X-ray diffraction topography, using both conventional and synchrotron sources, has been employd t reveal, to a resoltuoon of 1um, internal structural imperfections in diamonds from Brazil. Many of these diamonds were found to be twinned; and X-ray studies have been made of twinned diamonds from Brazil and elsewhere, in order to elucidate the mechanisms of twinning in diamond. Numerous X-ray topographs have been taken of contact twins (mcles), interpenetrant cubes and mulitple twins. The well collimated beam of synchrotron radiation at the SERV Daresbury Laboratory has proved most useful in revealing, in the forward reflexion Laue photographers, small twinned regions of diamons: the presence of which would have been mised by conventioanl methods.

abstract: Stress-related failure such as cracking are an important photovoltaic (PV) reliability issue since it accounts for a high percentage of power losses in the midlife-failure and wear-out failure regimes. Cell cracking can only be correlated with module degradation when cracks are of detectable size and detrimental to the performance. Several techniques have been explored to access the deflection and stress status on solar cell, but they have disadvantages such as high surface sensitivity. This dissertation presents a new and non-destructive method for mapping the deflection on encapsulated solar cells using X-ray topography (XRT). This method is based on Bragg diffraction imaging, where only the areas that meet diffraction conditions will present contrast. By taking XRT images of the solar cell at various sample positions and applying an in-house developed algorithm framework, the cell‘s deflection map is obtained. Error analysis has demonstrated that the errors from the experiment and the data processing are below 4.4 and 3.3%. Von Karman plate theory has been applied to access the stress state of the solar cells. Under the assumptions that the samples experience pure bending and plain stress conditions, the principal stresses are obtained from the cell deflection data. Results from a statistical analysis using a Weibull distribution suggest that 0.1% of the data points can contribute to critical failure. Both the soldering and lamination processes put large amounts of stress on solar cells. Even though glass/glass packaging symmetry is preferred over glass/backsheet, the solar cells inside the glass/glass packaging experience significantly more stress. Through a series of in-situ four-point bending test, the assumptions behind Von Karman theory are validated for cases where the neutral plane is displaced by the tensile and compressive stresses. The deflection and stress mapping method is applied to two next generation PV concepts named Flex-circuit and PVMirror. The Flex-circuit module concept replaces traditional metal ribbons with Al foils for electrical contact and PVMirror concept utilizes a curved PV module design with a dichroic film for thermal storage and electrical output. The XRT framework proposed in this dissertation successfully characterized the impact of various novel interconnection and packaging solutions. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2019

Die Herstellung von verspannten Schichten mittels Heteroepitaxie gewinnt in der aktuellen Festkörperphysik zunehmend an Bedeutung, insbesondere wenn es gelingt, Schichten mit unterschiedlichen Gitterparametern in hoher kristalliner Perfektion, wie sie für die Herstellung elektronischer Bauelemente notwendig ist, aufeinander abzuscheiden. Der Einsatz verspannter Schichtsysteme erlaubt es, bestimmte Materialeigenschaften, wie die Ladungsträgerbeweglichkeiten und den Bandabstand, gezielt zu beeinflussen. Im Rahmen der vorliegenden Arbeit wurde die frühe Phase der Relaxation von dünnen verspannten metastabilen Silizium-Germanium-Mischkristallschichten auf (001)-Siliziumsubstrat untersucht. Derartige metastabile Schichten bilden bei Temperaturbehandlung sogenannte Fehlanpassungsversetzungen aus. Die Ausbildung dieser Versetzungen in makroskopischer Ausdehnung in nahezu perfekt kristallinen Materialien setzt einen Nukleationsvorgang und die Ausbreitung durch Gleiten bzw. Klettern voraus. Diese Vorgänge wurden am o.g. Materialsystem systematisch untersucht. Die Untersuchung außerordentlich geringer Versetzungsdichten erfolgte mittels in-situ und ex-situ Röntgentopographie sowie ergänzender Messungen mittels hochauflösender Röntgendiffraktometrie. Die Plane-view-Transmissionselektronenmikroskopie sowie Atomkraftmikroskopie ergänzten