<p> Historically our understanding of the microscopic world has been impeded by limitations in systems that behave classically. Even today, understanding simple problems in quantum mechanics remains a difficult task both computationally and experimentally. As a means of overcoming these classical limitations, the idea of using a controllable quantum system to simulate a less controllable quantum system has been proposed. This concept is known as quantum simulation and is the origin of the ideas behind quantum computing. </p><p> In this thesis, experiments have been conducted that address the feasibility of using devices with a circuit quantum electrodynamics (cQED) architecture as a quantum simulator. In a cQED device, a superconducting qubit is capacitively coupled to a superconducting resonator resulting in coherent quantum behavior of the qubit when it interacts with photons inside the resonator. It has been shown theoretically that by forming a lattice of cQED elements, different quantum phases of photons will exist for dierent system parameters. In order to realize such a quantum simulator, the necessary experimental foundation must rst be developed. Here experimental eorts were focused on addressing two primary issues: 1) designing and fabricating low disorder lattices that are readily available to incorporate superconducting qubits, and 2) developing new measurement tools and techniques that can be used to characterize large lattices, and probe the predicted quantum phases within the lattice. </p><p> Three experiments addressing these issues were performed. In the rst experiment a Kagome lattice of transmission line resonators was designed and fabricated, and a comprehensive study on the effects of random disorder in the lattice demonstrated that disorder was dependent on the resonator geometry. Subsequently a cryogenic 3-axis scanning stage was developed and the operation of the scanning stage was demonstrated in the final two experiments. The rst scanning experiment was conducted on a 49 site Kagome lattice, where a sapphire defect was used to locally perturb each lattice site. This perturbative scanning probe microscopy provided a means to measure the distribution of photon modes throughout the entire lattice. The second scanning experiment was performed on a single transmission line resonator where a transmon qubit was fabricated on a separate substrate, mounted to the tip of the scanning stage and coupled to the resonator. Here the coupling strength of the qubit to the resonator was mapped out demonstrating strong coupling over a wide scanning range, thus indicating the potential for a scanning qubit to be used as a local quantum probe.</p>

<p> Silicon nitride passivation on AlGaN\GaN heterojunction devices can improve performance by reducing electron traps at the surface. This research studies the effect of displacement damage caused by 1 MeV electron irradiation as a function of the variation of passivation layer thickness and heterostructure layer variation on AlGaN/GaN HEMTs. The effects of passivation layer thickness are investigated at thicknesses of 0, 20, 50 and 120 nanometers on AlGaN\GaN test structures with either an AlN nucleation layer or a GaN cap structures which are then measured before and immediately after 1.0 MeV electron irradiation at fluences of 10¹⁶cm^-2. Hall system measurements are used to observe changes in mobility, carrier concentration and conductivity as a function of Si₃N₄ thickness. Models are developed that relate the device structure and passivation layer under 1 MeV radiation to the observed changes to the measured photoluminescence and deep level transient spectroscopy. A software model is developed to determine the production rate of defects from primary 1 MeV electrons that can be used for other energies and materials. The presence of either a 50 or 120 nm Si₃N₄ passivation layer preserves the channel current for both and appears to be optimal for radiation hardness.</p>

X-ray absorption spectroscopy (XAS) is a powerful probe of electronic and spatial structure that has been at the heart of many advances in physics, biology, chemistry, engineering and the earth sciences. Unfortunately, the existing experimental techniques are subject to fundamental limitations that complicate the interpretation of x-ray absorption spectra in many important cases. These limitations have motivated an effort to develop an alternative measure of the absorption cross-section that is not subject to the same set of limitations. In this thesis, a technique known as inverse partial fluorescence yield (IPFY) is described which addresses this problem. IPFY differs from existing approaches in a significant way — by using an energy-discriminating photon detector, one gains access to fluorescence information from both resonant and non-resonant x-ray emission processes. We will show that the non-resonant emission is fundamentally related to the total absorption cross-section of a material through an inverse relation. This will be proven by extension of the general theory of fluorescence yield for the case of a thick, homogeneous specimen. We will also demonstrate the utility of IPFY with measurements of NiO, NdGaO₃, LNSCO, and stainless steel 304 at soft and intermediate x-ray energies. These experiments will highlight some essential features of IPFY spectroscopy and demonstrate how it can be an invaluable tool when the other experimental techniques fail to provide reliable spectra. We will also demonstrate how one can exploit the geometry dependence of IPFY to quantitatively determine the composition of a sample and the total x-ray absorption coefficient. Additionally, we will consider the special cases of multilayers and powder specimens, where the theory of fluorescence yield requires approximations and is not as well-behaved as in thick, homogenous specimens. Ultimately, these experiments and theoretical developments will be used to support the claim that IPFY is a bulk sensitive measure of the total x-ray absorption coefficient. Moreover, we will show that IPFY is not affected by saturation effects, is insensitive to surface contamination layers and provides reliable spectra even for strongly insulating materials. These properties make IPFY a suitable spectroscopic technique for studying XAS in a wide range of materials.

Thesis (Ph.D.)--Lehigh University, 2007. / Adviser: Himanshu Jain.

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 1995" Wang-Chi Vincent Yeh. 12/12/2003. Report is also available in paper and microfiche from NTIS.

Thesis (P.D.)--Lehigh University, 2008. / Adviser: Nelson Tansu.

Thèse (M.Sc.A.)--Université de Sherbrooke (Canada), 2007. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6874. Adviser: Kenneth S. Schweizer. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1071. Adviser: Sheldon Katz. Includes bibliographical references (leaves 117-123) Available on microfilm from Pro Quest Information and Learning.

Over the last 4 years, perovskite solar cells emerged as an attractive, highly efficient, and low-cost alternative to established, conventional photovoltaic technologies. The power conversion efficiency of these devices recorded an unprecedented rise, currently exceeding certified values of 20%. This thesis covers a number of technological advancements which lead to improved photovoltaic performance, as well as vital insight into some more fundamental aspects of the perovskite device operation. The focus of this body of work is primarily directed towards the electric contact in the PV stack which is responsible for electron collection. The motivation of the study presented here is given in Chapter 1, and includes a brief summary of the current energy landscape. Chapter 2 introduces the theoretical background of photovoltaic technology, starting from the basics of semiconductor physics, through to the principles of solar cell operation, as well as some characteristic properties of the perovskite materials. Details of the experimental methods used in this study are reported in Chapter 3. Chapter 4 reports the development of a low temperature process (sub-150 &deg;C) for the manufacture of perovskite solar cells. Dispersions of pre-synthesised, highly crystalline TiO2 nanoparticles were used as an electron selective contact, which eliminated the high temperature sintering step. Chapters 5, 6 and 7, report the interface modification of an n-type contact, resulting in a substantially improved device operation and suppression of hysteresis phenomenon which is characteristic of perovskite photovoltaics. Fullerene-based materials have been found to make excellent electronic contact with halide perovskite materials, and are shown to be far superior to commonly used metal oxides. The facilitated electron collection allows enhancements in the photovoltaic performance of these devices. Furthermore, the organic layers used in this study can be processed at low temperatures. Finally, the development of transparent conductive electrodes based on silver nanowires is presented in Chapter 8. The fabricated electrodes exhibit low sheet resistance, high degree of transparency, and can be processed at low temperatures, allowing them to be compatible with processing on flexible substrates and multi-junction architectures. The application of silver nanowires in different perovskite solar cell architectures is also reported.