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The problem of recovering a wavefront or surface deviation from a fringe pattern image is investigated. The data sets generated in sampling a fringe pattern are considered in the frequency domain and errors that arise in analyzing the pattern are given an aliasing interpretation. Uniform sampling is shown to be superior to other sampling schemes. A variety of techniques for locating fringe centers are reviewed and three synchronous convolution methods are demonstrated that do not require the location of fringe centers. For the latter, direct phase measurements are obtained from fringe pattern photographs over a uniform grid with an accuracy comparable to temporal heterodyne interferometry. Two microprocessor-based video systems are described in which the traditional and synchronous convolution methods were implemented.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 15, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Ping Yu. Vita. Includes bibliographical references.

An algorithm to reduce data from the knife edge test is given. The method is an extension of the theory of single sideband holography to second order effects. Application to phase microscopy is especially useful because a troublesome second order term vanishes when the knife edge does not attenuate the unscattered radiation probing the specimen. The algorithm was tested by simulation of an active optics system that sensed and corrected small (less than quarter wavelength) wavefront errors. Convergence to a null was quadratic until limited by detector-injected noise in signal. The best form of the algorithm used only a Fourier transform of the smoothed detector record, a filtering of the transform, an inverse transform, and an arctangent solving for the phase of the input wavefront deformation. Iterations were helpful only for a Wiener filtering of the data record that weighted down Fourier amplitudes smaller than the mean noise level before analysis. The simplicity and sensitivity of this wavefront sensor makes it a candidate for active optic control of small-angle light scattering in space. In real time optical processing a two dimensional signal can be applied as a voltage to a deformable mirror and be received as an intensity modulation at an output plane. Combination of these features may permit a real time null test. Application to electron microscopy should allow the finding of defocus, astigmatism, and spherical aberrations for single micrographs at 0.2 nm resolution, provided a combination of specimen and support membrane is used that permits some a priori knowledge. For some thin specimens (up to nearly 100 atom layers thick) the left-right symmetry of diffraction should allow reconstruction of the wave-front deformations caused by the specimen with double the bandpass used in each image.

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No description available.

Electron BackScattered Diffraction (EBSD) systems can be considered as a tool providing three kinds of responses: EBSD patterns (EBSPs) themselves, an indexing response (orientation data), and an intensity response (also called Band Contrast "BC", Image Quality "IQ", or Pattern Quality "PQ or P"). This work focused on the characterization and development of the intensity response. For now, the intensity response cannot be used for quantitative microstructural analyses, including strain analyses of materials. Indeed, this response is affected by several material and experimental conditions. Moreover, properties of the intensity response (strain sensitivity, reproducibility, exact relation with EBSP quality or diffraction band intensities) are not well-known and understood. This project constitutes an exploratory study on the development of the intensity response for quantitative strain analyses of materials. A new modelling and statistical approach is presented and assessed for transforming the raw (current) intensity response (values and grey-tones of intensity images) of commercial EBSD systems into an accurate and reproducible parameter allowing objective visualization and measurements of strain. / Les systèmes de diffraction des électrons rétro-diffusés (EBSD) peuvent être considérés comme un outil offrant trois types de réponses: les patrons EBSD (EBSPs), la réponse d'indexation (données d'orientation) et la réponse d'intensité (aussi appelée Contraste de Bande «BC », Qualité d'Image « IQ », ou Qualité de Patron « PQ ou P »). Le présent projet s'est concentré sur la caractérisation et le développement de la réponse d'intensité. En effet, pour l'instant, la réponse d'intensité ne peut être utilisée pour réaliser des analyses microstructurales quantitatives des matériaux. En effet, cette réponse est influencée par de nombreux facteurs relatifs au matériau analysé et aux conditions expérimentales utilisées. De plus, les propriétés de la réponse d'intensité (sensibilité à la déformation, reproductibilité, relation exacte avec la qualité des EBSPs ou les intensités des bandes de diffraction) ne sont pour l'instant pas bien connues ni même compnses. Le présent projet représente donc une étude exploratoire visant le développement de la réponse d'intensité des systèmes EBSD commerciaux pour l'analyse quantitative de la déformation des matériaux. Dans ce projet, une approche de modélisation statistique est présentée et évaluée afin de transformer la réponse d'intensité actuelle (valeurs et tons de gris des images d'intensité) des systèmes EBSD commerciaux en une réponse précise et reproductible permettant de visualiser et de mesurer objectivement la déformation.

