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Single Particle Surface-enhanced Pump-Probe Raman Spectroscopy for the Direct Observation of Plasmon-Driven Chemistry

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Individual plasmonic nanoparticles have the potential to revolutionize all areas of energy science, catalysis, organic electronics, and solar technology. Owing to their light trapping and focusing ability, single nanoparticles can be utilized to efficiently drive chemical reactions at the sub-nanometer scale. Much of the fundamental science regarding how plasmons can be harnessed to efficiently drive chemical dynamics remains not yet fully understood. In this dissertation, we present the first direct detection of fundamental product (i.e. the radical anion) from a plasmon-driven electron transfer reaction. The radical anion is created through intense illumination of the nanoparticle surface with visible light, causing electrons to transfer to a nearby adsorbate molecule. The ionized species, or radical anion, is then directly detected using a form of vibrational spectroscopy known as surface-enhanced Raman spectroscopy (SERS). We demonstrate the plasmon-driven electron transfer effect across various molecular polypyridine complexes as well as provide a detailed description of the experimental energetics required to photo-initiate this reaction. In addition, we carefully correlate chemical information with nanoparticle structure, optical, and electronic information using localized surface plasmon resonance (LSPR) scattering, spectrally-resolved polarization dependent SERS, and high-resolution transmission electron microscopy (HRTEM) on the same nanoscale entity. The applications of this work are broad and far-reaching, with impact in the research areas of energy generation and storage, CO2 reduction, catalytic nanoreactors, and photovoltaic design.

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  • 11/25/2019
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