Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Outre leur fonction principale de correction visuelle, les verres ophtalmiques offrent des valeurs ajoutées supplémentaires, tels que des propriétés anti-rayures et antireflets, afin d'optimiser le confort visuel des porteurs. Ces caractéristiques sont apportées par des revêtements déposés sur le substrat polymère constitutif du verre ophtalmique. Plus précisément, un vernis anti-rayures de quelques microns d'épaisseur est déposé par voie humide, suivi par l'évaporation d'un empilement antireflet à l'échelle nanométrique. Le défi consiste à assurer la qualité de l'interface entre ces couches. Compte-tenu de leur faible dimension, l'évaluation de l'adhérence au sein de l’empilement ophtalmique est principalement effectuée qualitativement à ce jour. L’objectif de ces travaux de recherche est de fournir une estimation quantitative de l'adhérence à l'interface la plus sensible de la structure, située entre la couche de SiO2 de l’antireflet et le vernis. Parmi les 300 essais d'adhérence décrits dans la littérature, l’essai d'adhérence par compression a été choisi car il permet de reproduire des défauts observés dans les conditions d’utilisation réelles du verre ophtalmique. Par ailleurs, cet essai d’adhérence offre l'avantage de permettre une application mécanique uniaxiale et sans contact dans la zone d'observation. L'adhérence entre la couche de SiO2 et le vernis a été estimée quantitativement en étudiant les morphologies de cloques générées expérimentalement. Afin d'étudier les dimensions des cloques rectilignes, le développement de l’essai d’adhérence par compression in situ sous profilomètre optique, a été réalisé. Une attention particulière a été portée aux conditions d’essai lors de la mise en compression de l’éprouvette. La conception de la platine de compression et des dimensions d'échantillons ont été revues pour favoriser l'homogénéité de la déformation du substrat. L'adhérence des échantillons issus de différents procédés d’évaporation a été déterminée. L'influence des paramètres du procédé ainsi que l'impact du vieillissement sur l'adhérence ont été évalués. Afin de mieux décrire le scénario expérimental et de mieux comprendre les mécanismes d'adhérence entre la couche mince de SiO2 et le vernis, un modèle numérique a été développé. Les propriétés mécaniques des matériaux constituant le système étudié ont été caractérisées par nanoindentation et couplées à des modèles de nanoindentation prenant en compte l'influence du substrat sur la couche mince de SiO2 de faible épaisseur. Le délaminage interfacial par flambement de la couche de SiO2 a été simulé en utilisant la technique des surfaces cohésives. Les paramètres interfaciaux permettant de reproduire les résultats expérimentaux sont présentés. Des analyses de sensibilité ont été réalisées pour évaluer les facteurs principaux permettant une description correcte du scénario de flambage. / Besides its main function of providing visual correction, ophthalmic lenses offer additional benefits, such as anti-scratch and anti-reflective properties, in order to optimize visual comfort. These features are brought by coatings deposited on top of the plastic polymeric substrate constituting the lens. More specifically, an anti-scratch hardcoat of a few microns thick is deposited by wet chemical methods, followed by the evaporation of an anti-reflective stack within the nanometric scale. The challenge is to ensure interface quality between layers. Considering their small dimensions, assessment of mechanical adhesion within the ophthalmic stack is mostly performed qualitatively to this day. The aim of this research is to provide a quantitative estimate of the mechanical adhesion at the most sensitive interface of the structure, located between the SiO2 layer of the anti-reflective stack and the hardcoat. Among the 300 adhesion tests described in the literature, adhesion test by compression has been chosen because of its ability to replicate defects observed in real life. Moreover compression tests offer the advantage of allowing uniaxial and contactless mechanical application within the observation area. Mechanical adhesion at this interface has been estimated quantitatively by studying buckle morphologies generated by compression tests. In order to study dimensions of straight-sided buckles, development of in situ compression test under an optical profilometer was carried out. Special attention was given to experimental conditions during application of compressive stress on test specimen. Both designs of samples and compression testing stage were revised to promote substrate’s strain homogeneity. Mechanical adhesion of samples which underwent different deposition processes was assessed. Influence of process parameters as well as impact of ageing on mechanical adhesion was evaluated. In order to better describe the experimental scenario and gain a greater understanding of mechanisms of adhesion between the SiO2 layer and the hardcoat, a numerical model was developed. Mechanical properties of materials composing the interface were characterized by nanoindentation and coupled with nanoindentation models taking into account influence of substrate for thin SiO2 layer. Interfacial delamination through buckling of the SiO2 layer was simulated using cohesive surface technique. Interfacial parameters allowing close compliance with experimental results are presented. Sensitivity analyses were performed to evaluate leading factors allowing proper description of buckling scenario.

