their behavior. Molecular synthesis, self-assembly, and charge transport are essential components for realizing nanoscale devices with organic molecules. A coordinated team attack on such issues can advance the state of single-molecule devices. This project will be carried out by a team of two chemists, one solid-state physicist, one spectroscopist, and one theorist together with collaborators from industry, national labs, and foreign universities with expertise in polymer synthesis, surface chemistry, biochemistry, DNA self-assembly, DNA metallization, spectroscopy, charge transport, fluid dynamics simulation, and device fabrication. Broader Impacts. This project may result in a new approach to make electrical contacts to single molecules, which will allow study of charge transport through single molecules with different chemical functionalities and length as well as measurement of unique optical properties arising from a single molecule confined in a nanogap. The proposed work will not only answer fundamental questions of intramolecular charge transport mechanisms in molecules with length scale of 5-100 nm, it will also provide answers to technological questions of whether organic molecules have sufficient performance for nanoelectronics and whether the mobility of molecular devices will be dramatically increased by alignment of organic semiconducting molecules between electrodes. This project also utilizes methods to self- assemble DNA-polymer-DNA and nanoparticle-molecule-nanoparticle structures using electrophoresis and dielectrophoresis to allow electrical connections to be made to single organic semiconducting molecules. The PIs will work closely with existing NSF centers and the Stanford Office of Science Outreach to reach a broad population ranging from K-12, community college, undergraduate, and graduate students as well as to prepare teachers of tomorrow for new areas of science and technology. Two internship positions every year for minority and/or women community college students are integral to the project. One research position per year will also be provided to a middle school or high school teacher during the summer; PIs will continue to work with them to develop their education plans after their summer research. PIs will also reach out to the general public through a public website and participation in various community events. The graduate students and postdoc involved in the project will actively interact with each other and have the opportunity to interact with researchers from industry, national labs, and international collaborators. They will be well equipped with a combination of technical engineering skills, basic scientific understanding, and communication skills, and poised to contribute to nanoscience and nanotechnology.