abstract: Nanolaminate composite materials consist of alternating layers of materials at the nanoscale (≤100 nm). Due to the nanometer scale thickness of their layers, these materials display unique and tailorable properties. This enables us to alter both mechanical attributes such as strength and wear properties, as well as functional characteristics such as biocompatibility, optical, and electronic properties. This dissertation focuses on understanding the mechanical behavior of the Al-SiC system. From a practical perspective, these materials exhibit a combination of high toughness and strength which is attractive for many applications. Scientifically, these materials are interesting due to the large elastic modulus mismatch between the layers. This, paired with the small layer thickness, allows a unique opportunity for scientists to study the plastic deformation of metals under extreme amounts of constraint. Previous studies are limited in scope and a more diverse range of mechanical characterization is required to understand both the advantages and limitations of these materials. One of the major challenges with testing these materials is that they are only able to be made in thicknesses on the order of micrometers so the testing methods are limited to small volume techniques. This work makes use of both microscale testing techniques from the literature as well as novel methodologies. Using these techniques we are able to gain insight into aspects of the material’s mechanical behavior such as the effects of layer orientation, flaw dependent fracture, tension-compression asymmetry, fracture toughness as a function of layer thickness, and shear behavior as a function of layer thickness. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2016

The unprecedented ability of plasmonic metal nano-structures to concentrate light into deep-subwavelength volumes has propelled their use in a vast array of nanophotonics technologies and research endeavors. They are used in sensing, super-resolution imaging, SPP lithography, SPP assisted absorption, SPP-based antennas, light manipulation, etc. To take full advantage of the attractive capabilities of CMOS compatible low-cost plasmonic structures based on Al and Cu, nanolaminate coatings are investigated to improve their long-term stability in corrosive physiological environments. The structures are fabricated using phase-shifting PDMS masks, e-beam deposition, RIE, Atomic Layer Deposition and Rapid Thermal Annealing. An alternate approach using Nanosphere Lithography (NSL) was also investigated. Films were examined using ellipsometry, atomic force microscopy and transmission measurements. Accelerated in-situ tests of Hafnium Oxide/Aluminum Oxide nanolaminate shells in a mildly pH environment with temperatures akin to physiological environments emulated using PBS show greatly enhanced endurance, with stable structures that last for more than one year. / Master of Science

Thin films are an enabling technology for a wide range of applications, from microprocessors to diffusion barriers. Nanolaminate thin films combine two (or more) materials in a layered structure to achieve performance that neither film could provide on its own. Atomic layer deposition (ALD) is a chemical vapor deposition technique in which film growth occurs through self limiting surface reactions. The atomic scale control of ALD is well suited for producing nanolaminate thin films. In this thesis, ALD of two nanolaminate systems will be investigated: Al₂O₃-Ta₂O₅ and ZnO-SnO₂. Al₂O₃ and Ta₂O₅ are high κ dielectrics that find application as gate oxides for field effect devices such as metal oxide semiconductor field effect transistors and thin film transistors. Al₂O₃-Ta₂O₅ nanolaminate films of a fixed composition and total thickness, but with varied laminate structures, were produced to explore the influence of layer thickness on dielectric behavior. Layer thickness was found to have little impact on the dielectric constant but a strong impact on the leakage current. Thick layered nanolaminates (with 2.5 to 10 nm layers) performed better than either pure material. Showing structure provides a means of tailoring nanolaminate properties. ZnSnO is an amorphous oxide semiconductor used to make transparent TFTs. Although ALD is naturally suited to the production of nanolaminates, the deposition of homogenous ternary compounds is still uncommon. For very thin depositions, nucleation behavior can dominate, resulting in ALD growth rates different than for thicker films. Initial work on ALD of the ZnO-SnO₂ system is presented, focusing on nucleation and growth of each material on the other. It was found that both ZnO and SnO₂ inhibit the growth of one another and a method was developed to characterize the average growth rate for few cycle depositions. / Graduation date: 2011

