Metasurfaces are nanostructured interfaces capable of manipulating the phase, amplitude, or polarization of free-space light. ‘Local’ metasurfaces typically control the wavefront shape of spectrally broadband light to generate devices such as flat lenses, holograms, and beam steerers. In contrast, ‘nonlocal’ metasurfaces, such as photonic crystals, support spatially-extended optical modes that govern the transmission or reflection spectrum. Therefore, local metasurfaces typically offer spatial control over incident light but not spectral control, while nonlocal metasurfaces impose spectral but not spatial control. This thesis explores nonlocal dielectric metasurfaces with simultaneous spatial and spectral control such that they shape the wavefront only for spectrally narrowband resonant modes but act like an unpatterned substrate for non-resonant light. These devices are formulated from a rational design scheme based on symmetry arguments. Chapter 1 reviews the theoretical basis for these devices. Chapters 2 and 3 discuss experimental demonstrations of nonlocal wavefront-shaping metasurfaces in the near-infrared and visible wavelength regions, respectively. Our initial experimental demonstrations in the near-infrared in silicon metasurfaces were the first verification of their theoretical proposal. In the visible, experimental results of metasurfaces made of silicon-rich silicon nitride suggest potential applications in transparent displays, augmented reality headsets, and quantum optics. Significantly, our nonlocal metasurfaces form a versatile platform for multifunctional and multicolor meta-optics that shape the wavefront distinctively at several different resonant wavelengths, which we have experimentally demonstrated in both the near-infrared and the visible. Chapters 4 and 5 discuss conceptualization and experimentally demonstration of thermally-tunable nonlocal wavefront-shaping metasurfaces. Reconfigurable photonic devices such as zoom lenses and dynamic holograms have posed a substantial challenge and captured the interest of the optics community. We leverage the enhanced light-matter interaction in our nonlocal wavefront-shaping metasurfaces to realize tunable wavefront-shaping using conventional dielectric materials and standard nanofabrication procedures. The operating principle of these devices is that tuning the refractive index of the device with the thermo-optic effect can align or detune the resonant wavelength of a mode from the wavelength of a narrowband incident light source, and the wavefront is shaped only when the optical resonance is spectrally aligned with the incident light. Experimentally, we have demonstrated nonlocal metasurfaces based on structured germanium thin films whose functionality can be thermally switched between that of two different lenses. The thesis is concluded with a section on future prospects.

The main purpose of this work is to find a physical and numerical description related to the reaction of the multilayer nano energetic material (nEM) in dense film. Energy density of nEM is much higher than the conventional energetic material; therefore, nEM finds more applications in propulsions, thermal batteries, material synthesis, nano igniters, waste disposals, and power generations. The reaction model of a multilayer nEM in a dense film of aluminum and copper oxide deposits on a composite substrate of silica/silicon is studied and solved in different stages. The two main interests in this study are propagation speed and maximum temperature of the reaction. In order to relate speed of reaction and maximum flame temperature a number of other variables such as heat loss, the product porosity, and the reaction length should be estimated. The main aim of this study is to introduce a numerical model which estimates and relates these values in multilayer nEM in a dense film. The following is a summary of the execution steps to achieve this goal. In Part I of this thesis, flame front speed and the reaction heat loss were the main targets. The time-of-flight technique has been developed to measure the speed of flame front with an accuracy of 0.1 m/s. This measurement technique was used to measure the speed of propagation on multilayer nEM over different substrate material up to 65 m/s. A controllable environment (composite silicon\silica) was created for a multilayer standard thin film of aluminum and copper oxide to control the reaction heat loss through the substrate. A number of experimental results show that as the thickness of silica decreases, the reaction is completely quenched. Reaction is not in self-sustaining mode if the silica thickness is less