The localised corrosion behaviour of various grades of Austenitic Stainless Steels has been demonstrated by optical and electron microscopy. The effect of sensitisation upon subsequent corrosive attack has been investigated. A theoretical model based upon thermodynamic and kinetic considerations has been proposed to account for the observed experimental results. / Thesis / Master of Engineering (ME)

Scanning Electron Microscopy combined with Energy Dispersive X-ray Spectroscopy (SEM-EDS) is a widely applied elemental microanalysis method. The integration of silicon drift detectors (SDDs) has notably enhanced EDS performance, enabling precise elemental identification due to its large sensitive area and low output capacitance.  Accurate simulations of SDDs can provide insights that enable the design and optimization of future models without the need for costly and time-consuming experimental iterations. Moreover, the current model-based quantification methods for EDS applications have reached their maximum predictive accuracy. As such, creating a more accurate simulation model could help achieve a higher level of precision in these quantification models, which would be immensely valuable for all EDS applications.  With this objective in mind, a simulation framework for modeling SDDs in EDS was developed based on Geant4, Allpix Squared, and COMSOL Multiphysics. The simulation encompasses the entire physics pipeline, including characteristic X-ray emission from the target sample and its absorption in the detector. The generated charge carriers within the detector are propagated through the internal electric field of the SDD, and their individual charge contribution is measured to simulate EDS spectra. The simulated model was compared to existing literature and in-house experimental measurements, showing strong agreement in the case of a well-tuned SDD. Limitations of the simulation framework are discussed, and further research to enhance accuracy and speed is explored.

Ion channels are fundamental to the functioning of life, regulating processes as diverse as neural signaling, homeostasis, and environmental sensing, across the complexities of life from bacteria to the most advanced organisms. Among this vast diversity of ion channels, cyclic-nucleotide gated (CNG) channels hold particular significance and play a pivotal role in the sensory transduction across a variety of species. They transduce chemical signals into electrical signals, linking the external environment and our sensory perceptions. CNG channels were discovered almost 40 years ago and much knowledge has been gained on their physiological roles, biophysical properties, molecular characteristics, and channelopathies. However, the structural details of these channels remained elusive for a long time, mainly due to the lack of a full-length channel structure. It was only recently that atomic-resolution structures of full-length CNG channels became available, and structures of native mammalian CNG channels were only determined within the last two years. In my thesis, I use single particle cryogenic electron microscopy (cryo-EM) to determine the structures of native human cone CNGA3/CNGB3 channel in different biochemical environments and in different states, spanning the full spectrum of channel activation by its natural ligand cGMP. In addition, I use cryo-EM, electrophysiology, calcium imaging, and other biochemical techniques to characterize both wild-type and disease-associated mutant (DAM) CNG channels. Collectively, my thesis work contributes to a deeper understanding of the structural determinants of CNG channel properties, provides a detailed dissection of the CNG channel gating mechanism, demonstrates a potential CNG channel pathogenic mechanism, and calls for an interdisciplinary reevaluation of CNG channel DAMs.

In this thesis, we present three novel algorithms. The first algorithm is a method of identifying numerical landmarks (a definition coined in this thesis). The second algorithm uses the projection of image regions onto x- and y- axes and the matching of the resulting 1D projections to determine an overall 2D translation for use in registration. The third algorithm aligns SEM images of successive layers of a semiconductor device by first extracting the positions of vias in the lower layer, and then searching for the best translation for subsets of vias such that they all or mostly connect to metalization in the upper layer. / To acquire high-resolution Scanning Electron Microscopy (SEM) images over wide areas, we must acquire several images ``tiling'' the surface and assemble them into a single composite image, using a process called image stitching. While for some applications, stitching is now routine, SEM mosaics of semiconductors pose several challenges: (1) by design, the image features (wire, via and dielectric) are highly repetitive, (2) the overlap between image tiles is small, (3) sample charging causes intensity variation between captures of the same region, and (4) machine instability causes non-linear deformation within tiles and between tiles. In this study, we compare the accuracy and computational cost of three well-known pixel-based techniques: Fast Fourier Transform (FFT), Sum of Squared Differences (SSD), and Normalized Cross Correlation (NCC). We compare well-known 2D algorithms, as well as novel projection-onto-1D versions. The latter reduces the computational complexity from O(n^2) to O(n), where n is the number of pixels, without loss of accuracy, and in some cases, with greater accuracy. Another approach to reducing the computational complexity of image alignment is to compare isolated landmarks, rather than pixels. In semiconductor images, there are no natural fiducials and adding them would destroy the information required to reconstruct their circuits, so we introduce a new class of landmarks which we call numerical landmarks. Related to Harris corners, the novel numerical landmarks are insensitive to brightness variations and noise. Finally, we consider the alignment problem between layers of image mosaics. Unlike in the ``horizontal'' directions, the vertical dimension is only sparsely sampled. Consequently, image features and landmarks cannot be used for alignment. Instead, we must rely on the relationship between vias (through-plane metalization) and wires (in-plane metalization), and we have developed a novel algorithm for matching vias in the lower layer with wires above, and use this to align subimages. / Thesis / Doctor of Philosophy (PhD) / Applications in materials science often require the acquisition of images of semiconductor computer chips at very high resolution. Using cameras with even tens of millions of pixels might not give us enough resolution over a wide field of view. One approach is to acquire several images of parts of the sample at high magnification and assemble them into a single composite image. This way, we can preserve the high resolution over a wide area. Algorithms developed for assembling the composite image are known as tiling or mosaicing. This whole process is known as image stitching (and includes image registration). In this thesis, we develop specialized algorithms suited for the 2D stitching of semiconductor images, including the generalization to 3D. This case is challenging because slight alignment errors may completely change the reconstructed circuit, and the images contain both repeated patterns (such as many parallel wires) and changes in brightness and distortions caused by the scanning device.

