Página 1 dos resultados de 473 itens digitais encontrados em 0.044 segundos
Resultados filtrados por Publicador: Harvard University

Ultra-Thin Oxide Membranes: Synthesis and Carrier Transport

Sim, Jai S.
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
Português
Relevância na Pesquisa
715.9557%
Self-supported freestanding membranes are films that are devoid of any underlying supporting layers. The key advantage of such structures is that, due to the lack of substrate effects - both mechanical and chemical, the true native properties of the material can be probed. This is crucial since many of the studies done on materials that are used as freestanding membranes are done as films clamped to substrates or in the bulk form. This thesis focuses on the synthesis and fabrication as well as electrical studies of free standing ultrathin < 40nm oxide membranes. It also is one of the first demonstrations for electrically probing nanoscale freestanding oxide membranes. Fabrication of such membranes is non-trivial as oxide materials are often brittle and difficult to handle. Therefore, it requires an understanding of thin plate mechanics coupled with controllable thin film deposition process. Taking things a step further, to electrically probe these membranes required design of complex device architecture and extensive optimization of nano-fabrication processes. The challenges and optimized fabrication method of such membranes are demonstrated. Three materials are probed in this study, VO2, TiO2, and CeO2. VO2 for understanding structural considerations for electronic phase change and nature of ionic liquid gating...

GaN/InGaN Microcavities and Applications

Niu, Nan
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
Português
Relevância na Pesquisa
704.1325%
Semiconductor micro- and nano-cavities are excellent platforms for experimental studies of optical cavities, lasing dynamics, and cavity Quantum Electrodynamics (QED). Common materials for such experiments are narrow bandgap semiconductor materials with well-developed epitaxial growth technologies, such as GaAs and InP, among others. Gallium nitride (GaN) and its alloys are industrially viable materials with wide direct bandgaps, low surface re-combination velocities, and large exciton binding energies, offering the possibility of room temperature realization of light-matter interaction. Controlling light-matter interaction is at the heart of nanophotonic research which leads to ultra-low threshold lasing, photonic qubits, and optical strong coupling. Technologically, due to its blue emission, GaN photonic cavities with indium gallium nitride (InGaN) active mediums serve as efficient light sources for the fast growing photonic industry, optical computing and communication networks, display technology, as well as quantum information processing. The main challenges in fabricating high quality GaN cavity are due to its chemical inertness and low material quality as a result of strain-induced defects and threading dislocations. In this dissertation...

Physics-Based Visual Inference: Theory and Applications

Xiong, Ying
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
Português
Relevância na Pesquisa
928.2318%
Analyzing images to infer physical scene properties is a fundamental task in computer vision. It is by nature an ill-posed inverse problem, because imaging is a complicated, information-lossy physical and measurement process that cannot be deterministically inverted. This dissertation presents theory and algorithms for handling ambiguities in a variety of low-level vision problems. They are based on two key ideas: (1) explicitly modeling and reporting uncertainties are beneficial to visual inference; and (2) using local models can significantly reduce ambiguities that would exist in pixelwise analysis. In the first part of the dissertation, we study the color measurement pipeline of consumer digital cameras, and consider the inherent uncertainty of undoing the effects of tone-mapping. We introduce statistical models for this uncertainty and algorithms for fitting it to given cameras or imaging pipelines. Once fit, the model provides for each tone-mapped color a probability distribution over linear scene colors that could have induced it, which is demonstrated to be useful for a number of downstream inference applications. In the second part of the dissertation, we study the pixelwise ambiguities in physics-based visual inference and present theory and algorithms for employing local models to eliminate or reduce these ambiguities. In shape from shading...