Plasmonically enhanced molecular junctions for investigation of atomic-scale fluctuations in self-assembled monolayers

Molecular junctions represent a fascinating frontier in the realm of nanotechnology and are one of thesmallest optoelectronic devices possible, consisting of individual molecules or a group of moleculesthat serve as the active element sandwiched between conducting electrodes. As devices approachthe molecular scale, quantum mechanical effects become dominant, leading to a host of novelproperties that do not exist in larger-scale devices. This thesis delves into electrically integrated andplasmonically enhanced molecular junctions, which are instrumental in understanding interactionsat the metal-molecule interfaces. These junctions combine the optical capabilities of high fieldconfinement (and enhancement) and high radiative efficiency, with the electrical capabilities ofmolecular transport. They can probe the electronic structure and dynamics of the molecules withinthe junction, offering a view of the electronic transitions, molecular vibrations, conformationalchanges in the molecules, charge transfer, and quantum transport properties. Their potential inpioneering nanoscale optoelectronic applications, such as ultrafast electronics and nanosensing, issignificant. However, the complexity involved in creating scalable and robust molecular junctions atambient operating conditions poses a substantial challenge. In this thesis, we present the utilizationof a self-assembled molecular junction equipped with a nanoparticle bridge to explore the correlatedfluctuations in conductance and the light emission induced by inelastic electron tunneling at roomtemperature. Unlike large-area SAM junctions, both the electrical conductance and light emission areremarkably sensitive to atomic-scale fluctuations, even though hundreds of molecules are present inthe junction. This phenomenon mirrors the behavior observed in picocavities in Raman scatteringand the luminescence blinking seen in photo-excited plasmonic junctions. Moving localization ofthese point-like emitters (identified as the movement of gold atoms at the surface) is observed in thelight emission spectra and is supported by the conductance data. The research conducted for thisthesis demonstrates a scalable molecular junction platform that facilitates both optical and electricalinterrogation at the atomic level.