This thesis is concerned with the chemistry and physics of C(100) surfaces of diamond. The polished and cleaned C(100) surface is examined by surface microscopy (Atomic-force Microscopy), electron diffraction (Low-energy Electron Diffraction) and photoemission (X-ray Photoelectron Spectroscopy and Ultra-violet Photoelectron Spectroscopy). Results are presented on the presence of oxygen, nitrogen and hydrogen/deuterium on the C(100) surface. Finally, the valence band structure of diamond is probed by angle-resolved photoemission. We have confirmed by AFM that the grooves from the soft polishing process are present on a polished C(100) surface and found sporadic traces of hard polish on a surface polished in the soft polishing direction. XPS studies have verified heating cycles by electron beam bombardment as a suitable cleaning procedure for pure reconstructed C(100) surfaces. By allowing the crystal to cool slowly, the first experimental evidence of quarter-order LEED spots have been found, which suggest that buckled dimerisation might have occurred similar to those on Si(100) and Ge(100). We present the first experimental electron spectroscopy results for a nitrogen impurity in diamond by showing the N KLL Auger spectrum. An attempt to smooth a C(100) surface of diamond by an atomic hydrogen plasma did not succeed. AFM studies showed no evidence for the surface smoothing reported in other studies, but the results enable us to explain the different plasma published in the literature. The valence band of diamond is investigated by off-normal ARUPS. The features observed are consistent with possible transitions, which are determined using bulk band structure calculations and comparison with the experimental binding energies.

Electron backscatter diffraction is a method that is well described and commonly used for orientation image mapping, including grain size estimation. The use of this method for measuring elastic deformation and rotations caused by plastic deformations is not so well decribed. This diploma thesis first describes the typical EBSD system. The information regarding the standard coordinate systems, grain orientation notation and system calibration is then used to create an open-source software for mapping elastic deformations and rotations inside a single grain or a monocrystal. This software uses data acquired during standard EBSD mapping on a commercial system.

The high resolution structure of protein molecules and protein-protein complexes is important to investigate their functions. Today, large 3D or 2D crystals are required to obtain protein structures by X-ray crystallography or conventional Electron Microscopy, respectively. However, production of such crystals of good quality is a solely empirical procedure, which relies on screening numerous crystallization conditions. At the same time, multilayered protein crystals are often a by-product of attempts to grow 3D or 2D crystals and could be obtained more easily. So far, multilayered protein crystals have not been used in electron microscopy for structure determination, as the interpretation of an electron diffraction pattern is rather complicated. In this thesis we present the first protein structure bovine liver catalase at 4 Å resolution solved using electron diffraction data from multilayered crystals. 55 diffraction patterns (17 tilt series) were recorded and used for the reconstruction. The tilt geometry of each individual diffraction pattern was determined by a least-squares algorithm or Laue zone analysis to perform spot indexing. The phase problem was solved by molecular replacement. The influence of the missing data cone on the self-rotation function and interpretation of reconstructed map is discussed.

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.

No description available.

Thin metallic films with magnetic properties like magnetite are an interesting material in current technological applications. In the presented work the iron oxide films are grown by molecular beam epitaxy on MgO(001) substrates at temperatures between room temperature and 600K. The film and surface structure are investigated by x-ray reflectometry (XRR), x-ray diffraction (XRD) and low energy electron diffraction (LEED). The chemical properties are investigated by x-ray photoelectron spectroscopy (XPS). Furthermore, charge transfer multiplet (CTM) calculations are performed as a means to gain additional information from photoemission spectra. It is shown that only for temperatures higher than 500K the oxide film forms a spinel structure. A previously unobserved (2x1) surface reconstruction in two orthogonal domains is found for various preparation conditions. The application of CTMs results in good quantitative and qualitative agreement to other methods for the determination of the film stoichiometry. In addition CTMs can well describe the segregation of Mg atoms into the oxide film either during film growth or during film annealing. It is found that initially Mg substitutes Fe on all possible lattice sites, only for prolonged treatment at high temperature do Mg atoms favour the octahedral lattice sites of divalent Fe.

No description available.

No description available.

Measuring atomic displacement inside crystals has been an important field of interest for decades especially in semiconductor industry for its effect on the crystal structure and symmetry, subsequently on the bandgap structure. There are three different image based, diffraction based, and electron holography based techniques using transmission electron microscope (TEM). These methods enable measuring atomic displacement inside specimen. However, among all TEM techniques offering nano-scale resolution measurements, convergent beam electron diffraction (CBED) patterns show the highest sensitivity to the atomic displacement. Higher order Laue zone (HOLZ) lines split by small variations of lattice constant allowing the atomic displacement measurement through the crystal. However it is a cumbersome measurement and it can only reveal the atomic displacement in two dimensions. Therefore, the atomic displacement information at each depth through the specimen thickness is still missing. This information can be obtained by recovering the phase information across the split HOLZ line. The phase profile across the split HOLZ line can be retrieved by the electron interferometry method. The phase of the diffracted beam is the required information to reconstruct the atomic displacement profile through the specimen thickness. In this work, we first propose a novel technique of self-interference of split HOLZ line based on the diffracted beam interferometry which recovers the phase information across the split HOLZ line. The experimental details of the technique have been examined to report the parameters in order to implement the method. Regarding the novelty of the technique and the lack of the of a reference phase profile to discuss the results, phase profile simulation was a main contribution. For simulating the phase profile across the split HOLZ line the Howie-Whelan formula supporting the kinematical theory of diffraction is used. Accordingly, the analytical approach to simulate the phase profiles across the split HOLZ line for three various suggested atomic displacements are studied. Also, the effect of some parameters such as the atomic displacement amplitude, the specimen thickness, and the g reflection is investigated on the phase profile. This study leads to an equation used for fitting the experimental results with the simulated phase profile. Consequently, self-interference of split HOLZ line (SIS-HOLZ) is studied as a method of reconstructing the phase profile across the split HOLZ line which carries the information of atomic displacement through the specimen thickness. / Graduate / 0548 / 0794 / mananrp@uvic.ca

Properties of magnetic thin film devices cannot be understood without detailed knowledge of their structure. For this purpose, a variety of thin film and multilayer systems have been studied. Both reciprocal space (low energy electron diffraction, reflection high energy electron diffraction, X-ray diffraction and reflectometry) and direct space (transmission electron microscopy) as well as Rutherford backscattering spectrometry have been applied. To gain understanding of an oxidation procedure for the growth of magnetite layers, thermal stability of iron layers on molybdenum seed layers has been investigated. Following the mosaicity and the out-of-plane coherence length over different ratios between the constituting layers allowed a deeper understanding of the limits of metallic superlattices. This, together with an approach to use hydrogen in the process gas during magnetron sputter epitaxy, opens routes for the growth of metallic superlattices of superior quality. A non-isostructural multilayer/superlattice system, Fe/MgO, has been investigated. In turn, this gave more understanding how superlattice diffraction patterns are suppressed by strain fields. As an alternative route to single-crystalline superlattices, amorphous multilayers present interesting opportunities. In this context, crystallization effects of iron/zirconium layers on alumiunium oxide were studied. Understanding these effects enables significant improvement in the quality of amorphous multilayers, and allows avoiding these, growing truly amorphous layers. Both the substantial improvement in quality of metallic superlattices, approaching true single-crystallinity, as well as the improvements in the growth of amorphous multilayers give rise to opportunities in the field of magnetic coupling and superconducting spin valves.