than 200 nm. It is also observed that by ii increasing silica’s thickness in substrate, the quenching effect is progressively diminished. The speed of reaction seems to be constant at slightly more than 40 m/s for a silica layer with thickness greater than 500 nm. This would be the maximum heat penetration depth within the silica substrate, so the flame length was calculated based on the measured speed. In Part II, a numerical analysis of the thermal transport of the reacting film deposited on the substrate was combined with a hybrid approach in which a traditional two-dimensional black box theory was used, in conjunction with the sandwich model, to estimate the maximum flame temperature. The appropriate heat flux of the heat sources is responsible for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is based on the previous author’s work. This work highlights two important findings. One, there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon\silica. Secondly, by increasing the substrate thickness, the quenching effect is progressively diminished at given speed. These results also show that the average speed and quenching of flames depend on the thickness of the silica substrate and can be controlled by a careful choice of the substrate. In Part III, a numerical model was developed based on the moving heat source for multilayer thin film of aluminum and copper oxide over composite substrate of silicon\silica. The maximum combustion flame temperature corresponding to the speed of flame front is the main target of this model. Composite substrate was used as a mechanism to control the heat loss during the reaction. Thickness of the substrate, the length of flame front, and the density of the product were utilized for the standard multilayer thin film with 43 m/s flame front speed. The calculated heat penetration depth in this case was compared to the experimental result for the same flame front iii speed. Numerical model was also used to estimate three major variables for a range of 30-60 m/s. In fact, the maximum combustion flame temperature that corresponds to flame speed along with the length of the flame, density of the product behind the flame, and maximum penetration depth in steady reaction, were calculated. These studies will aid in the design of nEM multilayer thin film. As further numerical and experimental results are obtained for different nEM thicknesses, a unified model involving various parameters can be developed.

Polymer-derived Ceramics (PDCs) represent a unique class of high-temperature stable materials synthesized directly by the thermal decomposition of polymers. This research first focuses on the fabrication of high temperature stable siliconcarbonitride (SiCN) fibers by electrospinning for ceramic matrix composite (CMC) applications. Ceraset™ VL20, a commercially available liquid cyclosilazane, was functionalized with aluminum sec-butoxide in order to be electrospinnable. The surface morphology of the electrospun fibers was investigated using the fibers produced from solvents. The electrospun fibers produced from the chloroform/N,N-dimethylformamide solutions had hierarchical structures that led to superhydrophobic surfaces. A “dry skin” model was proposed to explain the formation of micro/- and nanostructures. The second objective of the research is to align the multiwalled carbon nanotubes (MWCNTs) in PDC fibers. For this purpose, a non-invasive approach to disperse carbon nanotubes in polyaluminasilazane chloroform solutions was developed using a conjugated block copolymer synthesized by ATRP. The effect of the polymer and CNT concentration on the fiber structure and morphology was also examined. Detailed characterization using SEM and TEM was performed to demonstrate the orientation of CNTs inside the ceramic fibers. Additionally, the electrical properties of the ceramic fibers were investigated. Finally, the structural evolution of polymer-derived amorphous siliconborocarbonitride (SiBCN) ceramics with pyrolysis temperatures was studied by solid-state NMR, Raman and EPR spectroscopy. Results suggested the presence of three major components: (i) hexagonal boron nitride (h-BN), (ii) turbostratic boron nitride (t-BN), and (iii) BN2C groups in the final ceramic. iv The pyrolysis at higher temperature generated boron nitride (BN3) with a simultaneous decomposition of BN2C groups. A thermodynamic model was proposed to quantitatively explain the conversion of BN2C groups into BN3 and “free” carbon. Such structure evolution is believed to be the reason that the crystallization of Si4.0B1.0 ceramics starts at 1500 ° C, whereas Si2.0B1.0 ceramics is stable upto 1600 ° C.

