Fundamentals and Applications of Surface-Enhanced Coherent Raman Scattering

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Plasmonic chemistry is an emerging field of research that contains great promise for new chemical reactivity, but thus far has been improperly observed. The goals of using plasmonic chemistry typically revolve around the use of nonequilibrium charge carriers that migrate to the surface of a plasmonic substrate to perform redox chemistry on surface adjacent molecular species. The process of plasmonic chemistry encompasses many different time scales from the first few tens of femtoseconds into the nanoseconds for full system relaxation - however, most claims of plasmonic chemistry report steady-state spectroscopic observations. To this end, the work contained in this thesis details the development of a new suite of tools to study plasmonic chemistry on time scales closer to the intrinsic lifetimes of the transient species being studied. This thesis discusses the expansion of surface-enhanced femtosecond stimulated Raman scattering (SE-FSRS), one form of plasmonically-enhanced coherent Raman scattering (PECRS) techniques that are ideally suited for observing the molecule-plasmon interactions involved in chemical change driven or enhanced by plasmonic nanomaterials. Development of new theories for SE-FSRS, experimental progress in improving SE-FSRS spectrometers, as well as new experiments showing stimulated Raman loss in SE-FSRS will be discussed. An important aspect of this work is the back-and-forth theory-experiment approach that has allowed for continued improvement in the SE-FSRS technique. The classical theory of SE-FSRS explained initial results well, but pushing the experimental techniques further resulted in the need for a new quantum mechanical theory of SE-FSRS. Further developing SE-FSRS experimentally and theoretically will allow for an improved analytical technique that can probe coupled molecule-plasmon interactions, potentially leading to a PECRS spectroscopy that can be used for initiating and tracking plasmonic chemistry.

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  • 10/21/2018
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