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Time-Resolved Interactions of Infrared Vibrations and Plasmonic Nanogaps https://doi.org/10.17863/CAM.126633 Bell, Fiona Baumberg, Jeremy The precise control of vibrational energy transfer at the molecular scale is crucial within the development of new platforms for quantum optics, optoelectronics, energy harvesting, and nanochemical reactions. Whilst the plasmonic enhancement offered by metal nanostructures can dramatically enhance these processes, the effects of metal-molecule coupling remain poorly understood due to significant challenges in probing the dynamics of nanoscale systems. In this Thesis, I present a comprehensive study of vibrational dynamics within plasmonic near-fields across a wide range of timescales, capturing ultrafast vibrational decay and microsecond thermal dissipation within nanoscale metal-molecule junctions. Novel spectroscopy approaches are developed which combine resonant mid-infrared (MIR) vibrational absorption with Raman scattering detection—employing precisely tailored plasmonic nanocavities to confine and enhance both wavelengths within the same nanoscale volume. Using a custom-built ultrafast microscope setup, sum-frequency generation from individual plasmonic nanocavities uniquely probes the coherent dynamics of collective vibrational modes. These measurements reveal how intermolecular coupling extends vibrational lifetimes by > 200% and protects molecules from local plasmonic induced dephasing effects. Complementary studies of thermal transport employ MIR heating to characterise thermal dissipation in metal-molecule junctions. The compatibility of plasmonic nanostructures with a wide variety of analytes allows the effects of molecular length and bond strength to be studied, revealing the emergence of an additional intermolecular channel for thermal transport within the highly confined system. These findings provide fundamental insights into vibrational dynamics within metal-molecule coupled nanostructures, opening up new possibilities in the control of nanoscale energy transfer and light-matter interactions. University of Cambridge 2025-05-31 Thesis Doctoral Doctor of Philosophy (PhD) eng https://www.repository.cam.ac.uk/handle/1810/397514 https://www.repository.cam.ac.uk/bitstreams/f1ec1f71-65b5-4687-aa3b-64d5f650d5b1/download d89c077014ac21192511262dd6550d8c https://www.repository.cam.ac.uk/bitstreams/dd7685fc-e371-42e3-bd5d-dc47d435373a/download 87eda9de84448d1f82354d60eee3eb5f http://purl.org/NET/rdflicense/allrightsreserved Plasmonics mid-infrared time-resolved vibrational spectroscopy