Microscopy of Functional Molecules

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Organic electronic materials are carbon-rich compounds with a composition and structure that is tailored to optimize a particular functional property such as charge mobility, photoconductivity or luminescence/phosphorescence. Because the manufacturing and processing costs of organic materials are low, and they can be deposited on low cost (flexible) substrates, organic thin films are now important parts of many commercial products, the most notable being the high efficiency, bright and colorful displays that have appeared on mobile phones and tablets. There is also significant research effort to develop stable thin-film transistors and photovoltaic devices for low cost energy generation with this technology.   Despite the recent commercial success of organic thin-film electronics, grand challenges remain to be solved before the full potential of molecule-based electronics can be realized. To fulfill this vision of using inexpensive, atomically precise molecules in electronic devices or as devices, new ways of measuring and controlling the functional properties of molecules embedded in a solid state device or sensor are required. This is because the properties of single molecule devices depend, crucially, on every detail of the molecule’s configuration, including the contact to the solid state host.      In the last five years, there have been dramatic improvements in the capabilities of scanning probes that have important implications for the study of molecules at surfaces. These include the ability to: measure electroluminescence from molecules with sub-molecular resolution, clearly resolve single covalent bonds between carbon atoms, discriminate the bond order of covalent bonds, and probe the charge distribution within single molecules. Some of these advances depend upon the ability to create atomically precise tips with 'probe' particles (CO or Xe). Others depend on the stability afforded by quartz cantilevers (qPlus sensors). In this proposal, we seek to address the grand challenges of molecule-based electronics by exploiting these new capabilities. Our long term goal is atomic-level control of the organic-inorganic interface. As a step towards this, we will measure and manipulate the functional properties of molecules at surfaces and investigate a new way of attaching molecules to metal surfaces using n-heterocyclic carbenes.  The research program is international, multidisciplinary and collaborative. It involves Chemists, who will synthesize molecules, three theoretical groups, who will perform first principles calculations, and three experimental groups, who possess complementary expertise to my group at Queen's. Canadian graduate students will work closely with theorists and travel to our experimental collaborators to take advantage of scanning probe microscopes that operate at low temperature (1 K), at high magnetic field (8 T) and with light detection.