Polymer thin films with the film thickness (h0) below ~ 100 nm often exhibit physical properties different from the bulk counterparts. In order to make the best use of polymer thin films in applications, it is important to understand the physical origins of these deviations. In this dissertation, I will investigate how different factors influence dynamic properties of polymer thin films upon nano-confinement, including glass transition temperature (Tg), effective viscosity (ηeff) and self-diffusion coefficient (D). The first part of this dissertation concerns the impacts of the molecular weight (MW) and tacticity on the Tg’s of nano-confined polymer films. Previous experiments showed that the Tg of polymer films could be depressed or increased as h0 decreases. While these observations are usually attributed to the effects of the interfaces, some experiments suggested that MW’s and tacticities might also play a role. To understand the effects of these factors, the Tg’s of silica-based poly(α-methyl styrene) (PαMS/SiOx) and poly(methyl methacrylate) (PMMA/SiOx) thin films were studied, and the results suggested that MW’s and tacticities influence Tg in nontrivial ways. The second part concerns an effort to resolve the long-standing controversy about the correlation between different dynamics of polymer thin films upon nano-confinement. Firstly, I discuss the experimental results of Tg, D and ηeff of poly(isobutyl methacrylate) films supported by silica (PiBMA/SiOx). Both Tg and D were found to be independent of h0, but ηeff decreased with decreasing h0. Since both D and ηeff describe transport phenomena known to depend on the local friction coefficient or equivalently the local viscosity, it is questionable why D and ηeff displayed seemingly inconsistent h0 dependencies. We envisage the different h0 dependencies to be caused by Tg, D and ηeff being different functions of the local Tg’s (Tg,i) or viscosities (ηi). By assuming a three-layer model, we were able to account for the experimental data and resolve the inconsistency. By extending the same ideas to the analogous data of silica-based polystyrene films (PS/SiOx), we found a resolution to the inconsistency regarding the effects of nano-confinement on the dynamics of polymer thin films.

The structural and magnetic properties of amorphous Cox(Al80Zr20)1-x multilayers with varying thicknesses of the magnetic bilayers have been investigated. The reduction of the thickness causes a reduction of the critical temperature, Tc, this is known as the finite-size effect. The multilayers were grown using DC magnetron sputtering, co-sputtering was used with cobalt and an Al80Zr20 alloy target to create an amorphous CoAlZr alloy. The total thickness of the multilayers was chosen to be held constant at 60 nm and the Al80Zr20 spacing layers were thick enough to suppress any interlayer exchange coupling effects. Estimating the composition using RBS proved difficult with great uncertainties in the measured amount of aluminium in the samples. The amorphousness of the samples was investigated using GIXRD and all measured samples display x-ray amorphousness. Fits of XRR measurements showed that the bilayers displayed a rather large roughness, the origin of this roughness is unknown. MOKE measurements showed that the CoAlZr alloys exhibit a noncollinear spin structure at magnetic bilayer thicknesses of 6 nm and below. The samples’ noncollinear spin structure lead to the loss of remanence. Attempts at measuring the critical temperature with DC measurements using the remanence at zero field were therefore unsuccessful. AC susceptibility with SQUID should allow an accurate measurement of the critical temperature.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14050号 / 工博第2962号 / 新制||工||1439(附属図書館) / 26329 / UT51-2008-F442 / 京都大学大学院工学研究科電子物性工学専攻 / (主査)教授 鈴木 実, 教授 髙岡 義寛, 教授 藤田 静雄 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14104号 / 工博第2968号 / 新制||工||1440(附属図書館) / 26392 / UT51-2008-L159 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 金谷 利治, 教授 伊藤 紳三郎, 教授 瀧川 敏算 / 学位規則第4条第1項該当

