Thesis deals with theoretical knowledge about scanning electron microscopy and environmental scanning electron microscopy. It describes principle of operation, signals generated by interaction between primary electron beam and specimen and means of detection of secondary electron signal in environmental conditions using scintillation detector. Furthermore, thesis focuses on optimization of detection od secondary electrons by adjusting electrode system of scintillation detector. Computer program Simion is used for modelling signal electron trajectories for proper adjustments. Simulation were starting-point for adjusting the design of the detector. Detection efficiency of adjusted detector was determined by evaluating signal magnitude from captured images, secondary electron detection capability from voltage contrast and quality of the captured images from signal/noise ratio.

Ce document présente les approches suivies et les résultats des investigations théoriques et expérimentales entreprises dans le cadre de l'étude du procédé de crêpage du papier depuis le début de la maîtrise faite en collaboration avec Kruger Produits Ltée. L'objectif du projet est de mieux comprendre les phénomènes reliant la qualité du papier a l'état d'usure des lames de crêpage. À cette fin, une méthode expérimentale basée sur les techniques de mesure par émission acoustique afin de suivre en temps réel le comportement mécanique et l'état d'usure des lames est proposée. Ce suivi en temps réel permet d'identifier par émission acoustique les mécanismes reliés à l'usure des lames par friction et d'établir une corrélation entre le comportement mécanique de la lame et les différents paramètres de qualité du papier, dont le crêpage. Ce mémoire présente donc en premier lieu la problématique du projet, les éléments fondamentaux qui entrent en jeu lors du procédé de crêpage, la description des lames utilisées dans le procédé industriel, l'analyse des principes de base des phénomènes d'usure des lames en relation avec les aspects métallurgiques du matériau et enfin, les principes du suivi de l'usure par la technique d'émission acoustique et le traitement numérique des signaux. La deuxième partie du mémoire s'attarde sur les procédures expérimentales suivies et sur la synthèse des résultats obtenus. La troisième partie présente la conclusion sur les résultats obtenus à partir de laquelle une série de recommandations sont mises de l'avant afin de permettre à l'entreprise d'améliorer l'opération de crêpage du papier.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / Dissertation presented for the degree of Doctor of Philosophy in Engineering at the University of Stellenbosch / ENGLISH ABSTRACT: Planar weak link structures, such as micro-bridges, variable thickness bridges and nanobridges, have always attracted a lot of attention. Their potential to behave as real Josephson elements make them useful devices, with numerous applications. Powerful techniques, such as focused ion-beam and electron-beam lithography, were successfully used and are well understood in planar weak link structure fabrication. In this dissertation the results of an experimental study on planar weak link structures are presented. For the first time these structures have been successfully fabricated using AFM nanolithography on hard high-temperature superconducting YBCO tracks, where diamond coated silicon tips were used as a ploughing tool. Superconducting YBCO thin films were deposited on different substrates, using inverted cylindrical magnetron sputtering. The films were used to fabricate micro-bridges, variable thickness bridges and nano-bridges, by using conventional photolithography, argon ion-beam milling and AFM nanolithography. The measured I-V characteristics of the fabricated micro-bridges (width down to 1.9 µm), variable thickness bridges (thickness down to 15 nm) and nano-bridge (width down to 490 nm) showed well defined DC and AC Josephson effect characteristics. For better understanding of the behaviour of these types of weak links, critical current versus temperature measurements, and magnetic field modulation of the critical current measurements, were also performed, with the results and discussions given inside the chapters. The major challenges that were experienced in the laboratory during the fabrication processes and the operation of the fabricated devices are also discussed, with the solutions given where appropriate. / AFRIKAANSE OPSOMMING: Swak-skakel vlakstrukture, soos mikrobr.ue, br.ue met veranderlike dikte en nanobr.ue, het nog altyd baie aandag getrek. Hul het die potensiaal om soos werklike Josephson-elemente te kan funksioneer en is, as gevolg hiervan, nuttige toestelle met veelvuldige toepassings. Kragtige tegnieke, soos gefokuste ioonstraal- en elektronstraal litografie, is suksesvol gebruik en word goed verstaan in die vervaardiging van swak-skakel vlakstrukture. In hierdie proefskrif word die resultate van ¡¦n eksperimentele studie van swak-skakel vlakstrukture voorgel.e. Vir die eerste keer is hierdie strukture suksesvol vervaardig, deur gebruik te maak AFMnanolitografie op harde, ho¡Le-temperatuur supergeleier YBCO (Yttrium Barium Koperoksied) spore, waar diamantbedekte silikonpunte gebruik is as ploeginstrument. ¡¦n Dun lagie van supergeleidende YBCO is op verskillende substrate gedeponeer, deur gebruik te maak van omgekeerde silindriese magnetron verstuiwing. Die dun lagies is gebruik in die vervaardiging van mikrobr.ue, br.ue met veranderlike dikte en nanobr.ue, deur die gebruik van gewone fotolitografie, argon-ioonstraal frees en AFM nanolitografie. Die gemete I-V eienskappe van die vervaardigde mikrobr.ue (met breedte so laag as 1.9 µm), veranderlike-dikte br.ue (dikte tot 15 nm) en nanobr.ue (breedte so min as 490 nm) toon goed gedefinieerde GS en WS eienskappe van die Josephson-effek. Ten einde die gedrag van hierdie tipes swak-skakels beter te kan verstaan, is metings gedoen van kritieke stroom teenoor temperatuur, asook magnetiese veld modulasie van die kritieke stroom. Hierdie resultate en besprekings daarvan word binne die toepaslike hoofstukke aangebied. Die grootste uitdagings wat in die laboratorium, sowel as met die toetsing van die vervaardigde toestelle ondervind is, word ook bespreek. Waar moontlik, word toepaslike oplossings voorgestel.

