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Strong Coupling of Gold Nanoparticle Plasmons on Quasi One-Dimensional AssembliesSlaughter, Liane 16 September 2013 (has links)
Single particle microscopy and spectroscopy strategies reveal hidden relationships between the surface plasmon resonances (SPRs) and the sizes, shapes, and arrangements of gold nanoparticles (Au NPs). The SPR, the coherent oscillation of the conduction electrons, leads to intense absorption and scattering of light at frequencies satisfying the resonance condition determined by the size, shape, and spacings between NPs. Growing and assembling NPs through wet chemistry yields a diversity of geometries. Together, optical spectroscopy, scanning electron microscopy (SEM), and computational modeling of individual NPs and NP assemblies elucidate the resulting variety of SPRs. Strong coupling of the SPRs in linear assemblies provokes particular interest for tunable structures that will benefit surface enhanced spectroscopies and optical computing. The influence of the constituents and imperfections in such assemblies, which deviate from idealized model systems, must be established one assembly at a time.
This thesis demonstrates previously unknown and sensitive relationships between the SPRs and these geometric parameters through systematic single particle experiments of self-assembled ring superstructures, nanorod dimers, individual nanorods populating different size regimes, and short linear chains of Au NPs through single particle spectroscopy. Dark-field scattering of self-assembled ring superstructures of 40 nm Au NPs reveals new plasmon modes that are redshifted from the single NP SPR by hundreds of nanometers, highly polarized along the axis of alignment, and indifferent to irregularities in the NP arrangement. SPRs of Au nanorod dimers, however, are dramatically altered by NP size heterogeneity, reduced symmetry, and metallic contact, consistent with previous studies of small assemblies. Broad band single particle extinction measurements of individual Au nanorods and short chains of 200-1000 nm long demonstrate the importance of the overall dimensions of an NP or an assembly of NPs. Finally, extinction measurements of these chains provide a compelling comparison to chemical polymers via the redshifting of the lowest energy SPR, tolerance to disorder, and the influence of the repeat unit. This result extends already well-defined analogies between plasmonic assemblies and chemical molecules to the ‘plasmonic polymer’. The findings presented in this thesis bring deeper and more detailed understanding to the tunable optical properties of real NP assemblies.
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Directed Self-Assembly of Gold Nanorods Using Surface ModificationWalker, David A 10 July 2008 (has links)
Metallic nanoparticles are unique materials for optical, electronic, catalytic, and sensing applications. Due to the vast flexibility in controlling the surface chemistry of these particles through functionalization there is a great deal of interest in using metallic nanoparticles as building blocks in the development of more complex nanostructures through the use of a 'bottom-up' approach. Using self assembly techniques, one can exploit spontaneous chemical interactions to build complex constructs on the nanometer scale.
Towards this end, gold nanorods have been synthesized and modified with various polymers, inorganic oxides and organic ligands to establish principles for self-assembly of these unique nanomaterials. Gold nanorods are of great interest due to their strong optical absorption in the visible and near infrared regions, which can be tuned through material preparation and modification of the surrounding environment. This thesis focuses on investigating approaches for both irreversible and reversible self-assembly of gold nanorods. Techniques such as dynamic light scattering (DLS), ultraviolet-visible (UV) spectroscopy, transmission electron microscopy (TEM), and polarization modulation infrared reflection absorbance spectroscopy (PM-IRRAS) were used to characterize the colloidal particles and gold surfaces. A novel contribution of this work is the successful demonstration of end-to-end linking of gold nanorods in a rapid and reversible manner using a pH responsive polypeptide.
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