Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 325-331).

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La technique Imagerie par Contraste de Canalisation d'Electron (ECCI) est utilisée en microscopie électronique à balayage (MEB) pour visualiser et caractériser des défauts cristallins tels que les dislocations. L’ECCI nécessite l'orientation, avec grande précision (meilleure que 0,1°), du cristal à analyser par rapport au faisceau d’électrons pour satisfaire les conditions très strictes de canalisation d'électrons. À cause de la limitation en résolution spatiale et angulaire des techniques actuelles permettant de déterminer l’orientation cristallographique, la caractérisation des défauts cristallins par ECCI est actuellement appliquée à des monocristaux (ou des polycristaux possédant des gros grains) et les conditions de canalisation ne sont pas toujours satisfaites. Dans ce projet de thèse, un mode de balayage Précession de faisceau (Rocking Beam en anglais) a été développé dans un microscope électronique à balayage. Il permet l’acquisition de diagrammes pseudo-Kikuchi haute résolution spatiale (500nm) et angulaire (0,04°) (High Resolution Selected Area Channeling Pattern en anglais (HR-SACP)) et de contrôler les conditions de canalisations nécessaire à l’ECCI. Ceci a permis d’améliorer considérablement la précision de l’ECCI (Accurate ECCI A-ECCI) et d’élargir son domaine d’application aux matériaux polycristallins à grains fins. Dans un deuxième temps, l’A-ECCI assistée par HR-SACP a été utilisé pour caractériser des défauts cristallins (dislocations, sous joint de grain, domaine d’ordre) dans des matériaux massifs polycristallins (Acier IF, UO2, TiAl). Des procédures similaires à celles utilisées dans la microscopie électronique en transmission (MET) sont alors appliquées en s’affranchissant de la préparation fastidieuse de lames minces et en profitant des autres avantages du MEB / Electron Channeling Contrast Imaging (ECCI) is a Scanning Electron Microscope (SEM) technique used to observe and characterize crystallographic defects. ECCI requires the crystal to be oriented relative to the electron beam with high accuracy (0.1°) in order to control the electron channeling conditions. The SEM techniques used to determine the crystallographic orientation, such as conventional Electron BackScattered Diffraction (EBSD) or Rocking Beam, don’t satisfy the high accuracy required for ECCI. Therefore, the characterization of crystallographic defects by ECCI is used only in single crystals or polycristals with large grains and channeling conditions are not always satisfied. In this thesis, a development of a new Rocking Beam mode in SEM is presented. It allows the collection of High spatial (500nm) and angular (0.04°) Resolution Selected Area Channeling Pattern (HR-SACP) and the control of channeling conditions required for ECCI with high accuracy (Accurate ECCI A-ECCI). In a second phase of this thesis, A-ECCI assisted by HR-SACP is used to characterize crystallographic defects like dislocation, sub-grains and order domains in fine grained bulk materials (IF-Steel, UO2, TiAl). In order to achieve this, several procedures (invisibility criteria) normally used in Transmission Electron Microscopy are applied. Using A-ECCI in SEM has many advantages over TEM such as the possibility of analyzing large areas and the relative easiness in sample preparation

In order to increase efficiency and lifetime of cutting tools it is typical to apply thin coatings by physical or chemical vapour deposition. Applying coatings on cutting tools has shown an increase in both efficiency and lifetime and are of large interest in further development. The study of coatings and their mechanical properties is a very active research area and produces tools extensively used in the industry.  The behaviour of materials on a macroscopic scale can typically be related to microscopic properties. Some coatings produced by Chemical Vapour Deposition (CVD) but especially Physical Vapour deposition (PVD) have crystal structures which are difficult to analyse by conventional methods due to crystal sizes in the nanometre scale. For nanocrystalline materials standard methods fall short due to a limited resolution of the methods.  Recently a method for electron diffraction of crystalline samples was suggested to be used differently in order to achieve a higher resolution. Unlike earlier when electrons were reflected from the sample, using Electron Backscattering Diffraction (EBSD), the electrons were transmitted through thin samples with thicknesses in the magnitude of 100 nm, which enabled the crystal structure to be determined. The new method is typically referred to as either Transmission Kikuchi Diffraction (TKD) or transmission EBSD (t-EBSD) with a resolution down to approximately 10 nm.  The goal with this master thesis has been to evaluate sample preparation methods and TKD studies on PVD samples. Each step has been divided into parameters which govern the sample preparation and analysis and optimized accordingly in order to achieve best possible results of the crystal structure of PVD coatings. From this it has been possible to show how TKD is optimally performed and which difficulties and limitations that are present.  In this thesis two coatings, TiN and (Ti,Al)N, have been studied with TKD and two different preparation methods have been attempted. These were precision mechanical polishing and in-situ lift out with a Dual Beam System. Mechanical polishing did not succeed in producing samples for TKD but was not ruled out as a possibility while the in-situ lift out method could both produce samples and achieve a crystallographic indexing around 80 %. The only areas which were difficult to index were crystal boundaries and crystal clusters where individual crystals were in the range of <30 nm. In these areas overlapping Kikuchi patterns were observed due to the resolution limit of TKD.

