UC San Diego

Metasurfaces are ultrathin, quasi-two-dimensional materials that are engineered to control and manipulate the flow of light, producing properties unattainable with naturally occurring materials. Metasurfaces designed to operate within the visible spectrum are of particular interest for advanced nanoscale light sources and chemical sensing. One promising approach to building optical metasurfaces utilizes plasmonic nanoantenna to funnel freely-propagating visible and near-infrared radiation from the far-field into confined nanoscale volumes using metallic antenna. Localized surface plasmon resonances (LSPR) supported by metallic nanoantenna strongly enhance the incident optical field, providing enhanced far-field coupling as well as enhancement of nonlinear optical processes. However, features significantly smaller than the wavelength of light are required and control over nanoscale morphology can be to achieve. In this thesis, I use bottom-up assembly methods to fabricate colloidal nanocrystal metasurfaces and experimentally demonstrate their capability as a tunable, ultrathin platform for controlling highly enhanced optical fields at the nanoscale. Shaped plasmonic nanocrystals are arranged using bottom-up self-assembly methods to produce metasurfaces operational throughout the visible and near-infrared spectrum. These metasurfaces exhibit extreme in-plane electromagnetic coupling that is strongly dependent on nanocrystal size, shape and spacing, displaying near-ideal electromagnetic absorbance tunable between 500–3,000 nanometers. I investigate their ability to mediate and enhance nonlinear optical processes such as second harmonic generation (SHG) and Raman scattering. By utilizing the double-resonance of metal thin-film coupled nanoantenna, we demonstrate colloidal metasurfaces as efficient sources for nonlinear light generation, achieving SHG enhancement of 104, with efficiencies of 5x10-10. Finally, I investigate colloidal metasurfaces for ultra-sensitive detection and hyperspectral chemical mapping, with uniform and predictable Raman enhancement factors of 106–107.