Materials on the edge: nanoscale understanding and control of interfacial and interaction-driven electronic properties of materials

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Today's technologies largely rely on the materials of the past 50-100 years. As we seek to solve human challenges and propel futuristic technologies, new materials and structures will be required to underpin these applications. Many of these will fall into the category of “quantum materials”, where properties differ substantially from the metals, semiconductors and insulators we rely on now, opening up many possibilities for novel applications. Still more opportunities arise from combining multiple materials in new ways. However, development of these materials and structures requires increasingly detailed understanding of their electronic states, arising from their atomic-scale structure, which dictate electronic and optical properties, reactivity, and more. Many of the most exciting emerging materials are those that are, in a variety of ways, “on the edge”: materials on the cusp of electronic phase transitions, at the edge of chemical stability, and interfaces between materials where electronic properties can vastly differ from the bulk and there is the greatest potential to engineer electronic landscapes. Just a few examples of these include molecules that form photoactive acceptor-donor interfaces for organic photovoltaic devices, adsorbed metal-organic complexes for energy and catalysis applications, atomically engineered graphene, and interfaces between materials with unusual electronic states such as topological materials and superconductors. In each of these cases, control over the structure and local environment is essential as small perturbations in structure (e.g. defects or structural disorder) can have a dramatic influence on the resulting properties we hope to use.Investigation of these emerging materials requires tools that can connect the local electronic structure to the atomic and molecular structure, especially where defects and interfaces dominate resulting properties. Scanning probe microscopy (SPM) techniques provide both local structural and electronic information on the atomic scale. Using pixel-by-pixel tunnelling spectroscopy and electrostatic force spectroscopy alongside imaging methods that reveal the atomic structure of materials we will correlate local structural information with electronic states at these key surfaces and interfaces to understand how structure drives important properties. To expand the already vast toolbox of SPM techniques, we are developing combined optical-SPM methods, undertaking complementary measurements to investigate the dynamics of electronic states at interfaces, and building new instruments that will bridge to complementary techniques such as angle resolved photoemission and transport measurements. These bridging experiments will provide much-needed connection of the atomic-scale understanding provided by SPM to the resulting macro-scale properties most applications are built upon.