Top-down and Bottom-up Integration of Engineered Nanostructures for Metamaterials
Open Access
- Author:
- Lin, Lan
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 10, 2015
- Committee Members:
- Theresa Stellwag Mayer, Dissertation Advisor/Co-Advisor
Theresa Stellwag Mayer, Committee Chair/Co-Chair
Douglas Henry Werner, Committee Member
Zhiwen Liu, Committee Member
Lasse Jensen, Committee Member - Keywords:
- Metamaterials
top-down
bottom-up - Abstract:
- The emergence of metamaterials has expanded the understanding of materials and their associated functionalities beyond the scope of naturally occurring substances. By properly engineering the electric and magnetic resonances of meta-atoms, which have a length scale smaller than the incident wavelength, novel artificial materials can be constructed. This research investigates novel optical metamaterials that are designed and fabricated with optimized subwavelength nanostructures and properly chosen constituent materials to meet user-specified criteria. Both top-down and bottom-up integration techniques were developed to explore the palette of materials and nanostructures that can be accessed. First, precisely defined subwavelength nanostructures fabricated using conventional top-down techniques were exploited to synthesize a metamaterial absorber, metamaterial waveplates, and a dielectric magnetic mirror. A single-layer metal nanostructure array that had been optimized by genetic algorithm was demonstrated to achieve near-ideal absorptivity from 1.77 μm to 4.86 μm and over incidence angles up to 45. The performance of the fabricated absorber was verified using Fourier transform infrared (FTIR) spectroscopy. A half-wave plate and a quarter-wave plate that exhibit polarization conversion ratios and reflectivity greater than 92% from 640 nm to 1290 nm with incident angles up to 40 were investigated. A Mie resonance-based amorphous silicon nanoresonator array was designed, resulting in a lossless magnetic mirror at 1 m with near unity reflectivity and zero reflection phase. The fabricated waveplates and magnetic mirror were characterized with custom-built measurement setups, and the results show excellent agreement with the design targets. Secondly, an alternative hybrid top-down and bottom-up integrated technique was developed to increase the range of materials and nanostructures beyond those available when using conventional top-down techniques and to synthesize optical metamaterials with reconfigurable structures/functionalities. A directed self-assembly strategy was investigated using an applied electric field to deterministically assemble pre-synthesized nanoparticles into predefined locations and to modulate the patterned structures. Based on this approach, reconfigurable two-dimensional ordered gold nanowire lattices with AC frequency-dependent lattice spacing were demonstrated. Electric field simulations and electric force calculations were performed to understand the formation of the lattices. Finally, a simplified electrical equivalent resistor and capacitor (RC) model was developed to explain the observed frequency dependent periodicity change.