UNT Theses and Dissertations - 6 Matching Results

Search Results

Core-Shell Based Metamaterials: Fabrication Protocol and Optical Properties

Description: The objective of this study is to examine core-shell type plasmonic metamaterials aimed at the development of materials with unique electromagnetic properties. The building blocks of metamaterials under study consist of gold as a metal component, and silica and precipitated calcium carbonate (PCC) as the dielectric media. The results of this study demonstrate important applications of the core-shells including scattering suppression, airborne obscurants made of fractal gold shells, photomodification of the fractal structure providing windows of transparency, and plasmonics core-shell with a gain shell as an active device. Plasmonic resonances of the metallic shells depend on their nanostructure and geometry of the core, which can be optimized for the broadband extinction. Significant extinction from the visible to mid-infrared makes fractal shells very attractive as bandpass filters and aerosolized obscurants. In contrast to the planar fractal films, where the absorption and reflection equally contribute to the extinction, the shells' extinction is caused mainly by the absorption. This work shows that the Mie scattering resonance of a silica core with 780 nm diameter at 560 nm is suppressed by 75% and only partially substituted by the absorption in the shell so that the total transmission is noticeably increased. Effective medium theory supports our experiments and indicates that light goes mostly through the epsilon-near-zero shell with approximately wavelength independent absorption rate. Broadband extinction in fractal shells allows as well for a laser photoburning of holes in the extinction spectra and consequently windows of transparency in a controlled manner. Au fractal nanostructures grown on PCC flakes provide the highest mass normalized extinction, up to 3 m^2/g, which has been demonstrated in the broad spectral range. In the nanoplasmonic field active devices consist of a Au nanoparticle that acts as a cavity and the dye molecules attached to it via thin silica shell as the ...
Date: December 2017
Creator: De Silva, Vashista C
Partner: UNT Libraries

Design, Construction, and Application of an Electrostatic Quadrupole Doublet for Heavy Ion Nuclear Microprobe Research

Description: A nuclear microprobe, typically consisting of 2 - 4 quadrupole magnetic lenses and apertures serving as objective and a collimating divergence slits, focuses MeV ions to approximately 1 x 1 μm for modification and analysis of materials. Although far less utilized, electrostatic quadrupole fields similarly afford strong focusing of ions and have the added benefit of doing so independent of ion mass. Instead, electrostatic quadrupole focusing exhibits energy dependence on focusing ions. A heavy ion microprobe could extend the spatial resolution of conventional microprobe techniques to masses untenable by quadrupole magnetic fields. An electrostatic quadrupole doublet focusing system has been designed and constructed using several non-conventional methods and materials for a wide range of microprobe applications. The system was modeled using the software package "Propagate Rays and Aberrations by Matrices" which quantifies system specific parameters such as demagnification and intrinsic aberrations. Direct experimental verification was obtained for several of the parameters associated with the system. Details of the project and with specific applications of the system are presented.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: December 2017
Creator: Manuel, Jack Elliot
Partner: UNT Libraries

Dynamic Screening via Intense Laser Radiation and Its Effects on Bulk and Surface Plasma Dispersion Relations

Description: Recent experimentation with excitation of surface plasmons on a gold film in the Kretschmann configuration have shown what appears to be a superconductive effect. Researchers claimed to see the existence of electron pairing during scattering as well as magnetic field repulsion while twisting the polarization of the laser. In an attempt to explain this, they pointed to a combination of electron-electron scattering in external fields as well as dynamic screening via intense laser radiation. This paper expands upon the latter, taking a look at the properties of a dynamic polarization function, its effects on bulk and surface plasmon dispersion relations, and its various consequences.
Date: August 2017
Creator: Lanier, Steven t
Partner: UNT Libraries

Fabrication of Photonic Crystal Templates through Holographic Lithography and Study of their Optical and Plasmonic Properties in Aluminium Doped Zinc Oxide

Description: This dissertation focuses on two aspects of integrating near-infrared plasmonics with electronics with the intent of developing the platform for future photonics. The first aspect focuses on fabrication by introducing and developing a simple, single reflective optical element capable of high–throughput, large scale fabrication of micro- and nano-sized structure templates using holographic lithography. This reflective optical element is then utilized to show proof of concept in fabricating three dimensional structures in negative photoresists as well as tuning subwavelength features in two dimensional compound lattices for the fabrication of dimer and trimer antenna templates. The second aspect focuses on the study of aluminum zinc oxide (AZO), which belongs to recently popularized material class of transparent conducting oxides, capable of tunable plasmonic capabilities in the near-IR regime. Holographic lithography is used to pattern an AZO film with a square lattice array that are shown to form standing wave resonances at the interface of the AZO and the substrate. To demonstrate device level integration the final experiment utilizes AZO patterned gratings and measures the variation of diffraction efficiency as a negative bias is applied to change the AZO optical properties. Additionally efforts to understand the behavior of these structures through optical measurements is complemented with finite difference time domain simulations.
Date: August 2017
Creator: George, David Ray
Partner: UNT Libraries

Interacting complex systems: theory and application to real-world situations

Description: The interest in complex systems has increased exponentially during the past years because it was found helpful in addressing many of today's challenges. The study of the brain, biology, earthquakes, markets and social sciences are only a few examples of the fields that have benefited from the investigation of complex systems. Internet, the increased mobility of people and the raising energy demand are among the factors that brought in contact complex systems that were isolated till a few years ago. A theory for the interaction between complex systems is becoming more and more urgent to help mankind in this transition. The present work builds upon the most recent results in this field by solving a theoretical problem that prevented previous work to be applied to important complex systems, like the brain. It also shows preliminary laboratory results of perturbation of in vitro neural networks that were done to test the theory. Finally, it gives a preview of the studies that are being done to create a theory that is even closer to the interaction between real complex systems.
Date: August 2017
Creator: Piccinini, Nicola
Partner: UNT Libraries

Nonlinear Light Generation from Optical Cavities and Antennae

Description: Semiconductor based micro- and nano-structures grown in a systematic and controlled way using selective area growth are emerging as a promising route toward devices for integrated optical circuitry in optoelectronics and photonics field. This dissertation focuses on the experimental investigation of the nonlinear optical effects in selectively grown gallium nitride micro-pyramids that act as optical cavities, zinc oxide submicron rods and indium gallium nitride multiple quantum well core shell submicron tubes on the apex of GaN micro pyramids that act as optical antennae. Localized spatial excitation of these low dimensional semiconductor structures was optimized for nonlinear optical light (NLO) generation due to second harmonic generation (SHG) and multi-photon luminescence (MPL). The evolution of both processes are mapped along the symmetric axis of the individual structures for multiple fundamental input frequencies of light. Effects such as cavity formation of generated light, electron-hole plasma generation and coherent emission are observed. The efficiency and tunability of the frequency conversion that can be achieved in the individual structures of various geometries are estimated. By controlling the local excitation cross-section within the structures along with modulation of optical excitation intensity, the nonlinear optical process generated in these structures can be manipulated to generate coherent light in the UV-Blue region via SHG process or green emission via MPL process. The results show that these unique structures hold the potential to convert red input pulsed light into blue output pulsed light which is highly directional.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: May 2017
Creator: Butler, Sween J
Partner: UNT Libraries