Nanostructuring Plasmonic Materials to Engineer Optical ResponsesPublic Deposited
Plasmonic nanostructures are capable of trapping and confining light at the nanoscale, leading to interesting optical phenomena involving enhanced light-matter interactions. These responses arise in two forms: surface plasmon polaritons propagating on the surface of metal films and localized surface plasmons confined to the surface of metal nanoparticles. Plasmonic modes can couple to free space light with a wavelength dependent on the size and shape of the nanostructuring, the metal material properties, and the surrounding dielectric environment. The properties and applications of these optical responses are discussed in Chapter 1, providing an introduction for plasmonics. In the remainder of this thesis I explore methods to tailor the plasmonic responses by controlling the nanostructuring of plasmonic devices.\ I explore this topic from the fabrication perspective in Chapter 2. I discuss and demonstrate a complete fabrication process using parallel patterning techniques for sequential feature density doubling of periodic silicon gratings. These silicon substrates were used for template stripping to produce plasmonic films with nanostructuring to support surface plasmon polaritons. The optical responses were characterized to illustrate their ultraviolet plasmonic activity and to examine the importance of developing scalable patterning methods that access shorter periodicities for manipulating surface plasmon polariton wavelengths across the UV spectrum. Chapter 3 and 4 describe progress toward tailoring optical cavities for enhancing the photoluminescence intensity of single-walled carbon nanotubes and few-layer black phosphorus, respectively. Both of these nanomaterials possess unique optical properties that show promise for applications in optoelectronics and telecommunications technology but suffer from weak fluorescence efficiency. Lattice plasmon modes were tested as optical cavities for enhancing the emission rate of these two nanomaterials. The lattice plasmon modes were engineered by controlling the geometry of nanoparticle arrays through fabrication methods and by selecting optimal materials for the substrates and superstrates. Chapter 5 investigates low-symmetry nanoparticle arrays as a way to examine the effects of geometry in photonic lasers. I developed a new, scalable fabrication procedure capable of patterning nanoparticle arrays composed of rhombus-shaped nanoparticles arranged in rhombohedral lattices. This low-symmetry platform provided insight regarding how nanoparticle shape can be used to engineer the electromagnetic hot spots of lattice plasmon modes. Examination of lasing behavior revealed that plasmon-exciton energy transfer is polarization dependent, with stronger coupling and faster dynamics observed when the dipolar orientations of plasmonic modes and gain materials are aligned. As a result, two lattice plasmon modes localized to the same nanoscale hot spots were shown to support lasing simultaneously by coupling to different polarizations of excited dye populations.