die Experimente auf der damit möglichen Längenskala insbesondere für die Beurteilung des Verhaltens von sich kreuzenden Versetzungen. Es wurden Versetzungsgleitgeschwindigkeiten in Abhängigkeit von verschiedenen Fremdstoffkonzentrationen und Epitaxieverfahren gemessen. Ein signifikante Einfluß dieser Verfahren auf die Gleitgeschwindigkeit konnte nicht nachgewiesen werden, jedoch veringert der Sauerstoffgehalt einiger Proben die Versetzungsgleitgeschwindigkeit. Eine Kohlenstoffdotierung von 0,1% führt bei Einbau auf Gitterplätzen zu keinem messbaren Einfluß auf die Ausbreitungsgeschwindigkeit von Fehlanpassungsversetzungen. Der Prozess der Nukleation von Versetzungen wurde durch die heterogene Nukleation an Einzeldefekten, deren Vorhandensein stark vom Epitaxieverfahren abhängt, dominiert. Dies wurde an einer Vielzahl von Proben verifiziert. Die Aktivität der einzelnen Nukleationszentren ist sehr unterschiedlich und lässt sich nur durch ein "Spektrum" von Nukleationszentren unterschiedlicher "Stärke" erklären. Starke Nukleationszentren können bis ca 100 Versetzungen, die zusammen Versetzungsbündel bilden, induzieren. Die Nukleationszentren werden sequentiell aktiviert. Es wurde gezeigt, dass Laserbeschuss schwache Zentren "aktiviert" und eine damit eine sehr gleichmäßige Relaxation von Schichten möglich wird. Durch in-situ-Beobachtungen konnte erstmals röntgentopografisch der Prozess des Versetzungsblockierens und des Quergleitens an sich kreuzenden Versetzungsbündeln über einen großen Skalenbereich verfolgt werden.Es konnte gezeigt werden, dass die Zweikristall-Röntgentopografie ein geeignetes Verfahren zur Untersuchung großer teilrelaxierter Proben mit extrem geringem Relaxationsgrad darstellt. / The deposition of metastable layers by means of heteroepitaxy is gaining more and more in importance in current solid state physics, especially if it is possible to deposit layers with rather different lattice parameters in perfect quality, necessary for the fabrication of electronic devices and semiconductor technology. The use of such layer systems enables to controlling specific material properties, for example the mobility of charge carriers and the energy gap. Within the framework of this work the early stages of the relaxation of very thin strained silicon-germanium layers deposited onto (001)silicon substrates were investigated. Such metastable layers create so-called misfit dislocations at annealing. The formation of dislocations in nearly perfect materials as silicon in macroscopic extension presumes a nucleation process and the propagation by means of gliding and/or climbing of the threading segments. These processes were investigated systematically at silicon-germanium-films on silicon substrates as a modelsystem. Very low densities of dislocations were investigated by in-situ and ex-situ X-ray topography as well as high resolution X-ray diffractometry. Plane-view transmission electron microscopy and atomic force microscopy complemented the experiments in order to study the behavior at the dislocation crossings at smaller length scale. Dislocation glide rates were measured at different concentrations of impurities (e.g. carbon) in the sample and for different growth techniques. There was no significant influence of the epitaxial method on the glide velocities but a very low amount of oxygen decreases the the velocity effectively. A low density of carbon (0,1%) wich occcupy silicon or germanium lattice sites had no significant influence on the propagation of dislocations. The process of nucleation is dominated by heterogeneous nucleation as was verified at a large number of samples and varies in detail for different epitaxial depostion methods. The activity of single nucleation centers is rather different and can interpreted with a "spectrum" of centers of different strength. A strong center can induce as many as 100 dislocations. These dislocations form bunches of dislocations as was observed with X-ray topography. The centers are sequentially activated. This was demonstrated at samples where a pretreatment with an excimer laser "activated" weak centers thereby inducing a comparatively homogeneous distribution of dislocations. By means of in-situ synchrotron radiation experiments the prozesses of propagation, blocking and crossslip could be observed for the first time in large areas of samples. The double crystal X-ray topography is a suitable method to observe these processes in comparatively large samples with a very low degree of relaxation.