Zr cladding alloys have been used for many years as the first safety barrier layer of a nuclear reactor. However, the recent Fukushima accidents and industrial demands to increase the burnup of fuels have led to increasing interest in a detailed mechanistic understanding of aqueous corrosion and hydrogen pickup and the performance at high temperatures. As part of an international MUZIC-2 programme (Mechanistic Understanding of Zr Corrosion and Hydrogen pickup), I have used a range of advanced microscopy techniques to study the microstructure, the nanoscale chemistry and the porosity in a series of zirconium alloys at different stages of corrosion and hydrogen pickup. Samples from both autoclave and in-reactor conditions were available to compare, I have focussed on RXA (recrystallised 580°C) Zr-1.0Nb and annealed (720°C) Zr-1.0Nb alloys. A set of samples from different exposures times were chosen to represent early, pre-transition and post-transition samples in order to compare the microstructure and microchemistry of the oxides, the metal-oxide interface and the metal. (Scanning) Transmission Electron Microscopy ((S)TEM), Transmission Kikuchi Diffraction (TKD) and automated crystal orientation mapping with TEM (ASTAR mapping) were used to study the grain structure and phase distribution. Significant differences in grain morphology were observed between samples oxidised in the autoclave with different corrosion rates, with more uneven metal-oxide interface, more parallel cracks and less organised oxide grains in the fast corroding samples. Comparing with autoclave samples, the in-reactor samples have shorter, less well-aligned monoclinic grains and more tetragonal grains. The rapidly oxidising annealed Zr-1.0Nb alloy also have much higher tetragonal grain fraction comparing with the slow corrosion rate RXA Zr-1.0Nb alloys. Porosity in the oxide is predicted to have a major influence on the overall rate of corrosion and hydrogen pickup, and there is much more porosity in the annealed Zr-1.0Nb alloy than found in either the RXA alloy or the similar alloy exposed to neutron irradiation. A combination of Energy Dispersion X-ray (EDX) mapping in STEM and Electron Energy Loss Spectroscopy (EELS) analysis of second phase particles can reveal the main and the minor element distributions respectively. The annealed Zr-1.0Nb alloys have Î2-Zr SPPs with nano crystalline structure and much larger size. Although they does not relate with the higher density of cracks in the oxide, the large SPP size can connect together all the small cracks that are generated by the huge amount of tetragonal to monoclinic phase transformation during corrosion and provides pathway for corrosion and hydrogen pickup. Two kinds of SPPs are found in the RXA Zr-1.0Nb alloys, one is Î2-Nb and another one is Zr-Nb-Fe Laves phase. Neutron irradiation seems to have little effect on promoting fast oxidation or dissolution of Î2-Nb precipitates, but encourages dissolution of Fe from Laves phase precipitates. Electron Energy Loss Spectroscopy (EELS) analysis of the oxidation state of Nb in Î2-Nb SPPs in the oxide revealed the fully oxidised Nb⁵⁺ state in the SPPs deep into the oxide, but Nb²⁺ in the crystalline SPPs near the metal-oxide interface. EELS, TKD and ASTAR mapping have also revealed the presence of suboxide layers with the hexagonal ZrO structure predicted by ab initio modelling. The combined thickness of the ZrO suboxide and oxygen-saturated layers at the metal-oxide interface correlates well to the estimated instantaneous oxidation rate, suggesting that the presence of this oxygen- rich zone combining with the part where porosity is not interconnected is the protective oxide that is rate limiting in the key in the transport processes involved in corrosion and hydrogen pickup.

