Focused Ion Beam (FIB) technology is a versatile tool that can be applied in many fields to great effect, including semiconductor device prototyping, Transmission Electron Microscopy (TEM) sample preparation, and nanoscale tomography. Developments in FIB technology, including the availability of alternative ion sources and improvements in automation capacity, make FIB an increasingly attractive option for many tasks. In this thesis, FIB systems are applied to photonic device fabrication and modification, semiconductor reverse engineering, and the production of structures for the study of nanoscale radiative heat transfer. Optical facets on silicon nitride waveguides were produced with plasma FIB (PFIB) and showed an improvement of 3 ± 0.9 dB over reactive ion etched (RIE) facets. This process was then automated and is capable of producing a facet every 30 seconds with minimal oversight. PFIB was then employed to develop a method for achieving local backside circuit access for circuit editing, creating local trenches with flat bases of 200 x 200 μm. Gas assisted etching using xenon difluoride was then used in order to accelerate the etch process. Finally, several varieties of nanogap structure were fabricated on devices capable of sustaining temperature gradients, achieving a minimum gap size with PFIB of 60 nm. / Thesis / Master of Applied Science (MASc)

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The flavor changing neutral current process b → dγ is a sensitive probe to the Standard Model of elementary particle physics. Using a sample of 386 × 10⁶ B meson pairs accumulated by the Belle detector at the KEKB e⁺e⁻ collider, we measure the branching fractions for the exclusive modes B⁻ → ρ⁻γ, B̅⁰ → ρ⁰γ and B̅⁰ → ωγ as follows: B(B⁻ → ρ⁻γ) = 0.55 _−0.36^+0.42_−0.08^+0.09 B(B̅⁰ → ρ⁰γ) = 1.25 _−0.33^+0.37_−0.06^+0.07 B(B̅⁰ → ωγ) = 0.56 _−0.27^+0.34_−0.10^+0.05 where the first error on each value is statistical and the second is systematic. Assuming that these three modes are related by isospin conservation rules, we find the combined branching fraction B(B̅ → (ρ,ω)γ) = 1.32 _−0.31^+0.34_−0.09^0.10. This result is used to determine the ratio of CKM matrix elements, |V_td/V_ts| = 0.199 _−0.025^+0.026_−0.015^0.018. / Ph. D.

An alternative approach to the problem of CP-violation is presented. It is based on the possibility of spontaneous CP-breakdown in models with two Higgs doublets. General features of the phenomenon such as stability of the vacuum and the existence of a light axion are discussed. We investigate the feasibility of spontaneously broken CP in the minimal supersymmetric models - the MSSM and NMSSM. The latter is shown to be experimentally viable. The phenomenological implications of the model such as CP-violating effects in the kaon systems and a nonzero neutron electric dipole moment are studied. / Ph. D.

This thesis contains an account of a measurement of the neutron energy spectrum from radiative pion capture in carbon, oxygen and calcium. The measurement was performed at six n-γ correlation angles for the case of carbon and oxygen, and seven n-γ correlation angles for the case of calcium. The observed energy spectra fall off approximately exponentially between 2 and 30 MeV. Evidence of resonance structure was observed at about 4 MeV in the energy spectra of carbon and oxygen. This is in agreement with a theoretical prediction of the giant multipole excitation model. The neutron yield versus n-γ correlation angles peaks at 180° for all three nuclei studied. This indicates the quasi-free mechanism also plays an important role in the radiative pion capture process. / Ph. D.

Humans have extensively altered terrestrial surfaces through land-use and land-cover change. This change has resulted in increased food, fiber, fuel, and wood that is provisioned by ecosystems to support the human population. Unfortunately, the change has also altered climate through carbon emissions and changes in the surface energy balance. Consequently, maximizing both the provisioning and climate regulation services provided by terrestrial ecosystems is a grand challenge facing a growing global population living in a changing climate. The planting of pine forests for timber and carbon storage and switchgrass fields for bioenergy are two land-cover types that can potentially be used for climate mitigation. Importantly, both are highly productive systems representing contrasts in albedo (grass are brighter than pines) and vegetation height (pines are taller than the grass) along with unknown differences in carbon and water balance that influence local to global climate. Here I use eddy-covariance data to investigate how a transition from a perennial bioenergy crop (switchgrass) to a planted pine plantation alters the local surface temperature, global carbon dioxide concentrations, and global energy balance. First, I found that switchgrass and pine ecosystems have very similar local surface temperatures, especially during the grass growing season. After the switchgrass is harvested, surface temperature in the pine forest is much lower than switchgrass because no vegetation is present to facilitate the evaporation of water. The surface temperature in a bare-ground system (a recent clear-cut) was also high relative to the pine and pre-harvest switchgrass ecosystems. This illustrates the importance of maintaining vegetation cover to reduce local surface temperature. Second, I found that the 30-year mean change in global energy balance (i.e., radiative forcing) from planting a pine ecosystem rather than a switchgrass field was positive (pine warms climate) when considering changes in albedo and carbon measured using eddy-covariance systems. When including harvested carbon, pine and switchgrass can have similar global radiative forcing if all harvested pine carbon is stored, but harvested switchgrass carbon is burned. However, no scenarios I explored resulted in a strong negative radiative forcing by the pine ecosystem relative to the switchgrass field. These results show that afforestation or reforestation in the eastern United States may not result in any climate benefit over planting a switchgrass field. However, the presence of vegetation in both ecosystem types offers a clear benefit by cooling local surface temperatures. / Doctor of Philosophy / Humans are changing the Earth's climate by using oil and gas as fuel that emits greenhouse gases, mainly carbon dioxide, into the atmosphere. Planting trees to reestablish forests is a natural solution for climate change because forests absorb carbon dioxide from the air, but reforestation also changes the Earth's climate in other ways. For example, forests are generally darker than crops and grasses and absorb more sunlight, which traps energy in the atmosphere that can warm global temperature. These non-carbon effects can potentially offset the climate benefit from absorbed carbon dioxide. An alternative natural climate solution is to replace oil and gas with fuels derived from plants, known as bioenergy. Here I compared the local and global climate influence of a tree plantation (loblolly pine) to a bioenergy crop (switchgrass). I found that the local temperature of pine and switchgrass were similar in the summer when the grass was growing, and both were cooler than bare-ground, which was unable to evaporate and transpire water to the atmosphere. Over 30 years, I found that pine and switchgrass absorb similar amounts of carbon. The pine forest absorbs more carbon than switchgrass when it is fully grown but releases carbon during the first five years of growth. As a switchgrass field is brighter than a pine forest, planting a pine forest instead of a switchgrass field warms the Earth's climate. However, assuming no carbon from the harvested trees is released to the atmosphere, the pine and switchgrass have the same influence on global climate. My findings show that a pine plantation and a bioenergy crop can have similar climate benefits when carbon is stored in forests.

