Molecular Optoelectronics in Plasmonic Nanocavities

Abstract

Creating functional optoelectronic devices using individual or ensembles of molecules is currently an active research area, driven by the ever-increasing demand for miniaturisation of electronic devices and the exploration of light-matter interactions at the molecular level. This thesis investigates the integration of molecules with plasmonic nanostructures to develop novel optoelectronic devices and gain deeper insights into nanoscale phenomena. The research focuses on two primary nanostructures: the nanoparticle-on-mirror (NPoM) geometry and monolayer aggregate (MLagg) films. These platforms enable the precise control of plasmonic fields at the nanoscale, facilitating the study of molecular behaviour under extreme confinement conditions. The thesis explores the photochemical restructuring of molecule-metal interfaces, revealing unexpected transformations that challenge conventional assumptions about their stability. The development of NPoM crossbar devices allows for simultaneous electrical and optical measurements of molecular junctions. This innovative approach combines electrical characterisation, photocurrent measurements, and surface-enhanced Raman spectroscopy (SERS) within a single device architecture, providing unprecedented insights into the interplay between molecular structure, charge transport, and light-matter interactions. The optoelectronic properties of MLagg devices are thoroughly investigated, demonstrating their potential as a versatile platform for various applications. Additionally, the integration of diarylethene (DAE) photoswitches into these plasmonic nanostructures is explored, offering new possibilities for light-controlled molecular devices. This research advances our understanding of quantum plasmonic effects, plasmon-induced hot electron generation, and molecular switching behaviours in nanoscale junctions. The findings pave the way for the development of next-generation miniaturised solid-state fast optical molecular switches and sensors, with potential applications ranging from ultrafast information processing to highly sensitive molecular detection systems.