The application of the entropy concept to stabilize oxide systems opens the possibility of discovering new materials with unique structural and functional properties. High-entropy alloys and oxides, which are based on the entropy stabilization concept and composed of multi-principal elements, have the potential to tailor structural and functional properties to meet specific needs. The study of lanthanum-based perovskite materials that benefit from the entropy stabilization approach is a promising area of research.However, the inherent randomness of multi-principal elements presents new challenges, making it difficult to predict their behavior. To understand these difficulties, we have initiated a methodical investigation of La-based medium- and high-entropy perovskite oxides. This study focuses on the synthesis, characterization, sintering mechanism, and electrical conductivity properties of nine La1-xCax(A1/3, B1/3, C1/3)O3 medium-entropy perovskite oxide systems (A, B, and C = three combination of Cr or Co or Fe or Ni or Mn) and one La1-xCax(Cr0.2Co0.2Fe0.2Ni0.2Mn0.2)O3 high-entropy perovskite oxide system (for x = 0.1 to 0.3). This research aims to provide better understanding of: (1) synthesis process, (2) temperature of single-phase formation, (3) the impact of various combinations of multiple B-site transitional elements and Ca doping on crystal structure, and microstructure (4) sintering mechanism and (5) electrical conductivity properties.

In dieser Arbeit wurde in situ TEM genutzt, um Phasendiffusionsprozesse in Echtzeit mit hoher räumlicher Auflösung während struktureller Übergangsphänomene in verschiedenen Systemen zu untersuchen, die durch eine zunehmende Anzahl von Einflussparametern wie Kristallorientierung oder Dehnung charakterisiert sind. Zur Entwicklung und Erprobung der Methode wurde die Interdiffusion an planaren Grenzflächen zwischen (Al,Ga)As-Schichten unterschiedlicher Zusammensetzung während des Glühens untersucht. Ein neuer hybrider Probenpräparationsansatz wurde verwendet, um die Interdiffusion in der Heterostruktur bei Temperaturen bis zu 800 Grad Celsius mit der in situ Weitwinkel-Dunkelfeld-Rastertransmissionselektronenmikroskopie (HAADF STEM) zu untersuchen. Die beobachtete Grenzflächenverbreiterung zeigte eine starke Abhängigkeit der Diffusionskoeffizienten von der lokalen Zusammensetzung von Al und Ga. Als nächstes wurde HAADF STEM verwendet, um die Phasenseparationsbildung von Bi-reichen Clustern in einem Ga(Sb,Bi)-Film direkt zu beobachten. Die Ergebnisse zeigten, dass sie sich durch spinodale Zersetzung bilden. Der komplexeste strukturelle Übergang, der in dieser Arbeit untersucht wurde, ist die Festphasenepitaxie (SPE) von Ge auf Fe3Si, die zur Bildung einer neuartigen epitaktisch stabilisierten FeGe2-Phase führt. Mittels in situ hochauflösendem (HR)TEM konnten die verschiedenen Schritte dieses Phasenübergangs alle in Echtzeit beobachtet werden. Die Ergebnisse zeigten, dass eine intermediäre CsCl-ähnliche Phase von FeGe2 zunächst durch einen diffusionsbegrenzten Prozess Schicht für Schicht von der Ge/Fe3Si-Grenzfläche aus wächst. Nach einer bestimmten Filmdicke wandelt eine zweite Umwandlung den Film in eine tetragonale Schichtstruktur von FeGe2 um. Dieser Prozess beginnt ebenfalls an der Grenzfläche zum FeGe2 und kann auf Gitterdehnung zurückgeführt werden. / In this work, in situ TEM was utilized to investigate phase diffusional processes in real time with high spatial resolution during structural transition phenomena in various systems which are characterized by an increasing number of impact parameters such as crystal orientation or strain. In order to develop and evaluate the experimental method interdiffusion at planar interfaces between (Al,Ga)As layers of different composition during annealing was investigated. A new hybrid sample preparation approach was used to investigate the interdiffusion in the heterostructure at temperatures up to 800 _C with in situ high angle annular dark field scanning transmission electron microscopy (HAADF STEM). The observed interface broadening revealed a strong dependence of the diffusion coefficients on the local composition of Al and Ga. Next in situ HAADF STEM was used to directly observe the phase separation formation of Bi-rich clusters in a Ga(Sb,Bi) film. The results showed that they form by spinodal decomposition. The most complex structural transition investigated in this work is the solid phase epitaxy (SPE) of Ge on Fe3Si resulting in the formation of a novel epitaxially stabilized FeGe2 phase. By using in situ high resolution (HR)TEM the different steps of this phase transition could all be observed in real time. The results showed that an intermediate CsCl-like phase of FeGe2 grows first by a diffusion limited process layer-by-layer from the Ge/Fe3Si interface. After a certain film thickness, a second transformation transforms the film into a tetragonal layered structure of FeGe2. This process also initiates at the interface to the FeGe2 and can be attributed to strain.

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