Depuis 1987, la palourde japonaise est sujette à une infection récurrente : la Maladie de l'Anneau Brun (MAB), provoquée par la bactérie Vibrio tapetis. Cette infection est caractérisée par la formation d'un anneau brun sur la face interne des valves et provoque souvent la mort de la palourde, suite à l'invasion de son système circulatoire par la bactérie. Cependant, quelques spécimens peuvent guérir de cette infection en sécrétant une nouvelle couche minéralisée qui recouvre l'anneau brun. Le but du travail de cette thèse est de comprendre et caractériser comment les palourdes japonaises sont capables de résister à la MAB, principalement en étudiant le mécanisme de réparation coquillière. Pour ce faire, des techniques comme la Microscopie Electronique à Balayage (MEB), la micro-spectrométrie confocale Raman, la microsonde WDS (Wave-length Dispersive Spectrometry), ainsi que des colorations cellulaires, la biochimie et la sérologie ont été utilisées. La couche de réparation est composée d'aragonite, de polyènes, de molécules luminescentes au Raman et de molécules sulfatées. La microstructure de la couche de réparation est souvent différente de celle de la couche interne saine et montre une grande variabilité. De plus, la matrice organique coquillière de la couche de réparation est quantitativement et qualitativement différente de celle de la couche interne saine et montre également une grande variabilité. Ces différences saines-réparées et ces variabilités pourraient être expliquées par une modification du régime sécrétoire des cellules calcifiantes du manteau, ainsi que par une mobilisation d'hémocytes préalablement chargés en sels insolubles de carbonate de calcium au niveau des sites de réparation coquillière.

Sensilla styloconica on the proboscis of 107 species of North American and tropical butterflies were comparatively studied using the scanning electron microscope. Focus was on 76 species of North American Nymphalidae representing 45 genera and 11 subfamilies. Nomenclature for generalized and specific types of nymphalid sensilla is proposed. Written descriptions and micrographs are presented for each species studied. Morphological features were generally consistent for all or most species within genera and sometimes within subfamilies, with specified exceptions. Statistical analysis revealed significant differences for six of eight variables tested between two distinct feeding guilds of North American Nymphalidae. Average number, density, extent of proboscis coverage with sensilla, their total length, and shoulder spine length were all significantly greater in the non-nectar feeding guild than in nectar feeders, and may indicate adaptation for greater efficiency in feeding on flat surfaces. The greater frequency of apical shoulder spines in non-nectar feeders may represent adaptation for protection of sensory pegs from mechanical abrasion during feeding, or for anchoring the flexible proboscis tip to the surface. Correlation analysis revealed 9 out of 28 positive correlations in nectar feeders and 5 out of 28 in non-nectar feeders. Results of preliminary cladistic analysis were not considered to be meaningfully robust due to few available characters. The stylar characters identified in this study should be more useful in future analyses when included with characters from other lines of evidence. The presence of sensilla styloconica in all subfamilies of Nymphalidae, except Danainae, largely supports Ehrlich's (1958) higher classification concept for the family. The presence of less conspicuous sensilla in the Danainae, and other characteristics are presented as further evidence that they should be reconsidered for full family status. Sensilla styloconica in nymphalid butterflies appear to function as extensions that provide greater sensory reach during feeding. The role of these sensilla in liquid uptake, pollen feeding, and host plant selection is discussed.