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<p> Electrochemical supercapacitors (ES) are urgently needed as components in many advanced power systems. The development of advanced ES is expected to enable radical innovation in the area of hybrid vehicles and electronic devices. Nanostructured manganese oxides in amorphous or various crystalline forms have been found to be promising electrode materials for ES. The use of composite electrodes of manganese oxide with carbon nanotubes is being proposed to improve the overall electrochemical performance of the ES.</p> <p> Electrodeposition methods have been developed for the fabrication of manganese oxide films with/without carbon nanotubes for applications in ES. Electrolytic deposition of manganese oxides was found to be possible using Mn2+ and Mn7+ species, co-deposition of multi wall carbon nanotubes (MWNT) and manganese oxide using cathodic electrosynthesis was successfully achieved.</p> <p> Novel chemical process has been developed for the synthesis of nano-size manganese oxide particles. Electrophoretic deposition of the nano-size manganese oxide particles was able to be performed in both aqueous and non-aqueous solutions. Electrophoretic co-deposition of the nano-size manganese oxide particles with carbon nanotubes was successfully achieved.</p> <p> The mechanisms and kinetics of all the deposition methods are discussed. Charge storage properties of the films prepared by different deposition methods are investigated and compared.</p> / Thesis / Master of Applied Science (MASc)

In this dissertation, simulation techniques are used to understand the role of surfaces, interfaces, and capillary forces on the deformation response of bicontinuous metallic composites and porous materials. This research utilizes atomistic scale modeling to study nanoscale deformation phenomena with time and spatial resolution not available in experimental testing. Molecular dynamics techniques are used to understand plastic deformation of metallic bicontinuous lattices with varying solid volume fraction, connectivity, size, surface stress, loading procedures, and solid density. Strain localization and yield response on nanoporous gold lattices as a function of their solid volume fraction are investigated in axially strained periodic samples with constant average ligament diameter. Simulation stress results revealed that yield response was significantly lower than what can be expected form the Gibson-Ashby formalism for predicting the yield response of macro scale foams. It was found that the number of fully connected ligaments contributing to the overall load bearing structure decreased as a function of solid volume fraction. Correcting for this with a scaling factor that corrects the total volume fraction to "connected, load bearing" solid fraction makes the predictions from the scaling equations more realistic. The effects of ligament diameter in nanoporous lattices on yield and elastic response in both compressive and tensile loading states are reported. Yield response in compression and tension is found to converge for the two deformation modes with increasing ligament diameter, with the samples consistently being stronger in tension, but weaker in compression. The plastic response results are fit to a predictive model that depends on ligament size and surface parameter (f). A modification is made to the model to be in terms of surface area to volume ratio (S/V) rather than ligament diameter (1/d) and the response from capillary forces seems to be more closely modeled with the full surface stress parameter rather than surface energy. Fracture response of a nanoporous gold structure is also studied, using the stress intensity-controlled equations for deformation from linear elastic fracture mechanics in combination with a box of atoms, whose interior is governed by the molecular dynamics formalism. Mechanisms of failure and propagation, propagation rate, and ligament-by-ligament deformation mechanisms such as dislocations and twin boundaries are studied and compared to a corresponding experimental nanoporous gold sample investigated via HRTEM microscopy. Stress state and deformation behavior of individual ligaments are compared to tensile tests of cylinder and hyperboloid nanowires with varying orientations. The information gathered here is used to successfully predict when and how ligaments ahead of the crack tip will fracture. The effects of the addition of silver on the mechanical response of a nanoporous lattice in uniaxial tension and compression is also reported. Samples with identical morphology to the study of the effects of ligament diameter are used, with varying random placement concentrations of silver atoms. A Monte Carlo scheme is used to study the degree of surface segregation after equilibration in a mixed lattice. Dislocation behavior and deformation response for all samples in compression and tension are studied, and yield response specifically is put in the context of a surface effect model. Finally, a novel bicontiuous fully phase separated Cu-Mo structure is investigated, and compared to a morphologically similar experimental sample. Composite interfacial energy and interface orientation structure are studied and compared to corresponding experimental results. The effect of ligament diameter on mechanical response in compressive stress is investigated for a singular morphology, stress distribution by phase is investigated in