The fundamental definitions of radiative transfer theory are given and the two-dimensional equation of transfer is derived, density of radiation is defined, and two-dimensional two-intensity transfer model is presented. An operational interpretation of the latter model is given interms of military truck transport supply and the functional dependencies of the terms in the transfer equations are evaluated. For this interpretation the density equations are given and the study state and time dependent solutions of the density equations are discussed in polar coordinates. This work was conducted for the U. S. Army Transportation Research Command, Fort Eustis, Virginia, 1961, Task 9R38-11-009-02. / Master of Science

Computational thermo-fluid models of a free surface flow under the dominant radiative transfer have been developed for the design and control of a modern optic fiber drawing process. Although modeling of the fiber drawing process has been of interest for the past three decades, most of the previous studies were limited to low draw speeds and small preforms. Large preforms drawn at high speeds have been used in modern fiber drawing systems to improve production efficiency and reduce cost. Several assumptions commonly made in previous studies have to be relaxed to address the new challenges. In this study, instead of using the Rosseland approximation, the radiative transfer equation (RTE) was solved directly for the radiation fluxes using the finite volume method (FVM). The complete two-dimensional free surface flow was simulated along with the coupling of the radiative transfer. Unlike most of the previous studies that only considered the furnace domain and that assumed the glass velocity at the exit, we included the post-chamber in the computation domain and predicted the fiber solidification location. Furthermore, the mixed convection of the air in the post-chamber was also considered, and was shown to have significant effects on the fiber solidification. On the basis of the computational model, a reduced order model (ROM) was developed for a mixed HŁ /LQG controller designed to regulate the fiber diameter under the effects of disturbances. The ROM was derived on the basis of the computational model. Optimal numerical eigenfunctions were obtained through the Karhunen-Loeve expansion using the computational model. The GalerkinŁ s method was then applied to obtain the state space ROM. The numerical model was shown to be efficient and was verified experimentally. The ROM characterizes the dynamics of the system accurately as compared with the computational model. The simulations using the full computational model showed that the closed-loop system is robust and superior to the open-loop system in the regulation of fiber diameter. The modeling and control methods can be applied to the design optimization and parameter regulation of the high-speed large-preform draw processes as well as other manufacturing processes that involve similar thermal-fluid transports.

This dissertation describes a theoretical and experimental study on coherent thermal emission from thin-film multilayer structures. A novel multilayer structure consisting of a one-dimensional photonic crystal and a polar material (or a metal) is proposed as a coherent thermal-emission source. Surface electromagnetic waves can be excited at the edge of photonic crystal, enabling coherent emission characteristics (i.e., spectral- and directional-selectivity in the emissivity). A near-infrared coherent emission source is designed and fabricated using vacuum deposition and chemical vapor deposition techniques. Measurements were performed using a Fourier-transform infrared spectrometer and a laser scatterometer. The agreement between the resonance conditions obtained from experiments and the calculated dispersion relation confirms that surface waves at the photonic crystal-metal interface can be utilized to build coherent thermal-emission sources. The second part of this dissertation focuses on the energy propagation direction in near-field thermal radiation. The energy streamline method based on the Poynting vector is applied to near-field thermal radiation by incorporating the fluctuational electrodynamics, in which thermal emission is viewed as originated from random motion of electric dipoles at temperatures above absolute zero. It is shown that the Poynting vector is decoupled for each parallel wavevector component due to the randomness of thermal emission. The spectral radiative energy travels in infinite directions along curved lines; this is a fundamental characteristic of near-field thermal radiation. The findings in this dissertation are important for the design of near-field optical sensors and energy conversion devices.

abstract: Recently, nanostructured metamaterials have attracted lots of attentions due to its tunable artificial properties. In particular, nanowire/nanohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire/nanohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field. This PhD dissertation aims to obtain a deep fundamental understanding of nanowire/nanohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire/nanohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017