<p>Energy harvesting is an interesting topic for today since we face running out of energy source, a serious problem in the world. Thermoelectric devices are a good candidate. They can convert heat (i.e. temperature gradient) to electricity. This result leads us to use them to harvest waste heat from engines or in power plants to generate electricity. Moreover, thermoelectric devices also perform cooling by applied voltage to device. This process is clean, which means that no greenhouse gases are emitted during the process. However, the converting efficiency of thermoelectrics are very low compare to a home refrigerator. The thermoelectric figure of merit (ZT_m) is a number which defines the converting efficiency of thermoelectric materials and devices. ZT_m is defined by Seebeck coefficient, electrical conductivity and thermal conductivity. To improve the converting efficiency, nanolaminated materials are good candidate.</p><p> </p><p>This thesis studies TiN/ScN artificial nanolaminates, or superlattices were grown by reactive dc magnetron sputtering from Ti and Sc targets. For TiN/ScN superlattice, X-ray diffraction (XRD) and reciprocal space map (RSM) show that we can obtain single crystal TiN/ScN superlattice. X-ray reflectivity (XRR) shows the superlattice films have a rough surface, supported by transmission electron microscopy (TEM). Also, TiN/ScN superlattices grew by TiN as starting layer has better crystalline quality than ScN as starting layer. The electrical measurement shows that our superlattice films are conductive films.</p><p> </p><p>Ca-Co-O system for inherently nanolaminated materials were grown by reactive rf magnetron sputtering from Ca/Co alloy target. The XRD shows we maybe get the [Ca₂CoO₃]_xCoO₂ phase, so far. The energy dispersive X-ray spectroscopy (EDX) reported that our films have Al conmination. We also discovered unexpected behavior when the film grown at high temperature showed larger thickness instead of thinner, which would have been expected due to possible Ca evaporation. The Ca-Co-O system requires further studies.</p>

Energy harvesting is an interesting topic for today since we face running out of energy source, a serious problem in the world. Thermoelectric devices are a good candidate. They can convert heat (i.e. temperature gradient) to electricity. This result leads us to use them to harvest waste heat from engines or in power plants to generate electricity. Moreover, thermoelectric devices also perform cooling by applied voltage to device. This process is clean, which means that no greenhouse gases are emitted during the process. However, the converting efficiency of thermoelectrics are very low compare to a home refrigerator. The thermoelectric figure of merit (ZTm) is a number which defines the converting efficiency of thermoelectric materials and devices. ZTm is defined by Seebeck coefficient, electrical conductivity and thermal conductivity. To improve the converting efficiency, nanolaminated materials are good candidate.   This thesis studies TiN/ScN artificial nanolaminates, or superlattices were grown by reactive dc magnetron sputtering from Ti and Sc targets. For TiN/ScN superlattice, X-ray diffraction (XRD) and reciprocal space map (RSM) show that we can obtain single crystal TiN/ScN superlattice. X-ray reflectivity (XRR) shows the superlattice films have a rough surface, supported by transmission electron microscopy (TEM). Also, TiN/ScN superlattices grew by TiN as starting layer has better crystalline quality than ScN as starting layer. The electrical measurement shows that our superlattice films are conductive films.   Ca-Co-O system for inherently nanolaminated materials were grown by reactive rf magnetron sputtering from Ca/Co alloy target. The XRD shows we maybe get the [Ca2CoO3]xCoO2 phase, so far. The energy dispersive X-ray spectroscopy (EDX) reported that our films have Al conmination. We also discovered unexpected behavior when the film grown at high temperature showed larger thickness instead of thinner, which would have been expected due to possible Ca evaporation. The Ca-Co-O system requires further studies.