the context of elastic moduli calculated from the full elastic tensor and pure elemental deformation tests. Dislocation evolution and its effects on strain hardening are put in the context of elastic strain, and plastic response is investigated in the context of a confined layer slip model for emission of a glide loop. The structure is shown to be an excellent, low interface energy model that can arrest slip plane formation while maintaining strength close to the theoretical prediction. Dislocation content in all samples was quantified via the dislocation extraction algorithm. All visualization, phase dependent stress analysis, and structural/property analysis was conducted with the OVITO software package, and its included python editor. All simulations were conducted using the LAMMPS molecular dynamics simulation package. Overall, this dissertation presents insights into plastic deformation phenomena for nano-scale bicontinuous metallic lattices using a combination of experimentation and simulation. A more holistic understanding of the mechanical response of these materials is obtained and an addition to the theory concerning their mechanical response is presented. / Doctor of Philosophy / Crystalline metals can be synthesized to have a sponge-like structure of interconnected ligaments and pores which can drastically change the way that the material chemically interacts with its environment, such as how readily it can absorb oxygen and hydrogen ions. This makes it attractive as a catalyst material for speeding up or altering chemical reactions. The change in structure can also drastically change how the material responds when deformed by pressing, pulling, tearing or shearing, which are important phenomena to understand when engineering new technology. High surface or interface area to volume ratios can cause a massive surface-governed capillary force (the same force that causes droplets of water to bead up on rain coat) and lead to a higher pressure within the material. The effect that both structure and capillary forces have on the way these materials react when deformed has not been established in the context of capillary force theory or crystalline material plasticity theory. For this reason, we investigate these materials using simulation methods at the atomic level, which can give accurate and detailed data on the stress and forces felt atom-by-atom in a material, as well as defects in the material, such as dislocations and vacancies, which are the primary mechanisms that cause the crystal lattice to permanently deform and ultimately break. A series of parameters are varied for multiple model systems to understand the effects of various scenarios, and the understanding provided by these tests is presented.

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Over recent decades, DNA-based methods for programmable self-assembly has tremendous progress in the design, synthesis, and three-dimensional (3D) organization of functional nanomaterials for practical applications. This dissertation will demonstrate how DNA binding interactions can be leveraged for the fabrication of complex nanoscale architectures through the use of isotropic and anisotropic DNA binding interactions. In Chapter 1, I will review recent progress in the field of DNA-based self-assembly strategies. Then, in Chapter 2, I will discuss our work that involves the use of DNA as a means of regulating the isotropic interactions of spherical nanoparticle shells to facilitate the programmable assembly of high- and low-coordinated 3D structures. Chapters 3-4 will demonstrate the “material voxels” self-assembly strategy where firstly, the valency and geometry of the nanoscale frames determine the crystallographic symmetry of the resultant assembled superlattice, and secondly, the use of addressable binding specificity can be utilized as a part of an inverse design strategy to both determine the number of unique voxels and binding motifs and assemble complex 3D architectures. This strategy was then used to design and fabricate a Distributed Bragg reflector (DBR) with enhanced tunability compared to traditional DBRs. Later, in Chapter 5, I designed DNA bonds with addressable binding specificity, in this case, using a series of orthogonal DNA strand displacement reactions to control the activity of the DNA bonds prescribed at the vertices of the DNA origami voxels. I also share work, in Chapter 6, that shows an additional parameter related to the addressability of the DNA bonds, the relative energies of the programmable sequences, to manipulate the morphology of the self-assembled domains. In addition to the organization of metallic particles via the material voxels assembly strategy, Chapter 7 reveals how DNA bonds can be used to organize functional proteins into ordered 2D and 3D organizations, while also retaining the biological activity of the captured proteins, in this case ferritin. In Chapter 8 I will describe how our DNA-based materials can be used to test the effectiveness of radioprotective agents to mitigate against DNA damage from sources of ionizing radiation. In Chapter 9, I will outline additional work that I have done, both published and ongoing, that are related to the DNA-based self-assembly strategies outlined in this thesis overall. Then lastly, in Chapter 10, I will discuss the conclusions we can draw from this dissertation overall, and detail further efforts that can use this research as foundational work.