| Description |
Plasmonic metasurfaces offer a unique capability to manipulate amplitude, phase and/or polarization of incident electromagnetic radiation using engineered surfaces. Here, one could explore this phenomenon with strong light-matter interaction (plasmonics) in conjunction with metamaterial design, where the resonant response is material as well as structure dependent. Moreover, due to the intrinsic properties of these materials being frequency dependent, particular materials need to be selected or designed for operation at different frequencies. In this regard, my work demonstrates devices based on plasmonic metasurface operating at ultraviolet (UV), visible, and terahertz frequencies. At UV frequencies, we developed a wetting system to fabricate Ga/Pt alloys system where liquid gallium was spread over sputtered platinum thin film; the excess gallium on the top was removed using focused ion beam (FIB). Furthermore, by fabricating nanoapertures on the film, using FIB, we experimentally demonstrated extraordinary optical transmission arising due to plasmonic response. The technique allows a uniform thin film of alloyed gallium/platinum that was found to be environmentally stable and showcased excellent UV plasmonic response. For visible spectrum, we designed an image encryption device using a spatial arrangement of nanoresonant antennas wherein the resonators have varied amplitudes of plasmonic absorption. To achieve different levels of modulation, we used a combination iv of weak and strong plasmonic material in form of cosputtered aluminum and titanium films. By fabricating a uniform array of nanoresonant antenna identical dimensions but different composition, we achieved spatial modulation of the intensity of transmitted light at a narrow band wavelength. Thus, our unique device approach allows us to encrypt data or images at optical frequencies. Lastly, at longer wavelengths corresponding to terahertz frequencies, we designed a frequency agile device based on electromechanical actuation of the metamaterial structure. Here, we employed shape-memory alloy wires integrated into a flexible structure injected with liquid metal, where an electrical bias on the wires induces the overall change in structural design, thus imparting the frequency tunable response to the metamaterial. Overall, the dissertation showcases novel materials and techniques towards the design of plasmonic metasurfaces for practical applications. |
