engineering optical materials with metal nanostructures

Open Access
Author:
Liu, Liu
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 19, 2016
Committee Members:
  • Theresa Stellwag Mayer, Dissertation Advisor
  • Zhiwen Liu, Committee Member
  • Thomas E Mallouk, Committee Member
  • Douglas Henry Werner, Committee Member
  • Theresa Stellwag Mayer, Committee Chair
Keywords:
  • surface-plasmon-polariton waves
  • solar energy
  • reconfigurable metamaterials
  • vanadium dioxide
Abstract:
Thanks to the development in nanotechnology, artificially engineered nanostructures have been exploited to manipulate the behavior of light. These nanostructures have critical dimensions on the same order of or smaller than the wavelength of interest and have unique properties other than naturally occurring materials. This research investigates novel approaches of applying metallic nanostructures for advanced optical materials. Both plasmonic quasiparticles and optical metamaterials were utilized to achieve exotic properties and exciting functionalities. The structures used in this research were carefully designed and fabricated and the physics for the observed optical response of the experimental devices were thoroughly discussed. First, a one-dimensional photonic crystal (1D PC) was coated on top of a two-dimensional metal grating to facilitate excitation of multiple surface-plasmon-polariton (SPP) waves and waveguide modes. The structures were found to be able to couple light into the guided-wave modes over a broad wavelength range in the visible spectrum regime over a broad incidence direction for both ¬s- and ¬p-polarization states. The individual excitations of the guided-wave modes were also theoretically predicted using the Floquet theory, surface-multiplasmonics theory, and the transfer-matrix approach with results well-matched to the experimental trends of the measured absorbance of the PC-metal structure. Second, the ability of the PC-metal structure to collect light efficiently and transport it over macroscopic distance were applied to realize a planar solar concentrator. The plasmonic concentrator was built as arrays of 1D PC coated 1D silver gratings, and micro-solar cells were attached to them to test their performance. The solar cells attached to the plasmonic concentrators had efficiencies three times higher than those not attached, validating the effectiveness of the plasmonic concentrators. In addition, the fabricated plasmonic concentrators showed optical transfer efficiency as high as 24% over the wavelength range of 450nm to 800nm and a concentration factor around 2X. Although these performance numbers were modest comparing to the state-of-art solar harvesting devices, the results open up new engineering opportunities to exploit the well-developed plasmonics theory for broadband, high-efficiency solar concentration devices. Moreover, the performance of the plasmonic concentrators was found to be insensitive to the angle of incidence of light, which makes them potentially applicable to stationary tracker-free roof-top solar harvesting devices. Finally, a self-sufficient reconfigurable hybrid optical metamaterial integrated with vanadium dioxide was demonstrated. The reflection spectrum of the hybrid metamaterial can be tuned electrically and the modulation contrast at the resonance frequencies can be as large as ~7500% and 500% at 3.05 and 3.85μm, respectively. Advanced functional meta-devices were demonstrated based on the drastic change in the optical response of the hybrid metamaterial. An electro-optical modulator was first demonstrated, with on-resonance reflectance controlled by sub-second electrical pulse-train input. The device was also shown to function as an electrically erasable and programmable read-only memory (EEPROM) with “0” and “1” reflectance contrast of ~10%. Finally, more sophisticated spatial modulation schemes of IR signals were demonstrated with this platform for IR display and surface emissivity control applications.