Die Arbeit beschäftigt sich mit zerstörungsfreien Untersuchungen von Kristalldefekten an kompakten Proben mittels röntgenographischer Kossel- u. Weitwinkel-Mikrobeugung im Rasterelektronenmikroskop. Das REM wurde durch ein neu entwickeltes Aufnahmeverfahren so erweitert, daß die äußerst intensitätsschwachen Kossel-Röntgeninterferenzen mittels Phosphorszintillator und hochauflösendem, extrem empfindlichen CCD-Flächendetektor registriert werden können. Das aufwendige Röntgenfilmverfahren wurde damit abgelöst. Die Aufnahme-Techniken wurden so kombiniert, daß die sich gegenseitig ergänzenden Methoden, v.a. die Kossel- u. Pseudo-Kossel-, aber auch die Rückstreu-Elektronen-Beugung, erstmals mit einem einzigen CCD-System im REM ausführbar sind. Die Aufnahme von Kikuchi-Bändern wurde so weit verbessert, daß diese erstmalig bei vertikaler Inzidenz des Elektronenstrahls auf der Probe beobachtet werden konnten. Durch Einsatz einer fokussierenden Polykapillarlinse in einem Röntgenfluoreszenzspektrometer konnte die Anregung von Kossel-Linien durch Bremsstrahlung und erheblich kürzere Belichtungszeiten sowie deutlich höhere laterale Auflösungen erzielt werden. Für die komplementären Mikrobeugungsmethoden wurde ein einheitliches Programm entwickelt, dessen neue Art der Simulation komplizierter Weitwinkel-Kurven 4. Ordnung die Lokalisierung von Gitterbaufehlern im kompakten Kristall ermöglichte. Entsprechende Simulationen und Verfeinerungen der Kanüle erlaubten in feinkörnigen Polykristallen, wie Bariumtitanat, eine Einzelkornanalyse mit der Weitwinkel-Beugung. Insbesondere wurden markante Erhöhungen der Versetzungsdichte nahe der Korngrenze einzelner Kristallite in FeAl festgestellt. An intermetallischen Fe-Al-Verbindungen wurden in Weitwinkel-Kurven Feinstrukturen gefunden, die sich durch Umweganregungen in Zusammenhang mit Überstrukturen erklären lassen. An zugverformten Ni-Kristallen wurden Kossel- u. Weitwinkel-Linienbreiten in Abhängigkeit des Azimuts im symmetrischen Bragg-Fall ausgewertet u. mit theoretischen Modellen verglichen. Anisotrope Linienverbreiterungen durch die Wirkung von Stufenversetzungen konnten quantitativ nachgewiesen werden. Erste Kossel- u. Weitwinkel-Untersuchungen an zyklisch verformten Ni-Einkristallen zeigten, daß beobachtete perlenkettenförmige Intensitätsanhäufungen an Weitwinkelreflexen die Konfiguration von Versetzungswänden aus Stufenversetzungsdipolen im Kristallvolumen widerspiegeln. Erstmals konnte der Einfluß von Stapelfehlern auf Weitwinkel-Linien, der sich durch linsenförmige Intensitätsaufspaltungen zeigte, experimentell nachgewiesen, theoretisch erklärt und quantitativ bestimmt werden. / The thesis deals with the nondestructive investigation of crystal defects by X-ray Kossel and Pseudo Kossel microdiffraction on compact specimens in the scanning electron microscope. The SEM was extended by means of a newly developed detection method in such a way that X-ray Kossel interferences, which are extremely faint in intensity, can be observed by a phosphor scintillator as well as a high resolution and ultra-sensitive CCD area detector. The demanding X-ray film method was thus replaced. The observation techniques were combined so that the mutually complementary methods, above all the Kossel and Pseudo Kossel, but also the electron backscattered diffraction, are made possible for the first time by using just one CCD system in the SEM. The detection of Kikuchi bands was improved to such a degree that these could be recorded even at vertical incidence of the electron beam on the specimen for the first time. It was shown that the lateral resolution of the Kossel technique under polychromatic X-ray tube excitation could be enhanced considerably and the exposure times strongly reduced by using a polycapillary lens in an X-ray fluorescence spectrometer. For the complementary microdiffraction methods a homogeneous simulation program was developed, whose novel way of simulating the complicated Pseudo Kossel curves of the fourth order enable the lattice defect