Neste trabalho apresentamos um modelo para bandas de energia do HxMoO3 tanto para baixos como para altos valores de x. A densidade ótica do MoO3 hidrogenado é descrita em termos deste modelo, considerando-se as transições intra-bandas e inter-bandas. Verificamos que a densidade ótica calculada está de acordo com os resultados experimentais / In this work we give a model for the energy bands of HxMoO3 for low and high values of x. The optical density of hydrogenated MoO3 is described in terms of this model including both intraband and interband transitions. The calculated optical density is shown to agree with the experimental results

In this dissertation, cross-sectional potential imaging of GaAs-based homoepitaxial, heteroepitaxial and quantum well structures, all grown by atmospheric pressure Metal-organic Vapor Phase Epitaxy (MOVPE) is investigated. Kelvin probe force microscopy (KPFM), using amplitude modulation (AM) and frequency modulation (FM) modes in air and at room temperature, is used for the potential imaging. Studies performed on n-type GaAs homoepitaxial structures have shown two different potential profiles, related to the difference in electron density between the semi-insulating (SI) substrate and the epilayers. It is shown that the contact potential difference (CPD) between the tip and sample is higher on the semi-insulating substrate side than on the n-type epilayer side. This change in CPD across the interface has been explained by means of energy band diagrams indicating the relative Fermi level positions. In addition, it has also been found that the CPD across the interface increases with electron density. This result is in qualitative agreement with theory. In addition, as known from literature, even under ambient conditions FM mode KPFM provides better lateral resolution and more realistic CPD values than AM mode KPFM. Compared to the case of AM mode analysis, where the experimental CPD values were on average of the theoretical values, the CPD values from FM mode analysis are on average of the theoretical ones. Furthermore, by using FM mode, the transition across the interface is sharper and the surface potential flattens/saturates as expected when scanning sufficiently far away from the junction. The non-neutral space charge region of the sample with an electron density of for example, is as measured by FM-KPFM, whereas for AM-KPFM, the width is even more than and the potential profiles do not saturate. For the p-type GaAs homoepitaxial structures, FM mode measurements from a sample with a dopant density of are presented. As in the case of n-type GaAs,a similar potential profile showing two main domains has been obtained. However, unlike the case of type GaAs where the potential measured on the epilayer side is higher than that on the substrate side, the potential on the epilayer side of the junction is lower in this case due to the fact that the Fermi level of p-type GaAs is below that of the substrate.

M.Sc. (Optometry) / The difference between objective automatic and subjective clinical refraction is studied using new statistical techniques. The question, by how much the two refraction techniques differ, is investigated by subtracting the subjective refraction finding from the auto refractory finding and then examining the distribution of the difference or excess as it will be called here. Computerized procedures were developed to automate mathematical and statistical methods of analysis. The methods were applied to two different samples: one of patients visiting an ordinary optometric practice (the clinical sample) and the other of children refracted in a screening program (the sample of school children) . The clinical sample, consisting of mainly older patients, is examined first. The difference between the autorefractor and subjective findings is studied and described. This difference could be used to compare different types of auto refractors assuming that the subjective refraction is correct. For the purpose of this study, however, the results of eight autorefractors are grouped together, combining left and right eyes, to serve as basis for studying the older population. The study shows that on the average there is no clinically significant excess. This means that there is on average no clinically significant difference between the automatic and clinical refraction for this population.

No description available.

No description available.

An automated ellipsometer was used to study field-induced optical anisotropy in anodic niobium oxide films. The oxide films were found to change from the optically isotropic state to the optically anisotropic state when an electric field was applied normal to the film surface. The anisotropic refractive indices of the oxide films decreased quadratically while the thickness of the films increased quadratically with the applied field. The quadratic electro-optic coefficients were determined. The changes in refractive indices and in thickness of the oxide films were found to be independent of time. Field recrystallization of the anodic niobium oxide films was investigated using a scanning electron microscope. The results are compared with those reported for anodic tantalum oxide films in the published literature. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22075号 / 農博第2367号 / 新制||農||1072(附属図書館) / 学位論文||R1||N5229(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 近藤 直, 准教授 小川 雄一, 教授 清水 浩 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Zinc oxide (ZnO) semiconductors have been utilized by many researchers, due to its unique properties beneficial for functional devices. In particular, gadolinium (Gd)–doped ZnO exhibits high ferromagnetic and electrical properties, which is attributed to defect/impurity bands mediated by Gd dopants. In this dissertation, I study the effects of Gd concentration, oxygen pressure using pulsed laser deposition (PLD), and thermal annealing on the optical and structural properties of undoped and Gd-doped ZnO films and nanostructures. Moreover, as the growth of practical ZnO nanostructures-based devices without catalyst, while presently challenging, is highly important for many applications. Thus, for the first time, a novel method is developed for growing well aligned ZnO nanorods (NRs) by optimizing PLD conditions using Gd-doped ZnO target without any catalyst in a single step. This study shows that, both the lattice orientation of the substrate and the Gd characteristics are significant in enhancing the NR growth. Our findings reveal that precise control of the NR density can be achieved by changing the oxygen partial pressure. Furthermore, due to the Gd incorporation, these NRs possess favorable electrical properties with a significant mobility of 177 cm2 (V.s)-1 compared to that reported in literature. Nonetheless significant challenges need to be overcome to achieve reproducible and stable p-type ZnO for commercial applications. Hence, several attempts based on n-type ZnO grown on foreign p-type substrates were made to achieve high-performance devices and overcome the issues arising when p-type doped ZnO is employed. Moreover, Growth of ZnO nanostructures on a foreign p-type substrates does not require a lattice-matched p-type substrate. Thus, for the first time, PLD conditions are improved to grow high quality ZnO nanotubes (NTs) with high optical, structural and electrical properties on a p-type Si (100) substrate without catalyst for high-performance devices. A fabrication of high performance UV photodetector (PD) based on ZnO NT/p-Si is demonstrated with superior responsivity (up to ~ 101.2 AW-1) compared to that reported in literature. This new and simple method demonstrates that the PLD system has a significant potential for improving the performance of materials used in a wide range of electronic and optoelectronic applications.