Plasmonic nanostructures can enhance light-matter interactions in the subwavelength domain, which is useful for photodetection, light emission, optical biosensing, and spectroscopy. However, conventional plasmonic devices are optimized to operate in a single wavelength band, which is not efficient for wavelength-multiplexed operations and quantum optical applications involving multi-photon nonlinear processes at multiple wavelength bands. Overcoming the limitations of single-resonant plasmonics requires development of plasmonic devices that can enhance the optical interactions at the same locations but at different resonance wavelengths. This dissertation comprehensively studies the theory, design, and applications of such devices, called "multiresonant plasmonic systems with spatial mode overlap". We start by a literature review to elucidate the importance of this topic as well as its current and potential applications. Then, we briefly discuss the fundamentals of plasmonic resonances and mode hybridization to thoroughly explore, classify, and compare the different architectures of the multiresonant plasmonic systems with spatial mode overlap. Also, we establish the black-box coupled mode theory to quantify the coupling of optical modes and analyze the complicated dynamics of optical interactions in multiresonant plasmonic systems. Next, we introduce the nanolaminate plasmonic crystals (NPCs), wafer-scale metamaterials structures that support many (>10) highly-excitable plasmonic modes with spatial overlap across the visible and near-infrared optical bands. The enabling factors behind the NPC's superior performance as multiresonant systems are also theoretically and experimentally investigated. After that, we experimentally demonstrate the NPCs application in simultaneous second harmonic generation and anti-Stokes photoluminescence (ASPL) with controllable nonlinear emission properties. By designing specific non-linear optical experiments and developing advanced ASPL models, this work addresses some important but previously unresolved questions on the ASPL mechanism as well. Finally, we conclude the dissertation by discussing the potential applications of out-of-plane plasmonic systems with spatial mode overlap in wavelength-multiplexed devices and presenting some preliminary results. / Doctor of Philosophy / Emergence of electronic devices such as cellphones and computers has revolutionized our lifestyles over the past century. By manipulating the flow/storage of electrons at the nanometer scale, electronic components can be very compact, but their speed and energy performance is ultimately limited due to ohmic losses and finite velocity of the electrons. In parallel, photonic devices and circuits have been proposed that by molding the flow of light can overcome the mentioned limitations but are not as integrable as their electronic counterparts. Plasmonics is an emerging research field that combines electronics and photonics using nanostructures that can couple the light waves to the free electrons in metals. By confining the light at deep subwavelength scales, plasmonic devices can highly enhance the light-matter interactions, with applications in ultrafast optical communications, energy-harvesting, optical sensing, and biodetection. Conventionally, plasmonic devices are optimized to operate with a single light color, which limits their performance in wavelength-multiplexed operations and ultrafast non-linear optics. For such applications, it is far more efficient to use the more advanced "multiresonant plasmonic systems with spatial mode overlap" that can enhance the optical interactions at the same locations but for multiple light colors. This dissertation comprehensively studies these systems in terms of the fundamental concepts, design ideas, and applications. Our work advances the plasmonic field from both science and technology perspectives. In particular, we explore and classify the strategies of building multiresonant plasmonic systems with spatial mode overlap for the first time. Also, we establish the black-box coupled mode theory, a novel framework for analysis and design of complicated plasmonic structures with optimized performance. Furthermore, we introduce the "nanolaminate plasmonic crystals" (NPCs), large area and cost-effective devices that can enhance the optical processes for both visible and near-infrared lights. Finally, we demonstrate NPCs ability in simultaneous frequency-doubling and broadband emission of light and come up with advanced theoretical models that can explain the light generation and color conversion in plasmonic devices.

Currently available solid lubricants only perform well under a limited range of environmental conditions. Unlike them, oxides are thermodynamically stable and relatively inert over a broad range of temperatures and environments. However, conventional oxides are brittle at normal temperatures; exhibiting significant plasticity only at high temperatures (>0.5Tmelting). This prevents oxides' use in tribological applications at low temperatures. If oxides can be made lubricious at low temperatures, they would be excellent solid lubricants for a wide range of conditions. Atomic layer deposition (ALD) is a growth technique capable of depositing highly uniform and conformal films in challenging applications that have buried surfaces and high-aspect-ratio features such as microelectromechanical (MEMS) devices where the need for robust solid lubricants is sometimes necessary. This dissertation investigates the surface and subsurface characteristics of ALD-grown ZnO/Al2O3 nanolaminates and ZrO2 monofilms before and after sliding at room temperature. Significant enhancement in friction and wear performance was observed for some films. HRSEM/FIB, HRTEM and ancillary techniques (i.e. SAED, EELS) were used to determine the mechanisms responsible for this enhancement. Contributory characteristics and energy dissipation modes were identified that promote low-temperature lubricity in both material systems.