Cette thèse s’intéresse à la croissance épitaxiale à basse température (~200°C) des couches minces de silicium par dépôt chimique en phase vapeur assisté par plasma (PECVD), pour des applications aux cellules solaires. L’objectif de départ était de mieux comprendre cette croissance épitaxiale, en utilisant la microscopie électronique en transmission (MET) comme principal outil expérimental. D’abord, nous avons étudié les premiers stades de cette croissance épitaxiale en chimie SiF4/H2/Ar, en menant une série de dépôts courts – quelques dizaines jusqu’à quelques centaines de secondes – sur différents types de substrats. Nous avons établi une corrélation entre les images MET de coupes et de vues planes et les mesures d’ellipsométrie in-situ. Nous avons discuté les mécanismes de croissance en nous basant sur l’hypothèse de la croissance traditionnelle à base d’atomes, radicaux et ions et l’hypothèse (relativement nouvelle) reposant sur la fonte des nanoparticules générées par le plasma au moment de l’impact avec le substrat. De plus, pour comprendre comment l’épitaxie par PECVD à basse température se maintient, nous avons étudié comment elle se brise ou se perd. Pour cela, des expériences de perte d’épitaxie ont été visées en augmentant soit la puissance de la source RF, soit le flux d’hydrogène, toujours pour une chimie SiF4/H2/Ar. Dans les deux cas, le mécanisme de brisure d’épitaxie fait intervenir des macles et des fautes d’empilement qui interrompent la configuration épitaxiale ; ceci est accompagné par une rugosification de surface. Grâce à cette nouvelle compréhension de la brisure d’épitaxie, nous proposons quelques moyens pour maintenir l’épitaxie pour de plus grandes épaisseurs. En outre, nous avons observé une fascinante quasi-symétrie cinq dans les diagrammes de diffraction pour ces couches et aussi pour d’autres élaborées par un plasma de chimie SiH4/H2/HMDSO/B2H6/Ar. Nous avons attribué une telle symétrie à une brisure d’épitaxie par l’intermédiaire d’un maclage multiple. Nous avons développé une méthode d’analyse quantitative qui permet de discriminer les positions de maclage de celles du microcristal aléatoire dans les diagrammes de diffraction et d’estimer le nombre des opérations de maclage. Nous avons aussi discuté quelques raisons probables pour l’incidence du maclage et du maclage multiple sous forme de symétrie cinq. Finalement, une importante réalisation pour le monde de la MET, durant ce travail doctoral, a été l’optimisation de la préparation traditionnelle d’échantillon (polissage par tripode). Nous l’avons transformée d’une méthode longue et ennuyeuse en une méthode rapide qui devient compétitive par rapport à la technique du FIB relativement chère. / This thesis focuses on low temperature (LT, ~200°C) epitaxial growth of silicon thin films by plasma enhanced chemical vapor deposition (PECVD) for solar cell applications. Our starting goal was to acquire a better understanding of epitaxial growth, by using transmission electron microscopy (TEM) as the main experimental tool. First, we investigated the initial stages of epitaxial growth using SiF4/H2/Ar chemistry by performing a series of short depositions – from few tens to few hundred of seconds – on different types of substrates. We made a correlation between cross-sectional and plan-view TEM images and in-situ ellipsometry measurements. We discussed the growth mechanisms under the hypotheses of the traditional growth mediated by atoms, radicals and ions and the relatively new approach based on the melting of plasma generated nanoparticles upon impact with the substrate. Additionally, in order to understand how epitaxy by LT-PECVD is sustained, we studied how it is lost or how it breaks down. For that, experiments of intentional breakdown of epitaxy were performed by either increasing the RF power or the hydrogen flow rate using the same SiF4/H2/Ar chemistry. In both cases, the breakdown mechanism was based on the development of twins and stacking faults thus disrupting epitaxial configuration; this was accommodated with surface roughening. Thanks to this new understanding of epitaxy breakdown, we can propose some ways to sustain epitaxy for higher thicknesses. Moreover, we fascinatingly observed a quasi-fivefold symmetry in the diffraction patterns for these layers and for layers deposited using SiH4/H2/HMDSO/B2H6/Ar plasma chemistry as well. We attributed such symmetry to the breakdown of epitaxy through multiple twinning. We developed a quantitative analysis method to discriminate twin positions from random microcrystalline ones in the diffraction patterns and to estimate the number of twin operations. We also discussed some probable reasons for the occurrence of twinning and multiple twinning in a fivefold symmetry fashion. Finally, one important achievement to the TEM world is the optimization, during this doctoral work, of the traditional TEM sample preparation (tripod polishing), transforming it from a long and boring method to a fast method that is competitive with the relatively expensive focus ion beam (FIB) technique.

Although the study of the interaction of acoustic and elastic waves with periodic surfaces and structures has a rich history dating back to Lord Rayleigh, it has recently been attracting new research efforts due to its value in the study of phononic crystals and in methods for ultrasonic non-destructive evaluation (NDE). The objective of the research described in this thesis is to provide new numerical and experimental tools capable of capturing important features that occur due to the diffraction of ultrasound on periodic solid surfaces. This thesis is divided into four main parts. First, the Rayleigh-Fourier (R-F) method will be used to simulate diffracted fields generated by structures containing multiple periodic surfaces and/or multiple solid layers. The second part of this thesis examines diffraction effects and compares ultrasonic NDE techniques for surfaces with imperfect periodicities. The third portion of this thesis focuses on one unusual phenomenon that has been observed on periodic surfaces, namely the lateral backward displacement of a bounded ultrasonic beam along the surface. This effect is currently understood to occur due to backward propagating surface waves that result from diffraction and mode conversion on the surface. The fourth and final part of this thesis describes the diffraction of bulk ultrasonic waves that can occur on the surfaces of phononic crystals.