Plasmonic Nanoshells: Synthesis, Functionalization, and Photonic Applications

The work presented in this dissertation focuses on the functionalization and application of hollow gold-silver nanoshells (GS-NSs). GS-NSs were chosen for this research because of their unique surface plasmon resonance properties, allowing for these nanostructures to be designed to absorb light at wavelengths from the visible to the near-infrared. Initial studies utilizing these nanoshell cores included coating the particles with porous silica, a protective layer that reduces aggregation but does not prevent access to the core by ions in solution. In addition, the silica coating afforded these nanostructures stability under a wide range of pH conditions. To demonstrate the utility of these composite particles, we employed silica-coated GS-NSs for plasmonically enhanced photocatalytic solar-to-fuel energy conversion and found that they increased hydrogen production up to 2.6 times as compared to an unmodified photocatalyst. This research has provided us a template for further investigations using alternative core-shell structures, with an example being the synthesis of unique tin oxide-coated gold-silver nanorattle particles. Nanorattle structures offer the potential for boosting hydrogen production due to the strong localization of the plasmonic enhancement between the metal and metal oxide interfaces. In separate studies, we synthesized hollow GS-NSs coated with doped tin-oxide shells for incorporation into a larger solar energy collection and conversion system with the goal of extending the active wavelength further into the visible and the mid-infrared range. These modifications are expected to enhance the coverage of the solar spectrum and optimize the dielectric environment around the metal oxide to improve the activity of the photocatalyst in the composite material. The targeted nanoparticles reported herein were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and UV-visible (UV-vis) spectroscopy. Nevertheless, since GS-NSs not only absorb/scatter light but also produce heat as the energy from the absorbed light dissipates, they have shown potential for photothermal drug-delivery applications. Therefore, we developed thiol adsorbates that contain a thermally-reversible Diels-Alder attached moiety and formed self-assembled monolayer on flat gold surfaces for analysis. Furthermore, we studied the thermally-activated release from these thin films as characterized by X-ray photoelectron spectroscopy (XPS) and ellipsometry.