localization in compact crystals. The corresponding simulations and refinements of the target tube allowed a single grain analysis also in fine-grained polycrystals like barium titanate with Pseudo Kossel X-ray diffraction. Particularly, a marked increase of the dislocation density was ascertained near the grain boundary of individual crystallites in FeAl. At intermetallic Fe-Al compounds Pseudo Kossel curves fine structures were found, which can be explained by umweg (detour) excitations in relation to superstructures. Kossel and Pseudo Kossel line widths were analyzed in dependence on the azimuth and compared with theoretical models at tensile deformed Ni-crystals in the symmetrical Bragg case. Anisotropic line broadenings through the effect of edge dislocations could be proved quantitatively. Conclusions could be drawn from the initial Kossel and Pseudo Kossel investigations of cyclically deformed nickel crystals with respect to the observed pearl-necklace-like intensity thickening at Pseudo Kossel lines reflecting the strong local variations of the dislocation density and, thus, the configuration of dislocation walls of edge dislocation dipoles inside the crystalline volume. For the first time, the effect of stacking faults on Pseudo Kossel reflections appearing by lens-shaped intensity splittings could be proved experimentally, explained theoretically and determined quantitatively.

Die Arbeit beschäftigt sich mit zerstörungsfreien Untersuchungen von Kristalldefekten an kompakten Proben mittels röntgenographischer Kossel- u. Weitwinkel-Mikrobeugung im Rasterelektronenmikroskop. Das REM wurde durch ein neu entwickeltes Aufnahmeverfahren so erweitert, daß die äußerst intensitätsschwachen Kossel-Röntgeninterferenzen mittels Phosphorszintillator und hochauflösendem, extrem empfindlichen CCD-Flächendetektor registriert werden können. Das aufwendige Röntgenfilmverfahren wurde damit abgelöst. Die Aufnahme-Techniken wurden so kombiniert, daß die sich gegenseitig ergänzenden Methoden, v.a. die Kossel- u. Pseudo-Kossel-, aber auch die Rückstreu-Elektronen-Beugung, erstmals mit einem einzigen CCD-System im REM ausführbar sind. Die Aufnahme von Kikuchi-Bändern wurde so weit verbessert, daß diese erstmalig bei vertikaler Inzidenz des Elektronenstrahls auf der Probe beobachtet werden konnten. Durch Einsatz einer fokussierenden Polykapillarlinse in einem Röntgenfluoreszenzspektrometer konnte die Anregung von Kossel-Linien durch Bremsstrahlung und erheblich kürzere Belichtungszeiten sowie deutlich höhere laterale Auflösungen erzielt werden. Für die komplementären Mikrobeugungsmethoden wurde ein einheitliches Programm entwickelt, dessen neue Art der Simulation komplizierter Weitwinkel-Kurven 4. Ordnung die Lokalisierung von Gitterbaufehlern im kompakten Kristall ermöglichte. Entsprechende Simulationen und Verfeinerungen der Kanüle erlaubten in feinkörnigen Polykristallen, wie Bariumtitanat, eine Einzelkornanalyse mit der Weitwinkel-Beugung. Insbesondere wurden markante Erhöhungen der Versetzungsdichte nahe der Korngrenze einzelner Kristallite in FeAl festgestellt. An intermetallischen Fe-Al-Verbindungen wurden in Weitwinkel-Kurven Feinstrukturen gefunden, die sich durch Umweganregungen in Zusammenhang mit Überstrukturen erklären lassen. An zugverformten Ni-Kristallen wurden Kossel- u. Weitwinkel-Linienbreiten in Abhängigkeit des Azimuts im symmetrischen Bragg-Fall ausgewertet u. mit theoretischen Modellen verglichen. Anisotrope Linienverbreiterungen durch die Wirkung von Stufenversetzungen konnten quantitativ nachgewiesen werden. Erste Kossel- u. Weitwinkel-Untersuchungen an zyklisch verformten Ni-Einkristallen zeigten, daß beobachtete perlenkettenförmige Intensitätsanhäufungen an Weitwinkelreflexen die Konfiguration von Versetzungswänden aus Stufenversetzungsdipolen im Kristallvolumen widerspiegeln. Erstmals konnte der Einfluß von Stapelfehlern auf Weitwinkel-Linien, der sich durch linsenförmige Intensitätsaufspaltungen zeigte, experimentell nachgewiesen, theoretisch erklärt und quantitativ bestimmt werden. / The thesis deals with the nondestructive investigation of crystal defects by X-ray Kossel and Pseudo Kossel microdiffraction on compact specimens in the scanning electron microscope. The SEM was extended by means of a newly developed detection method in such a way that X-ray Kossel interferences, which are extremely faint in intensity, can be observed by a phosphor scintillator as well as a high resolution and ultra-sensitive CCD area detector. The demanding X-ray film method was thus replaced. The observation techniques were combined so that the mutually complementary methods, above all the Kossel and Pseudo Kossel, but also the electron backscattered diffraction, are made possible for the first time by using just one CCD system in the SEM. The detection of Kikuchi bands was improved to such a degree that these could be recorded even at vertical incidence of the electron beam on the specimen for the first time. It was shown that the lateral resolution of the Kossel technique under polychromatic X-ray tube excitation could be enhanced considerably and the exposure times strongly reduced by using a polycapillary lens in an X-ray fluorescence spectrometer. For the complementary microdiffraction methods a homogeneous simulation program was developed, whose novel way of simulating the complicated Pseudo Kossel curves of the fourth order enable the lattice defect localization in compact crystals. The corresponding simulations and refinements of the target tube allowed a single grain analysis also in fine-grained polycrystals like barium titanate with Pseudo Kossel X-ray diffraction. Particularly, a marked increase of the dislocation density was ascertained near the grain boundary of individual crystallites in FeAl. At intermetallic Fe-Al compounds Pseudo Kossel curves fine structures were found, which can be explained by umweg (detour) excitations in relation to superstructures. Kossel and Pseudo Kossel line widths were analyzed in dependence on the azimuth and compared with theoretical models at tensile deformed Ni-crystals in the symmetrical Bragg case. Anisotropic line broadenings through the effect of edge dislocations could be proved quantitatively. Conclusions could be drawn from the initial Kossel and Pseudo Kossel investigations of cyclically deformed nickel crystals with respect to the observed pearl-necklace-like intensity thickening at Pseudo Kossel lines reflecting the strong local variations of the dislocation density and, thus, the configuration of dislocation walls of edge dislocation dipoles inside the crystalline volume. For the first time, the effect of stacking faults on Pseudo Kossel reflections appearing by lens-shaped intensity splittings could be proved experimentally, explained theoretically and determined quantitatively.

Crystalline films of vanadium dioxide were obtained through thermal annealing of amorphous vanadium dioxide thin films sputtered on silicon dioxide. An annealing process was found that yielded polycrystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated single-crystal particles. Orientation Imaging Microscopy (OIM) was used to characterize and study the phase and the orientation of the vanadium dioxide crystals obtained, as well as to diferentiate them from other vanadium oxide stoichiometries that may have formed during the annealing process. There was no evidence of any other vanadium oxides present in the prepared samples. Indexing of the crystals for the orientation study was performed with the Kikuchi patterns for the tetragonal phase of vanadium dioxide, since it was observed that the Kikuchi patterns for the monoclinic and tetragonal phases of vanadium dioxide are indistinguishable by OIM. It was found that a particle size of 100 nm was in the lower limit of particles that could be reliably characterized with this technique. It was also found that all VO2 crystals large enough to be indexed by OIM had a preferred orientation with the C axis of the tetragonal phase parallel to the plane of the specimen.