The field of spintronics emerged from the search for innovative concepts to comply with the ever increasing need for larger data storage. One major subject of spintronics are devices based on pure spin currents. Such devices usually rely on a combination of two materials: first, a magnetic insulator, to carry the spin information, and second, a spin Hall active metal, to convert from spin to charge information and vice versa and thus effectively act as electrical interface. While previously, such bilayers have been studied in detail in various planar structures, lately, curved and/or three dimensional (3D) geometries have gained more and more attention. Especially for magnetic systems, it has been reported that curvature can lead to the materialization of additional interactions such as curvature-induced anisotropy and the Dzyaloshinskii-Moriya-interaction. The latter is closely related to the magnetic topography of the system, which can be deduced from its essential role in the formation of skyrmions. To systematically study curvature- or topology-based effects, artificially designed systems with a controllable curvature are essential. Consequently, providing an experimental platform, which allows the realization of a variety of different geometries is a key step towards accessing this innovative field of magnetism research. In this thesis, we used atomic layer deposition (ALD) to establish such a platfrom. ALD is a chemical vapor deposition technique which enables the conformal coating of arbitrarily shaped objects while maintaining an excellent thickness control of the layers. In conjunction with 3D (nano)printed resist structures, which can be designed in a multitude of different designs, ALD serves as a powerful platform to fabricate 3D micro- or nanostructures. One of the most popular material combination in spintronics consists of yttrium iron garnet (YIG) and platinum. On the one hand, the ferrimagnetic insulator YIG is the ideal candidate for any kind spin transport experiments, due to its very low magnetic damping. Pt, on the other hand, has a large spin-orbitinteraction, which is necessary for an efficient spin to charge conversion. Therefore, the fabrication of 3D spintronic devices from YIG and Pt is highly desirable. In this thesis the successful fabrication of YIG and Pt by ALD is outlined. We validate the usability of the ALD-Pt layers for 3D spintronics by showing that the ALD-Pt layers are spin Hall active with a electrical quality comparable to other deposition techniques. For the fabrication of ALD-YIG, a nanolaminate approach was used, which is based on the alternate deposition of ultra thin layers of two binary ALD processes: ALD-Fe2O3 and ALD-Y2O3. Therefore, these two processes were optimized beforehand to establish the growth conditions. Furthermore, asdeposited ALD layers are often non-crystalline. To characterize, how this reflects in magnetotransport experiments, we used a model system of non-crystalline sputtered YIG and Pt. By rotating the magnetization in three rotation planes, we find the fingerprint of the spin Hall magnetoresistance. We demonstrate that 3D nanoprinted resist templates can be made fit for the deposition of ALD bilayers even at temperatures where the resist is not stable on its own. To enhance the stability of the resist templates, a layer of low temperature ALD-Al2O3 is used. Finally, the deposition of ALD-YIG is described. A subsequent annealing step is used to promote crystallization of the nanolaminates into YIG. Upon characterizing the structural properties, we find that our process is extremely stable with respect to changes in the stoichiometry within the nanolaminate. From additional measurements of the static and dynamic magnetic properties, we conclude that our ALD-YIG are of good quality comparable to other deposition techniques. By enabling the fabrication of high quality YIG and Pt via ALD, we lay the groundwork for studying the electrical and magnetic properties of systems with curvature and/or a nontrivial topography - effectively advancing the research field of 3D spintronics.