Tunable nanomaterials for infrared plasmonics
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Nanoparticles (NP) with tunable localized plasmon resonances in the infrared are useful for many applications, including molecular spectroscopy, nanoantenna design, energy harvesting, and thermal imaging to name only a few. In this thesis, tunable NP surface plasmon resonances in the infrared are achieved by adjusting either the optical constants of the material or the shape of the NPs. We synthesized indium tin oxide (ITO) nanocrystals and characterized their plasmonic properties. Importantly, we experimentally confirmed the existence of plasmonic coupling effects between ~ 6 nm ITO nanocrystals by evaluating the far-field resonance peaks, and the generated near-field enhancement on the vibrational spectra of surface ligands. In addition, we observed the evolution of standing wave patterns in AgAuAg nanorods (NRs) with lengths from ~70 nm to ~ 760 nm deposited on silicon with near-field scanning optical microscopy. We observed that on the high refractive index substrate under oblique illumination higher order multipolar modes with an even symmetry dominated due to strong interactions between metal and substrate. Moreover, we systematically investigated the near- and far-field optical response of dipole-multipole coupled Au NR dimer structure through numerical simulation. The antibonding modes of Au NR dimers is very similar to multipolar resonances of Au NR monomer of equivalent overall length in terms of far-field plasmon resonance peaks, near-field phase distribution, and far-field angular radiation distributions.
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