The salient issues of integrated biosensors on a complementary metal-oxide semiconductor (CMOS) platform are the limited transducer design and the need for post-processing. To overcome these issues, a heterogeneously integrated system, which employs both CMOS and large-area processing, was proposed and developed. The system presented, could become a rapid, low-cost and disposable sensing platform for point-of-care applications. The heterogeneously integrated system, comprising a CMOS front-end circuit and disposable electrodes, was applied to measure the impedance of suspended DNA at different concentrations. The measurement showed a double sensitivity compared to the one carried out on the CMOS platform only. The noise analysis of CMOS transimpedance amplifiers was performed, and the impact of technology scaling on low-noise transimpedance amplifiers was studied using the Enz-Krummenacher-Vittoz (EKV) model. It was found that the noise performance improves slowly with device scaling down to 90 nm. Further device scaling may increase the gate leakage current noise due to the very thin gate oxide. Disposable electrodes fabricated using large-area processing are low cost and flexible in terms of design. In particular, inkjet-printed silver electrodes on glossy paper and gold electrodes on the glass substrate were characterised. Both electrodes with the same dimension agreed well in determining solution resistance. In addition, the paper-based electrodes presented an improved sensitivity of impedance measurement at low frequencies. The amorphous oxide thin-film transistor (TFT) is promising for implementing active circuits on disposable substrates. In particular, the low-frequency noise of amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs was characterised, and a TFT-based regulated cascade transimpedance amplifier was designed and simulated with the extracted device parameters. The a-IGZO TFT showed a comparable noise performance to the PMOS device in deep submicron processes. The simulated circuit featured a transimpedance gain up to 120 dB, a bandwidth of 29.4 kHz, input-referred noise PSD of 2.91 pA/√Hz, and a power consumption of 18.55 μW, indicating that TFT-based front-end circuits are promising for implementing low-cost, low-noise and low-power biosensors.

abstract: Proton exchange membrane fuel cells have attracted immense research activities from the inception of the technology due to its high stability and performance capabilities. The major obstacle from commercialization is the cost of the catalyst material in manufacturing the fuel cell. In the present study, the major focus in PEMFCs has been in reduction of the cost of the catalyst material using graphene, thin film coated and Organometallic Molecular catalysts. The present research is focused on improving the durability and active surface area of the catalyst materials with low platinum loading using nanomaterials to reduce the effective cost of the fuel cells. Performance, Electrochemical impedance spectroscopy, oxygen reduction and surface morphology studies were performed on each manufactured material. Alkaline fuel cells with anion exchange membrane get immense attention due to very attractive opportunity of using non-noble metal catalyst materials. In the present study, cathodes with various organometallic cathode materials were prepared and investigated for alkaline membrane fuel cells for oxygen reduction and performance studies. Co and Fe Phthalocyanine catalyst materials were deposited on multi-walled carbon nanotubes (MWCNTs) support materials. Membrane Electrode Assemblies (MEAs) were fabricated using Tokuyama Membrane (#A901) with cathodes containing Co and Fe Phthalocyanine/MWCNTs and Pt/C anodes. Fuel cell performance of the MEAs was examined. / Dissertation/Thesis / Masters Thesis Technology 2014

abstract: Microwave dielectrics are widely used to make resonators and filters in telecommunication systems. The production of thin films with high dielectric constant and low loss could potentially enable a marked reduction in the size of devices and systems. However, studies of these materials in thin film form are very sparse. In this research, experiments were carried out on practical high-performance dielectrics including ZrTiO4-ZnNb2O6 (ZTZN) and Ba(Co,Zn)1/3Nb2/3O3 (BCZN) with high dielectric constant and low loss tangent. Thin films were deposited by laser ablation on various substrates, with a systematical study of growth conditions like substrate temperature, oxygen pressure and annealing to optimize the film quality, and the compositional, microstructural, optical and electric properties were characterized. The deposited ZTZN films were randomly oriented polycrystalline on Si substrate and textured on MgO substrate with a tetragonal lattice change at elevated temperature. The BCZN films deposited on MgO substrate showed superior film quality relative to that on other substrates, which grow epitaxially with an orientation of (001) // MgO (001) and (100) // MgO (100) when substrate temperature was above 500 oC. In-situ annealing at growth temperature in 200 mTorr oxygen pressure was found to enhance the quality of the films, reducing the peak width of the X-ray Diffraction (XRD) rocking curve to 0.53o and the χmin of channeling Rutherford Backscattering Spectrometry (RBS) to 8.8% when grown at 800oC. Atomic Force Microscopy (AFM) was used to study the topography and found a monotonic decrease in the surface roughness when the growth temperature increased. Optical absorption and transmission measurements were used to determine the energy bandgap and the refractive index respectively. A low-frequency dielectric constant of 34 was measured using a planar interdigital measurement structure. The resistivity of the film is ~3×1010 ohm·cm at room temperature and has an activation energy of thermal activated current of 0.66 eV. / Dissertation/Thesis / M.S. Materials Science and Engineering 2013