The exponential growth of data generation–driven in part by the proliferation of applications such as high definition streaming, artificial intelligence, and the internet of things–presents an impending bottleneck for electrical interconnects to fulfill data center bandwidth demands. Links now require bandwidths in excess of multiple Tbps while operating on the order of picojoules per bit, in addition to constraints on areal bandwidth densities and pin I/O bandwidth densities. Optical communications built on a silicon photonic platform offers a potential solution to develop power efficient, high bandwidth, low attenuation, small footprint links, all while building off the mature CMOS ecosystem. The development of silicon photonic foundries supporting multi project wafer runs with associated process design kit components supports a path towards widespread commercial production by increasing production volume while reducing fabrication and development costs. While silicon photonics can always be improved in terms of performance and yield, one of the central challenges is the integration of the silicon photonic integrated circuits with the driving electronic integrated circuits and data generating compute nodes such as CPUs, FPGAs, and ASICs. The co-packaging of the photonics with the electronics is crucial for adoption of silicon photonics in datacenters, as improper integration negates all the potential benefits of silicon photonics. The work in this dissertation is centered around the development of silicon photonic multi chip module transceivers to aid in the deployment of silicon photonics within data centers. Section one focuses on silicon photonic integration and highlights multiple integrated transceiver prototypes. The central prototype features a photonic integrated circuit with bus waveguides with WDM microdisk modulators for the transmitter and WDM demuxes with drop ports to photodiodes for the receiver. The 2.5D integrated prototype utilizes a thinned silicon interposer and TIA electronic integrated circuits. The architecture, integration, characterization, performance, and scalability of the prototype are discussed. The development of this first prototype identified key design considerations necessary for designing multi chip module silicon photonic prototypes, which will be addressed in this section. Finally, other multi chip module silicon photonic prototypes will be overviewed. These include a 2.5D integrated transceiver with a different electronic integrated circuit TIA, a 3D integrated receiver, an active interposer network on chip, and a 2.5D integrated transceiver with custom electronic integrated circuits. Section two focuses on research that supports the development of silicon photonic transceivers. The thermal crosstalk from neighboring microdisk modulators as a function of modulator pitch is investigated. As modulators are placed at denser pitches to accommodate areal bandwidth density requirements in transceivers, this thermal crosstalk will become significant. In this section, designs and results from several iterations of custom microring modulators are reported. Custom microring modulators allow for scaling up the number of channels in microring transceivers by offering the ability to fabricate variable resonances and provide a platform for further innovation in bandwidth, free spectral range, and energy efficiency. The designs and results of higher order modulation format modulators, both microring based and Mach Zehnder based, are discussed. High order modulators offer a path towards scaling transceiver total throughput without having to increase the channel counts or component bandwidth. Together, the work in these two sections supports the development of silicon photonic transceivers to aid in the adoption of silicon photonics into data generating systems.

<p>In the realm of tunable optical devices, 3D nanostructures with metals and dielectrics have been utilized in a wide variety of practical applications ranging from optical switching to beam-steering devices. 2D materials, on the other hand, have enabled the exploration of truly new physics unattainable with 3D systems due to quantum confinement leading to unique optical properties and enhanced light-matter interactions. Transdimensional materials (TDMs) – atomically thin films of metals – can couple the robustness of 3D nanostructures with the new physics enabled by 2D features. However, the evolution of the optical properties in the transdimensional regime between 3D and 2D is still underexplored. The optical properties of metallic TDMs are expected to show unprecedented tailorability, including strong dependences on the film thickness, composition, strain, and surface termination. They also have an increased sensitivity to external optical and electrical perturbations, owing to their extraordinary light-confinement. Additionally, the small atomic thicknesses may lead to strongly confined surface plasmons and quantum and nonlocal phenomena. The strong tunability and light-confinement offered by TDMs have resulted in a search for atomically thin plasmonic material platforms that facilitate active metasurfaces with novel functionalities in the visible and near infrared (NIR) range. In this research, we explore the plasmonic properties and tailorability of atomically thin titanium nitride (TiN). We experimentally and theoretically study the thickness-dependent optical properties of epitaxial TiN films with thicknesses down to 1 nm to demonstrate confinement induced optical properties. Overall, this research demonstrates the potential of TDMs for unlocking novel optical phenomena at visible and NIR wavelengths and realizing a new generation of atomically thin tunable nanophotonic devices. </p>