Die eingereichte Dissertation beschäftigt sich mit der messtechnischen Erfassung sowie der Modellierung von Haftkräften zwischen rauen Oberflächen. Dabei wurden durch Variation von Flüssigkeiten sowie dem Nutzen beschichteter Oberflächen verschiedene Benetzungseigenschaften eingestellt und untersucht. Zusätzlich wurden neben dem Kontaktwinkel der untersuchten Systeme die freien Ober- und Grenzflächenenergien bestimmt und mit den Kräften korreliert. Es zeigte sich, dass Haftkräfte auf rauen Oberflächen stets über mehrere Größenordnungen verteilt vorliegen. Die Beschreibung der ermittelten Verteilungen ist dabei entweder durch statistischer Funktionen oder zumindest teils auch durch eine im Rahmen der Arbeit entwickelten Modellierung möglich. Weiterhin zeigte sich, dass eine Unterteilung in verschiedene Haftmechanismen (durch Kapillarbrücken oder van der Waals- sowie polare Wechselwirkungen) vorgenommen werden kann. Kapillarbrücken bilden dabei die größten Kräfte aus. Sie entstehen auf Grund nanoskaliger Blasen (Nanobubbles), welche vor allem auf schlecht benetzenden Oberflächen existieren.

Doctor of Philosophy / Department of Physics / Bruce M. Law / Three diverse first author surfaces science experiments conducted by Sean P. McBride 1-3 will be discussed in detail and supplemented by secondary co-author projects by Sean P. McBride, 4-7 all of which rely heavily on the use of an atomic force microscope (AFM). First, the slip length parameter, b of liquids is investigated using colloidal probe AFM. The slip length describes how easily a fluid flows over an interface. The slip length, with its exact origin unknown and dependencies not overwhelming decided upon by the scientific community, remains a controversial topic. Colloidal probe AFM uses a spherical probe attached to a standard AFM imaging tip driven through a liquid. With the force on this colloidal AFM probe known, and using the simplest homologous series of test liquids, many of the suspected causes and dependencies of the slip length demonstrated in the literature can be suppressed or eliminated. This leaves the measurable trends in the slip length attributed only to the systematically varying physical properties of the different liquids. When conducting these experiments, it was realized that the spring constant, k, of the system depends upon the cantilever geometry of the experiment and therefore should be measured in-situ. This means that the k calibration needs to be performed in the same viscous liquid in which the slip experiments are performed. Current in-situ calibrations in viscous fluids are very limited, thus a new in-situ k calibration method was developed for use in viscous fluids. This new method is based upon the residuals, namely, the difference between experimental force-distance data and Vinogradova slip theory. Next, the AFM’s ability to acquire accurate sub nanometer height profiles of structures on interfaces was used to develop a novel experimental technique to measure the line tension parameter, τ, of isolated nanoparticles at the three phase interface in a solid-liquid-vapor system. The τ parameter is a result of excess energy caused by the imbalance of the complex intermolecular forces experienced at the three phase contact line. Many differences in the sign and magnitude of the τ parameter exist in the current literature, resulting in τ being a controversial topic.

Technology where a solitary dopant acts as the active component of an opto-electronic device is an emerging  field known as solotronics, and bears the promise to revolutionize the way in which information is stored, processed and transmitted. Magnetic doped semiconductors and in particular (Ga, Mn)As, the archetype of dilute magnetic semiconductors, and topological insulators (TIs), a new phase of quantum matter with unconventional characteristics, are two classes of quantum materials that have the potential to advance spin-electronics technology. The quest to understand and control, at the atomic level, how a few magnetic atoms precisely positioned in a complex environment respond to external stimuli, is the red thread that connects these two quantum materials in the research presented here. The goal of the thesis is in part to elucidate the properties of transition metal (TM) impurities near the surface of GaAs semiconductors with focus on their response to local magnetic and electric fields, as well as to investigate the real-time dynamics of their localized spins. Our theoretical analysis, based on density functional theory (DFT) and using tight-binding (TB) models, addresses the mid-gap electronic structure, the local density of states (LDOS) and the magnetic anisotropy energy of individual Mn and Fe impurities near the (110) surface of GaAs. We investigate the effect of a magnetic field on the Mn acceptor LDOS measured in cross-sectional scanning tunneling microscopy, and provide an explanation of why the experimental LDOS images depend weakly on the field direction despite the strongly anisotropic nature of the Mn acceptor wavefunction. We also investigate the effects of a local electrostatic field generated by nearby charged As vacancies, on individual and pairs of ferromagnetically coupled magnetic dopants near the surface of GaAs, providing a means to control electrically the exchange interaction of Mn pairs. Finally, using the mixed quantum-classical scheme for spin dynamics, we calculate explicitly the time evolution of the Mn spin and its bound acceptor, and analyze the dynamic interaction between pairs of ferromagnetically coupled magnetic impurities in a nanoscaled semiconductor. The second part of the thesis deals with the theoretical investigation of a single substitutional Mn impurity and its associated acceptor state on the (111) surface of Bi2Se3 TI, using an approach that combines DFT and TB calculations. Our analysis clarifies the crucial role played by the spatial overlap and the quasi-resonant coupling between the Mn-acceptor and the topological surface states inside the Bi2Se3 band gap, in the opening of a gap at the Dirac point. Strong electronic correlations are also found to contribute significantly to the mechanism leading to the gap, since they control the hybridization between the p orbitals of nearest-neighbor Se atoms and the acceptor spin-polarization. Our results explain the effects of inversion-symmetry and time-reversal symmetry breaking on the electronic states in the vicinity of the Dirac point, and contribute to clarifying the origin of surface-ferromagnetism in TIs. The promising potential of magnetic-doped TIs accentuates the importance of our contribution to the understanding of the interplay between magnetic order and topological protected surface states.

Coherence-Controlled Holographic Microscope (CCHM) and a Fluorescence Holographic Microscope (FHM) were developed particularly for quantitative phase imaging and measurement of live cell dynamics, which used to be a subject of digital holographic microscopy (DHM). CCHM and FHM in low-coherence mode extend capabilities of DHM in the study of living cells. However, this advantage following from the use of low coherence is accompanied by increased sensitivity of the system to its correct alignment. Therefore, the introduction of an automatic self-correcting system is inevitable. Accordingly, in the thesis, the theory of a suitable control system is derived and the design of an automated alignment system for both microscopes is proposed and experimentally proved. The holographic signal was identified as a significant variable for guiding the alignment procedures. On this basis the original basic realignment algorithms were proposed, which encompasses the processes for initial and advanced alignment as well as for long-term maintenance of the microscope aligned state. Automated procedures were implemented in both microscopes unique set of robotic mechanisms designed and built within the frame of the thesis work. All of the procedures described in the thesis were in real experimentally proved at real microscopes in the experimental biophotonics laboratory. In addition, the control software, which contains the needed automated procedures, was developed for FHM.

Le développement des senseurs protéiques et des outils optogénétiques au cours des dernières années a donné une place particulière à la microscopie pour l’étude des processus moléculaires in-vivo. L’équipe « Nano-optique et physiologie intégrée » développe des montages optiques originaux pour exploiter ces nouveaux outils chez le petit animal vivant en collaboration avec des neurobiologistes. Nous nous intéressons en particulier à l’organisation cellulaire et à l’activité des réseaux neuronaux impliqués dans la mémorisation associative olfactive de la drosophile. En amont, mon travail de thèse a été de mettre en place un microscope grand champ, basé sur le principe de la microscopie à HiLo, permettant l’acquisition rapide de sections optiques et la reconstruction tridimensionnelle de réseaux neuronaux. Après avoir prouvé la pertinence de l’approche choisie lorsqu’elle est associée aux outils génétiques permettant un marquage sélectif des neurones, le cœur de mon travail fut le développement d’un montage original permettant d’atteindre les objectifs de résolution spatiale et de vitesse. Son originalité se situe dans l’utilisation de la technologie des matrices de micro-miroirs (DLP) pour structurer l’illumination. Ce système de micro-miroirs pilotables peut moduler le faisceau d’une source LED haute puissance à haute cadence. Dans une seconde partie, j’ai caractérisé ce microscope et réalisé de premières expériences in-vivo avec les développements spécifiques nécessaires à ces expériences. En particulier, en utilisant un rapporteur protéique calcique fluorescent, GCamP3, j’ai montré que l’on pouvait suivre, dans des régions ciblées du cerveau, la réponse à des stimulations physiologiques à cadence vidéo. / In the last decades, optogenetic and protein reporter development have given a special place to optical microscopy for in-vivo investigation of biological molecular processes. Our team, “Nano-optics and integrated physiology”, develops optical set-ups to take advantage of these tools on small living animals, in collaboration with neurobiologists. We are particularly interested both in the cellular organization and neural activity involved in the olfactory memory formation in drosophila. Upstream to these investigations, my PhD research aimed at developing a new implementation for wide-field microscopy based on the HiLo concept. The new design took advantage of the micro-mirror array technology (DLP) to structure the illumination. This system can modulate the beam made by a high power LED illumination with high acquisition rates. I characterized this microscope and realized preliminary in-vivo experiments with specific developments made for physiological experiments under the microscope. Thus, I demonstrated both high spatial resolution imaging and a tenfold increase of speed with respect to confocal microscopy. I reached acquisition rates compatible with 3D monitoring of specific neural networks.